This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Wet Scrubbers – Set 2”.
1. Which of the following is the simplest type of wet scrubber?
a) Spray towers
b) Venturi scrubbers
c) Centrifugal scrubbers
d) Packed towers
View Answer
Explanation: The simplest kind of scrubbers is the spray towers. These devices spray the liquid from the top of the tower, and the gas inlet is at the bottom. The slurry containing the collected particles is collected from the bottom of the equipment.
2. How are the liquids and the gases introduced into the spray tower?
a) Liquid: bottom; gas: top
b) Liquid: nozzle, top; gas: bottom
c) Liquid: bottom; gas: nozzle, top
d) Liquid: top; gas: bottom
View Answer
Explanation: In the spray tower, the liquid is introduced through a nozzle at the top. This nozzle helps spray the liquid down into the tower where it comes into contact with the entrained gas. The impact of the two separates the particles.
3. Which mechanism is applied primarily for the separation in the spray towers?
a) Inertial impact
b) Diffusion
c) Centrifugal force
d) Electric field
View Answer
Explanation: In spray towers, inertial impact and interception are the primary mechanisms applied to collect particulates. Diffusion comes into play in the case of fine particles. Centrifugal force is utilised in centrifugal scrubbers.
4. Which of the following is the collection efficiency of the spray tower, not a function of?
a) Liquid droplet size
b) L/G ratio
c) Gas velocity
d) Particle size
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Explanation: The particle size does not affect the collection efficiency of the spray tower. It, however, depends on the droplet size of the liquid used to collect the gas. L/G ratio, gas velocity, and droplet pathway are all factors influencing efficiency.
5. The collection efficiency of the spray tower is independent of the size of the particle.
a) True
b) False
View Answer
Explanation: The collection efficiency of the spray tower is independent of the particle size when the liquid droplets fall under gravity. The condition is always true for the spray tower, where the liquid drops always fall under the influence of gravity. This collection efficiency is maximum for a droplet size of 8 * 10-1 mm.
6. What is the effectiveness of the spray tower is for the collection of particles of 5 microns?
a) 92%
b) 94%
c) 96%
d) 99%
View Answer
Explanation: The conventional spray tower has an effectiveness of about 94% when it comes to collecting particles of 5 microns. This property increases to 99%, for 25 microns. Effectiveness drops with the increase in particle size.
7. Which equipment can the spray towers be used in series to increase the collection efficiency?
a) Electrostatic precipitators
b) Cyclones
c) Centrifugal scrubbers
d) They already have high efficiency, so they are used alone
View Answer
Explanation: The spray towers are used in tandem with centrifugal scrubbers. Centrifugal scrubbers are attached in series to collect fine particles that haven’t already been collected in the spray towers. This addition dramatically reduces the particulate content in the gas phase.
8. Where do the liquid droplets entering the centrifugal scrubber act?
a) Gas in the inner vortex
b) Gas in the outer vortex
c) Particles in the inner vortex
d) Particles in the outer vortex
View Answer
Explanation: The liquid droplets remove the particulate matter from the gas phase. The particulates are separated into the outer phase of the centrifugal scrubber. So the liquid droplets act on the particulates in the outer vortex.
9. What is the particulate cut diameter for the centrifugal scrubbers?
a) > 0.3 microns
b) Equal to 0.3 microns
c) < 0.3 microns
d) 2 – 3 microns
View Answer
Explanation: The cut diameter is the particles of diameters that are collected with an efficiency equal to 50%. For the centrifugal scrubber, the cut diameter falls between the range of 2 microns and 3 microns.
10. For centrifugal scrubbers, for which particle size is the operating efficiency greater than 97%?
a) Larger than .10 microns
b) Larger than 0.25 microns
c) Larger than 1 micron
d) Larger than 0.5 micron
View Answer
Explanation: The efficiency of the collection of particles larger than 1 micron is greater than 97 per cent in commercial units. These devices are usually used in series with spray towers to increase the total collection.
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