1、30.1CHAPTER 30 INDUSTRIAL GAS CLEANING AND AIR POLLUTION CONTROLRegulations and Monitoring 30.1PARTICULATE CONTAMINANT CONTROL . 30.2Mechanical Collectors . 30.4Electrostatic Precipitators . 30.7Fabric Filters . 30.10Granular-Bed Filters 30.14Particulate Scrubbers (Wet Collectors) . 30.15GASEOUS CON
2、TAMINANT CONTROL. 30.17Spray Dry Scrubbing 30.17Wet-Packed Scrubbers 30.18Adsorption of Gaseous Contaminants 30.23Incineration of Gases and Vapors 30.26AUXILIARY EQUIPMENT. 30.27Ducts 30.27Dust- and Slurry-Handling Equipment 30.28OPERATION AND MAINTENANCE. 30.29NDUSTRIAL gas cleaning performs one or
3、 more of the follow-I ing functions: Maintains compliance of an industrial process with the laws orregulations for air pollutionReduces nuisance or physical damage from contaminants to indi-viduals, equipment, products, or adjacent propertiesPrepares cleaned gases for processesReclaims usable materi
4、als, heat, or energyReduces fire, explosion, or other hazardsEquipment that removes particulate matter from a gas streammay also remove or create some gaseous contaminants; on the otherhand, equipment that is primarily intended for removal of gaseouspollutants might also remove or create objectionab
5、le particulatematter to some degree. In all cases, gas-cleaning equipment changesthe process stream, and it is therefore essential that the engineerevaluate the consequences of those changes to the plants overalloperation.Equipment SelectionIn selecting industrial gas-cleaning equipment, plant opera
6、tionsand the use or disposal of materials captured by the gas-cleaningequipment must be considered. Because the cost of gas-cleaningequipment affects manufacturing costs, alternative processes shouldbe evaluated early to minimize the effect equipment may have on thetotal cost of a product. An altern
7、ative manufacturing process mayreduce the cost of or eliminate the need for gas-cleaning equipment.However, even when gas-cleaning equipment is required, processand system control should minimize load on the collection device.An industrial process may be changed from dirty to clean by sub-stituting
8、a process material (e.g., switching to a cleaner-burning fuelor pretreating the existing fuel). Equipment redesign, such as en-closing pneumatic conveyors or recycling noncondensable gases,may also clean the process. Occasionally, additives (e.g., chemicaldust suppressants used in quarrying or liqui
9、d animal fat applied todehydrated alfalfa before grinding) reduce the potential for air pol-lution or concentrate the pollutants so that a smaller, more concen-trated process stream may be treated.Gas streams containing contaminants should not usually bediluted with extraneous air unless the extra a
10、ir is required forcooling or to condense contaminants to make them collectible.The volume of gas to be cleaned is a major factor in the owningand operating costs of control equipment. Therefore, sourcecapture ventilation, where contaminants are kept concentrated inrelatively small volumes of air, is
11、 generally preferable to generalventilation, where pollutants are allowed to mix into and bediluted by much of the air in a plant space. Chapters 31 and 32of the 2011 ASHRAE HandbookHVAC Applications addresslocal and general ventilation of industrial environments. Regula-tory authorities generally r
12、equire the levels of emissions to becorrected to standard conditions taking into account tempera-ture, pressure, moisture content, and factors related to combus-tion or production rate. However, the air-cleaning equipmentmust be designed using the actual conditions of the processstream as it will en
13、ter the equipment.In this chapter, each generic type of equipment is discussed onthe basis of its primary method for gas or particulate abatement. Thedevelopment of systems that incorporate several of the devices dis-cussed here for specific industrial processes is left to the engineer.REGULATIONS A
14、ND MONITORINGGas-Cleaning RegulationsIn the United States, industrial gas-cleaning installations that ex-haust to the outdoor environment are regulated by the U.S. Envi-ronmental Protection Agency (EPA); those that exhaust to theworkplace are regulated by the Occupational Safety and Health Ad-minist
15、ration (OSHA) of the U.S. Department of Labor.The EPA has established Standards of Performance for New Sta-tionary Sources New Source Performance Standards (NSPSs),GPO and more restrictive State Implementation Plans (SIP 1991)and local codes as a regulatory basis to achieve air quality standards.Inf
16、ormation on the current status of the NSPSs can be obtainedthrough the Semi-Annual Regulatory Agenda, as published in theFederal Register, and through the regional offices of the EPA. Buo-nicore and Davis (1992) and Sink (1991) provide additional designinformation for gas-cleaning equipment.Where ai
17、r is not affected by combustion, solvent vapors, andtoxic materials, it may be desirable to recirculate the air to the work-place to reduce energy costs or to balance static pressure in a build-ing. High-efficiency fabric or cartridge filters, precipitators, orspecial-purpose wet scrubbers are typic
18、ally used in general ventila-tion systems to reduce particle concentrations to levels acceptablefor recirculated air.The Industrial Ventilation Committee of the American Confer-ence of Governmental Industrial Hygienists (ACGIH) and theNational Institute of Occupational Safety and Health (NIOSH) have
19、established criteria for recirculation of cleaned process air to thework area (ACGIH 2010; NIOSH 1978). Fine-particle control byvarious dust collectors under recirculating airflows has been inves-tigated by Bergin et al. (1989).The preparation of this chapter is assigned to TC 5.4, Industrial Proces
20、s AirCleaning (Air Pollution Control).30.2 2012 ASHRAE HandbookHVAC Systems and Equipment (SI)Public complaints may occur even when the effluent concentra-tions discharged to the atmosphere are below the maximum allowsemission rates and opacity limits. Thus, in addition to codes or reg-ulations, the
21、 plant location, the contaminants involved, and themeteorological conditions of the area must be evaluated.In most cases, emission standards require a higher degree of gascleaning than necessary for economical recovery of process prod-ucts (if this recovery is desirable). Gas cleanliness is a priori
22、ty, espe-cially where toxic materials are involved and cleaned gases might berecirculated to the work area.Measuring Gas Streams and ContaminantsStack sampling is often required to fulfill requirements of oper-ating and installation permits for gas-cleaning devices, to establishconformance with regu
23、lations, and to commission new equipment.Also, it can be used to establish specifications for gas-cleaningequipment and to certify that the equipment is functioning properly.The tests determine the composition and quantity of gases and par-ticulate matter at selected locations along the process stre
24、am. Thefollowing general principles apply to a stack sampling program:The sampling location(s) must be acceptable to all parties whowill use the results.The sampling location(s) must meet acceptable criteria withrespect to temperature, flow distribution and turbulence, and dis-tance from disturbance
25、s to the process stream. Exceptions basedon physical constraints must be identified and reported.Samples that are withdrawn from a duct or stack must representtypical conditions in the process stream. Proper stack traversesmust be made and particulate samples withdrawn isokinetically.Stack sampling
26、should be performed in accordance with approvedmethods and established protocols whenever possible.Variations in the volumetric flow, temperature, and particulate orgaseous pollutant emissions, along with upset conditions, shouldbe identified.A report from stack sampling should include a summary of
27、theprocess, which should identify any deviations from normal pro-cess operations that occurred during testing. The summary shouldbe prepared during the testing phase and certified by the processowner at completion of the tests.Disposal methods for waste generated during testing must beidentified bef
28、ore testing begins. This is especially critical wherepilot plant equipment is being tested because new forms of wasteare often produced.The regulatory basis for the tests should be established so that theresults can be presented in terms of process mass rate, consump-tion of raw materials, energy us
29、e, and so forth.Analyses of the samples can provide the following types of infor-mation about the emissions:Physical characteristics of the contaminant: solid dust, liquid mistor “smoke,” waxy solids, or a sticky mixture of liquid and solid.Distribution of particle sizes: optical, physical, aerodyna
30、mic, etc.Concentration of particulate matter in the gases, including aver-age and extreme values, and a profile of concentrations in the ductor stack.Volumetric flow of gases, including average and extreme values,and a profile of this flow in the duct or stack. The volumetric flowis commonly express
31、ed at actual conditions and at various standardconditions of temperature, pressure, moisture, and process state.Chemical composition of gases and particulate matter, includingrecovery value, toxicity, solubility, acid dew point, etc.Particle and bulk densities of particulate matter.Handling characte
32、ristics of particulate matter, including erosive,corrosive, abrasive, flocculative, or adhesive/cohesive qualities.Flammable or explosive limits.Electrical resistivity of deposits of particulate matter under stackand laboratory conditions. These data are useful for assessmentsof electrostatic precip
33、itators and other electrostatically aug-mented technology.EPA Reference Methods. The EPA has developed methods tomeasure the particulate and gaseous components of emissions frommany industrial processes and has incorporated these in the NSPSby reference. Appendix A of the New Source Performance Stan
34、-dards lists the reference methods (GPO, annual). These are updatedregularly in the Federal Register. Guidance for using these referencemethods can be found in the Quality Assurance Handbook for AirPollution Measurement Systems (EPA 1994).The EPA (2004) has promulgated fine particle standards foramb
35、ient air quality. Known as PM-10 and PM-2.5 Standards, theserevised standards focus particulate abatement efforts toward the col-lection and control of airborne particles smaller than 10 m and2.5 m, respectively. Fine particles (with aerodynamic particle sizesmaller than 2.5 m) are of concern becaus
36、e they penetrate deeplyinto the lungs. With the development of these standards, concern hasarisen over the efficiency of industrial gas cleaners at various parti-cle sizes.ASTM Methods. The EPA has also approved ASTM test meth-ods when cited in the NSPSs or the applicable EPA referencemethods.Other
37、Methods. Sometimes, the reference methods must bemodified, with the consent of regulatory authorities, to achieve rep-resentative sampling under the less-than-ideal conditions of indus-trial operations. Modifications to test methods should be clearlyidentified and explained in test reports.Gas Flow
38、DistributionThe control of gas flow through industrial gas-cleaning equip-ment is important for good system performance. Because of thelarge gas flows commonly encountered and the frequent need to ret-rofit equipment to existing processes, space allocations often pre-clude gradual expansion and long
39、-radius turns. Instead, elbowsplitters, baffles, etc., are used. These components must be designedto limit dust buildup and corrosion to acceptable levels.Monitors and ControlsCurrent regulatory trends anticipate or demand continuous mon-itoring and control of equipment to maintain optimum performan
40、ceagainst standards. Under regulatory data requirements, operatinglogs provide the owner with process control information and otherswith a baseline for the development or service of equipment.Larger systems include programmable controllers and comput-ers for control, energy management, data logging,
41、 and diagnostics.Increasing numbers of systems have modem connections to supportmonitoring and service needs from remote locations.PARTICULATE CONTAMINANT CONTROLA large range of equipment for the separation of particulate mat-ter from gaseous streams is available. Typical concentration rangesfor th
42、is equipment are summarized in Table 1.Table 1 Intended Duty of Gas-Cleaning EquipmentMaximum ConcentrationAir cleaners 40 10 50 25 to 125 1 1.5 to 3.0 None LargeBaffle chamber 20 10 50 125 to 625 1.5 5.0 to 10 None MediumSkimming chamber 20 2 70 10 2 80 75 to 500 1.5 to 6.0 10 to 20 15 MediumCyclon
43、e 15 2 85 125 to 750 1.5 to 9.0 10 to 20 25 MediumMulticyclone 5 2 95 500 to 2500 6.0 to 20 10 to 20 95 SmallImpingement 10 2 90 250 to 500 3.0 to 6.0 10 to 20 None SmallDynamic 10 2 90 Provides pressure 0.75 to 1.5 kW 10 to 20 25 Electrostatic precipitatorsHigh-voltage 0.01 0.2 99 50 to 250 0.1 to
44、0.6 kW 0.8 to 2.0 0.3 to 2.0 5 to 940 LargeLow-voltage 0.001 1 90 to 99 50 to 125 0.03 to 0.06 kW 0.5 to 1.0 1.0 to 3.5 0.5 to 50 MediumFabric filtersBaghouses 0.08 .1 99 500 to 1500 6.0 to 20 0.005 to 0.10 95 LargeCartridge filters 0.05 0.2 99+ 500 to 2000 0.0025 to 0.025 20 to 25 MediumWet scrubbe
45、rsGravity spray 10 2 70 25 to 250 140 to 690 70 to 270 L/s 5.0 0.5 to 1 50 MediumCentrifugal 5 2 90 500 to 2000 140 to 690 0.14 to 1.4 L/s 12 to 26 10 to 20 50 MediumImpingement 5 2 95 500 to 2000 140 to 690 0.14 to 0.7 L/s 9.0 to 31 15 to 30 50 MediumPacked bed 5 0.2 90 125 to 2500 35 to 210 0.7 to
46、 70 L/s 4.0 to 34 0.5 to 1.5 25 MediumDynamic 2 2 95 Provides pressure 35 to 210 0.14 to 0.7 L/s,2.25 to 15 kW30 to 200 15 to 20 25 Small25Submerged orifice 2 0.2 90 500 to 1500 None No pumping 9.0 to 21 15 25 MediumJet 2 0.2 90 Provides pressure 345 to 610 7 to 14 L/s 15 to 30 10 to 100 50 SmallVen
47、turi 0.1 0.2 95 to 99 2500 to 15 000 70 to 210 0.4 to 1.4 L/s 30 to 300 60 to 210 50 SmallSource: IGCI (1964). Information updated by ASHRAE Technical Committee 5.4.aMinimum particle diameter for which the device is effective.bAverage speed of gases flowing through the equipments collection region.3
48、0.4 2012 ASHRAE HandbookHVAC Systems and Equipment (SI)changes that occur in the gas stream due to air leakage in the system,condensation, and temperature and pressure changes.Penetration P is usually measured, and the efficiency for a col-lector calculated, using the following equations:P = 100wo w
49、i(2)with = 100 P (3)The fractional efficiency of a particulate collector is determinedby measuring the mass rate of contaminants entering and exiting thecollector in selected particle size ranges. Methods for measuring thefractional efficiency of particulate collectors in industrial applica-tions are only beginning to emerge, largely because of the need tocompare the fine-particle performance of collectors used under thePM-10 and PM-2.5 regulations for ambient air quality.Measures of performance other than efficiency should also beconside
