Question 21 : A fuel containing carbon and carbon monoxide (but containing no hydrogen or its compounds) is burnt in pure oxygen at constant pressure. Its gross calorific value as compared to net calorific value will be
1. less
2. more
3. same
4. data insufficient; can't be predicted.
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Question 22 : Softening temperature of coal ash is a measure of the __________ of coal.
1. caking tendency
2. coking tendency
3. clinkering tendency
4. size stability
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Question 23 : Dry air required to burn 1 kg of carbon completely may be around __________ kg.
1. 2
2. 11
3. 38
4. 20
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Question 24 : Pick out the wrong statement.
1. Regulation of furnace temperature and atmosphere (oxidising or reducing) is easily possible with pulverised fuel firing.
2. none of these.
3. Low grade coal can be used, but generally high volatile matter coals are more suitable for making pulverised fuel.
4. Pulverised fuel can be completely burnt with less percentage of excess air compared to lump coal.
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Question 25 : Temperature of preheated air used for the transportation of pulverised coal through pipes to the burner of a boiler furnace is restricted to a maximum limit of about 300° C to avoid the
1. risk of explosion.
2. requirement of large volume combustion chamber.
3. incomplete combustion of coal.
4. chances of clinker formation.
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Question 26 : Pensky-Marten apparatus is used for those oils, whose flash points are __________ °F.
1. 90-110
2. <120
3. <90
4. >120
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Question 27 : For every 10% increase in the excess air; the fuel consumption increases by __________ percent.
1. 0.1
2. 10
3. 2
4. 5
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Question 28 : The temperature at which plastic layer formation takes place during carbonisation of coal varies from __________ °C.
1. 700 to 850
2. 550 to 650
3. 100 to 150
4. 350 to 450
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Question 29 : Presence of free moisture in coal during its high temperature carbonisation
1. increases the loss of fine coal dust from the ovens when charging.
2. protects the volatile products from pyrolysis (cracking) in the presence of hot coke and hot oven walls.
3. reduces the coking time.
4. none of these.
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Question 30 : Fuel gases containing hydrocarbons (ie.g. coke oven gas) are not preheated before burning, mainly because
1. it reduces its calorific value tremendously.
2. the hydrocarbons crack thereby choking and fouling the heat transfer surface by carbon soot.
3. there are chances of explosion during preheating.
4. it reduces its flame temperature tremendously.
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