Question

What is the purpose of secondary fan’s air in under feed system?

(a) To support gases coming out of fuel bed

(b) To clear the ash from the upper beds

(c) To maintain constant pressure in system

(d) To support combustion of system

This question was posed to me in unit test.

This intriguing question originated from Principle of Stoker in chapter Steam Power Plant of Energy Engineering

Answer 1

The correct option is (a) To support gases coming out of fuel bed

The explanation: The gases coming out of raw fuel bed pass through a region of incandescent ash on the surface of the fuel and finally discharged to the furnace. As the gases coming out of fuel bed also contain combustible matter the supply of secondary air is required in this case. The ash left at the bottom of the stoker is at a higher temperature than the over feed stoker.