Cement Industry Process Technology - Holderbank Course (3 Of 3) 225u32

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III

B06 - PT III

© Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:33 PM

Page 1

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C01 - Emission Control

C01 - Emission Control


6/23/2001 - 5:13:33 PM

Page 2

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions

Sources and Reduction of NOx-Emissions P. Kutschera PT 96/14160/E 1. Introduction 2. Chemical And Physical Properties And Environmental Aspects Of Some Nitrogen Compounds And Ozone 2.1 Nitrogen (N2) 2.1.1

Physical Properties [1]

2.1.2

Chemical Properties [1]

2.2 Nitrogen Oxides (NO, NO2 N2O) 2.2.1


2.2.2

Toxicology [1]

2.2.3

Environmental Aspects [2]

2.3 Ammonia 2.3.1

Physical Properties

2.3.2

Chemical Properties

2.3.3

Toxicology

2.4 Ozone 2.4.1

Physical Properties

2.4.2

Toxicity

2.4.3

Formation of Trophospheric Ozone

3. Present Situation 3.1 Present State of Cement Kiln Emission 3.2 Present Legal Situation [16] 4. Nitrogen Input into the Kiln System 5. Behavior of Nitrogen in the Process 5.1 NO Formation 5.1.1

Nitrogen Monoxide Formation Reaction Mechanism

5.1.2

NO-Decomposition Mechanism in the Combustion Process

5.2 Formation of Nitrogen Monoxide in a Cement Kiln 5.3 Main Influencing Variables for NO Formation © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:33 PM

Page 3

"Holderbank" - Cement Course 2000 5.3.1

Temperatures

5.3.2

Temperature Peaks [6]

5.3.3

Excess Air

5.3.4

Retention Time

5.3.5

Burner Operating Parameters

5.3.6

Evaluation of Characteristical Burner Data (CETIC Working Group)

6. No Emission Reduction Possibilities 6.1 Reduction of Nitrogen Input 6.2 Primary Measures 6.2.1

Kiln / Clinker Cooler

6.2.2

Secondary Firing / Multi-Stage Combustion

6.2.3

Possible Negative Side Effects of Primary Measures

6.3 Secondary Measures 6.3.1

The Selective Non-Catalytic Reduction

6.4 Effectiveness of NOx Reduction Measures [9] 7. Examples Of Nox Emission Reduction 8. Literature

Summary: Cement kiln NOx emissions are between 300 and 2500 mg NO2 / Nm3. The degree of NOx emission is mainly determined by ♦ Flame temperature ♦ Oxygen content ♦ Residence time of exhaust gas in the kiln ♦ Fuel-N ♦ Primary measures against NOx ♦ Secondary measures against NOx

The NOx control technologies available for cement kilns include: ♦ Combustion Operational Modifications (COM) ♦ Low NOx Burners (LNB) ♦ Staged Air Combustion (SAC) © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:33 PM

Page 4

"Holderbank" - Cement Course 2000 ♦ Selective Non-Catalytic Reduction (SNCR) Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 1. INTRODUCTION

1.

INTRODUCTION

NOx is produced to different degrees in all stationary and mobile combustion sources. Because of the high flame temperatures the NO generation in cement kilns is relatively high. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE

2.

CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.1 Nitrogen (N2)

2.1

Nitrogen (N2)

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.1 Nitrogen (N2) / 2.1.1 Physical Properties [1]

2.1.1


At atmospheric pressure and room temperature, nitrogen is a colorless, odorless, non-combustible gas. Nitrogen condenses to a colorless liquid at -195.80°C and 101.3 kPa and forms a white solid at -209.86°C. Mr

28.0134

Triple point T

63.15 K

p

12.463 kPa

heat of fusion

25.8 kJ/kg

Boiling point (101.3 kPa) heat of vaporization

77.35 K 199 kJ/kg

Critical point Tcrit

126.2 K

pcrit

3.39908 Mpa

Qcrit

314.03 g/L

Properties at 0°C, 101.3 kPa: Relative density (air = 1)


0.967

6/23/2001 - 5:13:33 PM

Page 5

"Holderbank" Cement Relative density- (air = 1) Course 2000 0.967 Specific heat capacity

1.039 Jg-1 K-1

Dynamic viscosity

15.9 x 10-6 Pa s

Thermal conductivity

23.86 mWm-1 K-1

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.1 Nitrogen (N2) / 2.1.2 Chemical Properties [1]

2.1.2


Nitrogen has an extremely high heat of dissociation: N2 ↔ 2 N

∆H0 = 943.8 kJ/mol

No marked dissociation takes place even at 3000°C and standard pressure. The strength of the N º N bond is responsible for the inertness of N2. Important reactions of nitrogen with non-metals are those with hydrogen, yielding ammonia, and with oxygen. The latter, an endothermic reaction, gives nitrogen monoxide: N2 + O2 ↔ 2 NO

∆H0 = 180 kJ/mol

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.2 Nitrogen Oxides (NO, NO2 N2O)

2.2

Nitrogen Oxides (NO, NO2 N2O)

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.2 Nitrogen Oxides (NO, NO2 N2O) / 2.2.1 Physical Properties [1]

2.2.1


Compounds of oxygen with nitrogen are considered as a class and called nitrogen oxides (often denoted as NOx). The known oxides and their equilibrium reactions are as follows: +I N2O +II Nitrogen monoxide

NO

Dinitrogen monoxide

+II ↔

N2O2

Dinitrogen dioxide

+III N2O3 +IV Nitrogen dioxide

NO2


Dinitrogen trioxide

+IV ↔

N2O4

Dinitrogen tetroxide

6/23/2001 - 5:13:34 PM

Page 6

NO2 "Holderbank" - Cement Course 2000 +V N2O5 +VI Nitrogen trioxide

Dinitrogen pentoxide

+VI ↔

NO3

N2O6

Dinitrogen hexoxide

Table 1: Physical properties of nitrogen oxides Compound

N2O

NO

NO2 / N2O4

N2O3

N2O5

Oxidation state

1.000

2.000

+4 / +4

3.000

5.000

Tcr, °C

36.410

-93.000

157.850

pcr, MPa

7.245

6.485

10.132

Qcr, kg/m3

452.000

520.000

550.000

mp, °C

-90.860

-163.650

-11.200

-100.700

32.4*

bp, °C

-88.480

-151.770

21.150

-40 to +3

0.879

0.996

1.326

0.862

0.778

Standard enthalpy of formation ∆H°F, kJ/kg

1864.190

3007.684

721.199

1101.435

104.589

Heat of vaporization at bp, kJ/kg

376.070

459.031

414.257

517.416

1.9775 793

1.3402

3.4 (20°C) 1446.8

1.447 (2°C)

14.874

19.184

12.838

0.01718

0.02573

0.1124 0.1336

Specific heat , kJ kg-1 K-1

Density, kg/m3 Gas (0°C, 101.3 kPa) Liquid (20°C, 101.3 kPa) Dynamic viscosity, mPa -s Gas (25°C, 101.3 kPa) Thermal conductivity, W m K-1 Gas (25°C, 101.3 kPa) Liquid (20°C, 101.3 kPa)

2.05 (solid)

-1

* Sublimation point

N2O Under normal conditions (i.e. room temperature and atmospheric pressure), dinitrogen monoxide, also called nitrous oxide, N2O, Mr 44.01, is a colorless gas with a weak, pleasant odor and a sweetish taste. If inhaled, it can bring about a spasmodic inclination to laugh and a condition resembling drunkenness hence, its historic name, laughing gas. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:34 PM

Page 7

"Holderbank" - Cementresembling Course 2000 to laugh and a condition drunkenness hence, its historic name, laughing gas. NO Nitrogen monoxide, also called nitric oxide, NO, Mr 30.01, is a colorless, toxic, nonflammable gas at room temperature. As soon as it comes in with atmospheric oxygen, it is oxidized to nitrogen dioxide, a brown vapor. NO2 Nitrogen dioxide, NO2, Mr 46.01, is a brownish red, toxic gas with a pungent odor; for physical properties, see Table 1.

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.2 Nitrogen Oxides (NO, NO2 N2O) / 2.2.2 Toxicology [1]

2.2.2

Toxicology [1]

NO Pure nitrogen monoxide does not have any irritating effects. It reacts, however, with hemoglobin to form methemoglobin, resulting in cyanosis and possible death. The TLV-TWA value is 25 ppm (31 mg/m3). NO2 Nitrogen dioxide is an irritant gas. Its MAK value is 5 ppm (9 mg/m3). TLV-TWA 3 ppm (5.6 mg/m3), TLV-STEL 5 ppm (9.4 mg/m3). Inhalation of nitrogen dioxide causes pulmonary edema which may result in death (lethal dose 200 ppm). The substance is only slightly water-soluble but highly lipid-soluble. It therefore penetrates the alveoli where it damages the capillary walls resulting in exudative inflammation. The respiratory tract is obstructed due to formation of foam. Concentrations exceeding 60 - 150 ppm produce coughing and a burning sensation in the chest. Pulmonary edema becomes apparent after 2 - 24 h. The patient suffers respiratory distress and insomnia. Chronic exposure to low doses results in coughing, headache, loss of appetite and gastrointestinal disorders. Patients should be kept under clinical observation. Inhalation of ammonia from ammonium hydrogen carbonate is recommended. N2O Dinitrogen monoxide (laughing gas) does not irritate the mucous membranes. It has a powerful analgesic action but is only weakly narcotic. The gas displaces nitrogen from air-filled body cavities (middle ear, sinuses, intestines, brain ventricles) resulting in an increase in pressure. After chronic exposure, polyneuropathy and myelopathy have been observed. TLV-TWA value is 50 ppm (90 mg/m3).

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.2 Nitrogen Oxides (NO, NO2 N2O) / 2.2.3 Environmental Aspects [2]

2.2.3

Environmental Aspects [2]

Conditions which produce nitrogen oxides do not occur solely in stationary combustion sources. The © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:35 PM

Page 8

"Holderbank" - Cement Course 2000 exhaust gases from internal-combustion engines, particularly those of the gasoline-burning spark-ignition variety, contain traces of nitrogen oxides, and because of the sheer number of them they are estimated to contribute about 50% of the total anthropogenic NOx burden. Vehicle exhaust also contains the other ingredients needed to produce the effect known as photo-chemical smog; this has long plagued large conurbations in badly ventilated situations such as Los Angeles, Tokyo and Mexico City, and it has more recently become a feature of many other urban centers. The nitrogen oxides, activated by solar ultraviolet, react in the urban atmosphere with the unburned hydrocarbons from vehicle exhausts to produce a noxious cocktail of corrosive, oxidizing and irritating chemicals such as organic peroxides. They also interact with atmospheric oxygen to produce ozone. It is ironic that, at a time when one form of atmospheric pollution is destroying the ozone in the stratosphere, which provides vital protection against excessive solar radiation at the surface, another is creating it near ground level, where it is an economic and health hazard. Vehicle exhaust is, of course, discharged virtually at ground level, and its effects are "local" rather than global: the smog pall from Los Angeles sometimes extends 100 miles or more inland. But nitrogen oxides are now known to be a key component of a much more widespread problem which is even more serious in of its international implications than is photochemical smog. It is now plain that a sizable proportion of the blame for the very topical environmental concern of acid rain which was formerly perceived as an effect only of sulfur oxides, can in fact be attached to nitrogen oxides. Acid rain which ought really to be termed "acid precipitation" since the most spectacular manifestations tend to occur in snow rather than rain is no observer of national boundaries. Pollutants released in one country may come to earth in precipitation not just in neighboring countries but even in other continents. As the extent of the problem and its causes have become better understood and documented, it has become the subject of international dispute and negotiation. Ecological damage to the forests and lakes of Eastern Canada has been ascribed to (amongst other things) acidity originating from industrial sources in the US Mid-West. Similar damage which has ravaged the forests and lakes of Scandinavia has been blamed on pollution exported from the nearer EEC countries, especially the United Kingdom and , and former communist central European countries such as Poland, Czechoslovakia and Romania. And since the communist regimes in these countries collapsed the appalling extent of the devastation of their own forests has become only too apparent. By what mechanism acid rain causes forest damage is not known for certain. Two theories are currently given greatest credence. One proposes that the acidity leaches cationic nutrients such as calcium, magnesium and potassium away from the root zone and down into the subsoil, causing starvation. The other postulates that the acidity solubilizes normally immobile aluminum in the soil; this interferes with the normal uptake of other cationic nutrients and, if it reaches a threshold concentration (which varies according to the species of tree), it is directly toxic. This could also explain the dire effect on the aquatic life of lakes and rivers in the affected regions. Other pollutants reckoned to damage forests include heavy metals which are given off in coal smoke as well as in emissions from metal smelters and ozone which - as already mentioned - is generated in interactions between waste nitrogen oxides and atmospheric oxygen. Studies made in the United States for the National Acid Precipitation Assessment Program (NAPAP) a statutory body set up under the acid Precipitation Act of 1980 - have shown that the acidity is worse in high-level rain clouds than in lower-level clouds, suggesting that the pollutants causing it are carried up into the higher levels rather than diffu from ground level. So, while it is necessary to tackle exhaust emissions from vehicles to alleviate the smog problem and any strategy for curbing the contribution of nitrogen oxides to acid rain must center on the control of emissions from the © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:35 PM

Page 9

"Holderbank" - Cement Course 2000 large stationary sources. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.3 Ammonia

2.3

Ammonia

Ammonia, NH3, occurs in nature almost exclusively in the form of ammonium salts. Natural formation of ammonia is primarily by decomposition of nitrogen-containing organic materials or through volcanic activity. Ammonia and its oxidation products which combine to form ammonium nitrate and nitrite, are produced from nitrogen and water vapor through electrical discharges in the atmosphere. These ammonium salts, as well as those arising from industrial and automotive exhausts, supply significant quantities of the nitrogen needed by growing plants when eventually deposited on the earth's surface. Ammonia and its salts are also byproducts of commercial processing (gasification, cooking) of fuels with vegetable origins such as coal, lignite and peat. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.3 Ammonia / 2.3.1 Physical Properties

2.3.1

Physical Properties

Mr

17.0312

Liquid density (at -33.43°C, 101.3 kPa)

0.682 g/cm3

Gas density (at -33.43°C, 101.3 kPa)

0.888 g/L

Melting point (triple point)

-77.71°C

Vapor pressure (triple point)

6.077 kPa

Boiling point (at 101.3 kPa)

-33.43°C

Heat of vaporization (at 101.3 kPa)

1370 kJ/kg

Standard enthalpy of formation (gas at 25°C)

-45.72 kJ/mol

Net heating value, LHV

18.577 kJ/g

Gross heating value, HHV

22.543 kJ/g

Ignition temperature acc. to DIN 51 794

651°C

Explosive limits NH3 - O2 mixture (at 20°C, 101.3 kPa)

15 - 79 vol % NH3

NH3 - air mixture (at 0°C, 101.3 kPa)

16 - 27 vol% NH3

(at 100°C, 101.3 kPa)

15.5 - 28 vol% NH3

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.3 Ammonia / 2.3.2 Chemical Properties

2.3.2

Chemical Properties

Gaseous ammonia reacts very violently to explosively with nitrogen oxides to form nitrogen, water, © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:35 PM

Page 10

"Holderbank" - Cement Course 2000 ammonium nitrate or nitrite. The reaction with N2O does require ignition. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.3 Ammonia / 2.3.3 Toxicology

2.3.3

Toxicology

Ammonia is a strong local irritant. On mucous membranes alkaline ammonium hydroxide forms which dissolves cellular proteins and causes severe necrosis (corrosive effect). Ammonia or ammonium hydroxide can penetrate the cornea rapidly, leading to keratitis, damage of the iris, cataract and glaucom. Oral ingestion of aqueous ammonia can corrode the mucous membranes of the oral cavity, pharynx and esophagus and cause the shock syndrome, toxic hepatitis and nephritis. Ammonia is absorbed rapidly by the wet membranes of body surfaces as ammonium hydroxide, converted to urea and excreted by the kidneys. Human Exposure: Concentrations of 50 ppm are perceived easily; 50 - 72 ppm does not disturb respiration significantly. Levels of 100 ppm irritate nose and throat and cause a burning sensation in the eyes and tachypnoe. In addition to the symptoms described above, 200 ppm induce headache and nausea; 250 - 500 ppm, tachypnoe and tachycardia; 700 ppm, immediate onset of burning sensations in the eyes; 1000 ppm causes immediate coughing. The nitrogen metabolism is not significantly changed after exposure to 500 ppm of ammonia. The TLV value has been set at 25 ppm with a short-term limit exposure value at 35 ppm; the MAK is established at 50 ppm. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.4 Ozone

2.4

Ozone

Ozone is thermodynamically unstable and spontaneously reverts back into diatomic oxygen. This process is promoted by the presence of transition metals or their oxides. An irritating pale blue gas, ozone is explosive and toxic, even at very low concentrations. At -111.9°C it condenses to form a dark violet liquid which freezes at -192.7°C. In the Earth's stratosphere, it occurs naturally (5-10 ppm), protecting the planet and its inhabitants by absorbing ultraviolet radiation of wavelength 290-320 nm. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.4 Ozone / 2.4.1 Physical Properties

2.4.1

Physical Properties

Mr

48.0

bp (101 kPa)

-111.9°C

mp

-192.7°C

Critical temperature

-12.1°C

Critical pressure

5.53 MPa


6/23/2001 - 5:13:35 PM

Page 11

"Holderbank" - Cement Course 2000 Critical pressure 5.53 MPa Critical density

437 kg/m3

Critical volume

1.471 x 10-4 m3/mol

Heat capacity, gas 0°C

794 Jkg-1 K-1

25°C

818 Jkg-1 K-1

Heat of vaporization

15.2 kJ/mol

Heat of formation

144.8 kJ/mol

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.4 Ozone / 2.4.2 Toxicity

2.4.2

Toxicity

Ozone, being an extremely powerful oxidizing agent, readily oxidizes a variety of functional groups in biochemicals. Studies indicate that free radical formation, lipid peroxidation, carbonyl and aldehyde formation, and oxidation of SH groups, are some of the major sites of attack. Ozone readily reacts with olefinic compounds, particularly polyunsaturated lipids, forming unstable ozonides. Their decomposition results in the formation of toxic free radicals which can in turn amplify the primary cytotoxic or tissue damage. While ozone is considered to be a toxic gas, there are factors which mitigate the immediate danger to individuals working with it. Toxicity is dependent on concentration and length of exposure. OSHA has set an 8-h TWA-PEL of 0.2 mg/m3 (0.1 ppm) for ozone. Fig. 1 illustrates the relationship between various exposure levels and exposure time for humans. The odor threshold concentration for ozone is approx. 0.02-0.04 mg/m3 (0.01 - 0.02 ppm). Figure 1:

Human toxicity limits for ozone exposure

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME NITROGEN COMPOUNDS AND OZONE / 2.4 Ozone / 2.4.3 Formation of Trophospheric Ozone

2.4.3

Formation of Trophospheric Ozone CO + OH →


H + CO2 6/23/2001 - 5:13:36 PM

Page 12

"Holderbank" - Cement Course 2000 →

H + CO2

H + O2 H M →

HO2 + M

HO2 + NO → NO2 + Light (λ < 420 nm) → O + O2 + M → Net:

CO + 2 O2 + Light (λ < 420 nm) →

OH + NO2 NO + O O3 + M CO2 + O3

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 3. PRESENT SITUATION

3.

PRESENT SITUATION

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 3. PRESENT SITUATION / 3.1 Present State of Cement Kiln Emission

3.1

Present State of Cement Kiln Emission

There is no normal or average NOx emission from cement kilns. Many factors like kiln system and fuel characteristics are influencing the NOx emission. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 3. PRESENT SITUATION / 3.2 Present Legal Situation [16]

3.2

Present Legal Situation [16]

All combustion processes primarily produce nitrogen monoxide NO with a much smaller proportion of nitrogen dioxide NO2 (of the order of 5%). In the free atmosphere, i.e. at relatively low temperature, however, nitrogen monoxide is oxidized further to form nitrogen dioxide NO2. Owing to this oxidation, no difference is made between the two gases when emissions are concerned and they are referred to generally under the formula NOx (= NO + NO2 expressed as NO2), or nitrogen oxides. However, decisive for the NOx emission is the formation of nitrogen monoxide (NO) in the kiln system. Emission Limits Nm3dry = m3 at 273 K, 101300 Pa and 0% water Europe

200 - 1800 mg / Nm3

new plants / modification

500 mg / Nm3dry

existing plants

800 mg / Nm3dry

100% waste burning (17. BImSchV)

200mg / Nm3dry

USA

720 - 1100 mg/Nm3

US plants burning hazardous waste are regulated under BIF (Burners and Industrial Furnaces). Other © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:36 PM

Page 13

"Holderbank" - Cement Course 2000 plants do have a state permit defining certain parameters like NOx, SO2, CO and THC emission. The limits for these emissions are called emission standards. This standards are individually defined for each plant and usually represent the operating situation under certain conditions. Therefore, the US standards are different from the emission limits in Europe where emission limits are valid for a whole state or country. For comparison reason all emission limits/standards are indicated in mg/Nm3. The emission standards in the USA are usually not using mg/Nm3 but ppm, lb/tdry feed, gr/dscf, lb/1000lbgas, lb/hr, etc. To convert them into mg/Nm3 certain assumptions were necessary. All the above explained emission limits do include definitions how and when the compliance tests have to be carried out. It is, e.g. a very important difference whether the emission has to be measured continuously or not. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 4. NITROGEN INPUT INTO THE KILN SYSTEM

4.

NITROGEN INPUT INTO THE KILN SYSTEM

Nitrogen is introduced into the kiln system as molecular nitrogen (N2) in the combustion air (primary, secondary, tertiary) and as nitrogen compounds in the fuel. The quantity of the relevant N2 introduced into the kiln system is defined by the stoichiometric air required for the combustion plus excess air. The concentration of N2 in the air is always 78%. The quantity of fuel-N is defined by the fuel input and the nitrogen content in the fuel: Heavy oil:

700 - 1000 ppm by mass of N

Coal:

1000 - 4000 ppm by mass of N

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS

5.

BEHAVIOR OF NITROGEN IN THE PROCESS

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.1 NO Formation

5.1

NO Formation

NO formation only occurs at elevated temperatures (> 800°C). It is always connected with the combustion process. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.1 NO Formation / 5.1.1 Nitrogen Monoxide Formation Reaction Mechanism

5.1.1

Nitrogen Monoxide Formation Reaction Mechanism

The formation of nitrogen monoxide is not a simple process that can be described by a few equations. The complexity of the reactions involved has hitherto prevented the formulation of a conclusive theory regarding the formation of nitrogen monoxide NO. However, it appears to consist essentially of two phenomena, the products of which are referred to as "thermal NO" and "fuel NO". © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:36 PM

Page 14

"Holderbank" - Cement Course 2000 "Thermal NO" The "thermal NO" is produced by the oxidation of molecular nitrogen in the combustion air according to the formula: N2 + O2 → 2 NO (0) "Fuel NO" The "fuel NO" is produced by the oxidation of organically bonded nitrogen in the fuel. Formation of "Thermal NO" In the zone of combustion products that is after the flame front (oxidation zone), "thermal NO" is produced if the combustion gases remain for a sufficiently long time at temperatures above about 1600°C. This is determined by what is known as the Zeldovich mechanism according to the reactions: N2 + O• → NO + N• (K1) ; N2 + O• ← NO + N• (K2)

(1, 2)

N• + O2 → NO + N• (K3) ; N• + O2 ← NO + O• (K4)

(1, 2)

Here the speed is governed by that of the fastest reaction, i.e. the reaction between atomic oxygen (radical) and the nitrogen molecule. The rate of formation is therefore proportional to the concentration of atomic oxygen and molecular nitrogen. Assuming that combustion takes place in the presence of an air surplus, the following equation is obtained: (4)

d [NO ] ~ 2 • K 1 • [N2 ] • O • dt

[ ]

The pronounced dependence of K1 on temperature can be seen in Fig. 3. Thus, at high temperatures the equilibrium of the reaction is on the side of NO formation. In the flames of rotary cement kilns the atomic oxygen primarily comes from the thermal dissociation of O2: O2↔ 2 O•

(5)

Therefore, for the formation of NO the following equation is obtained:

d [NO ] = K • [N2 ] • O • dt

[ ]

Figure 3:

(6)

12

Dependence of K1 on temperature


6/23/2001 - 5:13:37 PM

Page 15

"Holderbank" - Cement Course 2000

The amount of nitrogen monoxide actually produced during technical combustion processes is a long way below equilibrium concentration (cf Fig. 4) owing to the marked dependence on temperature of the NO reaction and the relatively short time that it remains at this temperature. In air 50% of the equilibrium value is attained at temperatures around 2000°C but only after about 2.5 seconds. The dwell time of the gas in the flames of rotary cement kilns are obviously a whole order of magnitude below that. Thus, if the gases remain for a long time at high temperatures, the formation of NO is favored. Figure 4:

Equilibrium N2 + O2 → 2 NO

Hence, the formation of "thermal NO" is governed by the following parameters: ♦ Temperature ♦ Gas composition ♦ Dwell time at high temperature Formation of "Fuel NO" Fossil fuels contain varying proportions of nitrogen compounds: Heavy oil:

700 - 1'000 ppm by volume of N

Coal:

1’000 - 4'000 ppm by volume of N

Already during the pyrolysis of these fuels, i.e. at relatively low temperatures, the nitrogen compounds break off as secondary compounds, such as amines and cyanides, which are then oxidized by OH © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:37 PM

Page 16

"Holderbank" - Cement Course 2000 radicals or O2 to form nitrogen monoxide, or which react with nitrogen compounds (mainly NO) to form molecular nitrogen. The formation of NO from fuel nitrogen occurs almost regardless of how it is bonded, but is largely influenced by the amount of nitrogen contained in the fuel. It can be assumed that all fuel-bonded nitrogen compounds finally adopt a composition "I", where "I" may be either NH2 or atomic N. These are then converted into either NO or N2: I + OX → ... → NO + ...

(7)

I + NO → ... → N2 + ...

(8)

Hence, the formation of "fuel NO" is governed by the following parameters: ♦ The formation of NO depends on the quantity but not of the nature of nitrogen compounds contained by the fuel ♦ With increasing air surplus the proportion of nitrogen compounds in the fuel converted into NO increases ♦ Under sub-stoichiometric conditions it is possible for NO to be converted into N2. This takes place by combination of the NO with atomic nitrogen present in large proportions in the flame according to the formula: NO + N• → N2 + O•

(9)

♦ The conversion of nitrogen compounds in the fuel to NO depends to a large extent on the design of the burner of the precalciner. Here such operations as •

heating and distribution of drops or particles in the combustion air

•

driving off the volatile part

•

heterogeneous combustion

•

etc.

play a very important role Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.1 NO Formation / 5.1.2 NO-Decomposition Mechanism in the Combustion Process

5.1.2

NO-Decomposition Mechanism in the Combustion Process

Homogeneous Reaction NO reacts with hydrocarbon radicals according to equation 10. The product HCN reacts later like fuel-N and can form NO as well as N2. k10 CH x • +NO →  HCN + OH ( x −1)

(10)

For a significant NO-decomposition according to (10) high hydrocarbon concentration and low air factor (~0.6 - 0.9) are required. Also reactions between NO and HCN as well as ammonia from the fuel do have an influence on NO-decomposition. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:38 PM

Page 17

"Holderbank" - Cement Course 2000 Heterogeneous Reaction NO can also be reduced on catalytic active surfaces of solids outside of the flame. As catalyst can act coal and ash particles and metal oxides. Prerequisite for this reaction is the presence of CO or H2 in the exhaust gas. In case of coal particles also a gas-solid reaction between NO and the coal can decompose NO. The gas-gas reaction proceeds according to equations 11 and 12. k11 NO + CO  → 0.5 N2 + CO 22

(11)

k12 NO + H 2 →  0.5 N2 + H 2O

(12)

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.2 Formation of Nitrogen Monoxide in a Cement Kiln

5.2

Formation of Nitrogen Monoxide in a Cement Kiln

If the formation of nitrogen monoxide (NO) in a kiln has to be considered, it has to be distinguished between the formation of NO in the main firing system of the rotating part and its formation in a secondary firing system, if present. NO Formation in the Main Firing System (rotary part) In the firing system of a rotary kiln turbulent diffusion flames are used in which the greater part of the combustion air is only fed in after the fuel has been ignited (secondary air, proportion about 90%). As a result a severely sub-stoichiometric pyrolysis zone and flame front are produced. The nitrogen compounds in the fuel are therefore converted into NO to only a small extent. This means that only few "fuel NO" is produced, the nitrogen in the fuel is converted into N2. In the zone of the combustion products (flue gas) temperatures up to 1800°C are attained and there "thermal NO" is produced. Thus, in the flames of the main firing systems it is mainly "thermal NO" that is produced. NO Formation in Secondary Firing Systems In a secondary firing system the fuel fed in burns at much lower temperatures (800 to about 1200°C) than in the main firing system. This means that the NO produced in the secondary firing system cannot have formed thermally, i.e. from N2 and O2 of the combustion air. In other words, it is primarily "fuel NO" that is produced in a secondary firing system. Figure 5: Regions where NO formation occurs in a rotary kiln plant with cyclone preheater, calciner and tertiary air duct


6/23/2001 - 5:13:38 PM

Page 18


Kilns without secondary firing All kilns without secondary firing, i.e. wet process kilns, long dry process kilns and preheater kilns without riser duct firing, have one thing in common, viz. NO emission is determined exclusively by the conditions in the kiln burning zone. After leaving the burning zone, the kiln gases drop rapidly in temperature to a level at which the NO in the gas decomposes very slowly. Wet kilns are characterized by a specific heat consumption which is 1.5 to 2 times the specific heat consumption of a preheater kiln. This means a high specific amount of exhaust gas. On the other hand, the high specific combustion air consumption will also mean a somewhat lower secondary air temperature. This combined with the long material retention time in the burning zone should reduce the NOx concentration in the exhaust gas from the burning zone. SP kiln systems with riser duct firing In many SP kiln systems 10 - 20% of the fuel is fired into the riser duct. Measurements at several riser duct fired kiln systems indicate that firing coarse fuel (e.g. old tires) into the kiln riser duct will reduce NOx emission from the kiln system. This is probably explained by the fact that a large part of the fuel directly falls down into the kiln charge, creating a reducing atmosphere in the bottom part of the kiln back-end in which NOx from the burning zone is reduced. Conversely, when firing finely ground fuel into the kiln riser duct, the specific NOx content in the exhaust gas will often increase on ing through the riser duct. As the NOx emission from the kiln may also increase slightly due to an increased excess air rate the total NOx emission from the kiln system will often increase when starting up riser duct firing with finely ground fuel. Precalcining kiln systems In precalcining kiln systems with tertiary air duct, firing into the rotary kiln typically s for only 40 - 50% of the total heat consumption and the specific amount of combustion gases from the kiln burning zone is reduced proportionally. On the other hand, the NOx concentration in the kiln gas may be considerably higher than in preheater kilns. This is probably due to the shorter material and longer gas retention times in the precalciner kiln burning zone combined with a very high secondary air temperature. When examining the contribution from the calciner firing to the emission of NOx, we must distinguish between two basically different types of precalcining kiln systems, viz. the In-Line (ILC) type in which the kiln gas es the firing region of the precalciner and the Separate Line (SLC) type in which the © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:38 PM

Page 19

"Holderbank" - Cement Course 2000 kiln exhaust gas byes the firing region of the precalciner. ILC systems In these systems the fuel combustion in the calciner takes place in a mixture of kiln exhaust gas and hot air from the cooler (tertiary air). Some of the nitrogen in the fuel reacts with NO from the kiln exhaust gas while another part reacts with oxygen (from the tertiary air) to form NO. The result may be a net production as well as a net reduction of NO in the calciner. However, in most cases the calciner contributes a little to the NO emission. SLC systems In these systems the combustion in the calciner takes place in pure hot air. In the case of oil firing, NO production in the calciner is negligible, but when applying fuels containing nitrogen up to 50% of the nitrogen compounds in the fuel may be converted into NO. The specific NO production in the SLC calciner may be as high as 4 lb NO2/st (1400 mg NO2/Nm3). This was measured in a calciner fired with pet coke which has a high content of nitrogen and a low content of volatiles. The NO in the calciner exhaust gas is added to the NO in the gas from the rotary kiln which leaves this type of kiln system without being reduced. When fired with solid fuels, SLC systems must therefore be expected to generate somewhat higher NOx emissions than ILC systems. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation

5.3

Main Influencing Variables for NO Formation

Table 2:

NOx forming mechanisms in the kiln system

NO Formation

Main influencing variables ♦ temperature

thermal NO

♦ oxygen concentration

♦ residence time ♦ fuel nitrogen content

•

flame shape

•

temperature peaks in flame

•

secondary air temperature

•

burning zone temperature

•

flame shape

•

ignition point

•

burner momentum

•

excess air

•

recirculation

•

reducing zone

•

primary air component

•

swirl intensity

•

flame shape

•

kiln diameter

•

♦


6/23/2001 - 5:13:39 PM

Page 20

"Holderbank" - Cement Course 2000 ♦ ♦ oxygen concentration ♦ volatiles concentration in the fuel

fuel NO

♦ residence time

•

flame shape

•

excess air

•

recirculation

•

reducing zone

•

primary air

•

swirl intensity

•

flame shape

•

gas speed

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.1 Temperatures

5.3.1

Temperatures

In Chapter 3.1 it is shown that the NO forming reaction is accelerated exponentially with the temperature. The temperature of the combustion gas is defined by heat generated in the flame and the heat radiation from the burning zone. Temperature has a major influence on NO formation. Figure 8: gas

Influence of the sintering zone temperature on the NO concentration in the waste

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.2 Temperature Peaks [6]

5.3.2

Temperature Peaks [6]

Fig. 9 shows the increase in thermal NO formation due to temperature peaks in an ideal chemical reactor for different amplitudes of a given temperature behavior. For calculating the curves, first the NO concentrations for the temperatures T + ∆T and T - ∆T were calculated, averaged and then referred to the NO concentration for T . The subscript "L" in the diagram characterizes the combustion air temperature before the start of combustion. It appears from the diagram that the increase in NO formation becomes greater with increasing amplitude DT and decreasing average combustion air temperature. For practical purposes it is important that NO formation can increase by as much as 20 - 40 % even for very small amplitudes of the gas temperature, e.g. 100 K. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:39 PM

Page 21

"Holderbank" - Cement Course 2000 Temperature peaks arise more particularly if, in a given combustion chamber, the momentum and angle of exit of the swirl air and axial air of the rotary kiln burner cannot be optimally adjusted to each other or if short-term fluctuations in the fuel feed occur. Modern burners should therefore offer the greatest possible scope for varying their settings. Figure 9: Calculated increase in NO formation based on local or time-dependent temperature differences with the average combustion air temperature as parameter

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.3 Excess Air

5.3.3

Excess Air

Fig. 10 shows the behavior of NO concentration in the waste gas. The graph can be subdivided into two areas: A)

Air excess factor < 1.2. The NO concentration increases exponentially with the O2 concentration. This is according to the explanation in chapter 5.1 NO formation.

B)

Air excess factor > 1.2. The NO concentration is not anymore a function of O2. The high amount of excess air is cooling the flame, reducing the residence time of the gas in the kiln and diluting the exhaust gas. These 3 factors are reducing NO generation and concentration in the exhaust gas.

For most kiln systems the excess air factor is below 1.2. Therefore, oxygen concentration has a major influence on NO formation. Figure 10:

Influence of excess air on the NO concentration in the waste gas


6/23/2001 - 5:13:39 PM

Page 22


Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.4 Retention Time

5.3.4

Retention Time

The longer the combustion gas remains in the very hot part of the kiln (burning zone), the higher is the NO formation yield. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.5 Burner Operating Parameters

5.3.5

Burner Operating Parameters

The following burner operating parameters are influencing the flame characteristics (see [13]). For specific information about formulas and definitions of burner aerodynamics see chapter 6 report PT 96/14078/E. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.5 Burner Operating Parameters / 5.3.5.1 In-flame Air Level at Ignition

5.3.5.1

In-flame Air Level at Ignition

A minimum of air shall be entrained into the flame prior to ignition. This can be achieved by a low primary air input and the optimum use of an internal recirculation zone generated by a bluff body and/or swirl. Figure 11:


6/23/2001 - 5:13:40 PM

Page 23

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.5 Burner Operating Parameters / 5.3.5.2 Total Axial Momentum

5.3.5.2

Total Axial Momentum

Total axial momentum affects the overall entrainment into the flame jet. In general higher axial momentum result in enhanced mixing and higher NOx emission levels. For mono channel firing the axial momentum can be observed as a single parameter but for multi channel types a change in axial momentum also influences the tangential momentum. Figure 12:

Influence of Total Axial Momentum on NOx for Mono Channel Burners

From the Cemflame I research study it was finally concluded, that the total axial momentum should be in the range of 3 up to max. 7 N/MW. This matter of fact however can be confirmed by the old rule of thumb, which states that the kinetic energy of the primary air jet should be kept constant within certain limits. Applied for a typical kiln system, this formula illustrates as follows: Figure 13: Basic Data: Production 3000t/d, Heat consumption 3140kJ/kgc, CV Coal 27.2MJ/kg

Figure 14:

Influence of Total Axial Momentum on NOx for a Pillard Multi Channel Burner


6/23/2001 - 5:13:40 PM

Page 24


Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.5 Burner Operating Parameters / 5.3.5.3 Tangential Momentum and Swirl Level on the Swirling Channel

5.3.5.3

Tangential Momentum and Swirl Level on the Swirling Channel

The second parameter affecting the entrainment into the flame is the tangential momentum. In general higher tangential momentum results in more rapid heat release in the near burner zone and higher NOx emission levels. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.5 Burner Operating Parameters / 5.3.5.4 Swirling and Axial Air Amount, Distribution and Velocity

5.3.5.4

Swirling and Axial Air Amount, Distribution and Velocity

One of the main parameters affecting the tangential momentum is the swirling air and axial air distribution and injection velocities. In combination the product massflow (kg/s) times velocity (m/s) forms the momenta (N) on the different channels. It can be noticed that both swirling air velocity and amount may have a different influence on the flame characteristics. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.6 Evaluation of Characteristical Burner Data (CETIC Working Group)

5.3.6

Evaluation of Characteristical Burner Data (CETIC Working Group)

During the meetings 1995/96 of the CETIC working group focusing on kiln burners a database containing a total of 42 kiln burners could be established. In particular it was one of the main topics to investigate the NOx behavior of the individual kiln burner systems. Due to the heterogeneity of the kiln and cooler systems as well as the different fuels used, direct comparison and correlation of the existing data is limited. However certain operational guidelines and tendencies can be given. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.6 Evaluation of Characteristical Burner Data (CETIC Working Group) / 5.3.6.1 Burner Settings / Operational Figures / Correlations

5.3.6.1

Burner Settings / Operational Figures / Correlations

Mono Channel Burner The evaluation of a total of 12 industrial mono channel burners is showing the following application © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:40 PM

Page 25

"Holderbank" - Cement Course 2000 range: Primary air ratio

% Amin.

13 - 30

[%]

Injection velocity

v

60 -100

[m/s]

Specific axial momentum

Gax

4.5 - 8.5

[N/MW]

Percentage of petcoke burned

% Petcoke

0 - 100

[%]

Kiln inlet NOx at 0% O2

NOx @ 0% O2

1750 - 3400

[mg/Nm3]

Secondary air temperature

Tsec

550 - 1000

[°C]

Primary air ratio High primary air ratios must be avoided. This has negative effects both on kiln heat consumption and on NOx emissions. The CETIC data correlation for mono channel burners, primary air ratio vs NOx emission, clearly showed a rise in NOx at higher primary air ratios. Figure 15:

Multi Channel Burner

Primary air ratio

% Amin.

6 - 19

[%]

Percentage axial air

1.9 - 7.2

[%]

Percentage radial air

1.25 - 9.8

[%]

Percentage transport air

2.3 - 5.3

[%]

Injection velocity axial air

vax

90 - 300

[m/s]

Injection velocity radial air

vrad

60 - 130

[m/s]

Injection velocity transport air

vtr

14 - 38

[m/s]

Specific axial momentum

Gax

3.6 - 7.4

[N/MW]

Percentage of petcoke burned

% Petcoke

0 - 100

[%]

Kiln inlet NOx at 0% O2

NOx @ 0% O2

1160 - 3350

[mg/Nm3]

Secondary air temperature

Tsec

800 - 1010

[°C]


6/23/2001 - 5:13:41 PM

Page 26

"Holderbank" - Cement Course 2000 Specific axial momentum For multi channel burners the impact of the specific axial momentum on NOx emissions could be confirmed (see following graph). The specific axial momentum Gax [N/MW] is in the range of 3.6N/MW up to 7.4 N/MW - very good coincidence with the 3 - 7 N/MW indicated in the Cemflame 1 research report. Figure 16:

Radial air velocity From the CETIC test results further can be observed, that with increased radial velocity NOx emissions tend to be higher. This can be explained with a more rapid heat release in the near burner zone due to a higher tangential momentum. Figure 17:

Swirl number The CETIC attempt to correlate the swirl number with respective NOx emissions was not very successful. It is however noticeable, that the Pillard burners showed by far the highest swirl numbers. Figure 18:


6/23/2001 - 5:13:41 PM

Page 27


Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 5. BEHAVIOR OF NITROGEN IN THE PROCESS / 5.3 Main Influencing Variables for NO Formation / 5.3.6 Evaluation of Characteristical Burner Data (CETIC Working Group) / 5.3.6.2 Influence of Cooler System on NOx Emissions

5.3.6.2

Influence of Cooler System on NOx Emissions

The following graph from reference [14] is showing the important effect of the cooler system on NOx emissions. The grate cooler generating a hot, comparatively clean secondary air has considerable higher NOx output than the planetary cooler with its dusty secondary air, supposing identical kiln system for both cooler systems. Mean value and standard deviation of measured NOx emission from different types of kiln systems. Figure 19:

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 6. NO EMISSION REDUCTION POSSIBILITIES

6.

NO EMISSION REDUCTION POSSIBILITIES

To reduce the NO emission from a pyroprocessing system to a certain controlled level, three basically different methods are available: ♦ Maintain the existing process while reducing the nitrogen input into the system ♦ Modify the existing process (primary reduction measures) © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:41 PM

Page 28

"Holderbank" - Cement Course 2000 ♦ Maintain the existing process while adding a separate gas cleaning unit for the exhaust gas (secondary reduction measures) Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 6. NO EMISSION REDUCTION POSSIBILITIES / 6.1 Reduction of Nitrogen Input

6.1

Reduction of Nitrogen Input

It is not economical to reduce the nitrogen content in the combustion air. However, a reduction of fuel-N for the secondary or precalciner firing may be feasible under certain conditions. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 6. NO EMISSION REDUCTION POSSIBILITIES / 6.2 Primary Measures

6.2

Primary Measures

Primary measures are all actions which directly influence the burning process. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 6. NO EMISSION REDUCTION POSSIBILITIES / 6.2 Primary Measures / 6.2.1 Kiln / Clinker Cooler

6.2.1

Kiln / Clinker Cooler

♦ The criteria for a low NO generation are: ♦ constant fuel and kiln charge flow (short and long term) ♦ constant fuel and kiln charge composition ♦ constant secondary air flow and temperature ♦ lower burning zone temperature i.e. higher free lime ♦ lower LSF i.e. lower combinability (sintering) temperature ♦ lower flame temperature by •

dust injection

•

water injection

•

alternative fuels with high H2O content

♦ flame front closer to the burner by •

bluff body

•

higher volatile coal

♦ low excess air factor ♦ lower primary air i.e. indirect firing, low primary air burner ♦ optimum distribution of primary air i.e. customized multi channel burner ♦ short retention time of the exhaust gas in the flame and the kiln ♦ minimum temperature fluctuations in kiln and cooler To satisfy the first point an accurate dosing system and fuel transport is required. A constant fuel quality is difficult to achieve, especially if waste fuel is used. Therefore, additional effort is needed for homogenization, preparation and analysis of the fuels. The amount of heat from the secondary air depends mainly on operating characteristics of the clinker © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:42 PM

Page 29

"Holderbank" - Cement Course 2000 cooler. The new grate plates (for the recuperating zone) developed during the last years, help to stabilize the cooler operation and the heat input into the kiln. A constant kiln and cooler operation is a prerequisite for optimizing of the excess air factor without reducing conditions for the clinker burning. The excess air factor (l) for the main burner is always above 1. NOx reduction measures at the burner should achieve a reduction of temperature peaks and low oxygen content in the flame. Temperature peaks can occur if at a multi channel burner air volume and exit angle of swirl and axial air are not adjusted properly and if the fuel flow is fluctuating. Therefore, the burner should have a wide adjusting range. The optimum operating point has to be determined with systematic long time tests. The most important factor for NO generation is the ignition distance (= distance between burner exit and ignition of the fuel). An extension of the distance is increasing the NO generation. The reason for this behavior is the degree of total air (O2) mixed with the fuel which is higher for longer distances. To reduce the total air mixed into the fuel, primary air flow and total burner momentum should be kept as low as possible. The operation of LINKman is at most effective when burners are operated near their optimum momentum and can in fact lead to lower NO levels, due to lower burning temperatures via better control. To reduce the temperature of the secondary air the tertiary air should be extracted from the cooler at the kiln hood. To shorten the retention time of the exhaust gas in the hot kiln, the gas speed in the kiln should be as high as possible. The limits for the gas speed are dust circulations and mechanical stress for the refractory materials. The upper limit for the specific fuel heat input is 7 MW / m2 which is about equal to a specific exhaust gas flow of 2.5 kg/m2s. The minimum NO concentration with an optimized low NOx burner which can be achieved today is about 800 - 1000 mg NO2 / Nm3. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 6. NO EMISSION REDUCTION POSSIBILITIES / 6.2 Primary Measures / 6.2.2 Secondary Firing / Multi-Stage Combustion

6.2.2

Secondary Firing / Multi-Stage Combustion

Mainly fuel-N is contributing to the NO formation (fuel-NO). It is possible to design the secondary firing in such a way that only little NO is produced and that a portion of the NO from the kiln is reduced. This can be achieved with a multi stage combustion [8]. Multi-stage combustion has turned out to be a suitable method for conventional and also for highly sophisticated clinker burning processes. In the first combustion stage which extends over the sintering zone and the transition zone in the rotary kiln, combustion takes place in an oxidizing atmosphere (excess air coefficient > 1) to ensure good clinker quality. The nitrogen oxides which are inevitable formed in this high temperature zone are partially decomposed in a second combustion stage which has, at least locally, a reducing atmosphere (excess air coefficient < 1). Figure 20:

NOx reduction by Multi Stage Combustion


6/23/2001 - 5:13:42 PM

Page 30


By introducing fuel through a burner in the kiln inlet zone a reducing environment is set up in this second combustion stage. The resulting intermediate products from the consecutive reactions of combustion act as reducing agents for NO created in the sintering zone and at the same time prevent the formation of more NO. This reaction pattern is shown diagramatically in Fig. 12 for a precalciner plant of the PREPOL-AS type. Multi-stage combustion is logical in precalciner plants in order to avoid renewed formation of nitrogen oxides in the calciner from nitrogen in the fuel. A part of the precalcining fuel is introduced in the kiln inlet to form a reducing zone by arranging an air deficiency (< 1). The rest of the precalcining fuel is also supplied to the calciner, at least partially, in a reducing zone. This fuel burns here under sub- stoichiometric conditions (excess air coefficient < 1) and thus suppresses formation of NOx from the nitrogen in the fuel. In a fourth stage the unburned flue gas constitutients from the reducing zone are fully oxidized by supplying hot combustion air, whereby a turbulence generating gas flow in the calciner serves to enhance the burnout process. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 6. NO EMISSION REDUCTION POSSIBILITIES / 6.2 Primary Measures / 6.2.3 Possible Negative Side Effects of Primary Measures

6.2.3

Possible Negative Side Effects of Primary Measures

Kiln burner Temperature reduction: ♦ reduction of production capacity ♦ higher power and heat consumption ♦ clinker quality Oxygen (excess air, primary air) reduction: ♦ clinker quality ♦ additional CO formation ♦ additional SO2 volatilization ♦ additional TOC emissions Secondary combustion Lower fuel-N concentration: ♦ higher fuel cost Staged combustion: © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:42 PM

Page 31

"Holderbank" - Cement Course 2000 ♦ additional CO formation ♦ additional TOC emissions ♦ difficult to control Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 6. NO EMISSION REDUCTION POSSIBILITIES / 6.3 Secondary Measures

6.3

Secondary Measures

Secondary measures are exhaust gas treatments mainly SNCR (selective non-catalytic reduction) or SCR (selective catalytic reduction). In some cases combustion of coarse fuel (tires) in the kiln inlet is also considered as a secondary measure. Because of the reducing condition of the waste fuel combustion, NO is reduced to N2. This reaction is called NSNCR (non-selective non-catalytic reduction). The most efficient secondary measure which is already in operation in several kilns is the SNCR with NH3. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 6. NO EMISSION REDUCTION POSSIBILITIES / 6.3 Secondary Measures / 6.3.1 The Selective Non-Catalytic Reduction

6.3.1

The Selective Non-Catalytic Reduction

From tests in cement works it is known that ammonia, when injected into certain temperature zones of the cement kiln is able to reduce a large proportion of the nitrogen monoxide. In this chapter the NH3-injection is described. The Reaction Mechanism The desired process of reducing nitrogen monoxide (NO) by ammonia (NH3) is initiated by dissociation of the injected ammonia. At room temperature ammonia is stable, but at roughly 600 to 800°C a marked thermal decomposition is initiated by the reaction: NH•2 + O H• → NH2 + H2O

(13)

As the reaction proceeds, the NH2 radical is responsible for the reaction of nitrogen monoxide (NO). N H•2 + NO → N2 + H2O

(14)

The Influencing Factors Temperature Window Reduction of nitrogen monoxide (NO), defined as the decrease in NO relative to the original NO, is a function of the temperature where the ammonia is injected and the reaction is made. As Fig. 13 shows, a high NO reduction is only achieved in a narrow temperature band. This is generally referred to as the "temperature window". In a normal flue gas from a cement kiln the maximum reduction of nitrogen monoxide (NO) is attained at about 950°C. In a cement kiln at the most the temperature zone between 900 and 1100°C is technically "accessible". © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:43 PM

Page 32

"Holderbank" - Cement Course 2000 This means that the temperature zone is located in the preheater and this is where the ammonia can be injected. For this injection only the "lower" (left-hand) part of the NO reduction curve in Fig. 13 can be used. Figure 21:

NO-Reduction (Reaction-kinetic Model Calculation)

Dwell Time The formation of the NH2 radical from the ammonia (equation [?]) is dependent on the time. When ammonia is injected in to the cement process, this dwell time is fixed by the process. In any case the injection points in a cement kiln must be chosen that this dwell time is as long as possible. Ammonia Slip The proportion of injected ammonia that does not decompose to NH2 radicals is called the NH3 slip. This proportion leaves the reaction zone and travels with the flue gas to colder regions, during which a small proportion can decompose to NH2 radicals. The greater part of the slip, though, will remain stable as ammonia and, following various adsorption processes in the preheater, the cooling tower, the raw mill, or the electrostatic precipitator, will finally be emitted through the chimney as gaseous ammonia or adsorbed by aerosols. Because only the "lower" (left-hand) part of the NO reduction curve in Fig. 2 can be used, in any case a noticeable NH3 slip in this temperature zone occurs. Injection Rate The nitrogen monoxide reduction rate rises with increased NH3 injection rate, but work tests have shown that a greater injection rate will produce a greater ammonia slip. In cement kilns ammonia should only be injected up to a mol ratio of 1.5 at the most, or in extreme cases 2. [NH3]/[NO0]< 1.5

NO0 → N= without reduction

Form of Injected Ammonia Pure Ammonia Ammonia is already fluid at low pressures (15°, 7.28 bar). This substance can therefore be stored in a pressurized tank and pumped as a liquid. The entire ammonia system must be dimensioned for a pressure of 20 to 30 bar, which is certainly not optimal and can cause problems with the permission of such a tank in a cement plant. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:43 PM

Page 33

"Holderbank" - Cement Course 2000 Ammonia Water For an ammonia injection in a cement kiln ammonia water (NH4OH solution) should be used. In this solution the greater part of the ammonia is present in hydrated form as NH3H2O and only a very small proportion has dissociated to ammonium (NH4+) and hydroxide ions (OH-). When heated rapidly from ambient temperature to the reaction temperature, the solution decomposes into water (H2O) and ammonia (NH3). Thus ammonia water has the same effect as pure ammonia but the problems with transport, storage, handling, etc. are much less. Alternatives to Ammonia It is postulated and proved by works tests that the reduction of the nitrogen monoxide (NO) is effected via the NH2 radical. This means that all substances capable of supplying an NH2 radical may be used for reduction of NO. A component of this kind is, for instance, urea CO(NH2)2. This substance decomposes approximately in the same temperature zone, thereby producing NH2 radicals but unfortunately also a CONH2-radicals. That means urea decomposes according to reaction [4] and not according to reaction. CO (NH2) 2 → CO + 2 (N H•2)

(15)

CO (NH2) 2 → CO + N H•2 + NCON H•2

(16)

About the behavior of the CONH2-radical up to now nothing is know, but it is possible that cyanide compounds are produced in the kiln system. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 6. NO EMISSION REDUCTION POSSIBILITIES / 6.4 Effectiveness of NOx Reduction Measures [9]

6.4

Effectiveness of NOx Reduction Measures [9]

Figure 22: Control Technology CM LNB

Comparison of NOx Control Technologies for Cement Kilns Technical Feasibility

Potential NOx Reduction

Relative Cost

15 - 30%

Low

Medium (both kiln types)

Effect on Effect on Other Clinker Quality Emissions May be adverse

CO, THC, SO2 may increase

Improved •

15 - 30%

SAC

High (precalciner kilns)

20 - 50%

Low

None

CO, THC may increase

SNCR

Medium (precalciner kilns)

40 - 70%

Medium

None

Potential for NH3, PM10 emissions

Medium (all kilns)

20 - 30%

Low

None

CO, THC, SO2 may increase

NSNCR


Low

•

High (both kiln types)

•

6/23/2001 - 5:13:43 PM

CO, SO2 may increase

May vary with • may vary installation with installation

Page 34


CM

= Combustion Modifications

LNB

= Low NOx Burner

SAC

= Staged Air Combustion

SNCR

= Selective Non-Catalytic Reduction

NSNCR

= Non-Selective Non-Catalytic Reduction

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 7. EXAMPLES OF NOX EMISSION REDUCTION

7.

EXAMPLES OF NOX EMISSION REDUCTION

A collection of short descriptions of plants and their measures against NOx emissions is enclosed. Everybody is welcome to contribute to this collection. NOx emission reduction Plant:

Siggenthal (SG)

Capacity:

2000 t/d (design), 1900 t/d (standard)

Fuel type

Fuel oil, dried sewage sludge, complete tires [1]

Plant description:

Kiln with 4-stage preheater

Supplier/equipment:

Polysius kiln and preheater (Dopol), Fuller grate cooler

Initial NOx emission problem:

Very high NOx emissions of up to 2800 mg/Nm3dry (in direct operation) were reported in 1987. (LRV-limit = 1500 mg/Nm3dry, since 1991 LRV-limit = 800 mg/Nm3dry ) [LRV = Swiss clean air act]

Solutions investigated:

In 1988 trials to reduce the NOx emissions by injection of Ammonia-water in the raiser duct were carried out. Reductions of up to 46% were reached. The problem of this reduction method was the high NH3 emission due to the NH3 in the raw meal, which was already higher than the emission limit. So any small additional NH3 amount would not be acceptable. [3] Using a Pyrojet low-NOx burner, the emissions in 1990 were around 1500 mg/Nm3dry. [2] SG had a project to burn sewage sludge containing Hg and at the same time the NOx and SO2 emissions where much too high. To solve these problems, a 3-stage waste gas cleaning system was foreseen. In 1990 the system was successfully tested in a pilot plant with an Ammonia-water injection into the riser duct as well as an active coke filter. Using this SNCR, NOx could be reduced to N2 and H2O with ammonia injection. In these trials a reduction of the NOx emissions by more than 60% and hence below 800 mg/Nm3dry was reached.


6/23/2001 - 5:13:44 PM

Page 35

"Holderbank" - Cement Course more 2000than 60% and hence below 800 mg/Nm3dry was reached. Solution realised:

Based on the experiences of the pilot plant, a denitrification system, based on SNCR was built. This system is followed by the kiln EP and a POLVITEC (Polysius Environmental Technology) active coke scrubber, which is mainly filtering out SO2 and Mercury but also other pollutants like heavy metals, eventually occurring NH3 from the denitrification and organics. The whole system was successfully commissioned in 1994. Investment cost: 30'000'000 CHF Operating cost: 3.3 CHF/t cli

Emissions reached:

< 800 mg/Nm3dry [4]

Literature:

[1]

ATR, Annual Technical Report 1994,"Holderbank"

[2]

Stenger, Dr. R., Informationsveranstaltung der PCW Siggenthal zum Thema Klärschlamm-Verbrennung / Abgas -reinigung, HMB Bericht MA 92/93/D, VA-Dok: SG, Reg. 2

[3]

Waltisberg, J., Die Reduktion der NOx-Emission durch Eindüsung von Ammoniak in den Vorwärmer, HMB Bericht MA 88/10686/D, VA-Dok: SG, Reg. 2

[4]

Effektive Emissionsminderung bei Einsatz von Sekundärbrennstoffen im Zementdrehofen von "HCB Siggenthal, Dr. D. Rose, Dr. L. Brentrup, Krupp Polysius

Figure 22:

Integration of a POLVITEC-Filter in a cement plant

Figure. 23: Effect of SNCR of NOx at the Siggenthal plant. The NOx emission is controlled to below 800 mg/Nm3dry


6/23/2001 - 5:13:44 PM

Page 36

"Holderbank" - Cement Course 2000 NOx emission reduction Plant:

Untervaz (UV)

Capacity:

1900 t/d (standard)

Fuel type:

Coal, fuel oil; alternative fuels as dried sewage sludge, waste oil, distillation residue, plastics [1]

Plant description:

Kiln with 4-stage-suspension preheater and planetary cooler (kiln III)

Supplier/equipment:

KHD kiln, preheater and cooler


In January 1985 NOx emissions of 770 mg/Nm3dry were measured. After changing the original Pillard burner to a new Pyrojet burner, and additional changings on the lining (dam ring), in June 1985 a NOx emission 360 mg/Nm3dry was reported. [2]. In this time, only coal was used as fuel. Later, using a mixture of coal and oil, the flame was not any more as stable as before, and the NOx emission became higher. During measurements in 1989 for the office of environment the following NOx emissions were measured: [3] 880 mg/Nm3dry in compound operation 950 mg/Nm3dry in direct operation (LRV-limit = 1500 mg/Nm3dry, since 1991 LRV-limit = 800 mg/Nm3dry ) [LRV = Swiss clean air act]


In 1990 the reduction of NO by injection of Ammonia-water or urea was tested at different locations in the preheater tower. By injection of Ammonia-water in the raiser duct on stage 4 of the heatexchanger, a NO reduction of up to 42 % of the initial 840 mg/Nm3dry could be achieved [4]. After these short trials, a further test to add Ammonia-water to the preheater has been carried out in 1991. The achieved reduction was about 50 %, depending also on the ratio NH3/NO, i.e. approx. to 400 - 500 mg/Nm3dry. Compared to the addition of urea, the achievable reduction with Ammonia-water was twice as high.[5] The influence of water in the waste oil was investigated in 1992. Without negatively influencing the temperature of the sintering zone, a maximum of 5.7 g H2O/kg clinker could be injected, which resulted in a NO-reduction of 20 25%. [6] In 1993 a test to reduce NO selective and non-catalytic with pure hydrogen was carried out at temperatures between 600 and 1600 °C, without success. [7]

Solution realised:

Actually the NOx emissions are kept at a low level due to the low-NOx-burner and the water contained in the waste oil and in distillation residues. Additionally the Linkman control as well as a rather high CO concentration and the dusty atmosphere in the burning zone due to the planetary cooler contribute to a low NO-level.

Emissions reached:

In spring 1993 the following NO emissions of the kiln (calculated as NO2) have been measured: [8] 540 mg/Nm3dry in compound operation 600 mg/Nm3dry in direct operation The averaged values of 1994, measured after the heatexchanger, were in the same range.

Further Optimisation:

Is actually not necessary. If ever it would be necessary, the possibility of adding Ammonia-water to the preheater could be envisaged again.


6/23/2001 - 5:13:44 PM

Page 37

"Holderbank" - Cement Course 2000 Literature:

[1]


[2]

Waltisberg, J.: NOx-Messungen im Werk Untervaz, HMB Bericht VA 85/5230/D

Figure 24:

[3]

Waltisberg, J.: Emissionsmessungen für das Amt für Umweltschutz des Kantons Graubünden, HMB Bericht VA 90/5617/D

[4]

Waltisberg, J.: Nichtkatalytische Reduktion der Stickoxide über Salmiakgeist und Harnstoff - Kurzversuche im Werk, HMB Bericht VA 90/5698/D, VA-Dok: UV, Reg. 2A

[5]

Waltisberg, J.: Emissionsmessungen mit dem Massenspektrometer V+F CI-MS500, HMB Bericht VA 91/59/D, VA-Dok: UV, Reg. 2A

[6]

VA Datenbank, Blatt Nr. 1397

[7]

Waltisberg, J.: Selektive nichtkatalytische Reduktion von Stickoxiden mit reinem Wasserstoff, HMB Bericht VA 93/4096/D, VA-Dok: UV, Reg. 2A

[8]

VA Datenbank, Blatt Nr. 1428

NOx-Emissions BCU (kiln #1)

NOx emission reduction Plant:

Rekingen (RK)

Capacity:

2'200 mtpd (design), 2130 mtpd (standard)

Fuel type:

Coal, fuel oil, waste timber

Plant description:

4-stage-suspension preheater kiln

Supplier/equipment:

Polysius kiln and preheater


NOx emissions used to be very high in the past, and have not frequently been measured. In about 1984, the systematic observations and measurements of these emissions was started. As an example, in 1985 NOx emissions of about 1800 mg/Nm3 (based on 3 % O2) were measured. [1] (LRV-limit = 1500 mg/Nm3dry, since 1991 LRV-limit = 800 mg/Nm3dry) [LRV = Swiss clean air act]


6/23/2001 - 5:13:45 PM

Page 38

"Holderbank" - Cement Course 2000 [LRV = Swiss clean air act] Solutions investigated:

Initially the influences of different parameters on the existing plant have been investigated, as for example the temperature of the burning zone, the amount of primary- and secondary air, coal as well as raw meal [1]. In 1990 the actual NOx emissions were reported as 1'200 mg/Nm3dry in direct operation and 950 mg/Nm3dry in compound operation. These values have been below the actual valid LRV-limit of 1'500 mg/Nm3dry. Due to a regulation of the state of Aargau, a further reduction of the total NOx-emissions from 1200 t/year to about 300 t/y was required. It was expected to reach this reduction by installing a new Pyrojet burner (awaited REDUCTION OF ABOUT 30 - 40 %) and a additional denitrification based on SNCR (awaited reduction of about 60%) [2]. Through the installation of a new Pyrojet low-NOx-burner in 1990, the NOx-emissions were reduced to around 800 mg/Nm3dry. The denitrification has then first been investigated in trials, by adding liquid ammonia or urea to the preheater. The best results in the trials have been achieved, adding liquid ammonia into the raiser duct between preheater stage 3 and 4. Depending on the NH3/NO ratio NOx-reductions of up to around 50% could be detected [3] Due to unstable burning characteristics (design problem) which lead to higher NOx emissions, the Pyrojet low-NOx burner was exchanged in 1993 again to a Pillard 3 -channel burner (same type as earlier).[4] With this burner NOx emissions of 720 mg/Nm3dry could be reached.

Solution realised:

In 1994 a 4-channel Rotaflam burner was installed, mainly to be able to use waste timber as alternative fuel.

Emissions reached:

With the Rotaflam burner the NOx emissions were reduced by 10 20 % to an average value of 650 mg/Nm3dry.

Literature:

[1]

Waltisberg, J.: Untersuchung der NOx-Bildung im Ofen von Rekingen, Bericht VA 85/5166/D, VA-Dok: RK, Reg.17

[2]

Waltisberg, J.: Cementfabrik "Holderbank" AG, Rekingen, Reduktion des Stickoxid-Ausstosses, Bericht VA 90/5683/D, VA-Dok

[3]

Waltisberg, J.: Cementfabrik "Holderbank" AG, Rekingen, Stickstoffminderung durch Einbringung bestimmter Stoffe in den Vorwärmer, Bericht VA 90/5746/D, VA-Dok

[4]

Hasler, R.: HCB Rekingen, Brennervergleich Pyrojet Pillard-Dreikanal, Grundsätzliche Ergebnisse, Aktennotiz VA 93/16/D, VA Dok: RK, Reg. 2A

NOx emission reduction Plant:

Hardegsen (HD)

Capacity:

1'086 mtpd (standard)

Fuel type:

Coal (>98%), fuel oil, natural gas, landfill gas [1]

Plant description:

4-stage-suspension preheater kiln with grate cooler

Supplier/equipment:

MIAG kiln and Fuller cooler


6/23/2001 - 5:13:45 PM

Page 39

"Holderbank" - Cement Course 2000kiln and Fuller cooler Supplier/equipment: MIAG Initial NOx emission problem:

Until 1989 the NOx emissions using a Pillard VR-K3 three chanel burner were in the range of 1300 mg/Nm3dry (based on 10 % O2) [2,3]. (TA Luft-limit = 1800 mg/Nm3dry, since 1991 the limit is 800 mg/Nm3dry for old plants and 500 mg/Nm3dry for new plants.)


Different low-NOx burners were investigated. Finally the decision for a Pillard Rotaflam burner was influenced by the lower investment costs, the use of the existing pipe lines and the entire burner suspension system and the fact, that one of the existing fans could be reused.

Solution realised:

In 1990 a Rotaflam low-NOx burner was installed and is operated since then with good experience.

Emissions reached:

The NOx emissions could be reduced by about 22% under comparable conditions to 1004 mg/Nm3dry in the acceptance tests.

Literature:

[1]

ATR, Annual Technical Report 1994, "Holderbank"

[2]

Waltisberg, J.: NOx Reduktion im Werk Hardegsen, Aktennotiz VA 89/53/D, VA-Dok: HD, Reg.2

[3]

Adam, G.: Reducing NOx at Nordcement with a Rotaflam burner system, International Cement Review, July 1992, p.60/61

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of NOx-Emissions / 8. LITERATURE

8.

LITERATURE

[1]

Ullmann's Encyclopedia of Industrial Chemistry, Vol. A25 1994 VCH, 3-527-20125-4

[2]

Controlling Nitrogen Oxides, Nitrogen No. 197, May June, 1992

[3]

NOx Reduction in the Cement Industry by Application of Multi-Stage Combustion (MSC) and Selective Non-Catalytic Reduction (SNCR) Techniques, Dr. L. Bretrup, Krupp-Polysius, Cemtech April, 1991

[4]

An Overview of the Formation of SOx and NOx in various Pyroprocessing Systems, F.L. Smidth, Peter Bechtoft Nielsen, Ove Lars Jepsen, IEEE, May 1990

[5]

Stockstoffoxide NOx, Bildung im Zementofen und Reduktionsmöglichkeiten, NOx gerechte Konstruktion für den Ofen LD 11, U. Fankha, VA 92/6086/D

[6]

Reduction of NOx Emission in Cement Clinker Burning, A. Scheurer, VDZ, ZKG No. 3/1988


6/23/2001 - 5:13:45 PM

Page 40

"Holderbank" 3/1988 - Cement Course 2000 [7]

NOx Minderung durch Einsatz eines Stufenbrenners mit Rauchgasrückführung vom Vorwärmer, H. Xeller, ZKG 40 (1987) H.2, S. 57 - 63

[8]

Brennstoffstufung ein wirksames Mittel zur Nox-Emissionsminderung, ZKG 42 (1989)

[9]

Cement Kiln NOx Control, A.T. MacQueen and others, Radian Corporation California, 0-7803-0960-X/93, IEEE 1993

[10]

Flames "Semper Sursum", Tom "La Flamme" Lowes

[11]

International Flame Research Foundation (IFRF), Ijmiden Cemflame Consortium, VA 92/50/D, F. Schneider, 1992

[12]

Activities of VDZ Committee "NOx reduction", ZKG No. 1/88, J. Kirsch, A. Scheurer

[13]

The effect of burner design and operation and fuel type of cement kiln falmes, IFRF Research report CEMFlAME1, W.L. van de Kamp / J.P. Smart

[14]

Die SO2 - und NOx - Emissionen bei modernen Zementdrehofenanlagen mit Blick auf zukünftige Verordnungen, P.B. Nielsen

[15]

Die Bedeutung der 17. Verordnung zur Durchsetzung des BundesImmissions-schutzgesetzes (17. BImSchV) für die Zementindustrie (Verordnung über Verbrennungsanlagen für Abfälle und ähnliche brennbare Stoffe in der Bundesrepublik Deutschland) J. Waltisberg, HMB, Verfahrenstechnische Abteilung; "Holderbank" NEWS 2/91; 1991

[16]

Die Bedeutung der 17. Verordnung zur Durchsetzung des Bundes Immissions-schutzgesetzes (17. BImSchV) für die Zementindustrie (Verordnung über Verbrennungsanlagen für Abfälle und ähnliche brennbare Stoffe in der Bundesrepublik Deutschland) J. Waltisberg, HMB, Verfahrenstechnische Abteilung; "Holderbank" NEWS 2/91; 1991


6/23/2001 - 5:13:46 PM

Page 41

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions

Sources and Reduction of SO2-Emissions P. Kutschera 1. Introduction 2. Chemical and physical Properties and environmental aspects of some Sulfur compounds 3. SO2 Emission Limits / Normal Emission 4. Sulfur Input into kiln system [4] [6] 5. Behavior of S-Compounds in the Process 6. SO2-Emission Reduction Possibilities 6.1 Reduction of Sulfur Input into the System 6.2 Modification of the Existing Process 6.3 Secondary Reduction Measures 7. Examples of SO2 Emission Reduction 8. Literature

Summary: The SO2 emission of a cement plant depends on the ♦ type of the kiln ♦ quality of the raw material and fuel ♦ operating conditions of the kiln and the raw mill system ♦ secondary SO2 reduction measures To reduce the SO2 emission from a pyroprocessing system, three basically different methods are available: ♦ Maintain the existing process while reducing the sulfur input into the system ♦ Modify the existing process (primary reduction measures) ♦ Maintain the existing process while adding a separate gas cleaning unit for the exhaust gas (secondary reduction measures) With today's technology it is possible to reduce the SO2 emission to an acceptable level. The main methods are SO2 absorption with Ca(OH)2 in the preheater or in a separate scrubber and adjustments of the raw material. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 1. INTRODUCTION


6/23/2001 - 5:13:46 PM

Page 42

"Holderbank" - Cement Course 2000 1.

INTRODUCTION

SO2 was one of the first air pollutant with which the public made very negative experiences. Mainly SO2 but also other pollutants from coal fires in the city of London were responsible for the death of 4000 people between December 5 and 9, 1952. Today, the SO2 emission is known to be responsible for a part of the acid rain which is attacking plants and animals, for increased pH of lakes and for corrosion and decomposition of buildings. Today, the total worldwide SO2 emission is declining because of reduced sulfur content in the fuels and scrubbers for large SO2 sources like coal or fuel fired power stations. The SO2 emission of some cement plants is still on the high side and should be reduced in the future. The formation of SO2 in kiln systems and methods to reduce them are presented hereafter. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 2. CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME SULFUR COMPOUNDS

2.

CHEMICAL AND PHYSICAL PROPERTIES AND ENVIRONMENTAL ASPECTS OF SOME SULFUR COMPOUNDS

Sulfur (S) Sulfur is the 15th most common terrestrial element and the 9th most abundant element in the universe. It is widely distributed in nature in different compounds as well as in pure form. The main sulfur content of the lithosphere is estimated to be approx. 0.05%. Physical Properties [1] The melting / solidification point of normal sulfur is 119.3 - 114.5°C, depending on the mode of heating. Density of solid at 20°C, kg/m3 Rhombic α 2070 Melting point, °C, Natural Rhombic α 110.2 Density of liquid, kg/m3 115°C 1808 445°C 1614 Boiling point, °C

444.6

Density of vapor / density of air, 470°C 1.837 Chemical Properties Molecular weight: 32,1 g/mol Sulfur is one of the most reactive elements; it reacts directly with most elements except iodine, gold, platinum and the noble gases. In humid air it is weakly oxidized, forming traces of sulfur dioxide and sulfurous acid. At approx. 250°C, sulfur ignites in air and burns with a blue flame but the presence of sulfur dioxide significantly raises the ignition point. Pyrite / Marcasite (FeS2) © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:46 PM

Page 43

"Holderbank" - Cement Course 2000 Common and important iron and sulfur mineral Physical Properties [13], [2]

Pyrite

Marcasite

Cristalline form

cub.

rhomb.

Density t/m3

5

4.87

Melting point °C

1'171

450

Solvent

HNO3

HNO3

Pyrite

Marcasite

Molecular weight g/mol

119.98

119.98

Ignition temperature °C

350 - 550

Complete combustion °C

850 - 940


Four main reaction steps (Eqs. 3 - 6) make up the overall pyrite roasting reaction (represented by Eq. 7). The specified enthalpy values [7] refer to 298 K:

2 FeS2

→

2 FeS + S2 (g)

∆H

=

+ 293 kJ/mol

(1)

S2 (g) + 2 O2

→

2 SO2

∆H

=

- 723 kJ/mol

(2)

2 FeS + 3 O2

→

2 FeO + 2 SO2

∆H

=

- 948 kJ/mol

(3)

2 FeO + 0.5 O2

→

Fe2O3

∆H

=

- 282 kJ/mol

(4)

2 FeS2 + 5.5 O2

→

Fe2O3 + 4 SO2

∆H

=

- 1660 kJ/mol

(5)

Sulfur Dioxide (SO2) Sulfur dioxide is produced industrially in greater quantities than any other single sulfur compound. It is generated as the first stage in the manufacture of virtually all the sulfuric acid used by industry, irrespective of the basic raw material. Physical Properties [1] Sulfur dioxide, SO2, is a colorless, non-flammable, toxic gas with a characteristic pungent smell and acid taste.


6/23/2001 - 5:13:46 PM

Page 44

"Holderbank" - Cement Course 2000 Melting point (101.3 kPa)

- 75.5°C

Dynamic viscosity at 0°C

368 Pas

Critical temperature

157.5°C

Boiling point (101.3 kPa)

- 10.0°C

Latent heat of vaporization (at bp)

402 J/g

Standard density at 0°C (101.3 kPa)

2.93 kg/m3

Standard enthalpy of formation

- 4636 J/g

Specific heat capacity (101.3 kPa): 0°C 586 J kg -1 K -1 500°C 816 J kg -1 K -1

Chemical Properties [1] Molecular weight: 64.06 g/mol Sulfur dioxide is very stable; thermal dissociation becomes significant only above 2'000°C. It can be decomposed by shock waves, irradiation with ultraviolet or X rays or by electric discharge. The reaction of sulfur dioxide with oxygen to form sulfur trioxide is industrially the most significant of all its reactions because of its importance in sulfuric acid production. In the gas phase, it only takes place at elevated temperatures and, for a satisfactory yield of sulfur trioxide, it requires the presence of a catalyst. In aqueous solution, sulfur dioxide is oxidized to sulfuric acid at low temperature by air in the presence of activated coke or nitrous gases, or by oxidizing agents such a hydrogen peroxide. Environmental Aspects and Toxicology [1] A substantially larger amount of sulfur dioxide than utilized industrially is produced by the combustion of sulfurous fossil fuels and is discharged into the atmosphere with the flue gases. The calculated total emission of sulfur dioxide from power stations, traffic, households, industry and trade in the Federal Republic of in 1975 amounted to approx. 3.6 x 106 t. In contrast, only about 2.7 x 106 were used for that year's sulfuric acid production of approx. 4.2 x 106 t H2SO4. In the last years the SO2 emissions from power plants in were reduced continuously with the installation of flue gas desulfurization plant and with the utilization of low-sulfur fuels, but emissions from traffic, households, industry, etc. in 1990 still for 620 x 103 t/a. Emissions from power stations amounted to 320 x 103 t/a. For worldwide atmospheric emissions, only rough estimates are available. For 1970, while global emissions were estimated at 157 x 106 t SO2, only about 61 x 106 t were consumed in the production of approx. 94 x 106 t of sulfuric acid. The worldwide cement production (1985) is estimated to about 700 x 106 t/a. Based on an average SO2 concentration of about 1000 mg/Nm3, the portion of SO2 emitted by cement plants compared to the total anthropogenetic SO2 emission (200 x 106 t/a) is about 0.7% [5]. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:47 PM

Page 45

"Holderbank" - Cement Course 2000 Large-scale emission of sulfur dioxide close to ground level has indisputably been the cause of some spectacular environmental problems in the past. A large area around Sudbury, Ontario, was completely sterilized by sulfur dioxide from primitive ore roasting operations around the turn of the century and much of it is still barren as a result of the ensuing soil erosion. Calamitous sulfuric acid fogs occurred in Donora, Pennsylvania, and London, England, in 1948 and 1952, when adverse climatic conditions prevented sulfur dioxide from industrial sources and domestic coal fires from dispersing. The causes of these episodes were correctly identified and the action taken to control ground level smoke and sulfur dioxide concentrations has effectively prevented them from recurring. In the case of industrial sources, however, this has often been achieved by merely building taller chimneys to disperse the sulfur dioxide over a wider area and as the consumption of fuels has increased over the years it has been argued that the problem has merely been shifted from the location where the sulfur dioxide is produced to other locations downwind. Considerable publicity has been given to the apparently increasing problem of acid rain and there does, indeed, seem to be a correlation between the incidence of acid rainfall and the atmospheric transport of pollutants from major industrial locations. Establishing in any degree of certainty to what extent sulfur emissions are responsible for acid rain is, however, complicated by incomplete knowledge of the magnitude of sulfur emissions from natural sources, the atmospheric chemistry of sulfur and the importance of other potential acidulates such a nitrogen oxides. Nevertheless, the evidence linking sulfur dioxide pollution to acid precipitation has been mounting gradually. A recent report by the U.S. National Academy of Sciences, for example, has stated that there appears to be a direct proportionate relationship between sulfur dioxide pollution and the amount of acidic sulfates in precipitation. Ill-effects of sulfur dioxide on humans and animals are mainly related to irritation and damage of the moist mucous membranes by the formation of sulfurous acid. The odor threshold of sulfur dioxide in air is between 0.3 and 2.5 ppm. In most human beings, concentrations of 5 - 10 ppm will lead to irritation of the respiratory tract; in sensitive people they may produce spasms of the bronchi. Higher concentrations will cause heavy irritative coughing, while breathing sulfur dioxide at concentrations above 400 - 500 ppm, even for only a few minutes, is dangerous to life. The maximum workplace concentration is defined as 5 ppm (14 mg/m3). Long-term exposure may possible lead to bronchopneumonia and, in extreme cases, to toxic pulmonary edema with dyspnoea, cyanosis and cardiac-circulatory failure. Sulfurous acid absorbed by the body is converted to sulfate and discharged in the urine, as evidenced by an increase in urine acidity. Plants are impaired by sulfur dioxide at even lower concentrations than human beings. Sulfur dioxide levels of 1 - 2 ppm are enough to cause acute damage to the leaves of plants in only a few hours, followed by necrosis, probably resulting from impaired photosynthesis. Atmospheric Chemistry of SO2 [3]


6/23/2001 - 5:13:47 PM

Page 46


Sulfuric Acid Physical Properties Pure sulfuric acid H2SO4 is a colorless, water-white, slightly viscous liquid, mp 10.4 C, bp 279.6°C. It can be mixed with water in any ratio. Chemical Properties Molecular weight: 98.08 g/mol Sulfuric acid is a strong acid with characteristic hygroscopic and oxidizing properties. Sulfuric acid, like the sulfate ion, is chemically and thermally very stable.

SO2 + 1/2 O2

→

SO3

∆H°

=

- 99.0 kJ

(6)

SO3 (g) + H2O(l)

→

H2SO4 (l)

∆H°

=

-132.5 kJ

(7)

Environmental Aspects and Toxicology [1] Sulfuric acid has a highly corrosive effect on the eyes, the mucous membranes and the skin, even in low concentrations. Because it completely destroys living tissue, concentrated sulfuric acid causes burns that penetrate deeply and heal only slowly. Swallowing sulfuric acid produces extreme pain in the digestive tract, vomiting and shock and there is a danger of perforation. Sulfuric acid vapors or mists irritate the eyes and the mucous membranes of the nose, pharynx and respiratory tract, causing heavy coughing and breathlessness. Sulfuric acid releases are highly deleterious with respect to ground and surface waters. The substance is toxic to both fish and algae, both directly and as a result of reaction with other materials in the water. Any concentration ≥ 1.2 mg/L is considered lethal to fish: 6.3 mg/L or more causes death within 24 h. Sulfur Trioxide (SO2) Physical Properties Gaseous SO3 Nominal density, g/L (0°C, 1013 mbar)

3.57


6/23/2001 - 5:13:47 PM

Page 47

"Holderbank" - Cement Course 2000 Specific heat , kJ m-3 K-1 100°C 2.543 500°C 3.191 Liquid SO3 Density, g/cm3 (25°C) 1.9 bp, °C (1013 mbar)

44.8

Heat of evaporation (boiling point), J/g

538

Vapor pressure, bar 20°C 0.26 100°C 8 Critical temperature, °C

217.7

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 3. SO2 EMISSION LIMITS / NORMAL EMISSION

3.

SO2 EMISSION LIMITS / NORMAL EMISSION

Emission Limits

400 mg/Nm3 dry (no waste fuels)

Switzerland

500 mg/Nm3 dry

Europe

100 - 2400 mg/Nm3

Normal Emission There is no normal SO2 emission level for cement kilns. The SO2 emission depends mainly on quantity and quality of "S" input, kiln system and SO2 reduction systems. It is known that SO2 emission of cement kilns can be between very low values of less than 50 mg/Nm3 and very high values up to 3500 mg/Nm3. Figure 1

Average SO2 Emission according to a "Holderbank" Survey


6/23/2001 - 5:13:48 PM

Page 48


Figure 2

Result of PCA SO2 emission survey 1982 [4]

Assumption: wet: 2.1 Nm3 dry / kg cli (18 kilns) long dry: 1.5 Nm3 dry / kg cli (12 kilns) SP: 1.4 Nm3 dry / kg cli ( 5 kilns) Precalciner: 1.4 Nm3 dry / kg cli (12 kilns)

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 4. SULFUR INPUT INTO KILN SYSTEM [4] [6]

4.

SULFUR INPUT INTO KILN SYSTEM [4] [6]

Contained in the raw materials (mainly as FeS2) and the fuel, sulfur enters the process mainly in the form of sulfates (gypsum CaSO4, 2 H2O), sulfides (Pyrit: FeS2) and organic sulfur compounds. In the process, the sulfur compounds may either be reduced or oxidized to form gaseous SO2. Table 1: Sulfur content of kiln feed and fuels of the "Holderbank" Plants in 1994 % SO3 Kiln Feed

Average

Minimum

Maximum

0.46

0

1.93


6/23/2001 - 5:13:48 PM

Page 49

"Holderbank" - Cement Kiln Feed 0.46 Course 2000 0

1.93 %S

Fuels

Average

Minimum

Maximum

Coal

0.86

0.02

3.51

Pet Coke

4.22

1.01

8.3

Diesel Oil

2.61

0.02

3.5

Heavy Fuel Oil

2.86

0.12

11.6

Alternative Fuels Average

Minimum

Maximum

Liquid

0.56

0.11

2.01

Solid

0.92

0

3.9

Natural Gas

0.52

0

3.17

Tires

1.63

0.8

3.9

Waste Oil

1.16

0.5

2

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 5. BEHAVIOR OF S-COMPOUNDS IN THE PROCESS

5.

BEHAVIOR OF S-COMPOUNDS IN THE PROCESS

Wet Kilns A schematic representation of the sulfur circulation in a wet kiln is shown in fig. 3. Depending on the raw materials, the conditions in the kiln burning zone and the internal circulation, 30 - 80% of the sulfate compounds entering the kiln burning zone may decompose and form SO2 which leaves the kiln burning zone with the exhaust gas together with the SO2 formed by oxidation of the organic sulfur in the fuel fired into the kiln. On ing through the calcining zone, the preheating and the drying sections of the kiln, some of the SO2 will be reabsorbed in the raw materials but due to the poor between the kiln gases and the raw materials, especially in the calcining zone, 40 - 60% of the SO2 from the kiln burning zone will be emitted from the kiln. In the preheating section of the kiln, the SO2 concentration in the gas may even be increased if the raw materials contain sulfides which will burn here in accordance with equation:

+ II − I 4 FeS 2 + 11O

III - II 2

> 550 °C       →

IV - II

2 Fe 2 O 3 + 8 SO 2

(8 )

Having left the kiln, the exhaust gas usually only es through a precipitator before being emitted to the atmosphere through the stack. Depending on the type of precipitator between 10 and 30% of the SO2 in the exhaust gas may be absorbed in the raw materials at this stage. Taking into internal circulation and the evaporation and absorption rates mentioned, about 30% of the sulfur entering the kiln system will be emitted as © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:48 PM

Page 50

"Holderbank" - Cement Course 2000 SO2. The emission will increase roughly in proportion to the total input of sulfur compounds in raw materials and fuel. Since the specific heat consumption of wet kilns is high, SO2 emission depends very much on the sulfur content in the fuel. If the excess air is reduced below a certain level, a sharp rise in SO2 emission from the kiln may occur, as local reducing conditions will increase SO2 formation in the burning zone and make SO2 reabsorption in the kiln back-end more difficult. Long dry kilns Except for a possible slurry preheating section, the design of the long dry kiln is virtually the same as that of a wet kiln. Consequently, the SO2 absorption factors are comparable to those of wet kilns as mentioned above. However, with the same type of raw material and fuel the SO2 emission from the long dry kiln system will be lower than that from the wet kiln. This is due to the lower specific heat consumption and the fact that the exhaust gases from the long dry kiln are often used for drying in the raw mill in which 20% 50% of the SO2 might be absorbed by intimate with freshly ground raw meal particles. Figure 3

Behavior of sulfur in a wet or long dry kiln system without raw mill

Preheater kilns A schematic representation of the sulfur circulation in a dry-process preheater or precalciner kiln with by is shown in fig. 4. In 4 and 5-stage cyclone preheater kilns complete preheating of the raw meal takes place in intimate with the exhaust gas from the kiln and in the lower stages the temperature reaches 850°C at which point part of the raw meal starts to calcine. The SO2 coming from the kiln is thus brought into with free CaO and CaCO3 at a temperature at which the following reactions proceed relatively fast:

II - II

IV - II

CaO + SO 2

II IV - II CaCO 3

II IV - II +

1 O 2 2

IV - II + SO 2

→

CaSO 4

II IV - II   →

CaSO 3

(9 )

IV - II + CO 2

(10 )

In this way, nearly all SO2 formed in the kiln is absorbed by the hot meal and reintroduced into the kiln © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:49 PM

Page 51

"Holderbank" - Cement Course 2000 and bound into the clinker. Only if the sulfur circulation between the kiln and the lower preheater stage reaches extreme levels or in the case of local reducing condition in the kiln back-end and the riser duct SO2 may escape via the lower stage. This will often be the case if coarse waste fuel (e.g. rubber tires or pieces) is fired into the riser duct or kiln inlet. Except for this situation, considerable SO2 emission from preheater kilns (without by-) will only occur in case the raw materials contain non-sulfates such as pyrites which form SO2 already in the upper stage cyclones where the temperature and the concentration of free lime and alkaline materials are too low to ensure complete reabsorption of the SO2 formed, according to above two reactions (9, 10). Normally, 30 - 50% of the sulfur present in the raw meal in the form of pyrites will leave the preheater as SO2. Part of this is absorbed in the raw mill and the precipitator. Still, SO2 emission from the stack will amount to 15 - 30% of the sulfur entering with the raw materials in the form of non-sulfates. This means an SO2 emission of 500 - 1000 mg / kg cli for each per mil sulfur present as non-sulfate in the raw materials. Figure 4

Behavior of sulfur in a preheater kiln system

Precalciner kilns The precalciner kiln system in which the kiln gases the precalciner offers ideal conditions for absorption of SO2 from the kiln due to the high amount of free CaO and a temperature of approx. 900°C in the calciner. But also other precalcining systems where kiln gases enter into with sufficient free CaO in the kiln riser duct and the lower cyclones absorb SO2 from the kiln. The only source of SO2 emission from the preheater of a precalcining kiln system is therefore any content of non-sulfates in the raw meal which will generate SO2 in the upper preheater stages as explained above. Many precalciner kilns in the USA have a kiln gas by. On leaving the kiln riser duct the kiln gas is cooled by air dilution and/or water injection to 400 to 230°C (depending on the filter system). The by outlet is placed to ensure the lowest possible dust concentration in the by gas. This means limited possibility of absorption of the SO2 extracted with the kiln gases in the by duct. Very often, more than 50% of the SO2 contained in the by-ed kiln gases will thus enter the atmosphere via the stack. This might explain why the average SO2 emission from the precalciner kiln systems is higher than that from the SP kiln systems.


6/23/2001 - 5:13:49 PM

Page 52

"Holderbank" - Cement Course 2000 It should be borne in mind that the evaporation factor for sulfur components in the kiln and consequently the SO2 emission from the by may increase drastically if coal combustion in the precalciner is incomplete. In this case, residual carbon from the calciner will enter the kiln inlet where it will create reducing conditions, resulting in greatly increased sulfur "evaporation". Accordingly, improving the combustion in the precalciner is a mean of reducing the SO2 emission from a system with by. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 6. SO2-EMISSION REDUCTION POSSIBILITIES

6.

SO2-EMISSION REDUCTION POSSIBILITIES

To reduce the SO2 emission from a pyroprocessing system to a certain controlled level, three basically different methods are available: ♦ Maintain the existing process while reducing the sulfur input into the system ♦ Modify the existing process (primary reduction measures) ♦ Maintain the existing process while adding a separate gas cleaning unit for the exhaust gas (secondary reduction measures) Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 6. SO2-EMISSION REDUCTION POSSIBILITIES / 6.1 Reduction of Sulfur Input into the System

6.1

Reduction of Sulfur Input into the System

Raw Material A reduction of the total sulfur input or very important for preheater kilns the total input of sulfides is often possible. A sulfur-selective quarrying may not only reduce the total input of sulfur but also reduce its fluctuations. The maximum SO2 retention capacity of a kiln system as described above is reached at the lowest SO2 fluctuation. Because at very low sulfur input the absorption capacity of CaCO3 or Ca(OH) 2 is not used completely whereas during very high sulfur input the SO2 generation is over the absorption capacity of the raw meal. In some cases the SO2 emission stays below limit if the sulfur content in the raw material is not fluctuating too much. In the case of the Höver plant in , the desulfurization with Ca(OH) 2 injection into the preheater is working at its limit because of its very high sulfide input. As explained below, this method is only working up to an SO2 emission of about 1000 mg/Nm3 dry. If Höver would not have a very homogenous sulfur content in their raw meal it would not be possible to stay below the emission limit. Not even with Ca(OH) 2 injection. The costs of selective quarrying or opening a new quarry should be compared with the costs of the installation and operation of a system for secondary reduction measures. A selective elimination of sulfur in the raw material is not yet developed. Fuel Reduction of the sulfur input via the fuel can usually only be attained by accepting a considerable increase in fuel cost. Except for the case where the fuel can be replaced by alternative fuels. A reduction of the fuel-sulfur will under normal conditions not reduce SO2-emission from preheater kilns without by. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:49 PM

Page 53

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 6. SO2-EMISSION REDUCTION POSSIBILITIES / 6.2 Modification of the Existing Process

6.2

Modification of the Existing Process

Non-Preheater System → Preheater System As documented and explained above, preheater systems do have the lowest SO2- emission of all clinker production systems. This modification is reducing the SO2 emission significantly if: ♦ the SO2 emission is not mainly caused by non-sulfates input via the raw material ♦ the total input of circulating elements (S, alkali, Cl) is low enough to avoid a kiln by This modification is reducing the SO2-emission because of: ♦ retainment of sulfates and fuel-sulfur by embedding sulfur in the clinker ♦ SO2-adsorbtion during compound operation in the raw mill ♦ lower heat consumption Modification of fuel preparation and feed [8] A reducing atmosphere in the kiln is increasing the formation of CO and the volatility of "SO2". Therefore, the SO2 emission of preheater kilns with by, wet and long dry kilns and to a lesser degree also of normal preheater kilns is increased if a reducing atmosphere is present in the kiln:

2 CaSO

4

+ C

> 1000 °C      →

2 CaO + CO 2 + 2 SO 2

(11 )

This can be avoided by better fuel preparation and feed as well as with an increased O2 concentration in the kiln. Coal, Coke: ♦ no oversized particles (residues on 90 µm sieve = 0,5 x % volatiles) ♦ continuous feed (feeder, transport) Oil: ♦ good atomization: burner nozzle e.g. Pillard, Unitherm, temperature, pressure Alternative fuels: ♦ solid: no oversized lumps: e.g. chipped instead of whole tires, small bundles ♦ liquid: see "oil" above Besides fuel preparation and feed also the O2 concentration in the kiln should be optimized to reduce the sulfur volatility. To control the O2 in the kiln, a kiln inlet probe is recommended. O2 control with gas extraction after the preheater is also possible but because of fluctuation of the false air intake into the preheater it is less accurate. In most cases, a compromise in the O2 concentration (reducing atmosphere) has to be found, because the NOx-emission, fuel and power consumption can be increased by increasing the O2-concentration in the kiln. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:50 PM

Page 54

"Holderbank" - Cement Course 2000 SO2 adsorption in the raw mill The exhaust gas from preheaters and long dry kilns are usually used in the raw mills to dry the raw meal. The freshly ground raw meal in the raw mill has a large and very active surface where SO2 can be adsorbed. The highest degree of adsorption (100%) can be found at very low SO2 concentration whereas at very high concentrations (2500 - 3000 mg/Nm3 dry) like at the Untervaz plant only an adsorption of about 30% is possible. In systems with an emission of about 1000 to 1500 mg/Nm3 dry an adsorbtion of 50% is normal. The degree of adsorption in the raw mill is also influenced by the temperature and the humidity. A lower temperature or a higher humidity is increasing the adsorption capacity. Raising the proportion of compound to direct operation, time is reducing the time of high SO2 emission and therefore also the effort of secondary measures (e.g. amount of Ca(OH) 2 added to the kiln feed). Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 6. SO2-EMISSION REDUCTION POSSIBILITIES / 6.3 Secondary Reduction Measures

6.3

Secondary Reduction Measures

Catalytic or non-catalytic elimination of SO2 (as it is known for NOx) is not reasonable because oxidation would lead to SO3 and reduction to SH2, both would be more harmful than SO2. Therefore, only absorption or adsorption of SO2 can be used as secondary reduction measures. SO2 absorption with Ca (OH) 2 (slaked lime) [9] The most common measure against SO2 emission is SO2 absorption with Ca (OH) 2.

Ca(OH)2 + SO 2

  →

CaSO 3 + H2O

(12)

It can be added to the exhaust gas: ♦ at the upper cyclone stage of the preheater together with the kiln feed ♦ in a scrubber after the kiln system The addition of Ca(OH) 2 to the kiln feed is very successfully used in three "Holderbank" plants with preheaters (RK, HV, UV) (see chapter 7). However, this technology has its limits. For instance only concentrations not exceeding about 1000 mg SO2/Nm3 can be reduced. At the same time, the emission limit value should be less than 400 mg SO2/Nm3. If the normal SO2 emission is very high (> 1000 mg/Nm3) as it used to be in the Untervaz (UV) plant in Switzerland, a separate SO2 scrubber after the preheater has to be considered. The only slaked lime scrubber for a cement plant was built in the UV plant. There, the kiln exhaust gas flows through a Venturi reactor with an expanded fluidized bed formed by the absorbent which consists of a blend of hydrated lime (slaked lime) and raw meal [9]. A more detailed description of the UV reactor is attached (see chapter 7). Experience showed that the temperature for SO2 absorption with slaked lime is very important. Efficient absorption was only observed at temperatures above 350°C and below 70°C. Therefore, systems with Ca(OH) 2 injection into the conditioning tower or Ca(OH) 2 in bagfilters do not have a sufficient SO2 absorption efficiency [10]. Replacement of Ca(OH) 2 power by other Ca-compounds © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:50 PM

Page 55

"Holderbank" - Cement Course 2000 To save on the high cost of the fine slaked lime, other desulfurization agents were tested at the Höver plant of Nordcement for their suitability. These were coarser slaked lime, powdered chalk and partly calcined kiln meal. However, the results of these experiments were mostly unsatisfactory. The effectiveness of the slaked lime currently in use was in no case anywhere near achieved. Powdered chalk has the lowest effectiveness. The reactivity of the coarse slaked lime was also barely detectable due to the small surface area. In the case of the partly calcined raw meal which had been pneumatically withdrawn from the lowest cyclone stage of a preheater, a slight desulfurization effect could be discerned. However, the technical problems in handling were so great that its further use was abandoned. Tests with unslaked lime (CaO) were not carried out since on of its lower reactivity compared with slaked lime, the difference in cost does not justify the increased quantities required. Optimization, e.g. also for absorption of larger quantities of SO2, is only likely to be achieved by selecting a finer slaked lime. Thus a material with a BET specific surface of 18 or 36 m2/g could certainly lead to fixation of larger quantities of SO2. Untervaz started to use a Ca(OH) 2-mud from a former dump of a carbide manufacturer. The mud has a negative price and can be added to the raw material. This is reducing the Ca(OH) 2-feed to the scrubber. At the Fort Collins plant precalcined material (CaO) from the precalciner is added to the by exhaust gas to reduce SO2-emission. In addition to that, by dust is recirculated in the by to increase the concentration of SO2 absorbed in the dust. These measures are sufficient to stay below the SO2-limit. Activated Coke Absorber Activated coke is under presence of water a very efficient SO2 absorber. The only filter of this kind is installed in the Siggenthal (SG) plant of "HCB. The SO2 emission is reduced by the filter from above 500 to below 50 mg/Nm3. However, this type of absorber is very pricy. The Polvitec in SG is only economical because of the contribution from the village of Zurich for burning their sewage sludge. Sodiumbicarbonate Absorber Obourg. amaquoddy Absorber SO2 scrubbing is only a side effect of the amaquoddy scrubber. As described in chapter 7 the main purpose is to recover CKD to avoid dust dumping. The SO2 is first absorbed by the CaO in the CKD and reacts afterwards with the alkali oxides in the CKD to form an alkali salt. The alkali salt is extracted and if possible sold as a fertiliser. Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 7. EXAMPLES OF SO2 EMISSION REDUCTION

7.

EXAMPLES OF SO2 EMISSION REDUCTION

Below a collection of short descriptions of plants and their measures against SO2 emission. Everybody is welcome to contribute to this collection. SO2-emission reduction © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:51 PM

Page 56

"Holderbank" - Cement Course 2000 Plant:

Fort Collins (FC)

Capacity:

1500 t/d (design) / 1345 t/d (standard)

Raw material:

Containing kerogen and sulfur (~10% as Pyrite)

Fuel type:

Nat. gas, coal (0.44 % S), pet coke (4 to 5% S)

Plant description:

1-stage-preheater with precalciner

Supplier/equipment:

Polysius preheater, Allis-Chalmers kiln

Initial SO2-emission problem:

The SO2-limit of 150 ppm (i.e.~ 320 mg/Nm3) can not


[1], [2]

always be maintained, (sometimes up to 300 ppm) and limits the kiln output. The SO2 emissions originate from the by and not from the precalciner. Kerogen in the raw material is burned in the calciner, combusted into CO2 and SO2. At the same time CaO reacts with SO2 if sufficient Oxygen is available to form CaSO4 (SO2 scrubbing). The by is the control valve for the sulfur level in the clinker. The by rate is 100 %!

[2]

The reason for the emission from the by is believed to be due to a limited quantity of CaO being available in the by dust to combine with SO2 from the kiln. So adding some dust to the by-duct would help. Since a lot of sulfur input into the system is from coal, the specific fuel input has to be reduced. The sulfur content of the kiln feed is rather high with 3.6%. In order to control the SO2-emission, a splitter gate should be installed, in order to deviate a portion of return dust to the by scrubber.

Solution realized:

[4]

Dust return (mainly precalciner dust) from the by / precalciner bagfilter into the by duct has been installed before 1994, however the return dust system needs further modifications.

Emissions reached:

[3]

The necessary SO2-limit has been reached. Most of the time, no additional scrubber dust is used for stack sulfur control. Consequently the low stack SO2 (average 40 - 50 ppm) would allow a lower waste dust quantity.

Further Optimization:

[3],[4]

The plant capacity should be increased up to 1600 t/d with several modifications (and reduction of losses), without increasing the emissions. A modification of the kiln feed inlet is planned for 1995.


6/23/2001 - 5:13:51 PM

Page 57


Literature: [1]

POLYSIUS: Telefax (1989), VA-Dok: FC, Reg. 2D

[2]

Kupper, A.K.: HMC Report VA 91/5866/E, VA-Dok: FC, Reg.2A

[3]

Bachmann, R.: HMC Report VA 94/4263/E, VA-Dok: FC, Reg.2A

[4]

Kupper, A.K. and Bürki, Dr. P.: HMC Report VA 95/4288/E, VA-Dok: FC, Reg.2A

SO2-emission reduction Plant:

Höver (HV)

Capacity:

3'000 t/d (design), 2'900 t/d (standard)

Raw material:

Sulfur components: Pyrite 0.05 - 0.45 %w/w

Fuel type:

Coal (0.4%S), fuel oil, nat. gas; alternative fuels: whole tires (max. 10% of total heat input)

Plant description:

Kiln with 4-stage twin line suspension preheater and planetary cooler

Supplier/equipment:

KHD kiln and preheater


SO2 emissions of up to 1300 mg/Nm3 [1],[2]


(TA Luft = 400 mg/Nm3) In direct operation, up to 900 mg/Nm3 in compound operation

The following investigations were proposed: [3],[4],[5]

Reduction of SO2 emissions by lowering the exhaust gas temperature. Lowering the temperature in the raw mill in compound operation. Desulfurization with Ca(OH)2: different trials have been carried out. To reach an emission < 400 mg/Nm3, the SO2 concentration in the stack should be held at about 350 mg/Nm3. The calculated amount (based on trial results) of Ca(OH)2 needed to stay below the limit would have been 2.4 kg/t clinker in 1990 and 6.4 kg/t clinker in 1991.


6/23/2001 - 5:13:51 PM

Page 58


clinker in 1990 and 6.4 kg/t clinker in 1991.

Solution realized:

Desulfurization with Ca(OH)2 addition to the kiln feed (bucket elevator). The Ca(OH)2 is proportioned by speed control rotary valves with three independent pneumatic injection pipes, which can be used simultaneously when required. The Ca(OH)2 addition was started up in November 1991.

Emissions reached:

[1]

The addition of Ca(OH)2 is controlled by the measured SO2-concentration at the stack, in order to stay below the TA-Luft limit of 400 mg/Nm3.


[1]

Since the costs for slaked lime are quite high, different other desulfurization agents have been tested: powdered chalk:

low absorption efficiency

coarse slaked lime:

barely detectable effect due to small surface area

partly calcined raw meal:

slight desulfurization effect, but additional technical problems.

Tests with unslaked lime (CaO) have not been carried out, due to its low reactivity compared with Ca(OH)2. A further optimisation could be reached, using a finer slaked lime (higher surface area).

Literature: [1]

Boes, K.-H.: Measures to reduce the SO2 emission during clinker burning at Nordcement AG's Höver works. Zement, Kalk, Gips (1993), P.514-518

[2]

Waltisberg, J.: HMB Aktennotiz VA 86/66/D, VA-Dok: HV, Reg. 17

[3]

Hasler, R.: HMB letter to Nordcement AG, VA-Dok: HV, Reg. 17

[4]

Waltisberg, J.: HMB Bericht VA 87/5437/D, VA-Dok: HV, Reg.18

[5]

Waltisberg, J.: HMB Bericht VA 91/5904/D, VA-Dok: HV, Reg. 1

Figure A

Slaked lime chemical and physical data [1]


6/23/2001 - 5:13:51 PM

Page 59


"Blütenweiss slaked white lime from Fels-Werke GmbH

Chemical and physical data CaO

71.99%

MgO

0.65%

SiO2

2.00%

Fe2O3

0.45%

Al2O3

0.47%

SO3

0.27%

CO2

1.23%

Combined H2O

21.60%

Moisture BET

0.90% approx. 10 m2/g

Ca(OH) 2

90.0%

Fineness: R > 0.063 mm

Figure B

4.0%

SO2 reduction efficiency with slaked lime addition


6/23/2001 - 5:13:52 PM

Page 60


Keine KH-Zugabe

=

no slaked lime feed

KH-Zugabe

=

slaked lime feed

Zeit

=

time

SO2-Reduktion

=

SO2 reduction

Kalkhydratzugabe

=

slaked lime feed rate

Figure C

Slaked lime silo and dosing

SO2-emission reduction

Plant:

Rekingen (RK)

Capacity:

2'200 mtpd (design), 2130 mtpd (standard)

Raw material:

Sulfur component: 0.55 % Pyrite

Fuel type:

Coal 0.4%S, fuel oil 0.8%S, waste timber

Plant description:



6/23/2001 - 5:13:52 PM

Page 61

"Holderbank" - Cement Course 2000 Plant description:


Supplier/equipment:

Polysius kiln and preheater


SO2 emissions of up to 1200 mg/Nm3 (LRV-limit = 500 mg/Nm3) in direct operation [LRV = Swiss clean air act]


Reduction of SO2 emissions by lowering the exhaust gas [1],[2]

temperature. Reduction from 180°C to 150°C results in a reduction of 50 mg/Nm3, the same reduction is obtained by further lowering the temperature to 140°C. Desulphurization with Ca(OH)2, added to the kiln feed only during direct operation leads to a reduction of 400 - 450 mg/Nm3 at an initial emission of 750 1200 mg/Nm3

Solution realized:

[3]

Desulphurization with Ca(OH)2 addition to the kiln feed 3 kg/tcli (max. 17kg/tcli) during direct operation (20% of the operating time) Costs are about 60'000 CHF/year

Emissions reached:

The addition of Ca(OH) 2 is controlled by measuring the SO2 concentration in the stack, in order to reach the limiting values of LRV, i.e. below 500 mg/m3.

Literature:

[1]

Utzinger, K.: Reduktion der SO2-Emissionen durch Senkung der Abgastemperatur, Versuchsbericht (1986), VA Dok: RK, Reg.17

[2]

Scheuch, J.: Entschwefelungsversuche mit Ca(OH)2 im Ofendirektbetrieb, Versuchsbericht (1986), VA Dok: RK, Reg.17

[3]

"Holderbank" Cement Course: Source and reduction of emissions gaseous, VA 91/5882/E, P.7

Figure A

Dosing of slaked lime to the kiln feed


6/23/2001 - 5:13:52 PM

Page 62


SO2 -emission reduction Plant:

Siggenthal (SG)

Capacity:

2000 t/d (design), 1900 t/d (standard)

Raw material:

[2]

Sulfur: 0.7% S

Fuel type:

[2]

Fuel oil (2.3%S), dried sewage sludge, complete tires (1.3%S)

Plant description:

Kiln with 4-stage preheater

Supplier/equipment:

Polysius kiln and preheater (Dopol), Fuller grate cooler

Initial SO2 emission problem:

SO2 emissions of up to 1500 mg/Nm3 in direct operation, [1]

up to 900 mg/Nm3 in compound operation (LRV-limit = 500 mg/Nm3) [LRV = Swiss clean air act]


SG had a project to burn sewage sludge containing Hg and at the same time the SO2 and NOx emissions where too high. A pilot plant with an active coke filter as well as an ammonia injection into the riser duct was tested successfully. Mercury, SO2 and other pollutants were absorbed on the active coke. NOx was reduced to N2 and H2O with ammonia injection.

Solution realized:

A POLVITEC (Polysius Environmental Technology) active coke scrubber behind the kiln EP was successfully commissioned in 1994. Beside SO2 and Mercury it is also filtering out other pollutants like heavy metals, NH3, organic compounds and dust. The loaded coke is injected into the kiln as a fuel substitution.


Investment cost:

30'000'000 CHF

Operating cost:

3.3 CHF/t cli

Emissions reached:

[3]

6/23/2001 - 5:13:53 PM

< 12 mg/Nm3 dry Page 63

< 12 mg/Nm3 dry


Literature:

[1]

Dr. R. Stenger, : HMB Bericht MA 92/93/D, VA Dok: SG, Reg. 2

[2]


[3]

Effektive Emissionsminderung bei Einsatz von Sekundärbrennstoffen im Zementdrehofen von "HCB Siggenthal, Dr. 1§D. Rose, Dr. L. Brentrup, Krupp Polysius


Untervaz (UV)

Capacity:

1900 t/d (standard)

Raw material:

Sulfur components: Pyrite and Markasit, usually 10 - 16 g SO3/kg clinker

Fuel type:

[7]

Coal (0.07%S), fuel oil; alternative fuels as dried sewage sludge, waste oil (0.6%S), destillation residue (0.35%S), plastic (0.02%)

Plant description:

Kiln with 4-stage-suspension preheater and planetary cooler (kiln III)

Supplier/equipment:

KHD kiln, preheater and cooler; Lurgi SO2 -scrubber


SO2 emissions of up to 3600 mg/m3 (LRV-limit = 500 mg/Nm3) in direct operation [LRV = Swiss clean air act]


In 1984/85 trials to lower the SO2 emissions by changing

[1],[2],[3],[4]

the operating parameters have been carried out. Addition of Ca(OH)2 to the raw meal: Reduction of up to 50% of SO2, still insufficient.


6/23/2001 - 5:13:53 PM

Page 64

"Holderbank" - Cement Course 2000 50% of SO2, still insufficient. Because no possibility of lowering the SO2 emission of the Plant to the required 500 mg/Nm3 by simple means as the one explained above could be found, the use of a scrubber had to be considered. Because a wet SO2 absorber (washer) was too expensive (investment and operating costs) a dry absorber was chosen. Solution realized:

A system consisting of a circulating fluidized bed supplied [1],[2]

by Lurgi, , was started up in 1988. It works as follows: The kiln exhaust gas flow through a venturi reactor with an expanded fluidized bed formed by the absorbent that consists of a blend of hydrated lime (93% Ca(OH) 2) and raw meal (0.8-1.0t/h Ca(OH) 2 and 2.5t/h raw meal). The latter is mainly added to prevent caking of the very fine hydrated lime. Water is injected to operate the reactor as close as possible to the water dew point and to promote the reaction with the SO2. Due to the intensive of the exhaust gas with the absorbent in the fluidized bed at a temperature (approx. 65°C) close to the water due point (approx. 58 to 61°C), the SO2 becomes very effectively combined with the absorbent, whereby predominately calcium sulfite (CaSO3) is generated. The absorbent then es with the exhaust gas into an electrostatic precipitator. The bulk of the precipitated absorbent is returned to the venturi reactor (approx. 175t/h), while the remainder is discharged and either returned to the kiln feed or added to the cement. The stoichiometric factor of Ca(OH) 2 to SO2 is about 2.3 to 2.6. The pressure loss in the system is 2200 Pa. This results in a power demand for the fan of 315 kW. With the addition of 155 kW for the electrostatic precipitator and the transport systems, the total power consumption of the system amounts to 470 kW. Adding all the material to the kiln feed results in an increase of the SO3 content in the clinker from 1.0 to 1.3%. This is not desirable, but so far not of much concern, because it has turned out that the additional sulfates in the clinker act as a gypsum substitute, so that the SO3 content of the cement can be kept at 2.7% SO3 as before. The investment for the whole desulfurization plant, including auxiliary installations, amount to 15 million CHF. The operating costs are about 2.2 CHF/t cli (Slaked lime 1.6, electrical power 0.4, maintenance 0.5, gypsum substitution 0.3 CHF/t cli).


6/23/2001 - 5:13:53 PM

Page 65

"Holderbank" - Cement Course 2000 gypsum substitution 0.3 CHF/t cli). Emissions reached:


[5]

[6]

During the acceptance measurements in May 1989, the following values have been reached: Direct operation:

431 mg/m3

Compound operation:

418 mg/m3

In 1990 the circulating fluidized bed was operated with 1 t/h hydr. lime and 2.5 t/h raw meal. It has been investigated to use hot meal instead of hydr. lime. Due to analyses of hot meal, it seemed not to be possible to replace hydr. lime completely, but it should be tested whether a part of the hydr. lime could be replaced

Literature: [1]

Bonn, W., Hasler, R.: Verfahren und Erfahrung einer roh- stoffbedingten SO2-Emission im Werk Untervaz der Bündner Cementwerke. Zement, Kalk, Gips (1990), P. 139-143

[2]

"Holderbank" Cement Course: Source and reduction of emissions gaseous, VA 91/5882/E, P. 5 - 6

[3]

Hasler, R., Wickert, Dr.H.: HMB Bericht VA 86/5281/D, VA-Dok: UV, Reg. 17A

[4]

Berclaz, Ch.:HMB Bericht VA 85/73/D, VA-Dok: UV, Reg. 17A

[5]

Strahm, E., Waltisberg, J.: HMB Bericht VA 89/5665/D, VA-Dok: UV, Reg. 2

[6]

Waltisberg, J.: HMB Aktennotiz VA 90/6/D, VA-Dok: UV, Reg. 2

[7]


Figure A

Burning of dried sewage sludge in a cement kiln

Figure B

Circulating Fluidized Bed Absorber


6/23/2001 - 5:13:54 PM

Page 66



Aalborg Portland (not in Holderbank Group)

Capacity:

0.5 Mio. t/year of white clinker with 4 kilns

Raw material: Fuel type:

Fuel oil and pet coke

Plant description:

Wet process plant

Supplier/equipment:

FLS

Initial SO2 emission problem:

Due to the white color of white clinker, and since in the [1]


white kilns very little sulfur is retained, only special fuel quality could be used. Most of the sulfur was emitted as SO2 in concentrations of 500 - 800 ppm. Since the fuel consumption is generally higher for white clinker and for a wet process, in 1980 a conversion to a semi-wet process was considered. Due to high capital costs and technical risks this investigation was not followed further. The recovery of some of the waste heat seemed to be a more attractive solution. In combination with the SO2-problem, a combined heat recovery and desulfurization process seemed to be very attractive, and it was decided to build a pilot plant. From March 1989 to February 1990 a test program was carried out. The degree of desulfurization was found to be 75 %.

Solution realized:


The heat recovery and SO2 absorption unit for the four wet kilns consisting of 4 gas/water heat exchangers and 2 scrubber systems was commissioned in 1991.

6/23/2001 - 5:13:54 PM

Page 67


commissioned in 1991. The exhaust gas from the kiln es first the gas/water heat exchanger before it enters the SO2 scrubber at a temperature of about 115°C. In the scrubber SO2 is absorbed in a slurry loaded with 6 10% solids consisting of 98% CaSO4.2H2O and 2% CaCO3. The slurry is sprayed in counter current to the exhaust gas and collected in the recycle tank at the bottom of the scrubber where it is oxidized with air (CaSO3 + 0.5O2 → CaSO4). A part of the slurry is pumped to a centrifuge where water and gypsum are separated. The rest is reinjected through a circulation line into the scrubber. A chalk slurry of 30% moisture is injected into the circulation line before the spray nozzles to replace the used and extracted absorbens (CaCO3+SO2 → CaSO3 + CO2). The optimum pH for the circulated slurry has been found to be between 5.4 and 5.6 and is controlled by the amount of chalk slurry added to it. The circulated slurry es on its way from the recycle tank to the nozzles a heat exchanger to preheat the water for the gas/water heat exchanger. The exhaust gas leaves the scrubber with 75% less SO2 and a temperature of about 70°C.

Emissions reached:

The scrubber reaches an SO2 reduction of 75-80%, i.e. the remaining SO2-concentration is below 160 200 ppm.


Further optimization concerning the desulfurization is not foreseen.

Literature:

[1]

H.E.Borgholm: A new heat recovery and desulfurization plant for 4 wet kilns in Aalborg Portland. 35th IEEE cement industry technical conference in Toronto, IEEE catalogue (1993), 395 - 409.

Figure A

Heat recovery and desulfurization plant of Aalborg Portland / Denmark


6/23/2001 - 5:13:54 PM

Page 68


SO2-emission reduction Plant: Capacity:

Dragon Products, Thomaston (Maine, USA), (not in "Holderbank" group) [1]

4000'000 t/year

Raw material: Fuel type: Plant description:

Wet kiln

Supplier/equipment: SO2 emissions never were a problem (500 mg/Nm3).

Initial SO2 emission problem: [1]

During the time when Martin Marietta owned the plant (i.e., before 1980), the US EPA designed Thomaston, an upper class coastal residential area, a non attainment area (i.e. an area which had not attained the required level of emissions). This was due to dust emissions from both kiln and quarry (CKD). The Dragon plant discarded dust to produce a lower, but not a low alkali cement.

[1],[2]

The amaquoddy scrubber was commissioned in 1990. Conversion is accomplished in the Recovery Scrubber by reintroducing into CKD the CO2 that was released during calcining. Exhaust gas from the kiln is cooled in a heat exchanger (A) and bubbled through a reaction tank (B) containing a slurry of CKD and water. CO2 in the gas reacts with CKD in the slurry to reclaim CKD for kiln feed, while SO2 reacts with potassium sulfate in the CKD to form potassium sulfate in solution.

Solutions investigated: Solution realized:


6/23/2001 - 5:13:54 PM

Page 69

"Holderbank" - Cement Course 2000 CaO + SO2 0.5O2 → CaSO4 CaSO4 + 2KOH + CO2 → CaCO3 + K2SO4 +H2O Reclaimed CKD is separated in a settling tank (C), rinsed in a secondary settling tank (D) to remove potassium sulfate remnants, and returned to the cement plant as raw feed. Potassium solution is pumped to the crystallizer (E) for recovery as dry potassium sulfate. Heat for the crystallizer is obtained from the exhaust gas heat exchanger (F). Emissions reached:

[3]

The exhaust gas SO2 elimination is claimed to be over 90%. Beside SO2 also HCl as well as ammonia and some less volatile organic compounds are absorbed.

Literature:

[1]

Dust and Other Secondary Materials Management Using the amaquoddy Recovery Scrubber

[2]

The Recovery Scrubber , amaquoddy Technology

[3]

Clean emissions valuable by-products, International Cement Review March 91

Figure A

Recovery scrubber from amaquoddy

Process Technology / B06 - PT III / C01 - Emission Control / Sources and Reduction of SO2-Emissions / 8. LITERATURE

8.

[1]

LITERATURE

Ullmann's Encyclopedia of Industrial Chemistry, Vol. A 25, 1994 VCH, 3-527-20125-4


6/23/2001 - 5:13:55 PM

Page 70

"Holderbank" - Cement Course 2000 3-527-20125-4 [2]

Handbook of Chemistry and Physics, 60th Edition, CRC-Press, 0-8493-0460-8

[3]

Säurehaltige Niederschläge - Entstehung und Wirkung auf terrestrische Ökosysteme, 1984, VDI, Kommission Reinhaltung der Luft

[4]

F.L. Smidth, An overview of the formation of SOx and NOx in various pyroprocessing systems; P.B. Nielsen, O.L. Jepsen, No. 96

[5]

Der Anteil der Zementindustrie an den anthropogenen SO2- und NOx-Emissionen, H. Wickert, "Holderbank" News 6, 1985, p. 15-16

[6]

ATR-Databank 1994

[7]

Kiln Optimization Seminar, Circulation Phenomena VA 90/5714/E, U. Gasser

[8]

Kiln Optimization Seminar, Fuel Preparation / Firing Systems, VA 89/5653/E, F. Schneider

[9]

Environmental Protection Seminar, Sources Reduction of Emisisons (gaseous), VA 91/5882/E, J. Waltisberg

[10]

Parameter study on desulfurization in baghouse filter, VA 90/5687/E, A. Edlinger, R. Hasler

[11]

Massnahmen zur Minderung der SO2-Emission beim Klinkerbrennen im Werk Höver der Nordcement AG, K.H. Boes

[12]

Emissions of NOx and SO2 from cement clinker burning, V. Johansen, A.H. Egelov, Denmark

Figure 14

SO2-Reduction =f(Mol-ratio Ca/S)

Figure 15

SO2 REDUCTION WITH CA (OH) 2


6/23/2001 - 5:13:55 PM

Page 71


Figure 16

Influence of oxygen content in the kiln gas


6/23/2001 - 5:13:55 PM

Page 72

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C02 - Dedusting

C02 - Dedusting


6/23/2001 - 5:13:56 PM

Page 73

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C02 - Dedusting / General

General

1. INTRODUCTION 2. PRESENT STATE OF CEMENT KILN EMISSION 3. PRESENT LEGAL SITUATION 4. STANDARD TECHNOLOGY (ST) FOR DUST EMISSION REDUCTION 4.1 Reduction of Precursor Substances Input into Kiln System 4.2 Process Optimization (Primary Reduction Measures) 4.3 Secondary Reduction Measures 5. DUST CHARATERISTICS 6. DEDUSTING EFFICIENCY

Process Technology / B06 - PT III / C02 - Dedusting / General / 1. INTRODUCTION

1.

INTRODUCTION

Dust filters were the first secondary emission reduction measure in the cement industry. The motivation for dedusting of exhaust gas and vent air are: ♦ Compliance with environmental regulations ♦ Reduction of product loss ♦ Protection of employees and equipment from harmful dust impacts (irritation plugging, erosion) This paper is focused on the dedusting of kiln/raw mill exhaust gas and clinker cooler vent air. They are the largest dust filters of the entire clinker production line. Because they have to provide both very high reliability and efficiency under extremely severe conditions those filters have to fulfill the most difficult task among all cement plant dedusting equipment. The basic working principles of the presented filters are also valid for other applications. Process Technology / B06 - PT III / C02 - Dedusting / General / 2. PRESENT STATE OF CEMENT KILN EMISSION

2.

PRESENT STATE OF CEMENT KILN EMISSION

According to the very much varying dust emission limits in countries where cement plants are operated and the development in the dedusting technology, the average dust emission from cement kilns varies between 10 and 500 mg/Nm3 dry. Only a few exceptions are above 1000 mg/Nm3. Process Technology / B06 - PT III / C02 - Dedusting / General / 3. PRESENT LEGAL SITUATION


6/23/2001 - 5:13:56 PM

Page 74


PRESENT LEGAL SITUATION

Dust was one of the first stack emissions that were regulated and is today still the only emission limit for some plants. The reduction efficiency required is much higher compared to other emissions like SO2 or NOx. The dedusting efficiency of modern dust filters is about 99.999% compared to only 95% of very good SO2 filters. In Europe, emission limits are expressed as mass of particulates per gas volume: mg/Nm3 (N: 273 K and 101325 Pa). Usually the gas volume is calculated on dry base. In some countries the gas volume is referred to a certain oxygen concentration, mostly 10% O2. Emission Limits

Nm3dry= m3 at 273 K, 101300 Pa and 0% water Europe:

20 - 50 - 500 mg/Nm3

:

50 mg/Nm3 dry at 10% O2

In the United States of America not all plants do have a dust emission standard. But all of them do have an opacity limit which is to some degree correlated to the dust emission.

USA (e.g.):

0.3 lb/tfeed, dry

ca. 80 mg/Nm32%O2, wet

0.05 - 0.08 gr/dscf

ca. 115 - 180 mg/Nm3dry

0.015 gr/acf

ca. 60 mg/Nm32% O2, wet

5.5 lb/hr


Some US plants also have to comply with PM10 limits. PM10 stands for particulates smaller than 10 µm. Particulates smaller 10 µm are small enough to enter and mechanically damage the lungs. To express the limits the same units as discussed above are used.

USA PM10 (e.g.):

0.016 gr/dscf


4.7 lb/h


0.015 gr/acf

ca. 60 mg/Nm32% O2, wet t

US plants burning hazardous waste are regulated under BIF (Burners and Industrial Furnaces). Other © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:56 PM

Page 75

"Holderbank" - Cement Course 2000 plants do have a state permit defining certain parameters like NOx, SO2 CO, particulates (dust) and THC emission. The limits for these emissions are called emission standards. This standards are individually defined for each plant and usually represent the operating situation under certain conditions. Therefore, the US standards are different from the emission limits in Europe where emission limits are valid for a whole state or country. For comparison reasons all emission limits/standards are indicated in mg/Nm3. The emission standards in the USA are usually not using mg/Nm3 but ppm, lb/tdry feedgr/dscf, lb/1000 lbgas, b/hr, etc. To convert them into mg/Nm3 certain assumptions were necessary. All the above explained emission limits do include definitions how and when the compliance tests have to be carried out. It is, e.g., very important whether the emission has to be measured continuously or not. Some dust filters like electrostatic precipitators (EP) are very sensitive on process changes and can have an increased dust emission during transition periods and may not be in compliance during that time. Process Technology / B06 - PT III / C02 - Dedusting / General / 4. STANDARD TECHNOLOGY (ST) FOR DUST EMISSION REDUCTION

4.

STANDARD TECHNOLOGY (ST) FOR DUST EMISSION REDUCTION

(Technology frequently used in the cement industry) ST for cement kiln dedusting is the application of bagfilters or electrostatic precipitators. Both are very frequently used and can usually comply with today's dust emission regulations. Some of the older dedusting technologies like gravel beds or multiclones are still in operation but are not build any more, mainly because they do have difficulties to comply with today's more stringent dust emission regulations. To reduce the emissions from a pyroprocessing system to a certain controlled level, three basically different methods are available: ♦ Maintain the existing process while reducing the input of precursor substances into the system ♦ Modify the existing process (primary reduction measures) ♦ Maintain the existing process while adding a separate gas cleaning unit for the exhaust gas (secondary reduction measures) Process Technology / B06 - PT III / C02 - Dedusting / General / 4. STANDARD TECHNOLOGY (ST) FOR DUST EMISSION REDUCTION / 4.1 Reduction of Precursor Substances Input into Kiln System

4.1

Reduction of Precursor Substances Input into Kiln System

Dust input can obviously not be reduced because it is the raw material for our product. Process Technology / B06 - PT III / C02 - Dedusting / General / 4. STANDARD TECHNOLOGY (ST) FOR DUST EMISSION REDUCTION / 4.2 Process Optimization (Primary Reduction Measures)

4.2

Process Optimization (Primary Reduction Measures)

Modifications of the process can reduce dust emissions from existing dust filters (see below). However, the dust reduction achieved in the process is far below the efficiency of a dust filter. This means that process conditions can the dedusting equipment to work properly but the final dust emission is always determined by the filter type and its efficiency (secondary measure).


6/23/2001 - 5:13:56 PM

Page 76

"Holderbank" - Cement Course 2000 However, there are two exceptions where process changes can even be more efficient than a dust filter. If a grate clinker cooler with conventional vent air dedusting is converted into a ventless system or a satellite clinker cooler is used instead of a grate cooler, the dust emission of the clinker cooler becomes virtually zero. Process Technology / B06 - PT III / C02 - Dedusting / General / 4. STANDARD TECHNOLOGY (ST) FOR DUST EMISSION REDUCTION / 4.3 Secondary Reduction Measures

4.3

Secondary Reduction Measures

Almost all cement kilns are equipped with dust filters because of economical and ecological reasons. Nowadays, there are basically two different types of dust filters used: bagfilters and electrostatic precipitators. Some time ago also multiclones and gravel bed filters were installed. They are less efficient than modern systems and very often too sensitive on process changes. Process Technology / B06 - PT III / C02 - Dedusting / General / 5. DUST CHARATERISTICS

5.

DUST CHARATERISTICS

The characteristics of dust have a strong influence on the behavior and design of dust filters and on the impact of the dust on its environment. Dust is characterized by ♦

Size

♦

Shape

♦

Hardness

♦

Chemical composition

♦

Mineral structure

♦

Electrical resistivity

♦

Specific weight

♦

Angle of repose

♦

etc.

Fig 1. Comparison of sizes and physical characteristics of various dusts

The character of the dust is defined by its origin and the different treatments like grinding, blending, classifying or burning. Dust from a preheater kiln is much finer than dust from a clinker cooler and © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:13:56 PM

Page 77

"Holderbank" - Cement Course 2000 because of this more difficult to separate. Fig. 2: Particle size distribution of some dusts from cement kilns

Process Technology / B06 - PT III / C02 - Dedusting / General / 6. DEDUSTING EFFICIENCY

6.

DEDUSTING EFFICIENCY

To describe the performance of a filter or to compare different filter systems the non- dimensional dedusting efficiency η is used. It describes the filter performance independently from the filter load.

η =1−

r R

1)

where: ? = dedusting efficiency r

= clean gas dust content

R = raw gas dust content


6/23/2001 - 5:13:57 PM

Page 78

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP)

Electrostatic Precipitator (EP)

1. TECHNOLOGY BASICS OF EP 1.1 How does an EP work? 1.2 How EP Efficiency is determined 1.3 How EP Clean Gas Dust Content is determined 1.4 HT-Rectifier 1.5 Voltage-Current Curves


6/23/2001 - 5:13:57 PM

Page 79


Our companies, and thousands more throughout the world, will be faced with a substantial environmental challenge over the next few years. Increased governmental regulation and enforcement of clean air laws will require your air pollution control equipment to consistently meet rigid performance standards. And with an electrostatic precipitator that is always a challenge. Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP

1.

TECHNOLOGY BASICS OF EP

Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.1 How does an EP work?

1.1

How does an EP work?

Fig. 3 shows a schematic drawing of an electrostatic precipitator. An industrial precipitator has a number of ages through which the gases at a velocity of about 1 m/s. The ages are formed by two parallel rows of vertically mounted collecting plates and a number of discharge electrodes vertically suspended between the collecting plates. Normally the spacing of the discharge and collecting electrodes varies between 125 and 200 mm and the voltage applied between them is 35 to 110 kV negative DC according to spacing, gas and dust conditions. The high negative voltage applied to the electrically insulated discharge electrodes creates a strong electrical field between the discharge electrodes and the earthed collecting plates. The highest strength occurs near the discharge electrodes. As the voltage is raised, electrical breakdown of the gas close to the electrode surface takes place. This breakdown, called "corona", appears as a bluish glow extending into the gas a short distance beyond the surface of the discharge electrode. The corona produces large numbers of gas ions, the positive ions being immediately attracted to the discharge electrodes while the negative ions migrate towards the collecting plates. Some of the moving ions attach themselves to dust particles suspended in the gas between the electrodes. Dust particles are charged either by bombardment by the ions moving under the influence of the electrical field, or by ion diffusion, both types of charging taking place simultaneously. The particle size determines which type of charging is predominant, ion diffusion being the prevailing mechanism for particle sizes below 1 micron. Through the influence of the electrical field, the negatively charged particles migrate towards the collecting plate to which they adhere while being electrically discharged. These particles build up a layer of dust on the plate surface which is dislodged by rapping. The dislodged particles fall by gravity towards the bottom of the precipitator, ending up in the bottom hopper from where the dust is extracted by either mechanical conveyor (drag chain or screw conveyor) or pneumatic type system.

Figure 3

How electrostatic precipitators work


6/23/2001 - 5:13:57 PM

Page 80


Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.2 How EP Efficiency is determined

1.2

How EP Efficiency is determined

There have been many attempts over the years to develop satisfactory equations based on fundamental theories in order to enable the efficiency of a precipitator to be forecast. They are contained in a large number of technical papers, which are conveniently summarized in H.E. White's book entitled "Industrial Electrostatic Precipitation". Generally the performance of EPs can be expressed by the following Deutsch formula:

η EP = 1−e

(−

? ⋅L ) v ⋅s

2)

or

η EP = 1−e

( −?

A ) Q

3)

where

η

ω

A Q L v s

= = = = = = =

Efficiency of the electrical precipitator Particle migration velocity (m/s) Total projected collecting area (m2) Gas flow (m3/s) Field length (m) Gas velocity (m/s) Distance between collecting and discharge electrodes (m)

From equation 3 it follows that the dedusting efficiency of a precipitator depends on: I II III

the migration velocity w (m/s) the total projected collecting area A (m2) the gas flow Q (m3/s)

Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined

1.3

How EP Clean Gas Dust Content is determined


6/23/2001 - 5:13:57 PM

Page 81

"Holderbank" - Cement Course 2000 If equations 1 and 3 are combined then one can describe the clean gas dust content r in function of R

the raw gas dust content (g/m3)

ω

the migration velocity (cm/s)

A

the total projected collecting area (m2)

Q

the gas flow (m3/h)

r = R ⋅e

(−

A ⋅ϖ ) Q

[mg/m3]

4)

Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.1 Clean Gas Dust Content (r) in Function of the Raw Gas Dust Content (R)

1.3.1

Clean Gas Dust Content (r) in Function of the Raw Gas Dust Content (R)

With respect to equation 4, one would expect that the raw gas dust content (R) is directly proportional to the clean gas dust content (r). However, because the migration velocity is increasing with R, the effect of R on r is much weaker than expected. Figure 4 Example of correlation between raw gas dust content R and clean gas dust content r

Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.2 Clean Gas Dust Content (r) in Function of the Gas Flow (Q)

1.3.2

Clean Gas Dust Content (r) in Function of the Gas Flow (Q)

The equation 4 shows that r is an exponential function of the inverse gas flow (Q). However, the migration velocity ( ω ) is also influenced by the gas flow. Therefore, the correlation of r and Q is not exactly according to the equation 4 with ω = constant. Figure 5 Example of a correlation between gas flow Q and clean gas dust content r for a modern kiln EP during compound operation


6/23/2001 - 5:13:58 PM

Page 82


At relative gas flows above 100%, r is increasing exponentially because of the exponential correlation of r and Q (equation 4) and the amplifiying effect of turbulence and dust re-entrainment from the collecting plates. The latter is overlaid by other effects mainly based on physical and chemical changes of the particulates caused by the lower clean gas dust content (r). At this point we already realize that the calculation of r is very complex because, unfortunately, migration velocity ω is not constant but a function of R, Q and other variables. Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.3 Clean Gas Dust Content (r) in Function of the Total Projected Collecting Area (A)

1.3.3

Clean Gas Dust Content (r) in Function of the Total Projected Collecting Area (A)

The total projected collecting area (A) is

A =l ⋅ h ⋅ G ⋅ F ⋅ 2

[m2]

5)

where l h G F

= = = =

Length of field (m) Height of field (m) Number of gaps of one field (-) Number of fields (-)

The factor of 2 is required because both sides of the collecting electrodes are active during the dust extraction process. The correlation between A and r is about inverse to the correlation between Q and r (see equation 4). It is important to notice that the required collecting area is increasing exponentially with the reduction of the clean gas dust content.

Figure 6 Correlation between the projected collecting area A and the clean gas dust content r


6/23/2001 - 5:13:59 PM

Page 83


Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.4 Clean Gas Dust Content (r) in Function of the Migration Velocity (w)

1.3.4

Clean Gas Dust Content (r) in Function of the Migration Velocity (ω)

Among the variables in equation 4 the migration velocity is the one with by far the most practical significance. Not because it has a stronger impact on r than the others (see equation 4) but because it represents the effect of all other variables besides Q, R and A on the EP efficiency. Figure 7

Clean gas dust content r in function of the migration velocity ω


6/23/2001 - 5:13:59 PM

Page 84


The migration velocity can, somewhat simplified, be understood as the average velocity of the dust particles in their migration from the discharge to the collecting electrode in the electrostatic field. The migration velocity (ω) itself is a function of many other variables like ♦ Nature of dust •

Electrical resistivity

•

Size Gas condition

•

Temperature

•

Volume

•

Humidity

•

Chemical composition

•

Dust load

•

False Air

♦ Energization of electrical fields •

Voltage

•

Current

♦ EP design •

Gas distribution

•

Electrode design

•

Electrode cleaning

and these are only the most important ones. With this information we can rewrite equation 4 as follows:

r = R ⋅e

(−

A • ? (O , f , T, Q, t , c, r, R, l, U, s , ...)) Q

6)

For most of the mentioned variables there exist empirical graphs describing the correlation between the variables and ω. Some of these graphs were published but others are the secrets of the suppliers. Various attempts to calculate ω theoretically were not successful.


6/23/2001 - 5:14:01 PM

Page 85

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.4 Clean Gas Dust Content (r) in Function of the Migration Velocity (w) / 1.3.4.1 Electrical Resistivity of Dust

1.3.4.1

Electrical Resistivity of Dust

The electrical resistivity of the dust particles plays a very important part in the precipitation process and depends mainly on the type of the dust, the gas temperature and the gas humidity. Figure 8

Dust resistivity in function of temperature and dust source

Three ranges of electrical resistivity can be distinguished: ♦ less than 104 Ω cm ♦ 104 to 1011 Ω cm ♦ more than 1011Ω cm For particles having a resistivity of less than 104 Ω cm the electrical conductivity is so high that although they are charged in the normal manner and move normally under the influence of the electrical field, the attainable dedusting efficiency is poor. The reason thereof is that as soon as they reach the collecting electrodes, the electric charge leaks away so rapidly that the particles are repelled into the gas stream and most likely escape with the outlet gases. Dust types belonging to the range comprised between 104 and 1011 Ω cm show a favorable discharge behavior. This means that neither particle repulsion nor back-ionisation occurs, i.e. the particles are nicely deposited on - and sufficiently attached to the collecting electrode. Cement industry dusts usually belong to these "easily" separating dusts. Dusts stemming from long dry process kilns, suspension preheater kilns and grate clinker coolers, however, may occasionally develop dedusting problems. Particles having resistivities of more than 1011 - 1012 Ω cm can form within a very short period of time an electrically insulating layer on the collecting electrodes leading to the so-called back-ionisation (back corona) effect. With "back-ionisation" already captured dust is forced back into the gas flow and a reasonable dedusting efficiency of the precipitator becomes impossible to obtain. Figure 9

Back ionization of dust particles at high electrical resistivities


6/23/2001 - 5:14:02 PM

Page 86


Dust resistivity at temperatures below 200°C is primarily determined by the amount of moisture present in the gas. Therefore, a wet kiln will have a much lower resistivity than a standard long, dry or a preheater kiln. In fact that was the reason why a water spray / conditioning tower was added to these kiln systems to tread the exhaust gas. The variation of the resistivity as a function of the moisture content of the raw gas is due to an extremely thin conditioning layer on the particle surface which modifies the resistivity of the dust. At higher temperatures (above 350°C) the particles become increasingly conductive and the gas composition ceases to have much effect as a such. Figure 10

Dust resistivity in function of the temperature and the dew point

At middle-range temperatures of about 200 to 250°C the resistivity curve of some dust reaches a maximum. Figure 11

Dust removal efficiency as a function of the EP operating temperature


6/23/2001 - 5:14:02 PM

Page 87


Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.4 Clean Gas Dust Content (r) in Function of the Migration Velocity (w) / 1.3.4.2 Size of Dust Particulates

1.3.4.2

Size of Dust Particulates

According to Stoke's law for particles larger than 1 µm, the migration velocity is directly proportional to the particulates diameter. Figure 12:

Dedusting efficiency in function of the particle size

A dust with a mass mean diameter of 10 microns would require a precipitator only one-third the size of a system collecting dust with a mass mean diameter of two microns. As you can see, ϖ goes down when it is dealing with particulate in the 0.5 micron range and then starts to improve in efficiency when the particulate gets smaller (say 0.05 microns). That has to do with the two principals of particle charging which predominate in a precipitator. Field charging predominance for particulate greater than 1 micron in size and diffusion charging predominates for particulate less than 1 micron in size. That range around 1 micron is kind of a no-man's land where neither field charging nor diffusion charging has much effect. That is why the efficiency drops dramatically and then improves once the particles get even smaller. What are other consequences for the EP operation based on the correlation between ϖ and particle size: ♦ EPs are classifying the incoming dust. The coarse particles are found in the first fields and the fine fraction in the last fields. This classifying of the dust can be used to extract selectively a dust portion enriched with © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:02 PM

Page 88

"Holderbank" - Cement Course 2000 condensibles like K2O, SO3 and heavy metals, thus avoiding generation of larger quantities of "contaminated" dust or enrichment of certain compounds in the process. ♦ Fine dust particulates and condensibles can be accumulated in the system and reduce the EP efficiency if they are not extracted from the last field. ♦ The particle diameter of the clean gas dust is generally below 10 µm. Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.4 Clean Gas Dust Content (r) in Function of the Migration Velocity (w) / 1.3.4.3 Gas Temperature T

1.3.4.3

Gas Temperature T

Gas and particulate temperature are usually the same because the particulates are suspended in the gas and the retention time of particulates in the gas is sufficient to reach a temperature equilibration. The influence of the gas temperature T is mainly: ♦ Increased dust resistivity Ω at higher temperatures below 250°C (see para 1.3.4.2) ♦ Decreased dust resistivity Ω at higher temperatures above 250°C (see para 1.3.4.2) ♦ Increased actual gas flow Q at higher temperatures (see para 1.3.2) Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.4 Clean Gas Dust Content (r) in Function of the Migration Velocity (w) / 1.3.4.4 Gas Humidity (dew point t)

Gas Humidity (dew point τ)

1.3.4.4

The water of the raw gas is originating from: ♦ Combustion (4 CmHn + (4 m+n) O2 -> 4 m CO2 + 2n H2O) ♦ Water in ambient air ♦ Water in raw materials ♦ Water injection for gas conditioning

The dew point can be calculated as follows:

τ=

336 .48 −179 5 .3362 − 17 .045 +ln(V f •P tot )

[°C]

7)

where: Vf Ptot

= =

Volume fraction of water vapour in the wet gas (m3 H2O / m3wet gas) Total pressure (bar)

As described in para 1.3.4.1 the dew point is influencing the electrical resistivity of the dust particulates at temperatures below 250°C. This is responsible for the increased efficiency of the EP at higher dew points Figure 13

Example for clean gas dust content in function of the dew point τ at temperatures


6/23/2001 - 5:14:03 PM

Page 89

"Holderbank" - Cement Course 2000 below 250°C

The figure above shows the strong effect of gas dew point τ on EP efficiency η if no back ionization occurs. With back ionization the clean gas dust content r would increase even faster at lower dew points. A typical example for the influence of the dew point are preheater kilns switching from compound operation (mill on) to direct operation (mill off). When the raw mill is in service, the moisture conditioning (11 % to 12 % at 110°C) of the gas is optimum. When the raw mill goes off line, the spray tower preceding both the raw mill and the EP cannot catch up quickly enough to increase the volume of water to make up for the moisture content lost when the raw mill goes down. Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.4 Clean Gas Dust Content (r) in Function of the Migration Velocity (w) / 1.3.4.5 Gas Composition (not including water vapour)

1.3.4.5

Gas Composition (not including water vapour)

The gas composition of clinker cooler vent air is fairly simple, however, the composition of kiln exhaust gas is a complicated cocktail of many different compounds. Some compounds like SO2 can enhance the EP operation by reducing the resistivity of the particulate surface. Others like organic compounds or condensible alkalis reduce the EP efficiency. It is assumed that organic compounds attached to the particulate surface can increase their resistivity. Condensible alkalis can occur as very fine particulates < 10 µm significantly reducing the average migration velocity. Condensibles like chlorides can increase the stickiness of the deposited dust on the electrodes which leads to thicker dust layers on the electrodes. This would increase the total electrical resistivity of the dust layer and therefore reduce the EP efficiency. Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.4 Clean Gas Dust Content (r) in Function of the Migration Velocity (w) / 1.3.4.6 Gas Dust Load S, r and R

1.3.4.6

Gas Dust Load S, r and R

An increased raw gas dust load R has a positive effect on the migration velocity but cannot fully compensate the raise in the clean gas dust content according to equation 4. An increase of the clean gas dust content r is also increasing the migration velocity. According to the explanation under para 1.3.4.2 the lower the clean gas dust emission is the lower is the diameter of the © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:03 PM

Page 90

"Holderbank" - Cement Course 2000 dust particulates and smaller dust particulates have a slower migration velocity ϖ than larger ones. Therefore, the required collecting area A is increasing exponentially with the reduced clean gas dust content r (see Fig. 6). Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.4 Clean Gas Dust Content (r) in Function of the Migration Velocity (w) / 1.3.4.7 Energization of the EP

1.3.4.7

Energization of the EP

The collection efficiency of a precipitator is directly related to the total power for all fields on the precipitator. In general, the higher operating power levels that each field can achieve, the higher collection efficiency for that field. Figure 14

Example for clean gas dust content r in function of the relative power input

Many people believe that a precipitator cannot work (achieve power levels) unless the gas is loaded with dust. This question can be easily examined by energizing any field of an EP in air. By that, it is meant that the kiln is not in operation, and that the temperatures have settled to ambient conditions. Furthermore, the precipitator is not bottled up and dampers are open, allowing for a natural stack draft through the precipitator. It is important to have some air movement in order to obtain a good "air load". When a precipitator is energized in air, the following results could be obtained: Table 1:

Example of energization of an electrical field of an EP under pure air (without dust)

Precipitator Secondary Voltage (kV)


Precipitator Secondary Current (mA)

6/23/2001 - 5:14:03 PM

Page 91

"Holderbank" Course 2000 Precipitator- Cement Secondary Voltage (kV)

Precipitator Secondary Current (mA)

0 1 5 10 15 16.5 24 28 30.6 33.5 34 35.2 36.3 36.8

0 0 0 0 0 1 100 200 300 400 500 600 700 750

Actual results are dependent on T/R set size, type of high voltage electrode, and the electrical clearance between the electrodes. The mA readings are synonymous with the actual current flowing in the precipitator. Current flowing in a circuit is equivalent to the number of electrons that are moving past the point in that circuit. For current to flow in a precipitator, that means that electrons need to flow from the discharge electrode to the collecting electrodes in the precipitator. That means that the air in the precipitator must become a conductor. It is easy to think of the various conductors and realize that an insulator is a very poor conductor, a piece of copper wire is an excellent conductor, and an energized precipitator is somewhere in between. The air load demonstrates that current does not start to flow in a precipitator until (in this case) a voltage of 16.5 kV is achieved. That voltage is referred to as the corona onset voltage. With moderate increases in voltage, a correspondingly increasing current results. If the alignment is correct between the electrodes in the precipitator, then the air load test should achieve either the primary or secondary current rating of the T/R set being energized. In the above example, we ran out of secondary current (705 mA) first. Therefore, in order to get corona discharge in a precipitator, dust particles are not required. However, the concentration of particulate has a dramatic effect on the power levels in the precipitator. The term "space charge" is used to indicate a precipitator field that is collecting a significant number of fine particles or a heavy concentration of large particles. For our example, we will examine the latter, which is a common occurrence in cement plant precipitator applications. Space charge - high dust concentrations As we saw in the section on air load, since there are no particles (dust) in the inter electrode space, there can be no space charge. However, with the influence of a large concentration of large particles, see what affect it has on these two wet process cement kilns. Kiln No. 1 has a cyclone mechanical collector in series with the precipitator, whereas kiln No. 2 does not. The automatic voltage controls for those two precipitators were found to be operating as follows:


6/23/2001 - 5:14:04 PM

Page 92

"Holderbank" - Cement Course 2000 Table 2: Unit

Energization of two EPs with different dust loads Kiln No. 1: low dust load, kiln No. 2: high dust load Amps Volts

mA

kV

kW

Sparks/Minute

Kiln No. 1-1

123

337

664

50.1

27

0

Kiln No. 1-2

142

247

758

36.2

23

0

Kiln No. 2-1

9

232

39

57.5

1a

20

Kiln No. 2-2

16

324

71

52.0

2

14

Kiln No. 2-3

115

465

940

48.0

38

3

Kiln No. 2-4

120

346

924

35.1

28

0

Because kiln No. 2 does not have the mechanical collector preceding it, the dust loading (concentration) is significantly higher than kiln No. 1. The voltage control readings show the affect of space charge. Space charge is indicated by high voltages, but more importantly, by extremely low current. It is the absence of current flow that can be of significance. When asked what is the more important parameter, precipitator voltage (kV) or precipitator current (mA), often times people will say kV. They are partially correct in most cases, but not in this case. Precipitator voltage is responsible for pushing the dust particles toward the plates. Current is responsible for keeping them there. So although kiln No. 2, field 1 has a lot of pushing forced, (57.5), it has no holding force. Most of the dust re-entrains onto the next field. The other important point to note is that sparking in a precipitator (an electrical breakdown of the gas) is directly related to the precipitator voltage levels. That is why inlet fields have sparking (because of the high kV) whereas outlet fields sometimes do not. If one looks at the flow of current from the transformer / rectifier to set to the high voltage electrodes through the dust laden gas, to the collecting plate and back to the T/R set (through earth ground) as shown in Fig. 15 the effect of the ion mobility may become apparent. The air load demonstrated that in air without dust, the main current carriers are the free electrons and the negative ions. These two characters can be compared to running backs on a football team. They are very swift moving and seek the holes, and the mA meter counts a lot of them during an air load. With the introduction of dust into the precipitator, the ion mobility changes dramatically. The charged particles, which move very slowly, establish a "particulate space charge" in the inter electrode space. Fig. 15 gives an idea of their relative velocity. The affects of high space charge can be both influential and detrimental. On the positive side, high voltages created by space charge in turn create higher "electric fields". The electric field is the pushing force against the dust particles, accelerating them towards the collecting plates. Higher accelerations toward the collecting plates can result in increased efficiencies. However, as in our example in table 2, kiln No. 2 was operating with very low current levels. Therefore, the space charge enhanced the particulate collecting field (high voltages), but also contributed towards a suppression of the corona current. Corona current directly affects particle charging. The higher the particle charging ensure that the dust loss due to particle re-entrainment is diminished. If the corona is suppressed, this can promote re-entrainment. That is the case on kiln No. 2. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:04 PM

Page 93


Figure 15

Relative velocity (mobility) of current carriers

The peak value of the precipitator voltage is limited by the dielectric constant of the gas. The arc-over voltage is the only value which determines the maximum possible precipitator voltage. The total power input and therefore the EP efficiency η are strongly influenced by the applied voltage.

P c = lm ⋅

Up+Uv 2

8)

where Im Up Uv

= = =

Mean secondary current Secondary peak voltage Average secondary voltage

The factors determining the maximum possible precipitator voltage can change quickly. Therefore, the efficiency of the automatic voltage control, that is adjusting the voltage to operate at the maximum value, is directly correlated with the EP efficiency. The functioning of HT-rectifiers and automatic voltage control is explained in para 1.4. The electrical operating behaviour is also changing over the length of the field. Gas turbulence and distribution, dust content and particulate size at the EP inlet are very different from the ones at the EP exit. Therefore, to optimize the energization of the EP the electrodes should be subdivided mechanically and electrically in the length direction. Figure 16 Clean gas dust content r in function of the number of independent electrical fields at constant collecting area A


6/23/2001 - 5:14:04 PM

Page 94


Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.3 How EP Clean Gas Dust Content is determined / 1.3.4 Clean Gas Dust Content (r) in Function of the Migration Velocity (w) / 1.3.4.8 EP Design

1.3.4.8

EP Design

The equipment parts with the main influence on the migration velocity are: ♦ Gas distribution screens ♦ Electrode ♦ Electrode cleaning systems Gas distribution In general the ducting leading to the precipitator and the inlet and outlet funnels should be designed to ensure a proper gas velocity distribution in view of utilizing the whole collecting area and avoiding negative velocity effects. From a practical viewpoint this implies different requirements to the gas distribution in the different parts of the precipitator, and too strictly formulated numerical rules for deviation from uniformity may not be justified. The inlet gas distribution must be sufficiently uniform to secure a reasonable uniform current distribution. This is especially important for precipitators for processes with high resistivity dust and fine particles. A rule of thumb says that the standard deviation of the gas velocities in the EP should be below 30%. The velocity profile at the outlet should be specifically selected to reduce the risk of re-entrainment in the bottom region. Sneakage of dust laden gases around the electrically energized electrode system must be kept at an absolute minimum, in particular at the bottom part of the precipitator. And large eddies in the bottom hoppers caused by the velocity "slip" at the bottom of the electrode system may aggravate the influence from sneakage because particles already picked up by the hopper are swept into the main flow again. High local velocities may scour away already precipitated dust from the collecting plates. In this case a good gas distribution combined with high average velocity may not be superior to a bad gas distribution combined with low average velocity. The gas distribution may influence the dust space charge distribution and thereby the current distribution in a separately energized precipitator field. In areas with low velocities or, in extreme situations, areas with recirculating flow, the particle concentration will be much lower than in © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:05 PM

Page 95

"Holderbank" - Cement Course 2000 corresponding areas with higher velocities. Consequently the power input will be limited in the high velocity areas causing a reduction in overall efficiency. In particular with high resistivity dust such uneven current distribution will cause back ionization and frequent sparking, resulting in lower average voltage and current and increased dust re-entrainment. Due to the turbulence the gas distribution in each separate duct will tend to improve through the precipitator, thus smoothing the dust space charge. However, a skew cross distribution at the field inlet will not be smoothed to the same extent, and so the horizontal gas distribution should be fairly uniform in order to maintain a proper current distribution. Finally, high local gas velocity, combined with high dust content, can result in erosion of the edges of the collecting plates and other internal parts of the EP. Low gas velocity can cause dust build ups. The cross section of an ideal EP should be designed to achieve an average gas velocity of ♦ Kilns

0.8 - 1.0 m/s

♦ Clinker coolers

0.7 - 0.9 m/s

The gas velocity should not drop below 0.5 m/s to maintain a suitable gas distribution. Electrode design The electrodes have two duties. First emission of electrons (discharge electrode) and second the collection of the dust (collecting plate). The energization of the fields or in other words the supply with voltage and current is influenced by the discharge electrode design. Various electrode designs to achieve optimum voltage or / and current are employed by the suppliers. An important factor is the corona onset voltage which depends mainly on the radius of the electrode (plan strips) or the radius of spike peaks. The corona onset voltage is increasing with the above mentioned radius. Figure 17

Corona discharge voltage in function of the discharge electrode radius

In applications, where a high current is required (high dust load, low resistivity), the electrode radius should be small. In situations, where current must be reduced and voltage increased (high resistivity dust -> back corona) electrodes with larger radius (without peaks) can improve the efficiency. Since corona discharge is also greatly affected by dust settling, the discharge electrodes need rapping, which means that their oscillation behaviour is of utmost importance. Best results have been obtained with rigid frame-mounted electrodes or rigid electrodes. For maximum collection efficiency, the collecting plates must be rigid to maintain the critical spacing between the different electrodes and withstand bowing during operation. At the same time, they must facilitate the efficient transfer of rapping energy for effective cleaning. Not optimum cleaning can © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:05 PM

Page 96

"Holderbank" - Cement Course 2000 amplitude back corona effects and generally reduce the EP efficiency.

Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.4 HT-Rectifier

1.4

HT-Rectifier

The High Voltage Rectifiers are responsible for optimum energization of the EP under different operating conditions. Optimum energization means: ♦ Clean gas dust content r below the target ♦ Minimum energy consumption

The precipitator energization has a very strong influence on precipitator collection efficiency. As a result of this recognition, the microprocessor-based controller for precipitator high voltage power supplies have in recent years become the general standard. These programmable, fast reacting, digital controllers can implement sophisticated control strategies through their monitoring of secondary current and voltages, including differentiation of reactions according to type of arc or spark in the precipitator, arc quenching, fast voltage recovery after arcing without reignition of the arc, automatic current limitation to the nominal current at overload or short circuit conditions and operation at a precipitator current level just below the onset of "back corona". They continuously control flash-over rate and power input to the precipitator for optimum performance. Figure 18

Automatic voltage adjustment. Behavior of EP voltage at constant arc-over limit

Most microprocessor-based transformer / rectifier controllers have or can easily be supplemented with an option for semi-pulse energization, as described in the following: Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.4 HT-Rectifier / 1.4.1 Semi-Pulse Energization

1.4.1

Semi-Pulse Energization

An inexpensive method for reduction of precipitator power consumption, and in some instances also improvement of precipitator performance, is also known under various trade names such as semi-pulse intermittent energization and energy-control. Semi-pulse energization is implemented at a conventional thyristor controlled full wave transformer / rectifier simply by suppressing for instance two out of three, or four out of five half waves. The ripple of © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:05 PM

Page 97

"Holderbank" - Cement Course 2000 the precipitator voltage hereby becomes more pronounced than with conventional energization, resulting in a voltage wave form that resembles a DC base voltage superimposed with long duration pulses. The intermittent nature of the corona discharges gives this form of energization certain properties resembling those of the later discussed pulse energization. Semi-pulse has, in some cases, been able to improve the performance of precipitators operating with medium to high resistivity dust, but as a rule not to the same degree as pulse energization. Its main advantage is the resulting power savings. Power saving up to 90% and emission reduction of up to 50% were reported. Figure 19

Voltage wave form for semi-pulse energization

Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.4 HT-Rectifier / 1.4.2 Pulse Energization

1.4.2

Pulse Energization

Advances in high-power switching technology in recent years have made it possible to develop pulse energization systems with sufficient reliability and capacity to energize large precipitators. With pulse energization short duration, high voltage pulses are repetitively superimposed on a DC base voltage. Some energy conserving pulse energization systems utilize pulses with a duration in the order of 100 microseconds and pulse repetition frequencies up to 200 pulses per second. Pulse energization makes it possible to attain more favorable electrical conditions for high resistivity dust than is obtainable with conventional DC energization. Pulse energization, therefore, can successfully be used to improve the performance of an existing precipitator operating with high resistivity dust or to reduce the size of a new precipitator installation for a high resistivity application, as for instance with the so-called "hot" precipitators for kilns. Power saving of up to 90% and emission reduction of up to 60% were reported.

Figure 20

Voltage wave form for pulse energization


6/23/2001 - 5:14:06 PM

Page 98


Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.4 HT-Rectifier / 1.4.3 Improvement of Voltage and Current Wave Form Shape

1.4.3

Improvement of Voltage and Current Wave Form Shape

Modern precipitator power supplies include silicon controlled rectifiers (SCR's) and current limiting reactors (CLR's). SCR's and CLR's are designed to produce an optimum energization of the EP at one specified process condition. Since it is known that this condition can change very frequently, the current and voltage input have to be adjusted continuously. Operation of CLR's at conditions which are not according to the design specifications can produce a poor current wave form shape (poor form factor) which leads to a reduced power input. This can be corrected with a variable inductance current limiting reactor (VI-CLR). Figure 21

Improving wave form shape with variable inductance current limiting reactor

Another more expensive way to increase the power input is the utilization of a 3-phase energization. The transformer is operated with a square wave voltage with a frequency of 500 Hz. This produces a very flat direct voltage that can under certain circumstances result in a higher power input. Unfortunately, very little experience is available for this system. Figure 22

Improving current wafe form shape with 3-phase energization


6/23/2001 - 5:14:06 PM

Page 99


Intelligent EP control systems do limit the power input if additional power input does not result in significantly reduced dust emission (see Fig. 14). Process Technology / B06 - PT III / C02 - Dedusting / Electrostatic Precipitator (EP) / 1. TECHNOLOGY BASICS OF EP / 1.5 Voltage-Current Curves

1.5

Voltage-Current Curves

A voltage-current curve to a precipitator troubleshooter is like a stethoscope to a cardiologist. When a precipitator is running, we cannot see what is happening inside that might affect its performance. However, by a close examination of the relationship between the voltage and current levels in the operating precipitator, one can predict what is affecting performance. A V-I curve is run by taking the voltage controls to zero then slowly increasing the power levels, recording both the kilovolts and milliamps at convenient intervals (usually 50 mA or 100 mA) until the voltage control sparks over. A curve can then be drawn from the points collected utilizing the "X" axis for the kilovolts and the "Y" axis for the milliamps. Some typical V-I curves for a dry process cement kiln are shown on Fig. 23. Note that the voltage and current corresponding to each field reflects the voltage and current relationships as first shown in Table 2 of our precipitator example. When there are problems with the operation of the precipitator, Fig. 24, would be more helpful for troubleshooting. For example, the high resistivity dust as indicated by low current levels in the outlet fields may show up as the "moderately high" dust resistivity curve shown on Fig. 24. This short, stubby curve shows corona onset voltage as normal (say around 18 kV), but current level only increases to a very low level as opposed to the way an outlet field should, as shown on Fig. 23. This contrasts with a misalignment of the electrodes (wire-to-plate spacing) in the precipitator. Misalignment exhibits itself by a very low corona onset voltage (the electrical clearance is decreased), and the spark over. These curves can also be utilized to show if there is excessive dust buildup on the high voltage electrodes. Excessive dust buildup exhibits itself almost as if the wire diameter of the high voltage electrode has been increased. Dust buildup on the wire has the same effect of increasing the corona onset voltage from the normal range of 15 - 20 kV on up to 25 to 35 kV. The problem with wire buildup is that you are not able to achieve as high a current as if the wires were clean. , a precipitator needs both high voltage and high current levels. Figure 23

Normal precipitator voltage - current (V-I) curves


6/23/2001 - 5:14:06 PM

Page 100


Figure 24

Abnormal precipitator current-voltage curves

Table 3: Influence of some variables on EP's dedusting efficiency Variables

Variation

Efficiency

Dust Emission

Raw gas dust content R

ì

ì

ì

Gas flow Q

ì

î

ì

Collecting area A

ì

ì

î

Electrical resistivity of the dust Ω

ì

î/ä

ì/æ

Temperature T1 (<200°C)

ì

î

ì

Temperature T2 (>300°C

ì

ì

î

Particle size ∅ (> 1 µm)

ì

ì

î

Humidity (τ)

ì

ì

î

Organic emission c

ì

î

ì

Power input P

ì

ì

î

Standard deviation of gas distribution

ì

î

ì

Misalignment of electrodes

ì

î

ì


6/23/2001 - 5:14:07 PM

Page 101

"Holderbank" - Cement Course 2000 Speed of the controller for EP energization

ì

ì

Figure 25

Longitudinal Section of a 2-Field EP (Lurgi)

Figure 26

3D view on a 2-Field EP (ELEX)

Figure 27

Insulator Chamber FLS (Type C)

Figure 28

Electrode System (Lurgi)


6/23/2001 - 5:14:07 PM

î

Page 102


Figure 29

Collecting Electrode Rapping System (Lurgi)

Figure 30

Suspension and Rapping of Discharge System (Lurgi)

Figure 31

Gas Distribution Screen (FLS)


6/23/2001 - 5:14:08 PM

Page 103


Figure 32

Dust Removal System (FLS)


6/23/2001 - 5:14:08 PM

Page 104

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF)

Bag Filter (BF)

1. TECHNOLOGY BASICS OF BF 1.1 Categorizing Bag Filters 2. FILTER MEDIA 2.1 Selection Criteria 2.2 Properties of Various Media 2.3 Hydrolytic Influences 2.4 Woven Fabrics and Needle Felts 3. CLEANING SYSTEMS 3.1 Overall View 3.2 Reverse Gas Cleaning 3.3 Pulse Jet Cleaning


6/23/2001 - 5:14:08 PM

Page 105

"Holderbank" - Cement Course 2000 The history of bag filters begins in 1886, when engineer Wilhelm Friedrich Ludwig Beth, of Lübeck, was granted the Patent 38396 for a "suction tube filter with automatic cleaning device". Since then, the bag filter technology was continuously improved and is today at a level that makes it superior to any other dedusting system. Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 1. TECHNOLOGY BASICS OF BF

1.

TECHNOLOGY BASICS OF BF

Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 1. TECHNOLOGY BASICS OF BF / 1.1 Categorizing Bag Filters

1.1

Categorizing Bag Filters

To better understand one's bag filter, it is helpful to determine where it fits among the various types of BF. When one tries to group bag filters into a number of categories, it soon becomes obvious that the task is not simple. There appears to be an exception to each of the rules. The creation of certain categories, though they are not rigid, is yet very helpful. Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 1. TECHNOLOGY BASICS OF BF / 1.1 Categorizing Bag Filters / 1.1.1 Cleaning Method

1.1.1

Cleaning Method

One such approach is to group BF designs by cleaning method. There are three major cleaning methods: shakers, reverse gas and pulse jets. In addition to these three dominant cleaning methods, there exist a large number of other cleaning methods which are less often applied. Combinations of the three primary methods have been occasionally employed. For example, reverse air and shake have been used in combination and reverse-air with a pulse assist. Today, in cement plants mainly pure reverse gas or pulse jet BF are applied. Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 1. TECHNOLOGY BASICS OF BF / 1.1 Categorizing Bag Filters / 1.1.2 Capacity

1.1.2

Capacity

Another approach to grouping bag filters is by capacity. Generally, the groupings are small volumes (i.e. below 10'000 m3/h), medium volumes (i.e. 10'000 to 100'000 m3/h) and large volumes (> 100'000 to the multimillion m3/h level).

Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 1. TECHNOLOGY BASICS OF BF / 1.1 Categorizing Bag Filters / 1.1.3 Filter-Media Type / Temperature Capabilities

1.1.3

Filter-Media Type / Temperature Capabilities

The filter-media type and temperature capabilities provide two other ways to categorize and view bag filters. Woven vs. felted media are the media-type categories and high-temperature (> 200°C), medium-temperature (150 to 200°C) and low-temperature applications (< 150°C) are useful temperature groupings. One should be aware of these distinctions and attempt to find where the collector in question fits; thus, when considering operating or troubleshooting recommendations, one only applies recommendations that are suited to the type of collector being used. Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 2. FILTER MEDIA


6/23/2001 - 5:14:09 PM

Page 106


FILTER MEDIA

Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 2. FILTER MEDIA / 2.1 Selection Criteria

2.1

Selection Criteria

The filter medium is the all-important central feature of any dust collector operating on the filtration principle. With the correct or incorrect choice of the filter material the whole dedusting operation, however well received, will stand or fall in actual practice. Important criteria are: ♦ filter type, particularly cleaning principle ♦ gas temperature (average and peaks) ♦ composition and chemical properties of the gas ♦ raw gas dust load ♦ required dust load of the clean gas ♦ physical and chemical properties of the dust ♦ Furthermore, the filter medium must satisfy the following conditions: ♦ high air permeability (low pressure losses) ♦ good mechanical strength ♦ good thermal stability at operational temperature ♦ good dimensional stability at operational temperature ♦ Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 2. FILTER MEDIA / 2.2 Properties of Various Media

2.2

Properties of Various Media

Wool and cotton, the only two raw materials that were available to our grandfathers for making filter media have been nowadays, to a great extent, superseded by synthetic fibers. Even mineral and metal fibers are used for special applications. Table 1 summarizes the main properties of various fibers. The most extensively used ones in the cement industry are polyester, polyacrylnitrile, modificated polyamide (aramide) and glass fibre.

Table 1:

Properties of Various Fibers for Woven Fabrics and Needle Felts

Fabric, Trademark

Natural Fibers

Cotton

Chemical Tensile Classification strength N/mm2

max. Operating Acide Temperature Resist. long time °C

short time °C

Cellulose

70-90

120

410-670


poor

6/23/2001 - 5:14:09 PM

Alkali Resist.

Abrasion Moist Resist. Heat Resist.

Price Rating

Density g/m2

good

very good fair

$

150-400

Page 107

"Holderbank" - Cement Course 2000 Fabric, Trademark

Chemical Tensile Classification strength N/mm2

max. Operating Acide Temperature Resist. long time °C

short time °C

Keratin (protein)

90

120

fair-good

Dralon T, Polyacryl-} 200-570 Acrilan, nitrile pure Dralon, Orlon, mixed Zefran

120-140

150

very good good

100

120

Polypropylene Polypropylene 260-640 (PP)

100

120

excellent

excellent excellent

130-150

170

good

fair-good very good poor

Wool

Synthetic Organic Fibers

120-230

Price Rating

Density g/m2

fair

fair-good

fair

$$

400-600

good

excellent $$

400-600

fair

$

550

$

400-600

560-820

Nylon, Perlon

alipahtic polyamide

370-850

90-110

120

fair

very good

excellent

fair

$

300

Nomex

aromatic polyamide (aramide)

570-690

200-220

250

good in weak acids

excellent excellent at low temp.

fair

$$$$

500-600

Teflon

Polytetra-Fluorethylene 100 (PTFE)

260

280

very good very good

Ryton / PPS

Polyphenylene- 1000-1200 180

200

excellent

excellent good

(dry)

fair

max. 15%O2

max. 15% O2

260

280

excellent

excellent poor

350

fair-good

fair-good fair

P 84

Polyimid

850-900

Glass

Glass

1500-2500 270-230

Stone Wool

Mineral

120-260

300-350

fair-good

fair-good

500-750

up to 600

excellent

excellent excellent

870

excellent

fair

Anorganic Various Steels Metals Fibers

Abrasion Moist Resist. Heat Resist.

Trevira, Dacron, Tery- Polyester lene, Tergal, Vestan, Kodel

Sulfid

Synthetic

Alkali Resist.

Ceramic

Silicium Oxyde

fair

excellent $$$$$$$ $$$$$$

500-800

$$$$$$

550

good

$$$

300-400

0

$$$$$$$$

> 30

Special treatment of the fabrics and needle felts can significantly improve the properties of the bags. Table 2:

Special Treatment of the Bag Surface

Non-Fiberglass Finish Purpose

Available For

Singe

Recommended for improved cake release

Polyester, Polypropylene, Acrylic, Nomex, Ryton, P 84 (felts)

Glaze

Provides short-term improvements for cake release (may impede airflow)

Polyester, Polypropylene (felts)

Silicone

Aids initial cake development and Polyester (felt and woven) provides limited water repellany

Flame Retardant

Retards combustibility (not flame- Polyester, Polypropylene (felt and proof) woven)


6/23/2001 - 5:14:09 PM

Page 108

"Holderbank" - Cement Course 2000 Non-Fiberglass Finish Purpose

Available For

Acrylic Improves filtration, efficiency and Polyester and Acrylic felts Coatings (Latex cake release (may impede flow in base) certain applications) PTFE Surface For capture of fine particulate, Treatments and improved filtration efficiency, Laminates cake release

Nomex, Polyester, Acrylic, Polypropylene (felt) (Laminates available in Polypropylene, Ryton and Polyester only)

PTFE Penetrating Finishes

Improved water and oil repellency; limited cake release

Nomex (felt)

Acid Resistant

Improved acid resistance and water retardance

Nomex (felt)

Fiberglass

Finish Purpose

Applications

Silicone, Protects glass yarns from Graphite Teflon abrasion, adds lubricity

For non-acidic conditions, primarily for cement and metal foundry applications

Acid Resistant

Shields glass yarn from acid attach

Coal-fired boilers, carbon black, incinerators, cement, industrial and small municipal boiler applications

Teflon B

Provides enhanced abrasion resistance and limited chemical resistance

Industrial and utility base load boilers under mild pH conditions

Blue MaxCRF/70

Provides improved acid resistance and release properties, superior abrasion resistance, resistant to alkaline attack, improved fiber encapsulation

Coal-fired boilers (high and low sulfur) for peak load utilities, fluidized bed boilers, carbon black, incinerators

Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 2. FILTER MEDIA / 2.3 Hydrolytic Influences

2.3

Hydrolytic Influences

One of the greatest enemies of the textile filter media is hydrolysis. By this is understood the breakdown of the molecular chain of the polymerizate by the action of moisture. Hydrolysis is intensified by the action of heat, acids and alkalis. Polyester, for example, should not be used under conditions in which moisture and elevated temperatures occur in combination. Also aromatic polyamides (Nomex) are subject to hydrolytic influences at temperatures above 100°C, especially if acids or alkaline agents additionally act as a catalyser. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:10 PM

Page 109

"Holderbank" - Cement Course 2000 Fortunately, in recent years chemical modification processes have emerged which have enabled these polyamides and also polyester to be substantially improved in this respect. Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 2. FILTER MEDIA / 2.4 Woven Fabrics and Needle Felts

2.4

Woven Fabrics and Needle Felts

Filter media are available either in the form of woven fabric (cloth) or felt fabrics (more particularly needle felt). The structure of these two types of filter media is shown as follows: Figure 1

Woven fabric and needle felt with ing structure

Characteristic of woven fabric is its system of warp and weft threads crossing one another. Essentially the fabric pores, i.e. the holes between the warf and the weft threads, are decisive with regard to the filter properties. Effective fabrics for dust collection purposes have a free perforated area of about 40%. Therefore, they must have a permanent dust crust to maintain their good filtering effect. In contrast with woven fabrics, needle felts are "three-dimensional" filter media. Their active filtering surface is located both on the surface and in the interior of the medium. The dust collection process, beside the sieving effect as in woven fabrics, additionally takes place through inertia and barrier effects. For reinforcement, needle felt can be provided internally with a ing woven fabric interlayer which is only of secondary importance as regards its dust- collecting effect but which serves primarily to give tear resistance and dimensional stability to the material. The pore volume of needle felts is 60 - 90%. This porous structure allows higher ission velocities with lower pressure drops and higher dust collection efficiencies. The filtration process for both types of filter media is shown in Fig. 2: Figure 2

Dust Separation with Needle Felt and Woven Fabric


6/23/2001 - 5:14:11 PM

Page 110

"Holderbank" - Cement Course 2000 For the cleaning of the woven fabric bags reverse gas is usually used. The needle felt bag filters generally have a jet pulse system for cleaning. The high cleaning air pressure of the jet pulse allows the use of denser filter media which in turn achieve higher dust collection efficiencies. Special finishing or application of membranes on the bag surface become more and more important, especially for the jet pulse filters (see table 2). The purpose of those treatments is to give the bags improved resistivity against chemical and mechanical attack as well as optimum filtration efficiency and cake release (especially for fine dust particulates). Bags with such a treatment may have a very much improved filtering efficiency and therefore do not need any more cake formation on their surface to achieve a good dedusting efficiency. Such bags can be operated with a much thinner dust crust and have therefore a reduced flow resistivity. Figure 3

Needle felts without and with membrane

Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 3. CLEANING SYSTEMS

3.

CLEANING SYSTEMS

Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 3. CLEANING SYSTEMS / 3.1 Overall View

3.1

Overall View


6/23/2001 - 5:14:11 PM

Page 111

"Holderbank" - Cement Course 2000 Ten or twenty years ago, fabric filters used to be cleaned by rapping or shaking, sometimes in combination with low-pressure air purging but in the early 1960's a new agent for filter media cleaning was introduced: compressed air. Fig. 4 gives a summary of the various cleaning principles used for bag filters. Figure. 4

a, b: c: d: e:

Cleaning Principles of Bag Filters

manual or mechanical, by rapping or shaking mechanical, by vibrating pneumatic, by reverse air flow (often combined with shaking or vibrating) pneumatic, by compressed air (pulse jet)

Since most of the mechanically cleaned filters have been superseded by compressed air ones, mainly in the cement industry, the mechanical cleaning devices will not be described further here. Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 3. CLEANING SYSTEMS / 3.2 Reverse Gas Cleaning

3.2

Reverse Gas Cleaning

The reverse air cleaned bag filters usually contain woven filter bags. The raw gas enters the bags from the bottom. It flows from the bag center to the outside of the bag. The dust is deposited on the inner surface of the bag. Removal efficiency is improved and maintained by these particulate deposits (residual dust cake). With time excess particulates are deposited on the bags and increase the system resistance to the gas flow (pressure loss). To allow the filter fan to operate within the design parameters and to reduce the fan power consumption, this dust cake must be partly removed. Bag cleaning methods must be designed properly - not over cleaning or under cleaning. The bag cleaning process is triggered either by a timer or, better, when the pressure drop over the bag filter reaches some predetermined level. A reverse air bag filter consists of several compartments, usually of more than ten. When the bag cleaning process is started, the outlet valves of one of the compartments are closed (off-line cleaning). Then, an auxiliary fan forces a relatively gentle flow of filtered gas backwards through the compartment and bags to be cleaned. This causes the bags to partially collapse inward, dislodging the dustcake. This falls through the bags, the thimble and the tubesheet into the hopper. Metal anticollapse rings sewn into the bags along their length prevent complete bag collapse. Fig. 5 is a schematic of compartments in a reverse-gas-cleaned BF showing operation during filtering, cleaning and purging prior to shut sown or maintenance. To the cleaning of the bags low frequency, pneumatic horns ca be installed and used simultaneously with the normal reverse gas flow. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:11 PM

Page 112

"Holderbank" - Cement Course 2000 Table 3: Typical data of reverse gas filter Reverse gas pressure

30 - 40 mbar

Reverse gas flow

2.0 - 3.5 m3/m2h

Power consumption (installed capacity)

∼ 0.0075 kW/m2

Figure 5: Schematic of a shake / deflate-cleaned baghouse filtering flue gas, isolated prior to bag cleaning (null), with deflation gas entering the compartment prior to bag shaking, bag shaking and purging (or ventilation) prior to maintenance

The main criteria that are defining the size of a reverse gas by filter are: ♦ maximum actual flow ♦ maximum permissible air to cloth ratio (A/C) ♦ number of compartments ♦

Table 4:

m3 ) Recommended A/C m2h for reverse gas filter (net, net)1) (

Operating mode

Compound

Direct

Kiln exhaust gas

30

36

1)

A)

Because one compartment is usually isolated for reverse gas cleaning only the filtering area of n-1 compartments are used to calculate the A/C (net).

B)

m3 The h of the reverse gas must be added to the filter inlet flow to calculate the total gas flow ing the bags and the A/C (net).


6/23/2001 - 5:14:12 PM

Page 113

"Holderbank" - Cement 2000 gas flow ingCourse the bags and the A/C (net). A) + B) → A/C (net, net)

C)

Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 3. CLEANING SYSTEMS / 3.3 Pulse Jet Cleaning

3.3

Pulse Jet Cleaning

Pulse jet cleaned bag filters normally employ felted fabrics of various types. The raw gas enters the bags from the outside. The cleaned gas flows through the center of the bag to the clean gas plenum and from there to the stack. The dust is deposited on the outer surface of the bag. To prevent bag collapse during filtering, metal cages are inserted inside each bag. Just like the reverse-gas cleaned bag filter, periodic bag cleaning is required to remove excess residual dust cake. This is accomplished by pulsing compressed air down into each filter bag. Bag cleaning can be accomplished either with the compartment isolated or not isolated (on-line or off-line cleaning, see Fig. 6). The cleaning made is selected based on the particulates being filtered, process conditions and bag quality. Figure 6 Schematic of compartments in a pulse-jet cleaned baghouse filtering flue gas, purging (or ventilating) prior to maintenance, cleaning bags and filtering flue gas again

Most "jet" filters use injectors for the periodic purging of the individual filter elements with a nozzle, usually disposed centrally. Figure 7

Injector with central nozzle

Each row of bags or each individual bag is equipped with an injector which operates as follows: © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:12 PM

Page 114

"Holderbank" - Cement Course 2000 When the bag is in service, i.e. engaged in dust collecting, the clean gas flows from the interior of the bag through the injector into the clean gas plenum. When compressed air is released as a jet from the injector at a velocity which may be above or below the velocity of sound (depending on its type and design), secondary air is entrained from the clean gas chamber of the filter, and a purging air flow comprising the actual jet plus this entrained secondary air is introduced into the filter bag. The ratio of secondary flow to jet flow is called mass flow ratio. Cleaning the bags involves three stages: 1) The normal filtration gas flow is briefly interrupted by the barrier effect of the purging air flow in the opposite direction. 2) The purging air injected into the bag expands it to its original circular section (Fig. 7) and removes the dust cake which falls down into the dust bunker. 3) The purging air then flows outward through the filter medium in the direction opposite to that of the raw gas flow. A compressed air pulse of only 0.1 - 0.2 s duration is sufficient to perform all three above mentioned stages. The pulse is applied at intervals of 1 to 10 minutes. Thus, the duration of the cleaning operation amounts to only 0.02 - 0.3% of the overall operating time of the filter. Practically speaking, therefore, the whole filter surface area is always available for filtration, and the net area is virtually equal to the gross area. Figure 8

Jet pulse bag charged from the outside

Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 3. CLEANING SYSTEMS / 3.3 Pulse Jet Cleaning / 3.3.1 Guide Values for Jet Pulse Filters

3.3.1

Guide Values for Jet Pulse Filters

Although there exist many different forms of construction of jet pulse filters it is possible to give some guide values. For common jet pulse filters, with vertical bags and nozzle injectors, the following data can be given: Table 5:

Typical data of jet pulse filters

Compressed air pressure

bar

4-7

mass flow ratio

-

3-6

Compressed air flow rate

Nm3/m3h

0.05 - 0.10


6/23/2001 - 5:14:12 PM

Page 115

3 "Holderbank" - Cement Course 2000 Nm3/m h

spec. power consumption1)

kW/m2

0.005 - 0.010

1) installed capacity The main criteria that are defining the size of a jet pulse bag filter are: ♦ maximum actual gas flow ♦ maximum permissible air to cloth ratio (A/C)

Table 6:

m3 ) Recommended A/C m2h for jet pulse filters (

Kiln Exhaust Gas Clinker Cooler Vent Air 55 – 65

65 - 80

Cement Mill with Cyclone

without Cyclone

60 - 70

90.00

Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 3. CLEANING SYSTEMS / 3.3 Pulse Jet Cleaning / 3.3.2 Bag Dimensions

3.3.2

Bag Dimensions

Jet pulse bag filter bags are smaller than bags from reverse gas bag filters because of the different cleaning principles. The diameters of the bags are usually between 130 and 150 mm. The length of the bag should be between 4 and 3 meters, if a conventional gas flow pattern is applied, which means, that the gas enters through the hopper and then flows upwards, along the bags. In newer applications, the gas is distributed partially through the hopper and partially horizontally to the bags. Together with new low pressure cleaning, here larger bags of up to 6 m are applicable. Generally longer bags are more difficult to clean and have therefore an increased compressed air consumption. It is also very difficult to remove a bag of more than 3 to 4 meters length if it is filled with dust because of a hole in the felt. Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 3. CLEANING SYSTEMS / 3.3 Pulse Jet Cleaning / 3.3.3 Bag Material

3.3.3

Bag Material

As mentioned above, most bags for jet pulse filters are made with needle felt. This material allows a higher air to cloth ratio and resist the stress of the jet cleaning. For some exceptions (mainly by bag filter) and other high temperature applications, glass fiber bags are used which resist the high temperature and the aggressive environment. Experience during the last few years showed that jet pulse bag filter (operated at lower temperatures, < 130°C) are more reliable and economical than others. At temperatures below 130°C low cost bags like polyester or polyacrylnitril bags can be applied and the power consumption of the filter fan is reduced as well. The still on-going fast development of fabrics significantly improved the performance of bag filters. Due to this development it is possible to install very efficient bag filters at cost that are in the same range or © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:13 PM

Page 116

"Holderbank" - Cement Course 2000 below the cost of EPs. Special treatment of the bag fabric surface allows for more frequent cleaning without increased dust emission. The smaller dust cake on the bags is reducing the pressure drop and therefore saves fan power. Process Technology / B06 - PT III / C02 - Dedusting / Bag Filter (BF) / 3. CLEANING SYSTEMS / 3.3 Pulse Jet Cleaning / 3.3.4 Maintenance of Jet Pulse BF (for Kiln and Clinker Cooler)

3.3.4

Maintenance of Jet Pulse BF (for Kiln and Clinker Cooler)

Except for the valves and dust discharge equipment jet pulse BF have no moving parts. The most important aspect for maintenance are the bags. Holes in the bags can significantly increase the dust emission. Defective bags in reverse gas BF are replaced on line by isolating the respective compartment. Modern jet pulse BF do not need compartments like the reverse gas BF but usually consist of about 4 to 6 modules (static stability) with manual outlet and inlet valves for each module. It is proposed to only visually inspect the modules for defective bags through the inspection window or from the open door (values closed!). If a defective bag is found it does not need to be replaced immediately. It is sufficient to isolate the respective row of bags (~ 10) from the jet cleaning. The incoming dust will close the hole after a short while. The bag can be replaced during the next kiln shutdown. Figure 9

Figure 10 Jet Pulse Bag Filter designed for Off-line Cleaning with High Clean Gas Plenum (NEU Process)


6/23/2001 - 5:14:13 PM

Page 117

"Holderbank" - Cement Course 2000 Figure 11 Jet Pulse Bag Filter with High Clean Gas Plenum for 5’000 t/d Kiln. Dedusting of Kiln Exhaust Gas (Redecam)

Figure 12 Jet Pulse Bag Filter with Low Clean Gas Plenum for 5’000 t/d Kiln. Dedusting of Kiln Exhaust Gas (Redecam)

Figure 13 Air to Air Heat Exchanger and Jet Pulse Bag Filter with High Clean Gas Plenum. Dedusting of Clinker Cooler Vent Air (Redecam)

Figure 14

3-D View on Jet Pulse Bag Filter with Low Clean Gas Plenum


6/23/2001 - 5:14:13 PM

Page 118



6/23/2001 - 5:14:14 PM

Page 119

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns

Dedusting Concepts for Cement Kilns

1. COMPARISON BETWEEN ELECTROSTATIC PRECIPITATORS AND BAG FILTERS 2. CONCEPT 1 2.1 Kiln Exhaust Gas 2.2 Clinker Cooler 3. CONCEPT 2 3.1 Kiln Exhaust Gas 3.2 Clinker Cooler 4. CONCEPT 3 4.1 Kiln Exhaust Gas 4.2 Clinker Cooler 5. CONCEPT 4 5.1 Kiln Exhaust Gas 5.2 Clinker Cooler 6. CONCEPT 5 6.1 Kiln Exhaust Gas and Clinker Cooler Vent Air 7. CONCLUSION


6/23/2001 - 5:14:14 PM

Page 120

"Holderbank" - Cement Course 2000 Because of the changing needs and the different filter and cement production technologies, the concepts for cement kiln dedusting are numerous. Each of them has certain advantages and disadvantages. The dedusting of preheater kilns with waste heat utilization (raw mill) and great cooler is the most difficult case. Therefore, the following examples will be based on such a modern cement kiln system. Chart 1 shows the different possible dedusting concepts. Within the presented concepts there is still some differentiation possible; e.g. the bag filter concepts can be further differentiated by the fabric quality or the type of pulse jet that is applied. Figure 1

Different dedusting concepts

It can be seen that the first decision which must be made is, if the kiln and clinker cooler shall be dedusted separately or in one common filter. The standard solution is to use two filters, one for the kiln and one for the cooler, but we will see later that the simultaneous dedusting in one filter has some important advantages. The next decision is whether bag filters or electrostatic precipitators shall be used. Because of the more and more stringent dust emission limits and the superior dedusting efficiency of bag filters the present trend is to apply bag filters. Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 1. COMPARISON BETWEEN ELECTROSTATIC PRECIPITATORS AND BAG FILTERS

1.

COMPARISON BETWEEN ELECTROSTATIC PRECIPITATORS AND BAG FILTERS

The basic working principle of the two filters are completely different. The EP efficiency depends on many variables like gas volume collecting area, dust characteristics, dew point etc. Once the electrodes are not energized, the dust emission is increasing rapidly. The bag filter efficiency mainly depends on the quality of the bags and the sealing between clean gas plenum and raw gas plenum and is not affected by the process. The EP used to be a very popular filter in Europe and other places because of the low pressure drop, the little maintenance required and the high efficiency under normal operating conditions. Today, the main problem of the EP is its efficiency under not normal operating conditions. Changing the operating mode from compound operation to direct operation and start-up and shut down of the kiln always causes increased dust emission (reduced EP efficiency) because of unfavorable temperatures and © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:14 PM

Page 121

"Holderbank" - Cement Course 2000 dew point during the transition phase. Disturbances in the combustion process or excessive concentration or organics in the raw material can produce CO peaks in the exhaust gas which force the operators to shut the kiln EP down to prevent CO explosion. During kiln upset conditions the vent air (clinker cooler) temperature, volume and dust load are increased. This usually leads to elevated dust emission from the clinker cooler. Some decades ago, increased dust emission during such incidences where generally accepted by the neighbors and the authorities. Nowadays, with the stronger environmental awareness of the people and the more stringent emission limits (20 mg / Nm3, continuous dust emission control) it can be difficult to achieve the required long term efficiency with an EP. An important advantage of the EP can be the classification of the dust particulates. The coarse particulates are collected in the first hoppers, the fine ones in the last hoppers. Condensibles like alkalies and metals are enriched in the fine fraction of the dust. With an EP less dust has to be extracted from the filter to reduce the concentration of the condensibles in the system. Bag filters, if well maintained, have a very high efficiency unaffected by the process conditions. Their main disadvantage is the high pressure loss and the additional maintenance cost for the regular replacement of the bags. The new generation of jet-pulse filters have significantly reduced the pressure drop over the filter and the maintenance cost compared to the reverse gas filters. Table 1:

Comparison of jet pulse filter with reverse gas filter for 4-stage preheater: Kiln Bag Filters Jet Pulse

Reverse Gas

Bag quality

Polyacrylnitrile

Fiber glass

Relative cost for one set of bags

∼1

∼3-4

Pressure drop [mbar]

∼ 8 – 12

∼ 10 - 20

Bag cleaning 2) [Wh/kg cli]

∼ 0.6 - 0.8

∼ 1.1 - 1.5

CT water pump [Wh/kg cli]

∼ 0.6 - 0.8 1)

---

Filter fan [kWh/kg cli] 2)

∼ 6.7 - 7.5

∼ 6.5 - 9.0

1) 1) Only during direct operation 2) Installed capacity

A disadvantage of the bag filters is that they produce a not neglectible amount of waste (used bags). Depending on the local regulations for waste elimination and the quality of bags their elimination can be expensive. Generally, the investment cost for jet pulse filters and electrostatic precipitators are about the same. For installations above 3'000 t/d and 50 mg/Nm3 it is slightly in favor of the EP, below 3'000 t/dry in favor of the bag filter. This is only a general rule and because of the very strong competition this may be significantly different for individual projects. For very low dust emission like 10 mg/Nm3 EPs are higher in price than BFs because the required collecting area of the EP is growing exponentially with the reduction of the clean gas dust content: Table 2:

Additional equipment cost for reduction of the clean gas dust content from 50 to 10 mg/Nm3:


6/23/2001 - 5:14:14 PM

Page 122

"Holderbank" - Cement Course 2000 50 mg / Nm3 → 10 mg / Nm3 ∼ 20%

EP

∼ 5%

BF

The comparison of the operating cost is very difficult because of the variable cost of the bags and the electrical power. As a general rule it can be said that the operating cost of EPs are still slightly lower compared to BFs. For very low dust emissions (e.g. 10 mg/Nm3) the difference between EP and BF becomes neglectible because the power consumption of the EP is increasing exponentially with the reduction of the clean gas dust content. Conclusion of Comparison of EP and BF: For low clean gas dust contents the investment and operating cost of EP and BF (jet pulse) are about the same. The dedusting efficiency of bag filters are superior to EP because bag filters are less sensitive to process changes. Among the bag filters there are two major technologies available: ♦ the reverse gas filters ♦ the jet pulse filters Recent experience shows that the dedusting efficiency of jet pulse filters is the same as or better than the efficiency of reverse gas filters. Investment and operating cost of jet pulse filters are significantly lower compared to reverse gas filters. Below you will find six examples for cement kiln dedusting concepts with short comments on their advantages and disadvantages. Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 2. CONCEPT 1

2.

CONCEPT 1

Separate dedusting of kiln exhaust gas and clinker cooler vent air. Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 2. CONCEPT 1 / 2.1 Kiln Exhaust Gas

2.1

Kiln Exhaust Gas

Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 2. CONCEPT 1 / 2.1 Kiln Exhaust Gas / 2.1.1 Concept

2.1.1

Concept

♦ Conditioning tower before ID fan to cool the exhaust gas to below 150°C during direct operation ♦ 3 fan system (separate raw mill fan and cyclones) ♦ Electrostatic precipitator without pre-separation chamber Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 2. CONCEPT 1 / 2.1 Kiln Exhaust Gas / 2.1.2 Advantages

2.1.2

Advantages


6/23/2001 - 5:14:15 PM

Page 123

"Holderbank" - Cement Course 2000 ♦ Length of duct between preheater and conditioning tower very short because the conditioning tower is placed ahead of the ID fan. Therefore, the investment costs are reduced. ♦ Improved raw mill control because of separate mill fan ♦ Possibly reduced operating cost compared to bag filter ♦ Less false air intake and danger of corrosion at the electrostatic precipitator because of small negative static pressure (due to 3 fan system) ♦ No precollection required at the filter (due to raw mill cyclones) Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 2. CONCEPT 1 / 2.1 Kiln Exhaust Gas / 2.1.3 Disadvantages

2.1.3

Disadvantages

♦ Strong load changes on the ID fan because of different gas temperatures during direct and compound operation (due to conditioning tower before ID fan) ♦ More false air intake into conditioning tower and higher corrosion risk because of strong negative static pressure (60 - 40 mbar) compared to conditioning tower positioned after ID fan ♦ Slightly higher pressure drop between ID fan and filter fan because of the raw mill cyclones ♦ Over all dedusting efficiency of electrostatic precipitator is lower compared to bag filter Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 2. CONCEPT 1 / 2.2 Clinker Cooler

2.2

Clinker Cooler

Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 2. CONCEPT 1 / 2.2 Clinker Cooler / 2.2.1 Concept

2.2.1

Concept

♦ Electrostatic precipitator Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 2. CONCEPT 1 / 2.2 Clinker Cooler / 2.2.2 Advantage

2.2.2

Advantage

♦ Possibly reduced operating and investment cost Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 2. CONCEPT 1 / 2.2 Clinker Cooler / 2.2.3 Disadvantage

2.2.3

Disadvantage

♦ Efficiency of electrostatic precipitator is lower compared to bag filter Figure 2

Concept 1


6/23/2001 - 5:14:15 PM

Page 124


Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 3. CONCEPT 2

3.

CONCEPT 2


3.1

Kiln Exhaust Gas


3.1.1

Concept

♦ Conditioning tower before ID fan to cool the exhaust gas to below 150°C during direct operation ♦ 2 fan system (no separate raw mill fan and cyclones) ♦ Electrostatic precipitator Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 3. CONCEPT 2 / 3.1 Kiln Exhaust Gas / 3.1.2 Advantages

3.1.2

Advantages

♦ Length of duct between preheater and conditioning tower very short because the conditioning tower is placed ahead of the ID fan. Therefore, the investment costs are reduced. ♦ Slightly reduced pressure drop between ID fan and filter fan because of missing raw mill cyclones (compare Concept 1) ♦ Possibly reduced operating and investment cost compared to bag filters Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 3. CONCEPT 2 / 3.1 Kiln Exhaust Gas / 3.1.3 Disadvantages

3.1.3

Disadvantages

♦ Strong load changes on the ID fan because of different gas temperatures during direct and compound operation. ♦ Increased false air intake and corrosion at the filter because of very strong negative static pressure © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:15 PM

Page 125

"Holderbank" - Cement Course 2000 ♦ Electrostatic precipitator need separate precollector chamber ♦ Efficiency of electrostatic precipitators is lower compared to bag filter ♦ Gas recirculation to operate raw mill is increasing the required filter size (due to 2 fan system) Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 3. CONCEPT 2 / 3.2 Clinker Cooler

3.2

Clinker Cooler

♦ See concept 1 Figure 3

Concept 2


4.

CONCEPT 3


4.1

Kiln Exhaust Gas


4.1.1

Concept

♦ Fresh air intake before and / or after the ID fan to cool the exhaust gas to below 240°C ♦ 3 fan system (separate raw mill fan and cyclones) ♦ Reverse gas bag filter Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 4. CONCEPT 3 / 4.1 Kiln Exhaust Gas / 4.1.2 Advantages

4.1.2

Advantages

♦ No cooling tower and water injection required ♦ Higher overall dedusting efficiency than electrostatic precipitator © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:16 PM

Page 126

"Holderbank" - Cement Course 2000 ♦ Simple filter inlet temperature control ♦ Reduced corrosion in the filter because of high operating temperature and low dew point ♦ No precollection required at the filter (due to raw mill cyclones) Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 4. CONCEPT 3 / 4.1 Kiln Exhaust Gas / 4.1.3 Disadvantage

4.1.3

Disadvantage

♦ Higher operating cost than electrostatic precipitator and jet pulse bag filter ♦ Very large filter ♦ If the temperature control fails it is possible to burn the bags ♦ With a bad design it is possible that the pressure drop over the filter is increasing to a point where the capacity of the filter fan is not sufficient anymore to pull the gases Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 4. CONCEPT 3 / 4.2 Clinker Cooler

4.2

Clinker Cooler

Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 4. CONCEPT 3 / 4.2 Clinker Cooler / 4.2.1 Concept

4.2.1

Concept

♦ Cooling of the vent air with air to air heat exchanger (designed for up set conditions) ♦ Jet pulse bag filter; preferably equipped with polyester bags Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 4. CONCEPT 3 / 4.2 Clinker Cooler / 4.2.2 Advantage

4.2.2

Advantage

♦ The air to air heat exchanger serves as a compensator in case of upset conditions and allows therefore a very smooth operation of the filter. ♦ Higher overall dedusting efficiency compared to EP Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 4. CONCEPT 3 / 4.2 Clinker Cooler / 4.2.3 Disadvantage

4.2.3

Disadvantage

♦ If air to air heat exchanger and the jet pulse are designed properly, there are no real disadvantages in this concept. With a bad design it is possible to damage the bags during heat excursions or to increase the pressure drop over the filter up to the point where the capacity of the filter fan is not anymore sufficient to pull the gases. Figure 4

Concept 3


6/23/2001 - 5:14:16 PM

Page 127



5.

CONCEPT 4

Separate dedusting of the kiln exhaust gas and clinker cooler vent air. Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 5. CONCEPT 4 / 5.1 Kiln Exhaust Gas

5.1

Kiln Exhaust Gas


5.1.1

Concept

♦ Cooling tower before ID fan to reduce the temperature to below 150°C during direct operation ♦ Fresh air intake to reduce the gas temperature to below 120°C ♦ 3 fan system (separate raw mill fan and cyclones) ♦ Jet pulse bag filter; preferably with polyacrylnitrile bags. Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 5. CONCEPT 4 / 5.1 Kiln Exhaust Gas / 5.1.2 Advantages

5.1.2

Advantages

♦ Length of duct between preheater and conditioning tower very short because the conditioning tower is placed ahead of the ID fan. Therefore, the investment costs are reduced. ♦ Good mill control because of separate mill fan ♦ Reduced investment and operating cost compared to reverse gas bag filter ♦ Less false air intake and reduced corrosion risk at the filter because of low negative static pressure (due to 3 fan system). ♦ No precollection required at the filter (due to raw mill cyclones) Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 5. CONCEPT 4 / 5.1 Kiln Exhaust Gas / 5.1.3 Disadvantages

5.1.3

Disadvantages

♦ Strong load changes on the ID fan because of different gas temperatures during direct and © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:16 PM

Page 128

"Holderbank" - Cement Course 2000 compound operation ♦ More false air intake into cooling tower and higher corrosion risk because of strong negative static pressure 860 - 40 mbar) compared to CT after ID fan ♦ Slightly higher pressure drop between ID fan and filter fan because of the raw mill cyclones ♦ Very reliable temperature control required to protect the bags ♦ Higher risk for corrosion at filter because of low operating temperature ♦ With a bad design it is possible that the pressure drop over the filter is increasing to a point where the capacity of the filter fan is not sufficient anymore to pull the gases. Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 5. CONCEPT 4 / 5.2 Clinker Cooler

5.2

Clinker Cooler

See Concept 3. Figure 5

Concept 4


6.

CONCEPT 5

Simultaneous dedusting of the kiln exhaust gas and clinker cooler vent air in one jet pulse filter. Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 6. CONCEPT 5 / 6.1 Kiln Exhaust Gas and Clinker Cooler Vent Air

6.1

Kiln Exhaust Gas and Clinker Cooler Vent Air

Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 6. CONCEPT 5 / 6.1 Kiln Exhaust Gas and Clinker Cooler Vent Air / 6.1.1 Concept

6.1.1

Concept

♦ Reduction of the clinker cooler vent air dust concentration in a cyclone ♦ Direct operation: mixing of the clinker cooler vent air with kiln exhaust gas and reducing the temperature to below 120°C in an air to air heat exchanger Compound operation: reducing the clinker cooler vent air temperature and mixing it with the exhaust gas from the raw mill in a air to air heat exchanger © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:17 PM

Page 129

"Holderbank" - Cement Course 2000 ♦ 3 fan system (separate raw mill fan and cyclone) ♦ Jet pulse bag filter preferably with polyacrylnitrile bags Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 6. CONCEPT 5 / 6.1 Kiln Exhaust Gas and Clinker Cooler Vent Air / 6.1.2 Advantages

6.1.2

Advantages

♦ Only one filter ♦ No cooling tower ♦ No water injection ♦ Simple temperature control ♦ Reduced gas volume compared to all other solutions ♦ No precollection required at the filter (due to raw mill cyclones) ♦ Good mill control because of separate mill fan ♦ Reduced investment and operating cost compared to the other bag filter concepts ♦ Less false air intake and reduced corrosion risk at the filter because of low negative static pressure. ♦ Only one stack ♦ Clinker cooler gas can be used to dry raw material in the raw mill ♦ No visible plume at the stack because of the reduced dew point (no water injection and "dry" clinker cooler vent air) ♦ No load changes on the ID fan Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 6. CONCEPT 5 / 6.1 Kiln Exhaust Gas and Clinker Cooler Vent Air / 6.1.3 Disadvantages

6.1.3

Disadvantages

♦ Because of raw mill cyclones slightly higher pressure drop between ID fan and filter fan ♦ Kiln and clinker cooler not controlled by separate fan ♦ Portion of the clinker cooler dust is mixed with the kiln dust Figure 38

Concept 5


6/23/2001 - 5:14:17 PM

Page 130

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C02 - Dedusting / Dedusting Concepts for Cement Kilns / 7. CONCLUSION

7.

CONCLUSION

All concepts have certain advantages. Therefore, one cannot produce a ranking without respecting the individual situation of the plants. Those that require a very reliable dedusting without short time dust emission peaks should chose a bag filter concept. In case of water shortage the concepts 3 and 5 without cooling tower are most suitable. In case that bag supply cannot be guaranteed or short time dust emission peaks are accepted EPs may be the best solution. If alternative fuels are burnt it is possible that CO peaks are produced more frequently than without, especially during the commissioning phase of the waste feed equipment. The plants that are burning alternative fuels or those that are planning to do so are usually under more intensive observation by the neighbors and the authorities. Frequent dust emission peaks caused by EP CO-shutdown or changes of process conditions may be very embarrassing when asking for a permission to burn alternative fuels or when applying for extension of the permit. Therefore, bag filters, especially the pulse jet type, will for many plants be the preferred solution for the future.


6/23/2001 - 5:14:17 PM

Page 131

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance

C03 - Maintenance


6/23/2001 - 5:14:17 PM

Page 132

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT)

FOCUS PROGRAM MAC (MAINTENANCE CEMENT) CORPORATE PROGRAMS, October 1996 1. EXECUTIVE SUMMARY 1.1 Objectives and expected Results of the Program MAC 1.2 Content of MAC 1.3 Approach 2. OBJECTIVES 3. CONTENT 4. APPROACH 4.1 “Buy-in“ 4.2 Analysis 4.3 Ownership 4.4 Project-Implementation 4.5 Continuous improvement 5. PROJECT ORGANIZATION AND RESOURCES 5.1 Local resources 5.2 External : Peter Chadwick 6. TRAINING 7. COMPUTERIZED MAINTENANCE SYSTEM 8. COST/BENEFIT OF MAC


6/23/2001 - 5:14:17 PM

Page 133

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 1. EXECUTIVE SUMMARY

1.

EXECUTIVE SUMMARY

There is a gap between the actual state of maintenance in the cement plants of the "Holderbank" group and what could be expected: Lack of availability of the equipment, upward trend of maintenance cost and high inventories of spare parts. Corporate Programs of HMC together with four plants of the Origny group, of Alsen-Breitenburg and of Holnam designed, tested and fine-tuned the focus program MAC to bridge this gap. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 1. EXECUTIVE SUMMARY / 1.1 Objectives and expected Results of the Program MAC

1.1

Objectives and expected Results of the Program MAC

MAC is a program to improve substantially the maintenance activity in our cement plants. The objective is to maximize the total maintenance benefit which consists of three elements: ♦ plant output, measured by a new Key Performance Indicator: OEE (Overall Equipment Efficiency) ♦ direct maintenance cost ♦ NOA utilized It is estimated that MAC will have the following impact on those three elements Short-term (annualized benefit at the end of MAC)

Mid-term (2-3 years after Focus program)

OEE

+ 5%

+ 10%

Direct Maintenance Costs

- 10%

- 25-30%

Spares Inventory

- 5%

- 20-30%

Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 1. EXECUTIVE SUMMARY / 1.2 Content of MAC

1.2

Content of MAC

The program MAC reinforces or introduces a proactive and systematic way of doing maintenance. The main elements contributing to excellent maintenance can be presented in form of a pyramid


6/23/2001 - 5:14:18 PM

Page 134


The fundamental elements are at the bottom. As we move upwards the elements become more sophisticated. The program MAC results in some elements fully implemented (green color) and some elements in progress (yellow color). It must be stressed that the program MAC represents a back-to-basics approach, combined with a sustainable behaviour change. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 1. EXECUTIVE SUMMARY / 1.3 Approach

1.3

Approach

The program MAC is structured into four general phases followed by continuous improvement.

Going through those phases guarantees ♦ a shared understanding of the improvement potential of a specific plant ♦ sufficient training for a behaviour change ♦ a solid base for future continuous improvement The implementation will be done by a local team coached by HMC staff and external consultants. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 2. OBJECTIVES

2.

OBJECTIVES

The objective of the focus program MAC is to bridge the gap between the current state of maintenance © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:18 PM

Page 135

"Holderbank" - Cement Course 2000 in our cement plants and what could be called excellent or world class maintenance. This means substantially improving our maintenance activities. Doing so will maximize the Total Maintenance Benefit (Fig. 1) which consists of three elements: ♦ plant output, measured by a new Key Performance Indicator: OEE (Overall Equipment Efficiency) - see Fig. 2 for definition ♦ direct maintenance cost ♦ NOA utilized Fig. 1: Total Maintenace Benefit

OEE as a new Key Performance Indicator in “HOLDERBANK“ is defined as: Fig. 2: OEE Definition

OEE = Availability x Performance x Quality

OEE therefore gives an indication how well the installed equipment is used. The maintenance activity has a big impact on the availability; but there is also an impact on the other two factors. Expected MAC-Impact on Total Maintenance Benefit: Short term (annualized benefit at the end of MAC)

Mid term (2-3 years after Focus program)

OEE

+ 5%

+ 10%

Direct Maintenance Costs

- 10%

- 25-30%

Spares Inventory

- 5%

- 20-30%

Remarks: ♦ Additional benefits will also be a reduction of replacement - investments due to an increased equipment-life-time with improved maintenance. ♦ The benefits indicated in the table represent what can be expected on the average of all our plants; © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:18 PM

Page 136

"Holderbank" - Cement Course 2000 some individual plants, however, might have higher or lower results depending on what they have been doing in the past few years. ♦ The OEE-objective represents a potential for additional tons. The realization of this potential, however, cannot be done by MAC because it depends entirely on the market conditions. All those objectives are percentages. The impact in USD can be calculated as follows: ♦ OEE-improvement by 5%: Using the price, volume and margin situation 1996 of the Portland plant of Holnam as a basis, this works out to be an impact of USD 1.89 per short ton or USD 1.7/t. ♦ Maintenance cost: The average maintenance cost in the HBK group is estimated to be around USD 8.--/t. A reduction by 25% therefore has an impact of USD 2.--/t. ♦ Lower inventories: No calculation has been made. Based on German figures the impact is estimated to be within USD 0.2 to USD 0.5/t. Taken together the total impact will be between USD 2.2/t (without OEE) and USD 4.2/t (with OEE). Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 3. CONTENT

3.

CONTENT

The focus program MAC reinforces or introduces a proactive and systematic way of doing maintenance by: ♦ Concentration on fundamentals (back-to-basic approach), such as work-orders, machine history, break-down-analysis etc. ♦ Training on the job of the plant-workforce as well as of the management. ♦ Changing of the behaviour, thereby guaranteeing sustainability. ♦ Building the base for subsequent continuous improvement. The main elements of world class maintenance can be presented in form of a pyramid (Fig. 3 and full-size in Appendix 1). This pyramid has been drawn in such a way that the most fundamental elements are at the bottom. Subsequent layers of "bricks" can only be built on elements already existing. Fig. 3: Expected MAC-Attainment

The color code used in this pyramid shows the evolution towards world class maintenance: ♦ Fully installed at the end of the MAC program. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:19 PM

Page 137

"Holderbank" - Cement Course 2000 Status: satisfactory maintenance ♦ Process initiated during the MAC program. Fully installed within 1-2 years after the MAC program, resulting in good maintenance. ♦ To be addressed in the continuous improvement phase after MAC. Necessary to achieve world class maintenance. ◊

Input elements for maintenance

To measure the progress and control the systematic application of the maintenance system, a set of Key Performance Indicators (KPI's) are introduced in the management report system with MAC. These KPI's are: OEE:

Overall Equipment Efficiency as a factor of:

Availability x Performance x Quality where operating hours Availability = total hours Performance =

actual output best demonstrated practice

Quality = 1 (to be defined with MAC) Work-Order Coverage:

Ratio of available direct maintenance hours to hours covered by work-orders

Maintenance Productivity:

Ratio of earned standard labor hours compared to planned hours.

Backlog:

Amount of total direct maintenance hours needed to do all pending jobs on work-orders

Direct Maintenance Costs:

as the sum of: •

material cost

•

labour cost

• subcontracted services used in maintenance. Direct maintenance costs should be also split into: a) current maintenance b) major repairs Spare parts inventory:

indicating the amount of all spares on inventory.

Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 4. APPROACH

4.

APPROACH

In order to realize the necessary change, there has to be an approach with a twin focus on technical systems development and people organizational development as shown in Fig. 4. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:19 PM

Page 138

"Holderbank" - Cement Course 2000 Fig. 4: The development of world class performance in maintenance

Based on the information gathered so far most of our plants seem to be in stage 1. The MAC program will bring them to stage 2 or 3 depending on their actual status. Stage 5 - required for world class maintenance - will be achieved within 3 to 5 years after MAC, with the consequent usage and further development of the elements in the pyramid. In each plant the MAC program will run through five phases as shown in Fig. 5. Fig. 5: Basic Approach

Those five phases can be described as follows: Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 4. APPROACH / 4.1 “Buy-in“

4.1

“Buy-in“

to the need and benefits of such a program by management at company and plant level, through a shared understanding of the improvement-opportunities. This buy-in phase consists of two steps: a) A company-visit to: •

present MAC to the local management

•

get familiar with the actual situation and the specific needs of maintenance

•

propose and discuss the steps needed to carry out the analysis and ownership phases

Based on the result of that visit, local management will decide how to proceed with MAC in their © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:20 PM

Page 139

"Holderbank" - Cement Course 2000 company-specific case. b) A preparation of plant staff for the analysis with the objective to get commitment to the process as well as to integrate/co-ordinate other ongoing initiatives in the plant with MAC. Part of this preparation phase should be a visit to a plant where MAC is actually implemented. This will show the approach in praxis and help to understand better the whole process. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 4. APPROACH / 4.2 Analysis

4.2

Analysis

of the plant to determine on the one hand specific potentials in the areas of increased output, maintenance cost reduction and spare-parts reduction. On the other hand to identify the detailed implementation approach required to realize the potentials. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 4. APPROACH / 4.3 Ownership

4.3

Ownership

of the project by company and plant management and full commitment to the potentials and therefore objectives of the project. Based on the cost/benefit-ratio a decision how to proceed with the project will be made by local management. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 4. APPROACH / 4.4 Project-Implementation

4.4

Project-Implementation

with the 3 steps of: a) t definition in detail of the problems, obstacles, tools and skills to be tackled. b) Participative development and installation of the systems, processes and behaviours to be improved, in the form of cross-functional teams, each focusing on one of the three aspects of the overall maintenance benefit. c) Transition of activities from a project base to incorporation in the day-to-day activities at all levels of the plant and company, thereby fine-tuning them to adapt fully to the individual needs. By including them in the day-to-day activities and closing the information loop through the different levels of hierarchy the activities are essentially being sustained and can lead to the next phase. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 4. APPROACH / 4.5 Continuous improvement

4.5

Continuous improvement

of the maintenance level and results achieved to attain world class maintenance in the medium to long-term. The MAC program requires between 6 to 9 months per plant, depending on the actual situation of its maintenance activities and the readiness of management and staff to embrace change. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 5. PROJECT ORGANIZATION AND RESOURCES


6/23/2001 - 5:14:20 PM

Page 140


PROJECT ORGANIZATION AND RESOURCES

A key success factor to achieve a sustainable improvement is the continuous “take over“ of “project activities“ into the “day-to-day business“. To that process the typical project organization (see Fig. 6) is integrated into and works within the actual structure and not in parallel. Fig. 6: Typical Project Organization

To implement the MAC program in a plant requires a substantial number of resources. As indicated in the organization chart in Fig. 6 the Team (4-6 people) should comprise local resources working together with HMC staff and external consultants. There were and are two reasons for working with an external consultant: Know-how transfer and need of resources. The external consultant chosen - Peter Chadwick Ltd. - provides both: down-to-earth know-how in maintenance and trained consultants willing and able to work in all parts of the world. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 5. PROJECT ORGANIZATION AND RESOURCES / 5.1 Local resources

5.1

Local resources

The majority of the resources will come from the companies themselves. Therefore early on a list of potential candidates must be established, a selection made and the necessary training (see section 5) given. One of the beneficial consequences of the focus program MAC will be the creation of a group of very skilled individuals in the area of organization, planning and implementation in HMC and the companies. These individuals will develop into maintenance, production and plant management positions, or higher, in the future, thereby facilitating succession planning in management. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 5. PROJECT ORGANIZATION AND RESOURCES / 5.2 External : Peter Chadwick

5.2

External : Peter Chadwick

The know-how and skills for the maintenance program and specifically for the behaviour change required to perpetuate the results is provided by Peter Chadwick Ltd. Initially all plant projects will be led by consultants from Peter Chadwick. In a second phase HMC and company staff will take on more importance in the teams, to ultimately be able to run these projects without any Peter Chadwick . This “take-over“ from Peter Chadwick will depend upon the availability of trained local- and HMC-resources. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:20 PM

Page 141

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 6. TRAINING

6.

TRAINING

A number of training workshop modules (see Fig. 7) have been developed to properly prepare team or provide the context and conceptual groundwork for company and plant staff during the project. These modules on their own can not create the behaviour change required to achieve the sustainability of results - this is only done through the continuous on-the-floor involvement, coaching of management and employees and utilization of tools and skills - but it creates the framework and conceptual understanding to improve acceptance of change. Fig. 7: Training Modules

Most of the training, however, will be done on the job and will be given by the external consultants and the HMC staff. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 7. COMPUTERIZED MAINTENANCE SYSTEM

7.

COMPUTERIZED MAINTENANCE SYSTEM

As shown in the maintenance pyramid, the element "computerized maintenance systems" is located in level 4 and therefore not directly targeted by MAC. However, during the analysis the project team will check how efficient an eventually existents system is used and define the needs to optimize the usage if possible. The experience so far has clearly shown the need "go back" and practice with the maintenance staff the systematic application of the redefined maintenance manually, that means with "paper and pencil"! The move towards a "computerized maintenance system" should only be done, when all the know how to use system elements like work orders and reports in their daily routine. As many of our companies are in the process of installing SAP, a special task force is actually working with SAP with the objective to give a clear recommendation how MAC and SAP links together. So far it has been concluded, that (whenever possible) MAC should be done: a) before installing PM module, and b) in close coordination with the SAP project group. Process Technology / B06 - PT III / C03 - Maintenance / FOCUS PROGRAM MAC (MAINTENANCE CEMENT) / 8. COST/BENEFIT OF MAC


6/23/2001 - 5:14:21 PM

Page 142


COST/BENEFIT OF MAC

The one-time investment for the program would lie between USD 0,7 and USD 1,0 per ton of cement. This investment is to be compared with the projected saving of USD 2.5 to 4.2, half of which should be achieved at the end of the formal MAC project. These figures are estimates based upon experiences in the pilot plants. The specific costs and savings for each plant are estimated at the end of each analysis phase as basis whether or not to go for MAC.


6/23/2001 - 5:14:21 PM

Page 143

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements

The Maintenance Elements

1. MAINTENANCE REQUIREMENTS PYRAMID 1.1 Description 1.2 Purpose 1.3 Examples 2. CRITICAL ASSET 2.1 Description 2.2 Purpose 2.3 Examples 3. WORKS ORDER SYSTEM 3.1 Description 3.2 Purpose 3.3 Examples 4. DAILY / WEEKLY PLAN 4.1 Maintenance Master Schedule 4.2 Weekly Plan 4.3 Daily Plan 5. MAINTENANCE KPI’S 5.1 Description 5.2 Purpose 5.3 Examples 6. DAILY MAINTENANCE REPORT 6.1 Description 6.2 Purpose 6.3 Examples 7. MAINTENANCE COST STRUCTURE 7.1 Description 7.2 Purpose 7.3 Examples © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:21 PM

Page 144

"Holderbank" - Cement Course 2000 7.4 Description 7.5 Purpose 7.6 Examples 8. PRODUCTION PLAN 8.1 Description 8.2 Purpose 9. SPARES POLICY & MANAGEMENT 9.1 Description 9.2 Purpose 9.3 Examples 10. STANDARDS & SPECIFICATIONS 10.1

Description

10.2

Purpose

10.3

Examples

11. ASSET HISTORY SYSTEM 11.1

Description

11.2

Purpose

11.3

Examples

12. WEEKLY MAINTENANCE REPORT 12.1

Description

12.2

Purpose

12.3

Examples

13. MAINTENANCE COST REPORT 13.1

Description

13.2

Purpose

13.3

Examples

14. RESOURCE SKILLS MATRIX 14.1

Description

14.2

Purpose

14.3

Examples

15. BUDGET 15.1

Description

15.2

Purpose


6/23/2001 - 5:14:21 PM

Page 145

"Holderbank" - Cement Course 2000 15.3

Examples

16. BILL OF MATERIALS (BOM) 16.1

Description

16.2

Purpose

16.3

Examples

17. MAINTENANCE MASTER SCHEDULE 17.1

Description

17.2

Purpose

17.3

Examples

17.4

Overview

17.5

Description

17.6

Purpose

17.7

Examples

18. FMEA / RCM 18.1

Description

18.2

Purpose

19. RCM APPROACH 20. MTBF / MTTR / MTBCF 20.1

Description

20.2

Purpose

20.3

Examples

20.4

MTBF (Hours)

20.5

MTTR (Hours)

20.6

MTBCF (Hours)

21. PREDICTIVE ROUTINES / CONDITION BASED MONITORING 21.1

Description

21.2

Purpose

21.3

Examples

22. PLANT MASTER PLAN 22.1

Description

22.2

Purpose

23. MULTI-SKILLING 23.1

Description


6/23/2001 - 5:14:21 PM

Page 146


Purpose

23.3

Examples

23.4

Description

23.5

Purpose

23.6

Examples

24. COMPUTERIZED MAINTENANCE SYSTEMS 24.1

Description

24.2

Purpose

24.3

Examples

25. AUTONOMOUS MAINTENANCE 25.1

Description

25.2

Purpose

25.3

Examples

26. BUSINESS PLAN 26.1

Description

26.2

Purpose

27. AREA WORK TEAMS 27.1

Description

27.2

Purpose

28. PROCESS MAINTENANCE TEAMS 28.1

Description

28.2

Purpose

28.3

Examples

28.4

Description

28.5

Purpose

28.6

Examples

28.7

Examples

29. INTEGRATED PROCESS / MAINTENANCE SYSTEM 29.1

Description

29.2

Purpose

29.3

Examples

30. GLOSSARY OF


6/23/2001 - 5:14:22 PM

Page 147

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 1. MAINTENANCE REQUIREMENTS PYRAMID

1.

MAINTENANCE REQUIREMENTS PYRAMID

Asset Numbering System (HAC/PNS) Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 1. MAINTENANCE REQUIREMENTS PYRAMID / 1.1 Description

1.1

Description

♦ Unique asset numbering system describing : •

All assets (to the lowest discrete maintainable level)

•

Its physical location

♦ The equipment numbering system should be consistent for a plant and ideally, but not necessarily, across the whole business Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 1. MAINTENANCE REQUIREMENTS PYRAMID / 1.2 Purpose

1.2

Purpose

♦ Allow tracking of reliability, activity and costs against each item of maintainable asset ♦ It is a requirement for basic history reporting Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 1. MAINTENANCE REQUIREMENTS PYRAMID / 1.3 Examples

1.3

Examples

♦ HAC, PNS Code Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 2. CRITICAL ASSET

2.

CRITICAL ASSET

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 2. CRITICAL ASSET / 2.1 Description

2.1

Description


6/23/2001 - 5:14:22 PM

Page 148

"Holderbank" - Cement Course 2000 ♦ Failure of the asset (for more than n hours) interrupts production of the finished product ♦ Failure of the asset may result in a failure to meet legislative, safety or environmental requirements ♦ Failure to repair the asset immediately will result in significant damage to that or another item of equipment ♦ No other back-up equipment is available ♦ The equipment requires special or external attention Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 2. CRITICAL ASSET / 2.2 Purpose

2.2

Purpose

♦ To focus and prioritize maintenance effort for maximum gain Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 2. CRITICAL ASSET / 2.3 Examples

2.3

Examples

♦ Kiln Girth Gear, Mill Drive, Cooler Grates Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 3. WORKS ORDER SYSTEM

3.

WORKS ORDER SYSTEM

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 3. WORKS ORDER SYSTEM / 3.1 Description

3.1

Description

♦ Information and control system providing : •

- Instruction to perform a task

•

- The priority of the task

•

- Task description

•

- of what was done, lost time and parts used

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 3. WORKS ORDER SYSTEM / 3.2 Purpose

3.2

Purpose

♦ Controls and monitors maintenance activity ♦ Provides an auditable trail for all jobs ♦ Provides feed to other information systems Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 3. WORKS ORDER SYSTEM / 3.3 Examples

3.3

Examples

♦ Mapcon / SAP / Marcam / etc. Works Order System Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 4. DAILY / WEEKLY PLAN


6/23/2001 - 5:14:22 PM

Page 149


DAILY / WEEKLY PLAN

LEVELS OF MAINTENANCE PLANNING Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 4. DAILY / WEEKLY PLAN / 4.1 Maintenance Master Schedule

4.1

Maintenance Master Schedule

♦ Capacity and Resource Planning ♦ Medium Term (13 weeks) ♦ ‘What-If’ Modeling Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 4. DAILY / WEEKLY PLAN / 4.2 Weekly Plan

4.2

Weekly Plan

♦ Weekly Scheduling ♦ Task Prioritization ♦ Planning of skills, resource and equipment requirements Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 4. DAILY / WEEKLY PLAN / 4.3 Daily Plan

4.3

Daily Plan

♦ Allocation of tasks to individuals ♦ Flexing of the plan on a daily basis

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 5. MAINTENANCE KPI’S

5.

MAINTENANCE KPI’S

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 5. MAINTENANCE KPI’S / 5.1 Description

5.1

Description

♦ The key operational performance measurements which can be used to manage Maintenance or an area within Maintenance © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:23 PM

Page 150

"Holderbank" - Cement Course 2000 ♦ A KPI should have a base, plan and target ♦ For a KPI to be useful it should be timely and capable of being influenced by the person using it Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 5. MAINTENANCE KPI’S / 5.2 Purpose

5.2

Purpose

♦ Allows performance to be measured and reviewed ♦ Enables good fact based business decisions Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 5. MAINTENANCE KPI’S / 5.3 Examples

5.3

Examples

♦ Management Report, Daily/Weekly Operating Report (DOOR) and Short Interval Controls ♦ OEE, Availability, Performance, etc. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 6. DAILY MAINTENANCE REPORT

6.

DAILY MAINTENANCE REPORT

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 6. DAILY MAINTENANCE REPORT / 6.1 Description

6.1

Description

♦ Timely reporting of plan attainment of maintenance activities and equipment performance including cause of variation Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 6. DAILY MAINTENANCE REPORT / 6.2 Purpose

6.2

Purpose

♦ To allow structured review and to assign corrective actions to improve towards the agreed target levels Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 6. DAILY MAINTENANCE REPORT / 6.3 Examples

6.3

Examples

♦ SIC Log sheet Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 7. MAINTENANCE COST STRUCTURE

7.

MAINTENANCE COST STRUCTURE

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 7. MAINTENANCE COST STRUCTURE / 7.1 Description

7.1

Description

♦ Definition of the level of detail for cost reporting © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:23 PM

Page 151

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 7. MAINTENANCE COST STRUCTURE / 7.2 Purpose

7.2

Purpose

♦ Systematic cost roll up to enable analysis and reporting on all required asset levels Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 7. MAINTENANCE COST STRUCTURE / 7.3 Examples

7.3

Examples

SHORT INTERVAL CONTROL (SIC) Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 7. MAINTENANCE COST STRUCTURE / 7.4 Description

7.4

Description

♦ Regular monitoring and control of a process or activity ♦ The frequency of SIC should reflect the span of control that an individual has to influence the process or activity Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 7. MAINTENANCE COST STRUCTURE / 7.5 Purpose

7.5

Purpose

♦ To identify problems early and prevent them of becoming bigger ones Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 7. MAINTENANCE COST STRUCTURE / 7.6 Examples

7.6

Examples

♦ Maintenance activities ♦ Operation performance [t/h] ♦ Maintenance costs


6/23/2001 - 5:14:23 PM

Page 152


Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 8. PRODUCTION PLAN

8.

PRODUCTION PLAN

[Input Element to Maintenance System] Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 8. PRODUCTION PLAN / 8.1 Description

8.1

Description

♦ A Weekly Plan indicating production requirements for the week should be broken down into Daily Plans indicating target production levels ♦ The Production Plan should be linked to the Maintenance Plan to identify the agreed equipment availability for both maintenance activities and production needs Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 8. PRODUCTION PLAN / 8.2 Purpose

8.2

Purpose

♦ To the co-ordination of activities and requirements between Production and Maintenance Note: The production plan is not a development of “MAC”. However the production plan is an important input to the maintenance system as described above. The maintenance system as developed by “MAC” will feed the production plan with more accurate information and therefor help to improve its content. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 9. SPARES POLICY & MANAGEMENT

9.

SPARES POLICY & MANAGEMENT

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 9. SPARES POLICY & MANAGEMENT / 9.1 Description

9.1

Description

♦ Spares policy and management takes into : •

Spares criticality

•

Lead-Time of critical spares

•

Economic Order and Stocking Quantities


6/23/2001 - 5:14:24 PM

Page 153

"Holderbank" - Cement Course 2000 •

Parts Availability and Quality

•

Inter-plant parts sharing agreements

•

Systematical planning and control (reporting) of spare parts in order to maximize availability and minimize cost

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 9. SPARES POLICY & MANAGEMENT / 9.2 Purpose

9.2

Purpose

♦ To maximize critical equipment availability at minimum cost ♦ A stocking policy is a pre-requisite for maintaining a spares management system Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 9. SPARES POLICY & MANAGEMENT / 9.3 Examples

9.3

Examples

♦ Decision whether or not to store a kiln tyre Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 10. STANDARDS & SPECIFICATIONS

10.

STANDARDS & SPECIFICATIONS

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 10. STANDARDS & SPECIFICATIONS / 10.1 Description

10.1

Description

♦ Standard short Description of a planned or routine maintenance activity like : •

What needs to be done

•

How it should be performed

•

The optimum time to complete it

•

How many people are required

•

What skill or trade is required

•

What materials & tooling

•

Quality and safety requirements

•

Standard short description of failure cause

•

Standard short description of lost time causes

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 10. STANDARDS & SPECIFICATIONS / 10.2 Purpose

10.2

Purpose

♦ To enable the identification of lost time and to provide clear and consistent instruction of the best way to perform a task. ♦ Clear identification of failure causes in order to make statistical analysis Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 10. STANDARDS & SPECIFICATIONS / 10.3 Examples © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:24 PM

Page 154


Examples

♦ Instructions for a routine inspection or tensioning of a belt Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 11. ASSET HISTORY SYSTEM

11.

ASSET HISTORY SYSTEM

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 11. ASSET HISTORY SYSTEM / 11.1 Description

11.1

Description

♦ A performance history record for each item of asset including: •

Downtime and number of failure

•

Descriptions of major failures

•

Causes for those failures

•

Maintenance activities performed

•

Maintenance costs

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 11. ASSET HISTORY SYSTEM / 11.2 Purpose

11.2

Purpose

♦ Allows the simple analysis showing basic history and performance of all assets. ♦ s strategic or capital decisions. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 11. ASSET HISTORY SYSTEM / 11.3 Examples

11.3

Examples

♦ Equipment performance log book ♦ Work Order History Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 12. WEEKLY MAINTENANCE REPORT

12.

WEEKLY MAINTENANCE REPORT

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 12. WEEKLY MAINTENANCE REPORT / 12.1 Description

12.1

Description

♦ Timely reporting of maintenance KPI’s to allow the review and analysis of maintenance activity and equipment performance. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 12. WEEKLY MAINTENANCE REPORT / 12.2 Purpose

12.2

Purpose

♦ To allow structured review and to assign corrective actions to improve towards the agreed target levels © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:24 PM

Page 155

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 12. WEEKLY MAINTENANCE REPORT / 12.3 Examples

12.3

Examples

♦ Maintenance KPI Report. ♦ Management Report Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 13. MAINTENANCE COST REPORT

13.

MAINTENANCE COST REPORT

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 13. MAINTENANCE COST REPORT / 13.1 Description

13.1

Description

♦ A life-cycle cost analysis system to determine the true costs of operating and maintaining an item of asset. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 13. MAINTENANCE COST REPORT / 13.2 Purpose

13.2

Purpose

♦ To enable improved decision making including repair, replacement or re-engineer decisions. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 13. MAINTENANCE COST REPORT / 13.3 Examples

13.3

Examples

♦ Cost Report out of machine history (top ten spendings) Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 14. RESOURCE SKILLS MATRIX

14.

RESOURCE SKILLS MATRIX

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 14. RESOURCE SKILLS MATRIX / 14.1 Description

14.1

Description

♦ Matrix identifying the skills needed for all people who perform maintenance activities. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 14. RESOURCE SKILLS MATRIX / 14.2 Purpose

14.2

Purpose

♦ To identify the skills base, needs /gaps and training requirements for an individual or group of people in order to optimize skills flexibility. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 14. RESOURCE SKILLS MATRIX / 14.3 Examples


6/23/2001 - 5:14:25 PM

Page 156


Examples

♦ Human Resource Training records. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 15. BUDGET

15.

BUDGET

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 15. BUDGET / 15.1 Description

15.1

Description

♦ The Budget should explicitly identify projected maintenance costs by period including: •

Labor

•

Materials

•

Spare parts

•

Major Project

•

Contractors

♦ The Budget should be linked to the planned KPI’s levels. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 15. BUDGET / 15.2 Purpose

15.2

Purpose

♦ To identify and plan maintenance costs and to set operating targets. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 15. BUDGET / 15.3 Examples

15.3

Examples

♦ Annual maintenance budget Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 16. BILL OF MATERIALS (BOM)

16.

BILL OF MATERIALS (BOM)

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 16. BILL OF MATERIALS (BOM) / 16.1 Description

16.1

Description

♦ Explosion of all of the parts and consumables, to the level of each purchasable item, required to maintain an item of asset. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 16. BILL OF MATERIALS (BOM) / 16.2 Purpose

16.2

Purpose

♦ To identify the parts required to perform all maintenance activities. ♦ Maintenance Planning and Stock Management. ♦ Maintainability improvement. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:25 PM

Page 157

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 16. BILL OF MATERIALS (BOM) / 16.3 Examples

16.3

Examples

♦ Asset - Spare Part identification/relation, (HAC-PNS) Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 17. MAINTENANCE MASTER SCHEDULE

17.

MAINTENANCE MASTER SCHEDULE

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 17. MAINTENANCE MASTER SCHEDULE / 17.1 Description

17.1

Description

♦ A long term plan (3 month) indicating all maintenance activities and the resources required to complete them, considering : •

Labor Availability

•

Labor Productivity

•

Planned / Predictive Maintenance Routines

•

Task Priorities

•

Materials and Spare Parts Availability

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 17. MAINTENANCE MASTER SCHEDULE / 17.2 Purpose

17.2

Purpose

♦ To identify maintenance resource requirements and to optimize maintenance efforts. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 17. MAINTENANCE MASTER SCHEDULE / 17.3 Examples

17.3

Examples

♦ 13 week Master Schedule for the cement grinding area Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 17. MAINTENANCE MASTER SCHEDULE / 17.4 Overview

17.4

Overview


6/23/2001 - 5:14:25 PM

Page 158

"Holderbank" - Cement Course 2000 PLANNED MAINTENANCE ROUTINES (PMR’s) Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 17. MAINTENANCE MASTER SCHEDULE / 17.5 Description

17.5

Description

♦ Routine activities designed to minimize the risk of unplanned failures, including: •

Routine overhauls

•

Fixed frequency replacement of parts or equipment

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 17. MAINTENANCE MASTER SCHEDULE / 17.6 Purpose

17.6

Purpose

♦ To minimize unnecessary downtime and increase predictability by reducing the level of unplanned maintenance. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 17. MAINTENANCE MASTER SCHEDULE / 17.7 Examples

17.7

Examples

♦ Replacement of Cement Mill liners every 20’000 hrs. of production. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 18. FMEA / RCM

18.

FMEA / RCM

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 18. FMEA / RCM / 18.1 Description

18.1

Description

♦ Failure Mode Effect Analysis (FMEA) is an analytical tool to systematically establish the failure mode and effect of a failure. ♦ Reliability Centered Maintenance (RCM) is a process, utilizing FMEA, for determining what maintenance, if any, should be performed in order to respond to the demands for : •

Safe Operation

•

Environmental Protection

•

Production Quality

•

Plant Availability

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 18. FMEA / RCM / 18.2 Purpose

18.2

Purpose

♦ To proactively identify the optimum maintenance activity. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 19. RCM APPROACH


6/23/2001 - 5:14:26 PM

Page 159


RCM APPROACH A continuous process for determining the optimum preventive maintenance plan for each item of plant in its operating context.

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 20. MTBF / MTTR / MTBCF

20.

MTBF / MTTR / MTBCF

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 20. MTBF / MTTR / MTBCF / 20.1 Description

20.1

Description

♦ Indicators to measure maintenance effectiveness •

Mean Time Between Failure (MTBF)

•

Indication of the average time between failure for an item of asset.

•

Mean Time To Repair (MTTR)

•

Indication of the average downtime duration for an item of asset.

•

Mean Time Between Cause & Failure (MTBCF)

•

Indication of the MTBF by specific cause.

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 20. MTBF / MTTR / MTBCF / 20.2 Purpose

20.2

Purpose

♦ To measure and focus on the correct alignment of maintenance activity. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 20. MTBF / MTTR / MTBCF / 20.3 Examples

20.3

Examples

♦ Focus Maintenance activities in the “Bottle Neck” area. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 20. MTBF / MTTR / MTBCF / 20.4 MTBF (Hours)

20.4

MTBF (Hours)


6/23/2001 - 5:14:26 PM

Page 160

"Holderbank" - Cement Course 2000 Total Time Controlled - Duration of Breakdowns ________________________________________ Number of Breakdowns Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 20. MTBF / MTTR / MTBCF / 20.5 MTTR (Hours)

20.5

MTTR (Hours) Cumulative Downtime _____________________ Number of Breakdowns

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 20. MTBF / MTTR / MTBCF / 20.6 MTBCF (Hours)

20.6

MTBCF (Hours) Total Time Controlled - Duration of Breakdowns by Cause _________________________________________________ Number of Breakdowns due to that cause

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 21. PREDICTIVE ROUTINES / CONDITION BASED MONITORING

21.

PREDICTIVE ROUTINES / CONDITION BASED MONITORING

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 21. PREDICTIVE ROUTINES / CONDITION BASED MONITORING / 21.1 Description

21.1

Description

♦ Predictive inspection routines, condition based monitoring and condition based maintenance to asses the condition of equipment to predict failure and perform planned maintenance activities. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 21. PREDICTIVE ROUTINES / CONDITION BASED MONITORING / 21.2 Purpose

21.2

Purpose

♦ To minimize the level of intrusive maintenance. ♦ To optimize the use of asset lifetime. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 21. PREDICTIVE ROUTINES / CONDITION BASED MONITORING / 21.3 Examples

21.3

Examples

♦ Oil analysis to determine change. ♦ Vibration measurement to determine the optimal time to replace a rolling bearing. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 22. PLANT MASTER PLAN

22.

PLANT MASTER PLAN


6/23/2001 - 5:14:26 PM

Page 161

"Holderbank" - Cement Course 2000 [Input Element to Maintenance System] Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 22. PLANT MASTER PLAN / 22.1 Description

22.1

Description

♦ A long term plan (1 to 3 year) indicating : •

Production Requirements

•

Labor Availability

•

Training Plan

•

Major Maintenance Activities

•

Investments

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 22. PLANT MASTER PLAN / 22.2 Purpose

22.2

Purpose

♦ To identify planned major maintenance activities and investments in order to optimize resource requirements (capital, people, training). Note: The Plant Master Plan is not a development of “MAC”. However the Plant Master Plan is an important input to the maintenance system as described above. The maintenance system as developed by “MAC” will make a sound base for updating the Plant Master Plan. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 23. MULTI-SKILLING

23.

MULTI-SKILLING

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 23. MULTI-SKILLING / 23.1 Description

23.1

Description

♦ Training of all operational employees in the core maintenance skills either between Process Operators and Maintenance Technicians or between different trades. ♦ Note : Multi-Skilling does not mean that everyone should be expected to do everything. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 23. MULTI-SKILLING / 23.2 Purpose

23.2

Purpose

♦ To maximize labor utilization. ♦ Basic requirement for Autonomous Maintenance Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 23. MULTI-SKILLING / 23.3 Examples

23.3

Examples

♦ Quarry truck drivers doing their own oil changes. ♦ Production doing daily inspection. SHUTDOWN CYCLE TIME COMPRESSION (CTC)


6/23/2001 - 5:14:26 PM

Page 162

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 23. MULTI-SKILLING / 23.4 Description

23.4

Description

♦ Approach for planning, controlling and reviewing activities during a shutdown period in order to minimize downtime: •

Critical path planning to identify and manage parallel or critical activities

•

Value Added (VA) / Non-Value Added (NVA) analysis to identify and remove non-essential activities.

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 23. MULTI-SKILLING / 23.5 Purpose

23.5

Purpose

♦ To minimize equipment downtime by identifying activities which can be performed outside of a shutdown or in parallel ♦ To minimize equipment downtime by improving maintainability. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 23. MULTI-SKILLING / 23.6 Examples

23.6

Examples

♦ Kiln shut down ♦ Mill shut down Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 24. COMPUTERIZED MAINTENANCE SYSTEMS

24.

COMPUTERIZED MAINTENANCE SYSTEMS

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 24. COMPUTERIZED MAINTENANCE SYSTEMS / 24.1 Description

24.1

Description

♦ Integrated, comprehensive maintenance management system linked to all of the other relevant business systems including purchasing, stock control, engineering & finance. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 24. COMPUTERIZED MAINTENANCE SYSTEMS / 24.2 Purpose

24.2

Purpose

♦ To automate the development and management of maintenance information. ♦ Note : It is only appropriate to fully automate the maintenance system once it has been developed, tested and utilized in a live application. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 24. COMPUTERIZED MAINTENANCE SYSTEMS / 24.3 Examples

24.3

Examples

♦ Mapcon / SAP / Marcam / JDE / etc.


6/23/2001 - 5:14:27 PM

Page 163

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 25. AUTONOMOUS MAINTENANCE

25.

AUTONOMOUS MAINTENANCE

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 25. AUTONOMOUS MAINTENANCE / 25.1 Description

25.1

Description

♦ High frequency maintenance tasks which can be performed routinely by the immediate operator, outside the control of the planning system. Often utilizing check sheets or where the operator does not need to be told to do a task. ♦ Dependent upon behavioral change and true ownership of the process. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 25. AUTONOMOUS MAINTENANCE / 25.2 Purpose

25.2

Purpose

♦ To devolve and simplify maintenance tasks. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 25. AUTONOMOUS MAINTENANCE / 25.3 Examples

25.3

Examples

♦ Simple lubrication, cleaning to identify contamination, gauge marking. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 26. BUSINESS PLAN

26.

BUSINESS PLAN

[Input Element to Maintenance System] Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 26. BUSINESS PLAN / 26.1 Description

26.1

Description

♦ A long term plan (5 year) indicating the company's strategies and activities, and the resources required to complete them, considering : •

Market Development

•

Business Focus

•

Labor Availability

•

Training Plan

•

Investments

•

KPI’s Targets

•

Mission

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 26. BUSINESS PLAN / 26.2 Purpose

26.2

Purpose


6/23/2001 - 5:14:27 PM

Page 164

"Holderbank" - Cement Course 2000 ♦ To manage direction of business. ♦ To identify operation resource requirements and to optimize operation efforts. Note: The Business Plan is not a development of “MAC”. However the Business Plan is an important input to the maintenance system as described above. The maintenance system as developed by “MAC” will make a sound base for updating the Business Plan. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 27. AREA WORK TEAMS

27.

AREA WORK TEAMS

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 27. AREA WORK TEAMS / 27.1 Description

27.1

Description

♦ Individuals from the Maintenance and Process functions aligned to an area responsible for the operation, maintenance and improvement of all assets in that area, ed by specialists (assessor) when required. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 27. AREA WORK TEAMS / 27.2 Purpose

27.2

Purpose

♦ To create ownership of the process and to ensure continuous improvements. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 28. PROCESS MAINTENANCE TEAMS

28.

PROCESS MAINTENANCE TEAMS

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 28. PROCESS MAINTENANCE TEAMS / 28.1 Description

28.1

Description

♦ A Multi-Functional Team replacing discrete or Cross-Functional Maintenance and Process Operator teams. ♦ Everyone is a ‘Maintainer Operator’. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 28. PROCESS MAINTENANCE TEAMS / 28.2 Purpose

28.2

Purpose

♦ To minimize maintenance cost whilst maximizing flexibility. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 28. PROCESS MAINTENANCE TEAMS / 28.3 Examples

28.3

Examples


6/23/2001 - 5:14:27 PM

Page 165


RISK BASED MAINTENANCE (RBM) Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 28. PROCESS MAINTENANCE TEAMS / 28.4 Description

28.4

Description

♦ Extension of the RCM process to determine the optimum maintenance approach based upon cost and reliability requirements within a changing environment. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 28. PROCESS MAINTENANCE TEAMS / 28.5 Purpose

28.5

Purpose

♦ To achieve the optimum operational cost for a business. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 28. PROCESS MAINTENANCE TEAMS / 28.6 Examples

28.6

Examples

♦ When there are no sales and the silo is full, why incur the cost of fixing an item of asset? Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 28. PROCESS MAINTENANCE TEAMS / 28.7 Examples

28.7

Examples

♦ Risk Profile Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 29. INTEGRATED PROCESS / MAINTENANCE SYSTEM

29.

INTEGRATED PROCESS / MAINTENANCE SYSTEM

Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 29. INTEGRATED PROCESS / MAINTENANCE SYSTEM / 29.1 Description

29.1

Description

♦ Systems developed and utilized for process control used to take maintenance decisions. These would include expert systems, rate loss and downtime ing systems. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:28 PM

Page 166

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 29. INTEGRATED PROCESS / MAINTENANCE SYSTEM / 29.2 Purpose

29.2

Purpose

♦ To return rate to optimum or to predict the deterioration of plant condition in order to identify maintenance requirements. Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 29. INTEGRATED PROCESS / MAINTENANCE SYSTEM / 29.3 Examples

29.3

Examples

♦ Computerized maintenance system linked with a fully developed “TIS” Process Technology / B06 - PT III / C03 - Maintenance / The Maintenance Elements / 30. GLOSSARY OF

30.

GLOSSARY OF

MAC

MAintenance Cement

KPI

Key Performance Indicator

ESLH

Earned Standard Labor Hours

W/O’s

Works Orders

BOM

Bill of Materials

CTC

Cycle Time Compression

SIC

Short Interval Control

PM

Preventive Maintenance

PDM

Predictive Maintenance

CBM

Condition Based Monitoring

FMEA

Failure Mode Effect Analysis

RCM

Reliability Centered Maintenance

OEE

Overall Equipment Efficiency

MTBF

Mean Time Between Failure

MTTR

Mean Time To Repair

MTBCF

Mean Time Between Cause and Failure

RbM

Risk based Maintenance

HAC

Holderbank Asset Code

PNS

Part Numbering System

TIS

Technical Information System

DWOR

Daily / Weekly Operating Report

PMR

Planned Maintenance Routines


6/23/2001 - 5:14:28 PM

Page 167



6/23/2001 - 5:14:28 PM

Page 168

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management

The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management

1. AN INTRODUCTION TO THE OEE CONCEPT 1.1 Team Development 1.2 Design engineers have the skill to design the car ... 1.3 The driver competes on the track ... 1.4 The driver competes on the track ... 1.5 The team 1.6 If Design ignored input ... 1.7 The driver ignored the pit .... 1.8 And the pit team only focused on their needs .... 1.9 Successful and winning teams work together 1.10

Both the driver and the pit team have input into design

1.11

As the car is developed there are constant reviews of progress

1.12

It is not difficult to draw the parallel to cement production ...

1.13

Motor racing uses indicators to measure performance ....

1.14

Under the MAC we do not want complex measures of performance ...

1.15

A common unit of measure helps establish where we are and where we want to be

2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS 2.1 Why do we need effective maintenance systems? 2.2 Sailing a small ship within sight of shore requires little data - just the weather report perhaps 2.3 But in times of danger data is vital... 2.4 Behavioural Change 2.5 The need for behavioural change 2.6 Control the whole... 2.7 THREE TYPES OF BUSINESS SYSTEMS 2.8 What systems do 2.9 There are three major maintenance activities 2.10

Can we answer some of the following questions…


6/23/2001 - 5:14:28 PM

Page 169



2.12

PERFORMANCE SYSTEMS

2.13

BASIC SYSTEM ELEMENTS

2.14

THE COMMUNICATIONS STRUCTURE

2.15

SYSTEM CONCEPTS

2.16

Typical phases

2.17

SYSTEM CONCEPTS - GENERIC MGMT. CONTROL

2.18

What do Management Control systems do for our business?

2.19

Control the whole... by controlling the parts

3. SPARES MANAGEMENT 3.1 THE NEED TO BE COMPETITIVE 3.2 The financial performance of any plant can be evaluated by a simple formula 3.3 Costs are made up of many things, one of which is the costs of the spares held 3.4 Some of those will be critical… 3.5 One area often neglected in operations is the quality of maintenance spares held… 3.6 Where do we begin? 3.7 Set the policy 3.8 Spares Management is juggling 3.9 Spares Management is understanding 3.10

The Objective - Financial

3.11

The Objective - Operational

3.12

To manage spares we must understand spares

3.13

The two steps in bringing greater control to spares holdings

3.14

The 20 / 80 theory

3.15

COST

3.16

MOVEMENT

3.17

Stock Rotation

3.18

It is useful for the MAC teams to overlay certain definitions as they consider cost

3.19

ONGOING CONTROL

3.20

INDICATORS

3.21

THE KEY TO SUCCESS


6/23/2001 - 5:14:28 PM

Page 170


Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT

1.

AN INTRODUCTION TO THE OEE CONCEPT

Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.1 Team Development

1.1

Team Development

The principles that underpin the concept of OEE (Overall Equipment Efficiency) can be vividly illustrated by turning to the world of motor racing. Motor manufacturers assemble a team with the sole objective of winning Formula One Grand Prix’s and if possible, the World series. A Team Manager is selected and he is instrumental in selecting the various people he will need to achieve the goal. It is interesting to note that although racing drivers themselves are celebrities in their own right, the goal is for the Manufacturing team to win. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.2 Design engineers have the skill to design the car ...

1.2

Design engineers have the skill to design the car ...

The design team will be drawn from engineers with many different disciplines. There will be those who specialise in suspension systems. Others will be experts in aerodynamics, focusing on the vital job of reducing wind resistance. Others will specialise in the various aspects of engine manufacture, from © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:29 PM

Page 171

"Holderbank" - Cement Course 2000 ignition systems to lubrication systems. Each very knowledgeable in their own field. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.3 The driver competes on the track ...

1.3

The driver competes on the track ...

A Formula One driver who is successful is a celebrity. They seek fame and are blessed with a not inconsiderable amount of ego. They have to have skill - and courage, yet they must also have patience so that when lying in second place they can tactically choose the right point at which to challenge for the lead. They must know their machines and know the various circuits that go up to make the world series. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.4 The driver competes on the track ...

1.4

The driver competes on the track ...

Mechanics, like the engineers, will come from different disciplines. They are responsible for preparing the vehicle for the race and for maintaining it during the race. They need to be able to handle the stress of working under extreme pressure when a pit stop occurs and be able to work as part of a team. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.5 The team

1.5

The team


6/23/2001 - 5:14:29 PM

Page 172


Many different disciplines, many different personalities, all focused toward achieving victory. At the moment of victory the driver is the one who wears the laurels and gets the champagne. The team are left to celebrate away from the limelight and television cameras. Yet all participated in the victory. Victory would not - could not - be gained unless each had built their own personalities and skills into the achievement of one common goal - crossing the line first in one of the most competitive arenas that it is possible to envisage. But it could all have been so very different. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.6 If Design ignored input ...

1.6

If Design ignored input ...

Imagine how it would have been if the design team had totally ignored the needs of the remainder of the team. Let’s concentrate on deg a car that we like - that is a marvel of engineering - but not really suited to Formula One, let alone winning. Sometimes design niceties have to be sacrificed because of a maintenance requirement that will allow the pit team to meet the stringent times required for a pit stop if there is to be any hope of being in the first five - let alone out in front. Driver needs must be catered for. What use is a superb car if the driver becomes so fatigued that concentration has failed by the fifth lap. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.7 The driver ignored the pit ....

1.7

The driver ignored the pit ....


6/23/2001 - 5:14:30 PM

Page 173


Even when in front there are times when the car just has to come in for maintenance. It would be very little use for the driver to go blasting past the pit, when signalled to come in, then break down halfway round the circuit. At any given moment there will be decisions to be made that are in the interest of the goal of the team, not individual needs. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.8 And the pit team only focused on their needs ....

1.8

And the pit team only focused on their needs ....

There are often moments when, just having completed one pit stop, the car has to come back in again. Weather conditions might change quite dramatically and what were the right tyres one lap earlier are now totally unsuited for the new conditions. When this happens the pit team must effect a pit change on successive laps. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.9 Successful and winning teams work together

1.9

Successful and winning teams work together


6/23/2001 - 5:14:30 PM

Page 174


To be successful a team must all work together to meet the common goal - victory. Ideas must be shared. When a pit stop is taking too long then it has to be examined in detail, using everyone’s input. Is it a design problem or a skill problem with of the pit team? Is it a method change that’s required - or an engineering change? Personalities no longer count. Always the common goal of victory keeps the team focused on the goal. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.10 Both the driver and the pit team have input into design

1.10

Both the driver and the pit team have input into design

Problems are discussed and new ideas tried out, first in theory, then in practice. If engineering input is required then the engineering specialist will attend the group’s discussion. The problem is a team problem. The common function is winning - everything and everyone is secondary to that. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.11 As the car is developed there are constant reviews of progress

1.11

As the car is developed there are constant reviews of progress


6/23/2001 - 5:14:30 PM

Page 175


When the solution is found everyone included in the problem solving process is congratulated. There is only one common measurement for team success - winning. Because the measurement is so visible there can be no one function that is successful at the expense of the others. There may be secondary measurements under the umbrella of winning, for example the time taken for a pit stop, the top speed of the vehicle, the number of laps completed without breakdown, but each one of these indicators needs the input of more than one function in the solution. More importantly, no one function can solve its own problems at the expense of the others. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.12 It is not difficult to draw the parallel to cement production ...

1.12

It is not difficult to draw the parallel to cement production ...

It is not too difficult to draw the comparison between the world of Formula One and the less glamorous but more practical world of the cement industry. The roles are very very close to the roles undertaken in Formula One. The skills required are also very similar. The need to measure performance by the team remains the same need in cement business performance as it does in Formula One - a single overall indicator ed by other indicators for problem solving. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.13 Motor racing uses indicators to measure performance ....

1.13

Motor racing uses indicators to measure performance ....


6/23/2001 - 5:14:31 PM

Page 176


As we have already seen, the world of Formula One uses these series of indicators to measure performance. In production we need the total overall indicator by which the team - as a whole - can measure degrees of success and benchmark themselves against the competition. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.14 Under the MAC we do not want complex measures of performance ...

1.14

Under the MAC we do not want complex measures of performance ...

These indicators must be straightforward and reasonably simple to understand. Just as the Team Manager will look at lap times in Formula One (Short Interval Control) so we need something that is reasonably easy to calculate so that we can measure business performance on a short interval basis also. Trying to calculate the amount of oil in the gearbox by weighing the vehicle and subtracting from it the manufacturer’s specified weight is not an indicator that will be useful and straightforward. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 1. AN INTRODUCTION TO THE OEE CONCEPT / 1.15 A common unit of measure helps establish where we are and where we want to be

1.15

A common unit of measure helps establish where we are and where we want to be


6/23/2001 - 5:14:31 PM

Page 177


In the process of MAC such an indicator has been introduced and is termed Overall Equipment Efficiency (OEE) This measures the efficiency of the production team as a whole, where the production team is defined as being everyone involved in ensuring that the product is delivered to the client at the right specification, on time. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS

2.

MAINTENANCE MANAGEMENT CONTROL SYSTEMS

Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.1 Why do we need effective maintenance systems?

2.1

Why do we need effective maintenance systems?

You can get management books on a wide range of topics from strategic planning through to team building but it is very difficult to obtain books on the subject of “ Effective Management Control Systems “. Yet management can only be as good as the systems that them. Shipping spends a vast amount of money on navigational systems - companies put satellites into space to improve communications into space to improve communication speed and accuracy yet in many companies managers have to wait three to four weeks after the end of the financial period for the ing system to produce the numbers so that they can begin to see where they are financially. Many times the data input to these systems is suspect; often data is mismatched in that one statistic will be relating to a different time period or scope than another. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:32 PM

Page 178

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.2 Sailing a small ship within sight of shore requires little data - just the weather report perhaps

2.2

Sailing a small ship within sight of shore requires little data - just the weather report perhaps

In the same way that sailors need navigational systems to plot a course and to periodically check how they are doing against that course, managers need systems to plot the course of the company and to periodically check whether they are on course or are drifting. As seafaring companies need to know not only what money they will make at the end of the journey, but also how they are doing day to day in of longitude and latitude, speed and depth of water, companies need to know how much money they will make, providing they stay on course. On the high seas constantly checking latitude and longitude is the seafarers way of guaranteeing they will make port, so management need to be able to check the equivalent data to ensure that, at the end of each month, budgetary goals will be achieved. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.3 But in times of danger data is vital...

2.3

But in times of danger data is vital...

At sea conditions can change quickly. It is not always fair weather sailing. In business conditions can change quickly also and effective management control systems will help management navigate through difficult times. Management need to know, as soon as possible, if they are drifting off course so that action can be taken immediately. A small deviation from course on Monday will be large © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:32 PM

Page 179

"Holderbank" - Cement Course 2000 deviation by Friday if corrective action is not taken quickly. A Management Control system should be capable of telling management not only how well they have done but also how well they could have done. For without the process of continuous improvement the sunrise companies of today become the sunset companies tomorrow. For many years the Americans won the America cup in sailing until finally the Australians won. When asked what the secret of success was the skipper replied “ There wasn’t any one thing- it was lots of little things. If I had to choose one thing that made the difference it was attention to detail. Systems must provide attention to detail. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.4 Behavioural Change

2.4

Behavioural Change

When we consider upgrading systems the ultimate goal must never be forgotten. Systems are upgraded so that, through using them, management may improve operational performance, and therefore, financial results using the upgraded systems management must adopt new patterns of behaviour so the link between systems, change and results is developed. Upgraded systems provide the opportunity for management change; management change generates improved results. But it is not just management that need to change. Who will provide the upgraded data? Who will input data into the systems? The improvement of systems requires change at all levels. Not only must management embrace this change but they must also act as role models for the rest of the organisation. The essential factor that must be present in any system for it to be effective is compliance - that is everyone must play their part. No-one will play their part unless management comply to the system requirements, thereby acting as a role model for the remainder of the organisation. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.5 The need for behavioural change

2.5

The need for behavioural change


6/23/2001 - 5:14:32 PM

Page 180


There is a saying that if you continue to manage the business as you have always managed the business then the results will continue to be the same. The converse of this is true and this is the definition of madness. “ Madness is continuing to manage the business as you have always managed the business and expecting that, somehow, mysteriously, results will improve. Management cannot rely upon luck to improve the results of the business, neither can they live in a world of madness. To change the results being achieved something must be done differently. Too many companies focus upon investment in new machinery and technology and the only way towards improved results, ignoring that there are so many opportunities to create improvements within the organisation through behavioural change. The major behavioural change is to focus more upon detail. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.6 Control the whole...

2.6

Control the whole...

To be effective Management Control Systems must do this questioning for management. It must distinguish between activity that is productive and activity that is non productive, and naturally identify periods when activity has not occurred at all, although these are generally not filtered so effectively by the mind. An effective system will provide a continuous monitoring of an operation through its complete cycle from forecasting to planning, through the mechanisms of control to a reporting element that will alert management to situations where their intervention is required. By providing this continuous cycle management will be able to see when the decisions they have made have been effective. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.7 THREE TYPES OF BUSINESS SYSTEMS © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:33 PM

Page 181


THREE TYPES OF BUSINESS SYSTEMS

There are many types of system and one person’s perception of the word “ system “ may vary considerably from another. There are fire alarm systems, systems for working out numbers on the lottery, computer systems and rail systems or networks. The systems referred to in business fall into three major categories. Financial systems are the systems that forecast and track the financial performance of a company. These operate at the higher level of the business. Then, at the lower level, there are operational systems. These are the systems that control the product or service ordered and will contain data such as colour, quantity, due date etc. and are underpinned by the specifications of a product and the parameters of a service. These tell us what we have to do and to what standard. Finally there are Management Control Systems that tell us how well we did what we had to do.

Financial systems operate at the highest level of a company. They track the financial result of doing something. They are monthly in nature, use financial ( return on investment etc.) and use money as the common language. They tend to appear three to four weeks after the end of the period under consideration. Operational systems are one-off. Once the activity has occurred the system cycle is complete. Management Control Systems monitor the activity levels that occur because of the operational system and track how well we did what we had to do. Management Control Systems talk in of productivity, utilisation and focus on lost opportunity. By controlling these factors, on a shorter time base than the financial systems, the financial result will be more likely to occur as planned. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.8 What systems do © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:33 PM

Page 182


What systems do

Because Management Control Systems focus on activity levels the principles they are built upon will be applicable to almost any type of operation. Selling might be creative but it consists of activities. In some operations the activities might be less defined than in others but the underlying principles will remain true. An istration functions through activities in the same that a production unit does, so there is no reason to believe that one can be controlled - yet the other can not. ants would never accept that an operation which was predominantly istration should not have a budget, yet in many instances management fail to accept that the same principles of control that apply to production should also apply to istration operations. In the same way that a financial system will focus on the financial parameters of that operation a management control system needs to focus on the activities of that same operation. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.9 There are three major maintenance activities

2.9

There are three major maintenance activities

Viewing maintenance from the high ground there are three major types of activity. The first is routine maintenance. Routine maintenance tasks have frequencies attached to them and the work required to be done should be specified in the routine maintenance procedures (operational system) The second type of work carried out by a maintenance department is that of breakdowns - work on plant and assets that fail during service. The third type can be termed major overhauls, those activities that occur on a larger and less frequent basis than preventive maintenance, although it can be argued that overhauls are just larger types of © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:34 PM

Page 183

"Holderbank" - Cement Course 2000 preventive maintenance. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.10 Can we answer some of the following questions…

2.10

Can we answer some of the following questions…

A simple test of how effectively an operation is being controlled is to ask some basic questions about that operation. How many hours of routine maintenance is going to be done next week - and the week after. Do we have the resources for it? Are we maintaining our plan or is there routine maintenance work outstanding? If so - how many hours will be required to bring the backlog down to zero? How many hours are spent annually on breakdowns? Is there a pattern of how those hours are spent? How long should a job take? How long is it taking? Can we reduce the gap between the two. To be really in control the answers to all these questions - and many more beside - must be readily available. This can only be achieved through an effective management control system. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.11 Short Interval Control

2.11


The first principle that must be inherent in a system is that of short interval control (SIC) The more frequently performance is monitored the quicker management recognise, through he system, that a problem has occurred. For this to occur actual performance must be noted and recorded. This actual performance must then be compared to a realistic plan, that is a plan that has been derived from an © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:34 PM

Page 184

"Holderbank" - Cement Course 2000 accurate standard. The system must also show when a problem has been recognised and solved. This function is effected by the KPI’s which will rise back to planned level when the problem has been solved.

The short interval control function is the heart of the system. It occurs at the point of execution of the activities. Once an effective standard has been developed then this can form the basis of the planning capability. Planning can be set up on a weekly basis. This weekly plan can be lifted to a higher level by forecasting on a monthly basis giving the basic elements of the system as short interval control, ed by a weekly and monthly planning function.

At the monthly level of the management control system we have arrived at the same level as the budget and a link needs to be established between the budgetary system and the Management Control System. This can be done through what is termed the Master Schedule, which forecasts the resources needed to meet the budget forecast. So where the budget is forecasting labour cost the management control system forecasts hours. Where the budget forecasts material costs the master schedule will forecast parts and materials in of volume required. This link, between the management control system and the budget, illustrates how, by controlling activities and materials on a short interval basis, we can manage more predictability into the budget. It must be ed that so far generic principles have been discussed and these need to be tailored to differing situations. What is applicable to a fast moving production operation may not be translated into a maintenance function in the same way.


6/23/2001 - 5:14:34 PM

Page 185


The planning has now been structured on a short interval, weekly and monthly basis, linked to the budget through the master schedule, which encomes the forecasting and planning elements of the system. The link to the control element of a system is effected through the short interval control which both plans and reports against the plan. In the reporting function of the system the reporting elements can be matched against the planning elements to ensure that a clear focus is kept on what variances are occurring at a short interval period, weekly and monthly. This is important because the type of problems that occur at these frequencies will differ in nature. This difference in the nature of problems will direct how the management structure will align with the management control system. Many of the problems experienced at the short interval control level will be of short duration. Because this point of the system is at the point of execution of the activities this function can be handled by first line management (Level 1) Problems of a longer term nature but still linked to the execution of activities can be handled by mid-management (Level 2) At the monthly level problems of a longer term nature will need to be dealt with and these will more revolve around structural and strategic decisions. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.12 PERFORMANCE SYSTEMS

2.12

PERFORMANCE SYSTEMS

By constructing a system in this manner the four integral blocks of any system will be inherent in within that system. Obviously these are inherent in any system but will vary in nature according to the nature of the system under review. In both the financial system and the management operating system the forecast is annual and monthly. The management control system differs from the budgetary system in that it focuses upon the hours and materials required to meet the expected demand, not upon the cash value of those resources. The management control system differs from most financial systems in that beneath the monthly level it has a weekly and a short interval function. The short interval function may © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:35 PM

Page 186

"Holderbank" - Cement Course 2000 be as short as hourly or as long as daily, depending on the operation for which it is being designed. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.13 BASIC SYSTEM ELEMENTS

2.13

BASIC SYSTEM ELEMENTS

Looking at these elements in more detail: The forecast projects the hours required to meet the operational targets, together with the materials and tooling required to those hours and related back to the forecast budget levels of financial performance. The planning element breaks the overall monthly plan down into smaller elements of a weekly nature which builds in the basis for shorter term control underneath the monthly frequency of both the budget and the master schedule. The short interval control breaks this interval down even further, monitoring short term achievements through the Key Performance Indicators (KPI’s) and finally the repairing element will be matched to each level of the planning function, the focus being to provide a basis for review of planned performance against actual, with the KPI’s (planned and actual) indicating where variance shave occurred. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.14 THE COMMUNICATIONS STRUCTURE

2.14

THE COMMUNICATIONS STRUCTURE

As has been discussed earlier, the management structure must be aligned to the management control system so that communication concerning problems experienced and actions taken can be handled effectively and efficiently by the management structure. At the level of day to day activities the first line management (Level 1) will handle short term problems. Longer term problems need to be ed to the next level of management on a structured basis and this is done through a scheduled performance review meeting. As this is normally carried out on a daily basis this is termed the Daily / Weekly © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:35 PM

Page 187

"Holderbank" - Cement Course 2000 Operating Review Meeting. The document that records daily performance is termed the Daily/Weekly Operating Report (DWOR). Finally mid-management review performance with plant management (Level 3) on a weekly / monthly basis, the communication structure providing s structured pathway for the highlighting and solution of problems. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.15 SYSTEM CONCEPTS

2.15

SYSTEM CONCEPTS

In the development of a system which will meet the parameters of an effective “Management Control System” certain inherent characteristics must be in place. The whole of an operation can only be controlled by controlling the individual parts of the operation. How detailed these parts are must be taken into during system design. Systems are only effective when used and unless everyone who is required to use the system actually uses the system then that system will not be fully effective. We can only control what we can measure. We measure through Key Performance Indicators and these will restore to the planned level of performance when management action against any problem has been successful. Finally the information generated by the system must be timely, so that management can use it to proactively control and not posthumously review what has happened. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.16 Typical phases

2.16

Typical phases

The term “Installation” of a system means that the system has been designed, is in place and is being used by the management team to more effectively control the operation. To ensure this happens effectively five stages must be observed. The first stage is gaining acceptance of the need for © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:36 PM

Page 188

"Holderbank" - Cement Course 2000 upgraded systems. Unless people see the need then they will not see the need to be involved. The second stage is compliance; this means people will be involved in the design of the system, the development of the controls and the setting of the standards(if they don’t exist) that will be used for the planning element of the system. The third step is understanding what the system is communicating and this is a function of training. Fourthly, management must use the system and if the four first steps are undertaken correctly then the fifth step, commitment to continuing to use the system to maintain and improve on the results, will fall into place. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.17 SYSTEM CONCEPTS - GENERIC MGMT. CONTROL

2.17

SYSTEM CONCEPTS - GENERIC MGMT. CONTROL

The diagram of how the system links together is termed the “Generic System Flow” and is indeed generic. The elements of the system have already been covered in of the typical structure. The budget determines the levels of the master schedule which then enables the monthly plan, weekly plan and short interval control detail to be generated. Reporting is against the planning element. Systems need to be dynamic and the generic system flow shows a series of key meetings, all ed by an “Action Log”. An action log records what needs to be done, who will do it and the due date on which the action will be completed. The review meetings shown are either for the purpose of commitment to a plan or to review performance, highlight variances (which indicate problems) and to agree the actions to be taken to solve those problems. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.18 What do Management Control systems do for our business?

2.18

What do Management Control systems do for our business?


6/23/2001 - 5:14:36 PM

Page 189

"Holderbank" - Cement Course 2000 Effective Management Control Systems provide vital guidelines for management. Firstly they define clearly the managerial routines and disciplines that need to be observed to optimise the control over an operation. The major advantage is that these are not only clearly defined but agreed at all levels. Another key characteristic is that management is based upon fact rather than upon personality. Clear plans and regular reporting against those plans in meetings ed by Action Logs, avoids procrastination by any level of management. Everyone in the organisation has clearly defined goals, thus avoiding anxiety and ambiguity. By deg the system on how well we could do, not just on how well we did, the basis for a continuous improvement culture is put in place. By reducing the cycle of firefighting more time is freed up for management to focus of proactive rather than reactive management Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 2. MAINTENANCE MANAGEMENT CONTROL SYSTEMS / 2.19 Control the whole... by controlling the parts

2.19

Control the whole... by controlling the parts

An effective system must contain the elements of forecasting, planning, control and reporting. It must enable management to collect data, analyse the data make decisions based upon the analysis and then ensure that these actions are implemented. The inherent structure of the system must be such that the whole operation is controlled by controlling the parts. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT

3.

SPARES MANAGEMENT

Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.1 THE NEED TO BE COMPETITIVE

3.1

THE NEED TO BE COMPETITIVE


6/23/2001 - 5:14:36 PM

Page 190


How well a company is doing can be expressed quite simply as incomes minus outgoings. Companies need to make profit to set aside money for reinvestment in training, process development and product development. Therefore, one key aspect of asset management is the money spent on spares. Like every other aspect of upgrading performance it requires two stages. Stage 1 is a reassessment of current practices and the current levels of spare parts, their usage and applicability at this point in time, given other initiatives that are being taken in preventive maintenance. The second focus needs to be on ensuring that we have the systems for the future to ensure that whatever improvements are made are maintained. Management is not just about making one-off improvements. It is about generating a climate where continuous improvement is the natural way of life. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.2 The financial performance of any plant can be evaluated by a simple formula

3.2

The financial performance of any plant can be evaluated by a simple formula

As has been stated, profit is the difference between revenue and costs. There are many areas of costs ranging from the cost in losses when the plant should be operating to the loses incurred when maintenance staff are unable to work because of shortage of parts. The temptation is to generate a culture of just in case, where that little bit extra is held “just in case“ it is needed. The term “management“ when applied to levels of spare parts means balancing the need for “just in case“ a part may not be there with “just sufficient“ to ensure that the plant will be maintained but that the cost of holding such spares is not a burden on the business. Another way of looking at the the situation of spares is to ask the simple question: “Is this a maintenance organisation or a warehousing organisation?” Every time a spare part is purchased the difference between the revenue and the costs narrows. Every piece of spares bought that is not vital means that the organisation must sell more to maintain the margin. In the climate of today the market place is very competitive © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:37 PM

Page 191

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.3 Costs are made up of many things, one of which is the costs of the spares held

3.3

Costs are made up of many things, one of which is the costs of the spares held

It is not just the direct cost that hits the organisation. Costs for spares have hidden costs that often far outweigh the cost of the part itself, obviously depending on the actual price of the part. Requisitions have to be made out .. stationery costs are inflated. They have to be processed .. maintenance time and istration time is involved. Goods are received .. distribution costs are incurred. Finally they have to be stored and this soaks up more cost. Even stock checks take longer because higher levels of inventory are involved and we are now back on the circle of increased istration costs. An efficient company holds “just sufficient“ stock so that the plant is maintained but cost is kept to the minimum. This means managing stocks so that they move. Non moving stock is frozen money. The only exception to this rule is for strategic stock, that is stock that is maintained because the impact of not having it available when needed would be catastrophic. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.4 Some of those will be critical…

3.4

Some of those will be critical…

An examination of the stock held by maintenance departments shows that parts fall into three major categories. There are those stocks, as we have said, that are critical or strategic, spares that must be held because if they are needed and are not available there would be a complete and sustained loss of production. Some will not be so critical, where even if they are not held, the lead time to obtain them is not so long that production can not be protected. Finally the third type of spares .. left-overs from days © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:37 PM

Page 192

"Holderbank" - Cement Course 2000 gone by. It is easy to fall into the trap of using spares to cushion the effect of poor systems. Because the systems are unable to predict with reasonable accuracy when the parts will be needed the temptation is to hold some, sometimes a substantial some, just in case. Because the systems do not flash a light when a piece of equipment is replaced and spares become obsolete they sit on the shelf, gathering dust and incurring cost. Because the systems do not identify needs common to all plants, strategic parts are held by every plant. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.5 One area often neglected in operations is the quality of maintenance spares held…

3.5

One area often neglected in operations is the quality of maintenance spares held…

There is a term used by many organisations when referring to spares and that is quality. Quality, in this case, does not refer to whether the part is in good quality condition but refers to the need for holding the part. How essential is this part to the well being of production? There is a tendency for parts to be raised in quality in order to overcome shortcomings in the systems and procedures in place. To improve the level of parts management requires that this quality element is questioned, as are the systems in place. One additional part on the stock list may not seem much, but multiplied by that situation many times over in one location, then multiplied by the number of locations throughout the organisation, it soon builds up a figure that would build several additional plants; fund a much more aggressive stance in the market place; and give the competition cause for concern if it was realised. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.6 Where do we begin?

3.6

Where do we begin?


6/23/2001 - 5:14:38 PM

Page 193

"Holderbank" - Cement Course 2000 Because the sensitivity of parts’ availability is critical to production sustainability, it is vital that any approach is logical and well thought out. We can not afford to take risks or, if we do, they must be calculated risks that have been carefully evaluated. Anyone can reduce the level of stocks - just turn off the tap and the flow of spares will fall. But which of the spares that have been reduced are vital? How much of the stock in the stores is moving stock and how much is dead stock? The answers to these questions can only be arrived at by a systematic and detailed approach. The first steps are to tackle those areas that have a very low risk. As more data is developed then the more controversial and sensitive areas can be dealt with. It will take time to develop some of the data but we can not afford to sit and wait. We must not put off until tomorrow what our competitors are doing today. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.7 Set the policy

3.7

Set the policy

The MAC approach advocates that all functions within a company become involved in working together to identify opportunities for improvement and to realise them by working out solutions to the problems that have created the opportunity for improvement. The advantage of this approach can be seen in spares management where production can assess the impact on the production element of the company, and the maintenance function can assess the degree of difficulty in affecting the repair. Together the two viewpoints give a complete picture of the factors affecting a given situation and illustrates the value of treating maintenance not as a discreet focus but as a process that will benefit from input from all the disciplines. When dealing with factors that can have a major impact on production it is sensible to ensure that as broad an input of knowledge and experience as possible act as an input to the situation. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.8 Spares Management is juggling

3.8

Spares Management is juggling


6/23/2001 - 5:14:38 PM

Page 194


Spares management never will be, and can not be, a precise science. It is a case of using the best input available to weigh up all the factors impacting on the situations and then making the best possible decision in the light of the known facts. The more facts and data available the better the decision but there will always be the need for management expertise and experience in assessing the areas where data will not be available and in arriving at a decision that can be ed by all. The reality of the situation is that there will have to be a juggling of the commercial needs of the organisation, with the cost of carrying the level of spares held. Then there is the aspect of customer services which will vary from plant to plant. In some plants there may be excess capacity, in others none. The range of equipment will also vary from plant to plant; some plants may have a narrow range of equipment, others a wide range. Finally the availability of spares, or lead time, may vary from region to region. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.9 Spares Management is understanding

3.9

Spares Management is understanding

Criticality of parts will vary according to the impact on the production process. If the part is required for a item that will have no direct impact on the production process the rules governing the holding of those parts will vary from those of a part that can have a direct impact on production. The lead times for parts will also have an impact on holding levels. The lead time is the time between the time when the part is ordered and the time when it becomes available for maintenance use. This will vary according to not only the part type but also the supplier. For one supplier, two parts can have separate lead times. For one part two suppliers may have different lead times. Then for every part held there is a different usage rate. To begin to manage spares more efficiently all these aspects of parts need to be understood if they are not known already. Where data does not exist it has to be generated. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:38 PM

Page 195

"Holderbank" - Cement Course 2000 Spares Management / 3. SPARES MANAGEMENT / 3.10 The Objective - Financial

3.10

The Objective - Financial

Any spare part that is not being used represents money that is frozen. This money costs the organisation twice over. Firstly, there is the cost of carrying that money which means that interest will be incurred. Secondly, there is the lost opportunity to have invested that money and by earning an income from it rather than paying someone else for using it. The objective of spares management is to reduce the money that is frozen and not free for use. The objective is to achieve a position where the minimum of money is tied up in spares, but at the same time doing so in a climate where an emphasis is being placed upon the increment of plant availability. This will require management of a different nature than has been used in the past. One fact is indisputable; however efficient spares management has been in the past there will still be room for improvement. The amount of money involved in holding spares is not only phenomenal but represents money that is not value added. The financial objective of the spare parts initiative is to reduce this sum. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.11 The Objective - Operational

3.11

The Objective - Operational

The achievement of the financial objective for spare parts management will require a detailed examination of the systems and procedures currently in use. The objective of the operational section of the spare parts management approach is to ensure that the right systems are in place to see that the right part is available at the right time for the right piece of equipment. The parts must be held in the right quantity and be the right quality. To achieve this goal will require a detailed examination of the systems currently in use to understand how they deal with lead times, usage rate and criticality and to upgrade them if they are not effective for management needs. This will require understanding the © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:39 PM

Page 196

"Holderbank" - Cement Course 2000 documentation of the current system, developing a set of principles upon which effective spares management can take place, and then upgrading the systems to meet these principles. These are the actions that fall under the umbrella of the MAC approach. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.12 To manage spares we must understand spares

3.12

To manage spares we must understand spares

The message that comes through again and again when the subject of spares management is raised in any management seminar is “ in order to manage spares we must understand spares.” The beginning of the understanding of spares is to understand why spares are held in the first place. There are only two reasons why spares are held. The first is to ensure that plant availability is maximised. When a plant is running it earns an income but when it isn’t running it costs. Plant availability is the outcome of a good partnership between production personnel and maintenance. The second reason spares are held is to ensure that the maintenance team can remain productive at all times. When maintenance can not be productive, preventive maintenance falls behind and a back log develops. When a backlog of essential maintenance builds up the probability of failure increases. Spares availability has a direct impact on both plant availability and maintenance productivity. It makes the difference between a virtuous circle where maintenance catch failures before they occur or a vicious circle where maintenance are always one stage behind the failures. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.13 The two steps in bringing greater control to spares holdings

3.13

The two steps in bringing greater control to spares holdings

So the approach for improving the control of spares is two fold. The first is to analyse the current © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:39 PM

Page 197

"Holderbank" - Cement Course 2000 situation which will require developing data to understand a wide range of operational characteristics. In addition to an understanding of lead times and criticality it will be necessary to understand far more about the frequency of need. Preventive maintenance does not always meet the exact needs of the equipment and in many cases has been proven to actually do more harm than good. To ensure that preventive maintenance assists plant availability and doesn’t hinder it new maintenance indicators will need to be developed if they don’t already exist. Mean time between failures (MTBF) is critical to understanding when parts will be required but even this knowledge does not give the whole picture. What actually caused the failure, termed mean time between causal failures (MTBCF) is more meaningful and will indicate the exact focus of maintenance. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.14 The 20 / 80 theory

3.14

The 20 / 80 theory

The 20 / 80 theory is a common theory in management. It states that in any given situation 20 % of the causes will create 80% of the effects. Of course, it is not strictly accurate but it is a generalisation that is very useful in the management of many situations. Obviously once again up to date, accurate data is required. Where this is not available we must rely on the perceptions of the people involved as to which are the 20% of the root causes that are generating 80% of the effects. However, once again caution must be used in connection with statistics. They are there as a guide line and management must decide if a) the information makes sense and b) it is giving an accurate base of information from which good management decisions can be made. A 20/80 analysis of cause and effect in accidents highlighted the fact that 17% of drivers are company car drivers and cause 80% of the accidents. Suggested solution? legislation to force all companies to give their drivers advanced driving lessons. Impact high cost. Question: “how many miles do company drivers do in relation to ordinary drivers?” “Is kilometres per driver a more accurate key performance indicator?” Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.15 COST

3.15

COST


6/23/2001 - 5:14:40 PM

Page 198


In the investigation into the reduction of spares one objective is to reduce the amount of money frozen in spares and therefore it makes common sense to examine the relationship between categories of items and the value of those items. Do 20% of the items held for 80% of the cost, or a near approximation of this relationship? This relationship would, if it existed, give management the chance to focus first on high cost holdings. A small percentage reduction in the large cost areas will probably be far greater in impact than a large reduction in a small cost area. This does not mean that we focus only on the 20/80 relationship. It merely gives management a starting focus point where large gains may be made quickly with the minimum of effort. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.15 COST / 3.15.1 Actions

3.15.1 Actions

Step 1 in this process is to determine the number of items held by category. The detail to which this is taken has to be the subject of common sense and a very quick assessment can be made by using the estimated number of items and cost per item to give a guidance in this process. Once the range of items held and the detail to which it will be taken are established, then the next step is to determine the numbers held by time. By time infers reviewing the average holding levels over a given time period as usage of the parts may rise and fall dramatically, particularly if they are used in major overhauls. The value per item can then be inserted into the equation and the total cost of holding each item can be arrived at. Once this has been achieved then by plotting the value of each item as a percentage of the total cost against the total cost the “high ticket” items will appear. This process is termed Pareto analysis and in this exercise is being used only to determine if 20% of the items (cause) makes up 80% of the cost (effect) Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:40 PM

Page 199

"Holderbank" - Cement Course 2000 Spares Management / 3. SPARES MANAGEMENT / 3.15 COST / 3.15.2 Pareto analysis

3.15.2 Pareto analysis

A typical Pareto analysis chart is shown in the above illustration. On the vertical axis the percentage refers to the percentage of total cost generated by the items plotted along the bottom. Any spreadsheet application will automatically carry out the steps of calculating the cost of each item against the total cost and will then sort them into descending order. Setting up a spreadsheet in this way is a good investment for two reasons. Firstly, the spreadsheet can be used to generate “what if “ scenarios. What if we could reduce the cost of carrying these items by 15%? Secondly, as the level of cost of items is reduced by management actions the new levels can be entered into the spreadsheet. And thirdly, the situations with spares will never remain static. Actions taken under other initiatives, such as Failure Mode Effect Analysis (FMEA) will have an effect on spares holding levels and the spreadsheet model will act as a dynamic tool between these initiatives and the spares management focus. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.15 COST / 3.15.3 The ABC Analysis

3.15.3 The ABC Analysis

It is useful, as in so many management situations, to have a common language in which to converse and exchange information. Common language reduces the risk of misperception and breakdowns in communication through the misinterpretation of information. The items that fall into high cost areas are called A parts and should always be the focus of management actions. There will be a group of items that fall outside the 20% of the items ing for 80% of the cost and these are termed B items or parts. These should not be ignored but will be the second phase of management attention. Finally there will be a group of parts who cost level is minimal and where the effort of reducing the cost will be totally out of proportion to the management time and effort involved. These are termed C parts. As © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:40 PM

Page 200

"Holderbank" - Cement Course 2000 many actions are taken in other areas these categories may become fluid. A parts may become B parts; conversely B parts may become A parts. The analysis is an interactive link to all other initiatives Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.15 COST / 3.15.4 Under the MAC umbrella work teams will now examine these A class items…

3.15.4 Under the MAC umbrella work teams will now examine these A class items…

Under the concept of MAC working teams or groups will have been formed to examine the A class items. The analysis is just the beginning of the process. There are at least two important questions to be answered. The first is: “Are we holding too many?” The second is: “Can we reduce the level of current and average holdings?” The difference between these two - current and average holding - is that of a seasonality factor. Holding levels may vary according to the season - that is - different points in time. This is particularly pertinent to a maintenance situation where some items are held for frequent preventive maintenance routines and others are held for major/annual overhauls. This time element is of particular importance in maintenance, high value items being held for overhauls because money starts to cost the minute the items are received and paid for. This begs the question: “Can we hold off longer before we order the items?” followed by: “Can we gain more favourable payment ?” These questions illustrate the two aspects of spare parts management the teams must focus on. “What is the operational aspect of this situation?” and: “Can we manage the money flow better?” Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.15 COST / 3.15.5 To do this they will need to focus on…

3.15.5 To do this they will need to focus on…

The expertise of the group will be called into play to answer the first part of the three statements, © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:41 PM

Page 201

"Holderbank" - Cement Course 2000 namely, “how critical is this item to the production process?” Factors which will influence the answer to this question will be whether the item is a discreet item or not. Discreet can have two meanings in this situation. The first definition of discreet is whether the asset for which the item is held is a one off in the process flow. If this asset fails there is no alternative asset that can be brought into the production process. The second description relates to the points where this item can be used. Is this part common to many different types of plant items? Obviously an item which is discreet to one asset, which in turn is a discreet part of the process flow will be viewed differently from a part that is not discreet to one asset, that is it is used in many different types of equipment, none of which are discreet process items. The second factor that needs to be taken into is: “How long does it take to get one of these?” If they are off the shelf items from a local stockist this will have different connotations than an item that has to be especially ordered and takes three weeks to arrive. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.16 MOVEMENT

3.16

MOVEMENT

The Pareto analysis of cost per item as a percentage of total cost is a financial way of looking at spares holdings and brings into focus not just the value of the items but the management of cash flow as well. Lead times will have been considered and here the work team will have solicited the help of the purchasing function. The view of payment will have brought the finance department into the team arena but the work group, to be efficient, must only invite in those specialists that are needed when they are needed. To have specialists included in the standing composition of the work group will not be productive for them of the group. The work team will be a core of individuals who have a deep understanding of the core process and who have the authority to co-opt other people on to the team as and when they are needed. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.16 MOVEMENT / 3.16.1 Movement can be classified as zero, some a lot

3.16.1 Movement can be classified as zero, some a lot


6/23/2001 - 5:14:41 PM

Page 202


Another way in which the Pareto analysis principle can be applied is by looking into movement. The frequency of movement will indicate a degree of importance related to constant need and use, but will not indicate criticality. This frequency of use is important for one specific aspect of planning spare parts holding efficiencies. But first, the common language of movement. Some items will be high usage, frequently ordered but frequently used. Some will be of medium frequency usage and some will have zero usage or as near makes no difference. Naturally the time span under review needs to be the same for all items being reviewed and usually is defined as annual use. How many of these items are used on an annual basis? In general low usage items should should reflect a low level of holdings and vice versa, high usage, higher holdings. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.16 MOVEMENT / 3.16.2 Usage / Holdings matrix

3.16.2 Usage / Holdings matrix

To help in the process of evaluating holding levels against usage a matrix can be developed where one axis indicates the holding level and the other records the frequency of movement. The exact definitions for each of the three levels of holdings can be determined locally by the work teams but would be something in the order of zero, 1-5 and greater than 5. The movement categories would reflect the zero movement position, 1 - 20 and greater than 20 per annum. By analysing the holding levels and the movement frequencies items can be entered on the matrix. Once again the point must be made that this is not a precise statistical science; it is merely a way of focusing management onto those areas where there may be the greatest opportunity for improvement. Common sense must always prevail because of the strategic stock definition. A zero movement item with a holding of one may be strategically essential to the maintenance of maximum plant up time. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:42 PM

Page 203

"Holderbank" - Cement Course 2000 Spares Management / 3. SPARES MANAGEMENT / 3.16 MOVEMENT / 3.16.2 Usage / Holdings matrix / 3.16.2.1 The green area denotes where usage matches holdings

3.16.2.1

The green area denotes where usage matches holdings

With reference to the illustration above certain situations will appear natural for the relationship between holding levels and usage. Zero usage for example, related to zero holding (bottom left hand corner) would appear to make sense. A low holding level (1-5) allied to a low movement (1-20) would also appear to make sense. In general the area shaded (green) indicates where holding levels plotted against movements rates seem to have a common sense logic. However, the findings should always be questioned. A low holding level, an average of one half an item per annum ( the item is on stock for six months of the year) allied to a usage rate of one, may indicate that the item is ordered to far in advance. Is this because of excessive lead times or because purchasing have not been given specific guidelines? Could an alternative supplier be found to provide this item at a lower lead time? The interaction of conditions means that the work teams must stay very flexible in their thinking. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.16 MOVEMENT / 3.16.2 Usage / Holdings matrix / 3.16.2.2 Top left indicates excessive cost.

3.16.2.2

Top left indicates excessive cost.

Some general guidelines can be used when viewing the holding against the movement matrix. The top left area of the matrix generally indicates excessive cost being incurred with regards to spares holdings. The holdings are high whereas the movements are low. Likewise the bottom right hand side of the matrix will tend to indicate areas of plant risk, that is items that have a high movement but low holdings. This is where the knowledge of the work teams comes into its own. Nothing is seldom what it appears to be but then again nothing must ever be accepted at face value. The faithful serving words © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:42 PM

Page 204

"Holderbank" - Cement Course 2000 of management must always be in constant use: “Why, when, how, what, who, and where“; these valuable words will, in many cases, expose some flaw in the logic that was initially used to determine the organisational practices that are now reflected on the Movement / Holding matrix. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.16 MOVEMENT / 3.16.2 Usage / Holdings matrix / 3.16.2.3 The exception to the movement rule

3.16.2.3

The exception to the movement rule

Over-riding all the logical arguments for reducing stock levels will be two important aspects of any maintenance organisation: “Are these items strategic in that they need to be held to avoid a total plant shutdown in the event that the in process part fails?” and: “What is the lead time for this item?” However, the “criticality”, “strategic” and “lead times” can often cloud the thinking process, particularly when viewed solely from a maintenance process. The objective of the spares management process is to minimise the capital involved whilst maintaining or improving customer service. This does not mean that production availability must be 100% and that it must be protected at all costs. Availability is a function of demand and process management and it is possible to maintain customer service with less than 100% availability. A part is critical to production but production can stand downtime of four hours when this part fails. This part is held at another plant which is two hours away and can be fitted in one hour if work to remove the defective part is started when transport is despatched to collect the spare. Spare parts management is questioning all aspects of the holding and usage matrix. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.16 MOVEMENT / 3.16.2 Usage / Holdings matrix / 3.16.2.4 Non critical

3.16.2.4

Non critical


6/23/2001 - 5:14:42 PM

Page 205

"Holderbank" - Cement Course 2000 The top left hand side of the matrix, where holdings are high and movements are low may indicate a situation which is often referred to as a “dead stock “ situation. Why are a large number of items being held that are never used? With the vast amount of communication that is required in a plant, is it possible that the communication process has broken down and that a particular item of plant that used to require a high replacement of parts has been replaced by a more durable item that requires less replacements, but the communication to the stores function went adrift or never happened? Anything that does not move is “dead stock“ and must be viewed with suspicion. Why is money being frozen in something that never moves? Dead stock clutters up the system. Is it very valuable? Often not. But there are options. Is there another plant still using this item? If so perhaps it can be transferred there. Is this item still in use anywhere? - it could be sent back to the supplier and a credit obtained. Finally, when all other options are exhausted it could be sold for scrap; at least it will be out of the picture. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.17 Stock Rotation

3.17

Stock Rotation

The third aspect of spares management is a term called rotation. Rotation is a ratio that rates the levels of stock held against the annual usage. This is calculated by dividing the quantity of the part held by the annual usage. This will generate a ratio and once again the Pareto analysis principle can be used to relate the ratio for a particular item to the ratios of all other items held. In order for this relationship to be meaningful, an understanding of the ratio is needed. It is probably easier to understand this by taking some examples

An item has a rotation ratio of 0.25. This means that the annual usage is twelve and the average holding level is three. £ divided by twelve equals 0.25. What would be the rotation ratio for an item that has an average holding of 10 and a usage of 100 per annum? Holding (10) divided by usage (100) © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:43 PM

Page 206

"Holderbank" - Cement Course 2000 gives a rotation ratio of 0.1. In of the efficient use of money the lower the ratio the more efficiently money is being used. A number that is approaching zero is the most efficient ratio here is. Zero would indicate that the minute the part was received it was used - just in time maintenance. The most costly ratio is that of infinity - parts are held but never used. The objective of spares management is to achieve wherever possible, (compatible with he goals of the programme), the lowest possible rotation ratio for all parts. However, two factors will come into effect. The first is once again the criticality factor. The second is the return on investment of management time. Overall cost of the item will play a pat in this initiative. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.18 It is useful for the MAC teams to overlay certain definitions as they consider cost

3.18

It is useful for the MAC teams to overlay certain definitions as they consider cost

The whole process of making decisions based around the holding of spares is one where the generation of accurate and pertinent data, overlaid by knowledge of both the production and maintenance processes, plus a healthy dose of common sense, is the ideal situation. The work teams that focus on spare parts management must always wear 2 hats, that of the technical specialist and that of the ant. This requires a special degree of objectivity which will be enhanced if the team can focus on facts rather than historic practice, past experience etc... For example, past experience may be that a particular item has always been difficult to obtain. This does not necessarily mean that it will always be difficult to obtain. A deeper understanding of the factors affecting spares parts holding costs is also important so these will be explored a little deeper. Several factors affect spares holding costs, for eg. criticality (which has been raised on many occasions), expandability, rotability, prediction and obsolescence. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.18 It is useful for the MAC teams to overlay certain definitions as they consider cost / 3.18.1 CRITICAL PARTS

3.18.1 CRITICAL PARTS


6/23/2001 - 5:14:43 PM

Page 207


Critical parts have been defined before as those parts that will cause a major impact on production capability if a failure of a plant item occurs and there are no spares immediately available. This criticality is not a function of impact, rather a function of the degree of difficulty in either locating a source of supplier for the item or finding a supplier who can provide the item with minimum lead time. If the part is readily available and can be supplied at extremely short notice, the wisdom of permanently holding one of these items needs to be questioned. Just because historically this situation has occurred does not mean that these conditions still apply. Perhaps alternative suppliers could be, or indeed have been found. Perhaps the nature of the criticality has changed. Is it possible that, because of the market conditions a year ago the part was critical but now the market conditions have changed and we are set up for a condition that no longer exists? Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.18 It is useful for the MAC teams to overlay certain definitions as they consider cost / 3.18.2 EXPENDABLE PARTS

3.18.2 EXPENDABLE PARTS

Expendable parts is a term used to describe parts that are automatically discarded at the end of their life cycle. These are essentially parts that can not be over-hauled or are not deemed to be worth overhaul because the cost would not be in relation to their value. (Unless they are obsolete and can no longer be obtained). The major aspect of cost reduction in this situation is to locate a supplier who can generate shorter lead times. This will reduce the holding against use and reduce the rotation ratio. Another aspect of the management of this spares situation is the possibility that a supplier can be found who can provide the item to an improved specification, that is with longer life. By reducing the number of parts used per annum the number held can also be reduced. It is true that this move might well bring the rotation ratio right back to where it was before but this illustrates the interaction of the various aspects of spares management. The rotation ratio might have remained the same but the © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:43 PM

Page 208

"Holderbank" - Cement Course 2000 average holdings will have been reduced having an effect on the carrying costs for this item. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.18 It is useful for the MAC teams to overlay certain definitions as they consider cost / 3.18.3 ROTABLE PARTS

3.18.3 ROTABLE PARTS

Rotable parts is a term used to describe those parts that are overhauled at specific intervals or are overhauled when when there is an indication of need. These are normally of high value because the cost of overhaul must be justified in relation to the value of the part. There are two aspects that need to be looked at in respect to rotable parts. The first is the possibility of maintaining central holdings. The second is taking an objective look at the frequency at which the part is overhauled and the means by which overhaul is determined if it is being determined through a monitoring basis. If this is not the case then a means of monitoring the condition of the part needs to be considered and will probably already have fallen into the province of a work group looking at reliability centred maintenance (RCM) or risk based management (RbM). This is an example of where the work of one initiative may impinge on the work of another and stresses the need for effective intercommunication between work groups. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.18 It is useful for the MAC teams to overlay certain definitions as they consider cost / 3.18.4 PRODUCTION PARTS

3.18.4 PRODUCTION PARTS

Production parts are those parts whose life tends to be related to the volume of use. In many instances this relationship will be governed by the production hours scheduled. With a good system for tracking this relationship the need to replace these items becomes quite predictable and can be scheduled through the preventive maintenance (PM) system. The management of spare parts in this instance is © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:44 PM

Page 209

"Holderbank" - Cement Course 2000 much more straightforward than in most other cases. The stock needs to be managed against use. A low rotation ratio must be obtained through the management of lead times, minimum order batch sizes (MOBS) and quantity reorder levels (QRL’s) Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.18 It is useful for the MAC teams to overlay certain definitions as they consider cost / 3.18.5 OBSOLETE STOCK

3.18.5 OBSOLETE STOCK

Obsolete stock is indicated by no usage against some stock holding (the holding/usage matrix) or a very high rotation ratio (some stock level but no usage for a considerable time) The longer the period of non use the more likely it is that the stock has come become obsolete. Obsolete stock situations leave a working group with few options. Is there another plant where the asset for which the item was originally needed is still in operation? If so arrange to transfer it there. If not is the supplier still distributing this item to customers? If so perhaps it can be returned and a credit obtained. Finally, is there any scrap value? - an option which is a last resort but which at least brings in some revenue and clears the stores of items that will only cloud the spares management picture. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.19 ONGOING CONTROL

3.19

ONGOING CONTROL

The whole process of spares management in order to minimise financial cost whilst maintaining or improving customer service is an interactive process. New equipment is commissioned, old equipment becomes obsolete. Supplier practices change and lead times shorten. Preventive maintenance routines are reviewed and ways of extending them are found or criticality is designed out of something © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:44 PM

Page 210

"Holderbank" - Cement Course 2000 that was a critical item for years. Ongoing spares management, to be effective, must be continuous and can not be measured purely by looking at stock value levels. These tell us how well we are doing, not how well we could do. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.20 INDICATORS

3.20

INDICATORS

Effective spares management is all ing several indicators. The ones we have reviewed have been not just the financial indicators but operational indicators as well. Stock rotation, holding levels and usage levels are all influencing factors in the decision process which determines stock levels for maintenance spares. Because parameters will change due to changes in lead times, criticality, etc., the 20/80 theory (Pareto analysis) is not just a one off tool but part of a continuous process of data, analysis, decision and action, the whole underpinned by the financial and operational indicators. Process Technology / B06 - PT III / C03 - Maintenance / The main focus of MAC: Equipment efficiency, Maintenance Systems, Spares Management / 3. SPARES MANAGEMENT / 3.21 THE KEY TO SUCCESS

3.21

THE KEY TO SUCCESS

The key to success - to a competitive edge over the competition - the ability to not put off until tomorrow what our competitors are doing today - is an interactive spares management system that links financial performance to operational indicators through which management can continue to ask the question - why?


6/23/2001 - 5:14:45 PM

Page 211



6/23/2001 - 5:14:45 PM

Page 212

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING

CONDITION MONITORING

1. THE MAINTENANCE ENVIRONMENT TODAY 2. TYPES OF MAINTENANCE TASKS 3. WHAT IS CONDITION MONITORING 4. ADVANTAGES 5. IMPLEMENTING A CONDITION MONITORING TASK 6. THE P-F-CURVE 7. LIMITS 8. HOW OFTEN IS A TASK TO BE PERFORMED 9. CONDITION MONITORING METHODS WITHOUT INSTRUMENTS 10. CONDITION MONITORING METHODS USING INSTRUMENTS 10.1

Types of Techniques

10.2

On-Condition Techniques

10.3

Inspection Techniques

10.4

List of Techniques

11. OUTLOOK 12. CONCLUSION 13. REFERENCES 14. ANNEXES 14.1

Condition Monitoring Task

14.2

Condition Monitoring Techniques and their Applications

14.3

Annexes 3


6/23/2001 - 5:14:45 PM

Page 213

"Holderbank" - Cement Course 2000 Summary There have been many changes in the world of maintenance in the past few years. Predictive maintenance is one of the strategies to be used today to guarantee optimal performance at the lowest possible cost. Condition monitoring is a tool needed for predictive maintenance and the main requirement for it, is that it proves to be cost-effective. On-line condition monitoring techniques are gaining importance in the field of maintenance, sometimes incorporating on-line diagnoses of the results. These include: ♦ Data from the process side since it can give a hint of a maintenance related problem. ♦ Expert systems and statistical process control (SPC) techniques for the evaluation of trends used to decision making. For a proper selection of a specific CONDITION MONITORING task it is crucial to know the characteristic of the failure it is meant to prevent. Most failures give a warning that they are about to occur (potential failure). With condition monitoring deviations from the normal condition are detected. Based on these readings decisions can be made as to what corrective maintenance action has to be carried out and when. Suggestions are made of guidelines for the proper selection and implementation of condition monitoring tasks and the condition monitoring techniques described. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 1. THE MAINTENANCE ENVIRONMENT TODAY

1.

THE MAINTENANCE ENVIRONMENT TODAY

The world of maintenance has drastically changed in the past few years. The requirements have been growing and still are. The main aspects that maintenance has to cope with today are: ♦ Higher Plant Availability and Reliability ♦ Greater Cost Effectiveness ♦ Greater Safety ♦ Better Product Quality ♦ No damage to the environment ♦ Longer Equipment Lifetime The first two points are focused on, because they are easy to quantify by means of money. Maintenance strategies have to be selected to produce the lowest overall cost possible. Overall costs include: ♦ Prevention cost ♦ Repair cost ♦ Secondary damage cost (e.g. a bearing sizes due to a broken tube oil line) ♦ Loss of production (due to the down time of the equipment) Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 2. TYPES OF MAINTENANCE TASKS


6/23/2001 - 5:14:45 PM

Page 214


TYPES OF MAINTENANCE TASKS

Apart from servicing it is possible to split maintenance tasks into three types. Two of them do not need condition monitoring: ♦ Breakdown Maintenance; where the equipment is left in service until it fails. This can be both, dangerous and expensive. ♦ Scheduled Overhaul and Exchange; where the equipment, or part of the equipment, is restored or changed irrespective of its state. This is expensive and increases the risk of premature failures. The third type strongly depends on condition monitoring: ♦ Predictive Maintenance; where the equipment, or part of the equipment, is to be restored or changed the moment before it fails. One could say “Just in Time”. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 3. WHAT IS CONDITION MONITORING

3.

WHAT IS CONDITION MONITORING

For many people “Condition Monitoring” is vibration analysis. In this paper we will look at it in a much broader sense. Condition monitoring is everything which helps us to establish the state of equipment or the part to be maintained. Based on the findings, it is possible sometimes to estimate the residual lifetime of it. According to standards [1], condition monitoring can be explained as: ♦ Measures to establish and evaluate the actual condition. ♦ It serves to recognize that repair work has become necessary at a time sufficiently early to allow preparation for such work, thereby permitting the work to be performed according to a schedule and avoiding secondary defects. The term “Inspection” is also often used in this context. Most failures give some warning of the fact that they are about to occur. This warning is called a potential failure. It can be defined as an identifiable physical (abnormal) condition which indicates that a failure is either about to occur or in the process of occurring. With different techniques we intend to detect these deviations to the normal condition. These are condition monitoring techniques Condition monitoring detects deviations to the normal conditions The actual state of equipment can be established in different ways: ♦ Continuously or periodically On-line measurements or routine checks every certain time period ♦ Directly or indirectly E.g. weight belt / power consumption of the drive ♦ Qualitatively or quantitatively As a measured value or subjective (this noise is louder than normal) ♦ With or without instruments © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:46 PM

Page 215

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 4. ADVANTAGES

4.

ADVANTAGES

Predictive maintenance and therefore condition monitoring is applied to reduce overall cost. That means substituting secondary damage and down time cost, by the expense to avoid them (prevention cost). Therefore: Condition monitoring has to be cost-effective. Based on experience condition monitoring very often proves to be cost-effective. The benefits are: ♦ Prolonged equipment life time ♦ Minimized unscheduled downtime ♦ Fewer unnecessary overhauls ♦ Less stand-by equipment ♦ More efficient operation ♦ Increased safety ♦ Improved quality performance Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 5. IMPLEMENTING A CONDITION MONITORING TASK

5.

IMPLEMENTING A CONDITION MONITORING TASK

The need for a condition monitoring task can come from various sources: ♦ Out of the risk assessment process [2] ♦ From a cost/benefit analysis ♦ Dictated by law ♦ etc. The steps to establish a task can be seen on the flow sheet in Annex 1. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 6. THE P-F-CURVE

6.

THE P-F-CURVE

For the suitable selection of a specific condition monitoring task it is crucial to know the characteristics of the failure it is meant to prevent. The condition monitored has to have a correlation to the failure; e.g. there is no sense in monitoring the temperature if there will not be a temperature rise before the equipment fails. The characteristic’s in which failures occur can be visualized in a diagram which plots the condition against time. This forms a curve degrading in time. An example with some explanations can be seen in the following picture. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:46 PM

Page 216

"Holderbank" - Cement Course 2000 The P-F-Curve

The most common curves are degrading faster in time or are linear. The function of the curve is not necessarily age related. It can start at any time. But when a failure starts to occur it will progress according to that curve. The P-F-Interval is the time taken between the occurrence of a potential failure (detection possible) and its decay into the failure itself. In reality P-F-Interval’s are not necessarily consistent. In fact they can vary over a considerable range of values. For most purposes the shortest P-F-Interval should be taken into . A sudden impact from the environment (e.g. Overload, foreign object, etc.) can cause a immediate deterioration of the condition into a functional failure. There is no P-F-Interval associated to these kinds of occurrences. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 7. LIMITS

7.

LIMITS

There are some limits for the application of condition monitoring. The failure occurs without warning or too fast to undertake any action (P-F-Interval close to zero); there is no condition monitoring task to prevent it from occurring. The deviations are too small to be detected or if it is impossible to establish limits for the condition to be monitored. The P-F-Interval is so inconsistent, that no meaningful task interval can be established. The ultimate limit is given by the cost for the task in comparison to the money saved. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 8. HOW OFTEN IS A TASK TO BE PERFORMED

8.

HOW OFTEN IS A TASK TO BE PERFORMED

As a guidelines the frequency of a condition monitoring task has to be half of the (shortest) P-F-Interval of the failure. Therefore the frequency for the task depends mainly on two things: ♦ the characteristic in which a failure occurs ♦ the deviation needed to detect a potential failure © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:46 PM

Page 217

"Holderbank" - Cement Course 2000 The characteristics of the failure is predetermined mainly by design and equipment operation. This fact does not give maintenance the possibility to act directly on them. The only way to influence the frequency is to recognize a potential failure earlier in time. This means the deviation from the normal condition will be less and therefore the method of detecting the deviation has to be more sophisticated. In the case of a detected abnormal condition (potential failure), the frequency can be adjusted if the repair task will not be carried out immediately and the future development of the failure is not known well (lack of experience, inconsistencies of the P-F-Interval). The idea is to have the equipment, or part, remain in service for as long as possible. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 9. CONDITION MONITORING METHODS WITHOUT INSTRUMENTS

9.

CONDITION MONITORING METHODS WITHOUT INSTRUMENTS

The basic condition monitoring methods are use of the human senses: ♦ sight ♦ sound ♦ smell ♦ touch They exist as long as mankind and should not be forgotten even in the high-tech-times of today. These methods can be improved on by using simple instruments (magnifying lenses, mirrors, etc.). However, the disadvantage of inspections by human senses are that they are relatively unprecise, and therefore the associated P-F-Intervals are usually very short. Most of the smaller deviations tend to be beyond the range of the human senses and need specialized instruments to be detected. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 10. CONDITION MONITORING METHODS USING INSTRUMENTS

10.

CONDITION MONITORING METHODS USING INSTRUMENTS

We have learnt that a longer P-F-Interval means that the task needs to be done less often, and/or that there is more time to take whatever action is needed to avoid the consequences of the failure. In fact this will save money. This is why so much effort is being spent on trying to define potential failure conditions and develop techniques for detecting them with the longest possible P-F-Interval (as early as possible). Still one has to bear in mind that it has to be cost-effective. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 10. CONDITION MONITORING METHODS USING INSTRUMENTS / 10.1 Types of Techniques

10.1

Types of Techniques

In this paper the techniques using instruments are divided into two main groups: ♦ On-Condition Techniques; where the equipment remains in service ♦ Inspection Techniques; where the equipment has to be shut down or even dismantled © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:46 PM

Page 218

"Holderbank" - Cement Course 2000 The above mentioned division is not the only one, neither are the following ones. Some of the techniques can be used for more than one purpose. In Annex 2 a table can be found with various methods and their possible applications. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 10. CONDITION MONITORING METHODS USING INSTRUMENTS / 10.2 On-Condition Techniques

10.2

On-Condition Techniques

On-condition techniques have the advantage that the equipment can remain in service. In some cases they even have to be in service; e.g. dynamic measurements. Therefore there is no production loss cost associated with this type of measurement and they do not need special co-ordination with the production. For this reason on-condition techniques have become popular over the past few years. However, they are normally more expensive and the results are sometimes difficult to interpret. Often it is necessary to take baseline readings and decisions have to be based on trends rather than on single measurements. Very often this type of task is carried out on a regular basis by “inspectors” following a given route in the plant. A possible way of dividing them into smaller groups is by type of measurements: ♦ Dynamic; e.g. Vibration Analysis, Acoustic Emission, Torques ♦ Temperature; e.g. Thermography, Fibre Loop ♦ Particle and Chemical Analysis; e.g. Spectrometric Oil Analysis, Ferrography ♦ Electrical; e.g. Meggers, Resistance Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 10. CONDITION MONITORING METHODS USING INSTRUMENTS / 10.3 Inspection Techniques

10.3

Inspection Techniques

Many inspection techniques are well known and have been used in the cement industry for a long time. They include a wide range of solutions from simply determining the length with a tape measure to x-ray testing where expensive equipment is needed and good skills are necessary to handle them. A possible way of dividing them into smaller groups is by the failure they detect: ♦ Surface Degradation (Wear, Corrosion, Cracks, a.s.o.); e.g. Magnetic Particle Test, Dye Penetration Test, Endoscopy ♦ Internal Deficiencies; e.g. Ultrasonic Measurements, X-Ray Testing ♦ Properties; e.g. Hardness Test ♦ Dimensions; e.g. Meters, Calibration, Shell test ♦ Alignment; e.g. Laser Distance Measurements, Lead Wire ♦ Leaks; e.g. Pressure Testing, Ultrasonic Leak Detection Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 10. CONDITION MONITORING METHODS USING INSTRUMENTS / 10.4 List of Techniques

10.4

List of Techniques


6/23/2001 - 5:14:47 PM

Page 219

"Holderbank" - Cement Course 2000 In Annex 3 different condition monitoring techniques are described in detail. For every technique the following parameters are given: ♦ Condition moitored ♦ Applications ♦ Technical Base ♦ P-F-Interval ♦ Advantages/Disadvantages ♦ Skills necessary ♦ Standards applied ♦ Approx. Cost ♦ Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 11. OUTLOOK

11.

OUTLOOK

Taking into consideration all maintenance methods applied today a major movement towards on-condition monitoring techniques can be seen. This movement is expected to continue and to accelerate in the future. Together with the on-line monitoring the on-line diagnoses of the results will gain in attraction, because the expert systems have, and still are becoming more powerful and easier to handle. To involve process data into the condition monitoring is another step on the way to “Excellence in Maintenance”. A higher power consumption of the equipment or a quantity/quality decrease of the product can be a hint of a maintenance related problem. With the availability of long term data, statistical process control (SPC) techniques for the evaluation of trends can be used to help determine the actual condition of an equipment. Apart from others, two valuable tools to be applied for condition monitoring are: ♦ Moving X-bar Charts ♦ EWMA Charts (Exponentially Weighted Moving Average) Both of them cope with the small amount of measured values available over the time period. For the evaluation of on-line data (process or maintenance) a much wider field of SPC-techniques are worthwhile for consideration. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 12. CONCLUSION

12.

CONCLUSION

Condition monitoring is a tool needed for predictive maintenance. It is one of the tools for state of the art maintenance to cope with the requirements that it is confronted with; basically to guarantee optimal performance at the lowest possible cost. Therefore, every condition monitoring task has to prove to be cost-effective. For the proper selection of a specific task it is crucial to know the characteristic’s of the failure it is © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:47 PM

Page 220

"Holderbank" - Cement Course 2000 meant to prevent. Most failures give a warning of the fact that they are about to occur (potential failure). With condition monitoring, deviations to the normal condition are detected. Based on these readings, decisions can be made regarding what maintenance action has to be carried out and when. As a guideline the frequency of a task has to be half of the P-F-Interval of the failure, i.e. half of the time to elapse between the possible detection of a potential failure and its decay into the failure itself. The only way to lower the frequency is to recognize a potential failure earlier in time. This means the deviation from the normal condition will be less and the method of detecting it has to be more sophisticated. On-line techniques are gaining importance in the field of maintenance, sometimes incorporating on-line diagnose of the results. Data from the process side has to be involved as well, since it can give a hint of maintenance related problem. Expert systems and statistical process control (SPC) techniques for the evaluation of trends can be used to decision making. Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 13. REFERENCES

13.

REFERENCES

[1]

BS 3811; British Standard Nº 3811; Maintenance in tero technology, 1974

[2]

“Holderbank’s” Risk based Maintenance Policy; Information Brochure; Author: Holderbank Management & Consulting Ltd.; 1993

[3]

NDE Handbook Non-destructive examination methods for condition monitoring; Author: Knud G. Bøving; 1989

[4]

RCM II; Reliability-centered Maintenance; Author: John Moubray; 1993

[5]

VA 92/6008/E; Efficient Condition Monitoring of Rolling Bearings; Author: H. Burger, 1992

[6]

VA 83/5012/E; Author: W.H. Bürgi, 1983 Methods of Detecting Damage in Machine Parts;

[7]

VA 84/92/E; Scheduled Maintenance; Part A: Setting up a Maintenance Plan; Author: U.W. Hess, 1986

[8]

VA 82/4922/E; The HMC Maintenance Philosophy; Author: U.W. Hess, 1988

Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES

14.

ANNEXES

Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.1 Condition Monitoring Task


6/23/2001 - 5:14:47 PM

Page 221


Condition Monitoring Task

Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.2 Condition Monitoring Techniques and their Applications

14.2

Condition Monitoring Techniques and their Applications

Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.2 Condition Monitoring Techniques and their Applications / 14.2.1 Annex 2.1

14.2.1 Annex 2.1 On-Condition Techniques

Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.2 Condition Monitoring Techniques and their Applications / 14.2.2 Annex 2.2

14.2.2 Annex 2.2 Inspection Techniques


6/23/2001 - 5:14:47 PM

Page 222


Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3

14.3

Annexes 3

Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.1 Acoustic Emission

14.3.1 Acoustic Emission Conditions monitored Plastic deformation and crack formations caused by fatigue, stress and wear. Applications Metal materials used in structures, pressure vessels, pipelines and mining excavations. Technical Base Stress waves are emitted by the materials which are subjected to loads, due to the crystallographic changes. These stress waves are received by a transducer and amplified at an impulse analyser and fed to a X-Y plotter or an oscilloscope. The curve is evaluated visually. P-F Interval Several weeks, depending on the application Experience and knowledge necessary Equipment functioning and interpretation of the results: An experienced and trained technician Advantages Remote detection of flaws: Covers entire structures: Measuring system set up very quickly: High sensitivity: Only limited access to test objects required: Detects active flaws: Only relatively low loads are required. Can sometimes be used to forecast failure load. Disadvantages The structure has to be loaded: A-E activity is highly dependent on materials: Irrelevant electrical and mechanical noise can interfere with measurements: Gives limited information on the type of flaw: Interpretation of results may be difficult. Standards


6/23/2001 - 5:14:48 PM

Page 223

"Holderbank" - Cement Course 2000 ASTM in preparation Estimated Costs Ultraprobe USD 6’000.— Stethoscopes USD 1’000.— Supplier/Products SPM/ELS-12 Keel Engineering (CH) / Ultraprobe Westhill (South Africa) Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.2 Graded Filtration

14.3.2 Graded Filtration Conditions monitored Particles in lubricating oils (such as iron, copper, lead, chromium, aluminium, silicon, etc.) caused by wear, fatigue and corrosion. Applications Enclosed lubricating and hydraulic oil systems, such as gearboxes, engine sumps, hydraulic systems, etc. Technical Base An oil sample is diluted and ed through a series of membranes (filters) with decreasing particle ing size. The collected particles are counted under a microscope according to the element and size. Its statistical distribution is shown in a graphical form. The analysis of the characteristics of the distribution of the particles shows whether the wear is normal or not. P-F Interval Usually from several weeks to months. Experience and knowledge necessary Sample: a laboratory assistant; analysis of the characteristics for the distribution of the particles: An experienced laboratory technician or an engineer. Advantages Can determine whether wear is normal or not. Relatively cheap. Can be used to compare one element with another. Disadvantages It is not an on-line technique: A high degree of experience is necessary to interpret the results of the sample. Identification of particle elements is difficult Standards ISO 4406 Estimated Costs © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:48 PM

Page 224

"Holderbank" - Cement Course 2000 USD 2’000.— Supplier/Products Schak 01 (CH) Cortec Corporation (USA) Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.3 Ferrography

14.3.3 Ferrography Conditions monitored Wear, corrosion and fatigue Applications Enclosed lubricating and hydraulic oil systems such as gearboxes, engine sumps, hydraulics, etc. Technical Base Wear particles are separated magnetically from the lubricating oils onto an inclined glass plate by means of a instrument known as a ferrograph. The particles are distributed along the length of the slide according to their size. The slide is treated so that the particles adhere to the surface when the oil is removed. The total density of the particles and the ratio of large to small particles indicates the type of extent of wear and the analysis is made by means of a technique which is known as bichromatic microscopic examination. An electron microscope can also be used to determine the particles shapes and provide an indication of the cause of the failure. P-F Interval Usually several months Experience and knowledge necessary To extract the sample and operate the ferrograph: A semi-specialized operative suitable trained. To analyse the ferrogram: An experienced technician. Advantages More sensitive than the emission spectrometry at the at early stage of engine wear: measures particles shapes and sizes. Disadvantages It is not an on-line technique: measures only the ferrormagnetical particles: Requires an electron microscope for a more profound analysis. Standards Estimated Costs Supplier/Products BP, Mobil Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.4 Magnetic Plugs


6/23/2001 - 5:14:48 PM

Page 225

"Holderbank" - Cement Course 2000 14.3.4 Magnetic Plugs Conditions monitored Wear and fatigue Applications Equipment with closed lubrication systems, such as reductors, collectors of motor oil, compressors, etc. Technical Base In the lubrication system a magnetic plug is mounted so that it is exposed to the circulating lubricant. The small metal particles in suspension in the oil and the unfastened metal scales due to fatigue, are captured by the magnetic force. The probe is taken out by regular intervals and the adhering particles are examined under a microscope. An increase in the quantity and size of the particles indicates a potential failure. The particles have different characteristics (form, colour and structure) according to the type and location of the failure. P-F Interval From days to weeks Experience and knowledge necessary To pick up a sample: A semi-specialized operator trained accordingly. To analyse the particles: An experienced and trained technician. Advantages It is a cheap method to monitor the contamination of liquids. Only a ordinary microscope is required to analyse the particles. Some plugs may be taken out during operation. Disadvantages Short P-F interval: Experience is necessary to interpret the results. Standards Estimated Costs Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.5 SHELLTEST

14.3.5 SHELLTEST Conditions monitored The deformation of the shell of a rotary kiln, rigidity of shell and tyre and the play between them. Applications Shell of rotary kilns Technical Base The linear movements of a pin which is in with the surface of the shell is ed on a paper during a complete revolution of the kiln. There exist mathematical relations to the deformations of the © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:48 PM

Page 226

"Holderbank" - Cement Course 2000 shell. This procedure is carried out three times every 120° of the circumference of the kiln at various planes. Additionally the relative movement between the tyre and the shell is measured placing the pin on the shell and a plate with a paper on the tyre. P-F Interval Usually several months. Experience and knowledge necessary An experienced operator Advantages It is an on-line technique; long p-f intervals Disadvantages The evaluation of the results needs experience. Kiln operation does have a significant influence on the mesurement results. Standards Estimated Costs Shelltest equipment USD 10’000 Supplier/Products HMC “Holderbank” Phillips Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.6 Lead Wire Test

14.3.6 Lead Wire Test Conditions monitored Alignment, area Applications Alignment of tyre / roller kiln Technical Base A lead wire is ed between the tyre and a roller. The moulding of the wire is drawn on a sheet. This procedure is carried out three times per tyre every 120° of the its circumference for both rollers. The form of the wire is evaluated for: alignment, straightness of the surface, area and stress points. P-F Interval Usually several months Experience and knowledge necessary No experienced or special knowledge is required Advantages Cheap and easy, it is an on-line technique. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:49 PM

Page 227

"Holderbank" - Cement Course 2000 Disadvantages There is no quantitative result; additional measurements are required (oil film on the shoulders) for the evaluation of the alignment of the rollers. Kiln operation does have a significant influence on the measurement results. Standards Estimated Costs < USD 100 Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.7 Thermometer, Thermocouple

14.3.7 Thermometer, Thermocouple Conditions monitored Elevated temperatures due to wear, overloading, etc. at the surface or inside of an equipment Applications Refractory, reductors, motors, etc. Technical Base The electrical resistance of a wire changes with the temperature. The tension loss over the resistance is measured. In case of a PT100 the resistance at 20°C is 100 Ohm. P-F Interval From several hours to several days depending on the application. Experience and knowledge necessary Permanent installation: A specialist. Measurements with portable equipment: A suitable trained semi-specialized operator Advantages Cheap and easy to apply the portable equipment: often used as on-line measurement through the process control system Disadvantages In some cases the P-F interval is short - various hours Standards Estimated Costs PT100:

> USD 200

Digital thermometers: > USD 1’500 Supplier/Products Rikenta (CH); Ahlborn (D); Endress + Ha


6/23/2001 - 5:14:49 PM

Page 228

"Holderbank" - Cement Course 2000 Keithley, Bailey, Foxboro, Kent Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.8 Spectrometric Oil Analysis

14.3.8 Spectrometric Oil Analysis Conditions monitored The wear of the following elements can be detected: iron, copper, lead, chrome, aluminium, molybdenum, tin, silver, zinc, nickel, silicon, sodium, boron Applications Circulating oil systems Technical Base The contaminants in a sample of oil are measured by emission or atomic absorption spectrometry. The emission spectrometry excites the metallic impurities in the sample with a direct high voltage (15’000 V), causing the impurities to emit characteristic radiation’s which can be analysed. The atomic absorption spectrometry works on the principle that every atom absorbs light of its own specific wave length. The oil sample is diluted and vaporised in an acetylene flame, and the presence of each element is determined using a light source of the appropriate wave length. In this way, the wear particles are identified, quantified and qualified so that the source of deterioration can be located. The graphs of the wear rates for each metal show deteriorating or improving conditions. P-F Interval Usually from several weeks to months. Experience and knowledge necessary To take out a sample: A semi-specialized, suitable trained operator. To operate the spectrometer: a trained laboratory technician. To analyse the results of the sample: an experienced chemical analyst. Advantages This test, of atom absorption, is comparatively cheap (sometimes it can be included in the service of the oil supplier): More reproducible at lower concentrations: Emission spectrometry is much faster than the atomic absorption spectrometry. Disadvantages Normally the analysis have to be made by specialised contractors (or oil suppliers) because the equipment and experience is lacking (long response time). Standards Estimated Costs Supplier/Products BP, Mobil Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.9 Strain Gauges

14.3.9 Strain Gauges © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:49 PM

Page 229

"Holderbank" - Cement Course 2000 Conditions monitored Forces and deformations on parts Applications Gear reductor, structures, shafts, drives, etc. Technical Base The resistance of the wire changes linearly to the prolongation caused by the deformations. This resistance is measured by a bridge circuit. P-F Interval Several weeks to several months Experience and knowledge necessary An experienced technician is required to decide the position and affix the strain gauges as well as evaluate the results. Advantages Long P-F interval Disadvantages The measuring equipment are expensive, an external expert is required. Standards Estimated Costs Supplier/Products MEC; Brüel & Kjær Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.10 Stroposcopy

14.3.10

Stroposcopy

Conditions monitored Fissures, wear, direction, rotation speed and alignment in rotating and oscillating parts. Applications Rotary equipment such as shafts, ventilators, etc. for fissures or wear; check coupling for distance between the plates, loose screws, etc., balancing of rotary equipment (together with vibration measurement equipment) Technical Base The eyes follow the movement of one part in relation to the frequency in which it is illuminated. The frequency of the stroboscope is adjusted until the part appears to be stationary. Then the part can be inspected. P-F Interval Depends on the application; from several days to weeks © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:49 PM

Page 230

"Holderbank" - Cement Course 2000 Experience and knowledge necessary No experience or special knowledge is required. Advantages Easy to use and cheap, it is an on-line technique. Disadvantages Gives the impression that the part does not move, therefore security aspect should be kept in mind. Standards Estimated Costs USD 500 Supplier/Products Picostrob; Tourostrob Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.11 Test Coupon

14.3.11

Test Coupon

Conditions monitored General and localised erosion and corrosion such as metal loss and pitting Applications Petrol refineries, process plants, gas transmission plants, underground structures, monitoring of cathode protection, abrasive slurry transport, water distribution systems, atmospherique corrosion. Technical Base Usually coupons are produced from mild, low carbon steel with a low coal content or of a grade material which duplicates the wall of a vessel or pipe. The coupons are carefully prepared, weighted and measured before they will be exposed. After the coupons have been submerged in the process flow for a period of time (from several weeks to several months) they are removed and checked for weight loss and pitting. From these measurements, the relative metal loss of the tube walls can be calculated and pitting can be estimated. P-F Interval Several months Experience and knowledge necessary A suitable trained specialist Advantages Very satisfactory when corrosion is constant: Useful in dangerous areas where the electrical dispositives are prohibited: Fairly cheap: Indicates the type of corrosion: Widely used. Disadvantages Results take time: The response to dangerous corrosive conditions is low: The use of coupons requires several personnel: The determination of the rate of corrosion usually takes several weeks: Information © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:50 PM

Page 231

"Holderbank" - Cement Course 2000 about temporal or abnormal conditions are not supplied. Standards Estimated Costs Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.12 Thermography

14.3.12

Thermography

Conditions monitored Temperature variances caused by wear, corrosion, fatigue, leaks, poor electrical connections, etc. Applications Power transmission lines, transformers, refractories, electrical switchgear, building insulation, hydraulics, bearings, gas mains (dirt accumulations), etc. Technical Base Thermography extends the human vision to infrared waves. It is based on the principal that all objects above absolute zero (-273°C) emit infra-red radiation. An infrared camera that produces a live thermal picture detects this energy. Temperature differences of the surface are seen as light and dark areas and false colours. The thermal drawing can be recorded by a video camera attached to the display screen or directly onto a floppy-disk. P-F Interval A few days to several months depending on the application Experience and knowledge necessary Operation of equipment: A trained specialist. Interpretation of results: An experienced technician. Advantages Stationary or moving objects can be examined at any distance without touching or influencing the temperature of the object: Photographs and videotapes provide a permanent record: Examinations are carried out at safe distances from dangerous gases and high temperatures: Equipment portable and quick to use. Disadvantages Inaccessible components have to be uncovered: Costs: Needs specialist to interpret results: wide range of applications are needed to justify cost of the equipment. Standards Estimated Costs Portable systems USD 1’500 - 6’000 Complete systems (including software) USD 50’-100’000 Supplier/Products AGEMA: Thermovision © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:50 PM

Page 232

"Holderbank" - Cement Course 2000 AHLBORN: Raynger HENZ: Infratherm Land (USA); Williamson (USA); Kane May Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.13 Temperature Indicating Paint

14.3.13

Temperature Indicating Paint

Conditions monitored Equipment temperature at surface Applications Refractories, thermal treatment Technical Base A chemical substance is applied to the machine surface. If the temperature exceeds the design temperature of the substance, the state changes from solid to liquid. Although the temperature is lowered afterwards, the traces of the liquid are still visible. P-F Interval From days to several weeks depending on the application Experience and knowledge necessary No experience of special knowledge is required. Advantages Cheap and easy to use; provides a maximal temperature indication Disadvantages Indicates only a temperature limit; several paints are needed to cover temperature range; Once the temperature has been exceeded a new paint is required. Standards Estimated Costs USD 30 per tube or pencil Supplier/Products Medicina (FL): Tempil Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.14 Vibration Monitoring

14.3.14

Vibration Monitoring

Conditions monitored Changes in the vibration frequencies caused by wear, fatigue, corrosion, imbalances, disalingnment, loosening, etc. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:50 PM

Page 233

"Holderbank" - Cement Course 2000 Applications Rotating and oscillating machines in general such as reductors, ventilators, motors, etc. Technical Base Vibrations are produced by the movement of the machine or a part of it. The most important characteristics that can be measured are: displacement, speed, acceleration, frequency, phase, using an accelerator or a speed sensor, a vibrometer, filters, oscilloscopes, etc. Several methods exist to evaluate the vibrations (e.g. wide band, broad band, octave band, etc.) each of them has its advantage for a special problem P-F Interval From days to weeks depending on the application Experience and knowledge necessary To operate the measuring equipment: an appropriate trained technician; To interpret the results: An experienced technician, sometimes of superior level Advantages Cheap and compact: Test during service; can be portable or permanently installed. The interpretation can be based on established acceptance criteria for the condition such as VDI 2056 Disadvantages An in depth analysis requires an expert and a relatively long analysing time. Different evaluation techniques are needed to cover a case in detail Standards VDI 2056 ISO 3945 Estimated Costs Simple Instrument USD 1’000 Date collector, including software approx. USD 30’000 On-line system for several measuring points > USD 60’000 Supplier/Products IRD; Bruel & Kjaer; Karl Deutsch; Schenk, MAAG, ABB; SPM Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.15 Visual Inspection

14.3.15

Visual Inspection

Conditions monitored The range of conditions is enormous: Function, condition, surface, integrity, dimensions, shape, material, etc. of a piece of equipment in any industry not only for condition monitoring but also for damage analysis Applications For all equipment © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:50 PM

Page 234

"Holderbank" - Cement Course 2000 Technical Base Human sense is the technical base, sometimes ed with simple auxiliary instruments such as mirrors, lamps, etc. P-F Interval From several days to several months depending on the application Experience and knowledge necessary An attentive operator Advantages Most important method; cheap and easy, can be realised by operators of every level and education Disadvantages Human senses are limited: results are subjective and sometimes they can not be quantified. Standards DIN58220; DIN 8524; DIN 8563 BS 5289; BS 4080; ISO 3058; ASME sect V Art. 9 Estimated Costs Nothing for inspections that are carried out during the daily work. Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.16 Sight

14.3.16

Sight

Conditions monitored The range is enormous: Function, condition, surface, integrity, dimensions, shape, material, etc. of an equipment or of a part of any industry not only for condition monitoring but also for damage analysis. Applications For all equipment Technical Base Use of eyes P-F Interval From several days to several months depending on the application Experience and knowledge necessary An attentive operator Advantages Very important method; cheap and easy, can be realised by on an every day base. Disadvantages © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:50 PM

Page 235

"Holderbank" - Cement Course 2000 Human senses are limited; results are subjective and sometimes they can not be quantified. Standards DIN 58220; DIN 8524; DIN 8563 BS 5289; BS 4080; ISO 3058; ASME sect V Art. 9 Estimated Costs Nothing for inspections made by the operators during the daily work Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.17 Sound

14.3.17

Sound

Conditions monitored In majority: loosening, wear and forces Applications For all equipment or moving parts Technical Base Use of ears P-F Interval From several hours to several months depending on the application Experience and knowledge necessary An attentive operator Advantages Very important method: cheap and easy, can be realised by operators Disadvantages Human senses are limited, results are subjective and sometimes they can not be quantified. Standards Estimated Costs Nothing for inspections made by the operators during the daily work Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.18 Smell

14.3.18

Smell

Conditions monitored In majority leaks and forces (overloads) Applications © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:51 PM

Page 236

"Holderbank" - Cement Course 2000 For all equipment or moving parts, electrical, tubes, tanks, etc. Technical Base Use of nose P-F Interval From minutes to several hours depending on the application Experience and knowledge necessary An attentive operator Advantages Cheap and easy, can be realised by operators Disadvantages Human senses are limited; results are subjective and sometimes they can not be quantified, P-F interval is very short. Standards Estimated Costs Nothing for inspections made by operators during the daily work Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.19 Touch

14.3.19

Touch

Conditions monitored In majority loosening, wear and property Applications For all equipment Technical Base Use of hands P-F Interval From several hours to several months depending on the application Experience and knowledge necessary An attentive operator Advantages Cheap and easy, can be realised by operators Disadvantages Human senses are limited; results are subjective and sometimes they can not be quantified; can be dangerous (hot surfaces, splinters, etc.) © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:51 PM

Page 237

"Holderbank" - Cement Course 2000 Standards Estimated Costs Nothing for inspections made by operators during the daily work Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.20 SPM (Shock Pulse Method)

14.3.20

SPM (Shock Pulse Method)

Conditions monitored Shock waves due to fissures, wear, disalignment, insufficient lubrication, etc. Applications Rolling element bearings, pneumatic impact tools, valves of internal combustion engines Technical Base A accelerator detects the shock waves transmitted by the machine. The signals es through a band filter which selects only frequencies exceeding 10 kHz. This high frequency input is converted into square pulses. The peak values of these pulses are read off as a measure of bearing damage. P-F Interval Depends on the application, but usually several weeks to months Experience and knowledge necessary An experienced and suitably trained technician Advantages Long P-F intervals: Equipment portable: Simple to use, on-line technique Disadvantages Not suitable for slow-moving machinery with high levels of product impact noise unless adaptive noise cancelling” is also used. Application is limited to a shock impulse measurement and transitory signals. Standards Estimated Costs USD 3’000 Supplier/Products SPM Instrument AG AE Advanced Engineering, Rolle (CH) Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.21 Dye Penetrant Examination

14.3.21

Dye Penetrant Examination

Conditions monitored © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:51 PM

Page 238

"Holderbank" - Cement Course 2000 Surface discontinuities, fissures, etc. caused by fatigue, wear, surface shrinkage, grinding, heat treatment, laminations, corrosion, corrosion stresses Applications Ferrous and non ferrous materials such as welds, machined surfaces, shafts, boilers, plastic structures, compressor receivers, etc. Technical Base The penetrant liquid is applied to the test surface and sufficient time is permitted for it to penetrate the surface discontinuity. The excess surface penetrant is removed. A developer is applied which draws the penetrant from the discontinuity to the test surface where it is interpreted and evaluated. The liquid penetrants are categorised according to the dye type (visible dye, fluorescent or penetrates of double sensity) and the required procedure to eliminate them from the test surface (washable with water, post emulsified or solvent removed) P-F Interval From several days to several months depending on the application Experience and knowledge necessary To apply the penetrate: a semi-specialized suitable trained operator. Interpretation: A suitable experienced technician Advantages The sets of visible penetrate dye are very cheap but the fluorescent sets are a lot more sensitive. Detects surface discontinuities also on non ferrous materials. Disadvantages Fluorescent penetrates require an darkened area for inspection; Not an on-line technique, monitors only surface-breaking defects; It cannot materials with a porous surface; use is limited at temperatures from 0° to 50°C. Standards DIN 54152; BS 4416 ASTM-E 165; MIL-I-25135 Estimated Costs USD 40 per set Supplier/Products ARDROX; MAGNAFLUX; CASTROL Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.22 Eddy Current Testing

14.3.22

Eddy Current Testing

Conditions monitored Surface and sub-surface discontinuities caused by wear, fatigue and stress, detection of dimensional changes produced trough wear, strain and corrosion, determination of material hardness. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:51 PM

Page 239

"Holderbank" - Cement Course 2000 Applications Ferrous materials used for boiler tubes, heat exchanger tubes, hydraulic tubing, hoist ropes, railway lines, etc. Technical Base A test coil carrying alternating current between 100 kHz and 4 MHz induces eddy current in the part being inspected. Eddy current detours around cracks, becoming compressed, delayed and weakened. The electrical reaction on the test coil is amplified and recorded on a cathode ray tube or direct reading meter. P-F Interval Several weeks, depending on the application Experience and knowledge necessary An experienced and suitable trained technician. Advantages Applicable to a wide range of conducting materials. Can work without surface preparation. High defect detection sensitivity: Strip chart recorder provides a permanent record Disadvantages Poor response from non-ferrous materials. Usually an external specialist is required. Standards ASNT; DIN Estimated Costs from USD 3’000 Supplier/Products Förster () Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.23 Endoscopy

14.3.23

Endoscopy

Conditions monitored Surface cracks and their orientation, oxide films, weld defects, corrosion, wear, leaks Applications The internal visual inspection of narrow tubes, bores and chambers of engines, pumps, turbines, compressors, boilers, etc. in several industries Technical Base These instruments are known as endoscopes or borescopes. The light is channelled with mirrors or fibre cables to allow inspection of otherwise inaccessible points of view. If the light is insufficient, an external light can be sent through some of the fibre cables. For this an equipment producing cold light is used. It lightens the area so that photographs can be taken or video equipment used. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:52 PM

Page 240

"Holderbank" - Cement Course 2000 P-F Interval Several weeks depending on the application Experience and knowledge necessary An experienced and suitable trained operator Advantages A detailed inspection of the surface in inaccessible areas can be obtained without having to dismantle the pieces; photographs can be taken to provide permanent records. They can be magnified; portable equipment. Disadvantages Only surface defects can be detected; Not an on-line technique; when equipment with cold light source, video camera, etc. is used, the method becomes costly Standards Estimated Costs Inflexible: USD 2’000; with fibre cables USD 5’000-10’000 Complete systems: USD 30’000-50’000 Supplier/Products Volpi; Classen + Co; Olympus Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.24 Electrical Resistance (Corrometer)

14.3.24

Electrical Resistance (Corrometer)

Conditions monitored Integrated metal loss (i.e.: total corrosion) Applications Petroleum refineries, process plants, gas transmission plants, underground structures, cathodic protection monitoring, abrasive slurry transport, water distribution systems, atmospheric corrosion Technical Base The system is composed of a probe and an instrument to read it. The probe consists of a wire, strip or tube of the same metal in the plant being monitored. The electric resistance of the probe which is measured by a bridge circuit, increases as the probe cross-section decreases with corrosion. This increase in resistance enables total metal loss to be read out which is easily converted to corrosion rate P-F Interval Depends on the application and on the corrosion rate. Usually several months. Experience and knowledge necessary A trained specialist Advantages © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:52 PM

Page 241

"Holderbank" - Cement Course 2000 When plotted against a time scale, yields both corrosion rate and total metal loss; Can be used in any environment. Portable equipment available. On-line monitoring possible: In-plant equipment provides permanent records: Interpretation normally easy. Disadvantages Gives no indication of whether the corrosion rate at a particular time is high or low; portable equipment provides no permanent record. Standards ASTM D 1776-79 Estimated Costs Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.25 Hardness Test

14.3.25

Hardness Test

Conditions monitored Propriety of a material (hardness, crystallisation) Applications Shafts, gears, wear plates (i.e. clinker cooler), laminations, castings, welds Technical Base A test body is accelerated and collides with the test surface. The resistance of the material against penetration of the body into the surface is an indication of the hardness. Two types of evaluations are used depending on the method applied: A typical dimension (i.e.diameter) of the trace of the test body on the surface is measured or the energy difference of the test body is measured before or after the collision. For both methods the value is converted in hardness using tables. P-F Interval Depends on the application, but usually from several weeks to months Experience and knowledge necessary A suitable trained operator Advantages Rapid and simple measurements Disadvantages Application in a plant limited: inaccuracy of approx. 10%, Not an on-line technique. The measurement point has to be easily accessible. Standards Estimated Costs Equotip USD 4’000; Poldi USD 600


6/23/2001 - 5:14:52 PM

Page 242

"Holderbank" - Cement Course 2000 Supplier/Products Poldy Hammer Equotip Shore Hardness Tester Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.26 Dimension Measurement

14.3.26

Dimension Measurement

Conditions monitored Dimensions of parts and dimension changes due to deposits or wear Applications For all equipment or parts such as shafts, bearings, tubes, etc. Technical Base There exist a wide variety of methods A dimension is measured with a calibrator, a micrometer, etc. The results are in units of length and are compared with previous or basic values. A dimension is compared with a calibre. The results are in a digital form , it “DOES” or “DOES NOT” have the required value including tolerances. The contour of a part is formed with a wire and compared with the previous or basic contours. P-F Interval Depends on the application, but usually from several weeks to months Experience and knowledge necessary No experience or special knowledge is required. Advantages Cheap and simple to use and evaluate Disadvantages Difficult to apply to big dimensions; only a decision “YES” or “NO” in the case of calibre’s, not an on-line technique Standards ISO Estimated Costs Very depending on the technique selected, from USD 100 for calibrators, micrometers, etc. Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.27 Laser


6/23/2001 - 5:14:52 PM

Page 243


Laser

Conditions monitored In the majority dimensions or distances between two points are measured or it is used for alignment purposes Applications Kilns, transport ways, couplings, etc. Technical Base It is the modern form of the theodolite. A laser source is used to create an uniform and visible light of an exact wave length. This light is sent to a point on the surface. With a second instrument this point is also adjusted to this point, producing a triangulation measurements and evaluating them trigonometrically. With another Methode the beam is reflected and the difference at the source is evaluated. P-F Interval Depends on the application, but usually from several weeks to months Experience and knowledge necessary A suitable trained technician Advantages Rapid, can be measured without , measurement possible with the equipment in service. Disadvantages Relatively expensive, practice is required. Standards Estimated Costs Coupling alignment systems USD 10’000 Supplier/Products Optalign

FLS (kiln alignment service)

Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.28 Theodolite

14.3.28

Theodolite

Conditions monitored In the majority dimensions or distances between two points are measured or it is used for alignment purposes Applications Kilns, transport ways, coupling, etc. Technical Base Triangulation measurements and evaluating them trigonometrically © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:52 PM

Page 244

"Holderbank" - Cement Course 2000 P-F Interval Depends on the application, but usually from several weeks to months Experience and knowledge necessary A suitable trained technician Advantages Rapid and relatively cheap, can be measured without , sometimes possible with the equipment in service Disadvantages Practice is required, limited use in a cement plant Standards Estimated Costs Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.29 Leak Testing

14.3.29

Leak Testing

Conditions monitored Leaks in tube systems and tanks, etc. Applications Distribution systems, tanks and vessel for oil, petroleum, lubricants, chemicals, liquid alternative fuels, etc. Technical Base The range of methods is so great that only the types are mentioned: - by lost quantity - by pressure differences: see also Pressure Test - by tracing substances P-F Interval Depends on the application, but usually from several weeks to months Experience and knowledge necessary A semi-specialized suitable trained operator. In some countries a certification is required to be allowed to perform the tests Advantages/Disadvantages The range of techniques is so great that the advantage of one technique is the disadvantage of the other. Some are simple to use and cheap. Standards © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:53 PM

Page 245

"Holderbank" - Cement Course 2000 BS 3636; ASTM-E 432-71 Estimated Costs Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.30 Voltage Generator

14.3.30

Voltage Generator

Conditions monitored Resistance of electrical isolation Applications Electrical Circuits Technical Base The measurement is based on the ratiometer principle using two moving coils connected mutually at right angles (90°) within a permanent magnetic field. The reference coil is connected in series to a constant resistance, the other (deflecting coil) in series with the isolation resistance to be measured. The amount of deflection is a function of the resistance of the isolation. Test voltages of 250 to 10’000 V are used. P-F Interval From months to years Experience and knowledge necessary Operator or technician, depends on the voltage Advantages Simple and known technique Disadvantages No on-line technique Standards Estimated Costs Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.31 Magnetic Particle Test

14.3.31

Magnetic Particle Test

Conditions monitored Surface and near-surface cracks and discontinuities caused by fatigue, wear, laminations, inclusions, surface shrinkage, grinding, heat treatment, hydrogen embrittlement, laps, seams, corrosion fatigue and corrosion stress. Applications © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:53 PM

Page 246

"Holderbank" - Cement Course 2000 Ferromagnetic metals such as compressor receivers, welds, machined surfaces, shafts, steel structures, boilers, etc. Technical Base A test piece is magnetised and then sprayed with a solution containing very fine iron particles over the area to be inspected. If a crack exists, the iron particles will be attracted to the magnetic flux leaking from the area caused by the discontinuity and give an indication. These leakage fields act as local magnets. The indication is then interpreted and evaluated. Fluorescent magnetic particle sprays provide greater sensitivity and inspection should be carried out under ultra-violet light in a darkened room. P-F Interval From days to months depending on the application Experience and knowledge necessary Application: a suitably trained semi-specialized operator, Interpretation: an experienced technician. Advantages Reliable and sensitive: relatively cheap and simple; independent of temperatures Disadvantages Detects only surface and near surface cracks: Time consuming: Contaminates clean surfaces: Not an on-line monitoring technique; only for ferromagnetic materials. Standards DIN 54130 and following; BS 4397 MIL 1949; ASTM-E and ASME-SE various Estimated Costs USD 3’000 Supplier/Products Tiede; Magnaflux Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.32 Oilproof Lacquer

14.3.32

Oilproof Lacquer

Conditions monitored Alignment, area Applications Girth gear/pinion, gears Technical Base A coloured liquid is applied to the surface of one of the two parts. When the equipment is moved the coloured area comes into with the opposite part and leaves a “fingerprint” on it. Those are to be examined for colour distribution. P-F Interval © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:53 PM

Page 247

"Holderbank" - Cement Course 2000 Depends on the application, but usually from several weeks to months Experience and knowledge necessary No experience or special knowledge is required Advantages Cheap and simple to use Disadvantages There is no quantitative result; clean surfaces are required. Standards Estimated Costs USD 50 per 0.2 litres Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.33 Electron Fractography (Replica)

14.3.33

Electron Fractography (Replica)

Conditions monitored The growth of fatigue cracks Applications Metallic components in motor vehicles, industrial equipment, etc. Technical Base Every fracture has its own “fingerprint”, in that the history of the fracture process is imprinted on the fracture surface. By studying a replica of the actual fracture surface with an electron microscope, it is possible to establish the causes and circumstances of failures. P-F Interval Depending on the application Experience and knowledge necessary Replica of the fracture surface: suitably trained technician. Analysis and reading: experienced engineer. Advantages Failures can be analysed with a high degree of certainty: No damage caused the actual to fracture surface when replica is made. Disadvantages Electron microscope is expensive: High degree of specialisation required to read the results: Not an on-line monitoring technique: Inaccessible components must be dismantled. Standards


6/23/2001 - 5:14:53 PM

Page 248

"Holderbank" - Cement Course 2000 DIN 54150 ISO 3057 Estimated Costs Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.34 Pressure Test

14.3.34

Pressure Test

Conditions monitored Leaks, fissures, fractures and deformations in tanks, pressure vessels, etc. Applications Tanks for, gas, pressured air, etc. Technical Base For security reasons the tests should be carried out using water or oil if possible. The systems have to be adequately ventilated. Higher pressures than required during operation are introduced to the system to see if it can withstand them. The percentage of overpressure required before rupture, depends on the safety regulations applicable. P-F Interval “YES” or “NO” decision Experience and knowledge necessary A semi-specialized suitably trained operator. In some countries certification is required before testing can be carried out. Advantages This test can be combined with a leak test, cheap and simple to do. Disadvantages Not an on-line technique, The components have to be emptied and cleaned before and after the test. Standards BS 5430 Estimated Costs Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.35 Radiography (X-Ray)

14.3.35

Radiography (X-Ray)

Conditions monitored Surface and sub-surface discontinuities caused by fatigue, stress, inclusions, lack of penetration in welds, gas porosity, intergranular corrosion and stress corrosion. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:53 PM

Page 249

"Holderbank" - Cement Course 2000 Applications Ferrous and non-ferrous materials, welds, steel structures, plastic-structures, metallic wear components of engines, compressors, gearboxes, pumps shaft, etc. Technical Base A radiograph is produced by ing x-rays or gamma rays through materials which are optically opaque. The absorption of the initial x-ray depends on thickness, nature of the material and intensity of the initial radiation. The areas exposed become dark when the film is developed. The degree of darkening depends on the amount of radiation reaching the film. It will be darkest where the object is thinnest. A crack, inclusion or a void is observed as a dark patch. P-F Interval Several months Experience and knowledge necessary Use of equipment: a suitably trained and skilled technician. To interpret the results: a highly skilled technician or engineer. Advantages Provides a permanent record, detects defects in parts or structures not visually accessible Disadvantages Sensitivity often low on crack-line defects: Two-sided access sometimes needed; external expert required; security precautions elevated; costly Standards Estimated Costs USD 6’000 - 300’000 Supplier/Products Specialised companies Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.36 Linear Polarisation Resistance (Corrator)

14.3.36

Linear Polarisation Resistance (Corrator)

Conditions monitored The rate of corrosion in electrically conductive corrosive fluids Applications Cooling water systems, municipal water systems, heat exchanger, desalination plants and pulp and paper mills and in the plants where the measurement and/or the corrosion control is required in acid water systems Technical Base Corrosion rate is measured by the electro-chemical polarisation method with two or three probes and a measuring instrument. The principle is based on the fact that a small voltage applied between a metal specimen and a corrosive solution will produce a current. The ratio of voltage to current is inversely © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:54 PM

Page 250

"Holderbank" - Cement Course 2000 proportional to the corrosion rate so it provides a measure of the corrosion rate increase. P-F Interval Depends on the application and the corrosion rate. Usually several months Experience and knowledge necessary A suitably trained operator Advantages Provides a direct indication of the corrosion rate and pitting tendency: Measures corrosion as it occurs: Some instruments provide a record of the corrosion condition: Automatic detection and control available: Sensitive to very low corrosion rates: Portable equipment available: Rapid measurement: Interpretation normally easy Disadvantages Portable equipment does not provide a permanent record: Readings must be adjusted when taken in high sensitivity corrosive media: Gives no information on total corrosion. Standards ASTM D 2776 Estimated Costs Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.37 Liquid Chromatography

14.3.37

Liquid Chromatography

Conditions monitored Changes in lubricant properties such as alkalinity, acidity, ash, flash point, insoluble, viscosity, etc. Applications Enclosed oil systems such as transformers, engine sumps, compressor sumps, hydraulic systems, etc. Technical Base Liquids are selectively absorbed by ing through a column of finely divided absorbent material. The separate liquids are then set free by ing a mixture of two solvent liquids, with different polarities, through the column. Light liquids appear first from the column and complex liquids last. The analysis appears on a strip chart recorder, or a screen, and the area under each peak is measured to determine the respective liquid concentrations P-F Interval Depending on the degradation rate of the lubricant and the application, but usually several weeks. Experience and knowledge necessary Operating the equipment and interpretation of results: a laboratory technician who has ed a course of chromatography. Advantages © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:54 PM

Page 251

"Holderbank" - Cement Course 2000 High sensitivity: Quick sampling and analysis: Strip chart provides a permanent record Disadvantages Considerable skill is needed to interpret results: Equipment not portable: Wide range of applications required to justify purchase: Not an on-line monitoring technique: not widely used in maintenance Standards Estimated Costs Supplier/Products Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.38 Ultrasonic

14.3.38

Ultrasonic

Conditions monitored Surface and below surface discontinuities caused by fatigue, heat treatment, inclusions, lack of penetration and gas porosity in weld, laminations, etc. as well as material thickness. Applications Ferrous and non-ferrous materials related to welds, steel structures, boilers, boiler tubes, plastic structures, shafts, compressor receivers, etc. Technical Base A transmitter sends an ultrasonic pulse into the test surface and a receiver amplifies the return pulse to an oscilloscope. The echo is a combination of return pulses from the opposite side of the test piece and from any intervening discontinuity. The time elapsed between the initial and return signals and the relative height indicate the location and severity of the discontinuity. A rough idea of the size and shape of the defect can be gained by checking the test piece from another location. P-F Interval From several weeks to several months Experience and knowledge necessary An experienced and suitably trained technician Advantages Applicable to the majority of materials, relatively low costs, no expensive preparations needed Disadvantages Difficult to differentiate types of defects, evaluation relatively difficult; Problems with complex geometrical pieces, superficie has to be machined. Standards Estimated Costs USD 8’000 Supplier/Products


6/23/2001 - 5:14:54 PM

Page 252

"Holderbank" - Cement Course 2000 Krauträmer; Karl Deutsch Process Technology / B06 - PT III / C03 - Maintenance / CONDITION MONITORING / 14. ANNEXES / 14.3 Annexes 3 / 14.3.39 Potential Monitoring

14.3.39

Potential Monitoring

Conditions monitored Corrosive states of plant (active or ive) such as stress-corrosion cracking, pitting corrosion, selective phase corrosion, impingement attack, etc. Applications Electrolyte environments such as chemical process plants, paper mills, electrical generating plant, pollution control plants, desalination plants, etc. best suited to materials of stainless steel, nickel-based alloys and titanium Technical Base This technique takes advantage of the fact that, from the point of view of corrosion, a metal which is in a ive state (low corrosion rate) has a noble corrosion potential, while the same metal in an active state (higher corrosion rate) has a much less noble potential. The potential changes when ivity breaks down, and measurements can be made using a voltmeter of about 10 megohm input impedance and full-scale deflection of 0.5 to 2 volts P-F Interval Depends on the material and the corrosion rate Experience and knowledge necessary Signal detection is normally easy, but sometimes an experienced engineer is needed to interpretate de results further Advantages Monitors localised attack: Fast response to change Disadvantages Small potential changes can be influenced by changes in temperature or acidity: Does not give a direct measure of corrosion rate or total corrosion: Not widely used: Expert assistance may be required for interpretation Standards Estimated Costs Supplier/Products Rohrback Instruments


6/23/2001 - 5:14:54 PM

Page 253

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment

Quality Inspections for Cement Plant Equipment W. H. Bürgi, R. Burkhalter, T. Elvermann PT 97/14233/E (Revision 2, February 1999) 1. INTRODUCTION 2. OBJECTIVE OF QUALITY INSPECTIONS 3. EXAMPLES OF DAMAGES 4. REASONS FOR DEFECTS 5. INSPECTION METHODS / TESTS 6. SUPPLIER’S / MANUFACTURER'S INSPECTIONS 7. STEPS OF QUALITY ASSURANCE 8. QUALITY INSPECTION PROGRAM 9. HMC AS AN INSPECTION COMPANY – BENEFITS 10. CONCLUDING REMARKS 11. ANNEXES

Summary: Quality is not an invention of the twentieth century. Conscientious manufacturers have always been endeavored to assure the good quality of their products. But through the demand for substantial cost reduction, manufacturers reduced or outsourced their internal quality control. Suppliers also place their orders to manufacturers in low cost countries where quality control is not yet sufficiently observed. At the same time cement machines change to always larger dimensions and capacities. With this trend new problems appear as well. Our statistic shows that during the last few years only 60% of the items inspected are without any shortcomings. Out of the 40% rejected due to non-conformances, 2% could not be repaired and had to be discarded and re-fabricated. If not detected during the inspection, this would have caused substantial loss of production due to the down time, which means a loss of money and in the worst case even loss of customers. The Vision for our Quality Control Equipment was therefore clearly defined.

No break downs in the "HOLDERBANK" group due to components failures on purchases of new equipment

The objective of quality services is always the profit of the purchaser. The investment into quality will © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:55 PM

Page 254

"Holderbank" - Cement Course 2000 be paid back in lower production costs as the items are more reliable (less down time), lower maintenance costs (breakdown maintenance) and a longer live time (reduction of NOA). One of the most important points from the very beginning is to include adequate quality requirements (specifications) in the purchase order/contract to assure a trouble free roll-out. Following this procedure the quality requests have to be included in the contract and the supplier has to follow it. Each deviations from the specifications must be communicated with the inspectors and needs an agreement. After a seriously review of operating requirements it can lead into longer guarantee time, price reduction or manufacturing of a new part. Finally, from HMC experience we can say: Quality depends very much on the suppliers care – and regular quality inspections remind them for this responsibility.

Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 1. INTRODUCTION

1.

INTRODUCTION

For the purchaser of a production plant, new machine or component the mayor problem is normally the loss of production due to equipment break down and less the cost of a replacement. The failed item is sometimes still under guarantee. Due to production loss, substantial loss of sales or even loss of customers can occur. To avoid unexpected down time due to manufacturing defects of items, companies started to contract independent inspectors to supervise the quality control of the manufacturer. The history of the quality inspection service at "HOLDERBANK" shows typically this evolution. Recalculating the main items as girth gears, gear boxes and kiln tyres to influence its design was the first step. Anyhow, damages still occurred and it was found that some of the reasons were manufacturing defects. The experience with quality inspections showed that still nowadays it is necessary to supervise the fabrication through an independent body. This not only because the suppliers move their production into low price countries, but also because sometimes there is poor quality produced even in well-known companies with normally good products. Consequently "HOLDERBANK"'s objectives were set: ♦ Achieve high reliability of the equipment at adequate cost ♦ Maximize effective life time of assets ♦ Form the suppliers to deliver the expected quality ♦ Train our inspectors in supervising efficiently and precisely the quality inspections Full responsibility for the products remains with the supplier and the quality inspections have to be cost effective. Therefore our inspections are limited to important items as mentioned in Annex 1. Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 2. OBJECTIVE OF QUALITY INSPECTIONS

2.

OBJECTIVE OF QUALITY INSPECTIONS

The objective of quality inspection services is always the profit of the purchaser. The investment into quality will be paid back in lower production costs as the items are more reliable (less down time), lower maintenance costs (breakdown maintenance) and have a longer life time (reduction of NOA). © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:55 PM

Page 255

"Holderbank" - Cement Course 2000 Further valuable information with regard to applied materials and procedures, which normally are not supplied by the manufacturer, are handed out. Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 3. EXAMPLES OF DAMAGES

3.

EXAMPLES OF DAMAGES

In a cement plant the catalogue of possible examples of damages is quite long, e.g. ♦ Cracked / fractured girth gears and pinions ♦ Cracked / fractured kiln tyres, rollers, shafts ♦ Cracked kiln or mill shells ♦ Cracked mill end-castings and flanges ♦ Damaged roller mill bodies ♦ Damaged roller press rollers etc. Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 4. REASONS FOR DEFECTS

4.

REASONS FOR DEFECTS

Reasons for defects are many fold. In some cases it is lack of knowledge, unfavorable design or a price that was too low for a good quality product. It may be added that the production of large castings not only demands excellent knowledge and modern facilities but also involves a great deal of luck. Errors, such as insufficient supervision or checks, a carefree attitude, fatalism and taking calculated risks up to deliberate attempts to cheat have all been observed. The life cycle of an equipment/component explains very well that the quality of a part is “made” at different stages, starting with the design (specification) followed by the manufacturing (inspections) and finally at the installation.

The quality inspections focus on the manufacturing of the equipment/component, which is a very important step in its life. Defects can originate in every manufacturing step: casting, forging, welding, © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:55 PM

Page 256

"Holderbank" - Cement Course 2000 machining or assembling. The most common defects are: ♦ Material inhomogeneities ♦ Cracks ♦ Surface deficiencies ♦ Dimensional/Geometrical errors Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 5. INSPECTION METHODS / TESTS

5.

INSPECTION METHODS / TESTS

During the course of fabrication of components / machines quite a series of quality tests are carried out and different inspection methods are applied. ♦ Destructive Testing (Mechanical tests and Chemical analysis) ♦ Non-destructive testing ∗ Ultrasonic test ∗ Magnetic particle test ∗ Dye penetration test ∗ Hardness test ∗ Dimensional check ♦ Verification of procedures / documents Destructive Testing and Chemical Analysis Materials samples taken from the component in question are tested for the ultimate strength, yield strength, elongation, reduction of area and impact energy. Their chemical composition is analysed as well. The values received are compared with current standards and specifications. Visual Testing Visual testing includes checking of general appearance, surface quality, dimensions, conformity with drawing, functions and is the most often employed method and the one which has proved its worth for acceptance inspections of cement equipment. Ultrasonic Testing The most difficult of the above mentioned test methods might be the check for internal defects with ultrasonic sound waves. The microstructure of the material, the geometry and surface quality of the test piece has an important influence on the sound waves. A broad and permanent experience is needed to interpret the respective signals on the screen. A wide variety of ultrasonic probes is available, each of them has its special features. For the inspection of cement equipment it is not possible to take advantage of all technical possibilities (as for nuclear equipment) owing to the high cost. Therefore, a certain risk of failure during operation can not be excluded. Magnetic Particle Testing A test piece is magnetized and then sprayed with a solution containing very fine iron particles over the area to be inspected. If a crack exists, the iron particles will be attracted to the magnetic flux leaking from the area caused by the discontinuity and giving an indication. These leakage fields act as local © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:55 PM

Page 257

"Holderbank" - Cement Course 2000 magnets. The indication is then interpreted and evaluated. Fluorescent magnetic particle sprays provide greater sensitivity; the inspection should be carried out under ultra-violet light in a darkened room. Dye Penetration Testing The penetrant liquid is applied to the test surface and sufficient time is permitted for it to penetrate the surface discontinuity. The excess surface penetrant is removed. A developer is applied which draws the penetrant from the discontinuity to the test surface where it is interpreted and evaluated. The liquid penetrants are categorized according to dye type (visible dye, fluorescent or penetrates of double sensity) and the required procedure to eliminate them from the test surface (washable with water, post emulsified or solvent removed). Hardness Testing A test body is accelerated and collides with the test surface. The resistance of the material against penetration of the body into the surface is an indication of the hardness. Two types of evaluations are used depending on the method applied: A typical dimension (i.e. diameter) of the trace of the test body on the surface is measured or the energy difference of the test body before and after the collision is measured. For both methods the value is converted in hardness and/or strength using tables. Verification of Procedures / Documents No quality inspection is complete without the verification of the welding and heat treatment procedures/parameters (if applicable) and the complete documentation. This documentation includes all forms completed during the manufacturing and the quality inspection. It has to come along with the part for further reference at the plant in case of a failure during the operation phase. Inspectors Qualifications The inspectors carrying out quality checks on components and machines during fabrication must have knowledge, sufficient training and practical experience in the different testing methods and management of such jobs. Documents and Arrangements necessary for Quality Inspections In order to be able to carry out tests, certain specific information and documents about each component must be available. Also the necessary arrangements for the inspectors must be provided by the supplier. These needs are listed in Annex 2 which should become part of the purchasing contract in case HMC is entrusted with the quality control. Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 6. SUPPLIER’S / MANUFACTURER'S INSPECTIONS

6.

SUPPLIER’S / MANUFACTURER'S INSPECTIONS

In most cases the supplier is not or only up to a certain degree the manufacturer. He plans his order to a sub-supplier, e.g. a foundry, forge, gear maker etc. The manufacturer (sub-supplier) must perform quality inspections himself at various stages of manufacturing according to contractually agreed specifications, standards and procedures. He is, together with the supplier, fully responsible for ensuring that his products meet the specified qualities. In practice however we experience too often that the manufacturer does not bear sufficiently the responsibility for the quality of his products. Statistical data collected by "HOLDERBANK" show that only about 60% of the items inspected were without any shortcomings.


6/23/2001 - 5:14:56 PM

Page 258

"Holderbank" - Cement Course 2000 Out of 40% rejected due to non-conformances, 2% could not be repaired and had to be discarded and re-fabricated (see Annex 3). If not detected during inspection, many of these cases would have later caused substantial loss of production due to downtime of the installation. Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 7. STEPS OF QUALITY ASSURANCE

7.

STEPS OF QUALITY ASSURANCE

In order to avoid the above-mentioned shortcomings and non-conform behavior of manufacturers/suppliers it is recommended to engage an independent quality inspection company. This should, whenever possible, take place before g the purchasing contract, specially when working with a new supplier. The consultant can help to define and the expected quality level of the products as well as the inspection methods / procedures to be applied. The various steps of the proposed proceedings are shown in Annex 4.1 and 4.2. If the inspection company is contracted late, the purchaser will not get the full profit of their experience. Also the work for the company becomes much more difficult, since the manufacturer will not accept any directions from them towards better quality. Especially if it would cause additional work for fabrication or testing and if such activities will add cost (reduce his margin). In the worst cases experienced, at the time of involvement of the inspection company, fabrication had progressed so far that only a final inspection was possible. If there are any mayor deficiencies detected then, they can not be corrected anymore or only with a substantial loss of time and money. Both endanger the delivery and installation schedule of the item. Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 8. QUALITY INSPECTION PROGRAM

8.

QUALITY INSPECTION PROGRAM

Not all components and machines are in the same way critical for failures or for the time when failures occur. HMC established a list of the most important items regarding ♦ Highest stress ♦ Influence on the operation reliability ♦ History of similar items ♦ Long delivery ♦ High cost items The list is presented in Annex 1. For each component mentioned its priority for inspection is also indicated (1= high priority). Depending on its type of material, way of fabrication and complexity every component has an individual inspection program. While some are only checked once at the end of fabrication, others are checked two or three times at different stages. In Annex 5 a typical inspection program with three inspections is shown: ♦ After casting and pre-machining (before any welding repairs are carried out) ♦ After construction/repair welding and heat treatment © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:56 PM

Page 259

"Holderbank" - Cement Course 2000 ♦ Final inspection after completion Certain tests are performed on a random basis others are full-scale tests. The extent of the non-destructive test amounts generally to 100%, but can be reduced according to requirements. Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 9. HMC AS AN INSPECTION COMPANY – BENEFITS

9.

HMC AS AN INSPECTION COMPANY – BENEFITS

HMC of the inspection team can look back on a 20 years experience in machine techniques, maintenance and trouble shooting. Operational problems are therefore not new for them. HMC is now on the way of establishing their own inspection specifications for the key components. These can then be used as a "bar" for new suppliers specifications or directly for placing an order. Whether HMC sends their own or assigned inspector, all of them are highly trained and experienced inspectors. Training and knowledge exchange is a permanent issue also in the field of quality control. Once a customer entrusts HMC with the quality assurance and inspection of their purchases, an independent party will watch his interests as if they were their own. Some specific benefits are: ♦

The risk of unexpected sudden and premature failure is generally largely reduced. Such a failure could incur a downtime for carrying out of a (temporary) repair up to 3 weeks, resulting in a great loss of production with corresponding high monetary loss.

♦

If the quality inspection reveals shortcomings or deficiencies, action can be taken in time to avoid or shorten a delay in the delivery schedule of the item.

♦

Information that is not included in the documentation from the supplier will also be provided to the purchaser.

♦

An item unacceptable from a quality point of view will be disclosed to the client, the supplier will have to provide a replacement of acceptable quality.

♦

Due to the long time we have been in this business, we know most of the respective suppliers and their products very well; all the particularities and specialties, but, most of all, also their weak points. This allows for more effective inspections.

♦

Due to the well-structured documentation and the valuable hints given, lower maintenance cost can be expected and the lifetime of the parts may be increased.

Based on their knowledge, our inspectors can decide on the spot about the impact of any such problem. Furthermore, they have the full back-up of our department. Additionally, we are always able to call in specialists within our organization for process matters. This makes the inspections very efficient and effective, i.e. less time (and money ) is needed. All this will help that erection, commissioning and operation will be more efficient and economic. Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 10. CONCLUDING REMARKS

10.

CONCLUDING REMARKS

Quality inspections are not only a matter of costs but also an investment for the lifetime of new products and will be paid back by lower operation costs (reliability, lifetime). Besides the assurance of greater reliability in operation they also provide valuable information on the product. Therefore © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:56 PM

Page 260

"Holderbank" - Cement Course 2000 purchasers should look at it in the same manner as at an investment for a new line or an upgrade of a plant. However, no quality can completely exclude all risks. The quality requirements have to be determined together with the supplier and set down in the acceptance specification before g the contract. They should actually form an integral part of the purchase contract or order. In the long run the collaboration between the customer (plant) and the manufacturer/supplier has to become closer, so that only good quality items are delivered, even if there is no third party carrying out additional inspections. Unfortunately we are still far away from that point. Process Technology / B06 - PT III / C03 - Maintenance / Quality Inspections for Cement Plant Equipment / 11. ANNEXES

11.

ANNEXES Annex 1 No. of Inspections

Inspection Priority

Kiln Roller

2

1

Kiln Roller Axle

1

1

Recommended item to be inspected Kiln

Thrust Roller

1

2

2-3

1

Tyre Shell Section

1

1

Shell Section (10 pieces)

1

2

Planetary Carrier

1

2

Mill End

2-3

1

Mill Flange

1-2

1

2

1

Tyre

Tube Mill

Mill Body Mill Shell Section

1

1

2-3

1

Tube Mill Tyre (Bandage)

2

1

Slide Shoe

1

2

Grinding Table

2

1

Roller Yoke (Polysius)

2

1

Roller Carrier (FLS, Pfeiffer, etc.)

1

1

Rocker Arm (Loesche, Onoda)

1

2

Fork (Loesche, Onoda)

1

2

Mill Shell with Tyre

Vertical Mill

Roller Body [if GGG]

1-2

2

Roller Shaft

1

2

Table Liner (Segment)

1

2

Roller Wear Segment/Tyre

1

2

Roller Body (Studded/ Welded Design)

1

1

Roller Segments

2

1

Roller Shaft

1

1

Bearing Block

1

2

Roller Press Frame

1

2

Roller press


6/23/2001 - 5:14:56 PM

Page 261

"Holderbank" Roller Press Frame - Cement Course 2000

1

2

Girth Gear (Cast)

3

1

Girth Gear (Welded)

2

1

Pinion

1

1

Pinion Shaft

1

1

Mill Gear Drive

2

1

Mill Gear Planetary Carrier

1

1

Kiln Gear Drive (Mechanic Standard)

1

2

Kiln Gear Drive (Mechanic Direct)

1

2

Kiln Gear Drive (Hydrostatic)

1

2

Roller Press Drive

1

1

Hammer Crusher Shaft

1

1

Main Process Fan

1

2

Reclaimer Chain

1

2

Drives

Various

Annex 2

Documents and Arrangements necessary for Quality Inspections The following documents are to be provided to "Holderbank" at least one month before inspections: ♦ Fabrication program ♦ Inspection program of supplier ♦ Manufacturer for each item to be inspected (company address, telex, fax, telephone-No., responsible person for quality inspection, place of fabrication) ♦ Acceptance specifications for each item to be inspected (acceptance criteria, state of item when inspections take place, scope, etc.) ♦ Applied standards for non-destructive testing and other inspections ♦ Drawings (fabrication and assembly if available) ♦ Guarantee clauses of contract for items to be inspected Documents and certificates to be provided to "Holderbank" during inspections or latest at the final inspection (two sets): ♦ Non-destructive testing ♦ Surface quality ♦ Hardness test ♦ Materials (chemical composition, mechanical properties) ♦ Record of dimensions ♦ Heat treatment (indicating temperatures, heating, holding and cooling time) ♦ Welding (indicating properties of electrodes, preheating and post heating procedures, type of welding, welder legitimation) © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:57 PM

Page 262

"Holderbank" - Cement Course 2000 ♦ Map of defects of repair welds (indicating place and size of defects/repair welds) All the above mentioned documents have to be delivered in the language specified in the contract. This also applies to documents from sub-suppliers. Arrangements of Inspection The HMC's inspectors and additional inspectors from the client must be given access to manufacture at any time (time to be co-ordinated in advance). The HMC's inspector must be given due notice (at least 5 working days in advance) of the individual inspection stages by the supplier. Provision should be made by the supplier to allow the examination of several items at the same time (if possible) to minimize traveling expenses. All inspections will be carried out together with the supplier whereby all tests and measurements are to be performed by the manufacturers' personal using their own instruments and equipment. In case of suspect results of inspections the HMC inspector has the right to demand additional suitable inspections.

Annex 3

Annex 4.1 Quality Control of New Equipment


6/23/2001 - 5:14:57 PM

Page 263


Annex 4.2 Quality Control of Individual Spare Parts

Annex 5 GIRTH GEAR (CAST) INSPECTION PROGRAM For the quality assessment of a cast girth gear three inspections are to be carried out at different stages of the manufacturing. First Inspection After casting and pre-machining (before any welding repairs are carried out) ♦ Visual inspection ♦ Ultrasonic test of the internal material homogeneity (100%) ♦ Magnetic particle test of the surface in general and the areas of casting defects (100%) ♦ Dimensions ♦ Review of repair welding and heat treatment procedure Second Inspection After repair welding and heat treatment ♦ Visual inspection © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:58 PM

Page 264

"Holderbank" - Cement Course 2000 ♦ Magnetic particle test of repaired areas ♦ Ultrasonic test of the repaired areas ♦ Witness of material strength test (tensile and yield strength, elongation and reduction of area, impact work) ♦ Hardness test across repair welds and at gear rim ♦ Dimensions The second inspection can be dispensed if only minor repair welding is necessary. In this case the material strength test would be carried out either during the first or the last inspection. Third Inspection Final inspection after completion. The two gear halves must be assembled. ♦ Visual inspection ♦ Magnetic particle test of tooth (100%) and remaining areas ♦ Hardness test of tooth flanks ♦ Surface roughness test of teeth ♦ Tooth rectilinearity (if straight teeth) ♦ Tooth of pinion with girth gear (if possible) ♦ Dimensions in general and of toothing in particular ♦ Review of documents and certificates

The extent of the Non Destructive Tests amounts generally to 100%. It can be reduced on the HMC inspector's decision.


6/23/2001 - 5:14:58 PM

Page 265

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C04 - Gas Analysing Systems

C04 - Gas Analysing Systems


6/23/2001 - 5:14:58 PM

Page 266

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS

PRACTICAL GAS ANALYSIS IN CEMENT WORKS H. Nyffenegger PT 98/14340/E (substitute for 93/4080/D) 1. INTRODUCTION 2. PURPOSE 3. DEFINITIONS 4. MEASURING METHODS 4.1 In-situ measurement 4.2 Extractive measurement 4.3 Measuring points 5. GAS SAMPLING 5.1 Kiln inlet (measuring point A) 5.1.1

Preheater kilns (cyclone preheater and grate preheater kilns)

5.1.2

Wet kilns and long dry kilns

5.1.3

Special instructions for gas sampling at the kiln inlet

5.2 Other measuring points (B to G) 5.2.1

Kiln inlet chamber and riser duct (measuring point B)

5.2.2

Lower cyclone stages (measuring point C)

5.2.3

Upper cyclone stages (measuring point D)

5.2.4

Downstream of cyclone or grate preheaters (measuring point E)

5.2.5

Downstream of electrostatic filter (measuring points F, G)

5.2.6

Coal pulverising mill

6. GAS SAMPLING PROBES 6.1 Sampling probes in the temperature range 900 to 1500°C 6.1.1

Siemens type FLK

6.1.2

Harman & Braun type 60S (formerly type 13)

6.1.3

Hartmann & Braun type H (“Holderbank” probe)

6.2 Sampling probes in the temperature range 500 to 900°C 6.3 Sampling probes in the temperature range below 500°C 7. SAMPLE GAS PREPARATION


6/23/2001 - 5:14:58 PM

Page 267

"Holderbank" - Cement Course 2000 7.1 Sample gas pipe 7.2 Sample gas coolers 7.2.1

Specifications of a suitable sample gas cooler

7.3 Sample gas pump 7.4 Flow control and distribution 7.4.1

Simple gas control

7.4.2

Electronic gas volume control

7.5 Sample gas filters 7.5.1

Coarse filters

7.5.2

Fine filters

7.5.3

Valves

7.5.4

Pressure control valve

7.6 Adjustment 7.7 Further information on sample gas preparation 7.7.1

Sample gas discharge

7.7.2

Tightness test

7.7.3

Filter condition monitoring

7.7.4

Analyser room

7.8 Space requirement 7.9 Location 7.10

Climatic conditions

8. ANALYSERS 8.1 Infrared absorption 8.1.1

Space case, sulphur dioxide (SO2)

8.2 Ultra-violet absorption 8.3 Paramagnetism 8.3.1

Oxygen analysers

8.4 Flame ionisation (FID) 8.5 Solid-state electrolytic systems 8.5.1

Zirconium dioxide

8.5.2

Other electrochemical measuring methods

8.6 Multi-component measuring systems 8.6.1

Sick GM 31


6/23/2001 - 5:14:59 PM

Page 268


OPSIS AR 620; ER 650

8.6.3

LDS 3000 diode laser of AltOptronic (Sweden)

8.6.4

Advance Cemas FTRI of Hartmann & Braun

9. RECORDING AND EVALUATION 9.1 Trend curves, recorders 9.2 Averaging computers 9.3 Data logging 9.4 Emission computers 10. MAINTENANCE AND QUALITY ASSURANCE 10.1

Visual checks

10.2

Adjustment checks, cleaning

10.2.1 Tightness checks 10.3

Replacement of wearing parts

10.3.1 Sample gas pump 10.3.2 Cleaning sintered metal and ceramic filters 10.3.3 Fine filters 10.3.4 Gas analysers 10.4

Function test

10.5

Test gases

10.5.1 Mixing test gases 10.6

Fault signals

10.7

Automated maintenance equipment

11. MEASURING ERRORS 11.1

Sample gas sampling

11.2

Sample gas preparation

11.2.1 Sorption and chemical reaction 11.2.2 CO reduction 11.2.3 NO2 formation in the probe and sample gas preparation system 11.2.4 SO2 reduction in the probe and sample gas pipe 11.2.5 SO2 reduction of the filter dust of the sampling probe 11.2.6 Interaction with a liquid 11.3

Volumetric errors due to the solubility of accompanying components

11.4

Gas analysers


6/23/2001 - 5:14:59 PM

Page 269

"Holderbank" - Cement Course 2000 12. SPECIAL FUNCTIONS OF GAS ANALYSIS 12.1

CO monitoring for protection of electrostatic filter

12.1.1 Basic concept of filter shutdown 12.1.2 Optimisation of CO measurement 12.1.3 Specifications 12.1.4 Shutdown procedure 12.1.5 Special devices 12.1.6 Laser analysers 12.2

Monitoring of coal pulverising mills

12.2.1 Limiting values 13. CONVERSION FACTORS 14. LITERATURE


6/23/2001 - 5:14:59 PM

Page 270

"Holderbank" - Cement Course 2000 SUMMARY The measurement of individual process gas components in connection with emissions and for the purpose of process optimisation is increasingly becoming one of the most important procedures in cement works. Measuring techniques have advanced to the extent that there is now virtually no such thing as a problem that cannot be solved technically with the necessary specialised knowledge and means. In principle, distinction is to be made between analysers that measure (in-situ) directly in the measuring channel (process gas flow) and extractive measuring instruments. Extractive measuring instruments measure in a partial gas flow that is prepared prior to entering the analysers according to specifications (sampling). Extractive measuring instruments are mainly used in process measurement, as the conditions with respect to temperature and dust loading does not permit the use of the in-situ technique. The point at which measurements are carried out is mainly a question of the measuring problem involved. The extent of sampling increases with increasing process temperature at the sampling point. For gas sampling at the kiln inlet and up to gas temperatures in excess of 500°C, cooling and an emergency cooling or withdrawal system is required. Withdrawal devices with compressed-air drives are more reliable for emergency use, so that preference is given to electric drives. The separation of dust from the sample gas preferably takes place as close as possible to the entrance of the sampling probe. Sintered metal filters (alloyed steel) clog less quickly than the usual ceramic filters. Compared to the filters outside the sampling probe, internal filters require less maintenance and are smaller in volume. Wet sampling probes are considered out-dated. Three systems for gas sampling at the kiln inlet are described here in brief: Siemens type FLK, Hartmann & Braun type 60 and type H (Holderbank probe). The latter has proved highly reliable in use worldwide. For gas sampling below 500°C, in addition to standard products, proposals are submitted for the specific construction of sampling probes. The purpose of sample gas preparation is to supply the analysers with qualitatively and quantitatively specified sample gas. The apparatus used for this purpose must be generously dimensioned and equipped. This requirement applies in particular to the sample gas pump, sample gas cooler and sample gas distribution. The temperature in the measuring cabinet should be between 15° and 25°C. A monitoring system must inform the control system of any irregularities such as “insufficient sample gas”, “system being adjusted”, etc. The analyser room must provide the ambient conditions for the perfect functioning of the instruments, i.e. free from vibrations, as close to the sampling point as possible, free from dust and between 15° and 25°C. As it also serves as a workroom for maintenance personnel, it must offer sufficient space, good ventilation and a low noise level as possible. The analysers used for the determination of individual components in the sample gas are based on different physical effects such as light absorption. Paramagnetism, flame ionisation and solid-state electrolysis. The instrument functions and theoretical relationships will be dealt with only insofar as they are of significance for practical application. When choosing analysers, the manufacturing company is not as important as the specifications and local services offered. The majority of gas components (CO, NO, SO2, CO2) can be measured with NDIR (non-dispersive infrared analysers). They are simple, sturdy, robust, durable and maintenance-friendly. Disturbing cross-sensitivities to CO2 and water vapour are appropriately corrected. When measuring SO2 with NDIR analysers by the classic method, undefinable quantities of SO2 are absorbed in the sample gas cooler. Corrections are possible by acidifying the condensate in the © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:14:59 PM

Page 271

"Holderbank" - Cement Course 2000 sample gas cooler or using hot NDIR analysers. Preference is given to the use of in-situ analysers. Oxygen cannot be measured with light-sensitive analysers. The most reliable analysers are still considered to be those that exploit the magnetic properties of oxygen. The life of solid-state electrolytic systems such as zirconium dioxide probes is limited and depends on the gas composition. Improved electrochemical measuring cells have been more widely for the past few years and have a useful life of three years. They are small, lightweight, require a minimum degree of evaluation and are therefore used more and more in extractive multi-component analysers. The flame ionisation detector is used for measurement of the total hydrocarbons (VOC = Volatile Organic Compounds). The increasing requirements for continuous measurement of the VOC - in connection with alternative fuels - are maintenance-intensive. Microprocessor technology makes it possible to use well-known and new measuring methods and therefore to measure several components simultaneously. For the installation or replacement of measuring instruments, only the use of multi-component analysers is possible. The GM 31 in-situ analyser of Messrs Sick enables three gas components to be measured simultaneously. Compared with the earlier GM 21 (SO2 and dust) and GM 30 (additionally NO) series, the GM 31 does not offer dust measurement. The AR 620 and AR 650 series of Opsis are modern emission measuring instruments. Depending on the type and number of components to be measured, infrared or ultra-violet light used to the two together. The analyser or analysers are connected to the receiver at the measuring channel via glass-fibre cable (light conductor). Control, monitoring and evaluation is carried out by a standard PC. The analysers have been used several times with good experience. The new gas analysers with lasers are expected to have a promising future. These are in-situ analysers that offer the benefits of high sensitivity, short response times and high stability. They could provide the ideal preconditions for CO monitoring, but are (still) relatively expensive. Of the extractive measuring instruments, good experiences have been made with the CEMAS FTIR analyser of Hartmann and Braun. The analyser can be programmed with all IR selectable components. In order not to alter the originality of the sample gas, all gas conducting parts are heated. Recording the measured values with strip chart recorders should still suffice for a general overview. However, in the majority of countries, digital evaluation of emissions is required according to specific criteria. In the field of process optimisation, the measured values are also only useful when available in the required form, e.g. as mean values, spreadsheet for further evaluation, etc. At the kiln inlet, averaging or damping for lump fuel (tyres) feeding in precalcining is absolutely necessary. In modern plants, the measured values can be partly or wholly processed by the process control system. The reliable functioning of each measuring instrument depends largely on the maintenance provided. Visual checks and function tests must be carried out according to the age of the measuring instruments and the specifications of the supplier. Personnel must be suitably trained. Critical spare parts such as the sample gas pump, filters valves, seals, etc., must be carried in stock. The gas analysers must be checked according to the manufacturer’s instructions and emission measurements carried out in compliance with the local requirements and corrections made as necessary. If test gas should (still) be required, this must be obtained in good time. Any fault signalling devices must be checked for proper functioning. Theoretically, maintenance can be reduced by appropriate automation. Adjustment via internal analyser reference devices has proved highly disadvantageous in this respect. However, if solenoid © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:00 PM

Page 272

"Holderbank" - Cement Course 2000 valves should be required for the application of test gas, their usefulness is negligible or negative. Solenoid valves in sample gas are highly susceptible to faults. For this reason, sample gas changeover from two or more measuring points to the same analyser group is not considered worthwhile. The accuracy of gas analysis as a whole is often overestimated, whereby the analysers are least to blame in this respect. Significant errors occur when sampling (representative) due to sorptions and reactions in sample gas preparation. Gas analysis also has special monitoring functions for protection against explosions in the electrostatic filter and coal pulverising mills. Simple monitoring of the CO content is usually not sufficient for the protection of the electrostatic filter. The consequences are unnecessary shutdowns of the filter. In addition, reference is made to a new analyser of Messrs Sick, which has been designed specially for this task. Finally, a table is provided showing the various conversion factors from ppm to mg/m3 for the relevant gas components. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 1. INTRODUCTION

1.

INTRODUCTION

Gas analysis is among the most important, but also the most sophisticated methods of measurement in cement works. This is due to the constantly growing demands in the field of gaseous emissions and related requirements. Gas analysis fulfils an equally important function in the field of automation, where the reliable and exact measurement of certain gas components plays an essential role. Advances in the field of gas analysis have taken place parallel to the trend of demands, so that one can hardly speak of “technically unsolvable problems” any longer. If problems should nevertheless occur, they are mainly due to the following ♦ Incorrect choice of equipment ♦ Lack of specialised knowledge ♦ Underestimation of expenditure involved (investment and/or maintenance expenditure) ♦ The aim of this report is to prevent problems of this kind occurring when renewing and adding gas analysing apparatus. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 2. PURPOSE

2.

PURPOSE

The continuous measurement of the constituents of certain components in the gas flows (gas analysis) in cement works consists of three areas of activity: a) Emission measurements (pollutants, e.g. NO, SO2, CO, etc.). b) Safety measuring systems (e.g. CO monitoring in filtering plants, monitoring of coal dust silos, etc.). c) Process measuring systems (e.g. O2, CO, NO) for optimisation of the combustion process. Important for all these activities is a high availability of the measuring equipment and sufficient accuracy of the measured values. The report therefore attaches particular importance to sample gas sampling and preparation, maintenance and quality assurance as well as possible measuring errors. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:00 PM

Page 273

"Holderbank" - Cement Course 2000 Finally, hints and practical advice are given, based on many years of experience. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 3. DEFINITIONS

3.

DEFINITIONS

Indication delay (90% time) of an analyser or a measuring instrument: The time that elapses from a sudden change in the gas concentration at the entrance of the analyser or probe up to indication of 90% of this change. Downtime: The time during which faulty conditions of the measuring instrument and their correction unforeseeably make the generation of measuring or adjusting signals impossible. Accompanying gas: Sample gas without the gas components to be measured. Extractive sampling: The sample gas is extracted as a partial gas flow from the process gas prior to analysis and conditioned. Gradient monitoring: Monitoring the gas concentration change gradient (e.g. control of CO cut-off). In-situ: The measuring instrument is located in or on the process gas duct; analysis is carried out in the process gas (e.g. optical dust content measuring instrument or zirconium oxygen probe). Adjustment: Setting or adjustment of the gas analyser with test or zero gas with the aim of adjusting the indication of the gas analyser as close as possible to the gas concentration to be measured in the sample gas. With newer analysers, this can also take place with built-in gas-filled glass cuvettes. Calibration: For a given measuring instrument, determination of a valid relationship between the indicated measured value or the value of the output signal and a reference value that comes closest to the true measured quantity. Determination of the scale divisions of a measuring instrument with the aid of a reference measuring method (generally required only for officially specified continuous emission measurements). Life zero: A specific quantity (normally mA) prevails in the electric output signal when the analyser physically measures “zero”. The advantage of this system is that the output signal is electrically set to “zero” only if the electrical measuring circuit fails. Sample gas: That part of the process gas extracted from the process gas and ed to the analyser for measurement. Sample gas preparation: The entire equipment used for the qualitative and quantitative preparation of the sample gas to ensure that the same conforms to the specifications of the analysers. Measuring equipment: All devices and instruments required for the measurement of gas component concentrations. Measured quantity: Physical quantity, the numerical value of which is to be determined by measurement. Measured component: The gas component in sample gas, the concentration of which is to be measured. Zero gas: Test gas used for the adjustment or readjustment of the zero of a gas analyser. On-Line: The measured quantity is coupled directly with the process. Test gas: Gas with a known composition for adjustment or readjustment of gas analysers. It consists © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:00 PM

Page 274

"Holderbank" - Cement Course 2000 of the measured component and one or several accompanying gases (e.g. nitrogen/ carbonic acid + measuring component). Cross-sensitivity: Influence of the concentration of a disturbing component on the measuring result of another gas component under identical measuring conditions. Representativity: The correspondence of the measured signal with the definition of the measured quantity, e.g. the composition of the gas at the kiln inlet measured at a point in relation to the average gas composition over the entire cross-section. Disturbing component: Component in the sample gas that falsifies the measured value, e.g. if the gas analyser has a cross-sensitivity or chemical reactions distort measurements. Dead time of an analyser or measuring instrument: The time that elapses from a sudden change in the gas concentration at the entrance of the analyser or probe up to the start of the indication of this change. Availability: The time during which the measuring instrument generates usable signals. Supply pressure: The sample gas pressure necessary for supplying the analysers. VOC Volatile Organic Compounds: Volatile organic hydrocarbons. Maintenance time: Time required for maintenance of the measuring instrument (planned preventative maintenance). Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 4. MEASURING METHODS

4.

MEASURING METHODS

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 4. MEASURING METHODS / 4.1 In-situ measurement

4.1

In-situ measurement

In-situ measuring methods mainly offer the following advantages: ♦ No gas sampling ♦ Sampling forms a path in the measuring channel (as opposed to a point in extractive methods) ♦ Undelayed indication ♦ Less maintenance ♦ Good long-term stability In-situ measuring methods are used increasingly in modern measuring techniques. Two different measuring principles are in the foreground: ♦ Solid-state electrolytic and ♦ Optical systems Stabilised zirconium dioxide is a typical solid-state electrolyte with whose properties oxygen can be measured directly in the process (similar to thermocouples) (see chapter 8.5.1). This measuring method has proved reliable in the cement industry. In individual cases, the useful life of the zirconium sensors was unsatisfactory, as their activity was destroyed by certain accompanying gases. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:00 PM

Page 275

"Holderbank" - Cement Course 2000 Optical instruments are flanged directly on to the gas channel to be measured (e.g. chimney). These consist of a transmitter (normally light) and a receiver or reflector arranged opposite. While ing through the channel, the light beam emitted from the transmitter (infrared, ultraviolet or laser) is changed by certain gas components. After appropriate processing, this change results in the measured quantity (see chapter 8.6). Optical measuring instruments (8.6.1, 8.6.2, 8.6.3) are used mainly for the measurement of pollutant emissions, e.g. dust content, SO2, NO, etc. The range of instruments available for measuring further gas components is increasing in line with technological advances. The application of optical measuring in-situ instruments is restricted by two factors; the dust content and the given length of the measuring path, which is in direct relation to the sensitivity. For use in the cement works, these restrictions mean that they only function in pure gas and their application is limited solely to the measurement of emissions, although good experience has been made in this respect. Thanks to improved representativity, in-situ measuring methods are technically superior to extractive methods. Investments in-situ instruments are generally higher compared with extractive measuring instruments. As will be shown later, additional investments in in-situ measuring methods are justified under certain conditions. The level of maintenance is normally less, but partly more sophisticated than extractive measuring instruments, from a technical point of view. The measured values of in-situ instruments are always based on gas in an operational condition. However, values in a standard condition are usually required, .i.e. at 0°C, 1013mbar, dry. For conversion to the standard condition, the parameters pressure, temperature and moisture must be known or additionally measured. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 4. MEASURING METHODS / 4.2 Extractive measurement

4.2

Extractive measurement

The measuring procedure is subdivided into different stages: ♦ Sample gas sampling ♦ Sample gas supply ♦ Sample gas preparation ♦ Analysers With the exception of the dust content, the majority of components can be measured by the extractive method. In-situ measuring instruments offer the following advantages: ♦ Several analysers can be connected to the same sample gas preparation apparatus. ♦ The positioning of dust and heat-sensitive analysers is more flexible. ♦ Adjustment and calibration is simpler (with built-in reference cuvettes or test gas). Drying the gases during gas preparation by means of cooling to a dew point of about 3°C can be disturbing for certain components. These are logically water vapour (H2O) sulphur dioxide (SO2) and certain hydrocarbon compounds (VOC) (see chapter 8.4). To exclude disturbing influences during sample gas drying, there are instruments with operating temperatures that are far above the dew point (up to 250°C). The components of these instruments are subject to increased load when exposed to these temperatures, which inevitably leads to an increased susceptibility to faults. Experiences made with an instrument of this type are described in chapter 8.6.4. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:00 PM

Page 276

"Holderbank" - Cement Course 2000 The multiple advantages of extractive measuring instruments, compared with in-situ measuring methods, are confronted with a slightly higher level of maintenance, although the maintenance necessary for the extractive measuring method is less demanding than that required for in-situ measuring instruments. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 4. MEASURING METHODS / 4.3 Measuring points

4.3

Measuring points

Figures 1 to 3 show the typical measuring points at various kiln systems (cyclone preheaters, grate preheaters and wet kilns). The associated tables show the usually measured components as well as the purpose of their measurement. The choice of measuring point at the kiln system at which measurements are to be made, depends primarily on the purpose of measurement. Figure 1:

Measuring Points at Cyclone Preheater Kilns

Figure 2:

Measuring points at the grate preheater kilns

Figure 3:

Measuring points at wet kilns and long dry kilns


6/23/2001 - 5:15:01 PM

Page 277


Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING

5.

GAS SAMPLING

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.1 Kiln inlet (measuring point A)

5.1

Kiln inlet (measuring point A)

At the rotary kiln itself, only the measuring point at the feed end of the kiln is realisable with reasonable effort. The components normally measured there are needed as reference quantities for an optimal combustion process (usually O2, CO, NO). To prevent distortion of the measured signals due to false air from the kiln inlet seal, the probe tip must be located distinctly within the rotating part. The sampling conditions at the kiln inlet vary considerably, depending on the type of kiln (preheater kilns, long dry kilns and wet kilns). Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.1 Kiln inlet (measuring point A) / 5.1.1 Preheater kilns (cyclone preheater and grate preheater kilns)

5.1.1

Preheater kilns (cyclone preheater and grate preheater kilns)

Process conditions at the sampling point Gas temperature

1000 to 1300°C

Dust content

>100g/m3 (cyclone preheater)

Dust content

>5/g/m3 (grate preheater)

Dew point temperature

35 to 40°C

The process gas contains large proportions of alkalis, chlorides and sulphates that are subject to high local and time variations. Depending on the process and raw material situation, the alkali compounds combine with the dust to form strongly adherent deposits. To counteract their effects to make gas © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:01 PM

Page 278

"Holderbank" - Cement Course 2000 sampling possible at all, elaborate measures are necessary from a measuring point of view. Owing to the high temperatures, the provision of external cooling is necessary for all types of sampling probes in the area of the kiln inlet. Mounting sampling probes The principle mounting arrangement is shown in Figure 4. Owing to the wide range of kiln systems available, it is impossible to define an exact mounting point for all types of kilns in advance. The following criteria play a dominant role: ♦ Available space ♦ Accessibility ♦ Direction of rotation of the kiln ♦ Internals in the kiln inlet chamber According to experience, the gas composition at the kiln inlet is not homogeneous. In consequence, the sample is only representative of the average gas composition to a limited degree, irrespective of where the probe is positioned. The measuring point or sampling point in the rotating part of the kiln, as will be shown later, cannot be determined primarily on the basis of measuring criteria. An individually adapted interpretation of the measured values (averaging), correlation with disturbance variables, etc.) is far more important here than the position of the probe (see chapter 9). The mounting position shown in Figure 4 is for reference only. Positions and dimensions can vary considerably from plant to plant. The undisturbed, reliable function of the probe and the warranty that no false air will be drawn in from the kiln inlet seal always has the highest priority. The probe must be easily accessible. If necessary, special platforms must be erected. A lifting device placed above the probe will considerably facilitate maintenance. The minimum distance between the platform railing and probe axis should be about 1.3m (at least on one side). As the probe consists of relatively long sections, the access way must not be too narrow. The mounting position should be accessible via steps not ladders. Pokeholes, which must be operated regularly, are located in the immediate vicinity of the probe. It must be ensured that the sampling probe does not interfere with the working space provided for maintenance personnel. In principle, the probe must be mounted on the side where the direction of rotation of the kiln shell is directed downwards. If conditions do not permit, the other side can also be selected, provided the probe can be positioned at a sufficient distance to the material bed. Meal inlet pipes, pokeholes, measuring connections, etc., mostly restrict free selection of the mounting position, the main aim is to minimise hindrance of maintenance personnel. The inevitably cooled probe surfaces encourage the formation of deposits in the kiln inlet chamber. These deposits not only hinder subsequent removal of a probe, they can negatively influence the geometry of the kiln inlet chamber and also cause pressure loss. To prevent this happening, it is recommended to regularly blow-out the gap between the pipe and probe by means of a mounted air cannon. The pipe must be dimensioned, so that a gap of about 25mm is produced between the probe and inner pipe wall. Figure 4:

Mounting of the gas sampling probe at kiln inlet


6/23/2001 - 5:15:01 PM

Page 279


Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.1 Kiln inlet (measuring point A) / 5.1.2 Wet kilns and long dry kilns

5.1.2

Wet kilns and long dry kilns

Process conditions at the sampling point: Temperature wet kilns

150 to 200°C

Temperature long dry kilns

250 to 500°C

Dust content wet kilns

about 40g/Nm3

Dust content long dry kilns

about 300g/Nm3


60 to 70°C

Dew point temperature long dry kilns

35 to 40°C

Under these conditions, gas sampling is much simpler than for kilns with preheaters. No cooling of the probe is necessary and the measured signal has improved representativity, as better intermixture of the gases takes place due to the internals (chains, crosses). With regard to positioning, mounting conditions, etc. roughly the same conditions apply as for kilns with preheaters. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.1 Kiln inlet (measuring point A) / 5.1.3 Special instructions for gas sampling at the kiln inlet

5.1.3

Special instructions for gas sampling at the kiln inlet

Cyclone and grate preheater kilns The above process conditions show that gas sampling from this difficult environment requires particular measures: ♦ Owing to the high temperature, the sampling probe must be cooled. ♦ A filter system must ensure that the large amounts of diversely structured dust is removed prior to sample gas preparation ♦ Very often, deposits build up at the sampling system and clog the probe entrance, so that measures must be taken for their prevention. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:02 PM

Page 280

"Holderbank" - Cement Course 2000 Probe cooling Liquid cooling is used for all known probes. The cooling medium, which is usually water, transfers the heat in a closed system to water-air or water-water heat exchanger to prevent calcareous deposits. The energy produced varies considerably. Depending on the condition of the probe surface, a large amount (clean surface) or small amount (dust or deposits on the probe) must be removed. Based on experience, an energy flow of maximum 30kW per probe meter must be removed within the kiln (probe with 10cm outside diameter). In extreme cases, the energy flow varies between 1kW and 30kW per probe meter. According to experience, the risk of deposit formation increases with reducing probe or cooling circuit temperature. As a countermeasure, some probes are operated at higher temperatures. This takes place by controlling the cooling circuit or by internally heating the probe. If a water-air heat exchanger is used, it must be taken into in dimensioning that the maximum cooling capacity is still sufficient even with heavy clogging of the heat exchanger surfaces. It is also recommended to add an anti-freeze to the water in cold regions. In order to better control incrustations and deposit build-up in and on the probes, cooling systems were developed which enable the probes to be operated at higher temperatures. An example is the steam jacket probe. This probe functions as a heat conducting tube, whereby the heat of evaporation of water is used as a heat carrier to the directly flanged-on heat exchanger (condenser). The probe temperature is 120 to 150°C, the internal pressure is 1.5 to 5 bar. The probe only functions properly if it can be mounted almost vertically (less than 30° from the vertical axis). This requirement virtually excludes the mounting method shown in Figure 4 in an almost horizontal position, so that its possible applications are very restricted. If a synthetic heat carrying liquid is used instead of water, the probes can be operated at even higher temperatures (up to 200°C) (see chapter 6.1.1). Safety and maintenance equipment In the event of failure of the cooling system, the probe would be damaged within a few minutes. Countermeasures are essential. For emergency cooling purposes, water supplied from storage tanks can be used and feed directly into the probe circuit if required. Emergency cooling systems of this kind must also function in the event of a total power failure. Pneumatically operated withdrawal devices have proved more reliable than emergency cooling systems (see Figure 5). Since compressed air can be stored without problems, pneumatic operation has the advantage that the probe can be withdrawn from the danger, zone even in the event of a total power failure, within a reasonable time. The automatic insertion and withdrawal device also has further significant advantages: ♦ Regular insertion and withdrawal prevents the formation of deposits on the probe and their build-up. ♦ Maintenance is considerably facilitated. All connections to the probe (hoses, cables, etc.) must be flexible. Dust filtration in the probes With dry filtration, the sample gas is withdrawn from the process by suction in an unpurified condition. Dust separation takes place inside the probe or at its outer end. The produced dust must be removed from the filter from time to time. Whether this takes place manually by replacing the filter element or automatically by blowing back into the sampling space, the sample gas flow is always interrupted. This interruption has a negative effect on the availability of the measuring instrument. To prevent condensation of any kind, the filter must have a minimum operating temperature of 150°C. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:02 PM

Page 281

"Holderbank" - Cement Course 2000 Figure 5:

Probe extraction device

With wet filtration, the sample gas flows through a water curtain at the probe tip. This produces a slurry of water and dust, which together with the sample gas discharges through the wet probe, which in contrast to the dry probe is inclined outwards. The slurry discharges, the gas is dried and ed to the analysers. Wet filtration has the disadvantage that various gas components are also dissolved in water. SO2 is completely washed out and the CO2 concentration reduces to an uncontrollable degree. As a result of this change in the total composition, the relative contents of the other gas components increase, so that the composition of the sample gas is no longer correct. If the injector water circulates in a closed system, the circulated water becomes acidic and behaves virtually inert towards CO2. However, susceptibility to corrosion of all parts coming into with the water must be observed. The level of maintenance necessary with wet filtration is slightly less and above all technically less demanding than with dry filtration. However, in view of the distortion of measured values and the reliable dry systems that are currently available, its application is no longer recommended. Filter cleaning The dust separated in the dry filter must be removed from time to time. The degree of clogging of the filter, including the gas sampling probe, can be determined by means of a vacuum gauge arranged between the filter and sample gas pump. The maximum permissible value for cleaning differs from plant to plant and must be individually determined. Compressed air is normally used for cleaning and removing the dust from the filter. If the filter is arranged at the outer end of the probe, cleaning should take place in two stages. 1) Loosening the dust via the sample gas pipe. 2) Blowing out the dust via a separate compressed-air pipe. The compressed air must be free from oil and water. Oil in the purging air produces incorrect CO in the filter and excessive moisture encourages encrustation of the filter. With regard to gas sampling, the conditions for the wet kiln and long dry kiln are considerably simpler than for preheater kilns. The lower temperatures usually obviate the need of probe cooling. The lower dust load enables the use of simpler filter systems without special cleaning, as used following the heat exchanger in the case of dry kilns (see chapter 6.3). Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.2 Other measuring points (B to G)


6/23/2001 - 5:15:02 PM

Page 282


Other measuring points (B to G)

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.2 Other measuring points (B to G) / 5.2.1 Kiln inlet chamber and riser duct (measuring point B)

5.2.1

Kiln inlet chamber and riser duct (measuring point B)

Process conditions at the sampling point: Gas temperature

820 to 1300°C

Dust content

200 to 1200g/m3 (N.tr.)


35 to 40°C

In the kiln inlet chamber and riser duct, as at the rotary kiln inlet, local and time-related concentration differences can be expected. Above the meal inlet of the lowest cyclone, there is no longer any danger of a deposit build-up through circulated materials. However, the gas composition no longer corresponds at this point with the gas composition in the rotary kiln inlet. It is distorted by the reduction of CO in the riser duct and through dilution with false air and CO2 from deacidification of the burned product. When burning secondary fuel, the measuring point must be arranged below the secondary fuel inlet. With regard to gas sampling, virtually the same conditions apply as at the kiln inlet. This applies similarly to a large extent to sampling from the calcining chambers of grate preheater kilns. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.2 Other measuring points (B to G) / 5.2.2 Lower cyclone stages (measuring point C)

5.2.2

Lower cyclone stages (measuring point C)

From a measurement point of view, gas analysis in this area is virtually pointless, particularly in plants with pre-calcining. However, if measurements are still carried on a frequent basis, these are not for measurement reasons, but the more favourable conditions with regard to sampling (deposit formation and temperature) than further below, e.g. in the rotary kiln inlet. A cooling system is necessary in any event. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.2 Other measuring points (B to G) / 5.2.3 Upper cyclone stages (measuring point D)

5.2.3

Upper cyclone stages (measuring point D)


400 to 550°C

Dust content

200 to 1200g/m3 (N.tr.)


35 to 45°C


6/23/2001 - 5:15:02 PM

Page 283


Protection of the electrostatic filter against explosions due to impermissible CO concentrations, presupposes a rapid reaction of the gas analysis (see chapter 12.1). For this task, gas sampling below the uppermost cyclone stage is preferable, as the residence time of the main gas flow in the uppermost cyclone stage prolongs the reaction time of the monitoring device. Two-section preheater systems should always be provided with two complete measuring instruments (one for each section). The sampling conditions are relatively simple. No cooling is necessary. In order to achieve rapid reaction times, the maximum amount of gas must be drawn in (60 to 300 l/h). However, as the amount of gas increases, so too does the dust content in the sampling system, so that, depending on the particular system, it must be separated by the filter and blown back again. More suitable for this purpose are probes whose filters are located directly in the gas flow (internal filter probes) than those with external filters (see chapter 6.3). Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.2 Other measuring points (B to G) / 5.2.4 Downstream of cyclone or grate preheaters (measuring point E)

5.2.4

Downstream of cyclone or grate preheaters (measuring point E)

Process conditions at the sampling point: Gas temperature for rotary kilns with cyclone preheaters

300 to 400°C

Gas temperature for rotary kilns with grate preheaters

100 to 150°C

Dust content for rotary kilns with cyclone preheaters

20 to 70gm/3 (N.tr.)

Dust content for rotary kilns with grate preheaters

2 to 10g/m3 (N.tr.)

Dew point temperature for rotary kilns with cyclone preheaters

35 to 45°C

Dew point temperature for rotary kilns with grate preheaters 50 to 65°C

At the point, similar conditions prevail for gas sampling as in the riser duct (measuring point D). In the case of grate preheaters, this point approximately corresponds with the conditions downstream of the grate, but less dust loading. To be taken into for CO monitoring in grate preheater kilns is the fact that no cooling tower is usually available to delay the residence time of the gases in a positive sense. For this, the gas quantity can be increased on of the low dust loading. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.2 Other measuring points (B to G) / 5.2.5 Downstream of electrostatic filter (measuring points F, G)

5.2.5

Downstream of electrostatic filter (measuring points F, G)


100 to 150°C

Dust content

>50mg/m3 (N.tr.)


50 to 65°C


6/23/2001 - 5:15:03 PM

Page 284


In the majority of cases, the components relevant for emission are measured. Preference must be given to the point downstream of the fan, as the gas composition is no longer subject to change before the exhaust gas discharges from the stack. Owing to the turbulence of the process gas in the plant sections and fans, it can generally be assumed that the process gas is well intermixed. Owing to the probability of filter shutdowns, gas sampling requires a dust filter as provided at the measuring points in the raw gas flow. The high dew point makes it necessary for the probe to be heated at the critical points. No differences exist with regard to the type of kiln (cyclones, grate preheaters or wet kilns). Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 5. GAS SAMPLING / 5.2 Other measuring points (B to G) / 5.2.6 Coal pulverising mill

5.2.6

Coal pulverising mill

Gas analysis in the area of the coal pulverising mill serves solely for the purpose of quickly detecting smouldering fires and/or potentially explosive gas concentrations. The possible measuring points are shown in Figure 6. Figure 6:

Measuring points at the coal grinding plant

Upstream of coal pulverising mill (measuring point H)


250 to 350°C

Dust content

20 to 70g/m3 (N.tr.)


35 to 45°C

In filter (measuring point I)

Process conditions at the sampling point: © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:03 PM

Page 285

"Holderbank" - Cement Course 2000point: Process conditions at the sampling Gas temperature

90 to 110°C

Dust content

>50mg/m3 (N.tr.)


50 to 70°C

The measuring point in the filter serves especially for monitoring glow nests when the coal pulverising mill is stationary. Owing to the large filter volume, glow nests can only be detected quickly enough with sufficient circulation of the process gas. For this reason, 200-300m3/h process gas should be drawn out by suction via a separate gas pipe and fed back again at the filter inlet when the coal pulverising mill is stationary. The gas sampling probe is then arranged in the gas pipe. When the coal pulverising mill is in operation, the gas pipe is closed via a valve. Downstream of coal pulverising mill fan (measuring point E)


90 to 100°C

Dust content

>50mg/m3 (N.tr.)


50 to 70°C

Coal dust silo (measuring point L)


>60°C

Dust content

1 to 1000g/m3 (N.tr.)


>35°C

The gas sample is preferably positioned in the silo roof.

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 6. GAS SAMPLING PROBES

6.

GAS SAMPLING PROBES

In principle, gas sampling probes can be divided into three categories according to temperature range: •

Sampling probes in the temperature range 900 to 1500°C

•



6/23/2001 - 5:15:03 PM

Page 286

"Holderbank" - Cement Course 2000 •

Sampling probes in the temperature range up to 500°C

The following assessment of various gas sampling probes is based on the manufacturer’s documents as well as our own experience and information from the works, if available. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 6. GAS SAMPLING PROBES / 6.1 Sampling probes in the temperature range 900 to 1500°C

6.1


This category includes gas sampling at the inlet of preheater kilns with and without pre-calcining. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 6. GAS SAMPLING PROBES / 6.1 Sampling probes in the temperature range 900 to 1500°C / 6.1.1 Siemens type FLK

6.1.1

Siemens type FLK

Brief description Compact gas sampling system with special cooling fluid permitting probe operating temperatures up to 230°C. The condensation of alkali vapours and in turn the danger of incrustations is drastically reduced. The suction opening is arranged on the side of the probe tube and should be located in the flow slipstream. This arrangement offers selective dust separation. An electrically or pneumatically operated insertion / withdrawal device is an integral part of the probe. Design:

Extremely compact and professional design. Oval stainless steel sampling tube.

Suction opening:

Lateral, about 30mm in diameter

Mounting tube:

325mm diameter (relatively large)

Dust removal filter:

External, heated, blow-back with compressed air, large volume

Maximum probe length:

3200mm

Comment Despite effective measures, stubborn blockages can occur, particularly when kiln operation is loaded by high alkali circuits. Owing to the lateral arrangement of the suction opening, the gases within the probe tube flow through an elbow. The removal of incrusted deposits from this elbow is far more difficult due to poor access than if the gases were drawn out by suction at the end of the stem and through a straight tube. In view of the turbulent flow conditions at the sampling point, it is doubtful whether lateral suction results in selective dust separation. The large overall volume of the dust filter permits a relatively large gas throughput. The resulting delay and damping of the indication is of little significance from a measurement point of view. Available for the drive of the withdrawal device is either an electric motor or compressed-air drive. As compressed air can be stored without problems, the compressed-air drive offers more reliability than an electric motor in the event of a power failure. Emergency operation with crank handle is also provided. With difficult kiln operation, alkali condensation can occur and block the entrance of the probe, as already mentioned, despite increased operating temperature. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 6. GAS SAMPLING PROBES / 6.1 Sampling probes in the temperature range 900 to 1500°C / 6.1.2 Harman & Braun type 60S (formerly type © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:04 PM

Page 287

"Holderbank" - Cement Course 2000 13)

6.1.2

Harman & Braun type 60S (formerly type 13)

Brief description Gas sampling probe with closed cooling system (cooling medium water) and temperature control. Integrated emergency cooling system with fresh water. Lateral arrangement of two suction openings (Figure 7). Comment Widely used. Functions well in non-extreme alkali conditions. The same remarks apply here with regard to the lateral arrangement of the suction openings as for the Siemens system. With large amounts of dust, the filter must be blown-out at brief intervals, The resulting loss of signal can have a critical effect on the availability of the measuring signal. The operating temperature is too low to completely prevent alkali condensation. An automatic insertion and withdrawal device is optionally available. Figure 7:

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 6. GAS SAMPLING PROBES / 6.1 Sampling probes in the temperature range 900 to 1500°C / 6.1.3 Hartmann & Braun type H (“Holderbank” probe)

6.1.3

Hartmann & Braun type H (“Holderbank” probe)

Brief description The main features of this probe are the automatically functioning mechanical removal of any incrustations at the probe inlet as well as a new type of filter system (see Figure 8). Cooling takes place in a closed system (cooling medium water) with temperature controller. About 20 probes of this type are in use worldwide and are functioning efficiently. Marketing takes place via Messrs ELSAG BAILEY Hartmann & Braun in Frankfurt under the designation type H.

Design:

Probe body of alloyed steel

Suction opening:

At end of stem, about 40mm in diameter

Probe temperature:

External, 30 to 85°C, internal up to 250°C


6/23/2001 - 5:15:04 PM

Page 288

"Holderbank" - Cement Course 200030 to 85°C, internal up to 250°C Probe temperature: External, Mounting tube:

150mm in diameter

Dust removal filter:

Internal, heated filter of sintered metal, cleaning with compressed air

Maximum probe length:

3000mm

Thanks to its modular concept, the probe can be provided with the same insertion and withdrawal device as type 60. Figure 8:

Comment This sampling system has proved highly reliable in practical use, even under difficult conditions. The availability satisfies the high requirements of “high-level control systems”. The maintenance costs are low thanks to the simple and maintenance-friendly design of the system. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 6. GAS SAMPLING PROBES / 6.2 Sampling probes in the temperature range 500 to 900°C

6.2


With regard to the sampling probes, similar conditions prevail in this temperature as at higher temperatures (e.g. at the kiln inlet of preheater kilns). However, the danger of incrustations is lower. Cooling of the probes is essential down to 500°C, so that in principle, the same sampling probes can be used as in the higher temperature range. Temperatures between 500 and 900°C are typical for cyclone preheater kilns in the area of the lower cyclone stages (measuring point C). As already noted, measurements there are almost pointless, particularly in plants with precalcining. If measurements are still to be carried out despite this, steam jack probes are considered ideal for this purpose when mounted vertically in the cyclone roof. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 6. GAS SAMPLING PROBES / 6.3 Sampling probes in the temperature range below 500°C

6.3

Sampling probes in the temperature range below 500°C

Typical for the application of such probes are the measuring points downstream of the heat exchanger or grate preheater, upstream or downstream of the electrostatic filter as well as at the kiln inlet of wet © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:04 PM

Page 289

"Holderbank" - Cement Course 2000 or long dry kilns. Cooling is unnecessary. With regard to the place of use or purpose of measurement, there are certain differences in the design of the probes (e.g. mounting length). Decisive for the quality of these probes is the dust filtration. The discovery of fine-pore filter tubes of sintered stainless steel brought about great advances. The level of maintenance is low, a block-back device is unnecessary. The sample gas is clean and available for weeks to months without interruption. Probes with such filters are not available from established suppliers. They still use fine ceramic filters that enable a comparatively long useful life. However, it must be ensured that the gas conducting tube is heated at the penetration point (Figure 9). The optimal porosity of sintered metal filters is only 0.5m. As the main proportion of the dust particles is larger, the pores clog at a correspondingly slow rate. According to experience, they have a useful life of four weeks to several months, depending on the properties of the dust. If the pressure drop becomes excessive due to clogging, the filter tubes can be cleaned with acid. With wet kilns and long dry kilns, the probes must be lengthened, depending on the size of the smoke chamber. In order to ensure the necessary mechanical strength, ing tube of a larger diameter must be mounted, into which the probe is inserted. A further important element is the heating in the penetration zone from the measuring channel to the outside. In order to prevent any kind of condensation, the temperature must not fall below 100°C at any point. For all gas conducting parts, stainless steel, e.g. No. 1.4541 or 1.4571 must be used. Figure 9:

Gas sampling probe, up to 500°C

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION

7.

SAMPLE GAS PREPARATION

The purpose of sample gas preparation is to supply the downstream gas analysers with sample gas, so that it conforms qualitatively and quantitatively with the specifications of the analysers. Such an arrangement normally consists of the following elements: •

Supply

> Sample gas pipe

•

Drying

> Sample gas cooler

•

Delivery

> Sample gas pump

•

Dosage

> Controller


6/23/2001 - 5:15:04 PM

Page 290

2000 > Controller •"Holderbank" Dosage- Cement Course •

Distribution

> Pressure control valve

•

Calibrating option

> Manual or automatic

Experience has shown that the availability of a measuring instrument depends essentially on a properly functioning sample gas sampling and preparation. Insufficient sample gas preparation leads to fouling in the gas analysers and not infrequently to expensive damage. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.1 Sample gas pipe

7.1

Sample gas pipe

The probe itself as well as the sample gas pipe between the sampling probe and sample gas cooler should be heated to between 100 and 150°C (for measurements with FID devices up to 200°C). This heating has the following purpose: ♦ To prevent condensation and freezing of the condensate at low temperatures, because: •

Condensation in the sample gas pipe can distort certain measured values.

•

Incrustations and blockage of the sample gas pipe are accelerated by the formation of condensate.

♦ To delay the conversion of NO into NO2 during emission measurement. Heated sample gas pipes are available in various qualities: ♦ Low price pipes with a self-regulating heating band and ♦ Pipes with resistance heating and separate temperature controller For selection purposes, it should be noted that with heating band controlled pipes, the temperature is limited to a maximum of 105°C. This temperature does not normally suffice for process measurements but for emission measurements. The following specifications must be observed: •

Inner tube material:

Teflon

•

Inner tube dimensions:

Outside diameter 6mm Inside diameter 4mm

•

Connection ends:

Clamping ring tube fittings

•

Control:

Thermocouple with controller

•

Protective sleeve:

PVC or metal

Heated pipes are relatively expensive. When planning a measuring system, the sample gas pipes must therefore be as short as possible. The following points must be observed: a) If only O2, CO or NO is measured, heating can be dispensed with if the sample gas pipe (several metres) is short and can be laid with uninterrupted gradient from the sampling point to the ample gas cooler (no siphons). © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:05 PM

Page 291

"Holderbank" - Cement Course 2000 b) Possible installation of the sample gas cooler in the vicinity of the sampling point. For automatic compressed-air cleaning via the sample gas pipe, it must be ensured that this has sufficient pressure resistance. For connections, high-quality stainless steel clamping ring fittings, e.g. Swagelok, Serto or similar, must generally be used. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.2 Sample gas coolers

7.2

Sample gas coolers

Sample gas coolers serve to remove most of the water vapour from the sample gas at temperatures of about 3°C and keep the residual content at a constant value. The latter is important particularly for emission measurement. The temperature indication of the sample gas cooler normally shows the operating temperature of the cooling medium. If the sample gas cooler is subject to excessive load or ambient temperature, the sample gas temperature at the cooler outlet can be considerably higher than the indication. The dew point temperature then no longer corresponds with the cooling medium indication. The sample gas cooler is usually accommodated in a cabinet together with the analysers and the remaining sample gas preparation apparatus. Instead of using long heated sample gas pipes, it may be advantageous to install the sample gas cooler immediately downstream of the sample gas probe in a separate equipment cabinet. Condensate collecting tanks have the disadvantage that indication of the measured values is greatly delayed due to the additional volume. The produced condensate should therefore be pumped out using automatic hose pumps or diaphragm liquid pumps. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.2 Sample gas coolers / 7.2.1 Specifications of a suitable sample gas cooler

7.2.1

Specifications of a suitable sample gas cooler

Dew point at outlet

+5°C (±1°C)

Dew point stability

±0.25°C

Temperature at sample gas inlet

max. 180°C

Dew point at sample gas inlet

max. 80°C

Gas flow

max 100l/h

Ambient temperature

+5 to +45°C

Cooling capacity

860kJ/h, 25°C

Material of gas conducting parts

Teflon, PVDF

Permissible gas pressure

min. 3 bar

Volume

max. 100cm3

Sample gas connections

6mm or 1/4”

Time until ready for measurement

max. 30 minutes


6/23/2001 - 5:15:05 PM

Page 292

"Holderbank" - Cement Course 2000 Also available for the majority of sample gas coolers are moisture monitoring devices at the sample gas outlet. Such devices are urgently recommended. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.3 Sample gas pump

7.3

Sample gas pump

Mainly diaphragm and compressor pumps are used. The sample gas volume necessary for the gas analysers is between 30 and 100l/h. In order to keep indication delays to a minimum, a larger sample gas volume is often extracted from the process gas. The excess sample gas can be diverted via a by shortly upstream of the analyser. If possible, a large part of the measuring instrument should be operated under pressure, as false air can infiltrate during suction phase. Sample gas pumps installed upstream of the sample gas cooler must be heated. This arrangement has the advantage that no false air is sucked in the event of leaks in the sample gas cooler. However, according to experience, heated pumps are more susceptible to faults than cold operated pumps, so that arrangement downstream of the sample gas cooler is still more advantageous. The pump capacity should be generously dimensioned in respect of the suction pressure. The flow rate must be dimensioned, so that the available gas flow about 1.5 to 2 times higher than that required by the analysers according to specifications. Throttling of the flow preferably takes place on the low-pressure side. With throttling on the pressure side, a pressure control valve must ensure that the pressure downstream of the pump does not increase to an unnecessary degree. Significant pressure drops in the sample gas encourages the formation of powdery salts (white powder). The following diagram shows the characteristics of a suitable sample gas pump. ♦ Vacuum ♦ Excess pressure ♦ Gas flow [l/min] at 20°C Figure 10:

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.4 Flow control and distribution

7.4

Flow control and distribution


6/23/2001 - 5:15:05 PM

Page 293

"Holderbank" - Cement Course 2000 The arrangement for control and distribution of the sample gas depends on the number and specifications of the analysers to be supplied. Multi-component analysers with only connection solve the problem of gas distribution internally. However, as soon as two or more analysers have to be supplied with gas, the inlet pressure must be taken into in distribution. At a low supply pressure, the analysers can be connected in series. If analysers have to be connected with varying supply pressure, they must be connected in parallel via appropriate gas distribution. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.4 Flow control and distribution / 7.4.1 Simple gas control

7.4.1

Simple gas control

Figure 11:

The flowmeter monitors and controls the set sample and test gas volume. Rotameters fitted with variable limit transmitters are normally used for setting the flow rate. The signal transmitters should signal especially when the necessary flow is not reached. This is particularly important for gas analysers with safety functions. As already mentioned, not all gas analysers have the same conditions with respect to supply pressures. Optical analysers normally require less pressure than oxygen analysers, for example, which use the paramagnetic measuring principle. However, special attention must be given to the supply pressure of the analysers when dimensioning the sample gas preparation apparatus. As soon as several analysers have to be operated, parallel connection is recommended, despite the additional work involved. For this purpose, the sample gas flow must be divided appropriate to the number of gas analysers to be supplied. The following flow diagram shows how this division can take place. The sample gas pump supplies a common supply pipe, which is under increased sample gas pressure. A spring-loaded pressure control valve controls the pressure in this pipe. The excess sample gas is diverted. A further, slightly more elaborate option, is to use a separate sample gas pump for each analyser. Parallel connection with pressure control valve

Figure 12:


6/23/2001 - 5:15:06 PM

Page 294


Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.4 Flow control and distribution / 7.4.2 Electronic gas volume control

7.4.2

Electronic gas volume control

The available electronic flowmeters are reliable and should be used to an increasing extent for automatic gas volume control purposes. These are flowmeters whose measuring principle is based on a thermal measuring bridge, whereby the transported heat of a flowing substance is used as an indicator. The calibrated reference quantity is normally air. For other gas compositions, appropriate correction values (e.g. CO2) must be used for conversion.

Figure 13:

Tests with automatic control have confirmed that the reliability of the gas supply can be considerably improved with this system. It offers decisive functional advantages compared with rotameters and is less susceptible to faults. A constant gas flow positively affects overall gas analysis in every respect. Since the controllers have a throttling effect on the gas flow, they are preferably arranged on the suction side of the pump. For flow indication purposes, a volume-proportional signal is available. This enables ideal monitoring via the control system. In addition, a rotameter (without needle valve) can still be used for monitoring locally. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.5 Sample gas filters


6/23/2001 - 5:15:06 PM

Page 295


Sample gas filters

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.5 Sample gas filters / 7.5.1 Coarse filters

7.5.1

Coarse filters

Coarse filters are normally installed inside or downstream of the probe, so that a large proportion of the dust is already separated before the sample gas enters the sample gas preparation apparatus. If sintered metal filters with a porosity of <0.5m are already used in the probe, the sample would be sufficiently clean. Nonetheless, fine afterfiltration directly upstream of the analysers is recommended, as impurities can also infiltrate the system downstream of the probe. Ceramic filters of silicon carbide, mineral fibres or filter casings of borosilicate glass fibres are also frequently used. Silicone carbide composites have a high separation efficiency of about 99.9% at an average grain diameter of 1.2m and are temperature resistant up to 660°C. The disadvantage of all these filters compared to sintered metal filters, apart from their lower separation efficiency is that they have to be cleaned and blown out or replaced at shorter intervals Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.5 Sample gas filters / 7.5.2 Fine filters

7.5.2

Fine filters

For separation of the dust particles and sublimated salts left behind in the sample gas, membrane filter, e.g. of glass fibres or PTFE should be provided. Recommended is a combination of membrane filter and condensate monitor. The condensate monitor measures a change in the electrical conductivity between two electrodes. If a limiting value is exceeded, the sample gas pump is stopped and the fault is indicated in the control room. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.5 Sample gas filters / 7.5.3 Valves

7.5.3

Valves

Changeover valves If automatic blowing out of the filter and/or probes is required, the gas path must be able to be diverted automatically. For this purpose, stainless steel solenoid valves or mechanically/ pneumatically operated ball sliding valves of Teflon (housing) and stainless steel (ball) are used. Valves installed in moist sample gas (upstream of the sample gas cooler) must be mounted on a temperature-controlled valve plate in order to prevent corrosion as a consequence of the dew point not being reached. Valves, particularly solenoid valves, have the tendency to leak, even when slightly fouled. They enable a high degree of automation of the measuring instrument, e.g. automatic calibration, however, experience has shown that their susceptibility to faults almost cancels out the convenience they are expected to provide (see chapter 11.7). Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.5 Sample gas filters / 7.5.4 Pressure control valve

7.5.4

Pressure control valve

The purpose of the pressure control valve is to ensure that the supply pressure of the analysers © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:06 PM

Page 296

"Holderbank" - Cement Course 2000 remains fairly constant. The excess gas delivered by the pump discharges via a spring-loaded body. The nominal pressure of the valve must be slightly higher than the highest specified supply pressure of all parallel connected analysers. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.6 Adjustment

7.6

Adjustment

The necessity of regular adjustments depends on the purpose of the analysis and the stability of the analysers. For emission measurements, a rotation of one to two weeks is sufficient, provided the regulations in the country concerned do not contain any tighter requirements. During adjustment, a preferably manually-operated two-way directional control valve switches the gas supply to a bottle containing test gas. Newer gas analysers are normally provided with an automatic adjusting device. By means of an internal or external command a glass cuvette filled with the respective gas is inserted into the sensor and the analyser is automatically readjusted. During this time, the last measured value remains indicated, so that the subsequent signal processing system is not disturbed by the procedure. With older analysers that do not have this type of automatic device, operating personnel or the process control system must be informed of the adjustment. With CO monitoring systems, activation of the automatic filter shutdown system must be prevented. Analysers with so-called calibrating cuvettes have the big advantage that no more test gas is necessary. Manufacturers and most nationally customary regulations accept this type of adjustment over a period of 2...3 years. After this time, the analysers must be overhauled and inspected and readjusted by an appropriately licensed institute. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.7 Further information on sample gas preparation

7.7

Further information on sample gas preparation

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.7 Further information on sample gas preparation / 7.7.1 Sample gas discharge

7.7.1

Sample gas discharge

No sample gas must discharge into the analyser room. Every gas outlet must be connected to a pipe and discharged to the atmosphere or returned to the main gas flow. Pipes with large cross-sections must be used in order to prevent any back pressure. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.7 Further information on sample gas preparation / 7.7.2 Tightness test

7.7.2

Tightness test

An option should be provided to easily connect the sample gas pipe gas-tight to a nitrogen bottle directly downstream of the sampling probe. The complete measuring apparatus is purged with nitrogen with the gas preparation apparatus operating normally. The oxygen analyser shows “zero” indication soon afterwards. After several minutes, the nitrogen supply is interrupted, so that a vacuum is produced in the system. Caution! The regulating valves on the test bottles are often not vacuum-tight. If the measured value of the oxygen analyser should increase again within a space of about 20 seconds, this means that there is a leak in the system. An increase of several per cent within several minutes is considered normal. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:07 PM

Page 297

"Holderbank" - Cement Course 2000 GAS PREPARATION / 7.7 Further information on sample gas preparation / 7.7.3 Filter condition monitoring

7.7.3

Filter condition monitoring

The suction pressure is a good indicator of the condition of the filter or filters between the probe and sample gas pump. By measuring this pressure with a pressure transmitter or pressure gauge, the automatic cleaning process can be initiated when a certain level is reached. As a result of this optimising measure, the measured signal is not interrupted unnecessarily and the filters are cleaned or blown back before being irreversibly clogged. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.7 Further information on sample gas preparation / 7.7.4 Analyser room

7.7.4

Analyser room

The accuracy and reliability of gas analysis essentially depends on temperature variations, vibrations, draughts, dust, moisture and electrical interference fields being avoided. For this reason, the gas analysers including sample gas preparation apparatus should be installed in a closed room or equipment cabinet that can be locked to prevent unauthorised access. In the analyser room, the individual instruments and apparatus must be arranged with an emphasis on clarity and easy accessibility, so that rational operation and maintenance of the measuring equipment is ensured. Figure 14:

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.8 Space requirement

7.8

Space requirement

For the analysers and sample gas preparation apparatus, a double 19” equipment cabinet with one field respectively for the gas preparation apparatus and analysers is normally sufficient. However, other equipment is often installed in this clean, air-conditioned analyser room. In such cases, it must be ensured that sufficient room is provided to enable maintenance personnel to move freely and that there is adequate room for material (e.g. test gas bottles, tools, etc.) and additional space. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.9 Location

7.9

Location

In principle, the analyser room should be located as close as possible to the measuring point. This aspect is particularly important for CO monitoring, where fast indication is necessary. Unheated sample © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:07 PM

Page 298

"Holderbank" - Cement Course 2000 gas pipes must be laid descending to the sample gas cooler. It is therefore advantageous when the analyser room is located one floor below the sampling point. If space is available at a suitable location that is not exposed to excessive dust, heat radiation and noise, a switchgear cabinet is sufficient for accommodating the measuring equipment. A separate, closed room is unnecessary under such conditions. The volume to be air-conditioned can be considerably reduced as a result. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 7. SAMPLE GAS PREPARATION / 7.10 Climatic conditions

7.10

Climatic conditions

The temperature in the analyser room or cabinet should be able to be regulated between 15 and 25°C. For this purpose, heating and ventilation is necessary; a cooling unit must be provided to counteract heat radiation. The ventilation fans must be provided with efficient dust filters. All filters produced during gas analysis must be discharged to the atmosphere. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS

8.

ANALYSERS

The determination of individual components in the sample gas is based on various physical basic principles, such as: ♦ Light absorption ♦ Paramagnetism ♦ Flame ionisation and ♦ Solid-state electrolytic systems All newer analysers process the analogue signals output by the sensors digitally. Digitalisation has provided the following advantages: ♦ Increased operating convenience (menu guidance) ♦ Multi-channel technology ♦ Automatic adjustment ♦ More compact design ♦ Increased stability ♦ Remote monitoring and control via modem and/or data bus The internal functions of the analysers will not be dealt with here. Sufficient information in this respect is provided in the manufacturer’s documents and technical literature. Important for practical application is knowing how to use the various measuring methods effectively. The manufacturer plays a secondary role in analyser selection from a qualitative point of view. Measuring equipment faults are rarely attributed to faulty analysers. It goes without saying that only types designed for industrial purposes are suitable for use in cement works and certainly no laboratory equipment. Suitability for industrial purposes means, for example: ♦ Solid, totally enclosed housing (degree of protection IP 65 or IP 54) ♦ Insensitivity to vibrations © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:07 PM

Page 299

"Holderbank" - Cement Course 2000 ♦ Minimum temperature application range 15 to 35°C ♦ Insensitivity to system disturbances ♦ Isolated (floating) output signals The majority of established manufacturers are in a position to meet these specifications. Service and spare parts availability are therefore more important than the purchase price. If measuring equipment is already available and the above criteria are met, there is no reason to change manufacturers when purchasing new equipment or additions. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.1 Infrared absorption

8.1

Infrared absorption

With the exception of oxygen, the majority of interesting gas components can be measured by infrared absorption. Available are analysers for extractive and in-situ application. In the main, infrared is used for the extractive method. The following advantages are offered by these NDIR (non-dispersive infrared) analysers: ♦ Broad application spectrum ♦ Relatively simple method, favourable price ♦ Robustness ♦ Low wear, long useful life ♦ Good stability The not particularly high sensitivity of the NDIR analysers does not normally pose a problem in the cement industry. The smallest measuring range, e.g. for CO is about 100ppm, for NO about 500ppm and for CO2 about 20 %. Cross-sensitivities to water vapour and CO2 are present. Water vapour as a disturbing component plays a secondary role when the gases in the sample gas cooler are dried with sufficient stability. The cross-sensitivity of CO2 is usually within the tolerance when compensated in the analyser. The influence can be further reduced when an amount of CO2 corresponding to the average value of the sample gas is mixed with the test gas. As the CO2 content in the cement process is extremely high, unestablished analysers should be tested in this respect prior to their use. The most well known manufacturers today produce multi-channel NDIR analysers, enabling the prices per measured component to be distinctly reduced. The majority of manufacturers also offer analysers in different quality classes (low-cost analysers). As a rule, the low-cost analysers are not temperature-stabilised, but temperature-compensated and are therefore not as stable as the analysers at the top end of the price scale. However, if external fluctuations are kept to a minimum, the temperature-compensated analysers meet the requirements in the majority of cases. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.1 Infrared absorption / 8.1.1 Space case, sulphur dioxide (SO2)

8.1.1

Space case, sulphur dioxide (SO2)

In principle, NDIR analysers are suitable for the measurement of SO2. However, tests on kiln systems with cyclone preheaters have shown that insufficient SO2 is measured with extractive sample gas sampling and preparation (in accordance with DIN 2462, page 4). The magnitude of the deficiency can vary considerably and can therefore not be calibrated. These measuring errors are attributed to chemical reactions of the SO2 with NH3 (ammonia) in the sample gas cooler (see chapter 11.2). The © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:07 PM

Page 300

"Holderbank" - Cement Course 2000 following options are available to eliminate these errors: ♦ Acidification of the condensate by addition of phosphoric acid in the sample gas cooler (TÜV) tested method developed by and available from Hartmann & Braun). ♦ Use of a “hot analyser” (measurement with moist sample gas). ♦ In-situ measuring method With the addition of about 8 to 12ml phosphoric acid (5%) in the sample gas cooler, the pH of the condensate reduces to a value below 1.5. The reaction of the SO2 with ammonia is accordingly prevented. It is obvious that hot analysers, whose entire measuring system must function at temperatures between 150°C and 250°C, are more susceptible than cold analysers. According to experience, the heated sample gas pump causes the greatest problems. With in-situ measuring instruments, no distortion through chemical reaction is noticeable. As part of comparative tests, they showed to be more reliable than measuring instruments with extractive sampling and sample gas cooler. However, absolute measured values in mg/Nm3 are initially available after calibration using a reference measuring procedure. In addition, if “dry” standard values are required, the correction must be corrected with the moisture and temperature of the sample gas. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.2 Ultra-violet absorption

8.2

Ultra-violet absorption

The difference of the NDUV analysers compared with NDIR is mainly that they are less cross-sensitive to water vapour and CO2 and higher sensitivities can be achieved. In the cement industry, NDUV analysers were initially used for the measurement of NO components. Meanwhile, the less expensive NDIR analysers are being more widely used for NO and have proved reliable. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.3 Paramagnetism

8.3

Paramagnetism

Oxygen does not have a usable spectrum either in IR or UV light. In future, laser analysers /chapter 8.6.3) will be the first to be able to measure oxygen with light in addition to other components. The paramagnetic properties of oxygen (oxygen molecules are strongly attracted in a magnetic field) are still used for oxygen measurement, however with a declining trend. In practice, two methods are widely used: ♦ The magnetic torsion balance ♦ Thermomagnetic oxygen measurement Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.3 Paramagnetism / 8.3.1 Oxygen analysers

8.3.1

Oxygen analysers

In recent years, analysers operating on the torsion balance or also dumb bell principle have become increasingly popular. The measuring effect is based solely on the magnetic forces of the oxygen molecule and is therefore comparatively less cross-sensitive to other gas components. However, the measuring chamber reacts © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:08 PM

Page 301

"Holderbank" - Cement Course 2000 sensitively to dirt and condensate. The paramagnetism of oxygen reduces with increasing temperature. This thermomagnetic effect is used in so-called annual chamber or hot wire analysers for O2 measurement. The advantage of these analysers is that the measuring chambers contain no sensitive internals, so that they are less sensitive to dirt and are also easier to clean than analysers that operate on the torsion balance principle. However, the measuring method is cross-sensitive to other gases and only functions accurately with a known or more constant accompanying gas composition. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.4 Flame ionisation (FID)

8.4

Flame ionisation (FID)

This measuring method is used for measurement of the volatile content of unburnt hydrocarbons (VOC) (Volatile Organic Compounds). Organic carbon compounds contained in the sample gas are ionised in a hydrogen flame. The ion quantity is almost proportional to the number of carbon atoms involved in combustion. The ionic voltage is detected with the aid of an electrode and brought to indication via a high-resistance amplifier. Propane gas in nitrogen is normally used for calibration purposes. Continuous measurements with the flame ionisation detector (FID) are increasingly prescribed, as soon as alternative fuels are burned. FID analysers are unfortunately susceptible to faults and require considerable maintenance by suitably trained personnel. The entire sample gas preparation system must not fall at any point below the sample gas temperature, i.e. the sampler, sample gas pipe and pump must be heated. The temperature in the ionisation chamber of the FID analyser is normally about 200°C. Modern multi-component systems such as OPSIS are capable of measuring the majority of interesting VOC compounds as individual components. Programs for direct measurement of the volatile hydrocarbons (VOC) have also been developed. Initial tests have shown almost one hundred per cent correlation with FID values. This means that in countries where non-explicit FID measurements are required, an OPSIS or perhaps also some other type of multi-component analyser will preferably be used at a later time. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.5 Solid-state electrolytic systems

8.5

Solid-state electrolytic systems

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.5 Solid-state electrolytic systems / 8.5.1 Zirconium dioxide

8.5.1

Zirconium dioxide

Zirconium dioxide (ZrO2) has the characteristic of building up a differential voltage at varying partial pressures and temperatures between 500 and 1000°C due to the flow of oxygen ions. This effect is used for the purpose of oxygen measurement by exposing both sides of a ZrO2 membrane heated to about 800°C to varying oxygen concentrations (sample gas and reference gas). The supplied voltage is tapped and measured on the two surfaces of the membrane with thin, porous platinum electrodes. The measured potential difference increases exponentially with the oxygen concentration difference. To be noted is that the indicated measured values are based on gas in a moist condition. In addition to the advantageous zirconium dioxide based in-situ measuring instruments, there are also extractive types that are hardly worth mentioning. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:08 PM

Page 302

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.5 Solid-state electrolytic systems / 8.5.2 Other electrochemical measuring methods

8.5.2

Other electrochemical measuring methods

Electrochemical measuring cells (EC cells) have the characteristic of supplying a voltage in the presence of certain components proportional to the concentration. As they are small and lightweight and require only a small number of peripheral devices, they are used mainly for portable measuring equipment (e.g. flue gas controls), although they had proved unsuitable for use in the cement industry in the past. However, in recent years, suitable EC cells have been developed that offer advantages mainly for oxygen measurement. The oxygen sensor may not be used when the accompanying gas contains H2S, chlorine or fluorine containing compounds, as well as heavy metals and aerosols. The guaranteed useful life is three years. The many years of good experience prompted the majority of manufacturers to complement the NDIR analysers with EC cells for oxygen measurement. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.6 Multi-component measuring systems

8.6

Multi-component measuring systems

Development in the field of analysis has witnessed significant advances. Thanks to modern microprocessor technology, large computer capacities and high speeds, measuring methods are employed that enable disturbing secondary effects to be compensated by calculation and new techniques to be used, for example: ♦ Gas filter correlation technique (GFC) ♦ Fastfourier transformation technique (FTIR, FTUV) Differential Optical Absorption Spectroscopy (DOAS) ♦ Laser Diode Spectrometer (LDS), etc. Without going into details about the individual techniques, the following points are of importance: ♦ Multi-component analysers are less expensive for simple measuring tasks with more than one component than individual analysers in all respects. ♦ When using alternative fuels, the necessity may arise that new, particularly critical pollutant components have to be measured. This aspect justifies the use of flexible, programmable measuring instruments. The suitability of multi-component measuring instruments in the cement industry has been demonstrated by many years of reliable use. In the following, three instruments will be presented that have proved reliable and are state of the art. These are both extractive and in-situ measuring instruments. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.6 Multi-component measuring systems / 8.6.1 Sick GM 31

8.6.1

Sick GM 31

Sick, Waldkirch (D), is a pioneer of the design and construction of in-situ measuring systems. The instruments GM 21 for dust, and later, the GM 30 for NO SO2 and dust, have been used successfully for more than ten years. The successor instrument, GM 31, differs considerably from its predecessors in two ways: ♦ Dust can no longer be measured with this instrument. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:08 PM

Page 303

"Holderbank" - Cement Course 2000 The flanged design as a so-called lance instrument does not measure the whole channel cross-section. The GM 31 is designed for the components SO2, NO, NH3 and NO. A maximum of three of these components can also be measured simultaneously. Despite the lack of the benefit of dust measurement, the GM 31 is a low-cost emission measuring instrument, which complemented with a dust measuring instrument for systems not subject to particular requirements, meets all specific requirements. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.6 Multi-component measuring systems / 8.6.2 OPSIS AR 620; ER 650

8.6.2

OPSIS AR 620; ER 650

Within the Opsis measuring system, a light beam is projected on to a receiver and then ed through a glass fibre cable to the Opsis analyser. In emission measurement, the light beam or measuring path continues through the interior of a stack or exhaust gas duct. Every gas absorbs light in known spectral regions of the total light spectrum, in a manner that is characteristic of the respective gas. This enables the analyser to detect and measure gases defined by the . The results can be indicated in real-time or used for statistical and further processing purposes. Opsis uses a scientifically researched principle for the identification and measurement of concentrations of various gases: Differential optical absorption spectroscopy (DOAS) which is based on the Lambert-Beer Law. It describes the correlation between the absorbed quantity of light and the number of molecules in the light path.. As every gas has its own unmistakable absorption spectrum, the so-called “finger print”, the concentrations of several different gases can be determined simultaneously in the light path. With the DOAS method, a light beam is sent from a special light source - a Xenon high-pressure lamp - over a specific path; by means of complex, computer-aided calculations, the light losses through molecular absorption along the path are evaluated and analysed. The light of the Xenon lamp contains both the visible spectrum as well as the ultra-violet and infrared wavelengths. The light is detected by a receiver and ed on via a fibre optic cable to the analyser. This fibre optic cable makes it possible to install the analyser at a sufficient distance from any harmful environmental influences at the measuring point. The analyser consists, among other things, of a high-performance spectrometer, a computer and the associated control unit. The spectrometer breaks down the light with the aid of an optical grid in narrow wavelength bands. This optical grid can be adjusted for examining an optimal wavelength region. The light is converted into electrical signals. A narrow slot moves at high speed across the detector; this combines a large number of instantaneous values that provide an image of the spectrum in the relevant wavelength region This scanning procedure is repeated a hundred times per second; the recorded spectrums are added up in the multi-channel memory of the evaluation unit until their evaluation. Evaluation is carried out individually for each wavelength region and is based on the comparison of absorption curves. The respectively last recorded absorption spectrum is compared with a computer calculated spectrum. The calculated spectrum consists of a summation of the reference spectrums for the respective evaluation. The computer alters the size factors for each reference spectrum until optimal correspondence is achieved, so that the various gas concentrations can be calculated with high accuracy. In order to be able to measure a diverse range of gas components as possible, the light spectrums © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:09 PM

Page 304

"Holderbank" - Cement Course 2000 must be divided into IR and UV. Measurement is similarly divided into a UV spectrometer and an IR interferometer. Depending on the components to be measured, both or one of the two instruments is used. Both instruments are usually necessary for comprehensive measurement of cement kiln exhaust gases. The system is approved as a recognised emission measuring instrument worldwide. For calibration: In principle, each component must be calibrated at last once (as part of the commissioning procedure). This takes place either via a convention method or by inserting cuvettes circulated by test gas in the light path. In this simple way, the work involved in the normally usual convention method is avoided. In two works of the ChB, these measuring instruments have proved highly reliable and may be referred to as standard-setting technology. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.6 Multi-component measuring systems / 8.6.3 LDS 3000 diode laser of AltOptronic (Sweden)

8.6.3

LDS 3000 diode laser of AltOptronic (Sweden)

The design is basically comparable with OPSIS. However, as a light source, a semiconductor laser is used. The LDS 3000 enables measurements to also be carried out in aggressive atmospheres with a high dust content; this takes place in a way that the special features of the diode laser are utilised in conjunction with a patented signal evaluation method. The instrument can distinguish whether a change in transmission is due to dust or a change in the gases to be measured. The LDS 300 can be used for measurements in atmospheres with a varying dust content up to 50g/m3, depending on the size of the dust particles. The light spectrum of the semiconductor laser can be adjusted to the absorption lines of the gas component to be measured via temperature and current. This ensures that measurement can only take place on a selected absorption line of the respective gas. The absorption lines of the remaining gas components are on other wavelengths and do not influence measurement. In the three years in which the LDS has been used, continuous tests were carried out in order to determine the stability of the system. It emerged that no recalibration of either the zero or measuring range were necessary. The diode laser is located in the main unit, from where the laser beam is ed via an optical fibre to the sensors at the measuring points. The distance between the instrument and the measuring point can be up to 1000m. In the main unit, the laser beam is scattered in an optical distributor and so enables simultaneous measurements on three different process measuring levels. The short measuring time of the LDS 3000 provides direct information (t90<1 sec). This is made possible by in-situ measurement, the high efficiency of the diode laser and appropriate signal evaluation. The short resonance time depends on the number of measuring points, as the laser light is scattered in a fibre-optic distributor and ed on to all measuring points simultaneously. Each measuring point can therefore function independently of the other measuring channels. Thanks to its unusually short reaction time, this measuring system was to be able to considerably improve the CO monitoring of electrostatic filters. Measurement directly following WT would perhaps be possible, since the manufacturer mentions that up to 50g/m3 dust has no influence. Unfortunately, the measuring distance this value applies to is unavailable. The following gases can be measured at the present time: Gas

ppm, at 1m

mg/m3, at 1m

NH3

0.6

0.4


6/23/2001 - 5:15:09 PM

Page 305

"Holderbank" - Cement Course 2000 NH 3 O2

200

260

200/1

150/0.7

H2O

0.3

0.2

Hcl

0.3

0.4

HF

0.3

0.4

H2O/NH3

Also other gas components can be measured on request. The LDS 300 is one of the first laser analysers to appear on the market. At present, the price is (still) relatively high. Development is absolutely in line with the trend and could also be used advantageously in the cement industry in the near future. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 8. ANALYSERS / 8.6 Multi-component measuring systems / 8.6.4 Advance Cemas FTRI of Hartmann & Braun

8.6.4

Advance Cemas FTRI of Hartmann & Braun

Development has also continued with extractive measuring instruments. Hartmann and Braun builds in addition to the maximum four-component measuring NDIR systems a modern FTIR (Fastfourier Transformation Infrared) spectrometer, which has identical functions to those of the OPSIS, but is designed as an extractive measuring instrument. It offers high selectivity as well as easy upgrading to additional infrared components. Based on the measuring principle and automatic zero correction, calibration is only necessary twice a year to maintain the smallest measuring ranges. All parts coming into with the sample gas: Sampling system, sample gas preparation system and measuring cuvette are heated to 100°C. The instrument features a self-diagnosis system and, as with all modern instruments of this type, can be monitored by H & B Service and faults diagnosed via an integrated modem. A German cement works has had good experience over a two-year operating period. The instrument is overhauled twice a year as part of a maintenance contract. The weak point, the hot gas pump, is changed each time or the diaphragms replaced as a precautionary measure. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 9. RECORDING AND EVALUATION

9.

RECORDING AND EVALUATION

Following the measured values on the basis of recording strip charts is advantageous for the general assessment of a process sequence. In the area of emissions, the majority of countries require that measured values are prepared according to certain, adapted criteria; hourly and daily average value, criteria relating to the observance or non-observance of limiting values, etc. In such cases, digital processing of the measured values is unavoidable. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 9. RECORDING AND EVALUATION / 9.1 Trend curves, recorders

9.1

Trend curves, recorders

For the purpose of clarity, not too many components should be recorded simultaneously. Strongly varying signals must be appropriately dampened. Monitors or line recorders are better suited for this purpose than dotted-line recorders. Scaling should correspond with the actual physical values. This © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:09 PM

Page 306

"Holderbank" - Cement Course 2000 applies particularly to life-zero signals. For strip chart recorders, a paper feed rate of 20mm/h is standard. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 9. RECORDING AND EVALUATION / 9.2 Averaging computers

9.2

Averaging computers

When lump fuel (e.g. tyres) is fed into the precalcining zone, the measured values at the kiln inlet are subject to extreme fluctuations. Without damping of averaging, the signals are difficult to interpret. It has emerged that sliding, linear averaging is easier to interpret than logarithmic damping, as individual values are less important in linear averaging. The more favourable intervals for optimal averaging are between 10 and 15 minutes. Figures 15 and 16 show the behaviour of the signals of a 1500-7/d kiln with tyre feed without averaging and with various averaging times. Figure 15:


6/23/2001 - 5:15:09 PM

Page 307

"Holderbank" - Cement Course 2000 Figure 16:

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 9. RECORDING AND EVALUATION / 9.3 Data logging

9.3

Data logging

The interpretation of measured signals on the basis of trend curves is too rudimentary for sophisticated tasks. Visual comparisons of such curves easily lead to misinterpretations. In connection with optimisations or in the search for faults in the process, the signals from gas analysis must be processed with other measured quantities from the system in the PC. A precondition for this is that the data can be digitally acquired, logged and input into the PC. In plants with modern process control systems, this precondition is usually met. Where this is not the case or as part of temporary © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:10 PM

Page 308

"Holderbank" - Cement Course 2000 measurements, independent data logging systems should be used for data recording purposes. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 9. RECORDING AND EVALUATION / 9.4 Emission computers

9.4

Emission computers

The form of documentation of the measured emissions is prescribed in more and more countries. In Europe, there are plants whose emission computers are connected via a data line to the authorities concerned. The emission computers are normally designed for documentation of the following values: ♦ Half-hourly average values ♦ Hourly average values ♦ Daily average values ♦ Exceeded limiting values Emission computers primarily meet the officially prescribed evaluation and documentation of emission values. As the emission data also contains valuable process-relevant information, they are also useful for the operator. Depending on the regulations of the country concerned, the valuation of emission values can be taken over from internal process control systems. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE

10.

MAINTENANCE AND QUALITY ASSURANCE

Reliable continuous operation of continuous gas analysis is dependent not only on the efficient design of the measuring equipment, but also on systematic maintenance and repair. The maintenance work to be carried out can be subdivided into the following categories. ♦ Condition check ♦ Adjustment check, cleaning ♦ Replacement of wearing parts ♦ Function test Table 4 shows the maintenance intervals of a typical gas analyser. Maintenance must be carried out daily (D), weekly (W), monthly (M), quarter yearly (QY), half yearly (HY) or yearly (Y). The time cycle of the individual working procedures depends on the system-specific conditions and essentially on the age of the measuring equipment. The work undertaken is noted in a logbook for practical purposes. Table 4:

Maintenance Intervals

Function Test Replacement of worn parts Adjustments, checks, cleaning works Visual checks


6/23/2001 - 5:15:10 PM

Page 309

"Holderbank" Visual checks - Cement Course 2000 Sample gas preparation: Flow measurement (floating body instrument) Suction pressure (Manometer) Humidity in the sample gas pipes Function check of the wetness monitor Heated sample gas pipe temperature Sample gas cooler condensate pump Sample gas pump check and replace membrane Tightness check Cabinet air conditioning Magnetic valves, function and tightness check Cabinet cleaning

D D D

W M

HY HY Y

D QY

Y

D HY QY

HY

Y

Y

Y Probes: Tightness check Cooling Filter change Cleaning

QY D HY HY

Analyzers: Indication plausibility Adjustement Filter change Total overhaul

QY D W QY 3Y

The operating conditions and type of construction of the equipment used varies considerably. Instructions for maintenance and repairs must be adapted to local conditions and defined according to individual experience. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.1 Visual checks

10.1

Visual checks

The term visual check includes visual inspection of the equipment, indicating instruments, signal states and checking heated parts for a hot or cold condition by trained and experienced personnel. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.2 Adjustment checks, cleaning

10.2

Adjustment checks, cleaning

This category includes adjustments, readjustments, etc., of conditions which can change for different © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:11 PM

Page 310

"Holderbank" - Cement Course 2000 reasons. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.2 Adjustment checks, cleaning / 10.2.1 Tightness checks

10.2.1 Tightness checks Vacuum check The hose connections at the probe are sealed and the sample gas pump is started. The maximum vacuum which the pump can produce must be noted when commissioning the measuring equipment. At maximum vacuum, the part of the pump is closed and the pump stopped. The sample gas preparation system up to the sample gas pump (suction area) is considered tight when the vacuum does not change significantly for a period of 5 minutes following temperature equalisation. Nitrogen check See Chapter 7.7 Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.3 Replacement of wearing parts

10.3

Replacement of wearing parts

When replacing parts, it must be ensured that no leaks occur. According to experience, weak points in this respect are filter housings and connecting points in the sample gas pipe. Suitable sealing material must be available at all times, so that any type of seal, union, etc., can be replaced if there is the slightest suspicion of a leak. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.3 Replacement of wearing parts / 10.3.1 Sample gas pump

10.3.1 Sample gas pump The sample gas pumps are usually diaphragm pumps, whose diaphragm and valve plates should be replaced at least once a year. The ball bearings of the motor and eccentric should be replaced every two years in continuous operation. Standby sample gas pumps should be available. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.3 Replacement of wearing parts / 10.3.2 Cleaning sintered metal and ceramic filters

10.3.2 Cleaning sintered metal and ceramic filters Ceramic filters can be cleaned with diluted hydrochloric acid (1 part concentrated hydrochloric acid to 10 parts water). The filters must be placed in the acid for about 2 hours. The parts must subsequently be flushed with water pressure from the inside to the outside, blown out with compressed air and dried in a drying cabinet at about 100°C. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.3 Replacement of wearing parts / 10.3.3 Fine filters

10.3.3 Fine filters The filter element should be replaced at regular intervals, e.g. every three months. Fine filters with condensate monitor are tested by moistening the filter element. The instrument must then respond. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:11 PM

Page 311

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.3 Replacement of wearing parts / 10.3.4 Gas analysers

10.3.4 Gas analysers The gas analysers are tested with test gases or by means of the built-in calibrating cuvettes and readjusted if necessary. For testing with gases, it must be ensured that the flow rate roughly corresponds with the operating values. When selecting the test gases, the specifi-cations of the instrument manufacturer must be observed. The gas analysers should be adjusted at regular intervals, at least every two weeks. Adjustments must be noted in the maintenance report. If significant adjustments are required, or the adjustment range limits (greater than 80% or less than 20%) are reached, the instrument must be tested and inspected if necessary. Wearing parts are, e.g. emitter, receiver, diaphragm motor. For zero readjustment, nitrogen is normally used. With the exception of oxygen measurement, air can also be used as a zero gas if the analysers are not too sensitive. For sensitivity adjustment, a test gas is used that normally consists of the measuring components and nitrogen. For compensation of the residual moisture, it is advantageous to feed the test gas upstream of the sample gas cooler. The test gas concentration for sensitivity adjustment should be 80 to 90% of the respective measuring range end value. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.4 Function test

10.4

Function test

This term means that certain functions gas analysis are extensively tested, e.g. to ensure that the detector in the fine filter responds if moisture is present and the sample gas pump is stopped. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.5 Test gases

10.5

Test gases

As initially mentioned, new gas analysers no longer require any test gases. The internal calibrating and control options ensure that the accuracy is maintained over a long period (normally two years). After this time, the analysers should be tested by the manufacturer’s service department and in particular the internal control devices (calibrating cuvettes) checked. Test gases are available in various accuracy classes according to particular directives, e.g. VDI 3490, sheet 2. Depending on the manufacturing and analysis accuracy, distinction is made between three classes. The test gases are delivered with analysis certificates that contain all essential data, such as: ♦ Measuring component and accompanying gas ♦ Test gas production method ♦ Measuring component concentration ♦ Relative error of this concentration ♦ Pressure of container filling ♦ Minimum application pressure ♦ Minimum and maximum storage temperature and maximum test gas storage time (limit date)


6/23/2001 - 5:15:11 PM

Page 312

"Holderbank" - Cement Course 2000 The concentration specified on the analysis certificate should be written in large and easily readable letters on the test gas bottle. The test gases are available in bottles of varying size. A 10 litre bottle (about 1100mm high, preferably of aluminium) is normally sufficient for a two-year supply. The bottle pressure is between 100 and 200 bar, depending on the gas composition. The main valve must be closed after each use. Test gas deliveries max take time in certain regions; this should be taken into when the bottle pressure starts to get low. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.5 Test gases / 10.5.1 Mixing test gases

10.5.1 Mixing test gases Certain gas components can be combined as a mixture in a bottle. This possibility considerably facilitates maintenance (fewer bottle transports and savings on gas bottle hire charges). Caution! New multi-component gas analysers must only be tested with gas mixtures but not calibrated. Only individual components in nitrogen are permitted for calibration. With one exception, all standard components can be mixed together. This exception applies to oxygen O2. With oxygen analysers, the measuring range should be such that air can be used for calibration. Nitrogen must always be used as a residual gas. Example of a test gas mixture:

Component

Chemical symbol

Analyser measuring range

Concentration in test gas

Sulphur dioxide

SO2

3000ppm

2800ppm

Carbon monoxide

CO

5%

0.45%

Nitrogen monoxide

NO

2000ppm

1900ppm

Carbon dioxide

CO2

as accompanying gas

25%

Nitrogen

N2

as residual component

74.08%

The accuracy of the test gases reduces the more components are mixed. The number of mixing components is thus limited. Further, general information on test gases is provided in the annexed instructions. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.6 Fault signals

10.6

Fault signals

Faults in the measuring instrument should be indicated by status signals, e.g.: ♦ Insufficient pressure in the suction pipe (blockage of the probe or gas path) ♦ Excessive pressure in the suction pipe (possible failure or leakage of a solenoid valve) © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:11 PM

Page 313

"Holderbank" - Cement Course 2000 ♦ Status signals of the analysers (failure of the analyser or electrical fault) ♦ Operating temperature of the sample gas cooler or failure of the sample gas cooler ♦ Operation of the condensate monitor (can indicate failure of the sample gas cooler or faulty water-cooled probe ♦ Adjustment/operation changeover valve should automatically inform the control room that the measuring equipment is being serviced and is therefore not ready for operation ♦ Minimum of flowmeter (insufficient sample gas) Status signals for measuring equipment faults are checked for their plausibility by simulated operating deviations. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 10. MAINTENANCE AND QUALITY ASSURANCE / 10.7 Automated maintenance equipment

10.7

Automated maintenance equipment

Theoretically, numerous maintenance procedures can be automated, e.g. automatic zero and limit range adjustment, sample gas flow rate control, blowing out of the filter, etc. However, sample gases are media that can give rise to various difficulties. They have a corrosive effect, contain dust, must not be adulterated, can be very moist, etc., to mention but a few of the unpleasant characteristics that make automation difficult. Practice shows time and again that solenoid valves are the weak point within measuring equipment, so that only valves of the best quality must be used for evaluation. The number of necessary solenoid valves increases with an increasing degree of automation; due to their susceptibility to faults, the failure rate also increases, so that the savings expected from automation are accordingly lost. The same applies when a group of analysers is switched to two or more measuring points with the intention of saving on expensive analysers. Apart from the operating difficulties, experience has shown time and again that the saved investment costs are quickly absorbed by the corresponding maintenance costs. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS

11.

MEASURING ERRORS

The accuracy of gas analysers is often overestimated. The reason for gas analyses being relatively inaccurate is not because of the analysers, as is often assumed. The following examples explain the most important influences responsible for this. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS / 11.1 Sample gas sampling

11.1

Sample gas sampling

Significant measuring errors can occur as a result of non-representative sampling. In rotary kiln systems, these occur particularly at the rotary kiln inlet and kiln inlet chamber measuring points. These measuring errors occur mainly at the “filter” measuring points in coal pulverising mills. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS / 11.2 Sample gas preparation © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:12 PM

Page 314


Sample gas preparation

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS / 11.2 Sample gas preparation / 11.2.1 Sorption and chemical reaction

11.2.1 Sorption and chemical reaction In the probe and sample gas preparation system, sample gas components can react with each other. These reactions are reinforced by catalytic effects. Furthermore, reactions with dust or gas conducting components are possible. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS / 11.2 Sample gas preparation / 11.2.2 CO reduction

11.2.2 CO reduction At high temperatures (above 600°C), CO is reduced to a large degree depending on the residence time. This effect is the reason why only cooled probes may be used at temperatures above 500°C. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS / 11.2 Sample gas preparation / 11.2.3 NO2 formation in the probe and sample gas preparation system

11.2.3 NO2 formation in the probe and sample gas preparation system At temperatures of about 100°C and a concentration of 900ppm NO, the theoretical formation rate of NO2 is about 0.5ppm per second. At lower temperatures and high gas residence times, this formation takes place more rapidly. The indication delay of the NO measuring equipment should therefore be as short as possible. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS / 11.2 Sample gas preparation / 11.2.4 SO2 reduction in the probe and sample gas pipe

11.2.4 SO2 reduction in the probe and sample gas pipe Rust, dust deposits, non-ferrous metal parts (especially copper) in the gas path of the sample gas can reduce SO2 up to 100%. For the sample gas pipes and all other gas conducting parts, Teflon, high-alloyed steel or steel with special coating (e.g. PTFE) must therefore be used. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS / 11.2 Sample gas preparation / 11.2.5 SO2 reduction of the filter dust of the sampling probe

11.2.5 SO2 reduction of the filter dust of the sampling probe SO2 reacts with the CaCO3 and CaO contained in the filter dust of the sampling probe with the formation of CaSO4. With high dust contents in the process gas, measuring errors of up to 100% can occur. SO2 can therefore only be measured fairly accurately process gas with a low dust content. This applies in particular to SO2 measurements in the rotary kiln inlet. Tests have shown that SO2 is initially indicated only a short time after cleaning the filter. Within several minutes, the indication falls to zero again, because the SO2 is absorbed in the dust building up in the filter. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS / 11.2 Sample gas preparation / 11.2.6 Interaction with a liquid

11.2.6 Interaction with a liquid © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:12 PM

Page 315

"Holderbank" - Cement Course 2000 Errors due to the solubility of the measuring component The solubility of certain measuring components in water must be taken into for wet sampling probes. If the injector water of the wet sampling probe is not fed into the circuit, CO2, NO2 and SO2 can go into solution, depending on the probe design. Condensation of the water vapour which is separated as water in the sample gas cooler by the extractive method, can also distort gas analysis. This is of particular significance for SO2 emission measurement when low concentrations are present. The theoretical solubility of SO2 in water is low and could be compensated by appropriate calibration. However, tests on cement kiln systems in a direct operating mode have shown that measuring errors for SO2 are far above the theoretical distribution equilibrium when SO2 reacts with other gas components such as NH3. An SO2 measuring device can be tested for these errors by the sample gas being transferred from the sampling probe directly into concentrated sulphuric acid (H2SO4) as the drying medium and not via the sample gas cooler. If distinct differences in the measured value indication occur, a chemical reaction is most probably taking place in the sample gas cooler. Apart from SO2, NO2 also dissolves in the condensate of the sample gas cooler. However, since the proportion of NO2 in the total NO concentration can be disregarded with proper sampling, the resulting measuring error can normally be disregarded. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS / 11.3 Volumetric errors due to the solubility of accompanying components

11.3

Volumetric errors due to the solubility of accompanying components

If accompanying components, e.g. CO2 go into solution, the concentration of the other measuring components increases. The partial absorption of CO2 in an injector probe, increases, e.g. the O2 concentration. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 11. MEASURING ERRORS / 11.4 Gas analysers

11.4

Gas analysers

The accuracy of the gas analysers, provided they are in a perfect condition, is not an issue. If a gas analyser is viewed as a whole, the analyser is the most accurate link in the measuring chain, with a few exceptions. The analyser manufacturer’s specifications relating to cross-sensitivities, disturbing components as well as temperature and pressure influences must be observed. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 12. SPECIAL FUNCTIONS OF GAS ANALYSIS

12.

SPECIAL FUNCTIONS OF GAS ANALYSIS

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 12. SPECIAL FUNCTIONS OF GAS ANALYSIS / 12.1 CO monitoring for protection of electrostatic filter

12.1

CO monitoring for protection of electrostatic filter

If, for any reason, combustible gases should develop (ring fractures, faults in fuel dosage, etc.), in the kiln system, there is a risk of a potentially explosive mixture forming in the electrostatic filter. High-voltage discharges inside the filter cause sparks, which can lead to explosions in a gas atmosphere of appropriate composition. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:12 PM

Page 316

"Holderbank" - Cement Course 2000 As a safety measure, the CO component of the gas discharging from the kiln system is measured. Once a certain level is reached, the high-voltage should be switched off before the gases reach the electrostatic filter. Measurement can initially take place in precalcining plants following complete combustion in the auxiliary firing equipment, i.e. in the uppermost cyclone stage of the heat exchanger at the earliest. The residence time of the gases from this point to the electrostatic filter is relatively short (several seconds) and varies considerably from plant to plant (with or without cooling tower, combined/direct operation, etc.). Filter monitors, whose effect alone depends on an adjustable maximum value, reassure responsible personnel, however, they are not optimal solutions. On the one hand, unnecessary filter shutdowns are initiated, on the other hand, it is not ensured that they would operate promptly in an emergency. A tried and tested possibility of optimising this process is offered by sequential filter shutdown. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 12. SPECIAL FUNCTIONS OF GAS ANALYSIS / 12.1 CO monitoring for protection of electrostatic filter / 12.1.1 Basic concept of filter shutdown

12.1.1 Basic concept of filter shutdown Compared with the usual method, filter shutdown is optimised in two essential steps. The first step consists of shutting down the filter chambers step by step. The second step consists of taking into a “reducing” or “increasing” CO trend. The residence time of the gases in the electrostatic filter itself is used in order to further delay shutdown. The filter chambers are shutdown at approximately five second intervals, depending on the size and gas flow rate. However, as soon as CO measurement indicates a reducing trend, the shutdown cycle is stopped. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 12. SPECIAL FUNCTIONS OF GAS ANALYSIS / 12.1 CO monitoring for protection of electrostatic filter / 12.1.2 Optimisation of CO measurement

12.1.2 Optimisation of CO measurement The following measures must be taken in order to make CO measurement as efficient as possible: ♦ Short distance between sampling point and analyser ♦ Large sample gas volume (up to 300l/h setting;short delay time) ♦ Small volumes in gas path, particularly in sample gas cooler ♦ Select analyser with fast response time ♦ Use double measuring system for two-section WT systems ♦ Formation of logical signals “CO increasing” and “CO reducing” Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 12. SPECIAL FUNCTIONS OF GAS ANALYSIS / 12.1 CO monitoring for protection of electrostatic filter / 12.1.3 Specifications

12.1.3 Specifications ♦ Selection of measuring point according to Figure 1 ♦ Gas preparation system appropriately adapted according to Figure 12 ♦ NDIR gas analyser, measuring range 0 to 5%, CO with 3 adjustable maximum limiting values ♦ Arrangement of a shutdown procedure With regard to the CO analyser, it should be noted that the same must have a high measuring range © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:13 PM

Page 317

"Holderbank" - Cement Course 2000 for CO monitoring. It cannot be used simultaneously for continuous CO observation, as the normal CO content is below the detection limit of this analyser. If CO is to be continuously measured, a second analyser with a much lower measuring range of 5000ppm (0.5%) must be used. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 12. SPECIAL FUNCTIONS OF GAS ANALYSIS / 12.1 CO monitoring for protection of electrostatic filter / 12.1.4 Shutdown procedure

12.1.4 Shutdown procedure The procedure for shutdown of the individual filter chambers is shown on the basis of two examples in Tables 5 and 6. The specified numerical values of the shutdown sequences and the CO level are only guide values and must be adjusted to the respective plants. For CO values below 10%, a risk of explosion is virtually excluded. However, the threshold values must be set far lower, as the measurement reacts with delays despite optimal preconditions (dead time + indication delay). Table 5:

Switching procedure, for a simple heat exchanger kiln with 3-changer filter

Table 6:

Switch-off pocedure, for a two strings heat exchanger kiln with 3-chamber filter

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 12. SPECIAL FUNCTIONS OF GAS ANALYSIS / 12.1 CO monitoring for protection of electrostatic filter / 12.1.5 Special devices

12.1.5 Special devices Sick GM 950 © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:13 PM

Page 318

"Holderbank" - Cement Course 2000 Via an in-situ sensor (zirconium dioxide) CO is measured at a high response rate and processed to a shutdown command if required. As zirconium is fairly instable as a CO indicator, extractive supplied semiconductor sensors correct any deviations. The device is new and still in the testing phase. The currently available test results have been positive up to now. The measuring method is relatively elaborate and the device gives the impression of being somewhat complex. During the test, no functional disturbance occurred. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 12. SPECIAL FUNCTIONS OF GAS ANALYSIS / 12.1 CO monitoring for protection of electrostatic filter / 12.1.6 Laser analysers

12.1.6 Laser analysers In-situ laser analysers offer promising prospects as already mentioned in chapter 8.6.3. It is conceivable that low-cost options will soon be available, as several measuring points can be served with the same analyser, e.g. filter monitoring (upstream and downstream of the filter) and various points in the coal pulverising mill. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 12. SPECIAL FUNCTIONS OF GAS ANALYSIS / 12.2 Monitoring of coal pulverising mills

12.2

Monitoring of coal pulverising mills

In the safety concept of coal pulverising mills, the monitoring of critical gas components covers only a small part of the necessary equipment and measures. In addition, coal pulverising mills vary considerably in their design, so that the application and function of gas analysis is always determined as part of the entire plant. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 12. SPECIAL FUNCTIONS OF GAS ANALYSIS / 12.2 Monitoring of coal pulverising mills / 12.2.1 Limiting values

12.2.1 Limiting values In 1984, the following limiting values were listed by a working group of the Association of German Cement Works (VDZ): O2 content in moist exhaust gas downstream of the filter

14%

Temperature at mill inlet (coal moisture 12%)

400°C

Gas temperature downstream of mill upstream of filter

120°C

Gas temperature downstream of filter

120°C

Gas temperature upstream of filter minimum 30°C above dew point about

75°C

CO concentrate during filter shutdown

50ppm

Operation with hot gas generator

70ppm

Operation with kiln exhaust gase

not practical

Pressure upstream of mill

-1.5bar

Coal dust temperature

110°C

Air temperature of pneumatic transport

80°C

The limiting value for the oxygen concentration applies only to plants with inert gas operation. All other limiting values are the same for the safe operation of inert and non-inert gas operated plants. For coal © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:13 PM

Page 319

"Holderbank" - Cement Course 2000 pulverising mills heated with kiln exhaust gas, CO monitoring is not practical during operation, because the gases from kiln operation contain up to 10 times more CO than the limiting value of 70ppm permits. CO shutdowns of the electrostatic filter for the kiln, must be coupled with the filter of the coal pulverising mill. This information on the safety equipment of coal pulverising mills only contains the most important information and is intended to draw attention to the complexity and importance of such plants. Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 13. CONVERSION FACTORS

13.

CONVERSION FACTORS

Conversion of the gas components from volume to units of weight and vice versa, is often the cause of errors in adjustment or interpretation. Such errors occur most frequently in connection with NO and NO2. The problem with these NO components is that the instruments measure NO, but the emission must be converted to NO2. Furthermore, emissions are considered in weight-related units (mg/m3), but the instruments and the test gases are often specified in volume-related units (e.g. ppm or %)

Conversion from [ppm] to mg/m3

Factor f =

M 22.4

Whereby M = Mol mass (kg/kmol) of the gas components Table 7 Components

Converted to

Mol mass [M]

Factor (f)

1/f

CO

CO

28.01

1.25

0.80

NO

NO

30.01

1.34

0.75

NO

NO2

46.01

2.85

0.49

NH3

NH3

17.03

0.76

1.32

Example Given: ♦ Test gas with 8.75ppm NO ♦ NO analyser, measuring range 0-2000mg/m3NO Required: ♦ Analyser indication at 875ppm ♦ How much NO2 in mg/m3 corresponds to the adjusted value 875ppmNO? © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:14 PM

Page 320

"Holderbank" - Cement Course 2000 Solution: ♦ Analyser indication = 875 x 1.34

=

1172mg/m3 NO

♦ Emission value NO2= 875 x 2.05

=

1794mg/m3 NO2

♦ or from mg/m3 NO to mg/m3 NO2 1172 x 1.53

=

1794mg/m3 NO2

Process Technology / B06 - PT III / C04 - Gas Analysing Systems / PRACTICAL GAS ANALYSIS IN CEMENT WORKS / 14. LITERATURE

14.

LITERATURE

1) Verein Deutscher Zementwerke (VDZ) (Association of German Cement Works): 2) Continuous Gas Analysis in Cement Works, Notice VT9, June 1990 3) B. Thier: Safe Operation of Coal Pulverising Mills. ZKG 4/1984, page 163 4) M. Ascherfeld and W. Fabinski Multi-component Analyser for Oxygen and Infrared Active Gases. tm Technisches Messen 59 (1991) Volume 5 5) H.G. Loos, Erlangen: A New Operational Compact Gas Sampling Device for Cement Rotary Kilns. ZKG NO. 6/1987 6) M. Birrer, H. Nyffenegger: Gas Sampling at the Kiln Inlet with Improved Probe. 7) “Holderbank” NEWS 6/90 8) K. Utzinger: Reduction of Dust Emissions on Startup and CO Shutdowns of the Electrostatic Filter at the Rekingen Works. “Holderbank NEWS 7/8 (1986) 9) Bronkhurst High-Tech B.V., Ruurlo, Holland: Operating Manual for Mass Flowmeters and Controllers for Gases 10) KNF Neuberger (Switzerland) AG, CH 8362 Balterswil: Prospectus and Data Sheet for Diaphragm Compressors and Vacuum Pumps 11) Annette Schröck: Preparation of Decision-making Criteria for Plant Operators for Purchasing an Emission Measuring Instrument. Thesis SS 1992 (available from Messrs Sick) 1)


6/23/2001 - 5:15:14 PM

Page 321

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C05 - High Level Control

C05 - High Level Control


6/23/2001 - 5:15:14 PM

Page 322

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS

HIGH LEVEL CONTROL SYSTEMS U. Haberstich PT 98/14350/E (Revision of PT 94/4191/E) 1. INTRODUCTION 2. EVOLUTION OF HLC SYSTEMS 3. SPECIFIC REQUIREMENTS OF A HLC SYSTEM 4. PROCESS OPTIMIZATION WITH HLC 5. PRINCIPLES OF OPERATION 6. BENEFITS AND KEYS OF SUCCESS 7. HOW TO JUSTIFY AN INVESTMENT IN HLC 8. CONCLUSION 9. REFERENCES 10. ANNEX


6/23/2001 - 5:15:14 PM

Page 323

"Holderbank" - Cement Course 2000 Summary For more than 30 years, the cement industry has been exploring computer-based techniques to control and optimize the operation of cement kilns. The major reasons behind these endeavours are clinker uniformity, savings in energy consumption, increase in production, savings in refractory consumption and NOx reduction. Basically, cement kilns are difficult to control because of their non-linear, multivariable, behaviour and the poor quality of the available process signals. After several trials to describe the burning process with mathematical models a new approach in cement kiln control was investigated in 1980. Operator control strategies were studied, and a detailed record of the operator’s behaviour was made while controlling the kiln. These “fuzzy” rules can imitate multivariable control actions and can combine information from variables to identify the kiln conditions. Within the “Holderbank” group, specific requirements of such a High Level Control (HLC) system was defined to compare the several suppliers. The system from ABB LINKman is the most powerful real-time expert system with very advanced features and a high -friendliness. A standard implementation plan was made to reach a successful application of the system. The preparatory work in the plant must be carried out according to the recommendations made during the pre-project study. The identified process problems have to be solved. To achieve the “Best Operator Performance” the detailed and rigorous monitoring of the HLC performance is obviously essential at this stage. The optimization of the process with respect to product quality and related process factors, on a long-term basis, is the key to the ultimate level of savings arising from the HLC application. It is this optimization that can give the plant additional benefits over and above those arising from the average operator to „Best Operator Performance“. The experience shows that substantial benefits like higher kiln output, lower heat consumption, longer refractory life, lower NOx emissions and lower standard deviation of the key variables can be expected from HLC systems, if they are properly implemented and used. The experience shows that the payback of 1 to 2 years is realistic, when considering only the investment costs in the HLC system. Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS / 1. INTRODUCTION

1.

INTRODUCTION

For more than 30 years, the cement industry has been exploring computer-based techniques to control and optimize the operation of cement kilns. The major reasons behind these endavors are clinker uniformity, savings in energy consumption, increase in production, savings in refractory consumption, NOx reduction (Fig. 1 + 2, Annexes 1 + 2). The still high energy consumption of the cement manufacturing process, the stringent requirements on cement quality and the environmental aspects which are leading the governments to apply severe legislation regarding the emissions. The classical process automation approach, consisting in defining a mathematical model of the process, led to only a very few successful kiln control applications. The improvement in the performance of hardware equipment, combined with the advent of artificial intelligence, is leading to a major step toward kiln control and optimization. Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS / 2. EVOLUTION OF HLC SYSTEMS

2.

EVOLUTION OF HLC SYSTEMS

Basically cement kilns are difficult to control because of their non-linear, multivariable, behaviour and the poor quality of the available process signals. The control is then usually limited to a few secondary measurement loops, whereas the control of the primary parameters and the operating conditions are the responsibility of the kiln operators. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:14 PM

Page 324

"Holderbank" - Cement Course 2000 The first applied techniques were based on empirical or mathematical models. Although successful in simulating the kiln operation, these techniques were generally based on too many assumptions and used very complex theoretical models. For this reason they were not applicable and could not be extended to a broad selection of kilns. Other approaches such as the "hill climbing" techniques (Young et al, 1971) or statistical identification combined with optimal controller design by the state space method (Otomo et al, 1972) was also used but did not achieve any significant success. Since the mid-seventies, a new approach based on the analysis of the human decision making in cement kiln control has been investigated (Umbers and King, 1980). Operator control strategies were studied, and a detailed record of the operator's behaviour was made while controlling the kiln. Basically this approach rests upon the concept of fuzzy logic introduced by Prof. L. Zadeh in 1965. The basic operator control rules were already prescribed by Peray and Waddell (1972). These "fuzzy" rules can imitate multivariable control actions and can combine information from variables, they work by identifying the kiln conditions and prescribing suitable corrective actions. FL Smidth supplied the first commercially available kiln control system based on fuzzy logic in 1980. The concept of High Level Control was introduced at that time and is used to refer to systems, which provide not only supervisory control but also optimising control. Since then, many systems have been developed and are marketed. Some are using the concept of fuzzy logic and are called rule-based systems or are based on expert system shells. Others are more conventional and apply PID control or adaptive-predictive controllers. The penetration of HLC in the cement industry has been very intensive over the last decade, about 300 applications have been reported in kiln control applications. Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS / 3. SPECIFIC REQUIREMENTS OF A HLC SYSTEM

3.

SPECIFIC REQUIREMENTS OF A HLC SYSTEM

The following basic requirements were specified: 1) The provision of a high degree of -friendliness; this aspect is extremely important, since kiln control strategy needs to be adapted when process conditions change. The maintenance of the application control strategy must be easy for the plant engineers to carry out. 2) The concept of “autopilot” as used in the previous version of the supplier’s HLC system must be included to make it possible for the operator to switch the system on-line or off-line at any time without disturbing the process. 3) The use of a toolkit based on the G2 expert system shell which provides advanced features such as real-time facility, graphical interface and object-oriented programming; the toolkit, which is a software layer between G2 and the HLC applications, is the for developing and implementing control strategies without programming skills. 4) The possibility for having multiple applications on the same system, typically one kiln, one cooler, mills and the kiln simulator. 5) The provision of a system incorporating tools and facilities allowing for consistent process optimization. 6) Very helpful for the introduction is the inclusion of a standard interface between the HLC system and the tailor-made kiln simulator in order to provide a training platform for the operators; this platform would allow for the simulation of kiln upsets and disturbances. The plant engineer would thus be able to develop and test new strategies before real implementation in the actual plant application. Figure 3 (Annex 3) shows a typical configuration. 7) The standardisation of the control strategies, in order to shorten commissioning time and make © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:15 PM

Page 325

"Holderbank" - Cement Course 2000 exchange of experience easier between different s. It is important to have a standardised way of both configuring and maintaining the control strategies. Within the “HOLDERBANK” Group LINKman from ABB LINKman Systems Ltd, London, is applied. LINKman Graphic, the new version of this HLC system, is based on G2, a very powerful real-time expert system shell from Gensym Corp. LINKman Graphic is particularly -friendly and offers very advanced features [4]. Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS / 4. PROCESS OPTIMIZATION WITH HLC

4.

PROCESS OPTIMIZATION WITH HLC

As mentioned above, process optimization is the major target to be achieved. There are typically three phases associated with our concept of successful application. See also [3]. These phases are outlined below. Phase 1: Plant Preparation The preparatory work in the plant must be carried out according to the recommendations made during the pre-project study. Phase 2: Achievement of „Best Operator Performance“ Very often bottlenecks are detected, process problems are identified and experience is gained in the period immediately following HLC implementation. Detailed and rigorous monitoring of the HLC performance is obviously essential at this stage. The identified problems then have to be addressed during the secondary commissioning. Attempts must be made to achieve the highest possible run time of the HLC system, typically 90 % or more, using an adequate and consistent control strategy. At this stage, the HLC is expected to operate with the same performance as the best operator with respect to production output, product quality, heat consumption, etc. The associated benefits depend on the size of the plant and the performance previously achieved in manual operation. This phase, based on the best operator know-how, can be considered as the foundation of the whole HLC project. Phase 3: Process Optimization The optimization of the process with respect to product quality and related process factors, on a long-term basis, is the key to the ultimate level of savings arising from the HLC application. It is this optimization that can give the plant additional benefits over and above those arising from the average operator to „Best Operator Performance“. Process optimization mainly involves the plant technical staff. It requires an evaluation of the process performance, an estimation of the potential savings, which can be achieved, and an assessment of the control strategy performance. Since plant conditions change in respect to raw material quality, availability of alternative fuels, product quality requirements, etc., process optimization must be considered as a permanent task.

Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS / 5. PRINCIPLES OF OPERATION

5.

PRINCIPLES OF OPERATION

Basically, in the case of a conventional preheater kiln, HLC manages the control of the following parameters: ♦ the kiln feed rate © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:15 PM

Page 326

"Holderbank" - Cement Course 2000 ♦ the kiln speed ♦ the IDF speed (or damper position) ♦ the fuel to the kiln burner In case of a precalciner installation, the precalciner fuel and the position of the tertiary air damper (AS system) have also to be controlled automatically. The HLC system needs to access the process relevant data, such as preheater temperatures and pressures, the gas composition, the kiln amperage, the burning zone temperature, etc. The principles of kiln control operation depend on the HLC system used. The principles used in LINKman are hereafter presented. LINKman LINKman works in two basic modes: “Normal Actions” and “Interrupt Actions”. The approach used in LINKman is sequential. In a first phase, a specific logic checks whether the kiln is in normal operation or in upset situation.

Normal Actions If the kiln is in normal condition, then the parameters BZT, OX and BET are calculated. ♦ BZT (Burning Zone Temperature) represents the clinker burning degree, calculated out of NOx, Kiln Amps, and zone temperature. ♦ OX, the draught index, based on the gas composition at kiln inlet. ♦ BET (Bet End Temperature): the degree of preparation of the material when entering the kiln. LINKman selects then one of 4 ruleblocks to determine the required setpoint changes, depending on: ♦ the deviation between the actual feed rate and the desired target, ♦ the spare draught capacity, ♦ The process conditions. Rule Block

Actions on

General

Feed, Fuel, Fan

Top-feed

Fuel, Fan


6/23/2001 - 5:15:15 PM

Page 327

"Holderbank" - Cement Course 2000 Top-feed

Fuel, Fan

Top-damp

Feed, Fuel

Stable

Fuel

The changes calculated using the ruleblocks are scaled to physical changes. However these changes are merely based on the present kiln conditions. Specific actions are then carried out, if required, to take into the previous actions and the process dynamics, they are included in the "Post-Rule Block Processing" module.

Interrupt Actions If a kiln-upset condition is detected, a dedicated control action is applied. As these actions have a higher priority than the normal actions, they are called interrupt actions.

Examples: Break-Action

if the kiln is in unstable conditions for a longer period

Ring-Action

if a ring fall is detected

Hot-Action

if the kiln gets very hot

CO-Action

if a high amount of CO is detected

Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS / 6. BENEFITS AND KEYS OF SUCCESS

6.

BENEFITS AND KEYS OF SUCCESS

The experience shows that substantial benefits can be expected from HLC systems if they are properly implemented and used. The following table shows typical ranges of quantifiable benefits:

Item

Typical Range

Kiln output

+ [0 - 5 %]

Heat Consumption

- [0 - 5 %]

Refractory Life

+ [0 - 30 %]

Long-term clinker strength

+ [0 - 5 %]

Electrical energy for clinker grinding

- [0 - 10 % ]

NOx emissions

- [0 - 30 %]

Number of kiln stops

- [0 - 30 %]

Standard deviation of key variables

- [0 - 50 %]


6/23/2001 - 5:15:15 PM

Page 328

"Holderbank" - Cement Course 2000 In addition, the following qualitative benefits have to be mentioned: ♦ The working conditions of the operators are greatly enhanced. As the computer handles the routine tasks, the operator can concentrate on more important matters. ♦ Process analysis and optimization are made more easily since opportunities for testing new control strategies and new ideas are available, assuming that the HLC is -friendly enough. ♦ The use of HLC imposes to keep the instrumentation in a good operating state. The keys of success with HLC systems are: ♦ An adequate and reliable instrumentation (sensors, actuators, PID controllers, etc.) ♦ A stable and uniform raw mix chemistry ♦ An optimized combustion ♦ A highly motivated personnel ♦ A follow-up of the performance of the system Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS / 7. HOW TO JUSTIFY AN INVESTMENT IN HLC

7.

HOW TO JUSTIFY AN INVESTMENT IN HLC

In order to justify an investment in HLC, it is important to estimate the potential cumulative savings over the lifetime of the system. Figure 4 (Annex 4) gives an illustration of these savings over a period of ten years. In this figure, curves 1, 1a and 1b indicate the cumulative savings with HLC when achieving „Best Operator Performance“. If the HLC has a robust strategy and is permanently adapted to the evolution of the burning process, then the cumulative savings will increase consistently according to curve 1. However, if the system is not properly maintained or not adjusted to changing process conditions, sooner or later it will stop functioning and the savings will obviously stop. These situations can take place very shortly after installation (curve 1a) or later on (curve 1b). Curve 2 illustrates the cumulative savings, which can be realized in cases where the HLC is used as a tool for permanent process optimization. These extra savings are on top of the savings indicated on curve 1. The benefits resulting from this optimization can be achieved after reaching an HLC run time of more than 90 %. The savings through optimization can increase even more if the original HLC application is extended to other plant areas such as raw milling, stack gas flow control or integration of an efficient raw mix control strategy. To summarize, simply by achieving „Best Operator Performance“, the payback is generally less than two years (considering only the investment in HLC). Furthermore, if the HLC is used efficiently as a permanent optimization tool, then the cumulative savings will increase even more. The experience shows that a payback of 1 to 2 years is realistic, when considering only the investment costs in the HLC system. Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS / 8. CONCLUSION

8.

CONCLUSION


6/23/2001 - 5:15:16 PM

Page 329

"Holderbank" - Cement Course 2000 Over the last decade, HLC systems have penetrated the cement industry. About 300 applications have been reported which represents roughly 15 % of the cement manufacturing installations. There is no doubt that the proper implementation and use of a HLC system, although requiring relatively low investment costs, provide significant enhancements in of productivity. However it is of the utmost importance to select the adequate system, that means a system which has proven to be efficient and performant in the long term. It must be ed that the success of any HLC system depends upon: ♦ the quality of the instrumentation ♦ the raw meal preparation ♦ the quality of the combustion system ♦ the motivation of the works’ personnel and the acceptance of the system by the operators Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS / 9. REFERENCES

9.

REFERENCES

1) Bertrand I Automatic control of kilns and mills by expert systems. World Cement, July 1991. 2) Bauer C., G. Jäger, J. Patzer and K.H. Walen Cost-effective clinker production with the PYROEXPERT optimization system. Zement, Kalk, Gips Nr. 4/1993. 3) Hasler R. and E.A. Dekkiche Experience in kiln optimization with LINKman Graphic. IEEE Cement Industry Technical Conference, Seattle 1994. 4) Haspel D. and W. Henderson A new generation of process optimization systems. International Cement Review, June 1993. 5) Maynard B. Hall Kiln stabilization and control - A COMDALE/C expert system approach. IEEE Cement Industry Technical Conference, Toronto 1993. 6) Mende N. Erfahrungen mit dem Ofenführungssystem KCS an einer grossen Drehofenanlage in Südkorea. Zement-Kalk-Gips, Nr. 2/1993. 7) Ostergaard J.J. FUZZY II - The new generation of high level control Zement-Kalk-Gips, Nr. 11/1990. 8) Otomo T., T. Nakagawa and H. Akaike Statistical approach to computer control of cement rotary kilns. Automatica, Vol. 8, 1972. 9) Ruiz Navarro M., J.M. Martín-Sánchez and C. Corzo Carreno Minimizing energy consumption in kilns by the SCAP system. World Cement, March 1993. 10) Umbers I.G., P.J. King © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:16 PM

Page 330

"Holderbank" - Cement Course 2000 An analysis of human decision-making in cement kiln control and the implications for automation. Int. J. Man-Machine Studies, Nr. 12, 1980. 11) Young S.C.K., K.L. Todd and K.H. Lau On-line optimization of rotary cement kilns. 3rd IFAC/IFIP Intern. Conf. on Digital Computer Appl. to Process Control. Helsinki 1971. Process Technology / B06 - PT III / C05 - High Level Control / HIGH LEVEL CONTROL SYSTEMS / 10. ANNEX

10.

ANNEX

Figure 1:

Example of Improved Clinker Uniformity

Figure 2:

Example of Improved Heat Consumption


6/23/2001 - 5:15:16 PM

Page 331


Figure 3:

Operator Training

Figure 4:

Lifetime Benefits of Process Optimization with HLC


6/23/2001 - 5:15:17 PM

Page 332

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview

Field Preparation for High Level Control - Process Preview U. Haberstich PT 99/14495/E 1. INTRODUCTION 2. DETAILED SCOPE OF WORK 2.1 Definition of responsibilities and meetings 2.2 Data collection 2.3 Combustion check 2.4 Definition of the strategy 2.5 Control loops 2.6 Instrumentation check 3. APPENDIX 1 3.1 KILN MANUFACTURING DATA


6/23/2001 - 5:15:17 PM

Page 333

"Holderbank" - Cement Course 2000 Summary and conclusion: The introduction of a High-Level Control System requires a proper preparation of the plant to ensure an efficient and successful implementation and commissioning. For that purpose a so-called preproject from HMC is proposed in order to disclose eventual difficulties or even disability of the plant to implement such a system. A team of the Process Technology Department (HMC/PT) and Holderbank Engineering Switzerland (HES) will help the plant to achieve the best preparation. HES will check the possibilities to connect the LINKman system to the installed plant control system and the sensitivity of measuring and control devices. HMC/PT will check the quality aspects and the kiln behavior in order to disclose eventual process problems.

The main items of the LINKman preproject are: ♦ Kick-off meeting with explanation of the LINKman system and the procedure to implement it. ♦ Collection of all available plant data (Flow-sheets, technical descriptions of the installation). ♦ Collection of all available process data (Log-sheets, quality data, flow-sheets and trends). ♦ Combustion check. ♦ Description of the used strategy and rules for manual kiln and cooler control (which parameters were used) and a description of the most common kiln and cooler problems (dusty clinker, coating falls, etc.). ♦ Control of the adjustments of the most important control loops. ♦ Instrumentation check (type, position, sensitivity). ♦ Definition of the preparatory work to be done before the LINKman implementation. ♦ Conclusion meeting with the definition of the implementation schedule (ordering and commissioning). Definition of the project leader and of the responsible for the LINKman Hardware and Software (Strategy). Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview / 1. INTRODUCTION

1.

INTRODUCTION

The introduction of a kiln High-Level Control System like LINKman requires several preparatory works by the plant to ensure an efficient and successful implementation. The capability of the kiln to be driven by an automatic system has to be ensured by a pre-project. As in every project, the organization has to be determined and responsibles have to be nominated. The LINKman pre-project has to cover mainly the following capability checks of the kiln system: ♦ Disclosing eventual process problems ♦ Defining an adequate kiln and cooler control strategy ♦ Checking the instrumentation


6/23/2001 - 5:15:17 PM

Page 334

"Holderbank" - Cement Course 2000 ♦ Checking the sensitivity of the measuring and control devices (HES) ♦ Defining the connection of the LINKman system to the installed plant control system (HES). Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview / 2. DETAILED SCOPE OF WORK

2.

DETAILED SCOPE OF WORK

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview / 2. DETAILED SCOPE OF WORK / 2.1 Definition of responsibilities and meetings

2.1

Definition of responsibilities and meetings

A kick-off meeting has to be organized at the beginning of the pre-project. Experience has shown that a more detailed explication of the LINKman system avoids confusions. The implementation schedule (ordering and commissioning) has to be defined as well as the project leader and the responsibles for the LINKman Hardware and Software (Strategy). The responsible for the Hardware issues is usually an electrical engineer with knowledge of the plant control system and the automatic control loops. The responsible of the Software (strategy) needs detailed knowledge about the burning process and kiln control. Therefore, a process engineer is strongly recommended. He will be the future “LINKman – Champion” and doing all further modifications of the strategy after the commissioning. Before the implementation also the exact position of the Hardware has to be defined (location of the operator- and engineer-station in the control room and location of the LINKman cabinet). After finishing the study, all requirements will be discussed during the conclusion meeting at the end of the visit. The preparatory work has to be terminated until the first commissioning of ABB. If stronger process problems were detected, it may be recommended to postpone the order of the system. Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview / 2. DETAILED SCOPE OF WORK / 2.2 Data collection

2.2

Data collection

To prepare the system before delivering, ABB needs sufficient data about the plant. Therefore, a collection of all available plant data is required. This contains mainly:

Plant descriptions: ♦ Flow-sheet of the kiln system ♦ Flow-sheet of the plant control system (PLC-System) ♦ Kiln manufacturing data (see also Appendix 1) ♦ Layout of the control room (to place the Hardware and pre-configure the cabling) ♦ List of available control loops ♦ Instrumentation list.


6/23/2001 - 5:15:17 PM

Page 335

"Holderbank" - Cement Course 2000 Process data ♦ (During 1 week of representative production) ♦ Quality data of Raw meal, Hot meal and Clinker ♦ Operator log-sheets ♦ Statistical distribution of the freelime.

For 24 hours ♦ 1-day-trend of all important process values of that week (burning zone temperature, NOx, Amps, Calciner temperature, Preheater exit temperature, etc.)

Additional information ♦ Printout of all available kiln process screens (only 1 momentary printout) ♦ Short description of the used strategy and rules for manual kiln and cooler control (which parameters were used). Is there a correlation between the clinker quality and some kiln control parameters (NOx, kiln amps, burning zone temperature)? Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview / 2. DETAILED SCOPE OF WORK / 2.3 Combustion check

2.3

Combustion check

Process problems strongly influence the kiln behavior. Incomplete combustion leads to enhanced Alkali/Sulfur cycles within the kiln system. If the molar Alkali/Sulfur ratio of the total input of Alkalis and Sulfur is within the desirable range (0.8 to 1.5), minor encrustation and Sulfur ring formation take place. To avoid a bad or wrong implemented strategy and bad availability of the LINKman system, a combustion check is required. A combustion check contains: ♦ Description and analysis of all fuel at the main firing ♦ Gas analysis data at kiln inlet (O2, CO, NOx) ♦ Assessment of sintering zone, coating and the burner position ♦ Alkali/Sulfur balance. For this, sufficient samples of the raw meal, hot meal and clinker have to be taken and analyzed. ♦ Burner check (Primary air amount, fuel oil pressure, exit velocities, pressure fluctuations, etc.) ♦ Description and analysis of all fuels at the secondary firing ♦ Gas analysis data at preheater exit (O2, CO, NOx) Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview / 2. DETAILED SCOPE OF WORK / 2.4 Definition of the strategy

2.4

Definition of the strategy

LINKman offers standard strategies for almost every kiln type. One of those strategies will be © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:18 PM

Page 336

"Holderbank" - Cement Course 2000 pre-configured before delivery and modified on site during the commissioning. To ensure a proper predefinition of the kiln and cooler control strategy, a description of the current used strategy and the rules for manual kiln and cooler control is required. Kiln Control: Define the most important parameters estimating the burning zone temperature, the kiln inlet temperature and the oxygen level. A description of the most common kiln problems (dusty clinker, coating falls, etc.) will help defining required special actions. Cooler Control: Define the most important parameters to ensure proper clinker cooling and high efficiency. A description of the most common cooler problems (kiln rushes, red rivers, hot plates, etc.) will help defining required special actions. Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview / 2. DETAILED SCOPE OF WORK / 2.5 Control loops

2.5

Control loops

For a proper working High Level Control System, the in the PLC installed control loops have to work properly and smoothly. Therefore, the most important loops (kiln hood pressure control, under grate pressure control, etc.) have to be revised and adjusted, if required. A further possibility is the complete removing of a loop from the PLC in order to add it into the LINKman strategy or to switch it off during LINKman control. Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview / 2. DETAILED SCOPE OF WORK / 2.6 Instrumentation check

2.6

Instrumentation check

The instrumentation is the most important point for an automatic kiln control. The signals have to be convenient and reliable. Therefore, the type and position of the most important sensors have to be revised and corrected if required. Especially the gas analyzers need periodic calibrations and maintenance inspections. For a list with required process signals and its position see Report HES 98/6347/E. Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview / 3. APPENDIX 1

3.

APPENDIX 1

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control - Process Preview / 3. APPENDIX 1 / 3.1 KILN MANUFACTURING DATA

3.1

KILN MANUFACTURING DATA

Plant


6/23/2001 - 5:15:18 PM

Page 337


Kiln

Preheater: Precalciner:

Burner Cooler

No. : Supplier: Nominal Capacity: Max. Capacity: Type of fuels :

Heat Consumption: Length: Diameter: Slope: Number of strings: Number of stages: Type: Type of fuels:

% Fuel PC / Kiln: Type: % Primary air: Type: Number of grates: Number of fans: Width x length:


6/23/2001 - 5:15:18 PM

…………………… …………………… …………………… (t/d) …………………… (t/d) …………………… …………………… …………………… …………………… …………………… …………………… …………………… (kJ/kg) …………………… (m) …………………… (m) …………………… (%) …………………… …………………… …………………… …………………… …………………… …………………… …………………… …………………… …………………… …………………… …………………… …………………… …………………… …………………… ……………………

Page 338

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control

Field Preparation for High Level Control F. Fehr HES 98/6347/E 1. INPUT SIGNALS FOR HIGH LEVEL CONTROL 1.1 Checklist: Assignment of Input Signals 1.2 Example of a Checklist 2. OUTPUT SIGNALS FOR HIGH LEVEL CONTROL 2.1 Primary Control Loops, Actuators 2.2 Example of a check list 1 2.3 Example of a check list 2 3. INTERFACE TO PROCESS CONTROL SYSTEM 3.1 Data Exchange 3.2 Security 4. EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER 4.1 General 4.1.1

Definition:

4.1.2

Location of the Sensor

4.1.3

Calibration of the Transmitter

4.2 Examples 4.2.1

Temperature

4.2.2

Pressure

4.2.3

Speed

4.2.4

Current

4.2.5

Power/Energy


6/23/2001 - 5:15:18 PM

Page 339

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 1. INPUT SIGNALS FOR HIGH LEVEL CONTROL

1.

INPUT SIGNALS FOR HIGH LEVEL CONTROL

The Input Signals of the High Level Control system (HLC) are the measured variables of the controlled systems (kiln, cooler, mill). In the following a selection of the normally used input signals is indicated.

Selection of Input Signals

Wet kiln ♦ Sintering zone temperature (Pyrometer) ♦ Secondary air temperature (if available) ♦ Amps of kiln drive (Torque) ♦ O2/CO/NOx at kiln inlet ♦ Temperature at chain zone ♦ Backend temperature ♦ Backend pressure ♦ Kiln hood pressure ♦ Any other significant process variable used by the kiln operators

Preheater kiln ♦ Sintering zone temperature (Pyrometer) ♦ Secondary air temperature (if available) ♦ Amps of kiln drive (Torque) ♦ NOx at kiln inlet or at preheater exit ♦ O2/CO at kiln inlet ♦ Kiln inlet temperature ♦ Kiln inlet pressure ♦ Kiln hood pressure ♦ Preheater exit temperature or second stage from top ♦ Preheater exit pressure ♦ O2/CO at preheater exit ♦ Any other significant process variable used by the kiln operators Precalciner kiln


6/23/2001 - 5:15:19 PM

Page 340

"Holderbank" - Cement Course 2000 ♦ Basically the same signals as for preheater kilns, but additionally: ♦ NOx at kiln inlet ♦ Temperature exit lowest cyclone stage ♦ Tertiary air temperature

Lepol kiln ♦ Sintering zone temperature (Pyrometer) ♦ Secondary air temperature (if available) ♦ Amps of kiln drive (Torque) ♦ O2/CO/NOx at kiln inlet ♦ Temperature in hot chamber of Lepol grate (Pyrometer or Thermometer) ♦ CO/O2 after intermediate fan ♦ Temperature intermediate fan ♦ Pressure in hot chamber above grate ♦ Pressure in hot chamber underneath grate ♦ Kiln hood pressure ♦ Any other significant process variable used by the kiln operators

Clinker cooler ♦ Air rates of the individual fresh air fans ♦ Pressures of chambers 1, 2, 3 ♦ Exhaust air temperature ♦ Temperature of cooler plates ♦ Middle air temperature (if any)

Cement mill ♦ KW of mill motor ♦ KW of bucket elevator ♦ Rate of separator returns (t/h) ♦ Noise level by electronic ear ♦ Temperature/pressure at mill inlet and outlet ♦ Production rate, e.g. belt weigher, pressure of pneumatic transport, etc.


6/23/2001 - 5:15:19 PM

Page 341

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 1. INPUT SIGNALS FOR HIGH LEVEL CONTROL / 1.1 Checklist: Assignment of Input Signals

1.1

Checklist: Assignment of Input Signals

INPUT SIGNALS

Min.

Max.

Target

Name of Signal, Value Sensor: Location: Significance: Stability: Comment: Name of Signal, Value Sensor: Location: Significance: Stability: Comment: Name of Signal, Value Sensor: Location: Significance: Stability: Comment: Name of Signal, Value Sensor: Location: Significance: Stability: Comment: Name of Signal, Value Sensor: Location: Significance: Stability: Comment:

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 1. INPUT SIGNALS FOR HIGH LEVEL CONTROL / 1.2 Example of a Checklist


6/23/2001 - 5:15:19 PM

Page 342


Example of a Checklist

INPUT SIGNALS

Min.

Max.

Target

1)

650°C

1040°F

815°C

1200°F

1900°F

1500°F

Secondary air tempe rature

Sensor:

o.k.

Location:

o.k.

Significance:

Indication is sensitive. Tendency is o.k.

Stability:

o.k.

Comment:

Measuring equipment is adequate. Useful signal for LINKman II. Upper/lower limits are exceeded, therefore the limits have to be adjusted.

2)

3)

Cooler exhaust air temperature

95°C

230°C

150-175°C

200°F

450°F

300-350°F

Sensor:

o.k.

Location:

o.k.

Significance:

not looked at

Stability

not stable due to unstable cooler operation.

Comment:

Measuring equipment is adequate.

Clinker temperature

-

Sensor:

o.k.

Location:

Existing location gives no representative

-

signal. Significance:

not looked at

Stability:

not looked at

Comment:

As a better location is not available, this temperature should not be considered for automatic control.

4)

Grate speeds of cooler


6/23/2001 - 5:15:19 PM

Page 343

"Holderbank" Cement 4) Grate -speeds ofCourse cooler 2000

-

-

Sensor:

-

-

Location:

-

Significance:

-

Stability:

-

Comment:

unproblematic signal.

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 2. OUTPUT SIGNALS FOR HIGH LEVEL CONTROL

2.

OUTPUT SIGNALS FOR HIGH LEVEL CONTROL

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 2. OUTPUT SIGNALS FOR HIGH LEVEL CONTROL / 2.1 Primary Control Loops, Actuators

2.1

Primary Control Loops, Actuators

Basically all High Level Control output signals go as setpoints to primary control loops which then drive actuators. Example: Figure 1:

The behaviour of the variable controlled by the primary loop is influenced by the following factors: ♦ repeatability of the sensor (specifications) ♦ absolute accuracy of sensor (calibration) ♦ type of actuator: continuous, step-wise ♦ tuning of PID controller ♦ deadband to protect actuator ♦ disturbances from outside (e.g. flushing material) For HLC the primary loops have to fulfil the following criterias:


6/23/2001 - 5:15:20 PM

Page 344

"Holderbank" - Cement Course 2000 1)

Tolerable deviation from setpoint

Figure 2:

∆ x: max. tolerable deviation during a time > ∆ t ∆ x and ∆ t depend upon what is controlled by the primary loop (e.g. coal, slurry to a wet kiln) 2)

Sensitivity of setpoint change

What is the minimum applicable setpoint change that causes a reaction of the controlled variable? Figure 2:

The criterias which have to be fulfilled are given in the following list for every type of primary loop. Most of the loops are not critical so that no criterias for the tolerable deviation are given: Table 1 Tolerable Deviation from Setpoint

Sensitivity of Setpoint Change

x[% of Span]

SPmin [% of Span]


t [min]

6/23/2001 - 5:15:20 PM

Page 345

"Holderbank" - Cement Coursex[% 2000 of Span]

t [min]

SPmin [% of Span]

-

-

0.5% 1.0%

-

-

0.5% 1.0% 1.0% 1.0%

Kiln Kiln fan - fan speed - damper position Kiln drive Fuel rates Feed: wet preheater Dust insufflat. rate Tertiary air dampers Intermed. fan (Lepol) Lepol grate speed Water to granulator

3% 3% 3% 10% -

0.5 10.0 2.0 0.5 -

0.5% 1.0% 0.5% 0.5% 0.5% 0.5% 1.0% 1.0% 0.5% 1.0% 1.0%

Mill Mill feed Separator speed Cooling air fan - fan speed - damper position Water injection

3% -

0.5 -

1.0% 0.5%

Cooler Volume rate fresh air fans - speed - damper position Kiln hood pressure - speed - damper position Grate speed ratio Under grate pressure

0.5% 1.0% 1.0%

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 2. OUTPUT SIGNALS FOR HIGH LEVEL CONTROL / 2.2 Example of a check list 1

2.2

Example of a check list 1

PID Loop:

Kiln drive HAC Code

0%

to

100%

Unit

Setpoint:

.....

.....

to

.....

[

]

Actual Value:

.....

.....

to

.....

[

]


6/23/2001 - 5:15:21 PM

Page 346

"Holderbank" - Cement Actual Value: Course 2000 ..... Manipulated Variable: (actuator)

.....

.....

to

.....

[

]

.....

to

.....

[

]

Visual check of actuator: Tuned: Parameters:

KP = ....

Tl = ....

[

Max.

Delta x = Delta t =

.... ....

[ % of span ] [ min ]

....

[ % of span ]

deviation: during:

Sensitivity: SPmin =

]

TD = .... [

]

Remarks:

PID Loop:

Precalciner fuel rate HAC Code

0%

to

100%

Unit

Setpoint:

.....

.....

to

.....

[

]

Actual Value:

.....

.....

to

.....

[

]

Manipulated Variable: (actuator)

.....

.....

to

.....

[

]

Visual check of actuator: Tuned: PID Parameters:

Kp = ....

Tl = ....

[

Max.

Delta x = Delta t =

.... ....


....

[ % of span ]

deviation: during:


]

TD = .... [

]

Remarks: Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 2. OUTPUT SIGNALS FOR HIGH LEVEL CONTROL / 2.3 Example of a check list 2

2.3

Example of a check list 2


6/23/2001 - 5:15:21 PM

Page 347

"Holderbank" - Cement Course 2000 PID Loop:

Main burner fuel rate HAC Code

0%

to

100%

Unit

Setpoint:

.....

.....

to

.....

[

]

Actual Value:

.....

.....

to

.....

[

]


.....

.....

to

.....

[

]

Visual check of actuator: Tuned: Parameters:

Kp = ....

Tl = ....

[

Max.

Delta x = Delta t =

.... ....


....

[ % of span ]

deviation: during:


]

TD = .... [

]

Remarks:

PID Loop:

Kiln feed HAC Code

0%

to

100%

Unit

Setpoint:

.....

.....

to

.....

[

]

Actual Value:

.....

.....

to

.....

[

]


.....

.....

to

.....

[

]

Visual check of actuator: Tuned: PID Parameters:

Kp = ....

Tl = ....

[

Max.

Delta x = Delta t =

.... ....


....

[ % of span ]

deviation: during:

Sensitivity: SPmin = © Holderbank Management & Consulting, 2000 Query:

]

6/23/2001 - 5:15:21 PM

TD = .... [

]

Page 348


Remarks: Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 3. INTERFACE TO PROCESS CONTROL SYSTEM

3.

INTERFACE TO PROCESS CONTROL SYSTEM

For any process control application, the High Level Control System needs to read data from the process (inputs from sensors) and to write data to the process (outputs to primary control loops). Moreover, for kiln/mill control, the High Level Control System requires also operator inputs such as: ♦ operating targets (NOx, O2, etc.) ♦ operator setpoints (kiln feed, fuel feed, etc.) ♦ laboratory data (clinker factor, fuel heat value, % free lime etc.) These inputs can be entered either from the LINKman II or from the Process Control System (PCS) The data communication between the PCS and the HLC is mostly based on a RS 232/422 serial link with the PCS brand specific communication protocol. The data set for exchange has to be pre-processed and stored in a specific memory location to be available for the data communication software. For a kiln application for example, process data are accessed every 10 seconds and outputs are sent every 5 minutes, or with higher frequency if required, to update setpoints. The kiln strategy, for example runs every minute. To connect the LINKman II to the PCS, two possible configurations are proposed: ♦ If the PCS has a bus connecting the whole plant (plant loop), then the LINKman II is interfaced by using a serial link to the interface box of the loop. An example is presented on the next page where the LINKman II is interfaced through a CIU (Computer Interface Unit) to a Bailey Network 90. ♦ If the PCS is structured according to the plant departments, the LINKman II has access to the individual departments through individual serial lines. The second picture shows a typical interface in a application where an Allen Bradley Programmable Logic Controller is used in connection with the HOLDERBANK ODH system as Men Machine Interface (MMI). Figure 4:

Figure 5: © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:22 PM

Page 349


Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 3. INTERFACE TO PROCESS CONTROL SYSTEM / 3.1 Data Exchange

3.1

Data Exchange

The PCS does not only act as data acquisition system for the LINKman II, it serves also as operator interface (MMI, setpoint change, manual mode control), it hosts the basic loop controller, is responsible for automatic/manual switching including fail safe procedure if the LINKman II or communication breaks and does the alarm handling for the whole process (also HLC alarms). Because of this, the communication data set consists not only of anaputs and outputs, but also of digital signals: ♦ Digital control bits from the PCS (digital inputs) ♦ Digital alarm and status bit from the HLC (digital outputs)

DIGITAL INPUTS The PCS system has to provide different status bits from the process to indicate specific conditions which the LINKman II needs to work for proper operation. Example: ♦ LINKman II on/off ♦ failure of instrumentation ♦ group ready/running ♦ direct/indirect operation of raw mill ♦ select status (type of cement etc.)

DIGITAL OUTPUTS In a similar way, the LINKman II has to send status bits to the PCS to inform the operator about its status. Example: ♦ LINKman II available ♦ on/off line © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:22 PM

Page 350

"Holderbank" - Cement Course 2000 ♦ normal condition ♦ upset condition ♦ alarms ♦ etc. Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 3. INTERFACE TO PROCESS CONTROL SYSTEM / 3.2 Security

3.2

Security

The communication and proper execution of the program have to be guarantied. Therefore, a watch-dog function on the PCS has to be realised: Example: Communication/HLC watch-dog To check the communication as well as the LINKman II operating status (HLC on or off), a watch-dog toggle-bit has to be programmed. Figure 6:

The two on-delay timers control the on- and the off-time of the toggle-bit. If the time exceeds the pre-set delay time of the timers (typical 30 s), the toggle-bit has not been inverted and this means, that the LINKman II or the communication is off. The PCS is responsible to switch the HLC on- or off-line (on operator's request) and to monitor the HLC's on/off-state and to switch the setpoint signals accordingly (setpoint from operator MMI or from HLC). If the HLC goes off-line and the watch-dog detects a problem, the setpoint will be set to the operator control and an alarm has to be evoked. Note: The setpoint switching has to be made bumpless. (see PID subject) Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER

4.

EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:23 PM

Page 351

"Holderbank" - Cement Course 2000 IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER / 4.1 General

4.1

General

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER / 4.1 General / 4.1.1 Definition:

4.1.1

Definition:

Range = Max. - Min. of the sensor Example: 0°C - 1000°C Span = f

Used range for the electrical signal or monitoring the process

Figure 7:

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER / 4.1 General / 4.1.2 Location of the Sensor

4.1.2

Location of the Sensor

The location of the sensor is the most important thing in the instrumentation. There are a few locations which are really false and a lot which are good. For maintenance of the sensors it is quite frequently necessary (especially in the kiln area), that the location of the sensor should be above all easy accessible. Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER / 4.1 General / 4.1.3 Calibration of the Transmitter

4.1.3

Calibration of the Transmitter

The calibration includes first of all the checking of the transmitter. There are different methods how to check: 1) Reference measurement: The sensor will be tested on a well-defined media (boiling oil, known weight, etc.) 2) Comparison measurement: Measure the process value by an other measuring device (hand-held thermometer/multimeter, pressure U-tube, etc.) 3) Find out the actual physical measurement by measuring the electrical signal coming out of the © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:23 PM

Page 352

"Holderbank" - Cement Course 2000 sensor (only if the characteristics are well-known,should not be used on thermocouple due to the cold reference junction). 4) Simulating the process with an alternative source by entering a calibrated signal on the primary side. While applying method 1 or 2 as described above, the process value on the highest level (screen of the supervisor or high level control system) - if already installed - has to be monitored. If o.k., the procedure of course is quickly and successfully finished. If not, the output of the transmitter has to be measured by an Amp-Meter (4...20mA) and the transmitter has to be calibrated according its manual. In very seldom cases, the problem is in the scaling of the PLC or the supervisory system.

Note: Two hints on calibration ∗ Do a Plausibility Check. This means that the signal should be checked of its plausibility. Is it on its expected value? If not, there is something wrong. Do not accept everything you measure. Repeat the measurement if it is not plausible or try to make the calibration by an other way. ∗ Accuracy. If the sensor is not accurate enough or the transmitter has a too large range, try to calibrate it within the operating range. Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER / 4.2 Examples

4.2

Examples

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER / 4.2 Examples / 4.2.1 Temperature

4.2.1

Temperature

EXAMPLE 1: KILN INLET TEMPERATURE LOCATION: Figure 8:

♦ Easy accessible for maintenance ♦ Cleaned by pulling out (daily) © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:23 PM

Page 353

"Holderbank" - Cement Course 2000 ♦ Tip of sensor should be in the air-stream but not affected too much by incrustation ♦ Sensor should not be damaged by falling material ♦ The final position has to be evaluated

CALIBRATION: Figure 9:

♦ Inject a voltage in mV without the sensor into the transmitter, while measuring in the 4...20mA line. Take readings at the display for 0 and 100%. SPAN:

minimum:

0%

=

1000°C

=

4.0mA

maximum:

100%

=

1250°C

=

20.0mA

1%

=

2,5°C

=

0.16mA

80%

=

1200°C

=

16.8mA (16:100x80+4)

unit: typical value:

EXAMPLE 2: PYROMETER (at kiln hood for clinker temperature) LOCATION: Figure 10:


6/23/2001 - 5:15:24 PM

Page 354

"Holderbank" - Cement Course 2000 ♦ Aim spot 30 cm (1 foot) ♦ Do not point into flame (radiation) ♦ Aim the pyrometer below the flame into the clinker just before the clinker flows out of the kiln ♦ Dust on the lens of the pyrometer or between lens and clinker affects the measurement, therefore, choose a short measuring distance CALIBRATION: ♦ Calibration according to the manufacturer. (Does not have to be calibrated under normal circumstances) SPAN:

minimum:

0%

=

1100°C

=

4.0mA

maximum:

100%

=

1600°C

=

20.0mA

1%

=

5°C

=

0.16mA


depending on the kiln

Note: The absolute temperature is not so important, changes have to be monitored. EXAMPLE 3: PRECALCINER LOWEST CYCLONES LOCATION: Figure 11:

1

Dead zone

2

Good position for material temperature

♦ Find the 2 right locations out of 4 ♦ Parallel probes recommended

CALIBRATION: © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:24 PM

Page 355


SPAN:

minimum:

0%

=

600°C

=

4.0mA

maximum:

100%

=

1000°C

=

20.0mA

1%

=

4°C

=

0.16mA

72%

=

890°C

=

15.5mA (16:100x72+4)


EXAMPLE 4: PREHEATER EXIT TEMPERATURE LOCATION: Figure 12:

♦ Good for minimizing of exhaust gas temperature ♦ Equilibrium of tower streams ♦ If the temperature of the second stage is more indicative, it is advantageous to use this value

CALIBRATION:

SPAN:

minimum:

0%

=

0°C

=

4.0mA

maximum:

100%

=

500°C

=

20.0mA

1%

=

5°C

=

0.16mA


70% = 350°C = 5.2mA (16:100x70+4)

Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:24 PM

Page 356

"Holderbank" - Cement Course 2000 IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER / 4.2 Examples / 4.2.2 Pressure

4.2.2

Pressure

EXAMPLE 1: KILN HOOD LOCATION: Figure 13:

1

Measuring points (hood pressure)

2

ambient pressure (heated up air)

3

transmitter

4

U- Tube for calibration purpose

CALIBRATION: ♦ Measure the pressure by an U-Tube (differential measurement) grate cooler:

SPAN:

minimum:

0%

=

0.1mbar

=

4.0mA

maximum:

100%

=

-0.3mbar

=

20.0mA

1%

=

0.004mbar

=

0.16mA

unit:

typical value: 37.5% = -0,05mbar = 10.0mA (16:100x37.5+4) planetary cooler:

SPAN:

minimum:

0%

=

-2mbar

=

4.0mA

maximum:

100%

=

-3mbar

=

20.0mA

EXAMPLE 2: KILN INLET PRESSURE LOCATION: Figure 14:


6/23/2001 - 5:15:25 PM

Page 357


♦ Daily cleaning required ♦ Indicates ring formation, limits max. production

CALIBRATION:

grate cooler:

SPAN:

minimum:

0%

=

0mbar

=

4.0mA

maximum:

100%

=

10.0mbar

=

20.0mA

1%

=

0.1mbar

=

0.16mA

=

2-4mbar

unit: typical value: planetary cooler:

SPAN:

minimum:

0%

=

0mbar

=

4.0mA

maximum:

100%

=

10mbar

=

20.0mA

=

3-7mbar

typical value:

EXAMPLE 3: PREHEATER EXIST PRESSURE LOCATION: Figure 15:


6/23/2001 - 5:15:25 PM

Page 358


♦ Please note, that this pressure may be different from the ID-fan inlet pressure because of the resistance in the tubes. Typical value:

5mbar i.e. 5mbar pressure difference from preheater top to ID-fan (at bottom, difference in height : 100 m)

CALIBRATION:

grate cooler:

SPAN:

minimum:

0%

=

0mbar

=

4.0mA

maximum:

100%

=

10.0mbar

=

20.0mA

1%

=

1mbar

=

0.16mA

=

40-60mbar


Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER / 4.2 Examples / 4.2.3 Speed

4.2.3

Speed

EXAMPLE:

DC-DRIVE KILN

LOCATION: ♦ DC-Drive . Usually the transmitter is in the as well.

CALIBRATION: ♦ By a hand-tachometer (analogous or digital) on the kiln motor or motor coupling. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:26 PM

Page 359


SPAN:

minimum:

0%

=

0rpm

=

4.0mA

maximum:

100%

=

1500rpm

=

20.0mA

1%

=

15rpm

=

0.16mA

85%

=

1275rpm

=

17.6mA (16:100x85+4)


Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER / 4.2 Examples / 4.2.4 Current

4.2.4

Current

EXAMPLE:

KILN DRIVE CURRENT

LOCATION: ♦ DC-Drive . Usually the transmitter is in the as well.

CALIBRATION: ♦ By the Amp-meter on the DC-drive while measuring in the 4...20mA line.

SPAN:

minimum:

0%

=

0A

=

4.0mA

maximum:

100%

=

1000A

=

20.0mA

1%

=

10A

=

0.16mA

30%

=

300A

=

4.8mA (16:100x30+4)


IMPORTANT: ♦ The kiln amps are used to indicate the torque (and with the torque the: •

coating falling

•

hot or cold clinker) If the field current is not kept constant by a thyristor controlled unit, the kiln drive amps have to be multiplied by the field current.

♦ The value has to be filtered in case of a planetary cooler, but in a way that ring breaks still can be ed ♦ Span must be 100% nominal motor current Process Technology / B06 - PT III / C05 - High Level Control / Field Preparation for High Level Control / 4. EXAMPLES OF MOST IMPORTANT INPUTS IN RESPECT OF THE LOCATION AND CALIBRATION OF THE TRANSMITTER / 4.2 Examples / 4.2.5 Power/Energy


6/23/2001 - 5:15:26 PM

Page 360


Power/Energy

EXAMPLE:

POWER OF MILL DRIVE

LOCATION: ♦ Medium-voltage Switchgear.

CALIBRATION: ♦ Calibration is usually not necessary. For checking the value, it can be calculated: voltage (phase to phase) x current x 1.732 (square root of 3) x power factor (cosø, see motor data, typical 0.97).

RANGE:

minimum:

0%

=

0kW

=

4.0mA

maximum:

100%

=

2000kW

=

20.0mA

1%

=

20kW

=

0.16mA

98%

=

1960kW

=

19.68mA (16:100x98+4)



6/23/2001 - 5:15:27 PM

Page 361

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C06 - Practical Work

C06 - Practical Work


6/23/2001 - 5:15:27 PM

Page 362

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work

Control Technique - Practical Work

1. THE CONTROL LOOP 2. DYNAMIC BEHAVIOR OF THE PROCESS 2.1 Proportional Factor of the Process 2.2 Dead Time Element 2.3 Delay Element 2.4 Combinations 3. CONTROLLERS 3.1 Different Types of Controllers 3.2 PID - Controller 3.3 Analog and Digital Controller 3.4 Terminology 4. HOW TO TURN THE KNOBS - OPTIMAL SETTINGS OF THE CONTROLLER 4.1 Stabilization Point 4.2 Adjustments of the PID Settings 4.3 Optimal Settings of the Controller


6/23/2001 - 5:15:27 PM

Page 363


SUMMARY Lack of manpower, quality requirements and complicated processes have increased the importance of control to industry. This lecture gives an introduction into the basic control theory and its use. Because of the variety of today’s control techniques, applications are purposely omitted. Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 1. THE CONTROL LOOP

1.

THE CONTROL LOOP

The functioning and the components of a control loop are explained by the example of cooling tower control loop. Figure 1

Cooling tower control loop

1) Process: The Cooling Tower The process consist of those machines and equipment which are controlled to produce a desired output. 2) Process Inputs and Outputs For example: Process inputs: flowrate hot gas temperature hot gas flowrate cooling water Process outputs: flowrate cooled gas temperature cooled gas 3) Controlled Output (c): Outlet Gas Temperature The purpose of the cooling tower control is to achieve a constant outlet gas temperature. Variations of the other process outputs are of no importance. 4) Disturbances: Variations in Flowrate and Temperature of the hot Gas Variations of the process inputs cause disturbances to the process and therefore also to the process outputs, especially to the controlled output. 5) Manipulated Variable (m): Cooling Water Flowrate The cooling of the gas stream is achieved by spraying water into it. The degree of the cooling depends on the amount of water sprayed. Therefore, the outlet gas temperature can be controlled © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:27 PM

Page 364

"Holderbank" - Cement Course 2000 by manipulating the cooling water flowrate. 6) Set point (s): Desired Outlet Gas Temperature The level at which the controlled output shall be kept has to be defined. This reference input or setpoint can either come from an operator or from an other control system. 7) Elements (h): Thermocouple The process output you want to control has to be measured because you cannot control what you don’t know. The elements are always measuring devices. 8) Actual Value (x): Temperature Signal The signal which is delivered by the elements 9) Error (e): Deviation between measured Gas Temperature and the desired Temperature The actual value is compared with the setpoint (desired value). The controller will react according to the deviation of these two signals. Depending on the process it has to be selected between forward and reverse action: Forward Action: If the actual value is below the setpoint an increase of the controller output is required and vice versa. Example: If the temperature in a kiln is too low the fuel has to be increased to heat up the kiln. Reverse Action If the actual value is below the setpoint a decrease of the controller output is required and vice versa. Example: If the temperature after a cooling tower is too low, the flowrate of the cooling water has to be reduced to increase the temperature. The switching between the two actions can simply be done by calculating the error either by subtracting the actual value (x) form the setpoint (s) (forward action) or by subtracting the setpoint (s) from the actual value (reverse action). 10) Control Elements (g1) According to the error, the control elements act upon the manipulated variable. Two main elements: •

Controller: The controller is a device which generates the appropriate control signal according to the error (e) (see also the chapter “Controller”).

•

Actuator: The actuator transforms the controller output (y) into a change of the manipulated variable. In our example: A control value which acts upon the cooling water flow.

11) The commonly used expressions introduced above are summarized in the figure below: Figure 2

Cooling tower control loop

12) Block Diagram © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:27 PM

Page 365

"Holderbank" - Cement Course 2000 Every closed loop control system can be represented with the same diagram. Figure 3

Block disgram of control loop

Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 2. DYNAMIC BEHAVIOR OF THE PROCESS

2.

DYNAMIC BEHAVIOR OF THE PROCESS

Depending on the nature of the process the output response to an input change or a disturbance varies. The most important tool to characterize the dynamic behavior of a process is the “transient responses”: the reaction of the process to a step-change of the input. Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 2. DYNAMIC BEHAVIOR OF THE PROCESS / 2.1 Proportional Factor of the Process

2.1

Proportional Factor of the Process

The proportional factor describes how big the change of the output is caused by a one-unit change of the process input: Proportional factors of the process = B / A Figure 4

Proportional factor of the process

Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 2. DYNAMIC BEHAVIOR OF THE PROCESS / 2.2 Dead Time Element

2.2

Dead Time Element


6/23/2001 - 5:15:28 PM

Page 366

"Holderbank" - Cement Course 2000 Most processes require a finite response time, often with a magnitude of minutes or hours. The dead time is defined as the difference in time between an input change and the resulting output change. The dead time slows down controller response because the controller cannot act until an error in output is detected. An example for a typical dead time element is a belt conveyor. The dead time is given by the length and the speed of the belt. Figure 5

Dead time

The cooling tower as an example contains multiple dead time elements which can be added together: ♦ reaction time of the control value ♦ time the change in the water flow rate needs to reach the spraying nozzles ♦ time the gases need to the height of the cooling tower ♦ reaction time of the thermo-couple Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 2. DYNAMIC BEHAVIOR OF THE PROCESS / 2.3 Delay Element

2.3

Delay Element

The reaction of a process to an input change is depending on the physical and chemical reactions controlling this process: heat transfer, mass transfer, chemical reactions. As all these reactions do not just happen within no time but follow certain time laws, the whole process shows certain time delays. These time delays can be classified in different types. Example: First order element, second order element. The most frequent is the second order delay. Figure 6

Delay time


6/23/2001 - 5:15:28 PM

Page 367


The delay in the cooling tower system is the time between the first noticeable change in the outlet gas temperature and the moment when the new stable temperature is reached. Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 2. DYNAMIC BEHAVIOR OF THE PROCESS / 2.4 Combinations

2.4

Combinations

In most of the cases the process is a combination of a dead time and a delay element (second order). Figure 7

Dead time plus delay time

Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 3. CONTROLLERS

3.

CONTROLLERS

As mentioned before the controller is a device which generates according to the deviation between desired and actual value an appropriate control signal to bring this deviation to zero. Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 3. CONTROLLERS / 3.1 Different Types of Controllers

3.1

Different Types of Controllers

1) On-Off Controller The controller output can only have two positions;: fully open and fully closed. The controlled variable is controlled within a band. When the variable falls below the lower limit of the band, the controller output changes to “open”. The variable starts to rise again. When the upper limit of the © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:29 PM

Page 368

"Holderbank" - Cement Course 2000 band is reached, the controller output changes back to “closed”. The variable starts to fall again. Example: Temperature control of a refrigerator. 2) Continuous controller (PID-controller) The output can have any position between open and closed. 3) Adaptive controller The controller adapts automatically its parameters to changing process characteristics. It has to be differentiated between controllers which adapt themselves continuously and controllers that adapt only when this is desired. 4) Predictive Controller The predictive controller uses a mathematical model to predict the behavior of the controlled process. With this information the controller can optimize the control actions. Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 3. CONTROLLERS / 3.2 PID Controller

3.2

PID - Controller

The most frequently used controller is the PID-Controller. The total control action is a combination of three basic control actions: 1) P- Controller (proportional controller) The output of the proportional controller is the error (e) multiplied by a constant factor. This factor is called the proportional constant or the proportional gain. Figure 8

Proportional Controller

The control algorithm: y = Kp ⋅ e Kp: Proportional constant Characteristic Features: ♦ Increasing Kp causes stronger control actions and thus a faster return to the setpoint. But with increasing Kp the tendency of the system to cycle increases (see figure 9). ♦ Off-set: the P- controller is adjusted to work for one specific load of the controlled system (in the cooling tower example: one specific flowrate of the hot inlet gas). If the load changes, a permanent error.


6/23/2001 - 5:15:29 PM

Page 369


2) I-Controller (integral or reset Controller) As long as a deviation between setpoint and actual value exists, the I-controller sums the deviation up with time and produces an output proportional to this sum. Figure 10

Integral controller

The control algorithm: y = KI ⋅ ∫ edt KI:

integral constant or integral gain KI can be expressed with the proportional constant KI = Kp/TI

Kp:

proportional constant

T I:

integral action time - Time after which the output of the I-controller is equal the output of a P-controller (for a step).

Characteristic Features: ♦ As a permanent error leads to a continuously increasing control signal, an I-controller is very suitable to eliminate an off-set. ♦ With increasing KI increasing tendency to oscillate 3) D-Controller (differential, derivative or rate controller) The D-controller produces an output which is proportional to the rate of change of the deviation © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:29 PM

Page 370

"Holderbank" - Cement Course 2000 between setpoint and actual value. The D-controller weights the speed of a disturbance. Figure 11:

D-Controller

The control algorithm: Y = KD ⋅ de/dt KD:

derivative constant or derivative gain. KD can be expressed with the proportional constant KD = Kp ⋅ TD

Kp:

proportional constant

TD:

derivative action time. Time after which the output of the D-controller is equal to the output of a P-controller (for a ramp).

Characteristic Features: ♦ D-controller reacts earlier because it detects slope errors which occur before real errors. ♦ A D-controller cannot be used alone. It is used in combination with P or PI controller actions. ♦ As the D-controller reacts to slopes, it can be unstable for highly oscillatory systems. 4) PID - Controller The three basic control actions can be used alone (whit the exception of the D-controller) or as combinations like PI-Controller, PD-controller, PID-controller. In this case the total control action is the sum of the different basic control actions which means the controllers are arranged in parallel. Example: PID - Controller (three mode controller) Figure 12

PID Controller


6/23/2001 - 5:15:30 PM

Page 371

"Holderbank" - Cement Course 2000 The control algorithm when using the parameters Kp, KI, KD: y = Kp ⋅ e + KI ⋅ ∫ edt + KD ⋅ de/dt The control algorithm when using the parameters Kp, TI, TD: y = Kp ⋅ e + ( Kp / TI ) ⋅ ∫ edt + Kp ⋅ TD ⋅ de/dt Figure 13

Comparison of the different controllers

Which controller to choose depends on the plant behavior. Below you will find some guidelines on how to choose a controller for a given plant. In a cement plant a lot of controllers are just PI - controllers because many of the processes which have to be controlled are relatively slow and thus a derivative control action (D - controller) is not necessary Table 1

Guidelines how to choose a controller

Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 3. CONTROLLERS / 3.3 Analog and Digital Controller

3.3

Analog and Digital Controller

A PID - Controller can be realized as an analog or as a digital controller. a) Analog Controller © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:30 PM

Page 372

"Holderbank" - Cement Course 2000 The control loop is closed all the time. The control operations are executed at every point of the time scale. The control algorithms are realized on the hardware side with appropriate circuits. This means: the more sophisticated the control algorithms the bigger the hardware. Figure 14 Analog Controller

b) Digital Controller ♦ The control loop is only closed at certain sampling points. The different arithmetical operations of the control algorithm are not executed simultaneously but one after the other. ♦ The control algorithms are realized on the software side. Figure 15

Digital Controller

Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 3. CONTROLLERS / 3.4 Terminology

3.4

Terminology

Sometimes it can be very confusing that in the control technique a lot of different terminologies are used. Some of the used are listed below. We recommend strongly to stick to the used in the other chapters of this paper.

Kp Controller

Kp

KI *e +

Kp/TI

KD *∫edt +

KpTD

* de/dt

output = © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:30 PM

Page 373

"Holderbank" - Cement Course 2000 output = 100/PB

(100/PB)*(R/M)

(100/PB)*RT

Kp

=

100 / PB

proportional gain or proportional constant

PB

=

Xp

proportional band

KI

=

Kp / TI

integral gain or integral constant

1 / TI

=

R/M

reset gain or reset rate

R/M

reset per minute

TI

integral action time

KD

=

KpTD = (100/PB) *RT

derivative gain or derivative constant

TD

=

RT

derivative action time or rate time or rate gain

Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 4. HOW TO TURN THE KNOBS OPTIMAL SETTINGS OF THE CONTROLLER

4.

HOW TO TURN THE KNOBS - OPTIMAL SETTINGS OF THE CONTROLLER

Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 4. HOW TO TURN THE KNOBS OPTIMAL SETTINGS OF THE CONTROLLER / 4.1 Stabilization Point

4.1

Stabilization Point

Two possibilities to interrupt the process: ♦ changing the setpoint ♦ disturbing the process According to settings of the PID parameters Kp, TI, TD the reaction of the control system to such an interaction varies: Figure 16

Changing the setpoint


6/23/2001 - 5:15:31 PM

Page 374


Figure 17

Disturbing

Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 4. HOW TO TURN THE KNOBS OPTIMAL SETTINGS OF THE CONTROLLER / 4.2 Adjustments of the PID Settings

4.2

Adjustments of the PID Settings

the list and the figure below shall give you a better feeling about what happens if you change one of the PID parameters Kp, TI, TD.

Adjustment

Reaction

Increasing P action

Increasing Kp

Speeding up control action: - smaller amplitude, - smaller period of oscillation Decreasing offset Increasing tendency to oscillate

Decreasing P action

Decreasing Kp

Slowing down control action: - bigger amplitude - bigger period of oscillation Increasing offset Decreasing tendency to oscillate


6/23/2001 - 5:15:31 PM

Page 375

"Holderbank" - Cement Course 2000 Decreasing tendency to oscillate Increasing I action

Decreasing TI

Bigger amplitude Smaller period of oscillation Faster elimination of the offset Increasing tendency to oscillate

Decreasing I action

Increasing TI

Smaller amplitude Bigger period of oscillation Slower elimination of the off-set Increasing tendency to oscillate

Increasing D action

Increasing TD

Smaller amplitude Bigger Period First degreasing but beyond a certain point increasing tendency to oscillate

Decreasing D action

Decreasing TD

Bigger amplitude Smaller period First increasing, beyond a certain point decreasing tendency to oscillate

Adjustment of the PID Settings Kp

Adjustment of the PID Settings Ti

Adjustment of the PID Settings Td © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:32 PM

Page 376


Process Technology / B06 - PT III / C06 - Practical Work / Control Technique - Practical Work / 4. HOW TO TURN THE KNOBS OPTIMAL SETTINGS OF THE CONTROLLER / 4.3 Optimal Settings of the Controller

4.3

Optimal Settings of the Controller

Chien-Hrones Method The optimal controller settings are determined from the reaction curve of the opened control loop to a step disturbance. This method is also called ♦ process reaction curve method ♦ lag reaction rate method 1) open the loop (switch controller to manual) 2) create a step on the controller output signal Figure 18

Step in control element position

3) record the answer of the process to this step Figure 19

Process reaction curve


6/23/2001 - 5:15:32 PM

Page 377


4) determine the following expressions: Td: Dead time [min] Ts: Time constant [min] N: Slope = reaction rate in % of signal range per minute [%min]

C D*100 N= TS ∆P: % change in control element position [%]

A ∆p= *100 B 5) Optimal settings (rough estimation)

Output = Kpe+

Kp de edt +Kp * TD * ∫ TI dt

∆p N*Td

P-Controller

Kp

=

PI-Controller

Kp

=

TI

=

Kp

=

TI

=

2 * Td

TD

=

0.5 * Td

PID-Controller

0.92*

∆p N*Td

3.3 * Td

1.2*

∆p N*Td

Example: Cooling tower control loop

A step is made in the position of the cooling water control value from 60 % to 50 %. The measured outlet gas temperature signal shows the following picture (the range of the temperature signal is from © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:32 PM

Page 378

"Holderbank" - Cement Course 2000 100 °C to 300 ° C): Figure 20

Figure 21

Td = 5 min. Ts = 4 min.

180−150 * 100 300−100 N= =3.75% / min . 4 50−60 ∆p= *100 =10% 100 Optimal Settings for PID-Controller Kp

=

1.2*∆p N*Td

=

1.2*10 3.75*5

=

0.64%/%

TI

=

2 * Td

=

2*5

=

10 min.

TD

=

0.5 * Td

=

0.5 * 5

=

2.5 min.


6/23/2001 - 5:15:33 PM

Page 379



6/23/2001 - 5:15:33 PM

Page 380

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C06 - Practical Work / PRACTICAL EXERCISE - Fuzzy-Control

PRACTICAL EXERCISE - Fuzzy-Control F. Fehr 98/6346/E 1. INTRODUCTION 2. EXERCISE 2.1 Start / Set-up 2.2 Input/output Fuzzyfication 2.3 Implementing rules 2.4 Testing 2.5 Save 3. MISCELLANEOUS


6/23/2001 - 5:15:34 PM

Page 381

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C06 - Practical Work / PRACTICAL EXERCISE - Fuzzy-Control / 1. INTRODUCTION

1.

INTRODUCTION

This is an approach to teach the Fuzzy theories in a practical way, without a lot of paper and formulas. On behalf of a Siemens Demo Software, a Fuzzy controller will be shown and worked out empirically. The goal of this exercise is to get a basic idea about What is Fuzzy-Control How does it work There is a diskette included for every participant. Please take this diskette home as an example that you can recall anytime, whenever you are in a position to work with fuzzy-logic or explain to someone else what fuzzy is really about. The task of this exercise is: To set-up a temperature controller which uses a room and an outside temperature signal thus actuating a heater and an air-conditioner.

Room Temperature

Controller

Outside Temperature


Heater

Air Conditioner

6/23/2001 - 5:15:34 PM

Page 382

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C06 - Practical Work / PRACTICAL EXERCISE - Fuzzy-Control / 2. EXERCISE

2.

EXERCISE

Process Technology / B06 - PT III / C06 - Practical Work / PRACTICAL EXERCISE - Fuzzy-Control / 2. EXERCISE / 2.1 Start / Set-up

2.1

Start / Set-up

♦ Start Fuzzy.exe ♦ Create new Project with the name "TEMPCON" ("File" "New...") with 2 Inputs and 2 Outputs. ♦ Assign names to inputs and outputs (see pictures in 1. Introduction) ♦ Define 3 temperature ranges (hip functions) for room temp (e.g. chilli, comfortable, warm). ♦ Define 3 temperature ranges for outside temp (e.g. cold, warm, hot). ♦ Define 4 ranges for the heater (e.g. off, low, high, on) and 3 ranges for the air conditioner (e.g. off, med, on). ♦ Adjust the temperature scale to reasonable values (e.g. room temp. from 10…30°C). Process Technology / B06 - PT III / C06 - Practical Work / PRACTICAL EXERCISE - Fuzzy-Control / 2. EXERCISE / 2.2 Input/output Fuzzyfication

2.2

Input/output Fuzzyfication

Perform the Fuzzyfication of the 2 inputs and 2 outputs by asking the following questions and set the curves accordingly: … where is 0% cold… … from where to where is 100% warm… Out of 100 people, how many people would say that is chilli (first curve) at what temperature. Do the same for the other 2 curves. The number of people (in %) which is actually the degree of fulfilment (or the percentage of truth) is on the vertical axis, the temperature on the horizontal axis. On the example in the next picture below, it is 50% chilli (50 out of 100 people would call it chilli) at 20.5°C and after 22°C it is not chilly anymore.


6/23/2001 - 5:15:34 PM

Page 383

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C06 - Practical Work / PRACTICAL EXERCISE - Fuzzy-Control / 2. EXERCISE / 2.3 Implementing rules

2.3

Implementing rules

Now fill in the rules in "If…then".

Process Technology / B06 - PT III / C06 - Practical Work / PRACTICAL EXERCISE - Fuzzy-Control / 2. EXERCISE / 2.4 Testing

2.4

Testing

Use the menu "View" to simulate input values as constants or curves (sub menu "Curve Parameters…") and test the controller (sub menu "Curve Recorder"). Process Technology / B06 - PT III / C06 - Practical Work / PRACTICAL EXERCISE - Fuzzy-Control / 2. EXERCISE / 2.5 Save

2.5

Save

Save your project (“File” “Save” or “File” “Save As…”). For those who could not work through the exercise, there is an example of this exercise on the diskette, named exercise.txt. Rename it to *.fpl to be able to call it from the demo software. Process Technology / B06 - PT III / C06 - Practical Work / PRACTICAL EXERCISE - Fuzzy-Control / 3. MISCELLANEOUS

3.

MISCELLANEOUS

On the Cement Course CD-Rom, the directory \MISC\FUZZY contains all files and information being used for the practical work of fuzzy control logic described in the chapters above. Below a list of all files of the directory \MISC\FUZZY Files

Description

FUZZY.EXE

program file for the Fuzzy demo

FUZZY.ICO

icon for the above file


6/23/2001 - 5:15:35 PM

Page 384

"Holderbank" - Cement Course 2000 REE.TXT

supplementary supplier information about the fuzzy package

SHUTTERS.FPL

example "shutters controller"

PENDULUM.FPL

example "inverse pendulum"

EXERCISE.TXT

example "temperature control"

S7FUZ1EF.PPT

Power Point slides about the fuzzy package


6/23/2001 - 5:15:35 PM

Page 385

"Holderbank" - Cement Course 2000 Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work

Gas Flow Measurement - Practical Work H. Nyfenegger PT 97/14231/E 1. THEORETICAL BASIS 1.1 The Law of Bernoulli 2. LOCAL VELOCITY AND PRESSURE MEASUREMENTS 2.1 The Measurement of the Pressures 3. GAS FLOW MEASUREMENT BY THE PRANDTL TUBE 4. INTEGRAL GAS FLOW MEASUREMENT WITH NOZZLES AND ORIFICES 4.1 Standard Nozzles 4.2 Standard Orifices and Venturi-Nozzles 5. CALCULATION OF DENSITY 5.1 Requests, Calculation of Real Conditions 5.2 Gas Compositions 5.2.1

Calculation of a Heterogeneous Gas

6. PRACTICAL WORK IN GAS FLOW MEASUREMENT 6.1 Test Equipment 6.2 The Prandtl Tube 6.2.1

Calculation of the Gas Density

6.2.2

Numerical Calculation of Density

6.3 Calculation of the Gas Velocity 6.4 Calculation of the Gas Flow Rate 6.5 Anemometers 6.5.1

Type A (Vane Wheel Anemometers)

6.5.2

Type B Thermal Anemometers

6.5.3

Vortex Anemometers (not used in practical work)

6.6 Characteristic Curves of the Fan 6.6.1

Measurements

6.7 INLET NOZZLE 6.8 Manometers


6/23/2001 - 5:15:35 PM

Page 386


Inclined Stationary Manometer

7. SYMBOL LIST OF GAS FLOW MEASUREMENT


6/23/2001 - 5:15:35 PM

Page 387

"Holderbank" - Cement Course 2000 SUMMARY This paper shows the basic equations for gas flow measurement. Furthermore, the principles of gas flow measurement by the Prandtl tube as well as the Orifices and Nozzles are explained. Some of the presented principles and instruments will be used for the practical work carried out on a test equipment in the laboratory hall. Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 1. THEORETICAL BASIS

1.

THEORETICAL BASIS

Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 1. THEORETICAL BASIS / 1.1 The Law of Bernoulli

1.1

The Law of Bernoulli

(Daniel Bernoulli, 1700..1782 Swiss Scientist)

In aeronautics, a law or theorem state that in a flow of incompressible fluid the sum of the static pressure and the dynamic pressure along a streamline is constant if gravity and frictional effects are disregarded. Resultant from this law is that if there is a velocity increase in a fluid flow, there must be a corresponding pressure decrease. Thus an airfoil, by increasing the velocity of the flow over its upper surface, drives lift from the decreased pressure. As originally formulated, a statement of the energy conservation (per unit mass) for a non-viscous fluid in steady motion. The specific energy is composed of the kinetic energy v2/2, where v is the speed of the fluid; the potential energy gz, where g is the acceleration of gravity and z is the height above an arbitrary reference level; and the work done by the pressure forces of a compressible fluid ∫ v dp, where p is the pressure, v is the specific volume, and the integration is always with respect to value of p and v on the same parcel. Thus, the relationship v2/2 + gz + ∫ v dp = constant along a streamline is valid for a compressible fluid in steady motion, since the streamline is also in path. If the motion is irrational, the same constant holds for the entire fluid.

If the fluid is compressible © Holderbank Management & Consulting, 2000 Query:

If the fluid is incompressible:

6/23/2001 - 5:15:36 PM

Page 388


m& 1 =m& 2 ρ 1 ⋅ V&1 = ρ 2 ⋅ V&2

ρ 1= ρ 2 V& =V&

ρ 1 ⋅ A1 ⋅ w 1= ρ 2 ⋅ A2 ⋅ w 2

A1 ⋅ w 1 = A 2 ⋅ w 2

1

2

If the fluid is incompressible, that means ρ is constant:

ρ 1= ρ 2 = ρ 2

P1 w 1 P 2 w 2 + = + ρ 2 ρ 2

2

Symbols and units:

A

Cross section area

[m2]

d

Diameter of the smallest aperture

[m]

D

Diameter of the tube

[m]

m

Cross section area ratio m = d2 / D2

[-]

m⋅

Mass flow rate

[kg/s]

p

Pressure

N / m2]

∇

Volume flow rate

[m3 / s]

w

Velocity

[m / s]

ρ

Density

[kg / m3]

Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 2. LOCAL VELOCITY AND PRESSURE MEASUREMENTS

2.

LOCAL VELOCITY AND PRESSURE MEASUREMENTS


6/23/2001 - 5:15:36 PM

Page 389


The above figure shows a fluid flowing around an obstacle. One of the streamlines reaches the body at the point 2, called stagnation point. At this point the velocity of the fluid is zero. The Bernoulli equation, for the undisturbed flow at point 1 to point 2, 2

P1 w 1 P2 w 2 + = + 2 2 ρ ρ where P2 P1

ρ 2 w1 2

p2, p1 and

ρ 2

2

or (w2 = 0)

P2 =P1 +

ρ 2 w1 2

is the total pressure is the static pressure is the dynamic pressure

w 2 are pressures called total, static and dynamic pressure.

Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 2. LOCAL VELOCITY AND PRESSURE MEASUREMENTS / 2.1 The Measurement of the Pressures

2.1

The Measurement of the Pressures

The total pressure of a fluid can be measured at a stagnation point. For this purpose the so-called Pitot tube is used.

At the point 2 a stagnation point is created where the total pressure can be measured. A boring placed vertically to the flow (1) measures the pressure independent from the direction. This © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:37 PM

Page 390

"Holderbank" - Cement Course 2000 pressure is called static pressure. Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 3. GAS FLOW MEASUREMENT BY THE PRANDTL TUBE

3.

GAS FLOW MEASUREMENT BY THE PRANDTL TUBE

The dynamic pressure, defined as

ρ • w12 2 can be expressed as the pressure difference between the total and the static pressure. The relation is

p 2 − p1=

ρ 2 w1 2

This difference is measured with the Prandtl Tube.

The inner part of this instrument corresponds exactly to a Pitot Tube and the total pressure is measured there. The outer part has the function of the static pressure measurement. The difference between the two connections is the dynamic pressure. The direction of the flow should correspond to the axis of the Prandtl Tube. Deviations until ± 10° however, do not essentially influence the measuring accuracy. The error in the measurement of the pressure is below ± 1%.

With the dynamic pressure the fluid velocity can be calculated as follows:


6/23/2001 - 5:15:37 PM

Page 391


w 1=

2 ⋅ (P2 − P1 ) ρ

The Prandtl Tube measures a local velocity only. In order to get an integral velocity (e.g. the average value) the integration of several local velocities over the cross sectional area must be made.

w=

1 w ⋅ dA A ∫∫ A

The gas flow rate is finally calculated by multiplying the average gas velocity with the cross sectional area. Specific information on the gas flow measurement by the Prandtl Tube is given in chapter 6 "Practical work in gas flow measurement“. Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 4. INTEGRAL GAS FLOW MEASUREMENT WITH NOZZLES AND ORIFICES

4.

INTEGRAL GAS FLOW MEASUREMENT WITH NOZZLES AND ORIFICES

The idea of this method is to create a change of cross section of the whole fluid stream. By means of this change also the pressure and the velocity change and from the pressure difference the velocity can be calculated. A precondition for this measurement method is a more or less equalized velocity profile. Disturbances like ♦ Flow separation behind bends, valves, etc. ♦ Pulsation behind a piston type compressor ♦ High dust loading ♦ etc. falsify the measurement and make it useless in a lot of cases. As a rule of thumb it can be said that prior to such a flow measurement a straight tube length of more than 10 tube diameters is to be provided.


6/23/2001 - 5:15:38 PM

Page 392


Between point 1 and 2 the continuity condition can be formulated as A1 ⋅ w1 = A2 ⋅ w2 Between the same two points the Bernoulli equation (see 1.1) gives: 2

p1 w 1 p 2 w 2 + = + ρ 2 ρ 2

2

From the two relations the following equation is derived:

w 1=

2 ⋅ (P1 − P2 )  A  2  ρ ⋅  1  − 1  A2  

The velocity w1 can be calculated from the pressure difference between the undisturbed flow (point 1) and the accelerated flow in the smallest cross-sectional area. The pressure p2 is lower than pressure p1 and compared to the pressure p1, is p2 a negative pressure. The relation is 2   ρ 2  A1  (P1 − P2 )= W1   − 1 2  A2  

The pressure difference is a function of the ratio square of the cross sectional area. Great ratios produce therefore extreme underpressures! An example of such a great ratio is the reduction of the cross-sectional area during coating formation in preheaters. The change of the cross-section causes, especially when it is done suddenly, a disturbance of the flow. The fluid cannot follow the wall and a contraction of the stream is produced.


6/23/2001 - 5:15:38 PM

Page 393


The effective cross section Ae is now smaller than the real one and the calculated velocity must be corrected. The correction cannot be calculated, it must be measured. For this reason several types of integral measuring instruments are standardized by DIN 1952. In the following the 3 basic standard instruments are sketched: Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 4. INTEGRAL GAS FLOW MEASUREMENT WITH NOZZLES AND ORIFICES / 4.1 Standard Nozzles

4.1

Standard Nozzles

Standard nozzles are used for tubes with diameters from 50 to 500 mm and a cross-sectional ratio (smallest area against tube area) of 0.1 to 0.64.

The velocity in the tube and the volume flow, respectively, are calculated by the following relation:

w =α ⋅ ε ⋅ m ⋅

2 ⋅ ∆p ρ1

π 2 ⋅ ∆p V& =α ⋅ ε ⋅ m ⋅ ⋅ D 2 ⋅ 4 ρ1 The factor ε considers the change in the density of a compressible fluid. For incompressible fluids (e.g. water or air until a maximum velocity of 100 [m/s]) this factor has the value 1, otherwise it is tabulated © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:39 PM

Page 394

"Holderbank" - Cement Course 2000 in the DIN - Standards 1952. The value α is the correction factor for the contraction of the fluid. It is a function of the Reynold’s number and the ratio m of the cross-sectional areas. This factor is also tabulated in the DIN Standards 1952. The table below shows an output of these standards. Correction factors for the contraction α = f (m2, Re) for standard nozzles in tubes with smooth surfaces, valid for diameters D between 50 and 500 mm. Between the indicated values of m2 (not m) can be interpolated linearly.

Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 4. INTEGRAL GAS FLOW MEASUREMENT WITH NOZZLES AND ORIFICES / 4.2 Standard Orifices and Venturi-Nozzles

4.2

Standard Orifices and Venturi-Nozzles

Orifices and Venturi-nozzles are standardized in the same way as above-mentioned standard nozzles. The following figure shows the two standard orifices distinguished only in the pressure taps.

The following figure shows the two used Venturi nozzles distinguished only in the length of the diff part. © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:39 PM

Page 395


Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 5. CALCULATION OF DENSITY

5.

CALCULATION OF DENSITY

Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 5. CALCULATION OF DENSITY / 5.1 Requests, Calculation of Real Conditions

5.1

Requests, Calculation of Real Conditions

The methods based on the law of Bernoulli needs the knowledge of the density ρ of gas. For simple gases like dry air this request makes normally no problem. In case of kiln gases e.g. the density must be evaluated or approximated to the real condition.

 N  p 0 =760 [Torr ]=760 [mm Hg ]=1 . 01325 *10 5  2 or [ Pa ] m  T 0 = 273 . 16 [°K ]=0 [°C ]  N  1[mm Hg ]≅133 . 322  2 or [ Pa ] m  In case of air and in function of the relative humidity ϕ is almost invariant: Table 1 ϕ [%]

ρo [kg/m3]

100 80 60

1.290 1.290 1.291

Thus, the actual gas density ρG can be found with the following correlation:

ρG =ρ0

T 0 ⋅p G 273 . 16 ⋅ ρ G = 1 . 29 T G ⋅p 0 T G ⋅1 . 01325 ⋅10 where pG =


5

actual static gas pressure [N/m2] 6/23/2001 - 5:15:40 PM

Page 396

"Holderbank" - Cement Course 2000 TG = actual gas temperature [K] PG can be measured by adding the differential pressure between tube and the ambient to the barometric pressure. Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 5. CALCULATION OF DENSITY / 5.2 Gas Compositions

5.2

Gas Compositions

Mainly in the field of kiln, the gas compositions can be very different so that their density must be determining. The greatest influences to the density come from the components carbondioxide (CO2) and water content (H2O, humidity). Often both components are unknown and can’t be measured easily, so that the depend from approximations. Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 5. CALCULATION OF DENSITY / 5.2 Gas Compositions / 5.2.1 Calculation of a Heterogeneous Gas

5.2.1

Calculation of a Heterogeneous Gas

Density of dry gas composition: ρndr Component

Content [%]

Factor

Unit

CO2

1.977

[kg/m3,N, dr.]

O2

1.429

[kg/m3,N, dr.]

CO

1.25

[kg/m3,N, dr.]

N2

1.257

[kg/m3,N, dr.]

ρ ndr =

[kg/m3,N, dr.]

Σ 1.000

Density of wet gas composition:

ρnw= Where

Part of

W0 =

ρndr + W 0 1+fdr

Water content [kg/m3 n,dry] fdr =

W0 0.804

[m3/m3 n,dry]

Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 6. PRACTICAL WORK IN GAS FLOW MEASUREMENT

6.

PRACTICAL WORK IN GAS FLOW MEASUREMENT

Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 6. PRACTICAL WORK IN GAS FLOW MEASUREMENT / 6.1 Test Equipment

6.1

Test Equipment

The measurement of the velocity profile and the volume flow is shown on a special test equipment which is sketched in the following figure.


6/23/2001 - 5:15:40 PM

Page 397


The following measuring methods are demonstrated and applied: 1) Prandtl Tube: The velocity will be measured on several points of the cross sectional area by means of which the average velocity and the volume rate will be calculated. 2) Anemometers: At the outlet of the test equipment the mean velocity will be measured with two different anemometers. 3) Fan Characteristics: With the knowledge of the characteristic curves of the fan given by the supplier, the volume rate is determined by the pressure difference of the fan and the revolutions of the fan. 4) Inlet Nozzle (Piezometer): At the suction side of the fan an inlet nozzle is attached. This nozzle is calibrated and the volume rate can be calculated by means of the pressure difference between the nozzle inlet and ambient. Process Technology / B06 - PT III / C06 - Practical Work / Gas Flow Measurement - Practical Work / 6. PRACTICAL WORK IN GAS FLOW MEASUREMENT / 6.2 The Prandtl Tube

6.2

The Prandtl Tube

Prandtl tubes are mainly used for speed measurements of gaseous mediums. The application of a Prandtl tube is suitable for following measurements: ♦ Higher Temperatures (Until 500°C, depending of construction materials) ♦ Few dust loaded gas flows (approx. 50 g/m3 max.) ♦ Only for higher gas velocities (approx. 10 m/s min.) ♦ The density of the medium must be known The Prandtl tube itself is a very simple and cheap measuring instrument. Because the measuring is selectively for an integral gas flow measurement several measuring points must be measured. Therefore, the time consumption for the measurement itself and the evaluation is considerable. Most application in cement industry for Prandtl tubes are: ♦ Air output of grate coolers ♦ Riser ducts © Holderbank Management & Consulting, 2000 Query:

6/23/2001 - 5:15:41 PM

Page 398

"Holderbank" - Cement Course 2000 ♦ Tertiary air ducts ♦ etc. Generally, the application of Prandtl tubes are indicated when other instruments e.g. anemometers as a result of high temperatures or other reasons cannot be used. If a Prandtl tube is put into a flowing medium, the following pressures are produced:

The total pressure Ptot acts on the ball-shaped measuring head, composed of the static pressure Pstat and the dynamic pressure. The Bernoulli-equation formulated from the point 0 (ambient point) to the point 1 (pressure point) states:

ρG ⋅w 2 = p tot total pressure 2 ↑ ↑ dynamic pressure static pressure p stat +

(1)

The flow speed is only influenced by the dynamic pressure:

w =

⋅(p

2

tot

−p

stat

) (2)

G

Its value is obtained from the difference of the total pressure Ptot and the static pressure Pstat read on a differential pressure gauge.


6/23/2001 - 5:15:41 PM

Page 399

Cement Industry Process Technology - Holderbank Course (3 Of 3) 225u32

Overview 26281t

More details 6y5l6z

Related Documents 3h463d

Cement Industry Process Technology - Holderbank Course (3 Of 3) 225u32

Cement Industry Process Technology - Holderbank Course (2 Of 3) 6l2t66

Holderbank Cement Seminar 12e52

Cement Industry 5t2y34

Cement Types-3.ppt 4ts2g

Pest Analysis Of Cement Industry 392r1u

More Documents from "Nael" 1i7b

Formulas Kiln i1b5b

Cement Industry Process Technology - Holderbank Course (3 Of 3) 225u32

Monolithic Refractory Lining (calderys) 3j2w

Rotary Kiln - Refractory Lining Installation 1u4b66

Cement Industry Process Technology - Holderbank Course (2 Of 3) 6l2t66