US3483115A - Travelling grate shale retorting - Google Patents

Description

Dec. 9, 1969 J. H. HADDAD ETAL 3,483,115

TRAVELLING GRATE SHALE RETORTING Filed April 15, 1966 //2 1/6/7 fors James H Hack/0d United States Patent US. Cl. 208-11 5 Claims ABSTRACT OF THE DISCLOSURE A method of retorting oil shale in a horizontally moving bed wherein gaseous material flowing transversely through the shale bed, all in a downflow direction through a plurality of gas contacting zones establishes a restricted kerogen decomposition heat front in the top of the bed and drives the decomposition heat front progressively downwardly as the bed moves horizontally through the retorting section. Gaseous material obtained from an intermediate portion of the shale bed, from which oil mist was recovered, is employed to effect partial cooling of gaseous material recovered from a latter portion of the shale bed. This cooled gas is introduced to an initial portion of the shale bed to condense out entrained oil constituents and to preheat the shale.

This invention relates to an improved method for retorting oil shale to recover shale oil. More particularly, the present invention relates to the method and combination of process steps for retorting oil bearing shale in a horizontally moving bed.

Shale oil technology as we know it today has not reached an advanced commercially attractive stage and considerable work is yet to be done in developing systems having commercial acceptance for an economic recovery of valuable oil products. Oil shale is known as a sedimentary rock which contains a solid organic material known as kerogen. When this oil shale is heated to a suitable elevated temperature, the kerogen is decomposed by pyrolysis to shale oil, gas and a carbonaceous residue.

At the present time, a great number of shale oil retorting processes are available. Each of these processes are undesirable in at least one major respect which greatly reduces the economic incentive for their commerical application. Some of the major problems in shale retorting lay in controlling shale bed temperature, shale retorting time and otf gas temperature in a manner to maximize shale oil yield.

In shale retorting, large quantities of heat must be supplied to the shale bed to eifect substantially complete kerogen decomposition. The heat is supplied by a variety of methods including burning a portion of the shale off vapor or by burning the kerogen or organic carbon in a portion of the shale bed. In any event, the heat is usually passed through the shale bed by using very large quantities of gas. The desired hydrocarbon products produced by kerogen decomposition are vaporized, carried out of the bed by the gas moving through the bed and recovered from the otf gas. Since very large quantities of gas are employed, it is desirable that the olf-gas temperatures be sufficiently low to facilitate oil recovery. The alternative of cooling hot off-gas by heat exchange is not attractive due to the very large amount of necessary heat exchange surface and the problems associated with coking of hot-gas conduits and exchangers. The duel requirements placed upon the gas of (1) supplying sufiicient heat to the shale to eifect kerogen decomposition and (2) being of a sufficiently low temperature upon exit from the shale to facilitate oil recovery have resulted in retort operational problems which have not been satisfactorily solved by the prior art.

These problems are complicated by the presence of fines within the shale bed. To satisfactorily retort shale, it is necessary that the shale be in relatively small particle form to effect desirable heat transfer and to obtain high yields of shale oil. The most common method of forming relatively small shale particles is by crushing. When the shale particles are crushed there is a wide variance in particle size from a large quantity of fines which are particles less than A inch in size are formed. For example, where it is desirable to obtain shale particles which have a maximum size of 4 inches by present crushing methods, the quantity of fines produced will vary from a minimum of about 8 percent to 30 percent by weight depending on the types of crushers used. Under retorting conditions of high gas rates and high temperatures, the fines will reflux between the cool and hot portions of the bed in many of the presently known processes. For example, in shaft-furnace type retorts where the shale moves downwardly through the retort by gravity and the gas flows upward through the retort countercurrent to the shale flow, the oil vapors condense on and entrain the fines in the cooler upper levels of the bed and when refluxed to the hot lower portion of the bed will coke thereon. This results in an oil yield loss. Another result is the bridging of the particulate shale within the bed. Gadually the amount of fines and coke builds up in the bed and clinkers form. This results in additional restricted movement of shale particles through the retort. This condition is prevalent in the above-described shaft furnace type of retort even though the raw shale fines formed in the crushing operation are removed from the shale inventory prior to charging to the furnace. It has been found that the spent shale from these furnaces, even when operating with a fines-free raw shale charge, contains fines concentrations higher than 15-20 percent. These fines are formed during the heating and retort process due to weakening of the shale structure.

In addition, concentrated fines cause undesirable gas channeling through the shale bed. This results in nonuniform heating of the shale bed and further oil yield losses to coke. In addition, fines refluxing which causes fines buildup in the bed can result in undesirably high pressure drop throughout the bed. Further, the refluxed fines are subjected to excessive heating which results in carbonate decomposition. When excessive carbonate decomposition occurs, the amount of heat available for kerogen decomposition is decreased since carbonate decomposition is an endothermic reaction. The gross process heat requirements for kerogen decomposition then correspondingly increase.

An object of the present invention is to provide an improved oil shale retorting process which is thermally eflicient.

A further object of the present invention is to provide a shale retorting process which minimizes undesirable shale fines formation and refluxing or fines buildup in the shale retorting section.

A still further object of the present invention is to retort oil shale in a horizontally moving bed in a manner which more efiiciently utilizes heat carrying gasiform material to effect kerogen decomposition and recovery of oil from the shale bed.

A still further object of this invention is to provide a method for eificiently retorting the raw shale fines which are produced during the crushing step.

Other objects and advantages of the present invention will become more apparent from the following description.

Accordingly, the present invention relates to the method and sequence of processing steps for decomposing shale kerogen in a horizontally moving bed of shale with heat carrying gasiform material caused to move in a controlled and restricted manner through the shale bed. That is, gasiform material is employed to form a heat wave at kerogen decomposition temperature either on an upper or lower portion of the bed surface. In addition, the gasiform material is employed to move the heat wave progressively through the vertical height of the bed. The heat wave depth forms only a relatively narrow portion of the bed vertical height in any given bed section. In cross sectional representation, the heat wave appears to slope vertically away from the bed surface where gas is introduced to the bed and horizontally in the direction of the shale bed outlet. When the heat wave has passed through the entire bed height, substantially all of the kerogen in the shale bed has been decomposed to selectively produce oil product in high yields.

In accordance with the present invention, a bed of particulate shale of desired thickness or height is laid down on a traveling grate which moves horizontally and sequentially through a plurality of gas contacting zones. In the retorting operation, a heat wave carried by hot gasiform material and having a temperature sufiiciently elevated to effect kerogen decomposition is initiated on a portion of either the upper or lower surface of the shale bed as it moves horizontally into the retorting section. As the shale bed moves in its horizontal path, it is continuously subjected to contact with gasiform material which is caused to move through the shale bed thereby moving the kerogen decomposition heat wave in the form of a continuous relatively narrow band through the entire bed vertical height. The incoming gas is introduced in all contact zones on the same horizontal level of the bed where the heat wave is initiated. In the process of this invention, gas flow throughout the horizontally moving bed height can be either all downfiow or upflow. and one important aspect of the method and system of this invention is directed to maintaining the flow of gas all in the same direction for reasons herein described.

The gas inlet temperatures and gas flow rates to various horizontal areas of the bed from the shale inlet to the spent shale outlet may be varied and maintained in a manner to move the previously generated heat wave through the entire vertical height of the bed while at the same time cooling the spent shale as the bed progresses horizontally through the retort. The gas inlet temperatures and gas flow rates depend in part upon the shale particle size in the bed and the shale mass flow ratethrough the retort but in any event are regulated to obtain the desired kerogen decomposition heat wave progression through the bed. The heat wave in a given section of the retort is of sufiicient magnitude to effect substantial decomposition of the kerogen in a portion of the shale bed without effecting substantial overcracking of the kerogen decomposition product comprising oil vapors. The vapor outlet temperature of various sections of the retort are maintained sufficiently low to avoid substantial conversion of oil vapors to coke and to effect more efficient removal and recovery of oil products therefrom. Further, the vapor outlet temperatures from the various bed areas are maintained to effect a more desirable temperature and heating profile throughout the bed of shale and more efiicient utilization of available heat in the process.

Hereinafter, for purposes of convenience the process and system of this invention will be described in terms of an operation wherein all downfiow of gas is used. However, it is to be clearly understood that all upfiow can also be employed even though it is preferred to use all downfiow of gas through the shale bed. In the method and system of this invention, heat is supplied to a portion of the top of the horizontally moving shale bed to provide an initial heat wave having temperatures in the range of from about 1100 F. to about 1500 F. For purposes of convenience in controlling gas flow and temperature profile in the shale bed, it is preferred to introduce the hot gaseous material through a plurality of adjacent gas distributor means positioned throughout a portion of the length and at substantially the upper surface of the bed of shale. The thus distributed hot gaseous material causes a heat zone or band wherein kerogen decomposition takes place. Subsequent flow of colder recycle gases to the surface of the shale bed downstream from the hot gas inlet areas causes the hot band to move downwardly through the bed of shale as the bed moves horizontally through the retort thus causing a significant change in the bed vertical temperature profile. A bed in vertical cross-section view along its length would show a heat wave front wherein kerogen decomposition takes place sloping downwardly in the direction of the spent shale outlet. In the method of this invention the bed becomes gradually hotter in the lower portion of the bed while the upper portion of the bed becomes gradually cooler as the bed moves horizontally through the shale retort section. The incoming recycle gas to each retorting section removes heat from the top portion of the bed and releases the heat in a lower portion of the bed. The heat generated and/or picked up and carried by the gas from the hot retorted shale and subsequently released to colder raw shale below has been found to be sufiicient to maintain the heat wave above described and effect kerogen decomposition of the shale as the heat wave moves continuously downwardly through the bed. Thus the recycled gases cause the kerogen decomposition heat wave to move progressively downward through the entire vertical bed height as the bed moves horizontally through the retorting section.

Substantially downstream of the shale inlet and initial decomposition of oil shale, a relatively cool recycle gas from which condensible oil products have been removed is introduced to the top of the shale bed for flow downwardly therethrough. In this downstream portion of the bed, the kerogen decomposition heat wave is located in the lower portion of the bed. The incoming relatively cool gas is heated by the residual heat remaining in the shale in the upper portion of the bed and this heat is carried downwardly by the heated gas for release in a lower bed section to provide kerogen decomposition temperatures. The outlet gas temperature in the downstream portion of the bed is substantially higher than the outlet gas temperatures in the initial portions of the bed since the amount of cool shale underlying the kerogen decomposition heat wave diminishes as the bed moves horizontally through the retort. Therefore, a progressively smaller portion of the bed is available to extract heat from the vaporous material coming from the kerogen decomposition section of the shale bed. Therefore, in this portion of the retort, it is important to maintain close temperature contacts to avoid undesired cracking and heat damage to the horizontally moving grid supporting the shale bed and other related equipment.

It is clearly evident from the above that a continuous heat wave at kerogen decomposition temperatures is formed and maintained which appears in cross section to slope downwardly in the direction of the horizontal shale movement from the top of the bed to the bottom of the bed. Thus the bed temperature above and below the established heat Wave and kerogen decomposition portions of the bed will be below the heat wave temperature by virtue of the recycle gas and the shale bed not yet heated to the desired elevated temperature. Thus, advantage is taken of the vertical temperature profile in various portions of the bed to recover kerogen decomposition products and heat recycle gas more efiiciently. That is, when gas is introduced into the shale bed, after the heat wave is established, the bed gives up heat to the gas above the kerogen decomposition band but recovers heat from vaporous material below the band. In this manner, the bed erves as a most efificient heat exchange means to assist in effecting kerogen decomposition and recovery of condensible products from the vaporous material leaving the kerogen decomposition heat wave band. Further, when the heat Wave reaches the bottom of the retort, the bed is cooled to a sufficiently low average temperature that it can be removed from the retort without presenting unusual handling problems and without need for special heat resistant apparatus.

A further advantage is derived by the method and process of this invention in respect to problems associated with the presence of shale fines. In the present process solid particles fines refluxing and buildup is avoided because the gas flow through the bed is all in the same direction. The large majority of the fines remain entrapped in the voids between the large shale particles. However, a small portion of the fines are entrained in the moving gas. In the method of this invention, a wetted wave front containing partially condensed oil vapor obtained from kerogen decomposition precedes the heat wave in its vertical movement through the bed. This wetted wave front in the bed tends to trap those fines carried by the gas. The wetted wave front is formed by oil condensation on the shale particles in the relatively cool portion of the bed located below the kerogen decomposition heat wave. The condensed oil then removes the fines from the gas. As the heat wave progresses downwardly, the great majority of the condensed oil is revaporized and directed to a lower portion of the bed. A small portion of the condensed oil is converted to coke with the fines being retained in the formed coke. The downwardly moving oil is condensed and revaporized as described above and eventually is removed in the form of a mist from the bed. The amount of coke formed in the bed is relatively small and is distributed over a large surface provided by the shale particles.

Oil containing gases are removed at spaced intervals from the bottom portion of the bed of shale moving through the retort section at substantially different temperature levels in a plurality of separate gas recovery zones. Each gas recovery zone is associated with a particular oil separation step to which the recovered gases are directed for separation of oil therefrom. Generally, the average gas temperature in each recovery zone will be progressively higher in that portion of the shale bed wherein the kerogen decomposition heat wave is nearest the bed outlets. Advantage is taken of these varying temperature conditions to recover condensibles and condensed oil from the gasiform streams employed in the process and to heat and cool shale particles. Thus, the gases are sequentially subjected to a plurality of oil separation steps by passage through the shale bed in a manner that takes advantage of the temperature profile in any particular portion of the moving shale bed.

The oil recovered at higher temperatures is recovered in oil separation steps associated with those high temperature gas recovery zones so that substantially only the middle and/or higher boiling portions of the shale oil are recovered therefrom initially. The gases and uncondensed vapors are thereafter directed to that portion of the shale bed of lower temperature to affect a further cooling of the gases and vapors and recovery of condensible material therefrom. This usually comprises the initial portion of the bed nearest the shale inlet point. Simultaneously, in the initial portion of the bed the gases and uncondensed vapors are cooled and the bed is preheated. The reduced vapor temperatures in this portion of the shale bed cause the lower boiling fraction of the shale oil therein to condense. The condensed oil is recovered in the oil separation step associated therewith. In this manner, substantially all of the vaporous shale oil is recovered. In addition, it is unnecessary to provide an additional heat exchange step to recover substantially all of the shale oil from the bed off gas. Further, the heat removed from the shale bed by the off-gas and vapors in the downstream portion of the bed is substantially recovered in the initial portion of the shale bed thus adding to the thermal efficiency of the process.

In the process of this invention, a plurality of gas recovery zones are employed. For example, when only two gas recovery zones are employed, the first zone extends in the direction of shale movement from the shale inlet to that point of the bed wherein the heat wave is initiated. The second zone extends through the remaining horizontal bed length wherein oil containing vapors are emitted from the bed. The condensed oil in the gases from the second zone are removed from the gas in an oil separation step associated therewith. The gas and remainder of the uncondensed vapors are then recycled to the top of the bed in the first zone and passed there through to cool the same. The gases and condensed oil in the form of mist from the first zone are recovered and directed to an oil separation step different from the oil separation step associated with the second recovery zone to separately recover relatively low boiling shale oil from the gas. A portion of the gas from the first zone is then vented, while the remainder is directed to the portion of the top of the bed associated with the second gas recovery zone. The vapor directed to the top of the bed above the second recovery zone is split into at least two streams and is introduced in at least two separate bed sections. In the first section above the second recovery zone nearest the shale inlet, a heat wave having kerogen decomposition temperature is initiated on top of the bed. The heat can be supplied as for example by introducing air and fuel at combustion temperature to the top of the bed; burning a portion of the recycled vapors; by burning a portion of the kerogen in the shale bed or by a combination of these methods. In the second section on top of the bed associated with the second gas recovery zone, the gases from the first zone are introduced without additional heating or cooling thereof.

In another embodiment of the present invention, the recovery of oil from the shale bed can be effected in three main zones. The first recovery zone extends horizontally in the direction of shale movement from about the shale inlet to about that point of the bed wherein the heat wave is initiated. The second recovery zone corresponds to that portion of the horizontal bed wherein the heat wave is initiated and maintained at or near the top surface of the bed. The third recovery zone corresponds to that top portion of the horizontal bed wherein gases from the first zone are introduced without an intermediate gas heating or cooling step. The gases from the second and third vapor recovery zones are each directed to a separate oil recovery step. The gases and any uncondensed vapors from each of the oil recovery steps are directed to the top of the first zone to pass downwardly therethrough. The gases are cooled and vapors cooled and condensed while the bed is preheated in the first zone. The eifluent gases from the first zone are directed to an oil separation step associated therewith to remove the condensed shale oil from the gases obtained from the second and third oil separation zones. A portion of the first zone gases are vented. The remainder of the first zone gases are directed to the top of the second and third zones in respective amounts to maintain the desired heat wave progression through the bed vertical height.

In a preferred embodiment of the present invention the recovery of oil from the bed is conducted in three main zones. The three gas recovery zones are arranged as described above. The difference between this embodiment and that described above wherein three recovery zones are employed is the flow of gas from the second zone. In this embodiment, the off gas from the second zone is directed to the oil recovery step associated therewith. The gas from the recovery step is then directed to the third gas recovery zone prior to being recycled to the top of the first zone. In this manner, the off gases and vapor in the third zone are cooled prior to being subjected to an oil recovery step. Even though this cooling of the third zone off gas and vapor is obtained at the expense of heating the second zone oif gas, certain advantages are gained. The third zone ofi gas temperature is higher than the preceding two zones. Thus the gas contains higher boiling oil fractions which have a greater tendency to coke as compared to the lower boiling fractions. It is therefore desirable to quickly reduce this gas temperature before coke formation begins. In the alternative embodiment having three off gas zones described above, it is also possible to obtain desired low otf gas temperatures in the third zone without an additional heat exchange step. However, this is accomplished by using a bed having a horizontal length longer than theoretically necessary to obtain a complete kerogen decomposition. In the additional portion of the third zone after the kerogen decomposition has reached the bottom of the bed, gradually cooler vapor is passed therethrough. Thus, this cool gas mixes with the hot gas to lower the average gas temperature.

As discussed above, it is desirable to maintain the off-gas temperature in each recovery zone as low as possible while still effecting relatively complete kerogen decomposition in the bed. When two gas recovery zones are employed, the gas in the first gas recovery zone associated with the bed preheating zone should be maintained below about 150 F., while the gas in the second gas recovery zone associated with the retorting zone should be maintained below about 500 F. When three or more gas temperature in all the recovery zones are maintained tain the average gas temperature in the first gas recovery zone associated with the bed preheating zone below about 150 F., the gas in the last gas recovery zone associated with the last portion of the retorting zone below about 500 F. and the gas in at least one intermediate gas recovery zone below about 350 F. In any event, the gas temperature in all the recovery zone are maintained below about 500 F. to reduce coke formation. The average shale temperature at the retort outlet is maintained below that temperature will either thermally degrade the discharge apparatus or support. combustion of carbonaceous residue in the shale. In the process of this invention, this average shale outlet temperature is preferably maintained below about 400 F.

The figure represents in cross section the embodiment of this invention wherein three gas recovery zones are employed and gases from the second and third zones are mixed prior to being directed to the first zone.

Particulate shale which has been ground to a target average size of about 0.75 inch with a maximum particle size of about 4 inches is introduced into a hopper 1. The shale is directed from hopper 1 to classifier 3 through conduits 4 and 5. In classifier 3, the shale particles are classified according to size with the larger particles being directed to the bottom of the bed and the fines being directed to the top of the bed. Seal gas is introduced into conduits 4 and 5 to prevent air from entering the shale bed. In this embodiment, a double seal gas system is employed in conduits 4 and 5. The two seal gas flow rates are controlled so that the differential pressure between the two seal gas inlets 6 and 7 is essentially zero. The shale is introduced at a rate so that a relatively thick bed is formed on a horizontally moving perforated grate 8. The bed thickness on the grate 8 is maintained at about 6 feet. The small amount of fines which sift through the bed are recovered in hopper 9 and recycled through conduit 10 to the shale inlet hopper 1. The moving grate 8 causes the shale bed thereon to progress sequentially through zones 11, 12 and 13. The uncondensed gas from zones 12 and 13 are recycled to gas plenum 14 on top of the bed in zone 11 through conduits 15, 16 and 17. The uncondensed gas passes downwardly through zone 11 through the grate 8 and into a gas recovery zone 18 located below the grate 8. The gas in gas recovery zone 18 is maintained at a temperature below about 130 F. At this temperature, most of the shale oil is in the form of a condensed mist. The condensate and remaining gas are directed to an oil recovery step 19 through conduit 20. Oil recovery step 19 can be, for example, a cyclone separator or an electrostatic precipitator. Condensed oil obtained from oil recovery step 19 is directed through conduit 21 to storage not shown.

Uncondensed gas from recovery zone 19 is directed through conduits 22, 23, 24 and 25 to the top of the shale bed in zones 12 and 13. The uncondensed gas to zone 12 is first introduced into plenum chambers 26 and 27. Air is introduced to plenum chambers 26 and 27 through conduits 28 and 29. At start up, a fuel can be introduced to plenum chamber 26 through conduit 30 to a-dmix with the air and recycled uncondensed vapor under conditions to cause combustion in plenum 26. After start up it is usually unnecessary to add fuel to maintain combustion in plenum 26. In plenum 227, a portion of the uncondensed gas is burned. The resultant heat from the combustion in these two plenums is absorbed by the shale bed directly underneath these zones. By this heating, a heat wave at kerogen decomposition temperature is initiated on top of the bed in zone 12.

The kerogen decomposition zone is caused to move downwardly and toward the shale outlet in a configuration shown in FIGURE 1. Representative temperatures of the gas introduced to each zone as well as the bed temperature profile is shown in FIGURE 1. The ratio of gas rate to the shale rate in each zone is adjusted to provide the representative temperature profiles shown. The gas in vapor zone 12 is caused to move downwardly through the entire vertical height of the bed. This gas is recovered in plenum zone 35 at a temperature below about 225 F. At this temperature a major portion of the oil has condensed. The uncondensed and condensed oil and gas are directed through conduit 36 to an oil separator 37 wherein oil is recovered through conduit 28 and uncondensed vapor and gas are directed to plenum chamber 39 through conduit 40.

In zone 13, recycled gas from oil recovery step 19 is introduced into plenum chamber 41 on top of the bed at a temperature of about F. This gas is acused to move downwardly through the entire vertical height of the shale bed. In so doing, the top portion of the bed is cooled while the bottom portion of the bed is progressively heated until the kerogen decomposition heat wave reaches the grate 8. That portion of the bed lying between this point and the shale outlet in a horizontal direction is cooled through the entire vertical height. The off-gas from zone 13 is recovered in plenum chamber 39 at a temperature, when admixed with the uncondensed vapor from oil recovery step 31, of below about 400 F. At this temperature an additional portion of the higher boiling fraction of the shale oil is condensed. The uncondensed and condensed shale oil and gas is directed from plenum chamber 39 through conduit 42 to oil recovery step 43 wherein shale oil is recovered. The uncondensed vapor and gas from oil recovery step 43 is directed through conduits 44, 15, 16 and 17 to the top of zone 11 into the plenum chamber 14. The gas in plenum chamber 14 is caused to move through the vertical height of the bed in zone 11 in a manner described above. Blowers are provided in the various gas conduits to ensure gas flow downwardly through the bed. The gas flow rates to plenums 14, 27 and 41 are maintained respectively at about .765 ton vapor/ tons shale, .447 ton vapor/ tons shale and .483 ton vapor/ tons shale.

The grate 8', after progressing through zone 13 is contacted with a small portion of gas introduced through conduit 45 which removes any coke which has formed in the perforations of the grate. This gas moves only through a very small portion of the vertical height and is recovered in plenum chamber 39. The grate 8 is in sections and above hopper 47 the sections are tipped so that the shale thereon can be removed. The shale is broken up by the clinker breaker 46 and thereafter moves by gravity to hopper 47 and directed outwardly from the retort zone through conduit 48 onto a conveyor 49. Conduit 48 is sealed from the atmosphere by a dual-gas seal system by the introduction of seal gas through conduits 50 and 51 similar to that described above for the inlet seal system. The relative sizes of the gas inlet plenums are approximately proportional to the inlet gas flow rates thereto. To afford relatively complete clearing of the grate 8, it is subjected to a jet of fluid and/ or solids through conduit 52. The material entrained on the grate is directed to hopper 53.

In the process of this invention, the shale bed can be moved in a closed horizontal path as for example in a circular path or in an open horizontal path as for example in a straight line. In any event, the shale bed is continuously moved through a plurality of vapor contact zones. The vapors in each zone are introduced at a pressure sufficient to ensure vapor How in one direction through the bed vertical height. The gas pressure differential between the top and bottom of the bed to ensure this flow depends upon a number of factors including the average shale particle size, bed thickness, the gas flow rate used, and the temperature conditions of the bed. In the process of this invention, the average shale particle size is maintained below about 2 inches and preferably below about 0.6 inch. The shale bed thickness is maintained below about 15 feet and preferably between about 4 feet and about 8 feet.

In operation, the particulate shale can be directed onto the grate through a feeding device which stratifies the shale according to size with larger shale particles being located on the grate and the fines being located on top of the bed. In one embodiment of this invention, means can be provided below the bed and preceding the first vapor recovery zone to recycle the small portion of the fines sifting through the bed back to the top of the bed. The stationary gas plenum chambers above and below the moving retort are sealed from the atmosphere as for example by a liquid seal to contain the gases. The moving grate moves the shale bed serially through the gas con tact zones to effect complete kerogen decomposition. The temperature profile of the spent shale upon discharge from the grate may vary from about 150 F. at the top of the bed to as high as about 600 F. at the bottom of the bed. The spent shale is removed from the grate and directed to spent shale container wherein the shale is mixed and the temperature of the individual particles allowed to equilibrate by conductive heat transfer to reduce maximum particle temperature below 400 F. maximums. To assist removal of spent shale for the grate, apparatus can be used to break up the shale bed to assist in shale movement to storage. The spent shale container is also sealed from the atmosphere but is open to the retort vapors. The cool spent shale is removed from the container and disposed of. The moving grate is then directed to the shale inlet portion of the retort wherein fresh shale is introduced. After spent shale is removed from the grate and prior to introducing fresh shale thereon, any coke and/or particulate shale in the grate perforation is removed therefrom as for example with high velocity jet cleaning or by burning.

The vapors directed to each zone are first directed to inlet plenum chambers adjacent the bed. These inlet plenums operate to separate the vapors so that different conditions of vapor temperature and vapor flow can be maintained in various portions of the bed. In addition, the vapor inlet plenums provide relatively uniform vapor flow through the vertical height of a given portion of the shale bed. Each of the plenums can be subdivided into smaller chambers to provide more efficient vapor flow control. Similarly, the vapor outlet plenums can be subdivided into smaller chambers to improve vapor flow control. Compressors are provided in various vapor lines as needed to maintain the desired pressure gradient through the shale bed.

We claim:

1. A method for thermally decomposing a relatively deep bed of oil yielding granular material which comprises moving a bed of oil yielding granular material horizontally through a confined passageway under a temperature profile provided to raise the temperature of the bed to an oil yielding decomposition temperature followed by cooling of the oil depleted bed with gaseous materials of selected temperature conditions being flowed generally downwardly through said horizontaly moving bed, the preheating of said shale bed being initiated with partially cooled oil rich gaseous material hereinafter recovered at an elevated temperature from the bottom of the bed adjacent the end of its horizontal travel and cooling of the bed after removal of oil being particularly accomplished with oil lean gaseous material recovered from the bottom initial portion of said horizontally moving bed, gaseous material temperatures suitable for effecting thermal separation of oil component from the granular material being obtained by burning a portion of the separated oil lean gaseous material external to said bed and thereafter introducing the hot gaseous material thus formed to the top of said bed in a restricted area down stream of the inlet of the bed to the confined passageway, causing the thermal oil separation temperature profile to progress generally downwardly through said horizontally moving bed by the oil lean gaseous material thereafter passed downwardly through said bed and employing gaseous material removed from the bottom intermediate portion of the bed to partially cool oil rich gaseous material recovered from a latter portion of the bed for recycle to the initial preheat portion of the bed as above described.

2. A method for retorting a bed of oil shale particulate moving horizontally through a confined passageway which comprises establishing a restricted kerogen decomposition heat front area with hot gaseous material in the top of said bed adjacent the inlet thereof to the confined passageway, driving said kerogen decomposition heat front progressively downwardly through said horizontally moving bed with hereinafter obtained cooled gaseous material obtained from the initial portion of said bed introduced to said bed downstream of said heat front area to cool the kerogen depleted shale, recovering gasiform product material of increasing temperature in the direction of the bed flow from the bottom of said bed in a plurality of separate gas recovery zones, separating oil constituents from gaseous .material recovered from each of the gas recovery zones, effecting cooling of the highest temperature separated gasiform material with cool gaseous material recovered from an upstream portion of the shale bed and employing separated gaseous material of relatively high and low temperature after removal of oil constituents to maintain the desired temperature profile of said shale bed.

3. A process for retorting oil shale particles which comprises moving a bed of shale particles horizontally through a confined passageway provided with a plurality of gaseous material distributing sections on one side of said horizontally moving bed opposite to gasiform material collecting sections, causing gaseous material at preselected temperature conditions to move through said horizontally moving shale bed throughout the length thereof from said distributing to said collecting sections, employing gaseous material recovered at an elevated temperature from an intermediate section of said horizontally moving bed to effect partial cooling of higher temperature gaseous material recovered from a downstream portion of said shale bed to permit recovery of oily constituents therefrom, employing hot gaseous material recovered from the downstream portion of said shale bed after partially cooling as above described to give up heat to the bed of shale introduced in an initial portion of said confined passageway, initiating a kerogen decomposing heat front on the surface of said horizontally moving shale bed downstream of the shale preheating region, employing cooled gaseous material recovered from said shale preheating region to drive said kerogen decomposing heat front through said shale bed while effecting a simultaneous cooling of the kerogen depleted oil shale through which the gaseous material flows, separating retorted oil constituents from gaseous material streams of different temperature levels recovered from the shale in said confined passageway in a plurality of separation zones permitting the recovery of at least two separate gas streams of significantly different temperatures for use in the process as above described.

4. A method for retorting oil shale particles which comprises causing a relatively deep bed of said shale particles of varying temperature profile caused by the flow of gaseous material therethrough to move horizontally through a confined passageway generally transversely to the downfiow of the gaseous material, accumulating separate gasiform material streams varying considerably in temperature from the bottom of the shale bed in a plurality of at least three separate gasiform material collecting chambers, said collected gasiform material stream increasing in temperature in the direction of shale flow, separating oil mist from gaseous material in each of said collected gasiform streams at different temperature conditions, employing gaseous material of reduced oil content and obtained from an intermediate portion of said horizontal bed to effect a partial cooling of the highest temperature gasiform material recovered from a downstream portion of the shale bed whereby oil constituents are separated from the highest temperature material, employing elevated temperature gaseous material of reduced oil content thus recovered from a downstream portion of the shale bed to preheat the shale and con dense out entrained oil constituents on the shale thus contacted in the initial portion of the confined passageway, passing a portion of relatively cool gaseous material freed of oil constituent removed from the initial portion of the shale bed through a combustion section to establish a high temperature gaseous stream kerogen decomposing heat wave which will thereafter move transversely through the shale bed with the assistance of additionally supplied gaseous material to the horizontally moving bed downstream therefrom and effecting cooling of said kerogen depleted shale With said additionally supplied gaseous material.

5. In a process for retorting oil shale particulate in a horizontally moving 'bed wherein heating, thermal decomposition and cooling of shale particulate is accomplished with gaseous materials of different temperature levels flowing through said bed of shale, the method of improving the thermal efficiency of the process for effecting thermal decomposition of kerogen and recovery of shale oil product which comprises recovering separate streams of gasiform material of low, intermediate and higher temperature comprising kerogen decomposition product from the bottom of said horizontal moving bed in the direction of shale flow, Without further cooling, separating the low and intermediate temperature gasiform streams into separate gaseous streams and oil rich streams, using the separated gaseous stream of intermediate temperature to effect a partial cooling of the highest temperature gasifor-m material recovered from the shale bed to effect a partial separation thereof into an oil phase and a relatively high temperature gaseous stream, condensing additional oil constituents from the relatively high temperature gaseous stream by preheating fresh shale introduced to said horizontal moving bed with said high temperature gaseous stream and employing the lowest temperature gaseous material recovered as above recited to cool kerogen depleted shale and generate in an external combustion zone a high temperature kerogen decomposition gas stream which is thereafter passed through the kerogen rich shale bed intermediate the shale preheat step and shale cooling step.

References Cited UNITED STATES PATENTS 7/1931 Trent 202-417 6/1967 Ban 208-11 U.S. c1. X.R.

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