INDUSTRIAL AND ENGINEERING CHEMISTRY
Januarv. 1927
39
Low-Temperature Carbonization' The Situation in Great Britain By David Brownlie 46, GRANGE ROAD,EALING, LONDON, W 5, ENGLAND
OW-temperature carbonization in the broadest sense of the term is today a matter of such magnitude and complexity that any adequate consideration of it would require a volume of encyclopedic proportion. It is all the more necessary, therefore, to have a number of the main issues outlined clearly, and in the present contribution an attempt will be made to do this as regards Great Britain, first, from the historical point of view, and second in the way of a brief description of some of the newer processes that show signs of coming to the front. The term "low-temperature carbonization" is generally used in a vague manner. Originally it was intended to apply to the production of smokeless, free-burning, solid fuel containing 9 to 12 per cent volatile matter by carbonizing bituminous coal a t 900' to 1100' F. (480' to 595' C.), instead of about 2000' F. (1095' C.) as in the high-temperature carbonization industries for the production of household gas using soft, non-free-burning coke or very hard metallurgical coke. The tars are very different in quantity and quality. In fact, it was regarded a t one time-which does not hold good today-that low-temperature tar, about twice the yield per ton of coal tar, was essentially paraffinoid in character, the high-temperature tar being benzenoid and containing a much greater percentage of pitch. At present low-temperature carbonization means the subjection of coal or other carbonaceous material to heat treatment in a manner different from the existing high-temperature carbonization processes of the gas works and the coke oven, so as to extract the maximum amount of valuable by-products and to deliver either solid, residual, smokeless fuel, gas, or liquid fuel in a condition more suitable for general and efficient utilization than raw coal or high-temperature coke. This includes not only "straight" carbonization of coal, brown coal, lignite, shale, etc., but all kinds of other processes, such as briquetting before carbonization, total gasification with recovery of low-temperature oils, hydrogenation, and the production of synthetic fuels by way of carbonization, total gasification, and conversion of part of the gas to liquid fuels by catalytic methods. The whole subject of low-temperature carbonization is probably more important to Great Britain than to any other country in the world. Obviously, the burning of raw coal, with consumption of all the valuable by-products that can be obtained from it as mere fuel, is doomed. We in Great Britain have no petroleum and are almost unique in using the open household fire, so that black smoke is costing us a t least i€40,000,000 per annum in damage. Further, we have the great natural advantages of large deposits of good grade bituminous coal and very low freight rates. Probably the average distance from the coal fields to industrial centers does not exceed 50 to 75 miles, London, of course, being an exception. The enormous growth of water power throughout the world, especially on the continent of Europe, where during the past three or four years it has been even more rapid than in the United States also makes it impossible for the British mining industries to go on selling abroad every year about 60 million tons of raw coal. We shall therefore be compelled to adopt scientific methods of treating the coal on
L
Received September 11. 1926.
the spot. The writer has advocated on a number of occasions* that the British colliery industry tackle the whole subject of low-temperature carbonization on thoroughly scientific and cooperative lines and get a limited number of the more promising processes going on a commercial scale in order to solve the problem and convert the industry into a paying proposition again. History of Low-Temperature Carbonization There are a number of popular fallacies in low-temperature carbonization which apparently nothing will ever kill. One of these is that Thomas Parker "invented" low-temperature carbonization in 1906 when he heated bituminous coal in intermittent cast-iron retorts to about 800" to 1000" F. (428' to 540°C.)so as to produce hard, smokeless "Coalite" for the English open fire, the iron retort being externally heated and so arranged that the swelling plastic charge was subjected to internal compression. As a matter of fact, Parker commenced his work much earlier, his first British patent being in 1890, and it is, of course, nonsense to assume that he first used low-temperature carbonization methods. Thus the whole gas industry of Great Britain (and somewhat the same conditions applied to every other country) operated for the first forty years or so almost exactly on these lines. Up to about 1835 or 1840 the retorts used, nearly always horizontal, were of cast iron and the temperature did not exceed 1000-1200" F. (540-650' C.)-that is, red heat-simply because the metal would not stand it. Certainly somewhere about the year 1840 they got up to 1400" F. (760" C.), but the wear and tear and cost of upkeep on the retorts was ruinous. Millions of tons of coal were therefore carbonized in Great Britain under purely low-temperature carbonization conditions for about thirty or forty years, giving a yield of 6000 to 7000 cubic feet of rich illuminating gas per ton, and a residual high-grade coke, which was really low-temperature fuel, smokeless and free-burning although very soft and friable. What Thomas Parker originated was the simple carbonizationof bituminous coal a t low temperatures for the specific purpose of producing a hard, free-burning, smokeless fuel for household purposes, which could be handled without dropping to pieces. He intended primarily to cure black smoke, and had it not been for the English open fire his work would not have been started a t al1,while apparentiy he was quite unawareof the facts in connection with the early history of the gas industry. Long before the time of Thomas Parker coal was carbonized a t low temperatures, not to produce a solid fuel, but for the specific purpose of getting the maximum yield of oils without cracking. Most of the earliest investigators, particularly James Young in Great Britain, the pioneer of the shale carbonization industry, realized that as soon as the temperature of carbonization was raised in the retorts cracking took place, with a lower yield of inferior oils. Later many investigators attempted to get the maximum yield of oils by low-temperature carbonization, not only of shale and torbarnite, but of coal as well. One of the most interesting early pioneers in this field, about whom little is known today, was William Mattieu Williams, practically the founder of the principle of car-
* Trans. Inst. Mining Eng. (London), 71, 181 (1926).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
40
bonizing coal, shale, and other materials in shallow trays or thin layers. His British patents were taken out in 1861, 1862, and 1865, and during this period he specifically and deliberately carried out the low-temperature carbonization of shale and coal so as to improve the yield of oils and prevent cracking. The temperature was certainly not much more than 1100' F. (595' C.), and he states in his patents that he has discovered that gaseous products from the carbonization of coal and shale are due to cracking and decomposition of the solid and liquid products on the hot retort sides, and that if the temperature is properly controlled and kept under lowtemperature conditions, the yield of oils is much increased and that of the gas reduced. He used a series of shallow trays placed in an externally heated firebrick setting, and in
Vol. 19, No. 1
however, has fixed in it transversely and diagonally through the iron walls a t regular intervals in the height a series of cast-iron pipes, generally four, of relatively wide diameter, passing through the charge inside, which is thereby broken up in the passage downwards from a supply hopper a t the top. These pipes are open at each end and the arrangement is such that the flames and hot gases from the burners a t the bottom of the setting pass up and around the retort as well as through the transverse pipes so as to increase the rate of heat transmission. The heating is also progressive, with a maximum temperature at the bottom not exceeding 1200' F. (650" C.). Another feature of the Crozier retort is that the gases and vapors evolved are taken away separately a t four different points in the height of the retort. This is accomplished by means of a series of four small, triangular-shaped, cast-iron spouts or receivers pointing downwards in the charge, one being placed under each of the four transverse heating pipes connected through the side of the retort by small-bore pipes to the condensers operated under slight suction. A special point in connection with this process is the design of the condensing plant, which carries out simultaneously a considerable degree of fractionation. Four transverse, horizontal, closed iron troughs are arranged with a series of vertical air-cooled pipes in such a manner that the condensed light oils are discharged from the first section and the heavier oils pass on to the next, a second fraction being then withdrawn and so on, instead of the more usual arrangement of one large mixed fraction of crude oil. The retort is the invention of R. H. Crozier and is cgntrolled by the Mineral Oils Extraction, Ltd., of London, the first experimental installation having been erected a t Rangoon in 1922 for treating Burmese shale. In 1924 a demonstration retort with a normal throughput of 10 tons per 24 hours was erected and operated a t the Wembley Exhibition, London. This is still in use and in August, 1926, of the "Turfa" deposits from Brazil were treated, a peculiar variety of shale found a t Marahu, about 100 miles south of Bahia, which gives 50 gallons of oil to the ton. Dvorkovitz Process
-
F i l u r e I-Main
Desien
Filure 2-Modified
k. P. Hird Process
-
Desian
1868 he erected a complete battery of retorts on these lines at the Leeswood Oil Works, near Flint in North Wales.
Just as this plant was ready to start petroleum was discovered in America and the whole early shale carbonization industry in Wales collapsed, since the price of petroleum as placed on the British market was about one-fifth that of the oil produced from shale. Consequently, the works went to smash in 1868 and apparently the battery of retorts was never put into operation.
Low-Temperature Processes The following is the position today with regard to a number of British low-temperature processes, arranged in alphabetical order. This list is not intended to be complete, nor does inclusion in it necessarily mean that the particular process may be expected to be more important than others not mentioned. The Crozier Process The Crozier process is intended primarily for shale and non-swelling coals, blended or otherwise, and consists in the use of a vertical, continuous, externally heated, cast-iron retort, flat-sided and semicircular in plan, contained within a gas-fired brick setting in the ordinary way. The retort,
This is the invention of Paul Dvorkovitz, a Russian chemical engineer and authority on petroleum and gas oils for enriching gas, resident for many years in London, and is controlled by Motor Fuel Proprietory, Ltd., London. The modern Dvorkovitz low-temperature carbonization process originated in 1923, although the work on carbonization in general dates back to about 1893. A commercial plant is now being erected in Belgium and another is to be set up a t Slough near London. The retort used, for coal or other material, is of the vertical, intermittent, tapering, cast-iron type of circular cross section and relatively small diameter, which is both internally and externally heated to some temperature dependent on the conditions, but between the range of 932" and 536" F. (500' and 280" C.). The main heating is internal, by means of a stream of inert gas, such as water gas, passing continuously down through the charge from the top, which is raised to the exact temperature required in a gas-fired ''superheating'' section, the hot waste products of combustion then passed round the outside of the retort, entering also at the top. The gases and vapors evolved are withdrawn at the bottom. The principles of operation are, first, a very accurate control of temperature in the retort dependent largely on the inert gas which is easily adjusted as required, and second, that cracking is reduced t o a minimum because the gases and vapors under these conditions must always pass from a hotter to a colder zone. In a later patent (1924) there is added to this standard setting in the upper part of the retort only an
January, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
internal agitator device, intermittently operated, such as a screw or vertical rod with projections to prevent the charge from sticking a t this point. Fusion Retort Process This well-known British process for the low-temperature carbonization of coal, shale, brown coal, and other material is the invention of T. W. Stainer Hutchins, managing director of the Electro Bleach and By-products Co., Ltd., of Middlewich , Cheshire. The retort is of the long, horizontal, cylindrical, rotary type, externally heated, operating on the mechanically continuous principle, the crushed raw coal or other material being fed in a t one end and the residual product discharged a t the other. The externally heated rotary retort has a number of advantages, including efficient rate of heat transmission and the recovery of a very rich gas not diluted with any low-grade heating medium. The chief disadvantage is that with bituminous material a part of the charge sticks to the hot retort wall and is baked on, forming a scurf or layer which has to be removed a t intervals. The characteristic feature of the fusion process is the use inside the rotary retort of a heavy, loose, internal breaker made of boiler plate provided with a series of projecting arms or blades, 4 to 8 in number, arranged longitudinally. This breaker is generally made in several sections and placed end to end resting on the charge for the full length of the retort, and as the latter revolves the breakers fall over continuously, striking the material a series of glancing blows in such a manner that nothing can stick to the inside of the retort, while a t the same time stirring up and agitating the charge with the prevention of "balling" by breaking up any lumps as soon as they form. The temperature of carbonization used is very low, commencing by suitable adjustment on the externally fired setting on the progressive principle a t about 350" F. (175" C.) and rising to 850" F. (455" C.). The duration of the heating is 2 hours. It is claimed that in this way cracking is reduced to such an extent that 1 ton3 of 25 to 35 per cent bituminous coal will give 7 to 10 gallons4 of light oils (4to 5 gallons by fractionation from the tar and 3 to 5 gallons stripped from the gas) with from 10 to 20 gallons of oils less motor spirit, while the gas yield is only 2000 to 2500 cubic feet (700 B. t. u.). Practically no ammonia is produced because of the low temperature, while the residual fuel in practically a pulverized condition is 70 to 80 per cent of the raw coal. The fusion retort principle of the loose internal breaker inside a horizontal rotary cylinder has been applied to a number of operations in addition to carbonization, particularly the mechanical slaking of lime and the drying of extremely difficult material such as the wet lime residues in the manufacture of caustic soda from sodium carbonate. The original large-scale test fusion retort is a t Middlewich, while a number of installations are at work, including one in Lancashire for the carbonization of sawdust, as well as a number of drying units. I n Esthonia there is a plant for the low-temperature carbonization of the difficult Esthonian shale (Kukkersite), which includes two fusion retorts, each with a capacity of 20 tons per 24 hours, and a complete crushing, drying, by-product recovery, and fractionating plant. A plant of four fusion retorts for coal and colliery refuse is under construction near Nottingham and another installation a t a colliery near Edinburgh. Hird Process A new British low-temperature carbonization process for coal, shale, and other material, is that of H. P. Hird, of 1 Unless otherwise specified reference is t o long ton (2240 pounds) throughout this paper. 4 British Imperial gallons are meant throughout this paper.
41
Bradford, Yorkshire. An experimental retort has been operated for some time a t a colliery near Wakefield, and it is understood plans are now being prepared for a large installation. The general principle is the use of a vertical, intermittent, externally heated, cast-iron retort of relatively small cross section containing inside a slow-moving agitator, generally a shaft with small, heavy blades or projections. This stirs up the charge and a t the same time gives a crushing and grinding effect, thereby providing channels and passages, mainly a t 6he center of the charge, for the rapid escape of the gases and volatile products evolved, while a t the same time the material is always in a relatively thin layer. Internal heating by means of inert gases or steam can also be used if necessary. The main claim is that the rate of heat transmission to the charge is so increased that low-temperature carbonization can be carried out with absence of cracking of the oils while higher temperature carbonization conditions, such as 1202"F. (650" C.), can be obtained in the combustion chamber so as to increase the throughput. Figure 1 shows one of the designs of the cast-iron retort, R, externally heated with stout central agitator shaft, A , having cone-shaped agitator projections, A 2 , and driven by gearing continuous for intermittent a t the top. The cross section of the shaft is for the most part square, but a t the bottom, A', it is round passing through a bush a t the bottom of the retort. The gases and vapors evolved pass out at the top by the pipe, R2. Figure 2 is an alternative design, a slowly revolving coneshaped agitator, A", tapered to a point about the middle of the retort. The average yield per ton from normal bituminous coal, 25 to 35 per cent volatile, is as follows: Gas Motor spirit Low-temperature oils Sulfate of ammonia Smokeless fuel
5600 cubic feet at 720 B. t . u. 3 . 0 gallons 1 7 . 0 gallons 13.5 pounds 1568 pounds (70 per cent)
Illingworth Processes
The various Illingworth processes are the invention of S. Roy Illingworth, for a long time head of the chemistry department of the East Glamorgan School of Mines, Treforest, South Wales, and now associated with the Illingworth Carbonisation Co., Ltd., of Manchester. A considerable amount of secrecy appears to be attached to the work originally carried out a t Treforest followed by a large-scale experimental plant a t the Pontypridd Gas Works, Pontypridd, South Wales, and the principles involved are not easy to explain in a short space. The main idea, however, of the Illingworth processes, equally applicable to low- and high-temperature carbonization, in connection with which many patents have been taken out, seems to be that the ordinary coking theories, largely originated by S. W. Parr, are not correct. It will be remembered that according to these theories the bituminous constituent of the coal melts and permeates the mass so as to cement the whole into a dense, coherent coke, the melting point of the many different coking compounds covering a considerable range to allow time for this action to take place. A strongly swelling and therefore non-coking coal has excess of this cementing material and gives an unduly porous product, whereas the more usual non-coking coal has a deficiency so that the residue is more like a soft powder than a coke. Illingworth, however, states that a given bituminous coal swells because certain of the volatile constituents only cause this trouble and if they are eliminated then as a rule the pretreated coal can be carbonized directly without difficulty to give a dense, hard, smokeless fuel. Accordingly, in most cases he carries out the carbonization in two stages. The first consists in heating the swelling coal out of contact
42
INDUSTRIAL A N D ENGINEERING CHEMISTRY
with air to a temperature not exceeding 932' F. (500' C,), but generally not over 752' F. (400" C.), in such a manner that what Illingworth terms the "resinic content" is not less than 5 per cent and preferably 8 per cent or over. By this he means the amount soluble in boiling chloroform, phenol, or pyridine, calculating on the ash and moisture-free basis, while the freedom from air is to prevent the residual cementing material from being decomposed. The pretreated non-swelling coal is now heated, forming the second stage to 1112' F. (600" C.), giving a hard, smokeless, free-burning fuel without pressure, briquetting, or any other means with recovery of lowtemperature tars. Alternatively, metallurgical coke, claimed to be of an improved quality, is obtained by heating up to 1652" F. (900" C.), while if the resinic content is not sufficient blending can be carried out. A few coals are of the one-stage variety, which Illingworth explains by the fact they do not happen to have the bituminous materials that cause swelling, For this work almost any kind of retort can be used, but a number of Illingworth's patents relate to special designs, especially of the vertical, continuous, externally heated type. Included in the work are other principles, chiefly the sudden mixing of preheated coals a t 752' F. (400' C.) with wet coal from the washers so as to give direct for the low- or high-temperature carbonization retorts a product with not over 3 per cent moisture and 176' F. (80" C.) in temperature, as well as being non-swelling. One of the main claims is that small bituminous Welsh coal by two-stage heating in this way can be converted directly into large pieces of hard, smokeless fuel, giving from 1 ton, 25 to 35 per cent volatile coal, 5500 cubic feet of gas, 18 gallons low-temperature oils, 2.5 gallons of motor spirit scrubbed from the gas, and smokeless fuel equal to 70 per cent on the weight of the coal. Maclaurin Process
This is one of the most interesting low-temperature carbonization processes in Great Britain, being the invention of Robert Maclaurin, whose first patent was taken out in 1913. A plant of 100 tons per day capacity is now being installed a t the Dalmarnock Gas Works of the Glasgow Corporation, other plants having being a t Grangemouth, Striling, an earlier small retort a t Glasgow, and the original installation a t a colliery in Ayrshire. It consists essentially in the use of a vertical retort of great height, approximately 45 feet, and comparatively small cross-sectional area, something like a small blast furnace in appearance, operating continuously with bituminous coal direct, the residual solid fuel being withdrawn every hour. A blast of air and steam, the latter being 275 to 550 pounds per ton of coal, is blown in a t the bottom through tuyeres to gasify part of the charge and give internal heating, the mixed gases and vapors being withdrawn a t the top. Theretort holds about 30 tons of material. The chief distinguishing feature of the Maclaurin process is the extremely low rate of heating the charge, approximately 30 hours. In this way nearly all the volatile matter is driven off under low-temperature carbonization conditions, so that the coal does not expand when in the plastic condition, giving direct a hard and dense fuel which is free burning because of its structure, although subjected subsequently to high-temperature carbonization at the bottom of the setting. Thus, 1s hours elapse before the charge reaches 752" F. (400' C.) one-third of -the way down the retort and the hottest point, opposite the tuyeres, about 1472' F. (800" C.), is not attained for about 24 hours, the remaining 5 hours being steaming and cooling. A very large amount of coal has been carbonized in this plant. The yield per ton from average bituminous coal 25 to 35 per cent volatile for the production of hard, black, smokeless fuel for household purposes is as follows:
Gas (230 t o 250 B. t. u. per cubic foot) Light oils Dry low-temperature tar Sulfate of ammonia Hard smokeless fuel: Large pieces Smithy char and breeze
Vol. 19, No. 1 25,000 t o 35,000 cubic feet Not recovered 14 to 20 gallons 20 to 25 Ibs.
896 Ibs 40 0 per cent) 336 Ibs: f15:O per cent)
The process can easily be arranged to give a silvery gray coke by altering the air and steam blast, but the ordinary, black, household smokeless fuel contains about 4 per cent volatile matter and is quite free burning. It is all sold without diiliculty in Glasgow and the gas is used to heat the hightemperature carbonization retorts of the gas works. This plant was started last year and so far has carbonized about 13,000 tons of coal, but is a t the time of writing closed down because no coal is available due to the lock-out in the British mines that has been in force since May. Owing to the courtesy of Mr. Maclaurin and Mr. Mitchley of Blair Campbell and McLean, Ltd. of Glasgow, it is possible to give the results of detailed test runs of different length and various coals carried out in the plant in October and November, 1925: October November
Coal used: (a) Total tons ( b ) Tons per retort per 24 hours Pounds steam used per ton Gas yield : (a) Cubic feet per hour ( b Cubic feet per ton of coal (c] B.t. u. per cubic foot ( d ) Therms per ton Oils (dry) gallons per ton Li uor: ?a) Gallons per ton ( b ) Sulfate of ammonia, pounds per ton Smokeless fuel (5.5 per cent moisture): ( a ) Per cent of original raw coal ( b ) Large, pounds per ton (6) Medium and small, pounds per ton ( d ) Analysis (dry) of average smokeless fuel: Fixed carbon Volatile matter Ash
174 14.56 699
484 17.29 690
82,666 33,724 240 81.6 17.40
80,074 27,794 241 67.0 14.58
60.9 21.18
54.2 25.00
46.50 646 395
58.85 791 527
Per cent 88.50 4.70 6.80
Marshall-Easton Process
This has been developed primarily by F. W. Marshall, of London, previously associated with the Tozer and Nielsen processes. The process consists in the use of a mechanically continuous, vertical, internally heated, cast-iron retort having inside for the full height two screws, one intermeshing with the other, the invention of R. W. Easton. I n this way it is claimed that a viscous swelling coal does not jam a screw conveyer retort since one screw automatically cleans out the other even in the case of sticky and viscous material much more difficult than coal. The general principle is not novel, having been used in Great Britain in 1884, while two intermeshing paddle conveyers on the same lines formed part of the primary retorts of the Smith Carbocoal process, but it is applied by Esston according to a new modification, with both screws inside the charge. The crushed raw coal enters at the top of the setting and is conveyed continuously down through the retort externally heated within a firebrick setting on the ordinary lines from an adjoining producer gas plant, the residual low-temperature fuel being discharged from the bottom. In practice, the two screws, driven by gearing from the top of the retort cut the charge up into two segmental rings of material 6 inches deep by 4.5 inches thick, the practice effect being that of continuous carbonization of coal in layers 4.5 inches deep. The speed of the screws is 6 to 10 revolutions per minute, the heating period being about 3 hours under ordinary low-temperature conditions1000" F. (540' C.) in the combustion chambers and about 800" F. (425' C.) actually in the charge. As usual, also, the residual smokeless fuel has 7 to 12 per cent volatile matter with a yield per ton from average bituminous coal 5000 cubic feet of rich gas, 800 B. t. u. per cubic foot, 3 gallons motor
spirit,, 1: to 20 gillinis oils, 15 pounds sulfate of nitd 163'1 p ~ i i d (75 s per cent) of smokeless fuel.
ammonia,
A n cxinvintcntal retort has been in operation for some coitsiiierahle time in London, but this has now been disnutnt,lfdand a new Marshall retort is at present being erected cout:iining many modifications of the above design, psrticularb or which are not yet available for publication.
Midland Coal Products Process
This very interesting method is controlled by The Midland Coal Products, Lid., of Colwick Estates, Netherfield, Nottingham, a company formed in 1918. (Figure 3 ) The method consists essentially in hriqnetting small non-coking coal, if necessary blended with a certain amount of coking mal, in the ordinary way with 6 to 10 per cent pitch and then carbonizing the briquets Tujth internal heating obtained by gasification of part of the charge. The retorts are of the vertical continuous type of firebrick, inca.sed in sheet iron, the briquets heiug fed in at the top and withdra~mat the bottom, taking 5 hours to travel through. The present plant at Netheriield, started up in 1923, consists of four vertical retorts with a completo by-product recovery plant, gas engines of 3000 horsepower for the generation of electricity, and an installation for manufacturing bituminous paint using part of the tar. The throughput of each of the four retorts is approximately 1 ton of briquets-that is, 100 tons per 24 hours for the plant-and a blast of steam and air is blown in through tuyeres at the hottom of each retort amounting to about 25,000 cubic feet of air at 6'' W. G. and 200 pounds of steam at 20 pounds pressure per hour for each retort, as well as about 50 pounds of steam per hour for cooling the carbonized briquets. The mixed ynses and vapors are dis-
The gas is essentially a rich prodncw gas with very low carbon dioxide (1.5 per cent) having also 28.0 per cent carbon monoxide, 16.5 per cent hydrogen, and 4.5 per rciit methane and other hydrocarbon gases. It is all uscd i i i National vertical gas engines-two 750-horsepowr. U-cxlinder, and one 1500-horsepower, 12-cyliuder, tlie latter lu%vii!gonly just been installed. These engines drive electrical ge:icratms and supply current to the factories on the Culwiok Estates now being developed as an industrial center, and the whole plant runs very well. Nielsen or "L. N." Process
The low-temperature process, associated more prominently with the namo of Harald Nielsen, a Danish engineer long resident in Great Britain, is handled by the Sensible Heat Distillation, Ltd., of London, of which company Bryan Laing is managing director and Harald Nielsen, engineer and technical consultant. The basic principle is the use of the sensible heat of producer gas as given off from the generators at ahont 1022" to 1202' F. (5%' to 650' C.) for the low-temperature carbonization of bituminous coal. This itself is not novel, but in the Nielsen process a long, rotary, slightly inclined, cylindrical retort is used operated on the mechanically continuous principle and internally heated by passing through i t the hot producer gas in the reverse direction to the travel of the charge, tlie mixed gases and vapors being dischargedfrom the other end at about 392482' F. (200-250' C.), while the dorat,ion of tho heating is about 2.5 hours. With 3 normal bituminous coal at ?5 to 35 per cent volatile matter, the usual yields are ohtaineti, ineluding 18 gallons of low-temperature oils aud 70 per cent by weight of the raw coal in the form of smokeless fuel with 9 the retort at about fV2' to 13 per cent volatile F. (200° C.), whik! the matter. The process maximum temperature originated in 1918, and at the tuyeres is say very many p a t e n t s 21920 F. (12000 C.) athave been taken out in taioed after a h o u t 5 conjunction with i t rehours' travel as indilating to various modicsted. Many thousands fications in principle, of tons of coal have been such as blending and p u t through this indelivering the charge stallation, chiefly small partially carbonized in 0.5-incli ICirhy non3 plastic condition for coking slack (Derbydirect briquetting, as shire a n d S o t t i n g well as numerous dehamshire coal), and sirns of rotaryretort. the average yield calThcre is a complete cuhted as per ton of Nielsen experimental coal w i t h 8 per cent carbonization and byp i t c h b r i q u e t s is as product recovery plant follilws: FUure 3-MldIand Coal PTOdUcfs PIanr at Netherfield, Nofttngham situated at Barnsley, in . .- Ymkshire - -........ hnVina --Gas (190 to 200 B. t. U. per cuhic root) 68.T,O0 cubic ieei 3 capacity of 10 tons per 24 hours with 3 retort 48 feet 9 Light oils Not iccovrrcd Dry lor-temperature far 2 0 . 0 gn11oiis inches long and 3 feet 3 inches in diameter, where much inunonia Not recovered experimental work is being undertaken, including the lowCsrim.ized briquets 810poundn (36 per temperature carbonization of sewage residues. Sielseu now The carhonized briquets are smokeless and quite free burn- claims6 that his process "seems to be at present the only one ing because of the structure, the average analysis compared which can be relied upon to furnish proper heavier and with the original coal being as follows: ligliter lubricating oils," and that, so far as Great Britain is concerned, it is not necessary to resort to hydrogenation of RrRBr CoErlio 0.5-1Ncn SL*CZ the low-temperature fuel, which in any case "does not c A ~ ~ ~ Per cent Per cent according to independent authorities produce lubricating Fired carbon 52.5 84.8-86.5 bases, but only motor spirits and fuel oils." voirti1e matter 32.5 1.a$-a.z$ I
Ash
MOi.t"*e B. f u. per pound
5.5 9.5 12.500
9.2&12.60 2.00-2.10
12,15+12,750
5
Cor Wald. 84 (1828).
0
~
INDUSTRIAL A N D ENG INEERING CHEMISTRY
44
“Pure Coal Briquet” Process This is primarily the work of E. R. Sutcliffe, managing director of Sutcliffe, Speakman and Co., Ltd., of Leigh, Lancashire. Under the auspices of an associated company, Leigh Smokeless Fuels, Ltd., an extensive briquetting carbonization and by-product plant has recently been completed a t Leigh, although two retorts only have so far been installed, each of 50 tons per 24 hours capacity. At the time of writing (September, 1926) this installation is held up by the coal stoppage, although it is understood trial runs of parts of the plant have been made. The “pure coal briquet” process consists in the carbonization of briquets at medium or high temperature conditions so as to obtain an intensely hard carbonized fuel, which, however, in spite of its low volatile content, is free burning because of its extremely fine grained structure allowing maximum surface action, on c the same lines as charcoal. The feature of the process is the briquetting of bituminous coal blended with 10 to 15 per cent of coke breeze, oxidized coal, or other material to give a non-swelling mixture direct a t 8 to 10 tons pressure without the use of pitch or other binder, using a special Sutcliffe high-pressure b ri q u e t press These pure coal briquets can then be heated without sticking together and becoming distorted, the retort used being of the vertical, mechanically c o n t i n u o u s type, built of firebrick and of large size and i n t e r n a l l y heated by passing upwards through the charge a current of steam and inert gas a t a temperature of 1600’ to 1850’ F. (870’ to 1010” C.), the mixed gases and vapors being taken off at the top. The pure coal briquets are fed in a t short intervals by a gas-tight dumping device embodying the use of small traveling cars, and the hard briquets are withdrawn a t the bottom, the total duration of the heating being 6 to 8 hours. The average yield, based on consideraF i 8 d ; T + , & ~ ~ ~ ~ ~ble ~ m experience -with‘ an original experimental retort, calculated to 1 ton of 25 to 35 per cent bituminous coal, but with 10 to 15 per cent coke breeze added, all under the above conditions, is as follows:
.
Gas
10,000 to 1
Light oil (total) Low-temperature tar (less light oil) Sulfate of ammonia Carbonized fuel
Of the above amount of gas about 7000 cubic feet are required to heat the retorts and the method of working can be altered within wide limits by adjusting the temperature, the rate of travel of the charge, and the composition of the internal heating medium. Tozer Process This was one of the original British low-temperature carbonization processes, the invention of C. W. Tozer, for the production of a hard smokeless fuel from bituminous coal by heating to about 900-1000’ F. (480-540’ C.) in intermittent, vertical, externally heated, cast-iron retorts so that the strongly swelling viscous charge gives itself an internal compression up against the sides of the retort. It will be remembered that in the Coalite process Parker used in much of his work an intermittent, vertical, cast-iron pipe retort,
Vol. 19, No. 1
about 4.5 inches in diameter giving a hard, dense fuel because of the internal compression of the charge. The Tozer process is essentially an attempt to improve on this original design. The Tozer retort, shown diagrammatically in Figure 4 in its original form, which is subject to modifications, consists of a cast-iron tapering cylinder built up of three rings, one inside the other, joined together by transverse ribs. The small, central, circular aperture is for the passage of the gases and vapors evolved and the crushed coal is contained within the two rings-that is, eight separate compartmentsfour being in the outer ring and much larger than the other four inside. These partly circular slabs or layers of coal are nowhere more than about 3 to 4 inches thick, and the composite retort is then fixed in an outer firebrick setting and externally heated as usual. Also the gases and vapors evolved can come off both from the top and bottom of the charge into spaces left for the purpose connected by the central, smalldiameter, circular passage mentidned, and it is claimed this plays a very important part since the swelling plastic charge is not jammed by gases and vapors that cannot escape. A large Tozer plant, under the control of C. W. Tozer himself, is being operated a t Ballengeich, Natal, belonging to the South African Carbide and By-products Co., Ltd. This consists of eight Tozer retorts in a setting 28 feet 1 inch long and 17 feet 3 inches wide with a height to the charging stage of 23 feet together with a complete by-product recovery plant with light oil fractionating and purification apparatus. Based on a period representing 3838 tons (2000 pounds) of coal, the following is the yield obtained per ton (2000 pounds) of coal comprising dross, washed nuts, and washed peas, having an analysis within the range of 53.10 to 57.25 per cent fixed carbon, 24.30 to 25.20 volatile matter, 16.70 to 20.10 per cent ash, and 1.60 to 1.75 per cent moisture. Not stated (used on plant and process) Gas Motor spirit (stripped from gas only) 1.7 gallons 1 1 . 8 gallons Crude oils (dry) Not recovered Sulfate of ammonia Low-temperature, hard, smokeless, 1324 pounds (66.2 per cent) free-burning fuel
The average analysis of the smokeless fuel is: Per cent ~~. 69.25 7.80 0.40 22.55 ~
Fixed carbon Volatile matter
Ash
Moisture
~
while the crude oil fractionates to the following, per ton (2000 pounds) : Crude light oil Crude middle oil Crude heavv oil Pitch Tar acids
2 . 3 7 gallons (sp. gr. 0.926 at 25’ C.) 1 . 6 9 gallons (sp. gr. 0.953 at 25’ C.) 3.39 aallons (sp. gr. 0.994 at 2 5 O C.) 44 pounds 2 . 2 0 gallons
A Tozer plant for the low-temperature carbonization of lignite with complete by-product recovery equipment has also been erected a t the Mines de Laluque in the Landes area of France. The Winser Process This is the invention of Charles B. Winser and Percy Brown, both of London, and a retort has not yet been built, although arrangements are now being made to erect the first installation with a calculated throughput of 60 to 70 tons of coal per 24 hours. The Winser retort is based essentially on continuous ceramic kiln practice and consists essentially of a very large, 5at, horizontal, circular plate or platform device traveling on a ball-bearing device a t a very slow rate of speed. This contains fixed all around the outer edge about ninety small, vertical, metal retorts of rectangular cross section and tapering downwards to the full discharge end. These are charged
January, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
a t the top in rotation, and the flat circular platform, carrying all the vertical retorts fixed side by side, forming a complete circle, moves around so that the retorts travel in a circular firebrick channel or passage, which is externally heated by a series of gas burners in a concentric combustion chamber contained within an outer wall, the whole forming a very large circular brickwork construction like a kiln. After completing the circuit the retorts are each discharged through the bottom and again pass under the overhead hoppers. It is understood that for a setting with a throughput of 70 tons of coal per 24 hours the temperature in the combustion chambers will be 1202' to 1382' F. (650' to 750' C.), each retort being 5 to 6 feet high and 4 feet 6 inches wide, with a thickness of charge of 6 inches a t the top and 8 inches a t the bottom, while the total period of travel will be about 8 hours, of which, however, approximately one-third will be cooling off in the retort. Wollaston Processes The latest British developments in the fields of low-temperature carbonization and total gasification include the Wollaston processes, primarily the invention of T. Roland Wollaston and controlled by the Wollaston Gas Producers (Manchester), Ltd., the various patents commencmg in 1917. These are of two main types. The first is essentially, with numerous modifications, a combined vertical, mechanically continuous, preheating retort for low-temperature carbonization, placed on the top of a producer gas generator for total gasification on the usual lines by means of a steam and air blast, the gas passing up through the descending charge and mixing with the rich gases and vapors evolved by the advance low-temperature carbonization. The main object of the Wollaston process in its present stage of development is not so much the recovery of low-temperature oils, although this will be a valuable feature, as to render possible the use in producer-gas generators of every description of swelling bituminous or other difficult coals that would otherwise give rise to the familiar troubles of sticking together of the charge and irregular gasification, combined with the recovery of the maximum amount of sulfate of ammonia 70 pounds per 1 per cent nitrogen in the coal. The main feature is the design of the preheating vertical, cylindrical retort, which is arranged by means of transverse division in the form of a series of sections or compartments one above the other with scrapers or ploughs, so that the material is always in a thin layer, while being turned over and agitated as it passes down from one compartment to the other. The hot gases from the generator below enter a t about 1112' F. (600' C.), the time of travel in the preheating retort is 20 to 40 minutes, and the mixed gases and vapors leave the top a t 482' F. (250' (2.). The first plant on these lines was erected a t the Fishwick Dyeworks of George and R. Dewhurst, Ltd., Preston (Lancashire), and has been very successful, while a number of other installations are now a t work. The gas from small bituminous slack averages, without recovery of oils, about 45.5 per cent combustible, (17 per cent CO, 24.5 per cent H2, and 4 per cent CH,, etc.), with a heat value of 183 B. t. u. per cubic foot (net) and a yield of 125,000 cubic feet per ton, The second Wollaston process, which does not include recovery of by-products, is the combination in one setting of a producer-gas generator and a vertical, tubular, or locomotive type of boiler especially intended for the efficient utilization as fuel of coke breeze and general colliery refuse material, both high ash content, and general canneloid products. These are extremely difficult to use efficiently for steam generation in the ordinary way, but it is claimed that with a special design of small producer-gas generator the ma-
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terial can be gassed and all the gas burned direct in the setting with 16 to 19 per cent carbon dioxide, smokelessly and a t high efficiency. The principle of firing furnaces, not with solid fuel direct, but by means of an integral or adjacent generator in which the fuel is first gasified and the gas then burned, is ancient in origin, going back well over half a century. Wollaston, however, in his setting design adopts improved principles, in which, for example, the raw fuel is first preheated in the gasfired combustion chamber itself, any gases or vapors evolved being burned directly. The heated raw fuel then passes down gradually into the generator. Wollaston also uses this principle for vertical water tube and other boilers where it can be used efficiently. This is quite different from the internally fired cylindrical Lancashire boiler, with which so many of the earlier investigators worked. As typical performance figures using coke breeze with 19.5 per cent moisture, 25.5 per cent ash, and 8028 B. t. u. per pound in conjunction with a small vertical boiler, the carbon dioxide averaged 18.3 per cent, the combined efficiency of the generator and boiler being 73.8 per cent without feed water economizer, and 88.8 per cent for the generator only, while the gas had 22.2 per cent carbon monoxide, 13.7 per cent hydrogen, and 6.7 per cent carbon dioxide. Here also a number of installations are a t work and on order.
A Yellow Ink for Marking Rubber Tensile Strips' By Clifton G. Cashion PHILADELPHIA RUBBERWORKS Co., AKRON,OHIO
HE need of a light-colored ink for marking tensile and other test strips has long been felt by many rubber physical testing laboratories. The dark aniline inks and yellow crayons now employed are sometimes useless owing to the nature of the rubber or to the lighting conditions of the laboratory. A satisfactory ink may easily be prepared by any testing laboratory as follows: A soluble lead compound is precipitated as insoluble yellow lead chromate by the addition of potassium chromate. The solution containing the precipitate is boiled and then filtered. After filtering and before entirely dry the lead chromate is ground into glycerol. The proper consistency of the ink is best determined by practice.
This ink is used with a blank pad obtained at stationery supply houses. The pad is covered with the ink and dampened with glycerol as it dries. The right degree of dampness of the ink must be learned by experience, as a too wet or too dry ink will not give clean lines or the lines will be too broad for efficient work. It will be necessary to clean the markers often, if they are to give clear, clean-cut lines. Especially in stress-strain work a blurry line tends to throw the elongation a large percentage off the correct reading. This ink is especially valuable in working with black treads, both new and aged, as they have a tendency to absorb the aniline inks as soon as the rubber has stretched several hundred per cent. The use of this ink has entirely eliminated the loss of stress-strain determinations in this laboratory due to the elongation lines becoming invisible while stretching. In aging work, where the dimensions are marked previous to aging, this ink is valuable as it is permanent in the life oven. It is also permanent to a very high degree in water, steam, and fire. 1
Received September 4, 1026.
