Process for water-gas generation



Sept. l5, 1953 2 sheets-sheet 1 Filed Jan. 3, 1949 El MUN3m 10:1. Sept. 15, 1953 s. B. swEETsER ET AL 2,652,319V PROCESS FOR WATER-GAS GENERATION Filed Jan. ,3, 1949 2 Sheets-Sheet 2 CATALYST SOLUTION STEAM QESIDUE. OUT Sumner b. seis er B. t. u. content. The process as Patented Sept. 15, 1,953 2,652,319 PROCESS FOR WATER-GAS GENERATIDN Sumner B. Sweetser, Cranford, and Walter G. Scharmann, Westfield, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application January 3, 1949, serial No. 68,946 8 Claims. (Cl. 48-206) The present invention relates to the enhancement of catalytic activity of catalyst agents when supported on a char carrier. The invention relates more particularly to the production of gases from non-gaseous carbonaceous material, and specifically to the production of gas mixtures containing carbon monoxide and hydrogen, such as water gas, from such carbonaceous materials as coke and coals. i It has long been known that solid fuel materials, such as coke, coal, and the like, may be converted into more valuable gases which can more easily be handled and more eciently utilized for a greater variety of purposes. One of the most widely practiced gas-generating conversions is the so-called water-gas process in which solid fuels, such as coal or coke of any origin, are reacted with steam at temperatures of about 1400 to 2000 F. to produce water gas 'mixtures of carbon monoxide and hydrogen in varying proportions, depending mainly on the time of contact, conversion temperatures. and steam feed rate. The over-all water gas reaction being endothermic, heat must be supplied; this is usually accomplished by the combustion of a portion of the carbonaceous feed with an oxidizing gas, such as oxygen, at about 16002400 F. The combustion reaction may be carried out either simultaneously with the water gas reaction or alternately in a make-and-blow fashion. The water` gas process permits the production of gas mixtures of varying composition and such, therefore, is suited not only for the production of fuel gases but also for the production of gases for hydrogenation processes and particularly for the catalytic synthesis of hydrocarbons and oxygenated organic compounds from CO and H2, which process requires H2 CO ratios, depending on the `products desired and reaction conditions to be maintained, varying within limits of about 0.5 to 2.5 or more volumes of Hz per volume of CO. The technical utilization of the water gas process, particularly for hydrogenation and for production of synthesis gas has been impeded by diiiiculties encountered particularly in heat supply, continuity of operation, and limitations in temperature imposed by low ash fusion or softening points. The problem of continuity of operation has been satisfactorily solved heretofore `by the application of the uid solids technique wherein the carbonaceous charge is reacted in the form of a dense turbulent mass of finely divided solids iluidized by the gaseous reactants and products. Heat is generated either by partial 2 combustion of carbonaceous materials within the gas generator or a continuous circulation of suspended solid carbonaceous material to a separate heater in which heat is generated by combustion of the carbonaceous constituents of the residue, and recirculation of the highly heated .fluidizable combustion residue to the gas generation zone to supply the heat required therein. Whether heat is generated within the gas generator by combustion or whether it is supplied as sensible heat of the recirculated solids, it is generally desirable to operate the Water-gas generating unit at as low a temperature as possible commensurate with obtaining high yields of H2 and CO. Thus at the higher temperature ranges, ash tends to become plastic, making fluidization diliicult. Also, at the higher temperature ranges, the heat resistance of economical construction materials available for fluid solids equipment decreases substantially. Thus though the highest yields may be obtained at 2000 F. and above, prolonged operation at these high temperatures is increasingly accompanied by iluidization diiliculties and weakening of structural materials. However, as the operational temperatures are decreased, not only are the yields of CO and H2, and the rate of formation of these gases, also decreased, but also, in accordance with equilibrium considerations, the rate and quantity of CO2 formed is increased. These factors have been recognized and eiforts have been directed towards finding catalysts which permit lower temperatures of operation to obtain high yields of H2 and CO from the water gas reaction, and produce these gases at high rates. Thus it has 'been determined in laboratory experiments that the carbonates of sodium and potassium caused the Water gas reaction to take place some 180 F. lower and the carbon monoxide content of the gases was found to be higher than without the use of catalyst. When, however, this technique was transferred to larger scale operations, it was found that impregnating fresh coke or coal with catalyst and then subjecting the impregnated mass to the water gas reaction using the uid solids technique gave but indifferent results, and showed neither marked reduction of temperature requirements for producing water gas nor increased reaction rates at lower temperatures. These observations have also been confirmed in experimental operations involving the use of the fluidized solids technique. When a catalytic ma terial such as sodium or potassium carbonate is impregnated on fresh coal or coke, there is little tendency for the catalyst to be adsorbed on the the case of low coal or coke and it is sufciently volatile at the temperature of operation so that it is readily lost from the reaction zone by the stripping action of the product gases. The present invention overcomes the aforementioned difficulties and aifords various additional advantages. These advantages, the nature of the invention, and the manner in which it is carried out, will be fully understood from the following description thereof read with reference to the accompanying drawing. It is, therefore, the principal object of the present invention to provide an improved process for the production of gas mixtures containing carbon monoxide and hydrogen. Another object of the invention is to provide a process for the commercial production of water gas from carbonacecus materials and 'steam in volving the efficient and effective utilization of a catalyst promoting the gasification of carbon. l A more speciiic object of the invention is to provide an improved process for pretreating carbonaceous material such as coke or coal prior to impregnation to -provide a highly active surface for catalyst impregnation. i v'Other objects-andadvantages of the invention will appear hereinafter. i It has now been -found that these objects may be accomplished by employing in a uid solids gas generator solid carbonaceous charging material of `high surface Varea and chemical reactivity in conjunction with la catalyst promoting the gasification of carbon. En this manner, the steam conversion ata given temperature and under otherwise equal conditions may be considerably increased andthe gas generator maybe operated at temperatures considerably below the gas generation -temperatures required for other feed materials under similar conditions of pressure, steam concentration, contact time, carbon conc entration, etc., without detrimentally affecting -'the-steam conversion. Experimental research employing the fluidized solids technique has now established that wherefresh colte or coal has a very small surface area, after use for-a relatively short period of time in the uid watergas'vgeneratorto produce water gas, the carbonaceous material develops a very large'surface arearof the order of 500-800 square metersper gram. This has been most noticeable temperature coke, such as Disco coke, and coke produced by the fluid solids carbonization of coal at @LW-100()o E. Thus -'ithas been-found that the surfacearea of a low temperature coke undergoing gasification in the iluid water gasy generator goes through a maxi- 'mumfas shown-bythe following tabulation: Surface crea, vacoce 'carbon content Surface Percent Carbon Area, M2/ gm. #pfff-# f- 0. O4 /ff. a 27... 360 l7 200 60 tabl'ejitis readily seen that coke or coal, Athough initially having very low Vsurface area, develops ahigh surface area after a relatively minor portion of its carbon content has been removedby gasification, corresponding to a relatively short period of time. From this This ldiscovery has nowbeenV applied to the Cil ing to the l fluid catalytic gasification of coke or coal by means of the water gas reaction. Instead of impregnating fresh coke or coal with the gasification catalyst, as practiced by the prior art, in accordance with the present invention a highly active coke or coal is iirst produced, having a high surface area, and this material of high surface area, over l0,00`0-20,000times as high as the fresh colfze or coal, is then impregnated with the gasification catalyst. Because of the high surface area and the strong adsorption forces associated therewith, 'the impregnated catalyst is firmly held on the 'surface of the carbonaceous material despite the high temperature and the stripping action of the gases in the generator. Also, the uniformity of impregnation and the amount of catalyst that is associated with each unit of carbon is of a substantially higher order of magnitude than is the case with fresh coke or coal impregnated with catalyst, and as a result the catalytic effect of the gasification promoter is greatly enhanced las `compared with the impregnation of the promoter on the untreated coal or Veolie feed. In one form of operation of the process accordpresent invention, employing the fluidized solids technique, the operation is carried out in three steps involving two stages of gasification and an impregnation step. In the first stage steam and oxygen are injected into a reactor containing a luivdized bed -of coal vor coke under suitable conditions Yof temperature and pressure to lobtain a conventional water gas reaction, with the oxygen being the combustion kagent for supplying the heat of reaction. Fresh coke or coal is added to the first stage generator as required to maintain the desired inventory of the system. At the `desired level 4ef high surface area cf the solids within the generator, corresponding toa relatively short contact time, coke is `continuously withdrawn from the water gas generator and is impregnated with va suitable catalyst, for example, sodium-carbonate, to theextent of about 0.1 lto 3% by weight of `the coke. The impregnated colte is then sent to a second gasification stage wherein the carbon content is reduced to any'desired level to :producehighyields of CO and ated in a separate-exothermic Vreaction zone and transferred by the 'circulation of solids to the gasication zone of the water gas generation unit. In the vpresent'invention, any one-vessel or two-vessel water gas generation units `may be operated individually or in stages. Having set forth 4its .general nature and objects, the invention will best be `undc-:rstood from the subsequent more detailed description in which reference will-be made to the yaccompany ing drawings which illustrates'a system suitable forcarrying out a fpreferredeinbcdiment 1of the invention. Figure I is a diagrammatic representation of a two-stageiwater gas generation system. For illustrative, but not limiting purposes. lboth stages incorporate so-called one-vessel systems `for waterrgas generation. It is understood that the two stagesanay Icomprise two fone-vessel systems, two "itwo-evessel systems or any combination `of such systems. , time, etc. generator `comprising a one or two vessel system may be employed to carry out a modicationof the invention. Referring now to Figure I, fresh coke or coal ground to a finely divided form, preferably capable of passing through a 60 mesh screen and even through a hundred mesh screen, is fed from a supply hopper I into a standpipe 2 which is provided with a plurality of taps 3 through which slow currents of an aerating gas such as air, flue gas, synthesis tail gas, etc. may be injected in order to aerate the coke or coal. The suspension after preheating by means not shown is introduced into line 4 wherein it is dispersed and suspended in a stream of superheated steam. The mixture of fresh coke or coal and steam is discharged into the bottom of water gas generator 5, the suspension entering below grid 6 and then passing upwardly In some designs it may be unnecessary to employ a grid. Due to the superficial velocity of said steam, which is maintained within the limits of from about 0.2 to 3 feet per second, the coke or coal is formed into a dense, turbulent ebullient mass, having a well-defined upper level 1. An oxidizing gas such as oxygen, is admitted through line 8, and may also be added to the stream in line 4. The steam and carbonaceous material react to form water gas, a gasiform product containing CO and H2. The temperature in this noncatalytic zone is in the order of 1500 to 2000 F. and the gas pressure is preferably from 15 to 100 p. s. i. g., though pressure up to 400 p. s. i. g. and above may under certain conditions be ernployed. The heat required for the reaction is furnished substantially by the combustion of part cf the carbonaceous solids in reactor` 5 by the oxygen admitted through lines 8 and/or 4. The total supply of oxygen is carefully controlled to generate sufficient heat by combustion to satisfy the heat requirements of the process. The gaseous products are withdrawn from,I generator 5 through a dust separator 9, such as a cyclone which has a dip pipe `I extending below upper level 'I of the uidized bed for returning entrained dust particles. The water gas may be treated for the removal of sulfur or other impurities and then delivered to storage, preferably after combination with the product from the catalytic second stage water gas generator I'I. rEhe hot carbonaceous solids, now coke, are allowed to remain within reactor for a sumcient period of time to attain the surface `area desired, usually greater than 500 square gram meters, and then the hot carbonaceous solids are continuously withdrawn from water gas generator 5 through aerated bottom draw-off line II which extends above grid 6. The period of residence of the coke Within reactor 5 to form the high surface area desired, depends upon a plurality of operating factors, such as type of coal fed, temperature of gas generation, ratio of steam to carbon, solids hold-up The withdrawn solids are passed with the aid of steam to impregnation unit I2, which comprises a means suitable for impregnating finely divided carbonaceous solids with chemicals. One preferred method for accomplishing this consists of spraying a solution of the catalyst onto the char passing through the transfer line connecting both stages.` Other methn ods may be employed in any known mannersuch-` 6 as by mixing, evaporating, decanting, etc. `In unit I2 the high surface area coke is impreg- `nated preferably with an aqueous `solution of sodium carbonate. Other suitable catalytic materials may be potassium carbonate and zinc chloride, and as a result of the impregnation the coke contains 0.1 to 3% by weight of salt. Carbonate solution of the desired concentration may be admitted to I2 through line I3. The impregnated char passes from impregnation unit I2 throughline I4. Steam for suspendingmay be admitted through line I5. The suspended stream is passed through line `I6 into the lower portion of a water gas generator I'I which is of essentially the same type as vessel 5 and is fitted at its lower end with an inlet line I8 for admitting oxidizing gas, preferably oxygen. Said oxidizing gas may also be added to the fiuidized stream in line I5. As in reactor 5, the iiuidized impregnated carbonaceous material in generator I1 is in the form of a dense, turbulent mass fluidized by the upwardly flowing gases and superheated steam. Because of the catalytic effect, the gasication of the carbon by the steam in the catalytic reactor proceeds rapidly to form CO and H2. The heat required for the endothermic gasification reaction in this one-vessel unit is supplied by the combustion of part of the carbonaceous solids in reactor I1 by the oxygen admitted through lines I8 and/or I5. The total supply of oxygen is carefully controlled to generate suflicient heat by combustion to satisfyt-he heat requirements of the process. Thetemperature maintained in catalytic reaction zone I1 is in the range of about 1300 to 1800 F., which is substantially lower than that required for high steam conversion without the use of al gasification catalyst. Because of the higher rates of conversion associated with the use of the catalyst, substantially smaller reactors may be employed to obtain over-al1 yields of the same order of magnitude asthcse obtained without catalyst with large reactor volumes. The gasification products are withdrawn overhead through a dust separator 20 and line 2I and may go directly to product storage, to purification for sulfur removal and to a hydrocarbon synthesis plant after blending with the gasification products from the primary water gas reactor, or may be used as a fuel gas. With catalytic reactor I'I the bulk of the gasification is accomplished, and the coke is consumed in the gasication reaction to any desired residual carbon content. Ash of relatively low carbon content and surface area is continuously withdrawn from reactor I'I through line 24. If desired, the carbon associated with the ash may be completely utilized by combustion in a separate burner vessel (not shown) wherein the ash is burned at a temperature at least F. above the temperature level in the gasification zones, and the hot residue recycled to the latter zones to furnish sensible heat. Also, since the catalyst content of the ash is very high, it may be desirable to recycle a minor portion, say 5-25%, thereof, to generators 5 and I'I via lines 22 and 23to furnish a portion of the catalyst requirements of the system. In Figure II there is shown another embodiment of the invention wherein a high surface area is provided for catalyst activation without operating in two stages.` i l lReferringnow to this gure, fresh-coke or coal 9 by Weight of catalyst is incorporated into said char. SUMNER B. SWEETSER.. WALTER G. SCHARMANN. References Cited in the le of this patent UNITED STATES PATENTS Number 10 OTHER REFERENCES Taylor et al.: Journal of the American Chemical Society, September 1921, pp. 2055-2071. Godel: Chemical Engineering, July 1948, pp. Mantell: "Industrial Carbon, 2nd edition, page 164.



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