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

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

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Fuels and Combustion
Sometimes water is sprayed during coal charging in the coke oven, which helps in

Reducing the cracking of hydrocarbons in the gas and increasing the percentage of CO & H₂ in the gas (due to the endothermic reaction represented by C + H₂O = CO + H₂)
Controlling the dust nuisance while charging the coal
Prevention of clinker formation in the oven
All of these

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

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
It is abrasive to the coal pulveriser (ie.g. ball mill) and the combustion chamber
All of these

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Fuels and Combustion
A carbonaceous fuel (containing no H₂ or hydrocarbons) is burnt and the resulting flue gas contains 21% CO₂. It means that

21% excess oxygen has been used for combustion
Complete combustion of fuel has taken place
21% excess air has been used for combustion
No excess air has been used for combustion

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