US2654661A - Gasification of carbonaceous solid fuels - Google Patents

Description

Oct. 6, 1953 E. GORIN 2,654,661

GASIFICATION OF CARBONACEOUS SOLID FUELS Filed Nov. 19, 1949 2 Sheets-Sheet l METHANE HYDROGEN 34' HYDROGEN GENERATOR 3 l5 I-b O HYDROGEN GENERATOR 3 WATER HYDROGENATOR 23 FUEL GAS

RESIOUE PRODUCER- PRODUCER STEAM l4 "INVENTOR EVERETT GORIN ATTORN EY Oct. 6, 1953 E. GORIN GASIFICATION OF CARBONACEOUS SOLID FUELS Filed Nov. 19, 1949 GENERATOR 1 $6 74 HIGH B.T.U. GAS 94 az z 9 l- 3 Q In HYDROGENATQR 66 /64 m I m a: l 62 r HYDROGEN ll RESIDUE p FIG. 2 INVENTOR STEAM EVERETT GORIN 2 Sheets-Sheet 2 TO HYDROGEN ATTORNEY Patented Oct. 6, 1953 UNITED STATES ATENT OFFICE GASIFICATION F CARBONACEOUS SOLID FUELS Application November 19, 1949, Serial No. 128,435

1 Claim. 1

This invention relates to the gasification of carbonaceous solid fuels, and particularly to the production of hydrogen or high B. t. u. gas from such fuels.

In application Serial No. 99,561, filed June 16, 1949, a process for the gasification of carbonaceous solid fuels by reaction between steam and solid fuels in the presence of calcium oxide is described. In accordance with that process, calcium oxide is mixed with carbonaceous solid fuels in certain critical proportions and under certain critical conditions of temperature and pressure and then subjected to reaction with steam. A gaseous product is obtained which contains methane and hydrogen in varying relative proportions depending upon the particular temperature and pressure conditions. As a result of the reaction between the steam and the carbonaceous solid fuels, an inert solid residue or ash is formed in admixture with the lime. In order to reuse the lime, which is converted to calcium carbonate during the reaction, it is necessary to separate the lime from the ash and regenerate it at elevated temperatures. While various means are available for separating this ash from the lime, it would be desirable to conduct the conversion of the carbonaceous solid fuels to gas in a system in which the lime and solid fuels are not in admixture during the reaction, and yet in which substantially all the benefits of the use of lime in the process are secured. namely, high yields of hydrogen or methane as desired and under thermoneutral conditions.

The primary object of this invention is to provide an improved two-vessel system for converting carbonaceous solid fuels into gas under thermoneutral conditions. Another object of this invention is to provide a two-vessel system for making a high B. t. u. fuel gas which is rich in methane. A further object of the present invention is to provide a two-vessel system for converting carbonaceous solid fuels into a gas which is rich in hydrogen. Still another object of this invention is to provide a two-vessel system for gasifying carbonaceous solid fuels in which the gaseous products are substantially free of carbon dioxide.

For a better understanding of my invention and other objects and advantages, reference should be had to the following description and to the accompanying drawings, in which:

Figure 1 is a diagrammatic illustration of an apparatus comprising a two-vessel system adapted to carry out the preferred embodiment of my invention; and

Figure 2 is an illustration, partly diagrammatic and partly cross-sectional of a modified embodiment of a portion of the system shown in Figure 1.

In accordance with my invention, a two-vessel system is employed to convert carbonaceous solid fuels to a gas containing primarily methane and/or hydrogen as desired. In one of the two vessels a bed of carbonaceous solid fuels in granular form is maintained, while in the other vessel a bed of granular calcium oxide is confined. The temperature in each of the vessels, while not necessarily the same, must be between 1400 and 1750 F. The pressures in the two vessels, while preferably but not necessarily the same, must at least equal and preferably exceed that given by the empirical relation Where p is the minimum reaction pressure in atmospheres and t is the temperature of the reaction zone in F.

Steam and a gas containing methane are circulated through the vessel containing the lime, and under the conditions of temperature and pressure recited, the methane is converted to a gas containing a high percentage of hydrogen. The amount of calcium oxide maintained in the methane-steam reaction vessel must be suflicient to absorb substantially all of the carbon dioxide produced during the reaction in that vessel. Preferably, there are at least 250 parts by weight of calcium oxide present for each parts by weight of carbon contained in the hydrocarbon gas circulating through the bed of lime.

All or part of the hydrogen from the methanesteam reaction vessel (hereinafter sometimes re- 'ferred to as the hydrogen generator) is circulated through the bed of carbonaceous solid fuels confined in the other vessel. Under the conditions of temperature and pressure existing in that vessel, the fuel is hydrogenated and a high B. t. u. gas containing methane in substantial quantities is produced. If it is desired to produce only a high B. t. u. gas from the system, in preference to substantially pure hydrogen, then part of the methane-containing gas is recycled to the hydrogen generator for manufacturing hydrogen, all of which is then returned to the solid fuel hydrogenator vessel. If it is desired to produce hydrogen-rich gas, then only a part of the hydrogen produced in the hydrogen generator is circulated to the hydrogenator and all of the methane produced in the latter is recycled to the hydrogen generator.

As stated above, the temperatures and pressures of the two reaction zones do not necessarily have to be the same. But for practical reasons, it is desirable to maintain the same pressure 1n both vessels. In general, I prefer the pressures to be between 20 and 50 atmospheres. Preferably, the temperature in the solid fuel vessel is not higher than that in the steam-methane reaction zone. It may be less but should not be more than 200 F. lower. 'By operating under 7 these preferred temperature conditions the amount of recycled gas can be kept'at a minimum. I

The lime employed in the hydrogen generator is progressively converted to calcium carbonate by the carbon dioxide produced. It therefore is necessary to regenerate lime from the carbonate from time to time. This may readily be done by separately heating the carbonate to its calcination temperature in the same or different vessels. If the regeneration is effected in the same vessel, then it is necessary to operate a second vessel for carrying out the steam-methane reaction while the first vessel is on its regeneration cycle. Alternatively, the carbonate maybe continuously recycled to the generator.

The reactions in the two zones may be carried out using either fixed -or fluidized beds. The use of fluidized beds is preferred when ('l) the solid fuel used is a coking coal, and (2) it is desired to obtain precise temperature control in the lime regeneration step.

The use of a fixed or moving bed is preferred when it is desired to obtain a maximum concentration of hydrogen leaving the methane steam zone and a maximum concentration of methane leaving the male! char "hydrogenation zone. This is not only desirable in order to obtain a higher purity product but also to minimize the recycle of gas between the two zones. The purity of the hydrogen produced in the methane-steam reaction zonemay be increased for example, by establishing a'temperature gradient of at least 100 F. between the top and bottom of the lime bed, the higher temperature being at the methane inlet end. Similarly, the concentration of methane leaving the hydrogenation zone may be increased by establishing a temperature gradient such that the temperature of gases leaving are at least 100 F.'less than they are at the hottest point in the bed. The desired temperature gradient may be established in a fixed bed by cooling the outlet portion of the bed; and in moving or fluidized beds by maintaining a pluralityof successive beds at progressively lower temperatures.

Finally a fluidized bed may be used in one of the operations and not in the other. For example, due to the relatively low temperature prevailing in the methane-steam reaction zone, moderately long residence times of the order of one to ten minutes are required. Thus it is convenient to use relatively low velocities during the methane-steam reaction, i. e., 0.02-0.20 feet per second. These velocities using lime in the size range of to +325 mesh are either insufli- 4 cient to fluidize the lime or will effect only a bubbling type of fluidization. On the other hand, the lime regeneration step is most suitably carried out at a higher velocity, i. e., at 0.5-3.0 feet per second, i. e., sufiicient to maintain the lime bed in the streaming fluidization range.

The methane-steam reaction may be carried out, therefore, using either a fixed or bubbling fluidized bed, while the lime regeneration may be carried out using a streaming fluidized bed.

The rate of the methane-steam reaction may be increased substantially by the use of catalysts particularly the metals of the first transition group. The metals may be supported directly on the lime or on an independent porous support, 1. e., Ni, Co or Fe on a-alumina, Cu on silica gel, etc. The lime itself may be supported on a refractory basic oxide such as MgO to provide greater physical strength, i. e., dolomite in place of lime may be used as charge to the unit.

I have found that by operating the two vessels in the above manner, either hydrogen or a high B. t. u. gas containing methane in substantial quantities may be produced at will. In the lime vessel heat is supplied for the endothermic steam-methane reaction by the exothermic reaction between the lime and carbon dioxide produced in the reaction. The heat provided by the lime-CO2 reaction is not quite sufi'icient to maintain the methane-steam reaction. Consequently, it is necessary to add heat in any suitable manner to this reaction zone. One method of effecting the addition of heat to the methane-steam reaction zone is by the continuous addition of hot lime supplied from the regenerator. A'preferred method is described briefly below and in greater detail later. In the solid fuel vessel, on the other hand, the reaction between hydrogen and the fuel evolves heat, which is in excess .of the deficiency inthe hydrogen generator.

In one of the embodiments of my new process. I utilize the heat evolved in'the solid fuel hydrogenator to preheat'the steam which is circulated to the hydrogen generator. ,Not only i the necessary heat thus supplied, :but the steam conversion is increased as will be more fully explained below.

In the following description of a specific embodiment of my invention, by way of example only, my new process is applied to the carbonaceous solid residue obtained by the low temperature distillation or carbonization of hydrocarbonaceous solid fuels, such as the high volatile bituminous coal found in the Pittsburgh Seam. This residue, for the purpose of convenience, I shall hereafter refer to as char. It is to be understood, however, that the process is generally applicable to any carbonaceous solid fuels. Among such carbonaceous solids are included all ranks of coal, lignite, oil shale, tar sands, coke from coal or bituminous pitch, solid tar, etc., high reactive solid fuels such as char and lignite.

The apparatus shown in Figure 1 and its operation will now be described. A two-vessel system is employed comprising a solid fuels hydrogenation vessel It and a lime-containing methane-steam reaction vessel or hydrogen generator I2. A'fluidized bed .of granular char is maintained in vessel 10 by means of gases circulating therethrough. The char feed should be ground so that substantially all passes through a 20 mesh screen and the velocity of the gases circulating therethrough to effect fluidization should be of the order of 0.2 to 1.2 feet per second. The bed of calcium oxide may be maintained as a bubbling fluidized bed or as a fixed bed in vessel l2. The size consist of the lime is preferably in the range of to +325 mesh while the gas velocity is maintained at 0.02 to 0.2 feet per second.

A gas containing methane is introduced through a valved conduit i4 into vessel I2 along with steam fed to the conduit i l from conduits l6 and ii. The bed of lime through which the steam and methane are circulated is initially elevated to a temperature of 1400 to 1750 F. Once the reaction between the steam and hydrocarbon gas takes place, only a slight amount of heat need be added to maintain the reaction. The amount of lime present in vessel 12 is sufiicient to absorb substantially all of the carbon dioxide produced. There should be at least 250 parts by weight of oxide present for each 100 parts by weight of carbon contained in the methane passed through vessel I 2. The pressure in this system is that previously recited, that is, it must equal or exceed that given by the empirical relationship of Equation 1 but it is preferably maintained between 20 to 50 atmospheres. The gaseous product consisting essentially of hydrogen is withdrawn from vessel I2 through conduit l8. If it is desired to make a high B. t. 11. gas rather than hydrogen, then all of the gas from the lime vessel I2 is conducted through valved conduit Zil to the bottom of vessel l0. It is usually desirable to free the gas of water during its passage through conduit 20 by a condenser and a collector 22.

Fresh char is introduced into the stream of gas in conduit 21 through conduit 26 from a hopper 23 provided with a motor-driven screw 24. Reacted char or ash is withdrawn through a draw-off tube 2'! as necessary to maintain the level in the vessel. The gas circulates through the bed of solid fuels contained in vessel i0 and the hydrogen therein reacts with the fuel to produce a gas containing methane in substantial quantities. The latter is withdrawn from vessel H3 through a conduit 28 to a cyclone separator 30 where finely divided solids are returned to the vessel it through a dip leg 32. The solidfree methane gas is conveyed through a valved conduit 34 to suitable storage facilities. However, a part of the methane gas is recycled through the valved conduit 14 to vessel l2 to repeat the operation. The amount of methane recycled through conduit i4 is determined by the material balance in the system. In other Words, sufficient methane must be recycled to produce in vessel I2 the hydrogen requirements in vessel H]. The temperature and pressure maintained in Vessel Iii may be the same as those established in vessel i 2, but in any case must lie within the limits previously recited.

If it is desired to produce only hydrogen from the system, then substantially all of the methane produced is recycled to vessel l2 from vessel Ii] but only a portion of the hydrogen made in vessel !2 is recycled to vessel 10 for reaction with the solids. It is also possible by controlling the recycle from each of the vessels to produce hydrogen and methane concurrently, which is one of the inherent advantages of the twovessel system.

During the course of the reaction between the methane and steam in vessel 12 to make hydrogen, carbon dioxide is produced, and, as previously stated, is absorbed by the lime with the formation of calcium carbonate. It is necessary to regenerate the oxide periodically in order to maintain its effectiveness in the reaction. This regeneration is accomplished by raising the temperature of the carbonate to the decomposition point preferably 1750 to 1850 F. at atmospheric pressure. Since it is desirable not to suspend operation of the system during the regeneration, another vessel 48 corresponding to vessel I 2 is provided for continuing the steamcarbon reaction while the vessel i2 is on regeneration.

When the lime in vessel I2 is being regenerated, the flow of steam and methane through valved conduit [4 is stopped. The vessel I2 is reduced to atmospheric pressure by closing its communication with the remainder of the system and by opening the valve in an exhaust line 52. The necessary decomposition temperature is established in the bed of carbonate by burning producer gas introduced through a valved conduit 44 with air introduced through a valved conduit 46. Pulverized coal may be burned directly with air in vessel l2 in place of producer gas. A fine grind is employed, 1. e., through 200 mesh such that ash is not retained by the lime but is carried off in the flue gases.

While vessel I2 is on a regeneration cycle, vessel 40 is operating as the steam-methane reaction zone in the same manner as previously described for vessel I2. Steam is conducted through a valved conduit 48 into a valved conduit 50 which carries methane from the recycling conduit M to vessel 40. The gaseous product from vessel 40 is conveyed to the main outlet conduit it by a valved conduit 52. When vessel I2 is operating on a hydrogen generation cycle, vessel 40 is placed on a regeneration of oxide cycle in the same manner as is vessel It. Air and producer gas are introduced through valved conduits 54 and 56, respectively, and flue gases are discharged through a valved conduit 58 at atmospheric pressure.

The application of the above process to the production of a high B. t. u. gas from char may be illustrated specifically by the following example. The reaction zones in the two vessels are maintained at 1520 F. and at 40 atmospheres absolute. The recycle ratio of gas from the solid fuel hydrogenation vessel to net gas discharged through conduit 34 as product is 2.31. The molar ratio of steam to methane fed to the steam-methane reaction vessel is 3.09. A gas having a, heating value on a dry basis of 613 B. t. u./cubic foot and the following composition is obtained; H253.5 per cent by volume; CO3.8 per cent by volume; co -12 per cent by volume; and CH4- l1.5 per cent by volume. The overall steam conversion is 39 per cent and the net heat evolved over and above that required to maintain the system in operation is about 30,000 B. t. u./lb. mol. of carbon fed to the system.

The application of the above process to the production of a gas rich in hydrogen from char may be illustrated specifically by the following example. The reaction zones in the two vessels are maintained at 1520 F. and at 40 atmospheres pressure absolute. The recycle ratio of hydrogen gas from the steam-methane reaction vessel to the net hydrogen gas discharged through conduit 1 8 as product is 2.33. The molar ratio of steam to methane fed to the steammethane reaction vessel is 4.5. A gas having a heating value on a dry basis of 379 B. t. u./cubic foot and the following composition is obtained: H2-87.3 per cent by volume; CO2.8 per cent by volume; cog-1.4 per cent by volume; and.

CH4-8.5 per cent by volume. The overall steam conversion is 36.4 per cent and net heat evolved over and above that required to maintain the system in operation is about 23,000 B. t. u./l'o. mol. of carbon fed to the system.

In Figure 2 of the drawings, there is shown a modification of the solid fuel hydrogenator which provides for utilizing the heat evolved by the reaction between hydrogen and solid fuel to preheat the steam fed to the methane-steam reaction vessel to a sufficient temperature to render the reaction taking place therein thermoneutral and even exothermic. At the same time, the per cent steam conversion is increased by virtue of partial reaction of the steam with the solid fuel in the hydrogenator vessel.

Referring specifically to Figure 2, numeral 60 designates a modified solid fuel hydrogenator vessel in which carbonaceous solid fuel is reacted with hydrogen from a hydrogen generator in the manner described above. The vessel is di vicled into an inner hydrogenation zone 62 and an outer annular shaped steam preheating zone 64 by a cylindrically shaped chimney 66. The two zones communicate with one another at the bottom and the top of the chimney.

Finely divided solid fuel is carried into the inner hydrogenation zone 62 by the hydrogen gas produced in a hydrogen generator (not shown) which operates in the same manner as that described in connection with the system of Figure 1. The linear velocity of the hydrogen gas and the particle size of the solid fuel are regulated to produce a fluidized bed in the zone 52. A cone-shaped bafiie element 113 is provided at the foot of the chimney to support the bed and is spaced from the walls of the chimney to form an annular passage 12 permitting communication with the outer zone 64.

The gases produced in the hydrogenation zone are collected in a bell-shaped member 14 which is supported within the top of the chimney 68 in a spaced position with respect to the chimney walls to form an annular passage '16 for communication between the two zones. The bed level in the vesse1 60 is maintained sufiiciently high to at least cover the top of the chimney and thereby assure free circulation of solids between the two zones at the bottom and the top of the chimney. Preferably the solids overflow from the top of zone 64 into zone 62 in order to provide an effective seal between the gas bell 14 and the chimney 66. This may be accomplished by circulating the fiuidizing gas in zone '64 at a higher linear velocity than that circulating through zone 62. A conduit 18 serves to convey the high B. t. u. gas produced to a cyclone separator so which separates any entrained solids from the gas and returns them through a dip leg 82 to the feed line 68. The solid free gas is either discharged as product through conduit 84 or recycled through conduit 86 to the hydrogen generator.

Steam enters the outer zone 64 of vessel 60 through a conduit 88 and passes up through the hot solids at such linear velocity that the fluidized condition is maintained. Because the solids in vessel ED are continuously circulating between the two zones, the temperature in the outer zone fi l is nearly as high as that in the inner zone 62. The steam circulating through the outer zone is consequently preheated to reaction temperature. At the same time a small amount of the steam, of the order of 20 per cent,

is converted by reaction with the carbonaceous.

solids. The preheated steam'and gaseous reaction products are conducted from vessel 60 through a conduit to a cyclone separator 92 which separates the entrained solid fines and returns them to the outer zone 64 through a dip leg 94. The solid free steam and gases are discharged from the cyclone into conduit 86 where they become mixed with the methane rich gas from the .hydrogenation zone and are then fed to the hydrogen generator.

Operating temperature and pressure ranges are the same as previously given for the system described in connection with Figure l. I have found that preheating the steam to reaction temperature in vessel 60 is suflicient to convert the overall reaction in the steam-methane reaction zone from a slightly endothermic reaction to a thermoneutral and even exothermic reaction. Furthermore, while the steam conversion in the system shown in Figure 1 is of the order of 40 per cent, the steam conversion in the modified system of Figure 2 is in the neighborhood of 50 per cent. The composition of the products of the modified system remains substantially unchanged.

According to the provisions of the patent statutes, I have explained the principle, preferred construction, and mode of operation of my invention and have illustrated and described what I now consider to represent its best embodiment. However, I desire to have it understood that. within the scope of the appended claim, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

The method of making gas from carbonaceous solid fuels which comprises maintaining two separate reaction zones, the first or" which contains calcium oxide in granular form and the second of which contains carbonaceous solids in granular form, said second zone being divided into a hydrogenation section and a preheating section which intercommunicate and which are arranged in heat exchange relation with each other, maintaining said reaction zones at temperatures between 1400 and 1750 F. and at pressures which are at least those given by the empirical relationship where p is the minimum reaction pressure in atmospheres and t is. the temperature of the reaction zone in F., circulating a methane containing gas and preheated steam through said first reaction zone containing calcium oxide, the amount of oxide present in said zone being at least 250 parts by weight for each parts by weight of carbon contained in the methane containing gas, circulating at least a portion of the product hydrogen from said calcium oxide reaction zone through the hydrogenation section of the second reaction zone under fiuidizing conditions, passing steam through the preheating section of the second reaction zone under fluidizing conditions, circulating solids in the fluidized condition between said sections, recycling at least a portion of the gaseous reaction product from the hydrogenation section of said second zone together with the steam from the preheating section through said first reaction zone as the aforementioned methane containing gas and preheated steam, respectively, and recovering at 9 10 least a portion of the gas produced in one of said FOREIGN PATENTS zones- Number Country Date EVERETT GORIN- 491,453 Great Britain Sept. 2, 1938 519,246 Great Britain Mar. 20, 1940 mmmes one! in the Patent 6 522,640 Great Britain June 24, 1940 N b UNITEILSTATES PATENT Date OTHER REFERENCES ame 32 3 Williams 5, 1933 19lialbaeh, (5Jh1ert8nca1 Engmeermg, January 2,506,317 Rex May 2, 1950 4 Pages 2,609,283 Kalbach Sept. 2, 1952v

Claims (1)

1. 3.41X10-4(T-1431)2

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