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626 CHAPTER 36 1965 Guide And, Data Book- prepared coconut shell charcoals, qre sometime?* called activated charcoal$ or. activated gghon.^7-1.' These materials can ahaorh approximately 30 percent ottheir awn weight of many, organic gases at 70 F. The charcoal may be used for.a long time if reactivated at. high temperature?, to give up the adsorbedgases. Temperatures of approximately-1600 F are desirable for reactivation. Charcoals for use in air-handling systems should be able tQ. stand physical handling, without excessive loss by breakage- or dusting. Aa applied in air-handling systems, the charcoal is placed in perforated metal container which are grouped in frames and set in the air stream.-The percentage removal of an or ganic gas, such $3 carbon tetrachloride, is 95 percent or above, when placed, in intimate contact with the carbon at 70 F, In commercial apparatus there may be a bypass ef fect which depends-- on the physical arrangement of the charcoal containers. This bypassing reduces the, percentage removed' in the. total gaa passing through the adsorber. Resistance to air flow is' usually selected within the general range of resistance of- impingement filters. The required; quantity of* recirculated air to. be treated is determined-by dividing the requirements for contaminantfree air, minus the outdoor air, by the fraction denoting the percentage removal of- the gas in question in the adsorber bank, which is;to. boused.. Adsorbers may be applied to reduce objectionable gases entering through the outdoor air inlet. They may also be used to reduce the. odors caused by exhausts from process ing. Adsorber beds, in all cases, should be protected from dust, free oil, and grease. REFERENCES * G. W; Penney: A new electrostatic predpitatqr (Electrical Engineering, January 1937, p. 139). * Code for Testing Air Cleaning Devices Used tn General Ventila tion, Seaton /, Unit or Panel Type Air Filtering Devices (Air Filter Institute, 1963). * Ri 8. Dill: A test method for air filters (ASHVE Thanbao- TIONS, VoL 44, 1938m). 379). 4 AFI Dust 8pot Test Code (1960). (Air Filter Institute). * K. T; Whitby, A. B. Algren,;R. C. Jordan, and J. C. Annia: The ASHRAE alr-bome dust survey. (A8HRAJ3 Transactions Vol 64,1958, P- 129). * K, T, Whitby, A. B- Alxreq, and R- C. Jordan: Sire distri bution and. concentration of air-borne dust (ASHRAE Trans actions, Vo). 61, 1955, p. 463), ' C. E. dimmer, E. C. Tabor, and A. C, Stem: Particulate pollutants in the air of. the United 8ta,tea (Journal ofAir Pollution Centred Association, YoL 9, No. 3, November 1959). 1 M. W. First and R Drinker: Concentrations of-particulates found in air (Heating and Ventilating, November 1952). . '-.Chart: Concentrations of materials in the air (Mine Safety Appliance Co. No. 1500-1). ? K. T. Whitby et al.: Evaluation of air cleaners for occupied spaces (Technical Report No- 14, University of Minn&ota and 0. S. Public Health Service, February 1961). - u C, Y, C9ien: Filtration qf aerosols by fibrous (Chem, Reviews/VoL 55, No. 3, June 1955). ^ T. E. Wright, R j. Stasney, and C. E. Lapple: High velocity filters (WADC Technical Report 55-157, ASTIA Document No. AD 124075, October 1957), u Rans: Principles of inertial impaction (Engineering Research Bulletin B?66, Penn State University, December 1956). M G. W. Penney and G. W. Hewitt: Electrically charged dustin rooms (AIEE Transactions 1949). " Standards and Guidelines for tits Design and Operation of . Cl?fl-n, \Vwk Station. Air Force TO. * Clean Room and Work Station Requirements, Controlled Environments (Federal.Standard 209). 17 H. h. Barnebey: Activated charcoal for. air . purification (A8HAR {ourcal Section, Heating. Piping and Air CcmditUrri-' mg, March 1958, p, 153). M H. Sleik and A. Turk: Air Conservation Engineering (Connor. Engineering Carp., 1953). BIBLIOGRAPHY M. -W first, J B. Graham, G. M. Butler, G B. Walworth, and R. P. Warren: High temperatqre. gas filtration (Industrial and' Engineering Chemistry, VoL 48, No.'4, April 1956); .......... Leopold and Q. S. Leopold: Bronchial asthma and allied allergic disorders (Journal of the- American Medual Asen.. motion, March 7, 1925,,p. 730, ' -r- n-m . ...... I*. H. Criep, M.D., and. M. A. Green, M.D.: Air cleaning as an aid m the treatment of hay fever and. bronchial.' asthma (Jcwmn/ of Atiergy.Janqary 1^36, p. I?0), :I - - MowcR: The baaterial filtration efficiency, off an electrostatip air clever (Journal of the Institution, ofy.Heoting andVentilating cnpmeerz, London, June 1951, p.139). P. Drinker and. T. Hatch: industrial Dust. (McGraw-Hill Co., New York). J. W. May: Selecting the right air filter carefully CREmiGEa-' atino Engineering, March 1956, p. 53), ` ' . ~ ------ R. A, Nielsen: Dirt pattern ob walls (ASHVE Transactions. VoL 46, 1941, p. 247). - ' ......... ' - ^ Research Advisory Board, National Research Council/ Waa mgton, D. C., Research ConferenceReport, 1952). ' y"'* Air Cokdit*' 'juf ^1955 (fftwhnf, Piping, and H. C. Murphy: Design and*application of oil-coated air filters ' (ASHVE Transactions, Vol.`33, 192?, p. 73). . W. G. Frank: Operation and maintenance.of air filters (Heal* tng, Piping and Air Conditioning, May 1931, p. 378).' W. G. Eraqk : Size and:characteristics of air-borne impurities (Heatstig, Piping and Air, Conditioning, January 1932,'p. 35).: O. Wechaberg: Fundamental principles in the design of dry air filters (ASHVE Journal Section, Heating, Piping arid Air Conditioning, April 1933, p. 217). . . H. E. Ziefand HenrySleik: The economic factors inconvert^ mg.recirculated air.fop ventilation (ASHVE Journal Section Heating, Piping and Air Conditioning,'July, 1943, p. Sfi7). . F. B. Rowley and R. C. Jordan: ASHVE Research Report- No. 1094-^Air filter performance as affected by kind of dust, rate, of dust feed., and air velocity through filter. (ASHVE Transactions, Vol. 44, 1938, p. 415). F* B. Rowley and R. C. Jordan: Asuvn Research Report No. 1122--Air filter performance aa affected by. low rate of digist feed, various types of carbon, and dust partiole size and density (ASHVETransactions; Vol.'45,1939._p. 339). " F. B. Rowley and R. C. Jordan: ASHVE Research Report No, 1145-rrThe effect of lint on air filter performance (ASHVE TRANsAcnoNB, Vol. 46,1940, p. 25). " ' ` F. B. Rowley and R. C. Jordan: ASHVE Research Report No. 1169--^Comparison of the weight, particle count and dis coloration methods, of testing air filters (ASHVE 'Transac tions, Vol. 47,1941, p. 29). ...................~ " J ' F. B. Rowley and R. C. Jordan: ASHVE Rqajuvqop ReportNo. 1187--Economical sir velocities for mechanical air filtra tion (ASHVE Transactions, Vol. 47, 1941; p. 391). F. B. Rowley.and R. C.'Jordan: ASHVE Research ReportNo. 12l8rrOvertoading of visooiis air filters during accelerated tests (ASHYE Transactions,,Vol. 48,1942, p. 437)' H. E. Corbitt and N. J. Clark: Electrostatic precipitation for aircraft (Aero Digest, December 1940, p. 132). ' A. Nutting and R. F. Logsdon: New air filter oode (Heating, Piping and Air Conditioning, June 1953, p. 77). CHAPTER 37 INDUSTRIAL AIR AND GAS CLEANERS Degree of Air Cleaning Required, Factors Affecting Selection, Types of Application, Mechanical Collectors, Wet Collectors, Fabric Collectors, Electrostatic Precipitators, Absorbers, Adsorbers, and Combustion Devices NDUSTRIAL development mid growth of industrial areas I have bad a cumulative effect upon the problem of con trolling contaminants. Not only ha the atmosphere in many cities become mote polluted, but the intensity of pollu tion at the points of control has increased. Accompanying this infroftsfr in pollution there has been a growing consciousness of the need for more effective air cleaning among house wives, store managers, industrialists, and legal inspectors, and this has resulted in increasing severity of regulations pertaining to collection of dust and conthminarits. .This chapter deals with the cleaning of exhaust system air streams and flue gases, usually to avoid a neighborhood air pollution nuisance. Typical dust concentrations in such streams range from 100 to 20,000 grains per 1000 cu ft of air. .Air cleaning for the supply system id usually accomplished, by mfana of some .type of air filter. To prevent escape; of industrial dust into the atmosphere; some type of collector ts required. An industrial air-cleaning installation is de signed to perform one or more of the following 6 functions: 1. Prevent a nuisance or physical dainage U> an individual, a plant, or adjacent property. 2. Prevent re-entry of contaminants tb working spates. 3. Reclaim usable material. 4. Reduce fire, explosioh, or other hazards. ' 5. Permit recirculation of cleaned air to working spates. . 6. Allow utilization of cleaned gases for processes. DEGREE OF AIR GLEANING REQUIRED . . Hie amount of material which can be discharged lb the atmosphere is established by local or state regulations prepared by pollution control, labor, or health departments. Standards are established to prevent injury to persons or property. The need for control within the plant is often of prime interest io the industrialist for protecting his equipment, improving his product, and providing a clean working environment. The re-entry of contaminants, to working .spaces is prevented by effective air^cleaning devices since .only' a dean effluent is discharged tb the "ambient atmosphere. Public nuisance complaints often occtir even when the effluent concentration discharged to the. atmos phere is bdow the permissible limits of concentration and yisiblility. Plant location; contaminants involved,. and me teorological condition of the areas must be evaluated in addition to exiting regulations or codes of good practice. Fire and expiation hazards are created, by .combustible dusts, vapors, or gases. Safety may be affected by los& of Tha ztaertl 'iWpflairbilhy lot thl> fchAjrter ti kiltjaefl *TC iJl/Iadiirtfiti EftTinnmc&t. viability, settlement, or accumulation of various materials. -The fWning deviefe can prevent these hazards by provid ing an effluent below the inflammation limit, visibility index, and point where Settlement or accumulation will occur. The degree of air cleaning for the recovery of usable material is a matter of economic evaluation which will vary with such factors as quantity and value of material col lected, capital cost, and operating cost. Air cleanliness must be of the highest order where'toxic materials are involved and the cleaned air is recirculated to the workroom. Such recirculation is considered poor practice and is prohibited by many regulations where toxic materials are involved, except for those cases where dis charge tb atmosphere is impossible of decidedly impracti cable. Where air is recirculated, its contamination must hot exceed the established maximum allowable concentrations listed in Chapter 11. Usual requirements are a fraction, often t to t, of this standard, depending on: regulation involved, sir quantities recirculated in relation to the cubical con tent bf working space, and the presence of other exhaust systems "discharging tb the atmosphere. Cleaning requirements for the utilization of cleaned gases are dependfehb on the process and are generally of the highest order (usually comparable to atmospheric air cleanliness). Regardless of standards it is good practice to install the most effective collection equipment available in the light of practical operation features, installation, and equipment costs. This is warranted because the required degree of rlpftning is increasing continually. - The Industrial Gas Cleaning Institute was formed by a group of -Dust Control manufactorCre to assist in the establish ment of performance standards and ratings to help in the proper choice bf equipment to meet specific needs. . FACTORS AFFECTING SELECTION Selection of an industrial air cleaner for- a given applica tion requires an evaluation of the following 5 considerations: 1; Concentration, particle size, and size distribution of the contaminant; 2. Degree of cleaning required. `.,- 3. Conditions of air or gas stream with reference to tempera ture, tabistufe cbhtent, ana chemical composition. 4. Characteristics Of the contaminant,. corrOdyeneas, solu bility, edhiwtoit-, or parting, and its specific gravity* surface, and shape. ' 5. Methods of disposal or salvage that meet-the conditions imposed by material, process, or plant location. / 627 X