Document 2J3jx2k8XY1ZdN26rOQR3XV5b

168 CHAPTER 12 1965 Guide And Data Boole for effective cleaning of the air stream. Water is frequently used as the absorbent, though, in some cases, other, chemical solutions are necessary to increase collection efficiency.! In all absorption processes, the waste liquid may have to be treated to prevent a secondary pollution problem. When wastes have product, .value, the absorbent-gas solution is processed, and the absorbent is.reused. - A packed tower (fig. 5).is another means of contacting ob-. jectionable gas and absorbent. Ceramic rings, pebbles, ..tile, wood, and glass fiber pads are used for packing. When the contaminated air stream contains;,particulate matter,' the' tower has a tendency to plug up and must be cleaned periodi cally.to msintAin low pressure loss.- A venturi scrubber (Fig. 6), used'fOr absorbing objectionable gases contacts gas and.absorbent in the throat of aventuri nozsle/The gas-liquid nurture enters the'ehtraihmeht'sepa1 rator tangentially, and centrifugal force separates liquid from the contaminated air.' This mmii typeof collector.is aim used to collect particulates.' ' ` A variety of pairing materials are used in' order tb^increase the area of contact.--These are Raschig rings, Bert saddles'; egg- crate patterns, expanded metals, honeycomb,.'and many other' types. The equipment most extensively, used for mass transfer' operations in the air-conditioning industry for-odor removal, humidification, and dehumidification are tile spray air washer and the packed scrubber, because they.may.be designed to al low the flow, of air at high velocity with little-frictional re; sistance. Once the gas contacts the absorbing liquid, the diffusion of the gas in the liquid becomes knportaht.1 Where a gas is highly soluble in a liquid,-its.diffusion into the bulk of the liquid from the surface is relatively easy.-For,such applications, spraytype washers are used. If water is the absorbent, it is generally discarded to prevent it from becoming-concentrated with odors and returning the odors to the air stream.... More expensive absorbent liquids mayjbe!regenerated and purified. The mechanism of a regenerator is opposite that of the absorber. In the absorber, the concentration of odor solute must be small, and its partial pressure must be less than the partial pressure of the odor in the air. In the re generator, the absorbent' may be heated, which raises the partial pressure of. the odorant in solution. The odorant is removed from the solution' to' the stripping' air, provided that the partial pressure of the odorant in this air is lower than that in equilibrium with the solution. Odor removal efficiency of an air. washer depends on the extent of contact of air with the liquid and on:the concentra tion of odorant in the liquid. Thus, for ail practical purpose, deodorisation by physical absorption is never a process that operates at 100 percent efficiency. By the use of extended sur faces and freshly generated absorbent, p.fficipnriflfl approach 100 percent. Neutralization, Masking, and Counteraction Odors can be chemically destroyed, neutralised, or counter acted and masked. Antiseptic and disinfectant deodorisers are used to kill odor-producing bacteria.' The disinfectant' may in itself be odorless or have a masking or neutralizing odor. Where-the composition of the objectionable odor can be ascertained, it may be possible to compound another' odor that will cancel or counteract the objectionable odor;'The result may be an odorless atmosphere, or one having a more desirable or less objectionable odor than the basin objection able odor or the applied neutralizer. Obviously the selection of the antagonistic odor as well as the applicable amount requires considerable skill and is a matter for the specialist. The use of an odor counteractant results'in*, a lower odor intensity and removal of the malodor as sensed by the nose. -: f Odors can be masked by other more desirable odors applied in the proper concentrations. A change in odor quality and increased intensity occurs with this process. This has been the work of the perfumer from ancient times.' Chemical destruc tion of odors, neutralization,' and odor modification have come' into extensive use. Agents are available for deodorizing source materials such as rubber and plastics,** and industrial exhausts such as sulfur odors from 'a cement kiln,*7 or to remove'odor from the enclosed air space or atmosphere that may be con taminated by cooking or tobacco smoke.11. Some deodorants are standard items, while others are compounded for the special application. In some cases, the use of a deodorant re sults in the chemical destruction, neutralization, or masking of the odor, or a combination of them. Hie principles of odor masking are listed in Reference 6 as follows: 1. Odor masking is the process of candling one odor by superimposing another odor .to create a more overpowering sen sation. preferably pleasant. ' 2. The masking agent does'not alter the composition of pre existing odors, but amply covers such odors during the period of its addition to, and presence in, the air. 3. Masking is an effect produced at the point of sense percep tion in the respiratory paamges, together with final interpretation in the brain, and does not constitute an aromatic correction of the aerial components. 1 4. The application of an inherently pleasant masking agent to an offensive atmosphere may result in a final combination that is still objectionable as a consequence of odor} incompatibilities. 6. Hie objectionable odor concentration must not be so in tense that the masking agent a itself required in objectionable concentrations. -In such cases, other control methods are indi cated. Odor counteraction is defined as the process by which un desirable odors are eliminated of significantly reduced in olfactory intensity by the addition in the vapor phase of cer tain odorous components or mixtures. The result obtained from true counteraction is the lowering of odor intensity, and the elimination of malodor as sensed by the human nose to a degree where it is no longer objectionable. The counteraction process for controlling odors is'based on the fact that certain odorous substances are antagonistic and tend to compensate or neutralize their individual olfactory effects when mixed together in the vapor state. Zwaardemaker was probably the first to study the cancelling effects of two dissimilar odors. He found that when various pairs of odors are mixed in certain Odorsfc-f? 'j.-rA .o. I 69 proportions, their odor characteristics are cancelled, resulting in no^odor, or significantly reduced odor. Aronsohn and Back- -,, 1 Disposal of Refinery Waste*, Section llz Waste Ooses,-Va pors, Sludges and busts (American -Petroleum Institute, 193S). - 4 David Ronald: Offensive Trades (William Hodge and-Co., man's observations also demonstrated,the cancelling effect of odor pairs. During the past twenty years, developments based on this printiple have resulted in practical means of applica tion to' a wide variety'of malodorous conditions,1 including London, 1935). . * F. H.Munkelt: Air purification and deodorization by use of activated carbon' (Refrigerating Engineering Application Data No. it, Awehican Sooett or Refrigerating Engineers). C. P. McCord and W. N. Witheridge: Odors: Physiology application in air-conditioning systems. The threshold .concentration, Classification 1 (not objec tionable) on the sensory scale, of chemical and industrial odors and`their physiological reactions hss been devel oped by. DaOaValle and appears in References '6 and 29. TOese data show no agreement of threshold concentrations for the various substances. Care must-be taken never to.use 8 reodorsnt to mask or cover up a toxic concentration of Personnel in .refineries and other industries are accustomed to the presume of odor as the signal that dangerous con centrations of gas are bring reached. Combustion Methods Since the usual objectionable odors are combustible and can be destroyed by burning, combustion processes are em ployed for odor destruction in higher temperature gases. Where it is desired to remove odors from industrial exhausts at temperatures above 125 F, mid where the gas density is above 1000 ppm, the gases can be caused to flow over a catalyst at about 500 F and be destroyed by catalytic com bustion (see Chapter 37, Industrial Airand Gas Cleaners). For higK-temperature gases, direct combustion at temperatures of 1200 F and above is employed to destroy odors by passing the gas through a furnace to the exhaust stack." Partial com bustion may cause a more objectionableodor than the original gas. Incomplete burning of nitrogenous and sulfurous organic material with the resultantpungent oxides is not a satisfactory odor destruction process. Careful consideration should be given to the gases and to means of obtaining complete com bustion in order to assure effective odor control. Catalytic combustion has a major advantage of lowering the fuel or heating requirement for combustion. In some cases no additional fuel source is required, and beat recovery may amortize the investment. The catalyst may consist of a noble metal, such as a platinum alloy coating on porcelain rods, or and Control (McGraw-Hill Book Co.; New York, 1949). 7 C. P. Yaglou: ASHAE Research Repoax No. 1524--Venti lation requirements for cigarette smoke (ASHAE Transactions, VoL 61, 1955, p. 25). - W. F. Hopper: ASHAE Research Repost No, 1698-1--A method of measuring the odor adsorption and retention proper ties of surfaces (ASHRAE Transactions, VoL 65,'1959,- p. 735). *A- B. Hubbard: Winning the air conditioning'odor fight (Heating, Piping and Air Conditioning, VoL 31, No. 2, February 1959, p. 119). 11 Arthur D. little, Inc.: Flavor Research and.Pood'Acceptance (Remhoki Publishing Corp., New York, -l958, p.-71). 11 R. M. Hainer: An information theory of. olfaction (ed. A. G. Emalift and. Ada-'Jacobson,-. Annals of. the New York Academy of Sciences, VoL 58, Art. 2, March' 24, 1954, p. 161).- ' " Amos Turk et al: Approaches to sensory odor measurement (Conference on Recent Advances in Odor: Theory, Measurement and Control, New York Academy of Sciences, November 1963). UA. B. Hubbard, N. Deminger, and p. Sullivan: ASHAE Research Report No. 1547--Air conditioning coO odors (ASHAE Transactions, VoL 61,1955, p. til). 44 W. F. Kerka and C. M. Humphreys: ASHAE RgKEAarrg Report No. 1587--Temperature and humidity effect on odor perception (ASHAE Transactions, VoL 62, 1956, p. 531). u R. L. Kuehner: ASHAE Research Report No. 1569--Hu midity effects on the odor problem (ASHAE Transactions, VoL 62, 1956, p. 249). " G. W. Meek: Your place in the smart man's war (Healing Piping and Air Conditioning, Vol. 14, No. 8, August 1942, p. 463). 17 C. S. Leopold: ASHVE Research Report No. 12/7--To bacco smoke control--a preliminary study (AS5VE Trans actions, VoL 51, 1945, p. 255). 21J. C. White, J. K. Mustek, M. H. Boyer, R. S. Hartman, W. H. Scbecter, and R. R. Milien: Experimental Control of CO, and Oxygen Concentration Aboard the USS Sailfish (Naval Research Laboratory, P-2665, 1945). 11 Warren Vieesman: Air conditioning for protective shelters (Heating, Piping and Air Conditioning, VoL 26, No. 12, Decem ber 1954, p. 84). n Warren Vieesman: Cooling subterranean atomic attack shelters (Refrigerating Engineering, Vol. 59, No. 12, December 1951,0. 1175). " H. L. B&raebey: ASHAE Research Report, No. 1646-- Activated charcoal for air purification (ASHAE Transactions, a platinum alloy coating on nichrome wire. Catalyst effective ness and life are adversely affected by: (1) presence of metallic or organometallie vapors in the air, (2) deposits of car bonaceous material on the catalyst due to incomplete com bustion, and (3) mechanical loss of the catalyst by abrasion. For air free from particles and metallic vapors, a catalyst fife of 20,000 hours may be expected. A consideration of catalytic combustion should involve the following analytical approach." VoL 64, 1958, p. 481). " G. F. Hanna a al: A chemical method for odor control (Con ference on Recent Advances in Odor: Theory, Measurement and Control, New York Academy of Sciences, November 1963). ** J. Von Bergen: Industrial odor control (Chemical Engineer ing, August 1957, p. 239). u C. M. Bosworth and A. J. Barduho: Recent advances in odor control by air washing (Conference on Recent Advances in Odor: Theory, Measurement and ControL New York Academy of Sci ences, November 1963). " How to control gaseous emissions to abate air pollution (Engineering Data File, Heating, Piping and Air Conditioning, 1. Analyze the gas to determine quality and quantity of odor ous elements. 2. Determine the oxidizable elements in the air and the heat content per cubic foot based on concentration. 3. Obtain estimates from a competent manufacturer on cost of tngtidUtioo, life, maintenance, ana efficiency of heat recovery. 4. Make a coat comparison of owning and operating costs and ether methods including fixed charges, maintenance, and service tteta, similar to Table 5, Chapter 86 of the 1964 Guide And December 1959, p. 111). * Clean it Up (Industrial Bulletin No. StS, Arthur D. Little, Inc., July 1955). ^ 17 C. Lamoreaux: 8tack effluent reodorized (Plant Engineer ing, July 1955, p. 96). t* Killing an unpleasant smell (Factory Management and Maintenance, Nd. 114, No. 4, April 1956, p. 87). * B. K. Tremaine: Industrial reodorants (Air Conditioning, Beating and Ventilating, February 1955, p. 83). Data Book. BIBLIOGRAPHY REFERENCES ` F. M. Stead: Study and control of industrial atmospheric pollution nuisances (American Journal of Public Health, VoL 35. May 1945. p. 491). * J. M. DallaValle and H. C. Dudley: Evaluation of Odor Nui sance in the Manufacture of Kraft Paper (U. S. Public Health Service Reprint No. 2022, Public Health Reporta, VoL 54, Janu ary 13, 1939, p. 35). BL L. Barmbey: Odor removal in air-conditioned space (Con densation of speech at University of Missouri, Air Conditioning Heating and Refrigeration Ncvn} April 30, 1956). H. L. Baraebey: Air pollution control by activated carbon (Annual Meeting Air Pollution Control Association, Hotel Statler, Buffalo, N. Y., May 22, 1956). H. L. Barnebey: Odore--classification, detection and removal (Building Research Institute Conference, New York, April 6,1960).