Production Of Shale Oil

Abstract

Process for recovering shale oil from oil shale by retorting with synthesis gas, i.e., a mixture of carbon monoxide and hydrogen, generated by partial combustion of byproduct gas with oxygen, wherein part of the heat required for retorting is provided by the hot synthesis gas, and additional hydrogen is produced in the oil shale retort by the water-gas shift reaction, the shale acting as a catalyst; and the process being self-sufficient in requiring no external source of water.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for the recovery of oil from oil shale. In one of its more specific aspects, it relates to an improved process of hydrotorting oil shale with carbon monoxide and hydrogen generated by partial oxidation of gaseous byproducts to produce shale oil of improved quality and yield.

2. Description of the Prior Art

Oil shale consists of compacted sedimentary inorganic rock particles, generally laminated and partly or entirely encased with a high molecular weight organic solid material called kerogen, which is present in the amount of about 6 to 22 wt. percent.

Crude shale oil may be obtained by pyrolysis of raw oil shale. Thus, raw shale may be subjected to destructive distillation in a retort at a temperature of about 850.degree. to 950.degree. F. The chemical decomposition of the kerogen which takes place by the action of heat along yields crude shale oil vapors, together with water, gas, and spent shale containing a carbonaceous residue and mineral matter.

The application of hydrogen to the retorting of oil shale, for example by the processes of U.S. Pat. No. 3,117,072 and U.S. Pat. No. 3,224,954 issued to DuBois Eastman and Warren C. Schlinger, gives increased yields of shale oil of improved quality. Oil shales usually occur in desert areas where the lack of process water has traditionally been considered a drawback to development of the oil shale deposits for recovery of shale oil.

SUMMARY

We have devised a continuous process for retorting raw oil shale, thereby obtaining near maximum yields of shale oil of reduced nitrogen and sulfur content, as compared with the Fischer Assay. In our system, a synthesis gas generator produces a mixed stream comprising hydrogen and carbon monoxide at a temperature in the range of about 1,700.degree. -3,000.degree. F. by the partial oxidation of recycled byproduct gases from the process. At a temperature in the range of about 750.degree. to 1,500.degree. F. and a pressure in the range of about 100 to 20,000 p.s.i.g. the raw oil shale in a shale retort zone is then contacted by the effluent gas stream from the reaction zone of the synthesis gas generator, thereby supplying hydrogen and some of the heat for hydrotorting the raw oil shale. Further, water-gas shift reaction occurs simultaneously with the hydrotorting in the shale retorting zone. In such instance, spent shale serves as a shift catalyst so that some of the CO in the synthesis gas is converted into H.sub.2. Thus, a gaseous mixture comprising hydrogenated shale oil vapors, H.sub.2 O, and uncondensed H.sub.2 + carbon oxide gases is produced by the process. All or a portion of the uncondensed gases may be then introduced into a gas-purifying zone, where byproduct fuel gas is removed and is recycled to the gas generator as feed, along with the unpurified portion of said uncondensed gases and optionally with a minor amount of makeup fuel gas from an external source. Addition of H.sub.2 O to the gas generator or to the shale retort zone or both is optional. However, no external source of water is required as sufficient H.sub.2 O is produced by the process to fulfill any process requirements.

THe principal object of this invention is to provide an improved process for recovery of shale oil from oil shale.

Another object of this invention is to provide a process for pyrolyzing and hydrogenating raw oil shale to produce an upgraded shale oil, utilizing hot synthesis gas to provide heat and hydrogen for the process.

Still another object is to provide a process which is self-sustaining with respect to process water requirements, wherein fuel gases produced in the system are reacted with oxygen in the absence of H.sub.2 O in a synthesis gas generator to produce hot process gas for recovery of shale oil from oil shale.

A still further object of this invention is to provide a process for simultaneously retorting oil shale and hydrogenating the shale oil vapor released to produce increased yields of a shale oil with a substantially reduced nitrogen and sulfur content.

The accompanying FIGURE illustrates diagrammatically process steps in the method of this invention.

DESCRIPTION OF THE INVENTION

The present invention pertains to an improved hydrotorting process in which synthesis gas i.e., gaseous mixture comprising H.sub.2 and CO is used to recover high quality shale oil from raw oil shale at greater yields than the Fischer Assay.

The synthesis gas is produced by the partial oxidation of gaseous byproducts from the subject process in a separate conventional noncatalytic free-flow synthesis gas generator. A suitable gas generator for use in the process is described in U.S. Pat. No. 2,582,938 issued to DuBois Eastman. The synthesis gas is produced in the gas generator at a pressure in the range of about 100 to 3,500 p.s.i.g. and a temperature in the range of about 1,700.degree. to 3,000.degree. F.

Feed gas to the synthesis gas generator consists of a gaseous mixture substantially comprising the combustible gaseous byproducts from the subject process, optionally with a relatively minor quantity of supplemental makeup fuel gas from an external source. The feed gas mixture comprises mostly CO, H.sub.2, and CO.sub.2 and relatively smaller amounts of CH.sub.4 and H.sub.2 S. Preferably, the gaseous feed is introduced into the gas generator at a temperature in the range of 300.degree. to 750.degree. F. It is optional to provide water as part of the feed to the generator.

The oxidizing gas which is fed to the synthesis gas generator, preferably at a temperature in the range of 250.degree. to 350.degree. F., may be selected from the group consisting of substantially pure oxygen (greater than 95 mole percent 0.sub.2), and oxygen-enriched air (greater than 21 mole percent of O.sub.2). Suitably, sufficient free oxygen is introduced into the reaction zone so that the ratio of atoms of oxygen to atoms of carbon therein is in the range of about 0.08 to 1.5.

Raw oil shale in the shale retort zone is then contacted with the aforesaid synthesis gas at a temperature in the range of about 750.degree. to 1500.degree. F., and preferably below 1,000.degree. F. for example 800.degree. to 950.degree. F., at a pressure in the range of about 100 to 20,000 p.s.i.g. Preferably, to save on gas compression costs, the pressure in the synthesis gas generator and the shale retort zone are substantially the same, less ordinary pressure drop in the lines. Sufficient synthesis gas is supplied to the shale retort zone to provide a H.sub.2 +CO consumption in the range of about 1,000 to 20,000, and preferably about 1,300 s.c.f. of H.sub.2 +CO per ton of oil shale treated.

The oil shale may be in a dry form when treated or slurried with a liquid hydrocarbon fuel e.g., shale oil, crude oil. The shale retort zone may constitute a fixed or fluidized bed of raw oil shale particles, as described for example in U.S. Pat. No. 3,224,954 issued to Warren G. Schlinger and DuBois Eastman; a tubular retort, as more fully described in the aforementioned U.S. Pat. No. 3,117,072; or a fractured subterranean oil shale stratum as described for example in U.S. Pat. No. 3,084,919 issued to William L. Slater, thereby effecting pyrolysis and hydrogenation in situ. A particular advantageous method for retorting the raw oil shale is described in our coassigned copending application Ser. No. 786,951. Further, the oil shale retort zone may be externally heated; or substantially all or part of the heat required for retorting may be supplied by the synthesis gas.

Optionally, the raw oil shale is contacted with H.sub.2 O in the shale retort zone at the same time that the shale is contacted with hot synthesis gas. The H.sub.2 O, either in the form of supplemental liquid water or steam, may be introduced into the shale retort zone along with the synthesis gas, or the H.sub.2 O may be separately introduced. Introducing supplemental H.sub.2 O into the oil shale retort zone was found to have several new and unobvious results, making it a preferred mode of operation. It was unexpectedly found that when oil shale is contacted with H.sub.2 O in the shale retort zone, the endothermic decomposition of inorganic carbonates in the production of CO.sub.2 is repressed. This saves hydrogen, as CO.sub.2 would ordinarily react with H.sub.2 to form H.sub.2 O and CO. Thus by H.sub.2 O addition, there is a savings of energy in the form of heat ordinarily consumed by the decomposition of inorganic carbonates; and further, there is a considerable reduction of hydrogen consumption. Also, the mass velocity of the gas mixture through the shale retort zone, and the heat transfer coefficient of the mixture are increased by the addition of H.sub.2 O. In addition, vaporization and expansion of water in the oil shale tends to disintegrate the shale particles and facilitate the atomization of the shale oil. Also, coking of the shale may be minimized or eliminated at a substantially reduced hydrogen consumption.

Unobvious advantages for introducing H.sub.2 O underpressure into the oil shale during hydrotorting of shale slurries in a tubular retort include: (11 ) greater concentrations of shale may be incorporated in pumpable oil-shale slurries, and (2 ) clogging of the retort tubing is prevented. Thus, a portion of the water produced by our process, at a suitable temperature in the range of about 100.degree. to 500.degree. F. is preferably recycled to and introduced into the shale retort zone in an amount of about 0.01 to 0.6 ton of H.sub.2 0 per ton of raw oil shale, and preferably about 0.1 to 0.4 ton of H.sub.2 O per ton of raw oil shale. Both the synthesis gas and the supplemental H.sub.2 O may be supplied to the oil shale retort zone, for example, at a pressure of about 25 to 200 p.s.i.g. greater than the system line pressure.

In one embodiment of our invention a portion of the H.sub.2 O produced by the process may be used to cool the hot effluent gas from the synthesis gas generator from a temperature of about 2,200.degree. F. to about 1,000.degree. F. by recycling byproduct H.sub.2 O to a synthesis gas quench zone and quenching the effluent synthesis gas from the gas generator in the manner shown in U.S. Pat. No. 3,232,728 issued to Blake Reynolds. One advantage of this embodiment of the invention is that all of the water required in the shale retorting step may be picked up by the synthesis gas vaporizing the quench water during cooling.

It was unexpectedly found that spent shale in the shale reaction zone acts like a shift catalyst, and that simultaneously with the hydrotorting in the oil shale reaction zone the CO supplied by the synthesis gas undergoes an exothermic water-gas shift reaction to produce additional hydrogen gas and CO.sub.2. Thus the following additional savings are brought about by our improved process: (1 ) costly pure hydrogen may be replaced by relatively inexpensive synthesis gas containing H.sub.2 to effect denitrogenation and desulfurization of shale oil, (2 ) additional H.sub.2 is produced by the water-gas shift reaction from CO supplied by low cost synthesis gas, and (3 ) additional heat is released in the tubular retort during the water-gas shift reaction.

The residence time in the oil shale retort zone must be long enough to permit pyrolysis and disintegration of the raw oil shale and hydrogenation of the shale oil vapors. However, excess time in the shale retort zone may cause coking and result in degraded shale oil. Thus at the previously mentioned conditions, the preferred residence time is from about 20 minutes to 5 hours and generally about 30 minutes in a batch retort or a fixed bed of shale at a pressure in the range of about 1,000 to 2,500 p.s.i.g. Further, the residence time is preferably maintained at about one-fourth to 5 minutes in a tubular reactor at a pressure in the range of about 100 to 20,000 p.s.i.g. and preferably in the range of 300 to 1,000 p.s.i.g.

The gaseous effluent stream leaving the reaction zone comprises vapors of shale oil and water, unreacted hydrogen, NH.sub.3, CO, CH.sub.4, H.sub.2 S, CO.sub.2, and may contain a small amount of entrained spent shale particles (about 250 to 350 mesh). When necessary, the entrained spent shale particles may be separated from the remaining gaseous stream by means of a conventional gas-solids separator, or for example a chamber with a downwardly converging bottom equipped with baffling elements. The hot gaseous effluent leaving overhead from the reaction zone or the gas-solids separator is cooled below the dewpoints of the water and the shale oil. In a gas-liquids separator the shale oil and water are separated by gravity from each other and from the uncondensed gases.

Depending on the composition of the synthesis gas to the oil shale reaction zone, the uncondensed gases withdrawn from the top of the gas-liquids separator having the following approximate composition in mole percent dry basis: H.sub.2 45 to 85, H.sub.2 S 0 to 2.0, CO.sub.2 1.0 to 15.0, NH.sub.3 0.05 to 0.50, CO 3.0 to 30.0, and CH.sub.4 2.0 to 20.0. This gas may be compressed and recycled to the synthesis gas generator either alone or in combination with makeup fuel gas. However, to prevent the build-up of impurities all or a portion of this gas stream may be first diverted into a gas purifier. A suitable gas purifier of conventional type utilizing refrigeration and chemical absorption to effect separation of the gases, such as described in U.S. Pat. No. 3,001,373 issued to DuBois Eastman and Warren G. Schlinger may be used. A purified gaseous mixture, essentially comprising H.sub.2, and CO with a minor amount of CH.sub.4, is withdrawn from the gas purifier and recycled as feed to the synthesis gas generator.

In conclusion, by the process of our invention, oil shale is treated with a hot hydrogen-rich gas, i.e., synthesis gas, and preferably H.sub.2 O. As previously described, the following occurs: (1 ) kerogen in oil shale is raised to a high enough temperature to fracture, (2 ) pyrolysis of the kerogen and hydrogenation of the shale oil produced, (3 ) the porous structure of the shale is maintained during retorting to enable cracked kerogen in the interior to quickly escape before being converted to polymeric or gaseous products, and (4 ) rapid disintegration of raw oil shale into minute particles free of carbonaceous matter. In our process, shale oil, H.sub.2 O, and synthesis gas act as heat transfer agents by conducting heat to the surface of the shale particles. The H.sub.2 O also reduces the hydrogen consumption and heat load for a given yield of shale oil. The hydrogen is able to permeate into shale matrix so that it is available to properly terminate the hydrocarbon fractures before coke is formed plugging the pathway to the surface of the shale particle. By the process of our invention, the higher boiling hydrocarbons are subjected to viscosity breaking with substantially immediate hydrogenation of the molecular fragments and without further breakdown, thereby materially increasing the production of material boiling in the 400.degree. -700.degree. F. range without substantially increasing the lower boiling gasoline range materials or forming normally gaseous hydrocarbons and heavy tars and coke. Thus, the formation of heavy polymers, unsaturated hydrocarbons and carbonaceous residues, which characterize known processes, are suppressed.

Evidence of the success of this method can be seen by the unusually high yield of high quality product shale oil, the production of sufficient water to satisfy the needs of the process, and by the finely ground kerogen-free quality of the spent shale. For example, shale oil yields of about 34.0 gallons and more per ton of raw shale may be produced by the subject process in comparison with Fischer Assay shale oil of about 31.0 gallons per ton. This represents a minimum increase in yield of about 10 percent and marks an improvement over the yield from contemporary processes. Also, examination of the hydrotorted shale oil produced shows it to be of superior quality; that is, compared with Fischer Assay shale oil from the same shale, the sulfur and nitrogen content are each about 25 to 35 percent lower. Finally, the self-sustaining features of the process makes it particularly attractive for use in arid lands.

EXAMPLE OF THE PREFERRED EMBODIMENT

The following example is offered as a better understanding of the present invention but the invention is not to be construed as limited thereto.

In run 1, chunks of Colorado Oil Shale having a maximum cross-sectional dimension of about 4 inches and having a Fischer Assay of about 31.2 gallons of shale oil per ton of raw oil shale and 2.9 gallons of H.sub.2 O per ton of raw oil shale are charged into a fixed bed vertical oil shale retort 1 foot in diameter by 40 feet long. The retort is charged hourly with 2,000 pounds of oil shale per batch. The system is purged of air and 10,170 s.c.f.h. of synthesis gas, to be further described, at a temperature of about 950.degree. F., and 30 gallons per hour of supplemental H.sub.2 O at a temperature of 900.degree. F. are passed through the oil shale retort zone maintained at a pressure of about 500 p.s.i.g. The gaseous effluent stream leaving from the top of the oil shale retort comprises essentially vaporized hydrogenated kerogen products, e.g., shale oil, and water, as well as such gases as CO.sub.2, H.sub.2, CO, H.sub.2 S, NH.sub.3, and CH.sub.4. The gaseous effluent stream is then cooled below the dewpoint of the product shale oil and the water, which are thereby liquefied and separated by gravity in a gas-liquids separator from each other and from an uncondensed gaseous mixture. To prevent the build-up in the system of gaseous impurities, the uncondensed gas mixture is introduced into a conventional gas purifier.

A continuous stream of about 938 s.c.f.h. of noncombustible off-gas from the gas purifier is discharged from the system, while the remaining purified gas is introduced into the top of the synthesis gas generator. This fuel gas mixture comprises in mole percent dry Basis: H.sub.2 57.3, CO 38.2, CO.sub.2 0.0, CH.sub.4 3.5, H.sub.2 S 0.0, and N.sub.2 1.0. Further, about 550 s.c.f.h. of makeup gas from an external source having the following composition is also fed to the synthesis gas generator: CH.sub.4 95.1, C.sub.2 H.sub.6 2.0, and CO.sub.2 2.9.

About 71 lbs./hr. of 95+ mole percent of oxygen at a temperature of about 300.degree. F. are fed to the reaction zone of the synthesis gas generator. In this example, the synthesis gas generator operates without the addition of supplemental H.sub.2 O. About 10,170 s.c.f.h. of synthesis gas is produced in the reaction zone of the generator at a temperature of about 2,200.degree. F. and a pressure of about 550 p.s.i.g. The synthesis gas has the following composition (mole percent dry basis):

H.sub.2 58.5, co 38.2, co.sub.2 2.4, n.sub.2 0.8 and Ch.sub.4 0.1. The synthesis gas is cooled in a waste heat boiler to a temperature of about 950.degree. F. and is introduced into the shale retort zone, as previously mentioned.

For comparative purposes, run 2 was made under the same conditions as run 1 but with no supplemental H.sub.2 O being introduced into the shale retort zone.

A summary of the operating conditions and the products recovered for runs 1 and 2 are shown in table I along with, for comparison, shale oil produced by the Fischer Assay. ##SPC1##

By a comparison of the results in table I, it may be shown that in run 1 with supplemental H.sub.2 O being introduced into the shale reaction zone the consumption of hydrogen (as supplied by the synthesis gas) is less than in run 2 where no H.sub.2 O is added. However, the water yield for run 1 is less than that for run 2. This supports the theory that water injection into the shale retort inhibits the undesirable decomposition of shale carbonate, which reaction absorbs heat and liberates CO.sub.2 that reacts with hydrogen to form water.

The results clearly show that compared with the Fischer Assay (column 3 , superior yields of product shale oil are obtained from runs 1 and 2 and the quality of the shale oil is improved. Further, adding supplemental H.sub.2 O to the shale retort zone, as in run 1, is preferred.

The process of the invention has been described generally and by examples with reference to oil shale and gas mixtures of particular compositions for purposes of clarity and illustration only. It will be apparent to those skilled in the art from the foregoing that various modifications of the process and materials disclosed herein can be made without departure from the spirit of the invention.

Claims

We claim:

1. A process for hydrotorting raw oil shale to produce shale oil which comprises: generating synthesis gas comprising CO and H.sub.2 by the partial oxidation of byproduct gas from the subject shale hydrotorting process as defined hereinafter; contacting raw oil shale with said synthesis gas in a shale retorting zone at a temperature in the range of about 750.degree. to 1,500.degree. F. and for a sufficient time to pyrolyze said oil shale thereby producing a vaporous effluent stream comprising denitrogenated and desulfurized shale oil vapor, H.sub.2 O, H.sub.2, CO, CO.sub.2, and CH.sub.4; introducing said vaporous effluent stream into a separating zone; separately withdrawing from said separating zone hydrogenated shale oil and uncondensed fuel gases; and supplying at least a portion of said uncondensed fuel gases to said synthesis gas generator as feed.

2. The process of claim 1 with the added steps of introducing H.sub.2 O into said shale retorting zone and withdrawing water from said separating zone.

3. The process of claim 2 wherein said H.sub.2 O is introduced in the amount of about 0.01 to 0.6 tons of H.sub.2 O per ton of raw oil shale treated.

4. The process of claim 1 wherein sufficient synthesis gas is introduced into said shale retorting zone to provide 1,000 to 20,000 s.c.f. of H.sub.2 +CO per ton of raw oil shale treated.

5. The process of claim 1 wherein said synthesis gas is generated at a pressure substantially equivalent to the pressure in said shale retorting zone and is introduced into said shale retorting zone and is introduced into said shale retorting zone at a temperature in the range of about 800.degree. to about 1,000.degree. F. and at a pressure in the range of about 300 to 1,000 p.s.i.g.

6. The process of claim 1 wherein said shale retorting zone comprises a tubular retort, and said raw oil shale is pulverized and slurried with shale oil.

7. The process of claim 1 with the added step of cooling said synthesis gas in a quench zone with water obtained from said separating zone.