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Module 2: Characteristics of Gases - Treatment Time
Treatment (Residence) Time-
Animation #1:
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Treatment Time
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Practice Problems
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Animation #2:
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Space Velocity
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Animation #3:
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Gas Flow Rate and Emissions
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Practice Problems
Objective
- Calculate the treatment time and space velocity of a gas stream in an air pollution control device.
The flow rate of the gas stream through an air pollution control system determines the length of time that the pollutants can be removed from the gas stream. This is termed the treatment time or the residence time. These common equipment sizing parameters are defined mathematically in Equation 1 and are illustrated in Figure 1.
This animation helps you make the connection between gas flow rate, equipment size, and treatment time.
 Animation #1 
This animation allows (No audio)
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Note: Animations require a Netscape 4.7 or Internet Explorer 4.01 or higher browser and a Shockwave Flash plug-in (Netscape browsers) or Shockwave Flash ActiveX Control (Internet Explorer browsers). Shockwave Flash plug-in/ActiveX Control (version 3.0 minimum) can be obtained at the
Macromedia
web site. Before downloading or installing any software or plug-ins, please refer to your organization's network/computer policies or check with your system administrator.
Example Problem 1.
Calculating the Treatment Time
What is the treatment (residence) time of an 80,000 ACFM gas stream moving through a control device which is 24 ft high, 12 ft wide, and 30 ft long?
Solution:
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Calculate the volume of control device, V.
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Calculate the treatment time (in seconds).
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Practice Problems
Treatment Time
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Instructions:
- Complete the Practice Problems before proceeding to the next lesson. Click on the button below.
Space velocity is an alternative way to express the time available to treat a pollutant-laden gas stream and is defined by Equation 2.
It is obviously the inverse of treatment time and residence time. Space velocity has units of 1/seconds or 1/minutes. The term is often used for expressing the size of catalyst beds used for VOC incineration, NOx destruction, and CO destruction.
The space velocity is a value equivalent to the number of times that the control device will be filled with untreated gas in a given period of time. For example, if a control device has a volume of 100 ft3, and the gas flow rate is 200 ACFM, the space velocity is 2. This means that every 1/2 minute, the control device is re-filled with treated gas. If the space velocity were 4, the control device would be re-filled with untreated gas every 1/4 minute.
This animation illustrates the concept of space velocity by counting off the number of times the control device is filled per minute. Space Velocity depends on gas flow rate and equipment size.
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Animation #2
This animation allows (No audio)
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Note: Animations require a Netscape 4.7 or Internet Explorer 4.01 or higher browser and a Shockwave Flash plug-in (Netscape browsers) or Shockwave Flash ActiveX Control (Internet Explorer browsers). Shockwave Flash plug-in/ActiveX Control (version 3.0 minimum) can be obtained at the
Macromedia
web site. Before downloading or installing any software or plug-ins, please refer to your organization's network/computer policies or check with your system administrator.
Example Problem 2.
Calculating the Space Velocity (Actual Conditions)
What is the space velocity of a catalyst bed handling 15,000 ACFM of gas if the catalyst bed has a total volume of 3 ft3?
Solution:
In contrast to treatment time, which is always expressed in actual conditions, space velocity can be expressed in terms of both actual and standard conditions. In fact, some control equipment manufacturers prefer to state the size of their equipment in terms of standard conditions. In this case, the gas flow rate in ACFM must be converted to SCFM prior to calculating the space velocity. For clarity, the space velocity value should include the term "standard" in these cases.
Example Problem 3.
Calculating the Space Velocity (Actual and Standard Conditions)
What is the space velocity of a catalyst bed having a volume of 3 ft3 and a gas flow rate of 1,200 ACFM? Express the space velocity value in terms of reciprocal hours at both actual and standard conditions. Use an actual gas temperature of 200°F, a relative pressure of +10 in. W.C., and a barometric pressure of 401 in. W.C.
Solution:
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This space velocity indicates that the catalyst bed fills with untreated gas 24,000 times per hour at actual conditions.
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Calculate the absolute temperature and pressure.
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Convert the gas flow rate to standard conditions.
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Animation of Gas Flow Rate, Treatment Time, and Emissions
This animation presents three different gas flow rate scenarios for an air pollution control system. Gas flow rate affects treatment time, the amount of particles collected, and the amount of emissions.
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Animation #3
This animation illustrates (No audio)
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Note: Animations require a Netscape 4.7 or Internet Explorer 4.01 or higher browser and a Shockwave Flash plug-in (Netscape browsers) or Shockwave Flash ActiveX Control (Internet Explorer browsers). Shockwave Flash plug-in/ActiveX Control (version 3.0 minimum) can be obtained at the
Macromedia
web site. Before downloading or installing any software or plug-ins, please refer to your organization's network/computer policies or check with your system administrator.
Practice Problems
Space Velocity
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Instructions:
- Complete the Practice Problems before proceeding to the next lesson. Click on the button below.