Question

Why is air pre-heater used in the boiler?

(a) To draw in the atmospheric air

(b) To increase thermal efficiency

(c) To heat the air to superheated level

(d) To heat the air in advance

This question was posed to me in an interview for internship.

I need to ask this question from Feed Water and Steam Generation System, Working of Thermal Power Plant topic in portion Steam Power Plant of Energy Engineering

Answer 1

Right option is (b) To increase thermal efficiency

The explanation: the purpose of the air preheater is to recover the heat from the boiler flue gas which increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. As a consequence the flue gases are also conveyed to the flue gas struck at a lower temperature, allowing simplified design of conveyance system and flue gas stack.