Coal and Ash Circuit
Water and steam circuit
Air and flue gas circuit
Cooling water circuit
COAL AND ASH CIRCUIT:
It includes coal delivery, coal handling, boiler, ash storage and ash handling. Coal arrives at the storage yard after necessary handling.
The coal is transferred to the boiler by conveyor, elevator.
The coal is burnt in the boiler and ash is formed by burning of coal.
Then ash is transferred to ash storage. Usually the ash is quenched in reduced temperature.
WATER AND STEAM CIRCUIT:
It consists of feed pump, super heater, economizer, air-preheater.
Feed water is pumped from the hot well to the economizer.
This water is preheated in the economizer by the flue gas, then the water is supplied to boiler. Heat is transferred to the water by burning of coal. Now water is converted into steam.
The superheated steam is then expanded in a turbine to do work.
The turbine drives a generator to produce electric power. The expanded (exhaust) steam is then passed through the condenser.
In the condenser, the steam is condensed into water and re-circulated.
AIR AND FLUE GAS CIRCUIT:
It consists of forced draught fan, air pre heater, boiler, super heater, economizer, and chimney.
Air is taken by forced draught fan from atmosphere and passed to air-pre-heater.
The air is preheated by flue gas in the pre-heater. Then it is passed or supplied to the boiler furnace to combust the fuel.
Due to combustion of fuel, hot gases or flue gases are formed.
Then the flue gases pass through economizer to heat the feed water.
After that, it passes through the air pre-heater to pre-heat the incoming air.
It is then passed through a dust catching device (dust collector). Finally, it is exhausted to the atmosphere through chimney.
COOLING WATER CIRCUIT:
It consists pump, condenser and cooling tower etc.,
The exhaust steam from turbine is condensed in condenser.
In the condenser, cold water is circulated to condense the steam into water.
Thus the circulating water is heated. This hot water is then taken to a cooling tower, In cooling tower, the water is sprayed in the form of droplets through nozzles.
The atmospheric air enters the cooling tower from the openings provided at the bottom of the tower. This air removes heat from water.
This cold water is again circulated through the pump, condenser and cooling tower.
Thus the cycle is repeated again and again. Some amount of water may be lost during the circulation due to vaporization etc.
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