US 3616266 A
Description (OCR text may contain errors)
Unite States atent Inventors Robert N. Hall Boulder; Richard H. Beaver, Lakewood, Colo.; Roy Glenn Vawter, Los Angeles, Calif.; Charles ,1. Mains, Golden, Colo.
Appl. No. 820,140
Filed Apr. 29, 1969 Patented Oct. 26, 1971 Assignee The Oil Shale Corporation New York, N.Y.
HORIZONTAL RETORT WITH SOLID HEAT TRANSFER MEDIUM 3 Claims, 3 Drawing Figs.
Int. Cl Cl0b 1/06 Field of Search 202/1 18,
[ References Cited UNITED STATES PATENTS 1,712,082 5/1929 Koppers 202/118 X 2,913,344 11/1959 Stallings 23/273 3,251,751 5/1966 Lindah1eta1..... 201/20 X 689,723 12/1901 Hutchinson 202/265 X 1,461,614 7/1923 Harrison..,..... 202/265 X 1,561,735 11/1925 Lucas 202/265 X 1,741,573 12/1929 Kipper 202/265 x 2,008,270 7/1935 Willekcns 202/265 UX Primary Examiner-Norman Yudkoff Assistant ExaminerDavid Edwards Attorney-Brumbaugh, Graves, Donohue & Raymond ABSTRACT: A pyrolyzer or retort having a conveying section and a mixing section which latter section is composed ofa plurality of pyrolysis chambers having means for conveying and concurrently retarding the flow of intermixed solid raw material and solid heat carriers.
PATENTED E 2 6 3,6162 66 I/'J\"li/J'l HAS. ROBERT N. HALL, RICHARD H BEAVER,
ROY GLENN VAWTER a HARLES J. MAINS their ATTORNEYS HORIZONTAL RETORT WlTll-l SOLKD HEAT TRANSFER MEDIUM This invention relates broadly to a novel apparatus for efficiently carrying out the pyrolysis of solid carbonaceous and inorganic materials by means of solid-to-solid heat transfer techniques. Even more specifically, this invention pertains to a novel pyrolyzer for the production of carbonaceous fluids from solid carbonaceous materials by means of an intimate solid-to-solid pyrolysis technique wherein the pyrolysis residue serves as the primary heat source and heat carrier.
Numerous apparatus has been developed to carry out solidto-solid pyrolysis conversions. For the most part, the conditions effecting optimum pyrolysis procedures by means of solid-to-solid heat transfer techniques can be best satisfied through the use of: (l finely divided raw materials and solid heat carriers to provide maximum heat transfer surface; and (2 a pyrolysis zone which will provide for maximum conversion and product recovery. Accordingly, a pyrolysis apparatus has now been discovered which embodies the foregoing principles.
The pyrolysis apparatus according to this invention has been found to be particularly useful in the production of carbonaceous fluids, e.g., crude shale oil and gases, from solid carbonaceous materials although not limited thereto since the pyrolyzer may advantageously be utilized in the processing of various inorganic materials such as fluorspar, cinnabar, phosphate rock, etc. With respect to the recovery of carbonaceous values resident in the solid carbonaceous materials such as oil shale, bituminous sands, lignite, peat, wood chips, sawdust and the like, numerous pyrolyzers or retorts have been developed wherein the carbonaceous solids are thermally treated to produce an effluent vapor, which upon subsequent condensation yields a carbonaceous liquid comprising many organic compounds.
One of the more critical phases of all pyrolysis processes resides in the procedure carried out in the pyrolysis zone itself. A large variety of apparatus such as rotating drums, screw conveyors, etc., is available for carrying out pyrolysis reactions. By far, the majority of these are externally heated, although many have been developed for utilizing the direct solid-to-solid heat exchange concept. The latter technique is preferred since solid-to-solid heat transfer techniques are generally more efficient, however, apparatus which employ the solid-to-solid heat transfer concept are usually complicated by problems in mixing, solids separation, vapor recovery and the like, not found in externally heated pyrolysis units. These problems are further complicated and substantially increased when the physical and chemical properties such as the size ofthe heat carrier, composition, specific gravity, etc., more closely resemble those of the raw material. For example, it has been found that in the pyrolysis of finely divided oil shale by means of a more finely divided heat carrier composed of hot spent ash, that the standard pyrolysis retorts such as rotating drums, screw conveyors, pug mills, like the like fail to provide the degree of mixing and for an efficient and economical process. in many such retorts the oil shale and spent ash are inadequately mixed and the majority of the material flows laminarly through the retort. Even more significant is the reduction in oil yield caused by excessive contact of the pyrolysis vapor with the hot ash. Oil yield reductions as high as 50 percent and greater occur when compared to yields obtainable through the use of heat-carrying bodies such as alumina balls.
Accordingly, it is an object of the present invention to provide a pyrolyzer using solid-to-solid heat transfer technique which provides a high degree of mixing of raw material and heat carrier required for an efficient and economical pyrolysis process. Another object of the invention is the provision of a pyrolyzer which avoids excessive contact of the pyrolysis vapor with the heat carrier.
As previously pointed out, the pyrolysis procedure is one of the major factors leading to an efficient and economical process, particularly in the production of carbonaceous fluids from solid carbonaceous materials. Accordingly, the pyrolysis procedure should comprise the steps of intimately mixing a finely divided solid pyrolyzeable material, such as carbonaceous solids, with even more finely divided or pulverulent solid heat carriers in separate pyrolysis zones; moving the solids mixture through each of the separate pyrolysis zones and concurrently therewith retarding the solids flow through each of the zones; promptly withdrawing the pyrolysis vapors from contact with solid materials, and separating entrained solids from the pyrolysis vapors at substantially pyrolysis zone temperatures.
The foregoing procedure is accomplished by the pyrolyzer of the invention which is a substantially horizontal pyrolysis drum comprising a first inlet means for introducing the solid heat carriers, a second inlet means for introducing the raw material onto the surface of the heat carrier, an internal rotatable mechanism having a first conveyor section and a second mixing section. The conveyor section comprises a standard screw flight positioned so as to receive the heat carriers and raw material. The mixing section is positioned downstream from the conveyor section and comprises a series of longitudinally spaced pyrolysis zones or chambers, each zone terminated at the opposite ends thereof by suitable flowretarding means. It has been found that perforated screw sections wherein each section contains between one and two revolutions serve to both move as well as retard the solids flow through respective chambers. Each screw section is joined by means of rigid bladelike wiping members secured, preferably spirally, around the periphery thereof and extending between each section. in order to further insure adequate agitation throughout each zone, additional agitating means in the form of centrally positioned rotatable pugs, paddles, or the like are provided in each pyrolysis chamber. It should be noted that the perforations in each screw section allow passage of the pyrolysis vapors therethrough to an entrained solids separator.
The carbonaceous materials contemplated for pyrolysis treatment by the apparatus of the invention embrace any solid carbonaceous materials containing carbonaceous values which can be recovered by thermal treatment and which, upon such treatment, leave a combustible carbon-containing solid residue that is convertible to a solid ash after the available heat of combustion has been obtained therefrom. The solid materials which may be suitably pyrolyzed by the apparatus of the present invention include, without limitation, oil shale, bituminous sands, lignites, wood chips, peat and the like. The pyrolyzer of the invention is particularly adapted to the treatment of finely divided carbonaceous solids yielding pyrolysis residues of high available carbon content, e.g., spent oil shale residues typically containing 2 percent to 10 percent fixed carbon, although it may be used advantageously with carbonaceous solids yielding pyrolysis residues of lower carbon content as well. Upon subsequent combustion, hot solid heat carriers are produced comprising the relatively inert waste product. These heat carriers are generally finely divided; the size depending upon the nature of the raw material. The finely divided materials for use herein embrace crushed as well as finely divided or pulverulent materials. Materials which have been crushed to less than about one-half inch mesh are preferred, however, specific physical and chemical properties, such as specific gravity, will determine the desired size in each case.
The solid heat carriers utilized herein embrace particularly those solid pyrolysis effluents which are inert and maintain their physical characteristics under the conditions employed in the process to effect the pyrolysis of the particular solid carbonaceous or inorganic material. Since it is contemplated that the solid pyrolysis effluent constitutes the primary heat carrier, the size thereofwill generally be considerably smaller than that of the raw material, thereby providing greater heat transfer surface area and intimate contact during the pyrolysis reaction. For example, when oil shale crushed to about V; inch is pyrolyzed and the spent solid residue combusted, a fine dustlike ash is produced having a particle size in the order of 10 to 40 microns and smaller. lt will also be understood, of
course, that it may be necessary at times to add extraneous materials such as sand, powdered clay and the like to make up or maintain the heat carrier inventory. It should also be understood, that in processing some inorganic materials, it may be necessary to add extraneous combustible materials in the form of coke, coal, and the like, however, in such instances the materials should be added to and mixed with the solid pyrolysis effluent so as to absorb a portion of the sensible heat contained therein.
According to a preferred illustration of the use of the apparatus of this invention, the raw solid carbonaceous material to be thermally treated is initially crushed by any suitable method to a suitable particle size such that the largest particle possess the economic optimum surface area for retorting purposes. Usually the maximum particle size of the raw carbonaceous solid feed stream is in the range of from about inch to about as inch and the majority preferably less than about h inch. The crushed raw carbonaceous material at ambient temperatures may then be passed to a preheating zone and preheated therein to a maximum temperature of about 500 F.
The preheated carbonaceous material is then passed into the pyrolyzer wherein it is contacted in solid-to-solid heat exchange with spent ash having sufficient available heat to effect the desired degree of pyrolysis and produce an effluent carbonaceous vapor and a hot spent solid residue. The residence time in the pyrolyzer is usually between about 1 and 10 minutes, although longer residence times can be employed. The solid residue leaving the pyrolyzer comprises a mixture of hot spent solids and spent ash. The pyrolyzer is in the form ofa generally horizontal drum having a rotatable internal mixing mechanism designed to pass pyrolysis vapors while retarding the solids flow so as to insure intimate solid-to-solid contact between the spent ash and carbonaceous solids. The available heat in the spent ash is such that essentially complete pyrolysis ofthe carbonaceous solids is effected with a maximum yield of carbonaceous fluids being thereby achieved. For example, when oil shale is treated by the apparatus of the invention, the heat supplied by the bot spent ash to the oil shale preferably is such as to raise the temperature of the raw shale to the range of from about 750 F. to about 950 F., more preferably from about 800 F. to about 900 F. The actual temperature and amount of the spent ash introduced into the pyrolyzer will depend upon, inter alia, the type of carbonaceous material being treated, the degree of pyrolysis desired, the inlet temperature of the carbonaceous feed, and the heat transfer characteristics of the spent ash. Where oil shale is treated in accordance herewith, the ratio of spent shale ash to raw shale fed to the pyrolyzer usually is in the range of from about 1:1 to about l:l, preferably from about 1.4:1 to about 6:l. In such oil shale treatments the spent shale ash introduced into the pyrolyzer usually is at a temperature in the range of from about 1,150" F. to about 1,650 F., preferably from about 1,200" F. to about l,350 F.
Spent ash, cooled by giving up a portion of its heat for the pyrolysis, effluent vapor and spent solids residue, produced in the pyrolysis of the carbonaceous solids, are then removed from the pyrolyzer. The effluent vapor is immediately separated from the other materials and sent to a recovery section wherein the desired fractions thereof are recovered. Since the effluent vapor contains fine solid dustlike particles suspended therein which must be removed before being sent to the recovery section, provision is made by the apparatus of the invention for vapor solids separation in the reactor so as to prevent condensation and retain the hot solids in the system.
The invention will be more readily understood with reference to the accompanying drawings of which FIG. 1 is a longitudinal section of the pyrolysis apparatus. FIG. 2 is a cross section of the pyrolysis apparatus of FIG. 1 along line 2-2. FIG. 3 is a partial cross section of one of the filter elements designated as 80 in FIG. 1.
In the apparatus illustrated in FIG. 1, the pyrolyzer or retort is composed of a generally horizontal cylindrical pyrolysis chamber 60 and a vapor-solids separation chamber 61. The pyrolysis chamber is provided with inlet means 62 adjacent one end wall thereof for introducing hot ash and inlet means 63 juxtaposed the inlet means 62 for introducing preheated raw shale onto the surface of the hot ash. Within the pyrolysis chamber 60 is a horizontal rotatable conveying and mixing mechanism comprising a conveyor section 65 and a pyrolysis mixing section 66 positioned along shaft 64 which is rotatably driven by motor 85. The conveyor section 65 comprises a conveyor screw flight 70 secured to the rotatable shaft 64 along one end thereof so as to be positioned below shale inlet 63 and ash inlet 62. The pyrolysis mixing section 66 comprises a series of longitudinally spaced pyrolysis mixing chambers 67, 68 and 69, each chamber being terminated at opposite ends thereof by solids flow retarding members 71, 72, 73 and 74 distributed at spaced intervals along and secured to shaft 64. The diameter of the conveyor screw 70 should be substantially less than the internal diameter of the conveyor section 65 so as to permit convenient withdrawal of pyrolysis vapors. The flow-retarding members, as shown in greater detail in FIG. 2, are composed of perforated screw sections having a diameter substantially the same as the internal diameter of the mixing section 66. Each screw section 71, 72, 73 and 74 should contain not less than one or no more than two revolutions, and preferably about 1 /4 revolutions. Additionally, each screw section contains a plurality of perforations 75 for alternately passing vapors and solids as the section is rotated. Since each screw section contains between one and two revolutions, the solids flow will be impeded and at the same time conveyed from one pyrolysis chamber to the next. Each chamber is provided with a plurality of bladelike wiper members 76, preferably of angular cross section and secured in reellike fashion (see FIG. I) around the periphery of each screw section and extending therebetween for lifting and mixing unpyrolyzed pieces to the upper surface of the ash which is maintained at about V4 to reactor capacity. In addition to the bladelike members, each chamber is provided with a plurality of pugs or paddlelike mixing elements 77 secured to shaft 64 which serve to agitate the upper portion of the ash-shale mixture. The pyrolysis section may also be provided with an end dam 78 extending upwardly from the bottom of the pyrolysis mixing section 66 to further impede the solids flow.
The vapor-solids separation chamber 61 comprises a cylindrical vertically disposed housing 79 thermally connected to pyrolysis chamber 60. Within chamber 61 a plurality of cylindrical filtering elements 80, shown in greater detail in FIG. 3, are suspended from tube sheet 81 mounted in the upper portion of the housing for filtering entrained dustlike particles from the pyrolysis vapors. Above the tube sheet 81 is positioned a header 82 for gathering the filtered vapors which are thereafter removed via outlet 83. The lower portion of housing 79 serves as a hopper for the spent solids-ash mixture from the pyrolysis chamber 60 prior to removal therefrom via solids outlet 84.
FIG. 3 illustrates the construction of one of the filter elements 80. Each filter element comprises a perforated cylindrical support member 86 which is closed at its lower end by a cap 87. The upper end is open and has secured around the outer periphery thereof a flange 89 which is used to suspend the filter element 80 from the tube sheet 81 as illustrated in FIG. 1. The external surface of the perforated support member 86 is entirely covered by a spirally wound continuous wire 88 which is secured to the support member. The perforations are generally in the order of is to inch in diameter. The wire is so wound as to provide a spacing between adjacent winds. The spacing determines the minimum size of the particles to be filtered. It has been found that entrained dustlike shale ash particles may be satisfactorily filtered from the oil vapor by utilizing filters having 6 to 40 micron spacings between winds. During operation a filter cake of shale ash is formed on the surface of the filter which further aids in the filtering process. The support member 86 and wire 88 are composed of any suitable material (e.g. stainless steel or the like) capable of withstanding pyrolysis temperatures in the order of 750 F. to 950 F.
Since modifications of the apparatus of the invention which do not depart from its spirit will become apparent from the general description and specific embodiment appearing in the specification, it is intended that this invention be limited solely by the scope of the appended claims.
What is claimed is:
1. An apparatus for pyrolyzing finely divided solid raw materials by means of solid-to-solid heat transfer contact with finely divided solid heat carriers to provide an effluent vapor comprising a generally horizontal cylindrical pyrolysis chamber, a first inlet means adjacent one end wall of said chamber for introducing said heat carriers into said chamber, a second inlet means juxtaposed said first inlet means for introducing said raw material onto the surface of said heat carriers, an elongated rotatable shaft extending through said pyrolysis chamber, said shaft having a first conveyor section and a second mixing section secured thereto, said conveyor section being disposed below said first and second inlet means, said mixing section being disposed longitudinally adjacent to said conveyor section and communicating therewith, said mixing section being composed of a plurality of longitudinally spacemeans defining a series of pyrolysis chambers therebetween for conveying and concurrently therewith retarding the flow of said solids through said pyrolysis chambers, a plurality of elongated bladelike members secured around the periphery of said spaced means and extending therebetween, means secured to said shaft between said spaced means for agitating said raw material and heat carriers, means for discharging said effluent vapors, and means for discharging the heat carriers and solid pyrolysis products from said pyrolysis chamber.
2. The apparatus according to claim 1 wherein said solids conveying and flow-retarding means comprises a plurality of longitudinally spaced apertured screw sections secured to said shaft, each of said screw sections defining between about one and two revolutions.
3. The apparatus according to claim I including means secured to said pyrolysis chamber for receiving and separating entrained solids from said effluent vapor.