Fuels and Combustion

201.Higher fuel combustion efficiency cannot be achieved by

1. Preheating of fuel gases & combustion air
2. Reducing sulphur content in the fuel
3. Adopting proper fuel firing technique & fuel preparation
4. Supplying correct amount of combustion air

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202.Higher percentage of ash in coal meant for the production of metallurgical grade coke

1. Decreases the hardness of coke
2. Decreases the abrasion resistance of coke
3. Causes brittleness in steel
4. None of these

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203.Highly caking coals

1. Produce weak coke
2. Produce strong coke
3. May damage the coke oven walls during carbonisation
4. Both (B) and (C)

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204.Highly reactive coke have lower

1. Porosity
2. Coke reactivity index (CRI)
3. Critical air blast (CAB) value
4. Both (B) and (C)

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205.If CO₂ is not fully absorbed by the KOH solution meant for its absorption in the orsat apparatus, it will appear as

1. O₂
2. CO
3. N₂
4. SO₂

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206.If oxygen content in the flue gas rises too high, fuel is being wasted by

1. Incomplete combustion
2. Dry gas/stack gas loss
3. Moisture loss
4. None of these

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207.If the specific heat of gaseous products of combustion of a fuel is high, the abiabatic flame temperature will be

1. Low
2. High
3. Very high, if the fuel is of low calorific value
4. None of these

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208.Ignition temperature decreases progressively from anthracite to lignite, because

1. Volatile matter content increases
2. Carbon content decreases
3. Moisture content increases
4. Ash content increases

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209.Ignition temperature of a fuel in air is _________ that in pure oxygen.

1. More than
2. Less than
3. Equal to
4. Either more or less; depends on the type of fuel

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210.Improper storage condition results in the weathering of coal and spontaneous combustion, which increases its

1. Caking index
2. Yield of carbonised products
3. Friability & oxygen content
4. Calorific value

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