US2595979A - Underground liquefaction of coal - Google Patents

Description

May 6, 1952 E. F. PEVERE ET Al. 2,595,979

UNDERGROUND LIQUEFACTION OF COAL Filed Jan. 25, 1949 Patented May 6, 1952 UNITED STATES PATENT ofi-Fics UNDERGROUND LIQUEFACTION OF COAL Ernest. F'. Revere,` Beacon, and Georgev vB. Arnold,

Glenham.. N.v Y.,. assignors to The Texas Company; New York, N. Y., a corporation of Del- Application January 25, 1949, Serial N o. 72,582`

( Cl. 19E-53) 2' Claims. l.

` This invention relatestoa process for the recovery of coal substance from. underground deposits in the formv of a liquid In oneof. its more specific aspects, this invention relates tov the underground Iiquefaction oi. a liqueable fraction. of a coal deposit. by hydrogenation to produce a liquid extract suitable for use in the. production ofmotor fuels.

In accordance with the present invention, coal in an underground deposit is hydrogen-ated in situ by contact with a. hydrogenating agent. The hydrogenation is carried out. at an elevated temperature and pressure, which may be controlled from above ground. The. hydrogenation reaction produces a liquid product which is readily recovered` as a relatively heavy oil. The crude liquid product may be subject to further hydrogenation and refining operations. to produce motor fuels and other desired products after recovery from the undergroundformation.

The hydrogenating. agent used in the present process may be free hydrogen or an organic compound capable of liberating hydrogen. Hydroaromatics, such as hydrogenated naphthalenes, e. g., tetralin and decalin, and heavy oils obtained by hydrogenation of` coal are suitable hydrogenating agents. Hydroaromatic oils act as solvents in the liquefaction of coal, due primarily to their ability to transfer hydrogen to the coal.

In general, from about 70 to about 90 per cent by weight of av bituminous coal may be liqueed by hydrogenation, the extent of the liquefaction depending largely upon the grade of the coal. Approximately 65 per cent by weight of massive or lump coal may be readilyA liquefied' by hydrogenation. The hydrogen consumption' generally' ranges from about 1.5 to about 3 percent by weight based on the Weight of the coal reacted. The liqueed coal, or extract, obtained on hydrogenation is fluid and substantially free from ash.

This liquid may be recovered from thefcoal seamY by the process of this invention in a manner analogous to the. production. of crude oil. The residual or unhydrogenated portion of the coal comprises unreacted carbon and the mineral matter or ash. The residue may also. be utilized advantageously as will be brought out hereinafter.

The process of the present invention has many advantages over prior methodsof producing hydrocarbons from coal.` The methods. of the prior art include conventional hydrogenationa of powdered coal, and methods for thev gasication of coal to produce a mixture of carbon monoxideand hydrogen followed by conversion of the carbon monoxide and hydrogen to liquidv hydrocarbons by theFischer-Tropsch synthesis.

In the conventional coal hydrogenation process, the coal is mined in the usual manner.. dried, pulverized and made into a paste by. admixing the powdered coal with a heavy oil. The paste is mixed with hydrogen and. reacted at a temperature of from about 800 to about 900' F. and at pressures ranging from about 43000. to about 10,000 pounds per square inch.

An important elementr of cost in conventional coal hydrogenati'on processes is. the cost .of preparation of the coal for hydrogenation. The. ne grinding of the coal to obtain a. powder requires the expenditure of large amounts of' power. In addition, costly high. pressure. reactors, pumps, transfer lines and related equipment. are required.

The mining of bituminous coal., for. example, is in itself a wasteful. procedure. It has been. estimated that on an overall average,v about per cent of the coal in place is recovered from the mines, the remainder being left, as supporting pillars, etc. There is another l0 per. centv loss incurred in the handlingoperations so. that` only about 55 per cent of. thecoal in place is recovered as marketable coal. In addition, a. considerable amount of methane is lost. from` every ton of coal produced. Contact with atmosphericA oxygen results in some chemical. reaction.. rendering the coal somewhat less reactive for hydrogenation.

than is the virgin coal. The recovery of. coal substance from the. deposit iby the-present. process is, therefore, comparable in eiliciency to modern mining methods..

The. present process does not. suffer from the depth limitations which are. imposed upon mining operations. At4 adepth of 5,000 feet.. for example, the temperature of' the. earths. crust is about, F'., which makes. the cost @airconditioning and Ventilating the coal seams too.4 expensive to work them by conventional mining. methods. Such underground temperatures. are an advantage of the process of the present. invention.

Another. important. advantage of this invention derives from the fact that. the unhydrogenated portion of the coal seam is left in a porous or honeycomb state whichv is. almost ideallyl suited for underground gasification. The present invention also contemplates recovery of carbon values from the unhydrogenated residue by gasication of the residue.` in situA by contact with an oxygen-containing gas. cation of coal with an oxygen-containing gas is already known inthe art.. Much diiculty has been experienced with previous methods of gasication due to the fact. that a. complicated system of passagevvays must rst be provided through the coal seam to permit passage of the oxidizing gases therethrough.. In the present process, the passageways. are provided by the removal of the hydrogenatable. portion of the coal so that a pervious massief reactivecarbonaceous material remains for the gasication reaction. The oxygen-containing. gas mayv be passed directly through this residue-without' the4 Underground gasinecessity of drilling passageways therethrough.

An object of the present invention is to provide an improved process for the recovery of coal from underground deposits.

Another object is to provide a process for the liquefaction of coal substances in underground seams.

Still another object is to provide an improved process for recovery of coal as a liquid from underground deposits.

Another specific object is to provide an improved method of recovery of coal from underground deposits, partly as a liquid hydrogenation product and partly as a gaseous product of underground gasification.

Other objects and advantages will be apparent to those skilled in the art from the following detailed description.

In the process of this invention, coal is liquefied at a temperature above about 550 F. and generally within the range of from about 550 to about 850 F. by direct contact between the virgin coal and the hydrogenating agent. Preferably the temperature is maintained within the range of 700 to 750 F. Pressures above about 1,000 pounds per square inch are suitable. The pressure may range up to about 10,000 pounds per square inch where such pressures may be used without excessive loss of hydrogen due to leakage from the coal seam. Structural limitations usually require the use of pressures in the lower portion of this range; higher pressures are desirable wherever practical.

The rate of reaction, and the reaction temperature, may be controlled by control of the pressure at which the reaction is carried out. As the pressure is increased, the rate of reaction and the reaction temperature increase; as the pressure is decreased, the rate and temperature decrease.

In carrying out the present process, a well bore is drilled into the coal seam through which the hydrogenating agent may be admitted and the resulting liquid product withdrawn. The hydrogenating agent is forced under pressure through the well bore into direct contact with the virgin coal in the underground seam. Gaseous hydrogen is preferable as the hydrogenating agent. The hydrogen permeates the residue relatively thoroughly and produces by reaction with the coal an oil which is an excellent solvent and hydrogen transfer agent. The heavy oil or liquefied coal substance obtained by hydrogenation is one of the best hydrogen carriers known at the present time. The hydrogen diffuses upwardly into the coal seam, liquefying the more readily liqueable coal substance. This liquid then drains down over the less readily liquefiable portion of the coal, thus acting as a hydrogen carrier to facilitate the liquefaction.

The reaction is initiated by raising the temperature at the coal face to the reaction temperature.

Any means of supplying heat may be used; preferable are those involving liberation of heat near the face of the coal seam by chemical means. An electrical heater may be placed in the well bore to preheat the reactants. Superheated vapors of a hydroaromatic may thus be supplied to the coal whereupon heat is transferred to the coal upon condensation of the vapors to supplement the heat liberated by the reaction. Once initiated, the exothermic heat of reaction and the heat transfer between the reactants and reaction products serve to maintain the reaction temperature.

The `well bore is preferably drilled into a low portion of the coal seam to permit the liquid product to drain down to the well bore for removal. The process is well adapted to working those seams which are inclined at an angle too steep for conventional mining. The process is particularly adapted to working those coal seams which are overlain by a relatively impervious stratum. Generally, the coal seams are overlain with a layer of clay and shale which is relatively impervious and is a good heat insulator.

The loss of hydrogen into pervious adjacent formations may often be largely eliminated by operating at high temperatures for a period of time such that some of the fusible metal salts in the formations are melted or some of the volatile metal salts associated with the coal are vaporized, thus plugging the walls of the adjacent formation. The temperature may be increased by operating at very high pressure to increase the rate of reaction and hence the rate of heat at which heat is liberated by the exothermic heat of reaction. Volatile metals may be supplied to the coal seam in the form of a concentrated solution of a soluble salt of one of the metals during the course of reaction. Halides of zinc and lead, for example, are suitable for this purpose.

A typical product obtainable by underground hydrogenation comprises 60 to 70 per cent liquid hydrocarbons and l0 to 30 per cent gaseous hydrocarbons. About 31/2 to 4 barrels of oil are obtained from each ton of coal reacted. Approximately 27 per cent of the liquid hydrocarbon fraction has a boiling range within the gasoline range that is up to 392 F., 50 per cent between 392 and 572 F. and 23 per cent above 572 F.

A solvent extraction, based on hydrogenation by hydrogen transfer, may be carried out by using one of the liquid hydrogenating agents for recovery of the coal. Among the hydrogenating agents which are suitable for this purpose are tetrahydro-naphthalene, decahydro-naphthalene, crude cresols, oil from the hydrogenation of coal, aromatic crude oil, and the like. Preferably the liquid hydrogenating agent is supplemented with gaseous hydrogen. The liquid hydrogenating agent may be injected into the coal seam and recovered therefrom either intermittently or continuously. The liquid hydrogenating agent may be injected into the upper part of the seam and the liquid product recovered from a lower portion of the seam. Appropriate passages may be provided in the coal seam for injection of the hydrogenating agent and recovery of the product. A portion of the product, preferably a heavy fraction, may be used effectively as the hydrogenating agent, most suitably after hydrogenation aboveground.

Often the coal seam is pervious due to structural anomalies, sometimes resulting from foi'- ing or faulting of the strata. The permeability of the coal may be increased by dissolution of part or all of the mineral matter, thus opening pores in the coal. A concentrated mineral acid, preferably sulfuric acid, may be used for this purpose.

A catalyst may be used for the hydrogenation reaction. Iodine is an effective catalyst for this purpose. The iodine may be employed in either the elemental state, as hydrogen iodide, or in the form of an organic compound of iodine, e. g., methyl iodide, iodoform, methyl iodoform, etc.

The accompanying drawing illustrates diagrammatically the process of this invention.

With reference to the drawing, the numeral i designates an underground seam of coal above which is a relatively impervious stratum 2, generally of clay and shale, and below which is another relatively impervious stratum 3, e. g., a layer of clay. A well bore is drilled from the surface of the earth #i to a low point in the coal seam adjacent the underlying stratum `3. Separate conduits 5 and 6 extend through the well bore into the coal seam. These conduits may be placed in any convenient manner analogous to the placement of tubing and casing in oil wells. As illustrated in the drawing, conduit 6 is placed within conduit 5 leaving an annular passageway 'l therebetween.

An enlarged cavity 8 may be formed at the terminus of the Well bore to serve as a collection chamber for liquefied coal. The conduit 5 preferably is closed at its lower end and provided with a number of perforations 9 adjacent the coal stratum as outlets for the hydrogenating agent. The hydrogenating agent is admitted to conduit 5 through pipe I6, flowing through the annular passageway 'l and the perforations 9 into the coal stratum. The liqueed coal or liquid hydrogenation product is withdrawn through pipe 6.

As the hydrogenation progresses, a porous, honeycomb-like residue i2 is left in place in the formation. The liquid resulting from the liquefaction drains away from the residue, collects in the cavity 8 and flows through pipe 6 to the surface where it may be subjected to appropriate refining methods.

Obviously, a plurality of well bores may be employed in carrying out the process, with injection of the hydrogenating agent into one or more wells and recovery of the liquefied coal from one or more additional wells. The well may be used alternately for injection and recovery, either alone or in combination with other wells.

The crude product comprises not only the liquid and gaseous hydrocarbons but also tar acids, tar bases, ammonia, carbon dioxide, carbon monoxide, water, and hydrogen sulfide. The crude product is preferably maintained under an elevated pressure of at least 100 pounds per square inch until a separation of the oil and water layers has been effected at the surface of the earth.

In this way, most of the carbon dioxide, ammonia and hydrogen sulfide remain in the water layer, the ammonia in the form of salts of carbon dioxide or hydrogen sulde.

After the separation of the Water layer, the pressure is released to permit the escape of the excess carbon dioxide from the water fraction. The ammonia may then be recovered by makingf the water layer alkaline and heating the water layer to release the ammonia. Ammonium carbonate may be produced by combining the recovered ammonia with some of the carbon dioxide originally released from the water layer. Sulfur may also be obtained as a by-product by oxidation of the hydrogen sulde in a neutral solution by blowing with air and recovering the resulting sulfur from the water layer by filtration.

The hydrocarbon gases and carbon monoxide dissolved in the liquid hydrocarbon product are separated by stabilization and these gases used for the liquefaction process. Hydrogen from any suitable source may be employed in the process.

The stabilized hydrocarbon may be treated to remove the tar acids and the tar bases. The tar acids are suitably removed by a caustic wash and the tar bases by an acid wash, as is known in the art. Tar acids and bases may be recovered from the resulting solutions by neutralizing and skimming although it is sometimes desirable to extract the neutral solution with a suitable sol- 'vent such as ether, acetone, or the like. The tar acids and bases may be separated into various constituent compounds by conventional methods or, as is often the case, sold and used as mixtures.

After removal of the tar acids and bases, the residual stabilized hydrocarbons may be separated into the usual fractions by distillation and by other refining methods. The hydrocarbon fraction contains relatively large quantities of aromatic constituents. In some instances, it may be desirable to separate some of these materials for chemical uses.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof and, therefore, only such limitations should be imposed as are indicated in the appended claims.

Vle claim:

. 1. A process for the recovery of coal from underground deposits which comprises contacting the coal in situ with a hydrogenating agent selected from the group consisting of free hydrogen and hydroaromatic compounds at a temperature within the range from about 550 F. to about 850 F. and a pressure above about 1,000 pounds per square inch gauge effective tohydrogenate a portion of the coal substance to form a liquid, and recovering the resulting liqueed coal substance from the underground deposit.

2. A process for the recovery of coal substance from a subterranean coal deposit which comprises drilling a well bore from the surface of the earth into the coal seam, introducing hydrogen through the well bore into Contact with the coal in situ at a pressure above about 1,000 pounds per square inch gauge,'initiating the reaction between hydrogen and coal in said deposit by heating the coal in the area adjacent the well bore to a temperature above about 550 F. whereby hydrogen combines with a portion of the coal substance to form a liquid, maintaining the temperature within the range of from about 550 to about 850 F., collecting the resulting liquefied coal substance in a well bore, withdrawing said liquid from the subterranean deposit through a well bore.

ERNEST F. PEVERE. GEORGE B. ARNOLD.

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

UNITED STATES PATENTS Number Name Date 345,586 Hall July 13, 1886 947,608 Betts Jan. 25, 1910 1,532,826 Lessing Apr. 7, 1925 1,669,439 Bergius May 15, 1928 2,039,459 Seguy May 5, 1936 2,119,647 Pier et al June 7, 1938 2,165,940 Pier et al. July 11, 1939 2,177,376 Pier et al Oct. 24, 1939

Claims (1)

1. A PROCESS FOR THE RECOVERY OF COAL FROM UNDERGROUND DEPOSITS WHICH COMPRISES CONTACTING THE COAL IN SITU WITH A HYDROGENATING AGENT SELECTED FROM THE GROUP CONSISTING OF FREE HYDROGEN AND HYDROAROMATIC COMPOUNDS AT A TEMPERATURE WITHIN THE RANGE FROM ABOUT 550* F. TO ABOUT 850* F. AND A PRESSURE ABOVE ABOUT 1,000 POUNDS PER SQUARE INCH GAUGE EFFECTIVE TO HYDROGENATE A PORTION OF THE COAL SUBSTANCE TO FORM A LIQUID, AND

Images