US2634233A - Fluid-type retorting of oil shale - Google Patents

Description

1 April 7, 1953 NICOLA] ET AL 2,634,233

FLUID-TYPE RETORTING OF OIL. SHALE Filed June 16 1949 4 Sheets-Sheet 1 Q 04 e o z o o g v o n BURNER :rznpsnnrunz F zzo z z MW Mrs April 7, 1953 A. NlCOLAl ET AL 2,634,233

FLUID-TYPE RETORTING OF OIL. SHALE Filed June 16, 1949 4 Sheets-Sheet 2 CARBON AOSORBED on Bunmso SHALE PER PASS THROUGH RETon-l; m

84 88 42 46 so 5.4 5.8 5425mm TE cnnaou on swans sHALE w7.'%

gea d meu'fiwwors .25 9. gm Afi'orrvey WEIGHT 7. co; EVOLVED April 1953 L. A. filcoLAl ET AL 2,634,233

FLUID-TYPE RETORTING OF OIL SHALE Filed June 16, 1949 4 Sheets-Sheet 3 lo I 200. 400 600 600 I000 I200 I400 I600 TEMPERATURE F fig. 5

4. WM Mrs Ap 1953 L. A. NICOLAI ET AL 2,634,233

FLUID-TYPE RETORTING 0F on. SHALE Filed June 16, 1949 '4 Sheets-Sheet 4 Patented Apr. 7, 1953 2,634,233 FLUID-TYPE RETORTING OF OIL SHALE lzl rd A- Rouge,

Nicolai and Byron V. Molstedt, Baton I La., assignors to Standard Oil Development Company, f a corporation of Delaware Application June 16, 1949, Serial No. 99,459 Claims (01. 2021-14) combustion residue to the distillation zone. More particularly, the present invention relates to improved means for preventing losses of product by excessive combustion thereof in the combustion zone and for reducing solids entrainment in the gases and vapors leaving the fluid bed in the distillation retort.

The invention will be. fully described hereinafter with reference to the accompanying drawing wherein Figures 1, 2, and 3 are graphical summaries of experimental data demonstrating the utility of the invention; and.

, Figure 4 is a schematical illustration of a system suitable for carrying out a preferred embodiment of the invention.

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 f. about 4 ch diameter in a h y turbulent fluidized state while supplying the heat required by this reaction as sensible heat of hot solid ombus i n r s e in the m ner indi at abov t h s been o se e n this type of ope ation that substantial product losses are caused by an x es iv b il up o arb n in the distil ime zo e a d the ubs uent combu tion of s carbon the combustion zone. Another prob m arises as the result or"- a strong tendency of the ha e o di teg a ra idly in t e co o h P mb'tie treatme t. t P ri es ha in n sm lr mall s z f. a u 0-2 mic ons wh ch is the at Pa ticle. the sha s For am e; Co o do sh le hen. Su cte o a fluidtype distillation quickly form a mass containing ab ut 7 oi n s o MD micr n Si e and hi even if the shale is charged in rather coarse aggregates. At the conditions of fluid shale distillation, these fines are fully entrained by the t dir'm'ei g te and ra d c r d o rh a #9 1 iliefl i l zfld 3315 in thedisfillat o an combustion zones, comp ic t g li u drmdi ft eth 1 53i bf tho flui ized: beds. The

. n rainm nt ra e f th se. shale fines is not only a 2. function of their particle size but, in addition, in creases as the carbon concentration of th lines increases.

It has now been found that this carbon cor- 1- centration in the retortis strongly influenced by the temperature to which the spent shale is subjected in the combustion zone. Experimental data indicate that a substantial portion of; the carbon on the spent shale in the retort has bee picked up in the retort by burned shale returned to the retort from the combustion zone. These burned particles have a high adsorption and/or polymerization activity which results in the adsorption of oil vapors evolved in the retort and i the formation of a carbon deposit on these particles whereby their gas buoyancy and-entrainment rate is substantially increased and the products so adsorbed are lost by combustion in the combustion zone. It is this adsorption and/or polymerization activity and with it the carbon concentration of the fines in the retort, which have been found to be strongly affected by the burner temperature. More particularly, it has been found that within certain limits said adsorption activity and carbon concentration are the higher, the higher the temperature to which the spent shale is subjected in the combustion zone or burner.

Based on this discovery, the present invention in its broadest aspect proposes to maintain the temperature in the combustion zone or burner of a two-vessel shale retorting system of thetype identified above, at the lowest level possible for efficient retorting of the shale, while simultaneously reducing'the organic carbon content of the spent shale by combustion in the burner so as to maintain a total carbon concentration in the retort as low as possible, preferably substantially below 0.7 weight percent. o I

This proposal differs fundamentally from the tendency strongly established in the art of twovessel al dis illat n to ma a n t e bur e t m er ure as hi h s ssi l i Order o u he c rcu i rate of hot sol s- T min m m burner tember ture ract c in a two-vessel system of the type here involved is fi e by t e m im tem era re e ire for eflicient retorting of the fresh shale.

the heat required to maintain these retorting temperatures, hot burned shale must be circulated from the burner to the retort at a temperature at least differentially higher than said minimum retorting temperature and at a circulation rate which is a high multiple of the fresh shale feed rate. This circulation rate is the higher the smaller the temperature diiferential between the burner and the retort. Since circulation rates in excess of about 30 times the fresh shale feed rate are commercially impractical, the lowest burner temperature is practically fixed at the level at which the heat required in the retort may be supplied at circulation rates below about 30 times the fresh feed rate. This level lies about 50 F. above the minimum efiicient retorting temperature. Therefore, in accordance with one embodiment of the invention, the burner of a two-vessel system of the type here involved is operated at a temperature exceeding the retorting temperature of about 850-1200 F. by not more than about 50 F., while simultaneously reducing the organic carbon content of the spent shale by combustion in the burner to the degree .described above.

Experimental data have demonstrated that the amount of adsorbed carbon varies between about 0.07 to about 0.35 weight percent for burner temperatures between 1000 and 1150 F. The pertinent data were obtained in pilot plant experiments wherein shale of 26 gals/ton Fischer assay was retorted in a two-vessel retort-burner system. The amount of adsorbed carbon was determined by determining the carbon content of the burner flue gases and deducting therefrom the residual organic carbon of the retorted shale as determined by fluid batch experiments evaluating the shale in a manner similar to Fischer assay analyses.

The results of these experiments are summarized in Figure 1 showing a graph wherein weight percent of carbon adsorbed on burned shale in the retort is plotted against burner temperature. The curve illustrates qualitatively and quantitatively the direct relationship between these two variables. In accordance with a preferred embodiment of the invention, therefore, the burner temperature in a two-vessel shale retorting system of the type here involved is maintained at the lowest possible level within the range of about 900-1200 F., which is compatible with the required heat supply to the retorting zone. while simultaneously reducing the organic carbon content of the spent shale by combustion inthe burner to the degree specified above.

These experiments have further shown that there also exists a definite relationship between adsorption-activity or adsorbed carbon concentration of the burned shale and its content of inorganically bound carbon determinable as carbonate carbon.

The results of these experiments with respect to the influence of carbonate carbon are summarized in Figure 2 in the graph of which weight percent of carbon adsorbed on. burned shale is plotted against weight percent of carbonate carbon. The curve shows that the higher the carbonatecarbon content the lower is the adsorption activity or adsorbed carbon content of the shale. It is indicated that, between about 3.5 and 6 weight percent, the carbonate carbon content should be held as closely to the'upper limit of this range or to complete COzsaturation of the spent shale as is compatible with the heat requirements of the process, in order to prevent excess e ca on adsorption.

The data reported in Figure 2 have been supplemented by experiments establishing the relationship between combustion temperature and carbonate carbon content of the shale. In these experiments, freshly retorted shale was subjected successively to different temperatures in a nitrogen atmosphere for about 30 minutes at each temperature and the CO2 evolved was determined during each 30 minute period. The results are summarized in Figure 3 showing a graph wherein weight percent of CO2 evolved is plotted against temperature. Residual carbonate carbon may be derived from this plot by deducting weight percent COz evolved from the total 002 content of about 22 weight percent of the freshly retorted shale. The curve of Figure 3 shows that residual carbonate carbon falls off very rapidly at temperatures above about 1000 F. From Figures 2 and 3 together it follows that in order to maintain the carbonate carbon content of the spent shale within the above-mentioned desirable range of about 3.5 to 6 weight percent the burner temperature should be maintained below about 1100 F. and as low as is.compatible with the heat requirements of the process. Therefore, in accordance with another embodiment of the invention the burner temperature is maintained at a level below about 1100? F., which is conducive to a carbonate carbon content on the burned shale in excess of 3.5 weight percent and preferably closely approaching 6 weight percent or complete CO2 saturation of the burned shale, while simultaneously removing carbon from the spent shale by combustion in the burner to the degree specified above.

The present invention has utility in all conventional fluid-type two-vessel shale retorting systems wherein the shale is retorted in one or more fluidtype vessels and heat for retorting is supplied as sensible heat of hot spent shale burned in a separate heater and returned to the fluidized shale in the retorting zone substantially at the burner temperature. A typical system of this type is schematically illustrated in Figure 4 and will be hereinafter briefly described with special reference. to a preferred application of the present invention. 7

Referring now to Figure 4, the system illustrated therein essentially comprises a distillation vessel or retort Ill, a stripper or second stage retort 30, and a combustion chamber or burner 40, the functions and cooperation of which will be forthwith described using as an example the retorting of a Colorado oil shale having a Fischer assay of about 26 gals. of oil per ton of shale.

In operation, fresh shale crushed to a particle size of'about 4-30 mesh is supplied through line I to retort ID at a rate controlled by valve 3.

Simultaneously, a gas such as product tailgas,

steam, CO2 or other inert gas containing suspended therein hot solids supplied from burner 40 as will appear more clearly hereinafter, is fed to the lower portion of retort [0 from line [2 through a suitable distributing device, such as grid I 8. Betort lfi-is so designed that at the prevailing conditions of solids circulation andcarrier gas rates, the superficial linear velocity of the gasiform medium in retort H] is about 0.5-1.5 ft. per second. Sufficient hot solids from burner 40 are supplied 1 with the gas through line l2 and grid l 4 at an adequate temperature to maintain within retort l0 a solids temperatureof about 900-,l200 'F., for

example about 950 F., suitable for shale distillation. At the conditionsspecified, a fluidized high- 1y turbulent relatively dense Shale bed M10 having The average carbon concentration of the most readily entrainable fines of 20 microns size is maintained substantially below 0.6-0.7 weight percent, say at about 0.2-0.4 weight percent, by the combined action of carbon removal and temperature control in burner 40 inaccordance with the invention as will appear more clearlyhereinafter. As a result, the fines entrainment rate from retort I is relatively low, say about 0.002 to 0.004 lb. per cu. ft., of overhead gases and vapors and bed M may be readily maintained in a relatively dense fluidized state. Simultaneously, the product transfer rate from the retort to the burner is maintained at a desirable minimum.

The mixture of product vapors and gases with fluidizing gas passing overhead from level L10 together with entrained solids enters a gas-solids separator system, such as one or more cyclones l6, wherein most of the entrained solids may be separated and returned to bed M10 through one or more dip-pipes l8. Vapors and gases now containing merely about 00001-00005 lb. per cu. ft.

of entrained solids fines are passed through line 20 to a conventional product recovery system (not shown). Such concentration of solids fines in the product vapors may be readily removed by scrubbing and filtering without causing appreciable difficulties by slurry formation. If desired, solids so removed may be returned to retort I0 in the form of an oil slurry.

A mixture of freshly retorted and burned spent shale particles is withdrawn from retort 10 through line 22 and may be passed into a fluidtype stripper 30. A stripping gas, such as steam or CO2 is supplied to the bottom of stripper 30 through line 24 and grid 26 at a rate adequate to establish in stripper 30 a turbulent fluidized mass M30 having an upper interface L30 similar to mass M10 in retort l0. Stripper 30 may be operated at conditions similar to those maintained in retort I0. Such operation serves the dual purpose of removing adhering product vapors from the shale flowing from retort l0 and of completing the retorting process. In other words, stripper 30 may represent a second shale retorting stage whereby the total holding time of the shale charged may be substantially reduced at any given temperature as compared with single stage operation. Stripper overhead passes through line 28 into retort l0, to be mixed therein with the overhead from bed M10. I

Shale now substantially denuded of distillable constituents and containing an average of about 0.2-0.4 weight percent of organic carbon and about 5-6 weight percent of'carbonate carbon is passed from stripper 30 through line 32 into line 35 .wherein it is picked up by a combustion-supporting gas, such as air, which may be preheated to about 600-800 F. in heat exchange with process flue gases. The amount of air supplied to line 35 is preferably sufiicient for a substantially com- 6* plete combustion of the organic carboncn the solids carried by line 35. About 5-7 normal cu. ft. of air per lb. of fresh shale charged are usually suiiicient for this purpose. The suspension formed in line 35 is passed through a distributing grid 31 or the like to' the lower portion of burner 40 which is so designed that the gases flow upwardly therein at a superficial linear velocity of about 1-3 ft. per second so as to form a relatively dense fluidized bed M40 having a well defined upper interface L40.

The temperature in bed M40 is preferably maintained about 50 Rhigher than that of bed M10, say at about 1000" F. For this purpose, bed M40 may be cooled by any'suitable cooling means, such as cooling coil 42,"in heat exchange with water or steam. Steam so generated and/or superheated may be used in the process. If desired, heat may be withdrawn by continuously circulating burner solids through extraneous cooling means and backto bed M40 in a manner known per se. A dilute suspension of spent shale fines in flue gases is passed overhead from' interface L40 through a gas-solids separation system 44 comprising one or more cyclones and/or electrical precipitators from which separated solids may be returned to bed M40 through line 46 or discarded through line 48. Flue gases substantially free of entrained solids may be vented through line 50, if desired after suitable heat recovery. Additional burner solids may be discarded through line 52 from bed M40 if desired for a proper maintenance of the solids balance in the system.

Solid combustion residue substantially free of organic carbon is withdrawn from the bottom of bed M40 via line 55 at a rate controlled by valve 5?. The solids flowing through line 55 enter line i2, are suspended therein in fluidizing gas and supplied to retort II] as described above substantially at the temperature of bed M00. These solids may have an average organic carbon content of about 0 to 0.05 weight percent and a carbonate carbon content of about 5.5 weight percent. Their adsorption activity is insignificant as a result of the relatively low burner temperature and the high carbonate carbon content of the solids.

The solids circulation rate through line l2 which is approximately the same as that through line 35 depends on the exact temperature differential between burner 40 and retort [0. At the conditions specified above, it may be about 15 to 25 lbs., say about 20 lbs. per 1b., of fresh shale fed through line I.

Various modifications of the system described with reference to the drawing 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 during distillation, wherein the subdivided minerals are subjected to a distillation temperature in the form of a highly turbulent dense mass fluidized by an upwardly flowing gasiform medium in a distillation zone and the heat required by the distillation is supplied by burning solid distillation residue with a combustion-supporting gas in the form of a fluidized mass of solids in a separate combustion zone at a combustion temperature and returning solid combustion residue substantially at said combustion temperature to said distillation zone, the improvement which comprises maintaining said combustion temperature at the lowest level within the approximate range of about 10001100 R, which is compatible with a substantially complete distillation of said minerals and reducing the organic carbon content of said distillation residue by said combustion substantially below 0.7 Weight percent, whereby the adsorption of oil vapors on shale fines and the entrainment of shale fines in said distillation zone are maintained at a minimum.

2. The process of claim 1 in which said combustion temperature is maintained not more than about 50 F. higher than said distillation temperature.

3. The process of claim 1 in which said combustion temperature is so controlled that the carbonate carbon content of said solid distillation residue remains substantially unchanged during said combustion.

4. The process of claim 1 in which said com- 8v bustion temperature is maintained at a level below about 1100" F. which is conducive to a carbonate carbon content on the burned shale in excess of 3.5 Weight percent.

5. The process of claim 4 in which said level is so chosen that said carbonate carbon content closely approaches complete CO2 saturation of the burned shale.

LLOYD A. NICOLAI. BYRON V. MOLSTEDT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,379,408 Arveson July 3, 1945 2,392,036 Blanding Mar. 5, 1946 2,432,135 Barr Dec. 9, 1947 2344936 Corson et a1. June 29, 1948 2,480,670 Peck Aug. 30, 1949

Claims (1)

1. IN THE PROCESS OF DISTILLING OIL-BEARING MINERALS OF THE TYPE OF OIL SHALE WHICH DISINTEGRATE DURING DISTILLATION, WHEREIN THE SUBDIVIDED MINERALS ARE SUBJECTED TO A DISTILLATION TEMPERATURE IN THE FORM OF A HIGHLY TURBULENT DENSE MASS FLUIDIZED BY AN UPWARDLY FLOWING GASIFORM MEDIUM IN A DISTILLATION ZONE AND THE HEAT REQUIRED BY THE DISTILLATION IS SUPPLIED BY BURNING SOLID DISTILLATION RESIDUE WITH A COMBUSTION-SUPPORTING GAS IN THE FORM OF A FLUIDIZED MASS OF SOLIDS IN A SEPARATE COMBUSTION ZONE AT A COMBUSTION TEMPERATURE AND RETURNING SOLID COMBUSTION REDISUE SUBSTANTIALLY AT SAID COMBUSTION TEMPERATURE TO

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