., N-T-U Retorts,
Sm t
Bins. and Crushing Plant (leJt to r i g h t ) at I‘.S. lhiroau of Demonatration Plant, Rifle, Calo.
A S t af f-lndustrly WILLIAM Q. HULL Assmiom Editor
lllaboratiue Report
Mines
Oil-Shale
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BOYD GUTHRIE AND E. M. SIPPRELLE U. S. Bureou of Mines, Rifle, C o b .
in mhboration w i t h
T.
ever, with the discovery of large American petroleum fields, the enterpriaes failed to survive the resulting competition, and the distillation plants were compelled to close. Later some were remodeled into refineries for well petroleum. The processing of coal and shale into syntbetic liquid fuels then became a subject merely of academic interest. The annual per capita we of oil in the United States has increased from 4 to 14 barrels in the last 30 years. Natural gas consumption shows B similar etartliig growth from 7503 to 35,ooO cubic feet sinre 1920. During the same period, coal consumption dropped from 6 to 4.5 tons per person. However, the energy derived from coal in 1948 was approximately the same as in 1920. The trend toward greater usage of ail and gas, the reserves of which have limitations, has resulted in a change from the former academic interest in synthetic fuels to thorough investigations of the feasibilityof the development of a synthetic fuels industry. The United States Government 6rst became seriously concerned in the production of liquid fuels from shale and coal shortly after World War I, when a growing interest in the importance of liquid motor fuels was io evidence. In 1925, the Bureau of Mines conshcted an ail-shale experiment plant near Xifle, Colo., where fundamental work in the minina and retortima of Colorado ehale w~lswnduvted until 1929, when the plant ;as closed following the discovery of large oil 6clds in California, Oklahoma, and Texas, and an ahundanw, rather than a scarcity. uf petroleum was indicated. During World War 11, when the Cnitcd Statpa faced the poeaihility of a serious pemleum shortage, plans were made fur the Bureau of Mines t a conduct comprehensive studies of the technical urd economic problems in.
HE distillaboo of “an oyle from some kind of stone” wasde. ’ . . s c n W in a Bntish patent (8)in 1694. The reference is presumably to shale and is believed to be the first recorded interest in the subject (3). Even earlier, in the middle of the 14th century, the term “petroleum” was used in England in referring to oils derived from rocks (10). Thus, long before the beginning of our modern industry founded on flow oil, “petroleum” was a p plied to shale and similar rock oils, sod since the term is derived from the Latin pelra or rock, and oleum or oil, its earlier application was literally correct. However, the term has long been a m eiated with that mixture of hydrocarbans d e r k d in a liquid form from wells drilled into the earth’s surface. Oils derived from naturally occurring d i d formations are included today in the field of synthetic liquid fuels. The United States, endowed with abundant supplies of w t n rally occurring gas and petroleum, also has extensive deposits of oil &ale, coal, and other s b t i n g materials for the preparation of synthetic fuels. Although early American we of synthetic oil dates back as early as 1855 when the Mormons retorted oil ahale in Utah (l),interest in the development of a synthetic fuel i n d w try has been characterbed by revivals and subsidences beginning in Pennsvlvania in 1859. The with the diseoveni .. of Detroleum . fluctuating interpst wasa result of the phe~omrnalincrease in pemleum wage aud growth of the pcmleurir industry and the rver changing and c.onfiicting opinions of the extent of ow u o d pemleum mrrvcs. During thr derad? beginning with 18.50, mom than lifty plants were erected in the s t a t p ~along ihe Atlantic Coast to retort imporird Boghcad cod and local coals nnd shales, as well as plants fa treat the Albert Mines +halein Canada. How2
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January 1951
*
INDUSTRIAL A N D ENGINEERING CHEMISTRY
volved in the production of synthetic fuels. In 1944, Congress passed the Synthetic Liquid Fuels Act (18), authorizing the expenditure of $30,000,000 over a 5-year period, to construct and operate demonstration plants to produce synthetic liquid fuels from coal, oil shales, agricultural and forestry products, and other substances. The act further authorized the Secretary of the Interior, acting through the Bureau of Mines, to carry out the provisions of the act. Two extensions to the act have authorized the expenditure of 187,600,000over a total period of 11 years and increased its scope to include work on secondary recovery of petroleum. The Bureau of Mines delegated the responsibilities for work on agricultural and forestry products to the Department of Agriculture and work on secondary recovery to the Petroleum and Natural Gas Branch of the Fuels and Explosives Division of the Bureau of Mines. The Office of Synthetic Liquid Fuels was created as a branch of the fuels and explosives division to carry out the research and demonstration plant work on the production of synthetic liquid fuels from coal and oil shale. The United States Department of Agriculture is conducting research and developing methods for the production of alcohol and other liquid fuels from agricultural residues including corncobs and hulls of cottonseed, oats, and rice. A liquid fuels plant was constructed in 1946 on the site of the Northern Research Laboratories a t Peoria, Ill., in order that the programs of the two groups might be coordinated. Studies of the fermentation of pentose and dextrose sugars to liquid fuels are being made, and the various fuels produced are undergoing extensive testing. The secondary recovery phase of the program deals with stripper oil fields and refining processes. Bureau of Mines field headquarters, acting as centers of activities on secondary recovery research, include Bartlesville, Okla., Laramie, Wyo., San Francisco, Calif., Dallas, Tex., and Franklin, Pa. Measurable technical progress has been made to lessen the quantity of oil previously classed as unrecoverable in stripper fields and to improve the utilization potentialities of the so-called marginal crudes, especially those with a high sulfur content. The Officeof Synthetic Liquid Fuels established research laboratories a t Bruceton, Pa., Morgantown, W. Va., and Laramie, Wyo., and demonstration projects at Louisiana, Mo., and Rifle, Colo. The Bruceton laboratory carries on research work in connection with coal hydrogenation; the Morgantown laboratory devotes its efforts to synthesis gas production from coal; and the laboratory a t Laramie works on research problems concerned with oil shale and shale oil (14-16). The demonstration project a t Louisiana, Mo., works on coal and in reality consists of two demonstration plants employing two basically different processes for converting coal to liquid products; the direct hydrogenation or Burgess process and the gas synthesis or modified Fischer-
3
Tropsch process. The direct hydrogenation plant was dedicated May 7, 1949, and has been described in detail (7). The gas synthesis demonstration plant is scheduled to be in operation in 1950. The oil-shale demonstration project a t Rifle is divided into two major phases: one dealing with mining of the oil shale and the other with the extraction of the oil from the shale and refining of shale oil into liquid fuels (Figure 2). Research and demonstration activities are closely coordinated, with the research laboratories working in the main t o obtain basic research data and to develop processing techniques on a bench scale size, whereas the demonstration plants design, construct, and operate pilot plant processing units to obtain the required process and engineering data which are used to build and operate demonstration scale units of sufficient size that accurate designs and cost information can be projected to commercial size installations.
A 3-Inch Cube of Oil Shale Yields 6 Fluid Ounces of Shale Oil by Gas-Flow Process Shale assaya 38 gallons per ton by modified Fischer assay method
Some 150 cooperative agreements with industry, universities, research institutions, and the armed services on oil shale and shale-oil processing are in existence. These agreements in the main provide for furnishing raw materials for testing to the cooperators, and in return the Bureau of Mines is furnished the information resulting from these investigations. The bureau reviews and coordinates these results and disseminates the information obtained therefrom, with consent of the cooperators, to augment the general knowledge of the subject of oil shale. This article describes the work of the Bureau of Mines and work under a few cooperative agreements with private investigators on the recovery of liquid fuels from oil shale. OIL SHALE AND HISTORY OF SHALE-OIL RECOVERY
Oil shale has been defined by the American Society for Testing Materials (9)as: A compact rock of sedimentary origin, with ash content of more than 33% and containing organic matter that yields oil when destructively distilled but not appreciably when extracted with the ordiTABLEI. SUXMMARY OF DIRECT MININGCOSTSPERTONOF SHALE nary solvents for petroleum. (Top heading and middle bench test run) A large variety of rocklike Maintenance Bits materials occurring throughout Labor and Operatthe world and known by variand ExploDrill ing Labor Parts Power Fuel sivea Rod Other Total ous names including oil shale, $0.020 $0.04 Drillinga $0.018 torbanite, kukersite, and others .. ro:002 0.0s Blastinga 0,010 - 0.002 .. .. . . 0.037 have the common characteristic Loadingb 0.018 0.024 . . 0.004 .. . . 0 . 0 5 1 TransDortationb 0.023 of containing the large propor0.001 .. .. .. .. 0.018 Scaling 0,017 FoTemin and surveytion of carbonaceous oil-yield.. .. .. .. .. 0.013 Ing 0,013 ing material, as specified in the Electrical distribu.. .. .. .. 0.016 0.016 tion A.S.T.M. definition, but have .. .. 0 : 002 .. 0.004 0.007 Miscellaneous 0:001 ,. .. .. 0.019 0.019 Labor burdenc .. other characteristics that dif- - _ _ _ _ _ _ Total $0.100 $0.043 $0.009 $0.007 $0.072 $0,020 $m$0.292 ferentiate them. Howevw, oila Maintenance costs on thess units are based on calculated cost of continuous operation at the oil-shale mine for soaked sands such as are 1 year b M’aintenance costs on these units are based on the Der hour cost of maintenance parts and maintenance labor found in California, Utah, and as supplied by the manufacturers of the units. Disposition is 0 Labor burden based on actual operating and maintenance labor charged during the test run. Alberta, Can., are not oil shales based on 260 working days: annual leave, 10.0%; holidays (8 days leave with pay), 3.1%; sick leave, 4.0%: because the oil can be extracted total, 17.1%. by organic solvents. True oil
.. .. .. ..
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INDUSTRIAL AND ENGINEERING CHEMISTRY
shale is a fine-grained sedimentary rock with a laminar structure quite similar to slate. It varies in color from gray or bluish gray or brovm or reddish brown to almost black, and there is little outward appearance or feel of oiliness. Homver, rich, thin pieces can be ignited with a match and nil1 burn with a sooty flame and
Vol. 43. No. 1
a t the Pumpherston refinery. -1dditional commercial oil-fihalc industries exist today in Australia, Manchuria, Estonia, anti Sweden. DERIONSTRATIOS PIAS'r
The Bureau of Mines experimental oil-shale mine and demonstration plant are located on Kava1 Oil-Shale Reserves 1 and 3 a t Anvil Points, about 10 miles west, of Rifle, Colo. The mine is at, an altitude of 8200 feet and overlooks the plant site 3000 feet beloa.; these are connected by a 5.5-mile winding, mountain road. The mined shale is hauled in Diesel trucks to the crushing plant. From here the shale is available for retorting and the crude oil for storage and eventual refining. The oil-shale mine is in the Parachute member of the Green River formation, which extends t'hrough western Colorado into Utah and TTyoming. The main oil-shale measurc is near the t,op of the Green River formation and averages 500 feet in t'hickness. The shale yields approxiinabely I5 gallons or 0.36 barrel of shale oil per ton. The lower horizon of the 500-foot measure, called the Mahogmy ledge, varies from 50 to 100 feet in thickness and averages a yield of approximately 30 gallons or 0.7 harrel per ton. The oil-shale measure outcrops in bold cliffs for a distance of 145 miles in t,he area, and sampling of outcrops and core drilling iiidicate the oil-shale measure in the surrounding 1000-square mile area contains 300 billion barrels of shale oil. The Mahogany ledge alone, n-hich appears most practical for t,he first commercial exploitation, represents 100 billion barrels. Jlining
Underground Quarry Electric sho\el loading dump iruclr o n bench levcl; bench-level drilling operation (upper r i g h t ) ; portahle compressor and utiliti unit (upper / e f t )
petroleumlike odor. The shale contains up to 25y0 of a solid organic material knon-n as "kerogen" xhich x a s derived by cambining tn-o Greek \voids: meaning "producer of wax." Kerogen is a complex organic niixt,ure and not a definite chemical compound; and the kerogen ccntent of different shales varies considerably (18). The kerogens have the common property of reacting to form a liquid hydrocarbon oil on distillation of the rock. Oil vapors appear a t temperatures of 482" to 662' F., and all kerogen is converted if t,he temperature is increased t,o 842" to 1022" F. Oil shale is distributed in many parts of the world; the composition, properties, and oil yields of deposits vary ividely as shown in Tables I, 11, and I11 of Thorne et al. (16) in which Colorado ahale is compared n-ith several foreign shales. France is credited n-ith having developed the first commerc,ial exploitation of oil shale. Using the process patented by Selligue (13),in vihich superb-eated steam is t,he source of heat for retorting, a French shale-oil industry had its birt,hin 1839 and expanded to about 1865, n-hen the lower cost of imported American products threat,ened the industry. Hon-ever, subsequent tariff protection has pernlitted its survival to the present day. Follo~~ing shortly after the beginning of the industry in France, commercial shale oil extraction was started in Scotland; the first establishment, treating shale exclusively in Broxburri in 1859. James Young (1811-83) developed an int,ermitt,ent horizontal type retort in which oil shale was dry dist,illed a t a, low temperature, and shortly after in 1860 the forerunners of the vertical type retort, in use today, made their appearance. Twelve mines are in operation a t the present time and supply shale to five crude oil works producing crude oil, naphtha, and ammonium sulfate. The crude oil and naphtha are processed t o marketable products
Lon- cost iiiining of oil shale was the first. problem to be solved in order that a commercial industry might receive practical consideration. The experimental mine has adopted surface mining practices to a great degree, since mining costs are considerablv lower in quarries and open-cut mines; the operating mine is rcferred to as the "underground quarry." In the actual mining operation, entries are driven into the oil shale from t,he outcrop of the Mahogany ledge. The mine is laid out with BO-foot-square pillars t o support t'hc overlying formation, and the pillars are spaced 60 feet apart in both directions and staggered in one direction, as shom-n in Figure 1. A loose1,y cemented bedding plane exists a t the top of the Mahogany ledge, and the rock above this parting is a low grade marlstone of sufficient strength to serve as a roof stone Tvithout any t,imbnriiig or roof supports what,soever. A test, room SO feet wide and 100 fwt, long stands unsupported, and from accurate microseismic noise level readings and roof and floor convergence measurements there has been no indication of failure of the roof stone to datp. The
TABLE 11. PRODLTT~OK ( T o p heading and middle bench te.-t. r u n )
Tons mined in 20 shifts Labor Tons per 8-hour man-shift (underground labor) Tons per 8-hour man-shift (total labor force, including direct supervision engineering and all maintenance) 1,abor percentage of total direct cost Power and supply items Power, kw.-hr. per ton Drilling Loading Utilities Tons broken pes pound of exp1osii.e Tons broken per foot of drill hole Feet of drill hole per drill bit Feet of drill hole per drill rod used Tons of oil sha!e transported per gallon of fuel used Gallons of mater per ton Drilling Wetting broken oil shale Spraying road
32,560 148.2
118.1 43.8
0.321 0.223 0,164
0,708
2.54
1.986 1171 513
27.66 I .75 0.377 0,773 0.398
January 1951
INDUSTRIAL A N D E N G I N E E R I N G C H E M I S T R Y
room is currently being lengthened to 200 feet and will be widened to 90 feet in the near future. Advance top-level headings 60 feet wide by 27 feet high are first driven immediately under the roof stone by means of horizontal blast hole drilling and blasting. In a commercial operation, the remaining shale would be mined by following the advance headingq with 22-foot benches similar to quarry operations. I n the experimental mine, one bench is mined, since it is considered that costs and techniques established on the middle level will be the same as in the third level.
X goal of a minimum of 100 tons per man-shift was set up. It \vas established that standard equipment would be adequate for loading and transporting the broken oil shale, but it was evident that convrntional drilling and blasting practices would have to be modified in order that the required tonnage per man-shift might be realized. A unique heading jumbo was developed for drilling horizontal blast holes. The unit consists of two platforms mounted 011 a framework a t the rear of a Diesel truck. Each platform has two 4-inch percussion drills mounted on 16-foot feed slides. The vertical inclinations of the feed slides are controlled by screws and ratchets; air hoists are used for raising and lowering the platforms; and spur gear devices permit swinging the platforms to various horizontal angles. A water tank and air hoist are mounted on the truck. Preparatory to drilling, it is only necessary to connect a 3-inch air hose. The four drills mounted on the carriage are operated by two men. By use of the multiple-drill carriage, two miners drill out a round comprising seventy-two 15-foot holes in less than 6 hours, breaking nearly 1700 tons of shale. A second drilling rig has been developed for drilling vertical holes on benches. Similar to the heading carriage, it mounts four 16-foot drill feeds, each carrying a 4-inch percussion drill. A Diesel tractor forms a mobile base for the rig. The carriage is operated by two men who drill a bench round consisting of fortyeight 22-foot holes in approximately 7.5 hours. Each vertical drill round breaks approximately 3400 tons of shale. The horizontal blast holes, 25 feet above the floor in the top headings, required the development of a special piece of equipment for charging. The unit consists of a 5 X 10 foot wooden platform mounted on a fork-lift truck. The truck, powered by a Diesel engine, has a power hoist for raising and lowering the platform from which the powdermen charge the explosive into the blast holes. A charge of 680 pounds of 45% semigelatin dynamite in l7/8 X 12 inch cartridges is required to blast a top level heading round. A standard 2.5-yard electric shovel with a short boom to permit Tvorking under a %-foot height is used for loading the broken shale. Since shale is relatively light in weight, averaging 15 cubic feet to the ton, the 2 5-yard dipper was replaced with one of 3cubic yard capacity. The shovel handles as much as 300 tons of shale per hour. Three &ton Diesel end-dump trucks are used for transporting the shale, which is loaded directly into the trucks by the shovel. A caterpillar bulldozer is used for cleanup work during the loading operations. Water for n rtting down the broken piles of stone and for spraying the roadqays is supplied from a water truck with a 700-gallon tank and a high pressure pump. Drilling water is also supplied by this truck. After each blast loose rock must be scaled from the heading face. The roof and the pillars in other parts of the active mine workings are also inspected and scaled periodically. Another special unit of equipment has been developed for this purpose. It consists of a telescopic mast mounted on a fork-lift truck. With the tower fully extended, the platform is 65 feet above the mine floor, and the scaling rig can be used on any level of the oil-shale mine. Two men working on the platform pry loose lock from the roof and upper parts of pillars by means of aluminum rods with steel tips. A small percussion drill is used foi drilling loose slabs of rock not easily removed. An early study showed that the cost of laying and moving air and water lines on the advancing levels of the underground quarry nould be a considerable item of expense; air and water lines xould interfere with other work; and pressure lossss would reduce drilling speed with pneumatic drills. T o overcome these difficulties, a movable compressor assembly was designed. The
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utility station is constructed on a 30-ton trailer, 30 feet long and 12 feet wide. I t is equipped with steering dollies at both ends and may be towed from either. The trailer carries two 770-cubic foot-per-minute compressors, a 2500-gallon water tank, and a 200-cubic foot air receiver. The compressors are driven by two 150 hp., 2300-volt electric motors. The assembly is operated by the mine mechanic who also maintains other mining equipment underground. Water uspd in the mine is supplied through a diamond drill hole from a 10,000-gallon tank located on a plateau
Figure 1. Method of Mining Developed in Bureau of Mines Underground Quarry
above the cliffs in which the mine is located. Two earthen dams, capable of impounding 700,000 gallons of water, have been constructed on the plateau. Water for the housing area and plant is taken from the nearby Colorado River. Production Test R u n
In the autumn of 1949, a production t2st run was conducted utilizing the mining practices that had been developed and the equipment that has been described. During this test run, the top level was mined for 2 weeks and a bench level for the following 2 weeks, since sufficient equipment was not available t o operate both levels concurrently. The operational procedures during the test run were identical to those that would be employed in one unit of a commercial mine, but do not necessarily repre-ent the optimum results that ultimately may be obtained. The toplevel mining crew consisted of a total of thirteen men, including one shovel operator, one bulldozer operator, three truck drivers, two drillers, two blasters, two scalers, one mechanic, and one foreman. A labor crew of eleven men worked the bench level. Tables I and I1 show summaries of costs and production during the test run. Mining Rehearch
An extensive research program is being conducted at the oilshale mine to obtain solutions to several significant problems, all of which will contribute to further lowering of mining costs and improvements in mining techniques. At the present time, efforts are being concentrated in four fields: 1. 2. 3. ment 4.
Development of a successful rotary drill Improvement in blasting technique Development of more efficient underground loading equipFurther study of roof and pillar stresses
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 43, No. 1
January 1951
INDUSTRIAL A N D ENGINEERING CHEMISTRY
1
Crushing
The &st step in the preparation of the oil shale from the mine is the reduction of the shale to proper size for various retorting procems. Retorting requirements dictated that the crushing plant be able to crush all existing grades of shale from lean to rich and to produce a crushed shale of &inch maximum siSe a t a rate of 30 to 60tons per hour. The shale resulting from bl& ing in the mine ranges in size from dust to 75 inches, the larger pieces being of cubical or 56 slab form. A maximum particle size of 24 X 24 x 18 inches was eatabliied for the crushing plant and over-rb? pieces are broken to this size
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before delivery to the plant. The maximum crushing plant output is 80 tons per hour, depending on the grade and particle Size range of the crushed oil shale produced. The nature 6f retorting characteristics indicate^ that a crushed Pilot Plant Gas-Flow R e t o n i n g Proms shale as near cubical in form an possible, with R a O m n g r a r s l is at leftbodinstmmsnt pndli t u b d u o o n d - ~ minimum henes, is desirable. equipmanf at -ht The crushing plant includes primary, see ondary, and tertiary crushers. Ore is unthe retorting equipment (18). One property which varies widely loaded from mine trucks directly i n b a receiver hopper. An among different shalea is tbe tendency of a ahale t o agglomerate apron feeder carries the shale from the hopper to the primary when heated. The differencesin the mineral carbonate and orcrusher, which is a double-toggle type jaw crusher with 36 X ganic composition of the kerogen are at leaat partly responsible 42 inches intake. The jaw crusher opening can be varied from for this phenomenon. This coking and clinkering tendency p m 4 to 6 inches giving product sizes within these ranges includdominates in Green River shales a w y i n g more than 30 gallone ing approximately 15% avers& above maximum opening. The of oil per ton but is of minor coneideration in retorting some capacity is 100 tons per hour. Belt wnveyers transfer the shales, auch a8 Swedish alum shales. Unlees the temperatures crushed shale to a twodecked vibrating sereener above the secare controlled accurately during retorting, shales having a proondary crusher. The particle size range de-d in the crushed nounced coking tendency will produce oil-free shale residues that product is obtained by using semens of the proper mesh on the will clog the discharge mechanisms of a continuous retort. The upper and lower decks. The fines pa-g thmugh both screens presence of relatively large p-'^"*Lages of mineral carbonates in go to a belt conveyer below and are discharged to a stock pile to await future retmtbg studies or to be used for grading and surfacing of roads in the plant area. Material passing through the upper screen and retaiied on the l o r n Bereen is conveyed to om of ,$he 15o-toa storage b i m The materjal retained on the upper 8 c m is wnveyed to the sewndary d e r , which is a Blake-type, all-steel, single-toggle, roller-bearing jaw crusher. The intake is 10 X 30inches and jaw Srping is 0.5 inch with dosed jaw opening ranging from 1to 6 inches. The capacity is 15 to 30 tons per hour. The discharge from the secondary crusher is returned to the head of the vibrating sereens hy a bucket conveyer and recycled through the semning operation. A tertiary cruaber if provided to supply extra-fine shale for experimental $ot plant retorting owrations. It is a gearless, lowhead gyratory d e r with maximum receiving opening of 3 inches and delivers 20 tons of minus &mesh crushed shale per hour. RetortiIIg
When oil shale is destructively distilled, the evolution of oil from the kerogen takes place in two stages (If). A primary decomposition occurs, in which the insoluble kerogen changes into a soluble d i d , or semisolid, bitumen. The intermediate bitumen is unstable and a secondary decomposition changes it into lighter oils of m a t e r stgbility and higher saturation. The characteristics of,oils.mauered.fmm different shale deposits vary greatly. Like petroleum, they may he classified as of para5nic, asphaltic, or mixed base. The oils from Scottiah and Tasmanian shales are of para&c base; oils from Nevada shales are of parafh i c b m , fmm Kentucky of asphaltic base, and from &lorado and Utah, intermediate. The yields of oil from various oil shales and from varioua locations and strata of the same deposit may vary mafly. %me of the properties have very definite effects on retorting, and these must be conaidered in the design of
.,
oil shale limits the heat efficiency of those r e t o d g pmcesses in which the shale is heated to temperatnres su5ciently high for carbonate dewmposition. This dewmposition oocurs at elevated temperatures yielding carbon dioxide amounting to about 20% of the weight of the raw shale. Since the deTmpesitions 81'e endothermic and it is highly desirable that the heat for retorting he supplied from a portion of the retort products, auch as gas or fixed carbon on the spent shale,delicate contml of retorting temperatures is necessary.
INDUSTRIAL A N D ENG INEERING CHEMISTRY
Vol. 43, No. 1
advantages include a comparatively low production rate in relation to capital expenditure and required operating labor and relai tively inefficient heat transfer. In Scotland, the production of good vielde of ammonia, in addition to oil, offaetathe d i d v a n e age of inefficient heat transfer. During 1946, the Bureau of Mines wnducted experimental o p eration with a low temperature coal-carbonization pilot plant known as the Hayes retort. This work wss done in eooperatiou with the Colorado Fuel & Iron Corp. at the company's plant in Pueblo, Colo. The testa were primarily made to produce crude shale oil for laboratory investigations prior to the completion of the retorting plant a t Ri0e. The Hayes retort consists e w n tially of a rotating tube containing a screw Conveyer. The retort tube is set in a furnace and the oil shale is carried through the tube by the screw conveyer. Oil vapors are drawn from the r e tart into a coudensing system by an exhauster operating at a slight suction. Although no difficulties were encountered due to coking, yields were poor and the shale oil contained large quautities of duet formed by the breakage of shale as it traveled along the screw conveyer. Heat transfer through the metal shell wan also slow, and high capital and operating coats precluded cousid-
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F i v r e 4. Se&ionnl View of N-T-U Retort Vessel Although hundreds of retorts have been designed and patented, they may be divided into four major classes baaed on the method by which heat is applied to produce oil, as follows: Class I
Method of Heat Application H u t is t r a m f e d t o theahale through B wall
EXample Pumphemton; Ha-; Berr
I11
H u t is t m m f d to the &le by sssiw . leviousl heated or &qui& t k d &e shale bed H u t i trand-d to the a h i s by intd,uction of hot soli& into the retortlnz bed .
6aedi.h Industrial; Buns" of Mines 086 Flow; Rovatar Sttandad Oil Co. FluidFloa. Buraau ol Mi& Hot-blidaContaat
IV
A number of retorts of the various classes have been Btudied and tested at the Bureau of Mines o i l d a l e demonstration plant. class I Retorts. A Pumpheraton retort was used in the pilot plant investigations at Rifle from 1925-29 and WBE operated experimentally to determine the suitability of this retort for proceae ing Green River oil shale. Pumpherstons have been ueed to produce shale oil and ammonia in Sootland for over 50 years and have also been used in France and Australia. The rctort consists baaically of a cylindrical inner "easel of firebrick which itr surrounded by an outer limbrick shell. The space between the two strwturelr is divided into several comhuatinn chambers. The inner vessel is charged with oil shale, and retorting heat is supplied from burning th? e d shale gas, which is re: wvered during the retorting operabon rn the wmhuation chambers. The heat is tranaferred through the inner fire wall to the shale. Raw shale is fed into the top of the retort intermittent1 +d discharged $ontinuonsly from the bottom. Steam is ad: rmtted to the Wtom of the retort, flows u thmugh the shale be4 and leaven the retort with the shale o# vapors and gases which are drawn hy turhoexhansters through the condensing and scrubbing system. I ~
~
~
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Nonw!&g k p r i c m shale p r o g r e a d satisfactorily in the Pumpherstnn a d recovery of oil averaged 89.3% of the m y value. However, the retort became plugged when richer shalea were retorted, and the Pumpheraton WBE found generally unsstS a c t o r y for prucedng Green River oil shale. Additional die
Class II Retorts. The Nevada-Texas-Utah retort, commonly called the N-T-U but also known a8 the Dundae-Howe retort, wan invented and developed in the United States (6)and has been uaed in commercial operations in Austrdia and ERgland. Two N-T-U's were constructed a t the Oil-Shale Demonstration Plant for the purpose of studying retorting rates, heat t r a d e r , and other thermodynamic relationship with plant sire equipment and to develop retorting techniques, h i n pemnnel, and produce shale oil for other experimental operations. It is to be emphasiaed that the b a t h N-T-U is not wnaidered or suggested as a practical retort for a commercisl operation in the United States, hut it has been uaed as a tool for gathering fnndamental data. Nevertheleae, it has played an importeat role in providing a fund of plant operating experience that is applicable to other processes, and ita we has contrihuted greatly to a better knowledge of shale handling, maintenance of equipment, and design of equipment to meet the peculiar need8 of Colorado oil ahsle and shale oil. The N-T-U retorting and condensing system wnsists of the retort, a shale trap, a contact condensing system, a reflux accumu-
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January 1951
latotor, air and gas blowers, and a wastegasstack (Figure 3). The retort is a cylindrical steel vessel with tapered firebrick lining and dome (Figure 4). The inside diameter of the retort is 10 feet 4 inches, tapering to 8 feet 8 inches a t the top, with a dome radius of 4 feet 4 inches and an over-a11 height of 22 feet. A manhole is provided a t the top for charging, and the bottom is closed by a hinged grate operated through a toggle mechanism and carriage
7iigure
6,
F l o w Diagram of Gas Gmhuslion
Retorting Plant
by B hydraulic cylinder. Each of the two retorts holds approximately 40 tons of shale. A gas seal between the grate and retort is provided hy filling a channel-shaped ring on the grate periphery with clay-oil luting.
'
demonstrated at the company's Wihnington, Calif., refinery. The demonetration waa carried out under simulated commercial plant conditions, and representatives from the Bureau of Mines and other governmental agencies as well as observers from numerone oil and construction companies in the United States, Brazil, and England were in attendance. The shale pmceased in the retort was from the Green River formation in Colorado and was ohtamed through . the cooperation of the Bureau of Mines.
Process flow and pertinent structural features of the semiworks Union retort me illustrated d ammatidly in Figure 5. Raw shale is fed upward through th%ottomof the retortin vessel b a hydraulically operated piston which oscillates throug%an arc {etween the shale charge hopper and the retort. The entire feeding mechanism is submer d in oil to the level of the transfer line, providing both a IiquiTseal to prevent air from entering thro h the feed hopper and lubrication of the moving parts. S 8 e moves countercurrent to a stream of air which enters through the top of the vessel. Residual carbon in the shale$ burned m the upper portion of the retort, and the hot combusbon gases f l o m g down through the shale bed heat the incoming shale. As the shale moves upward through the retort, it passes through a cool zone where oil condenses, then to a retorting mue where the temperature is raised to 900' F., to R combustion zone where residual carbon is burned from the oil-free material and the temperature raised to2000" V., and finally through a zone at the top of the retort where the spent shale is cooled to 800" F. by the incoming air, and the air is thereby reheated. Li uid distillation products are withdrawn from tEe bottom of &e unit, and ash and clinker are removed overhead by a revolving plow mechanism.
The N-T-U batch-type retort is operated on a cycle which consista of charging, runomg, and discharging. After the retort is charged with approximately 40 tons of shale (-8.5 to +0.5 inch) a fire is started on the top of the shale bed using approximateiy 200 ounds of oil-soaked kindling. The manhole 18 left open and a &aft is drawn downward throu h the shale bed by the gas blower. As soon as combustion is un&r way, the manhole is closed, and air is forced into the top p f the retort with mr blower. The air stream is d h t e d m t h combustmn gas m the retort. Excess gaa is vented to the atmosphere through the waste gas smek. Rriorting takes place helow the combustion zone brmusr of thP hot gases passiug downward through the shale bed. I a rlie retortin. zone. shale-il vawr. fixed mms. and coke arc formed by d e s t k t i v k distillationbf the ker&en,'and the coke remaining in the shale serves as fuel when the downward moving combustion eone reaches it. %me of the oil va or condenses on the cold shale in the lower a r t of the retort and% ?moved from the system through the shaE trap. The condensedod removed at this point amounts to about half of the oil produced, the balance being recovered in the condeneing system. After the c h a r r has heen retorted, the blowers are shut off and the spent shale 18 discharged by opening the hinged bottom. Following experimental tests, the N-T-U retorts were operated on a production basis to determine the signiiicance of operating variables and their relationship to the entire operation. At a rerting rate of 35 pounds of ahale per hour per quare foot of retort 088 section, a maximum recovery efficiency of 90% of Fimher y wa8 obtained. The best oil recovery rate was 110 gallons our, which waa obtained with no recycle gas and an air rate superficial cubic feet per minute corresponding to the o p gas velocity of 15 superficial cubic feet per minute per foot of cromctional m a . The superficial gas velocity is calculated at standard cenditions assuming the retort empty. In retorting systems ,such as the N-T-U and Uniou Oil Co. proceaees, definite benefitsarerealizedthro~the "down burning" of the oil shale, These advantages include: (1) gravity flow of the oil produced to the product withdrawal point at the hottomof the retort; (2) better heat economy by concurrent condensation of the'oil vapom on the cold shale in the area below the combustion aone and preheating of the shale in this area; and (3) better heat t r a d e r to those ahale particles which are wet with shale oil. Union Oil Co. Retort. A continuaus, internally fired, underfwd retort has been developed by the Union Oil &. of California, and a 6Chton semiworks unit has recently been formally
9
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A. .I** I.. O I l l U L *nr*T
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..WT
?L*n
,*.LE
Figure 7.
Gas Combustion OilShale Retort
The Union Oil Go. retort represents a distinct depanure from conventional retorting proceases and has the advantage of requiring no condensing equipment and no combustion or heat transfer facilities outside the retort. I n addition, it has been demonstrated that the full range of particle size and h e s probe efficiently proceaeed in the unit. duced in crushing of shale The ability of the Union retort to tolerate hea, which normally c a w plugging and excessive clinker formation, is attributable to the continuous nature of the moving bed and the action of the plows which control particle Pj5e in the m a of clinker formation, termed the plastic ash zone. These advantages contribute niate rially to a low capital i n w t m e n t in a commercial retorting plant &B well a8 to decreased mining costa and handling prohlem-
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Vol. 43, No. I
INDUSTRIAL AND ENGINEERING CHEMISTRY
10
TaBLE
111. GAS COMBUSTION RETORTING DATASUMMARY (Heat and material balances)
R u n KO. 60 Material balances (Ib./ton raw shale) Lb./ton % In R a w shale 2000 91.7 182 8.3 Air Total 2182 100.0 out Sgentshaleash 1740 79.8 Product gases 218 10.0 Oil 76 3.5 0,2 Condensed water 4 Unaccounted for 6.5 Total 2182 1 0 0 . 0 Heat Balances (B.t.u./ton raw shale) B.t.u./ ton R In Heat of combustion 254000 91.2 Sensible heat of air 0 0 Sensible heat of 24400 8~ .8 recycle ~ Total 278400 1 0 0 . 0
61 _____
62
Lb./ton 2000
88.8
~-'2254 _254 _ _ _ 1_1_. 2 100.0
out Sensible heat of ash Sensible heat of eas Sensible heat of liquid Heat of vaporization of H20 Heat of reaction of kerogen Carbonate decomposition Heat loss b y diff. Total
1650 354 164 15 -71 2254
73.3 15.7 7.3 0.7 3.0 100.0
Lb./ton
Lb./ton
2000
85.2 2000 1 4 . 8~ 427 100.0 2427
350 ~ 2350
1542 532 152 10
65.7 27.6 6.5 0.2
2350
100.0
114
64 65 _______-
63
~
1554 618 146 11 __ 98 2427
%
Lb./ton
82.4 -1 7 . 6 100.0 64.0 25.5 6.0 0.5 4.0 100.0 ~
%
Lb./ton
%
1548 597 151 11 __ 69 2376
65.2 25.1 6.4 0.J 2.8 100.0
1672 71.8 500 21.5 158 6.8 5 0.2 __ -6 __ -0.3 2329 1 0 0 . 0
-
% '
B.t.u./ ton
70
B.t.u./ ton
76
355000
94.2
487600
95.7
595000
97.1
543000
96.5
0
0
0
0
0
0
0
2.9 _ 20000 _ _
1614 558 I54 9 -15 2320 ~
563000
2000
90.2
220 9.8 __--2220 100.0 1738 78.3 332 l5,O 165 7.4 4 0.2 __ -19 ___ -0.9 2220 100.0
B.t.u./ ton
%
B.t.u./ ton
70
456000
95.8
458000
95.8
309000
92.5
0
0
0
_4 . 2_ 20300 _
4.2 _
0
1 0 0 . 0 478300
100.0
a
0
25000_ _ 334000
7 ._ 5 100.0
30450
10.9
54680
14.5
40100
7.9
78200
12.8
69600
12.4
41900
8.8
53500
11.2
34760
10.4
40500
14.6
34700
9.2
39100
7.7
37400
6.1
38400
6.8
36600
7.7
33500
7.0
44000
13.2
2591
0.9
6006
1.6
5240
1.0
6626
1.1
5000
0.9
5000
1.1
5000
1.0
5600
1.7
37800
13.6
28000
7.4
30600
6.0
28400
4.6
29900
5.2
32700
6.9
40500
8.5
36800
11.0
25 I00
9 0
41800
11.1
40400
7.9
39400
6.4
41200
87600
31.5
120000
31.8
180700
35.5
264800
43.2
234000
54359 278400
2 58 _ 144900 19.5 91815 _ 2 4_ . 4 _173510 _ - - _3_4 . 0_ 158054 100.0 376900 100.0 509650 100.0 61.2880 100.0 563000
through utilization of the fines. A description of the 50-ton semiworks unit has been published ( 1 2 ) . Gas Combustion Retorting Process. The Bureau of Mines is currently investigating a vertical countercurrent retorting process in a 500-pound-per-hour pilot plant. This process has several novel features that depart from former concepts of retorting. Although simple mechanically, it is capable of a high yield of liquid products a t high shale thioughput rates. It is indicated that cost figures for the process will be less than for other retorting processes studied to date.
A schematic flow diagram of the pilot plant process is shown in Figure 6. A portion of the product gases is introduced a t the bottom of the retorting vessel. These gases pass up through the bed of descending hot spent shale and recover the sensible heat from this material. A portion of the preheated gases then passes up through the spent shale tube and is mixed with air introduced through opposite sides of the tube This mixture of air and gases passes out under the cone into the shale bed where combustion of the combustible constituents in the gas and a small amount of the carbonaceous residue remaining on the spent shale takes place. Enough air is introduced to provide the minimum of heat required by the process, The resultant hot flue gases from the combustion section pass up through the shale bed and cause the shale to be heated to retorting temperature. The oil is released from the shale presumably as a vapor and is swept away by the flue gas stream to the heat exchange zone where the gas stream is cooled; most of the oil vapors are condensed as a very fine stable mist and are carried out of the retort by the gas stream in this form. A small portion of the oil vapors condenses on the surface of the shale particles, This material is revaporized in the retorting zone. The liquid products are recovered from the gas stream by passing the mixture through a centrifugal separator, a positive displacement blower, a second centrifugal separator, and a concurrent water scrubber, Ordinarily 25 to 3594 of the liquid products are recovered in the first separator, 60 to 70Tc in the second separator, and 2 to 10% in the concurrent water scrubber. Since some gas is produced in the process, part of the gas stream must be vented, and the balance is recycled.
7.3
42200
12.6
I29000
27.0
105700
31.6
2 5 . 8 _123400 ______2 - -5-. 8- 175400 100.0 476000 100.0 478300
36.6 100.0
64940 334000
19.5 100.0
41.6
40400 196000
8.5 41.2
41400
8.7
_
70
%
20000 _ 476000
100.0
85.8 14.2 100.0
_
B.t.u./ ton
0
3_ .5 100.0
69.6 24.1 6.6 0.4 ___ -0.7 100.0
~~
67 ~
Lb./ton
2000 329 2329
B.t.u./ ton
17880 _ 100.0 612880
Lb./ton
84.2 2000 86.2 15.8_ _ 320 _ - 13.8 100.0 2320 100.0
%
-4 . 3 -
%
_
2000 376 _ 2376
~~
B .t .u./ ton
21900 8 22150 ~ 5 .~ ~ 376900 100.0 509660
-____ 66
The essential features of the retorting vessel are shown in Figure 7 . The vessel proper consists of three flanged steel sections 30 inches in diameter lined on the inside with 5 inches of insulating refractory and 2.5 inches of insulation on the outside. The total height of the three sections is 12 feet. However, a %inch steel maring plate is attached to the lower flange and an 8-inch diameter feed leg extends down 18inches from the top so that the depth of the shale bed is actuallv about 11feet. Raw shale is charged through twin hoppers mounted on the t o p of the retorting vessel. Each of the hoppers has a capacity of about 350 pounds of raw shale. The raw shale is conveyed from floor level in buckets to the hopper platform by use of an electric hoist mounted on the roof beams. The hoppers discharge the raw shale into the vessel through an 8-inch feed pipe. Shale ash is discharged from the retorting vessel by means of a rotating disk driven by a variable speed direct current motor. The disk is enclosed in a pressure-tight housing into which the recycle gases are injected. The ash is carried to a common discharge point in the housing by chains attached to the outer edge of the disk. The ash drops through a slide valve into removable 55-gallon drums flanged to the slide valve for easy removal. Two centrifugal separators are used in the recovery system for separating the product oil from the gas stream. A packed concurrent water scrubber is located in the recovery system after the second centrifugal separator. The capacity of the two blowers, which are operated in parallel, limits the maximum shale rate a t which the retort can be operated a t the present time. Another distinct advantage of the process is that elaborate instrumentation is not required. Two temperature strip-chart recorders are used for the necessary temperature measurements and all process flows and pressures are measured by U-type manometers, Gas flows and pressures are controlled by manual positioning of butterfly valves.
_
-
During normal operation of the pilot plant unit, the air and recycle gas rates are maintained constant. Since the air rate is constant, the amount of heat released from combustion is also approximately constant. The tem erature of the product stream leaving the retort can thus {e controlled indirectly by changing the temperature of the ash discharged. This is accomplished by varying the rate a t which ash is discharged from the retort. The net effect is to move the temperature profile of the retort up or down. Shale from the upper bench of the experimental mine waR used for the gas combustion runs reported here since it was available a t the time. However, middle-bench shale has been successfully processed in the countercurrent retort and no operational difficulties were encountered. Operating and yield data for a series of pilot plant runs have been correlated and are presented in Figures 8 through 11. Figure 8 shows that for a constant recycle gas-air ratio and constant shale grade increasing the space velocity of the gases out of the retort causes a gradual increase in the efficiency of the liquid oil recovery from the shale. The shale rate increases linearly and the pressure drop through the bed increases a t a greater rate. From these data it is believed that a satisfactory oil recovery could be realized a t much higher shale rates than those studied to date. The effect of space velocity on the gas volumes and mineral
carbonate decomposition is shown in Figure 9. The curves indicate that a t the higher space velocities less heat input is required; this is reflected in the lower air requirements and gas volumes. Likewise, a t the higher space velocities the shale is subjected to the combustion zone temperature for a shorter period of time and less mineral carbonates are decomposed. I n Figure 10 the effect of recycle gas-to-air ratio on the oil yield, spent-shale assay, and the shale rate is shown. The oil yield improves a t a gradual rate with increasing recycle gas-toair ratio until a point is reached a t which the bed temperatures drop to such a level that complete retorting is not realized. Although the inlet gas space velocity was constant for these runs the outlet gas velocity was not, and this also has influenced the shape of the shale rate relationship. However, it is apparent that the ratio can be varied over a wide range without influencing the oil yields appreciably. The relationship of other process variables are shown in Figure 11. Material and heat balances for each of the runs are presented in Table 111. Class I11 Retorts. A Ropster retort was the first in this class to be operated a t the oil-shale demonstration plant. This is a batch process in which the uncondensed gas from the distillation
Aerial View of N-T-U Retorts Crushing plant at right; three raw shale storage bins are between mushing plant and retorts
12
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE IV. GAS-FLOWRETORTIXG SLXl\L4RY (Effect of recycle-gas inlet temperature on retorting conditions a n d yields) Low High TemperaTemperature ture Shale processed 21.5 21.5 Fisher assay, gal./ton 16.9 16.9 Mineral COz content, wt. % 0.5-1.0 0.5-1.0 Particle m e , inches Retorting conditions 12.4 18.6 Shale charge rate, tons/day 40 60 Shale residence time, niin. 0 5 0.5 Recycle-gas \ elocity5, ft.isec. 50 8 34.4 Recycle-gas, thous. stand. cu. ft./ton shale 1073 1360 Recycle-gas inlet temperature, F. 95.5 1020 Temperature retorted shale, O F. 317 283 Heat transferred to shale, B.t.u./lb. shale Heat-transfer rate, B.t.u./lb. shale/min. 4 8 7.9 residence time Product yields 107 100 Oil6 (Fischer assay), vol. 70 22.9 21 a Oil, gal./ton 833 1277 Gas, cu. ft./ton shale Product gas coiiiponents 288 401 Hydrogen Hydrocarbons C (principally methane) 23 1 171 38 33 Unsaturates 113 352 Carbon monoxide 3 1 Hydrogen sulfide 80 193 Carbon dioxide TO 123 Water vapor a Velocity of gas corrected to standard conditions paqsing through empty retort. b Water- a n d sediment-free basis. C 'From Orsat analysis; other alkanes are possibly present, b u t mass spectrometer analyses on similar gases shorn methane t o predominate.
of shale is circulated through a heater, the retort, and the oil ITcovery system. 9 pilot plant was operated in 1948 and the results have been reported in considerable detail ( 1 7 ) . T h e Royster process is not considered to have commercial possibilities, principally because it is a batch operation. However, it. led to the development of a similar process which is continuous in operat,ion and has definite commercial possibilities; it is known as the gas-floiT retorting system. The gas-flow process is shown in Figure 12. Crushed r a ~ shale, 0.25 to 1 inch in particle size, enters the top of the retort through a rotary gas seal. The shale flows by gravity t.hrough the retorting vessel, which is 10 feet high and 18 X 12 inches in cross sect,ion; it has a capacity of 1500 pounds per hour (Figure 13). Product gases, raised to a temperature of 1075" to 1350" F. in the propane-fired gas heater, enter the retort through a gasdistribution manifold and flow transversely through the moving bed of shale particles which is bound on two opposit,e sides by louvers. Conversion of the kerogen occurs as a result of the exchange of heat between the circulating gas stream and the shale. The inlet gas manifold distributes the gas to various portions of the shale bed in order to control the temperature gradient from the top to the bottom of the retort. Spent shale a t 955' F. is discharged from the bottom of the retort by a vibratory feeder which also controls the shale throughput rate. The circulating gas stream containing the oil, gas, and v-ater produced during retorting passes through a scrubber where part of the oil is condensed and entrained shale is removed; product oil is used as the scrubbing medium. The overhead stream from the scrubber passes to a tubular condenser where the remaining . oil and water are condensed. After repressuring, the excess make gas is vented through a pressure controller arid burned; the heat-carrying gas required for retorting is recycled through t,he gas heater and back to the retort. A part of the cool recycle gas is by-passed around the gas heater and mixed with the hot gas stream from the heater to control the temperature of the gas entering t,he retort. Experimental operations of the gas-flow pilot plant, began in 1948 and are still in progress. The test program has included raw shale preheating studies, determination of the optimum out,let shale temperature, and the studyof the effect of recycle gas inlet temperature. The shale preheater, originally mounted above the retorting vessel, was removed after tests indicatrd pcor heat economy and other disadvantages. For residence periods of 55 minutes and longer, the oil content of the retorted shale is low when the shale is heated to tempt~raturess h o w 923' J?.; for resi-
Vol. 43 No. L
dence periods of less than 55 mmuteb, the oil content 01 i c i t o i trtl shale having an outlet temperature of 925' I?. is greatci . T,rblr~ IV and V show the effect of recycle gas inlet temperalurc o i i product yield and quality, and on circulating gas rquircnicni R and energy consumption. The crude shale oils from the lo\? and high tempetittuic i u i i aere very similar, as shown in Table V. Gas-flow oil apprais to he similar to P\'-T-TI and Roystw shale oils, except that IL IS sonicM hat heavier In R commercial plant, the pas produced by the gai.-How piocess could be utilized to generate power, burned in gas cngir1c.s 01 turbines, or under steam boilers. Should it be desirable i o gcneiate power and heat from other sources, the shale gases could b~ used as a source of hydrogen for a hydrogenation step in rctining or as a source of synthesis gas for the production of liquid fuck hy Fischer-Tropsch synthesis. In addition, the Fischer-'l'wpecl\ process would yield organic chemical by-products such as ethanol, propanol, butanol, acetic acid, propionic acid, acetoric, niethvl rthyl ketone, and acetaldehyde. Preliminary operation has been conducted with a, spcn t,-dinlc burner, using cool retorted shale from the gas-flow pilot plant The tests indicate that retorted shale will support corrtbristion, nnd that by using recycle gas, the combustion tempeiatiiic c a n h r controlled to minimize carbonate decomposition. Approximately 61 B.t,u. are generated per pound of retorted shale, and using R spent-shale burner receiving hot retorted shalc djic~ctli from the retort, this quantity of heat plus the sensible h a t in thv hot shale charged to the burner would be sufficient lo ietort aii equivalent amount of raw shale. Class IV Retorts. The Standard Oil Development Co. hn.; developed R fluidized method of retorting (Figure 14). 'rc have been conducted 011 a pilot plant, previously used Jor expc'iimental work on fluid catalytic cracking of pe'croleum F~actionis. which has been converted to an oil-shale ietorting pi101 phiit. Under a cooperative agreement, the Bureau of R h c i hat. iunnished the company 1000 tons of - 3/16-inchshale for I h i - ~ o h.i
(Effect of recycle-gas inlet tempemtiire oil prnd,ii,h)
Product gasa Nolecular weight Net heating value, B.t.u. ' C I I . ft Composition, mole % Hydrogen Methane Ethane Unsaturates Carbon monoxide Hydrogen sulfide Carbon dioxide Water vapor Retorted shale Organic residue content, wt. LG Crude oil Gravity, A.P.I. Viscosity, S.U.S. a t 130' I: Viscosity, S.U.S. at 210' F Pour point F. Flash poi& (C.O.C.), ' F . Conradson carbon, wt. Yo Sulfur, x t . %, h-itrogen, r t . yo Water, vol. 70 Sediment, wt. yo 100 ml. distillation (cor. t.o 760 mill.), 1:. Initial boiling ooint % recovered' . 2 5 10 20 30 40 50 60 70 Overhead recovery, c/c Corrected for air and Rue-gar leakage. Q
I a n u w 1951
INDUSTRIAL AND ENGINEERING CXEMISTRY
I n t h i process, raw shale is charged continuously to a fluidized bed in the retort. Gas, oil, and water are removed overhead through a cyclone and recovered. The retorted shale, stripped of residual liquid hydrocarbons, is diacharged from the retort and carried by a stream of air to the fluidieed combustion chamber, where the retorted shale ie burned. A stream of hot ash from the burner is mixed with steam and fed to the retort to provide heat for retorting. Another stream of ash is withdrawn continuously also be from the burner and disposed of ae waste. The unit operated a8 a single-vessel system in ehich burning and retorting take place in the same vessel.
tar, and in some it is quite similar to petroleum. m omer respects, it is different from both coal tar and petroleum, Cod tar has a specific gravity of 1.192 and sulfur content of 0.04 or lesa Volume percentages of wid oil, middle oil, heavy oil, and pitch in typical coal tars average 16, 25, 12,and 47%, re~ this is ~not a god ~ ~ ~since the~ spectively, H light Oil, representing 1% of the products from tbe coking of coal, is a k n t from coal tar. b p e d e s of a typical mid-continent crude are included in Table VI. Important difference between shale oil and petroleum are the shale oil's higher percentagesof olefins, aromatics, and compounds of sulfur, nitrogen, and oxygen and lower percentages of p a r a 5 8 and naphthenes. As rompared to petroleum, shale oil is also deficient in hydrogen, owing to its unsatnration. REFINING
The fluid-Aow proceea has the advantages of high-heat transfer rates which result in high throughput rates. Heat efficiency should be high, since a fairly good fuel gas is recovered in addition to the oil. No moving parts are required for transporting the shale through the system, and maintenance costs should be reasonable. R e t o r t i i Process in Design Stage. The pilot plant design of a recently devised continuous retorting process is under way at the demonstration plant at the present time The hotsolids-contact process combines the principle of solid-to-eolid heat transfer with the use of cold shale aa a cooling medium for oil vapms produced during retorting, and w s the residual carbon on retorted shale to supply the heat for retorting. It is anticipated that the process will retort shale fines as well as coarse particles, since the velocity of the gases will be low enough that there should be no tendency for the gas stream ta carry fines from the retort. Power requirements are also estimated to be smaller than for proceases using hot gages as the medium far carrying beat to the shale.
The refinery at the oil-shale demonstration plant is designed 80 that atmospheric distillation, reforming, single-coil recycle cracking, visbreakin^, or delayed coking can be performed with G i m u m changes in-the refining equipment. The refinery was designed as the smallest semicommercial plant that could be constructed using conventional petroleum refining equipment. It has a capacity of 300 barrels per stream day based on the minimum practical siae of heater tube that could be utilized under the conditions nf +.he various proposed operations.
NATURE AND MARACl'EBISTlCS OF SHALE OIL
P
The characteristics of crude shale oil as produced in retorta vary to a considerable extent depending on the nature of the organic material in the shale and the retorting proms8 used. In general, the crude ail is a black, waxy oil having a gravity of about 21' A.P.I. and, because of its high wax content, a pour point of about 90" F. It is composed chiefly of hydrocarbons, consi&ing of olefins, paraffins, uaphthenes, and aromatics; appreciable amounts of sulfur, nitrogen, and oxygen compounds are present but no light ends. Table VI compares the properties of Colorado shale oils produced by several retorting processes. The oils from all pmcesse~ in which the shale is heated by pasaage of hot gas through the shale bed are quite similar but differ from those produced by a process in which heat is transferred through a metal wall. In some of its physical and chemical properties, the oil resembles coal
Figure 13. Gpe-Flow Retorting V-l The refinery consists of the following equipment: designed to operate under all 1. A singleeail crackina furconditions of atmospheric Xiatillation, tbcrmal erackiog, and reforming. The c e l l - c y upshot, heater incorporates features for maximum Eexihility, eat ditribution control, and maiatenanar
,
. - ..
, ;.,,>..;. ,.' . ,. t, ..... . ,
~~, j
14
INDUSTRIAL AND ENGINEERING
CHEMISTRY
"ol, 43, wo.
refining processes that have been investipated and nresenta Hempel Dirtn. Yielda. Vol. %preliminary dsta representaPour spm.. s N. Point, Napli- Light "ivy R e s tive of the refinery's first proRetort 60 60' F. Wt.'% Wt. % ' F. thi disk dist. due 2.5 15.5 28.4 54.1 duction (8). P e r f o r m a n c e Gaa-Boa 0.8581 0.73 2.12 85 Royatv 0.8287 0.72 1.85 85 5.0 18.0 35.8 42.1 testa conducted with shale 0.9248 2.50 55 Hayes 0.80 28.2 20.3 30.2 20.8 14.9 20.4 37.1 27.2 Diesel fuel and cracked shaleP%rW 85 0.9321 0.87 1.81 N-T-U 0.8321 0.78 2.10 eo 2.8 18.5 31.2 48.3 oil gasoline have indicated Pumpherston 0.8930 0.77 1.57 Bo 17.6 28.4 40.0 12.7 Typioal mid-continent arvde 0.8283 .. 5 0.14 28.4 25.0 18.8 26.3 that the early products from the refinery are quite =tie f a c t o r y . Table V I 1 compares shale Dieeel fuel with petroleum Diesel fuel. The shale fuel was prepared by batebtreating visbroken ligbbgas oil and was uaed for B period of 1month in the Diesel equipment in the experimental mine; this included three &ton dump trucks operated far 170 hours each and a fourth operated for 184 hours. The performance of the fuel under regular load and operating conditions was very sa& factory and comparable to the performance of commercial fuel normally wed. On being dismantled, the engine of the fourth truck sbowed no unusual carbon or other fouling deposita and only normal wear of the fuel injection system. Dynamometer tests on the fuel showed greater engine horsepower output over the entire-rangeof engine speed testa, a range of 1400 to 2100 engine r.p.m., as compared with the engine output when petroleum fuel was used. This c o n h e d the observations of drivers, who claimed greater power when using the shale fuel. Limited performance testa have also been conducted with cracked s h a l e 4 gasoline, which had been treated to approximate Figure 14. Fluid Shale-Oil Retorting P r o m s the specifications of commercial gasoline of petroleum origin. The Developed by Standard Oil Development Co. gasoline was msde from a composite of recycle cracked naphtha produced during the firstrefinery operations. The finished product has a sulfur content of 0.41% (Table VIII), but its color and simplicity. Flexibility is obtained b a system of elrternal constorage stability were satisfactory after the addition of 0.005 version piping which provides for d r e e possible flow schemes weight % of Universal Oil Products No. 5 inhibitor. Tbongb throu thebeater. only a limited quantity of gasoline was made for the first road 2. k o coke chambers: One of these is suitable for 330pounds per square inch pressure a t design temperature and is used as testa, ita performance was entirely satisfactory. It is believed either a cracking-reaction chamber during recycle-cracking o rathat cold weather use will require the addition of casing-head gasoThe second vessel a tions or as a coke drum during coking. line for greater volatility to improve starting characteristics. design preasure of 125 pounds per square inch and ISuaed for cokAlthough the fuel contained high percentages of olefins and aming only. The capacity of the chambers was based on a &hour cycle, 24 hours being allowed for amling and decoking. Wmch matics, there was little audible detonation in the engine. and cable-coking eqmpment are used in the intarest of econom 3. A hh-fractionator which will separate the oil into s o k e MATERIALS OF CONSTRUCTION (9) l i b t g a oil, heavy gas oil, and heavy fuel oil. The h b - E c t i o n l ator is 30 inches in diameter and 37 feet high, and is over a 42 X Since a study of the corrosive characteristics of shale oil was desired, minimum material sllowsnces were made far corrosion in the thermal processing unit of the refinery. Materials were selected primarily on the basis of strength requirementa. It w beTABLEVI.
PRUPEUTIES OF cOUX3ADO SHALE
-
OILS
::::T
TABLEVII. C O H P ~ S O OFN SHALEOIL m u P E T B ~ ~DIESEL ~WM
FUELS
24 feet and is acked with 0.75-inch Raachig regs. Stripping heat is supplied$ a conventional kettle-type reboiler. 7. A continuous low temperature aci&treatmg unit to rovide for treating of motor fuel fractions for nitrogen, sulfur, cog,, and gum control. 8. A rerun distillation unit for removing high-sulfur polymers from the gasoline after the acid treatment. The rerun unit consists of a packed fractionator, 16 inches by 14 feet, with a reboiler, feed prebeater, and the usual fractionating auxiliaries, including the overhead condenser, receiver, and reflux ump Heat is supplied to the reboiler by a bot-oil circuit from tge fla& fractionator. 9. A continuous doctor sweetening unit to convert objectionable odorous components of the gmoline or other distillate fractions to sweet compounds.
The refinery was completed in 1949 and limited operations have been conducted. An accompanying article describes the
Physical Properties Gravity. e A.P.I. at 80' F. F h h LPPamky-Martem), F. Pour. F. Visoarity. S.U.S. et 100' F. color^ C o d s o n carbon (10% bottoms) Flulfur. .at. % Nitrogen. nt. 7 ~ s acids, r sol. Tar bases ~01.~9 Aniline p&t. 8. Diesel index Cetane No. (motor)
k,
~ . t i ~ Petrolaum d h e . standsrd.
Shale Oil 38.0 198 0
38.8 8 0.87 0.8% 0.12 Uil
PStmleum 38.8 130 0 38.8
-1
0.021 0.18
Nil Nil Nil
172.4 88.8 54.6
i
3%
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
January 1951
TABLE VIII.
SHALEGASOLINEUSEDFOR PERFORMANCE TESTS Raw Gasoline 63.5 7.8
Gravity, A.P.I. Reed vapor pressure Sulfur, wt. yo Nitrogen, wt. yo T a r acids, vol. % Tar base, vol. %
Gum, A.S.T.M.
0.64
Doctor test Induction period, min. Corrosion copper strip Octane N a b (motor method) Octane No. b (research) A.S.T.M. didillation, F. Initial boiling point 10%
20 %
E% End point
1.27 1.6 6.6 521.7 Sour 3-5 Nea. 71.7 78.6 108
141
202 293 395 442
Treated Gasoline 58.0 5.6
0.41 0.013 0 0
8.3 Sweet
480+a
Neg. 71.3 77.9 117 161 190 274
463 Gasoline contains 0.005 weight % U.O.P.No. 5 inhibitor. b With 3.0 00. of tetraethyllead per gallon.
Typical Petroleum Gasoline 59.0 8.5 0.1 Nil 0 0 5.0 Sweet
15
The cost of finding new reserves and producing natural petroleum is increasing each year. The progress already attained in the short time devoted to the production of liquid fuels from shale indicates that steady advances are yet to be made with corresponding decreases in the costs of such fuels. The rising cost of liquid fuels from petroleum and the decreasing cost of liquid fuels from shale will meet some day, and although this day is as unpredictable as i t is inevitable, it is thought by many that it will not be many years hence.
480+
Neg. 73.0 78.0 90
130
180 260 370 390
Q
-
lieved that corrosion will not be severe since the sulfur compounds are of a less reactive type than those found in petroleum, and the nitrogen compounds have a corrosion-inhibiting effect. The cracking heater tubes are 2% chromium and 5% molybdenum alloy, A.S.T.M. A 200-46, Grade 4, with fittings containing ‘2.25y0 chromium and 1% molybdenum. Tubes and headers are rated for 1000 pounds per square inch a t 1050” F. I n the transfer line and heater crossover connections, steel containing 4 to 6% chromium and 0.5% molybdenum, A.S.T.M. A 158-44TJ p-5aJ was used to give the desired tensile strength with some corrosion resistance. Pumps, exchangers, and control valves were all specified in accordance with the usual practice for high sulfur crude oils. Kone of the vessels is lined, but the coke drums and flash chamber are designed to permit the addition of ganister, a highly siliceous lining, if necessary. Carbon steel is used throughout the chemical-testing plant except in dilute acid and ammonia handling equipment. The dilute acid and water settlers are lead-lined and served by Hastelloy B jet mixers and stainless steel pipe, Nos. 20 and 304. Carbon steel piping and cast-iron fittings are used in the ammonia refrigeration system. Carbon steel is used throughout the N-T-U retorting plant, except in the water-cooled reflux oil cooler in the condensing system, where tube bundles made of Admiralty metal have replaced the original carbon-steel tubes because of the corrosive nature of water from the Colorado River. A firebrick lining is used in the N-T-U retorts as the temperature of the fire bed is 1800” to 2200’ F. All firebricks are made of high heat-duty fire clay. I n the hottest parts of the gas-flow pilot plant, heat-resistant materials are used. I n the pebble stoves there are two outer linings of insulating brick whose total thickness is 7 inches and one inner lining of firebrick 3.5 inches thick. The retort vessel is stainless steel, G.I.S.I. Type 304,and the louvers are cast-iron alloy specified to stand 1400’ F. I n a commercial plant, the retorting vessel would be made of mild steel with a refractory lining. Stainless steel was used as an expedient and for ease in operation, Brick-lined piping is used from the stoves to a point where the quench gas enters, and from this point to the retort, stainless steel is used.
b
FUTURE PROSPECTS
The Bureau of Mines’ work a t the oil-shale demonstration plant is directed toward the development of satisfactory processes and techniques for the commercial production of liquid fuels from oil shale. These methods will be made available to any American industry that may wish to engage in such an oil-shale industry. Most of the major oil companies in this country own shale deposits and have displayed a keen interest in the work being done by the Bureau of Mines; many of the companies are engaged in cooperative work on oil shale and its products. Instead of being a competitive source of liquid fuels, oil shale actually is a supplement to those produced from petroleum.
Multiple-Drill Jumbo for Drilling Heading on Top Level
ACKNOWLEDGMENT
The authors wish to acknowledge the full cooperation and assistance of the entire staffs of the Bureau of Mines Experimental Oil-Shale Mine and Demonstration Plant, Rifle, Colo., in the preparation of this article. Particular appreciation is expressed to J. D. Lankford, Boyd Morris, and J. R. Ruark for their many helpful suggestions in gathering the data presented and to D. Z. Hobbs, chemist in the demonstration plant’s laboratory, for the pictures used in the report. BIBLIOGRAPHY
Alderson, V. C., “The Oil Shale Industry,” p. 39, New York, Frederick A. Stokes Co., 1920. American Society for Testing Materials, D 288-47, supplement to A.S.T.M. Standards, Part 111-A, pp. 33-4, 1947. (3) Bell, H. S., “Oil Shale and Shale Oils,” p. 1, New York, D. Van Nostrand Co., Inc., 1948.
(1)
(2)
(4) Ibid., p. 17.
( 5 ) Dundas, R. C., and Howe, R. T., C . S. Patent 1,469,628 (1923). ( 6 ) Eele, M., Hancock, T., and Portlock, W., Brit. Patent 330
(Jan. 29, 1694).
(7) Kastens, M. L., Hirst, L. L., and Chaffe, C. C., IND.ENG.
CHEM.,41, 870-85 (1949).
(8) Lankford, J. D., and Ellis, C. F.,Ibid., 43, 27 (1951). (9) Lankford, J. D., and Morris, B., presented before Second OilShale and Cannel Coal Conference, Institute of Petroleum, (10)
Glasgow, Scotland (July 1950). McKee, R. H., “Shale Oil,” A.C.S. Monograph 25, New York, Chemical Catalog Co., Inc., 1925.
p. 14,
(11) Ibid., p. 79-82. (12) Reed, H., and Berg, C., Mech. Engr., 7 1 , No. 8 , 639 (1949). (13) Selligue, A.-F., French Patent 9467 (Nov. 14, 1838). 43, 33 (1951). (14) Sohns, H. W., et al., IND. ENG.CHEM., (15) Stanfield, K. E., and Thorne, H. M., Ibid., 43, 16 (1951). (16) Thorne, H. M., etal., I b i d . , 4 3 , 2 0 (1951). (17) U. S. Bur. Mines, Rept. Invest. 4457 (January 1949). (18) U. S. Congress, 78th session, Public Law 290 (April 1944).
RECEIVED October 31, 1950.
