Gaseous Pollutant Control Questions and Answers

Q: Effect of operating variables on activated carbon working capacity. VariableChangeEffect on capacity TemperatureIncreaseDecreaseHumidityIncreaseDecreasePollutant concentrationIncreaseIncreaseCompeting organicsIncreaseDecrease What pre-treatment does the table suggest for a warm humid stream?

Correct answer: Cool and dry the gas beforehandThe table shows capacity falling with both temperature and humidity, so a warm humid stream is doubly disadvantaged. Cooling raises the capacity directly and, by condensing out moisture, removes the water that would otherwise compete for the adsorption sites - though cooling alone raises the relative humidity, so a condensing cooler or a subsequent reheat is used. Heating would lower the relative humidity but reduce capacity through the temperature effect.

Q: Selective catalytic and non-catalytic reduction compared. AttributeCatalyticNon-catalytic Removal efficiency80 to 90 per cent30 to 50 per centOperating temperature300 to 400 C850 to 1100 CCatalyst requiredYesNoRelative capital costHighLow Why might a plant choose the non-catalytic route despite its lower removal?

Correct answer: Its far lower capital cost, and no catalystThe non-catalytic route needs only injection lances into the furnace: no reactor vessel, no catalyst to buy, house, monitor and replace every few years, and no additional pressure drop for the fans to overcome. Where the emission limit can be met with 30 to 50 per cent removal, that saving decides the matter. Its operating temperature is far higher, not lower, and its reagent consumption is greater rather than less.

71.

Effect of operating variables on activated carbon working capacity.

Variable	Change	Effect on capacity
Temperature	Increase	Decrease
Humidity	Increase	Decrease
Pollutant concentration	Increase	Increase
Competing organics	Increase	Decrease

What pre-treatment does the table suggest for a warm humid stream?

A.Humidify the gas further
B.Dilute the pollutant
C.Cool and dry the gas beforehand
D.Heat the gas before the bed

Answer: C

Correct answer: Cool and dry the gas beforehand

The table shows capacity falling with both temperature and humidity, so a warm humid stream is doubly disadvantaged. Cooling raises the capacity directly and, by condensing out moisture, removes the water that would otherwise compete for the adsorption sites - though cooling alone raises the relative humidity, so a condensing cooler or a subsequent reheat is used. Heating would lower the relative humidity but reduce capacity through the temperature effect.

Discuss in Forum

72.

Selective catalytic and non-catalytic reduction compared.

Attribute	Catalytic	Non-catalytic
Removal efficiency	80 to 90 per cent	30 to 50 per cent
Operating temperature	300 to 400 C	850 to 1100 C
Catalyst required	Yes	No
Relative capital cost	High	Low

Why might a plant choose the non-catalytic route despite its lower removal?

A.Its higher removal efficiency
B.Its lower operating temperature
C.Its lower reagent consumption
D.Its far lower capital cost, and no catalyst

Answer: D

Correct answer: Its far lower capital cost, and no catalyst

The non-catalytic route needs only injection lances into the furnace: no reactor vessel, no catalyst to buy, house, monitor and replace every few years, and no additional pressure drop for the fans to overcome. Where the emission limit can be met with 30 to 50 per cent removal, that saving decides the matter. Its operating temperature is far higher, not lower, and its reagent consumption is greater rather than less.

Discuss in Forum

73.

Absorption tower sizing for four separations.

Separation	Transfer units required	Height of a transfer unit (m)	Packed height (m)
Easy, very soluble gas	2.0	0.45	0.90
Moderate	4.0	0.50	2.00
Difficult	6.4	0.55	3.52
Very difficult	9.0	0.60	5.40

What does the table separate into two distinct factors?

A.Separation difficulty and packing efficiency
B.The gas flow and the liquid flow
C.The capital cost and the running cost
D.The pressure drop and the removal efficiency

Answer: A

Transfer units measure how hard the separation is and the height of a transfer unit measures how well the packing performs. Improving the packing shortens the tower without changing the number of units the duty demands.

Discuss in Forum

74.

Assertion (A): Adsorption beds are switched at breakthrough rather than at saturation.

Reason (R): Continuing past breakthrough buys the remaining capacity at the price of an emission.

Select the correct answer from the options below.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: B

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

Both are true and the reason states the trade exactly. Between breakthrough and saturation the bed still has capacity, but every hour of that capacity is bought by emitting pollutant at a rising concentration. Since the whole purpose of the bed is to prevent that emission, it is switched at breakthrough, and the design capacity used is the working capacity up to that point rather than the equilibrium capacity.

Discuss in Forum

75.

Assertion (A): Catalytic incineration is preferred where fuel cost dominates.

Reason (R): A catalyst allows oxidation at roughly four hundred degrees rather than eight hundred.

Select the correct answer from the options below.

A.A is true but R is false
B.A is false but R is true
C.Both A and R are true, and R is the correct explanation of A
D.Both A and R are true, but R is not the correct explanation of A

Answer: C

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. The fuel needed is what it takes to raise the whole gas stream to the operating temperature, so halving that temperature roughly halves the heat duty. Where fuel dominates the operating cost - a continuous stream of moderate concentration - catalytic incineration wins, provided the stream is free of the halogens, sulphur and metals that would poison the catalyst.

Discuss in Forum

76.

Assertion (A): Wet limestone desulphurisation usually requires flue gas reheat.

Reason (R): The gas leaves the absorber cooled and saturated with water vapour.

Select the correct answer from the options below.

A.Both A and R are true, but R is not the correct explanation of A
B.A is true but R is false
C.A is false but R is true
D.Both A and R are true, and R is the correct explanation of A

Answer: D

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

Both are true and the reason gives the cause. The gas leaves a wet absorber at 50 to 60 degrees and saturated, so it has little buoyancy and will condense acid in the ductwork and stack. Reheating it by 20 or 30 degrees restores plume rise and protects the downstream metal, at the cost of fuel or of a gas-to-gas heat exchanger. Avoiding this is one of the arguments for the semi-dry routes.

Discuss in Forum

77.

Assertion (A): Ammonia slip rises as removal efficiency is pushed higher.

Reason (R): Higher removal requires a higher ammonia to nitrogen oxide molar ratio.

Select the correct answer from the options below.

A.Both A and R are true, and R is the correct explanation of A
B.Both A and R are true, but R is not the correct explanation of A
C.A is true but R is false
D.A is false but R is true

Answer: A

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

Both are true and the reason explains the mechanism. Mixing between reagent and flue gas is never perfect, so pushing removal higher requires injecting more ammonia than stoichiometry demands; the fraction that finds no nitrogen oxide passes through as slip. Removal and slip therefore rise together, and the practical limit on removal is usually set by the slip the downstream equipment and the permit can tolerate.

Discuss in Forum

78.

Assertion (A): Biofiltration suits large dilute odorous streams.

Reason (R): Incinerating such a stream would require prohibitive fuel to heat the whole volume.

Select the correct answer from the options below.

A.A is false but R is true
B.Both A and R are true, and R is the correct explanation of A
C.Both A and R are true, but R is not the correct explanation of A
D.A is true but R is false

Answer: B

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

Both are true and the reason is the decisive argument. The fuel required by an incinerator scales with the volume of gas to be heated, while the benefit scales with the mass of pollutant destroyed, so a very dilute stream is the worst possible case for combustion. A biofilter treats the same stream at ambient temperature with almost no energy input, needing only that the compounds be biodegradable and the bed kept moist.

Discuss in Forum

79.

Assertion (A): Chemical absorption is used for sparingly soluble gases.

Reason (R): Reacting the dissolved gas keeps its liquid-phase concentration near zero.

Select the correct answer from the options below.

A.A is true but R is false
B.A is false but R is true
C.Both A and R are true, and R is the correct explanation of A
D.Both A and R are true, but R is not the correct explanation of A

Answer: C

The driving force is maintained the whole way up the tower, which the reason explains, and a physical absorber would saturate long before. The cost is a consumed reagent and a pollutant that cannot be recovered unchanged.

Discuss in Forum

80.

Assertion (A): A packed tower must be operated below its flooding velocity.

Reason (R): Packing gives a large interfacial area at a modest pressure drop.

Select the correct answer from the options below.

A.Both A and R are true, and R is the correct explanation of A
B.A is true but R is false
C.A is false but R is true
D.Both A and R are true, but R is not the correct explanation of A

Answer: D

The assertion is true and the reason is true, but the reason is about the choice of packing rather than about flooding. Flooding is avoided because liquid cannot drain against the rising gas and the tower ceases to operate.

Discuss in Forum

Loading…

Topics

Other Subjects

Tags: Gaseous Pollutant Control Questions and Answers || Gaseous Pollutant Control MCQ Questions and Answers || Gaseous Pollutant Control GK Questions and Answers || Gaseous Pollutant Control GK MCQ Questions || Gaseous Pollutant Control Multiple Choice Questions and Answers || Gaseous Pollutant Control GK || GK on Gaseous Pollutant Control || 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

Gaseous Pollutant Control Questions and Answers

Topics

Other Subjects

About Us

Stay informed about all important Dates & Notifications