July 19-50
Atmospheric Pollution This month's column is the first of two reports on the U. S. Technical Conference on Air Pollution b g Louis C. IMcCabe
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HE summaries and recommendations of three of the seven panels of the United States Technical Conference on Air Pollution (Washington, D. C., May 3-5, 1950) are reported here essentially as presented by the panel chairmen. The summaries and recommendations of the four remaining panels will appear in this column in the August issue. Instrumentation. One of the major problems in instrumentation is t o obtain representative samples. The problem is more difficult when particulate matter is involved, and a fundamental investigation of the theory of sampling and development of methods, which might become more or less standard, would be advantageous. Some aspects of instrumentation could well become the subject of research for a federal agency, a university, or a research institution. It would be unfortunate if each locality and each group working in air pollution should have to duplicate this work.
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There was considerable discussion of appropriate time periods for sampling and the relative merits of what might be called cumulative or integrated samples as against the so-called instantaneous sample. Samples may be analyzed in a second or microsecond, but there is always some finite period involved. Whether this period should be seconds or months depends or1 the particular application. In Great Britain, the major emphasis is placed on long-time average samples. For example, in the apparatus for dust-fall determination and SO2 determination a sample is collected for a period of 1 month. After a lapse of a sufficient number of years, it is possible to draw contour lines of pollution on the map. This is in sharp contrast to the feeling in this country. There are practical reasons also why short-sampling periods are essential. For example, with growing crops, there may be damage by emission which can happen in a short period, perhaps a n hour or so. Continuous average samples over days or a month would not show anything of great benefit in this case. Short sampling periods are advisable for locating the source of pollution and, of course, for instrumentation where plant control is necessary to ensure that industrial processes are operated in conformity with control measures. Continuous sampling with short-time periods is, in general, likely to give much more valuable information than long-time cumulative or average type samples. Obviously, it is possible t o accumulate records of samples for short-time periods, whereas it is not possible to use average values over a longer period of time t o find what happens a t some particular instant. The instrument makers indicated that they could make any instrument which might be required, if specifications are furnished, including: substances to be determined; concentration ranges involved; accuracies required; operating conditions; and whether the equipment will be required to work in an airplane or bolted down in a plant, Of the fourteen papers presented, four were on sulfur dioxide determination, and these included three distinctly different methods for determining sulfur dioxide. From the health standpoint, not only the chemical nature of substances must be measured but also form, particle size, and particle size distribution. Many instrument makers are postponing development work until they can get more specific information on the types of instruments which would be most useful to investigators. These considerations are important in health and crop damage, both physiological phenomena, Ordinary nuisance value is important when concentrations are far below those which would cause injury to health, and there are the economic factors: factors which affect visibility, the operation of airlines, and shifts in population, both on a temporary and on a permanent basis. All of these and many other considerations will determine what types of instruments are needed. Virtually all the chemical and physical phenomena are available for use in instrumentation; physical methods include everything from gravity to electrical and optical phenomena. Physical methods are advantageous, and it is always desirable to obtain a continuous record, as it is more valuable than the discontinuous or grab-sample type of analyses.
Analytical Methods and Properties. When two chemicals are dispersed, either of them alone may not be of great importance but the combination of the two may be of serious consequence. This phenomenon occurs not only during dispersion but it is a major ~- m-oblem in collection. A sample containing a variety of components may not in any way represent the material which was originally in the air because of the reactions which occurred in the collecting apparatus. The need for further knowledge of organic contaminants is apparent. There remains considerable confusion in the collection and analysis of sulfur-containing components such as sulfur dioxide, hydrogen sulfide, and the mercaptans. The optimum for analysis, of course, is t o analyze for the unchanged molecule. The task of the analytical chemist is t o obtain methods which characterize and are specific for components which he wishes to find. It was noted during the presentation of papers t h a t concentrations were expressed in mg. per liter, grains per cubic foot, mg. per cubic meter, and mg. per cubic foot. It would be useful if there were some agreement of dimensions per unit of concentration. The separation and identification of compounds in multicomponent systems presented a major problem which needs further research. Study of the effects of sunlight and oxygen on atmospheric components t o form obnoxious compounds was recommended. There should also be further research on the changes which occur in sampling collections. Study of the physical chemistry of sampling and collection procedures is considered in order, and fundamental studies on the properties of aerosols relating to atmospheric pollution should be continued. Equipment Panel. The Equipment Panel was concerned largely with means of collecting, a t the source, or preventing the formation of atmospheric contaminants. The properties of aerosols were of particular interest because they give clews and point to the possibilities of arresting, retaining, and depositing them. Scientific knowledge has no end, and it wag recommended t h a t research be continued. It was concluded that the knowledge we have on the pro erties and behaviors of particulate matter and aerosols genera&, even though it is not complete, is substantial and entirely satisfactory for progress in the a r t of development and use of equipment for control of atmospheric contamination. The greatest impediment seemed to be not in knowing how'to proceed but in knowing what is needed and wanted, so that present knowledge may be better directed to the solution of problems. It was pointed out that there is no evidence to show that odors cause disease. There is evidence to show that odor might affect the state of well-being such as the appetite or sleep and might be a cause of hysteria. Much is known of the principle of design, construction, application, and limitation of the fibrous filter, and filtering performance can be modified to meet a variet of requirements. Following wartime developments and, recentfy, through sponsorship by the Atomic Energy Commission, there has been developed a commercial filter in a package-type unit. This is now declassified and is very effective in the collection of submicron dusts. It is rated on air velocity, size, and pressure drop just as are other pieces of collection equipment. Granular coke beds were used long ago for collecting sulfuric arid mists, and fibrous or granular beds are high1 effective in collecting small aerosols. Other research is needediin this field, however, and some is going on now. The uses and limitations of spray towers and packed towers in atmospheric pollution, par(Continued on page 74 A ) ticularly in connection with
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Atmospheric Pollution
WHAT KIND OF DUST CONTROL APPARATUS
chemical processing equipment, is understood, hut further research is needed if they a.re to be used in aerosol collection. I n spray towers, there is difficulty in producing small droplets below 50 microns in size, and the effectiveness of such droplets i i i collection of submicron dust and mists i s not great. The characteristics of cyclonic spray toil-ers and the venturi scrubber n . e ~ cited as examples of sedimentary-type equipment which provitiocl improved contact. These have now been used rather widely i i i plant operations, and t h m has been good collrction of information on performance over a wide variet of practical prohlemr. The technique of introducing dust particl s into u. stream of superheated steam to secure condensation and sedimentation is a iiovel approach which shows promise and is crrtainly worthy of furthrr exploration. The use of activated carbon collectors is highly developed. They have good application when irritating substances or odor..; must be removed. There are possibilities of improving inactive carbon by impregnating i t t,o make it active. The electro,ytw precipitator is one of the oldest and most effective of collecto but there is considerable research in progress to develop i t I'urtii The sonic flocculator has proved itself in several installations an(1 development and research are going on. There was a paper on the usefulness of high stacks, and t,hc locat,ion, populat,ion, and other requirement,s which must IP satisfied, along with meteorological conditions, came in t'or considerable discussion. A paper was presented on the design fundamentals of large incinerators. There were four papers on the mitigation of atmospheric pollution from solid fuels. Coal-burning locomotives may m u terially improve operating conditions by the use of douLI(,screened coal. This not only reduced the amount of fly as11 released over the count'ryside but increased the efficiency of t h e fuel. A saving of 25% in fuel cost was indicat,ed where thi-: practice was followed. Smokeless household st,oves have bcrit developed a t Battelle Memorial Instit,ute, under the auspices Bituminous Coal Research, Inc., and a t the Gniversity of Illinoi This equipment, which has been field-tested and is in productio , eliminates smoke and is more convenient to operate. ..llt,hougli costs are 10 to 20% higher than costs for conventional type equipment, there are fuel savings of 20 to 30%. Power plants have been particularly active in the improvement of stoker and furnace designs and in t'he installation of precipit,at'ors and duyt collectors.
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If all dust and fume control e We, problems were alike, there oir cleaning usin would be no need for specialized "Rotoclone." engineering service. But these problems vary widely, depending upon manufacturing processes and raw materials used, including many recently developed materials which present entirely new problems. For these reasons, selection of the right units for a really efficient dust or fume control system is definitely a job for engineering specialists. Kirk & Blum with 43 years of experience in this field, first makes a thorough analysis of your special dust or fume control problem. Next, our Staff selects the right - units for your job from among the various makes available-then designs and installs a complete system that is guaranteed by Kirk & Blum to give the results you want.
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Engineering knowledge is available for the solution of almwt all the collection problems. Before there is intelligent dcsign, development, selection, and use of equipment, there must, be soiiie definition of cleanliness. Degree of cleanliness i s important because in a precipitator a change in collecting efficiency from 90 to 99% doubles the cost of the unit. There is need fo: ii uniform standard procedure for determining the performancr: oi' equipment. Without it, much of our experience in performancc data becomes worthless. Efficiency figures do not mean mucli in this field unless one is dealing with a homogeneous dust in t1.e size ranges which are responsible for the difficulty. Some filtering devices are 99% efficient, but against what? Air-pollution equipment should be planned on the drafting board before a plant is built. This means that, engineers, familiar with such equipment, n d l be a t the drafting boards; this, t o sonic extent, requires an educational program in the universities and some inoculation with the idea that things are designed in relatioil to people. Equipment that is satisfactory in one situation may not 1 ) ~ ' satisfactory in another if conditions are not identical. Currently, the selection and design of equipment is in the hands of specialists. Ihowledge is not yet of the type that can be put into a hanclbook so that anyone can use it. Concensus of opinion is that where control equipment i y installed for the public good, there might be some t,ax relief oi' election of rate of amortization.
0 Centrifugal separator suitable - - - fa. - haavv _ - , dud -concentration.
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0 Combination of centrifuge1 separator ond dry filter.
T h e tltomic Energy Commission's "Handbook o n Aerosols," which contains basic discussions a n d descriptions of theoretical a n d experimental importance in the field of aerosols, i s now available through tho Superintendent of Documents, Washington 2 5 , D. C. (60 cents). An annotated bibliography "Biological Aspects of Air Pollution,'' prepared by the Public Health Service, was published in M a y . Copies m a y b e obtained through t h e Publicity Department, United Steelworkers of .4merica, Room 1500, Commonwealtli Building, Pittsburgh 22, P a . ( 5 0 cents).
FOR CLEAN A J R . . . THE O L T ~ ~ J rooL I~IM ~-
DUST CONTROL S Y S T E M 5
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