This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Gaseous Pollutants – Control of Hydrocarbons – Set 2”.
1. Where is condensation employed for the removal of hydrocarbon vapours from industries?
a) Metallurgical industries
b) Process industries
c) Dry cleaning operations
d) Power plants
View Answer
Explanation: Hydrocarbon vapours can condense at relatively low temperatures. It is used to recover solvent vapours in dry cleaning operations. Additionally, it is used in those processing industries where the air is used as a drying agent.
2. Which of the following equipment cannot be used as a direct-contact condenser that can recover hydrocarbons?
a) Spray chambers
b) Venturi scrubbers
c) Electrostatic precipitators
d) Cyclone scrubbers
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Explanation: In direct-contact condensers, the condensing liquid is brought into direct contact with the vapours that need to be condensed. Scrubbers that can provide direct contact with liquid and gas are ideal. Spray chambers, cyclones, and venturi scrubbers are such examples.
3. Which of the following is the advantage of biological reactions that are used to capture hydrocarbons?
a) Biological reactions are not used
b) Low energy consumption
c) High-temperature operation
d) Produce lots of CO
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Explanation: Biological reactions use microorganisms to remove hydrocarbons from the flue. Biological reactions take place are room temperatures, and the consumption of energy is low. Additionally, they do not produce high emissions of nitrogen oxides, unlike incineration.
4. When are biofilters most effective?
a) When hydrocarbon concentration is below 1 mg/m3
b) When the load capacity is low
c) At high temperatures
d) When hydrocarbon concentration is above 1 mg/m3
View Answer
Explanation: Biofilters use microorganisms to remove hydrocarbons from exhaust streams. Such devices are very effective when hydrocarbon concentrations are below 1 mg/m3. This condition does not necessarily mean that the load capacity should be low.
5. Which of the following is not a disadvantage of using biofilters to remove hydrocarbons from exhaust streams?
a) High retention time
b) High space requirement
c) Limited application
d) High energy consumption
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Explanation: Biofilters have a high retention time because microorganisms require several days to reach required efficiencies. Additionally, they have a high space requirement because of high retention time. However, energy consumption is low. They are most effective at hydrocarbon concentrations below 1 mg/m3.
6. What are biological reactions ideally used for?
a) Odour control
b) Colour control
c) Processing industries where the air is the drying agent
d) Pharmaceutical industries
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Explanation: Biofilters can be used to remove hydrocarbons from emissions. Biological reactions are ideal for the removal of the odour. Odour removal from processes like fermentation and food industries are typical for biofilter applications.
7. The installation cost of adsorbers is high, but the operating and maintenance costs are relatively lower.
a) True
b) False
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Explanation: The main drawback of using an adsorber is that its installation cost is high. However, operating and maintenance costs are significantly low. Activated carbon, the adsorbent, is inexpensive as well.
8. What is the main advantage of condensing hydrocarbon vapours to reduce emissions?
a) High load capacities
b) Condensation occurs at low temperatures
c) Low installation costs
d) Low operating costs
View Answer
Explanation: The hydrocarbon vapours can condense at relatively low temperatures, which makes condensation a viable method of capture. There are various types of condensation equipment available for this process.
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