Entrained-Solids Retorting of Colorado
Oil Shale EQUIPMENT AND OPERATION H. W. SOHNS, E. E. JUKKOLA, R. J. COX, F. E. BRANTLEY', W. G. COLLINS, AND W. I. R. MURPHY Petroleum a n d Oil-Shale Experiment Station, Bureau of Mines, Laramie, Wyo.
M
OST of t h e shale oil being processed today is produced in
Results of the study are reported here together with a description of the equipment and its operation.
conventional, countercurrent, internal-combustion retorts in which oil vapors are swept out of the retort as rapidly as formed, t o minimize thermal cracking after t h a t involved in forming the oil from t h e shale organic matter. Although such retorting processes (1,9 ) produce a high yield of oil (about 65 weight % of the organic matter in the shale), the unique combination of molecular structures in the oil often requires the use of several refining steps t o produce from it commodities of desired quality. It contains compounds ranging from completely saturated to completely aromatic, with considerable quantities of material of many types and. degrees of unsaturation between these extremes. I n addition, large percentages of sulfur, nitrogen, and oxygen compounds are found throughout t h e boiling range of the oil, some of which interfere in processes t h a t might otherwise be used t o advantage in refining it. Nitrogen in particular is troublesome, in t h a t it limits application of catalytic cracking, a process that would be useful in producing high-octane gasoline components from the straightchain aliphatics. Some of the unsaturated compounds also are detrimental in both thermal and catalytic processes, because they readily form carbonaceous deposits in heaters and on catalyst surfaces. These considerations suggest that, if the quality of oil produced from the retort could be controlled, refining of the oil t o gasoline might be simplified. One method of control is to subject t h e retort vapois to additional cracking before condensation. B y this method some of the aliphatics of high molecular weight can be converted t o olefins of low molecular weight for processing by standard polymerizing methods, some aliphatics may be cyclized and aromatized, and some of the unstable unsaturated cyclic compounds may be dehydrogenated further t o stable aromatic structures. This aromatic oil or its fractions may then be converted to gasoline in a one-step hydrogenation process which at the same time removes the undesirable sulfur, nitroU P E R H EATER gen, and oxygen. T o study t h e effects of retorting variables upon quality and quantity of oil produced, apparatus was constructed in which fine particles of shale entrained in steam or other media can be retorted a t controlled temperatures , a n d residence times. A study has been completed of the variation in yieId and quality of products obtained in this equipment at several temperatures over the range 1000" t o 1650" F. with steam as t h e entraining fluid. Present address, Monsanto Chemical Co., Anniston, Ala.
EQUIPMENT
Figure 1 is a flow diagram of t h e equipment used. It consists of five main operating units: (1) the furnace and the superheater; (2) t h e shale feeding and retorting system; (3) the solidsseparation system; (4)the liquid-product-recovery system; and ( 5 ) the noncondensable gas-handling system. The furnace and the superheater are of steel and firebrick construction. Two groups of three automatically controlled, inspirating-type natural gas-air burners along opposite sides of the furnace supply the necessary heat. Flue gases from t h e furnace enter the superheater chamber through two flues in opposite ends of the common side wall. Here they come in contact with a bundle of superheater tubes before being admitted t o the stack and exhausted to the atmosphere. T h e retorting system consists of four straight Duraloy tube sections, each approximately 9.5 feet long, which are joined by three 24-inch center-to-center return bends. T h e tubes and return bends have an inside diameter of 33/s inches and a wall thickness of 3/8 inch. The tube assemblies are supported within the furnace by brick columns. At the inlet end of the retort tube, shale and the entraining steam are mixed, the shale dropping a t the desired rate from a variable-speed screw feeder into the stream of superheated steam. Steam flow is automatically maintained a t the desired rate. A differential-pressure controller maintains a positive helium pressure on the feed hopper t o prevent steam from entering the hopper, condensing on the shale, and upsetting feeder operation. The retorted or spent shale is separated from the product stream in a series of five cyclone-type separators. Liquid products are recovered in three stages. I n the first stage two condensers, one contact and the other shell and tube, remove most n W e
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Entrained-solids retorting equipment
GAS METERS
INDUSTRIAL AND ENGINEERING CHEMISTRY
462
Vol. 47, No. 3
cally. Temperature and pressure histories at, point? throughout the pilot plant system are recorded continuously. SOURCE AND PREPARATION OF SHALE
The shale used in thie series of tests was obtained from the Bureau of Mines Anvil Points mine near Rifle, Colo., and consisted of a blend of 75% upper-bench and 25% EF-bed shale. T o prepare it for t h e retorting tests it was pulverized in a hammer inill and the crushed product wits passed over a 12-mesh screen. A typical Fischci assay (4)of the finished product is shown in Table I and the screen analysis in Table 11. RETORTING T E M P E R A T U R E WAS CONSIDERED
TO B E THAT OF T r i E PRODUCT S T R E A M LEAVING RETORT A F T E R T H E 2 n d PASS
OPERATION
Initial experinients were made t o determine the effects of temperature upon product yieldP and qualities. The survey included runs a t apL proximately 100" F. intervals through the tern-10 0 20 40 60 80 IO0 I20 I40 160 D U R A T ON or R U N , M I N U T E S perature range of 1000" to 1650" F. .4 steam flow rate of 60 pounds per hour was used for Figure 2. Temperature histories during typical run at 1200" F. all runs, and the shale feed for most of them approximated 300 pounds per hour, resulting in a of the water and oil from the product stream. The next stage steam-shale ratio of 1 to 5. The average gaseous stream velocity is a high-speed centrifugal agglomerator which removes the mist produced in the retort a t shale and steam rates of 300 and 60 of fine oil particles from the stream. In the last stage, the pounds per hour, respectively, varied from 17.8 feet per sccproduct stream is compressed to approximately 90 pounds per ond a t lOOb" F. to 29.3 a t 1500' F. These velocities, calculated square inch gage, then passed successively through an aftercooler and a refrigerated tube-condenser, the tubes of which are mainfrom the quantity of steam, oil vapors, and shale gases enteiing tained a t 10" t o l 5 O F. Pressure on this stage of the liquidand leaving the tube, produced calculated shale-retention times recovery system is maintained by a back-pressure regulator. of 6.0 and 3.7 seconds, respectively. Gases being bled off by the regulator go t o the gas-handling A temperature history of a typical run a t 1200' F. i v repiosystem, where they are metered and split into two streams. One of the streams, approximately 10% of the total, is stored in duced in Figure 2. Temperature equilibrium and good control floating-roof-type gas holders for sampling, and the other is of the process are obtaincd rapidly. flared. T h e equipment is instrumented so that steam flow, furnace temperature, feed hopper-pressure differential, and pressure of DISCUSSION O F R E S U L T S the high-pressure condensing stage are all controlled automatiFigure 3 shows the oil arid gas yields obt'ained a t various tcinperatures, and Figure 4 compares the oil yield, including all C4+ hydrocarbons in the gas, with Fischer-assay oil yield. These Table I. Modified Fischer Assay ol a Typical Oil Shale as figures show that, oil yield decreased with increase in temperature Charged and ranged from 168 pounds or 21.2 gallons per ton of 3O-gallori-Gallons pel Ton of Shale Wt. yo per-ton shale a t 1000" F. t o 55 pounds or 5.6 gallons per ton a t Charge 100 0 1650" F. When C4+ hydrocarbons in the gas are included, the. Oil 10.4 27.2 Water oil yield varied from 77.2 volume % of Fischer assay a t 1000" F. 3.2 1.4 83.6 Spent shale t o 23.5'% a t 1650" F. Although the oil yield a t the lower temGas plus loss 2.6 perature was less than 80% of the Fischcr assay, subsequent work Characteristics of Products Spent Shale 011 Ignition loss, % 22.71 Bgecific gravity: 77.29 100° F . / l O O O F. Ash, % Tendency t o coke Slight 60' F./60° F. (calcd.) Ignition loss (original shale basis), % 19.4 Consistency a t 77' F. Ash loss (original shale basis), % 66.2
0.904 0.918 Liquid
Table 11. Typical Screen Analysis of Raw Shale as Charged Screen Size, Mesh +8 -8, +IO -10, + I 4
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Effect of retorting temperature on oil and gas yields
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1955 80
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Effect of retorting temperature on Ca+ oil yield
has resulted in oil yields approaching those obtained by Fischer assay. Mineral-carbon dioxide-free gas yield (see Figure 3) increased with increase in temperature and ranged from 70 pounds per ton of shale at 1000' F. to 417 pounds a t 1650' F. The formation of water gas during the run at 1650" F., as evidenced by an apparent loss in the water balance and a corresponding gain in the organic balance, accounts for the excessive amount of gas formed a t this temperature. Deducting the amount of water gas formed (approximately 165 pounds per ton) from the total amount of gas obtained brings the value in line with the others (see Figure 3). Although the amount of oil produced by this series of runs was less than by Fischer-assay retorting, total oil and gas produced were equal to or greater than that produced by Fischer-assay retorting. Organic removal, as determined by raw- and spentshale analyses, varied from 71 to 86% (see.Figure 5). This compares favorably with the 78% usually removed during Fischer assay retorting of Colorado oil shale. Carbonate decomposition varied from 4% a t 1000" F. to 89% a t 1650' F. At temperatures below 1500' F., decomposition was less than 40%, and below 1400, less than 30%. Hest economy considerations make it desirable that carbonate decomposition be kept a t a minimumvia., the heat required to decompose carbonates in Colorado oil shale amounts to approximately 1490 B.t.u. per pound of carbon dioxide liberated. The heat required to retort 28-gallon-per-ton Colorado oil shale a t 1200' F. with zero carbonate decomposition is approximately 425 B.t.u. per pound ( 3 ) . Decomposition of all the carbonates would result in an additional heat requirement of 238 B.t.u. per pound of shale, or slightly over half the amount required for retorting without carbonate decomposition. Figure 6 shows the effect of retorting on shale particle size during a typical run. Screen analyses of raw and spent shales show that some disintegration takes glace during retorting.
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Charged, Lb. Raw shale Steama Total 858.0 763.0 857.0 681.0 790.0 930.0 700.3
369.0 273.0 269.1 242.7 255.5 263.0 463.8
1227.0 1036.0 1126.1 923.7 1045.5 1193.0 1164.1
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Figure 7.
Effect of retorting on shale particle size
Distribution of organic matter in retorting products
Recovered, Lb.
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Effect of retorting temperature on carbonate decomposition and organic removal
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Spent shale
Water
744.4 613.3 723.7 575.8 646.1 736.4 500.2
373.0 303.5 287.8 244.3 261.9 273.6 418.5
Oil 69.5 52.3 50.8 27.8 34.0 36.6 18.1
Gas 34.4 38.6 68.5 73.2 116.8 184.0 235.6
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Total 1221.3 1007.7 1130.8 921.1 1058.8 1230.6 1172.4
Loss Lb. 5.7 28.3 4.75 2.6 13.35 37.6b 8.35
% 0.5 2.7 0.45 0.3 1.35 3.26 0.7b
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Table I11 shows the material balances obtained for this series of runs. Except for the relatively large gain for run 11 (1500' F.), probably due to shale holdup from run 10 (1100O F.) which showed a comparable loss, t h e excellent material balances obtained are indicative of the reproducibility of results obtainable in this equipment. Figure 7 shows the distribution of shale organic matter among the various products of retorting. I t also compares the distributions obtained a t different retorting temperatures with those obtained by Fischer assay retorting. SU-MMARY
Oil yields obtained by retorting in an entrained-solids system ranged from 55 pounds or 5.6 gallons per ton of 30-gallon-per-ton shale a t 1650" F. t o 168 pounds or 21.2 gallons per ton a t 1000° F. Based upon Fischer assay, oil yields ranged from 23.5% at 1650" F. to 77.2% a t 1000' F. if C4+ hydrocarbons are included. Yields of mineral-carbon dioxide-free gas varied from 70 pounds per ton of 30-gallon-per-ton shale a t 1000" F. to 417 pounds per ton a t 1650' F. Removal of organic matter from the shale ranged from 71 t o 86 weight %. Decomposition of the carbonates present in the shale varied from 4 weight yo,a t a retorting temperature of 1000" F., to 89% a t 1650' F. Screen analyses of the ran- and spent shales indicate that some disintegration occurs during retorting.
Vol. 47, No. 3
Excellent material balances n-ere obtained for this series of runs, losses varying from 0.3 to 2.7 TTeight % of the material charged. ACKiYOWLEDGMENT
This project was part of the Synthetic Liquid Fuels Program of the Bureau of Mines and was performed a t the Petroleum and Oil-Shale Experiment Station under the general direction of H. P. Rue and H. M. Thorne. Special thanks are due various members of the personnel of the station for their valuable assistance in carrying out this project. The work was done under a cooperative agreement between the University of Wyoming and t h e U. S. Department of the Interior, Bureau of Mines. LITERATURE CITED
(1) Cattell, R. A., Guthrie, Boyd, and Schramm, L. W., Oil Shale and
Cannel Coal, 2nd Conference,p. 345 (1951). ( 2 ) Guthrie, Boyd, and Klosky, Simon, U. S. Bur. Mines, liept. Invest. 4776 (1951). ( 3 ) Sohns, H. W., Mitchell, L. E., Cox, R. J., Barnet, W. I., and ENG.CHEM.,43,33 (1951). Murphy, W. I. R., IND. (4) Stanfield, K. E., andFrost, I. C., U. S. Bur. Nines, Rept. Invest.
4477 (1949). RECEIVEDfor review M a y 7, 1054, ACCEPTEDNovember 3, 1054. Presented before the Division of Gas and Fuel Chemistry as part of the Symposium on Synthetic Liquid Fuels and Chemicals a t the 125th Meeting of the AMERICAN CHEhrICAL SOCIETY, Kansas City, hlo., March 1984.
(Entrained-Solids Retorting of Colorado Oil Shale)
PRODUCT YIELDS AND PROPERTIES S. S. TIHEN, J. F. BROWN, H . B. JENSEN, P. R. TISOT, N. 31. RIELTON, d K D W. I. R. RIURPHY Petroleum and Oil-Shale Experiment Station, Bureau of Mines, Laramie, Wyo.
RJ
ETORTIXG oil shale in an entrained state ( 4 )permits control of composition as well as of quantity of volatile products, an advantage over most conventional retorting systems where quality cannot be controlled. However, these are not independent variables, and knowledge of the relationship between then1 and the retorting variables is iiiiport,ant in establishing optimuin retorting conditions. The purpose of the present investigation, conducted a t the Laramie, Wyo., station of the Bureau of Mines, rras to establish this relationship over the retortingtemperature range 1000" to 1650" F. SAMPLE PREPARATION
Two liquid-product streams vere collected from the retort: (1)a heavy oil together wit,h condensed entraining steam gathered from the contact condenser, the tube and shell condenser, and the mist separator, and (2) a light oil containing a small amount of condensed steam gathered from the aftercooler and the refrigerated condenser. The heavy-oil fraction mas dried by distillation, while the light oil was dried, and stabilized in a st,ill fitwd with a packed column and a refrigerated condenser. The stabilized light oil and the dried heavy oil were combined to form a composite sample representative of the oil produced in the retorting experiment. This composite was fractionated into a naphtha, cut at, 400" F. vapor temperature; a light gas oil, cut at 397" F. vapor temperature a t 40 mm.; Ftheavy gas oil, cut when the still-pot t,emperature reached 623 F. a t 3 t o 6 mm.; and the bottoms. These fract,ions were tested to determine their suit,ability as synthet,ic liquid fuels and t.o ascert,ain the effects of the retort temperature on their properties.
The gases froin the retort and from stabilizing the light oil were analyzed separately by mass spectrometry, and the calculated analysis of the total gas yield is reported here. PRODUCT YIELD
Although product yields, and composition, are affected by both temperature and residence t,ime, no attempt was made in this n-orlr to correct the data for the variations of the latter variablc. The effect of temperature on the yield of liquid products is shown in Figure 1. The highest yield of C;+ crude oil, approaching t h a t obtained from conventional retorts, vias obtained a t 1000" F. As the retort temperature vias raised, the yield of the Cs+ crude oil steadily decreased, as did that, of the C8 plus C4 saturates, which was about 1 gallon per ton of shale a t 1000" F. The production of C3 plus C4 olefins increased to a maximum a t about 1300' F., and the production of C3f crude was greatest a t 1100" to 1200" F. Production of lighter gases, including ethane, ethylene, methane, hydrogen, carbon monoside, and carbon dioxide, brought t h e total weight per cent yield after correction for mineral carbonat,e decomposition over most of the temperature range t o more than 100% of the Fischer assay oil plus gas yield. DISTRIBUTION ANI) QCALITY O F PRODUCTS
The volatility of the C j + oil was also affected by the retort temperature. Oils produced from Colorado shale by conven-
