US2796390A

US2796390A - Process of retorting of oil shale

Info

Publication number: US2796390A
Application number: US269180A
Authority: US
Inventors: Kenneth M Elliott
Original assignee: Socony Mobil Oil Co Inc
Current assignee: ExxonMobil Oil Corp
Priority date: 1952-01-31
Filing date: 1952-01-31
Publication date: 1957-06-18
Anticipated expiration: 1974-06-18

Description

, June 184, -1957 f K. M. ELLIOTT PRocEss oF RETORTING oF OILSHALE Filed Jan. 31.. 1952 wwmz W. B M Z aLl W MM .U ZE

i INVENTOR. Bflnntfl 1% lh'dff lq TT? N E Y ISRGCESS F RETRTHNG @F 0E SHALE Kenneth M. Elliott, Woodbury, N. lf., assignor to Socony Mobil Oil Company, Inc., a corporation of New York Application lanuary 31, 1952, Serial No. 269,180

l Claim. (Cl. 2in-6) 'Ihis invention relates to a method and apparatus for obtaining valuable hydrocarbons from shale and the like. More particularly, the present invention is concerned with an improved process and apparatus in which shale is retorted in lan efiicient manner utilizing the cold shale feed as a medium for effecting condensation of oil vapors emitted upon roasting the shale.

It is common practice in the art to recover oils from solid oil-bearing or oil-producing materials and particularly to recover shale oil from oil shale. As is well recognized, ordinarily oil shale does not contain oil as such but a solid bitumen type material known as kerogen which, when heated, breaks down into gases, petroleumlike liquids, and carbon.

The manufacture of oil from oil shale has heretofore been accomplished by heating the shale at elevated temperatures suicient to educt the oil and separate it from residual mineral matter. However, commercial shale retorting operations previously employed have been generally cumbersome and expensive, involving large equipment and operating costs per unit of shale throughput. Important factors contributing to these economic burdens have been poor heat recovery in the retort systems and the expense, equipment, and time consumed in subsequently recovering the products of retortation.

A major object of this invention, accordingly, is the provision of a method and apparatus in which oil shale and the like may be eiciently retorted without the excessive heat loss which has been generally prevalent in the processes `and the equipment heretofore used. A further object is to provide a method and apparatus for retorting oil shale wherein intimate contact between vaporous shale oil products and condensed liquid shale oil is obtained. A still further object is the provision of la compact apparatus for retorting oil shale affording convenient means for subsequent recovery of the liquid shale oil. A specific object is the provision of an internal gas seal zone in the retorting system. These and other objects which will be apparent to those skilled in the art are accomplished in accordance with the present invention.

In my copending application Serial No. 246,462, filed September 13, 1951, now Patent No. 2,723,225, there is described a process and apparatus involving the continuous passage of crushed shale downwardly as a solid moving bed through an elongated vertical vessel having a condensing zone wherein gaseous products rising from a Ilower retorting zone of said vessel undergo condensation While flowing counter-currently to the solid moving bed. As set forth in the above-identified application, the crushed shale and gaseous products pass through a zone in the vessel intermediate the condensing and retorting zones wherein a gas seal is maintained by the introduction of an external stream of an inert gas in an amount sufficient to prevent the downward flow of condensed liquid shale oil without substantially inhibiting the downward passage of crushed shale.

In accordance with the present invention, it has now Patented June 18, 1957 V"ice been found that the maintenance of a gas seal within the retort intermediate the condensing and retorting zones thereof may be accomplished without the introduction of an external stream of gas. Operation of the process and apparatus described herein involves the initiation and maintenance of an internal gas seal intermediate the aforesaid condensing and retorting zones and at a fixed position relative to the walls of the retort by control of the amount of combustion-supporting gas introduced into the retorting system. More particularly, the operation of the instant process land apparatus comprises the continuous passage of crushed shale downwardly as a solid moving bed through an elongated vertical retort having a condensing zone wherein gaseous products rising from a lower retorting zone of said vessel undergo condensation while flowing counter-currently to said solid moving bed. An intern-al gas seal intermediate the condensing and retorting zones and at a fixed position relative to the Walls of the retort is maintained by control of the air or other combustion-supporting gas introduced into the burning zone of the retorting system. It has been found that by proper control of the amount of combustion-supporting gas into the retorting system, an internal gas seal between the retorting and condensing zones is formed at a fixed position relative to the walls of the retorting vessel, thus preventing downward ilow by gravity of the condensed liquid shale oil into the retorting zone of the retorting vessel.

The invention may be further understood by reference to the attached drawings wherein:

Figure 1 represents a schematic arrangement of apparatus for carrying out the process of the invention;

Figure 2 illustrates a detailed section of the apparatus of Figure 1, and

Figure 3 shows in schematic form a preferred embodiment of the invention.

Turning now to the drawings, and particularly to Figure 1, cold, crushed, raw oil shale is introduced into hopper 1i). The shale moves by gravity from hopper 10 through feed leg 11 provided with a suitable flow control means not shown and passes into the upper portion of retorting vessel 12. A gas, such as flue gas or steam, is desirably introduced into feed leg 11 through conduit 13 to forestall the upward flow of gaseous retort products therethrough. As the shale descends through the retorting vessel, it passes rst through a condensing zone where liquid shale oil condensed from gases generated during retorting is collected in the form of a pool. The liquid product, together with non-condensable gases, is withdrawn through outlet pipe 14 leading to a liquid gas separator 15. Liquid shale oil collects in the bottom of separator 15 and is withdrawn therefrom through draw-off pipe 16. Non-condensable gases are removed from separator 15 through pipe 17. A baiile 18 is afxed to the interior wall of retorting vessel 12 overlying the outlet connection of pipe 14 to prevent entrainment of granular solid shale particles in the product oil.

The descending shale, now wet with shale oil, passes from the condensing zone of retorting vessel 12 through a gas seal zone wherein the upward ilow of shale oil vapors, together with other gas present, is such as to permit sufiicient condensed shale oil to fiow downward which, in turn, is revaporized and flows upward to the condensing zone. Such internal gas seal zone is maintained by control of the amount of oxygen-containing gas introduced into the burning zone underlying the retorting zone. The oxygen-containing gas is suitably introduced into the burning zone of the retorting system through conduit 19 furnished with control valve 2t).

The downwardly moving shale in the retort vessel is further heated in the gasseal zone by counter-current heat exchange with the hot vapors rising from the retorting zone immediately below. As the rising hot vapors give up their heat to the descending shale passing through the gas seal zone, the condensable portion of the vapors isliqueed. YIt is for the purpose of minimizing the natural downward ow of this condensate and of preventing the poolv of liquid in the overlying condensing zone from flowing down into the retorting zone that the above-mentioned seal zone is' maintained at a point intermediate the condensing zone and the retorting zone.

Upon emerging from the seal zone, the preheated shale continues its downward passage through a retorting zone and a burning zone wherein it is contacted with an oxygen-containing gas suchas air introduced through conduit 19. Upon contact of the oxygen-containing gas with hot shale, residu-al combustible matter is burned from the shale, thereby providing the heat required for retorting, The combustion products flow upward in admixture with the vapors resulting from decomposition of the kerogen contentof the shale, and sai-d combustion products ultimately leave the top of retorting vessel 12 along with non-condensable retorting gas and liquid shale oil through outlet pipe 14. ln accordance with the instant invention, the amount of oxygen-containing gas introduced into the burning zone is such as-to provide sufficient gaseous products and a suicient temperature to initiate and maintain a seal zone intermediate the condensing and retorting Zone, as described above.

The hot shale flows downwardly from the burning zone and is further cooled by the introduction of a cooling medium such as water, steam, or theV like, suitably introduced through conduit 21 providedV with control valve 22. For initially heating the shale, hot fluegas is` introduced through conduit 23, valve 22 being closed and valve 24 being open. After operation ofthe retortv is begun, valve 24 is closed and valve 22 is opened as the introduction of cooling medium is desired. Spent shale'ows out of the bottom of retorting vessel 12 through outlet pipe 25, the rate of ow being conveniently controlled by valve 26. The introduction of a cooling medium is not considered essential to successful operation of the instant retort but is advantageous in that it assists in' upward transfer of heat to the retorting zone and further provides a seal by some downward leakage on outlet pipe 25, thereby serving to facilitate the desired upward movement of gaseous retort products.

It is essential, in accordance with the present method of operation, that the amount of oxygen-containing gas introduced into the burning zone of the retort system be controlled in amount s'uch vthat a seal zone is maintained between the condensing zone and the retorting zone of the retort system. The manner in which such seal zone is effected may be readily understood from an inspection of Figure 2. By' careful control of the amount of oxygen-containing gas introduced into theburning zone, it is possible in accordance with the instant invention to operate the retorting system-without providing a high velocity gas seal from an external source. Referring to Figure 2, which illustrates a portion of the retort containing the condensing and retorting zones, hot gases and shale oil vapors from the retorting zone pass upwardly and the shale oil vapors condense upon contact with the cold shale. The upward gas velocity is too' low in and of itself to prevent the condensed shale oil from liowing back to the retorting zone. The condensed shale oil, upon contacting the hot shale in the retorting zone, then revaporizes and passes upwardly to the condensing Zone wherein it re-condcnses. This cycle repeats itself until the upward flow of shale oil vapors, together with non-condensable gases present in the retorting system, is just the rate required to permit sutlicient oil to llow downward to vaporize and to flow backup the retort. After this internal recycle is established, it is maintained by control of the amount of oxygen-containing gas introduced into the burning zone of the retorting system so that the net amount of shale oil produced in the retorting zone would be condensed and removed as product from the retort. As will be realized, it is essential, in accordance with the above-described operation that the downtlowing shale carry as much heat down through the retort as the shale oil vapors carry upwardly. If such were not the case, the retorting Zone would gradually rise in the retorting vessel until it would be at the shale feed hopper and no cold shale would be available for condensing the shale oil and cooling the gases. One purpose in accurately controlling the amount of oxygen-containing gas fed to the bottom of the retort, is to control the location of the gas seal zone at a predetermined fixed position relative to the walls of the retort. A suitable automatic control means for such purpose is shown in Figure 3.

Referring to Figure 3, a preferred embodiment of the invention is depicted wherein the amount of air or other oxygen-containing gas introduced through conduit 19 is responsive to a variable condition such as temperature or pressure maintained in the seal zone of the retorting system. Thus, responsive device 27 extends from control point 2S to throttle valve 20 so that the quantity of air passing through said valve is directly responsive to a variable condition at said control point. It is contemplated that any of the commercially available temperature or pressure responsive devices may be employed for the above purpose. With the installation of such responsive device, the retorting system becomes substantially automaticsin'ce the amount of oxygen-containing gasintroduced through conduit 19 to the burning zonev is responsive to a variable within the seal zone. For example, the responsive device may be regulated by the temperature at some predetermined point in the seal zone. If, during operation of the retort, the temperature at the control point starts to increase, this means that the rising shale oil vapors and non-condensable gases are carrying more heat upv through the retort than the shale is carryingdown. Consequently, the retorting Zone beginsv to move up the retort, which movement is detected by the increase in temperature at the control point. The temperature responsive device, actuated by the increase in temperature, effects an increase in the amount of oxygencontaining gas being introduced through conduit 19 to the burning zone. This increase in supply of oxygencontaining gas effects an increase in the amount of noncondensable gases in the' rising gaseous stream coming. into contact with the temperature control point and thereby lowers the heat capacity per cubic foot of rising gas. Since the volume of seal gas required for Amaintenance of the seal zone is constant, the amount of shale oil liquid reflux required is lowered and the rate of said reflux is automatically reduced by the increase in rate of feed of the oxygen-containing gas being conducted to the retort. Consequently, the amount of latent heat of vap'oriz'ation transferred from the retorting zone up through the seal zone to the condensing zone is also lowered. The over-all effect of increasing the oxygencontaining gas rate to the retort accordingly is a decrease in the amount of heat carried up by the rising vapors from the retorting zone through the seal zone to the condensing zone and a stopping of the upward movement of the retorting zone initially caused by a minor upset in the retorting system.

It is particularly to be noted in conventional shale retorting operation, as heretofore practiced, in which shale oil reflux was not used to aid in maintenancek of a seal zone between retorting and condensing zones that the rate of `oxygen-containing gas conducted to the retort would be decreased under the above circumstances instead of being increased as described to lower the heat carrying capacity of the upward flowing vapors through the seal zone. Operation in accordance with the instant retorting process is accordingly quite different frorn prior practice.

If, on the other hand, the temperature at the control point begins to decrease during operation of the retort, this means that the descending shale is carrying more heat down through the retort than the oil vapors and noncondensable gases are carrying up. Accordingly, the retorting zone begins to move down the retort. Such downward movement is detected by the decrease in temperature at the control point. The temperature responsive device thereupon effects a decrease in the amount of oxygen-containing gas being introduced to the burning zone of the retort. The resulting `decrease in supply of oxygen-containing gas decreases the amount of noncondensable gases in the rising gaseous stream and consequently increases the heat capacity yof said gaseous stream. The amount of shale oil liquid reflux is increased, the rate of reux being increased by the decrease in the rate of feed of the oxygen-containing gas being conducted to the retort. The latent heat of Vaporization being transferred from the retorting zone up through the seal zone to the condensing zone is also increase-d. The net result of decreasing the oxygen-containing gas rate to the retort is an increase in the amount of heat being carried up by the vapors passing from the retorting zone to the condensing zone which, in turn, stops the downward movement of the retorting zone. In this case, also, it is to be noted that operation in accordance with the process of the invention is just the reverse of prior practices in which shale oil reux was not used as an aid in maintaining the seal zone. Thus, operation in accordance with prior practice would have dictate-d that the rate of oxygen-containing gas conducted to the retort be increased under the above given conditions instead of being decreased as in the present method of reto-rting.

In a less preferred embodiment, the responsive device employed may be actuated by changes in pressure at some predetermined point in the gas seal zone so that the upward pressure of non-condensable gaseous products and vaporized shale oil, including shale oil reflux, can be controlled so that it is always sufficient to support the overlying pool of condensed liquid shale oil. In this case, if the pressure at the control point should begin to decrease, the rate of introduction of oxygen-containing gas to the retort is automatically increased to compensate for such pressure drop. Conversely, should the pressure at the control point start to increase, then the rate of introducing oxygen-containing gas to the retort is decreased responsive to said pressure increase. In either case, the gas seal Zone is maintained at a xed position relative to the walls of the retort.

Modifications and refinements of the foregoing process may be made, depending largely on the nature of the shale oil product desired. Thus, where the presence of water in the retort is considered detrimental, it may be advantageous to preheat the raw shale being introduced into hopper to a temperature above the dew point of the retort gas to obviate possible condensation `of w-ater in the condensing zone.

In practice of this invention, the shale is suitably crushed. The preferred size should pass a 2-inch mesh sieve and be retained on a 1t-inch mesh sieve. However, crushed shale outside of this preferred mesh size may also be used. The temperature in the retorting zone is generally between about 800 and about 1500 F., depending `on the type of shale employed `and the nature `of the products desired.

It is to be understood that the crushed shale flows downward through the apparatus of this invention as a compact moving bed and that the unit is so designed that vapor velocities do not reach a value suiciently high t?) cause the descending solids to boil to any appreciable extent. The elimination of a high velocity gaseous stream within the retorting system affords several advantages. Thus, erosion of equipment and shale is minimized by substantial elimination of high vapor velocities. Collection of the liquid shale oil in a pool inside the retorting vessel is also advantageous in that a high degree of contact between the rising vapors and the liquid oil is achieved, resulting in greater heat recovery and improved adsorption of light hydrocarbons from the retort gas. The intimate contact between liquid shale oil and retort gas is further advantageous in eliminating the tendency of the retorted shale oil to disperse itself as a finely divided mist in the retort gas such as is `ordinarily the case when recovery by condensation is attempted in conventional equipment. This problem of dispersion is so troublesome in some instances that expensive electrical precipitators must be employed to resolve the shale oil mist. Operation in accordance with the present process eliminates the need for such precipitators.

While the method and apparatus described herein have been particularly directed to the recovery of shale oil from oil shale, the present invention may be adapted for the recovery of oils from any solid substance. Accordingly, it is to be understood that the above description is merely illustrative of preferred embodiments of the invention, of which many variations may be made within the scope of the following claim by those skilled in the art without departing from the spirit thereof.

I claim:

A process for the recovery of shale oil from oil shale, which comprises feeding crushed, raw oil shale to an elongated vertical retort, passing said shale downwardly through said retort, while bringing the same to ignition temperature, contacting the resulting hot shale with a stream of oxygen-containing gas to effect combustion of combustible matter present therein, flowing hot vaporous products emitted from the heated shale upwardly through a zone wherein a gas seal is maintained at a fixed position relative to the walls of the retort solely by control of the amount of said stream of oxygen-containing gas such that the upward ow of shale oil vapors and non-condensable gases passing through said gas seal zone sufficient to permit adequate liquid shale oil to llow downward to said retorting Zone, vaporize, and flow back up to said condensing zone, thereby eiecting an overall upward vapor flow suflicient to prevent the bulk 'of condense-d shale oil from passing into said retorting zone but insufficient to prevent the downward passage of crushed oil shale therethrough, passing said vaporous products from said gas seal zone and immediately condensing a portion thereof to liquid shale oil by contacting with cold, crushed raw shale feed, maintaining a pool of the liquid shale oil so obtained, passing said cold, crushed raw shale, wet with oil, through the aforementioned gas seal zone, removing a stream of non-condensable gases and liquid shale oil from the upper portion of said retort and Withdrawing a stream of spent shale on the lower portion of said retort.

References Cited in the le of this patent UNITED STATES PATENTS 1,130,001 Maclaurin Mar. 2, 1915 1,426,159 Doherty Aug. 15, 1922 1,467,757 Day Sept. 11, 1923 1,509,667 Catlin Sept. 23, 1924 1,738,202 Plantinga Dec. 23, 1929 1,866,399 DeBaufre July 5, 1932 2,079,586 Atwell May 4, 1937 2,396,036 Blanding Mar. 5, 1946 2,534,051 Nelson Dec. 12, 1950 2,550,677 Dalin et al May 1, 1951 2,626,234 Barr et al. Ian. 20, 1953 2,637,683 Kassel May 5, 1953 OTHER REFERENCES Synthetic Liquid Fuels, Annual Report of the Secretary of the Interior for 1950. Part II. Oil from Oil Shale February 1951. (Only Fig. 27 and p. 21 relied upon.)