Steam Power Plant Ppt r1r4i

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Criteria In general, both the construction and operation of a power plant requires the existence of some conditions such as water resources and stable soil type. Still there are other criteria that although not required for the power plant, yet should be considered because they will be affected by either the construction or operation of the plants such as population centers and protected areas. The following list corers most of the factors that should be studied and considered in selection of proper sites for power plant construction: Transportation network: Easy and enough access to transportation network is required in both power plant construction and operation periods. Power transmission network: To transfer the generated electricity to the consumers, the plant should be connected to electrical transmission system Therefore the nearness to the electric network can play a roll. Geology and soil type: The power plant should be built in an area with soil and rock layers that could stand the weight and vibrations of the power plant. Earthquake and geological faults: Even weak and small earthquakes can damage many parts of a power plant intensively. Therefore the site should be away enough from the faults and previous earthquake areas Topography: It is proved that high elevation has a negative effect on production efficiency of gas turbines. In addition, changing of a sloping area into a flat site for the construction of the power plant needs extra budget. Therefore, the parameters of elevation and slope should be considered.

Rivers and floodways: obviously, the power plant should have a reasonable distance from permanent and seasonal rivers and floodways. Water resources: For the construction and operating of power plant different volumes of water are required. This could be supplied from either rivers or underground water resources. Therefore having enough water supplies in defined vicinity can be a factor in the selection of the site. Environmental resources: Operation of a power plant has important impacts on environment. Therefore, priority will be given to the locations that are far enough from national parks, wildlife, protected areas, etc. Population centers: For the same reasons as above, the site should have an enough distance from population centers. Need for power: In general, the site should be near the areas that there is more need for generation capacity, to decrease the amount of power loss and transmission expenses. Climate: Parameters such as temperature, humidity, wind direction and speed affect the productivity of a power plant and always should be taken into . Land cover: Some land cover types such as forests, orchard, agricultural land, pasture are sensitive to the pollutions caused by a power plant. The effect of the power plant on such land cover types surrounding it should be counted for. Area size: Before any other consideration, the minimum area size required for the construction of power plant should be defined.> Distance from airports: Usually, a power plant has high towers and chimneys and large volumes of gas. Consequently for security reasons, they should be away from airports. Archeological and historical sites: Usually historical building …are fragile and at same time very valuable. Therefore the vibration caused by power plant can damage them, and a defined distance should be considered.

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1. A furnace to burn the fuel. 2. Steam generator or boiler containing water. Heat generated in the furnace is utilized to con- vert water in steam. 3. Main power unit such as an engine or turbine to use the heat energy of steam and perform work. 4. Piping system to convey steam and water. In addition to the above equipment the plant requires various auxiliaries and accessories depending upon the availability of water, fuel and the service for which the plant is intended. The flow sheet of a thermal power plant consists of the following four main circuits : Feed water and steam flow circuit (ii) Coal and ash circuit (iii) Air and gas circuit (iv) Cooling water circuit. A steam power plant using steam as working substance works basically on Rankine cycle. Steam is generated in a boiler, expanded in the prime mover and condensed in the condenser and fed into the boiler again. The different types of systems and components used in steam power plant are as follows : (i) High pressure boiler (ii) Prime mover (iii) Condensers and cooling towers (iv) Coal handling system (v) Ash and dust handling system (vi) Draught system (vii) Feed water purification plant (viii) Pumping system (ix) Air preheater, economizer, super heater, feed heaters.

Underfeed stoker

Pulverised coal firing is done by two system : (i) Unit System or Direct System. (ii) Bin or Central System. Unit System. In this system the raw coal from the coal bunker drops on to the feeder. Hot air is ed through coal in the feeder to dry the coal. The coal is then transferred to the pulverising mill where it is pulverised. Primary air is supplied to the mill, by the fan. The mixture of pulverised coal and primary air then flows to burner where secondary air is added. The unit system is so called from the fact that each burner or a burner group and pulveriser constitute a unit. Advantages (i) The system is simple and cheaper than the central system. (ii) There is direct control of combustion from the pulverising mill. (iii) Coal transportation system is simple.

Bin or Central System. It is shown in Fig. Crushed coal from the raw coal bunker is fed by gravity to a dryer where hot air is ed through the coal to dry it. The dryer may use waste flue gases, preheated air or bleeder steam as drying agent. The dry coal is then transferred to the pulverising mill. The pulverised coal obtained is transferred to the pulverised coal bunker (bin). The transporting air is separated from the coal in the cyclone separator. The primary air is mixed with the coal at the feeder and the mixture is supplied to the burner. Advantages l. The pulverising mill grinds the coal at a steady rate irrespective of boiler feed. 2. There is always some coal in reserve. Thus any occasional breakdown in the coal supply will not effect the coal feed to the burner. 3. For a given boiler capacity pulverising mill of small capacity will be required as compared to unit system. Disadvantages 1. The initial cost of the system is high. 2. Coal transportation system is quite complicated. 3. The system requires more space.

A large quantity of ash is, produced in steam power plants using coal. Ash produced in about 10 to 20% of the total coal burnt in the furnace. Handling of ash is a problem because ash coming out of the furnace is too hot, it is dusty and irritating to handle and is accompanied by some poisonous gases. It is desirable to quench the ash before handling due to following reasons: 1. Quenching reduces the temperature of ash. 2. It reduces the corrosive action of ash. 3. Ash forms clinkers by fusing in large lumps and by quenching clinkers will disintegrate. 4. Quenching reduces the dust accompanying the ash. Handling of ash includes its removal from the furnace, loading on the conveyors and delivered to the fill from where it can be disposed off.

ASH HANDLING EQUIPMENT Mechanical means are required for the disposal of ash. The handling equipment should perform the following functions: (1) Capital investment, operating and maintenance charges of the equipment should be low. (2) It should be able to handle large quantities of ash. (3) Clinkers, soot, dust etc. create troubles, the equipment should be able to handle them smoothly. (4) The equipment used should remove the ash from the furnace, load it to the conveying system to deliver the ash to a dumping site or storage and finally it should have means to dispose of the stored ash. (5) The equipment should be corrosion and wear resistant.

The size of dust particles is designated in microns (1 μ = 0.001 mm). Dust particles are mainly ash particles called fly ash intermixed with some quantity of carbon ash material called cinders. Gas borne particles larger than 1μ in diameter are called dust and when such particles become greater in size than 100µ they are called cinders. Smoke is produced due to the incomplete combustion of fuels, smoke particles are less than 10µ in size.

The disposal smoke to the atmosphere is not desirable due to the following reasons : 1. A smoky atmosphere is less healthful than smoke free air. 2. Smoke is produced due to incomplete combustion of coal. This will create a big economic loss due to loss of heating value of coal. 3. In a smoky atmosphere lower standards of cleanliness are prevalent. Buildings, clothings, furniture etc. becomes dirty due to smoke. Smoke corrodes the metals and darkens the paints. To avoid smoke nuisance the coal should be completely burnt in the furnace.

The various types of dust collectors are as follows : 1. Mechanical dust collectors. 2. Electrical dust collectors. Mechanical dust collectors. Mechanical dust collectors are sub-divided into wet and dry types. In wet type collectors also known as scrubbers water sprays are used to wash dust from the air. The basic principles of mechanical dust collectors are shown in Fig. As shown in Fig. by increasing the cross-sectional area of duct through which dust laden gases are ing, the velocity of gases is reduced and causes heavier dust particles to fall down. Changing the direction of flow of flue gases causes the heavier particles of settle out. Sometime baffles are provided as to separate the heavier particles. Mechanical dust collectors may be wet type or dry type. Wet type dust collectors called scrub scrubbers make use of water sprays to wash the Drygases. type dust collectors include gravitational, cyclone, and baffle dust collectors. dust from flue

Electrostatic Precipitators. It has two sets of electrodes, insulated from each other that maintain an electrostatic field between them at high voltage. The flue gases are made to between these two sets of electrodes. The electric field ionises the dust particle; that through it attracting them to the electrode of opposite charge. The other electrode is maintained at a negative potential of 30,000 to 60,000 volts. The dust particles are removed from the collecting electrode by rapping the electrode periodically. The electrostatic precipitator is costly but has low maintenance cost and is frequently employed with pulverised coal fired power stations for its effectiveness on very fine ash particles and is superior to that of any other type.

4.13.1 FLY ASH SCRUBBER It is similar to a mechanical ash collector but has a flowing water film on its inner walls. Due to this film, the collected ash is removed more rapidly from the apparatus to the bin. The degree of ash collection in scrubbers varies from 0.82 to 0.90. The dust laden gas enters through the inlet pipe. Cinder Catcher. Cinder catcher is used to remove dust and cinders from the gas. In this catcher the dust laden gas is made to strike a series of vertical baffles that change its direction and reduce its velocity. The separated dust and cinders fall to the Hopper for removal. Cinder catchers are ordinarily used with stoker firing.