This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Wet Scrubbers – Set 3”.
1. What is the contact surface when it comes to the packed bed towers?
a) The packing
b) The equipment walls
c) The sieves
d) The plates
View Answer
Explanation: In the packed bed, the packing provides contact between the liquid phase and the gas phase. The entrained gas and liquid have to go through the packing, where the particulates are collected.
2. How are fine particles in the packed bed collected?
a) By inertial impact
b) By diffusion
c) By adsorption
d) Diffusion, and adsorption
View Answer
Explanation: Diffusion is predominant in collecting very fine particles in the packed bed setup. Here, the contact time allowed between the gas and the liquid is very high, allowing for good mass transfer. Thus, small particles are collected by diffusion.
3. What kind of packings cannot be used in the packed tower?
a) Raschig rings
b) Saddles
c) Coke
d) Acid
View Answer
Explanation: Acids are not used as packing. Packings are solid in nature, either inert or reactive. Raschig rings, saddles, intalox saddles, et cetera are common types of packing used. Coke may be used on a case by case basis.
4. When are packed towers chosen as the scrubbing unit?
a) Higher loads
b) When more collection is required
c) For higher efficiency
d) When particulates are soluble in liquid
View Answer
Explanation: Packed towers are chosen only when the particulates are soluble in the scrubbing liquid. It allows for satisfactory efficiencies, and it also avoids clogging of the tower. The latter might be a problem when the liquid does not dissolve the particles.
5. When does the packed tower encounter clogging problems?
a) When the particulates are not soluble in the liquid
b) When maintenance is not done frequently
c) These happen regardless of any factors
d) The load is very high
View Answer
Explanation: The packed tower runs into clogging problems when the particulates to be collected are not soluble in the scrubbing liquid. The pores in the packed tower are small, so it is easily susceptible to clogging.
6. Both the size and shape of the packing affects the efficiency of collection.
a) True
b) False
View Answer
Explanation: This statement is untrue. The size of the packing affects the efficiency of collection, but it is independent of shape. It means that smaller sizes give improved efficiencies, but there is no advantage of 5 mm Raschig rings over 5 mm saddles.
7. How can clogging problems be avoided in the packed tower?
a) Use big packings
b) It cannot be, use other equipment
c) Low-density packings
d) Use low load capacities
View Answer
Explanation: Low-density packings are a suitable way to reduce plugging problems in the packed bed towers. Another way to reduce plugging is to spray the packings with liquid or use high gas flow rates. Recently, chemical foam is being used.
8. The venturi scrubber is ideal for the collection of particles of which sizes?
a) 4 microns
b) 3 microns
c) 2 microns
d) 1 micron
View Answer
Explanation: Venturi scrubbers are very efficient at the collection of fine particles. The particles it can collect efficiently have sizes that fall below two microns. Among the given options, only 1 micron falls below this value.
9. Particles with which of the following properties are readily collected by venturi scrubbers?
a) Hard and smooth
b) Coarse and big
c) Sticky and flammable
d) Big and slimy
View Answer
Explanation: Venturi scrubbers are viable for the collection of particles that are sticky in nature. They are also suitable for the recovery of flammable or corrosive particles. This niche application makes them very useful for the collection of such particles.
10. What is the reason for the high performance of venturi scrubbers?
a) Their ability to collect small particles
b) Entrained gas acceleration
c) High pressure drop
d) They can collect sticky particles
View Answer
Explanation: High performances are ensured by the acceleration of the particle-containing gas. The gas is accelerated to very high velocities, above 60 m/s, which atomises the liquid used to collect the particulates. The separation of the entrained liquid takes place in another separation unit.
11. Which is the primary mechanism of separation in the venturi scrubbers?
a) Condensation
b) Agglomeration
c) Inertial impaction
d) Diffusion
View Answer
Explanation: All the mechanisms listed in the options help with the collection of particulates in venturi scrubbers. Additionally, electrostatic precipitation also plays a role. Condensation helps with agglomeration. However, the primary mode of recovery is due to inertial impaction.
12. Which of the following factors is affected by the high-efficiency collection of fine particles in venturi scrubbers?
a) Pressure drop
b) Time of operation
c) Velocity of particles
d) Length of the device
View Answer
Explanation: The high-efficiency collection of fine particles is accompanied by higher pressure drops. Operation of the device in such conditions implies a higher power consumption. This condition is true for the high-efficiency collection of any particle size.
Sanfoundry Global Education & Learning Series – Air Pollution Control.
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