Discuss the engineering options available, the mode of action for capturing gas-phase pollutants from air, and the benefits and limitations of each as an option in air quality system designs. the answer must be at least 300 words in length UNIT VIII STUDY GUIDE Utilizing Pollution Control Technologies for Engineered Air Quality Control Course Learning Outcomes for Unit VIII Upon completion of this unit, students should be able to: 7. Evaluate air pollution control technologies. 7.1 Discuss air pollution control technologies for particulate-phase pollutants. 7.2 Discuss air pollution control technologies for gas-phase pollutants. Course/Unit Learning Outcomes 7.1 7.2 Learning Activity Unit Lesson Chapter 9, pp. 331-352 Chapter 10, pp. 355-385 Unit VIII Assessment Unit Lesson Chapter 9, pp. 331-352 Chapter 10, pp. 355-385 Unit VIII Assessment Reading Assignment Chapter 9: Control of Motor Vehicle Emissions, pp. 331–352 Chapter 10: Control of Emissions from Stationary Sources, pp. 355–385 Unit Lesson Independent Variables 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 general systems, theory-based engineering perspective. We can most likely agree that engineering air quality has demonstrated to be an interdisciplinary science of its own! In this unit, 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 in our air. Consequently, we must first understand that our air quality control options are going to largely fall into one of two categories: particulate-phased pollutants or 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 (2014), particulate-phased pollutants (measured as a percentage of particulate matter or PM) really have about three main capture strategies that are effective for improving air quality. These include cyclonic collection, electrostatic collection, and numerous methods of filtration collection. Controls 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 MEE 6501, Advanced Air Quality Control 1 aerosol centrifuges). The documented benefits include their relatively lower costs, operation, UNITsimplicity x STUDYofGUIDE durability, and generally low maintenance. However, disadvantages include relatively Title low 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., 2014). Electrostatic precipitators (including mist precipitators) are designed to operate at high temperatures while creating a 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., 2014). 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 off-set with higher bag replacement costs (such as replacing entire bag houses during maintenance shut-downs), and the potential for fire hazards seem to be intrinsically higher in these designs (Phalen & Phalen, 2013; Godish et al., 2014). More advanced filtration options include spray chambers and wet scrubbers (to include venturi scrubbers and wet cyclones). These afford very small particle captures, constant pressure drops (not unlike electrostatic precipitators), and no dust generation. Still, one of the disadvantages of the design is that the process involves water. As such, the waste water 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., 2014). According to Godish et al. (2014), 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 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 from 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 are normally very few 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) are still potential outcomes as byproducts of combustion (Phalen & Phalen, 2013; Godish et al., 2014). 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., 2014). 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., 2014). MEE 6501, Advanced Air Quality Control 2 UNIT x STUDY GUIDE Title This is a close-up view of cross section of honeycomb interior structure of a catalytic system. The precious elements used in these systems, such as platinum and palladium, cause a cost-disadvantage for these systems. (Baloncici, 2011) 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 by Godish et al (2014), 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 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 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 is possible as well as the potential that flammable media—like activated charcoal—could become compounded with the adsorption of other flammable organics (Phalen & Phalen, 2013; Godish et al., 2014). 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 are the increased costs associated with many of the liquids effective at capturing the select gas molecules, corrosion problems, and the strong potential for accidental contamination of the system (Phalen & Phalen, 2013). Absorption systems (gas adsorption through liquid) or scrubbers are discussed by Godish et al. (2014) as also 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 captures 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, then subsequently semi-dried in a reaction chamber. Liquid-phase media scrubbers include water mixed with select mineral slurries or even acids. For example, a common industry practice for cleaning an ammonia nitrogen (NH 3) gas stream is by scrubbing with a wet scrubber that mists 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., 2014). 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 are discussed by Godish et al. (2014) with several different design types. The advantages of these systems include their relative efficiency. Still, disadvantages include the higher maintenance requirements, the cost of the microbes MEE 6501, Advanced Air Quality Control 3 necessary to keep the biofilters and packing beds charged, and the temperature andx pressure sensitivity UNIT STUDY GUIDE differences among microbes (Phalen & Phalen, 2013; Godish et al., 2014). Title This discussion completes our in-depth study of air quality engineering, and it prepares us as graduate-level engineers to specify the appropriate control technology for applications not unlike the industrial 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 these eight units has prepared you to understand the steps required to actively engineer air quality rather than to passively monitor and manage it. You can be proud of your demonstrated applied learning in this course. This course has effectively challenged you to pull from your growing knowledge of chemistry, physics, and atmospheric science, gained throughout this entire graduate-level program. You are ready. Let’s go engineer some air quality into our environment! References Baloncici. (2011). Catalytic converter, (ID 29963108) [Photograph]. Retrieved from https://www.dreamstime.com/royalty-free-stock-photos-catalytic-converter-honeycomb-interiorstructure-emissions-control-image29963108 Godish, T., Davis, W. T., & Fu, J. S. (2014). 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. MEE 6501, Advanced Air Quality Control 4 
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