US3808119A

US3808119A - Process for refining carbonaceous fuels

Info

Publication number: US3808119A
Application number: US00297093A
Authority: US
Inventors: W Bull; B Schmid
Original assignee: Pittsburgh and Midway Coal Mining Co
Current assignee: Chevron USA Inc
Priority date: 1972-10-12
Filing date: 1972-10-12
Publication date: 1974-04-30
Anticipated expiration: 1991-04-30
Also published as: KR780000159B1; ZA733362B; JPS4974201A; AU466761B2; JPS5438601B2; AU5600273A; CA990675A; IN139155B; DE2326707A1

Abstract

HYDROGEN THE UNDISSOLVED PORTION OF THE TREATED CARBONACEOUS MATERIAL IS MORE READILY SEPARATED FROM THE SOLUTION CONTAINING THE UPGRADED CARBONACEOUS FUEL. IN ADDITION, WHEN SUBBITUMINOUS COAL OR LIGNITE IS TREATED BY THE METHOD OF THIS INVENTION, THE CONVERSION THEREOF AND THE YIELD OF UPGRADED CARBONACEOUS FUEL AS WELL AS THE YIELD OF THE LIQUID BY-PRODUCTS IS SIGNIFICANTLY INCREASED. MOREOVER, WHEN A GASEOUS MIXTURE COMPRISING CARBON MONOXIDE, STEAM AND HYDROGEN IS EMPLOYED, AN UPGRADED FUEL HAVING A LOWER ASH CONTENT IS, GENERALLY, OBTAINED.
AN IMPROVED PROCESS FOR PREPARING A LOW-ASH, LOWOXYGEN, LOW-SULFUR CARBONACEOUS FUEL WHEREIN AT LEAST A PORTION OF THE AVAILABLE FUEL FRACTION OF A CARBONACEOUS MATERIAL CONTAINING ASH, OXYGEN AND/OR SULFUR IS DISSOLVEC D IN A SUITABLE AROMATIC SOLVENT IN THE PRESENCE OF A GASEOUS MIXTURE COMPRISING EITHER CARBON MONOXIDE AND STEAM OR CARBON MONOXIDE, STEAM AND HYDROGEN. IT IS ESSENTIAL TO THE PRESENT INVENTION THAT THE SOLVATION BE EFFECTED WITHIN A RELATIVELY NARROW RANGE OF TEMPERATURES AND PRESSURES AND THAT THE PERIOD OF TIME AT WHICH THE CARBONACEOUS MATERIAL IS IN CONTACT WITH THE SOLVENT AT ELEVATED TEMPERATURES AND PRESSURES BE LIMITED WITHIN A RELATIVELY NARROW RANGE. IN A PREFERRED EMBODIMENT, THE CARBONACEOUS MATERIAL TO BE TREATED BY THE METHOD OF THIS INVENTION WILL BE GROUND AND SLURRIED WITH THE SOLVENT PRIOR TO TREATMENT. MOREOVER, IT IS PREFERRED THAT THE AROMATIC SOLVENT EMPLOYED TO BE DERIVED FROM A CARBONACEOUS MATERIAL HAVING THE SAME OR SUBSTANTIALLY THE SAME COMPOSITION AS THAT BEING TREATED. PRODUCTION OF A LOW-ASH, LOWOXYGEN, LOW-SULFUR CARBONACEOUS FUEL BY THE METHOD OF THE PRESENT INVENTION RESULTS IN HIGHER YIELDS OF THE MORE VALUABLE PRODUCTS AND IN PRODUCTS HAVING HIGHER HYDROGEN CONTENTS THAN WHEN HYDROGEN ALONE IS PRESENT DURING THE SOLVATION STEP. MOREOVER, BY USING A MIXTURE OF CARBON MONOXIDE AND STEAM OR CARBON MONOXIDE, STEAM AND

Description

April 30, 1974 w. c. BULL ETAL 3,808,119

PROCESS FOR REFINING CARBONACEOUS FUELS Filed Oct. 12, 1972 United States Patent 3,808,119 PROCESS FOR REFINING CARBONACEOUS FUELS Willard C. Bull and Bruce K. Schmid, Prairie Village, Kans., assignors to The Pittsburgh and Midway Coal Mining Co., Merriam, Kans., and the United States of America as represented by the Secretary of the Interior,

a fractional part interest to each Filed Oct. 12, 1972, Ser. No. 297,093 Int. Cl. Cg 1/04 U.S. Cl. 2088 11 Claims ABSTRACT OF THE DISCLOSURE An improved process for preparing a low-ash, lowoxygen, low-sulfur carbonaceous fuel wherein at least a portion of the available fuel fraction of a carbonaceous material containing ash, oxygen and/0r sulfur is dissolved in a suitable aromatic solvent in the presence of a gaseous mixture comprising either carbon monoxide and steam or carbon monoxide, steam and hydrogen. It is essential to the present invention that the solvation be effected within a relatively narrow range of temperatures and pressures and that the period of time at which the carbonaceous material is in contact with the solvent at elevated temperatures and pressures be limited within a relatively narrow range. In a preferred embodiment, the carbonaceous material to be treated by the method of this invention will be ground and slurried with the solvent prior to treatment. Moreover, it is preferred that the aromatic solvent employed be derived from a carbonaceous material having the same or substantially the same composition as that being treated. Production of a low-ash, lowoxygen, low-sulfur carbonaceous fuel by the method of the present invention results in higher yields of the more valuable products and in products having higher hydrogen contents than when hydrogen alone is present during the solvation step. Moreover, by using a mixture of carbon monoxide and steam or carbon monoxide, steam and hydrogen the undissolved portion of the treated carbonaceous material is more readily separated from the solution containing the upgraded carbonaceous fuel. In addition, when subbituminous coal or lignite is treated by the method of this invention, the conversion thereof and the yield of upgraded carbonaceous fuel as well as the yield of the liquid by-product is significantly increased. Moreover, when a gaseous mixture comprising carbon monoxide, steam and hydrogen is employed, an upgraded fuel having a lower ash content is, generally, obtained.

BACKGROUND This invention relates to an improved method for refining carbonaceous fuels. More particularly, this invention relates to an improved solvation process for refining carbonaceous fuels.

This invention results from work done under Contract l4010001496 with the Oflice of Coal Research in the Department of the Interior entered into pursuant to the Coal Research Act, 30 U.S.C. 6612668.

It is, of course, well known in the prior art to refine solid, carbonaceous fuels, such as coals, lignites, peat and the like, by dissolving at least a portion thereof in a suitable solvent at elevated temperatures and pressures and in a hydrogen atmosphere. Generally, however, the use of these processes has been limited to the preparation of highly specialized products such as waxes and other low volume, high priced materials due principally to the economics associated therewith as well as other operating difliculties, and few have been concerned with the production of a low-ash, low-oxygen, low-sulfur carbonaceous fuel in combination with other liquid and gas products. One such process is, however, disclosed and claimed "ice in U.S. Pat. No. 3,341,447 which issued Sept. 12, 1967 to Willard C. Bull, Lawrence G. Stevenson, Dean L. Kloepper and Thomas F. Rogers and which is assigned jointly to the United States of America and Gulf Oil Corporation.

In accordance with the disclosure of this patent, a lowash, low-oxygen, low-sulfur carbonaceous fuel is obtained in combination with both liquid and gas by-products by dissolving a substantial portion of the available fraction of a naturally occurring carbonaceous fuel in a suitable solvent. Generally, the solvent will be derived from the original fuel feed stock. In accordance with the disclosure, it is essential that the solution be formed under critically controlled conditions of temperature, pressure and atmosphere and that the same be formed within a relatively narrow, critical range of holding times. Generally, this process has proven quite successful from the standpoint of both economics and performance. Notwithstanding this, however, difliculty has been encountered in separating the ash residue from the solution. Moreover, the hydrogen content of the liquid product from this process is generally low and it is sometimes necessary or desirable to further hydrogenate this product so as to enhance both its usefulness and value. In addition, the relatively high yields of gas product when compared to the yield of liquid product detract from the economic attractiveness of the process. In addition, the total yield of useful product, which is, generally, economically acceptable with all feed stocks, is undesirably low with certain feed stocks such as the lignites and subbituminous coals. As will be readily apparent, it would be most desirable to recover a low-ash, low-oxygen, low-sulfur carbonaceous fuel in the highest possible yields from any feed stock and to recover by-products therewith having the maximum possible utility and value. It would also be most desirable to obtain these materials with a process having a minimum of operating difficulties.

SUMMARY OF THE INVENTION It has now been found that the foregoing and other disadvantages of the prior art processes can be overcome by the method of the present invention and a lowash, low-oxygen, low-sulfur carbonaceous fuel recovered from naturally occurring carbonaceous materials in relatively high yields and in combination with valuable byproducts with a minimum of operating difiiculties. It is, therefore, an object of this invention to provide an improved process for refining carbonaceous fuels. It is another object of this invention to provide an economical process for preparing low-ash, low-oxygen, low-sulfur fuels from naturally occurring carbonaceous fuels. It is still another object of this invention to provide an improved process for refining carbonaceous fuels wherein the ash may be separated more readily. It is yet another object of this invention to provide an improved process for refining carbonaceous fuels which will yield liquid products having a higher hydrogen content. It is a still further object of this invention to provide an improved process for refining carbonaceous fuels wherein the liquid by-products are obtained, generally, in higher yields. It is yet a further object of this invention to provide an improved process for refining carbonaceous fuels wherein the total yield of product from carbonaceous materials such as the lignites and subbituminous coals is significantly increased. Still other objects and advantages of the present invention will become apparent from the disclosure set forth hereinafter.

In accordance with the present invention, the foregoing and other objects and advantages are accomplished by dissolving all or a substantial portion of the potentially available fuel fraction of a naturaly occurring carbonaceous fuel in a suitable solvent and in the presence of both carbon monoxide and steam or carbon monoxide, steam and hydrogen, then separating the undissolved portion of the carbonaceous fuel from the solution, and thereafter recovering a low-ash, low-oxygen, low-sulfur solid, carbonaceous fuel from the solvent. The liquid and gas products will be obtained by flashing and/ or fractionation of the liquid media from the solvation step. As is pointed out more fully, hereinafter, it is important to control the operating parameters such as temperature, pressure and atmosphere and to affect the solvation within a relatively narrow range of holding times.

BRIEF DESCRIPTION OF THE DRAWING The figure is a schematic flow diagram of a process within the scope of the present invention wherein the refining of a carbonaceous fuel is effected continuously.

DETAILED DESCRIPTION OF THE INVENTION Broadly, and as has been noted, supra, the present invention relates to an improved process for refining or upgrading naturally occurring carbonaceous fuels. The refining or upgrading is effected by first dissolving so much of the available fuel portion of the carbonaceous material as is consistent with good operation in a suitable solvent. As will be pointed out more fully hereinafter, it is essential that the fuel fraction of the carbonaceous material be dissolved at an elevated temperature and pressure and in the presence of both carbon monoxide and steam. The refined or upgraded carbonaceous fuel is then recovered by first separating the ash portion (undissolved portion) of the carbonaceous feed material and thereafter separating the dissolved fuel fraction from'the solvent and any liquid and gas by-products produced during the dissolving step.

In general, any carbonaceous fuel may be refined or upgraded to a low-ash, low-oxygen, low-sulfur fuel by the method of the present invention. The process is, however, most suitable for the upgrading of naturally occurring canbonaceous fuels such as bituminous and subbituminous coals and lignites. Broadly, the carbonaceous material may be treated by the method of the present invention in essentially any shape or size. As will be readily apparent, however, the carbonaceous material will be most easily handled and most readily dissolved when the same is in a relatively small particle size. For these reasons, then, it is, generally, advantageous to grind or otherwise pulverize the coal such that 100 percent will pass through a mesh screen (U.S. Standard) and such that at least 50 wt. percent will pass through a 40 mesh screen (U.S. Standard). In a preferred embodiment, the particle size of the carbonaceous material treated in accordance with the method of the present invention will range between about 0.006 and 0.008 inch in diameter.

It should be noted, that while any carbonaceous material may be treated by the method of the present invention, the advantageous obtained as a result of processing by the method of the present invention will vary with the particular carbonaceous feed material subjected to treatment thereby. In this regard, and as will be pointed out more fully hereinafter, certain advantages are realized by the method of the present invention in the treatment of bituminous coal while the same and/or other advantages will be realized in the treatment of subbituminous coal and these and/or still other advantages will be realized in the treatment of lignites.

In general, any of the solvents known in the prior art to be useful for the purpose of dissolving the available fuel portion of a carbonaceous material may be used in the method of the present invention. Suitable solvents include the highly hydrogenated aromatic materials, generally, boiling within a range of about 200 to about 900 F. such as anthracene oil or creosote oil. A particularly preferred solvent, however, is one obtained by the extraction of the carbonaceous fuel itself. In this regard, it should be noted that a liqu d y-p' is obtained as a result of dissolving the carbonaceous feed material and a portion of this liquid material is suitable for use as a solvent therein. Moreover, a sufi'icient quantity of such a solvent will be produced during the extraction to satisfy the process needs therefor in either a batch or continuous operation. As will be readily apparent, the composition of the solvent thus produced will vary with the particular carbonaceous feed material but that portion of the liquid by-product having an initial boiling point within the range of about F. to about 700 F. and a final boiling point within the range of about 700 F. to about 1100 F., a density of about 1.1 and a carbon to hydrogen ratio in the range of about 1.0209 to about 10:03 will be satisfactory for use in the method of the present invention.

During the solvation step, it is essential that sufiicient solvent be employed to effectively dissolve the available fuel portion of the carbonaceous material being treated without forming a high viscosity slurry which would be difficult, if not impossible, to process upon dissolution of the dissolved fuel fraction therefrom. It is, therefore, essential that the ratio of hydrocarbon solvent to the carbonaceous material being treated (on a dry basis) be at least 05:1 and ratios of hydrocarbon solvent to dry carbonaceous material within the range of about 0.5:1 to about 5:1 will be operable in the method of the present invention. Higher ratios will, of course, also be operable but such higher ratios provide no functional advantage in the process of the present invention. Moreover, the use of such higher ratios will require additional energy or work for the subsequent separation of solvent from the upgraded carbonaceous product and for recycling in the system. Lower ratios within the broad range are, therefore, preferred.

In general, the fuel fraction of the carbonaceous material being treated by the method of the present invention will be dissolved at a temperature sufficiently high to facilitate the solvation but not so high as to cause excessive decomposition of the fuel fraction, which is sought to be recovered, or the solvent employed in the extraction or solvation step. Temperatures within the range of about 700 to about 950 F. have been found suitable for use in the present invention. In this regard, it should be noted that the rate of solvation below about 700 F. is too slow to permit reasonable recovery of the available fuel fraction. At temperatures above about 950 F., on the other hand, decomposition of the desired products and the solvent become excessive. As will be readily apparent, from the standpoint of economics, the use of the lower temperatures within this range which are consistent with good yields is most desirable.

Since the solvation of the available fuel fraction of the carbonaceous material is accomplished at an elevated temperature and in the presence of hydrocarbon materials having a boiling point below these temperatures, it is essential that the extraction or solvation step be accomplished at an elevated pressure. Moreover, since elevated pressure enhances the solvation of the available fuel fraction of the carbonaceous material, it is most desirable to effect the solvation at elevated pressures. In general, pressures within the range of about 500 to about 5000 p.s.i.g. will be effective. In this regard, it should be noted that at pressures below about 500 p.s.i.g., the yield of deashed carbonaceous fuel is unreasonably low. Pressures above about 5000 p.s.i.g., on the other hand, are operable but provide no functional advantage when employed in the method of the present invention. As will be pointed out more fully, hereinafter, it is essential that at least a portion of this pressure be provided by a gaseous material or materials capable'of providing hydrogen ions to the products produced by the method of the present invention.

As has been noted, supra, the essence of the present invention resides in the discovery of unexpected advantages which are realized when part or all of the available fuel fraction of the carbonaceous material is dissolved in an atmosphere containing both carbon monoxide and steam. Generally, these advantages will be realized when carbon monoxide is present in an amount ranging between about 1.5 and 40 s.c.f. of CO per pound of dry coal in combination with steam within the range of about 0.2 to 1.5 pounds per pound of dry coal. It is not, however, essential that carbon monoxide and steam be the only gaseous components present in the gas phase during the extraction or dissolving step and, in fact, it has been found beneficial in many cases to also have hydrogen available in the gas phase. In this regard, and when hydrogen is employed, the ratio of hydrogen plus carbon monoxide to dry carbonaceous feed material will range between about 1.5 and 40 s.c.f. per pound of said carbonaceous material and the ratio of steam and/or water to dry carbonaceous material will range from about 0.2:1 to 1.5 :1 on a weight basis. Moreover, when hydrogen is employed, the ratio of hydrogen to carbon monoxide will range between about 0.1:1 to 10.011.

In general, the length of time during which the solvent and carbonaceous fuel will be contacted at the process temperature will vary between about 3 and 180 minutes. The optimum holding time for each carbonaceous material will, however, vary with each such material. In this regard, it should be noted that, in general, the viscosity of the solu tion obtained during processing of the carbonaceous material will, initially, increase with time, then decrease and then increase again as the holding time is extended. As will be readily apparent, separation of the undissolved portion of the carbonaceous material from the solution and the recovery of the dissolved fuel portion from the solution will be most readily accomplished when the viscosity of the mixture from the reactor is at a reasonably low value. For this reason, then, it is most desirable to continue the solvent-carbonaceous material contacting at process temperature until the viscosity first begins to decrease but to discontinue the contacting before the viscosity again increases to a point where the mixture from the dissolver would be difiicult to process. In this regard, it should be noted that the viscosity of the solution in the dissolver can be used to provide an accurate guide to determine the optimum holding time in the extraction or solvation step and that this may conveniently be accomplished by reference to the relative viscosity of the solution formed in the dissolver. In this regard, it should be noted that the relative viscosity here referred to is the ratio of the viscosity of the solution in the dissolver to the viscosity of the solvent used therein. It will, of course, be appreciated that this ratio should be established by determining the viscosities of both the solution and the solvent at the same conditions and different values might be obtained at different temperatures. For this reason, then, the term relative viscosity as used herein is restricted to and defined as the ratio of the viscosity of the solution at 210 F. and the viscosity of the solvent, also at 210 F., employed in the system.

As has been noted, supra, during the extraction or solvation step, there is, initially, an increase in the solution viscosity followed by a decrease therein and then a second increase. There is, then, a corresponding increase in the relative viscosity followed by a decrease therein and a second increase. Generally, the relative viscosity will rise, initially, to a value well above 20 before the same begins to decrease as the holding time is continued. This value will, of course, depend somewhat upon the particular carbonaceous material being treated and the solvent employed in the solvation step. In all cases, however, a value of at least 20 will be reached during the initial increase. Following this increase, the relative viscosity will reduce to a value below 10, and, generally, to a value well below 5 before the same again begins to increase. In this regard, it should be noted that mixtures from the dissolver having relative viscosities less than 10 can be processed by the method of the present invention and a low-ash, low-oxygen, lowsulfur carbonaceous fuel recovered therefrom. The extraction or solvation will, therefore, be continued at least until the relative viscosity of the solution from the dissolver is less than 10 but the same will be discontinued before the relative viscosity has passed through its minimum and then increased to a value of 10 or more. In a preferred embodiment, the extraction or solvation step will be continued until the relative viscosity of the solution in the dissolver has reached a value of 5 or less but will be discontinued before the relative viscosity has increased back to a corresponding value of 5. In a most preferred embodiment, the extraction or solvation step will be discontinued when the relative viscosity has reached a value of about 1.5 to 2.

While applicants do not wish to be bound by any particular theory, it is believed that the solvation of the available fuel portion of the carbonaceous material being treated is effected via a depolymerization of the relatively high molecular weight components thereof, "and that when this depolymerization in accomplished in the presence of a hydrogen ion donor the free radicals thus formed are neutralized by the hydrogen ions, thereby preventing repolymerization of the free radicals. The neutralized free radicals, as well as any other decomposition products, are then soluble in the solvent and may be subsequently recovered by flashing or otherwise separating the solvent therefrom.

During the extraction or solvation step, materials other than those which are soluble in the solvent are either formed or liberated. Such materials include hydrogen sulfide, carbon dioxide, methane, propane, butane, and other higher hydrocarbons and these materials will comprise part of the atmosphere in the dissolver. Generally, however, their presence therein will not adversely affect the extraction or solvation of the carbonaceous material. Care should, however, be exercised so as to prevent a buildup of these materials to the extent that the partial pressures of carbon monoxide and steam (and hydrogen, when used) are reduced to inoperable values. In this regard, it should be noted that these materials may be separated from any recycled gas by conventional means. Moreover, during the extraction or solvation, step, hydrogen is consumed by the extracted or dissolved portion of the carbonaceous material in an amount rang ing between about 0.5 and 4.0 wt. percent of the initial dry coal feed and this amount should be made up if the gas phase is recycled and the presence of hydrogen desired initially. In addition, about 5 to about 50 mol percent of the carbon monoxide and steam will be converted to hydrogen during the extraction or solvation step and this amount, too, should be made up if gas recycle is employed.

After the extraction or solvation step of the method of this invention has been completed, the upgraded, low-ash, low-oxygen, low-sulfur carbonaceous fuel can then be recovered from solution. Generally, this recovery will involve: the separation of the undissolved portion of the carbonaceous feed material from the solution; the separation of the carbon monoxide, steam and hydrogen, as well as any other gaseous components present in the system, from the solution; the separation of the low-ash, low-oxygen, low-sulfur carbonaceous fuel from the solvent; and the separation of any gas and liquid by-products from the solvent. The manner and order of these separations is not, however, critical to the present invention and the same may be accomplished in essentially any order which will yield the upgraded fuel free of the undissolved portion of the carbonaceous feed. Generally, however, it will be advantageous to first reduce the pressure to a value suitable for separation of the undissolved portion of the carbonaceous feed from the solution and thereafter separating the gaseous components from the liquid and solid components and then the solid (undissolved portion of the carbonaceous feed material) components from the liquid. The upgraded, low-ash, low-oxygen, low-sulfur carbonaceous fuel can then be conveniently recovered from solution. Fractionation of the solvent phase may then be employed to effect recovery of the liquid by-product and to separate any dissolved or entrained gases therefrom.

In general, any suitable means, such as filtration and centrifugation, can be employed to effect the separation of the undissolved portion of the carbonaceous feed from the solution. With either of these methods, however, it will, generally, be desirable to subject the recovered solids to a drying step so as to recover entrained solvent therefrom. Moreover, the dried solids from a centrifugal separation and/or the dried filter cake from a filter will have a definite fuel value with fuel ratings running as high as 7000 B.t.u./lb.

As will be readily apparent, the gaseous components may be separated from the slurry containing the undissolved portion of the carbonaceous feed material either prior to or simultaneously with the separation of the solid material. After separation, the gases may then be subjected to any subsequent treatment, such as scrubbing to remove acid gas components, and then recycled or used for other purposes, as desired. In this regard, it should be noted that when gas recycle is employed, a buildup in hydrogen gas will, often, occur, initially, due to the formation thereof through the reaction of carbon monoxide with steam. This inital buildup is not, however, detrimental and, at steady-state operation, within the operating ranges heretofore set forth, the concentration of carbon monoxide and steam in the dissolver can easily be maintained within the operable limits set forth, supra.

After the undissolved portion of the carbonaceous feed has been separated from the solution, the low-ash, lowoxygen, low-sulfur carbonaceous fuel may then be recovered therefrom with any suitable means such as by vacuum distillation or flash evaporation. In any case, however, the solvent and other lower boiling liquids therein will be separated by exposure to temperatures just slightly above the boiling point of the highest boiling component thereof.

The upgraded, low-ash, low-oxygen, low-sulfur carbonaceous fuel may be recovered as either a liquid or a solid, depending upon the particular method used to separate the same from the solvent, and the same may be used in either form. Moreover, when the upgraded fuel is recovered as a liquid, the same may be solidified simply by cooling.

As has been noted, supra, the method of the present invention offers several advantages over prior art processes wherein hydrogen alone is used to supply the hydrogen required during the extraction or solvation step. The advantages oifered do, however, vary with the particular carbonaceous material subjected to treatment. For example, when bituminous coal is upgraded by the method of the present invention, the yield of all products (gas, liquid and upgraded fuel) from the feed is, often, substantially identical to that obtained through the use of hydrogen alone. Separation of the undissolved portion of the carbonaceous feed material from the solution is, however, significantly enhanced, and as a result, smaller filtration equipment is required to effect the desired separation. Moreover, when bituminous coal is treated by the method of this invention, the yield of the more valuable liquid by-product is, generally, increased with a corresponding decrease in the less valuable gas by-product and the hydrogen content of all products is, surprisingly, higher. When subbituminous coal, on the other hand, is treated by the method of this invention, the advantages noted above and associated with the treatment of bituminous coal are again generally realized. In addition, the total yield of the more valuable products is significantly increased over the full range of operating conditions normally employed. Similarly, when lignite is treated by the method of this invention, all of the advantages derived in the treatment of subbituminous ooal are, generally, realized and an upgraded fuel containing less sulfur is, generally, obtained.

In addition to the foregoing advantages, which advantages will be realized when the solvation is accomplished in an atmosphere comprising carbon monoxide and water and any reaction products therefrom either with or without hydrogen being added in the range of concentration heretofore specified, it has, surprisingly, been found that the addition of hydrogen within the range of concentrations heretofore specified, will, generally, yield an upgraded fuel having a lower ash content than that obtained through the use of hydrogen alone. Moreover, since mixtures of hydrogen and carbon monoxide are, generally, less costly than either pure hydrogen or pure carbon monoxide, there is a distinct economic advantage associated with the use of the three component mixture. In addition, since the presence of steam during the solvation step is essential to the present invention, there would be no advantage in drying the carbonaceous material prior to subjecting the same to treatment by the method of this invention. In this regard, it should be noted that many carbonaceous materials which may be upgraded by the method of this invention will contain all of the water required for such treatment, and when these materials are treated it will be unnecessary to add additional steam and/or water.

Having thus broadly described the present invention, it is believed that the same will become readily apparent by reference to the appended drawing. Referring then to FIG. 1, there is shown a schematic flow diagram of one embodiment of the present invention wherein a carbonaceous feed material is upgraded in a continuous process. As illustrated in the figure, a finely ground carbonaceous feed material is fed to mixer or slurry tank 1 through line 2 where the same is slurried with a suitable solvent therefor. As illustrated, the solvent enters through line 3. After the carbonaceous material has been slurried, the same is withdrawn from the slurry tank through line 4 and passed through preheater 5 and into dissolver 6 through line 7. In the preheater, the slurry is heated to the desired solvation temperature and then held in the dissolver until the desired portion of the available fuel fraction of the carbonaceous material has been dissolved therein. As has been noted, supra, it is essential to the present invention that the solvation be accomplished in an atmosphere comprising carbon monoxide and steam and it is important that the carbonaceous material be in contact with these components at all times during which the same is exposed to elevated temperatures. For this reason, then, it is important that the slurry be mixed with the desired gas prior to passing the same through the preheater 5. In the embodiment illustrated, the desired gas feed is brought in through line 8 and mixed with the slurry in line 4. As has been previously noted, the gas fed to the preheater may be pure carbon monoxide, when there is suflicient water in the coal to provide the required steam or when sulficient water is added thereto, or the same may be a mixture of carbon monoxide and steam or a mixture of carbon monoxide, steam and hydrogen. It will, of course, be appreciated that other gaseous components could be present in the gas feed and this will, generally, be the case when recycle gas is employed or when impure sources of the gas are used. When the solvation step is completed, the solution containing any undissolved portion of the carbonaceous feed material is withdrawn from the dissolver through line 9 and passed to filter 10. As has also been noted, supra, other means of separation could be employed at this point; however, a conventional rotary drum pressure filter suitably adapted for pressure let down and venting of gases has proven quite satisfactory. In the embodiment illustrated, the separation of the gaseous components and the undissolved portion of the carbonaceous feed material is effected simultaneously in the filter. As illustrated, the gases pass overhead through line 11 to scrubber 12 where any undesired components are separated. The treated gas then passes overhead through line 13 and all or a portion of the same may be vented through line 14 or recycled to the preheater through line 8. Any make-up gases required may then be added through line 15. As will be readily apparent, the undissolved portion of the carbonaceous feed material is deposited on the filter cake and may be withdrawn from the filter through line 16. The filter cake may then be processed by any suitable method for the purpose of recovering absorbed solvent or other materials. For example, the same may be passed through a rotary drum drier 17 and then withdrawn from the process through line 18. The solvent or other recovered material may then be recovered through line 19 and either recycled to the slurry tank or withdrawn from the process as desired. The solution containing the dissolved fuel fraction of the carbonaceous feed material, on the other hand, is withdrawn from the filter through line 20 and passed through a second preheater 21. In the preheater, the solution is heated to a temperature suitable for vacuum flash separation and is then withdrawn through line 22 and passed to vacuum flash vessel 23. The vacuum flash vessel may, of course, be heated as required. In the vacuum fiash vessel, the solvent and any other liquid materials will be flashed and will pass overhead through line 24. The overhead product may then be subjected to distillation in distillation column 25. As will be readily appreciated, any number of products may then be recovered from the distillation column. In the embodiment illustrated, the recovered solvent is withdrawn through line 26 and may be recycled to the slurry tank through line 3. The lighter liquid materials will pass overhead through line 28 and may be withdrawn from the process through this line. In the embodiment illustrated, the upgraded, low-ash, lowoxygen, low-sulfur product will be withdrawn from the vacuum flash vessel as a liquid through line 29. The liquid product may then be cooled and solidified and withdrawn from the process by any suitable means such as watercooled conveyor 30.

PREFERRED EMBODIMENT In a preferred embodiment, the method of the present invention will be employed to upgrade a carbonaceous material selected from the group consisting of the lignites, the subbituminous coals and the bituminous coals and the upgrading will be effected continuously. In the preferred embodiment, the carbonaceous feed material will first be ground such that approximately 80% thereof will pass through a 200 mesh (U.S. Standard) screen and then slurried with a solvent derived from the carbonaceous material and having an initial boiling point within the range of about 400 to about 600 F. and a final point within the range of about 800 to about 1000 F. Preferably, the ratio of solvent to dry coal in the feed slurry will range from about 1.0:1 to about 25:1. The slurry will then be mixed with a gaseous mixture comprising both hydrogen and carbon monoxide. Preferably, from about -00 to about 5000 standard cubic feet of these gases will be added per barrel of slurry. Steam will also be added to the slurry, when required, such that the ratio of water to dry coal ranges between about 0.5:1 to about 1:1. The ratio of hydrogen to carbon monoxide will be within the range of about 0.321 to 4:1. The slurry will then be heated to a solvation temperature within the range of about 775 to about 875 F. and the solvation will be effected at a pressure within the range of about 1000 to 2500 p.s.i.g. Preferably, the liquid space velocity in the reaction zone will be within the range of about 0.5 to about 3.0.

p.s.i.g. In this run, 96.6% of the available fuel fraction The following examples demonstrate the effectiveness of the present invention but are in no way intended to limit the same.

Example 1 In this example, a Kentucky No. 11 bituminous coal was ground such that wt. percent thereof passed through a 100 mesh (U.S. Standard) screen and then slurried with amixture of water and a highly aromatic solvent. The solvent to dry coal ratio in the slurry was 2 to 1. The ratio of water to dry coal was 0.25 to 1. The slurry was heated in an atmosphere comprising 50 mol percent carbon monoxide and 50 mol percent hydrogen at an initial pressure of 1500 p.s.i.g. and held at these conditions for 30 minutes (at 425 C., the autogenous produced pressure was 3800 p.s.i.g.). During the 30 minute residence time, 94.1% of the available fuel fraction of the carbonaceous feed material was dissolved in the highly aromatic solvent or otherwise converted to a lower molecular weight liquid or gas material. After the 30 minute residence time, the undissolved portion of the carbonaceous feed material was separated from the solution by filtration and the gaseous materials flashed so as to yield a solution containing an upgraded carbonaceous fuel. The upgraded carbonaceous fuel was then recovered by vacuum distillation of the solvent and other liquid products. The upgraded carbonaceous fuel was recovered in a yield of 48.7 wt. percent based on initial coal feed. A liquid product boiling within the range of 100 and 800 F. was obtained in a yield of 25 wt. percent based on initial coal feed and a gas product consisting of C to C hydrocarbons was recovered in a yield of 1.4 wt. percent based on the initial coal feed. The hydrogen to carbon ratio in the upgraded carbonaceous fuel was 0.73:1 while that in the liquid product was 0.86: 1. The separation of the undissolved portion of the carbonaceous feed material from the solution was accomplished in a laboratory filtration apparatus in 1 hour.

Example 2 The run of Example 1 was repeated except that the ground Kentucky No. 11 bituminous coal was heated to a temperature of 425 C. in an atmosphere of pure hydrogen and held for 30 minutes. The initial pressure was 1500 of the carbonaceous feed material was dissolved and an upgraded carbonaceous fuel was obtained in a yield of 48.3 wt. percent based on the initial coal feed. A liquid product having a boiling range between 100 and 800 F., on the other hand, was obtained in a yield of only 18 wt. percent based on initial coal feed while a gas product containing C -C hydrocarbons was obtained in a yield of 9 wt. percent. Moreover, the hydrogen to carbon ratio in the upgraded fuel was only 0.60:1, while that of the liquid product was 0.82:1. In addition, separation of the undissolved portion of the carbonaceous feed material from the solution took 4 hours for the same volume in the same laboratory filtration apparatus under identical conditions.

From the foregoing, then, it is readily apparent that when the solvation step is accomplished in an atmosphere containing steam, carbon monoxide and hydrogen there is a significant increase in the yield of liquid product without any decrease in the yield of upgraded carbonaceous fuel and that the hydrogen contents of the major products are significantly higher. Moreover, it is readily apparent that when the solvation step is accomplished in an atmosphere of steam, carbon monoxide and hydrogen the undissolved portion of carbonaceous feed material can be separated more readily by filtration.

Example 3 In this example, a Kentucky No. 9 bituminous coal containing 3.58 wt. percent sulfur was ground to a particle size such that 100 wt. percent passed through a 100 mesh (U.S. Standard) screen and then slurried in a highly aromatic solvent having an initial boiling point of 550 F. and a final boiling point of 800 F. The ratio of solvent to available fuel fraction in the carbonaceous feed material was 2.4 to 1. The slurry was then processed in a continuous flow unit at a temperature of 425 C. in an atmosphere containing steam, carbon monoxide and hydrogen at a pressure of 1000 p.s.i.g. The hourly liquid space velocity in the reaction zone (preheater plus dissolver) was 0.8 while the hourly gas space velocity (STP) was 225. The weight ratio of steam to coal in the available fuel fraction was 0.3 to 1 and the mol ratio of hydrogen to carbon monoxide in the atmosphere was 1 to 1. At these conditions, 87% of the available fuel fraction of the Kentucky No. 9 coal was dissolved in the highly aromatic solvent and an upgraded carbonaceous fuel was obtained in a yield of 54.8 wt. percent based on initial coal feed. The sulfur content of the upgraded fuel was 0.8 wt. percent.

Example 4 The run of Example 3 was repeated except that the sol vation of the available fuel fraction in the carbonaceous feed material was accomplished in an atmosphere of pure hydrogen. In this run, 90% of the available fuel fraction was dissolved in the aromatic solvent and an upgraded carbonaceous fuel was obtained in a yield of 47.1 wt. percent based on initial coal feed. The sulfur content of this product was, however, 1.02 wt. percent.

A comparison of Examples 3 and 4 clearly reveals that when the available fuel fraction of a bituminous coal is dissolved in an atmosphere containing steam, carbon monoxide and hydrogen the sulfur content of the product is significantly less than when hydrogen alone is used. This is, of course, particularly significant in light of recent emphasis on the use of low-sulfur fuels in power plants and other industrial installations.

Example 5 In this example, a Big Horn, Wyoming subbituminous coal was ground to a particle siZe such that 100 wt. per cent passed through a 65 mesh (U.S. Standard) screen and then slurried in a mixture of water and a highly aromatic solvent having an initial boiling point of 550 F. and a final boiling point of 800 F. The solvent to dry coal ratio in the slurry was 2 to 1. The water to dry coal weight ratio in the slurry was 0.4 to 1. The slurry was then heated to 400 C. in an atmosphere containing 50 mol percent carbon monoxide and 50 mol percent hydrogen and held for 30 minutes. The initial pressure in the reactor was 1500 p.s.i.g. During the 30 minute holding time, 76.9% of the available fuel fraction of the Big Horn, Wyoming subbituminous coal was dissolved in the solution. After the 30 minute holding time, the undissolved portion was separated from the solution by filtration. An upgraded carbonaceous fuel was then recovered from the solution by vacuum distillation of the solvent and other liquid components present therewith. The upgraded carbonaceous fuel was obtained in a yield of 42 wt. percent based on initial coal feed. In addition, a liquid product having an initial boiling point of 100 F. and a final boiling point of 800 F. was obtained in a yield of 11.4 wt. percent.

Example 6 The run of Example 5 was repeated except that the solvation was accomplished at a temperature of 450 C. in an atmosphere of pure hydrogen and the solvation step was allowed to continue for 94 minutes. In this run, only 60% of the available fuel fraction of the Big Horn, Wyoming subbituminous coal dissolved in the solvent and an upgraded carbonaceous fuel was recovered in a yield of only 34.7 wt. percent based on initial coal feed. Moreover, the yield of total liquid product was less than 1 wt. percent based on initial coal feed.

1 2 Example 7 In this example, Elkol, Wyoming subbituminous coal was ground to a particle size such that 100 wt. percent passed through a 65 mesh (U.S. Standard) screen and then slurried in a mixture of water and a highly aromatic solvent having an initial boiling point of 550 F. and a final boiling point of 800 F. The solvent to dry coal ratio in the slurry was 2 to 1 on a weight basis. The water to dry coal ratio was 0.4 to l on a weight basis. The slurry was then heated to 400 C. in an atmosphere comprising 50 mol percent carbon monoxide and 50 mol percent hydrogen and held at these conditions for 30 minutes. The initial pressure in the dissolver was 1500 p.s.i.g. During the 30 minute residence time, 92% of the available fuel fraction of the Elkol, Wyoming subbituminous coal was dissolved in the solvent. After the 30 minute residence time, the undissolved portion of the carbonaceous feed material was separated from the solution by filtration. An upgraded carbonaceous fuel was then recovered by vacuum distillation of the solvent and other liquid materials therewith. The upgraded carbonaceous fuel was recovered in a yield of 58 wt. percent based on initial coal feed. At the same time, a liquid product having an initial boiling point of 100 F. and a final boiling point of 800 F. was recovered in a yield of 17.6 wt. percent based on initial coal feed.

Example 8 The run of Example 7 was repeated except that the solvation was accomplished in an atmosphere of pure hydrogen and at a temperature of 425 C. In this run, only 73% of the available fuel fraction of the carbonaceous feed material was dissolved in the highly aromatic solvent. Moreover, the yield of upgraded carbonaceous fuel was only 53 wt. percent based on initial coal feed while that of the liquid product was less than 1 wt. percent based on initial coal feed.

A comparison of Examples 5, 6, 7 and 8 clearly show that when a subbituminous coal is upgraded by the method of the present invention in an atmosphere comprising steam, carbon monoxide and hydrogen a higher percentage of the available fuel fraction thereof is recovered and the yield of both upgraded carbonaceous fuel and liquid by-product is significantly increased.

Example 9 In this example, a Beulah lignite was ground to a particle size such that 100 wt. percent passed through a 65 mesh (U.S. Standard) screen and then slurried with a mixture of water and a highly aromatic solvent having an initial boiling point of 550 F. and a final boiling point of 800 F. The solvent to dry coal ratio in the slurry was 2 to l on a weight basis, and the water to dry coal ratio was 1 to l on a weight basis. The slurry was then heated to a temperature of 410 C. in an atmosphere of pure carbon monoxide and held at these conditions for 10 minutes. The initial pressure in the dissolver was 1000 p.s.i.g. During the 10 minute residence time, over 95% of the available fuel fraction of the Beulah lignite was dissolved in the aromatic solvent. After the 10 minute holding time, the undissolved portion of the lignite feed was separated from the solution by filtration and an upgraded carbonaceous fuel then recovered from the solution by vacuum distillation. A liquid product having an initial boiling point of F. and a final boiling point of 800 F. was obtained in a yield of 24 wt. percent based on initial coal feed and a gas product containing C -C hydrocarbons was obtained in a yield of 1.6 wt. percent. The sulfur content of the upgradedcarbonaceous fuel was only 0.13 wt. percent.

Example 10 The run of Example 9 was repeated except that the solvation was accomplished at a temperature of 425 C.

in an atmosphere of pure hydrogen. In this run, only 85% of the available fuel fraction of the Beulah lignite was dissolved in the aromatic solvent. The yield of a liquid by-product having an initial boiling point of 100 F. and a final boiling point of 800 F., on the other hand, was only 4 wt. percent based on initial coal feed yvhile the gas product, containing C -C hydrocarbons, was obtained in a yield of 8 wt. percent. The sulfur content of the upgraded carbonaceous fuel was 0.37 wt. percent.

Example 11 In this example, a Baukol-Noonan lignite containing 31 wt. percent water was ground to a particle sizesuch that 100 wt. percent thereof passed through a 65 mesh (US. Standard) screen and then slurried with a highly aromatic solvent having an initial boiling point of 550 F. and a final boiling point of 800 F. The slurry was then mixed with a gas stream consisting of pure carbon monoxide and heated to a temperature of 425 C. for 30 minutes. Sufiicient gas was added to make the initial pressure in the dissolver 1000 p.s.i.g. During the 30 minute holding time, more than 90% of the available fuel fraction of the Baukol-Noonan lignite feed was dissolved in the solvent. After the 30 minute holding time, the undissolved portion of the carbonaceous feed material was separated from the solution by filtration. An upgraded carbonaceous fuel was then recovered by vacuum distillation to remove the solvent and other liquids associated therewith. The upgraded carbonaceous fuel was recovered in a yield of 31.8 wt. percent based on dry coal feed. -At the same time, a liquid product having an initial boiling point of 100 F. and a final boiling point of 800 F. was obtained in a yield of 32.8 wt. percent based on initial coal feed and a gas product containing C C hydrocarbons was obtained in a 7 wt. percent yield based on feed coal.

Example 12 The run of Example 1 was repeated except that the slurry was mixed with a gas stream comprising 50 mol percent hydrogen and 50 mol percent carbon monoxide. In this run, again more than 90% of the available fuel fraction in the lignite feed was dissolved in the highly aromatic solvent. Moreover, the yield of upgraded carbonaceous fuel, liquid by-product and gas by-product were substantially identical with those of the previous run and the hydrogen to carbon ratios were not significantly changed. The ash content of the upgraded carbonaceous fuel was, however, significantly lower; viz., 0.12 wt. percent versus 0.45 wt. percent.

Example 13 The run of Example 11 was again repeated except that the slurry was mixed with a gas stream comprising pure hydrogen rather than pure carbon monoxide. In this run, only 59% of the available fuel fraction of the lignite feed was dissolved in the aromatic solvent and the yield of all products was significantly reduced and the hydrogen content thereof was significantly lower. Moreover, the undissolved portion of the lignite feed was separated from the solution at a much slower rate. 1

A comparison of Examples 9, 10, 11, 12 and 13 clearly indicate that when lignite is upgraded by the method of the present invention and in the presence of either-steam and carbon monoxide or steam, carbon monoxide and hydrogen the conversion of the initial materials is significantly higher and the yield of desirable products significantly increased. Moreover, the yield of liquid byproduct is significantly higher when the solvation is accomplished in the presence of either carbon monoxide and steam or carbon monoxide, steam and hydrogen than when hydrogen alone is used without any decrease in the yield of upgraded carbonaceous fuel. These examples also demonstrate that the hydrogen content of the productsis; generally, higher when the gas mixture is employed than when hydrogen alone is used and that the' sulfur content of the upgraded carbonaceous fuel is significantly lower. Moreover, it is clear from the comparative examples that when a mixture of steam, carbon monoxide and hydrogen is employed, the ash content of the upgraded carbonaceous fuel is lower. Further, it is readily apparent from a comparison of these examples that when the carbonaceous feed material contains a sufiicient amount of water therein it is unnecessary to add steam during the solvation step.

Although the present invention has been described and illustrated by reference to particular embodiments thereof, it will be readily apparent that the same lends itself to various modifications which will be obvious to those of ordinary skill in the art. Accordingly, reference should be made solely to the appended claims to determine the scope of the invention.

Having thus described and illustrated the present invention, what is claimed is:

1. A solvation process for preparing a substantially ash-free solid carbonaceous fuel from a charge consisting essentially of coal containing ash, an aromatic solvent, a. gaseous carbon monoxide-containing stream, with or without a gaseous hydrogen-containing stream and with or without added water, comprising the steps of:

(a) dissolving in the aromatic solvent at least a portion of the carbonaceous fuel fraction from the ash of the coal at a temperature within the range of about 700 F. to about 950 F. and at a pressure between about 500 and 5,000 p.s.i. in contact with between about 1.5 and 40 standard cubic feet of carbon monoxide per pound of dry coal and between about 0.2 and 1.5 pounds of steam per pound of dry coal to form a dissolved solution;

(b) establishing the dissolving conditions so that the relative viscosity of the solution measured at 210 F. rises to a value at least 20 times the viscosity of the solvent alone measured at 210 F. due to extration of carbonaceous fuel from the coal by the solvent and then falls to a value below 10 times that of the solvent alone measured at 210 F. due to depolymerization of said carbonaceous fuel;

(c) the dissolving conditions permitting the relative viscosity of the solution to again rise above 10 with increased dissolving time due to repolymerization of said carbonaceous fuel but terminating dissolving conditions which permit the relative viscosity to again rise above 10;

(d) separating the undissolved portion of the coal from the solution;

(e) recovering an upgraded substantially ash-free carbonaceous fuel from the solution; and 1 (f) cooling and solidifying said fuel and removing solid, substantially ash-free fuel from the process.

2. In the process of claim 1, terminating the dissolving conditions when the relative viscosity has fallen from a value above 20 to a value below 5, the dissolving conditions permitting the relative viscosity to again rise above 5 except for termination of the dissolving conditions which permit said rise.

3. In the process of claim 1, terminating the dissolving conditions when the relative viscosity has fallen to a value below 2, therdissolving conditions permitting the relative viscosity to again rise above 2 except for termination of the dissolving conditions which permit said rise.

4. The process of claim 1 wherein the ratio of solvent to dry coal is within the range of about 0.5 to 1 to'about 5 to 1 5. The process of claim 4 wherein said solvent has an initial boiling point within the range of about to about 700 F. and a final boiling point within the range from about 700 F. to about 1100 F.

6. The process of claim 4 wherein said solvent is derived from a coal having a composition substantially identical to that of the coal being treated.

7. The process of claim 1 wherein said coal is first ground and then slurried in said solvent.

8. The process of claim 1 wherein the carbonaceous fuel fraction of the coal is dissolved at a temperature within the range of about 775 to about 875 F.

9. The process of claim 1 wherein the carbonaceous fuel fraction of the coal is dissolved at a pressure within the range of about 1000 to about 2500 p.s.i.g.

10. The process of claim 9 wherein the ratio of solvent to dry coal is within the range of about 1.0 to 1 to about 2.5 to 1.

11. The process of claim 1 wherein hydrogen is included in the charge to said dissolving step.

References Cited UNITED STATES PATENTS 3,075,912 1/ 1963 Eastman et al. 2088 3,692,662 9/1972 Wilson et al. 2088 5 3,733,183 5/1973 Singh 2088 3,748,254 7/1973 Gorin 208-8 DELBERT E. GANTZ, Primary Examiner 10 V. OKEEFE, Assistant Examiner US. Cl. X.R. 208-l0