US2497898A - Method of changing the composition of a combustible gas by diffusion - Google Patents

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' G. v. MOGURL ZALQKWQ METHOD OF CHANGING THE COMPOSITION OF A COMBUSTIBLE GAS BY DIFFUSION Filed Nov. 16, 1946 CGOLEQ 'Lm MET'E HEATER 4o Patented Feb. 21, 1950 I METHOD OF CHANGING THE COMPOSITION OF A COMBUSTIBLE GAS BY DIFFUSION Gilbert V. McGurl, Newark, N. J., assignor to Koppers Company, Inc., Pittsburgh, Pa., a cor-;

poration of Delaware Application November 16, 1946, Serial No. 710,327

9 Claims. (Cl. 48-197) This invention relates to gas diffusion for rearranging the composition of fuel gases. More particularly the invention relates to the revision of the composition of coke oven gas by diffusion producer gas.

daily or seasonal demand cycle.

properly burn such gas.

when using producer gas as a sweep gas and 5 is flowing. The sweep gas is used to control the thereby revising both the coke oven gas and the pressure distribution of the two gases on opposite sides of the boundary. The sweep gas has The carbonization of coal in byproduct coke a. flow through the boundary into the feed gas ovens produces a comparatively uniform quality and also acts to sweep from the face of the boundof gas which, when the aromatic hydrocarbons ary the hydrogen and other gases that have are removed, has a heating value of 530 to 580 penetrated through the boundary from the feed B. t. u. and a comparatively low specific gravity. gas side by diifusion. This gas is being widely used in cities for heat- The pressure distribution of the feed and ing purposes. The construction of a coke oven sweep gases on opposite sides of a boundary inbattery requires that all of the ovens be operated volves several factors: simultaneously so that the total or average out- First, the size of the pores which determine put of gas is quite uniform and cannot be conthe porosity of the boundary or diaphragm. For veniently and economically varied to follow the the revising of fuel gas, the boundary should have a pore size which is many times larger than the To take care of this variation in gas demand, mean free path of the gas molecules. This mean it is customary to supplement the coke oven batfree path of the molecules is the average distery with water gas generators and then to mix tance which a molecule travels before colliding the water gas with the coke oven gas to meet with another or an adjacent molecule. Dependthe demand. Some mixes of coke oven gas and ing upon the length and the desired resistance to water gas are not satisfactory because the B. t. u. flow of the gas through the pore, the width or values may vary considerably and the gravity of diameter of the pore may be from 1 to 10,000 the gas will also vary quite widely. The gas times the mean free path of the molecule. burning appliances do not operate satisfactorily se n th pressure of t gas streams t opwith these varia yp o a 50 that it is posite sides of the boundar or the average presportant to deliver a comparatively uniform qualsure differential across the pores of the boundary, ity of gas for city distribution. It has been found or across the boundary. that when the specific gravity of the domestic Third, the area of the boundary, which takes gas is quite uniform, then the appliances will into consideration the pressure differentials at the inlets or outlets of the boundary, or the aver- The most desirable method of changing the age pressure difierential over the entire area of composition of coke oven gas is to vary the hydrothe boundary. When the feed and sweep gas gen content. When hydrogen is removed from streams flow concurrently or in the same directhe gas, the specific gravity and the B. t. u. value tion across the opposite faces of the boundary, are increased. Therefore coke oven gas may be the pressure differential at the entrance end is revised to obtain the desired heating value and dependent on the pressure differential of the Another object of' the invention is to provide a method of separating hydrogen from coke oven gas by diffusion. In the diffusion method of hydrogen separation from coke oven gas, the hydrogen passes through a porous boundary as the gas flows in a continuous stream across one face of the boundary. The diffusion is substantially aided if another gas commonly termed a sweep gas" is movedacross the face of the boundary opposite the face across which the coke oven gas two inlet gas streams, and there will be a gradual decrease or increase of the pressure differential as the streams advance across the boundary area, depending upon whether the pressure drop due to flow resistance in the sweep stream is more or less than the pressure drop in the feed stream. If the feed and sweep gas streams flow in countercurrent direction along the faces of the boundary, then the pressure differential across the boundary at the entrance end of the sweep gas is at its maximum because the resistance to flow and the diffusion of the feed gas through the boundary has altered and lowered the pressure of the feed gas while the pressure of the sweep gas is at its maximum. Therefore, with countercurrent flow the diffusion rate will be the highest at the entrance end of the sweep gas, and lowest at the entrance end of the feed gas.

Fourth, the hydrodynamic flow of the sweep gas through the pores of the boundary. This hydrodynamic flow is the free flow of sweep gas through the boundary pores not due to diffusion but due to the pressure differential across the boundary.

I have found that a low B. t. u. producer or blast furnace gas which has a radically different composition than the composition of coke oven gas is an excellent sweep gas for facilitating the separation or redistribution of hydrogen in coke oven gas. Producer and blast furnace gases have comparatively high specific gravities so that there is relatively small amount of diffusion of these gases through the boundary into the coke oven gas. On the other hand, the low specific gravity hydrogen readily passes through the boundary and is swept away from the boundary by the high specific gravity gas. If hydrogen is passed through the boundary from coke oven gas into producer or blast furnace gas, the addition of hydrogen to these gases is very advantageous in that it lowers the specific gravity of the gases and substantially increases the B. t. u. heat values.

Accordingly, a further object of the invention is to utilize producer or blast furnace gas as a sweep gas in the diffusion separation of hydrogen from coke oven gas.

In accordance with the relative volumes of sweep gas and feed gas being revised, it is desirable to maintain a fixed difierential pressure on opposite sides of the boundary, this differential pressure across the boundary being high if the boundary is only slightly porous and being comparatively -low if the boundary is quite porous. The temperature of the gases flowing across the boundary should be maintained above the dew points of any constituents in the gases and the velocity of the sweep gas should be such that it will sweep away from the face of the boundary the constituents difiusing through the boundary.

The pressure distribution of the sweep and feed gases with reference to the porous boundary of a diffusion apparatus depends upon the specific gravity of the gases, the pressure differential across the boundary, the velocity of movement of the gases across the face of the boundary and the area of the boundary. It is possible by the control of these various features to obtain a selective separation of hydrogen from coke oven gas.

Typical compositions of coke oven, producer and blast furnace gases are shown in the following table.

My tests have shown that at the same time that the coke oven gas is being revised, the sweep of a diffusion apparatus.

gas may also be revised so that a large number of different types of gas may be produced. The revised producer or blast furnace gas which is enriched with the hydrogen and hydrocarbons of the coke oven gas is a good heating gas for coke ovens. Further, the revision of the sweep gas may be controlled to distribute the hydrogen and carbon monoxide in the ratio of molecular volumes of 1:1 or 2:1 to provide an excellent synthesis gas for the hydrogenation of carbon monoxide in the Fischer-Tropsch reaction.

A still further object of the invention is to provide a method of changing the composition of coke oven gas with a producer sweep gas to simultaneously upgrade the producer gas into a predetermined type of gas.

With these and other objects in view, the invention consists-in the method of revising the composition of gas by diffusion as hereinafter described and particularly defined in the claims.

The various features of the invention are illustrated in the accompanying drawing which is a diagrammatic fiow sheet of an apparatus in which the preferred method of revising coke oven gas by diffusion may be carried out.

Coke oven and producer gases are generally maintained at a. comparatively low pressure (6 to 12 inches of water pressure). Accordingly the diffusion process for revising coke oven gas is carried out at substantially atmospheric pressure, that is, these gases will have a sufficient pressure to control their flow through the diffusion apparatus.

Referring to the drawing, the diifusion revision of coke oven gas may be carried out as follows:

Coke oven gas is introduced through a line 10 and flow regulator [2 into a meter 14 to establish a definite flow rate. The gas passes through a heater 56 which is preferably heated by steam to a temperature above the condensation temperature or dew point of any of the constituents in the gas at the boundary. From the heater t6 the gas passes through a line I8 into a chamber 20 This gas is then distributed throughout the area of the chamber 20 and passes through tubes 22 which connect with porous diffusion boundaries 24 that form a continuation of the tubes 22. The streams of coke oven gas pass through the diffusion boundary tubes. then through tubes 26 into a chamber 28 and thence flow through a line 30 into a cooler 32. The cooler 32 is preferably cooled by water or other cooling medium in order to standardize the temperature of the gas so that it may flow through a line 34 through a meter 36 to measure its volume.

The producer sweep gas is introduced into the apparatus through a line 38 and flow regulator 40 to establish a definite predetermined flow rate of producer gas. The producer gas then passes through a meter 42 into a heater 44 where it is heated by steam to raise it to substantially the same temperature as the coke oven gas as maintained by the heater I6. This preheated gas then passes through a line 46 to a line 48 or a line 50 in accordance with the manner in which the sweep gas is circulated through the diffusion apparatus. If the sweep gas is to pass through the diffusion apparatus in a parallel concurrent stream with the feed gas then the sweep gas will enter a chamber 52 of the diffusion apparatus through the line 48. The sweep gas will then be distributed throughout the chamber 52 and pass upwardly through the tubes 54 around the porous boundary tubes 24. After passing across the porous boundaries,the sweep gas enters a chamber 56 and then flows out through a line 58 through a cooler 50 to be conditioned for passing through a line 62 into a meter 64. If the sweep gas is-to pass across the porous boundaries in a stream parallel to the coke oven gas stream but countercurrent to the flow of the coke oven gas, then the sweep gas will pass through the line 50 to the line 58, thence into the chamber 56, then down across the porous boundary tubes 24 into the chamber 52, and out through the line 48. From the line 48 the gas will pass through the line 66 to the line 58 and thence through the cooler 60 and meter 64. To assist in obtaining a good temperature condition for diffusion, the tubes 54 are surrounded by a heating jacket 68 into which steam is introduced through an inlet and water of condensation taken out through a line 12.

The pressure distribution across the porous boundary tubes 24 is maintained by means of a regulating valve 14 in the sweep gas line 58 and a regulating valve 16 in the feed gas line 30. The flow regulators l2 and 40 in the coke oven and producer gas lines respectively control the flow rate of coke oven gas and producer gas. The pressure of the gas flowing across the opposite sides of the porous barrier of the difiusion tubes is controlled by the valves I4 and 16. The valve 74 is controlled to maintain a pressure of the sweep gas on the outside of the tubes 24 slightly higher than the pressure of the feed gas within the tubes 24. This pressure difierential then controls the hydrodynamic flow of sweep gas through the porous tubes and the difiusion of constituents from one gas stream into the other gas stream. The pressure differential is small but is suflicient to maintain a hydrodynamic flow and definite diflusion through the diaphragm.

From Table I it will be seen that the hydrogen content of coke-oven gas is much higher than the hydrogen content of producer gas or blast furnace gas. Hydrogen has a very much lower specific gravity than carbon dioxide, carbon monoxide, nitrogen or the hydrocarbons in coke oven gas. Since the rate of difiusion through a porous diaphragm is roughly inversely proportional to the square root of the molecular weights of the gases, the hydrogen will have the highest velocity of any of the constituents in the feed and sweep gases. Therefore, the revision of coke oven gas when using producer gas as a sweep gas will consist principally in the redistribution of hydrogen by diffusion through the porous boundary. By maintaining a higher pressure on the sweep gas side of the boundary than on the feed gas side of the boundary, the free flow will be from the sweep gas into the feed gas. On the other hand, the coke oven gas constituents tend to set up a counterdiffusion through the boundary which is opposed by the free flow and diffusion of the constituents of the producer gas through the porous boundary. The net result is an exchange of constituents passing through the boundary from each stream into the other. However, the higher difiusion velocities of the lighter constituents in the coke oven gas, particularly hydrogen, will result in a net addition of hydrogen to the producer gas from the coke oven gas and a small redistribution of other constituents between the two gas streams.

In Tables II to VII inclusive are shown data of the revision of a coke oven gas, of substantially the composition cited above, through a porous boundary in which tubes are used which have a TABLE II Feed (ooke oven gas) in- 643 C. F. H. (coke oven gas) out- 708 C. F. H. Sweep (producer gas) in- 520 These 1 out- 455 Sweep Feed In Out In Out Per cent Per cent Per cent P H; by Conductivity Cell. 10. 5 29. 5 61. 7 Orsat:

N; (By difference). 53. 2 38. 9 4. 6 20. 6

Specific Gravity 0. 870 0.097 0. 370 0. 538

TABLE III Feed (coke oven gas) in= 643 C. F. H. (coke oven gas) out= 816 C. F. H. Sweep (Producer Gas) in= 530 C. F. H. out- 357 C. F. H.

Sweep Feed In Out In Out Per cent Per cent Per cent Per cent 11 by Conductivity Cell. 10. 5 2s. a 51. 7 39. 2

rsa

00 4.9 3.7 1.6 2.6 I11uminants.. 0. 9 0. 7 3. 0 2. 2 O2 0. 5 1. 0 0. 6 l. 7 112... 10.8 30.1 55.6 39.8 C0 28.5 21.1 5.6 12.8 CH4 1.2 4.5 29.0 13.4 N. (By diflerence) 53. 2 38. 9 4. 6 27. 5

Specific Gravity 0.870 0. 699 0. 370 0. 576

TABLE IV Feed (coke oven gas) in=l87 C. F. H

(coke oven gas) out=307 C. F. H. Sweep (Producer Gas) in=476 C. F. H. out-=356 C. F. H.

Sweep Feed In Out In Out Per cent Per cent Per cent Per cent H2 by Conductivity Cell- 10. 5 23. 1 54. 3 31. 8 Orsat:

4. 0 3. 8 1. 7 2. 8 0. 0 0. 0 2. 8 2. 2 0.8 1. 0 1. 5 1. 3 11. 8 22. 1 53. 9 31. 6 m. 7 24. 6 6. 7 15. 8 0. 0 2. 0 17. 2 16. 1 OiHs 1. 5 1. 8 2. 9 0. 0 N, (By difference)..- 58. 2 44. 7 l3. 3 30. 2

Specific Gravity 0. 874 0. 783 0. 431 0. 637

ide to hydrogen in the reformed sweep gas may be quite widely varied. In accordance with the data of Tables IV and V the molecular ratios of hydrogen to carbon monoxide in the revised producer gas are approximately 1:1, while in accordance with the data of Tables VI and VII the molecular ratios of hydrogen to carbon monoxide in the revised producer gas are substantially 2:1. Such gases are well suited as synthesis gases for the Fischer-Tropsch process. Although nitrogen is present in these gases, it has been found that a high percentage of nitrogen is not detrimental to the catalytic hydrogenation of carbon monoxide with a catalyst in the Fischer-Tropsch reaction.

In the apparatus illustrated in the drawing, seven porous boundary tubes have been used. It is apparent, however, that the apparatus may be designed to use any desired number of tubes and the porous area may be varied in accordance with the gases being treated in order to get the desired diffusion separation of products. In the diffusion operation there is always an exchange of gas from one side of the boundary into the gas at the' other side of the boundary but the rates of diffusion of the gaseous constituents may be controlled and modified in order to get a comparatively selective separation of the desired components.

The preferred form of the invention having been thus described, what is claimed as new is:

1. A method of simultaneously changing the composition and specific gravity of coke oven gas and producer gas comprising: feeding coke oven gas as a stream along one side of a porous boundary, passing producer gas in a stream to sweep across the opposite side of the boundary and controlling the pressure differential and the rate of flow of the gases on opposite sides of the boundary of a predetermined area to cause a movement of hydrogen by difiusion through the boundary to the producer gas and nitrogen and carbon monoxide to the coke oven gas so that the specific gravity of the coke oven gas will be increased in the range of 42 to 50%.

2. The method defined in claim 1 in which the gases on opposite sides of the boundary are conducted in concurrent paths.

3. The method defined in claim 1 in which a slightly higher pressure is maintained on the sweep gas side of the boundary than on the coke oven gas side of the boundary to cause a hydrodynamic flow of producer gas through the pores of the boundary.

4. The method defined in claim 1 in which the composition of the coke oven and producer gases are brought to a finished composition in a single pass across the boundary 5. The method defined in claim 1 in which the pore size of the boundary is in the range of one to one hundred times larger than the mean free path of the coke oven gas molecules.

6. A method of simultaneously changing the composition and specific gravity of coke oven gas and producer gas comprising: feeding coke oven gas as a stream along one side of a porous boundary, passing producer gas as a stream to sweep across the opposite side of the boundary, controlling the pressure differential and the rate of fiow of the gases on the opposite sides of the boundary of a predetermined area to increase by diffusion the hydrogen content of the producer gas and the carbon monoxide and nitrogen content of the coke oven gas while increasing the specific gravity of the coke oven gas in the range of 42 to 50 '7. A method of simultaneously changing the composition and specific gravity of coke oven gas and producer gas comprising: feeding coke oven gas as a stream along one side of a porous boundary, passing producer gas as a stream to sweep across the opposite side of the boundary, controlling the pressure differential and the rate of flow of the gases on the opposite sides of the boundary of a predetermined area to increase by diffusion the hydrogen content of the producer gas and the carbon monoxide and nitrogen content of the coke oven gas while decreasing the specific gravity of the producer gas in the range of 12 to 20% 8. A method of increasing the specific gravity of coke oven gas while converting a producer gas into a Fischer-Tropsch synthesis gas comprising: feeding a coke oven gas having a gravity of approximately O.4 as a stream along one side of a porous boundary, passing a producer gas having a specific gravity of approximately 0.9 along the opposite side of the boundary as a sweep gas, controlling the rate of flow and pressure differential of coke oven gas to producer gas on opposite sides of a boundary of a predetermined area to increase the hydrogen content of the producer gas by diffusion in the range of two volumes of hydrogen to one volume of carbon monoxide while simultaneously increasing the specific gravity of the coke oven gas and decreasing the specific gravity of the producer gas in the range of 25 to 28%.

9. The method defined in claim 8 in which the coke oven and producer gases are caused to flow on opposite sides of the boundary in countercurrent paths.

GILBERT V. McGURL.

REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS 2,255,069 Maier Sept. 9, 1941

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