Fuels and Combustion
The main function of primary air in pulverised coal fired burner is to

Preheat the tertiary air used for complete combustion of CO to CO₂
Have proper combustion by supplying it around the burner
Dry and transport the coal
Burn CO to CO₂

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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 accelerated by storage in large heaps with small surface to volume ratio
Is more for low volatile coal compared to high volatile coal
Decreases with increase in surface area

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