This set of Engineering Chemistry Objective Questions & Answers focuses on “Secondary Solid Fuels – 2”.
1. At what temperature does the H2S and olefin gases are evolved in the process of carbonisation?
Explanation: In the process of carbonisation, the bituminous coal is slowly heated to remove moisture and occluded gases. Then at 270oC H2S and olefin gases are evolved. At about 450oC the liberated gases consist of hydrocarbons and at 700oC hydrogen gas is liberated.
2. What happens when coal is expanded during the plastic stage of caking?
a) Closed texture coke is obtained
b) Highly swollen open texture coke is obtained
c) There is no change in the coal
d) Coal breaks into a number of pieces
Explanation: If the coal is free to expand at plastic stage, it produces a highly swollen open texture coke produced from strongly coking coal. If this expansion is suppressed by the retaining wall, a dense coke having fine pore structure is produced.
3. Coal is a good conductor of heat and electricity.
Explanation: Coal contains maximum carbon inside it which is not a good conductor of electricity (except graphite). Coal produces a large amount of heat on its combustion but is not a conductor of heat.
4. Which of the following forms a heat barrier in the process of carbonisation?
a) Impurities present in the coal
b) Moisture present in the coal
c) Different structure of the machine
d) Thin plastic zone formed by caking coal
Explanation: The plastic zone so formed by the caking coal results in a considerable temperature gradient. There may be a drop of about 250 oC across half an inch thickness.
5. Which of the following coals have high rates of carbonisation?
a) Non-caking coal
b) Caking coal
c) Coking coal
d) Non-coking coal
Explanation: Caking coal form a plastic zone which acts as a heat barrier. Non-caking coal does not forms this plastic material due to which it has high rates of carbonisation. Coking coals are formed by caking coals.
6. In which type of plant does the carbonisation process is done?
a) Thermal power plant
b) Blast furnace process
d) Destructive distillation plant
Explanation: Coke-ovens are used for the completion of process of carbonisation. The final product obtained by carbonisation is coke. Destructive distillation plants are used to generate charcoals.
7. Which type of carbonisation method is used for obtaining particular types of by-products?
a) High temperature carbonisation
b) Medium temperature carbonisation
c) Low temperature carbonisation
d) No by-products are formed
Explanation: The temperature in this type of carbonisation varies from 700-900 oC. The yields of NH3, tar, light oils are obtained from this carbonisation. The yields of tar obtained from this process are different from the yields obtained by high temperature carbonisation.
8. What is done when the coke is too friable for use in carbonisation process?
a) It is divided into small pieces
b) Its maturity is made decreased
c) The ash content is reduced
d) It is pulverised
Explanation: By pulverising the coal, the rate of combustion of coal can be easily controlled which helps in the easy formation of coke. Coal can also be briquetted for using under friable condition.
9. How much yield of coke is produced in low temperature carbonisation?
a) 75-80 %
b) 60-70 %
c) 100 %
Explanation: The coke produced by this method is used as a domestic fuel. The coke formed contains 5 to 15 % of volatile matter and is not sufficiently strong for metallurgical processes.
10. High temperature carbonisation process is used to produce ______________
a) Brown coal
b) Gas coke
c) Coal tar
d) Coal gas
Explanation: The by-product gas produced in this process is about 370-480 m3/tonne. Gas coke is produced at the gas works of cities. The calorific value of the coke obtained is less than that of the coke obtained by low temperature carbonisation process.
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