This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Electrostatic Precipitators”.
1. Which of the following equipment has the most widespread use in the industry to remove particulate matter?
a) Gravity settlers
b) Electrostatic precipitators
c) Cyclone separators
d) Filtration
View Answer
Explanation: Electrostatic precipitators have broad industrial applications. From powerplants to refineries, from paper to cement manufacture, it is widely used to remove particulates from gaseous emissions. These devices have high efficiencies.
2. For which of the following operations is the electrostatic precipitator most widely used?
a) Removing dust
b) Removing combustion particulates
c) Removing fumes
d) Removing water vapour
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Explanation: The electrostatic precipitator is used widely to remove the particulates produced during combustion. In addition, it is also used for the removal of dust and acid mists, but the application is not as widespread.
3. Which of the following is not a widespread application of electrostatic precipitators?
a) Combustion particulate removal
b) Acid mist removal
c) Basic mist removal
d) Dust fibre removal
View Answer
Explanation: Particulates from alkaline mists are not removed by electrostatic precipitators. On the other hand, particulates produced during combustion (like fly ash), acid mists and dust (like cement dust) are all commonly removed by electrostatic precipitators in the industries.
4. Which kind of process is electrostatic precipitation?
a) Physiochemical process
b) Biological process
c) Chemical process
d) Physical process
View Answer
Explanation: The process of electrostatic precipitation is a physical process. It involves application of an electric field to ionise the particulates present in the gas and then separating them. There is no chemical or biological processing involved.
5. Which gaseous components are ionised during electrostatic precipitation?
a) The particulates
b) The gas
c) Both the particulates and the gas
d) It cannot be said
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Explanation: The particulates and the gas are charged during this process. The electric field supplied to the system ionises the gas, which then ionises the particulates. The particulates are driven to the grounded surface, where they are collected.
6. To obtain high efficiency for high capacities, how is the electrostatic precipitator used?
a) Multiple precipitators in parallel
b) One big unit
c) Pre-treatment is done
d) Another equipment is used
View Answer
Explanation: To get high efficiencies, multiple precipitators are used in parallel. This arrangement also allows for continuous operation of the process. One big unit is utility-consuming and occupies a large space.
7. What is the most frequent use of the multiple unit electrostatic precipitator?
a) Collecting liquid particles
b) Collecting gases
c) Collecting solid particles
d) Collecting semi-solids
View Answer
Explanation: The multiple-unit electrostatic precipitator utilises the arrangement of multiple precipitators in one single cylindrical unit. This allows for continuous operation. It has limited applications but is used prominently for the collection of liquid particles.
8. Which kind of electrostatic precipitator used most widely in the industries?
a) Singular unit
b) Multiple-unit
c) Wire and pipe type
d) Parallel-plate type
View Answer
Explanation: For industrial applications, the parallel-plate type has the most widespread applications. This type of precipitator uses two vertical parallel plates to act as collectors. The particulates get collected at the plates.
9. Which of the following factors determines the collection efficiency of the electrostatic precipitators?
a) The gas flow rate
b) The nature of the gas
c) The period of operation
d) The voltage of electricity
View Answer
Explanation: The gas flow rate, along with the size of the precipitator are important factors used to determine its collection efficiency. This efficiency is given by the Deutsch equation, which can be used for the cylindrical and plate type precipitators.
10. In the collection efficiency equation for the electrostatic precipitator, what does the term vpm represent?
η = 1 - exp(- vpm * Ac / Q)
a) Volume of the gas
b) Migration velocity of particles
c) Volume of the particulates
d) Migration velocity of the gas
View Answer
Explanation: The term vpm represents the migration velocity of the particles. When the particle velocity term is divided into its components, the y-component is given by vpm. It is also known as the drift velocity.
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