Suppose the combustion air is preheated with the heat recovered from the POC in a heat exchanger which is having 50% relative efficiency. Calculate the fuel consumption

First we have to find amount of air. In this problem note that composition of coal is not completely given. Amount of air has to be calculated from the amount of POC:

One notes that GAH increases with the addition of sensible heat in air.

Fuel saving = 580 kg/hr; if the furnace operates for 20 hrs/day then coal saving is 11140 kg/day. Carbon saving is 8127 kg/day. This saving means that now less carbon will be discharged in the environment. This illustrates that preheating of air not only save fuel but also reduces carbon emission into the environment.