大氣污染控制工程-Lecture 7-1 General ideas in air pollution control.PPT

1、Prof. Jiakuan YangHuazhong University of Science and Technology Three alternatives for air pollution control Air pollution control systems and equipment Fluid velocities in air pollution control equipment Minimizing volumetric flow rate and pressure drop Efficiency, penetration, nines Three alternat

2、ives for air pollution controlImproving the dispersion of our emission and thereby diluting the pollutants and lower the concentration near the ground level where people often exist .Basic ideaThreshold value(1) improve dispersion The population density is 1 person/km2In a sparely populated area, th

3、e pollutant emissions are eliminated by natural removal mechanisms and without causing any damage to the neighbors.In a densely populated world, dispersion is not a satisfactory approach .For exampleThe population density is 29,000 persons/km2 ( Manhattan ) (1) improve dispersion (1) improve dispers

4、ion Tall stack the ground-level concentration22222exp2expzyzyHyuQcHchProblem(1) improve dispersionIt will certainly decrease all the ground-level concentration near the stack, but it may increase some concentration far from stack with a tall stack .SO2 ultimately comes to ground , mostly with rain o

5、r snow for far away from the tall stack .Raising the emission point of stack, may raise the concentration far downwind .For example: Acid-rain controversy Tall stack 2001 年年 度二度二 氧氧 化化 硫硫 濃濃 度度 區(qū)區(qū) 域域 分分 布布2001 年年 度度 全全 國(guó)國(guó) 將將 水水 pH 值值 分分 布布(1) improve dispersion Intermittent control schemes Example 1

6、, predictive control scheme down wind StackA fire-electric plant morning exercise 6:30 8:00 A.M. Opening center-park(1) improve dispersionhTBefore 9:00 A.m. Shut off the production and stringent control of stack emission. Temperature Inversion Intermittent control schemes (1) improve dispersionExamp

7、le 2, observation control system Homes wood stoves: PM10Oxygenated motor fuels: CO Intermittent control schemes (1) improve dispersion relocate the plantThe emission source should be far away from populated areas. Such as residential areas, commercial centers . Reduce emission by process change , po

8、llution prevention water-based paintsCleaner production, from raw material, old process, old technology, changed into a cleaner process, to prevent pollution. Basic ideaCoal is replaced by natural gas as a home or business fuel .(3) Use a downstream pollution control device tailpipe end-of the pipe

9、control device Designing air pollution control systems and equipment Emission source Hood Blower Control device stack Collected pollutant Reduce emissionResource recovery and ultimate fate of pollutantsFluid velocitiesRun costEfficiency室內(nèi)空氣速度分布（三）風(fēng)壓作用下的自然通風(fēng)風(fēng)洞模型實(shí)驗(yàn)風(fēng)洞模型實(shí)驗(yàn)A Typical continuous-feed mass-

10、fired municipal CombustorResource recovery If the pollutant is valuable material or a fuel , it may be more economical to collect and use it than to discard it. Generally, reclamation or recovery is economical only if the concentrations are high enough in waste stream .The ultimate fate of pollutant

11、sMost particulate pollutant , e. g . fine dusts, to be captured and placed in a landfill. Most organic compounds will burn.Hazardous wastes disposal cost is higher . Fluid velocities in air pollution control equipmentMinimize sum of pumping cost and capital cost of pipes and ducts .Almost all indust

12、rial-sized flows of air or gases are turbulent .40 to 60 ft/s (12 to 18 m/s ) Diametervelocitycost of pumpingCost of the pipe Minimizing volumetric flow rate and pressure dropIn the air pollution control system , fan or blower is the power source that propels the gas stream through the control devic

13、e and the associated ductwork and exhaust stack . Minimizing volumetric flow rate and pressure drop n = molar flow rate R = universal gas constant T1 = inlet absolute temperature k = heat capacity ratio = 1.4 for air and most waste gases = fan or blower efficiency P1 = inlet absolute pressure of the

14、 fan P2 = outlet absolute pressure of the fan 11/1121kkppkknRTPowerPage 171 Minimizing volumetric flow rate and pressure dropPQPPRTnkkPPkkRTnpowerPPwhenPPP 111111211111. QP Power Efficiency, penetration, ninesDownstream control deviceC0Q1C1Q0C0C1Q0C0Mass flow rate of contaminant into the deviceQ1C1M

15、ass flow rate of contaminant out of the device Efficiency, penetration, nines00110011001CQCQCQCQCQ00111CQCQefficiencyp1pEfficiencypenetrationnines99%99.9%90% Efficiency, penetration, nines(2) 112112211222CQCQCQCQ00331CQCQoverall) 1 (111001100111CQCQCQCQQ1C1Q3C3Q2C2Q0C0(3) 113223322333CQCQCQCQ Effici

16、ency, penetration, nines12311223312311111overalloveralloverallPP PPPPPPP P 3210033111(3) in to (2) and (1) CQCQsubstitute321331111 in to CQ overalloverallsubstituteIn the terms of penetration Homogeneous and non-homogeneous pollutantsCO, SO2 are homogeneous Every CO molecule is identical to every other CO molecule .Particles are not homogeneous different particle with various sizes .This Lecture and the Next Lectureq This Lecture:v Chapter 7 Page 160196 Page 202205q The Next Lecture:v Chapter 8 Page 209246Exerciser Page 203, 7.5Page 204, 7.12Page 205, 7.19, 7.21DIS