Fuels and Combustion

141.During combustion of coal on grate, clinker formation is increased by the

1. Use of thick fire bed
2. Low fusion point of ash (< 1100° C)
3. Use of preheated primary air
4. All (A), (B) & (C)

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142.During combustion of gaseous fuels, deficiency of air

1. Lengthens the flame
2. Tends to shorten the flame
3. Does not affect the flame length
4. Increases the flame temperature

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143.During its calorific value determination by bomb calorimeter, coal is combusted by

1. Air
2. Oxygen
3. Oxygen enriched air
4. None of these

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144.During the carbonisation of coal

1. All tar is evolved at < 600°C
2. Evolution of H₂ and formation of methane and aromatics occur at > 700°C
3. Hard semi-coke starts shrinking at 600°C
4. All (A), (B) and (C)

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145.Dust content in raw blast furnace gas is about _________ gm/Nm³; hence it is cleaned to the dust level of about < 10 mg /Nm³ before use.

1. 15-30
2. 43862
3. 70-100
4. 150-200

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146.Efficiency of the combustion of a fuel is judged by the _________ the flue gas.

1. % of CO₂ in
2. % of O₂in
3. Temperature of
4. Colour of

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147.Efficient burning of anthracite coal requires

1. Low preheat of air
2. Fine grinding
3. High excess air
4. All (A), (B) and (C)

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148.Emission of dense white smoke out of the chimney of a thermal power plant is an indication of the use of

1. Less air for combustion
2. Correct amount of air for combustion
3. Too much air for combustion
4. Pulverised coal in boilers

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149.Eschka mixture, which is used for the determination of sulphur in coal, is a mixture of

1. MgO & Na2CO3
2. MgSO4 & BaCl2
3. BaSO4 & NaCl
4. MgCO3 & NaCl

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150.Explosion limit of blast furnace gas is 37 to 71% gas in gas-air mixture. It means that the blast furnace gas will explode when burnt in a confined space, if its concentration in the gas-air mixture is _________ percent.

1. < 37%
2. > 71%
3. In between 37 & 71%
4. None of these

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