GB2057007A - Gasification of Solid Carbonaceous Materials to Produce Gas Suitable for Ammonia Synthesis - Google Patents

Abstract

Coal is contacted with air and steam in a fluidized bed and heat is provided by downward flowing hot char or hot thermal refractory material through the fluidized bed. The char or refractory material is heated externally of the fluidized bed by combustion of fuel and/or a portion of the char. Control of the ratio of steam and air to the coal provides a gasification product of approximately 3 moles carbon monoxide plus hydrogen per mole of nitrogen. <IMAGE>

Description

SPECIFICATION Gasification of Solid Carbonaceous Materials to Produce Gas Suitable for Ammonia Synthesis Background of the Invention This invention relates to the production of a mixture of hydrogen and nitrogen from solid carbonaceous materials and air. Ammonia synthesis gas is such a mixture having a molecular ratio of about 3 hydrogen to 1 nitrogen.

Ammonia synthesis gas is generally prepared by two-stage steam reforming of natural gas, with air in the correct proportion being introduced between stages. The air is introduced to provide nitrogen; however, combustion of part of the synthesis gas reduces the heat necessary to drive the endothermic reforming reaction to completion. This system produces an intermediate synthesis gas containing hydrogen, carbon monoxide and nitrogen, with the carbon monoxide plus hydrogen being approximately three times the moles of nitrogen. This gas is then catalytically reacted with steam in the so-called water gas shift reaction. In this well-known reaction, carbon monoxide reacts mole for mole with steam to produce one mole of hydrogen per mole of carbon monoxide. Thus, in a hydrogen-carbon monoxide mixture, carbon monoxide can be viewed as "potential" hydrogen.After the shift reaction, the gas is processed to remove water, carbon dioxide, and any traces of sulfur which may have been introduced in the hydrocarbon feed, resulting in a gas containing only hydrogen and nitrogen in the desired ratio.

With the decreasing reserves of natural gas, it has become apparent that other carbonaceous raw materials will ultimately be used in the manufacture of ammonia, methanol, and other synthesis gas derived products. Coal can be reacted with oxygen and steam to produce a mixture of hydrogen and carbon monoxide with minor amounts of carbon dioxide and sulfur compounds. If ammonia synthesis is the object of the gasification, the mixture is shifted and purified to produce pure hydrogen, after which an appropriate amount of nitrogen derived from air separation is blended with the purified hydrogen. A number of physical systems have been proposed to effect oxygen fueled gasification; however, generally they require an air separation plant or a purchased supply of pure oxygen.This adds to the capital cost and operating complexity; or, if purchased oxygen is used, the raw material costs chargeable to the product are greatly increased.

U.S. Patent No. 2,795,559 discloses the production of a gas mixture of 3 volumes of hydrogen per volume of nitrogen by oxidatively gasifying a carbonaceous fuel, such as coal, with air as the sole source of oxygen at an elevated temperature and pressure to produce a synthesis gas containing a mixture of carbon monoxide, hydrogen and nitrogen, the latter being present in greater than one volume of nitrogen per three volumes of hydrogen. The carbon monoxide in said mixture is then reacted with steam, i.e., water gas shift reaction, to convert the carbon monoxide to carbon dioxide with the concomitant production of hydrogen. The carbon dioxide and water vapor are removed from the mixture leaving essentially a hydrogen and nitrogen mixture.The hydrogen and nitrogen mixture is then further refined by a series of steps wherein nitrogen in excess of 1 volume per 3 volumes of hydrogen is condensed at cryogenic conditions and removed to obtain the ammonia syn gas mixture. It is noted that the process described in this patent utilizes air in the gasification of the coal as the only source of oxygen and the reaction of air with the fuel, coal, is exothermic to maintain the gasification autogenously and supply heat for the endothermic water gas shift reaction.

U.S. Patent No. 2,276,343 describes a continuous process for gasifying lignite to produce hydrogen by preheating a lignite containing 25 40% water to drive off water-containing vapor and render the lignite highly reactive. The mixture of highly reactive lignite and water vapor are reacted at an elevated temperature to produce a hydrogen rich gaseous mixture which is then separated from the lignite and purified. The lignite is heated and maintained at 5000C. to 8500C. in the described process by external means. External steam may be introduced to the reaction to produce additional hydrogen.

U.S. Patent No. 3,620,697 discloses a process for producing hydrogen by reacting carbon, such as coal, with water utilizing a circulating inert particulate material as the heat source for the endothermic reaction. The inert particulate material is heated by burning a carbonaceous material therewith while being conveyed to the reaction. Similarly, U.S. Patents No. 3,968,052 and No.

3,850,839 disclose processes for gasifying coal-derived char with steam in a fluid bed system where the heat for the endothermic gasification reaction is supplied by circulating through the system inert pellets which are heated by burning fines from the gasifier in their presence externally of the gasifier.

Summary This invention provides a unified process for producing a raw gaseous product which is readily converted to gas suitable for conversion to ammonia from solid carbonaceous starting materials. This gas, as derived from the teaching of this invention, contains essentially carbon monoxide plus hydrogen and nitrogen with hydrogen plus carbon monoxide in a molar ratio to nitrogen of about three to one. In this process, coal char, resulting from the charring (carbonisation) of coal and comprising carbon and a small amount of ash, or a chemically inert, thermally refractory solid particulate material is used to supply endothermic heat for oxidatively gasifying solid carbonaceous material with air and steam.In a major aspect of this invention, the solid carbonaceous material is maintained in a fluidized reaction zone and heated char particles or inert solid particles flow downward through the fluidized bed losing heat to the reaction mass as they progress downward.

Typical objects of this invention are (1) to provide a process for gasifying solid carbonaceous materials, (2) to provide a process for production of crude ammonia synthesis gas comprising hydrogen plus carbon monoxide and nitrogen in a desired ratio, and (3) to provide an improved process for the gasification of solid carbonaceous materials with air and steam to form a gaseous mixture of about 3 volumes of carbon monoxide plus hydrogen and 1 volume of nitrogen.

Various other objects, aspects and advantages of this invention will become apparent to those skilled in the art from the accompanying description, drawings, and appended claims.

According to this invention, solid carbonaceous materials, as typified by coal of rank ranging from lignite through anthracite are gasified by partial oxidation in the presence of steam. Partial oxidation in this context refers to oxidation of carbon, or a carbon-hydrngen material with a deficiency of oxidant, usually oxygen, so that the highest oxidation products cannot be obtained. Thus, at the temperatures employed in this invention, the oxidized carbon would exist essentially as carbon monoxide rather than carbon dioxide and hydrogen would be essentially non-oxidized. The overall reaction of solid carbonhydrogen materials with steam and a deficiency of air is endothermic; that is, heat must be supplied to maintain the reaction at a temperature necessary to obtain desired products.The amount of heat supplied is a function of the heat of formation of the carbonaceous materials and the temperature(s) at which the various reactants are introduced into the reaction zone. A primary aspect of this invention is the use of heat carrier particles comprising coal char particles or a chemically inert, thermally refractory particulate solid to carry heat from a heating device outside the reactor into the reaction zone. This invention embodies a fluidized bed reactor comprising a primary gasification zone of a vertically cylindrical section immediately above and contiguous to an elutriation/fluidization zone of a circular conical section. Solid carbonaceous particles entrained in the reactant steam are injected into the fluidized bed of particles at the bottom of the cylindrical section.In the fluidized bed operation mixing and thermal equilibrium are rapidly attained; thus, the solid carbonaceous particles are very rapidly heated to temperature and react with steam and air which is introduced as an elutriation/fluidization gas near the base of the conical section. As has been previously discussed, the solid carbonaceous material-air-steam reaction conducted in a deficiency of air is endothermic. The heat carrier particles, heated to a temperature above the reaction temperature, are introduced near the top of the gasification zone and are cooled rapidly to bed temperature while supplying heat necessary to maintain the reaction temperature.The quantity of heat carrier particles and temperature at which they are introduced into the bed are directly related to the heat required to maintain bed temperature and optimized conditions can readily be calculated from heat balance relations for a specific solid carbonaceous material. As the heat carrier particles reach the conical section, the cross-sectional area available for solids flow downward and gas flow upward decreases with the result that the smaller, lighter solid carbonaceous particles are, for the most part, blown back into the gasification zone while the heat carrier particles flow from the bottom of h e e I the elutriation/fluidization zone into a conduit leading to a riser-burner.The heat carrier particles, after removal of aggregates of ash, carbon and heat carrier, singly or in concert, flows up the riser-burner due to a pressure balance to the point where preheated combustion air is introduced, engages the particles and transports them on up the riser-burner.

Immediately above the combustion air inlet, a stream of coal char, essentially pure carbon with a small amount of ash from the gasification zone, can be fed into the riser-burner as additional fuel to the char entrained in the heat carrier particles from the elutriation/fluidization zone. Combustion of the fuel supplies heat to the heat carrier particles for ultimate release into the gasification zone.

The heat carrier particles plus gas flow to a separator where the disengaged particles then flow back to the gasification zone, thus completing this cycle, while the combustion gas, nitrogen plus carbon monoxide are cooled to recover heat, filtered of particles by auxiliary equipment and are discharged harmlessly to the atmosphere.

Suitable conditions employed for carrying out this process can be generally typified as follows: From To Preferred Superifical gasification velocity, 1 5 2-3 feet per sec. (meters per sec.) (.305) (1.52) (.610--.915) Superificial elutriation gas velocity, 4 10 6-7 feet per sec. at bottom of cone (1.22) (3.05) (1.83-2.13) (meters per sec.) Superifical riser-burner gas velocity. 12 40 1 8-22 feet per sec. (meters per sec.) (3.66) (12.2) (5.49-6.71) Reactor Temperature, OC. 925 1200 1000 Riser-BurnerTemperature, OC. 1050 1300 1150 System Pressure, atmospheres 1 65 28-32 The ratio of air and steam to solid carbonaceous material in the gasifier feed will depend entirely on the elemental analysis of the coal to obtain the 3/1 molar ratio of carbon monoxide plus hydrogen to nitrogen which will generally be desired. Generally, a weight ratio of 0.25 to 0.75 kg. H20/kg. coal is present in the gasifier and a weight ratio of 0.6 to 10 kg. air/kg. coal is present in the elutriation/fluidization zone. Also, solid carbonaceous solids, e.g., coals of various ranks, are not of uniform composition even in a given mine.Regulation of the process can be accomplished by airsteam-coal ratio control based on continuous analysis of the gas product. Although a molar ratio of 3 hydrogen to 1 nitrogen is desirable for ammonia synthesis gas, a broad molar ratio of carbon monoxide plus hydrogen to nitrogen such as 2:1 to 4:1 can be prepared in accordance with this invention by varying the steam and/or air additions. Additional hydrogen or nitrogen may be added to bring the ratio to 3 to 1 for ammonia synthesis.

In the preferred method of operation of the various zones, heat carrier particles are continuously circulated through the reaction system. Throughout the system linear gas velocities are maintained such that the particles are entrained in the gases in the riser-burner zone and flow downward through the fluidized bed of solid carbonaceous material in the gasifier and elutriation zones. Gas velocities of 1 2 to 40 feet (3.6 to 12.2 meters) per second are employed in the riser-burner zone and 1 to 5 feet (0.3 to 1.5 meters) per second in the gasifier zone and 4 to 10 feet (1.2 to 3 meters) per second in the elutriation zone. Actual gas velocities employed will be dependent upon the apparatus, size and shape, employed and the densities of the solid materials.In this type of operation, means will be provided externally of the gasification zone for separating solid materials entrained in the gaseous effluent withdrawn from the gasifier zone.

Any chemically inert material capable of being a.heat carrier is usable in the present invention.

The heat carrier will generally be used in a particulate form of a size suitable for fluidization. Any refractory metal oxide such as aluminum oxide, silica-alumina oxide, spinels, zirconia, mullite and the like can be used as the inert material; The temperature employed in the gasification zone can vary over a wide range. Preferably, such reaction will be conducted from 9250C. to 1 2000C. Pressure on the system can also vary. The system can be operated under pressures from 0 psig to 1000 psig (6.89x 106 Pa). Temperatures in the riserburner zone will generally be from 1050C to 1 3000C.

As previously indicated, the process of this invention utilizes a fluidized bed of solid carbonaceous material in the gasifier zone. The fluidization of the solids is obtained by introducing air, also a reactant, into the system. Air is introduced at such rates to fluidize the solids.

This invention will be more specifically described with reference to the drawings. Figure 1 is a diagrammatic illustration of the apparatus in the system described with regard to gasifying coal using coal char and Figure 2 is a diagrammatic illustration of the apparatus using the refractory material.

According to Figure 1, coal char in particulate form from gasifier 1 is introduced through conduit 2 to riser-burner zone 3. Combustion air is introduced through conduit 4 and distributor 5 into riserburner zone 3. Riser-burner zone 3 is maintained under conditions whereby the char particles are heated. The exothermic burning reaction heats the char particles. The char particles are transported upwardly through riser-burner zone 3 through conduit 7 into gas-solids separator 8. Combustion gases are removed through conduit 6 and vented. The heated char particles flow through conduits 9 into gasifier zone 1. Coal from supply 12 is introduced through conduit 1 3 to gasifier 1. Steam is introduced through conduit 14 into conduit 1 3 to transport the coal therethrough and introduce steam to gasifier 1.Below gasifier 1 is elutriation/fluidization zone 1 5 where the char particles after flowing downward through the bed of coal in gasifier zone 1 are separated from the coal and flow from elutriation/fluidization zone 1 5 through conduit 2 into the lower portion of riser-burner 3. Air is introduced through conduit 1 6 into the lower portion of elutriation/fluidization zone 1 5 to aid in separation of the char particles and to fluidize the bed of and react with coal in gasifier 1. Gasification product gases are removed from the upper portion of gasifier 1 through conduit 1 7 for recovery of ammonia syn gas.

According to Figure 2, chemically inert, thermally refractory material in particulate form, as needed, from supply 20 is introduced through conduit 21 to riser-burner zone 22. Combustion air is introduced through conduit 23 into the lower portion of riser-burner zone 22. Riser-burner zone 22 is maintained under conditions whereby the inert particles are heated. In one aspect heat is supplied by burning fuel introduced through conduit 24. In another aspect heat is supplied by burning carbon from gasifier zone 29, introduced through conduit 30 to riser-burner zone 22. Air is introduced into conduit 30 through conduit 31 to control movement of the carbon therethrough. The exothermic burning reaction heats the inert particles. The inert particles are transported upwardly through riser-burner zone 22 through conduit 25 into gas-solids separator 26.Combustion gases are removed through conduit 27 and vented. The heated inert particulate material flows through conduit 28 into gasifier zone 29.

Coal from supply 32 is introduced through conduit 33 to gasifier 29. Steam is introduced through conduit 34 into conduit 33 to transport the coal therethrough and introduce steam to gasifier 29.

Below gasifier 29 is elutriation/fluidization zone 35 where the inert particulate material after flowing downward through the bed of coal in gasifier zone 29 is separated from the coal derived char and flows from elutriation/fluidization zone 35 through conduit 36 into the lower portion of riser-burner 22. Air is introduced through conduit 37 into the lower porttdn of elutriation/fluidization zone 35 to aid in separation of the inert particulate material and char-and to fluidize the bed of and react with coal in gasifier 29. Gasification product gases are removed from the upper portion of gasifier 29 through conduit 38 for further processing and recovery of ammonia synthesis gas.

Examples The practice of this invention will now be more fully illustrated in the following Examples. In these Examples unless indicated otherwise, the reactor employed for carrying out the particular coal gasification runs comprises a 20-inch (50.8 cm.) RA 330 schedule 40 pipe with a 1.61-inch (3.89 cm.) inside diameter main having a Type 310 stainless steel conical section at the bottom fitted with a water-cooled injection nozzle for introducing finely divided coal conveyed with air.

RA 330 schedule 40 and type 310 are alloys having the following compositions by weight: RA 330 Sch. 40 Type 310 Carbon 0.5% Carbon 0.5% Manganese 1.5% Manganese 1.5% Silicon 1.25% Silicon 0.5% Chromium 19% Chromium 25% Nickel 35% Nickel 20% Iron-Balance to 100% Iron-Balance to 100% In each run using char, the reactor contains sufficient char to provide a fluidized bed height of 1 8 inches (45.7 cm.). The reactor is equipped with two dip tubes, one extending from the top through the inert material to about 1/4 inch (0.635 cm.) above the coal injection nozzle for the introduction of steam and the other extends to the top of the fluidized bed for removal of reaction gases and excess solids (ash and unreacted coal). The reactor is enclosed in an insulated electric radiant heater.

Example 1 This Example illustrates the gasification of various solid carbon-containing materials, steam and air to produce ammonia synthesis gas using hot char in accordance with this invention.

Characterization and results of each run is given in Table 1.

Example 2 This Example, with reference to the drawing of Figure 1 illustrates the continuous stable gasification: Table 1 Run B Run C Run D Coal Run A N. Dakota Wyoming Wyoming Analysis (Wt. %) Texas Lignite Lignite Sub-Bituminous Sub-Bituminous C 41.23 44.60 61.48 61.48 H 3.79 5.95 6.07 6.07 N 0.81 0.69 1.20 1.20 S 0.22 0.31 0.74 0.74 0 16.10 13.57 12.40 12.40 H20 30.00 29.93 15.82 15.82 Ash 7.84 4.95 2.29 2.29 Inert Solids Lignite Char Lignite Char Coal Char Coal Char Weight(gms) 73 36.42 54.17 39.10 Temperature ( C.) 1002 943 977 1050 Pressure atm. abs. 1 1 1 3 Feed Coal (gm/min.) 1.007 0.483 0.472 1.057 Steam (gmZmin.) 0.285 0.150 0.130 0.520 Air (Std.Liters/min.) 0.622 0.350 0.320 0.750 Run Time (min.) 120 1 50 1 50 120 Gas Residence Time (sec.) 5.1 10.8 10.2 10.5 Product Analysis (gram moles) C 2.99 1.43 0.83 1.63 02 0.03 0.02 0.02 0.00 N2 2.53 1.70 1.55 3.54 CO2 0.14 0.17 0.18 0.20 CO 3.96 2.72 2.48 5.68 H2 3.91 2.41 2.68 5.71 CO+HJN2 Ratio 3.11 3.02 3.33 3.22 of Wyoming sub-bituminous coal according to this invention. Additions to or modifications of flows and conditions during periods of non-steady state operation will be apparent to those skilled in the art.

These periods include transient conditions of start-up and shut-down as well as inevitable upsets caused by changing feedstock and/or production rates imposed by operations of auxiliary equipment necessary to, but not integral with this invention. Further, ancillary equipment necessary to the operation of a process utilizing this invention, but not germane to the invention as disclosed here include heat exchangers, compressors, coal handling and conditioning equipment, solids conveying equipment, and gas solids separators.

Powdered coal (-50 mesh), 100 pounds (45.35 kg) is fed via conduit 13 where it is joined by 3.1 pounds (1.4 kg) of steam at 500 psig (3.4x 106 Pa) and 35O0C. from conduit 14 which pneumatically conveys the coal into the lower portion of the fluidized bed in gasifier 1. The coal is very rapidly heated to the reaction temperature, 1 O250C., in the fluidized bed and reacts with 843 Scf (Standard cubic feet) (23.8 cubic meters) of air preheated to 8250C. fed via conduit 16 and the conveying steam to product a gas containing 6.7 pounds (3.04 kg) hydrogen, 66.7 pounds (30.2 kg) carbon monoxide, 53.6 pounds (24.3 kg) nitrogen, and 18.5 pounds (8.38 kg) carbon dioxide. Traces of hydrogen sulfide will also be formed if the coal contains sulfur impurities.The raw synthesis gas exits the reactor through conduit 1 7 and is processed by downstream equipment, not shown, to recover heat (7 1.3 x 1 03 BTU) (75.1 5x 106 J), preheating incoming air, remove sulfur, entrained ash, and carbon particles, and further chemical reaction. Since the gasifier 1 is operated below the ash fusion temperature, the mineral content of the coal will be removed as a fine dust, fly ash. The reaction, with coal entering at 250C., steam at 3250C. and air entering at 8250C. is endothermic requiring 161 x103 BTU to be supplied.

This endothermic heat requirement is supplied by a flow of coal char heat carrier of a size suitable for fluidization. The heated char is introduced near the top of the fluidized bed of coal in the gasifier 1 from riser-burner 3 and separator 8 through conduit 9 at a rate of 1 909 pounds (864.8 kg) per minute and a temperature of 11 250C. The char passes downward through the fluidized bed by virtue of its particle size and density rapidly giving up heat to maintain bed temperature at 1 0250C. Char, 1930 pounds (874.3 kg), is essentially separated from coal in the conical lower section of gasifier 1 by elutriation in the incoming air and leaves the reactor at a temperature of 10250C. via standpipe 2.Any large, relative to the heat carrier particles, particles of coal are trapped at the bottom of the riser-burner 3 and intermittently removed via conduit 18. Combustion air, 2351 Scf (66.5 cubic meters) at 8250C.

is introduced stagewise through conduit 4 and distributor 5, and transports the char upward in the riser-burner where it is heated from 10250C. to 1 1250C. by combustion of 21 pounds (9.5 kg) char fed into the riser-burner 3 from the gasifier 1. The mixture of hot combustion gas and heated char is separated in separator 8 with solids at 11 250C. being returned to the gasifier 1 via conduit 9 and combustion gas, 24.5 pounds (11.1 kg) carbon monoxide, 38.4 pounds (17.4 kg) carbon dioxide and 146.7 pounds (66.5 kg) nitrogen, at 11 250C., leaving the separator through conduit 6 for heat recovery (183.1 x 103 BTU) and cleanup before being vented to the atmosphere.

The product gas contains CO+HN2 in a ratio which, after water gas shift of the CO, provides a hydrogen-nitrogen mixture suitable for ammonia synthesis. At theoretical conversion of the synthesis gas to ammonia, gasification of 100 pounds (45 kg) of coal results in 65.1 pounds (29.5 kg) of ammonia (1 ton of ammonia requires gasification of 1.54 tons of coal) and produces 5.63x 106 BTU of heat.

As shown in Fig. 1 and Example 2, stagewise introduction of combustion air into riser-burner 3 results in non-equilibrium burning of the char to a higher CO2 content than anticipated by thermodynamic equilibrium and thus less char is required to be burned to sufficiently heat the char to provide the heat for the gasification.

Example 3 In this Example, the reactor employed for carrying out coal gasification comprises a 20-inch RA 330 schedule 40 pipe with a 1.61-inch inside diameter main having a Type 310 stainless steel conical section at the bottom fitted with a water-cooled injection nozzle through which 0.539 gram per minute of finely divided Kentucky bituminous coal conveyed with 0.250 standard liters per minute of air are introduced. The reactor contains 1 95 grams of alpha aluminum oxide to provide a fluidized bed height of 1 8 inches. The reactor is equipped with two dip tubes, one extending from the top through the inert material to about 1/4 inch (0.635 cm) above the coal/air injection nozzle through which 0.250 gram per minute of steam is introduced and the other extends to the top of the fluidized bed for removal of reaction gases and excess solids (ash and unreacted coal). The reactor is enclosed in an insulated electric radiant heater. The reaction is conducted at 1051 0C., a pressure of 1 atmosphere absolute anda gas residence time of 10.1 seconds for 120 minutes.Characterization of the feed and product is as follows: Analysis Feed (wit. /0) Product (grams/moles) C-68.61 C-2.58 H-5.25 20.02 N-1.39 N2-1.15 Analysis (contd.) Feed (wt. /0) Product Kgrams/moles) S--0.70 C02-O.O6 0--9.56 CO--1.52 H20-2.82 H2-1 .92 Ash1 1.67 The product gas contains a molar ratio CO+H2 to N2 of 2.99, which after water gas shift of the CO provides a H2/N2 mixture suitable for ammonia synthesis.

Example 4 This Example, with reference to the drawing of Figure 2 illustrates the continuous stable gasification of Kentucky bituminous coal according to this invention. Additions to or modifications of flows and conditions during periods of non-steady state operation will be apparent to those skilled in the art. These periods include transient conditions of start-up and shut-down as well as inevitable upsets caused by changing feedstock and/or production rates imposed by operations of auxiliary equipment necessary to, but not integral with this invention. Further, ancillary equipment necessary to the operation of a process utilizing this invention, but not germane to the invention as disclosed here include heat exchangers, compressors, coal handling and conditioning equipment, solids conveying equipment, and gas-solids separators.

Powdered coal, 2.1 grams per minute is fed via conduit 33 where it is joined by 0.73 grams per minute steam at 500 psig and 3500C. from conduit 34 which pneumatically conveys the coal to the lower portion of the fluidized bed in gasifier 29. The coal is very rapidly heated to the reaction temperature, 10250C. in the fluidized bed and reacts with 2.04 grams per minute (1.59 standard liters per minute) of air preheated to 8250C. fed via conduit 37 and the conveying steam to produce 0.235 gram mole per minute (5.27 standard liters per minute) of a gas containing 41.3 mole percent hydrogen, 32.4 mole percent carbon monoxide, 24.6 mole percent nitrogen, and 1.7 mole percent carbon dioxide. Traces of hydrogen sulfide will also be formed if the coal contains sulfur impurities.The raw synthesis gas exits the reactor through conduit 38 and is processed by downstream equipment, not shown, to recover heat, preheating incoming air, remove sulfur, entrained ash, and carbon particles, and further chemical reaction. The reaction, with coal entering at 250C., steam at 3250C. and air entering at 8250C. is endothermic requiring heat to be supplied at the rate of 3.07 kilocalories per minute. This endothermic heat requirement is supplied by a flow of a chemically inert thermally refractory heat carrier typified by alpha aluminum oxide of a size suitable for fluidization. The heat carrier is introduced near the top of the fluidized bed of coal char in the gasifier 29 from riser-burner 22 and separator 26 through conduit 28 at a rate of 102 grams per minute and a temperature of 11 250C.

The heat carrier passes downward through the fluidized bed by virtue of its particle size and density rapidly giving up heat to maintain bed temperature at 1 0250C. The heat carrier is essentially separated from carbon in the conical lower section of gasifier 29 by elutriation in the incoming air and leaves the reactor at a temperature of 1 0250C. via conduit 36. Any large, relative to the heat carrier particles, particles of coal are trapped at the bottom of the riser-burner 22 and intermittently removed via conduit 39. Combustion air, 5.41 grams per minute (4.21 standard liters per minute) at 8250C. is introduced through conduit 23, and transports the heat carrier upward in.riser-burner 22 where it is heated from 10250C. to 11 250C, by combustion of 0.45 gram of carbon per minute fed into the riserburner 22 from the gasifier 29 via conduit 30 with the rate being controlied by very small amounts of aeration air flowing through conduit 31. The mixture of hot combustion gas and reheated heat carrier is separated in separator 26 with solids being returned to the gasifier 29 via conduit 28 and 0.188 gram mole per minute (4.21 standard liters per minute) of flue gas leaving the separator through conduit 27 for heat recovery and cleanup before being vented to the atmosphere.

Claims (1)

1. Claims

   1. A continuous process for the gasification of solid carbonaceous materials in a fluidized bed system comprising a lower elutriation/fluidization zone and an upper gasifier zone and an associated riser-burner zone characterized by: a) introducing particulate solid carbonaceous material and steam into the lower portion of said gasifier zone, b) introducing air into the lower portion of said elutriation/fluidization zone, c) entraining and fluidizing said particulate solid carbonaceous material in said air, d) introducing coal char particles or a finely-divided chemically inert, thermally refractory solid material at an elevated temperature into the upper portion of said gasifier zone, e) allowing said char particles or said inert solid material to flow downward through said fluidized bed of solid carbonaceous material in said gasifier zone, f) maintaining said gasifier zone under conditions so that said carbonaceous material, steam and air are endothermically reacted to a mixture of carbon monoxide, hydrogen and nitrogen, g) said char particles or said inert solid material being the source of heat for said endothermic reaction, h) withdrawing a gaseous effluent comprising carbon monoxide, hydrogen and nitrogen from the upper portion of said gasifier zone, i) separating said char particles or said inert solid material by elutriation with said air introduced into said elutriation/fluidization zone, j) introducing said separated char particles or said inert solid material into the lower portion of said riser-burner zone, k) introducing air to the lower portion of said riser-burner zone, I) maintaining exothermic conditions in said riser-burner zone to heat said char particles or said inert solid material to an elevated temperature sufficient to effect gasification of said solid carbonaceous material in said gasifier zone, and m) withdrawing said char particles or said heated inert solid material from said riser-burner zone and reintroducing it into said gasification zone.

   2. A process according to Claim 1, wherein separated char particles are introduced into the riserburner zone and said exothermic conditions are maintained therein by burning a portion of the char particles in said riser-burner zone.

   3. A process according to Claim 1, wherein separated inert solid material is introduced into the riser-burner zone, fuel is introduced into the lower portion of said riser-burner zone, and said exothermic conditions are maintained by burning said fuel therein.

   4. A process according to Claim 1, wherein separated inert solid material is introduced into the lower portion of said riser-burner zone, wherein separated inert solid material is introduced into the riser-burner zone, carbon from said. gasifier zone is introduced into the riser-burner zone, and said exothermic conditions are maintained by burning said carbon therein.

   5. A process of any of Claims 1 to 4, wherein said solid carbonaceous material is coal.

   6. A process of Claim 5, wherein said coal is a coal of rank ranging from lignite through anthracite.

   7. A process of Claim 6, wherein said coal is lignite.

   8. A process of any of the preceding claims, wherein said inert solid material, is present, is alpha alumina, silica-alumina or spinel.

   9. A process of any of the preceding claims, wherein the temperature maintained in said gasifier zone is from 9250C. to 1 2O00C. and in said riser-burner zone is 1 0500C. to 1 3000C.

   1 0. A process of any of the preceding claims, wherein said gaseous effluent contains carbon monoxide plus hydrogen to nitrogen in a molar ratio of 2 to 1 to 4 to 1.

   11. A process of any of the preceding claims, wherein the superficial gas velocity in the gasifier zone is 1 to 5 feet per second, in the elutriation/fluidization zone is 4 to 10 feet per second and in the riser-burner zone is 12 to 40 feet per second.

   12. A process of Claim 1 characterized by: a) introducing particulate coal selected from the group consisting of lignite, bituminous, subbituminous and anthracite and steam at a weight ratio of 0.25 to 0.75 Ibs. H20/lb. coal into the lower portion of said gasifier zone, b) introducing air to provide an air to coal weight ratio of 0.6 to 10 ibis. air/lb. coal into the lower portion of said elutriation/fluidization zone at a rate to provide a superifical gas velocity of 4 to 10 ft./sec. in said elutriation/fluidization zone and of 1 to 5 ft./sec. in said gasifier zone to entrain and fluidize said particulate coal, c) introducing coal char particles at a temperature of 10500 C. to 1 3000C. into the upper portion of said gasifier zone, d) allowing said char particles to flow downward through said fluidized bed of coal in said gasifier zone to maintain said gasifier zone at a temperature of 9250C. to 1100 C. so that said coal, steam and air are endothermically reacted to form a mixture of carbon monoxide, hydrogen and nitrogen, said char particles being the source of heat for said endothermic reaction, e) withdrawing a gaseous effluent comprising said mixture of carbon monoxide, hydrogen and nitrogen from the upper portion of said gasifier zone, f) separating said coal from said char particles by elutriation with said air introduced to said elutriation/fluidization zone, g) introducing said separated char particles into the lower portion of said riser-burner zone, h) introducing air to the lower portion of said riser-burner zone, and i) withdrawing said heated char particles from said riser-burner zone and reintroducing them into said gasification zone.

   14. A process according to Claim 1 substantially as described in any of the Examples.