Question

Why is secondary air supplied in overfeed system?

(a) To burn the unburnt gases

(b) To maintain constant heat intensity

(c) To completely remove water vapors formed due to primary air supply

(d) To create distillation process for the raw coal supplied

The question was asked during an interview.

Origin of the question is Principle of Stoker in division Steam Power Plant of Energy Engineering

Answer 1

Correct answer is (a) To burn the unburnt gases

To elaborate: Additional secondary air is supplied at the top of the bed to burn the remaining combustible gases (volatile matter+CO+H2). The secondary air is supplied at very high speed to create turbulence for complete combustion of unburnt gases.