此文档是毕业设计外文翻译成品（含英文原文+中文翻译），无需调整复杂的格式！下载之后直接可用，方便快捷！本文价格不贵,也就几十块钱！一辈子也就一次的事！外文标题：Air Pollution Prevention and Control - An Integrated Designed Approach外文作者：Dr. Akshey Bhargava, M.tech, Ph.D., LLB文献出处：International Journal of Engineering Science and Computing,April 2018,Volume6,Issue No.4(如觉得年份太老，可改为近2年，毕竟很多毕业生都这样做)英文2873单词， 14698字符(字符就是印刷符)，中文4589汉字。

Air Pollution Prevention and Control - An Integrated DesignedApproachAbstract:The Planning, Management and Control of Air Pollution need to be addressed simultaneously to achieve the maximum output. The present paper signify the importance and high light an integrated approach needs to be infused into the system which inter-alia include Source control, Pathway control, and Receptor control . An effort has been made in the present paper to briefly describe Pathway and Receptor control with main emphasis on design of the Air Pollution Control Systems, particularly Bag Filters to control dust emissions and Wet Scrubbers to control gaseous emissionsby way of Throwaway scrubbing processes, Regenerative Scrubbing Processes, Dry Processes and Spray Towers.Key Words: Air Pollution, Integrated Approach, Design of Control Systems.Introduction:The term “Air Pollution” is used to describe substances that are artificially introduced in to the air in the form of gases and airborne particles which, in excess, are harmful to human health, buildings and ecosystems. Air pollution is mainly caused by combustion of fossil fuel, processing of materials and decomposition of organic matters. The main sources of air pollution is from industrial activities, transport sector, house hold fuel burning, and other commercial activities. The present paper high light an integrated approach which inter-alia include Source Control, Pathway control, and Receptor control . An effort has been made in the present paper to briefly describe Pathway and Receptor control with main emphasis on design of the Air Pollution Control Systems, the details of which are as under:Pathway Control:Pathway control is a control system through which the air pollutants are restricted or arrested between a source and receptor through the mechanism of scavenging and filtration.This can be achieved by having a green belt of suitable species between source and receptor. Such a green belt would be able to absorb the air pollution gases and would also act as filtering media for the particulate matter. Sometimes in certain situations, curtains in the form of high walls or other means are also provided between sources and receptor to restrict air pollutants to reach receptors.Receptor Control:Receptor control is governed by an integrated urban and rural planning which should invariably incorporate environmental policy parameters in the form of following:-Atmospheric stability condition-Aerodynamic effects-Albedo-effect-Heat island effect-Ventilation coefficients-Optimization between concreting and non-concreting surface area-Optimization between vertical to horizontal expansion of urban areaIf the above issues are adequately and scientifically addressed, the level of air pollution at the receptor urban area shall be significantly low.Source Control:Main stress is usually laid on source control techniques with the focus on two fronts, one on “transformatio n of waste gasses / materials into usable products” and second on “end of the pipe treatment “. The first approach is gradually coming to fore front with the advancement of research and developmental activities and which has economic value addition. The second approach is cost intensive in which pollution control equipment or devices are installed to restrict air pollution into atmosphere. Source control is also associated with introduction of cleaner technologies, optimization of processes, controlled combustions, use of cleaner raw materials or fuels etc.Design of Air Pollution control systems:A.Particulate Matter control:There are various air pollution control equipment for the control of dust emissions depending upon particle size, minimum loading, desired efficiency, typical velocity, maximum gas pressure drop, and space requirements. These control equipment’s are dry collectors, as well as, wet collectors depending upon the basic characterises of gas and local conditions.The dry collecting devices are:1.Settling chambers2.Baffle chambers3.Lower chambers4.Cyclone chambers5.Multiple cyclones6.Impingement7.Fabric Filters8.Electrostatic precipitatorsThe wet devices are used where in water or scrubbing media is usually used to control emissions. These control devices are1.Gravity spray tower2.Centrifugal Collectors3.Impingement chambers4.Packed tower5.Jet spray scrubbing tower6.Ventury scrubberBag filters design: Introduction:Filtration is among the most reliable, efficient, and rather economical methods by which particulate matter may be removed from gases.∙Such type of filters are represented by various fabric bag arrangements and capable of high dust loading, more than 1gm / m3∙In-depth or bed filters∙Represented by fibrous array, a paper like mat, and occasionally, as a deep packed bed.Packed beds are applied when particulate concentration is much less. Deep packed beds are prepared from crushed stone or bricks, wire screens, or fibers of many types arranged individually or in combinationFabric bag filters:∙Employed to control emissions involving abrasives, irritating chemical dusts, and exhausts from electric furnaces, oil fired boilers, oxygen fed converters for steel making.Principle of operation:Filtration is principally accomplished by the particle layer that accumulates on the fabric surface. Pressure loss increases with accumulated dust layer, thereby gas velocity decreases. Thus, dust dislodging operation is undertaken to have proper filtration. Many fabric bag filters assembled in one unit is called bag house.Classification of filters:∙Fabric or cloth filtersProperties of fiber materials:Design of Bag Filter:Collection efficiency and pressure drop for a single layer or bag filter∆P = (K1+K2*C ma)*V o = (K1+K2*C ma)*Q/A f Where,C ma = mass area concentration in kg/m2 and represents mass of dust present in the dust cake attached tounit area of filter, also proportional to thickness of dust cakeK1, K2 = constants in N-sec/m3 or kg/m2/s Typical values of K1 and K212000 < K1 < 120000 N-s / m310000 < K2 < 130000 s-1The thickness of dust cake increases with time, its growth can be predicted if flow rate and dust concentration are known. The equation is:C ma = Q*C mv*t / A f = V o*C mv*t Where,C mv = mass volume concentrationt = time since filter was last cleanedBag filters and Bag houses:∙Bag filter most commonly used is in the shape of a long cylinder where filter is clamped around a sleeve at the bottom and around a cap at the top.∙The air enters at the bottom, flows through filter along its sides, leaving the dust to form a cake on the inside of the filter, and flows outside the filter to the exit duct.∙Generally, bags diameter ranges from 12.5 to 30 cm with lengths from 2 to 6 meters. Length to diameter ratio should not usually exceed 20 : 1∙Bags in the bag house are sewed to a strap which is fastened to a hanger at the top end of each bag. The hanger is attached to the shaker mechanism.∙Large bag houses are built with several compartments out of which atleast 2 compartmentsshould be off-line, one for cleaning and one for repair or replacement of bagsBags should be arranged within each compartment in such a way as to utilize the space effectively and yet provide access to each individual bag for replacement. This is done by placing the bags close together, about 5 cm apart, while leaving wide spaces of 1/3 to 2/3 meter between every fourth to eighth row of bags.Cleaning cycles for bag houses∙Cleaning is essential whenever the pressure drop across the filter reaches a certain preset value. The length of cleaning cycle, that is, the time period between the start of onecleaning process and the start of next cleaning process needs to be calculated. Followingassumptions are made:n = number of compartments in bag house Q = total flow raten – 1 = active compartments, as one will always be kept for cleaning∆P= pressure drop∆P m = maximum value of pressure dropC mai= weight of dust cake on each filter, where subscript i represents the ithcompartmentt1= length of cleaning cycleQ i= flow rate through i th compartmentA fi= filter area in each compartment which is same for all compartments∆t c= length of cleaning processø1and ǿ1 are the constants, value of ø1 can be obtained from graph drawn between ø1 andQK1/A fi*∆P mǿ1 can be calculated from equation below: ǿ1= ø1 – 2K2*C mv*∆P m*∆tc / K12t1 can be calculated from equation:t1= (A fi*K1/K2*C mv*Q)*(√1+ǿ1+ ø1* (n – 1)-1))Design of Wet Scrubber: Particulate scrubberIn all scrubbers droplets of the scrubbing media are formed, generally much larger than the particles to be collected.∙In most cases, scrubbing media is water,occasionally a different substance is used∙Different types of scrubbing devices employ different means of forming water droplets and different means of ensuring a relative velocity between water droplets and the gas to becleaned∙In all cases the cleaning mechanism involves attachment of particulates to the droplets. The droplets are then collected and drained to a sump.∙Scrubbers in common use are:∙Spray chamber or spray tower∙Centrifugal or cyclone scrubber∙Orifice or self-induced sprayVentury scrubber: Spray tower:∙The scrubbing liquid, usually water for particulate matter removal, is sprayed into the chamber from a series of nozzles located at the top chamber while the air-particle mixtureenters the bottom of chamber and flows upward, encountering the droplets formed from thesprays which fall to the bottom by gravity. The droplets remove the particles by scrubbingaction, the resulting slurry so formed is collected at the bottom and sent for treatment forremoval of collected particles and treated water is recirculated.Collection efficiency of spray tower, using following:L = length of tower D sc= diameter of towerV a= velocity of upward airV d= velocity of dropping dropletsV∞= relative velocity between drops and air Re d= Reynolds number = 10 <Re d > 700D = diameter of droplet ρd= density of dropletρ= density of airμ= viscosity of airn = no of droplets encountered by a group of particlesN d= rate of drop formation in number per secondA sc= area of towerUpward velocity of air in chamber:V a= Q / A sc, which must not exceed drop velocity V d to prevent air from carrying drops outof the top of chamberF = Force acting on the dropF = π*ρd*D3*g / 6 = 5.135* ρd*D3 If spray liquid is water,F = 5135 D3If Reynolds number for the drop motion is between 10 and 700:V∞= (4.8/ρ*D)*√ ((447*μ2)+(ρ*ρd*D3*g/6)) –20.4*μFor standard air as gas and water as spray liquid. The above equation becomes:V∞= (178.3/D)*√(0.7814*10-10+D3) – 1.520*10-3/DThe Reynolds number becomes:Re d = V∞*D / v = 11.50*106*√ (D3+0.7814*10-10) – 98.06If Reynolds number is greater than 700,V∞= (2.4/D)*√ (π* ρd*D3*g/6*ρ) = 5.44*√ (ρd*D/ρ)For standard air and water V∞ = 158 √ D Re d > 700Reynolds number is given by Re d = 1.020*107*D 3/2Since the drop falls with velocity V d Where,V d = V∞ - V a, (particle travel upward with velocity V a)Time period for impaction, diffusion becomes: L / V a + L / V d , and n becomes:n = (N d* π* D2 / 4* A sc)*(L / V a + L / V d)Total drop formation rate is related to mass flow rate of spray fluid as:N d = 6* m s/ π* d3* ρd n becomes,n= (1.5*m s*L / ρd*D)*(1/Q+1/ (A sc*(V∞-V a)) For water as spray fluid,n = (0.0015*m s*L/ D)* (1/Q+1/ (A sc*(V∞-V a)) If spray chamber is circular, thenA sc= π D sc2/4Collection efficiency for a single droplet = ηd, is defined as ratio of no. of particles collected to no. of particles initially contained in the volume swept through by the droplet.∙To predict the behavior of the particles as they flow around and into the droplet, a particle of given diameter and density will strike the droplet if it lies initially within a certain distance y1of the axis of motion of the droplet. If it lies away from axis than this, it will pass by thedroplet and not collected.∙The collection efficiency of the individual droplet due to interception and inertial impaction combined ηdi can be defined as the ratio of the area of circle having radius y1 to the projectedarea of the droplet. This ratio is modified by an attachment coefficient σ.∙From above, efficiency is defined as :ηdi= (π* y12* σ) /(π* D2/4) = 4* σ* y12 / D2, and β = ( 5 / 72 )*( ρp* d2* V t* C / μ* D ) Now considering boundary layer conditions,ηdi= 8.811* σ*√(v/V∞*D) *((y2/∂2)2– 1/6*( y2/∂2)4))When, y2 < ∂2 And,ηdi=7.342* σ*√v/V∞*D, when y2 = ∂2 And,ηdi=7.342* σ*√v/V∞*D+(2* σ)*(y2/D-∂2/D)*(3+6*y2/D+4*(y2/D)2) , when y2 > ∂22. Control of NOx:In general, the main parameters which effect NOX, formation are temperature, residence time, concentration of various species, and extent of mining. From the experimental view point, the factors which control NOX formation include1)Air-fuel ratio 2)Combustion air temperature3)Extent of combustion zone cooling 4)Furnace-burner configurationConsideration of these basic design factors leads to the combustion techniques known as flue-gas recirculation and two stage combustion. Type of fuel is also a major influence on performance.Among the possible removal techniques for oxides of nitrogen are catalystic decomposition, catalytic reduction, absorption and adsorption.In catalytic decomposition the direct decomposition of NO into N2 and O2 would be highly desirable whereas but in catalytic reduction a reaction with another compound reduces NO to molecular nitrogen. Two types of reduction must be considered-selective and non-selective. In selectivereduction, the excess O2 must be consumed first. Selective reduction is too preferred, since it minimizes the amount of reactant required.Selective reduction can be carried out with H2, CO, NH3, or H2S as reactant gas, and with suitable catalyst.2CO + 2 NO 2CO2 + N2 and4CO + 2 NO24CO2 + N2Rather than the combustion reaction 2CO + O22CO2The use of CO has the disadvantage that any amount which is unreacted adds to the general CO pollution of the atmosphere. Using hydrogen is preferable to using CO. However, some catalysts for H2 are not effective in the presence of CO (present from the main combustion reaction). The catalysts found to be most effective are the platinum-type metals.Infect absorption is quite prominent in the reduction of NOx. The oxides of nitrogen can be absorbed by water, hydroxide and molten alkali carbonates and hydroxides. When aqueous alkaline solutions, such as NaOH and Mg OH are used, complete removal requires that one-half of the NO must first be oxidized to NO2 (or NO2 gas added to the gas stream). Best absorption occurs when the NO/NO2 molar ratio is 1:1, which indicated the absorption of the combined oxide, N2O3, is the most favorable. The absorption of NO2 by alkaline solutions has been confirmed during desulfurization of power plant emissions by such solutions. In the desulfurization process, apparently about 10 % of the NO was oxidized to NO2 before the flue gas reached the scrubber.The scrubber then removed about 20% of the total NO2 in equal parts of NO and NO2.Conclusions:Air Pollution is an area where integrated approach needs to be infused into the system of planning, strategy formulation, and technological advancement in the form of cleaner technology, transformation of waste into usable product, process optimization, andinter-linkage of pollution control devices with production. Significant focus needs to be given on Receptor Control coupled with Pathway Control.References:1. Air Pollution Book, by M.N. Rao and H.V.N. Rao, Tata McGraw-Hill Publishing Company Limited, New Delhi, Page No 160-1672. Handbook of Air pollution Prevention and control by Nicholas P. Cheremisinoff, Ph.D., N & P Limited3. Book on Performance criteria of Air pollution control equipment by Sinclair Knight Merz, Final August 2000 International Journal of Environmental Science and Development, Vol. 2, No. 5, October 20114. Shepherd, C. B., and C. E. Lapple. 1939. Air Pollution Control: A Design Approach. InCyclones. 2nd Edition, ed. C. David Cooper, and F. C. Alley, pp 127-139. Illinois: Woveland Press Inc.5. Parker, R., R. Jain., and S. Calvert. 1981. Particle Collection in Cyclone at High Temperature and High Pressure. Environ. Sci. Technol., 15: 451- 458.大气污染的防控–一条综合性的设计方法摘要：为了实现最大效益的产出，大气污染的规划、管理和控制问题需要进行同步解决。