US3691056A - Process for retorting oil shale in the absence of shale ash - Google Patents

Abstract

IN THE PYROLYSIS OF OIL SHALE TO SHALE OIL, THE LOSS OF THE SHALE OIL PRODUCT BY SORPTION ON POROUS SHALE ASH IN THE PYROLYSIS ZONE IS PREVENTED BY ATTRITING THE SHALE ASH PARTICLES TO FINES AND ELUTRIATING THE FINES FROM THE HEAT

CARRIER CIRCUIT SO THAT THE HEAT CARRIERS RECYCLED TO AND USED IN THE PYROLYSIS ZONE ARE SUBSTANTIALLY FREE OF SHALE ASH.

Description

Sept. 12, 1972 J. H. BARNEY ETAL PROCESS FOR RETQRTING OIL SHALE IN THE ABSENCE OF SHALE ASH Filed Aprll 1a. 1971 1NVE.\'TORS. BARNEY JOHN H.

FRANKLIN B. CARLSON nited States Patent 3,691,056 PROCESS FOR RETORTING OIL SHALE IN THE ABSENCE OF SHALE ASH John H. Barney, Denver, and Franklin B. Carlson, Bloomfield, Colo., assignors to The Oil Shale Corporation,

New York, N.Y.

Filed Apr. 13, 1971, Ser. No. 133,507 Int. Cl. C10b 53/06 U.S. Cl. 208-11 5 Claims ABSTRACT OF THE DISCLOSURE In the pyrolysis of oil shale to shale oil, the loss of the shale oil product by sorption on porous shale ash in the pyrolysis zone is prevented by attriting the shale ash particles to fines and elutriating the fines from the heat carrier circuit so that the heat carriers recyled to and used in the pyrolysis zone are substantially free of shale ash.

The present invention relates to a process for the recovery of shale oil from oil shale which contains substantial amounts of carbonate-containing minerals.

BACKGROUND OF THE INVENTION As the worlds petroleum reserves become more depleted and/or nationalized, increasing attention and interest is being directed to the recovery of shale oil from the plentiful reserves of oil shale located in the western states of Colorado and Utah and elsewhere throughout the world.

When oil shale of the type found in the Green River shales of the western United States is pyrolyzed at about 800 F. to 1000 F., the kerogen decomposes to gas, oil and spent shale. The oil and gas are recovered for down stream processing and upgrading. The spent shale is a waste product comprising coke-like residue which contains large quantities of calcite (CaCO and dolomite (MgCO -CaCO having a particle size as small as /1- inch and smaller. This shale matrix is to be distinguished from other oil-bearing matrixes such as coal which contains minor amounts of ash and tar sands which consist mainly of dense particles of silica.

Green River shale typically contains carbonate minerals in the range of about 35 weight percent dolomite and 15 weight percent calcite. The spent shale also averages about 3 to 6 weight percent fixed organic carbon, depending, of course, on the specific pyrolysis process employed. This amount of fixed carbon in terms of energy constitutes enough heat to sustain a very large retorting facility without resorting to the use of a portion of the oil or gaseous pyrolysis products for supplying the heat requirement. In this regard, many processes have been envisioned which contemplate the use of this available energy source for conducting the pyrolysis reaction, but none of these processes have fully anticipated the gamut of problems inherent in actually recovering and utilizing this energy source. At least one process (see U.S. Pat. No. 3,281,349) has attempted to cope with a portion of the problem that arises when spent shale decomposes and produces fines which contaminate the oil product as base sediment. The solution in this instance was directed to avoiding the destruction of the original shape of the raw shale particle by controlling the size of the feed material so as to easily remove the major portion of the spent shale prior to combustion of carbon deposited on the process heat carrier, i.e., catalyst beads. This procedure also sought to avoid the heat consuming endothermic reaction which occurs as a result of carbonate decomposition when spent shale is combusted. This endothermic reaction is considered therein as undesirable because it consumes heat and produces very fine micron and sub-micron size shale ash particles that contaminate the oil product.

A number of other processes have also described burning the carbon, or a portion thereof from the spent solid residue to furnish hot spent combustion residue, char, coke or the like, which is recycled to the retort to effect the pyrolysis reaction. Processes of this type, for example, those disclosed in U.S. Pat. Nos. 2,983,653 and 3,251,751, also disclosed adding extraneous heat carriers such as fuel ashes, fireclay, alumina, silica, silicates, catalyst beads, magnesium oxide or like materials to the heat carrier circuit in conjunction with combustion residue to maintain an inventory of heat carrier for effecting the pyrolysis reaction. For the most part, the data presented in prior art of this type were derived primarily from tests conducted relative to the degasification of coal and, then, only broadly relate to the processing of oil shale.

It has now been found that the presence of the combusted spent shale residue, i.e., shale ash, in the pyrolysis zone is detrimental to the economical recovery of shale oil from oil shale containing substantial amounts of carbonate minerals. This is because the shale ash sorbs a significant quantity of the product shale oil during the pyrolysis reaction which is subsequently lost to the recovery system. The sorbed oil is burned during the combustion of the spent shale used to provide the heat for reheating extraneous heat-carrying bodies. This sorption is believed to be peculiar to oil shales containing substantial carbonate mineral concentrations because upon decomposition of the carbonates, the residue or shale ash is converted to an extremely fine (50 to weight percent smaller than 325 mesh or 44 micron), porous and oleophilic material. If this shale ash is allowed to remain in the heat-carrier circuit, the total hydrocarbons available for recovery will be adversely affected by sorbing more of the oil product than is necessary to furnish the overall process heat requirements. As previously noted, the fixed carbon content of the spent shale alone is generally more than sufiicient to provide the pyrolysis heat requirement. As to the endothermic carbonate decomposition reaction, it has been determined that for spent shale combustion tempertaures up to about 1400 F.-the process heat requirement is still in balance. Additionally, because of the minute particle size of shale ash, substantial levels of base sediment contaminate results from vapor entrainment of this fine ash if it is not purged from the circuit.

SUMMARY OF THE INVENTION It is therefore, the principal object of the present invention to provide a process for the recovery of shale oil from oil shale whereby the loss of shale oil by sorption on porous shale ash in the pyrolysis zone is prevented entirely or at least substantially.

In general, the process of the present invention provides for the recovery of shale oil from oil shale via solid-to-solid heat transfer techniques while preventing the loss of shale oil by sorption on porous shale ash in the pyrolysis zone. This is achieved to the process herein described by insuring that the heat-carrying bodies recycled to the pyrolysis zone are free entirely or substantially of shale ash. The heat-carriers used herein may be any small attrition resistant material such as silica, minute alumina beads, or the like. The shale ash is removed from the heat carrier body circuit by attrition and elutriation steps. These steps are preferably carried out in conjunction, however, each step may be performed independently of the other. Thus, in combusting the fixed carbon on the spent shale or shale coke by-product of the pyrolysis of oil shale in a dense phase fluid bed combustion zone containing the cooled heat-carrying bodies, the spent shale is converted to friable particles of shale ash which are attrited to fines by frictional contact in the turbulent dense phase fluid bed combustion zone and the fines elutriated therefrom by the hot flue gas by-product of combustion. The remainder of the friable shale ash particles are separated from the reheated heat-carrying bodies by attriting them to fines at a location downstream of the fluid bed combustion zone. This is conveniently accomplished in the present process While transporting the shale ash from the combustion zone to an accumulation zone wherein the recycle heat-carrier is stored prior to being returned to the pyrolysis zone by subjecting the shale ash to a second attrition and elutriation step. The hot heat-carrying bodies, now free entirely or substantially of shale ash, are recycled to the pyrolysis zone to effect the pyrolysis of oil shale to shale oil in the absence of sorbent porous shale ash so as to prevent the loss of shale oil by sorption on the porous shale ash in the pyrolysis zone.

The process further provides for the economical recovery of the heat content of the hot flue gas. This heat may be used to preheat raw oil shale fed to the pyrolysis zone if the sorbent shale ash is first removed from the gas stream. The heat may be more conveniently recovered via indirect heat exchange with the combustion air to the dense phase fluidized bed.

DETAILED DESCRIPTION OF THE INVENTION The process of the invention will be further illustrated and described in detail in connection with the accompanying drawing which represents a flow diagram of the process of the invention.

Oil shale, previously crushed to a particle size of nominal minus /2-inch, is fed from source 1 to the pyrolysis zone (retort) 2. The shale may be preheated prior to being fed to the retort by passing the cold shale at about 60 F. through preheater 3. Shale preheating may be accomplished by recovering the sensible heat from the discharge flue gas product of spent shale combustion described below. The sensible heat may be recovered either directly by entraining the cold shale in a stream of hot flue gas from which the solid combustion zone products have been removed, or indirectly by passing the flue gas through a heat exchanger of the type resembling a bundle of fin tubes. Regardless of the preheat procedure, it is desirable to preheat the shale to at least 220 F. to remove as much of the free moisture as possible and reduce the size of the downstream shale oil recovery equipment.

In one pilot plant test run, the crushed oil shale was preheated to about 230 F. in a dilute phase fluid bed and fed at an average rate of about 1180 pounds per hour into the retort 2 operating at a pressure of 0.75 p.s.i.g.

Hot heat-carrying bodies substantially free of shale ash and having an average temperature of about 1215 R, which are preferably highly attrition resistant silica sand particles having the granular particle size distribution set forth in Table 1 below, are fed from the heat-carrier accumulator 4 to the retort 2 via line 5 at an average rate of about 4000 pounds per hour. The present process contemplates the use of all attrition resistant heat-carrying fluidizable solids having a particle size range in the order of 100 mesh to about 4.0 mesh.

TABLE 1 Cumulative weight percent In the retort 2, the hot heat-carrying sand particles are mixed with preheated oil shale and conveyed therethrough. The retention time required in the retort is in the order of 2 to 5 minutes. The hot sand particles exchange heat with the preheated oil shale to convert the kerogen content thereof into shale oil vapors at a temperature of about 950 F. and a spent shale residue. The shale oil vapors comprise noncondensable or gaseous hydrocarbons as well as vaporized condensable hydrocarbons. The spent shale or shale coke contains fixed residual carbon in amounts ranging from about 3% to about 6%.

The typical carbon content of the Green River oil shale found in western Colorado and processed via solidto-solid heat exchange techniques is in this range. The fixed carbon content of oil shale usually varies with its origin or location and can be as high as 10% or more by weight. Since the fixed carbon represents an available energy source, all efforts should be exerted to recover or utilize it efiiciently.

The solids blend of cooled heat-carrying bodies, i.e., sand, and spent shale particles plus the shale oil vapors pass from the retort 2 into a solids-vapor separator vessel 6. The shale oil vapors collect in the upper portion of the separator 6 and are removed therefrom via conduit 7 and passed to a vapor recovery zone or fractionator 8 for further downstream processing.

The solids blend of cooled heat-carrying bodies and spent shale particles is withdrawn from the bottom of the separator 6 through the solids flow control valve 9 via line 10 and passed therethrough to a dense phase fluidized bed combustion zone 11 by conventional dense phase transport procedures. If the solids blend contains a substantial quantity of large spent shale particles, for example, minus one-inch to plus Az-inch size, the particles may be comminuted via crusher 12 prior to entry into the combustion zone 11. Because spent shale is somewhat friable and easily crushed, the crusher rolls are disposed to impose only moderate pressure on the larger spent shale particles without fracturing the heat-carriers.

In the fluidized bed combustion zone 11 the carbon content of the solids blend is combusted to provide the heat for reheating the heat-carrying bodies therein. The heat-carrying bodies are generally covered with deposited coke, while the spent shale contains coke throughout its fine-grained matrix. If the fuel requirement provided by the carbon content of the solids blend fed to the combustion zone 11 is insufficient to accomplish the desired retorting, additional extraneous fuel may be added to the fluid bed in the form of heavy oil, tar or the like. The fluidized bed is operated to provide turbulent frictional contact within the bed section 13 and freeboard section 14 to thereby cause severe attrition of the friable spent shale ash into shale ash fines having a particle size preferable less than 200 mesh. The fluidized bed is operated at temperatures ranging from about 1100 F. to about 1650 F. and at fluidizing superficial air velocities of from about 2.5 to 6.0 feet per second. The higher combustion temperatures of 1400 to 1650 F. are desired because carbonate decomposition of the spent shale more readily occurs, thereby enhancing the breakdown and degree of attrition of shale ash in the combustion zone. A further product of the combustion reaction is hot flue gas. The attrited shale ash fines are elutriated from the reheated heatcarrying bodies by the hot flue gas and withdrawn from the freeboard section 14 via cyclone separator 15 and line 16. The cyclone separator 15 returns any of the larger heat-carrying bodies which may be jetted out of the fluidized bed back to the bed. The hot flue gas which contains shale ash fines is conveyed via line 25 through a cooler 17 and into a solids removal zone 18, i.e., bag filter, prior to being discharged to the atmosphere via line 19.

The reheated heat-carrying bodies and any larger remaining particles of the friable shale ash not removed with the hot flue gas are withdrawn from the dense phase fluid bed combustion zone 11 via standpipe 20. The reheated heat-carrying bodies and the small remainder of the friable shale ash particles are fed through line 22 by hot air transport gas from source 21 into the heat carrier accumulator 4 having therein an elutriator 23 equipped with a plurality of attriter bars or baflles 24. The friable shale ash particles are attrited and comminued by impacting against the attriter bars 24 and thereby converted into shale ash fines having an average particle size of about 200 mesh (U.S. sieve) or smaller while the attrition resistant hot heat-carrying bodies are not significantly attrited. The elutriator also serves to disperse the shale ash fines so as to significantly improve the elutriation thereof from the heat-carrying bodies. The suspension of shale ash fines in the hot air transport gas is withdrawn from the elutriator 23 via line 25 which joins line 16 and passes through cooler 17 for cooling prior to subsequent fines-gas separation and disposal.

The hot heat-carrying bodies, now entirely or substantially free from shale ash, accumulate in a bed 26 within the base of the heat carrier accumulator 4. The heat carriers are fed from the accumulator 4 via line at a temperature of from 1100" F. to 1650 F. into the retort 2 to eifect pyrolysis of fresh oil shale introduced therein. Excess solids are withdrawn from accumulator 4 via line 27.

In one test conducted over a 16-hour period, the shale ash fines were allowed to build up in the recycle sand circuit to determine the effect of shale ash fines on the product oil yield. The overall effect was determined by noting the decrease in the fluid bed fuel (natural gas) requirement to maintain an average temperature of about 1400 F. It was observed during this test that the whole oil yield decreased as the test progressed, and that the decrease in oil yield was accompanied by a corresponding decrease in the fluidized bed fuel requirement. The data are presented in Table 2. Visual inspection of the recycle sand circuit confirmed that the ash content increased substantially over the test period.

TABLE 2.COMPARISON OF OIL YIELD AND FLUID BED FUEL REQUIREMENT NECESSARY TO MAINTAIN 1,400 F. BED TEMPERATURE 1 Weight percent at modified Fischer assay.

From the foregoing discussion and the data in Table 2 it is evident that product oil was sorbed and burned in the combustion zone. Extraneous fuel was required in all of these pilot plant tests to compensate for heat losses from the small-scale equipment.

In another test conducted to determine the effect of removing the shale ash from the recycle sand circuit on the overall product oil yield, a total of 8.9 tons "of the same Green River oil shale as used in the above test were preheated to 230 F. and processed over a test period of eleven hours. A charge of clean silica sand having the particle size distribution set forth in Table 1 above was used for this test. The fluid bed combustion zone was operated at a superficial air velocity of 4.2 feet per second to remove all solids of less than about 200 mesh. Upon completion of the test, it was determined that the recovered oil plus C and heavier gaseous hydrocarbons amounted to 100.5 weight percent of Fischer assay. The total amount of hydrocarbons recovered, which also includes C through C hydrocarbons, oil, and C and heavier gaseous hydrocarbons was 107.2 weight percent of Fischer assay.

From the above description of the process of the invention, it is clear that it provides for the recovery of shale oil from oil shale without the loss of shale oil by sorption on porous shale ash in the pyrolysis zone and subsequent combustion thereof and loss in the combustion zone or reheater. This is achieved by insuring that shale ash is not fed into the pyrolysis zone. Using the process described herein, the shale ash was removed from the heat carrier circuit by means of a primary attrition and elutriation step conducted in the dense phase fluid bed combustion zone and a secondary attrition and elutriation procedure performed downstream of combustion zone in the heat carrier accumulation zone. By such attrition and elutriation of the shale ash, it is removed from the reheated heat carriers so they are fed to the pyrolysis zone free entirely or substantially of shale ash.

It will be appreciated that various modifications and changes, in addition to those set forth above, can be made in the process of the invention by those skilled in the art without departing from the essence of the invention and that accordingly the invention is to be limited only within the scope of the appended claims.

What is claimed is:

1. A process for the recovery of shale oil from oil shale which comprises:

(a) pyrolyzing oil shale containing substantial quantities of mineral carbonates by heating the oil shale with attrition resistant hot heat-carrying bodies substantially free of shale ash in a pyrolysis zone to form shale oil vapors and a solids blend of cooled heat-carrying bodies and spent shale particles containing fixed carbon;

(b) separating the shale oil vapors from said solids blend in a separation zone and passing the separated shale oil vapors to a recovery zone;

(c) attriting the spent shale particles and combusting the carbon content of the solids blend in a combustion zone to reheat the cooled heat-carrying bodies and to form hot flue gas and fine shale ash particles;

(d) separating the hot flue gas and fine shale ash particles from the hot heat-carrying bodies to provide hot heat-carrying bodies substantially free of shale ash particles; and

(e) recycling the hot heat-carrying bodies substantially free of shale ash to the pyrolysis zone to pyrolyze fresh oil shale fed therein;

whereby loss of shale oil by sorption on porous shale ash in the pyrolysis zone is prevented.

2. The process as defined by claim 1 wherein the heatcarrying bodies are attrition resistant silica sand particles.

3. The process as defined by claim 1 wherein the shale ash fines are separated from hot heat-carrying bodies by elutriation of the shale ash fines fromthe combustion zone with hot flue gas.

4. The process as defined by claim 1 wherein the spent shale particles of the solids blend are comminuted prior to entering the combustion zone.

5. A process for the recovery of shale oil from oil shale which comprises:

(a) pyrolyzing oil shale by heating the oil shale with hot heat-carrying bodies substantially free of shale ash in a pyrolysis zone to form shale oil vapors and a solids blend of cooled heat-carrying bodies and spent shale particles containing fixed carbon;

(b) separating the shale oil vapors from said solids blend in a separation zone and passing the separated shale oil vapors to a recovery zone;

(c) reheating the cooled heat-carrying bodies in a dense phase fiuid bed combustion zone by combusting therein the fixed carbon contained in the spent shale particles to form hot flue gas and friable shale ash particles;

(d) attriting a portion of the friable shale ash particles to fines in the dense phase fluid bed combustion zone 7 and elutriating therein the fines from the reheated heat-carrying bodies by the hot flue gas;

(e) attriting the remainder of the friable shale ash particles to fines in a heat carrier accumulation zone and elutriating therein the fines from the reheated heat-carrying bodies by hot air transport gas to provide hot heat-carrying bodies free of shale ash; and

(f) recycling the hot heat-carrying bodies free of shale ash to the pyrolysis zone to pyrolyze fresh oil shale fed therein;

whereby loss of shale oil by sorption on porous shale ash in the pyrolysis zone is prevented.

CURTIS R.

References Cited UNITED STATES PATENTS DAVIS, Primary Examiner

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