US 2832725 A
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Description (OCR text may contain errors)
April 29 .1958 J. w. SCOTT, JR 2,8
FLUID SHALE RETORTING WITH INTERMEDIATE OIL RECOVERY Filed March so, 1955 FRESH SHALE GAS GAS,-
' SHALE on.
PREQHEAT SECTION 'RETORTING HEAT- SE CONSERVATION 8b ZONE AIR 7-. 30
2a CONDENSER COOLING SHALE OIL SECTION RECYCLE GAS INVENTOR Joflgpw. scorr, JR. I2
SPENT SHALE OUT ATTO NEYS Unite FLUID SHALE RETGRTING WITH INTERMEDIATE OIL RECOVERY Application March 30, 1955, Serial No. 497,924
2 Claims. (Cl. 202-6) This invention relates to a method of the solids fluidization type for retorting oil-bearing minerals to recover valuable liquid and gaseous hydrocarbon products therefrom. More particularly, this invention relates to a fluidized shale retorting process in which intermediate product recovery is accomplished. This application is a continuation-in-part of my copending application Serial No.-4l8,030, filed March 23, -1954, now Patent No. 2,710,828.
The recovery of hydrocarbon liquids and gases from shale and similar solids by countercurrently contacting the solids, either in ordinary moving bed or fluidized bed operations, with hot gas in a retorting zone to vaporize oil from the solids has long been known. However, in practicing these methods it has been found .that a substantial proportion of the hydrocarbon material formed in the retorting zone is condensed during its contact with the incoming fresh cold shale and forms a distinct liquid phase which refluxes in the unit. This condition increases the tendency of the shale particles to agglomerate, with the result that clinkering in the retorting zone is aggravated. Further, vaporized normally liquid hydrocarbons in contact with the cold incoming shale condense in the form of a fog which is not precipitated in the condensation zone and which emerges therefrom in suspension in the gaseous product. This latter condition requires either that a substantial loss of liquid product be accepted or that unusually elaborate recovery equipment be provided to capture the suspended oil droplets.
Accordingly, it is an object of the present invention to provide a process for the fluidized retorting of carbonaceous material by which liquid refluxing in the retort is considerably reduced, thereby reducing the undesirable agglomeration of the fluid solids. Another object is to provide a method for recovering the liquid present in the aforementioned fog without the expensive apparatus heretofore thought necessary. Still another object of the subject invention is to provide a staged fluidized retorting process in which improved thermal efficiencies and recoveries are obtained. Other objects will be apparent from a consideration of the description to follow.
Pursuant to the present invention, the retorting of finely divided oil-bearing particles is performed by contacting them in a shale treating zone with hot gas to vaporize oil from the particles. Oil is recovered from the upper portion of the treating zone and substantially oil-free solid particles are withdrawn from the lower portion of said zone. A substantial proportion of the vapors produced in the zone are withdrawn from a withdrawal point in the zone 'where the temperature of the solid particles contained therein is at or somewhatabove the average dew point of the normally liquid components of the vapors, i. e., from about 400? to 800 F., and are then passed into a heat conservation zone wherein the normally liquid components are condensed out and the uncondensed vaporsare returned to the treating zone at a point immediately above the withdrawal point. In this manner,
States Patent 'ice 2 refluxing in the treating zone is considerably reduced and misting or fogging is avoided by recovering the normally liquid components of the vapors produced in the zone.
The process of the invention will be better understood by reference to the appended drawing which is a diagrammatic illustration of apparatus and process flow suitable for its practice.
Vessel 1, constituting a shale treating zone, contains a preheat section 2, a retorting section 3 and a cooling section 4. Cold, finely divided shale (of a size of from about 15 to 400 mesh) is introduced into the preheat section of the treating zone from hopper 5 through standpipe 6, the latter containing slide or star valve 7. In preheat section 2 the downwardly moving cold fresh shale is maintained in staged fluidized beds by the combination of staging means and the countercurrent contact with hot gases flowing upwardly through the treating zone, the source of these hot gases to be described in more detail in the description to follow. As shown in the drawing, staging can be accomplished by known means, for example by inserting in the preheat section a series of screens and trays 8a which will allow the upward passage of the gas therethrough but whichimpair or restrict the downward passage of the shale particles. The hot gases introduced into the preheat section pass through grid 9a (which also allows the upward passage of the gas but restricts the downward passage of the solids) and thence upwardly through the trays 8a at such a rate that the downwardly moving shale particles are maintained as a fluidized bed divided into regions of increasing temperature (in the direction of solids flow) by said screens 8a.
The preheated shale is withdrawn from preheat section 2, usually at a temperature of from about 250 to 650 F., and passed by standpipe 10 into the retorting section 3 of the treating zone. I In the retorting section, the preheated shale is passed downward through another series of fluidized beds also divided into regions of increasing temperature by the action of screens 8b and the countercurrent contact with gas. The latter, being ordinarily at a temperature of from 1100 to 1500 F., serves both as a heat conveying and fluidizing medium. The source of this gas will also be hereinafter described.
Hot spent shale is withdrawn from the retorting section and passed by standpipe 11 into the cooling section 4 where it flows downward through another series of fluidized beds segregated by screens and fluidized by the countercurrent contact with cold recycled product gas entering the zone by lines 18 and 20. Here the flow of shale is downward through regions of decreasing temperature. Cold, spent shale is withdrawn from the cooling section through line 12 and slide or star valve 13 at a temperature usually in the range of from about 200 to 350 F.
Substantially all of the gas produced in the process and a minor proportion of the normally liquid materials produced in the process are withdrawn from the upper portion of the treating zone through separator 14 and line 15 into condenser 16. Separator 14 may be any type of apparatus that will separate the solid particles from the gaseous stream. A cyclone separator in which the solid particles are returned by a standpipe to below the level of the fluid particles in the preheat section is preferred. The normally liquid components of this stream are condensed and collected in condenser 16- and withdrawn as product through line 17. The normally gaseous components of the stream withdrawn from the treating zone through line 15 are passed from condenser 16 through line 18, blower 19 and line 20 into the lower portion of coolingv section 4 of treating zone 1. A portion of the gas from line 18 is withdrawn through line 21 as product.
3 The recycled gas introduced into cooling section 4 contacts hot spent shale countercurrently, cooling the shale, and being itself heated usually to 700 to 900 F. The gases pass from line 20 upwardly through grid 9c at a velocity suflicient to maintain the downwardly moving shale in cooling section 4 in a series of fluidized beds created by partial isolation between screens 8c. A superficial velocity from about 0.5 to 3.0 ft./sec. has been found to be suflicient for all of the fluidization steps of the present operation. The heated gas flowing upwardly from cooling section 4 passes through separator 22 wherein solids are removed and returned to the cooling section and the hot vapors pass into the open annular space be tween the cooling section 4 andthe retorting section 3 of the treating zone. Air is introduced into this annular space through line 23 to burn a portion of the gas flowing upward from the cooling section. The actual burning may be conducted in a special combustion space as an in-line burner, etc. The quantity of air introduced through line 23 ordinarily amounts to from about 10 to about 30% of that stoichiometrically required for complete combustion of net make gas. ,Putting it another way, the amount of air introduced is sufficient 'to burn from to 15% of the gas entering the annular space from the cooling section. The amount of air is varied ordinarily within these limits depending uponthe composition of the gas flowing upward from the cooling section, but may exceed this if heat requirements are unusually high as when a very wet shale is run, when carbonate decomposition is encountered, or when the gas yielditselfis low. The quantity of air introduced through line 23 is adjusted so that the temperature of the mixture of unburned gas and combustion products produced in the annular space between the cooling section and the retorting section is raised to a temperature sufficiently high that the gaseous mixture can supply all of the heat required to decompose the kerogenic constituents of the shale inthe retorting section. This temperature is usually in the'range of from about l100 to 1500" F. As an alternative, air may be introduced directly into the fluid bed at the indicated location with the staged retorting and cooling zones interconnected so as to be substantially contiguous. This alternative is not attractive if staging is not employed.
In the retorting section 3, the down flowing shale is.
countercurrently contacted with the hot gas flowingupwardly from the annular space between the coolingsection and the retorting section'through grid 9b and is maintained in the same type fluidized bed as is maintained in both the preheat and cooling sections. This moving shale is so heated by contact with the hot gases that substantially all of the kerogenic constituents of the shale are converted to normally gaseous and normally liquid hydrocarbons. Normally gaseous hydrocarbons and vaporized normally liquid hydrocarbons (usually at temperatures from about 400 to 800 F.) flow upwardly fromthe retorting section through separator 24 and line 25 into the heat conservation zone. The heat conservation zone contains vessel 26, packed with inert solid heat exchange inaterial, indirect heat exchange zone 27, and vessel 23 packed with inert solid heat exchange material. The stream withdrawn from the space above the retorting section 3 through line 25 is passed through line 29 into vessel 26. This stream is cooled by direct heat exchange with the inert solid packing in vessel 26 (vessel 26 operating as a partial condensation zone) and is passed from that vessel at a temperature from about 200 to 300 F. through line 30'into indirect heat exchangezone 27. In indirect heatexchange zone 27 the effluent from vessel 26 is further cooled, if desired, to approximately atmospheric temperature by indirect heat exchange with a cooling medium such as water. If the normally'liquid product is unusually viscous, the cooling in exchanger 27 may be deliberately limited so that the liquid product is sufliciently hot that it is easily handled as a liquid. A
substantial portion of the normally liquid hydrocarbon components of the elfluent are condensed in condensation zone 27 and withdrawn therefrom through line 31 as a product. Uncondensed gases comprising normally gaseous hydrocarbons and products of combustion are passed from condensation zone 27 through line 32 into vessel 28. At the start-up of the unit, the solid packing in vessel 28 will be cold, but as the operation is under way, this packing will be hot by reason of its having served to cool the material carried by line 25 in an earlier cycle of operation. Accordingly, in the usual operation of the process, the uncondensed gases passing from indirect heat exchange zone 27 into vessel 28 will be heated by contacting with the hot solid packing in vessel 28 (said vessel operating as a reheating zone) and then passed through lines 33 and 34 into the lower portion of preheat section 2 of treating zone 1. A two-way valve 35 is placed in the junctions of lines 25, 29, 33, and 34. The material withdrawn from treating zone 1 through line 25 is passed through line 29, vessel 26, condenser 27, vessel 28, and line 33, until the solid packing in vessel 26 has been heated to the point where its capacity to cool the product is exhausted, i. e., the solid packing has attained an average temperature of 500 to 800 F., or the temperature of the efliuent product rises to an undesirably high value, for example, to 350 or higher. When this condition is reached, valve 35 is turned so that the flow of gas from line 25 through the heat conservation zone is reversed, i. e., the gas passes successively through line 25, line 33, vessel 28, condenser 27, vessel 26, line 29, and line 34.
By operating in this manner, refluxing of the liquid product in treating zone 1 is prevented, and also the loss of product due to fogging is very substantially reduced. These results are attained with only very small losses of heat. Most of the heat contained in the product withdrawn from treating zone 1 through line 25 is stored in the solid packing of vessel 26 during one cycle of operation of the heat conservation section and is returned to the uncondensed gas when the flow through the heat conservation section is reversed in the succeeding cycle of operation. The only net loss of heat sustained is the relatively small amount of heat lost to the cooling water during indirect heat exchange of the partially cooled products with cooling water in condenser 27.
Those skilled in the art may vary operation of the process of the invention, for example, by the employment of a Ljungstrom type of heat exchanger instead of packed vessels 26 and 28, by adding heat to line 34 if a big heat load is encountered in the preheating section, or by conductingthe partial combustion of the gases efiluent upwardly from the cooling section of the treating zone in a burner exterior to the treating zone, as shown in mycopending application Serial No. 244,620, filed August 31, 1951, now Patent No. 2,752,292.
Furthermore, the drawing'and above description describe a preferred embodiment of the present invention, in that in the three distinct sections of the treating zone, all have been'staged by screens or trays (8a, 8b and Although operation of the present invention can be accomplished by maintaining one large fluid bed of shale particles in each section, it has been found that by staging the solids'within the sections, that the function of each separate section is best obtained. For example, by staging preheat section 2, more complete heat transfer is accomplished from the relatively hot gases entering the section through line 34 to the cold fresh shale particles entering through line 6, thereby achieving more efficient preheating of the shale and cooling of the gas than can be obtained by operating the entire preheat section 2 as one single fluidized bed of shale. In the staged operation, an approach to a true countercurrent contacting step is attained in that a temperature gradient is built up with the shale leaving section 2 by standpipe 10 considerably hotter than the shale on'a middle tray 'or' above." This must be contrasted with the operation in which the entire section is fluidized. In such an operation, the mixing is so complete that the particle mass attains an essentially average temperature, with no such temperature gradient as is obtained by staging, and therefore, the gases leaving the reaction have not been cooled to the point that the gases leaving the staged operation have. The same reasoning applies to the other sections in performing their functions, i. e., retorting and cooling.
In the drawing, staging has been accomplished by employing trays or screens that hinder the free flow of solids passing down through them but which readily permit the upward passage of gases. An example of another method of staging is disclosed in my copending application Serial No. 419,993, filed March 31, 1954, now Patent No. 2,759,889. It must be understood that any apparatus or means of accomplishing this result is intended to be within the scope of this invention.
Also, it is feasible to operate the process of the present invention by staging one or more of the sections while allowing one large fluidized bed to exist in the other sections. Obviously, many variations can be made that are within the scope of this subject.
The heat conservation section is desirably operated so that a minimum amount of heat is lost to the cooling water in the indirect heat exchanger of that zone. No difficnlty is encountered in pre-cooling the product stream in either vessel 26 or 28 down to a temperature in the range from about 250 to 300 F. so that relatively little heat is lost in heating the water. This heat may, in part, be transferred back to the process by preheating air stream 23 in condenser 27. This reduces both combustion and cooling water requirements.
Obviously it is not necessary for the particular sections to be in vertical arrangement, but such alignment is preferred. Solids may be transferred between the sections by any means known in the fluid solids art.
1. In a process for removing hydrocarbons from oilbean'ng mineral solids comprising passing said solids in particulate form downwardly through a solids preheating zone, a retorting zone, and a gas preheating zone in countercurrent contact in each of said zones with rising recycled gaseous retorting products, withdrawing from said retorting zone a substantial portion of the oil vapors produced therein, separating the normally liquid components from said vapors, passing at least some of the re maining gaseous components of said vapors into said solids preheating zone to heat the solids therein and thereby to cool said gaseous components, recycling gases so cooled from said solids preheating zone to said gas preheating zone for preheating in the presence of the hot spent solids therein, burning at least a portion of said preheated gases, and passing to said retorting zone the combustion products of said burning and any remaining unburned preheated gases, the improvement which comprises passing said solids in an indirect pathway through a series of stages in each of said zones, maintaining the particle size of said solids small enough so that they may be fluidized in said zones with available flow rates of system gases, including recycled product gases, and adjusting said system gas flow rates to maintain said fluidization.
2. A process as in claim 1, wherein gases withdrawn from each of said solids preheating, retorting, and gas preheating zones are first separated from solids entrained therein, and said solids are returned to the main body of solids in the zone from which they came.
References Cited in the file of this patent UNITED STATES PATENTS 2,367,281 Johnson Jan. 16, 1945 2,396,036 Blending Mar. 5, 1946 2,588,076 Gohr Mar. 4, 1952 2,626,234 Barr et a1. Ian. 20, 1953 2,627,499 Krebs Feb. 3, 1953 2,673,177 Buell Mar. 23, 1954 2,710,828 Scott June 14, 1955 2,719,115 Russell Sept. 27, 1955 2,757,129 Reeves et a1. July 31, 1956