This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Gaseous Pollutants – Control of Nitrogen Oxides – Set 2”.
1. What is the disadvantage of using stack emission control methods for the control of nitrogen oxides?
a) Methods are expensive
b) Quantity of pollutants is low in the emissions
c) Methods are not suitable
d) Selectivity for nitrogen oxides is low
View Answer
Explanation: The flue gases contain low volumes of nitrogen oxides when compared to the flue gas volume being handled. This factor creates considerable issues in the design and implementation of the equipment.
2. Which of the following two methods are used for nitrogen oxide recovery from the flue gas stream?
a) Scrubbing and catalytic decomposition
b) Adsorption and adsorption
c) Catalytic reduction and adsorption
d) Absorption and combustion
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Explanation: Scrubbing and catalytic decomposition are used to recover nitrogen oxides from the emission streams. Adsorption and adsorption are methods of scrubbing. Catalytic decomposition and reduction are often done together.
3. What does the catalytic decomposition of nitric oxide involve?
a) Reaction with oxygen
b) Formation of nitrogen dioxide
c) Formation of nitrogen and oxygen
d) Reaction with carbon dioxide
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Explanation: In the catalytic decomposition of nitric oxide, nitric oxide is reduced to its components: nitrogen and oxygen. Carbon monoxide is used as the other reactant for this operation. The formation of nitrogen oxide is the oxidation reaction, which is unfavourable.
4. Which of the following is false about the scrubbing of nitrogen oxides from effluent streams?
a) Scrubbing is divided into two methods
b) Adsorption by solids is a scrubbing method
c) Absorption by liquids is a scrubbing method
d) Absorption by solids is the only scrubbing method
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Explanation: Scrubbing is divided into two types of methods. One uses solids so that nitrogen oxides get adsorbed onto them. The other uses liquids so that nitrogen oxides get absorbed by them. The suitability of the method depends on various factors.
5. The absorption of nitrogen oxides from emission streams helps with sulphur dioxide recovery as well.
a) True
b) False
View Answer
Explanation: The process employed for the removal of nitrogen oxides by absorption also helps in sulphur dioxide removal. The absorbents used to absorb NOX also absorb some of the sulphur dioxides, thus, helping with their removal.
6. Which of the following is not an absorption method used to recover nitrogen oxides?
a) Treatment with lime slurry
b) Absorption with HCl
c) Absorption with magnesium hydroxide
d) Absorption in sulphuric acid
View Answer
Explanation: Nitric oxides do not get absorbed by nitric acid. Treatment with lime slurry recovers nitric acid and gypsum. Nitric oxide is recovered by magnesium hydroxide. Sulphuric acid recovers both nitric and sulphur oxides.
7. Magnesium hydroxide absorbs which nitrogen compound from the flue gases?
a) Nitric oxide
b) Nitrogen dioxide
c) Dinitrogen trioxide
d) Nitric acid
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Explanation: Nitric oxide is absorbed by magnesium hydroxide. Upon absorption, nitric oxide is oxidised to nitrogen dioxide. Part of this nitrogen dioxide is recycled into the absorber, while the rest is used to make nitric acid.
8. Why are the common absorption recovery methods of nitrogen oxides so complex?
a) Because of high-temperature operations
b) The methods are not complex
c) Difficult to source raw materials
d) Concentration maintenance
View Answer
Explanation: The absorbers have to maintain equimolar concentrations of nitrogen dioxide and nitric oxide. This restraint makes the process complex. The need for such maintenance is that the absorption of dinitrogen trioxide is favourable.
9. When is ammonium bisulphite used for scrubbing nitrogen oxides?
a) When the concentration of oxides is sufficient
b) When NOx present can react at NTP
c) When no other methods are viable
d) When the operating cost is low
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Explanation: Ammonium bisulphite is used for nitrogen oxide absorption when the ones present in the flue gases can react at nominal temperature and pressures. This reaction results in the formation of ammonium sulphate, which can be used as a fertiliser.
10. What is the advantage of using continuous catalytic absorption for the recovery of nitric oxides?
a) Recovers NO as nitric acid
b) Produces fertilisers as products
c) The efficiency of recovery is high
d) Reduces the oxide content to the least value
View Answer
Explanation: The advantage of using the catalytic absorption process is that it recovers nitric oxide as nitric acid. This advantage is in addition to reducing the nitrogen oxide contents to adequate limits in the flue. The absorption medium here is stripped nitric acid.
Sanfoundry Global Education & Learning Series – Air Pollution Control.
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