AMIE Study Circle

The minimum amount of air which supplies the requisite amount of oxygen for complete combustion of fuel is called theoretical or stoichiometric air . The reaction is, however , not likely to proceed to completion if the fuel is supplied just with stoichiometric air. The objective of complete combustion is achieved by supplying excess air ; excess air means the amount of air supplied in excess to that theoretically needed to burn fuel completely. The quantity of excess air depends on the type of fuel and the method of combustion used and may vary from 25 to 100 percent. 

Chimney height and Draught head (i) h w = 353[(1/T a ) - {(1/T g )(m a + 1)/m a }] mm of water. (ii) h w = P/(ρ a - ρ g ) Assuming that the same draught is produced by gas column of height H 1 H 1 = H[{(T g /T a ) - 1}x {m a /(m a + 1)}] Here T a = absolute temperature of atmosphere T g = Average absolute temperature of chimney gas h w = equivalent mm of water head m a = mass of air H = height of chimney Condition for Maximum Discharge through a Chimney H 1,max = H WhatsApp channel " BOE Adda " Example A chimney is 28 m high and the temperature of hot gases inside the chimney is 320°C. The temperature of outside air is 23°C and furnace is supplied with 15 kg of coal burnt. Calculate the following: (i) Draught in millimetre of water (ii) Draught head in metres of hot gases Solution (i) h w = 353[(1/T a ) - {(1/T g )(m a + 1)/m a }] = 353 x 28 [(1/298) - {(1/593)(15 + 1)/15}] = 15.61 mm of water (ii) H 1 = H[{(T g /T a ) - 1}x {m a /(m a + 1)}] = 28[{(593...

A fuel generally has the number of constituents. Some constituents react exothermally and thereby generate heat, and some others do not react chemically at all. The heat generated due to combustion of a unit mass of solid (or liquid) fuel is called its calorific value and is expressed in terms of kJ/kg. For gaseous fuels, the calorific value is expressed as heat liberated by combustion of unit cubic metre of gas at standard temperature and pressure (15 0 C and 760 mm of mercury).