Air Pollution Control Questions and Answers – Wet Scrubbers

This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Wet Scrubbers”.

1. What is the advantage of wet collectors over dry collectors?
a) They remove particulates and gases
b) Low pressure drops
c) High capacities
d) High efficiencies
View Answer

Answer: a
Explanation: Wet collectors, like scrubbers, are capable of collecting gases in addition to particulate matter. This feature is advantageous when compared to dry collectors, which can collect only particulates. Factors like pressure drop, capacities, and efficiencies vary with equipment.

2. What is the disadvantage of using a dry collector over using a wet collector?
a) Low efficiencies with dry collectors
b) Corrosion problem with wet collectors
c) High space requirement with wet collectors
d) Low pressure drops with dry collectors
View Answer

Answer: b
Explanation: Wet collectors, like scrubbers, utilise contact with a liquid to remove both particulates and gases. Although advantageous, it has problems of its own. The use of liquids can cause corrosion problems as well as additional liquid waste disposal.

3. Which of the following is not an advantage of using wet collectors?
a) It can remove particulates and gases simultaneously
b) High performance over various load capacities
c) Low energy costs
d) Presence of moisture does not affect performance
View Answer

Answer: c
Explanation: Wet collectors are very advantageous because of the use of a third contact medium. They can capture particulates as well as gases and have high performance. The presence of moisture in the gas does not inhibit their performance. A disadvantage is that the nature of operation does increase utility requirement and energy costs.

4. Which of the following is not a disadvantage of using wet collectors?
a) They encounter corrosion problems
b) Minute particles may not be captured
c) Added problem of liquid effluent disposal
d) High space requirement
View Answer

Answer: d
Explanation: Wet collectors have a few disadvantages to accompany their myriad of advantages. Since operation requires the use of liquid, corrosion problems persist, along with issues of effluent disposal. The devices do, however, need lesser space than dry collectors.

5. What is the primary function of the wet scrubber?
a) Provide contact between gas and liquid
b) To remove dissolved gases
c) To separate two liquids
d) To wash gas before processing
View Answer

Answer: a
Explanation: The main function of the wet scrubber is to provide contact between the particulate to be removed and the scrubbing liquid. Depending on the type of scrubber to be used, contact is provided in different ways.

6. Which of the following is not an impaction target used to bring about contact between particulate and liquid in the wet scrubber?
a) Equipment walls
b) Air molecules
c) Sieve
d) Packings
View Answer

Answer: b
Explanation: The impaction targets are any wet surfaces or the surface of the liquid itself. Among the given options, only air molecules do not fall into either of these categories. Equipment walls, sieves, and packings fall into the wet surface category.

7. Wet scrubbers work based on several principles. Which of the following is not one of its principles?
a) Inertial impaction
b) Diffusion
c) Adsorption
d) Interception
View Answer

Answer: c
Explanation: Among the given options, only adsorption is not one of the working principles of wet scrubbers. Generally, mass transfer by diffusion occurs in the case of minute particles. Inertial impact and interception both happen in the case of large particles.

8. The working principles used for the working of wet scrubbers are similar to another particle collector. Which of the following is the particulate collector in question?
a) Electrostatic precipitators
b) Cyclones
c) Gravity settlers
d) Filters
View Answer

Answer: d
Explanation: The principles on which the wet scrubbers operate are inertial impact, interception, and diffusion. The same working principles are applied to filters, especially packed filters. The other listed devices run on different working principles.

9. Which particle sizes are collected primarily by inertial impact in wet scrubbers?
a) > 0.3 microns
b) Equal to 0.3 microns
c) < 0.3 microns
d) Particles of all sizes
View Answer

Answer: c
Explanation: Generally, large particles are collected by inertial impact and interception. Such particles are greater than 0.3 micrometres. Small particles are captured usually due to mass transfer by diffusion.

10. For particles smaller than 3 * 10-1 micron, what is the predominant mechanism of the collection in wet scrubbers?
a) Interception
b) Diffusion
c) Impaction
d) All mechanisms are active
View Answer

Answer: b
Explanation: For very small particles, as the ones mentioned, mass transfer by diffusion is predominant. When the liquid and the entrained gas is brought into contact, the particles diffuse into the bulk of the liquid. Interception and impact are predominant in large particles.

11. Which of the following is not a primary type of wet scrubber?
a) Spray tower
b) Venturi scrubber
c) Plate and frame filter scrubbers
d) Packed bed columns
View Answer

Answer: c
Explanation: Except for plate and frame filter scrubbers (there is no such scrubber), all the given options are primary types of wet scrubbers in industrial use. Another prominent scrubber is the centrifugal scrubber.

12. Which of the following is a low energy scrubber?
a) Packed towers
b) Venturi scrubbers
c) Centrifugal scrubbers
d) Spray tower
View Answer

Answer: d
Explanation: An example of a low energy scrubber is the spray tower. It is used to collect relatively larger particles in the range of 5 to 100 microns. Venturi scrubbers, on the other hand, are high energy scrubbers.

13. Which of the following is a high energy scrubber?
a) Venturi scrubber
b) Spray towers
c) Packed towers
d) Centrifugal scrubbers
View Answer

Answer: a
Explanation: Among the given options, the venturi scrubbers are high energy scrubbers, i.e. they have high energy costs because of their operation. They can collect fine particles (smaller than 3 microns). On the other hand, spray towers are low-energy units.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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