WO1986003510A1

WO1986003510A1 - Shale oil production process and apparatus

Info

Publication number: WO1986003510A1
Application number: PCT/US1984/002033
Authority: WO
Inventors: Earl Mullins; Robert H. Pettey, Jr.; Chang Yul Cha; Donald L. Morris
Original assignee: Gemini Research Inc
Current assignee: Gemini Research Inc
Priority date: 1984-12-12
Filing date: 1984-12-12
Publication date: 1986-06-19
Anticipated expiration: 1987-06-12
Also published as: EP0203920A1

Abstract

Apparatus and process for producing a combustible liquid from solid oil shale. The process comprises the steps of: (a) heating particles of shale to an elevated temperature in a heating liquid bath in the abscence of air at which vapor of the combustible liquid may be evolved from the shale; (b) retorting the shale at the elevated temperature at substantially an isothermal condition for a time sufficient to evolve vapor of the combustible liquid and to produce retorted shale; and (c) condensing the vapor to produce the combustible liquid. Preferably, shale removed from the retorting process is subjected to a stripping operation to strip from the removed retorted shale additional vapor of the combustible liquid and vapor from heating liquid retained on the removed retorted shale.

Description

SHALE OIL PRODUCTION PROCESS AND APPARATUS

Background of the Invention

The present invention relates to an improved shale oil production process and apparatus. More spe¬ cifically, this invention relates to an apparatus and process for producing shale oil from oil shale under a substantially isothermal condition, and preferably including solvent extraction by which up to about 98% of the potential shale oil content of the kerogen con¬ tained in the shale can be recovered. The present invention is based on the discovery that high quality light shale oil usable as fuel oil can be produced by heating the oil shale to the retorting temperature as fast as possible at the lowest possible reaction tem¬ perature.

Oil shale is a term which generally refers to a wide variety of laminated sedimentary rocks usually containing more than one-third mineral matter and vary- ing amounts of organic matter. The organic matter is

released by destructive distillation. The organic portion of oil shale (hereinafter "shale") is the kero¬ gen. The composition of kerogen varies, since the composition of the shale from which it is obtained varies, depending upon the location of the shale de¬ posits. In the United States, vast shale deposits are present in the Green River formation, including por¬ tions of the states of Colorado, Utah and Wyoming. Other significant deposits in the United States are located in the states of Alaska, Indiana and Kentucky. Considerable shale deposits have been found throughout » the world, including Australia, Brazil, France, Ger¬ many, New Zealand, South Africa, Spain, Sweden, Swit¬ zerland, the United Kingdom, the U.S.S.R. and Yugo- slavia, to mention a few.

Various combustible liquids can be obtained from shale. Generally, they are referred to as shale oil, and can be used for fuel oils, gasoline, jet fuels, by-products such as asphalt, waxes and deter- gents, and gas production, for example. Because of the extensive deposits and innumerable uses for shale oil, the economic commercial production of shale oil would be extremely beneficial. Major obstacles for commer-

cialization of shale oil are the high cost associated with mining and transporting shale, producing shale oil from the shale and upgrading and refining shale oil to produce saleable products. If saleable petroleum pro- ducts such as diesel fuel and home heating oil can be produced directly from oil shale, oil production costs would be reduced by eliminating the upgrading and re¬ fining costs.

Customarily, shale oil is produced by heating either a fixed or a moving bed of oil shale to a tem¬ perature of about 427°C (800°F) to about 537°C (1000°F) long enough to convert the kerogen to gas, oil and coke, and to distill the volatile conversion products from the inorganic residue or spent shale. Conven- tional retorting processes result in a recovery gene¬ rally not exceeding 80% of the kerogen in the shale as volatile products. Moreover, the shale oil produced from the prior art retorting processes typically is of low quality and must be upgraded and refined to sale- able products.

The present invention overcomes the disadvan¬ tages of prior art processes and apparatus and can be used to produce high quality shale oil in a commer-

^ cially economical manner, even from shale which hereto¬ fore has been difficult to treat, such as that found in the Eastern United States. Apparatus of the present invention may be constructed on a scale commensurate with the type and size of the shale deposit and can be engineered to perform the process of the present inven¬ tion in an efficient manner. Where desired, the appa¬ ratus of the present invention can be transported to different deposit sites. Even though the equipment may be small enough to transport, it still can be operated efficiently and on a commercial basis.

Summary of the Invention One aspect of the present invention relates to a process for producing a combustible liquid from solid oil shale comprising the steps of:

(a) heating particles of shale to an elevated temperature in a heating liquid bath in the absence of air at which vapor of the combustible liquid may be evolved from the shale; (b) retorting the shale at the elevated tem¬ perature at substantially an isothermal condition for a time sufficient to evolve vapor of the combustible liquid and to produce retorted shale; and (c) condensing the vapor to produce the com¬ bustible liquid.

Preferably, shale removed from the retorting process is subjected to a stripping operation to strip from the removed retorted shale additional vapor of the combustible liquid and vapor from heating liquid re¬ tained on the removed retorted shale.

Another aspect of the present invention re¬ lates to apparatus for producing a combustible liquid from oil shale comprising retorting means for retorting shale particles in a heating liquid bath in the absence of air at an elevated temperature sufficient to evolve vapor of the combustible liquid from the shale, tem¬ perature maintaining means for maintaining the te pera- ture of the heating liquid bath at a substantially isothermal condition during retorting, condensing means for condensing the vapor to produce the combustible liquid, and conduit means through which the vapor moves from the retorting means to the condensing means. Again, it is preferred that the retorted shale be removed from the retort to a stripper for further extraction of vapor of the combustible liquid remaining after the shale has been retorted. Brief Description of the Drawing For the purposes illustrating the invention, there is shown in the drawing a schematic form of the invention which is presently preferred; it being under- stood, however, that this invention is not limited to the precise arrangement and instrumentalities shown.

The single drawing figure illustrates a gene¬ ral schematic diagram of apparatus used to perform the process of the present invention indicating the inter- relationships of the various components.

Detailed Description of the Preferred Embodiments

Referring to the drawing in detail, apparatus

10 of the present invention is illustrated in a gene- ralized or schematic representation. The specific structure of each component is not deemed to be a matter of importance for the purpose of understanding the present invention. Rather, based on the disclosure contained herein, one of ordinary skill in the art could acquire or make the individual components and connect them without undue experimentation. The appa¬ ratus will be described in connection with an explana¬ tion of the process from the initial treatment of the

OMPI shale to the final production and separation of the shale oil.

Shale from the deposit is mined and crushed to have an average maximum dimension of about 0.5 cm (3/16 inch) to about 3.8 cm (1-1/2 inches) and prefer¬ ably from 0.6 cm (1/4 inch) to about 2.5 cm (1 inch). Since a key to the present invention is the rapid heat¬ ing of the shale to the retorting temperature, the shale particles should not be too course. While finer particles may be used, no further advantage may be obtained to offset the increased cost of producing the smaller particles. The shale particles are stored in hopper 12 and fed at a controlled rate through valve 14 unto a conveyor 16. Hopper 12 may include feeding aids, such as vibrator means or the like, but need not be so sophisticated. Valve 14 preferably is a rotary metering valve, but could also be any other type of valve capable of delivering a measured amount of the crushed shale onto conveyor 16. Valve 14 can be either a manual valve, or preferably a remote controlled valve. Weighing means could be built into hopper 12 or associated with conveyor 16.

O F1

WIPO Typically, conveyor 16 is an inclined con¬ veyor so as to feed the shale particles into the upper portion of the apparatus. As illustrated, the shale is delivered from the discharge end of conveyor 16 into a feed hopper 18 adjoining an airlock assembly 20. Air¬ lock assembly 20 can be of any desired construction using water seals or the like to prevent a significant amount of air from entering the retort which may cause an explosion. The preferred airlock is shown schema- tically as including two valves which open and close in an alternating sequence with each other. Thus, first valve 24 is closed and then valve 22 is opened and to permit the shale to enter the airlock. Thereafter, valve 22 closes prior to the opening of valve 24 by which the shale is allowed to enter the bottom of an airtight conveyor 28. Preferably, steam is injected into the feed tube below the airlock from steam injec¬ tion conduit 26 so as to further reduce the possibility of explosions. Conveyor 28 may be of any suitable type. A screw conveyor is presently preferred. The shale par¬ ticles are delivered from conveyor 28 through feed tube 30 to the upper portion of a retort 32. After leaving

the feed tube, the shale particles are dispersed within the retort by means of a distribution device, such as an assembly comprising a series of concentric frusto- conical rings in which the upper rings are of a smaller diameter than the lower rings. Other distribution devices, such as a deflection grate arrangement, a series of baffle plates or the like, could be used. The purpose of the distribution device is to provide a reasonably uniform distribution of the shale particles at the upper portion of the retort, so that as they fall by gravity through the retort the maximum surface area of the shale particles are exposed to the heating liquid bath within the retort resulting in a substan¬ tially uniform bulk heating rate. This is also impor- tant in achieving the rapid heating of the particles to a substantially isothermal temperature.

A heating liquid bath is maintained within retort 32 by a fluid system to be described herein¬ after. It is critical to the present invention that the proportion of heating liquid to shale within the retort be controlled to rapidly heat the shale par¬ ticles to a temperature at which vapor of the com¬ bustible liquid to be produced (such combustible liquid

OMPI

^So being referred to hereinafter as "shale oil") will be evolved and to maintain the shale at the evolution temperature at substantially an isothermal condition. As used herein, a condition is "substantially iso- thermal" when the temperature of the heated materials after reaching equilibrium is maintained within a range of plus or minus 10 C (18 F). This technique, together with the use of a low evolution temperature as set forth below, produces the lighter, high quality shale oil which has not been produced by conventional pro¬ cesses.

Although the relative proportions of shale and heating liquid must be determined by the location of the processing plant, the type and composition of the shale, the weather conditions and other such fac¬ tors, rapid heating of the shale and the maintenance of the shale and heating liquid bath at a substantially isothermal condition should be achieved if the weight ratio of heating liquid to shale is at least 10:1. Other ratios may be suitable, depending on the circum¬ stances. The process may be efficient with such a ratio within a range of about from 10:1 to about 50:1, and preferably from about 20:1 to about 35:1. For

example, in hot, arid regions with dry shale being fed into the retort, the shale could be fed at a faster rate and, therefore, the heating liquid to shale ratio would be lower compared to cold and/or rainy locations where the shale may be wet or frozen, requiring a higher ratio of heating liquid to shale.

To attain the rapid heating to the shale oil evolution temperature, the heating liquid bath must be preheated before the shale enters the retort. Again, depending upon the composition of the shale being pro¬ cessed, the temperature of the bath should be main¬ tained in a substantially isothermal condition within a range of about 338°C (640°F) to about 354°C (670°F), and preferably from about 343°C (650°F) to about 349°C (660°F). It is preferred to use the lowest tem¬ perature possible to achieve evolution of better qua¬ lity and lighter shale oil vapor from the shale.

The heating liquid can be any liquid which will have a boiling point and decomposition temperature significantly above the shale oil vapor evolution tem¬ perature within the retort environment. A presently preferred heating liquid is a heavy gear oil, such as ASHLAND TRA SAE 140 gear lubrication oil. Heavy motor oil or other stable, high boiling point liquids would also be suitable for use as the heating liquid.

In addition to maintaining the proper propor¬ tions of shale and heating liquid within the retort to sustain a substantially isothermal condition, it is important to control the temperature and flow of the heating liquid within the retort. The drawing illus¬ trates an efficient apparatus to achieve this result. Heating means 38 is arranged to heat the heating liquid for the retort and to generate steam and super-heated steam. Heating means 38 comprises a heater 40, which may be a gas or oil burner, an electric furnace, or any other source of heat. Preferably, it is an oil burner or gas burner or a combination oil/gas burner. In this instance, a combustion air inlet 42 allows the entry of combustion air into burner 40. A heating chamber 44 which may include a mixing air inlet 46 includes the usual heat exchangers. Heating means 38 preferably also includes a super-heated steam generating means 48, a heating liquid heat exchanging means 50 and steam generating means 52. Suitable heating means may be ob¬ tained commercially. One source is The Trane Company of La Crosse, Wisconsin, U.S.A. The heating means typically includes a stack 53. Gas scrubbers or other pollution control equipment and the like may be used with the heating equipment to comply with local en¬ vironmental laws or regulations. The heating liquid is heated by heat ex¬ changer 50 to the desired shale oil vapor evolution temperature. From the heat exchanger, the heating liquid is pumped through conduit 54 in the direction indicated by the arrow adjacent the conduit to an upper portion of a jacketed conveyor 36. In a like manner, the other arrows in the drawing indicate the direction of flow of fluids through the conduits adjacent the arrows. The hot liquid is heated within insulated jacket 56 and flows downwardly through the jacket to conduit 58 to manifold 60 located in a lower portion of retort 32. The heating liquid is removed from an upper portion of the retort through conduit 62 by a pump 64 driven by motor 66. The heating liquid is returned to heat exchanger 50 through conduit 68. It should be understood by those skilled in the art that the heating liquid pump could be located at any convenient location within the above-described loop. It is important that the proper volume of the heating liquid at the proper

temperature be circulated through the retort, prefer¬ ably in a countercurrent flow to the descending shale particles, to sustain a substantially isothermal con¬ dition within the retort. The shale must be in contact with the heating liquid bath for a time sufficient for- most of the kero¬ gen and shale oil contained therein to be converted to vapor. If the time is too short, valuable shale oil may be lost. If the residence time is too long, the process and apparatus will not be operated efficiently and economically. A suitable residence time for the shale to be in the heating liquid bath is about 15 minutes to about 30 minutes, and preferably about 20 minutes to about 25 minutes. These time periods at a substantially isothermal condition within the above- identified temperature range result in an efficient production of vapor which can be condensed and sepa¬ rated into high quality light shale oil readily sale¬ able without further refining for use as fuel oil. The shale oil vapor evolved during retorting, along with steam and other volatile components, are removed continuously from the upper portion of retort 32 through retort oil vapor and steam conduit 110.

gE5ά The production of high quality, light shale oil is enhanced by combining the thermal decomposition of kerogen in the retort with solvent extraction in¬ volving the kerogen remaining in the retorted shale. Solvent extraction occurs in' the retort, with the heat¬ ing liquid and product oil being the solvents. The solvents extract the bitumen, but leave the sulfur com¬ pounds and nitrogen compounds in the shale particles. The retorted shale is removed from the lower portion of retort 32 on a continuous basis through airtight heated conveyor 36. While conveyor 36 may be of any suitable type, it is preferably a screw conveyor. Conveyor 36 is an ascending inclined conveyor. This allows the heating liquid retained on the shale particles to drain by gravity to the bottom of the conveyor. The sub¬ stantially isothermal temperature of the retorted shale particles is maintained as the shale travels through conveyor 36 by the heating liquid flowing through jacket 56 in a countercurrent flow path. The retorted shale is delivered from conveyor

36 through feed tube 70 to stripper feed conveyor 72. Any shale oil vapor, steam or other volatile components evolved within conveyor 36 are vented through vent pipe

OMH 112 to conduit 110. Sludge formed in conduit 36 may be removed through conduit 57 and valve 59 by a pump (not shown) for disposal.

Conveyor 72 may be any type of airtight con- veyor which can be heated, such as a jacketed screw conveyor. Retorted shale particles removed by conveyor 36 from retort 32 are transported by conveyor 72 through a feed tube 74 into a stripper preheater 76 which is connected to the top of a stripper 78. After additional shale oil vapor, heating liquid vapor and other volatile materials are removed from the retorted shale in the stripper preheater and the stripper, the then-spent shale is discharged from the stripper through any suitable metering valve 80, such as a manual or preferably a remote controlled rotary valve. An auxiliary knife valve or gate valve (not shown) may be used initially to seal the stripper and keep it airtight before the retorted shale fills the discharge tube. The spent shale is deposited onto discharge conveyor 82. The spent shale can be transported to a furnace where it can be burned to produce electricity, for example, or it can be disposed of as clean land¬ fill. By subjecting the retorted shale to treatment in both the stripper preheater and the stripper itself, almost all of the kerogen in the shale, in excess of about 98%, can be decomposed. In the retort, most of the kerogen in the shale is converted to hydrocarbon vapor, but due to a balancing of the vapor pressure within the shale particles and in the environment within the retort surrounding the shale particles, a significant amount of kerogen remains in the shale. By heating the retorted shale to a higher temperature, the internal vapor pressure of the kerogen components within the shale is greater than the external pressure in the stripper preheater and in the stripper, so that the additional shale oil components can be evolved and stripped from the shale.

Stripper preheater 76 is heated by super¬ heated steam from generator 48. The super-heated steam is conveyed from generator 48 through conduit 84 to a lower portion of an insulated jacket 86 which surrounds preheater 76. Conduit 84 also delivers super-heated steam to the lowermost of a series of interconnected baffle plates 88 within preheater 76. The super-heated steam is removed from an upper portion of the stripper

preheater through conduit 90, where it passes into an insulated jacket 92 surrounding conveyor 72. The steam is then returned to generator 48 through conduit 94. Suitable pumps (not shown) and valves (not shown) can be used to control the flow of the super-heated steam. The super-heated steam is heated to a tem¬ perature of about 371°C (700°F) to about 537°C (1000°F) and preferably within a range of about 482°C (900 F) to 509°C (950°F). As the shale passes through heated conveyor

72, its temperature is raised from its temperature in the retort of say 354°C (670 F) to the temperature of the super-heated steam of say over 398 C (750 F). Within preheater 76, the shale is heated when it flows through the preheater by gravity adjacent to the series of baffles 88 heated by the super-heated steam. The temperature of the retorted shale in the stripper pre¬ heater reaches about 371°C (700°F) to about 537°C (1000°F), and preferably 482°C (900°F) to about 509°C (950°F). At this temperature additional shale oil vapor is evolved from the retorted shale. The counter- current flow of super-heated steam and shale within the conveyor and preheater provides for a more efficient

OMPI_ A^ WTO ό heating process. The retorted shale flows through preheater within about two minutes. At the indicated temperatures, this residence time within the preheater is sufficient to convert almost all of the remaining kerogen within the shale to gaseous products.

From the stripper preheater, the very hot shale flows by gravity into stripper 78. Steam flows from steam generator 52 through conduit 96 having branches 98, 100 and 102 to manifolds 104, 106 and 108 at three different levels within the lower portion of stripper 78. Again, steam pumps and valves are not shown but may be used. The steam enters the stripper at several different levels to assure complete contact with the shale particles as they flow downwardly through the stripper by gravity.

Stripper 78 is used for the purposes of cool¬ ing the shale discharged from preheater 76, heating the steam as it passes through the stripper so that it is at a high temperature when it reaches the preheater to aid in the evolution of the shale oil vapor, and re¬ moving the last portion of the obtainable shale oil vapor and other volatile components from the retorted shale. Steam entering the bottom of the stripper is generally at a temperature of about 104 C (220°F) to about 176°C (350°F) and preferably at a temperature of about 107°C (225°F) to^' 121°C (250°F). The steam thus cools the shale so that it is discharged from the stripper at a temperature of about 121 C (250 F). As the steam travels through the stripper, the steam is heated by the hot shale particles to a temperature of about 482°C (900°F) to about 509°C (950°F). The steam flows through the stripper at a space velocity of about 6.3 standard m 3/minute/m2 to about 25.2 standard m 3/minute/m2 and preferably from about 12.6 standard m 3/minute/m2 to about- 18.9 standard m3/minute/m2. At this flow rate, the retorted shale is treated so as to remove substantially all of the removeable components within a residence time of about 20 minutes to about 40 minutes, and preferably from about 25 minutes to about 35 minutes.

The following discussion relates to the flow and treatment of vapors evolved from the shale during the various processing steps discussed hereinbefore. The majority of the vapor of the combustible liquid shale oil product is removed from the shale at iso¬ thermal conditions in retort 32. The vapor travels through the top of the retort into retort oil vapor and steam conduit 110. Any vapor evolved during the con¬ veying of the retorted shale in conveyor 36 is vented from conveyor 36 to conduit 110 by vent pipe 112. Pro- duct vapor and heating liquid vapor evolved in stripper preheater 76 and stripper 78, together with the steam used in this portion of the process, flow through the stripper and stripper preheater to conduit 116. The gases in conduits 110 and 116 are condensed in con- denser 114. Heat transfer cooling fluid flows in a countercurrent manner through coils in the condenser. The cooling fluid, preferably water, flows from a source (not shown) into condenser 114 through conduit 118 and out of the condenser through conduit 120. Condensed liquid flows from condenser 114 through conduit 122 into a gas-liquid separator 124. The separator may be one of any number of conventional devices well known to those skilled in the art. Pro¬ duct gas is removed from separator 124 through conduit 126 and can be recycled to the burner for heating pur¬ poses, stored or used for other purposes. The liquid remaining in the separator is an oil-water mixture. This mixture flows through conduit 128 into an oil-

water separator 130 where the different components are separated, preferably by specific gravity. Other types of separators can be used if desired. Oil is removed through conduit 132 and water can be removed through conduit 134. The water can be treated and recycled for use in the process either to generate steam or as con¬ denser cooling water.

The shale oil produced from the present in¬ vention can be used directly as fuel oil and need not be upgraded and refined to be saleable as was the case with shale oil produced by prior art processes.

The entire apparatus can be automated with conventional computer controlled equipment. In this manner, the process and apparatus can be fine tuned to account for the various factors, such as the type of shale, its moisture content and temperature, the tem¬ perature of the environment, the feed rate for the shale onto the feed conveyor, the operation of the airlock valves, the retorted shale removal conveyor speed, the temperature of heating liquid and its pump¬ ing rate, the steam generating and super-heating equip¬ ment, the stripper feed conveyor speed, the stripper discharge valves and discharge rate, and the other

variables mentioned above. The automated control pro¬ vides the best way of maintaining the isothermal con¬ dition within the retort and for optimizing the produc¬ tion of the shale oil. The present invention may be embodied in other specific forms without departing from the spirit or the central attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

Claims

1. A process for producing a combustible liquid from solid oil shale comprising the steps of:

(a) heating particles of shale to an elevated temperature in a heating liquid bath in the absence of air at which vapor of the combustible liquid may be evolved from the shale;

(b) retorting the shale at the elevated tem¬ perature at substantially an isothermal condition for a time sufficient to evolve vapor of the combustible

» liquid and to produce retorted shale; and

(c) condensing the vapor to produce the com¬ bustible liquid.

2. A process according to claim 1 further comprising the steps of:

(d) removing the retorted shale from the heating liquid bath;

(e) stripping vapor from heating liquid re¬ tained on the removed retorted shale and additional vapor of the combustible liquid from the removed re¬ torted shale and to produce spent shale;

(f) condensing the vapor from the heating liquid, the additional vapor of the combustible liquid and any steam to produce condensed liquids; and

(g) separating the condensed liquids from each other.

3. A process according to claim 1 wherein a weight ratio of at least 10:1 of heating liquid to shale is maintained during retorting.

4. A process according to claim 1 wherein the heating liquid bath is maintained at a substan¬ tially isothermal temperature within a range of about 338°C to about 354°C.

5. A process according to claim 4 wherein the shale is retorted for about 15 minutes to about 30 minutes.

6. A process according to claim 2 wherein the stripping comprises subjecting the removed retorted shale to a countercurrent flow of steam initially at a temperature of about 220 C to about 350 C.

7. A process according to claim 6 wherein the steam has a flow rate of about 6.3 standard m 3/minute/m2 to about 25.2 standard m3/minute/m2 , and the steam contacts the removed retorted shale for about 20 minutes to about 40 minutes.

8. Apparatus for producing a combustible liquid from oil shale comprising retorting means (32) for retorting shale particles in a heating liquid bath in the absence of air at an elevated temperature suffi¬ cient to evolve vapor of the combustible liquid from the shale, temperature maintaining means (28, 36, 38, 64) for maintaining the temperature of the heating liquid bath at a substantially isothermal condition during retorting, condensing means (114) for condensing the vapor to produce the combustible liquid, and con¬ duit (110) means through which the vapor moves from the retorting means to the condensing means.

9. Apparatus according to claim 8 wherein the temperature maintaining means includes heating means (38) for heating the heating liquid and means for metering the flow of shale particles (28, 36) and heated heating liquid (64) into and out of the re- torting means at a rate whereby a weight ratio of heat¬ ing liquid to shale of at least 10:1 is maintained.

10. Apparatus according to claim 8 further comprising conveying means (72) for conveying retorted shale from the retort to a stripping means (76, 78), the stripping means including means (52, 96, 98, 100, 102, 104, 106, 108) for directing steam in a counter¬ current flow with respect to the retorted shale whereby vapor is evolved from heating liquid retained on the retorted shale and additional combustible liquid vapor is evolved from the shale.

11. Apparatus according to claim 10 wherein the conveying means is at least one airtight heated conveyor (36, 72).

12. Apparatus according to claim 11 wherein the conveyor includes at least one screw conveyor (36, 72).

13. Apparatus according to claim 11 further comprising first conduit means (54) through which the heating liquid flows from the heating means to an upper portion of an outer jacket (56) around at least one of the heated conveyors (36), second conduit means (58) through which the heating liquid flows from a lower portion of the jacket to a manifold (60) in a lower portion of the retorting means (32), third conduit means (62, 68) through which the heating liquid flows from an upper portion of the retorting means to the

OMPI heating means, and pump means (64) for circulating the heating liquid through the conduit means, retorting means and heating means.

14. Apparatus according to claim 13 further comprising means for generating steam (52) and means for generating superheated steam (48), fourth conduit means (96, 98, 100, 102, 104, 106, 108) through which steam flows from the steam generating means to at least one level of a lower portion of the stripping means (78), a fifth conduit means (84) through which super¬ heated steam flows from the means for generating super¬ heated steam to a lower portion of a stripper pre¬ heating means (76) for heating retorted shale prior to the stripping means, the stripper preheating means being connected to an upper portion of the stripping means, a second heated conveying means (72) by which the retorted shale is conveyed from the one conveying means (36) to the stripper preheating means, a sixth conduit means (90) through which the superheated steam flows from an upper portion of the stripper preheating means to an upper portion of a jacket (92) surrounding the second heated conveying means, and a seventh con¬ duit means (94) through which the superheated steam

flows from a lower portion of the jacket surrounding the second conveying means to the means for generating superheated steam.