The Chemist’s Interest in-
Air Pollution H. B. MELLER 3lellon Institute of Industrial Research, and Department of Public Health, Pittsburgh, Pa.
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If the present discussion were limited to the smoke-making possibilities of anthracite, it would suffice to restate an earlier sentence: Anthracite does not smoke under any conditions. But anthracite is not everywhere available as a remedy for the city smoke nuisance; nor a t present are other smokeless fuels-gas and coke-everywhere economically applicable. Even in the northeastern portion of the United States and adjacent Canadian areas, where one or more of these smokeless fuels is generally available and where their compulsory use might conceivably be ordained by law, reasons of economy appear to have dictated that. considerable quantities of potentially smoky fuels be burned; this sit,uation is apt to continue for some time. The smoke problem does not, therefore, lend itself to a solution as simple as the universal adoption of anthracite or its equivalent from the standpoint of interest and smokelessness. The present complication must continue to be faced and be attacked by bringing currently exempt fuel-burning groups under regulation, and by stiffening requirements of all anti-smoke ordinances until they say, in effect, “burn smokeless fuel, or burn potentially smoky fuel smokelessly.” This is a national problem and the solution must be largely the work of technologists; a conspicuous part of this work must be undertaken by chemists. The shortcomings of antismoke ordinances are handicaps. The average individual will consider that he need not go farther than the requirements imposed by his city, upon the assumption that he is receiving the full practicable measure of protection. Generally, legal limits are based on the density of the issuing column of smoke. If the smoke is so dense as to be opaque as it leaves the stack, and if that density continues for a specified time-for example, 2 minutes in a period of 15 consecutive minutes-it is a violation; anything less, either in density or in time, is permissible. The number of inspectors to enforce such an ordinance usually will not exceed 1 per 100,000 to 200,000 population in the larger cities; in smaller municipalities it is customary for one man t o be responsible for all of the work, often in connection with inspection of buildings. Considering that the goal is the elimination of excessive visible smoke, damaging cinder and ash, and injurious and objectionable gases, it is evident that municipal laws as now framed can be only partially effective against the smoke, and
AS the chemist given adequate consideration to the effect upon community life of the release into urban atmosphere of products of incomplete combustion of potentially smoky fuels? The average small user of fuel is not sufficiently aware that smokeless combustion of potentially smoky fuels depends entirely upon equipment and operation. Hence he is likely to attempt to burn bituminous coal, for example, in a boiler or furnace designed for anthracite (a fuel which will not smoke under any conditions). Recently there has been voiced strong realization that such individuals are not being supplied with fundamentally necessary information concerning fuels and their use. Probably chemists and other scientists should assume a larger share of the responsibility for seeing that adequate information is supplied in understandable form. Between the gathering of scientific data and their dissemination to the fuel-using public (except the larger industrial organizations that are adequately staffed with chemists and engineers to work out their own combustion problems) there is a lamentable gap. Nold (9) recognizes this gap when he says: “Obviously, members of the Coal Division have devoted, not too much time and energy, but too great a proportion of their time and energy, to developing information and publiqhing papers on the purely scientific aspects FIFTY-YEAR A C C U M U L ~ T I O SOF SOOT BEIUCCLE.4YED of coal uses. The files of coal users, coal producers, FROM GRAYITE F.~cEOF PITTSBURGH JAIL and, in fact, of i n d u s t r i a l organizations in g e n e r a l , contain many manuscripts explaining in great detail the results of expensive and v a l u a b l e researches that have never paid dividends to industry because they have never been adapted to industrial practices. Some practical application should be m a d e of this accumulated information.” It is true that the files of technical journals abound in articles on smoke and dust, their effects, and their control. T h e “ m a n o n t h e street” who pays the bill gets little of this information and then only after it has gone through a series of filters.
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only occasionally operative in so far as colorless solids and gases are concerned. The problem is to find ways and means most rapidly to approach the goal. The interest of chemists and chemical engineers lies in the determination of the part they may logically take in the development of a workable plan.
Fuels and Combustion Complete combustion is smokeless combustion, in the lay acceptance of the term. To secure it requires either the use of smokeless fuel or of a potentially smoky fuel burned under proper conditions. It is not sufficient for the chemist to say that from his viewpoint combustion is a simple process; for the engineer to say, “Here is a furnace-fhd a satisfactory fuel for it,” and leave the purchaser to learn that something is wrong, but not what it is and what to do about it. Except for plants of such size that technical skill and advice may be had within the organization or are sought as a matter of course, it is surprising how few purchasers of equipment or fuel secure the unbiased opinions of competent consultants. The owners or operators of small industrial or commercial plants, of the considerable number of heating plants in office buildings, churches, institutions, apartment houses, etc., and the vastly greater number of householders, as a rule are not familiar with the technical phases of their problems, except as uncorrelated bits may a t e r through the more popular press. They depend largely upon the representations of salesmen, too many of whom have little or no technical knowledge of their products but who argue from catalog claims which may be as roseate as possible in view of competition. This is not criticism of the salesmen but simply a statement of fact. To these dependents upon the knowledge and fairness of others, fuels are known only as gas, oil, coke, hard coal, and soft coal. They, and often even their community officials, are unfamiliar with reports of committees on classification which discuss the burning characteristics of fuels, the composition of ash, and other qualities that affect combustion. Not all fuel producers know enough about the characteristics of the product they mine and sell. In connection with a recent relief project, i t was desired to know the composition of ash in a half-dozen coals. The chemist who made the determinations has been for five years in charge of the analytical work for a large coal mining company. He said that in that time he had not been required to make a single complete analysis of ash. Distributors and retail dealers vary in their ability to be helpful, from those who maintain corps of employes to study individual cases and to recommend the right fuel, to those who have little or no specific knowledge beyond the price of the commodity they sell and who therefore may be potentially harmful to the cause of smoke abatement. An example of this latter type is the signer of a letter recently received by the writer: “I have been referred to you for information on the use of soft coal. Our particular problem is the excess amount of smoke. At the present time we are selling company’s -coal. The local police department is threatening to serve summons on the consumers. All the soft coal is hand k e d . Will you kindly send me any hints that remedy such a condition.” The coal referred to is medium volatile semi-bituminous. The uninformed user will decide between gas, oil, coke, and coal. If he chooses a solid fuel, it may be coke or anthracite because of smokelessness; but it is probable he will want to use bituminous coal on a price-per-ton basis, regardless of whether or not his furnace is designed to burn high-volatile fuel and, if it is not, without consideration for any discomfort and damage that the resultant incomplete combustion may cause his neighbors.
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As an illustration, the renter of a nice home in one of Pittsburgh’s best residential districts remarked recently that, although his landlord always used coke while living in this house, he (the renter) had purchased bituminous coal because it cost so much less per ton. After three months of the heating season he was ashamed to face a neighbor who lived to leeward of him. He was chagrined to see how much damage the soft coal smoke for which he was responsible had done to the paint on the neighbor’s house. Considering the amount of coal he had burned, he was convinced that coke would have cost no more, if as much.
Fuel-Burning Equipment Combustion is a chemical process and requires a proper combustion train and the right technic to produce desired results, whether in the laboratory or in a plant. Industrial plants and all heating plants, except those in private residences and small apartment houses are regulated by law in those cities that have antismoke ordinances. Regulated owners and operators can secure advice and direction from the city’s enforcement officer, but that official must approve any equipment or fuel that can, in normal operation, meet the lenient requirements of the law. Since those requirements generally have been fixed with reference to easily available equipment and fuels, and since equipment manufacturers need not produce appliances that will do more than the present l a m require, there is a circle that can be vicious. In practically all cities the man who operates a house-heating boiler or furnace is exempt from regulation and may buy whatever type of fuel burner and fuel he wants, and any amount of smoke his chimney emits is legal.
Boilers, Furnaces, and Fuel Feeds Without discussing engineering design, we will consider briefly some of the difficulties, from the standpoint of smoke abatement, that are met in the use of medium- and small-size boilers and furnaces burning bituminous coal-difficulties that affect the chemical process of combustion. With gas there is no smoke problem because there is no difficulty in supplying air intimately mixed with the fuel, and the necessary furnace conditions can readily be maintained. The use of oil is not as simple as that of gas; adjustment of the burner must be watched more closely and the burner must be kept clean. There is no reason why oil cannot be burned smokelessly if fed through a correctly designed and adjusted burner to a properly proportioned combustion chamber; the difficulty comes with unconsidered attempts to adapt it to boilers or furnaces not designed for its use. Rose and Lasseter developed a chart (3) which shows that, with solid fuels, potential smoke production (appreciable yield of low-temperature tar) does not begin until about 10 per cent volatile matter (dry, mineral-matter-free basis) is reached. Fuels in the range of typical Pennsylvania anthracite, then, are shown to be smokeless under all conditions of test or use. More data are needed before drawing a final conclusion regarding the important coals of semi-bituminous rank, but, according to Rose and Lasseter, after about 13 per cent volatile (dry, mineral-matter-free basis) the potential smoke production increases and is practically in direct proportion to the volatile matter content. Hence all coals of bituminous rank are potentially smoky; where they are burned smokelessly, it is because proper combustion conditions have been met. It is obvious that a furnace designed to use smokeless fuel only may give results approaching the ideal when burning that type of fuel, but may be inefficient and smoky with highvolatile coal because of lack of provision to take care of the low-temperature tar as it is distilIed. Such necessary pro-
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LEFT: No SMOKEIS VISIBLE
RIGHT: THEREIs No RESTRICTION ON SMOKE OF THIS DENSITY
(CORRESPONDS
TO
RINGLEMANN CH.4RT)
0
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1
CE-TER:
THE AVERAGE OHDIN.&VCE: O F SMOKEO F T H I S
Any AhiounT
(CORRESPOKDS TO K O .
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LEFT: SMOKEOF THISDENSITY Is A VIOLATION(CORRESPONDS TO hTo. 3 RINGLEMANN CHART)
RIGHT: P O W D E R E D C O A L PRODCCES No VISIBLE SMOKE, BUT ON AN AVERAGEWINTER DAYTHISSTACKEXITSABOUT 20 Tom OF FLYASH
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visions are ample combustion space, secondary air for oxidation, and thorough mixture of air and gases. A glance a t newspaper and magazine advertising and a t commercial catalogs would indicate that the problem was solved with the development of the so-called smokeless boiler for high-volatile coal and the extension of automatic feed devices into the smaller size field. The solution, however, is dependent not only on design but on practical operation as well with, for the most part, firemen who know little or nothing about combustion except that more coal makes more steam. Failure correctly to operate such a combustion train within the comparatively narrow limits of tolerance will result in smoke which may be the result of firing too much green coal a t one time and thus overloading with rapidly released volatiles, failing to supply sufficient secondary air, covering too large a percentage of the fire with green coal and thus chilling the fire box, disturbing the fuel bed too much by poking-in many ways even an experienced fireman may fail to maintain correct conditions in the furnace. On the other hand, with smokeless solid fuels it is little more than a matter of loading up, setting drafts, and occasionally shaking down the ash. Clinker troubles are not considered in either group of cases. Estep (1) says: “TO expect a high degree of skill in combustion from a domestic consumer is asking too much. . . . . The domestic consumer can never be made a fuel technologist.” That is true also of most of the consumers being considered in this discussion. The question seems to be whether the unnecessary pollution of communities is to be permitted to continue indefinitely because of ignorance of available remedies. The extension of automatic stokers to this field of mediumand small-size plants has been of decided help in smoke abatement. It remains for designers to make such improvements as will rectify specific smoke-promoting conditions and to bring the price level to a point where the use of such devices can be required with bituminous coal-in other words, t o a point where the hand firing of fuels other than those inherently smokeless can logically be prohibited.
Fly Ash The physicist and the engineer are more concerned with this trouble than the chemist, since it is a matter of separation within the combustion train. L4 large part of the airpollution nuisance is caused by solids that could be prevented from entering the atmosphere.
Sulfur The chemist is directly interested in volatile sulfur compounds because of their possible damaging action on building materials, furnishings, etc. A few large plants have installed equipment to eliminate a high percentage of the sulfur that would otherwise be expelled, but as yet there is no practical method for universal application. An illustration of what can be done is shown by an investigation recently made at Mellon Institute, by request, to determine the amount and effects of volatile sulfur compounds from locomotives moving mail cars into and from the basement floor of Pittsburgh’s new post office building. Between the track level and the working floors above are mail chutes (not tightly sealed) and open-top traveling belts which act like chimneys, Tests were made while locomotives were in the building and a t periods of 5 to 10 minutes after their departure. With a semi-bituminous coal containing 3.1 per cent sulfur, fifty-seven tests on the first working floor gave an average concentration of 1.00 part volatile sulfur compounds per million parts of air (by volume), with a maximum of 3.64 parts per million. The fuel was readily changed to
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one of similar price that analyzed 1.2 per cent sulfur. Eightysix subsequent tests a t the same locations gave an average concentration of 0.29 part of volatile sulfur compounds per million parts of air (by volume); with a maximum of 2.13 parts per million. Such steps taken to reduce the amount of sulfur put into fire boxes will result in a relative reduction in the total amount of sulfur compounds escaping into the air.
Conclusion The question in point is the extent to which the chemist and chemical engineer may feel willing to assist in remedying a condition which is the subject of condemnatory discussion wherever fuel is burned for power or heat. When the chemist prepares to make a laboratory analysis, he first sets up the necessary apparatus. If he does not have it and cannot get it on the market, he makes it. He would not be content to use a makeshift with which he might lose some of the products he is seeking. When he develops a chemical process, he directs the proportioning of the equipment t o the extent’ that he specifies what must be accomplished in each operation. Should he do any less in the matter of the combustion of fuel? Classification of fuels is necessary; the burning characteristics, the composition and clinkering qualities of ash, the disposition of noxious and obnoxious gases-the chemist is doing splendid work in these directions and is publishing his findings in the technical press and making them available to industrial concerns. The mass of fuel users who, in the aggregate, burn a large percentage of the fuel, would understand comparatively little of this literature if they saw it. The individual in this mass buys a boiler or a furnace when he needs one and periodically goes to the telephone to order a load of coal or coke or anthracite. The manufacturers of equipment have only two imposed restrictions: they must satisfactorily combat competition and they must meet the smoke abatement regulations in such cities as have antismoke ordinances. Probably one of the largest factors in the development of the smoke nuisance, and a t the same time the tolerance of the public toward it, has been the low price of fuel. This point has had its effect in tending to inhibit regulatory action on the part of many whose qualifications would make their participation of great value in movements for cleaner air. There is, however, a definite movement under way, not only among those who have been closely allied with smoke abatement but also among national technical societies. The American Society of Mechanical Engineers, the ilmerican Institute of Mining and Metallurgical Engineers, the American Society of Heating and Ventilating Engineers, the American Public Health Association, and others have committees st,udying phases of the air-pollution problem. Much valuable time might be saved if an effort were made to secure intersociety cooperation, to arrange for thorough discussion of the problems, and to prepare to assist distressed fuel users mho need help badly but do not know where to seek it.
Literature Cited (1) Estep, T. G., Heating, Piping, Air Conditioning,6 , 520-4 (1934). (2) Nold, H. E., MiningandMet., 16 (337), 34-5 (1935). (3) Rose, H. J., and Lasseter, F. P., paper presented before Division of Gas and Fuel Chemistry, 88th Meeting of American Chemical Society, Cleveland, Ohio, Sept. 10 to 14, 1934. RECEIVEDMarch 28, 1935.
