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

All of these
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
It is abrasive to the coal pulveriser (ie.g. ball mill) and the combustion chamber
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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Fuels and Combustion
A liquid/gaseous fuel containing hydrocarbons and high amount of sulphur is burnt with 40% excess air. The flue gas still contains large amount of carbon monoxide. This may be due to the

Low calorific value of the fuel
Presence of large quantity of hydrogen in the fuel
Lack of thorough mixing of fuel with air
High sulphur content in the fuel

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Fuels and Combustion
A good metallurgical coke

Should be brittle
Should have low fusion point of its ash
Should have high porosity
Must contain moderate quantities of ash, moisture, sulphur and volatile matters

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