US3025223A - Method for the treatment of oil shale - Google Patents

Description

3 March 13, 1962 o. E. A. ASPEGREN ETAL. 3,025,223

METHOD FOR THE TREATMENT OF OIL SHALE Filed March 11, 1957 AI R f HEAT 2 L500? E XCHA NGEQ.

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BALL BLEED-OFF INVENTOR 0L 0: E, A). flJPEGBE/V flAlu-es JEgLU/Va WM 477 NEH- United States Patent Ofiice iifiZSflii Patented Mar. 13, 1952 3 025 223 ivinrnon son THE Thnririunrsr or on snare Olof Erik August Aspegren and Anders Josef Eldund,

dtoclrholm, Sweden, assignors, by direct and mesne assignments, to The Oil Shale Qorporation, Beverly Hills,

Calih, a corporatinn of Nevada Filed Mar. 11, 1957, Ser. No. 645,139 5 Claims. (Cl. 202-14) This invention relates to a process for the treatment of solid-pieced material and relates especially to the destructive distillation of solid fuels which leave a carbonaceous residue after distillation. More specifically, this invention relates to the recovery of shale oil from oil shale, wherein oil shale is stripped, leaving a carbonaceous residue, the carbonaceous residue then being burned with an oxygen-containing gas to provide heat for the stripping phase of the process.

The term stripping as referred to hereinafter, denotes the actual conversion of kerogen in the oil shale to oil or oil vapors, and the term distillation will refer to the complete process for both stripping the shale and for the combustion of the resulting carbonaceous residue to thereby provide heat for the stripping phase of the process. The stripped carbon-containing shale residue is referred to hereinafter as shale coke and the combusted shale coke is referred to hereinafter as shale ash.

This application is a continuation-impart of our copending United States application Serial No. 257,657, entitled Method for the Treatment of a Fuel, now abandoned.

in the past, some processes for the destructive distillation of solid carbonaceous fuel, such as oil shale, have employed fixed bed or moving bed processes in which steam or flue gas is the stripping gas. Fluidized bed processes have also been used, the tluidizing gas acting as the stripping gas.

The use of gas as the stripping medium is not advantageous for the following reason. In the destructive distillation processes of the type under consideration, it is important that the shale oil produced be either substantially uncracked, or, at most, lightly cracked, in order to produce as close to a maximum oil yield as possible. To this end, a close temperature control during the stripping phase of the distillation process is essential. It is found that the most satisfactory method of providing the required temperature control is to employ a purely solid-tosolid heat transfer during the stripping step, rather than by employing gas-to-solid heat transfer or by a combina tion of gas-to-solid and solid-to-solid heat transfer, the reason being that the heat capacity per unit volume of stripping gas is substantially lower than the heat capacity of solid heat transfer bodies, such as metal or ceramic balls. Thus, substantially larger flow rates of gas per unit of heat input to the stripping zone are necessarily employed in comparison to the through-put of heat transfer bodies. The accurate control of large volumes of gas is substantially more diflicult than the control of the smaller volume of solid bodies, and, correspondingly, the control of temperature within the stripping zone is relatively more diflicult with gas as the stripping material.

In addition to the large volumes of gas necessarily employed during stripping, and the consequent difliculty in temperature control, further temperature control problems arise in those distillation processes wherein combustion, as well as stripping take place in a single kiln employing oxidizing gas as the stripping medium. For a greatly variable amount of heat produced during the additional combustion step causes the stripping gas to vary in temperature considerably.

There is another inherent disadvantage in employing gas as the stripping material. As mentioned, the heat capacity per unit volume of gas is relatively low compared with the heat capacity of solid heat transfer bodies, such as metal balls, and for this reason, the stripping gas must be introduced at a considerably higher temperature than the optimum stripping temperature in order to heat the oil shale to the required point. In such a case, local superheating of the oil shale takes place. To avoid such superheating, larger flow rates of gas may be employed, in which case considerable loss of carbonaceous fine particles is encountered. Of course, both superheating and loss of carbonaceous fines by entrainment are highly disadvantageous and are to be avoided.

The conditions stated herein of accurate temperature control and lack of superheating within the stripping zone can be met if the required heat is added by means of preheated heat transfer bodies, since these have a small volume in relation to the heat capacity ,and, consequently, their temperature drop within the stripping zone need not be as great as when employing gas, even if the throughput volume per unit of time is kept within reasonable limits.

In accordance with the process of our invention, it has been found advantageous to employ as solid heat exchange bodies for the stripping step, ash bodies having a high heat conductivity which are directly intermixed with shale ash residue to be heated thereby.

Employing the sensible heat of the carbon-containing stripped shale or shale coke is not, per se, novel. It is known, too, in the prior art to burn the shale coke by oxygen or other oxygen-carrying gases in a combustion zone to raise the temperature of the resulting material or shale ash that is produced, and to then impart the heat of the shale ash in some manner to the fresh shale. However, the problem faced by the art has been the fact that known solid-to-solid heat exchange distillation processes do not economically impart the heat energy present in the shale coke to the oil shale.

In the prior art, processes are known which strip the oil shale employing solid-to-solid heat transfer mechanisms and which employ inclined rotary kilns, the oil shale and solid stripping material flowing, by gravity, downwardly through the kiln. Such distillation processes are, of necessity, co-fiow in nature because of the nature of the kilns employed. However, the most etficient meth od of retorting oil shale is a method wherein solid stripping material flows countercurrently to the oil shale and in continuous admixture therewith-rather than by concurrent fiow, so that the rate of heat transfer is maximized. Other processes that have utilized solid-to-solid heat transfer in the distillation of oil shale have been unduly complex in nature, have required substantial capital investment, and have generally been of little practical utility and importance.

Bearing in mind the foregoing facts, it is a major object of the present invention to provide a simple and eflicient method of producing shale oil from oil shale.

It is another object of the present invention to provide a process for the destructive distillation of oil shale wherein the maximum rate of heat transfer from a given amount of solid stripping material at a given temperature to a given amount of fresh oil shale is obtained.

It is yet another object of the present invention to provide a method for the destructive distillation of oil shale wherein oil shale is stripped by means of solid stripping materials flowing countercurrently to the oil shale and in intimate heat transfer contact therewith, and in which the rate of heat transfer between the stripping material and the oil shale is maximized.

Another object of the present invention is to provide a method for the destructive distillation of oil shale wherein the stripping phase of the process utilizes solid-to-solid 3 heat transfer means, and in which a stripping material is heated for the stripping phase of the process by means of a solid-to-solid heat transfer means.

It is still another object of the present invention to provide a method for the destructive distillation of oil shale wherein the stripping material is heated by means of a combustion step in which the stripping material moves countercurrently through shale coke, and in intimate heat transfer contact therewith, as the solid shale coke is being combusted, to maximize the heat transfer to the stripping material.

The necessity of maintaining a low temperature for the stripping of oil shale to produce a maximum yield of oil is known. However, it may be desirable, in some instances, to lightly crack or visbreak the oil during the stripping phase of the distillation process in order to produce a lighter oil of lower viscosity for the purpose of ease of transportation through pipelines and the like. Such 'visbreaking requires a somewhat higher, but closely controlled, temperature than is usually employed in distillat-ion processes. The solid-to-solid heat transfer system herein contemplated is ideally suited for such processes.

Accordingly, it is another object of the present invention to provide a process for obtaining oil from oil shale wherein a close temperature control of the stripping phase of the process is maintained by means of a wholly solidto-solid heat transfer system employed in the stripping step, the temperature control enabling either low-temperature distillation to be accurately controlled, or, alternatively, enabling the visbreaking of the oil to be accurately controlled.

It is still another object of the present invention to produce oil from oil shale by means of the destructive distillation process of the present invention which has improved chemical and physical characteristics.

These and other objects of the present invention will be best understood by referring to the following description, and to the accompanying figure, which is a diagrammatic flow sheet of one preferred form of the process embodying our invention.

Generally speaking, the process of invention employs two horizontal rotating kilns, one of which functions as a stripping zone wherein the shale is stripped, the other kiln acting as a combustion zone wherein the carbon, in the shale coke, is combusted to provide heat for the heating of the stripping material. In both the stripping and combustion zones or kilns, the shale and shale coke, respectively, flow countercurrently to heat transmitting solid bodies, these bodies acting as the sole media for transferring the heat produced in the combustion kiln of the distillation process to the stripping kiln.

Referring now to FIGURE 1, fresh oil shale is first crushed to a suitable size which is preferably less than one-half inch, and is supplied to line by any conventional means (not shown). Pressure hoppers, mechanical conveyors, or the like may be used for this purpose. The ground oil shale passes from line 10 into a horizontal rotating drum or stripping kiln 12 of the type described in US. application Serial No. 662,890, filed April 17, 1946,

entitled Rotary Heat Exchanger, and now issued as Patent No. 2,592,783 to Olof E. A. Aspegren. Hot solid stripping material enters the opposite side of the kiln 12 from that of the oil shale along line 14, the stripping material being composed of inert heatand wear-resistant materials, such as ceramic, aluminum oxide, or metal bodies. These are preferably generally spherical in shape for ease of conveyance from point to point in the process and are of a different size than the oil shale, for example, greater than one inch, so that they can be separated and removed from the shale. It will be noted that the hot solid stripping material is an extraneous solid, as opposed to a process solid, i.e., a solid produced in the process. The use of ceramic balls as the stripping material is at present preferred because of their high heat conductivity,

wearing qualities during the solid-to-solid milling contact characterizing the process, and their inertness.

The rotation of the kiln 12 causes the hot stripping balls to come into intimate heat transfer contact with the countercurrently moving oil shale, the balls being previously heated, in a manner to be described, to a temperature sufficient to cause the oil shale to be completely stripped. The oil may be stripped from the oil shale at temperatures ranging from about 750 to about 1300 F., depending on the particular oil shale and product desired. However, maintenance of temperatures of between 900 to 1025" F. in the stripping kiln is usually preferable where maximum oil yield is sought. Temperatures of from 1025 F. to approximately 1300 F. are sometimes employed where light cracking is desired.

The resulting oil vapors and gases produced in the stripping kiln 12 exit from the hot end 16 thereof via line 18 and pass to a condenser 20. The oil and noncondensible gases are there separated, being removed from the condenser along lines 22 and 24, respectively.

The combustible shale coke residue formed during the stripping kiln 12 contains approximately 4% to 8% fixed carbon, or higher, depending upon the temperature at which the stripping of the material takes place. The residue is passed from the hot end 16 of the stripping kiln 12 along line 26 into the end 28 of a ball-heating or combustion kiln 30. The balls, cooled because,of their transfer of heat to the oil shale, pass from the cold end 32 of the stripping kiln 12 along line 34 to enter the end 36 of the ball-heating kiln 30.

Preheated air is fed to the ball-heating kiln 30 via line 40 and a substantial portion of the fixed carbon in the shale coke is combusted thereby producing a substantial amount of heat which is transmitted to the balls flowing countercurrently within the ball-heating kiln. In addition, the balls within the kiln 30 are raised considerably in temperature by direct contact with the substantially higher-temperatured shale coke. Thus, it can be seen that the balls are raised to a high temperature by means of both the sensible heat of the shale coke and its residual heat of combustion.

The heated balls are separated within the ball-heating kiln 30 by any suitable means, for example, by the screening means described in the aforementioned U.S. Patent No. 2,592,73 8, and are recycled along line 14 to the stripping kiln 12, to strip fresh incoming oil shale, as previously described. The combusted shale ash is separated from the balls in the ball-heating kiln 30 and passes therefrom along line 42, its sensible heat being employed in various heat exchange systems, such as, for example, in the preheating of the combustion gases or in the preheating of balls, as will be described.

The hot exhaust gases produced by the combustion in the kiln 30 exit from the kiln along line 44 and preferably pass through a dust separator 46, for example, of the cyclone type, where suspended soilds are removed along line 48. The exhaust gases then pass along line 49 to a heat exchanger 50 to preheat the incoming combustion gases, such as air, the air entering the heat exchanger along line 52. The cooled exhaust gases leave the heat exchanger 50 along the line 53, while the preheated air is sent to the kiln 30 along line 40.

A preheat burner 54 is required for initiation of the combustion within the ball-heating drum (kiln) and is otherwise unnecessary for the proper functioning of the process. Worn balls are bled olf from line 34 along line 56, and are replaced by fresh balls entering line 34 from line 58.

While it will be appreciated that the nature and condition of the oil shale varies considerably and requires any specific example of the process to be only approximate, the following example is herein set forth for the sake of clarity of operation:

Approximately 2000 lbs. of oil shale at 70 degrees F., and 8000 lbs. of balls at 1100 degrees F. enter the stripping kiln 12. The halls flow countercurrently to the shale, as described, to thereby strip the shale, producing approximately 250 lbs. of oil and gas at a temperature of 900 degrees F., and 1750 lbs. of shale coke at a temperature also of approximately 900 degrees F. The amount of non-condensible gases produced is approximately 30 lbs.

The halls leave the cold end 32 of the stripping kiln 12 at a temperature of approximately 250 degrees F., and enter the ball-heating kiln 30 at this temperature along with approximately 720 lbs. of air preheated to a temperature of 500 degrees F., and the 1750 lbs. 900 degrees F. shale coke produced in the stripping kiln 12. Heat transfer takes place within the ball-heating kiln such that the balls are heated to an average stripping temperature of 1100 degrees F the exhaust gases leaving at a temperature of approximately 1000 degrees F., and the shale ash passing from the kiln at a temperature of approximately 500 degrees F. The shale ash is approximately 40 lbs. lighter than the shale coke, thi amount representing the total residual carbon in the shale coke burned off to provide the additional heat requirements for the heating of the balls. The amount of carbon burned in the ball-heating kiln represents over half the 4% residual carbon in the shale coke. The exhaust gases are then sent to a heat exchanger 50 to preheat the incoming air to a temperature of approximately 500 degrees F., as previously described.

The balls employed in this example are composed primarily of steel. Where ceramic balls are used, the amount of balls circulated is approximately twice the input rate of oil shale.

In the process just described, complete stripping of the oil shale is accomplished by means of solid-to-solid heat transfer occasioned by the solid-to-solid milling contact in the stripping zone, no additional fuel or stripping gases being employed therein or at any other point in the process.

Accurate control of temperature is possible by use of heat-carrying bodies, and the temperature in the stripping zone is readily raised or lowered, depending upon the nature of the product desired, by merely increasing or decreasing the rate of flow of the heat-carrying bodies. For example, if the oil is to be lightly cracked, the amount of hot heat-carrying bodies circulated to the stripping zone 12 may be immediately increased by the addition of previously heated balls along line 58 into line 34, and thence into the combustion zone 30. These additional reserve balls, may be heated for example, by the sensible heat of the 500 degrees F. shale ash leav ing the combustion Zone 30 along line 42 in a rotary drum. The additional heat thus imparted to the system is sufficient to raise the temperature of the incoming oil shale to as high as 1300 degrees R, if necessary.

Alternatively, the amount of fresh oil shale introduced per unit of balls circulated may be decreased, thus increasing the amount of stripping heat available per unit of oil shale. The oil shale may then be stripped at the higher temperature desired.

It can be seen that the amount of change required in the rate of flow of the heat-carrying bodies or oil shale is substantially less than that necessary when employing gaseous strippin materials for reasons previously described.

Further, the particular counterfiow-solid-to-solid process employed in both stripping and combustion stages of the distillation process results in maximum heat utilization of the shale coke. The process is thus capable of controlled distillation at a variety of temperatures, from a low-temperature process where a greater oil yield is obtained, to a higher-temperature process in which the oil yield is less, but in which the oil is of lower viscosity, thus leading to greater convenience and economy in transportation.

The oil produced in the stripping zone by means of 6 the above-described processes has several advantageous chemical and physical properties. Perhaps one of the most significant physical properties of the oil produced is its extremely low pour point. The pour points of shale oil hitherto produced have been, on an average, ranging between degrees and degrees F. However, it has been found that the pour point of the oil produced according to our process is approximately 55-70 degrees F.

An important chemical property of the oil produced by the process of this invention is its substantial freedom from nitrogen. The removal of nitrogen prior to, or during the refining of the oil is an expensive process. For this reason, it is advantageous to produce a crude shale oil which is substantially free of nitrogen. The nitrogen content of the oil produced by the process herein described ranges from 1.0 to 1.3%, while oils produced by other processes generally range between 1.7% to 2.1%.

While one preferred embodiment of the invention has been described herein, it will be understood that substantial changes and modifications may be made that lie within the scope of the invention. Hence, the applicants intend to be bound only by the scope of the appended claims.

We claim:

1. A method for the continuous stripping of a solid fuel in a stripping zone, said fuel upon being stripped leaving a combustible residue, which comprises the steps of: continuously contacting fresh solid fuel in a stripping zone in solid-to-solid milling contact with substantially hotter solid extraneous inert heat-carrying stripping bodies larger in particle size than said combustible residue, the heat-carrying bodies imparting their heat to said solid fuel to cause the stripping thereof, and the production of a gaseous eflluent; burning said combustible residue to produce hot ash and hot combusted gases; reheating said heat-carrying bodies by means of said hot ash and combusted gases, said combusted gases and said gaseous efiluent never intermingling; and recycling said reheated heat-carrying bodies to said stripping zone to strip additional fresh incoming solid fuel.

2. The method of claim 1 in which the heat-carrying bodies are continuously intermixed with additional solid fuel as these materials pass through the stripping zone, and further characterized in that the heat-carrying bodies are passed through a combustion zone and are continuously intermixed with the combustible residue.

3. The method for the continuous stripping of the solid fuel in a stripping zone, said fuel upon being stripped leaving a combustible residue, which comprises the steps of: continuously contacting fresh fuel in a stripping zone in solid-to-solid milling contact with substan tially hotter solid extraneous inert heat-carrying bodies larger in particle size than said combustible residue, the heat-carrying bodies imparting their heat to said solid fuel to cause the stripping thereof in a noncombustion supporting atmosphere, and to produce thereby a gaseous effluent and cooled heat-carrying bodies; separating the cooled heat-carrying bodies from said combustible resi due; reheating said heat-carrying bodies by means of both the gaseous products of combustion and the combusted residue, said gaseous products of combustion and gaseous eflluent never intermingling; and recycling said heat-carrying bodies to said stripping zone to strip additional fresh incoming fuel.

4. A shale oil product of low pour point and low nitrogen content produced according to a method which comprises the steps of: continuously contacting fresh oil shale with substantially hotter inert heat-carrying bodies in a stripipng zone, the heat-carrying bodies imparting their heat to the oil shale by direct contact therewith to cause the stripping thereof; transferring the cooled heat-carrying bodies and combustible residue formed in said stripping zone to a combustion zone; comhusting said residue in the presence of said heat-carrying bodies to reheat 5. A shale oil product having a pour point of between approximately 55 to 70 F.

References Cited in the file of this patent UNITED STATES PATENTS Everest Feb. 23, 1869 Gibbons Mar. 9, 1869 Danckwardt Oct. 17, 1922 Bussey Oct. 17, 1922 McKee:

8 Koppers May 7, 1929 Iohansson May 13, 1947 Barr et a1. Mar. 4, 1952 Riblett June 17, 1952 Moore Mar. 2, 1954 Martin et al Nov. 29, 1955 Young et al July 17, 1956 Aspegren Apr. 9, 1957 FOREIGN PATENTS Great Britain Dec. 19, 1949 OTHER REFERENCES Shale Oil, The Chem. Catalog Co. Inc.,

Claims (1)

1. A METHOD FOR THE CONTINUOUS STRIPPING OF A SOLID FUEL IN A STRIPPING ZONE, SAID FUEL UPON BEING STRIPPED LEAVING A COMBUSTIBLE RESIDUE, WHICH COMPRISES THE STEPS OF: CONTINUOUSLY CONTACTING FRESH SOLID FUEL IN A STRIP PING ZONE IN SOLID-TO-SOLID MILLING CONTACT WITH SUBSTANTIALLY HOTTER SOLID EXTRANEOUS INERT HEAT-CARRYING STRIPPING BODIES LARGER IN PARTICLE SIZE THAN SAID COMBUSTIBLE RESIDUE, THE HEAT-CARRYING BODIES IMPRATING THEIR HEAT TO SAID SOLID FUEL TO CAUSE THE STRIPPING THEREOF, AND THE PRODUCTION OF A GASEOUS EFFLUENT; BURNING SAID COMBUSTIBLE RESIDUE TO PRODUCE HOT ASH AND HOT COMBUSTED GASES; REHEATING SAID HEAT-CARRYING BODIES BY MEANS OF SAID HOT ASH AND COMBUSTED GASES, SAID COMBUSTED GASES AND SAID GASEOUS EFFLUENT NEVER INTERMINGLING; AND RECYCLING SAID REHEATED HEAT-CARRYING BODIES TO SAID STRIPPIG ZONE TO STRIP ADDITIONAL FRESH INCOMING SOLID FUEL.

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