Fuels and Combustion
Which of the following would require least amount of secondary air for combustion?

Anthracite containing 10% volatile matter and 8% ash
Bituminous coal containing 20% ash and 25% volatile matter
Coke breeze containing 25% ash and 2% volatile matter
Semi-bituminous coal containing 25% ash and 20% volatile matter

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Fuels and Combustion
Ratio of primary air to secondary air increases with increase in the rank of coal, because the

Calorific value of the coal increases
Oxygen content progressively decreases
High rank coals have higher amount of volatile matter
Ratio of fixed carbon to volatile matter increases

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