Exersise-3
3) In a continuous heating furnace 750 kg/hr coal is burnt with 3% moisture and the following ultimate analysis (dry basis); C 77%, H 7%, O 4%, N 1%, S 2% and ash  In normal operation, the Orsat analysis of products of combustion (POC) is  and  . The operator has opened the furnace door for charging. He closes the door and operates the furnace with the same firing rate and burner adjustment as was in the normal operation He does again Orsat analysis of POC. The Orsat analysis now is  and 80.3% N2. He is surprised to see change in Orsat analysis.
The operator wants an explanation both qualitatively and quantitatively.
SOLUTION:
Explanation : The operator has neither changed the firing rate nor adjusted the burner. When the door was opened, atmospheric air is leaked into the combustion chamber and CO of POC was combusted. This has resulted in change in POC. We have to calculate excess air
Basis of calculation is 1 kg / hr.
Performing Carbon balance we get amount of  moles for normal operation.
Again we perform carbon balance when the door was opened. Now we get amount of  moles.
Amount of air leakage for combustion of 750 kg/hr coal=23m3/min
Calculations on excess air has been done in problem 1 and 2.
Percen excess air = 21.46%
For further problems refer
A. Butts: Metallurgical problems
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