Particulate Control Devices Questions and Answers

Q: Which of the following is NOT an inertial collection device?

Correct answer: Electrostatic precipitatorThe precipitator charges the particles and moves them to a plate by an electric field, which does not depend on particle inertia - and that is why it works on very fine material. The cyclone, the settling chamber and the venturi scrubber all rely on the particle’s failure to follow a change of direction in the gas, whether around a bend, downward under gravity, or past a droplet.

Q: Which of these is NOT a disadvantage of a wet scrubber?

Correct answer: It is damaged by hot or sticky particulateTolerance of hot, sticky and near-saturated gas is a scrubber’s chief advantage, and precisely the condition under which it is chosen over a baghouse. The other three are genuine disadvantages: a high pressure drop, the fan power that follows from it, and the slurry that must be thickened, dewatered and disposed of.

Q: Which of these is LEAST relevant to selecting a particulate control device?

Correct answer: The colour of the collected dustColour has no bearing on how a particle is captured. What decides the selection is the particle size distribution, which determines whether an inertial device can work at all; the gas temperature and dew point, which decide whether a fabric filter is possible; the dust resistivity, which decides whether a precipitator is; and whether an aqueous effluent can be handled, which decides whether a wet device is acceptable.

101.

Match each remedy in List I with the problem it addresses in List II.

List I

A. Sulphur trioxide conditioning

B. Raising the cleaning set point

C. Adding a cyclone upstream

D. Selecting a higher temperature fabric

List II

1. Excessive coarse dust loading on a baghouse

2. High dust resistivity causing back corona

3. Bag failure from heat

4. Over-cleaning that strips the dust cake

Select the correct match.

A.A-2, B-4, C-1, D-3
B.A-1, B-2, C-4, D-3
C.A-2, B-1, C-4, D-3
D.A-3, B-1, C-4, D-2

Answer: A

Each fault has a specific and well established remedy, and applying the wrong one wastes money without improving anything. Diagnosing which problem is present is the whole of the work in most cases of poor performance.

Discuss in Forum

102.

Which of the following is NOT an inertial collection device?

A.Venturi scrubber
B.Electrostatic precipitator
C.Cyclone
D.Gravity settling chamber

Answer: B

Correct answer: Electrostatic precipitator

The precipitator charges the particles and moves them to a plate by an electric field, which does not depend on particle inertia - and that is why it works on very fine material. The cyclone, the settling chamber and the venturi scrubber all rely on the particle’s failure to follow a change of direction in the gas, whether around a bend, downward under gravity, or past a droplet.

Discuss in Forum

103.

Which statement about fabric filters is FALSE?

A.Air to cloth ratio is the primary sizing parameter
B.Condensation blinds the fabric irreversibly
C.Efficiency is at its highest immediately after cleaning
D.The dust cake does most of the collecting

Answer: C

Correct answer: Efficiency is at its highest immediately after cleaning

This is the false statement and it inverts the mechanism. Cleaning removes the dust cake, which is what does the collecting, so efficiency is at its lowest just afterwards and recovers as the cake rebuilds. The other three are all true: the ratio is the sizing parameter, condensation blinds the fabric irreversibly, and the cake rather than the weave is the filter.

Discuss in Forum

104.

Which change would NOT raise a precipitator's efficiency?

A.Adding plate area
B.Adding a further field in series
C.Conditioning the dust to lower its resistivity
D.Increasing the gas flow rate through it

Answer: D

A higher flow shortens the residence time and moves the Deutsch exponent the wrong way. The other three each raise the product of area and migration velocity relative to the flow, which is what the equation depends on.

Discuss in Forum

105.

Which of these is NOT a disadvantage of a wet scrubber?

A.It is damaged by hot or sticky particulate
B.It produces a slurry requiring treatment
C.Its pressure drop is high
D.Its fan power dominates the running cost

Answer: A

Correct answer: It is damaged by hot or sticky particulate

Tolerance of hot, sticky and near-saturated gas is a scrubber’s chief advantage, and precisely the condition under which it is chosen over a baghouse. The other three are genuine disadvantages: a high pressure drop, the fan power that follows from it, and the slurry that must be thickened, dewatered and disposed of.

Discuss in Forum

106.

An engineer proposes a settling chamber to meet a PM2.5 standard. This is

A.Unworkable only for hot gases
B.Unworkable: settling velocity is far too low
C.Sound if the chamber is long enough
D.Sound at low gas velocity

Answer: B

Correct answer: Unworkable: settling velocity is far too low

A 2.5 micrometre particle settles at a fraction of a millimetre per second, so a chamber long enough for it to reach the floor before the gas leaves would be measured in hundreds of metres. Lowering the gas velocity helps only in proportion, and no practical length can close the gap. A settling chamber is a pre-cleaner for material above about fifty micrometres, and nothing else.

Discuss in Forum

107.

Which statement about cyclone design is TRUE?

A.Cut diameter is independent of body diameter
B.Efficiency is highest for the finest particles
C.A narrower body cuts finer, at more pressure drop
D.A narrower body gives a lower pressure drop

Answer: C

Both effects follow from the higher centrifugal acceleration a smaller radius produces at the same tangential velocity. Multiclones exist to obtain the small cut diameter without the pressure drop of a single narrow body at full flow.

Discuss in Forum

108.

Which of the following would NOT explain a precipitator's poor performance?

A.Dust resistivity above the workable window
B.Excessive gas flow rate
C.Rapping that re-entrains the collected layer
D.An unusually low pressure drop across the unit

Answer: D

Correct answer: An unusually low pressure drop across the unit

A precipitator’s pressure drop is low by design and is not an indicator of its collection performance at all - the gas passes between plates with nothing obstructing it whether the fields are working or not. The other three are all genuine causes of poor performance: resistivity above the window brings back corona, excess gas flow reduces the residence time in the field, and over-vigorous rapping re-entrains the layer that has just been collected.

Discuss in Forum

109.

Which statement about efficiency in series is FALSE?

A.Efficiencies of devices in series are added together
B.Penetrations multiply
C.Two devices at 90 per cent give 99 per cent overall
D.A pre-cleaner protects the device behind it

Answer: A

Adding efficiencies would give figures above one hundred per cent for any reasonable pair. Multiplying the penetrations is the correct treatment and it makes the diminishing returns of further stages immediately clear.

Discuss in Forum

110.

Which of these is LEAST relevant to selecting a particulate control device?

A.The ease of handling an aqueous effluent
B.The colour of the collected dust
C.The particle size distribution
D.The gas temperature and dew point

Answer: B

Correct answer: The colour of the collected dust

Colour has no bearing on how a particle is captured. What decides the selection is the particle size distribution, which determines whether an inertial device can work at all; the gas temperature and dew point, which decide whether a fabric filter is possible; the dust resistivity, which decides whether a precipitator is; and whether an aqueous effluent can be handled, which decides whether a wet device is acceptable.

Discuss in Forum

Loading…

Topics

Other Subjects

Tags: Particulate Control Devices Questions and Answers || Particulate Control Devices MCQ Questions and Answers || Particulate Control Devices GK Questions and Answers || Particulate Control Devices GK MCQ Questions || Particulate Control Devices Multiple Choice Questions and Answers || Particulate Control Devices GK || GK on Particulate Control Devices || Air Pollution and Control Questions and Answers || Air Pollution and Control MCQ Questions and Answers || Air Pollution and Control GK Questions and Answers || GK on Air Pollution and Control

Particulate Control Devices Questions and Answers

Topics

Other Subjects

About Us

Stay informed about all important Dates & Notifications