Abstract:
A process and apparatus for production of liquid and gaseous fuels from solid organic carbonaceous materials by reacting free falling solids in a countercurrent gas stream. The process is conducted with a lean solids phase which provides good process control and uniform flow of solids even in the presence of condensation and refluxing of liquids on the solid particles. Rapid heatup rates provide high carbon conversions. Oil shales of the eocene period are particularly well suited for the process of this invention. A reactor particularly suited for conducting reactions between free falling solids and countercurrent flowing gas streams is disclosed together with preferred methods for introduction of solid feeds to the top of the reactor.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part of co-pending application Ser. No. 386,721 filed June 9, 1982, now U.S. Pat. No. 4,431,509. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to production of principally hydrocarbon liquid and gaseous fuels from organic carbonaceous solids by countercurrent flow of heat-containing gas with free fall solids through a reactor, the solids passing sequentially through a solids preheat and pretreatment zone, a reaction zone, and a gas preheat zone. Liquid and gaseous fuels may be produced from organic carbonaceous materials such as oil shale, coal, peat and biomass. 
     2. Description of the Prior Art 
     The worldwide energy shortage has encouraged consideration and improvement of various processes for production of hydrocarbon fuels which do not involve petroleum products. Non-petroleum materials such as oil shale, coal, peat and biomass represent a large potential energy resource. 
     The production of hydrocarbon fuels by hydroconversion of oil shale is well known. For example, U.S. Pat. No. 4,003,821 teaches production of liquid hydrocarbons from oil shale by passing a hydrogen-rich gas stream countercurrent to a packed moving bed or fluidized bed of oil shale particles. The &#39;821 patent teaches use of hydrogen sufficient to meet chemical requirements and the desirability of a sufficient excess of hydrogen to convert all of the hydrocarbons and carbon monoxide produced to methane. U.S. Pat. No. 3,922,215 teaches production of liquid hydrocarbons from oil shale by passing a hydrogen-rich gas stream in contact with oil shale particles in a moving bed. The &#39;215 patent teaches the preferability of passing the hydrogen-rich gas stream in cocurrent relation with the oil shale particles to avoid condensation of hydroretorted liquids. The problems of condensation of liquids on the solid particles has been recognized by the prior art, for example, in U.S. Pat. No. 3,619,405. U.S. Pat. Nos. 3,891,403 and 3,929,615 teach production of high methane content gas from oil shale by hydrogasification. 
     Several patents teach various methods of retorting hydrocarbonaceous solids utilizing moving solids beds wherein gas passes countercurrently, such as U.S. Pat. Nos. 3,841,992; 3,619,405; 3,503,869; 2,899,365 and 3,297,562. 
     Free fall oil shale hydrogasification is taught by U.S. Pat. No. 3,421,868. The &#39;868 patent teaches production of relatively high Btu gas from oil shale by passing freely falling oil shale in contact with hydrogen which is passed either cocurrent with or countercurrent to the free falling shale. The &#39;868 patent teaches the desirability of low gas to shale ratios and flow rates of hydrogen gas much lower than flow rates of shale solids, resulting in much longer gas residence time than solids residence time within the reactor. The process of the &#39;868 patent does not require heat input to the reaction zone. The &#39;868 patent teaches that the disclosed free falling shale process substantially reduces decomposition of mineral carbonates while providing substantially the same gaseous yield as previous moving bed processes. 
     U.S. Pat. No. 4,012,311 teaches a process for high yield of coal tars by contacting coal in a series of free fall reaction zones with a cocurrent flow of hydrogen followed by quick quenching and removal of coal tar prior to entry to the next reaction zone. The &#39;311 patent teaches low hydrogen to coal ratios and the importance of very rapid heat-up, short residence time, and quenching. 
     SUMMARY OF THE INVENTION 
     This invention relates to a process for increased production of liquid and gaseous fuels from solid organic carbonaceous materials of the type having a sufficiently high density, such as oil shale, coal, peat and biomass, to free fall in a lean solids stream countercurrent to a heat-containing gas stream. The process of this invention involves the solid organic carbonaceous material passing in free fall countercurrent flow relation to heat-containing gas sequentially through a solids preheat and pretreatment zone, a reaction zone, and a gas preheat zone. The gas may be reactive or non-reactive with the solids. The gas provides heat to the solids for the solids pyrolysis reaction which may be liquefaction or gasification. Suitable gases include any heat transfer gas such as air, steam, flue gas, synthesis gas, hydrogen, and mixtures such as steam-oxygen and steam-carbon monoxide. A high gas to solids ratio of about 5 to about 35 Standard Cubic Feet per pound of solids is maintained in the reaction zone. This provides a lean solids stream so that the heat content of the gas is sufficient to rapidly heat the solids to reaction temperature. Hydrogen is a preferred gas resulting in higher methane yields by hydroconversion and hydrogen pretreating of the solids. In the case of hydrogen, a high hydrogen to organic carbon ratio of about 10 to about 30 Standard Cubic Feet of hydrogen per pound of carbonaceous material is maintained in the reaction zone. Further, short gas residence times, as compared to solid residence times, are provided by the heat-containing gas moving countercurrently to the organic carbonaceous solids at a higher velocity than the solid material. A solids residence time in the reaction zone of about 2 to about 400 seconds at temperatures of about 500° to about 2000° F. forms predominately the desired liquid and gaseous products which are removed from the upper portion of the vertical reactor vessel and the spent carbonaceous material is removed from the lower portion of the reactor vessel. For preferential liquid production, the reaction zone temperatures are about 800° to about 1300° F. and for preferential gas production about 1400° to about 2000° F. 
     The process of this invention in one embodiment provides that the solid organic carbonaceous material and the gas are introduced at about ambient temperatures. The problems of liquid condensation and clogging, previously encountered in moving bed reaction processes, are considerably reduced or eliminated in the process of this invention, thereby providing a higher useful yield of the more desired liquid products. When liquid production is desired, it is frequently advantageous to remove the liquids from the gas stream between the top of the reaction zone and the bottom of the solids preheat zone to further avoid liquid condensation on the cooler solids. Variation of process conditions within specified limits provides for utilization of a wide variety of organic carbonaceous containing feed solids. 
     It is an object of this invention to provide a process for production of liquid and gaseous fuels from solid carbonaceous materials, which have a sufficiently high density to free fall in a lean solids stream countercurrent to a the gas stream, by passing the carbonaceous material in free fall countercurrent flow relation to upwardly flowing gas in a single vertical reactor. 
     It is another object of this invention to provide a process for production of liquid fuels from heavy organic carbonaceous materials in a free fall countercurrent flow reactor free from clogging problems experienced in prior moving bed reactors. 
     It is yet another object of this invention to provide a process for production of liquid fuels from carbonaceous materials in which prior problems of liquid condensation in moving bed reactors is greatly reduced. 
     These and other objects and advantages will become apparent upon reading the detailed description of preferred embodiments with reference to the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a reactor vessel according to one embodiment of this invention suitable for carrying out the process of this invention; and 
     FIG. 2 is a cross-sectional view of the upper portion of a reactor of another embodiment for use in the process of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Carbonaceous materials useful as feed materials in this invention are solid organic carbonaceous materials having sufficiently high density to cause solid particles of a size providing reasonably high reactive surface area to fall in a lean solids stream countercurrent to a gas stream. The particle size may vary over quite wide ranges dependent upon the density of the solids. Suitable particle sizes are generally about -6 to about +400 U.S. Sieve, preferably about -10 to about +200 U.S. Sieve. Suitable solid organic carbonaceous material is selected from the group consisting of oil shale, coal, peat and biomass. 
     Oil shales of the Eocene period generally found in the western United States, particularly the northwestern area of Colorado and in the adjoining areas of Utah and Wyoming are suitable for use in this invention. These oil shales have an organic carbon to hydrogen weight ratio typically of less than 8/1 and usually of 7/1 to 8/1 and Modified Fischer Assays in the order of 25 gallons per ton or more. Oil shales from deposits such as Devonian and Mississippian, generally found in the eastern portion of the United States are especially suitable for use in this invention. These oil shales have been found to have organic carbon to hydrogen weight ratios typically in the order of 10/1 up to about 13/1 and Modified Fischer Assays of less than about 15 gallons of oil per ton and frequently as low as less than 5 gallons of oil per ton. The Modified Fischer Assays have been found to not represent the organic carbon actually present in the &#34;eastern&#34; type shale having the higher organic carbon to hydrogen weight ratios. Further, the inorganic carbon present in the &#34;eastern&#34; type oil shales is lower than that of the &#34;western&#34; type oil shales by a factor of greater than 10 and up to 30 to 40. The following table shows compositions of both the organic and inorganic portions of a typical &#34;eastern&#34; and &#34;western&#34; oil shale. 
     
                       TABLE I______________________________________        Source of Oil Shale        Clark County, Ind.                    Colorado        (Eastern)   (Western)        Weight Percent______________________________________OrganicCarbon         13.7          13.6Hydrogen       1.2           1.9Sulfur         0.3           0.3Nitrogen       0.4           0.5Oxygen         1.0           1.7Carbon/Hydrogen          11.4          7.2InoroanicCarbon Dioxide 0.5           15.9Water          4.0           1.8Sulfur         4.4           0.2Ash            78.3          66.8Modified Fischer Assay          10            30gal/ton______________________________________ 
    
     The excess of the totals over 100 percent is thought to be due to weight gain by oxidation of metals in the mineral component during ashing. It is readily observed from Table I that while the organic carbon content of the two oil shales is almost identical, the Modified Fischer Assay varies by a factor of 3. Oil shales having the properties set forth above as typical of &#34;eastern&#34; shale are particularly preferred for use in the process of this invention. Suitable coal for use in the process of this invention includes anthracite, bituminous and lignite. Peat suitable for use in this invention includes new peat and old peat. 
     Biomass materials suitable for use in this invention include heavy biomass materials such as organic solid sanitary, agricultural, and municipal wastes and woods. 
     Suitable sizes for introduction of the solid organic carbonaceous material are particles predominantly about -6 to about +400 U.S. Sieve, preferably about -55 to about +300 U.S. Sieve, about -55 to +200 U.S. Sieve being most preferred. The size of the particles is dependent upon the density of the particle so as to provide desired free fall velocity as set forth further herein. The solid organic carbonaceous materials useful as feed stock in this invention generally have a true density of about 50 to about 200 pounds per cubic foot. 
     Referring to FIG. 1, the solid organic carbonaceous material may be pretreated in any desired fashion, such as reduction of moisture content, and provided to solids storage hopper 21 which, together with solids introduction conduit 22 and solids introduction feed means 23, make up solids feeding means 20. Any suitable solids feeding means as known to the art may be used. The feed solids are introduced to reactor 10 through vessel top bell 14 and pass over solids distribution baffles 24 to provide even distribution of the introduced solids across the area of the reactor. The solids pass downwardly by gravity and pass sequentially through solids preheat and pretreatment zone I, reaction zone II, heat addition zone III and gas preheat zone IV. Heat addition zone III is provided between gas preheat zone IV and reaction zone II to provide the necessary addition of heat to maintain the reaction zone II at temperatures of about 800° to about 2000° F. The spent solids leave the reactor by spent solids discharge conduit 19 through reactor vessel bottom 16. 
     Gas passes upward through reactor 10 countercurrent to the downward passage of the solid organic carbonaceous material. Gas at or near ambient temperature conditions may be introduced to the lower portion of the reactor vessel through gas introduction conduit 31 controlled by valve V 1  and pass upwardly through gas distributor plate 32 and through gas preheat zone IV wherein the free falling solid particles transfer heat to the countercurrent flowing gas stream. The gas stream is further heated in heat addition zone III which may be considered, and is meant to be considered for the purpose of this disclosure and claims, as the lower portion of reaction zone II since further reaction may take place in zone III. Hot heat-containing gas or hot non-reactive solids may be introduced through hot gas/solids conduit 44 controlled by valve V 4 . Any suitable means may be used to distribute the hot gas or hot solids generally uniformly across the reactor cross section. The amount of heat necessary to add in heat addition zone III is that amount sufficient to maintain the reaction zone II at desired temperatures of about 800° to about 2000° F. In preferred embodiments the temperatures in reaction zone II are maintained at about 800° to about 1200° F. for the production of liquids and at about 1400° to about 2000° F. for the production of gases. In one embodiment of this invention, the spent particles removed through discharge conduit 19, particularly when coal or peat is used as feed solids, may be combusted in a separate combustion process to heat the gas or non-reactive solids for introduction through conduit 14. It will be apparent that the amount of heat-containing gas introduced through each of conduits 31 and 44 may be advantageously adjusted to provide the desired heat to reaction zone II. Thermal energy may also be provided to heat addition zone III by addition of combustible material through conduit 41 controlled by valve V 3  and mixing the oxygen-containing gas, such as air, introduced through conduit 42 controlled by valve V 2  in an amount sufficient for internal combustion within heat addition zone III to provide the desired temperatures in reaction zone II. When the heat-containing gas contains sufficient oxygen for combustion, it is not necessary to add additional oxygen-containing gas through conduit 42. When hydrogen is used as the heat-containing gas, hydrogen may be combusted in heat addition zone II and such combustion may be controlled by control of the addition of oxygen. 
     The upwardly flowing heat-containing gas stream entering reaction zone II is in an amount of about 5 to about 35 and preferably about 10 to about 30 Standard Cubic Feet of gas per pound of raw carbonaceous material in countercurrent flow thereto. A frequently used amount of heat-containing gas introduced to the reaction zone is an amount of about 15 to about 25 Standard Cubic Feet of gas per pound of the countercurrent flowing carbonaceous material. The solid carbonaceous material moves downwardly through the reaction zone at about 0.1 to about 5 feet per second, preferably about 0.5 to about 2 feet per second, while the heat-containing gas moves countercurrently upward at a higher flow rate of about 0.3 to about 15 feet per second, preferably about 2 to about 4 feet per second, providing solids residence time in the reaction zone of about 2 to about 400 seconds. In a preferred embodiment, the solids residence time in the reaction zone is about 20 to about 200 seconds. These velocities are expressed as absolute rates of travel, not relative to each other. These rates have been found suitable for desired heating of the solid particles to reaction temperatures. 
     One feature of this invention is high carbon conversion with high heatup rate of the solid particles. Heatup rates to desired reaction temperatures of about 1,000° to about 30,000° F. per minute are suitable for use in the process of this invention, about 2,000° to about 10,000° F. per minute being preferred for most carbonaceous materials. Laboratory tests using shale particles of -170 to +200 U.S. Sieve size in a nitrogen stream at 1 atmosphere pressure show that during the rapid heatup at 4,000° F./minute to 899° F., without any retention at that temperature, high total carbon conversions are obtained. 
     
         ______________________________________             &#34;Eastern Shale&#34;             New Albany,             Indiana______________________________________Feed Analysis:(dry basis, wt. %)Ash                 76.96Total Carbon        13.73Hydrogen            1.80Nitrogen            0.48Residue Analysis:(dry basis, wt. %)Total Carbon        6.54Hydrogen            0.55Nitrogen            0.32Modified Fischer Assay               12Total CarbonConversion:Expected Basis Fischer Assay                 35%Actually Obtained   59.8%______________________________________ 
    
     In another emobodiment baffles may be used in any of the various reactor zones to periodically impede the freely falling solid particles decreasing their average downward velocity, thereby decreasing the height of the particular reactor zone necessary to achieve the desired solids residence time. Any type of appropriate baffles, such as distribution baffles 24, can be used for this purpose. The preferred baffle arrangement should impede the particles about every 2 to 10  feet, preferably about every 3 to 7 feet of reactor zone length. 
     The upwardly flowing heat-containing gas stream leaving reaction zone II passes upwardly through preheat and pretreatment zone I. In the solids preheat and pretreatment zone, thermal transfer between the heat-containing gas and carbonaceous solids takes place cooling the gas and heating the solids. When hydrogen-rich gas is used it additionally pretreats the organic carbonaceous material by contact with it in such a manner as to improve production of desired substantially saturated liquid and gaseous hydrocarbon products in the reaction zone. The upwardly moving gas stream also carries the gaseous and vaporized liquid products from conversion of the solid organic carbonaceous material in the reaction zone. The height of the solids preheat and pretreatment zone may be sufficient to allow substantial thermal exchange to take place which heats the free falling solids to near the desired temperature of the reaction zone and for pretreatment of solid organic carbonaceous material to render it more suitable for conversion of the organic carbonaceous component to liquid and gaseous fuel products in the reaction zone. This is practical due to the lean solids phase which will continue to flow uniformly even in the presence of condensation on cold feed material as encountered by the prior art with moving bed reaction systems. The gas stream passes upwardly from the solids preheat and pretreatment zone to a solids/gas separator means 33 located in upper zone 12 of the reactor. Solids/gas separator means may be conventionally used cyclones as are well known to the art or any other means for separation of entrained solids from the product gas. The solids/gas separator means is preferably located within the reactor vessel so that the solids may be returned directly to the solids preheat and pretreatment zone for recycle. Gas with entrained product vapor and gases passes from the reaction system through product conduit 34. 
     The fuels produced according to the process of this invention vary with the gas used. When hydrogen is used as the upflowing gas, the product stream comprises principally hydrocarbon liquids and low molecular weight paraffinic gases. The desired low molecular weight paraffinic gas products include molecules of 4 and less carbon atoms, namely, methane, ethane, propane, butane and isobutane which are removed through product conduit 34. When air, oxygen, steam, flue gases or mixtures thereof are used as the gas, the product stream will also contain steam, carbon dioxide, carbon monoxide and nitrogen in amounts depending on the type and quantity of gas used. 
     When liquid products are desired, in one embodiment of the invention, they may be withdrawn and separated from the gas in the upper region of reaction zone II. The entire system for liquids separation from gas at the upper region of the reaction zone is optional and used when it is desired to obtain the highest yield of liquid products. Separation of liquids at this stage prevents later gasification and possible condensation in the solids preheat zone I. As shown in FIG. 1, withdrawal conduit 50 removes gas with entrained liquids and vapor from the upper region of reaction zone II. The gas stream is passed through cooler 51 to cool the gas stream sufficiently to condense desired liquids from the gas. The gas stream with condensed liquids is then passed to liquid/gas separator 52 and liquids are withdrawn through withdrawal conduit 53. The gas stream is heated by passage through heater 54 to the temperature necessary to heat the solids to reaction temperature in solids preheat zone I. Heater 54 may be supplied heat from cooler 51 by heat exchange conduit 59 and/or from any other source. The heated gas is returned to upward flow through the solids preheat zone by passage through conduit 55 to the plenum defined by gas distributor plate 56 and solid plate 57. Solids falling through preheat zone I are directed into solids conduit 60 and pass through valve V 6  such as a trickle valve, a seal-pot valve, or a J-valve, and are redistributed across the cross section of reactor vessel 11 in the upper portion of reaction zone II by distributor baffles 58. In another embodiment, the entire gas/liquid withdrawal and reintroduction system in the upper portion of the reaction zone may be omitted and the liquid products entrained in the gas stream may be removed through product conduit 34. The desired hydrocarbon liquids produced by the process of this invention are especially suited for further processing, such as production of naphtha, gasoline, kerosene, jet fuel, diesel oil and light fuel oils, and other low boiling distillate oils as well as for conversion to high methane content pipeline quality gas. When liquid product is desired, the process conditions may be adjusted as described above so that less than about 20 percent of the organic carbonaceous material is converted to the gas form. 
     When hydrogen is used as the heat-containing gas, the terminology &#34;hydrogen-containing gas&#34; throughout this description and claims, means gases having sufficient hydrogen partial pressure to effect high organic carbon hydroconversion from the organic carbonaceous feed material. Such hydrogen-containing gases may be obtained by a number of processes well known in the chemical process industry. It is preferred to use hydrogen containing gas having a partial pressure of hydrogen greater than about 100 psia. The upper operating pressures are limited only by equipment and economical considerations. Higher hydrogen partial pressures allow higher reaction rates and thus smaller reactors. Total operating pressures throughout the process system are usually substantially the same. Normally, the process of this invention may be carried out at total pressures of about 1 atmosphere to 1500 psia, preferably about 15 to about 500 psia. 
     A particularly well suited reactor for carrying out the process of this invention is shown in FIG. 1. Vertical reactor vessel 10 has substantially vertical walls 11 through its central portion, the wall extending outwardly shown as expanded vessel walls 12 forming an expanded volume in the upper portion of the reactor. A bell-shaped reactor top 14 has depending walls 17 substantially in line with the reactor vessel walls 11 and extend downwardly in the expanded volume having their bottom ends spaced from reactor walls 11 forming an annular solids/gas separation zone between depending walls 17 and expanded vessel walls 12. Depending walls 17 define a solids distribution zone having solids distribution baffles 24 capable of distributing the feed solids substantially evenly across the area of the reactor vessel. Solids feed means 20 introduces feed solids into the upper portion of the solids distribution zone and may be any suitable feed means capable of supplying solids to the pressurized vessel. Solids/gas separator means 33 are located within the annular solids/gas separation zone and may feed the solids directly back to the straight wall portion of the reactor vessel. Product conduit 34 is in communication with the gas exit of the solids/gas separator means 33 and conveys the products from the reactor. In the lower portion of the reactor, gas distribution means 32 is capable of distributing passing gas across the cross section of the reactor vessel. Gas introduction and supply means 31 allows the entry of hydrogen-containing gas to the portion of the reactor vessel below gas distribution means 32. While normally the spent solids will be removed by discharge conduit 19 with valve 5 with some organic carbonaceous feed materials the ash will be carried out with the product stream. 
     The process of this invention requires addition of heat. A particularly suitable means for introduction of heat to a heat addition zone in the lower portion of the reaction zone is shown in FIG. 1 wherein upwardly extending expanded vessel wall 13 and downwardly extending vessel wall 15 form an annular volume around the heat addition zone to provide for introduction of hot particulates, hot gases or combustible materials for internal combustion within the heat addition zone. 
     FIG. 2 shows another preferred embodiment for solids introduction and distribution substantially evenly across the area of the reactor vessel. Fluidized bed support 25 extends across the lower portion of depending walls 17 and a plurality of overflow tubes 27 extend from the height of the fluidized bed 26 downwardly through support plate 25 distributing solids substantially evenly across the area defined by reactor vessel walls 11. It is preferred that the lower ends of overflow tubes 27 have valves 29, such as trickle vales, seal pots, or J-valves, to prevent entry of product vapor. 
     The apparatus of this invention may be constructed of materials apparent to those skilled in the art upon reading this disclosure and are principally dependent upon desired operating temperatures and pressures as well as overall reactor size. 
     While in the foregoing specification this invention has been described in relation to certain preferred embodiments thereof, and many details have been set forth for purpose of illustration, it will be apparent to those skilled in the art that the invention is susceptible to additional embodiments and that certain of the details described herein can be varied considerably without department from the basic principles of the invention.