1、30.1CHAPTER 30INDUSTRIAL 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 CONT
2、AMINANT 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 materia
4、ls, 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 objectionabl
5、e 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 operat
6、ionsand 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 alterna
7、tive 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 a
8、 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 liquid
9、 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 ai
10、r 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 re
12、quire 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 ent
13、er 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 AN
14、D 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-ministr
15、ation (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.Info
16、rmation 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 air
17、 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 typica
18、lly 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) havee
19、stablished 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 Process
20、 AirCleaning (Air Pollution Control).30.2 2012 ASHRAE HandbookHVAC Systems and Equipment 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 plan
21、t 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 priority, e
22、spe-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 regulatio
23、ns, 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 stream. T
24、hefollowing 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 disturbances to
25、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 shoul
26、d 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 thepr
27、ocess, 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 before t
28、esting 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 use, an
29、d 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, aerodynamic,
30、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 expressed at
31、 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 characteristi
32、cs 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 precipitato
33、rs 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-dard
34、s 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 forambient
35、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 because the
36、y 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 Metho
37、ds. 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 Distr
38、ibutionThe 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-radi
39、us 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 performanceaga
40、inst 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, and
41、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 this eq
42、uipment are summarized in Table 1.Table 1 Intended Duty of Gas-Cleaning EquipmentMaximum ConcentrationAir cleaners 40 5 50 0.1 to 0.5 1 300 to 600 None LargeBaffle chamber 20 5 50 0.5 to 1.5 1.5 1000 to 2000 None MediumSkimming chamber 20 1 70 10 1 80 0.3 to 2.0 1.5 to 6.0 2000 to 4000 30 MediumCycl
43、one 15 1 85 0.5 to 3.0 1.5 to 9.0 2000 to 4000 50 MediumMulticyclone 5 1 95 2.0 to 10.0 6.0 to 20 2000 to 4000 200 SmallImpingement 10 1 90 1.0 to 2.0 3.0 to 6.0 2000 to 4000 None SmallDynamic 10 1 90 Provides pressure 1.0 to 2.0 hp 10 to 20 50 Electrostatic precipitatorsHigh-voltage 0.01 0.1 99 0.2
44、 to 1.0 0.1 to 0.6 kW 0.8 to 20 60 to 400 10 to 2000 LargeLow-voltage 0.001 0.5 90 to 99 0.2 to 0.5 0.03 to 0.06 kW 0.5 to 1.0 200 to 700 0.1 to 100 MediumFabric filtersBaghouses 0.08 0.5 99 2.0 to 6.0 6.0 to 20 1.0 to 20 200 LargeCartridge filters 0.05 0.1 99+ 2.0 to 8.0 0.5 to 5 40 to 50 MediumWet
45、 scrubbersGravity spray 10 1 70 0.1 to 1.0 20 to 100 0.5 to 2.0 gpm 5.0 100 to 200 100 MediumCentrifugal 5 1 90 2.0 to 8.0 20 to 100 1 to 10 gpm 12 to 26 2000 to 4000 100 MediumImpingement 5 1 95 2.0 to 8.0 20 to 100 1 to 5 gpm 9.0 to 31 3000 to 6000 100 MediumPacked bed 5 0.1 90 0.5 to 10 5 to 30 5
46、 to 15 gpm 4.0 to 34 100 to 300 50 MediumDynamic 2 1 95 Provides pressure 5 to 30 1 to 5 gpm,3 to 20 hp30 to 200 3000 to 4000 50 Small50Submerged orifice 2 0.1 90 2.0 to 6.0 to None No pumping 9.0 to 21 3000 50 MediumJet 2 0.1 90 Provides pressure 50100 50 to 100 gpm 15 to 30 2000 to 20,000 100 Smal
47、lVenturi 0.1 0.1 95 to 99 10 to 60 1030 3 to 10 gpm 30 to 300 12,000 to 42,000 100 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.30.
48、4 2012 ASHRAE HandbookHVAC Systems and Equipment 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 wi(2)wi
49、th = 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 beconsidered in
