Gaseous Pollutant Control Questions and Answers

Answer: A

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason is the mechanism. Above roughly 50 per cent relative humidity, water condenses in the micropores of the carbon and occupies sites that would otherwise hold the organic vapour, so the working capacity falls - by half or more in a saturated stream. The remedy is to condition the gas first, by cooling and condensing the moisture out or by warming it to lower the relative humidity.

Answer: B

Correct answer: 1 and 2 only

Statements 1 and 2 are correct. Statement 3 is the reverse of practice: random or structured packing is prone to plugging and channelling when solids are present, whereas plate towers, with their open downcomers and larger passages, tolerate them far better and can be cleaned. Packed towers are chosen for low pressure drop, corrosive service and small diameters, not for dirty gas.

Answer: C

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: breakthrough precedes saturation because the mass transfer zone has finite depth, and humidity competes for sites. Statement 3 is wrong. Regeneration requires energy to drive the adsorbate off - low pressure steam is the usual agent, sometimes hot inert gas or a vacuum - and cold air would achieve nothing at all.

Answer: D

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: the three T’s of temperature, time and turbulence must all be adequate, and a catalyst lowers the temperature required. Statement 3 is seriously wrong. Incomplete oxidation produces carbon monoxide, aldehydes and, from chlorinated feedstocks, dioxins and furans - products often far more objectionable than the compounds being destroyed. This is why combustion conditions are monitored rather than assumed.

Answer: A

Correct answer: 1 and 2 only

Statements 1 and 2 are correct: the catalytic route reaches 80 to 90 per cent against 30 to 50, and both use ammonia or urea. Statement 3 assigns the wrong temperature. It is the catalytic route that works at 300 to 400 degrees; the non-catalytic route needs the furnace window of about 850 to 1100 degrees, since without a catalyst nothing else will drive the reaction at a useful rate.

Answer: B

Three of these capture the pollutant and one destroys it, which is the first distinction to draw when choosing between them. Capture leaves something to handle afterwards, and that residue is often what settles the decision.

Answer: C

Correct answer: A-2, B-1, C-4, D-3

Each route has its own signature. Wet limestone gives the highest removal and saleable gypsum but leaves the gas saturated and needing reheat. Spray dryer absorption produces a dry solid and no liquid effluent. Dry sorbent injection is the cheapest to install and the most wasteful of reagent. What all three share is the underlying chemistry: an alkaline reagent neutralising an acid gas.

Answer: D

Correct answer: A-2, B-1, C-4, D-3

Each term belongs to one process and identifies it. The breakthrough curve is the defining plot of fixed bed adsorption. The height of a transfer unit is an absorption tower design quantity, multiplied by the number of transfer units to give the packed height. Ammonia slip belongs to nitrogen oxide reduction. And the three T’s - temperature, time and turbulence - are the classical conditions for complete incineration.

Answer: A

Correct answer: A-2, B-1, C-4, D-3

Each condition points to one method. A large dilute odorous stream of biodegradable compounds goes to biofiltration, since heating it would be prohibitive. A concentrated recoverable solvent goes to condensation or adsorption, both of which return the material in usable form. Moderate concentrations of mixed organics suit catalytic incineration, which destroys them at modest fuel cost. Acid gas from coal combustion is neutralised by alkaline scrubbing.

Answer: B

Incineration oxidises the compound to carbon dioxide and water, leaving nothing to handle afterwards. The other three transfer the pollutant to a liquid, a solid or a condensate which must then be treated, recovered or disposed of.