US 2618589 A
Description (OCR text may contain errors)
N 1952 E. w. s. NICHOLSON ETAL 2,618,589
CONTINUOUS RETORTING OF OIL SHALE Filed June 21, 1949 OWN sank uzimmwiq worm Patented Nov. 18, 1952 UNITE S'lf'i'ES OFFICE CONTINUOUS RETGRTING OF OIL SHALE Delaware Application June 21, 1M9, Serial No. 100,314
2 Claims. 1 The present invention relates to the art of distilling oil-bearing minerals, such as oil shale, oil sands, tar sands and the like, maintained in the form of subdivided particles in a highly turbulent state, fluidized by upwardly flowing gases.
toresemble a coiling liquid, wherein the fresh charge undergoes rapid disintegration to form an excessive amount of particles having sizes below a properly fiuidizable range. More particularly, the invention relates to improved means for maintaining properly fluidized beds of such materials during distillation.
Prior to the present invention, it has been proposed to carry out the distillation of oil shale in the form of subdivided solids varying in particle size from a fine powder up to rather large aggregates of, say, about inch diameter in a highly turbulent fluidized state. The heat re quired for distillation has been supplied either as sensible heat of preheated process materials, by indirect heat exchange of the fluidized bed with suitable heating means, by combustion of combustible shale constituents within the retorting zone, or as sensible heat of hot spent shale highly heated in a separate combustion zone 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 the shale to disintegrate rapidly in the course of the distillation to particles having an extremely small size of about -20 microns which is the unit particle size of the shale silt. For example, Colorado shale when subjected to a fluid-type distillation quickly forms a mass containing about 60 per cent of fines of 0-20 microns size, and this even if the shale is charged with rather coarse aggregates. Attrition further increases the proportion of these fines in the highly turbulent or circulating solids masses. At the conditions of fluid shale distillation such fines tend to be entrained and carried overhead by the fiuidizing gases. This situation is further aggravated by relatively frequent localized spurts or jets of gasiform materials caused in the fluidized bed by the flashing of water and oil from the cold fresh shale dropped into the hot fluidized bed. Even gas-solids separators of normally highest efficiency have been found inadequate to cope with this degree of solids entrainment. severe losses of valuable carbonaceous constituents removed from the distillation zone with these fines, the carry-over of excessive amounts of fines seriously complicates liquid product recovery due to heavy slurry formation and detrimen- Aside from tally afiects the fluidity of the fluidized bed which may be rapidly converted into a dilute phase which cannot be retained in the distill-a tion zone unless special precautions are taken. The present invention provides means for eiiectively counter-acting the detrimental effects of this type of fines entrainment.
In accordance with the present invention, losses of shale flnes having particle sizes of 020 microns from a fluidized shale bed undergoing distil ation, by entrainment and carry-over oi the fines in the fluidizing gases and gasiform distillation products, may be materially reduced by obstructing the upward flow of the 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 obstruction completely while a portion of the entrained solids is deflected back into the fluidized bed. This obstruction may have the form of inclined or horizontal cit-set baffles prescribing a zig-zag flow for the solids-in-gas suspension, or of e. non-fluidizable stationary packing having irregular passageways, or the like. However. in accordance with a preferred embodiment of the invention the obstruction has the form of a horizontal perforated plate or grid capable of supporting a second fluidized solids mass and permitting entrained solid particles to penetrate the perforations so that a second fluidized bed of particles will form above the grid within a relatively short time of operation. Such fluidized solids, particularly when of a particle size slightly larger than 20 microns, have a strong capacity for collecting fines of 020 microns size up to a concentration of about 50 per cent. More specifically, the invention provides, therefore, for the maintenance of a fluidized bed of solids supported by a horizontal grid plate above the interface of the fluidized shale bed undergoing distillation, wherein said second bed consists predominantly of solids having a particle size slightly larger than 20 microns.
The formation of such a second fluidized bed by direct carry-over of particles from the retorting bed is preferably supplemented by the addition of subdivided solids of the proper particle size by means other than immediate carryover from the retorting bed. Another modification of this embodiment involves the supply to the second bed, of spent shale which has been subjected to combustion in a separate combustion zone for the purpose of generating the heat required for distillation.
The two fluidized beds are preferably connected 3 by a conventional downcomer pipe which permits flow of solids from the upper fluidized 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, the entire amount of 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 fines 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 in which:
Figure 1 is a schematical illustration of the basic concept of the invention;
Figure 2 is a similar illustration of a specific modification of the invention; and
Figure 3 illustrates in a similar manner the application of the invention to a conventional system including a retorting zone and a separate heat-generating combustion zone.
Referring now in detail to Figure l, the numeral i designates a mostly conventional distillation vessel or retort adapted for fluid-type shale distillation and containing a fluidized shale bed M1 supported by a gas distributing device, such as grid 2, and having a well defined interface L1. Above this interface a second perforated grid 14 is provided. An overflow downcomer l6 leads from a point above grid I4 to a point below 3 interface L1.
In operation, fresh coarse shale, which may have a particle size of about 4-50 mesh, may be supplied through line it into the space between interface L1 and grid i i. A fiuidizing gas, such as steam, product tail gas, other inert gas, CO2 and/or air, is supplied through line 2?] and grid l2 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. M1 may be maintained at a distillation temperature of about 850-l100 F. by any of the conventional methods described above which need not be specifically illustrated for a proper understanding of the invention.
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 10 80 microns35 mesh On mesh 20 A portion of the entrained solids impinges on the imperforate portions of grid ill and is thus returned to bed M1. The remainder of the entrained solids penetrates the perforations of grid l4. Initially the fines of 0-20 microns size carried through grid M remain entrained in the gases and vapors and are carried therein to a gassolids separator 22 in which a substantial proportion of the entrained fines, say, about to 90%, may be separated. The separated fines may be likewise returned to bed M1 via dip-pipe 2d. The slightly coarser solids which have penetrated grid 14 gradually are building up thereon until they form a second fluidized bed M2 having an interface L2 abovegrid I4. Thereafter, a major pro- Bed fi l
portion of the fines penetrating grid I4 is retained in bed M2, the remainder being carried into separator Equilibrium of the system is established and maintained by overflowing and returning solids ircm bed M2 via downcomer IE to bed M1 and withdrawing spent shale from bed M1 through line 38. In this manner, about -99% of the solids leaving bed M1 entrained in gases and vapors will be returned to bed M1 via downcomer I6 and dip-pipe 2 1. Product vapors and gases are withdrawn through line 26.
A further improvement of the solids recovery in accordance with the invention may be accomplished by a system'of the typ illustrated in Figure 2.
Referring now to Figure 2, the system illustrated thereinxdifiers from that described with reference .to Figure 1 essentially in the operation of the gas-solids separation system 22a, 22b, and 220 replacing separator 22 of Figure 1.
The operation of the system of Figure 2 is likewise analogous to that described with reference to Figure 1, system elements similar to those of Figure 1 being identified by like reference characters, with the exception of the gas-solids separation system. The gases and vapors contain-- ing entrained solids pass in series through cy-- clone separators 22a, 22b and 220. The material separated in any one or these cyclones may be returned either to bed M1 or bed M2, as required to maintain the desired particle size distribution in bed M2. In the example illustrated in Figure the coarsest material which is separated in cyclone 22a and the finest material separated in cyclone 220. are both returned to bed M1 while the particles of intermediate size separated in cyclone 2219 are returned to bed M2.
In this manner, bed M2 is enriched in particles slightly larger than 20 microns size whereby the retention of fines of 0-20 microns particle size is favored.
As previously indicated, the invention has par- I ticular 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 specifically adapted to the application of the invention is illustrated in Figure 3 wherein liKe reference charactersare used to identify system elements similar to those of Figures 1 and 2.
Referring now to Figure 3, there is shown a fluidized combustion zone or burner 50 inaddi Spent shaletion to the elements of Figure l. withdrawn through line 39 from bed M1 may be passed to line 35 and suspended therein in air suificiently preheated to support combustion of the shale. The air is supplied at a rate suflicient to carry the spent shale through grid 52 into burner 52!, to substantially completely burn the carbon off the spent shale at a temperature about 50-300 F. higher than that in retort i0, and to maintain a superficial gas velocity within burner passed substantially at the temperature of mass M50 to bed M2 in retort ID. The circulation rate Dip-pipes 2 301, 24?) and 24c are provided for this purpose.-
of hot shale through line 6!] depends on the temperature differential between burner 50 and bed M1. A ratio of burned, hot shale to fresh shale charged of about 520:1 is usually adequate for the purposes of heat supply. Approximately the same solids circulation rate is maintained in lines 30 and 35 to establish equilibrium. Excess solids may be withdrawn from burner 58 through line 62.
The particle size distribution of the solids circulating through line 60 may be about the same as that specified for bed M1 of Figure 1.
In addition to containing material coarser than 20 microns, these particles are 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 63 to retort 19 above grid M are, therefore, ideally suited to form a well fluidized, relatively dense bed of solids, M2, above grid l4, adapted to retain substantial proportions of fines entrained from bed M1 and penetrating grid i l. The hot solids then flow through downcomer It to supply the heat required in retorting bed M1 and to rep at the cycle described above. As a result of the extremely high circulation rate of hot low-carbon solids from burner 50, bed M2 will at all times consist predominantly of particles of sufficiently low gas buoyancy to retain an adequate proportion of the fines of 0-20 microns size entering bid M2 from bed M1.
When operating in the manner last described,
the fines concentration of the effluent of retort leaving through line 29 will be substantially less than in the absence of a second bed M2.
Various 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 when subjected to distillation, in the form of a dense turbulent mass of subdivided solids fluidized by an upwardly flowing gasiform medium to form a well defined interface within a distillation zone at a distillation temperature, the improvement which comprises partially obstructing the free upward fiow of said medium containing entrained solids within the distillation zone by a flow obstruction arranged at a level above said interface, passing said medium upwardly over the entire height of said distillation zone past said obstruction, forming above said obstruction a second fluidized mass of solids consisting predominantly of retorted mineral particles from which at least a major proportion of residual car-- bon has been removed by combustion and which have a size slightly larger than 20 microns diameter, passing said medium containing fully entrained solids particles upwardly from said second mass through a multi-stage gas-solids separation zone, classifying said fully entrained particles in said separation zone into a first fraction of particles of a size larger than said slightly larger particles, a second fraction of particles of said slightly larger size and a third fraction of particles not exceeding 20 microns in size, returning said first fraction to said first-named mass, returning said second fraction to said second mass and returning at least a portion of said third fraction to said first-named mass.
2. The process of claim 1 in which retorted mineral particles are continuously circulated from said first-named mass to a separate fluidtype combustion zone, subjected to combustion therein and returned to said second mass.
EDWARD W. S. NICHOLSON. LINDSAY I. GRIFFIN, J R.
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 LeiTer Mar. 19, 1946 2,420,542 Jahnig May 13, 1947 2,444,990 Hemminger July 13, 1948 2,471,119 Peck et a1 May 24, 1949 2,480,670 Peck Aug. 30, 1949 2,483,485 Barr Oct. 4, 1949