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Wheeler and Hague were the first to show that the time element is of great importance in cracking methane to produce liquid products, just as in oil cracking operations. At still higher temperatures, of the order of 1500” to 1600” C., acetylene is formed by cracking natural gas: CHa
CHz
+ HB
+ CHI C - CZHB CZHB e CzHz + 2H2 CZHz e 2C + H? CHz
Seither of these processes appears to be far from the commercial stage, in localities where natural gas is rich, cheap, and abundant. Much work has been done by many experimenters to utilize natural gas by methods other than burning, but only a negligible quantity of the gas is so consumed.
REFINERY GAS The amount of gas produced a t refineries in 1929 was 520 billion cubic feet, according to Egloff and Morrell, of which 270 billion came from cracking stills and 250 billion from straight-run refining stills. This is greater than the amount of manufactured gas in the United States-that is, gas manufactured from coal and oil in gas plants for domestic and
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industrial purposes. This refinery gas is burned mainly as fuel under stills and boilers, although some is sold for outside purposes, and a small quantity is cracked (reformed) to produce a lower heating value gas of greater volume. Most of this gas is scrubbed, or compressed and cooled, to extract the gasoline, and in a few cases liquefied gases, propane, and butane are prepared from it. The first plant (called “vapor recovery plant”) to extract gasoline from the refinery gases, to the author’s knowledge, was built a t the Bayonne refinery of the Tidewater Oil Company, in 1917. Improvements in vapor recovery plants followed in natural gasoline plants (at first compression plants) ; oil absorption plants were then developed which were later equipped with stabilizers. By-products from refinery gases consist of the absorption of the unsaturates in sulfuric acid to make higher alcohols by the Standard Oil Company of New Jersey, and the Empire Refineries Company. I n cracking oil to make highly unsaturated gases for their line of solvents the Carbide & Carbon Chemicals Corporation produces ethyl alcohol from ethylene, which is sufficient for its own process needs. Ethylene is first made and absorbed in a mixture of sulfuric acid and ethyl hydrogen sulfide, and then diluted with water and distilled. Much that has been said in this review on natural gas is applicable to refinery gas. RECEIVED August 9. 1933
Progress in Coal Carbonization, Gas-Making, and By-product Recovery HORACE C. PORTER, 1833 Chestnut St., Philadelphia, Pa.
D
IFFICULTY has been The past twenty-jive years have seen much imof other Ikll-grade solid fuels, encountered in forcing provement in and eficienciesof producthere is no commercial inducethe growth of coal carment for carbonization. Altion and in quality of products; volume of bythough the development of gas bonization merely on the grounds of improving the raw coal, renProduct )*ecOuerY,especially gas, has gained; but and by-product sales has gone ahead in a measure, it has of late dering i t smokeless, or providing carbonization growth as a whole is disappointing because of the competition of natural gas and oil years s l a c k e n e d and may go valuable chemical by-products. This Was m u c h t a l k e d of a Slowly in the future. as fuels, and of synthetic chemicals. Coke for Burning p r o c e s s e d c o a l i n q u a r t e r - c e n t u r y ago, and a domestic fires has gained and, together with bypower plants has not been, nor strong effort was made through government and industrial chanProduct coal gas for Public distribution where can be, p r o m o t e d w i t h o u t natural gas cannot projitably reach, offers the best demonstration of financial adnels, on these grounds, to decrease the burning of coal raw outlook for future growth. Low-temperature capvantage to the operator. Coal gas, especially as a bywith attendant smoke and loss bonization has made no commercial progress in of by-products. There has been product from coke ovens, has the bTnitedStates but in England and Germany is been enjoying increasing sales, accomplished, to be sure, during the last 20 to 25 years a considercoming to the front slowly, assisted by the demand since gas in general is growing in there f o r free-burning fireplace fuel and for oils popularityas afuel. But of late able growth of carbonization with by-product recovery. The other than petroleum. years large expansion of natural gas distribution and a consideruse of nonrecovery or ‘(beehive” able growth of the use of refinery ovens in the United States has fallen to 10 per cent or less of all carbonization and is retained g a j and “bottled” petroleum gases have retarded the rate of merely as a cushion or reserve for handling at lower cost the coal gas growth. By-products, as later noted in detail, now offer little help peak requirements of industry. Beyond, however, the demands of the metallurgical indus- in the expansion of coal carbonization. Our requirements of try for coke and of the gas utilities for by-product coal gas, the coal-tar fractions necessary for the making of dyes, plasit has been difficult to carry carbonization profitably. Fuel tics, and pharmaceuticals are more than met by present home consumers in general, except to some extent the domestic, production; the ammonia market is oversupplied ; motor fuels will not pay a premium price merely for the sake of smokeless- of antiknock quality are obtained as cheaply from other sources ness. Unless therefore the gas and by-products of carboniza- as by benzene blends. This does not mean that coal by-prodtion can be sold for enough to keep the coke price to the level ucts cannot be sold in increasing quantities, but it does
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mean that large financial inducement cannot be depended upon from them to boost carbonization into rapid growth. I n those parts of the country where natural gas cannot profitably enter, coal carbonizing plants can be and are being installed with profit for supplying city gas and domestic coke. This outlet willcontinue to grow, by virtue of the established advantages of these products, but carbonization confined largely to these ends will from now on have a slower growth than it has had during the last 25 years under the favoring influences of growing metallurgical demand, lesser competition from natural gas, and satisfactory return on by-product ammonia. We are concerned here mainly with carbonization, and with gas manufacture by that method but may mention briefly the progress of gasmaking bv other methods. Ur,to about 1910, FIGURE I . MODERV BY-PRODUCT COKEPLANT;BECKER OVENS OF YOUNGSwater gas- and oil gas produc6on had a rapid 1'O\%Y SHEET AND T u n E COtlPANY, SOUTH CHIC.4G0, ILL. growth but since then have remained almost s t a t i o n a r y . Advances have been made in technic, and efficiency has been improved; the use of cheaper Luiness activity when the reserve capacity of the beehives oils has been made possible, and reformed refinery gas has was drawn upon, partly for economic reasons. Total producbecome a successful factor, But these advances hare served tion of coke has not increased during the last 15 years. Coke-oven gas and retort coal gas, publicly distributed, only to lessen the dropping off of this branch of gas manufacture forced by the growth of natural gas and coke oven gas. have risen to the large figure of 205 billion cubic feet in 1931, Some commercial progress has been attained in low-tem- more than treble its amount in 1908. It now constitutes perature carbonization in England and in other countries about half of all nianufactured gas in public distribution. where prices of the competitive petroleum oils are on a higher \BLE I IN THE T;NIpED STATES, INCLrDlevel with respect to coal than they are in America. I n EngING PETROLEUM COEE land hydrogenation of the tars and a demand for open-fire(In thousands of tons) BEEBYGAB PEplace fuel may well be the saving factors for this type of YEAR HIYE PRODUCT RETORTT R O L E L I I TOT%L carbonization. I n America no commercial suwess has as 1896 12,000 100 12,100 yet been attained in spite of 20 years of effort and great ex1900 19,500 1,100 1500 22,100 42,300 1907 35,100 5,500 penditure of capital. A few projects are still under way ex1912 32,870 11,110 2400 46,400 1916 35,460 19,070 2900 300 57,700 perimentally. The best prospect here seems to lie in plants 1920 20,510 30,830 3200 600 55,100 2800 700 59,100 installed at the mines for improving those grades of screenings 1923 17,960 37,530 2800 1500 57,100 1928 4,500 48,300 which have a low market value. Only semicoke and tar 1929 6,470 53,410 2800 1900 64,600 1,130 32,360 2100 2100 37,700 would be shipped, the gas being used in the process. Success 1931 would depend on the demand for the coke. But M hile there has been a large increase in the makine of Statistically, progress is shown in Table I. These figures show impressively the rapid rise of by-product coking since 1909 and the continuous decline of beehive production since 1907, except for the years 1916 and 1929, periods of unusual
FIGURE2.
slowly, if a t all, during the last 15 years. We are carbon& ing now practically the same percentage of our total coal production as we did 30 years ago-namely, 16.0 to 16.5 per cent. There has been no progress in the displacing of raw coal for steam generation with products of carbonization, and such growth as there has been in the use of coke and of coal gas in domestic h e a t i n g is n e a r l y Counterbalanced by a decreased demand in the metallurgical industry arising from improved fuel efficiencies. The future rests on the possibility of a boom in the steel trade, through exports or general industrial expansion, and on building up the demand for domestic coke and coal gas. Domestic coke consumption, it should be noted, rose to the encouraging figure of 10 million tons in 1931, about three times what it was 15 years ago. From a technical standpoint there has been great progress in the coking of coal in ovens and retorts. This may be outlined briefly as follows :
BY-PRODUCT RECOVERY A P P A R ~ T U S , PHIL4DELPHIA COKECOMPANY, PHILADELPHIA, Pi.
MODERN
Gas coolers, scrubbers, and purifiers are e h r , a n
( I ) Increase of output capacity per unit of building the oven higher and longer. ( 2 ) Same as 1, secured by use of silica refractories, permitting higher heats and shorter coking coht, due t o
timep.
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FIGURE 3. PLANT OF WISCONSIN GASAXD ELECTRIC COMPANY, RACINE,WIS., SHOWING U. G. I. VERTICAL CHAMBER OVENS (Equipped with gravity coke discharge, proviaion for steaming of charge, and by-product recovery)
(3) +me as 1, secured by better design of heating flues, giving more uniformity of heats and more even coking. (4) Careful control of ressure inside of the oven, and of leakage through walls and joor jambs, thereby reducing air and inerts in the oven gas and combustion within the oven. (5) Development of oven heating by producer gas (made from coke breeze) and by blast-furnace gas, thus releasing all of the oven gas for outside disposal. (6) Steaming of the hot coke in the oven to make water gas during a small part of the coking period, thereby increasing therm yield in the gas without corresponding decrease in the coke. (7) Admixing of fine coke or dust with the coal charge to the extent of 3 to 8 per cent, thereby improving coke strength and lessening coal cost per ton of coke made. (8).Development of dry quenching of coke, whereby the large item of loss in sensible heat of the coke is much reduced by utilizing a part of it to produce steam. (9) In gas retort practice, the design of vertical chamber ovens with gravity discharge, and of continuous retorts saving labor and other operating costs and facilitating steaming of the charge for gain in therm economy.
LOWTEMPERATURE CARBONIZBTION As has been noted above, no commercial progress has been made in this country in this field; but on account of the great amount of experimentation under way, and the more favorable conditions in other countries, we are justified in examining the progress that has been made abroad and its technical aspects. In England probably more commercial progress has been attained than in any country, but it is admitted by impartial analysts there that, without governmental subsidy on the oils and with present competitive prices of imported petroleum oils, the profit on this kind of carbonization is insufficient to attract large investment of capital. They are encouraged to believe however that conditions will become more favorable. As an indication of this confidence, the government has recently announced a “guaranteed preference” on home-produced gasoline of 4 pence per gallon and the press states that Imperial Chemical Industries, Ltd., will erect a plant costing $12,000,000 for hydrogenation of coal, to be ready in 1935. It is reported (a) that the firm of Low Temperature Carbonisation, Ltd., for one year’s operation ending October 31, 1932, showed a credit balance of 15,138 pounds sterling. This firm uses the Coalite process in modernized Parker retorts.
Total coal coked by the low-temperature method in 1932 in England was 220,000 tons. It is assumed that practically all of this was by the Coalite process, since other plants are still operating only experimentally. The above named profit was made without the aid of the subsidy on motor fuel. It may amount to between 6 and 8 per cent on the necessary invested capital, although no figures are available on the investment requirements. The tar has not so far been hydrogenated to make light fuel, but the yield of 17 gallons per short ton, plus 2 gallons of light oil stripped from the gas, has been redistilled to make fuel oil and high-antiknock motor fuel, the output of which has been contracted for, respectively, by the Admiralty and the Air Ministry. There are three plants of the Parker Coalite retorts in England, with a combined capacity of 322,000 tons of coal per year. Each retort consists of twelve vertical tubes, of a resistant metal alloy, cast in a monobloc, the tubes being 9 feet long and 41/s to Y/, inches in diameter (tapering). They are heated to 600-650’ C., externally, and carbonize the 600pound charge in 4 hours. The coke has had a ready sale as an open-fireplace fuel. The gas (4000 cubic feet per ton, of 750 B. t. u. per cubic foot) may be used to enrich city gas, or compressed into cylinders for use as motor fuel. Other processes of low-temperature carbonization which have been installed on a commercial scale in England (some also in France, Belgium, and Italy) are: (1) The Illingworth, using a stationary charge in vertical retorts 12 feet high, 9.5 feet long, 14 inches wide, and heated externally, in which are iron “conductor” plates to facilitate heat transfer. They discharge downwards. A system of quenching the coke by direct contact with fine wet coal and screening of the mixture leaves coke breeze in the coal charge, preheats the charge slightly, and results in an unusually dense semicoke (0.90 apparent specific gravity). In America the development of this process has been taken over by the Pittsburgh Coal Company. (2) The Salermo, using a group of parallel inclined troughs with paddle stirrers, and making small-sized coke for stokers. Recharging of a part of the coke is now practiced. Plants have been successfully operated in the Saar district and in conjunction with a large power station at Langerbrugge, Belgium. (3) The Salerni rotating cylindrical retort for which a commercial contract has been let. By a system of blending it produces a semicoke of high density.
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(4) The modified Bussey producers, at Glenboig, Scotland, again Put into operation on a Of 240 tons Per making gas for brick kilns. (5) The L & N rotating cylindrical retorts, using internal heating by hot gases and briquetting the roduct. One 100-ton plant operated intermittently at mines in leicester.
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oil. Lately these have been much reduced. Ammonia recovery, in fact, now usually brings no profit, owing to the cornpetition Of ‘(air nitrogen” and an overproduction thereof. Recent development by The Koppers Company of a process of recovery of sulfur from the oven gas (the Thylox process) and use of the sulfur to make sulfur6 acid for fixing t h e ammonia from the oven plant, promises to reduce the cost of sulfate recovery and again make it profitable. As for light oils, the competition from low-priced gasoline has reduced the profit obtainable as motor fuel, and the markets for them in organic chemical manufacture are oversupplied. Phenol and cresols, for use in Bakelite and other such plastics, are encountering competition from other and newer resins. The growth of creosoting of timber is one of the promising outlooks for tar products. Road surfacing still offers a good outlet, and pitch coke is being made in increasing quantities by better methods. That all of these outlets, however, in the aggregate fall short of providing a good return to the industry on this by-product is well shown by the fact that 40 to 50 per cent of the tar produced is burned as fuel. Phenol recovery, and that of naphthalene, by direct washing of the oven gas are developments of recent years. Purification of the oven gas from hydrogen sulfide by wet-washing
A recent American invention (S), not yet put into practice, proposes a vertical continuous retort, internally heated by hot gas circulation, with central core of coke extending down from the top. The gases are drawn out by suction from an annular space above the coal, traveling inward in the retort away from the heat. Arrangements for a pilot plant, of 30 tons daily capacity, are said to have been made with commercial interests. Another process that is undergoing semi-commercial scale development in the United States is the Wisner, which uses a thorough preheating of the coal, short of the point of softening or decomposition, and then, in a second stage, tumbles the coal in a cylindrical retort a t higher temperatures until it has formed itself into “balls.” A plant to try out this process on the scale of 100 tons per day is now being built near Pittsburgh by the Pittsburgh Coal Company. For the last 8 or 10 years the British Fuel Research Station has carried on experiments with low- and medium-temperature carbonization in vertical retorts, 21 feet high, continuously or semi-continuously operated. Up to 1930 these retorts were of cast iron, but recently fie-brick retorts have been experimented with a t temperatures of 600650” C. on the inner wall in the upper zone of the setting, and about 1150” C. in the upper flues. The main part of the carbonizing occurs in this upper zone. Steaming, up to about 10 per cent of the coal, is used during certain periods. This is really medium-temperature carbonization and it is reported (1) that the fire-brick retorts have proved very satisfactory; they show little if any wear or distortion after a year of use; give adequate coking capacities, the control of heats being both by rate of throughput and rate of fuel-gas combustion; make a coke of 4 to 10 per cent volatile matter and of a Qw O K W suitable combustibility rate for open-fireplace use (although of low density); give a high therm yield of gas (40 to 60 therms per ton DIRECT-TARRECOVERYEQUIPMENT from high-grade coking coal, depending on the FIGURE4. DIAGR.4M OFONB.4RRETT COKE-OVEN B.ATTERY rate of throughput), and 14 to 20 gallons of a. Distilling main with rotating cylindrical tar sprayer b . Preheater and heavy-oil condenser etc. tar. The caDacitv mav range from 6 to 9 tons per retort per day, depending on the nature of the coal. Plant cost, up to the condensing equipment, has methods (using generally sodium carbonate solutions) has been 1500 pounds sterling on a setting of two retorts (about been put on a successful commercial basis. $450 per ton-day) and could be reduced on larger settings. The coke-oven tar still, whereby the sensible heat of the oven gas is utilized to distill and fractionate the tar, sprayed HYDROGENATION OF TAR back into the hot mains, is a recent invention (Figure 4). The British Research Station reports that small-scale exPOWER-PLBNT PRETREBTMENT O F COAL periments have shown a yield by hydrogenation cracking of tar of 13 gallons of refined motor fuel and 6 gallons of Diesel This has been tried out on a commercial scale a t a consideroil per ton of coal, using molybdic acid as catalyst, suspended able number of power stations in Germany, France, and Belon aluminum oxide or charcoal. The motor fuel has a high gium, and a t one in England (the Dunstan station a t Xewoctane (antiknock) number (85 to 88) but is somewhat defi- castle-on-Tyne). All these have had a measure of success cient in low-boiling constituents. The cost for hydrogen is when a favorable market was at hand for the oils produced. claimed to be 1.8 pence and for catalyst renewal 0.5 pence They afford economies in boiler firing by virtue of sensible heat per gallon of motor spirit. in the fuel as fired, greatly reduced moisture content of the Tars obtained by carbonization a t inner-wall temperatures waste combustion gases, and increase of capacity in the boilunder 800” C. appear to be suited for good yields by hydro- ers. A drawback, however, is the difficulty of running the genation, but above that the yields are less. retorts on a good load factor when directly connected to boilers. *
“
“
V
PROQRESS IN BY-PRODUCT RECOVERY During the early days of rapid growth of by-product coking, important revenues were obtained from ammonia and light
CARBONIZATION RESEARCH
A great deal has been accomplished of late leading to a better understanding of the mechanism of carbonization and the
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formation of by-products. The correlating more effectually of small-scale tests with industrial practice has been advanced by giving a definite interpretation and usage to the term “carbonizing temperature”-namely, the temperature immediately at the surface of the carbonizing mass next to the hot wall of its container. The question of what constituents give the coking property, and how they do it, is by no means settled. It seems probable, in the author’s opinion (based on experiment), that by reason of the fluid quality of many good
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coking coals, shown by their extrusion possibilities through very small orifices, a large proportion of a12 the organic constituents of coal softens more or less by heat. LITERATURE CITED (1) Rept. Fuel Research Board (Gr. Brit.) for year ended March 31, 1933, H.M.Stationery Office, London. (2) Sinatt, F. S., private communication, 1933. (3) Warner, A. W., U. S. Patents pending. RECEIVED September 8, 1933
Progress in Low-Rank Coals IRVIKLAVINE,TJniversity of North Dakota, Grand Forks, N. Dak. The importance of the low-rank coal reserres of this country becomes clearly evident when a comparison is made of the distribution and amount of coal in the fields of the LTnited States with the output of these mines. Such a study shows that, although the bulk of the coal in this country is low rank, the greatest output has been coming from the high-rank deposits. This discrepancy cannot CORtinue forever. The low-rank coals are characterized by a high moisture content, slacking upon exposure to the atmosphere, disintegration in the fire, and noncoking quality. The first attempt at eliminating some of these nondesirable qualities was the briquetting of these coals by the German process. It was soon found that the American fuels are not adaptable to this method, but that good briquets could be made from the carbonized residue obtained f r o m these coals.
T
HE low-rank coals of this country represent a vast tonnage of fuel of commercial value. For many
years these fuels were given only little attention, but their economic importance from a national point of view is being discerned. The term “low-rank coal” will be applied to those coals that are lowest in the U. S. Geological Survey classification-namely, lignite and sub-bituminous coal (16). Lignite can be considered as the first stage in the transformation of peat into coal. I n color lignite is brown or, in the better qualities, often deep black. The black variety upon being dried and pulverized turns dark brown. The luster of lignite varies from dull to brilliant, depending on the composition and structure. A woody specimen of freshly mined lignite shows a dark dull luster. Some specimens of lignite upon being mined expose pitchy, jetlike, bright layers and inclusions which upon close examination are found to be fragments of more or less rotted wood. These pieces may range in size from small slivers to chunks of wood or parts of tree trunks. I n other specimens the woody structure may be entirely obliterated. Lignite burns with both flame and smoke and often gives off a disagreeable odor in the process. Furthermore, in spite of its relatively high volatile content, lignite lacks the properties of fusing and coking in the fire that bituminous coals possess. I n consequence of this tendency to slack in the fire, special grate construction or firing methods are necessary to prevent excessive loss of unburned fuel in the ash pit.
The low-runk coals are now burned in modern power plants with eficiencies that approach that obtained with high-rank f u e l . These fuels can be used successfully in the manufacture of producer gas. Microstructure and extraction studies haae provided valuable information as to the physical and chemical make-up of the low-rank fuels. The moisture in low-rank coals is held colloidally. Studies with lignite have indicated many of the properties of the moisture in these coals. They do not possess a n abnormally high tendency f o r self-heating owing, primarily, to the large proportion of water naturally contained which requires a large expenditure of energy to bring about its evaporation. Recent studies on the coking o j these coals have shown definite possibilities in this direction. Dehydration and the production of a n active carbon are other phases that offer possibilities. Lignite is a noncoking and noncaking coal. Its destructive distillation leaves a noncoherent char in contradistinction to the solid coherent coke obtained with certain bituminous coals. Jeffrey (34) has reported, however, that a coke can be obtained from certain lignites, but unfortunately the method for accomplishing this was not given. The term “sub-bituminous coal” has been adopted by the U. S. Geological Survey for the “black lignite” coals between bituminous coal and brown woody lignite (16). A subbituminous coal can generally be distinguished from a lignite by its dense black color and its lack of a distinctly woody texture and structure. I n common with lignite, this coal has a high moisture content, slacks freely on weathering, and is noncoking. These latter characteristics have heaped a national disgrace upon a natural resource which some day will play an important role in our economic welfare.
COALRESERVESIN THE UNITEDSTATES The United States is fortunately situated with respect t o abundant supplies of coal. Twenty-eight of the forty-eight states, Blaska, and the Philippine Islands have a bountiful supply of coal; eight states possess only a small amount, and twelve states and the Hawaiian Islands are absolutely void of coal. The total United States reserve represents nearly 52 per cent of the world’s coal reserve (16). Table I gives the estimated tonnage of coal in the United States and the reserves a t the end of 1930 according to data
