Question

How can exhaust gas be recovered in the induced draught?

(a) By installing the forced draught fan at the starting point

(b) By extending the chimney’s height

(c) By inletting high amount of air from multiple air ducts

(d) By installing air preheater and economizer along the gas path

I got this question during an online interview.

Origin of the question is Draught System topic in division Steam Generators & Accessories of Energy Engineering

Answer 1

The correct option is (d) By installing air preheater and economizer along the gas path

For explanation I would say: The heat in exhaust gases can be recovered as much as possible by installing an air preheater and economizer along the gas flow path. As the draught produced in this system is independent of flue gas temperature care should be taken such that the fan handles gas at its lowest possible temperature.