INBUSPRIAL A N D ENGINEERING CHEMISPRY
April, 1923
935
Coa,l Carbonization and the World’s Fuel’ By Horace C . Porter 1833
HE w 0 r l d ’ s f u e 1 is basic in Our Civili-
T
CHESTNUT S T . , PHILADELPHIA,
PA.
they handle. BY electrification this is very greatly reduced. The use of coal for heating houses and for making into gas for cooking and lighting is comparatively among the minor forms of application. From 15 to 20 per cent would easily cover these needs. The large accomplishments in fuel economy, therefore, are to be looked for in the industrial field. By a reasonable amount of centralization of industrial power production and by improvement of efficiency therein, coupled with electrification of a reasonable part of the railway system, the country’s coal donsumption on the basis of present power requirements may readily be cut by 30 per cent. Still greater reductions are to be expected from future improvements as yet undeveloped in the application and distribution of energy. The mercury-vapor engine, and the powdered-coal, explosion-driven turbine are in the minds and on the work-benches of inventors-destined possibly a t some time in the future to turn into useful channels a large part of the 90 per cent loss commonly occurring to-day in the realization of the energy of coal through steam-power application. With increase of .population and continued development of industry in this country, now sparsely settled and relatively undeveloped, the need for increased fuel economy will be felt more and more strongly. Efficiency and technical skill must ease the burden of expanding requirements and slowly diminishing natural resources. Now comes the question, how far can coal carbonization enter into this fuel-economy program? Is it true that for highest efficiency, as some have said, bituminous coal should not be, and eventually will not be, burned raw? We frequently have our attention drawn, through appeals from economists and conservationists, to the immense possibilities in the saving of by-products from coal now burned raw under boilers. It has been said that large, central power stations located a t coal-mine mouth could utilize carbonization methods, produce power thereby, and save vast quantities of coal by-products now going to waste. The needs of agriculture for the fixed nitrogen, of motor transportation and the Diesel engine for the oils, of industry and the household for a larger and cheaper public fuel-gas supply-all these seem to cry out’ against the waste of byproducts from the furnace stacks.
After stressing the eoer-increasing need for greater fuel economy which is broughf about by the growth of industry and the S ~ O W ~ Y diminishing natural resources, the author has discussed the possibilifies of coal carbonization as a solution of the problem. The dificulfies involued. principally the excessive costs of the process, due to high expenditure of energy, heauy plant expense, and insuficient “form values’’ of its products, are pointed out; and the progress of the industry in eliminating these dificulfies. particularly the possibilities of the low-temperature carbonization processes in increasing the “form value” of the products, is described.
Zation. Not O d Y does it give heat for homes, ofice% and factories, but, more importanti as the main Source of industrial Power-jt Provides 90 Per cent of all mechanical energY for railways, streetcars, steamships, manufacturing. Each household in this country-averaging the many small with the few large ones -uses directly and indirectly 20 tons of coal per year and spends for it $150 to $200. The industrial fabric would go to pieces without fuel-without coal. The savage in primitive times used no coal-in fact, but little fuel of any kind-and yet for his own ends he got along very well. He was more healthy, as a rule, than the present generation, highly ornamented and educated and pampered by civilization. Our fuel goes to meet the needs of our complex civilization, elaborately organized and developed as it is, to give us clothing, food, and shelter of-a high order, communication, education, luxuries, and pleasuremuch of it, indeed, to the latter two ends. But, notwithstanding all this, we are not a generation utterly abandoned to waste and extravagance. The figures in respect to fuels will confirm this fact. We devote, in increasing measure and with favorable results, a great deal of attention to research looking toward improvement in the utilization of fuel and the securing of economies. We do waste, to be sure, a great deal of coal. Under industrial and locomotive boilers, for example, where nearly 70 per cent of our coal consumption is applied, we waste on the basis of efficiencies now possible by best engineering practice, one-third or more of what is being used. But the encouraging feature is that in large centralized stations now in actual operation, we obtain by condensing steam turbine equipment and entirely practical furnace and boiler operation, twice as much power from a pound of coal as was obtained in average practice a few years ago. As it becomes practicable gradually to scrap the old equipment and to concentrate more and more the production of power into large central units, our expenditure of coal for a given output in this field will steadily decrease. As to the railroads which consume nearly one-third of our bituminous coal, and are admittedly extravagant in its use, we are able to answer the pessimist by pointing to the increasing favor which is accorded to electrification. A western division of the Chicago, Milwaukee & St. Paul Railway has been converted from steam to electric operation and by actual records has secured a gain in train locomotive power cost of 53 per cent. The Pennsylvania Railroad, according to announcement in the daily press, will electrify its Mountain Division in Pennsylvania in the near future. This step by the railroads is a real advance in fuel economy. We are to consider here, of course, the large indirect savings in addition to that of the fuel on the locomotives. For example, the haulage of coal by the railroads has been estimated to amount to one-third of the total ton-miles of freight which 1Presented before the Syracuse Section of the American Chemical Society, Syracuse, N. Y.,December 8, 1922.
DIFFICULTIES TO BE OVERCOME But we must be reasonable in this boosting for carbonization-we must analyze the difficulties involved. There is the cost of carbonization, excessive under the present methods, and therefore standing as an obstacle to wide development for the purpose of general fuel application. If power is to continue to be obtained through steam, the carbonization products coke and gas, applied thereto, have not, under present conditions, a “form value” sufficiently great to pay the costs of their manufacture. Furthermore to even Of ammonia and Oils the supplementary the balance.
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The cost of carbonization is made up of two factors, the energy expenditure, and the plant operation and maintenance. First, in energy expenditure we have a loss of 18 per cent of the original heat value of the coal. (Figures of average, high-
FUEL- 1QO$
LOSSES :
ZO$
G A J PRODUCER
COOLING-
19%
EXHAUST- 30
J
ENGINE & GENERATOR-
FIG. ENERGY
CONVERSION I N
7$
GAS-ENGINEELECTRIC PLANT*
*Illustration from pamphlet of W. S. Rockwell Company.
temperature industrial carbonization, not the “optimum” figures.) In other words, there result from carbonization available fuels having a heating value of 82 per cent of that of the original coal. The loss is not only in the gas burned in the oven flues but inlleakage, carbon, and soot, and the unavoidable mechanical losses of operation. This energy is lost, it is not stored or converted so as to be available in the products. S. W. Parr’s researches on carbonization a t the University of Illinois look to the reduction of this item of loss by utilization in greater measure of the exothermic reaction occurring in carbonization, the inducing of a coking process in part from the inside of the charge by its own heat of reaction. Other advances in reducing this energy expenditure are constantly being made through practical improvements in plant-operating methods and design of apparatus. It may be noted that the newer types of by-product coke ovens are now expending in the form of fuel gas only about 1000 to 1100 B. t. u. per lb. of coal carbonized, as compared to 1500 to 1600 B. t. u. common in the practice of ten years ago. The other factor in carbonization costs-plant expense-is larger even than the energy cost. It is difficult, however, to put it into figures of dollars and cents or in percentage of the coal value, owing to fluctuation in labor and materials costs. The latter, however, parallel ordinarily the fluctuation in coal cost, so that we may say, with some approximation of a general rule, that the plant and conversion cost of carbonizing coal in a modern plant of medium size will amount to a figure between 25 and 35 per cent of the cost of the coal. These plant costs, both investment and operating cost, are of course lowered as the rate of output is increased. Late developments in coke-oven design make possible a
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decided advance in rate of operation without undue increase in the temperatures used or deterioration of products. The Semet-Solvay regenerative six-flue-high, silica oven, with its large charges, its high degree of heat economy, and successful application of the principle of efficient and uniform heat transfer by high velocity of heating gases, attains remarkable coking velocities, and is able to coke, a t some of the later plants, 26 to 27 tons of coal per oven per day. The newtype Koppers oven, recently developed in this country under patents of J. Becker, secures an advantage through the use of cross-over flues from the row of vertical-heating flues on one side, over the top of the oven to the row on the other side, enabling the oven to be built higher than has formerly been possible with vertical-flued ovens, and securing much more uniform heating. This oven is built narrower than the older type, but higher and longer, and attains a great increase in coking capacity. A small battery of these ovens built a t Chicago a year ago for experimental purposes has been successful in securing very uniform heats and high capacities. It cokes, if required, 28 tons or more ofcoal per oven per day. These capacities, compared to those of 8 to 12 tons per oven per day prevailing fifteen years ago in this country, or even now in Europe, illustrate how investment and operating costs can be cut in two by careful attention to engineering design and operating methods. Yet, with the best of design and of operating method so far attained, coal carbonization must carry a burden of costs amounting to 25 to 30 per cent for plant and operation and 17 per cent for heat expenditure, a total of, say, 45 per cent of the cost of the coal. In average practice to-day it exceeds 50 per cent. Following a graphic method used by W. S. Rockwell Company, in showing the losses in various energy conversion
FIG. 2-cOAL CARBONIZATION. I N P U T AND OUTQO OF BY-PRODUCT AUXILIARY. (WITHOUTDISPOSAL OF COKEFLANT,APPLIEDAS STEAM BY-PRODUCTS)
*
* This chart is based strictly on fuel value relationships, assuming eq?ial values per unit for B. t. u. in whatever form occurring; for example, the item “heat used,” 13.5 cents (equal to 17.5 per cent of the va1i:e of the coal), is the proportionate value of the loss of B. t. U. in rarbonizing obtained by difference.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April, 1923
t-
337
TnT--’ana
HEAT USED IN PROCESS-
OPERATING EYPENSE. R A N T &DEPRECIATION
TOTAL LOSSES s 36 9
pJT!rE;:ypFzk. LIGHT OIL
54
AMMONIA 6Q
NET
PROFIT :
- 22%
FIG. 8-cOAL CARBONIZATION. I N P U T AND OUTGO OF BY-PRODUCT COKEPLANT,APPLIEDAS STEAM POWER AUXILIARY. (ASSUMINOENHANCED FORM VALUES FOR BY-PRODUCTS AND FUEL V A L U E FOR COKB)
* Possible
FIG. &-COAL
CARBONIZATION.
I N P U T AND OUTGO OF
BY-PRODUCT
C O K E PLANT, APPLIEDTO FAVORABLE OUTLETS FOR C O K E AND B Y PRODUCTS. (FIELD LIMITZDBY DEMAND FOR COKEAND GASAT ENHANCED VALUES SHOWN)
improvements, if and when developed, would utilize some portion of this loss-e. g., the sensible heat of the coke if fired hot directly under boilers. *These by-products are assumed a t favorable disposal values, light oil for motor fuel, tar for chemical conversion or special fuel, and gas for city distribution.
eThese are the relative values referred t o the outlay of $1.00 in coal and plant; with coal, for instance, a t $7.75 per ton, assumption is made of coke at $11.00 per ton, coke breeze a t $2.00, ammonium sulfate a t 3 cents per lb., light oil (suited to motor fuel) a t 17 cents per gal., tar at 5 cents per gal., and gas at 25 cents per M. C U . ft.
processes, there may be depicted. the energy distribution and losses in coke-oven carbonization. Fig. 1 merely illustrates the diagrammatic method used, and shows the energy distribution in the gas-engine electric plant. Fig. 2 shows the losses and the recoveries based on use of the products strictly as fuels in steam production-in other words, making the coke-oven plant a fuel feeder to the steam-power plant, with no attempt to find better markets outside. Figs. 3 and 4 illustrate in the same manner how the dollar investment (77l/2 cents in coal and 221/2 cents in plant and operating cost) yields returns by the aid of carbonization-Fig. 3 on the basis of fuel values, with ammonia added as a by-product, and Fig. 4 on the basis of enhanced form values which the products command in a limited market. On the basis, therefore, of relative heat units contained, ready for application to steam raising (Figs. 2 and 3), it is evident that the products of carbonization leave a large margin between their value and that of the investment in plant, labor, and coal. Obviously, on this basis alone the carbonization plant as a steam-power producer is a failure. But now there come the by-products, chiefly ammonia and the “form values” of the fuel products-coke, gas, and light oils-to even up the balance. I n Fig. 4 we add, without question, 6 cents for ammonia and a 4-cent “bonus” to the light oil for enhanced “form
value” used as motor fuel, for both of which no immediate danger of an over-supplied market and thereby reduced valuation appears to threaten. Tar and gas also are given an enhanced “form value,” assuming special uses wherein their adaptability and convenience make the demand, but it is problematical to what extent the market would absorb them and sustain the higher valuation in case of great expansion of the carbonization industries. Dyestuffs and coal-tar chemicals and the increasing industrial demand for gas at something more than its fuel value (compared to coal) do now justify some degree of boosting of the “form value” for the tar and surplus gas from carbonization. But until the public acceptance of these products (and coke as well) can be obtained a t an average valuation 60 to 70 per cent higher than their mere heat unit value, carbonization can hardly be expected to overstep greatly the metallurgical coke and domestic gas fields. Certainly, for power production through steam, concluding from the charts and analysis above shown, carbonization processes leave now, on the wrong side of the balance sheet, too great a margin to justify hope of conservation through their wide application therein. The gas-engine power plant is a possible aid in this connection for future development, but, under the present status of relative costs, it offers only uncertain advantages. Further improvements in the effi-
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INDUSTRIAL AND ENGINEERING CHEMISTRY
ciency of heat-energy recoveries in carbonization-as, for example, the utilization of the sensible heat in the discharged coke-will aid materially. NEWDEVELOPMENTS IN THE CARBONIZATION FIELD From the foregoing considerations it readily becomes apparent that carbonization of coal, in order t o gain ground as an aid in the application of fuel, especially if applied in steam-power production, must make improvement along one or all of three lines. It must (1) lower its expenditure of heat energy, or (2) lower its plant and operating costs per unit of output, or (3) increase the “form value” of its products more nearly t o balance the costs of conversion. The prevailing high temperature coke- and gas-making processes are progressing in some small degree along the first-named line, in more marked degree along the second, but almost not at all along the third line. Their progress on the second line is notable and creditable. Rate of output is being increased by improvements in design and in structural materials, and operating costs are being reduced. Vertical gas-retort plants with their simplified charging and discharging equipment, their lower operating labor cost and their adaptability t o steaming for increase of gas-making capacity, contribute in important measure t o the advance in this direction. Low-temperature carbonization processes and those “complete gasification” processes which embody low-temperature carbonizing as an element in their operation, lead toward advances along the third line named above; in other words, they show prospects of yielding tars, oils, and coked residues of an enhanced “form value” for special purposes. If they do not succeed in doing this in marked degree, they will fail. For in capacity or rate of output, and therefore in production costs, the low-temperature processes compare very unfavorably with the established high-temperature processes. The great virtue of low-temperature carbonizing is the saving of the oils from the coal-the preserving of these presumably “high form-value” materials from cracking and degradation into soot and gas carbon. The oil yield is doubled; and, if all or nearly all is found‘applicable to motor fuel use, both in light-fuel motors and the Diesel heavy-oil motor-as is claimed to be possible-the form value in this product should compensate for much of the increased plant and operating costs. The coked residue, however, must also create for itself, perhaps in the domestic field, a high form value and win its way in public favor before these processes can satisfactorily overcome their handicap of high costs. COMPLETE GASIFICATION ” PROCESSES
/
“Complete gasification” processes are those effecting complete conversion of the coal into gas, except for the ash residue and a certain amount of tar. Ordinarily, the term is now applied to those processes involving destructive distillation in one zone, and the making of producer gas or water gas in an adjoining zone of the same apparatus. The distillation is usually effected, in part at least, by the sensible heat of the producer gas or water gas passing directly through the raw coal in the upper or distilling zone. This is an application where low-temperature carbonization finds great promise. It is an adjunct here to a gas-making process of a high degree of heat economy and low operating cost. Its special virtue of yielding rich, uncracked vapors and oils may be utilized, and its solid residue converted to the higher “form-value” gas. Such gas, however, being lower in heat value per cubic foot than the now-used public gas supply-say, 350 B. t. u. as against 570-will have to await public acceptance as of suitable quality. It has
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been shown in some countries to answer well the requirements for fuel purposes. In projects for expansion of the public use of gas fuel, industrial and domestic, the serious problem of distribution costs enters as a factor fully as important as production cost. The “form value” of this kind of fuel is high, but it is counterbalanced in a measure by high delivery costs. The Tully gas-making process-a complete gasification process used in England since the war in a large number of plants-may be cited merely as an example. It is said t o secure, under favorable conditions, 50,000 cu. ft., of 360 B. t. u. gas from a ton of coal, together with 8 to 9 gal. of tara yield of about 20 million B. t. u., or 70 to 72 per cent of the original in the coal. This is a slight improvement in heat economy (3 to 5 per cent) over the two-stage, water-gas processes now in common use, and the operating costs are lower. To illustrate the general principle applied in many “complete gasification” processes, such as the Dellwyk-Fleischer in Germany, and H. L. Doherty’s recently patented process in this country, the Tully process may be outlined as follows: A vertical shaft or retort surmounts a shaft generator or producer wherein the fuel is intermittently blasted with air to raise the heats. The blast gases pass around the superimposed retort in checquer brick chambers where their heat is largely recovered. After an interval of blast, the “make” period starts, steam being blown through the hot charge in the generator and the hot water gas thus made being passed through the raw coal in the retort. The latter is thus carbonized (under low-temperature conditions) by the heat of the gases supplemented by the external heat of the surrounding checquer brick chambers. “Low-temperature’’ condensation products are carried off, with a mixture of blue water gas and coal-distillation gases.
In this country “complete gasification” has not yet obtained a commercial footing, nor, in fact, have any of the numerous tentative low-temperature carbonization processes. Much experimental work along both of these lines is being carried on, however, some of which has been brought to an industrial scale of operation. In this work there is great promise of an improved efficiency in coal carbonization and gasification, and an increase in the aggregate “form value” of the products. Abroad, Bergius has made recent researches worthy of note on distilling coal mixed with oil under high pressures whereby a hydrogenation is accomplished and remarkable yields of the lighter hydrocarbon oils are obtained.
An Efficient Reflux Air Condenser By George T. Dougherty A M ~ R I C ASTEEL N FOUNDR~ CHICAGO, S, ILL.
In the saponification of oils and fats in an alcoholic solution of potassium hydroxide it has been found convenient to use an air condenser made from a condenser tube, with adapter sealed to it, such as is furnished by all apparatus dealers for Liebig condensers. The condenser tube is inserted through the cork stopper of the flask with the adapter in the top. A test tube nearly filled with cold water is placed in the adapter and kept from fitting tightly by extending a wire between the adapter and test tube, nearly to the bottom of the latter. This prevents blocking of the outlet by any alcohol fumes. In making these extractions the flask is placed in a sand bath heated by a Bunsen burner. In case the flask breaks, the alcohol is absorbed in the sand and not ignited. This apparatus is also available for the determination of crude fiber in flour and core compounds, and for other purposes where it is desired to maintain a fairly constant volume of liquid during boiling.
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