Module 2: Characteristics of Gases - Treatment Time - Practice Problems

Instructions:: Work these problems on a sheet of paper and check your answers against those provided below.
Helpful Calculators:: The following calculators may be useful in solving these problems. You can access them either from the "Calculators" button on the screen or from the links below.; Temperature Converter; Pressure Converter; Gas Flow Rate Converter (Actual Standard Conditions)

#1

If the volume of an air pollution control device increases by 50%, what is the change in the treatment time?

The treatment time increases by 50%.
The treatment time increases by 200%.
The treatment time decreases by 50%.
The treatment time decreases by 200%.
The treatment time remains unchanged.

: Answer: a. The treatment time increases by 50%.; Solution:; The treatment time increases by 50%, which can be confirmed by substituting the problem information into the equation that defines treatment time.

#2

If the gas flow rate (ACFM) in an air pollution control device increases by 50%, what is the change in the treatment time in the control device?

The treatment time increases 50%.
The treatment time increases 33.3%.
The treatment time decreases 50%.
The treatment time decreases 33.3%.
None of the above.

: Answer: d. The treatment time decreases 33.3%.; Solution:; This can be confirmed by substituting the problem information into the equation that defines treatment time.

#3

An air pollution control device has a volume of 100,000 ft³. The gas flow rate is 25,000 SCFM. What is the treatment time?

4 min
15 sec
It cannot be determined from these data.

: Answer: c. It cannot be determined from these data.; The gas flow rate is expressed in standard conditions. Gas temperature and pressure data are needed to convert the gas flow rate to actual conditions. All velocities and treatment times are calculated using gas flow rates in actual conditions.

#4

How does the treatment time usually affect the pollutant removal efficiency in an air pollution control device?

Longer treatment times usually increase efficiency.
Longer treatment times usually decrease efficiency.
Treatment time is not related to the collection efficiency.

: Answer: a. Longer treatment times usually increase efficiency.; There are many factors that can affect the overall collection efficiency of an air pollution control device. Increased treatment times usually improve collection efficiency slightly.

#5: What is the residence time of a gas stream with a flow rate of 300,000 ACFM through an electrostatic precipitator with a height of 30 ft, a width of 45 ft, and a length of 40 ft?

: Answer: 10.8 sec; Solution:; Calculate the treatment time using the following equation:

Calculate the volume of the precipitator.
Calculate the residence time.

#6: What is the treatment time of a gas stream in an electrostatic precipitator based on the following information?

: Answer: 12.5 sec; Solution:

Calculate the absolute temperature and pressure.
Convert the gas flow rate from SCFM to ACFM.

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Treatment Time

Practice Problems

Space Velocity

Instructions:: Work these problems on a sheet of paper and check your answers against those provided below.
Helpful Calculators:: The following calculators may be useful in solving these problems. You can access them either from the "Calculators" button on the screen or from the links below.

#1

The gas flow rate through a catalytic incinerator has increased by 50%. What is the change in the space velocity of the catalytic incinerator?

The space velocity increases by 50%.
The space velocity decreases by 50%.
The space velocity remains the same.

: Answer: a. The space velocity increases by 50%.; Solution:; This can be confirmed by substituting the data into the equation that defines space velocity.

#2

If the volume of catalyst in a catalytic incinerator is doubled, what is the effect on the space velocity of the gas moving through the catalyst bed?

The space velocity increases 50%.
The space velocity decreases 50%.
The space velocity remains unchanged.

: Answer: b. The space velocity decreases 50%.; Solution:; This can be confirmed by substituting the data into the equation that defines space velocity.

#3

The space velocity in a catalyst bed of a catalytic incinerator has decreased to one-third of the original value. What is the usual effect of this change on the pollutant oxidation efficiency in the incinerator?

The efficiency usually increases with a decreased space velocity.
The efficiency usually decreases with a decreased space velocity.
The efficiency is unaffected by the space velocity.

: Answer: a. The efficiency usually increases with a decreased space velocity.; Solution:; The oxidation efficiency of a catalytic incinerator usually increases when the space velocity of the catalyst bed has decreased. This means that there is more catalyst available to oxidize the contaminants. It is important to remember that space velocity is the inverse of the treatment time.

#4: What is the space velocity of a catalyst bed having a volume of 3 ft³ and a gas flow rate of 1,500 SCFM?

: Answer: 30,000 hr^-1; Solution:

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Treatment Time

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Module 2: Characteristics of Gases - Treatment Time - Practice Problems

Practice Problems

Space Velocity

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