Power Plant Control Ppt 734h26

Power Plant Dynamics and Control

Power Plant Dynamics & Control

Prof. Dr. Amitava Gupta

Power Plant Dynamics and Control

A plant in general

disturbances

control inputs

Dynamic System or Plant

outputs to be controlled

measurements

Power Plant Dynamics and Control

A typical control loop and its dynamics

PID Step

1 0.036s2+0.022s+1

PID Controller

Scope Transfer Fcn

Power Plant Dynamics and Control

Power Plant Dynamics and Control

Power Plant Dynamics and Control

Root Locus 15 0.02

0.0135

0.0095

0.0065 0.0042 0.002

14 12

10

Imaginary Axis

5

0.032

0.06

0

-5

10 8

System: sys_pl Gain: 2.1 Pole: -0.306 + 9.27i Damping: 0.0329 System: sys_pl Overshoot (%): 90.2 Gain: 0.000901 Frequency Pole: -0.306(rad/sec): + 5.26i 9.28 Damping: 0.0579 Overshoot (%): 83.3 Frequency (rad/sec): 5.27

6 4 2

2 4

0.06

6 8

-10

10

0.032

12 0.02 -15 -0.35

-0.3

0.0135 -0.25

-0.2

0.0095 -0.15

Real Axis

0.0065 0.0042 0.002 -0.1

-0.05

14 0

Power Plant Dynamics and Control

Root Locus

6

6 0.64

0.5

0.38

0.28

0.17

0.08

0.8

4

4

Imaginary Axis

5

System: sys_ol Gain: 0.573 0.94 2 Pole: -5.99 Damping: 1 Overshoot (%): 0 Frequency (rad/sec): 5.99 0

System: sys_ol Gain: 1 Pole: -1.32 + 0.657i Damping: 0.895 Overshoot (%): 0.184 Frequency (rad/sec): 1.47

3 2 1

1 -2 0.94

2 3

-4

4

0.8 0.64 -6 -6

-5

0.5 -4

0.38 -3

Real Axis

0.28 -2

0.17 -1

0.08

5 60

Power Plant Dynamics and Control

Bode Diagram Gm = Inf dB (at Inf rad/sec) , Pm = 9.4 deg (at 7.43 rad/sec)

Magnitude (dB)

20

0

-20

-40

-60 0

Phase (deg)

-45 -90 -135 -180 -1

10

0

1

10

10 Frequency (rad/sec)

2

10

Power Plant Dynamics and Control

Bode Diagram Gm = Inf , Pm = 88.8 deg (at 21.3 rad/sec) 30

Magnitude (dB)

20 10 0 -10 -20 90

Phase (deg)

45 0 -45 -90 -135 -1

10

0

1

10

10 Frequency (rad/sec)

2

10

Power Plant Dynamics and Control

Desirable properties of a controller

Should track input (zero steady-state error) Should have enough stability robustness: gain and phase margins should be  comfortable Robustness to variations of gain: performance robustness Robustness to high frequency noise Good output disturbance rejection

Power Plant Dynamics and Control

Power generation as a process

4 4

2

3

t

5

2

3

1 6 5 1

s 6

Power Plant Dynamics and Control

Process control of power generation process Change prime-mover input Maintain this pressure

Change generation to match demand

Maintain this temperature

Maintain this level

Power Plant Dynamics and Control

Process control of power generation process: in simplest

Power Plant Dynamics and Control

Modulating control loops in a thermal power plant

Load demand control Firing rate control Air and fuel flow control Secondary air-flow control Drum-level control Furnace draft control

Superheater steam temperature control

Power Plant Dynamics and Control

Load demand control: Boiler following turbine

Governor valve opens/closes based on steam demand.

PT Boiler Boiler firing rate demand, Air and fuel demand,

Pressure drop sensed by transmitter

Master control signal actuates related loops

Power Plant Dynamics and Control

Load demand control: Turbine following boiler

Steam pressure sensed by the transmitter controls pressure at the first stage

PT

Boiler Boiler firing rate demand, Air and fuel demand,

Demand signal

Set boilers fuel, air and feed-water flow based on demand

Power Plant Dynamics and Control

Load demand control: Sliding Pressure mode

PT Boiler Boiler firing rate demand, Air and fuel demand, MW

Demand for steam is corrected by powerfrequency signal

f

f(x)

Power Plant Dynamics and Control

Load demand control: Co-ordinated control mode Demand signal

Co-ordinated Control

PT

FT

Boiler Boiler firing rate demand, Air and fuel demand,

MW

Power Plant Dynamics and Control

Air and fuel-flow control: Requirements

Control the heat supplied to the boiler by controlling the flow of fuel and air. The ratio of fuel and air is maintained so that incomplete burning due to excess fuel or excessive losses due to excess oxygen do not occur. Problems due to excess fuel: Increased pollution Production of poisonous Carbon Monoxide Dangerous collection of unburnt fuel in the furnace Problems due to excess oxygen: Total loss Heat losses Chimney loss

Unburnt loss Excess Oxygen

Power Plant Dynamics and Control

Air and fuel-flow control: Requirements contd..

When demand increases, air-flow must increase first followed by increase in fuel flow. When demand decreases, fuel-flow must decrease first followed by decrease in air-flow

Power Plant Dynamics and Control

Air and fuel-flow control: A ratio controlled loop

Power Plant Dynamics and Control

Air and fuel-flow control: A simple scheme for an oil-fired boiler PT

PIC

Steam pressure sensed by transmitter

Controller compares it with steam pressure corresponding to demand Setpoints of fuel flow and air flow controllers altered

If more flow is required, valve opens, else closes if less flow is required

Oil flow control valve

Damper is adjusted accordingly to maintain air-fuel ratio

Air flow damper

Power Plant Dynamics and Control

Inadequacies of the simple scheme

The response of the fuel control loop is much faster than the response of the air-flow control loop. As a result, increase in load shall cause momentary increase in fuel compared to air leading to black smoke and increased CO content. Similarly, decrease in load will lead to an Oxygen rich mixture.

Power Plant Dynamics and Control

The remedy: Cross-linked scheme for an oil-fired boiler Oil flow

FT

PT

Air flow

Steam pressure

PIC

H

FT

Airflow increases

χ

Setpoint raised

H

+ve

<

0 This signal now increases

+ve 0

>

+ve raise setpoint

PIC 0, no change in setpoint +ve signal, setpoint raised, valve opens till FT o/p matches setpoint

Oil flow control valve

PIC Damper opens till FT o/p matches setpoint

Air flow damper

Power Plant Dynamics and Control

Air-fuel flow control for a pulverizer Air-flow demand

FC

FC

X

Raw coal feed

DPT

Set mill load-line

DPT

Coal Feeder

Coal and air to burners

Hot air

Mill

TT Tempering air

f(x) FC

Power Plant Dynamics and Control

General schematic of mill control Set mill loadline

Mill diff

PA diff

PA temp

DPT

DPT

TT

Fuel-oil pressure

PT

Number of Burners alight

f(x)

Gain compensation (no. of mills in service)

X

X

Oil flow per burner

f(x)

H/A

Temperature Compensation of PA differential f(x) Pressure signal Coal equivalent of oil burning at this group

PID Mill H/A

H/A Feeder speed controller

Master Demand

H/A

Oil burning At this group

f(x)

X

<

To other Mill groups

TT Minimum PA Flow limit Coal flow demand

PID

PID

H/A

H/A Tempering Air damper actuator

Mill outlet temperature

Power Plant Dynamics and Control

Furnace draught control Furnace pressure PT

PT

PT

PT +

+ Desired furnace pressure Bias

PIC

-

H/A

H/A

CD

CD

+

f(x)

Furnace pressure cut-back (Progressively reduces FP set point if pressure approaches safety limit for the furnace design)

Induced-draught fan vanes

Power Plant Dynamics and Control

Control of air flow: Parallel Operation of FD Fans

FT

FT

+

FC

CD

Fan A

CD Fan B

Power Plant Dynamics and Control

Control of air flow: Operation of FD Fans with single controllers

FT

FT

Demanded air flow

FC

FC

CD

CD

Fan A

Fan B

Power Plant Dynamics and Control

Drum-level control: Single element control steam

LT

LC

Feed-water

Power Plant Dynamics and Control

Drum-level control: Two element control steam

FT 2

LT

LC

1

FC

Feed-water

Power Plant Dynamics and Control

Drum-level control: Three element control steam

FT 2

LT

LC

3

1

FC FT

Feed-water

Power Plant Dynamics and Control

Steam temperature control

Primary super-heater

secondary super-heater

TT

TT

1

TC TC

Power Plant Dynamics and Control

Steam temperature control

Primary super-heater

secondary super-heater

2

1

TC

TC

G2(s)

G1(s)

TT

TT

1

TC 2

TC

Δho(s)/ Δhi(s) secondary super-heater

Δho(s)/ Δma(s) primary super-heater

Power Plant Dynamics and Control

Dynamics of steam temperature control loop explained

Power Plant Dynamics and Control

Dynamics of steam temperature control loop explained

Power Plant Dynamics and Control

Dynamics of steam temperature control loop explained

mi  m0  ma  V

d (0 ) dt

mi hi  m0 h0  ma ha  Qmf  V Q gm  Qmf  M

d (  0 h0 ) dt

d (Tm ) dt

m g (hgi  hgo )  Qgm  Vg  g

d (hgo ) dt

p 0  p i  f .mo2 Qmf   mwa(Tm  0.5 f (h0 , p0 )  0.5 f (hi pi ))

Qgm   gmca(0.5

hgi C pg

 0.5

hgo C pg

 Tm )

Time constants of each transfer function 0 V is ss

moss

Power Plant Dynamics and Control

Dynamics of steam temperature control loop explained SL. No.

Parameter

Value

1

V

0.102 m3

2

Vg

35.04 m3

3

M

380.3 kg

4

a

11.8

m2

5

o

1000

kg/m3

6

g

0.67

kg/m3

7

f

35.96

8



0.47 kJ/kg.K

9

g

1.41 kJ/kg.K

10

ms

140.0 W/m2.K

11

gmc

30.0 W/m2.K

Power Plant Dynamics and Control

Auxiliary control loops

The typical auxiliary control loops are the following: Closed cycle cooling water system Feedwater heater level control

De-aerator storage tank and hotwell level control Boiler feed-pump recirculation control Controls associated with air heater

Power Plant Dynamics and Control

Control using digital hardware Programmable Logic Controllers Typically for on-off controls mainly those which are not affected by change of plant operating conditions. Distributed Control Systems Boiler controls, including the combustion (firing rate) furnace draft, steam temperature and feed-water control loops. Burner control and pulverizer control Control loops in the plant auxiliary systems that need to be monitored and/or operated the main control room. Data acquisition and reporting functions

Power Plant Dynamics and Control

Model predictive control

Usually employs an estimation algorithm for correction of control inputs to tackle uncertainties Can be used for multi-regime operation

Example: Use of a simulator to correct the demand for steam with compensation for bled steam in co-ordinated control

Power Plant Dynamics and Control

Conclusion

Use of thermal energy is older than civilization itself- mankind mastered lighting a fire much before learning to draw or write. Harnessing thermal energy to produce electricity is as old as old man Faraday himself, but the technology for this is ever evolving and always in a nascent state.

Thank you….