US 3929615 A
A process for the production of hydrocarbon gases from oil shale comprising the steps of gradually preheating oil shale in a preheat and prehydrogenation zone to a temperature of about 700 DEG to about 950 DEG F. in the presence of hydrogen-rich gas without substantial production of liquid or gas in the preheat and prehydrogenation zone, then hydrogasifying the preheated and prehydrogenated oil shale in a hydrogasification zone at a temperature of about 1,200 DEG to about 1,500 DEG F. in the presence of hydrogen-rich gas to form predominately low molecular weight paraffinic hydrocarbon gases from the preheated and prehydrogenated organic hydrocarbon portion of the oil shale. The hydrogen-rich gas may be passed countercurrent in thermal exchange relation to the spent shale to recover heat from the spent shale heating the hydrogen-rich gas for passage countercurrent and in thermal exchange relation to fresh oil shale in the preheat and prehydrogenation zone. The improvement of this process lies in the exceptionally high conversion of the organic component of oil shale to products of high value having high content of low molecular weight paraffinic hydrocarbon gases.
Description (OCR text may contain errors)
Unite States Linden et al.
atent [1 1 51 *Dec. 30,1975
1 PRODUCTION OF HYDROCARBON GASES FROM 01L SHALE  Assignee: American Gas Association, Inc.,
[ Notice: The portion of the term of this patent subsequent to Dec. 25, 1992, has been disclaimed.
Filed: Oct. 26, 1973 Appl. No.: 409,914
Related US. Application Data  Continuation-impart of Ser. No. 365,973, June 1,
 US. Cl. 208/11; 48/197 R  Int. Cl. C10B 53/06  Field of Search 48/197 R, 211, 202', 208/1 1  References Cited UNITED STATES PATENTS 2,991,164 7/l961 Elliott etal. 48/197 R 3,118,746 1/1964 Stratford 48/197 R 3,347,647 10/1967 Feldkirchner et a1. 48/202 3,484,364 12/1969 Hemminger 208/11 3,556,979 1/1971 Needham 208/11 3,619,405 11/1971 Smith 208/11 FOREIGN PATENTS OR APPLICATIONS 654,289 12/1962 Canada 48/197R Primary ExaminerS. Leon Bashore v Assistant ExaminerPeter F. Kratz Attorney, Agent, or FirmThomas W. Speckman  ABSTRACT A process for the production of hydrocarbon gases from oil shale comprising the steps of gradually preheating oil shale in a preheat and prehydrogenation zone to a temperature of about 700 to about 950 F. in the presence of hydrogen-rich gas without substantial production of liquid or gas in the preheat and prehydrogenation zone, then hydrogasifying the preheated and prehydrogenated oil shale in a hydrogasification zone at a temperature of about 1,200 to about 1,500 F. in the presence of hydrogen-rich gas to form predominately low molecular weight paraf- 12 Claims, 1 Drawing Figure I l warm smm'oa ---------t T Ms ram 1 I l '0ll.. me I usrumnon PREHEAT mo 2: menvonoezumou Putin-Isa g :f PREHEATED mo 22 g pasnvonoeannrao l 1, i 5 gig I on. SHALE c E 83 f'L uoum a: 1 alsll'filh as u \X SEPARA E zone-u w COOLERO m I 1 HEAT in son 2 I mg 1 INPUT I u r'a h bcm i vi l I MEANSI uoums I t.. uouw I HEAT HEAT SEPARATOR I RECOVERY MEANS b ZONE-l2 l5 1 a PIPEUNE XYLENE QUALITY ens i I sesur SHALE coouso waggig gn HYDROGEN- PRODUCTION OF HYDROCARBON GASES FROM OIL SHALE CROSS REFERENCE TO RELATED APPLICATION This is a continuation-in-part of copending application Improved Process for Production of Hydrocarbon Liquids and Gases from Oil Shale, Ser. No. 365,973, filed June 1, 1973.
This invention relates to an improved process for the production of predominately low molecular weight paraffinic hydrocarbon gases from oil shales. Low molecular weight paraffinic hydrocarbon gases include molecules of4 and less carbon atoms, namely methane, ethane, propane, butane and isobutane. The production of small amounts of aliphatic and alicyclic hydrocarbon liquids including straight or branched chain molecules which may be saturated or unsaturated and alicyclic hydrocarbon molecules substantially free from aromatic double bonds, is not detrimental since they are especially suited for various further processing. Such liquids may be used for preparing a high methane content pipeline-quality gas suitable as a substitute for or as a supplement to natural gas by direct recycling to the hydrogasifier. The process of this invention provides high methane content pipeline-quality gas.
Oil shales are sedimentary rocks which are thought to have been formed from finely divided mineral matter and organic debris from aquatic organisms and some plant matter which were deposited on the bottoms of shallow lakes and seas and later solidified. The resulting oil shales are fine-grained impermeable rocks in which it is almost impossible to separate the organic component and the inorganic mineral matter without changing the structure of the organic component. One of the major inorganic constituents of oil shales is carbonates. Oil shales vary in the amount and in the constitution of the organic component which is called kerogen. Typical oil shales contain about to 30 weight percent kerogen. Kerogen is a high molecular weight hydrocarbon having a molecular weight of over 3000 and a carbon to hydrogen weight ratio (C/l-I) typically of about 7/1 to 8/1.
Due to the high demands upon natural gas supplies and their limited reserves, synthetic pipeline gas will be needed to supplement such natural gas in the United States and other countries of the world. The interest in an economical process for producing synthetic pipeline gas from oil shales is high. There are abundant reserves of commercial grades of oil shales in the United States, particularly in the northwestern areas of Colorado and adjoining areas of Utah and Wyoming.
To be suitable as use for pipeline gas, the heating value must be about 900 to l l00 BTU/SCF which results from high methane content, normally 80% by volume or greater. Such specifications require that for pipeline-quality gas the carbon to hydrogen weight ratio be low, approaching as low as 3/1.
To produce a high yield of pipeline-quality gas from oil shales, it is desirable to limit the coking and aromatiz ation of the oil shales organic component to limit torrnation of aromatic oils and carbon or coke during gaslfication. It is also desired to limit decomposition of mineral carbonates present in the oil shale and resultant carbon dioxide formation which increases process heat requirements, consumption of hydrogen, and increases the cost of purification.
Previous processes for the production of hydrocarbon fuels from oil shale have the disadvantages of lower thermal efficiency and/or lower conversion of the organic component of oil shale to suitable gas.
It is an object of this invention to optimize the production of paraffinic hydrocarbon gases from oil shale.
It is another object of this invention to provide a process for the production of low molecular weight paraffinic hydrocarbon gases from oil shale wherein the oil shale is preheated and prehydrogenated by countercurrent flow of hydrogen-rich gas and may be hydrogasified by countercurrent or cocurrent flow of hydrogen-rich gas.
It is still another object of this invention to provide a process for high yield production of pipeline-quality gas from oil shale by a process characterized by its high thermal efficiency.
Further objects of this invention will appear to one skilled in the art as this description proceeds and by reference to the figures.
Preferred embodiments of this invention are illustrated in the drawing wherein:
FIG. 1 is a block flow diagram illustrating the production of low molecular weight paraffinic hydrocarbon gases from oil shale using one embodiment of the process of this invention.
The process of this invention is applicable to a wide variety of oil shales. For high efficiency it is desired that the Fischer Assay, which indicates the oil yield obtained by conventional retorting of the oil shale, be 25 gallons per ton or more. However, the process of this invention is also'applicable to oil shales having lower Fischer Assays, down to about 10 gallons per ton.
The size of the shale particles used in the process of this invention is not important, but particles generally of the size one-sixteenth inch to 1 inch diameter are utilized. Use of very fine particles may give difficulty in plugging during processing and large particles have a lower surface area and may result in longer processing times.
The fresh oil shale is fed into a preheat and prehydrogenation zone and gradually preheated to a temperature of about 700 to about 950 F. in the presence of hydrogen-rich gas. It is preferred that the temperature to which the oil shale is heated in the preheat and prehydrogenation zone is about 750 to about 850 F. At 700 F. the rate of adequate prehydrogenation is slow, but may be achieved by a residence time of several hours. At the higher temperatures of about 950 F. prehydrogenation occurs in a few minutes. The criteria of adequate prehydrogenation is the ultimate increased recovery of organic matter from the shale which is expressed most conveniently in terms of organic carbon recovery. By the process of this invention, as much as about percent of the organic carbon can be removed from oil shale in the form of valuable liquid and gaseous hydrocarbons. Longer residence times at the higher temperatures lead to undesired production of oil and gas by hydroretorting in the preheat and prehydrogenation zone. It is desired to limit oil production in the preheat and prehydrogenation zone to avoid plugging of the shale in this zone. It is desired not to produce substantial quantities of hydrocarbons in the pre- .heat and prehydrogenation zone, preferably less than about 15 to 20 weight percent of the organic component of the shale is converted to normally liquid or gaseous hydrocarbons. It is especially preferred to confrom prehydrogenated oil shales which had an original organic carbon content of 21.1 weight percent. The maximum temperature to which the shale was heated was 1300 F. and the data was obtained at sustained hydrogen partial pressures as shown in Table I.
TABLE I the art. Such variety of heating means allow both cocurrent and countercurrent operation of the preheat and prehydrogenation zone with respect to the shale and hydrogen-rich gas. One method which is preferred is the introduction of oil shale at ambient temperatures at one end of the preheat and prehydrogenation zone and the introduction of the hydrogen-rich gas at the other end of the preheat and prehydrogenation zone at a temperature in quantities sufficient to heat the oil shale to about 700 to about 950 F. by countercurrent flow of the hydrogen-rich gas in thermal exchange relation to the oil shales.
The preheated and prehydrogenated oil shale is hyd'rogasified in a hydrogasification zone at a temperature of about 1200 to about 1500 F., preferably about l300 to about 1400 F., in the presence of hydrogen- Percent Organic Carbon Recovery The data in Table I show that increases in hydrogen partial pressure are beneficial to organic carbon recovery. Hydrogen partial pressure should be maintained above about psia throughout the system. In practical operation, the hydrogenpartial pressure is substantially constant throughout the preheat and prehydrogenation zone. However, the hydrogen partial pressure decreases from the inlet to the outlet of the hydrogasification zone due to the formation of gaseous hydrocarbons by reaction of hydrogen and organic carbon. To maintain sufficient hydrogen partial pressure throughout the system, while avoiding hydrogen dilution of the product gas from the hydrogasifier and resultant lowering of the heating value of the final gas, the hydrogen concentration at the outlet of the hydrogasification zone should not exceed about 20 volume percent. Therefore, the lower limit of total pressure in the hydrogasification zone should be maintained above about 100 psia since the minimum hydrogen partial pressure should be above about 20 psia. Inasmuch as zones 10, 11 and 12 are at substantially the same total pressure, this lower total pressure limit applies to the entire system. At higher total pressures, the benefits of higher hydrogen partial pressures are obtained. The upper operating pressure is limited only by equipment and economic considerations. Normally the process of this invention is carried out at total pressures of about 100 to about 2000 psia, preferably about 500 to 1500 psia.
It is preferred that the oil shale not be thermally shocked by abrupt temperature changes, but that it be gradually heated at a rate in the order of less than about 100 F. per minute in the preheat and prehydrogenation zone. It is preferred that the heating rate be less than about 50F. per minute above about 500 to.
600F. The oil shale and hydrogen-rich gas may be heatedby external heating means or internal heating means in the.
rich gas to form predominately low molecular weight paraffinic hydrocarbon gases from the preheated and prehydrogenated organic portion of the oil shales. It is necessary to reach a temperature of about 1200 F. in order to obtain the desired hydrogasification in a reasonable period of time. The residence time of the shale in this zone is not considered critical since most of the organic material or kerogen in the shale will be rapidly removed from the shale due to prehydrogenation in the previous or oil shale preheat zone 10. The light oils from the organic material in the shale are vaporized immediately upon reaching the high temperatures. Therefore, in the hydrogasification zone 11, the shale may be in a free fall condition or a moving bed condition, whichever is convenient. The length of time at which the shale is at the hydrogasification temperature need not be more than about ten seconds. although longer times, as up to several minutes, is not considered detrimental. The residence time of the gas in the hydrogasification zone is more significant.
The hydrogen-rich gas stream is preferably introduced at the bottom of the hydrogasification zone 11 and flows upwardly or countercurrent to the shale passing downwardly. The hydrogen rich gas stream may also flow cocurrent with both the hydrogen rich gas and shale being introduced at the top of hydrogasification zone 11. The hydrogen-rich gas flow rate and size of the hydrogasification zone 11 is designed for a gas residence time of about 20 to 50 seconds within the hydrogasification zone, to allow conversion of vaporized hydrocarbons to low molecular weight paraffmic hydrocarbons, although somewhat longer periods of the time are not considered detrimental to the process; This gaseous mixture is carried upwardly and out of the hydrogasification zone 1 1 to a series of processing steps for the separation of paraffiuic hydrocarbons from the other gases or volatilized liquids in the gaseous mixture.
The hydrogasification zone may be heated by any suitable means aswill be obvious to one skilled in the art. One method is to supply hydrogen-rich gas of sufficiently high temperature to raise the temperature of the shale to the desired temperature by direct thermal exchange. The hydrogasification zone may be optionally internally heated by any suitable means such as a fuel oil/oxygen burner. Carbon dioxide may be added to the hydrogasification zone with the hydrogen-rich gas input and methanated to methane providing heat by methanation. The actual hydrogasification reaction is exothermic and when hydrogasification is established, the heat requirements become lowered.
The hydrogen-rich gas supplied to the hydrogasification zone should contain sufficient hydrogen to meet the chemical requirements sufficient to convert the organic portion of the oil shale to paraffinic hydrocarbon gases and hydrogasifiable aliphatic and alicyclic hydrocarbon liquids. It may also be desirable to add a controlled excess of hydrogen to the hydrogasification zone. For example, sufficient excess hydrogen may be added to the hydrogasification zone to ultimately convert all of the hydrocarbons recovered, and the carbon monoxide remaining after final purification, to methane. However, such excess hydrogen may be added at a later stage. Less than such excess may lead to undesired carbon deposition when the aliphatic and alicyclic hydrocarbon liquids are hydrogasified. Lesser than the amounts of hydrogen required chemically for conversion of the prehydrogenated component of oil shale to low molecular weight paraffinic hydrocarbon gases results in lower organic carbon recovery.
Referring to FIG. 1, the fresh oil shale is supplied to preheat and prehydrogenation zone wherein hot hydrogen-rich gas passes countercurrent and in thermal exchange relation to the oil shale at a temperature sufficient to gradually preheat the oil shale to a temperature of about 700 to about 950F. The preheated and prehydrogenated oil shale is then passed to hydrogasification zone 11 wherein it is passed countercurrently and in thermal exchange relation with hydrogen-rich gas of sufficient temperature to heat the oil shale to a temperature of about 1200 to about l500F. In hydrogasification zone 11, the organic component of the oil shale is hydrogasified to form low molecular weight paraffmic hydrocarbon gases. The mixture of predominantly low molecular weight paraffmic hydrocarbon gases, containing some aliphatic and alicyclic hydrocarbon liquids, remaining hydrogen-rich gas and carbon dioxide are removed from the hydrogasification zone. The mixed stream may be purified by further treatment to form desired products such as pipelinequality gas.
The spent shale is removed from hydrogasification zone 11 and passed through heat recovery zone 12 in countercurrent and thermal exchange relation to hydrogen-rich gas which cools the spent shale to less than about 300F., preferably to about 150F. The hydrogen-rich gas is heated in heat recovery zone 12 for recycle to preheat and prehydrogenation zone 10.
One advantage of the process of this invention is the high thermal efficiency wherein the hydrogen-rich gas may remove a large portion of the thermal energy of the spent shale for reutilization in preheating of the fresh oil shale. FIG. 1 shows a preferred embodiment of this invention wherein hydrogen-rich gas from preheat and prehydrogenation zone 10 passes through separator 13 for removal of liquids, namely water and hydrocarbon liquids which may be formed in preheat and prehydrogenation zone 10. The organic hydrocarbon liquids from separator 13 may be recycled to hydrogasification zone 11.
The hydrogen-richgas leaving separator 13 follows a split stream, one portion recycling to heat recovery zone 12 and another portion supplying hydrogasification zone 11. Valve 17 adjusts the split in the hydrogenrich gas flow dependent upon the chemical hydrogen requirement in hydrogasification zone 11. The hydrogen-rich gas passing from separator 13 to hydrogasification zone ll may be heated by passing through heat exchanger 20 in thermal exchange relationship with the output stream of hydrogasification zone 11 followed by further heating by any suitable heating means shown as 15, prior to introduction to hydrogasification zone 11. Alternatively, the hydrogen-rich gas may be supplied directly to the hydrogasification zone 11 without preheating and'hydrogasification zone 11 may be heated by any suitable means shown in FIG. 1 as heat input means 16. Heat input means 16 may be combustion of fuel withv oxygen.
The other portion of the stream of hydrogen-rich gas from separator 13 is recycled to heat recovery zone 12. The amount of hydrogen-rich gas makeup is determined by the amount of hydrogen consumed in the prehydrogenation and hydrogasification zones and discharged from hydrogasification zone 11. The hydrogen-rich gas is heated in heat recovery zone 12 and upon passing from heat recovery zone 12 may be further heated by any suitable heating means 14 prior to introduction to preheat and prehydrogenation zone 10 to obtain the desired temperature for entry to preheat and prehydrogenation zone 10. A larger volume of hydrogen-rich gas passes through preheat and prehydrogenation zone 10 than passes through hydrogasification zone 11.
The advantages of the process'of this invention appear to be achieved by the controlled gradual preheating and prehydrogenation in zone 10 followed by higher temperature hydrogasification of the preheated and prehydrogenated oil shale in zone 11. While prior processes of hydrogasifying oil shale without gradual preheating and prehydrogenation of the organic component have resulted inless than percent recovery of the organic carbon from the shale, we have found that with our two-zone hydrogenation process, it is possible to recover as much as about percent of the organic carbon from the oil shale.
A preferred embodiment of this invention in the production of pipeline-quality gas results in further increases in thermal efficiency of the process being obtained by utilization of heat from heat exchanger 20 cooling the gas output of the hydrogasifier to heat hydrogen-rich gas input to hydrogasifier zone 11.
The effluent gas from hydrogasifier 11 generally including methane, hydrogen, carbon dioxide and vaporized liquids is passed through heat exchanger 20 wherein the hydrogen-rich gas passing to hydrogasification zone 11 may be heated by thermal exchange with the hydrogasified gas. The cooled hydrogasified gas is then passed through liquidgas separator 21 removing liquids including water, benzene, toluene, xylene and other organic liquids which are passed through liquid separator 18 which separates water, high boiling hydrocarbon liquids fraction which gives greatest coking difficulties; and low boiling hydrocarbon liquids including benzene, toluene and xylene from middle boiling hydrocarbon liquids which are recycled to the hydrogasification zone. The low-boiling hydrocarbon liquids prehydrogenation zone and hydrogasification zone'or the preheat and prehydrogenation zone and the hydrogasification zone may be physically contained in one vessel appropriately separated. When operated on a "batch basis, the preheat and prehydrogenation conditions may first be subjected to a single zone to which same zone the hydrogasification conditions'are later applied. It is readily apparent the process of this invention may be carried out on either a batch or continuous flow basis. A continuous flow process is preferred.
While no specific means of distribution of the hydrogen-rich gas throughout the zones containing oil shale is. shown, it is readily apparent that it is desirable to have a suitable gas distribution means such as a gas manifold distribution system at the introduction area of the gas to the particular zone. The desirable factor is that the hydrogen-rich gas be effectively distributed to the crosssectional area of the zone upon its introduction or shortly thereafter.
Suitable materials for construction of an apparatus suitable for the process of this invention are well known to persons skilled in the art and need only be sufficient to contain the pressures obtained in the process and to effect suitable heat retentions in the different thermal zones of the process of this invention.
While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to 7 those skilled in the-art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without departing from the basic principles of the invention.
1. In the process'for the production of pipeline quality gas by gasification of organic components of oil shale wherein above about 77 percent of the organic carbon in said oil shale is converted to liquids and gases the improvement comprising:
introducing fresh oil shale into a preheat and prehy- 7 about 20 psia.
8 hydrogasifying the preheated and prehydrogenated organic components of oil shale in a hydrogasification zone at a temperature of about l200 toabout 1500F. in the presence of at least a stoichiometric amount of hydrogen-rich gas to form low molecular weight paraffinic gases and liquid hydrocarbons from the preheated and prehydrogenated organic portion of said oil shale;
said hydrogen-rich gas being supplied to said preheat and prehydrogenation zone in larger volumes than the hydrogenrich gas supplied to said hydrogasification zone;
removing spent shale from the hydrogasification zone separate from said gases; and
purifying and upgrading said gases by removing liquids and undesired steam, carbon monoxide, carbon dioxide, ammonia and hydrogen sulfide followed by methanation to provide pipeline quality gas.
2. The process of claim 1 wherein spent shale is passed from said hydrogasification zone to a heat recovery zone wherein hydrogen-rich gas recycled from said preheat and prehydrogenation zone passes countercurrent and in thermal exchange relation to said spent shale cooling the spent shale and heating the hydrogen-rich gas for introduction directly to said preheat and prehydrogenation zone.
3. The process of claim 2 wherein said heated hydrogen-rich gas is further heated during passage from said heat recovery zone tosaid preheat andprehydrogenation zone.
4. The process of claim 2 wherein the hydrogenrich gas stream leaving said preheat and prehydrogenation zone is split, with one portion, containing sufficient gas to provide at least the chemical hydrogen requirements in the hydrogasification zone, being passed to said hydrogasification zone and the other portion being recycled to said heat recovery zone.
V 5. The process of claim 4 wherein said one portion of hydrogen-rich gas stream is further heated during passage to said hydrogasification zone. I
6. The process of claim 1 wherein .the oil shale is preheated to about 750 to about 850F. in said preheat and prehydrogenation zone.
7. The process of claim 1 wherein the preheated and prehydrogenated oil shale is heated to about l300 to about 1400F. in said hydrogasification zone.
8. The process of claim 7 wherein said hydrogasification zone is heated by methanation of carbon dioxide.
9. The process of claim 7 wherein the input hydrogen-rich gas to the hydrogasification zone is heated by thermal exchange with the output of the hydrogasification zone. A 1 I 10. The process of claim 1 wherein the preheat and prehydrogenation zone and the hydrogasification zone is at a total gas pressure of about to about 2000 psia.
11. The process of claim 10 wherein said total gas pressure is about 500 to about 1500 psia.
12. The process of claim 1 wherein the preheat and prehydrogenation zone and the hydrogasification zone is maintained at a hydrogen partial pressure above l l i I