US 2618588 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
NOV. 18, C. E JAHNIG F'LUIDIZED SHALE DISTILLATION Filed June 2l, 1949 :EF-f 0 a4 S /5 m2/1512"L l 72 -72 f FEED nafs" HOPPER. @f'f 52 Pa oa uc -rs "f' M ze 77 sanne/z 22 60d 60 S l l L2 l M2 s-' SRE W 24 8 /8 /6 lg 9753; Ml- -Mr 92 l2 'f l0 E/ uTR/A-ron IJ# r'/ 20 l 3o T .94
a Am. s ,35 gq l Patented Nov. 18, 1952 FLUIDIZED- VSIIALE DISTILLATION Charles E. Jalinig,` Red Bankg'Nf'J.,` assigner to l StandardY Oil Development Company, A a corporation of Delaware VApplication'June'21, 1949, Serial No; 100,327-
4 Claims. 1
The present-invention relates to the art of distilling oil-bearing minerals such-as oil shale, 4oil sands, tar sands and the like, maintainedl in the form of subdivided particles ina highly turbulent state, iluidized by upwardly flowing gases `vto resembled a boiling liquid, wherein the fresh charge undergoes rapid disintegration to form an excessive amount of particles having sizes below a properly fluidized range. More particularly, the invention relates to improved means -ior maintaining properly iluidized beds of rsuch materials during-distillation.
Prior to the present invention, it'has been proposed to carry out the distillation of oil shale in the form oi subdivided-solids varying in particle size from a line powder up to rather large aggregates of, say, about 1A; in. diameter-in a highly turbulent'fluidized state. 'The heat required for distillation has been supplied either as sensible heat of preheatedV process materials,`by o indirect heat exchange ofA the -fluidizedbedwith suitable heating means, by combustionof combustible shale `constituents within the retorting zone, or as sensible heat of hot spent shalehigh'ly heated in a separate combustion zoneV` and `circulated to the fluidized bed in the retorting` zone. The principal problem encountered `in all these operations arises as the result of the strong tendency of ltheshale to disintegrate rapidly in the course of the distillation to particles having an extremely small size of aboutO--ZO microns Which'is the unit particle size of the'shale'silt.
For example, Colorado shalewhen subjected to a fluid-type distillation quickly forms a mass containing about 6()y per cent of fineso'O-ZO` microns size, and this even if the shale is charged in rather coarse aggregates. Attrition further increases the proportion of these nes in the .highly turbulent'or circulating solidsimasses. At the condition Vof `uid shale distillation such fines tend tobe entrained and carried overhead'by theifluidizing gases. This situation is further .aggravated by relatively frequent localized spurts or jets of gasiiorm materials caused in the uidized bed by the flashing of water and oilfrom the cold fresh shale dropped into the hot fluidized bed. Even gas-solids separators of normally highest eiliciency have been found inadequate to cope with this degree of solids entrainment. Aside from severe losses of valuable carbonaceousv constituents removed from the distillation zone with these nes, the carry-over of excessive amounts of fines seriously complicates liquid product recovery dueto heavy slurry formation and detrimentally affects the fluidity of the'luidizecl bed which may be rapidly converted into a dilute `The present Ainvention provides means for eilec- -tively counter-acting the detrimental effectsv of this type ofines entrainment.
In accordance with the present invention, in `its broadest aspect, losses of shale fines having particlesizes oft-20 microns from ak luidized shale bed undergoing distillation, by entrainment and carry-over of the iines in the fluidizing gases and gasiform distillation products, may be materially reduced by obstructing the upward now of lthe gases and entrained solids above the interface of the fluidized bed and within the distillation zone in such a manner that gasiform materials may pass the obstructionV completely while a proportion of the entrained solids is deilected back into the nuidizedbed. This obstruction may have the form. of `inclined or horizontal offset baiiles. prescribing a zig-zag flot/'forl the solids-in-gas suspension, or of a non-iluidizable stationary packing havingirregular passageways, or thelike. However, in accordance with a preferred embodimenty of the invention, the obstruction has the form of a horizontal perforated plate or grid capable of supporting a second iluidized solids mass above that undergoing distillation.
All types of obstructions mentioned aoid the advantage oi returning a proportion of entrained nes' by deilection continuously to the shale bed undergoingdistillation and thusof reducing fines carry-over into the product recovery' system and. its detrimental effects. However, when a grid plate is used, permitting solid particles to penetrate the perforations, a second Iiuidized bedof particles will form above the grid within a relatively short time of operation. Such fiuidized solids have a strong capacity' for collecting ines of 'li-20 microns size up tola concentration oi about 30-50 per cent. A more specic and preferred embodiment of the invention provides, therefore, for the maintenance of a fluidized bed of solids supported by `a horizontal grid plate above the interface of the liluidized shale bed undergoing distillation.
The formation of such a second iluidized bed by `direct carry-over of particles from the retorting bed may be. replaced or supplemented by vthe addition of subdivided solids by means other than immediate carry-over from the retorting bed. The preferred embodiment of the invention involves-the supply to the second bed of spent. shale which has been subjected to combustion in a separate combustion zone for the purposes of generating the heat required for distillation.
The two' 'iluidized beds are preferably connected by a conventional downcomer pipe which permits flow of solids from the upper :Iluidized bed to the lower retorting bed. In this manner, a substantial proportion of the solids carried over from the retorting bed into the second bed may be returned to the retorting bed. In addition, part or all of the heat-carrying burned shale recirculated from a separate combustion zone may be passed through the upper bed to the retorting bed and thus serve the dual purpose of preventing loss of shale lines from the distillation zone and supplying heat to the retorting bed.
Having set forth its objects and general nature, the invention will be best understood from the following more detailed description wherein reference will be made to the accompanying drawing, the single gure of which is a semi-diagrammatic illustration of a system suitable to carry out a preferred embodiment of the invention.
Referring now in detail to the drawing, the numeral I! designates a mostly conventional distillation vessel or retort adapted for fluid-type shale distillation and containing a iluidized shale bed M1 supported by a gas distributing device, such as grid I2, and having a well defined interface L1. Above this interface a second perforated grid I4 is provided. An overflow downcomer IS leads from a point above grid I4 to a point below interface L1.
In operation, fresh coarse shale, which may have a particle size of about 4-50 mesh, may be supplied from feed hopper I through line I8 into the space between interface L1 and grid I2. A uidizing gas, such as steam, product tail gas, other inert gas, CO2 and/or air, is supplied through line 2b and grid I2 at such a rate that a linear superficial gas velocity of about 0.5-3 ft. per second, suitable for fluidization, is established within bed M1. Bed M1 may be maintained at a distillation temperature of about 850-1l00 F. by any of the conventional methods described above.
The fresh shale upon entering bed M1, undergoes distillation and disintegrates rapidly. As a result, bed M1 may have a particle size distribution about as follows:
Size: Weight per cent 0-20 microns 55 20-80 microns l0 8f) microns, 35 mesh l5 On 35 mesh 20 A portion of the entrained solids impinges on the imperforate portions of grid I4 and is thus returned to bed M1. The remainder of the entrained solids penetrates the perforations of grid I4. Initially the fines of 0 20 microns size carried through grid I4 may remain entrained in the gases and vapors and may be carried therein to a gas-solids separator 22 in which a substantial proportion of the entrained nes, say, about '70- 90%, may be separated. The separated fines may be returned to bed M2 via dip-pipe 24, gradually building up thereon until a second fluidized bed M2 having an interface L2 is formed above grid I4. Thereafter, a major proportion of the lines penetrating grid I4 is retained in bed Mz, the remainder being carried into separator 22. Equilibrium cf the system is established and maintained by overflowing and returning solids from bed Mz Via downcomer I6 to bed M1 and withdrawing spent shale from bed M1 through line 30. In this manner, about 80-99% of the solids leaving bed M1 entrained in gases and vapors will be returned to bed M1 via downcomer I6.
As previously indicated, the invention has particular advantages when used in connection with a system wherein hot spent shale is circulated from a separate combustion zone to the retorting zone for the purposes of heat supply. A system specically adapted to the application of the invention is illustrated in the drawing.
As shown in the drawing, a fluidized combustion zone or burner 50 is provided in addition to the elements just described. Spent shale withdrawn through line 30 from bed M1 may be passed to line 35 and suspended therein in air sufficiently preheated to support combustion of the shale. The air is supplied at a rate sufficient to carry the spent shale through grid 52 into burner 5I), to burn part or all of the carbon olf the spent shale at a temperature about 50300 F. higher than that in retort IIJ, and to maintain a superficial gas velocity within burner 50 of about 1-3 ft. per second, adequate to establish a lluidized mass M50 of burning shale having an interface L50 within burner 50. The gas containing entrained shale fines passes overhead from level L50 and may be further handled in any desired manner.
Burned spent shale is withdrawn from bed M50 through line 6I) which may be an aerated standpipe or the like and passed substantially at the temperature of mass M50 to bed M2 in retort I0. The circulation rate of hot shale through line 50 depends on the temperature differential between burner 50 and bed M1, and upon the heat requirement in vessel I0. A ratio of burned, hot shale to fresh shale charged of about 5-20:1 is usually adequate for the purposes of heat supply. Approximately the same solids circulation rate is maintained in lines 39 and 35 to establish equilibriurn. Excess solids may be withdrawn from burner 50 through line 62.
The particle size distribution of the solids circulating through line 60 may be about the same as that specified above for bed M1.
In addition to containing material coarser than 20 microns, these particles are relatively low in carbon or practically carbon-free and have, therefore, a substantially lower gas buoyancy than the high carbon particles of similar size which are entrained and carried overhead from bed M1. The burned shale particles supplied through line 60 to retort I0 above grid I4 are, therefore, ideally suited `to form a well fluidized, relatively dense bed of solids, Mz, above grid I4, adapted to retain substantial proportions of fines entrained from bed M1 and penetrating grid I4. The hot solids then flow through downcomer I6 to supply the heat required in retorting bed M1 and to repeat the cycle described above. As a result of the high circulation rate of hot lowcarbon solids from burner 50, bed M2 will at all times consist predominantly of particles of suiliciently low gas buoyancy to retain an adequate proportion of the fines of 0-20 microns size entering bed M2 from bed M1. When operating in the manner last described, the fines concentration of the effluent of retort Il! leaving through line 26 will be substantially less than in the absence of a second bed M2.
As an alternative to the procedure described above, the system shown in the drawing may be operated as follows.
Heater 50 may be divided by a second grid 'In into two sections with the burning taking place in the lower section. The hot flue gases from this lower section then pass up through grid 'I0 into a second dense phase M70. The gases are cooled in this section, withdrawn through line 12 and used to supply the fresh shale to the system as follows.
Feed hopper l is replaced by hopper 'I5 from which the fresh charge may be supplied to line 'l2 by any suitable means, such as a screw conveyor ll. 'Ihe gases in line 'I2 are then used for conveying the shale feed to an elevated feed hopper 80. separators 82 may be located in the top of elevated feed hopper 80 to remove entrained solids. The shale from hopper 80 then ows through line 84 to bed M70 wherein it is preheated by the flue gases penetrating grid 1D. The preheated shale may thereafter be fed via lines 86 and I8 to bed M1 in retort l0.
The advantages of this type of ow are as follows. The flue gases are cooled immediately so that piping and equipment following the heater are at a low temperature. This avoids expansion problems and expensive materials of construction. The feed shale is preheated by the flue gases so that less burning is required and less air is used. The flue gases are under suiilcient pressure to be used in conveying the feed shale to the elevated feed hopper. This eliminates the necessity of compressing recycle make gas for this purpose. A hindered settler is used as heat exchanger, thus eliminating expensive exchanger surface.
The system illustrated in the drawing permits of various modifications. Bed Mz may serve as a cracking zone for the distillation products liberated in bed M1. Cracking may be controlled by the amount of hot burned shale introduced through line B9. For this purpose, a portion of the hot shale in line 60 may be fed directly to bed M1 through lines 6l and I8. Instead of pass- ,ing all of the spent shale from line through line directly to burner 50, any desired portion of the suspension of spent shale in air may be passed from line 35 through line 90 to an elutriator 92 where shale of undesired particle size may be removed through line 94, the remainder being passed through line 96 to burner 50 to be further treated as above described.
While most of the volatile components present ln the feed shale will be recovered by retorting in vessel l0, it has been found that further quantities of valuable products often can be obtained by further heating to a higher temperature. For example, ammonia and light fuel gases can be recovered by heating the spent shale from vessel l0 or vessel 50 to temperatures of the order of 12001800 F. Such heating may be accomplished using indirect heating, or by recirculation of heated solids from a heater Vessel, or by direct injection of an oxygen containing gas.
In many cases the spent shale rejected from the retorting system will still contain appreciable amounts of combustible material. These spent solids can be used as fuel, as for example in a boiler house. Moreover, they may be used for the generation of fuel gas o-r synthesis gas by contacting with steam, and/or carbon dioxide at suitable conditions. Heat for this process can be supplied by solids recirculation from a heater vessel, or by direct injection or an oxygen containing gas.
Other modifications of the systems illustrated may appear to those skilled in the art without deviating from the spirit of the invention.
The above description and exemplary operations have served to illustrate specific embodiments of the invention but are not intended to be limiting in scope.
What is claimed is:
1. In the process of distilling oil-bearing minerals of the type of oil shale, which disintegrate lwhen subjected to distillation, in the form of a dense turbulent mass of subdivided solids fluidr ized by an upwardly flowing gasiform medium to forni a well defined interface within a distillation zone, the improvement which comprises feeding said oil-bearing minerals to said mass, obstructing the upward flow of said medium containing entrained solids within the distillation zone at a level above said interface by an obstruction, which permits said medium to flow upwardly over the entire height of said distillation zone past said obstruction, forming a second fiuidized mass of solids within said zone above said obstruction, continuously circulating retorted mineral particles from said first-named mass to a separate fluid-type combustion Zone, maintaining at least two superimposed fiuidized beds in said combustion zone, subjecting said retorted minerals to combustion in the lower one of said beds, pasing hot nue gases from said lower bed through the upper one of said beds, supplying fresh minerals to said upper bed to be dried and preheated therein by said flue gases, and passing preheated minerals from said upper bed to said first-named iiuidized mass.
2. The process of claim 1 in which volatile products of distillation are subjected to cracking in said second mass.
3. The process of claim 1 in which ue gases produced in said combustion zone are used to lift fresh minerals to an elevated point.
4. The process of claim 1 in which solid combustion residue from said lower one of said beds is returned to said second fluidized mass.
CHARLES E. JAHNIG.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,396,036 Blanding Mar. 5, 1946 2,396,709 Lefer Mar. 19, 1946 2,420,542 Jahnig May 13, 1947 2,444,990 Hemminger July 13, 1948 2,471,119 Peck et al May 24, 1949 2,480,670 Peck Aug. 30, 1949 2,483,485 Barr Oct. 4, 1949 FOREIGN PATENTS Number Country Date 586,992 Great Britain Apr. 10, 1947