UNIT PROCESSES
Pyrolysis of Coal and Shale R E S E A R C H in coal carbonization continued on a wide front on both the fundamental and the practical scale. Studies on fundamentals of coal pyrolysis included isolation of fusible primar! pyrolysis fractions of coal by chloroforni extraction, kinetics of evolution of gases other than tar, and use of the molecular still and the refractometer for following thermal decomposition. Other studies included the relationship of coke quality to plastic properties, to petrographic nature. and to thermal pretreatment of coals. Interest in low temperature carbonization has continued, with most of the processes previously reported under development still under study. A comprehensive compilation of Fischer loit temperature assay data for 400 coals was published, as well as a n investigation of free radicals trapped in low temperature
CHARLES H. PRIEN, who prepares our annual reviews on coal and shale pyrolysis, i s head of chemistry and chemical engineering division, Denver Research Institute, and professor of chemical engineering at the University of Denver. In addition to these activities, he has published articles on the teaching of unit processes and has conducted research on shale and synthetic fuels. Prien is a graduate of Purdue University, receiving his Ph.D. there in 1948. He is a registered engineer of the state of Colorado and holds memberships in the ACS, AIChE, ASEE, Sigma Xi, and Phi lambda Upsilon. MICHAEL PERCH is Senior Chemical Engineer in the Research Department, Koppers Co., Inc., Verona, Pa. Perch i s a 1939 graduate of Carnegie Institute of Technology with B.S. and M.S. degrees in Chemical Engineering, He is a member of ACS, Eastern State Blast Furnace and Coke Oven Association, and is active in ASTM committee work on coal. He is author of several publications in the coal carbonization field.
1 142
carbons. Consolidation Coal Co. and Standard Oil of Ohio announced a joint venture on a 5 to 10-year research program for developing marketable hydrocarbon liquid fuels from low temperature tars. Similar studies were continued by Battelle Memorial Institute, Union Carbide Corp., University of Wyoming, .\labama Pobver Co., and others. Pilot Plants. This year marked the year of consrruction of large-scale pilot plants for studying coals, cokes! and coal chemicals. T h e U. S. Steel Corp. built a pilot plant consisting of five fullscale ovens for experiments on methods of preparing and blending of coals for the coke ovens and measurement of yields and assessment of the quality of cokes, gases, and coal chemicals. Similar plants were built in England by the British Coke Research Association and at the Emil coking plant of the Altessener Bergwerks A.-G. in Germany. Smaller scale pilot plants were installed in this country by the Island Creek Coal Corp., Consolidation Coal Co..Pittston-Clinchfield Coal Co., and Eastern Gas and Fuel Associates. T h e impetus for such installations is the growing desire on the part of steel companies to improve production efficiencies of coke ovens and blast furnaces as well as the quality of coke. Blast furnace men capitalizing on the benefits from ore benefication and new operating techniques have set targets for reduction in coking rates from 1800 to 1250 pounds per ton of iron and the more optimistic are shooting for a coking rate of 900 pounds. This is the face of considerable recent excitement over direct reduction methods for iron ore. T h e U. S. is gradually becoming aware of the importance of its vast oil shale deposits. .A growing volume of opinion is being voiced that a commercial oil shale industry here may begin much sooner than has been expected. Several retorting processes are stated to be competitive in cost Lvith domestic petroleum production. A proposal to detonate a nuclear device in the U. S. western oil shale deposits, to recover shale oil, stimulated public attention to oil shale. A more careful examination of the economics of the proposal: however, indicated that shale oil so produced was no cheaper than that by the most advanced of present retorting
INDUSTRIAL AND ENGINEERING CHEMISTRY
techniques. T h e technical probletns associated with such a process are formidable. Fundamental research on U.S. oil shale continues to be lacking. By contrast, the Russians have considerably increased their fundamental research on oil shale. and a t present dominate this area of oil shale activity. Greater industrial support of basic oil shale research is sorely needed. T h e Union Oil Co. discontinued operation of its pi101 plant a t Grand \-alley: Colo., upon completion of its scheduled testing program. T h e Oil Shale Corp. is continuing its laboratory and pilot plant activities a t the University of Denver. A demonstration plant there resumed operation in June 1959.
Coal Pyrolysis Mechanism, Kinetics, Thermochemistry. Brown ( 6 A ) isolated the fusiblc primary pyrolysis fractions of coal by chloroform extraction and concluded that the lack of coking properties in a low-rank coal is due partly to the greater volatility and thermal instability of this primary pyrolysis product, compared to that of a high rank coal. Fitzgerald and van Krevelen (9.4) studied the kinetics of evolution of gases other than tar during carbonization by determining the flow rates of each gas concerned under a vacuum a t rising temperatures by measuring flow rates of the combined gases a n d frequent gas analyses. Methane flow takes place as a first-order reaction u p to 500' C. and becomes larger than expected above that temperature. Hydrogen flow follows first-order reaction to the same temperature, but thereafter becomes less than expected. Coals of 92Yo carbon content give the greatest total arnounr of hydrogen; coals of 89% carbon give the greatest total amount of methane; coal of 86% carbon give the largest amount of the other hydrocarbons. Shapiro (13.4) experimented with solid distillation of a variety of coals and assessed the characteristics of the plastic mass of coal by the rate of separation of tar and gas ivith rise in temperature. T h e colloidal properties of the plastic mass determine the coking properties of the coal. T h e most important property is rhermal stability; the higher
PYROLYSIS OF COAL AND SHALE _ _ _ _ ^_____._._....___________._______.----.-..---..-. .________.___._.____~~~~~
its decomposition temperature, the better the caking properties. Using a molecular still to study the primary thermal decomposition products of coal: Sun (74'4)showed that the distillate from coal Lvith the strongest agglutinating properties is richest in high molecular weight components. Coke formation is dependent on the liberation of certain high molecular lveight but fusible components in the early stages of the decomposition. Van Krevelen and Huntjens (77.4) determined the fluidity of undecomposed coking coals by measuring the viscosities of solutions of coal in tar-pitch made at 200' C. Because the temperature of the solution does not exceed this temperature, during dissolution or during the measurements. the viscosity measured is that of the completely dissolved but undecomposed vitrinite. By comparing the viscosity thus measured \vith that of coal measured during coking it was concluded that the degree of agglutination attained during coking is primarily a function of the nature and quantity of the decomposition products formed. Sadziakiewicz ( 7 2 4 found that the yield of chloroform-soluble extract of coals a t various plasticizing temperatures bore a direct relation to the logarithm of the maximum fluidity as measured by the Gieseler plastometer. He concluded that the fluidity of the coals is attributable to a substance that is formed as a product of primary decomposition a n d is extractable with chloroform. T h e residue shows no plastic behavior after chloroform extraction: although an additional ? to 9% extract is obtained by using pyridine as a solvent. Austen (3A) in an investigation of free radicals trapped in low temperature carbons observed the effect of carbonization a n d chemical treatment on the concentration of free radicals. H e concluded that the unpaired electrons are little influenced by the particular edge groups present but are closely associated Lvith the aromatic skeleton. By partial hydrogenation of a noncoking coal, Ahuja (2'4) converted the coal into one of coking variety a t 200 atm. and 375' C . without the use of a catalyst a n d a t 30 arm. with a n iron oxide-chromic acid-ammonium molybdate catalyst. T h e coke was similar to that from a high rank coal but the yield was lower. O n the other hand, the yield of tar \vas higher than that obtained from a high rank coal. Delvaux a n d Grace (7.4) reported a study of the decrepitation of anthracite under the action of thermal shock, to permit use of this fuel in the foundry cupola. Their study pointed to the fundamental importance of the rate a n d amount of volatile matter released during carbonization. Eckerd and Ten-
ney ( 8 A ) attempted to stabilize anthracite thermally by calcination in r e t o r t . Bond and others ( 4 A ) attempted to follow changes in carbonized coal structure with temperature u p to 900' by measuring the light-reflecting power. Changes in optical properties were greatest in the curves when changes in physical a n d chrmical structure were most evident. Subject Change in heat conductivity and temperature conductivity when coals are heated Transient fusion of coals Formation of chloroform-soluble material in coking coal
Lit. Cited
(fA) (;Ai
U0A)
Low and High Temperature Carbonization. Lee ( 8 B ) surveyed the carbonization of coal in coke ovens and attempted to set out in broad terms the problems facing the coking industry and the efforts being made to overcome them. H e stressed the advantages of coke uniformity in both analysis and physical properties for industrial purposes and rcferred to theoretical aspects now under study, to achieve a better understanding of the process. Mohr (73B) speculated on the future size of the coke oven with the vie\v of producing a more productive oven. H e imagined a n oven 19 feet high, SO feet long, and 20 inches in average width, which would have approximately double the charge of the present-day coke oven. H e claimed reduced direct labor, operating, a n d investment charges per ton of coke. T h e maximum fluidity of coal as determined in the Gieseler plastometer was the factor having the largest effect on coke quality. McKellar (IOB) expressed coke quality by conventional indexes a n d by a "quality index'' composed of both the shatter and Micum d r u m test results. About 4470 of the variance of the quality of the coke was explained by variation in coal properties. Selvig and O d e (79B) summarized the results of Fischer-Schrader low temperature assays a t 500' C. for 400 coals from 19 states, Alaska, a n d British Columbia. This represents the most comprehensive compilation of such data available. Kennedy and Evans (6B) developed a neir fuel from noncoking bro\cn coal suitable for metallurgical a n d domestic purposes. L u m p char in the form of briquets was produced, having strength comparable to conventional metallurgical cokes. Gillmore (5B) studied the factors influencing the strength of carbonized briquets prepared from anthracite fines using a pitch binder: amount of binder, briquetting pressure, carbonization tem-
perature and rate, and heat pretreatment. Increasing the amount of binder produced stronger briquets u p to a maximum, then the strength decreased. Temperature of carbonization had a favorable effect u p to 1050" C.; while the rate had little effect. Heat treatment before briquetting decreawd the briquet strength. Gayle and Eddy ( d B ) used a sole-heated test oven for studying the expansion properties of coal. For binary blends, the expansion results Jvere nonadditive in behavior? and depending on the coal, both positive and negative deviations from additive behavior Lvere observed. T h e effect of addition of inerts on the expansion behavior of coals could be predicted from the amount of inert added and its specific gravity. Dense inerts such as coke breeze, anthracite fines. and particularly iron ore markedly reduced coal expansion. I n some inscances, low density inerts actually increased expansion properties. Marshall a n d others ( 9 B ) made an important contribution to the study- of the relationship of petrographic composition to the coking character of Illinois coals. They found that the petrographic constitution importantly influenced coking properties. Optimum cokes \\'ere produced for coal in the KO. 6 seam that had 87Yc vitrinite and a vitrinite median thickness of 15 microns Coke strength increased with increased content of inertinite u p to about 957,. A swelling meter for coal during lo\v temperature carbonization was consiructed by Diamant (,?B). Degree of swdling was found to be inversely proportional to the time required to pass through the swelling zone. Two regions exist-the stable zone rvhere the coke produced possesses fine pores. and the unstable region where coke nf large vapor pockets is produced. Sadiakieivicz (74B) reported that fissures arise in coke as a result of the decrease in volume between the bulk volume of granulated coal and thc resulting true volume (without fissures) of the coke. This volume reduction takes place in two periods. u p to the end of the plastic stage (500' C.) and from 500' to 1000' C. T h e E. S. Bureau of Mines (ZOB) reported the results of thermal pretreatment of coals a n d its effects on coke and other products. High-oxygen coals on preheating to 250' to 300' C. produced cokes of improved physical strength; the yield of tar increased and that of gas decreased. Perch and Russell (75B) obtained results which confirmed those of the Bureau of Mines and suggested new procedures for charging the hot coal into coke ovens. Yields and quality of products in rapid
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SEPTEMBER 1959
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By far the most intensive basic research on oil shale is being done by the Russians. In the U. S. considerable attention is being - devoted to detonation of a nuclear explosion in the Colorado oil shale deposits.
coal carbonization \cere studied by Peters ( 7 S B ) . Fine coal was in contact with a finely divided heat carrier a t 500' to 900" for about 5 minutes. Products xvere withdrawn rapidly to avoid secondary cracking. T a r yields much higher than predicred by the Fischer assay were obtained but gas yield was lower. 'The tar had a relatively high pitch content. Mitchell and Sedlachek (IZB) reported a full year's production and use of iron-coke in a coke plant. Carbonization of blends of coal and blast furnace flue dust \vas reported an economically and technically feasible xvay of disposing of flue dust kvith added credit for reduction of oxides to metallic iron. T h e presence of iron ore may have an adverse catalytic action on coke formation, but according to Barking and Eymann (2%) this effect can be decreased by adding small amounts of oil to the coal before coking.. Syskov and Angelova ( J I B ) studied the dynamics of evolution of total and organic sulfur of various coals of different rank during carbonization. They concluded that sulfur evolution is mainly a function of the changes occurring in rhe structure of the coal substance as determined by its rank and not the proportion of pyritic and organic sulfur. Mirev a n d Zlateva ( 7 7B) also studied the evolution of sulfur both during normal low temperature carbonization and in a stream of ammonia. T h e amount of sulfur removal depends on the degree of carbonization and the volatile constituents of the coal. Removal of sulfur in the case of coking coal is more difficult because of the fusion properties of the coal. Lit. Cited
Juhjert
Improving foundry coke Significance of dilatometric contraction of coal Semicarbonization in a fluidized bed Influence of inserts on dilatometric properties of coal Guaranteed mechanical strength of metallurgical coke
(1B) (7B) (27B) (18B) (82B)
Oven O p e r a t i o n , Products, and Byp r o d u c t s . Glenn and Rose (5C) made a comprehensive compilation of typical yields. typical end products and their uses. and coal and po\cer requirements for a wide variety of metallurgical, chemical, and other processes using coal. Boyer and others (7C) developed a laboratory procedure for measuring the reactivity of coke in which pieces weighing 10 to 100 grams are gasified a t temperatures u p to 1500' C. T h e reactivity of carbon dioxide toward
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The project, however, does not appear economically feasible
coke has special significance in the foundry cupola. Under normal conditions, the rate of the C02-carbon reaction is controlled by the diffusion of the gases into the pores of the coke instead of by the arrangement of carbon atoms, the surface area of the coke, or the chemical properties. T h e pore structure of coke during carbonization and gasification was studied by Cameron and Stacy (ZC). Apparent specific volume, internal surface area, and mercury penetration measurements showed that coke contains two distinct pore systems. Micropores with entrance diameters of less than 10 A . and macropores with entrance diameters varying between 400 and 130,000 A. were found. but no pores had diameters between 10 and 400 A . A s the carbonization temperature is increased, both the macroand the micropores became less accessible. O n gasificarion with steam at 800' C. many of thr constrictions are destroyed. lrlott and Rucklidge ( S C ) Lvorked on the effect of test conditions in the determination of the apparent specific gravity of coke. Nandi (IOC) studied the true density of cokes from coal blends and found that the density of coke from blends is higher than the densities of cokes made from the individual coals. Herein may be a n explanation for the behavior of blends in coking. T h e blend acted during carbonization as a coal higher in rank than either of the individual coals. Resistance of coke to breakage on impact was studied by Mott (9C) in the shatter test method. T h e number of drops, height of drop, and initial size of the coke were evaluated. Mean size of coke after impact is related linearly to the logarithm of the number of drops. Larger sizes of coke have greater liability to breakage because of fissuring. A "fissure index!' was developed, based on Kick and Rittinger laws, which increases \2;ith the mean size and for a given coke size increases as the shatter index decreases. Very strong foundry cokes have a zero fissure index. Lit.
Subject High purity aromatics from cokeoven oil Fluorocarbons from coal Handbuch des Kokereiwesens, VOl. I1 Physical properties of coke and relations to blast furnace practice
Cited (4Ci
(SC) (6C)
(7C)
Oil Shale Pyrolysis T h e greatest artention given to oil shale in the United States during the
INDUSTRIAL AND ENGINEERING CHEMISTRY
-
_I___I-
year was devoted to a joint proposal of the Bureau of Mines a n d the AEC to detonate a nuclear explosion in the Green River formation in northwestern Colorado. A meeting seeking industry financial participation in the experiment was held in Dallas, Tex., in January 1959. Briefly summarized, the tivo government agencies involved proposed that nuclear blast be detonated deep in the oil shale beds, and that fire-flooding techniques be attempted on the resulting cushed shale, to recover shale oil in iitu ( 8 0 ) . Initial tests with a 10-kiloton nuclear device would create a cavit!. of crushed rock 200 to 300 feet in diamerer: from which u p to 150,000 barrels of oil could theoretically be recovered by subsequent in situ combustion. O n a commercial scale a I-megaton blast a t 300O-foot depth would shatter .iO.OOOjO0O tons of shale and permit rheoretical recovery of u p to 30,000.000 barrels of oil. I t was originally cstimated a t Dallas that the cost of production of shale oil Mould be approximatrlv S I .OO per barrel: but this figure was subsequently revised upward to $2.88 per barrel ( 7 0 0 ) . This latter cost is in thc same range or higher than has been quoted recently for shale retorting by present above-ground retorting methods. It icould appear that any economic ndvantage in "nuclear retorting" of Colorado oil shale is considerably in doubt. in the light of present retorting research. From a strictly scientific viewpoint. of course, the experiment would be intensely interesting. However. the nuclear technique might be more economically and technically feasible if applied to Athabasca tar sands ( 2 0 ) . Hartley ( 4 0 , 5 D ) has attempted to analyze the factors influencing initiation of an oil shale industry in the United States. It is apparently the Union Oil Co.'s viewpoint that present costs of production of semirefined products from shale oil compare favorably with similar costs from natural crude oil. Because of the uncertain foreign crude price picture, however, Union does not deem it advisable to commercialize its own process for the present. Savage and Hough ( 7 7 0 ) have reviewed the status of an oil shale industry in the United States today, including title problems in patenting claims! recent progress in mining, in situ retorting, and current retorting technology. .4n up-to-date map of private oil shale holdings is shown. Particularly interesting figures show further reductions in mining costs as a result of the use of rotary
PYROLYSIS drilling and ammonium nitrate explosives. Duncan ( 3 0 ) has re-estimated total L-nited States \vestern reserves of 25-gallon-per-ton oil shale a t over 500 billion barrels. This richness is deemed commercially minable by known techniques. The 3000-ton-per-day Spanish oil shale industry south of Madrid has been described in detail ( 9 0 ) . Rotary drills are used in mining, and Scotch Pumpherston-\Yest\\$ood retorts for oil recovery. The resulting shale oil is hydrogenated and refined to yield light oils and lube stock. Kirss ( 6 0 ) has compiled an excellent review of postwar Estonian oil shale research by the Russians. including basic research, retorting research, and characterization of products. One is struck by the intensive research effort being conducted on all aspects of oil shale in Russia. T h e only active oil shale development in the \vestern hemisphere outside the United States is in Brazil. Cameron
and Piper ( I D ) have described recent pilot plant work on these shales, under their direction, using a 13-ton-per-day retorr. .i\ larger continuous retort is no\v under construction. Present production costs for Paraiba shale are approximately $3.60 per barrel. Labuntsovite. a rare complex silicate first found in the Russian Arctic, has been idrntified by the L-. S. Geological Survey in a Green River formation shale from Sweetwatcr County. Wyoming. Lit. Cited
Suhj err
U.S.S.R.resources of oil shale Index of U.S.oil shale and shale oil patents, 1946-1956
(12D) (70)
Basic Research. By far the most intensive basic research on oil shale is being done bv the Russians. An excellent re\*ie\z of postwar fundamental research on Estonian shale appeared (60).
Oil shale demonstration plant, Denver Research Institute, Denver, Colo.
OF
COAL AND SHALE
Only a few studies of any consequence on United States shales were published during the year. Robinson and Cummins (76E) extracted Colorado oil shale kerogen Lvith Tetralin at 2.5' to 350' C., fractionated the extracts, and attempted to characterize the products obtained. Molecular weight of the extracts varied from 410 to 625. I t was concluded that Colorado oil shale kerogen is composed primarily of saturated heterocyclic structures, Isith lesser amounts of straightchain and cyclic paraffins and aromatic structures. Previous oxidation studies have led to similar conclusions. Hubbard ( 7 7E) subjected a 5070 kerogen concentrate to hydrogenolysis a t 355' C. and obtained 88c0benzene-soluble product. No further elucidation of krrogcn structure resulted trom the study. Vimba and others (7QE) report the result of a thermal solution study on shale a t temperatures up to 300' C., using cylinder oil? mazut. anthracene oil. and similar unrefined solvents. The work is similar to that previously done by Dyakova. Results are of more applied significance than in deducing kerogen structure. Brower and Graham ( J E ) subjrcred Colorado oil shale kerogen to chlonination. hydrobromination. nitration, sulfonation, air oxidation, and acetylation. This kerogen is largely nonbenzenoid, with 16 to 22 carbon atoms per "polymeric" unit, and one double bond or active hydrogen atom per unit. Iida (72E) has begun a study of the nitrogenous compounds in a n hT.T.U.Colorado shale oil. Preliminary separations and identification indicate the presence of aliphatic nitriles. phenanthrenes or fluorenes. allyl pyridines-e.g.. 2,4.6triundecylpyridine-and quinolinrs. The presence of polycyclic aromatic hydrocarbons is particularly interesting. .4mong the 20-odd Russian basic papers reviewed, the following are of particular interest. Aarna (2E) has continued his investigation of the structure of Baltic shale kerogen. He reports aromatic nuclei equal to 15 to 20% of total carbon present, and naphthenic nuclei equal to 50 to 75y0of total carbon. Distribution of oxygen was studied and 70yc found to exist as phenol-ether and hydroxy groups. Solubilization of kerogen is stated to be related to destruction of the phenol-ether bonds. Vpon oxidizing a Baltic shale kerogen a t 120' to 170' C.. Polozov (75E) found little change in the carbon-hydrogen ratio. harna (7E) studied the thermal decomposition of a kerogen concentrate prrpared by centrifuging in a calcium chloride medium. Oxygen concentration of the resulting tar was independent of temperature, primarily because of the manner in which dihydric phenols decompose. T'aldek (78E) studied the physico-
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UNIT PROCESSES chemical properties of Estonian kukersite. Polished disks 60 mm. in diameter and 10 mm. thick were retorted a t 520' to 900' C. Heat conductivity decreased sharply as semicoke formation began, and porosity increased. Gubergrits (7OE) measured the heat transfer characteristics of kukersite by isothermal heating of pieces heated from one side only. a t 500' to 800' C.: as a basis of studying thermal conductivity. Diffusion and kinetic properties of kukersite coke were measured by Shilov (77E), who found a coefficient of diffusion of 4 X sq. meter per second at 600' C. It was established that combustion of small coke particles at 600' to 850' C. is controlled by rate of diffusion and not reaction kinetics. .A series of model studies on kukersite gasification has been reported. including measurements of gas prrmeability (7,?E) on cylindrical samples ; heating rates ; on parallelepiped-shaped pieces (GE) heat conductivity under preheat conditions (7E) and during pyrolysis ( S E ) ; and factors controlling underground gasification (7dE). Subject Review on chemical nature and origin of kukersite Composition of bitumens from Volga shales Sulfonation of Colorado shale to produce desiccants and ion exchange materials Geochemical investigation of Athabasca tar sands
Lit. Cited
@E) (2OE)
(W (;E)
Retorts a n d Retorting Processes. Probably the most interesting retorting paper on U.S. shales was a study by the Institute of Gas Technology on the production of pipeline gas by hydrogenolysis of Colorado shale (7OF). A 22.9-gallon-per-ton shale was hydrogenated a t 1200' to 1300' F. and 1100 to 5700 p.s.i.g. with 90 to 100% gasification of organic matter to 800 to 900 B.t.u. per cu. foot gas. Particle sizes varied from 5 to 325 mesh. While not economically competitive at present, hydrogasification offers definite promise as a future method of supplementing dwindling natural gas reserves. Shell Development has patented a vertical retort ( 7 3 F ) in Lvhich off-gases are recirculated in part to the raw shale preheat zone at the top of the retort: and the temperature of the combustion zone a t the bottom of the retort is controlled by cooling tubes. Esso Research and Engineering (72F) proposes thermal solution (and hydrogenation) of finely divided oil shale, using a partially hydrogenated aromatic oil fraction. The dehydrogenated oil is regenerated from hydrogen produced by fluidized water-gas reaction of the
1 146
carbonaceous residue on the spent shale. A Russian patent describes a three-step liquid phase hydrogenation of oil shale ( 4 F ) a t 50- to 100-atm. pressure, in the presence of a solvent and iron catalysts. Scott ( 8 F ) has patented a method of shale retorting involving successive and separate fluidized beds arranged vertically for preheat, retorting. combustion, and cooling Excessive areosol formation and refluxing \
