US3647379A

US3647379A - Method of gasifying water-containing coal

Info

Publication number: US3647379A
Application number: US852430A
Authority: US
Inventors: Werner Wenzel; Hermann Schenck
Original assignee: Rheinische Braunkohlenwerke AG
Current assignee: Rheinbraun AG
Priority date: 1968-08-22
Filing date: 1969-08-22
Publication date: 1972-03-07
Anticipated expiration: 1989-03-07
Also published as: DE1796050A1

Abstract

For gasifying coal, a coal-water mixture is pumped in the form of a viscous mass into a treating chamber where the mixture is heated, causing, in immediately successive steps and in said chamber, first, dehydration of the mixture by vaporizing its water content, second, gasification thereof and, third, endothermic reaction of the products precedingly obtained by the heat treatment.

Description

United States Patent Wenzel et al.

[ Mar. 7, 1972 [54] METHOD OF GASIFYING WATER- CONTAINING COAL [72] Inventors: Werner Wenzel; Hermann Schenck, both of Aachen, Germany 1 Assigneel Rheinische Braunkohlewerke A.(1.,

Cologne. Germany [22] Filed: Aug. 22, 1969 211 Appl. No.: 852,430

[30] Foreign Application Priority Data Aug. 22, 1968 Germany ..P 17 96 050.8

52] u.s.c1 ...48/202,48/92,48/99 [51] lnt.Cl ..Cl0j3/00,C10j3/46 [5s] FieldofSearch ..48/73,99,92,202,206,210, 48/197, 226, DIG. 7; 23/284, 260, 262, 212 B, 212,

[56] References Cited UNITED STATES PATENTS Royerson et al ..48/202 2,485,875 10/1949 Gorin et al. ..48/206 X 2,659,668 11/1953 Mayland 2,768,935 10/1956 Watkins... 1,392,788 10/1921 Paris, Jr... 1,592,860 7/1926 Leonarz 1,592,861 7/1926 Leonarz 3,533,739 10/1970 Pelczarski et al. ..48/92 X FOREIGN PATENTS OR APPLICATIONS 465,548 5/1937 Great Britain ..48/92 Primary Examiner-Joseph Scovronek Attorney-Edwin E. Greigg [57] ABSTRACT For gasifying coal, a coal-water mixture is pumped in the form of a viscous mass into a treating chamber where the mixture is heated, causing, in immediately successive steps and in said chamber, first, dehydration of the mixture by vaporizing its water content, second, gasification thereof and, third, endothermic reaction of the products precedingly obtained by the heat treatment.

9 Claims, 2 Drawing Figures METHOD OF GASIFYING WATER-CONTAINING COAL BACKGROUND OF THE INVENTION This invention relates to a method of and apparatus for gasifying water-containing coal or the like.

Coals used for obtaining combustible gases often have a very high water content. Thus, brown coal at the time of its recovery from deposits may contain 50-60 percent of water. Other coals may be dry in their deposits, but are recovered from open pits by a flushing process resulting in a coal-water mixture of 40-50 percent water.

In order to gasify coal having such substantial water content, the coal-water mixture has heretofore been first subjected to a separate drying step for dehydrating the wet coal by separating the water therefrom. Thereupon, the dry coal has been introduced into a reaction chamber for heat treatment under elevated temperatures resulting in the generation of combustible gases and coal residue.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to provide an improved method and apparatus for practicing the same to permit a simple and economical gasifying of water-containing coal without the necessity of subjecting the coal-water mixture to a separate prior drying or water-separating step.

It is a further object of the invention to provide an improved method and apparatus for practicing the same to utilize directly the water vapors, obtained during the dehydration of the coal, in aiding the endothermic reaction following gasification of the dried coal.

Briefly stated, according to the invention the coal-water mixture is introduced into a reaction chamber as a viscous or fluid mass. In the reaction chamber the mixture first loses its water content by vaporization and then the vapor is reduced directly with the solid gasifiable coal components while a combustible gas is generated. Thus, the water of the coal-water mixture itself is utilized in the gastifying process.

The invention will be better understood, as well as further objects and advantages will become more apparent, from the ensuing detailed specification of two exemplary embodiments taken in conjunction with the drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic side elevational view of a first embodiment of the apparatus according to the invention; and

FIG. 2 is a schematic side elevational view of a second embodiment of the apparatus according to the invention.

DESCRIPTION OF THE FIRST EMBODIMENT Turning now to FIG. 1, the embodiment illustrated therein is particularly adapted for the treatment of a mixture of brown coal and approximately 60 percent of water. This mixture is introduced into the apparatus through a hopper 13. Immediately adjacent the outlet of hopper 13 there is disposed a piston pump generally indicated at 11 having a reciprocating piston 12. Downstream of the hopper 13 there is disposed a check valve assembly generally indicated at 14 having a housing 14a, a reciprocable ball 15, a spring 16, a spring seat disc 17 and a valve seat 14b formed in the valve housing 14a. The spring 16 urges the ball against the valve seat 14b in opposition to the feeding force exerted to the coal-water mixture 30 by the pump 11. Thus, during operation of the latter, pressure strokes of piston 12 cause a downstream displacement of ball 15 so that the mixture 30 may pass through the valve opening contoured by valve seat 14b, whereas during return strokes of piston 12, the ball 15, by virtue of spring 16, is in its seat preventing backflow and maintaining pressure of the mixture downstream of valve assembly 14.

A valve 14 is joined in the downstream direction by a connecting conduit 18 which continues in one or several reaction tubes 20 (only one shown) surrounded by a jacket or heating chamber 19. The latter has an inlet 22 for admitting, and an outlet 23 for discharging, a heating medium. The heating chamber 19 is joined by a separating chamber 25 by means of a conduit 24. The separating chamber 25 has at its upper end a gas discharge outlet 26 provided with a control valve 27. At the lower end of the separating chamber 25 there is disposed, for the discharge of solid, nongasifiable products, an outlet 28 controlled by a pair of sliding gates 29.

THE METHOD PRACTICED BY THE FIRST EMBODIMENT In operation, the water-coal mixture 30 is introduced into the apparatus shown in FIG. 1 through the hopper 13. By means of reciprocating piston 12, the mixture is urged as a viscous mass against the ball 15 of the check valve 14. As the ball 15 yields and is unseated downstream, the mass is advanced through check valve 14 and the connecting conduit 18 and is introduced as mixture 31 into the reaction tube 20. Through the inlet 22 there is introduced into the heating chamber 19 a fluid heating medium which, for example, may be high-temperature helium taken from the cooling system of a nuclear reactor. It is also feasible to use a part of the obtained combustion gases for furnishing the necessary heat, Subsequent to the heat exchange in chamber 19, medium is discharged therefrom through the outlet 23. By virtue of heating the reaction tube 20, the mixture 31 forced thereinto is first dried to obtain a mass of dry coal 32. Thereafter, the dry coal is gasified and reacted upon in the reaction tube 20. The products of the reaction, i.e., gas 34 and the residue 33 which is mostly coal ash-are introduced into the separating chamber 25 through the connecting conduit 24. The gas 34 is taken out from the chamber 25 through the outlet 26 in a rate determined by control valve 27. The residue 33 accumulating at the bottom of the separating chamber 25 is discharged through outlet 28 by alternately opening and closing the dual sliding gate 29.

DESCRIPTION OF THE SECOND EMBODIMENT Turning now to the apparatus shown in FIG. 2, the coal water mixture 42 is fed through a hopper 41 and forced through a conduit 44 by a rotary pressure pump 40 having a worm 43. It is seen that in this embodiment the feeding means does not contain a valve assembly (such as valve assembly 14 in the first embodiment): a backflow of material is nevertheless prevented by an appropriate design of the cross section and length of conduit 44 for generating a sufficient frictional resistance.

The conduit 44 ends, with an extension 53, in a treating chamber 45 where both the gasification and separation take place as hereinafter described.

At the upper lateral portion of the chamber 45 there is provided an outlet 46 through which the residue is admitted into a collecting tank 47. The latter is at its lower end providing with a sliding gate 48 which, similarly to the gate 29 of FIG. 1, may be designed as a dual gate. The residue may be discharged from the tank 47 upon operation of the gate 48.

At the upper terminus of the reaction chamber 45 there is provided a gas discharge nipple 49 containing a control valve 40 for permitting a metered removal of the gas obtained from the coal during the reaction process.

The heat necessary for raising the temperature of the coalwater mixture for the purpose of vaporizing the water, for decomposing the coal and for performing an endothermic reaction, may contact the mixture directly or indirectly. It is noted that in the first embodiment (FIG. 1) such heat treatment of the coal is indirect inasmuch as the heating medium circulated through jacket 21 does not directly contact the material to be treated. In the apparatus according to the second embodiment (FIG. 2), however, the heat exchange takes place in chamber 45 by virtue of a direct contact between the heating medium and coal-water mixture introduced into chamber 45 through conduit 44. For effecting the aforenoted direct contact, at the base of the chamber 45 and in the sidewall thereof there are provided, respectively,

ports

51 and 55 associated with

respective control valves

52 and 56. Through these ports-one serving as an inlet and the other as an outleta heating medium, such as molten metal, preferably molten lead, may be circulated.

THE METHODS PRACTICED BY THE SECOND EMBODIMENT According to a first method of practicing the invention by means of the apparatus shown in FIG. 2, the heating medium (molten metal, such as liquid lead) circulates through the chamber 45 in an upward direction. Thus, port 51 serves as an inlet, while port 55 serves as an outlet for the molten lead. Since the material 44 introduced into chamber 45 at the lower portion thereof also proceeds upwardly, the flow of material 44 and that of the heating medium, i.e., the molten lead, are codirectional. The temperature of the molten lead is, e.g., I000 C. upon introduction through port 51 and is cooled to, e.g., 750 C. after heat exchange and upon discharge through port 55. The level of the molten lead bath 57 is indicated at 54. Externally of the treating chamber 45 the temperature of the lead is again increased (for example, by means of heat taken from a nuclear reactor) and the lead may be submitted to a purifying process during which, for example, sulphur may be used.

The coal-water mixture introduced into the lead bath 57 through the extension 53 is promptly dried and gasified, whereby the separated gases cause in the lead bath a strong turbulence of the coal and the products of gasification. Hereby an intensive reaction takes place between the water vapor, the carbon dioxide (obtained from the degasification) and the carbon, while permanent combustible gases are generated. These gases 58 accumulate in the upper portion of the reaction chamber 45 above the lead bath 57 and are discharged through the outlet 49. The residue 59mostly coal ashsettles on the .top of the lead bath 57 and flows over to tank 47 from which it is discharged upon operation of gate 48.

A second method of practicing the invention by means of the apparatus shown in FIG. 2 will now be described.

In process including a counterflow-type heat exchange, it has been assumed heretofore that, from both technical and economical points of view, the best results could be obtained when the heat exchange was performed indirectly through separating walls. Stated in different terms, the medium carrying the heat, on the one hand,,and the material or material mixture to be heated, on the other hand, do not enter into direct contact with one another. A counterflow-type heat exchange with no direct contact may be effected by means of the apparatus of FIG. 1.

If a heat exchange by direct contact between the two material flows is to be effected, a counterflow process in general has not been deemed possible because the fluid medium which is used as heat carrier often carries away material particles from the opposite flow unless the latter meets certain conditions with respect to particle weight and volume. In case of coal-water mixtures of the type with which this invention is concerned, such conditions are not met. For this reason, raw brown coal, which is particularly adapted for use in the present invention, has been heretofore directly contacted with hot gases only by means of concurrent flow process.

Contrary to expectations based on processes performed ac- I cording to the prior art, it has been found that in case a molten metal, preferably liquid lead, was used as a heat-carrying medium, the transfer of heat by direct contact to the mixture could be performed in a counterflow process without experiencing the aforenoted difficulties.

According to a second method of practicing the invention by means of an apparatus shown in FIG. 2, a direct contact heat exchange by counterflow is effected. For this purpose, the molten lead passes through the chamber 45 downwardly, that is, in a direction opposing the upward flow of the coal mixture introduced into the lower portion of chamber 45 from conduit 44. To effect a downward flow of the lead bath 57, the molten lead is introduced into chamber 45 through port 55 and discharged from chamber 45 through port 51. It was found, as noted hereinabove, that the molten lead did not carry with it particles from the opposed flow. This disadvantage being absent, the process may fully benefit from a dual advantage of the counterflow contact. In the first place, the heat exchange is more efficient than in the case of a contact between coinciding flows: It has been found that the molten lead, which upon its entering the treating chamber 45 through port 55 had a temperature of 1000 C. cooled to about 450 C. upon its discharge through port 51. In the second place, the different temperatures along the flow path of the molten lead are best suited for the optimal temperature requirements during the successive different heat treatments to which the upwardly flowing coal material is exposed at different heights. Thus, following the introduction of the coalwater mixture 44 into the lower portion of treating chamber 45, the first step is to withdraw the water from the mixture. This is effected by vaporizing the water. The temperatures for this step may be relatively low: The temperatures of 450-650 C. of the lead bath in this part of the chamber (close to discharge port 51) are well suited for this purpose. As the dehydrated coal proceeds upwardly, it is submitted to a gasification step. In this region of the lead bath 57 the prevailing temperatures are 650-750 C. Finally, adjacent the upper level 54 of the lead bath an endothermic reaction takes place which requires the high temperatures of approximately 750- 1,000 C. prevailing in the upper part of the lead bath.

In all other aspects the precedingly described method is identical to the method in which direct contact between codirectional flows takes place, identified hereinabove as the first method for practicing the invention by means of an apparatus shown in FIG. 2.

As set forth in the foregoing description relating to both embodiments according to FIGS. 1 and 2, the dehydration of the coal is carried out immediately preceding the gasification and successive endothermic reaction and all the water vapors obtained as a result of said dehydrating step participate in the endothermic reaction and form part of the equilibrium thereof. It may be consequently stated that at given gasifying temperature and pressure, the amount of water vapors determines substantially the composition of the obtained gas which may be, for example, a mixture of two or more of the following gases in varying proportions: hydrogen, carbon monoxide, carbon dioxide and methane.

The quantity of generated water vapors, in turn, is determined by the water content of the coal-water mixture. The pumpability of this mixture, as well as the frictional resistances opposing the flow of the mixture through the conduits to the treating chambers are functions of the mixture consistency which, again, is determined by its water content. It was found, for example, that a mixture of brown coal and water may be pumpable when the water content is upward of approximately 20 percent.

It follows from the foregoing that different types of pumps may be selected to advance mixtures of different consistency.

If necessary, the aforenoted frictional forces may be reduced by adding oil or other lubricant to the coal-water mixture, particularly to marginal regions that are close to or in contact with the walls of conduits. It is advantageous to add such lubricants only to the marginal zones of the coal-water mixture for keeping the required quantities of such lubricants small. Thus, the lubricants may be introduced into the advancing mixture through orifices in the conduit wall.

The determination of temperature, pressure and water vapor conditions for obtaining a predetermined composition of the final gas product is well known from the thermodynamics of this process. Thus, by selecting the proper temperature and pressure conditions and, in particular, by using a coal with a determined initial water content, gases for the reduction of iron ore, gases for various gas syntheses, or high-calorie gases for heating purposes may be obtained.

That which is claimed is:

l. A method of gasifying solid fuel with high water content, comprising the following steps:

A. circulating molten lead as a heat-carrying medium through a treating chamber,

B. forming a bath of sad circulating molten lead in said treating chamber, C. heating said molten lead externally of said treating chamber, D. introducing a coal-water mixture into the molten lead bath, E. effecting in said molten lead bath as a result of direct contact l. a dehydration of said mixture by vaporizing its water content and 2. an immediately successive gasification of the dehydrated coal and F. discharging from said treating chamber the gases and the solid residues obtained as a result of step (E). 2. A method as defined in claim 1, wherein said mixture is introduced into said bath in a viscous condition.

3. A method as definedin claim 1, wherein said mixture is introduced into said bath in a fluid condition.

4. A method as defined in claim 1, wherein said molten metal and said mixture are in a codirectional flow in said chamber.

5. A method as defined in claim 1, wherein said molten lead and said mixture are in a counterflow in said chamber.

6. A method as defined in claim 1, wherein said mixture is introduced into said chamber through a tubular conduit; a lubricant is added to said mixture prior to step (D) for reducing the frictional resistance encountered in said tubular conduit.

7. A method as defined in claim 1, wherein said solid residues accumulate on the top of said bath and are discharged therefrom.

8. A method as defined in claim 5, wherein the temperature of said molten lead bath in said chamber increases in the direction of flow ofsaid mixture.

9. A method as defined in claim 1, wherein step (E)(2) includes an extraction of gases from said dehydrated coal and an immediately successive endothermic reaction of said gases with the water vapors obtained as a result of step (E)( l

Claims

2. an immediately successive gasification of the dehydrated coal and F. discharging from said treating chamber the gases and the solid residues obtained as a result of step (E).
2. A method as defined in claim 1, wherein said mixture is introduced into said bath in a viscous condition.
3. A method as defined in claim 1, wherein said mixture is introduced into said bath in a fluid condition.
4. A method as defined in claim 1, wherein said molten metal and said mixture are in a codirectional flow in said chamber.
5. A method as defined in claim 1, wherein said molten lead and said mixture are in a counterflow in said chamber.
6. A method as defined in claim 1, wherein said mixture is introduced into said chamber through a tubular conduit; a lubricant is added to said mixture prior to step (D) for reducing the frictional resistance encountered in said tubular conduit.
7. A method as defined in claim 1, wherein said solid residues accumulate on the top of said bath and are discharged therefrom.
8. A method as defined in claim 5, wherein the temperature of said molten lead bath in said chamber increases in the direction of flow of said mixture.
9. A method as defined in claim 1, wherein step (E)(2) includes an extraction of gases from said dehydrated coal and an immediately successive endothermic reaction of said gases with the water vapors obtained as a result of step (E)(1).