Question

What are effect of fines on coal combustion and how to overcome it?

Answer 1

Proper coal sizing is one of the measures to ensure effective combustion of coal. Proper coal sizing helps in even burning, reduces ash losses and gives better combustion efficiency.

But the fines present in coal sample creates problems in combustion on account of segregation effect. Coal conditioning with water helps to a greater extent to reduce the segregation of fines from larger coal pieces. Due to present of water, fine particles stick to the bigger lumps. This prevents the fines from falling through the grate bars or from being carried away by the furnace draft. Therefore, while crushing the coal lumps, care should be taken that the moisture addition is uniform.

If the percentage of fines in the coal sample is very high, wetting of coal can decrease the amount of unburnt carbon and excess air is required for combustion. Extent of wetting the coal sample depends on the percentage of fines present in the coal as given below.

Fines(%) Moisture(%)

10-15 4 - 5

15-20 5 - 6

20-25 6 - 7

25-30 7 - 8

In case of coal having excessive fines, the predominantly lumped coal can be blend with the coal having excessive fines. Thus coal blending may also helps to limit the extent of coal fines in coal being fired, but not to more than 25%.