Gaseous Pollutant Control Questions and Answers

Answer: A

The gas must be soluble in the chosen liquid, and the driving force is the difference between the partial pressure in the gas and the equilibrium pressure over the liquid. Packed and plate towers both exist to maximise the area over which that transfer takes place.

Answer: B

A low Henry's constant means a very soluble gas and therefore an easy absorption, while a high one means the reverse. Adding a reagent that reacts with the dissolved gas removes it from solution and keeps the driving force high throughout the tower.

Answer: C

Activated carbon and zeolites present enormous internal surface areas on which molecules are held by physical or chemical forces. Because nothing is consumed, the bed can be regenerated by steam or by heat and the pollutant recovered.

Answer: D

The mass transfer zone travels through the bed and eventually reaches the outlet, at which point the effluent concentration climbs. Beds are switched at breakthrough rather than at saturation, since the last part of the capacity is bought at the price of emission.

Answer: A

The surface has an affinity for organic molecules and its capacity is well characterised for them. High humidity competes for the same sites and reduces the working capacity considerably, which is one of the method's practical limits.

Answer: B

The method recovers the material as a liquid, which makes it attractive where the vapour has value and is concentrated enough to justify the cooling. At trace concentrations the refrigeration cost becomes prohibitive for the mass recovered.

Answer: C

Adequate temperature drives the oxidation, sufficient residence time lets it complete, and turbulence brings fuel and oxygen together. Failing on any one of the three produces partial oxidation products that may be worse than what went in.

Answer: D

A catalyst lowers the activation barrier so the reaction proceeds at three to four hundred degrees rather than eight hundred or more. The fuel saving is large, but catalyst poisoning by metals, halogens and sulphur is a real operating risk.

Answer: A

Forced oxidation gives saleable gypsum, which is what makes the process economically tolerable at large scale. It reaches over ninety-five per cent removal but produces a cooled, saturated gas that usually needs reheat.

Answer: B

The heat of the gas evaporates the water so the product leaves as a dry solid collected downstream. Removal is lower than wet limestone at around eighty to ninety per cent, but there is no liquid effluent and no reheat requirement.