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Basis of calculation is 298K and 1 kg coal

By carbon balance, the amount of POC is 0.486 kg mol with the following composition

Heat to POC can now be calculated by using Cp values. The calculated value of heat to POC is 22063kJ.

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. 

Now assume that the heat exchanger is  not used. Coal is burned with a mixture of cold air and oxygen. Excess of oxygen (air + pure oxygen combined) over theoretical for combustion will be kept same as with preheater. Calculate the amount of oxygen required in kg/hr to obtain the same fuel consumption as obtained with the heat exchanger

Pre-heater adds sensible heat into furnace. When pre-heater is not used, nitrogen of air must be reduced so that heat taken out by nitrogen equal to 9833 kJ.

Let Y kg mol oxygen is required, this corresponds to 3.76Y of nitrogen

This problem illustrates the method of reduction of fuel by adopting technologies like preheating of air and oxygen enrichment of air. Both the technologies are in use to reduce the fuel consumption in industrial practice. Which technology suits has to be evaluated locally keeping in view the available resources and expertise.