Fuels and Combustion
Fuel gases containing hydrocarbons (ie.g. coke oven gas) are not preheated before burning, mainly because

It reduces its calorific value tremendously
There are chances of explosion during preheating
It reduces its flame temperature tremendously
The hydrocarbons crack thereby choking and fouling the heat transfer surface by carbon soot

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Fuels and Combustion
Rate of low temperature oxidation of coal due to bad storage conditions

Does not vary with increase in surface area
Is more for low volatile coal compared to high volatile coal
Decreases with increase in surface area
Is accelerated by storage in large heaps with small surface to volume ratio

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