Catalytic incineration differs from thermal incineration principally in that it
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.
Please log in or register to report this question.
Wet limestone flue gas desulphurisation removes sulphur dioxide by
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.
Please log in or register to report this question.
Spray dryer absorption for sulphur dioxide uses
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.
Please log in or register to report this question.
Dry sorbent injection is characterised by
Answer: C
Correct answer: Simplicity, at poorer removal and sorbent use
Dry sorbent injection blows powdered lime or sodium bicarbonate straight into the duct, and the reacted solid is collected with the fly ash. There is no absorber vessel, no slurry handling and no liquid effluent, so it is by far the cheapest route to install. The price is a removal of only 50 to 70 per cent and a large stoichiometric excess of reagent, since the gas-solid contact is brief and imperfect. Saleable gypsum and the highest removal both belong to wet limestone scrubbing.
Please log in or register to report this question.
Selective catalytic reduction removes nitrogen oxides by
Answer: D
The catalyst allows the reaction to proceed at around three hundred to four hundred degrees with high selectivity. Ammonia slip and catalyst poisoning are the two operating concerns, and the catalyst itself is a substantial part of the cost.
Please log in or register to report this question.
Selective non-catalytic reduction differs from the catalytic route in that it
Answer: A
Ammonia or urea is injected into a narrow temperature window of about eight hundred and fifty to eleven hundred degrees. Removal is typically thirty to fifty per cent, against eighty or ninety for the catalytic route, but capital cost is far lower.
Please log in or register to report this question.
Ammonia slip refers to
Answer: B
Injecting more reagent than the reaction consumes raises removal but sends the excess up the stack, where it forms ammonium salts and fouls downstream equipment. The trade between removal and slip is the central control problem of both reduction processes.
Please log in or register to report this question.
A biofilter removes gaseous pollutants by
Answer: C
Correct answer: Passing it through a moist microbial bed
A biofilter passes the gas slowly through a bed of compost, peat or wood chips carrying a moist biofilm. The pollutant partitions into the water layer and is metabolised by the microorganisms to carbon dioxide, water and biomass. It works only on biodegradable compounds at low concentration, needs the bed kept moist and near neutral pH, and requires a long residence time - but it consumes almost no energy, which is what makes it right for large dilute odorous streams.
Please log in or register to report this question.
A packed tower is generally preferred to a plate tower for absorption when
Answer: D
Packing gives a large interfacial area with a modest pressure drop and is easily built in corrosion-resistant materials. Plate towers handle solids and large turndown better, since a packed bed fouls and channels when solids are present.
Please log in or register to report this question.
The height of a transfer unit in an absorption tower expresses
Answer: A
Multiplying it by the number of transfer units gives the packed height required, which separates the equipment's efficiency from the separation's difficulty. A more efficient packing shortens the tower without changing the number of units needed.
Please log in or register to report this question.
