Posted: November 16th, 2022

MEE 6501, Advanced Air Quality Control 1

MEE 6501, Advanced Air Quality Control 1
Course Learning Outcomes for Unit VIII
Upon completion of this unit, students should be able to:
6. Estimate the impact of air pollution on the environment.
7. Evaluate air pollution control technologies.
7.1 Describe air pollution control technologies for particulate-phase pollutants.
7.2 Explain air pollution control technologies for gas-phase pollutants.
Reading Assignment
Chapter 9:
Control of Motor Vehicle Emissions
Chapter 10:
Control of Emissions from Stationary Sources
The Guide for Obtaining Air Authorization in Texas is used with the permission of the Texas Commission on
Environmental Quality. You can access the document from their website, or you can click on the link
in the Unit II Mini Project in the syllabus.
Texas Commission on Environmental Quality. (2011). Surface coating facilities: A guide for obtaining air
authorization in Texas. Retrieved from
https://www.tceq.texas.gov/searchpage?cx=004888944831051571741%3Auk3yh4pey8&cof=FORID%3A11&q=Surface+Coating+Facilities%3A+A+Guide+for+Obtaining+Air+Auth
orization+in+Texas
Unit Lesson
To date, we have discussed a tremendous amount of chemistry, particle science, atmospheric science, and
statistical analysis. We have worked within these different disciplines using mathematics as the common
language in order to effectively approach air quality from a systems engineering perspective. We can agree
that engineering air quality has been demonstrated to be an interdisciplinary science of its own!
In Unit VIII, we want to comprehensively consider all of the work that we have done to understand the
independent variables causally related to air quality. If we take this critical view now, we have a much better
opportunity to carefully select the appropriate engineering control for the independent variables of concern to
our air. Consequently, we must first understand that our air quality control options are going to largely fall into
one of two categories: (a) particulate-phased pollutants, or (b) gas-phased pollutants. Understanding each will
inform us to make the best possible decision when engineering the air quality controls for our systems.
According to Godish, Davis, and Fu (2015), particulate-phased pollutants (measured as percentage of
particulate matter or PM) really have three main capture strategies that are effective for improving air quality.
These include cyclonic collection, electrostatic collection, and numerous methods of filtration collection.
Settling chambers, impingers, and cyclones are designed to capture large to medium-sized particles of all
types of pollutants. These may include elutriators for aerosol particle collection, as well as cyclones (to
include aerosol centrifuges). The documented benefits include their relatively lower costs, simplicity of
operation, durability, and generally low maintenance. However, disadvantages include relatively low
UNIT VIII STUDY GUIDE
Utilizing Pollution Control Technologies
for Engineered Air Quality Control
MEE 6501, Advanced Air Quality Control 2
UNIT x STUDY GUIDE
Title
efficiencies for smaller particles, the propensity for erosion of components due to abrasive actions of particles,
and the large space required to accommodate the equipment (Phalen & Phalen, 2013; Godish et al., 2015).
Electrostatic precipitators (including mist precipitators) are designed to operate at high temperatures while
creating moisture-laden air as the capture medium. This makes electrostatic capture very efficient for very fine
particles. The advantages include the compact nature of the equipment, the lack of dust generation during the
capture process, and the constant pressure drop to the system during particle capture. Still, among the most
significant disadvantages of the design are the large space requirements for the equipment, the relatively
higher initial costs, and the phenomena of some pollutant particle charges not being matched well enough to
the system for efficient capture (Phalen & Phalen, 2013; Godish et al., 2015).
Filtration options include traditional filtration systems (such as medium filters) that are excellent for capturing
dust, fumes, and non-sticky particles with a wide disparity of sizes. This makes for highly efficient systems,
moderate power requirements, and a nice, dry disposable waste. However, the low initial cost is often offset
by higher bag replacement costs (such as replacing entire bag houses during maintenance shutdowns), and
the potential for fire hazards seem to be intrinsically higher in these designs (Phalen & Phalen, 2013; Godish
et al., 2015).
More advanced filtration options include spray chambers and wet scrubbers (to include venturi scrubbers and
wet cyclones). These afford very small particle capture, constant pressure drop (not unlike electrostatic
precipitators), and no dust generation. But, one of the disadvantages of the design is that the process
involves water. As such, the wastewater generated from the process creates another waste stream that must
be handled properly for pre-treatment and ultimate disposal (Phalen & Phalen, 2013; Godish et al., 2015).
According to your textbook, gas-phased pollutant capture strategies include a few more options than PM
capturing. These include thermal oxidizing (thermal oxidizers, flaring, and catalytic systems), adsorption
(packed sorbent beds), absorption (scrubbing), and biological treatment. The different options available within
each of these strategies afford the air engineer to aptly match the diverse types of gas pollutants to the
control.
Thermal oxidizers or “afterburners” are gas combustion chambers with temperatures typically ranging 540ºC
to 815ºC. These systems are robust enough to accommodate a moderate range of gases and work similarly
to a flare in terms of simply combusting the gas mixtures into less complex gases. There is normally very little
maintenance requirements for this technology, and the process is very efficient. However, as with any
combustion-related process, carbon dioxide (CO2) and carbon monoxide (CO) is still a potential outcome as a
byproduct of combustion (Phalen & Phalen, 2013; Godish et al., 2015).
Flare systems are typically used specifically for hydrocarbon-rich gases within a range of concentration just
below the upper explosive limit (UEL) and just above the lower explosive limit (LEL). The benefit is that the
explosive gases are combusted, often close to or exceeding 99% efficiency. The disadvantage is that, not
unlike afterburners, natural gas is often used as a prime for the flare system to keep the pilot lit, even while
producing other byproducts of combustion (Phalen & Phalen, 2013; Godish et al., 2015).
Catalytic systems (catalytic oxidizers or catalytic converters) are actually catalyst-filled filters that typically
operate at elevated temperatures between 370ºC to 480 ºC to treat gases at or near the LEL (Phalen &
Phalen, 2013). Benefits include the low maintenance requirements associated with thermal oxidation, as well
as the low system pressure drop that is also indicative of electrostatic precipitators. However, one of the most
routinely leveraged benefits is the use of this technology to reduce the footprint (size) and fuel use of other
systems. Disadvantages include the inefficiencies inherent in the design during colder temperatures, the
strong potential for particles to clog the catalytic converter, and the seemingly growing expense of catalyst
replacement (Phalen & Phalen, 2013; Godish et al., 2015).
Adsorption systems (packed beds) are designed to leverage the adherence (sticking nature) of gas molecules
through the van der Waals attractional force phenomena. These can be through either solid or liquid
adsorption systems. As discussed at length in your textbook, this is often accomplished with solid media
systems by packing beds with various packing media of metal, glass, plastic beads, and activated charcoal in
order to create a sorbent environment for the molecules traveling through the system. The polarity of the
molecules helps to inform the air engineer of the appropriate media to use in the system, targeting the gas
molecules of interest for capture. This specificity of gas molecule targeting is among the benefits of this type
of technology, as well as the relative ease of incorporating higher temperature gases for destruction of
MEE 6501, Advanced Air Quality Control 3
UNIT x STUDY GUIDE
Title
specific gases (such as heating potassium permanganate for destruction). However, disadvantages include
the fact that since there is a pressurized gas stream, clogging of the system, as well as the fact that
flammable media like activated charcoal is only compounded with the adsorption of other flammable organics
(Phalen & Phalen, 2013; Godish et al., 2015). Liquid media systems may also be used, given the benefit of
collecting the fluid media for recycle and reuse. However, disadvantages of the liquid media system is the
increased costs associated with many of the liquids effective for capturing the select gas molecules, corrosion
problems, and contamination issues often cited as being problematic in these types of system designs
(Phalen & Phalen, 2013).
Absorption systems (gas adsorption through liquid) or scrubbers are discussed in your textbook as having the
options of either solid or liquid-phased media designs. For example, solid-phased media scrubbers include
packed tower scrubber designs that can accommodate select gas molecule capture through sodium
carbonate, lime or other pack media. Additionally, flue gas and other similar gases may be dry scrubbed with
aerosol or aerosol slurries injected as an atomized mist and subsequently semidried in a reaction chamber.
Liquid-phase media scrubbers include water mixed with select mineral slurries or acids. For example, a
common industry practice for cleaning an ammonia nitrogen (NH3) gas stream is to scrub with a wet scrubber
misting water and sulfuric acid (H2SO4) in order to reduce the ammonia to the ammonium salt of ammonium
sulfate ((NH4)2SO4). Interestingly, both the benefits and disadvantages of these system designs are similar to
adsorption systems (Phalen & Phalen, 2013; Godish et al., 2015).
Biological treatment system options are appropriate when attempting to digest (rather than capture) gases
such as organic acids, ketones, esters, and other toxic gases. These “bioscrubbers” have several different
design types, as described in your textbook. The advantages of these systems include their relative efficiency.
Still, disadvantages include the higher maintenance requirements, costs of the microbes necessary to keep
the biofilters and packing beds charged, and the temperature and pressure sensitivity differences among
microbes (Phalen & Phalen, 2013; Godish et al., 2015).
This discussion completes our in-depth study of air quality engineering, and it prepares us to specify the
appropriate control technology for applications like our interior coating (paint) spray booth in our course
project scenario. We now understand that we have options for capturing both solid aerosol particles and
organic gas molecules within our work system, prior to discharging the air through the ventilation system and
out into the ambient air environment. Your work over the last eight units has prepared you to complete your
project successfully, carefully finishing the last few steps of engineering the air quality for your organization in
the scenario.
You can be proud of your demonstrated applied learning in this course. This course has challenged you to
pull from your growing knowledge of chemistry, physics, and atmospheric science gained through this
program. You are ready. Let’s go engineer some air quality into our environment!
References
Godish, T., Davis, W., & Fu, J. (2015). Air quality (5th ed.). Boca Raton, FL: CRC Press.
Phalen, R. F., & Phalen, R. N. (2013). Introduction to air pollution science: A public health perspective.
Burlington, MA: Jones & Bartlett Learning.
Pollution Control Technologies and Process Flow Diagram
Read the Unit VIII Study Guide (see attached), then consider the control technology options available for our scenario. Make your first Unit VIII section level 1 heading titled “Pollution Control Technologies.” Select appropriate control technologies to be used in the final exhaust air from the spray booth for the following pollutants: (a) gases and vapors, (b) aerosol particles, and (c) noise levels of 90 dBA at 1,000 Hz. Be sure to defend your suggested engineering controls with literature. Next, make your second Unit VIII section level 1 heading titled “Process Flow Diagram.” Map out the entire process by developing a drawing of the process. You might consider reviewing the drawings located within Appendix G and Appendix J in the TCEQ (2011) document and Figure 10.12 on page 381 of your textbook as good examples of clear and understandable process drawings to help you construct your own Process Flow Diagram.

Note: Since this section has two headings and a process flow diagram, . Thanks (As always please cite and reference as required using APA formatting).

Pollution Control Technologies
Environment conversation is important for today and future generations. Therefore, pollution control technologies are important in improving the quality of air. In this discussion, the control technologies which can be integrated into spay booth to control gas and vapors, noise levels of 90 dB at 1000Hz, and aerosol particles are presented. A flow diagram representing the process is also described.
Wet scrubber: the method applies the use control equipment useful for the removal of gaseous and vapor contaminants. The contaminants are removed through absorption process. The absorption process applies the principles of mass transfer. The liquid used is set to contain less of the contaminant to be absorbed. In physical absorption, the contaminant is dissolved in aqueous solvent. The scrubber may be countercurrent, cross flow or concurrent scrubber (De Nevers, 2010). The wet scrubbers attain very small particle capture, no dust generation and produces constant drop of pressure. All these desirable qualities suit the extraction of polluted gases and vapor from the exhaust air. The method is also cost effective with the major problem being wastage of water (Phalen & Phalen, 2013: Godish, 2015 quoted by the University of Columbia). Finding solution on how to control water wastage would highly boost the feasibility of the method.
According to Jacko and La Breche (2009), noise level can be controlled through shielding muffling, enclosing, and maintaining the machinery equipment. The spray booth is not an exceptional in this scenario. Therefore, the spray booth should be designed in a manner that high level of noise are absorbed and must be regularly maintained to so as to function properly without producing high levels of noise beyond the set limits.
Electrostatic precipitation forms the best appropriate control method for the aerosol particles. The aerosol particles are fine particles that can only be handled with the use of electrostatic precipitation rather than methods like cyclone collection. The method is very efficient since moisture laden air created from the high temperature of operation become the capturing medium, as stated by Phalen & Phalen (2013, quoted by the University of Columbia). Allied Environmental Technologies states that through utilization of the combined single stage and two stages electrostatic precipitation, the multistage collector provides the best combination of the uniform and non-uniform high tension electric fields of high efficiency for charging and collection of aerosol particles.
Process Flow Diagram
According to the TCEQ Regulatory Guidance (2011), process flow diagram or process description is one of the requirements that must be submitted at the registration time. It entails a step by step description of the input up to the final output. For the purpose of this discussion, electrostatic precipitation as a method of control technology for maintaining quality of air is described below. Buekens, Bhaskar, & Cholakov (2005) states that dust particles or dust are carried by the gas through the corona discharge created by the high potential voltage. The particles collect mainly negative ions. In accordance with their charge, the particles are attracted towards the collecting or discharging electrodes. Eventually, they are precipitated on those electrodes. The collecting roads are continuously removed in a periodical manner to dislodge the collected particles.

Figure 1Electrostatic Precipitation Process Flow Diagram
In conclusion, one method may not curb all the types of the pollution. Thus the use of hybrid methods should be enforced to ensure that the quality of air is maintained.

References
Allied Environmental Technologies, Inc. Control of Ultra-Fine Particulate Emissions Compendium: State-of-the Art Technology Review. Retrieved from http://www.alentecinc.com/papers/MSC/Control%20of%20Ultra-Fine%20Particulate.pdf
Buekens, A., Bhaskar, N., & Cholakov, G. S. (2005). Pollution Control Technologies. Encyclopedia of Life Support Systems.
Columbia southern university. Unit VIII Study Guide: Utilizing Pollution Control Technologies for Engineered Air Quality Control.
De Nevers, N. (2010). Air pollution control engineering. Waveland press.
Jacko, R., & La Breche, T. (2009). Air pollution and noise control. Environmental Engineering: Environmental Health and Safety for Municipal Infrastructure, Land Use and Planning, and Industry, Sixth Edition, 309-393.
Texas Commission on Environmental Quality. (2011). Surface coating facilities: A guide for obtaining air authorization in Texas. Retrieved from https://www.tceq.texas.gov/searchpage?cx=004888944831051571741%3Auk-3yh4pey8&cof=FORID%3A11&q=Surface+Coating+Facilities%3A+A+Guide+for+Obtaining+Air+Authorization+in+Texas

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