1. What is the main purpose for a blending of coal?
a) To produce more amount of coal
b) To produce good quality of coal
c) To decrease the cost of coal
d) To produce different types of coal at same time
Explanation: The process to mix different types of coal at the same time to increase the efficiency of coal is called blending of coal. This is due to the fact that different types of coal are produced during the coal processing
2. Which of the following is a disadvantage of storing coal for a long period of time?
a) Increase in the friability of coal
b) Decrease in its ignition temperature
c) Increase in its calorific value
d) Increase in the proportion of fine
Explanation: When the coal is stored for a long period of time, it leads to slow oxidation which causes deterioration of the coal. This process causes an increase in the proportion of fine which are not easy to cure. Also the oxidation of coal can lead to its spontaneous combustion.
3. How do the chances of spontaneous combustion of coal can decrease?
a) Decrease in the maturity of coal
b) By washing the coal time to time
c) Increase in the maturity of coal
d) By the reducing the quantity of coal
Explanation: The coal of high maturity (anthracite) contains less impurities due to which it does not gets oxidise easily, also the volatile matter present in them is less. Washing of coal can cause an increase in moisture content due to which the coal produced will not be of good quality.
4. 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.
5. 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
6. In which state does the pulverised coal burns?
a) Gaseous
b) Liquid
c) Solid
d) Colloidal
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.
7. 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.
8. The rate of combustion cannot be easily controlled in combustion of pulverised coal.
a) True
b) False
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.
9. 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.
10. 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.