US 2717869 A
Description (OCR text may contain errors)
Sept. 13, 1955 E. E. TURNER DISTILLATION OF OIL BEARING MINERALS Filed Dec. 9, 1949 United States Patent O y 2,717,869 DISTILLATION OF OIL BEARING MINERALS Earl E. Turner, Baton Rouge, La., assignor to Esso Research and Engineering Company, a corporation of `Delaware -Application December 9, 1949, Serial No. 132,093
Z Claims. (Cl. 202-33) The present invention relates to the art of distilling oilbearing minerals such as oil shales maintained in the formof subdivided particles in a highly turbulent state iluidized by upwardly flowing gases to resemble a boiling liquid, wherein the heat required for distillation is supplied by burning spent solid distillation residue in a separate combustion zone and circulating hot solid combustion residue to the distillation zone. More particularly, the present invention relates to improved means for controlling the particle size distribution of the iluidized solids masses by controlling the percentage of .rich and lean shale in the feed to the fluid type distillation retort.
Prior to the present invention, it has been proposed to carry out the pyrolytic treatment or distillation of oil shale in the formof subdivided solids ranging in particle size from a fine powder up to rather large aggregates of, say, about 1A inch diameter in a highly turbulent lluidized state while supplying the heat required by this reaction as. sensible heat of hot solid combustion residue in the manner indicated above. The principal problem encountered in this type of operation arises as the result of al strong tendency of the shale to disintegrate rapidly in the course of the pyrolytic treatment to particles of extremely small size which complicate and frequently even prevent proper lluidization and solids circulation. The maintenancev of proper fluidization conditions normally requires a relatively low percentage, say, less than about 2li-55% of particle sizes below 20 microns diameter. However, it is desirable in commercial operation to maintain the fines concentration between 20 and25% because relatively high apparent densities of the circulating solids permit the use of lower standpipes and a lower surface area of the particles reduces undesirable oil adsorption on the circulating solids, in the retort. The oil shale powder formed in conventional fluid type distillation has a particle size generally below 40 microns and mostly below 20 microns, independent of the particle size of the raw shale. In addition, spent shale, that is the solid residue from the distillation stage, has a very high attrition rate amounting to about -20 times the attrition rate of other iluidizable siliceous material, such as conventional fluid cracking catalyst.
It will be appreciated that this disintegration causes a rapid accumulation of shale nes in a system of the twovessel type described above wherein the shale is maintained for a considerable length of time at and above dis` tillation temperatures and continuously subjected to attrition in the turbulent fluidized beds as well as during circulation Vbetween the combustion and distillation zones. As this fines accumulation proceeds, iluidization becomes irregular and all solids are eventually carried overhead by the tluidizing gases. The present invention is designed to overcome this diillculty.
The breakdown of the raw shale in the course of the distillation reaction results from the removal of the kerogen content, i. e., the hydrocarbonaceous constituent, which acts as a binder for the silt particles in the raw shale. This breakdown is particularly pronounced in systems of the type referred to above where, in addition to.I
the hydrocarbonaceous constituents, the residual carbon having itself an appreciable though relatively weak binding power, is substantially completely removed in the combustion zone and thus weakened shale particles are subjected to excessive mechanical impact in the course and relatively lean shale in proportions vsuch that upon,
disintegration of the shale the concentration of fines 'of microns size will not exceed the limits referredto above. Y
More specifically it may be stated that shales assayingv about 60 gallons of oil per ton of shale or more break down in the course of the distillation process to a particle size distribution involving an excessive proportion of.
nes of -20 microns in size. Shales assaying about 30- 50 gals. of oil per ton disintegrate to assume readily fluidizable particle size distributions while leaner shales of say 5-20 gals. of oil per ton yield relatively large-sized disintegration products averaging about 40 to 200 microns and above. In accordance with the preferred embodiment of the invention the distillation process is initially run on the richest shale available until the fines concentration of the circulating solids reaches about 20- 55%. Thereupon-relatively leaner shale is added to the charge until the lines concentration of the circulating solids has dropped to about or lower. s
Specific proportions of rich and lean shale to be charged of course depend on the relative richness of the shale fractions available, `their rate of disintegration andj- By way of example, it-
their disintegrated particle size. may be stated that when using a relatively rich shale assaying about -100 gals. of oil per ton as the basic charge to the lluid retort the addition of about 10.40% by weight of a relatively lean shale assaying about 5-20 gals. per ton will afford continuity of operation at a de sirable particle size distribution, i. e., a lines concentration of about 25%.
The practical application of the present invention-,is facilitated by the fact that in most cases the richness of the shale varies considerably between different sections of the same large deposit. For example, the mahogany ledge of the Colorado deposit consists of various layers alternating in richness from gals. to a layer containing about 40 gals. per ton so as to average about 30 gals. per ton. Adjacent sections are as lean as l5 gals. per ton. Australian deposits have sections assaying as high as 80 gals. per ton and higher with adjacent sections containing shale as lean as 1-5 or 20 gals. per ton. lt will be appreciated'therefore, that the different shale fractions required for the purposes of the invention may normally be mined at the same general location.
The process of the invention may be carried out in a layer containing about-26 a system of this type will be briefly described hereinafter.
Referring now to the drawing the system illustrated comprises essentially a fluid type distillation retort and a fluid type combustion zone 30 of largely conventional design, which cooperate in the manner known for twovessel shale distillation systems of this type. In operation, the fresh shale charge crushed to a particle size of about 80% through l0 mesh enters the top of retort 10 through line 9. Simultaneously, a gas such as product tail gas, steam, CO2 or other inert gas containing suspended hot soli-ds supplied from burner 30 as will appear more clearly hereinafter, may be fed to the lower portion of retort 10 from line 12 through a suitable distributing device such as grid 14. Retort 10 is so designed that at the prevailing conditions of solids circulation and carrier gas rates the superficial linear velocity of the gas in retort 10 is about 0.5-1.5 ft. per second. Sufficient hot solids from burner 30 are supplied through line 12 to maintain within retort 10 a proper distillation temperature of say about 900-l200 F. At the conditions specified, a fluidized highly turbulent relatively dense shale bed Mio having a more or less well defined upper level L10 is formed in retort 10 and distillation takes place.
At equilibrium conditions, bed Mio may have an apparent density of about -40 lbs. per cu. ft. and should have a particle size distribution about as follows:
200-400 microns 20-30 400 microns 5 This particle size distribution may be maintained in accordance with the present invention as follows:
Relatively rich oil shale crushed as indicated above and containing for example about 40-80 gals. of oil per ton may be originally charged from feed hopper 1 via line 3 provided with metering device 4, and through line 9 to the top of retort 10. Distillation may be continued as described above until the concentration of nes of .-20 microns in size approaches or exceeds about Thereupon relatively lean shale similarly crushed an-d containing for example about 10e20 gals. of oil per ton may be cut in from hopper 2 via line 6 provided with metering device 7, while the shale supply throughA line 3 is correspondingly reduced to maintain a constant solids feed. The feed rate of the lean shale through line 6 may then be so adjusted and maintained that the fines concentration in bed M10 stays continuously substantially below about 25%. At the relative richness of the rich and lean charge here specified, this may be accomplished by feeding a total charge consisting to about 60 to 90% of rich shale and to about l0 to 40% of lean shale. Rather than adding lean shale continuously in this manner, it may be added intermittently in relatively large increments. In order to prevent the relatively coarse and heavy fresh shale particles from dropping through the liuidized bed to the bottom of retort 10 within undesirably short contact times and from reaching burner in a partially retorted state, retort 10 may be provided with horizontal baies 16 of the disk and doughnut type to prevent the fresh shale from falling freely through bed Min and thus to increase the retorting time of the fresh particles. Suitable perforated plates may take the place of the disk and doughnut type baies.
A mixture of product vapors with tiuidizing gas may be withdrawn overhead from level L10 and passed preferably after separation of entrained solids (not shown) through line 18 to conventional product recovery equipment schematically indicated at 20. Carbonized shale is withdrawn from the bottom of retort 10 through standpipe or the like 22 at a rate controlled by valve 24 to Je picked up in line 26 by air. The suspension formed :nters burner 30 through grid 32. The amount of oxygen supplied through line 26 should be sufficient to maintain by combustion a burner temperature about -200 F. higher than the temperature maintained in retort 10. Burner 30 is so designed that at the prevailing conditions a iluidized solids bed M30 is formed having an apparent density of about 10-30 lbs. per cu. ft. and an upper level L30. Elue gases are withdrawn through line 34 to be used for heat recovery preferably after removal of solids in any conventional manner (not shown).
Hot solid burner residue is withdrawn from bed Mao through standpipe 36, supplied to line 12 and returned to retort 10 as described above. A solids circulation rate between vessels 10 and 30 of about 10-20 lbs. of hot solids from burner 30 per lb. of fresh shale charged is normally sufficient to maintain the system described in heat balance. Excess solids may be discarded either through the gas-solids separators mentioned or through line 3S, or in any other convenient manner, as desired. Rather than mixing the different shale fractions in feed line 9 as shown in the drawing, these fractions may be: mixed in one of the hoppers 1 or 2, or olf-site in any suitable manner. Various other modifications of the system illustrated will appear to those skilled in the art without deviation 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:
l. ln a process wherein finely divided relatively rich4 oil shale having an oil content of 40 to 80 gals. of oil' per ton is distilled in the form of a dense turbulent mass liuidized in a distillation zone by an upwardly flowing gasiform medium and wherein the shale disintegrates so that the concentration of the fines of a particle size of less than 20 microns increases in said iluidized mass to about 25%, the improvement which comprises adding to said distillation zone containing about 25% fines a relatively lean shale fraction containing about l0 to 20 gals. of oil per ton at a rate sufficient with respect to the rich shale feed to prevent increase of said fines in said fiuidized mass to a concentration substantially above about 25%.
2. A process according to claim l wherein the relatively lean shale fraction is added to the distillation zone intermittently in a ratio equal to about l0 to 40% of total shale fed, both shale fractions being originally crushed to a size of about through 10 mesh.
References Cited in the file of this patent UNITED STATES PATENTS Peck et al. May 24, 1949 Peck Aug. 30, 1949 OTHER REFERENCES