28-09-2012, 05:05 PM
E. BOILER
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A Boiler is a closed pressure vessel in which a fluid is heated for use
external to itself by direct application of heat resulting from the combustion of
fuel (solid, liquid, gaseous) or by use of electricity or nuclear energy.
A steam boiler is a closed vessel in which steam or other vapour is generated.
Fuel and ash circuit:
Fuel (coal) from the storage is fed to the boiler through fuel feeding device known as coal handling plant (chp).Ash is produced as a result of combustion of coal at the back of boiler and is removed to ash storage through ash handling equipment.
Air and flue gas circuit:
Air from the atmosphere is supplied to the combustion chamber of the boiler through the action of force draught (F.D.) fan and/or induced draught (I.D.) fan .The air before being supplied to the boiler passes through the air preheater where it is heated by the heat of flue gases which are then made to pass to the chimney. The flue gases first passes around the boiler tubes and super heater tubes
and then from the outlet of the combustion chamber the flue gas passes successively through the evaporator tube bank, baffle type dust collector (BDC), mechanical cyclone dust collector (MDC), economizer, electrostatic precipitating unit, induced draft fan to the chimney. (Finally exhausted to the atmosphere).
Feedwater and steam circuit:
The water first comes from the DM plant and then passes through the economizer.
A small part of the steam and water (around 1%) in passing through the
different components lost. Therefore water is added in a feed water system as makeup water.
In the boiler drum and tubes water circulates because of difference in
density in the lower and higher temperature sections of the boiler. Wet steam from the drum is further heated in the super heater before it is supplied to the prime mover.
In the boiler steam pressure is set to 24.6kg/〖"cm" 〗^"2" and the temparature of the combustion chamber is set to 343°C.