22What is Air Pollution?The release of harmful substances that can harm the environment and humansEPA created the Clean Air Act to have regulations against acts against the environmentTwo main approaches to reducing emissions into the atmosphereChange the process that contributes to emissionsAdding pipe to the end of a process to remove and treat contaminants
33Clean Air ActEPA Clean Air Act violations and the resulting punishments
4High Priority Violators of CCA 4High Priority Violators of CCA
5Advantages of the Clean Air Act 5Advantages of the Clean Air ActFor over 40 years the CAA has cut pollution in the U.S.The health benefits of the CAA exceed the costs of reducing pollutionNew types of technology have been developed because of it etc. automobiles, plants, and factoriesThe act also promotes heavily for the develop and deployment of cleaner technologies
6Advantages of the Clean Air Act 6Advantages of the Clean Air ActHealth Effect Reductions (PM2.5 & Ozone Only)Pollutant(s)Year 2010Year 2020PM2.5 Adult MortalityPM160,000230,000PM2.5 Infant Mortality230280Ozone MortalityOzone4,3007,100Chronic Bronchitis54,00075,000Acute Bronchitis130,000180,000Acute Myocardial Infarction200,000Asthma Excaberation1,700,0002,400,000Hospital AdmissionsPM, Ozone86,000135,000Emergency Room Visits120,000Restricted Activity Days84,000,000110,000,000School Loss Days3,200,0005,400,000Lost Work Days13,000,00017,000,000This table demonstrates how air emissions are dropping from 2010 to 2020 and in what categories
7Clean Air Act violation 7Clean Air Act violationAugust 2009 in IllinoisA guy named O’Malley was hired by a guy named PinskiPinski was the manager of Dearborn Management Inc.O’Malley was the owner and operator of Original Fire ProtectionO’Malley’s company was hired to remove and dispose of asbestos from Dearborn’s piping systemDuring investigation O’Malley was found out to be a fraud in the removal of abestos. His company was not trained and he also accepted to perform the job at a cheaper price than a competing company who was trained in the removal.O’Malley fines120 months in jail, 36 months probation, and he had to pay a fine of $15,000 to the federal government, and $47,086 to the EPA for having to clean up their messPinski finesSentences to half a year in prison, 2 years of release from work,and half a year home detention
8Pollution Prevention Change the way we use fuel 8Pollution PreventionChange the way we use fuelSubstitute less toxic materialsReduce the formation and fabrication of materials and byproductsCapture and conduct studies on potential pollutants
9Air Pollution Control (APC) Equipment 9Air Pollution Control (APC) EquipmentAPC equipment can help control emissions by these ways:Destroy and capture possible pollutantsConvert these pollutants to less-toxic materials or compoundsRemove all pollutants from the air
1010Gas AbsorptionOne of the most common methods for reducing air pollutionPollutants are removed by dissolving into the scrubbing solution (usually water).
11Gas Absorption 11 Commonly used to reduce CO2 amounts in furnaces. The final product is leaving the scrubber at less than 500 ppm CO2
1212Gas AbsorptionReactants can also be added into the scrubbing solution to remove pollutants via chemical reaction.Ex: adding hypochlorite to the scrubbing solution allows sulfur- containing compounds to react with the solution, which can reduce odor.Conditions necessary for gas absorption:Water-soluble pollutantsParticulatesThis figure shows 2 types of absorbers
1313Gas AbsorptionThe most common type of absorption for reducing pollutants in air is through a Gas-liquid interface, as shown in figure (a) to the left.When gas is bubbled through the liquid, gas molecules are absorbed.Note that this is not adsorption (which can also be used to reduce pollution). Adsorption requires that the molecules adhere to the surface of other molecules.
14Visualizing Gas Absorption 14Visualizing Gas AbsorptionThis is another way to visualize the absorption process.The red arrow represents polluted gas entering a chamber.The pollutants (red) are then absorbed by water molecules as they rise through the chamberPurified air (white) is then released through the top of the chamber
1515Measuring Air qualityAfter the absorption process, it is useful to be able to measure the quality of purified air. This can be done using the following Matlab code:% I = Air quality Index% C = Pollutant Concentration% Clow = Concentration breakpoint less than C% Chigh = Concentration breakpoint greater than C% Ilow = Index breakpoint for Clow% Ihigh = Index breakpoint for ChighClow=35.5Chigh=55.4Ilow=101Ihigh=150I=((Ihigh-Ilow)/(Chigh-Clow))*(Chigh-Clow)+IlowI=% AQI approx. 150 means air is potentially unhealthy to the population
16Optimizing Gas Absorption 16Optimizing Gas AbsorptionAdding arsenite increases the rate of absorption of CO2 with respect to NH3.Arsenite allows absorption to continue past a 1:1 ratio. With no arsenite, absorption becomes very ineffective at this point
17Condensation 17 Highly effective for VOC’s Separates pollutants by rapidly decreasing temperature or increasing pressure, causing them to condense and drop outThis tower is used for Cryocondensation. Cryocondensation can purify many solvents. These include toluene, acetone, methanol, chlorinated derivatives, and hydrocarbons.
18Thermal Oxidizers/Incinerators 18Thermal Oxidizers/IncineratorsDestroys volatile organic compounds (VOCs) and volatile hazardous air pollutants (HAPs) by high temperature destruction (~ °F)High thermal energy breaks covalent bondsPros -high efficiency (>99.9% if well- designed)good for variable VOC loadshighly reliableCons -insufficient residence time causes toxic byproductsrequired fuel is expensive, produces CO2 and NOx gassesmust be fabricated from highly temperature resistant materials
19Thermal Oxidizers - Liquid Injection 19Thermal Oxidizers - Liquid InjectionUsed primarily in chemical industry to destroy the liquid wastes that contain organic toxinsLiquids get atomized through nozzles, exposed to burner flames, get vaporized and become superheatedSuperheated gas combined with air in a turbulent zoneResidence time varies based upon flow volume, usually ~ sToxic liquid waste gets oxidized to produce CO2, H2O, O2, N2, and acid gasesAcid gases must be cleaned from exhaust stream by using wet scrubbers
20Improvements to Thermal Oxidizers 20Improvements to Thermal OxidizersRecuperative Thermal Oxidation:Utilizes shell-and-tube heat exchanger to capture excess heat, which can be used to preheat incoming waste gasRegenerative Thermal Oxidation:Recovers and reuses >90% of thermal energy from combustion chamber by utilizing a ceramic material as a heat sink to remove heat from the exhaust downstream of the unitThe ceramic material preheats incoming waste gas, reducing the amount of fuel required for oxidationimages from original paperImages from original article
21Catalytic Oxidizers/Incinerators 21Catalytic Oxidizers/IncineratorsDestroy VOCs and volatile HAPs by high temperature destructionUtilizes catalyst to lower destruction temperature (~ °F)Pros -high control efficiencygood for variable VOC loadsvery reliablelower temperature compared to thermal oxidizers, means significant fuel savingsCons -catalysts may plug and become ineffectiveexpensive to dispose of spent catalystsCan utilize same improvements as thermal oxidizers (regen. & recup.)
2222Carbon AdsorptionRemoves some VOCs which have a high affinity for carbon by surface adsorptionbenzene, phenol, vinyl chloride, xylene, toluene, acetone, sulphur-containing compoundsPros -able to recover contaminants for reuseVery high control efficiencyCarbon is relatively cheapCons -only removes some VOCsnot as effective if load variesparticulate matter can plug the carbon bed
23Carbon Adsorption 23 Most systems consist of two beds Waste gas is passed over one bed and undergoes adsorbing process, while steam passes over the other bed and undergoes a desorbing processAfter a period of time the process streams are switched, so that the beds alternate between adsorption and regeneration processesMost carbon adsorption processes utilize a prefilter to remove particulate matter that would otherwise plug the carbon beds
24Carbon Adsorption - Freundlich 24Carbon Adsorption - FreundlichThe Freundlich Adsorption Equation is used to compare adsorptive capacity of different activated carbonsX/M=KC^(1/n)It is often more convenient to express in logarithmic form to perform calculations and fit dataThese logarithmic plots are referred to as Freundlich Adsorption Isotherms (FAI)These plots are useful because they:determine if a desired purity level is possible with the specific carbonallow for calculation of carbon loading at equilibriumcan be used to predict the relative performance of different types of carbonhigher isotherm line means better adsorptive capacityA MATLAB function to calculate carbon loading at equilibrium , plot the FAI and compare two different carbons is shown on the next slide.
25Carbon Adsorption - MATLAB 25Carbon Adsorption - MATLABfunction [Crate] = carbadsorp(M,C,X,Co)%function to generate Freundlich Adsorption Isotherm%M(1) must correspond to lowest C dosage%C(1) must be initial impurity%INPUTS:%X = amount of impurity adsorbed at equilibirum (mg/L)%M = carbon dosage (g/L)%C = concentration of impurity remaining in solid (mg/L)%Co= desired final impurity level%OUTPUTS:%CL = carbon loading at Co (mg/L)%delC= impurity removal (mg/L)%Crate= carbon usage rateMold=M;Cold=C;Xold=X;n=length(C);if n ~= length(M) && n~= length(X)error('length of M,C, and X must be same');endb=X./M;if M(1)==0for k=1:n-1b(k)=b(k+1);C(k)=C(k+1);endb=b(1:n-1);C=C(1:n-1);n=length(C);endblog=log10(b);Clog=log10(C);a=polyfit(Clog,blog,1);xx=linspace(Clog(1),Clog(n));for i=1:length(xx)yy(i)=a(1)*xx(i)+a(2);endplot(log10(C),log10(b),'xr',xx,yy,'--k'),gridxlabel('log(C), impurity remaining'),ylabel('log(X/M), carbon loading'),title('ADSORPTION ISOTHERM')CL = 10^(polyval(a,log10(Co)));delC = Cold(1)-Co;Crate = delC/CL;endPlot for carbadsorp(M2,C2,X2,20)From scipt on next slide
26Carbon Adsorption - MATLAB Results 26Carbon Adsorption - MATLAB ResultsThe following script can be used as an example:>> M1 =[ ];>> C1 =[ ];>> X1 =[ ];>> M2=[ ];>> C2=[ ];>> X2=[ ];>> carbadsorp(M1,C1,X1,20);>> (ans-carbadsorp(M2,C2,X2,20))/ans*100ans =Plot for carbadsorp(M1,C1,X1,20)These results show that approximately 55% more of Carbon 2 is required to obtain the same treatment results as Carbon 1. This data can now be used to determine which carbon is more suitable for use in a regenerative carbon adsorber by comparing the cost and efficiency of each.
27Electrostatic precipitation overview 27Electrostatic precipitation overviewESP Industrial Air Filter, image from:The Electrostatic precipitation (ESP) technique is another effective solution to reduce air pollutant in the air.Utilizes induced electrostatic charge to remove particulars from the gas.Very effective at removing particles from the gas because the flow is uninterrupted and energy is only used removing the particles.With regards to air pollution, ESP first polarizes the pollutants and collects them while allowing the cleaner air to flow through.
28Electrostatic precipitation continued 28Electrostatic precipitation continuedESP process microscopic view, image from:Electrostatic precipitator has two important steps: the charging step and the collection step.During the charging step the particles in the gas are charged (positively) from the wires. Afterwards, the particles are collected by the negatively charged collecting plates while clean air is unimpeded. Picture to the right illustrates the process.One very important characteristic to consider therefore is the resistivity of the particle. Resistivity is the measure of resisting power of a material to flow current.Resistivity= Resistance*Area cross-section/LengthIf the resistivity is too high, the particle will not be charged sufficiently, too low and the particle will not stick on the collecting plates.Ideal resistivity of the particles is 107-2*1010 ohm-cm as shown on the left.Graph of efficiency versus resistivity, image from:
29Dust collection efficiency calculations 29Dust collection efficiency calculationsThe effectiveness of an electrostatic precipitator separating particles of medium resistivity can be determined by its dust collection efficiency.η = 1-exp(-a*k*t) Where a=area, k=device constant, and t is the treating timeMatlab m-file for calculation of efficiency assuming spherical particle:function ElectroStaticEff(r, k, t)% r is the radius of the particle being removed% k is a device constant defined by experiments% t is the treating timea=4/3*pi*r^3;n=1-exp(-a*k*t)endAs shown above, the effectiveness of electrostatic precipitator is highly dependent on the area of the particle. Smaller particles greatly reduces the efficiency of the process.Typical values range , efficiency below .8 are better off using a different filtration process.Visualization of process, image:
30Electrostatic precipitator conclusion 30Electrostatic precipitator conclusionHowever, small particles do not stick to wallPros for ESP:Efficient process to separate pollutants from the air.Low operating costTemperature independentVery high efficiency for medium to large sized particles.Cons for ESP:Very large machineCannot separate very high or very low resistivity particles-- needs a certain rangeCannot separate very small sized particles.Currently, the most popular industry uses for ESP process are smokestack to remove harmful air pollutants from the exhaust.Large enough particles stick to the collecting stationsAir passes through along with pollutants
31Baghouse introduction 31Baghouse introductionBaghouse filtration is a different method which can control emissions.Focuses on removing the pollutants from the air, as with electrostatic precipitation.Baghouse filtration is always very efficient, very common collection efficiency rate is 99.9%. Furthermore, collected pollutants can be recycled to the parent process to be used as heat.Particle size is not a limiting factor for baghouse filtration, can collect particles large and small.Example of baghouse filtration, picture taken from:
32Baghouse filtration continued 32Baghouse filtration continuedDuring the baghouse filtration process dirty gas is run through the walkways and out through the exhaust.The walkways are made from felted fabric which can be as small as the particles needed to be filtered.The particles are left behind and form a cake layer on the fabric.Once the cake layer is so dense that the flow of gas has stopped, the walkways are shaken which drops the particles into a collector to be recycled if capable. The process is then repeated.Example of walkways, picture from
33Baghouse filtration calculations 33Baghouse filtration calculationsPressure drop across the baghouse filter is necessary to know in order to utilize the filter. Pressure drop is the sum of the pressure drop across the filter and the pressure drop across the cake, numerically given below. Matlab program given below.∆Pf=k1*Vf ∆Pc=k2*Ci*Vf2*tWhere k1:fabric drag, Vf: filtration velocity, k2: Resistance of cake, Ci: Dust concentration loading, t=filtration timeFiltration Velocity (or air-to-cloth ratio) is another quantity helpful to define.Vf= Q/(Ac)Where Q: volumetric flow rate, Ac: Area of cloth filterClean air passes throughfunction BaghousePressure(k1, Q, Ac, k2, Ci, t)% k: fabric drag coefficient% Q: volumetric flow rate% Ac: area of cloth filter% kk: cake resistance coefficient% Ci: Dust concentration loading% t: filtration timeVf= Q/ACPF=k*VfPC=kk*Ci*Vf*Vf*tP=PF+PCendCake layer builds up on the endDirty air enters the walkway
34Baghouse filtration conclusion 34Baghouse filtration conclusionPros for baghouse filtration:Very efficient filtration over 99%.Able to separate the small particles that other filtration methods cannot.Collected particles can be recycled and used for heat.Cons for baghouse filtration:Time must be spent cleaning the walkways once the air flow stops.Cost can be higher upfront.If an air bag breaks, the entire process must be stopped in order to replace the bag. Often times the particles are toxic to humans and difficult to clean if it breaks.Example process of baghouse, taken from:
35Conclusions-Prevention Methods 35Conclusions-Prevention MethodsThe most cost effective way to reduce air emissions is by implementing pollution prevention method and improving efficiency of process to consume less materials and energyHowever, efficiency improvements have limits and APC technologies will be needed to overcome these limitations.The figure shows gives an example of how and plant first attempts to change their process using prevention methods to reduce pollution before moving on to other less preferred options.
36Conclusions-Air-Pollution-Control 36Conclusions-Air-Pollution-Control•Due to diverse nature of plant’s processes, raw materials, and emissions, certain plants may require different types APC equipment.•It is important to understand the fundamental principles behind:•APC technologies•Processes being used•Contaminants to be controlled•Exhaust stream composition•To determine which APC will be most efficient, reliable, and cost-effective as an air pollution strategy.•This table summarizes the APC technologies basic fundamentals.Table from original articleTable from original article
3737Future work in topicImprovements are ideally made at the upstream level, decreasing the pollutants originally formed.Future work in APCs could include more efficient designs of any of the procedures outlined above.Otherwise new methods could be created which could combine methods used above or reduce their disadvantages.