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80 CHAPTER 7 I960 Guide odor retention of wool was comparable to that of cotton. Wood lost its odor after 300 min. These data are meager, but indicate a trend useful for design. Application of the quantitive values should not be made without due consideration of the finish, weight, weave, and thread count of the fabrics. Further research is needed relative to these items. On a qualitative basis, wood quickly gives up odors adsorbed. Wool has low odor adsorption at oil temperature and humidity combinations tested. Nylon and cotton adsorb large quantities of odors at an optimum con dition of 75 F and 50 percent relative humidity. They act as a sponge, readily adsorbing odors from a tobacco-smoke filled room, and releasing them more slowly over a longer period. While it has been shown that smoke, cooking, and body odor perception is decreased with humidity increase, where the odor source is intrinsic with the materials, as in the case of linoleum, .paint, rubber, and upholstery, a reduction of relative humidity would be beneficial," and would decrease the rate of odor release. A--Air roqvind to proviso aeemtsary oxygon content. ft--Air requirod to pnvont CO* eoocanfraftoo front riting obon 0,6 percent. C--Air required fo remove objeefionabt* body odon from sedentary adutte O--Data from curve C nwreamd by 50 percent (and projected) to allow tor moderate piya'cat activity and odon. Fig. 5.... Ventilation Requirements to Avoid Vitiation and Obnoxious Body and Smoking Odors ODOR REMOVAL Odor removal may be accomplished by physical or chemical means Ventilation with clean outdoor air, air washing or scrubbing, charcoal adsorption, and masyjng are physical methods available to the engineer. Chemical adsorption or destruction of odor sources, vapor neutralization, and cata lytic combustion are other means. Air washing or scrubbing and combustion are of considerable value to process indus tries. Washing and scrubbing, like filtering, are applicable to the removal of particulates and in some cases are means of recovery of valuable product. Odors associated with the particulates are removed indirectly in such processes. Com bustion of obnoxious gases is quite effective and practicable where indicated by economy. These methods are employed to alleviate the effects of harmful exhaust gases mid particulates on people, vegetation, and property. . .. .Ventilation,, charcoal .adsorption, and neutralization are effectively utilised in air conditioning for odor removalrTbe removal of odorous gases or vapors by water sprays in airconditioning systems has been found to be of little practical value to the air-conditioning engineer, since other available methods are more effective. Rg. A... .Odor Retention for Nylon at 50 percent Relative Humidity Ventilation Ventilation is an effective means of removing the con taminated air in an enclosed spaceby dilution. In this process, the vitiated air containing objectionable gaseous odors, ir ritants, particulates that obscure virion, and toxic matter are replacedby clean outdoor air. It has been shown by ASHRAE and other research that ventilation requirements for human occupancy are a function of the space per person and the de gree of activity (see Table 1, Chapter 6). Data from tins table and other sources have been presented in a readily usable form in Fig. 5. The values from Curve D of Fig. 5 have also been found to apply reasonably well to densely populated heavy-smoke-laden atmospheres such as sports arenas where vision and irritation are more of a problem than odor. It has been found that 30 cfm per person are necessary for effective commercial ventilation for such arenas, to avoid objectionable eye irritation, odors, and impaired viability.0 The actual oxygen requirement.per person varies with activity. It is normally about 0.89 cu ft per man hour when walking at a rate of 1 mile per hour. About 0.74 cu ft of carbon dioxide is liberated per mao hour for norinai activity* Nor mal air contains about 0.03 percent carbon dioxide. Fig. 6 shows the effect of carbon dioxide on lung action. A concen tration of 0.6 percent has little effect on lung action, increas ing it only about 10 percent above normal * As shown in Fig. 5, the oxygen and carbon dioxide require ments can be met with an outdoor-air ventilation rate of less than 4 cfm per person* This may include infiltration. An outdoor-air ventilation rate above 4 cfm is required to dilute odors, irritants, smoke density, or other nontoxic conditions. The amount of ventilation required per person to remove hu man odors, or dilute them to an acceptable value, can be found from Curve D of Fig. 5 for the space occupancy. Smoke and other solid and liquid particulates can be ef fectively removed by electronic precipitators or absolute filters (see Chapter 24, Air Cleaning). Odors, gases, and vapors can effectively be removed by charcoal adsorbers or by counteraction. If the room is conditioned during summer or winter, a considerable fuel and power saving can result from use of these methods to reduce high ventilation rates." - Charcoal Adsorption Charcoal adsorption is the physical condensation of a gas or vapor sorbate on the charcoal sorbent. The charcoal or Air Contaminants 81 1 Of. cowfCIOOTMtM - irrttuLT t -n u/ r/ 7 / T BSfN 3H - KRCtKT or MOftUAL LUMB ACTION 00 Rg. 6.... Physiological Effect of Various Concentrations of Carbon Dioxide carbon is especially prepared from coconut shells, peach kernels, or other materials. To increase the surface area and thereby increase the sorption capacity, the charcoal or carbon is activated. The preparation of activated charcoal usually involves two steps, first, is.the carbonization of the raw ma terial by controlled heating in a neutral atmosphere. The second is a high-temperature oxidizing process, the purpose of which is to remove from the capillaries of the raw material those substances which cannot be carbonized in order to create extensive, surfaces on which adsorption, can take place." -r'". Coconut charcoal properly prepared is considered the standard high quality material for air or gas purification in air-conditioning systems. The quality of charcoal as an ad sorber of gases is rated oh the break-through time when sub-., jeeted to the standard Accelerated Chloropicrm Test. The capacity of charcoal to adsorb gases or vapors varies with the gas or vapor. Some are readily adsorbed, while others are not. Improved adsorption for certain gases can be obtained by impregnation of the charcoal with certain mineral salts.** The relative adsorption qualities of high quality 50-minute unimpregnated coconut shell charcoal for some vapors are given in Table 3 The values used are baaed on the removal of the substance from dilute concentrations in air, as en countered in air-recovery and air-conditioning systems. If the weight of the vapor to be adsorbed is known, then the quan tity of charcoal required for the period under consideration can be obtained by use of Table 3. If analytical determination or knowledge of specific odor- cauring compounds and their amounts are not available, other means can be employed to determine the charcoal require ments. These may be an inventory of individual odor sources, type of occupancy and volume to be purified, dilution of purified air, using the curves of Fig. 5, or other means. Table 4 provides the necessary data to determine the carbon re quirement based on an inventory of individual odor sources. It is to be noted that odor control by activated charcoal ad sorption may also remove other gases present that are toxic or otherwise objectionable, but which might not have an odor. The relative odor levels of the various types of occupancies listed in Table 5 are for average conditions existing prior to installation of special odor removal equipment. The occu pancies are classified into four odor levels; A, B, C, and D. Odor level A contains the lowest amount of odor, and level D, the highest. One pound of 50-min activated coconut-shell charcoal will suffice for one year to purify 2000 cu ft of space at odor level A, 800 cu ft at level B, 300 at level C, and 100 at level D. If 40-min charcoal is to be used, then the amount of charcoal required would be 20 percent greater. Activated charcoal is available in cylindrical canisters, flat plate, or accordion pleated frames. In some cases the char coal can be reactivated at a temperature of about 1000 F. If the charcoal is heavily loaded with a high molecular weight or unstable organic material, the processing may have to be very similar to that used in the original manufacture of the charcoal, that is, approximately 900 C (1652 F), plus stems. The adsorbers are provided with a fan system for recirculation or placed in the return air stream of an air-conditioning sys tem. If a percentage of the return air is purified, the outdoor air requirement as indicated on Fig. 5 could be reduced ac cordingly, without affecting the odor level and with a saving in outdoor air heating, cooling, and blower costs. Four cubic feet of outdoor air would still be required to supply oxygen and to prevent the carbon dioxide concentration from exceed ing 0.6 percent. In cases where no outdoor air can be provided, such as in a submarine protective shelter, oxygen can be provided and the carbon dioxide adsorbed. Washing and Scrubbing Where odorous vapors are soluble or emulsifiable in a liquid, with or without chemical reaction, odor removal by liquid absorbents may be suitable. Absorbents may be water, modified water solutions, or oils. Where a gas is highly soluble in a liquid, its diffusion in the liquid from the surface is rela tively easy. For such' applications spray type washers are used. For relatively insoluble gases, odor removal by the ab sorption process may preferably be accomplished by scrub bing methods. In this process, odors may be removed from air by-flowing countercurrent to water, oil, acid, and some ab sorbing liquid. This process is frequently used for the re covery of valuable vapors. For relatively insoluble gases some types of bubbler equipment, packed towers, or scrubbers (centrifugal or cyclone) are commonly employed. Physical solution, without chemical reaction, is involved in these absorption methods. The partial pressure of the odorous gas in equilibrium with the solution of the gas is a limiting factor. For all practical purposes deodorization by physical absorption is never a process which removes all odors, some odors may be returned from the liquid if the equilibrium is disturbed and the water not removed from contact with the air in the system. Neutralization, Masking, and Counteraction y Odors can be chemically destroyed, neutralized, or counter acted and masked. Antiseptic and disinfectant deodorizers are used to kill odor-producing bacteria. The disinfectant may in itself be odorless or have a masking or neutralizing odor. Ozone is one deodorant that chemically destroys the odor source, is a tdasking agent, and counterodorant. Its use has been limited by the difficulty of devising adequate control techniques. Where the composition of the objectionable odor can be ascertained, it is possible to compound another odor that