This set of Engineering Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Pulverised Coal”.
1. How can we increase the rate of combustion of solid fuel?
a) By storing it in the right conditions
b) By the process of pulverisation
c) By removing the impurities present in it
d) By blending of coal
Explanation: The rate of combustion can be increased by bringing the air in contact with the fuel. The coal powder is pulverised from 75-85% below 74µm. Blending of coal produces a good quality of coal. The impurities are somewhat useful.
2. On what factors does the burning of pulverised coal depends?
a) The calorific value of fuel
b) Bulk density
c) Percentage of volatile matter
d) On the texture of coal
Explanation: Coal having high volatile matter is used for making pulverised coal. As soon as it is fired, the volatile matter starts burning which helps in increasing the rate of combustion. The degree of fitness of particles also helps in the burning of pulverised coal.
3. In which state does the pulverised coal burns?
Explanation: The air-fuel mixture of the pulverised coal is sent along with air under suitable burner which burns just like the gaseous fuel. This is because of the mixing of coal powder with air.
4. How can we transport pulverised coal?
a) Maintaining suitable conditions of temperature and pressure
b) By suitable packaging of the coal
c) With the help of air compressors
d) By forcing a stream of air
Explanation: It becomes easy to handle and transport the pulverised coal if a strong stream of air is continuously passed though the coal powder. This work can also be done by using screw conveyer to keep the pulverised coal fresh.
5. The rate of combustion cannot be easily controlled in combustion of pulverised coal.
Explanation: The combustion of pulverised coal occurs in gaseous state due to which its rate of combustion can be controlled easily. This also helps us to increase the calorific value of the coal depending on its rate of combustion.
6. The combustion process of pulverised coal is ________________
a) Non-uniform and incomplete
b) Non-Uniform and complete
c) Uniform and complete
d) Uniform and incomplete
Explanation: Pulverised coal intimately mixes with air and undergoes uniform and complete combustion. This happens because the pulverised coal is sent along with suitable burners for its combustion.
7. Which of the low grade coal is suitable for pulverising?
a) Coals containing high moisture content
b) Coals with more percentile of impurities
c) Coals with low fixed carbon rating
d) Coals containing high percentile of ash
Explanation: Ash contains many minerals, due to which when coal powder is allowed to mix with air most of its minerals form oxides and escapes out, due to which it helps in increasing the rate of combustion of coal. This process is very useful for Indian coals because they contain a lot of ash content in them.
8. Which type of burners are used for mixing of coal powder and air?
a) Turbulent burner
b) Pressure jet burner
c) Rotatory cup burner
d) Dual fuel burner
Explanation: Turbulent burner is an atomising burner which is used to mix fuel and air to produce a flow. Dual fuel burner cannot be used in this case as the physical state of both are different.
9. Which type of firing technique is employed for pulverised coal?
a) Oxidation firing
b) Reduction firing
c) Front wall firing
d) Raku firing
Explanation: The pulverised coal is burnt along the front side of the burner. It can be done in more three ways, i.e. side wall firing, U-flame firing and corner firing respectively. U-flame firing is not used so much as it produces a very long flame.
10. Which method is used for reducing fly ash?
a) Dry bottom
c) Cyclone burner
d) Corner firing
Explanation: Fly ash is the ash produced by burning the pulverised coal. 75% of fly ash is deposited around the surrounded places. When the pulverised coal is burnt is slag-tap furnace, its flame is directed towards and sweeps over the bed of molten slag where the particles of ash are caught.
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