This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Gaseous Pollutants – Control of Sulphur Dioxide Emissions”.
1. By how much can coal washing can remove pyritic sulphur content?
a) 20%
b) 30%
c) 40%
d) 50%
View Answer
Explanation: The inorganic sulphur present in coal is in pyrites, marcasites, sulphide form, et cetera. The washing of coal is simple and results in the reduction of sulphur content by 30%. However, it may also result in the loss of combustible material.
2. What is the disadvantage of removing sulphur content by coal washing?
a) Increases the cost of coal
b) Reduces the sulphur
c) Makes the coal unsuitable for combustion
d) Adds more steps to the process
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Explanation: Washing of coal significantly reduces the sulphur content in coal. However, the combustible matter may be lost in the process also. Additionally, the cost of coal may also increase by 20%, which is not ideal.
3. How is organic sulphur removed from coal?
a) Washing
b) Size reduction
c) Chemical processing
d) Biological treatment
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Explanation: The organic sulphur present in coal is removed by chemical processing only. Organic sulphur exists in forms like cystin, thiols, et cetera. Hydrodesulphurisation is one such method. Washing and size reduction are physical methods.
4. Which method removes both inorganic and organic sulphur in coal?
a) Combustion
b) Reinluft process
c) Washing coal
d) Hydrodesulphurization
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Explanation: Washing is a physical process, which removes inorganic sulphur only. The Reinluft process is used to remove sulphur from flue gases. The hydrodesulphurization process removes both organic and inorganic sulphur from coal.
5. Which of the following methods is preferred to recover hydrogen sulphide in the coal gasification process?
a) Adsorption
b) Absorption
c) Incineration
d) Oxidation
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Explanation: During the gasification process, sulphur in the fuel is converted to hydrogen sulphide. Although both adsorption and absorption can be used, the former is preferred. Absorption causes heat loss because the gases are cooling, which is undesirable.
6. Which method is effective at removing sulphur from fuel oil?
a) Washing
b) Hydrodesulphurization
c) Absorption
d) Adsorption
View Answer
Explanation: Hydrodesulphurization is very effective at removing sulphur content from fuel oil. This process has many disadvantages, though, especially so because it is not very economical. The catalyst used for the process is very susceptible to poisoning.
7. Which of the following reasons cause the hydrodesulphurization to be uneconomical?
a) Catalyst fouling
b) High-temperature operations
c) No value-added products recovered
d) Recovery is low
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Explanation: Asphaltenes, which contain sulphur, cause catalyst fouling. Additionally, the catalyst used for the process is susceptible to poisoning by organometallics present in fuel oils. Since the process needs hydrogen, the construction of the plant is expensive.
8. By how much would the cost of fuel oil increase if the hydrodesulphurization unit removes 50% of the sulphur in fuel oils?
a) 5%
b) 15%
c) 25%
d) 35%
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Explanation: The cost of the fuel oil increases by about 25% if a hydrodesulphurization unit is incorporated into the plant. The construction of the unit is expensive because it makes use of hydrogen. Additionally, the organometallics need to be removed to avoid poisoning of the catalyst.
9. Which sulphur compound is the sulphur content converted to during fuel oil gasification?
a) Sulphur dioxide
b) Hydrogen sulphide
c) Sulphuric acid
d) Sulphur trioxide
View Answer
Explanation: During gasification, which is essentially catalytic creaking, the sulphur content is converted to hydrogen sulphide. The hydrogen sulphide in the flue gases is recovered and then converted to sulphur in the Claus process.
10. Which of the following processes is preferred over hydrodesulphurization to remove sulphur from fuel oils?
a) Washing
b) Pyrolysis
c) Gasification
d) Claus process
View Answer
Explanation: Gasification is preferred because of the carbon to hydrogen ratio. Since it is low in fuel oils, gasification is an easy process. The Claus process converts recovered sulphur compounds to sulphur. Washing can only remove inorganic sulphur.
11. How can sulphur content in flue gases be reduced using the combustion process?
a) Increase pressure
b) Pretreatment
c) Increase temperature
d) Using dry limestone
View Answer
Explanation: During the combustion process, limestone can be added during processing to convert the sulphur dioxide formed to calcium sulphate. The salt, thus formed, can be removed along with the slag. This addition reduces the sulphur dioxide in the flue gases.
12. Why does the dry limestone technique only reduce about half of the sulphur oxides formed?
a) Short residence time
b) Low selectivity
c) Temperature is too low
d) Inhibition of combustion
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Explanation: Directly adding limestone to the combustion process is not very inefficient. It is because the gases have a low residence time, and the chemical reaction producing calcium sulphate produces a low amount of it. Additionally, calcium sulphate is unstable at the temperatures of combustion (1500 degrees Celsius).
13. How can limestone be incorporated into the process to remove sulphur more efficiently during combustion?
a) Add limestone
b) Use a fluidised bed
c) Lower the temperature
d) During gasification
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Explanation: Directly adding limestone during the combustion process is inefficient. To sustain the benefits of limestone addition, without the shortcomings of direct addition, a fluidised bed combustion unit is used. Here, crushed coal and limestone form the bed, and the air is the fluidising medium.
14. How efficient is the fluidised bed combustion unit at removing sulphur dioxide from the gas stream?
a) 50%
b) 60%
c) 80%
d) 90%
View Answer
Explanation: Using the fluidised bed is very efficient. It increases the efficiency of the process to 90%. The operating temperatures are low, which allows the calcium sulphate to be stable. The residence time is sufficient for the chemical reaction to occur.
15. What is one advantage of the fluidised bed combustion unit over the dry limestone technique?
a) Higher operating temperatures
b) Lower efficiency
c) Less expensive
d) Lower operating temperatures
View Answer
Explanation: The fluidised bed combustion unit operates at lower temperatures than the conventional combustion unit. Such temperatures prevent the formation of ash fusion and inhibit the corrosions of the boiler tubes.
Sanfoundry Global Education & Learning Series – Air Pollution Control.
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