US2899365A

US2899365A - scott

Info

Publication number: US2899365A
Authority: US
Publication date: 1959-08-11
Anticipated expiration: 1976-08-11

Description

1959 J. w. SCOTT, JR 2,899,365

SHALE RETORTING Fild Sept. 20. 1956 3 Sheets-Sheet 1 SHALE IN GAS-LIQUID SEPARATOR LIQUID P ODUCT I /7 I6 GAS FLUE GAS PRODUCT OUT AIR m GAS CARBON 2 5 A N COMBUSTION 9 \coMausnoN 27 ZONE ZONE 6 a PREHEATER HG 1 9 NVENTQR GAS m K JOHN w. scorr, 25 LA BY SHAL-E OUT ATTORNEYS 1959 J. w. SCOTT,- JR 2,899,365.

SHALE RETORTING Fi led Sept. 20.

3 Sheets-Sheet 2 FLUE GAS GAS-LIQUID SEPARATOR LIQUID PRODUCT PRODUCT OUT GAS

ZONE

HQ COMBUSTION GAS IN- 26 F l G. 2

SHALE OUT INVENTOR JOH% sc TT JR. BY

IATTORN EYS Aug. 11, 1959 J. w. SCOTT, JR

SHALE RETORTING 3 Sheets-Sheet 3 Filed Sept. 20. 1956 FLUE GAS .OUT

o a o a m w m MA LR v .A SP AE G5 2 6 a 6 T DC w mo LR P 67 GAS f PRODUCT ZONE COMBUSTION INVENTOR JOHN W SCOTT, JR.

ATTORNEYS SHALE OUT Unite 1 Research Corporation, San Francisco, Calif., a corporation of Delaware Application September 20, 1956, Serial No. 611,009

2 Claims. (Cl. 202-87) This invention relates to an improved process and ap paratus for retorting oil shale and bituminous solids of similar character in order to recover valuable liquid and gaseous hydrocarbon products, and particularly to a process and apparatus wherein downwardly moving retortable solids are countercurrently contacted with a gaseous medium for supplying said solids with retorting heat; and an object of the invention is to provide improved methods and apparatus for developing the necessary retorting heat carried by said gaseous medium and supplied by said gaseous medium to said solid.

Many processes have been proposed for removing hydrocarbon products from retortable solids, including oil shale and bituminous solids of similar character, for example, tar sands and lignites. These processes include solvent extraction processes and pyrolytic processes. However, few of these proposed methods are commercially attractive for various reasons, including excessive cooling water requirements, solvent losses, excessive fuel requirements, and inadequate handling flexibility. Solvent extraction processes are generally considerably less attractive than pyrolytic processes. The possible pyrolytic processes heretofore proposed may be divided into processes wherein heat is transferred indirectly from a heat source to the hydrocarbon-containing solids, and processes wherein such heat transfer is accomplished directly. Examples of both types of heat transfer, and some disadvantages usually associated with each example, are as follows:

(1) Indirect heat transfer;

(a) Through walls of retorting vessel. Expense for materials and equipment is generally prohibitive.

(b) Through solid particles mixed with the bituminous solids, for example steel balls. Involves inefficient heat utilization.

(2) Direct heat transfer:

(a) Steam. Involves high costs for steam generation and for condensing equipment.

([1) Heated air or flue gas. Involves high yield losses due to high dilution and excessive combustion.

(c) Recycle hot shale gas. Inflexible especially when the bituminous solids being processed are wet or are low in hydrocarbon content.

From the standpoints of economics, possible hydrocarbon recovery, and trouble-free operation, indirect heat transfer methods and direct heat transfer involving steam are considerably less attractive than methods involving 2(b) and 2(c) above, for recovering hydrocarbons from retortable solids, i.e., from oil shale, tar sands and bituminous solids of similar character. For example, a given retorting system may be satisfactory for retortable solids having given water and hydrocarbon contents and yet may not be satisfactory for the development of ade- States Patent quate retorting heat when the hydrocarbon content of ice the incoming retortable solids decreases or the water con-' tent increases, or both.

It is known that heat from a source external to the retorting system may be-supplied to the system for re torting purposes, and also that retorting heat may be developed by burning combustible product gases produced by the system. However, inadequate flexibility hereto fore has existed in developing suflicient retorting heat by these means, especially when more retorting heat was required because of an increased water content of the retortable solids entering the retort, and when less gas product from the retortable solids was available for burning because of an increased leanness of the incoming retortable solids. In view of the foregoing, it is an object of the present invention to provide novel methods and apparatus for developing retorting heat and for provid ing operating flexibility for the retorting of retortable solids of varying degrees of leanness and wetness.

Further, excessive decomposition of carbonates, for example, calcium carbonate and magnesium carbonate, that are contained in many retortable solids, has been heretofore a serious limitation on the development of retorting heat in processes involving gas or carbon combustion within the bedof retortable solids. When heated, such carbonates give off CO and in so doing heat is consumed in amounts which can rise to intolerably enormous proportions in the processes under consideration. For example, CaCO when heated reacts thusly:

CaCO Ca0 CO With each unit of temperature rise increasing amounts of carbonate decomposition take place, so that it is desirable to supply a given increment of heat to a bed of retortable solids at retorting temperatures as low and as uniform as practicable, and thereby to minimize carbonate decomposition. In these processes involving combustion of gas or carbon within a bed of retortable solids to obtain retorting heat, the high temperatures in the combustion area limit the amount of combustion that can be accomplished to obtain the necessary retorting heat to that amount of combustion that will not result in intolerable amounts of carbonate decomposition. Heretofore in these processes it frequently happened that the maximum tolerable rate of carbonate decomposition was reached before the amount of combustion occurring was high enough to produce adequate amounts of effective retorting heat. It is an object of the present invention to provide novel methods and apparatus for developing adequate amounts of effective retorting heat without exceeding the maximum tolerable rate of carbonate decomposition, in those processes for retorting retortable solids which involve gas or carbon combustion within the bed of retortable solids.

In accordance with one aspect of the present invention, downwardly moving particles of retortable solids are passed through a retorting zone, a carbon combustion Zone, and a gas preheating Zone; product gas from said retorting'zone is passed to said gas preheating zone; a portion of the preheated gas from said gas preheating zone is passed to a gas combustion zone so located that gas burning therein may be accomplished out of contact with the solids in the stream of downwardly moving solids, at least a portion of the gas entering said gas combustion zone is burned therein; the contents of said gas combustion zone are passed to said retorting zone; and carbon is burned in said carbon combustion zone from theparticlesof retortable solids entering said carbon combustion zone, to further heat thesaid particles in their passage to saidpreheating zone. In accordance with another aspect of the present invention the above-described operation is modifiedby passing an additional portion of the preheated gas from said preheating zone to said carbon combustion zone and burning said second portion preferentially in said carbon combustion zone in lieu of burning the carbon therein. In accordance with still another aspect of the present invention, downwardly moving particles of retortable solids are passed through a retorting zone, a carbon combustion zone, a first gas combustion zone, and a gas preheating zone; product gas from said retorting zone is passed to said gas preheating zone; a portion of the preheated gas from said gas preheating zone is passed to said first gas combustion zone and burned therein, another portion of the preheated gas from said gas preheating zone is passed to a second gas combustion zone so located that gas burning therein may be accomplished out of contact with the solids in the stream of downwardly moving solids, at least a portion of the gas entering said second zone is burned therein, carbon is burned in said carbon combustion zone from the solids therein, the contents of said second gas combustion zone are passed to said retorting zone, and the proportions of gaseous combustible products from said first gas combustion zone and said carbon combustion zone that are passed upwardly to said retorting zone through said downwardly moving particles, and. that are withdrawn from the system, respectively, are regulated as desired.

It may be seen that when the moisture content of solids entering the retort increases, the present invention provides a plurality of sources from which additional amounts of retorting heat may be derived in order to satisfy the increased retorting heat requirements, and that the proportions of heat obtained from these sources may be varied as desired to give a high degree of operating flexibility.

Further, it may be seen that when additional amounts of retorting heat are desired when gas or carbon combustion within the solids bed is resulting in carbonate decomposition at rates approaching the maximum tolerable rate, the additional retorting heat may be developed by burning additional gas in the external gas combustion zone. The high temperatures that may exist in that zone result in efficient gas burning, but cannot cause carbonate decomposition because they are not in close proximity to the retortable solids. Additional gas may be added to the external gas combustion zone beyond the amounts burned there. This additional gas acts as a quench to reduce the temperature of the gas stream entering the retort from the-external gas combustion zone to a temperature well below the burning temperatures in the external gas combustion zone. Thus, the heat developed by the gas burning in the external zone may be carried to the retorting zone at reduced uniform temperatures that are no higher than necessary to accomplish retorting, and therefore that do not result in the carbonate decomposition that wouldhave occurred had the gas burning in the external burner taken place in close proximity to the retortable solids.

It will be noted that the foregoing advantages are obtained without bulky and expensive tubular heat exchangers and condensers.

The novel features of the present invention are set forth with particularity in the appended claims. The invention will best be understood, however, both as to organization and operation, and additional objects and advantages thereof will be apparent from the-following description of specific embodiments when read in con nection with the accompanying drawings. In the following description shale retorting specificallyis discussed, although it will be understood that the description also applies to other retortable solids. In the accompanying drawings:

Fig. 1 is a diagrammatic illustration of an embodiment of apparatus and flow paths for retorting shale in the presence of hot gases, in which non-condensible gases recovered from the shale, together with recycled combustion gases, are preheated by contacting them with hot spent shale in a preheating zone, in which at least a portion of said preheated gases is burned out of contact with the shale, in which the heat obtained by said fixed gases from said hot shale and from said gas burning is carried by said fixed gases to -a retorting zone, and in which the hot spent shale entering said preheating zone may have received part of its heat from the burning of carbon therefrom in a carbon combustion zone.

Fig. 2 is a diagrammatic illustration of an additional embodiment of apparatus and flow paths for retorting shale, in which a single major enclosure is provided for the retorting, carbon combustion, and preheating zones, and in which a gas combustion zone is so located that combustible gas may be burned therein out of contact with the shale particles.

Fig. 3 is a diagrammatic illustration of an additional embodiment of apparatus and flow paths for retorting shale, in which a downwardly moving stream of shale particles travels successively through a retorting zone, a carbon combustion zone, a first gas combustion zone, and a gas preheating zone; and in which a second gas combustion zone is provided for gas burning out of contact with the shale particles.

Referringnow to Fig. 1, fresh crushed shale is introduced through line 1 and gas-tight valve 2 into retorting zone 3, where it is retorted in the presence of hot gases' that are heated as hereinafter described. The hot spent shale from retort 3 passes downwardly through gas-tight star feeder valve 22, carbon combustion zone 5, gas-tight star feeder valve 23 and gas preheater 8, from where it is withdrawn through gas-tight valve 9 and line 10. A vaporous product containing normally liquid and normally gaseous hydrocarbons is withdrawn from retort 3 I through line 11 and is passed to gas-liquid separator 12,

where said normally liquid and normally gaseous components are separated. The normally liquid components are withdrawn as a product through line 13. The normally gaseous components are withdrawn from gas-liquid separator 12 through line 14 by pump 15, and are passed through line 16 to preheater 8. A portion of said gaseous components may be withdrawn as a product from the system through line 17. In preheater 8 heat is exchanged from the hot shale therein to the gases entering preheater 8 through line 16.

A portion of the preheated gases from preheater 8 may be passed through line 18 to gas combustion zone 19, located as shown or in any position which will permit gas burning therein out of contact with the shale particles. The amount so passed may be controlled by valve 25 to control the temperature level of the gases entering line 21. At least a portion of the heated gases entering gas combustion zone 19 is burned therein in the presence of air admitted to zone 19 through line 20. If desired, only the amount of gas to be burned in zone 19 may be passed thereto through line 18. Alternatively, additional preheated gas from preheater 8 may be passed through line 18 into combustion chamber 19 in addition to the amount of 'gas that is to be burned therein. In the latter case, in order that the gas burning in combustion chamber 19 be limited to the desired amount, there may be introduced into combustion chamber 19 a gas containing free oxygen in an amount stoichiometrically sufiicient to support combustion of only so much of the preheated gas enten'ng combustion chamber 19 as it is desired to burn. Any excess gas in combustion chamber 19 over the amount that is burned will simply be further heated and passed into retort 3 through line 21. This excess gas thus serves as a quench gas to absorb heat of combustion and prevent unnecessarily high local temperatures in equipment and in the shale bed.

The normal 21% 0 content of the air entering zone 19 through line 20 may be lowered as desired by passing recycle gas from line 16 through line 30 and valve 31 to line 20. The gaseous contents of gas combustion zone 19, having been further heated by gas combustion, are

passed from gas combustion zone 19 through line 21 to retort 3, where heat is exchanged from the heated gases to the shale.

The hot spent shale from retort 3 may be further heated before it reaches preheater 8 by burning carbon therefrom in carbon combustion zone 5 in the presence of air admitted to zone 5 through line 6. In such case gas valve 35 in line 34 may be closed, thus preventing gas from preheater 8 from reaching carbon combustion zone 5, where it would have a tendency to burn in preference to the carbon therein. Further in such case it may be desired to close gas valve 37 in line 36 and withdraw gaseous products of combustion in zone 5 from the system through line 24, thus preventing them from diluting and contaminating the recycle gas stream flowing in

lines

14 and 16. In this manner the recycle product gas stream emerging from retort 3 through line 11 can be maintained at a higher Btu. value per unit yolume than if the flue gases from zone 5 were allowed to enter it. However, when operating conditions and shale oil and moisture content are such that dilution of the recycle gas stream may be tolerated, it may be desired to conserve system heat by passing the hot flue gases from zone 5 through valve 37 into retort 3.

The amount of heat carried away when flue gas is withdrawn from the system through line 24 can be minimized by introducing the line 6 combustion air into the bottom of combustion zone 5, so that most of the heat development will take place away from the flue gas exit, thus enabling the downwardly moving shale to carry to preheater 8 a greater amount of the heat developed in zone 5.

If desired, a portion of the flue gas in line 24 may be passed through line 32 and valve 33 to line 6, or an inert gas from another source may be used, to lower the oxygen content of the air entering zone 5 through line 6, and thus to prevent clinkering and fusion tendencies of the shale particles in zone 5, and also to minimize carbonate decomposition, by controlling the burning and hot spots in zone 5.

As an alternative to burning carbon only in zone 5, gas valve 35 may be opened and a portion of the preheated gas from preheater 8 passed to carbon combustion zone 5 for burning therein in the presence of air admitted to zone 5 through line 6. This gas will tend to burn in zone 5 preferentially to the carbon therein, especially at lower ratios of air to gas therein. Again it may be desirable to close gas valve 37 and withdraw the gaseous combustion products in zone 5 from the system through line 24, although when the recycle gas stream in line 16 will not thereby be excessively diluted, it will be preferable to conserve system heat by passing the hot combustion products through line 4 to retort 3. As in the case with carbon burning only in zone 5, recycle gas may be passed from line 24 through line 32 to line 6 to control the oxygen content of the air entering zone 8.

If desired, a portion of the preheated gas from preheater 8 may be passed through valve 28 and line 29 directly to retort 3, thus lay-passing combustion zones 5 and 19.

It may be seen from the foregoing that the system described is extremely flexible and is easily adjusted to develop retorting heat most efliciently, regardless of variations in hydrocarbon and moisture content of the shale entering retort 3 through line 1. By manipulation of

valves

25, 28 and 35 it is possible to control the relative proportions of the preheated gas from preheater 8 that are passed through

lines

18, 29 and 34, respectively. By this control, and by control of the oxygen entering combustion zones 19 and 5, burning of the amounts and proportions of carbon and gas that will result in the most eflicient development of retorting heat for various shale I types and conditions may be accomplished;

normal conditions with shale of average hydrocarbon and moisture content to burn in combustion chamber 19 a small proportion, for example, less than 50%, and preferably from 5 to 30% of the true make gas of the process in order to add to the heated gas leaving preheater 8 enough additional heat to enable the heated gases entering retort 3 to accomplish retorting.

However, more heat may be required in some cases than can be obtained by burning up to 30%, or even 50%, of the true make gas of the process in combustion chamber 19. The additional heat may be required, for example, because a large amount of water in abnormally moist shale must bevaporized, or because the incoming shale is abnormally lean, or yields its oil with a relatively small gas yield. In these cases where more heat is required than can be developed by burning up to 50%, and preferably up to 30% only, of the true make gas of the process in combustion chamber 19, the present invention provides flexible means for developing the additional heat efliectively. Burning of over about 30% of the true make gas of the process in combustion chamber 19, gen:- erally should be avoided, because such burning may result in a recycle gas stream containing an excessive quantity of inert diluents. If additional heat is required it may be developed as heretofore described by burning carbon or gas in combustion chamber 5. Carbon burning in zone 5 requires more air, and thus higher compressor and pumping costs, than gas burning in zone 5, so that generally it may be preferable to burn gas rather than carbon only, in zone 5.

Further flexibility may be provided by augmenting the recycle gas stream flowing in line 16 by introducing fuel gases or residues from external sources into the system as desired. These may be introduced, for example, into line 16 through line as, or directly into gas combustion zone 19 through line 27.

Referring now to Fig. 2, it may be seen that the embodiment shown in Fig. 1 may be modified if desired by providing a more Vertical downward pathway for the shale particles, and by providing a common envelope for the retorting, carbon combustion, and preheating zones, to aid in conserving system heat. In this modification the parts, reference numbers, and operations correspond exactly to those of Fig. 1, except that a common envelope 38 is provided, in which the channelling members 39 are provided to define the various zones.

The following table is illustrative of the amounts and temperatures of the process materials involved in an exemplary operation of the process of the present invention in the embodiment and modification thereof shown in Figs. 1 and 2, respectively.

Table Material Amo/unt, Temp, F.

(1) Fresh shale (Me in. to 4 in.) 25,000 60 (2) Retorted shale (line 4) 20, 705 950-1, 050 (3) Retorted shale (line 7).-. 20, 655 1, 050-1, 500 (4) Cooled shale (line l0) 20, 655 200- 300 (5) Shale oil (line l3) 2, 790 (6) Shale gas (line 17) 1, 525 200 (7) Recycle gas (line 1 12, 200 150- 200 (8) An (line 220 100- 150 (9) Recycle gas (line 18)... 8,000 600-1, 200 (10) Recycle gas (11116 29) 4, 200 600-1, 000 (11) Tina lgake gas burned in combustion chamer 5 (l2) Flue gas (line 24)-" 800 1, 000-1, 500 (13) All (line 6) 750 100- 150 Referring now to Fig. 3, there shown is an alternate embodiment of the present invention, in which gas burning may be carried out in two separatestages as in the embodiment shown in Figs. 1 and 2, but in which both of the gas burning zones are separate from the carbon burning zone, in contrast to the embodiment shown in Figs. 1 and 2, which includes a common carbon burning and gas burning zone.

Still referring to Fig. 3, fresh crushed shale is introduced through line 50 and gas-tight valve 51, into retorting zone 52, where it is retorted in the presence of hot gases that are heated as hereinafter described. The hot spent shale from retort 52 passes downwardly through gas-tight star feeder valve 53, carbon combustion zone 54, gas-tight star feeder valve 55, gas combustion zone 56, gas-tight star feeder valve 57, and gas preheating zone 58, from where it is withdrawn through valve 59 and line 60. A vaporous product comprising normally liquid and normally gaseous hydrocarbons is withdrawn from retort 52 through line 61 and is passed to gas-liquid separator 62, where said normally liquid and normally gaseous components are separated. The normally liquid components are withdrawn as a product through line 63. The normally gaseous components are withdrawn from gas-liquid separator 62 through line 64 by pump 65, and are passed through line 66 to preheater 58. If desired, a portion of said gaseous components may be withdrawn as a product from the system through line 67. In preheater 58 heat is exchanged from the hot shale therein to the gases entering preheater 58 through line 66.

A portion of the preheated gases from the preheater 58 may be passed through line 68 to gas combustion zone 69. The amount so passed may be controlled by valve 70. At least a portion of the heated gases entering gas combustion zone 69 is burned therein in the presence of air admitted to zone 69 through line 71. If desired, only the amount of gas to be burned in zone 69 may be passed thereto through line 68. Alternatively, additional preheated gas from preheater 58 may be passed through line 68 into combustion chamber 69 in addition to the amount of gas that is to be burned therein. In the latter case, in order that the gas burned in combustion chamber 69 be limited to the desired amount, there may be admitted into combustion chamber 69 a gas containing free oxygen in an amount stoichiometrically suflicient to support combustion of only so much of the preheated gas entering combustion chamber 69 as it is desired to burn. Any excess gas in combustion chamber 69 over the amount that is burned will simply be further heated and passed into retort 52 through line 72. This excess gas thus serves as a quench gas to absorb heat of combustion and prevent unnecessarily high temperatures in equipment and in the shale bed.

The normal 21% content of the air entering zone 69 through line 71 may be lowered as desired by passing recycle gas from line 66 through line 73 and valve 74 to line 71. The gaseous contents of zone 69, having been further heated by gas combustion, are passed from zone 69 through line 72 to retort 52, where heat is exchanged from the heated gases to the shale in retort 52.

The hot spent shale from retort 52 may be further heated before it reaches preheater 58 by burning carbon therefrom in carbon combustion zone 54 in the presence of air admitted to zone 54 through line 75. In such case gas valve 76 in line 77 may be closed, thus preventing either burned or unburned gases from gas combustion zone 56 from reaching zone 54. Further in such case it may be desired to close gas valve 78 in line 79 and withdraw gaseous products of combustion in zone 54 from the system through line 86, thus preventing them from'diluting and contaminating the recycle gas stream' flowing in

lines

61 and 66. In this manner said recycle gas stream can be mainatined at a higher B.t.u. value per unit volume, a

passed through line 81 and valve 82 to line to lower the oxygen content of the air entering zone 54 through line 75, and thus to control burning and hot spots in zone 54, thereby preventing clinkering and fusion tendencies of the shale particles in zone 54,

Whether or not carbon is being burned in carbon combustion zone 54, it may be desired to pass a portion of the preheated gas from preheating zone 58 through line 83 and valve 84 for burning in gas combustion zone 56 in the presence-of air admitted to zone 56 through line 85. The oxygen content of the air entering zone 56 may be controlled if desired by recycling flue gas from zone 56 through

lines

86, 87 and valve 88. It may be desired to close valve 76 in line 77 and withdraw the gaseous products of combustion from zone 56 from the system through line 86. Alternatively, system heat may be conserved by passing the burned gases from zone 56 through valve 76 in line 77 and, if desired, through valve 78 in line79 to retort 52. It should be noted that if less than all the combustible gas entering zone 56 is burned therein, it may be undesirable to pass the unburned gas from zone 56 to zone 54 if carbon burning is being attempted in zone'54 at thesame time, because the combustible gas will tend to burn in zone 54 preferentially to the carbon therein.

If desired, a portion of the preheated gas from preheater 58 may be passed through valve 89 and line 90 directly to retort 52, thus by-passing

combustion zones

54, 56 and 69.

Common envelope 91 for

zones

52, 54, 56 and 58, in which channelling members 92 define the various zones, serves to aid in the conservation of system heat.

The recycle gas stream flowing in

lines

61 and 66 may be augmented, if desired, by combustible gas introduced into the system from an external source, for example through

lines

93 and 94.

It will be understood by those skilled in the art that the various gas-tight star feeder valves shown and described herfein are only one possible gas sealing means. Alternative gas sealing means may be used in lieu thereof, for example, conventional gas seal legs without a sealing fluid, or conventional gas seal legs with a sealing fluid, for example steam or other gas. These alternative sealing means may be desired to avoid various problems that may arise with star feeder valves, for example differential expansion of parts at high temperatures, corrosion and wear from abrasive materials in the retortable solids.

The amounts and temperatures of process materials set forth in connection with Figs. 1 and 2 are generally indicative of amounts and temperatures for corresponding portions of the embodiment shown in Fig. 3, for an exemplary operation thereof.

From the foregoing it may be seen that the present invention provides a very high degree of process flexibility, which is of great practical value, particularly when in 'field operation a wide range of shale moisture and hydrocarbon contents must be dealt with, and when adequate retorting heat cannot be developed only by burning in contact with the shale because of carbonate decomposition. With the present invention a small amount of recycle gas burning under normal shale and operating con ditions will supply suflicient heat to the retorting zone that when combined with other heat carried to the retorting zone from the preheater, retorting may be accomplished. Under abnormal conditions, for example when shale of high moisture content or low hydrocarbon content, or both, must be dealt with, and recycle gas stream dilution dangers prevent burning of enough gas in one gas combustion zone to obtain suflicient retorting heat, additional gas may be burned in a second zone, from which flue gas diluents may be withdrawn from the system if desired. Further retorting heat may be developed by burning carbon from the hot spent shale, and the products of combustion thereof may be withdrawn from the system if desired. Additional combustible gas may be introduced into the system if desired to augment the gas produced by the process. The present invention thus provides many possible combinations of operating process steps that are necessary to meet changing field condi' tions, and thus removes many previous limitations on process flexibility.

It is to be understood that many modifications in process techniques and apparatus could be made without departing from the basic features of this invention or from the spirit and scope thereof, and that the only limitations to the present invention intended herein are those indicated in the appended claims.

I claim:

1. Apparatus for removing hydrocarbons from retortable solids, comprising a retorting zone, a first burning zone, a gas preheating zone and a second burning zone, means for passing said solids successively through said retorting zone, first burning zone and preheating zone, means for passing combustible product gases from said retorting zone to said preheating zone, means for passing preheated gas from said preheating zone to said first burning zone, means for passing preheated gas from said preheating zone to said second burning zone, means for selectively burning in said first burning zone carbon from solids therein and gas, means for burning in said second burning zone out of contact with said retortable solids at least a portion of the combustible gases in said second burning zone, and means for passing the gaseous effluent from said second burning zone, along with unburnt gases from the preheating zone, to the retorting zone.

2. Apparatus for removing hydrocarbons from retortable solids, comprising a housing, means for dividing said housing in vertical spaced relationship, into a top retorting zone, a bottom gas preheating zone, and two intermediate burning zones, means for providing a gastight seal between each adjacent two of said four zones, means for passing retortable solids downwardly through said four zones, means for burning carbon from the retortable solids in the first of said intermediate burning zones encountered by the solids, means for supplying combustible gas to the other of said intermediate burning zones and for burning said gas therein, means for recycling a combustible gas product from said retorting zone to said preheating zone, and means for burning a portion of the preheated gases from said gas preheating zone and for passing the resulting burnt gases, along with unburnt, preheated gases, to said retorting zone.

References Cited in the file of this patent UNITED STATES PATENTS 1,551,956 Hubmann Sept. 1, 1925 2,131,702 Berry Sept. 27, 1938 2,560,767 Hufi July 17, 1951 2,710,828 Scott July 14, 1955 2,757,129 Reeves et al July 31, 1956 FOREIGN PATENTS 484,050 Great Britain Apr. 29, 1938 107,907 Australia July 20, 1939

Claims

1. APPARATUS FOR REMOVING HYDROCARBONS FROM RETORTABLE SOLIDS, COMPRISING A RETORTING ZONE, A FIRST BURNING ZONE, A GAS PREHEATING ZONE AND A SECOND BURNING ZONE, MEANS FOR PASSING SAID SOLIDS SUCCESIVELY THROUGH SAID RETORTING ZONE, FIRST BURNING ZONE AND PREHEATING ZONE, MEANS FOR PASSING COMBUSTIBLE PRODUCT GASES FROM SAID RETORTING ZONE TO SAID PREHEATING ZONE, MEANS FOR PASSING PREHEATED GAS FROM SAID PREHEATING ZONE TO SAID FIRST BURNING ZONE, MEANS FOR PASSING PREHEATED GAS FROM SAID PREHEATING ZONE TO SAID SECOND BURNING ZONE, MEANS FOR SELECTIVELY BURNING IN SAID FIRST BURNING ZONE CARBON FROM SOLIDS THEREIN AND GAS, MEANS FOR BURNING IN SAID SECOND BURNING ZONE OUT OF CONTACT WITH SAID RETORTABLE SOLIDS AT LEAST A PORTION OF THE COMBUSTIBLE GASES IN SAID SECOND BURNING ZONE, AND MEANS FOR PASSING THE GASEOUS EFFLUENT FROM SAID SECOND BURNING ZONE, ALONG WITH UNBURNT GASES FROM THE PREHEATING ZONE, TO THE RETORTING ZONE.