Particulate Control Devices Questions and Answers

Answer: A

Correct answer: Statement I is incorrect but Statement II is correct

Statement II is correct and it is precisely why statement I is wrong. A scrubber transfers the dust from the gas to the water; it does not destroy it. The resulting slurry must be thickened, dewatered and the solids disposed of, and the water treated or recirculated. The air problem has become a water and solid waste problem, which is the standing objection to wet collection.

Answer: B

Correct answer: Both Statement I and Statement II are correct

Both are true and the second gives the consequence. If the gas falls below its acid dew point, sulphuric acid condenses within the cake and turns it into a paste that cleaning cannot dislodge - the bags are blinded, the pressure drop climbs and they must be replaced. The remedy is to keep the whole filter, including the hopper and casing, above the dew point by insulation and by heating during start-up and shutdown.

Answer: C

The three inertial devices improve as the acceleration acting on the particle rises, and the filter then works by an entirely different mechanism. Capital cost and pressure drop generally rise along the same sequence, which is what makes the choice a real one.

Answer: D

Charging and collection are separate steps performed by the same field, and removal of the collected dust is a third. Rapping too gently leaves an insulating layer and too hard re-entrains the dust, so its timing is a matter of some care.

Answer: A

Efficiency is at its lowest immediately after cleaning and at its highest just before, which is the opposite of what intuition suggests. Setting the cleaning trigger too low strips the cake and keeps the filter in its least effective state.

Answer: B

Size distribution and gas condition together rule most options in or out before any cost is considered. Choosing a device before characterising the stream is how baghouses end up on gases above their fabric's temperature limit.

Answer: C

Each step follows from the one before, and the whole chain is set off by a dust property rather than by any fault in the equipment. Sulphur trioxide conditioning attacks it at the second step by making the layer conductive.

Answer: D

Correct answer: Only three

Cyclone, fabric filter and precipitator are correctly described. The fourth is wrong: a venturi scrubber collects by impaction, accelerating the gas through a throat so that particles cannot follow the streamlines around the injected water droplets and strike them instead. Gravity settling is the mechanism of the settling chamber, and it is far too weak to catch what a venturi is built for.

Answer: A

Correct answer: Only three

Cut diameter belongs to the cyclone, air to cloth ratio to the fabric filter, and migration velocity to the precipitator, where it appears in the Deutsch-Anderson equation. The fourth pair repeats the air to cloth ratio for a venturi scrubber, which has no fabric at all; the venturi’s characteristic parameters are its throat velocity, its liquid to gas ratio and its pressure drop.

Answer: B

Correct answer: Only three

The first three are correctly paired. The fourth is wrong - a gravity settling chamber has the lowest pressure drop of any device, a few tens of pascals, since the gas simply passes slowly through a large box. That is its one virtue, and it is why it survives as a pre-cleaner despite being useless on anything fine.