Fuels and Combustion
Which of the following is not increased by using preheated combustion air in place of ordinary air at room temperature?

Speed of combustion of fuel
Calorific value of the fuel
Flame temperature achieved
Heat transfer rate to the stock in the furnace

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Fuels and Combustion
A coal with high ash content is undesirable, as

It is abrasive to the coal pulveriser (ie.g. ball mill) and the combustion chamber
The ash in molten condition gets absorbed in the pores of the refractory lining of the furnace and causes its spalling due to different co-efficient of expansion/contraction of the refractory and the
The ash retains the sulphur & phosphorus and thus affects the quality of products in metallurgical furnace apart from increasing the slag volume. Besides, it may fuse and stick to the boiler tubes
All of these

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