大氣污染控制工程英文課件

1、1大氣污染控制工程Air Pollution Control Engineering21 Introduction to Air Pollution control2 Air Pollution effects3 Air Pollution control philosophies4 Air Pollution Measurement, Emission Estimates5 Meteorology for Air Pollution control Engineers6 Air Pollutant Concentration Models7 General Ideas in Air Poll

2、ution control 8 Nature of Particulate Pollutants 9 Control of Primary Particulates10 Control of Volatile Organic Compounds11 Control of Sulfur Oxides12 Control of Nitrogen Oxides13 Other topicsContents31 Introduction to Air Pollution control1.1 Definition of Air Pollution 1.2 Source of Air Pollution

3、1.3 Results of Air Pollution 41.1 Definition of Air PollutionAir pollution is the presence of undesirable material in air, in quantities large enough to produce harmful effects.It causes harmful effects on human health, property, aesthetics, and the global climate.Key point: (1) it is harmful to veg

4、etation, biotic or abiotic. (2) The quantities are too great to be accepted (The pollutant concentration exceeds the acceptable lever)61 .2 Source of Air PollutionParticulate pollutantsCOXSOXNOXVOCsBurning fossil fuels such as coal, gasoline, and oil fuels Polluted air Greenhouse effect Ozone deplet

5、ionAcid rain Structure of the Electricity generation in ChinaCoal 82.6%Hydro 15 %Nuclear 2.3%Wind/ Biomass/Solar/Other 0.1%9Polluted Air101.3 Results of Air PollutionA. Global Warmingcaused by Carbon Dioxide, Other Greenhouse Gases, AerosolsB. Ozone Depletioncaused by （CFCS） Chlorofluorocarbons 氯氟碳化

6、合物，氟里昂C. Acid Rain11Global Warmingimprove12A. Global Warming Carbon Dioxide Other Greenhouse Gases Aerosols131415Caused by（CFCS）-Chlorofluorocarbons 氯氟碳化合物，氟里昂 ozone is about 1040km in height from the surface of the earthUse the thickness of the ozone to measure it：1 Dobson unit=110-3cmIf the ozone

7、is less than 220 DU, Ozone hollow turns up. The cavity in the Antarctic pole (the south pole) is becoming larger and larger. Ozone( O3) Depletionconsumption16Ozone Depletion18C. Acid Rain -pH12. some pollutant has no threshold limit valuesFor instance: arsenic; isocyanate (異氰酸鹽); carcinogens(致癌物)27B

8、. Air pollution Effects on Property28C. Air Pollution Effects on Visibility3 Air Pollution Control PhilosophiesEmission Standard*Air Quality Standard *Emission Tax (稅）*Cost BenefitWhat is Emission Standard? Answer: It is the regulation of the upper limit concentration values of the pollutants emitte

9、d from the smoke stack. These maximum values are determined by the acceptable pollutant concentration value on the ground according to the diffusion theory calculation. What is Air Quality Standard? Answer: It is the regulation of the maximum (threshold) value of the pollutant concentration in air.

10、These (threshold) values will not lead to air pollution damage on human and property.What is Emission Tax？ Answer: It is an air pollution law about that the money must be paid by the pollution emitters according to the emission rate, e.g., dollars/(kg pollutant/h). A. Emission StandardDifferent coun

11、try has different emission standard, Why?It depends on the economy, The technology, the living condition , the knowledge and the requirements of people. So it is a Philosophy. For Example: Emission Standard of cement factory (kiln窯爐 )Country Kiln Dust（mg/Nm3）SO2（mg/Nm3）NOx（mg/Nm3 ）Germen50400500Fran

12、ce505001200England40200900China (GB4915-1996)100400800China (GB4915-2004)50200800Japan50750500Malaysia1002002000Turkey120300400Italian1530400700UAS70750900 New Emission Standard for the Main Pollutants in China(GB16297-1996)pollutantLimit concentration of emission from stack(mg/m3)Limit of discharge

13、 rate(kg/h)Limit concentration of emission from disorder source(mg/m3)Height of stack(m)ClasstwoClassthreeSO2Production 96020304050801004.31525391101706.62238581602700.40Application 550NOxProduction 140020501001.312522.018780.12Application 240particulateCarbon black 18InvisibleAsbestos, quartz, 601.

14、0Others 1201.0B. Air Quality Standard GB3095-1996 pollutantTime averageconcentration Limit (mg/m3)Class ClassClass SO2year0.020.060.1Day0.050.150.25hour0.150.500.70 TSPyear0.080.200.30Day0.120.300.50PM10year0.040.100.15Day0.050.150.25NOxyear0.040.080.08Day0.080.120.12hour0.120.240.24C. Emission Tax

15、The polluters must pay the emission tax if they do not want to install the pollution control equipment.In this case, the pollutants discharged could possibly cleaned by the natural removal ability. Otherwise the pollution control equipment should be put in to use except bearing the emission tax. How

16、ever, the disadvantages of the emission tax (fee) is obvious. Why? Since this may lead to the managers to have less consideration about the effect on the environment due to the pollutant discharge. D. Cost-Benefit PhilosophyThe air pollution control philosophy is not to eliminate the pollution total

17、ly, but to minimize the costs of both control and damage in the condition of the economy and technology at present. Pollutant concentration in airCostCost of pollutant control equipment Pollutant damage costTotal cost (control + damage)acceptable concentrationProblem (Classwork)1. Explanation (1) Ai

18、r pollution(2) Dobson unit (3)（CFCs） (4) Threshold limit values of the pollutant breathing 2. composition Advantages and Disadvantages of Emission Forfeit or Penalty in China (more than 150 wards)4 Air Pollution Measurement, Emission Estimates4.1 A representative sample 4.2 Concentration determinati

19、on4.3 Averaging4.4 Determining pollutant flow rate 4.5 Isokinetic sampling384.1 A representative sampleTwo main tasks for any air pollution measurement are involved:One is to obtain a suitable representative sample.The other is to determine the concentration of the pollutant of interest in it correc

20、tly.HoodDuctPollution control equipmentFan Stack Measuring systemAir pollution control system and Measuring system394.2 Concentration determinationMeasuring systemExample: particle concentration determination Air pumpDuctParticle generator Valve FilterRotameterprobestepsWeigh the original filter m1

21、and put the filter into the holderTurn on the fanUse the thermo-ball meter to measure the velocity in the ductCalculate the flow rate Q according to the velocity since the diameter of the sampling tube is knownTurn on the air pump and adjust the rotameter（轉子流量計） at the calculated flow rateGenerate t

22、he particulateTake out the filter from the holder after 3 or 5 minutesWeigh the filter m2 because the particles are collected on the filterThe concentration C is: 414.3 AveragingAlmost all the experimental results have certain fluctuation due to the measurement error (deviation偏差) at different time.

23、 the average value is, therefore, much more reliable (reasonable) in scientific research. There are two cases:(1) An experiment is repeated several timesAverage value:(2) An experiment has been done over some period of timeAverage value4.4 Determining pollutant flow rateThere are two flow rates, mas

24、s flow rate and volume flow rate. Qm=vA, orwhere, v-gas velocity, A-area of the duct, and -the density of the polluted air QV=vA, orExample If the velocity distribution is and the radius of tube is R=0.1m. Please find the volume flow rate in the tube.m/s,434.5 Isokinetic samplingequivalent velocity

25、samplingThe gas velocity inside the sampling probe is equal to the gas velocity in the duct.Why? (Page 73)If the gas velocity is too great in the probe, less particles get into the probe due to the inertial （慣性）effect.If the gas velocity in the probe is slower than the gas velocity in the duct, more

26、 particles get into the probe. Therefore, isokinetic sampling is necessary to reduce the measuring deviation in the experiment.445 Meteorology for Air Pollution Control Engineers5.1 The atmosphere5.2 Horizontal atmosphere motion5.3 vertical motion in the atmosphere5.4 Winds5.5 Temperature inversion5

27、.6 Fumigations, stagnation 455.1 The atmosphereThe composition of the atmosphere: 78% nitrogen, 21% oxygen, 1% argon (氬）and other trace(微量) gases.The humidity of the atmosphere: changing significantly with place and time, and increasing rapidly with increasing temperature. of the mass of the atmosph

28、ere is within 6 km above the earth surface. Almost all the mass of the atmosphere and the moisture are within 20 km above the surface. The thickness of the atmosphere: Its upper boundary is not well defined. Fortunately, the air pollution problems we discussed are often within 2km.465.2 Horizontal a

29、tmosphere motion1. Atmosphere motion caused by temperature differenceKey point: hot air goes up, cold air goes down.EquatorSouth poleNorth pole472. Atmosphere motion caused by Coriolis force the force acts at right angles to the motion of the bodyEquatorEarth rotationNorth poleAtmosphere motioncanno

30、nbomb485.3 vertical motion in the atmosphereIn the atmosphere any parcel of air that is less dense than the air that surrounds it will rise by buoyancy. Otherwise, any parcel of air more dense than the surrounding air will sink by negative buoyancy. Most vertical motions in the atmosphere are caused

31、 by changes in air density. 5.31 Air density changes with temperature and humidityThe density of gas is given by perfect gas lawWhere, Mmolecular weight, Ppressure, Rgas constant, Ttemperature (1) 49ExampleEstimate the change in air density due to 1 increase in temperature for dry air1percent increa

32、se in relative humidity (both at 20)Solutiona. Differentiating Eq. (1), If M and P are constant, we have(2)we find50b. The molecular weight of dry air is 29. The mol fraction of water vapor at 20 is 0.023RH. And the molecular weight of water is 18.Thus The molecular weight of the air with water vapo

33、r isThe variation of temperature has much more effect than that of the humidity. Therefore, most of the vertical motion of the atmosphere is driven by changes in temperature rather than by changes in humidity.relative humidity515.3.2 Air density change with pressureThe basic equation is The negative

34、 refers to the pressure in the opposite direction of the coordinate z . Substitute Eq. (1) into Eq. (3), yields(3)The changes of M can be negligible, but the changes of temperature are not . (4)52 Suppose a parcel of air in a invisible flexible balloon moving upward in the atmosphere. The air in the

35、 balloon does not work on its surroundings as it expands. It undergoes a reversible, adiabatic（絕熱） process. According to thermodynamics, we have Where CP is the heat capacity of gas at constant pressure.Divided Eq. (4) by Eq. (5) on both sides, we find(5)(6)Here, g=9.81m/s2, M=29g/mol, Where CP =3.5

36、R=3.58.314m3Pa/molKs.So thatballoon/kmUFO This is called dry adiabatic lapse rate（干絕熱直減率）535.3.3 Atmosphere stability z Super-adiabatic UnstableTemperature InversionVery stableSub-adiabaticStable Adiabatic NeutraldT/dz10dT/dz10054Vertical temperature distribution on a cloudless day with low windz158

37、-9AM 10AM-1PMT6-7AM 222-5 PMdry adiabatic lapse rate linestable5.3.4 Mixing Height (混合層高度） Since the temperature reduces 10 when the height increases 1km, if the ground temperature is 15. The temperature will become 0 at 1.5km in height. The humid air must be condensed. The cloud can forms above 0 （

38、05 ). 150 0 cloudMixing heightzTThe mixing height the height where the cloud can get to. The pollutant diffusion happens within the mixing height.lapse rate line565.4 WindsSeacontinent windCool air Wormer air At day timeCool air Wormer air 4 A.M.mountainvalley wind575. 5 Temperature inversions warm

39、air layer on the top of the cold layer 5.6 Fumigations(熏煙）, stagnations（滯流）T5.7 City island effectSuburb Countryside Urban zPlume（煙羽）stagnationFumigation6 Air Pollutant Concentration Models 6.1 Introduction The purpose of establishing the concentration modelsTo meet the requirements of the air pollu

40、tion law, we should predict the concentrations of contaminants. To plan air pollution control programs or to build up some new projects, we should predict the emission concentrations of the pollutant from the sources. The basis of the concentration models: principle of mass balance.6.2 Fixed-box mod

41、els (箱式模型）Assumptions:1. The pollution area is rectangular with W and L.2. Pollutants are complete mixed up to the mixing height H（混合層）.3. The concentration is uniform in the box due to the turbulence.4. The wind velocity u is constant and uniform .5. No pollutant leaves or enters through the top of

42、 the box, nor through the sides that are parallel to the wind direction. 60Let: the concentration of pollutant in the air entering pollution area is C0 (g/m3), the emission rate per unit area is q (g/sm2).The mass flow rate(質(zhì)量流量）is:The creation mass flow rate in the pollution area is: yHxWind veloci

43、ty, uzWLThe mass flow rate out of the pollution area is: According to the material (mass) balance theory, we have616.3 diffusion models6.3.1 The Gaussian plume ideaThe pollutant gas comes out as a point source.The coordinates of the point source is 0, 0, H, where H is the effective stack height. Whe

44、re, h is the stack height, h is the plume rising height.The plume appears to have a twisting, snake like shape. However, time averages out the variations of the plume, the shape of the plume appears uniform and symmetrical. The concentration distribution follows the Normal distribution function. 626

45、.3.2 Gaussian plume derivation1. Basic Gaussian plume equationWhere, are called horizontal and vertical dispersion coefficients (彌散參數(shù)， m）. If are determined, the concentrations of the plume at any point can be calculated .2. How to determine the are proportional to the square root of the downwind di

46、stance. At the different point (x, y, z), are the function of wind speed and the degree of solar heating. These can be related with the atmosphere stability. (1)63Surface wind speed(10meters 6CDDDDStability categoriesSurface wind speed(10meters above ground)m/sDayNightIncoming solar radiationThinly

47、cloud Or 4/8Clear or3/8strongmoderateslight0-2AA-BB-2-3A-BBCEF3-5BB-CCDE5-6CC-DDDD6CDDDD64Example: estimate the valu of at a point 0.5km downwind from a point sourceon a bright summer day. wind speed greater than 6m/s. From the above table, atmosphere stability C should be selected. Using the fig. 6

48、.7 and fig. 6.8, we find the horizontal dispersion coefficient and vertical dispersion coefficient at a point 0.5km downwind respectively: Then we can use the equation (1) to calculate the concentration at any point of x, y, z. 3. The effect of the ground Equation (1) is a diffusion model in unlimit

49、ed space for the point source, which can be used to predict the concentration approximately in the fume considerably far from the ground. It means that the effect of the ground can be negligible.However, we are often interested in concentrations at the ground level since people and property are expo

50、sed there (living on the ground). But near the ground, because the boundary condition is changed, the concentration distribution will not follow the Equation (1).(1) “reflection wall hypothesis”(反射壁假設） When the plume goes down and touches to the ground surface, the ground looks like a mirror, the po

51、llutant is reflected upward to the atmosphere again. (2) principle of superposition（疊加原理） The pollutant concentrations from different sources can be added directly. 66In order to know the concentration in the reflection area, suppose there is an image point source symmetrically under the ground. The

52、 original plume concentration distribution is HH0Reflection areaReal sourcezxImage sourceThe image plume concentration distribution, obviously, is 67According to superposition principle, the concentration in the reflection area is 4. the concentration on the ground Let z=0, the concentration on the

53、ground can be found directly from Equation (3)5. the concentration on the ground under the centerline of the plume For this condition, y=0, z=0, therefore, the concentration on the ground under the centerline of the plume is6.4 plume riseWe have known that , Where, h is the stack height, h is the pl

54、ume rising height. The h is determined by : smoke exit velocity from the stack vs, stack diameter D wind speed u, the pressure around the stack P, smoke temperature Ts and the atmosphere temperature Ta. There are many formulae for calculating the plume rising height h. Now we just give the Hollands

55、formula Example (page 143)7 General Ideas in Air Pollution control7.1 AlternativesThree control options are available ( three methods can be made use of to control the air pollution).1. Improve dispersion first option(1) Tall stackFrom Eq.(6), when the stack height h is determined, to increase the s

56、moke exit velocity vs, the difference of the smoke temperature Ts and the atmosphere temperature Ta is the main ways to increase the plume rising height h. The smoke dispersion can be improved. (2) Intermittent control schemes (the plan to control the emission quantity at different time and deferent

57、 place)For instance, in the afternoon, the diffusion ability is stronger, the amount of pollutant discharged could be higher. But in the morning, the amount of pollutant discharge should be reduced due to the temperature inversion.Similarly, Seacontinent wind and mountainvalley wind, and others fact

58、ors should also be considered. 2. Reduce emissions by process change, pollution prevention - second option The idea of reduce emissions by process change means that using the less pollution production techniques to substitute the heavy pollution processes. In this book (page 165), many examples were

59、 given:Painting: water-based paint replaces the oil-based paint to reduce the hydrocarbon emission;Burning: Open burning is substituted by the close burning in incinerator; Traveling: get people from home to workcarpool. Taking buses with others, instate of driving a car individually. Lighting: repl

60、acing low efficiency incandescent lights with higher-efficiency fluorescent lights to save energy (less fuel is used, less air pollutants are emitted). And so on.The key point is: preventing pollution is much better than control it.3. Use a downstream pollution control device-third option a downstre