Fuels and Combustion
By-products recovery process from coal carbonisation is termed as direct, indirect and semi direct process depending upon the method of recovery of

Ammonia
Benzol
None of these
Tar

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

All of these
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

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