|Publication number||US3247092 A|
|Publication date||Apr 19, 1966|
|Filing date||Mar 19, 1963|
|Priority date||Mar 19, 1963|
|Publication number||US 3247092 A, US 3247092A, US-A-3247092, US3247092 A, US3247092A|
|Inventors||Morgan G Huntington|
|Original Assignee||Pyrochem Corp|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (12), Referenced by (12), Classifications (13)|
|External Links: USPTO, USPTO Assignment, Espacenet|
April 19, 1966 M. GA HUNTINGTON 3,247,092
QUADRI-PHASE LOW PRESSURE METHOD FOR PARTIAL LIQUEFACTION OF COAL Filed March 19, 1963 LD L; I IJ 5 6o lis TRAcTloNATTNG l SYSTEM i |66 LL! 5 E2! g Zd. E# j+- i E D Z Q LT :D j Q S E 22 Zu.: E?
MORGAN G. HUNTINGTON CHAR 8T ASH ATTORNEYS1 United States Patent O 3,247,092 QUADRl-PHASE LUW PRESSURE METHD FR PARTIAL LTQUEFACTIN F CUAL Morgan G. Huntington, Washington, DC., assigner, by mesne assignments, to Pyrochem Corporation, Salt Lake City, Utah, a corporation of Utah Filed Mar. 19, 1963, Ser. No. 266,255 The portion of the term of the patent subsequent to (let. 22, 19%, has been disclaimed 14 Claims. (Cl. 208-8) This application is a continuation-impart of my allowed copending yapplication Ser. No. 41,679, lfiled July S, 1960, now Patent No. 3,107,985.
This invention relates to a quadri-phase method for the recovery of the more readily liquefiable petrographic constituents of coal under relatively low pressure hydrogenating conditions and to apparatus for carrying out this method.
This invention relates to continuous drying, destructive hydrodistillation and hydrocarbonization of coal and other solid hydrocarbonaceous material. More particularly, this invention concerns a continuous multi-stage pressurized coal hydrodistillation system in a vertical vessel. The system includes the functions of coal drying, p-reheating, `destructive distillation with coincidental mild hydrogenation and immediate vapor phase catalytic hydroreining and hydrodealkylating of the condensable volatiles, and coincidental redistilling, hydrorefining and hydrodealkylating of re-cycled heavy bottoms and selected fractions with whatever entrained solids, partial combustion of char to furnish heat to the system, and thermal cracking of recycled methane to produce elemental hydrogen.
The destructive distillation of coal by heating in the absence of air is carried on for the production of coke, gas, tar and oils, and other by-products. There have been a large number of different approaches to the carbonization of coal, most of which attempt to accomplish the destructive -distillation of the coal and to maximize the recovery of coal tars, and at the same ltime to produce a minimum of uncondensable gases `and of solid residue. There are also a number of different, but complex and expensive, approaches to the total liquefaction of coal such as high pressure hydrogenation and solvent extraction.
The present quadri-pbase method of coal liquefaction is devised as an economic and technical compromise between the mechanically complex and economically impractical systems which are 4aimed at the total liquefaction of the coal by high pressure hydrogenation, and the primitive, unsophisticated and equally economically unsound destructive distillation of coal commonly known as low temperature carbonization.
The present invention provides means for thermally cracking whatever permanent hydrocarbon gases may be distilled from the coal and thereby making avai-lable to the system all of this hydrogen in its elemental state. As is known in the art, most bituminous coals have two or three times as much surplus hydrogen as is required to hydrorefine the primary distillate into hydrocarbon cornpounds consisting only of carbon and hydrogen and to saturate the more reactive molecules. Therefore, it is the purpose of this quadri-phase method to substantially increase the yield of liquid distillate over what is normally considered the Fischer Assay volumetric yield of condensable liquid distillate, based solely upon the thermal destruction of the coal in the absence of air.
Low temperature coal Itars would be practically identical to some natural crude naphthenic petroleums, if it were not for the fact that certain chemical functional groups are attached to most of the hydrocarbon molecules. These chemical functional groups of oxygen, sulfur and nitrogen alter the primary hydrocarbon molecules and promote the combination and complexity of molecules, and thereby so complicate the entire tar r-elining problem as to render it almost insoluble without extensive high pressure catalytic hydrogenation as is described in Bureau of Mines Report of Investigations 6124, Hydrogenation of Pitch From Low Temperature Carbonization of Coal.
AIt is emphasized that prior known proposed processes which distill liquids from high volatile coals or perform high pressure hydrogenation retain a considerable proportion of the troublesome chemical lfunctional groups of oxygen, nitrogen and sulfur in the product oil. 'Extensive catalytic hydrogenation and hydrogenolysis are, therefore, necessary before the iinal refining into saleable products may be accomplished. It should be further emphasized that once the coal volatiles have been allowed to condense from the Vapor phase, polymerization and interrnolecular lreaction produces a tar which is at least as diicult to hydrogenate as the original coal.
The coal still system of this invention eliminates the chemically troblesome functional groups of oxygen, sul- -fur and nitrogen by the coincidental, continuous hydrogenation and by the subsequent catalytic surface hydrogenolysis of the primary volatile matter as it is distilled from the coal at system pressure and before it condenses from the initial vapor phase.
The total gasification and liquefaction processes lead to the synthesis of petroleum substitutes and the yield of products such as gasoline, diesel fuel, oil, lubricants, etc. At the present state of development, the total coal liquefaction systems are expensive to construct and to operate and while capable of producing satisfactory petroleum substitutes from coal, their present product cost is too high to be competitive with natural petroleum. This invention goes beyond the simple destructive distillation process which is common to practically all the known coal carbonization systems, but does not go as far as the total synthesis and liquefaction systems.
In all of the known coal gasification and carbonization systems of the internal-ly fired type the products of combustion inevitably mix with the primary volatile matter and the presence of substantial partial pressures of CO, CO2 and H2O aifect the character of the products. This is undesirable lparticularly when the direct utilization of hydrogen is of paramount importance since an expensive separating step then becomes necessary to recover specific constituents from the mixed gases. It is an important object of this invention to provide a method for coal distillation and gasification in an internally fired retort without mixing any products of combustion with the primary volatile matter, in a manner similar to my allowed copending application Ser. No. 41,679. Therefore, the uncondensable gases which result from the destructive distillation of coal, mainly hydrogen and methane, are continuously available invpractically a pure state and after removal of ammonia, hydrogen sullide and |water, can be re-cycled through the system, including a heat exchange portion thereof, while at the same time the re-cycled methane and whatever other hydrocarbon gases are dissociated into hydrogen and colloidal carbon before entering the coking and distillation zone. With this arrangement, practically all the hydrocarbon gases can be made available for cracking into hydrogen and essentially no other gases are present to lower the partial pressure of hydrogen.
An important object of -this invention is to provide an internally heated coal distillation and partial liquefaction system in which practically all of the distillable, uncomb-ined hydrogen which was originally present in the coal is conserved without dilution with combustion gases and is available at system pressures. That is, since the products of combustion utilized to heat the system are not mixed with the coal being distilled, -they do not mix with the primary volatile matter evolved. The uncondensable gases of the primary volatile matter are principally hydrogen and methane, and may include C2 and C3 gases. These hydrocarbon gases may then be cracked in the heat exchange portion of the system as the thermal carrier gases are re-cycled through the hot char below the combustion zone so that no hydrogen need be consumed in the incidental production of light hydrocarbon.
It is also an object of this invention -to provide for hydrogenation coincidental with the destructive distillation to produce a tar which is much higher in hydrogen and which is practically completely free of sulfur and oxygen while at the same time the spent char itself will be desulfurized and a substantial part of its nitrogen content recovered as ammonia. Since hydrogen is actually the thermal carrier fluid which, in the system of this invention, must raise the temperature of the preheated, dried coal from about 650 F. to 1600 to 1800" F., and since the thermal carrier hydrogen mixed with the primary and secondary volatiles and with nothing else, the hydrogen leaving the retort exerts 80 -to 95 percent of the system pressure while that of the combined primary `and secondary (volatiles from contact coking of the re-cycled heavy bottoms) volatile matter, exert but 5 to 20 percent of the system pressure of l5 to 30 atmospheres.
The coal utilization concept of this invention presents a novel method of skimming the oils from high volatile coals, or any mixture of coals in which the oxygen to hydrogen ratio at 650 F. does not exceed three to one, such that all of the coals hydrogen which is uncombined in C3 and heavier compounds is conserved at substantial pressure and in such purity and amount as to accomplish the complete, economic hydrogenolysis and hydrogenation of the condensable volatile matter. In this method the low volatile char (either gasified or pulverized) may be utilized for the generation of electric power, and much of the atmospheric pollution normally resulting from the utilization of sulfurous coal `can be eliminated.
All of the known prior coal carbonization systems have rigid requirements for the type and size of coal which may -be used. It is an object of this invention to provide a continuous system for the distillation and carbonization of coal which may operate on various types of coal irrespective of their agglomerating and ash fusion properties. Also, because of the particular construction of the system using gyratory shelves to feed and to support the series of zone-separating beds of broken solids, controlling the amount of coal and char on each gyratory shelf and uniformly feeding the solids over the periphery thereof into -a uniform annular cascade, any coal which tends to coke or agglomerate and to form scabs on the retort walls may be broken off by the gyrations of the supporting shelf and passed through the system. Further, any large agglomerated chunks too large to pass will be broken down as they are fed over the periphery of the shelf. The structural features of the gyrating shelf system per se are disclosed in my allowed and co-pending application Seria-l No. 17,293 (Series of 1960), filed March 24, 1960, now Patent No. 3,083,471.
In general, the capital investment in coal carbonization and processing plants is quite high and the interest on the investment plus the depreciation usually far outweights the direct cost of operation. Obviously, for any such process to succeed, the net sales of all products must exceed by a comfortable margin the cost of the coal plus the operation and investment charges. However, at least for the present, i-t is evident that the entire operational cost of any coal skimming process must be borne by the revenue from the sale of the distilled liquids, since the monetary value per heat unit of the solid fuel residue and of surplus gases for steam raising is little different from that of the original coal. Therefore, the economic justiiication of any such process must hinge upon the enhanced yield and value of its liquid products. The only chance for commercial success of such a process will depend entirely upon the feasibility of producing a petroleum equivalent product at a low cost and which can be refined into gasoline, jet fuel and diesel fuel in existing reneries.
It is unlikely that any very large new market can be developed for the principal chemicals historically derived from coal tar. Moreover, these chemicals -are presently manufactured more cheaply from petroleum refinery byproducts than from coal. Further, it is evident that the only very large outlet for special liquid fuels is that of the four million barrel a day demand of automotive and `aircraft fuels.
The attractiveness of this specialty motor fuel market becomes at once apparent when one compares the current price per million B.t.u. for motor fuel with the price per million B.t.u. for coal (motor fuel is 5 times as expensive). The economic feasibility of this quadri-phase process for the partial liquefaction of coal becomes possible -through increasing, by ya factor of five or more, the market value of some one-fifth of the coals initial caloric content.
This process invention provides the means of substantially augmenting the manufacture of high octane motor fuel from petroleum more cheaply than such increase in quality motor fuel production can be obtained from petroleum alone. Furthermore, the quadri-phase partial liquefaction system involves a lesser overall investment than is currently required for finding, developing, producing and refining of new pet-roleum by itself into motor fuel Iof comparable quality.
The basic knowledge of coal chemistry and of chemical engineering processing has developed to the stage at which greatly improved techniques are available for converting coal into more convenient forms of fuel and chemicals. Liquid fuels, chemicals, gases and coke can be produced from coal by the use of modern hydrocatalytic methods which employ poisoning resistant catalysts using the techniques of modern catalytic petroleum refining. Coal re- `fining hydrocatalytic processin-g applies catalysts in the form of hydrosolvation, hydrogenolysis, hydrocracking, hydroalkylation, and similar reactions with hydrogen to produce liquid fuels in the gasoline boiling range. The wide use of hydrocatalytic processing methods by the petroleum and chemical industries and their applicability to coal processing is well known. Commercialization of c'oal processing by such methods has not yet proven economically feasible.
The simplest and by far the least expensive of all processes which would extract liquid fuels and chemicals from coal is destructive distillation. Parenthetically, the chief objective of commercial high temperature carbonization of coal in America today is the production of metallurgical coke. Byproductliquid fuels and chemicals are currently of minor and quite incidental economic importance to the metallurgical fuel. Practically all of these hitherto essential coal tar chemicals can now be produced more cheaply and conveniently from petroleum as refinery by-products.
Many attempts have been made toward commercializing flow-temperature coal carbonization processes which would yield a greater amount of liquid fuels and organic chemicals and at the same time, produce a smaller proportion of low Value, solid residual fuel. All of these prior efforts toward the commercialization of low-temperature carbonization have failed economically for these chief reasons:
A. The coke or char produced by such systems is no more valuable than the original coal and, therefore, it can bear no part of the processing cost. Earlier attempts to commercialize such carbonization processes hopefully it ascribed an improved value to smokeless, high volatile char, but the demand for such premium solid fuel was never firmly established.
B. The condensable volatile matter distilled from coal contains a very large number of different interreactng organic compounds and the characteristics of such coal tars vary between Wide limits depending upon the conditions imposed by the system of carbonization. No such low temperature tar has found acceptance as a commercial source of organic chemicals.
C. More than half of all coal tar distillates constitute a very high boiling refractory rubber-like polymer called pitch (The distillate of the present process invention contains no pitch at all.)
D. The throughput rates of coal per unit of capital investment have been low and maintenance costs have proved to be excessively high.
The characteristics of the oils and tars produced and the nature of the compound which result from the destructive distillation of coal are specifically unpredictable without statin-g a number of conditions under which the carbonization is performed. The more important of these conditions are:
(l) The method of retorting the coal to effect carbonization and the physical preparation and condition of the coal. That is, whether, (a) the retort is externally heated; (b) the retort is internally heated; (c) the coal is heated en masse and whether batch charging or continuous charging is employed; (d) whether the coal is ground and dispersed in a thermal carrier or thermal transfer gas; (e) whether the coal itself is catalyzed; (f) whether the coal particles are saturated or coated with a hydrogen donor such as Decalin or tetralin or coated by hydrogen transfer agent such as phenanthrene; (g) if the ground coal is in the dispersed phase, whether the thermal carrier gas fiow concurrently or countercurrently with the coal; (h) whether the partial pressure of the volatile matter is above or below its critical pressure and therefore, whether or not the heavier boiling constituents can pass into the vapor phase before being thermally destroyed during carbonization.
(2) Temperature of the heat source, that is, (a) the temperature of the retort Walls if internally heated; (b) the temperature of the thermal carrier medium if internally heated.
(3) The residence time of the coal Within the carbonizing environment, i.e., the rate of evolution of the volatile matter.
(4) The size of the coal particles if `ground and the temperature to which the outer part of the coal particle (or the coal mass if unground) rises before all of the volatile matter is expelled from the cooler portion of the particle or the mass.
Although essentially all of the condensable volatile matter is expelled from coal between the temperatures of 700 F. and 900 F. when destructively distilled under conditions at which the partial pressure of the volatiles does not exceed atmospheric pressure, the character and the amount of the primary condensable matter may be drastically altered, depending mainly upon the several conditions to which the vapors are subjected following its distillation from the coal:
(a) The temperature to which the primary volatile matter is raised after it is evolved and the length of time the vapors are held above the vaporizing temperature.
(b) The type of surface with which the vaporized distillate comes in contact and the length of time such contact continues.
(c) The atmosphere during the carbonization, that is, the extent to which the partial pressure of the condensable volatiles is reduced by dilution with hydrogen, methane and other `gases such as hydrogen sulfide, water vapor, carbon monoxide, carbon dioxide, and ammonia, during distillation and while the volatile matter vapors remain at reaction temperatures.
Vapor phase catalysis or" the hydrogen entrained volatiles prior to initial condensation is the third and most important means of producing a coal distillate of desirable qualities. The character of the catalyst, the time of contact of volatiles with a catalytic surface, the temperature and the pressure during catalysis are the controlling variables. Vapor phase catalysis can affect the coal distillate in a number of ways including the removal of oxygen and sulphur and most of the nitrogen as their respective hydrides, producing an essentially neutral oil; rings can be caused to open or to condense and chain compounds can be caused to vform rings; cycloparafiins can be dehydrogenated to form aromatics and aromatics can hydrogenate to form cycloparafiins; alkyl groups can be transferred from one ring compound to another such as the formation of two mols of toluene from one mol of xylene and one mol of benzene; at higher temperatures, all aromatics can be completely de-alkylated so that the ultimate products, before complete carbonization into carbon and hydrogen, are benzene, naphthalene, anthracene, chrysene and their homologs.
As indicated above, vapor phase surface catalysis of the coals volatile matter immediately following destructive distillation of the coal, offers a wide range of control over the character of the quadri-phase system distillate. For example, over certain combinations of catalysts arranged in sequential fiuidized beds and subject to separate temperature control, the following reactions can be accelerated toward equilibrium Within a single continuous hydrogen entrained vapor stream:
(l) Sulphur, oxygen and nitrogen can be removed as their respective hydrides. Oxygen can be eliminated completely, thereby removing all tar acids and sulphur can be reduced below parts per million. Noncyclic nitrogen can also be eliminated and the remaining stable heterocyclic nitrogenous compounds such as pyridine and its homologs are water-soluble and/ or soluble in acid solutions and are separated thereby.
(2) Cycloparafhns (naphthenes) can be dehydrogenated to aromatics at temperatures above 900 F.
I (3) Benzene can be recycled and alkylated to ethylbenzene and to toluene by the partial dealkylation of the higher homologs.
The quadri-phase system of partial coal liquefaction offers a further means of product control: Dealkylation of alkyl naphthenes and the elimination of close boiling nonaromatics can be coincidentally effected by recycling the 207 2l7 C. fraction and the 2l9270 C. acidscrubbed fraction into the high temperature distillation Zone by spraying these fractions against the incandescent carbon cascade at the horizon at which it has reached `temperatures in the order of 1200 to l600 F. Residual petroleum refinery stocks can also be injected into the incandescent carbon cascade to accomplish contact coking and the recovery of aroma-tic compounds.
The present quadri-phase method and apparatus for low pressure coal liquefaction provides for the fiash melting of coking coals and the liquid and vapor phase hydrogenation of active sites formed by the thermal breaking of oxygen and sulfur intermolecular fonds, and subsequent distillation of the more easily liquefiable petrographic constituents of ground coal while it is falling freely countercurrently with respect to a stream of heated hydrogen at moderate pressure.
This process also concerns the manner and the sequence of heating the coal particles in order to autogenously create on each particle a liquid surface film by melting, and into and upon which liquid film is absorbed and adsorbed hydrogen and continuously distilling off the surface film of liquid and removing `the same from the system as a vapor. This process may also include the recycling of phenanthrene and other condensed nuclear compounds which, when melted, are favorable to the absorption and transfer of hydrogen to coal particles.
This process particularly concerns the effective increase of hydrogen concentration by adsorption and absorption upon the particle liquid surface. The process also includes the autogenous formation of this liquid vehicle as a lmolten or liquid iilm upon the particle surface and its continuous removal from the particle by distillation into thermal carrier hydrogen and the subsequent and immediate vapor phase hydrogenation of the whole stream of volatile matter upon one or more sequential beds of selected catalysts.
This invention further provides automatic control of the liquid phase temperature by the absorption of the exothermic heat of hydrogenation as enthalpy of vaporization, thereby minimizing disproportionating reactions and the formation of unreactive coke.
This process produces a primary neutral oil from the two-stage hydrogenation of coal, which oil contains less than two hundred parts per million of oxygen and sulfur and less than one percent of asphaltenes (organic material soluble in benzene but insoluble in normal hexane).
This process is entitled Quadri-Phase Method of Low Pressure Coal Liquefaction because during the free fall of particles of ground coal against the rising stream of hot, pressurized hydrogen in addition to the solid phase, liquid vapor and gaseous uid phases all exist simultaneously in or near each particle as it changes from dry coal to nonreacting char:
(1) The Solid Phase-because the coal enters the system dry and without liquid vehicle and exits from the system as dry, low volatile, low sulfur char.
(2) The Lz'quid Phase-because a molten liquid phase is formed primarily by the melting of the outer surface of each coal particle. Liquefaction is promoted by the rapid surface adsorption of hydrogen, some of which becomes chemically combined, reducing both the melting temperature and the boiling temperature of the liqueable coal constituents.
(3) The Vapor Phase-As the liquid surface film rises in temperature to its boiling point at system pressure, it is continuously distilled as a vapor into the thermal carrier stream of hydrogen until nothing but the unreactive char remains with its original ash and nonvolatile catalyst.
(4) The Gaseous Phase-Hydrogen is the thermal carrier and the principal reacting uid.
This process is aimed primarily at the partial liquefaction of coal' under moderate pressure using the hydrogen initially contained in coal to the fullest extent and to the best advantage in order to produce the maximum volume of useful liquid in a system normally operating below 500 p.s.i. except when more severe hydrogenating eifects should be desired.
Although this process of coal utilization goes somewhat beyond the simple `destructive distillation processes which are classical and common to practically all coal carbonization systems, this process does not go so far as total coal liquefaction as in the Frederick Bergius high pressure coal hydrogenation process. Rather, the present multiple-phase method of low pressure coal liquefaction is, in effect, an autogenous hydrogenation system which maximizes the advantages of the natural phenomena of destructive distillation performed in a hydrogen atmosphere at moderate pressures.
Also, in one embodiment of the present method, the degree to which disproportionating thermal reactions take place is controlled and the rate of chemical combination of hydrogen with coal is promoted by the judicial use of specific catalysts and hydrogen transfer agents coating the ground coal particles.
This process is, therefore, a median method which might be classified as lying about midway between simple coal carbonization and the very complex high pressure hydrogenation of the whole coal.
The present method also accomplishes what neither of the two early concepts contemplate by yielding a reiinable, neutral oil from coal without tar acids or tar bases as the direct product of the process, and without the form-ation of any refractory pitch complex.
Other objects of this invention will be pointed out in the following detailed description and claims and illustrated in the accompanying drawings which disclose, by way of example, the principle of this invention and the best mode which has been contemplated of applying that principle.
In the drawing:
The single figure is a semi-schematic illustration of a coal still capable of carrying out a preferred embodiment of the process of this invention.
In general, the schematic representation of the coal still includes a single, continuous, pressurized, vertical vessel ltl'having means for measuring and charging coal thereinto and discharge means for removing the char or ash therefrom. The coal still, between its top (solid materials charging) and its bottom (solid materials removal), is divided into Ia number of zones for accomplishing various functions. The single continuous, pressurized vertical vessel 10 performs various functions in four different zones. The zones are labeled on FIG. l of drawings. The zones include a concurrent ow drying and preheating zone A, a distillation zone and thermal treatment B, a partial combustion zone C, and a heat transfer and methane cracking zone D, somewhat similar to the allowed column of solid fuels in accordance with the function of the various zones.
Zone A performs the triple function of drying, preheating and removing carbon oxides from the crushed raw. coal. The heat for zone A is furnished by the sensible heat of the high temperature flue gas from the partial combustion of char in zone C. The hot flue gas llows concurrently with the raw fuel cascade and effects the preheating of the coal to 650 F. without any destruction of the coal substance beyond the expulsion of water and carbon oxides.
Zone B performs the function of distilling olf the primary volatile matter and heatingthe coal completely through its plastic range within a fraction of a second while the coal particles are in suspension and while they are cascading against hot ascending hydrogen preheated in contact with incandescent char in zone D below. Little or no agglomeration of the coal particles occurs, and in the pressurized, vessel 10 the volume of the char increases only about live times as compared to some times which is possible in such systems operated at atmospheric pressure. Also zone B allows for thermal treatment of recycled products and contact coking of heavy bottoms and mixed ground coal, if desired.
Zone C is a combustion chamber within which the partial combustion of the char to carbon dioxide is achieved in two stages, i.e., some carbon monoxide is generated inthe fuel cascade by the injection of a limited amount of oxygen, then the carbon monoxide is separated physically from the solid carbon and subsequently is burned to carbon dioxide by a secondary injection of oxygen. About one-half of the heat of the secondary combustion of carbon monoxide to carbon dioxide is radiated back to the fuel cascade and about half is conveyed to zone A as sensible heat of the ue gas leaving the combustion zone D. A preferred partial combustion zone is shown in my co-pending application Serial No. 186,920 tiled April l2, 1962.
The temperature of the char and the temperature of the flue gas are regulated by the rate of oxygen admission into the combustion zone. The apportioning of the sensible heat content of flue gas in relation to the sensible heat content of the char is controlled by varying the oxygen enrichment by the degree of preheat of the combustion blast.
As is shown in FIG. l, when necessary char is recycled through the combustion and heat transfer Zones C and D. The purpose of recycling the char is to increase the total heat capacity of the fuel cascade through the lower two functional Zones by a factor of about four, as is explained in detail hereinafter. This becomes necessary only in very high volatile coals when the low volatile char is less thanSS or 60 percent of the initial moisture and ash-free coal.
Zone D performs three functions: It thermally cracks recycled methane in contact with cascading, incandescent char; it transfers heat from the incandescent char, heated in the combustion Zone D above to the recycled hydrogen and to products of thermal disassociation (hydrogen and carbon black) which become the thermal carrier media for zones C and B above; it also recovers useful heat from the low volatile spent char.
The char produced in the system is typical of that formed by dropping ground, melting coal against streams of gases heated above l500 F. with three very important and distinct improvements: 1t has a higher bulk density, lower sulfur content and greater surface activation.
Each of the zones contains one or more gyratory shelf feeders for solid materials and zone gas zonal gas diffusion barriers. Each gyratory shelf is of the nature disclosed in my allowed cti-pending application Serial No. 17,293 led March 24, 1960 and reference may be had thereto for a further description of the details of the mechanical features of each gyratory shelf. The gyratory shelves dening the concurrent flow drying and preheating zone A are shelves 12 and M. Shelf 12 serves as the solid material feeder shelf for the entire system. Shelves 12 and 14 carry enough solid materials thereon so that they function as gas separating beds. In other words, the solid unsorted material on the shelf is controlled in depth and density such that gaseous fluids will not readily flow therethrough and will not pass from one zone to another in significant amounts at thesmall differential pressures which are automatically maintained. The distillation thermal treatment Zone B may be detined by separating beds on gyratory shelf units 14 and 16. Gyratory feeder unit 16 likewise includes solid materials carried thereon of such depth and density to function as a separating bed and also to prevent ow of gaseous fluids between the zones above and below the bed. The partial combustion zone C is defined gyratory feeder shelf units 16 and 1S. The particular construction and operation of the partial combustion zone is clearly set out in my co-pending application Serial No. 186,920 led April l2, 1962 and now Patent No. 3,190,245. Gyratory shelf feeder unit l@ also carries a separating bed for effectively separating the combustion and gas producer zone C from the next lower zone which is the heat transfer and methane cracking zone D.
For the sake of simplicity only, the gyratory shelves de- -ning the separation of the various zones have been shown.
It will be understood, however, that additional gyratory shelves can, if desired, he utilized with any Zone, although the additional gyratory shelves would not carry the materials in such a depth and density that it would serve as a gas separating bed.
It is noted that the separate functions are performed in zones which are separated within the continuous vertical vessel by beds containing deep layers of crushed char or coal which substantially prevent the flow of gaseous fluids between adjacent Zones. The beds themselves are comprised of unsized, unsorted solid material through which heated gases simply cannot pass in volume at existing small pressure differentials.
Control of the depth of solids on the separating beds may be accomplished by any suitable known type of level sensing c-ontroller, such as a gamma ray level detector adapted to control solids being fed to the separating beds. Two positionable gamma ray level detectors can be provided for controlling the maximum and minimum depth of each separating bed.
At the top of the vertical cylindrical retort is a measuring bin 20 which is charged with only enough raw, crushed coal so that its entire contents may be dumped into a charging lock 2.2, thus' leaving bell valve 2li completely clear for unobstructed closing. After the raw coal is dumped into the charging lock 2.2 and valve 24 is closed, the coal may be pressurized by closing a valve 26 and opening a valve Z3 allowing non-explosive ue gas from flue gas receiver 32 to flow into the charging lock through conduit 30 at system pressure. The charging loclt 22 is closed at the bottom by hopper-like arrangement and a movable bell valve 34. Thus, when the charging lock contents are pressurized, valves 26 and 2S are closed and bell valve 34 may be opened to dump the pressurized charge of solid carbonaceous material on to the system gyratory feeder shelf l2. After dumping the valve 34 may be closed and the vent valve 26 opened to allow the pressure in charging lock 22 to vent to atmospheric through conduit 36. 1n the pressurizing of charging lock 22 with the flue gas, the purpose is not only to use a gas more readily available and cheaper than steam but the ue gas will be entirely non-explosive since it contains principally products of combustion.
Below the system gyratory feeder shelf 12 in zone A, there may be additional gyratory shelves (not shown) and there may be a core-baffle 3S or similar means to ensure that the falling cascade is generally annular in section. Leading into the top of zone A below the gyratory system feeder shelf l2 is an inlet itl for hot flue gas and there may be a plurality of inlets (not shown) equally spaced to ensure good solid and gaseous material contact. At the bottom of zone A, is a conical collector hood 42 for removing the ue gas after its heat exchange purposes in the drying, deoxidizing and preheating Zone.
Below the separating gyratory shelf 14 in the flash carbonization zone B, there is a conical offtalre hood 44 for the volatile matter distilled from the coal as well as thermally treated recycled products of the process as will be described. Also in zone B are a plurality of spreader inlets 45, 46 and 47', for introducing recycled intermediates for thermal treatment in an atmosphere of hydrogen plus heavy 4bottoms for contact coking and for redistillation, together with whatever solids they may include or have included therein. The inlets 45, i6 and i7 in zone B allow for different degrees of severity of thermal treatment, ranging from merely redisti-llation into the vapor.
phase at 900 F. to mild dehydrogenation of naphthenes to aromatics in the central injection, to the lowest injection where the alkylated naphthalenes are completely thermally dealltylated in contact with incandescent carbon. The introduced liquids (and gases) are spread out to contact the annular cascade by similar baffles dit and the cascade is kept in annular shapeby a core baffle 50 which also functions to prevent the solids from boiling up at the bottom of zone B. Also near the bottom of zone B, there is an inlet conduit 52 for hot thermal carrier hydrogen and this inlet is arranged so that the hydrogen contacts the entire annular cascade and flows countercurrently thereto. There is also a solid material inlet 54 underneath the separating bed carried on shelf 16 and this solid material inlet Se is for recycling char as will he described.
Zone C includes a conical hood 56 with a flue gas offtake 58 at its apex and an oxygen inlet 60 into the lower portion of cone 56 as well as additional inlets for oxygen and air 62. The operation for accomplishing partial combustion of char to carbon monoxide and the further combustion of carbon monoxide to carbon dioxide is per se not a part of this invention, but rather is covered in copending application Serial No. 186,920 led April l2, 1962.
Below the gyratory shelf 18 Within the vertical vessel 10 and in the methane cracking zone D, there is a conical hood otftake 6a for hot hydrogen. Below the hood is another core baffle 66. Core bafe 66 and the other core baffles mentioned above, would preferably have a diam- 1 1 eter such that the clear annular space between the edge of the core battle and the inside of an insulated and possibly cooled shell of the pressurized vessel, will preferably be one to three feet in width.
Below core baiiie 66 is a collector 68 for recycling a predetermined quantity of char when the yield of char is less than 60 percent of the M.A.F. Coal and/or when additional sensible heat is necessary for methane cracking, as will be described hereinafter.
At the bottom of methane cracking zone D there may be a hopper 70 closed by a bell valve 72. Alternatively, there may be another system in the same or adjacent vvessel so that the char may be heated up again and used for gas making as shown for example in my copending allowed application, Serial No. 74,907 led December 9, 1960, now Patent No. 3,088,816.
Below hopper 70 is an isolating bin 74 closed at the bottom by hopper 76 and a `bell valve 78. This isolating chamber 74 enables the char to be dumped in toto into a char lock chamber 80. Char lock chamber 80 is similarly closed at the bottom by hopper 82 and a bell valve 84. Flue gas from ue gas receiver 32 may enter through .conduit 86 under the control of valve 88 into char lock 80 and may be vented therefrom through conduit 90 under control of valve 92. The bottom of the vessel may, if desired, include a hopper 94 for removal of the char product which in turn may be used to raise steam or for other industrial fueling purposes.
As can be seen from the foregoing, the passage of the solid materials, which consist of ground, unsized coal, is vertically downward in the vessel controlled at various horizons by the gyratory shelves, and including when necessary a recycling through the combustion and heat exchange zones, some portion of the char. The recycling of the char includes in addition to the collector 68, a char conduit 96 which is controlled by a star valve 98. Star valve 98 controls the entire feed of the recycled char and may be driven from suitable motor controls interrelated to the other parameters of the system. The solid materials which are fed by star valve 98, enter conduit junction 100 which functions as a heavy .solids trap, and the heavier or coarse materials fall downwardly into conduit 102 and may be periodically removed by opening a venting arrangement including interlocked valves 104 and 10S. Gas
at system pressure circulated by a fan 106 draws the recycled char from juncture 100 upwardly through conduit 108 and deposits it into a gas separator 110. Within the gas separator 110 the gas is taken off in hood 112 and recirculated through line 114 to juncture point 100. Meanwhile, the recycled char falls downwardly through inclined inlet 54 to below the level of solid materials on separating bed 16 to be recycled through the partial combustion zone C and methane cracking zone D. Thus, the solid materials iiow vertically downward but are recycled as required to furnish the heat exchange capacity necessary for the system.
In addition to the solid material ow as described above, there are two separate fluid circuits. One of the circuits is that of thermal carrier gas consisting essentially of hydrogen, and the other is that of combustion flue gas consisting essentially of carbon dioxide and inert gas (nitrogen). Mixing of the carbon dioxide in the hydrogen circuit is prevented by deep separating beds 16 and 18 adjusted by suitable controls and a very small counterow of hydrogen into the ue gas circuit is maintained by positive displacement metering of the fluids into and out of the two circuits of the system. The hydrogenous and oxygenated fluid circuits are separated by the mechanically controlled gyratory shelf separating beds as described below.
The thermal carrier hydrogen circuit may be described starting with a Conduit 116 for recycled hydrogen and methane from a condenser and scrubber and this recycled gas passes through a positive displacement metering valve 118 through an inlet conduit 120 into the annular cascade 12 of freely falling hot solid materials which have left the partial combustion zone C and have been fed by gyratory shelf 18 through the methane cracking zone D. Methane is cracked into hydrogen and colloidal carbon in zone D as it flows countercurrently to the hot hydrogen. The very hot hydrogen passes ot through oiftake cone 64, ottake conduit 122 (which may include a mechanical cleanout 124) and into a knockout chamber 126 with a bottom outlet valve arrangement 128 for solid materials. The knockout chamber 126 for the hot thermal carrier hydrogen contains the hydrogen at a temperature of around 2500" F. and bypasses the partial combustion zone C to pass the hot hydrogen through conduit 52 into the bottom of the distillation and thermal zone B so it ilows countercurrently with the falling hot annular cascade. As the hot hydrogen flows countercurrently with the falling cascade of coal in zone B, it also flows countercurrently with any recycled intermediates and entrained solids. The volatile matter distilled off the coal, the thermally treated recycled intermediates, etc., ow through offtake hood 44 through conduit 130 where it may be mixed with additional hot hydrogen from line 132 under the control of metering valve 134. Additional offtakes (not shown) may also be provided at diferent horizons. The mixture of volatile matter and hydrogen passes into a knockout drum 136 with the bottom valve 138 and with a mechanical cleanout 140. The knockout drum may contain sized uidized char onscreen 139 and the tar in the products passing therethrough will be removed by impingement on the char. The gases and vapors from the knockout drum 136, which includes volatile matter and entrained solids with thermal carrier hydrogen at a temperature of about 1000 F., passes out line 146 to three catalyst chambers in series, these are catalyst chambers 147, 148 and 149. Additional hot or cold hydrogen may be admixed into line 146 for temperature control through line under control of valve 152.
rlfhe three catalyst chambers 147, 148 and 149 in series perform the following functions on the stream:
Catalyst chamber 147 deoxidizes, desulphurizes and saturates the olens, preferably on a cobalt molybdate catalyst.
Catalyst chamber 148 performs the -function of reforming whichis a common type of renery operation and which removes hydrogen from naphthenes to leave aromatic compounds.
Catalyst chamber 149 has the further purpose of causing an alkylation shift using a third type of catalyst which promotes the transfer 0f alkyl groups such as methyl, ethyl, propyl, etc. from one molecule to another. For example, practically 100% yield is obtainable when benzene accepts one methyl group from xylene to produce practically all toluene.
Cool or cold hydrogen from line 142 may be admitted selectively as desired to each catalyst chamber 147, 148 or 149 through control valves 141, 143 and 145 respectively for the purpose of temperature control.
The outlet from catalyst chamber 149 includes a line 154 leading into a fractionating system 156. The fractionating system 156 may comprise several smaller lfractionators (not specifically shown) known as strippers. However, since this invention is not concerned with the art of fractionating per se, fractionating system is merely disclosed in general.
From the bottom of the fractionator system 156 a takeoff 174 is provided with a control valve 176 for pumping heavy bottoms through line 178 into a selected inlet cone within zone B of the coal still. Additional heavy bottoms from the knockout drums may be mixed into line 178 and ground coal or other solid particulate hydrocarbonaceous material may be added into line 178, for example through inlet 180 controlled by valve 182. Also, instead of recycling for contact coking or other thermal 13 treatment the bottoms could be removed through line 131 under control of valve 183.
The fractionating system will also have a number of other outlets as is known in the art. Overhead passes out line 158 to conventional condensers, gas scrubber-s, etc., as is known in the art. is the fact that a number of different outlets 160, 162 and 164 at the side of the fractionator system represent different boiling range products as will be `set out in detail hereinafter.
The different boiling range streams which appear in outlets 160, 162 and 16d (as enclosed by bracket 166) may be selectively recycled for reheating and revaporization. This is accomplished by selective fluid interconnections between the fractionator system outlets of bracket 166 and zone B coal still inlets enclosed by bracket 168.
Therefore, in order to obviate the use'of pipe stills, recycle streams may be sprayed into the cascading `hot carbonaceous material in zone B. Those fractions which require the least thermal exposure, for example, benzene which is being recycled for alkylation say to toluene while at the same time dealkylating xylene to toluene, will be sprayed into the upper portion of zone C. At the same time, very intense dealkylation of alkylated naphthalenes require that these compounds, that is, those boiling above 218 C. and below 290 C., be recycled into the lower and bottom part of zone C.
The remaining fluid circuit is that of the combustion gases. In the partial combustion zone C, metered amounts of oxygen and air are admitted through inlet line 62 from oxygen manifold 184 and compressed air line 186 under the control of metering valves 138 and 120 respectively to mix in required proportions for entrance into the falling cascade for oxidizing the carbon of the coal to carbon monoxide. The carbon monoxide within the combustion cone 56 is further oxidized to carbon dioxide by oxygen introduced through line 60 under control of valve 192 from oxygen manifold 184. The CO2 flue gas at very high temperatures e.g., around 3000 F., passes from offtake S into a flue gas knockout chamber 194 having an intermittent mechanical cleanout 196 for the inlet passage and the usual bottom valve 198. Hot flue gas passes out the top thereof through line 200 into inlet 40 in the top ofthe drying, deoxidizing and preheating zone A. The outlet of the gas from Zone A after owing concurrently with the falling annular cascade and preheating the same to about 650 F. is through outlet offtake cone 42, conduit 202 into a gas knockout drum 2011; at approximately 700 F. The usual bottom valve 206 is provided as is a mechanical cleanout20. The flue gas from the knockout drum 204 passes to a cooler and flue gas condenser 210 from where the stream distilled condensate passes out through line 212 under control of valve 21e, and the cooled flue gas passes through outlet 216 under control of metering valve 213 into the flue gas receiver 32 through check valve 220. The gas for carrying and transporting the char during recycle may be obtained through line 222 under control of valve 22d for making up any gas loss in the gas transport.
The operation of the coal still and the process of this invention will now be described.
The input coal is ground but not sized and may be coated either with a catalyst or a recycled hydrogen transfer agent such as phenanthrene either sprayed on while liquid or crushed and mixed with the coal.
The optionally pretreated ground coal is dumped into measuring bin 20 and then into charging lock 22 by opening valve 24. Charging lock 22 is brought up to system pressure by closing valve 26 and opening valve 28. Upon attaining system pressure in charging lock 22, bell valve 34 in the bottom thereof may be opened so that the crushed coal from charging lock 22 is dumped upon the system gyratory shelf feeder unit 12. After the crushed coal has been discharged through bell valve 34, the charging lock 22 may be depressurized by closing bell valves 2d Most important howeverv 141 and 34, closing valve 28 and opening valve 26 which discharges the contained liue gases through line 36 to the atmosphere. The charging lock may be then reloaded as before.
The rate at which the crushed coal is fed off the system gyratory shelf feeder unit 12 or any of the other gyratory feeder shelves is a function of the amplitude and rate of gyration of each gyratory shelf feeder unit.
ln the drying deoxidizing and preheating Zone A, the crushed coal and hot drying tiue gas admitted at 40 mingle in concurrent downward ow. In drying deoxydizing and preheating ground coal, two primary functions are effected at precisely limited temperatures. First is the removal of superficial moisture at steam saturation temperature at system pressure. For example, at a system pressure of about 20 atmospheres (300 p.s.i.) the steam saturation temperature is 417 F. A large amount of heat may be rapidly transferred to cold moist coal from a very high temperature gas without thermal destruction of fine coal particles. If for example, the drying gas enters the Zone A through line i0 at about 2800" F., the saturation tem perature of steam at system pressure cannot be exceeded untilpractically all of the superficial moisture has evaporated. At that same time, the coal particles must have also risen in temperature to the saturation temperature of 418 F. At this point, some three-quarters of the available heat has been transferred from the drying gas to the coal and to the surroundings and the temperature of the drying gas has dropped from about 2800 F. to about 1200 F. Therefore, in flowing concurrently the very hot drying flue gas can at no time have sufficient thermal heat to destroy even the nest coal fragments.
The other function performed in this zone A is the removal of oxygen from lower ranked coals as carbon oxides and as water vapor, and this occurs primarily between the temperatures of 400 F. and 650 F. without significant evolution of hydrogen or of hydrocarbons. In this temperature range many oxygenated compounds break down to form water, carbon monoxide and carbon dioxide. However, it is important that the temperature of the coal in zone A is n ot raised above 650 F. at which point distillation of hydrocarbon begins because any hydrocarbon evolution in Zone A must represent a net loss to the system.
The elimination of the carbon oxide gases and water vapor before the distillation and producing the hydrocarbon volatiles is a very important advantage and improves the operation for two principal reasons. First of all, the available hydrogen to carbon ratio of the coal is markedly improved and the significance of this increases with the lower ranks of the coal. Secondly, whatever carbon oxide gases appear in the volatile stream must be scrubbed from any recycle of gases because their diluent effect is cumulative. Morever, any recycled carbon dioxide in thermal carrier hydrogen becomes, to some extent, a reactive oxydizing agent at system temperatures and interferes with the production of neutral oil. Therefore, coal enters zone A at system pressure and at a relatively cool temperature. The coal is preheated by incoming flue gas coming in about 2800 F. and exiting at a temperature of about 700 F. so that the coal is dried and preheated to about 650 F. as it lies on gyratory shelf 14 and this temperature is just below its temperature range at which evolution of hydrocarbon gases begins to any important extent. Also, the freed carbon oxides and water vapor will be expelled from the system through offtake 202 and after being cooled, the steam condensated will drain off through line 212.
The dried, deoxidized, and preheated coal is then fed off the periphery of gyratory feeder unit 14 into the dis tillation and thermal treatment zone B. In zone B, a thermal carrier fluid, which consists principally of hydrogen is passed countercurrently through the annular cascade of descending coal to drive oif the primary volatile matter through offtake cone 44 and flue 130.
I have discovered that finely ground melting coal dropping freely through heated gases can be carbonized at rates in the order of some 50,000 times faster than has been achieved by any system which carbonizes coal en masse. Further, the limiting factor of flash carbonization capacity is the rate at which heat can be supplied to the system rather than the rate at which coal can absorb the heat available.
Most bituminous coals melt and many actually become liquid between 700 F. and 900 F. However, the plastic condition usually encompasses a temperature range of no more than 100 F. The fact that some coals soften to the extent of actually becoming fluid, greatly complicates the mechanics of handling coal while it is in the intumescent stage or temperature range. Sticky coal in the 700 F. to 900 F. temperature range adheres to practically all surfaces cooler than 900 F. with which it comes in contact. Equally serious is the fact that caking coals agglomerate in passing through the plastic range. The worstsituation, if heated en masse without movement, strongly caking coals will actually form a chunk of solid coke the size and shape of the containing vessel. Even those coals which are not considered strongly caking will tend to melt in an atmosphere of hydrogen which is the thermal carrier uid in this invention. However, even sticky coal will not adhere to surfaces which are maintained above the thermal setting temperature of about 900 F. Furthermore, when dispersed and freely falling, agglomeration is negligible.
After being dried and preheated and deoxydized in zone A wherein about half the total heat requirement of the system is supplied, the coal being fed olf gyratory shelf 14 falls evenly and freely as an annular cascade into a rising column of pressurized hot hydrogen admitted through line 52, the hydrogen having sufficient heat capacity per unit time so that all of the coal must pass through its intumescent range and become thermally set before arriving at a pile in the bottom of the chamber including the flash carbonization zone B. At the same time, in order to scale off any scabs which may occasionally adhere to the sides of the apparatus, large chunks of refractory tirebrick may occasionally be cycled through the system.
It is also important that high sulfur coal can be used in the system and the resultant char will be substantially desulfurized. If coal is heated rapidly in a stream of diluting hot hydrogen as it is in this process in zone B and if the organic molecules of volatile matter which contain sulfur are immediately removed from the solid carbon as they are in this process through offtake cone 44 and line 130, the resultant char will be desulfurized to the extent that a large part of the organic sulfur and half of the pyritic sulfur (but none of the sulfate sulfur) is removed with the stream of volatiles. Much of the remaining portion of pyritic sulfur (FeS) is removed as SO2 and COS during partial combustion of char at temperatures in the order of 2500 F. to 3000 F. in combustion zone C. The resulting char exiting from hopper 94 at the bottom of the vessel after also being contacted with hot hydrogen in zone D would contain only a small part of the original sulfur of a high sulfur coal and this, of course, is a desirable characteristic of the char for steam raising, metallurgical use and the like.
Falling coal in zone B, ground to pass through a 30- mesh screen can be heated from 650 F. through its plastic range in less than half a second during a free fall of less than ve feet against rising hydrogen at 1500 F. It is important to note that the coal particles with a terminal velocity in hydrogen less than the superficial velocity of the hydrogen and which are therefore entrained may be recycled with the recycled heavy bottoms entering through inlet cone 46 in zone B and sprayed against descending solids.
The coal entering zone B is preferably of such a neness that its terminal velocity in hydrogen at system pressure may lie between two feet and twelve feet per second. For optimum liquefaction, a catalyst and/or hyfv drogen transfer agent (phenanthrene) may be coated on the coal particles in a manner most suitable to distribute the catalyst on the surface of each particle of coal. The coal, of course, is dried and preheated in zone A as described above and is dropped into the rising stream of hot thermal carrier hydrogen which partial pressure is from ten to twenty times the partial pressure of the desirable oils in order that they may freely evaporate at system temperature and pressure.
As the coal particles drop countercurrently in zone B through the thermal carrier hydrogen, there is established a reaction zone whose upper limit is dened by the initial melting point of the coal and the formation of a liquid lm on the surface of the coal particles. The lower limit of the reaction zone is that horizon in which all the liquid surface lm has been completely distilled from the particles and only char and catalyst remain. The vertical extent of the coal melting and hydrogenation reaction zone is principally a function of four controllable parameters of the system including the inlet temperature of the preheated coal particles, the size and size range of the coal particles, the volumetric heat content of the thermal carrier hydrogen per unit time, and the partial pressure of the condensable volatiles.
In general, the hydrogenation characteristics of various coals can be predicted by the comparison of the opacity of thin petrographic sections and those sections which are more translucent will hydrogenate more rapidly and under milder conditions than those of less translucence. A further reliable prediction as to the hydrogen acceptance of the petrographic constituents of coal may be obtained from the determination of sulfur, oxygen and nitrogen which may form cross bonding between segments of the original coal molecule and which bond may be thermally broken to form active sites which readily hydrogenate. The thermal breaking of such cross bonds is the primary mechanism by which the original coal molecule yields liquid fragments which have molecular weights in the order of one tenth of the coal. Hydrogenation of these active sites increases liquefaction and pressures below 500 pounds per square inch. v
The contact coking of recycled bottoms and mixed solids may also be accomplished in zone B. By introducing the bottoms into the lower part of Zone B for some thermal treatment secondary distillation up to l800 F. is accomplished and redistillation and contact cokng of selected recycled fractions with whatever entrained solids may be therein, is also accomplished. Furthermore, the tars from the various knockout drums can be admitted to line 178 for recycling through inlet 46 with the heavy bottoms and in addition, nely ground coal may be mixed with the heavy bottoms after being admitted through inlet 180.
Thus, as the falling char reaches gyratory shelf 16, it
has been heated to a temperature of at least l600 F. and
the volatile matter has been distilled off so that it contains only about 2% of volatile matter. The coal at this point is joined by recycled char from char inlet 54 to provide the necessary heat capacity for the system, as is explained above.
The stream of hydrogen thermal carrier gas and primary volatiles is withdrawn through conduit l and is introduced into -knockout and tar removal drum 136 at about 900 F. with Ithe vapor pressure of the highest boiling components about one tenth to one twentieth of system pressure. Next, the combined gas stream is subjected to vapor phase hydrogenation in sequential catalytic chambers 147, 148 and 149. Additional hot hydrogen may be diverted from the main stream of thermal carrier gas through line 1'3-2 to conduits l130 and 150 for combination with the mixed gas stream. This'further addition of hot hydrogen maintains the gas stream at lthe desired high temperature of about l000 F. and prevents any undesired condensation of valuable hydrocarbons, by increasing the compounds) 15 Tar acids and tar bases 15 Aromatics Refractory pitch, 1boiling above 600 F 50 The fina-l coal still distillate, operating on bituminous coal under rather severe hydrodealkylating conditions may be expected to produce a distillate of lthe following approximate analysis:
18 Oleins none Aromatics (average molecular weight less than 115) 95.0 Pitch none Tar Acids none rTar bases, chiefly pyridine and quinoline 1.0 Sulfur Less than 100 pp ni.
In order to illustrate the great chemical complexity of coal distillate which is produced 'by conventional processes,
and Vparticularly so as to point up the very distinct advantages of the coal still system, presented herebelow is a list of the chief organic compounds which have been identied yin coal tars and light oils. Several of the compounds listed in column three are recovered commercially in byproduct colte oven practice.
Column one identies many of the compounds which exist in the coal still distillate under mild operating conditions. Column eight lists the final coal still products when operating under the most severe hydrorevning and Percent hydrodealkylating conditions and indicates the initial com- Parafns 4.0 pounds from which they are derived.
Mild conditions Compound Initial compound Compound Classification Name of compound Compound formula retained Severe conditions appearing of compound group under Seyer@ in straight coal still l Final coal still run coal still conditions M.P., Boiling distillate distillate C. point, C.
Alkane n-Pentane 36. 2 Hydrogen, methane,
ethane, etc. Naphthene Cyclopentane 49. 5} D0 Cyclo-slkene Cyclopentene C H 44. 2 Alkene Pantone-1...-- 29. 9 Do. Alkene n-Hexylene 67. 5 D o. Cyelo-olen 1-3 cyclopentadiene.. 42` 5 Do. Alkane n-Hexane 69. 0 Seine benzene. Aromatic E tetained as benzene.
C clohexane 8 enzene. iNaphthene iThiophene gzS plus butane.
C clohexene 00H10 enzene. icycwlefm ipiethyismnde.. s2. o Hts pius ethane.
Alkfirie n-Heptane C H 98. 4 Toluene. Naphthene Methyleyclohexane 100. 3 Toluene or benzene. Aromatic Toluene 110. 6 Do. Naphthene 1,3 dimethyl 4 121. 0 Xylene to benzene.
cyclohexane. Naphthene 1, 4 dimethyl CH12(CH3)2 No 119. 0 Do.
cyclohexane. Naphthene Cycloheptane 01H14-. 118. 1 Light hydrocarbons. Wbater soluble tar Pyrz'dzne CsHN 115. 3 Pyridine.
ase. 2methylthiophene CH3C4H3S 112. 5 HQS plus light HC's. 3-metliylthiophene CHaCiHgS.- 115. 4 Do.
Alkane n-Octane CEHIL-. 125. 8 Light HCs. Allrene Octylene CgHm 123 Do. Water soluble tar 2-Picoline CHgCHiN 128 Pyridine.
base. Dirnetliyl- (CHW C4HgS 136-138 HzS plus light HCs.
thiophene. Aromatic Ethyl benzene C5H5C2H5 136. 15 Ethylene benzene or benzene. do p-zylene C5H4(CH3)2 138.4 Xylene or benzene. do m-zyZene-- C6H4(CH3)2 139.1 Do. do o-zylene CEHACHQL-. 144.4 Do.
Aromatic; arylal- Styrene CeHsCHzCHz 146 Ethyl benzene kene. onbenzene. Water soluble tar Dimethyhpyridines- (CH3)2C5H3N 143-163 Pyridine.
bases. lutidines. Armn atie Isoropylbejnzene CeHCHHg); No -96. 9 152. 4 Benzene or toluene.
umene Propyl benzene. CGH5CH3C2H5 No -101. 6 2 Toluene or benzene' Ethyl toluenes CGH4CH3C2H5.. Do. i Trimethyl-thio- (CH3)3C4HS H13 plus light.
phene. HCs. Mesztylene CHMCHsk Toluene or benzene. 1,2,4 trimethyl ben- CeH3(CH3)3 Do zene (pseudocuxnene). Thiophenol H2S plus benzene. D ieyclo-pentadiene Naplithalene. n-Decane Light HCs. Coumarone Toluene or benzene. Hemimellitene Do. isopropyl toluene Do.
(Cymenes). Indene CnH4CH2CH:CH Benzene. 1,3, diethyl benzene- CuHi(C2H5)2 Do. PheHOl a 50H D0. 1,4, diethyl benzene CnH4(CzH5)2 Do. Durene (CHaMCsHz No 80 194 Toluene, xylene, or
Mild conditions Compound Initial compound Compound Classification Name of compound Compound formula retained Severe conditions appearing of compound group under severe in straight coal s Final coal still run coal still conditions M.P., Boiling distillate distillate C. point, C.
Tar acid 30 191.5 Toluene or benzene.
do 11 202.8 Do,
do 36 202. 5 D0.
I-lydrogenated -30 207. 2 Naphthalene.
Tar acid. (CHmCHaOH 26 211. 5 Xylcne or benzene.
Tar base m-Tolunitrile CHQCBHCN 23 v 214 N131; plus xylenc or enzcne.
, do o-Ethyl analine Cz`H5CH4NHq -43 215 Ethyl benzene or benzene.
Tar acid 2,6, xylenol 49 212 Xylene or benzene.
do 2,5 xylenol 74. 5 211.5 D0.
Hydrogenated l 1,4 dihydro-naph- -43 194. 6 Naphthalcne.
Tar base 2,5 xylidine. (CHghCHsNHz 15. 5 217 Ng; plus xylcne to enzene.
dO 2,4 Xylid11e (CH3)2C5H3NH2 216 D0.
Alkane Dodecane CHa(CHn)rCH3 -12 214 Possible ring forma- Tar acid m-Ethyl phenol CzHCaH40H -4 214 Ethyl benzene t0 Jenzcne.
Tar base p-Tolunitrile CHaCtHrCN. 29. 5 217 N131; plus xylcne to Tar acid p-Ethyl phenol CzHCeHrOH.- 46 219 Ethyl benzene t0 enzene.
Bicyclic aromatic.. Naphthalene C H 80.2 218 Naphthalene.
Tar ac' 2,3 xylenol (CHa)zCH3OH 75 218 Xylene to benzene.
do 3,5 xylenol (CHmCnHaOIL- 68 219 Do.
Tar base 3,5 xylidinc. (CHahCHaNHn No 221 NbHa plus xylcne to enzene. Tar acid o-Propyl phenol CaHCHrOH No 220 Pzgnpyl benzene to enzcne. Mesitol (CHmCtHZOH No 69 220 Mcsitylene tobenzenc. Thio naphthalene CGH4SCH:CH No 32 221 HZS plus ethyl benzcne to benzene. 2,3, xylidine (CHmCHNHz No 223. 8 NH3 plus xylene to benzene. 3,4, xylenol (CHahCHrOH No 65 225 Xylcne to benzene. m-Propyl phenol C3H1CH4OH N o 26 228 Prpyl benzene to cnzene. p-Isopropyl-phenol.. CHmCHCHrOH N o 61 229 Do. p-Propyl phenol CaHrCeHiOH No 22 232 Do. Pscudocumcnol (CHmCaHrOH N0 72 235 Mesitilenc to bcnzene. Quinoline CaHrNrCHCHH... Yes -19 237 Quinoline. Aromatic 2-rtnhctlhyl-naph-- CmHrCHa No 35 245 Naphthalene.
a ene. Tar base Isoqui'noline CGH4CH:NCH:CH Yes 23 243 Isoquinoline.
Quinaldine. CHrCs No 246 Quinolinc. Lepidine CHJCQHBN-- No -1 260 Do. Ditrkrlielthyl-naph- CraH(CHa)r No 255-270 Naphthalene.
Acenaphthene C10H(CH2)2 N0 95 277.5 Do. 1naphthol 96 288 Do. 2naphthol 122 295 Do.
Fluorene 116 295 Two mols benzene or one mol naphthalcne.
3-ring aromatic Phenanthrene 100 340 Phemmthrcne.
3-ring aromatic Anthraccne. 217 354 Anthracenc.
Tar base Acridz'ne 108 346 Ac'rldine.
Tar base Carbazole 246 354 NH3 plus two mols benzene or one mol naphthalene.
Yes 4-rlng aromatic Pyrene CMHm Yes 150 393 Pyrene. Yes 4-ring aromatic CM1/sane. CrrHw Yes 258 l 448 Chrysene.
Coal, freed of mineral matter, is comprised of ve elements-carbon, hydrogen, oxygen, sulfur and nitrogenwhile hydrocarbons (neutral oil) are combinations of carbon and hydrogen only. Recent studies indicate that 92%, plus or minus 2%, of the carbon in coal is combined with hydrogen in the form of aromatic and alicyclic molecules.
For the most part, oxygen, sulfur and nitrogen in chemically functional groups such as OH, CO, COOH, NH2, CN, S, SH, etc., are attached to, and are integral part of, the basic very large coal molecules. After the primary volatile matter has been allowed to condense from the vapor phase, these functional groups promote intermolecular reactivity which results in the progressive formation of the huge molecular structures which typify refractory coal tar pitch. Once allowed to form, the complex coal tar polymers are as diflicult to hydrogenate as is the original coal itself.
The composition of primary tar is closely related to that of the coal from which it is distilled in that the tar saturated hydrocarbons, the chemical character and molecular Weight of coal tar changes from minute to minute; and such instability may to some extent, persist for years.
The condensable products of all earlier processes retain oxygen, sulfur and unsaturated hydrocarbons in highly reactive forms. Therefore, the liquids produced by normal destructive distillation are constituted of complex chemical combinations of literally thousands of 0rganic compounds which cannot be separated and refined by fractional distillation or by routine petroleum refinery methods,
Evidently, the earlier in the pyrolysis of coal that oxygen, sulfur and nitrogen can be removed as hydrides and unsaturates stabilized in the uid stream (destructive distillation iof coal is also essentially a dehydrogenating and disproportionating process), the less chemically complex and the more useful is the primary'liquid product.
In the coal still with a system pressure of 15 to 30 atmospheres and with hydrogen as the thermal carrier fluid, advantage is taken of the fact that the boiling point of a material, is effectively lowered by the fact that hydrogen effectively reduces the partial pressures of high boiling of a material component vapors. For example, as shown in the following materials balance, if the condensable volatile stream in outlet 130 per 100 pounds of M.A.F. Coal is 1/10 mol, the total hydrogen in 3.44 mols and methane is present as 0.35 mol, the partial pressure of condensables is evidently in the order of lo of the total system pressure or less than l pounds per square inch absolute.
As a non limiting example, the following is a summary of a materials balance drawn upon the Huntington Coal Still when treating Eastern Kentucky Elkhorn Coal, Bureau of Mines No. C-66286.
other type of catalyzing systems be positioned immediately following the primary retort to take advantage of these temperatures. The first bed of solids through which the volatile system must pass is comprised of char on screen 139, which physically removes whatever liquid phase dispersoids by impingement without seriously lowering the temperatures. Such impingement and removal of resins and other liquid phase high boilers is necessary because even small amounts rapidly coat and deactivate the catalyst.
The hydrogenation which is effected upstream from the fractionator 156 removes practically all of the trou- Coal still charge, pounds per 100 pounds of moisture and ash-free Coal still products, after direct vapor phase catalysis coal Component Kentucky Combustionblast, Coal still Stabilized Hydrogen lkhorn 68.5 weight perchar liquid gas (surplus) Oli gas Flue gas HVAB 1 coal cent oi nitrogen distillate Hydrogen:
As combined H- A H O As NH3 As CH., (No CHl per se is thermally cracked) As free H2 Carbon:
As combined C As C As C02 from pyrolysis As CO2 from C0mbustion AS CH4 Nitrogen:
As combined N 1. 5 0.50 Nil 0 8 s As tree N2 0.2 32. 59 Oxygen:
As combined O 7. 5 Nil H r 6. 49 0.32 0. 26 Nil 0.75 14.
0.1 As free O2 0.1 Sulfur:
As combined S Nil As HES 0.3 As SO2 U. 1 As sulfate Pounds per 100 pounds MAF coal 100. O 47. 51 61. 35 16. 3 0. 89 15. 92 53. D5 Coal Moisture 2 7. 28 7. 28 Coal Ash 2 7. 7 7.7
1 HVAB =High Volatile A Bitmninous.
2 Moisture and ash content adjusted to American Power Company sample.
In the pressurized coal distillation process of this invention wherein the dilution is 20 or more `moles of hydrogen per mole of coal tar vapor, coal distills at temperatures even somewhat below those encountered in externally heated retorts operating at atmospheric pressure. Also, it is possible to directly distill and recover somewhat higher boiling point lcompounds from coal under these conditions at 20 atmospheres pressure than is conventionally possible at atmospheric pressure.
The thermal carrier iiuid will be present in an amount by Weight of two to four times greater ,than the primary volatile matter from coal distillation vplus the secondary volatile matter from contact coking which passes out through tiue 130. Therefore, the partial pressure of hydrogen will be high even at modest system pressures of 15 to 30 atmospheres. Without a catalyzer, at these pressures, relatively little hydrogenolysis will take place in the time available even though active hydrogenation does begin at about 750 F. In hydrogenating `such materials, it has been established that maximum liquid product yield, at least in respect to fractions in the gasoline and kerosene boiling range, occurs between 750 F. and 950 F. when a suitable catalyst is present. Therefore, it is important that, in this system, a series of moving bed or blesome functional groups of oxygen, sulfur and nitrogen from the tar and many of the alkenes are saturated. However, the lower ranked hydrocarbons require more severe treatment in order to satisfactorily dealkylate these into reformer 4stock for the production of high octane gasoline blending stock. Therefore, a series of sequential moving bed catalyst chambers under separate temperature control may be employed.
The stream leaving catalyst chamber 149 passes to the fractionator system 156. The lighter gaseous fractions pass off through line 150 to a condensor and absorber system (not shown) which also recovers sulfur compounds and ammonia. Stripped hydrogen with sucient methane to make up the hydrogen requirement of the system is recycled from the condensor through line 116 into the methane cracking and heat exchange zone D of the vertical retort 10. Excess methane from the absorber may be sold as fuel gas.
As explained above, the intermediate liquid products from the fractionator system 156 as enclosed by brackets 166 may be selectively recycled into the column in Zone B through selected ones of the inlets in bracket 168.
The purposes of the recycle are multifold; it gets rid of solids by recycling heavy bottoms. If thermal exposure beyond redistillation or vaporization is required the recycle is to an upper spreader inlet 45. If destructive distillation is desired the recycle of bottoms is to the lowermost inlet 47. Also by recycling benzine and close way of notes in the right hand column how the inspection of the iinal distillate can be predictably modied by the recycling of selected fractions into various horizons of the solid fuel cascade in zone B.
COMPOUNDS COMPRISING COAL STILL DSTILLATE WHEN OPERATED FOR MAXIMUM YIELD OF STABLE, NEUTRAL DISTILLATE The Most Tliermally Stable Compounds are Italicized Class of compound Name of compound Compound formula Mol weight Melting Boiling Disposition of point, C. point, C. distillate compounds Allmne Pantano 05H12 72 131. 5 36. 2 (Naphtliene) cycloalkane. Cyelopentane... 70 -93. 3 49. 5 LS? 2'0% 0I total Aiken@ n-Hexane--- so 94. 3 e9. o S 1 a Aromatic Benzene 78 5. 5 80. 1 Either sold separately or recycled for alkyla- (N mii o i h s4 e 5 si 4 tion' ap ene ye o exane Aiken@ n-heptane 01H1@ 10o -9o. 5 es. 4 Rfcmd t0 dehydo' (Naphthene cycloalkane 98 -126. 4 100. 3 e' Aromatic oluene CHCHa 92 -95 110.0 Added to 1gasoline blending stoc Water soluble tar base Pyridi'ne C5H5N 79 -42 115.3 Removed in aqueous solution. Cycloalkane Cyeloheptane 98 -12 118.1 Do 1,4,dimethy1 cyclo- 114 -86 120. 5
hexane. Recycled to dehydroge- Do 1,3,dimethyl cyclo- 114 85 121. 0 nate to xylenes.
hexane. Alkane ri-Oetane Cs 114 50. 5 125.8 Water soluble tar bases 2-picolines 92 128-143 Renliotved in aqueous so u ion. Aromatic Ethyl benzene 106 93. 9 13G. 15
Do p-Xylene 106 13. 2 138. 4 Do.- m-Xylenc--. 106 53. 6 139. 1 w D0"i`i3i""z` iiiyliieimi R 1m31 29' 0 143 4 atei' so u e tar ass. me y pyr ines emove n aqueous (Lundines). solution lslglkofgt r i, Aromatic Isopropyl 120 1023 5% Dimmi distiiiate, D0 Etiiyi wineries cuiiionaoin.. 12o 2o 162. 2-164. 9 lncudm tomem- Do 1,3,5,trimetl1yl benzene CuH3(CHa)3 114 52; 7 104. 7
(Mesitylene) Do 1,2,4,trimethyl benzene C@H3(CH)3 114 57. 4 169. 3
(Pseudo-cumene) Allmnn ri-Derane Cmloq 144 -30 174 Aromatic IstZ-ropyl toluenes CuH4CH:(CHa)zCH3 134 -25-75- 175-176 enes Do 1,3,diethyl benzene CsH4(CzH5)z 134 -20 181. 1 Alicyclic Indcne CeHiCHiCH 116 -2 182. 4 Aromatic 1,4,diethyl benzene.. CaH4(CzHs)z -35 183. 7 Recycled for dealkyla- Do 1,2,4,5,tetrametliyl CHi(CHa)4 134 80` 194 tion and deliydrobenzene (Durene). gcnation. Hydrogenated naplitlia- Tetrohydronaplitha- CioHi2 132 -30 207. 2
Iene. lene (Tetralin). Naphthalene Decahydro naphtha- CioIIia.. 138 -43 194. 6
lene (Decalin) Alkane CH3 CH2 10CH3 170 -12 214. 5 Bicyclic aromatic CioHs 128 80. 2 218 Oilcred at 2 cents a pound for plithalic acid manufacturing; about 20% of total distillate. Removed in aqueous C5H4N:CHCH:CH 129 -19 237. 7
soln tar base. Removed in acid Wash Isoquinoline CH4:CHNCH;CH.-.-. 129 23 243 Removed in acid tar base. aqueous solution.
Do 2-methy1 quinoline CHaCpHN. 143 246 (Quinaldine). Bioyelic aromatic 2-methyl naphthalene CioH1CH3 142 35 245 Removed in acid solution Removed in acid wash 4-Methy1 quinoline CHaCpHN- 148 0 260 Recycled.
tar base. lepidine. Aromatic Dimethylnaphthalene... CiuHt(CHa)i 156 Z55-270 Alicyclic `l1uorene l CGlEIICHzCH 045 3-ring aromatic-- criant rene 14 10.... 0
D0 Anthraeene omnia.-- 17s 217 354 Aqutilofogota t Removed in acid so ution 1s l l te' o ere d? Tar base Aeridine oHiCHzNoHi 10s 34s of@ C2 la POU of 4-ring aromatic.. Pyrene mm 202 150 300 c lemma use' Do Chrysene 0181112 228 258 448 1 Also used on input coal as a hydrogen transfer agent.y
boiling compounds for revaporization the proportion of benzine in the vapors is increased so that benzine will be alkylated to toluene at the expense of Xylene in catalyst chamber 149. Also dehydrogenating of naphthenes under selected conditions of recycle may be accomplished in catalyst chamber 148.
The following tabulation of compounds explains by blending stock for the production of high octane gasoline.
75 The following tabulation sets out the comparative costs of manufacturing high octane gasoline and illustrates the utility of this invention.
Catalytic cracking and alkylation; no reforming Catalytic cracking, alkylation, isomerization and reforming Case One Case Two Case Three Case Four No outside blend Coal still blend 1 No outside blend Coal still blend 1 Unit Clear 3 ce. TEL Unit Clear 3 cc. TEL Unit Clear 3 ce. TEL Unit Clear 3 cc. TEL volumes F-l F-l volumes F-l F-l volumes F-l F-1 volumes F-l F-l octane octane octane octane octane octane octane octane Catalytic gasoline,
425 F. E.P 36 92 99 36+!) 94 101 3G 92 99 364-9 94 101 ropylene alkylate- 16 94 102 l6|8 104 111 16 94 102 l6+8 104 111 Reformate Pool volume, percent F-l pool octane 78. 5 91.6 89. 4 Estimated pool cost per bbl $4. 62 $4. 90 $4. 62 Refinery output capacity, perccnt 100 100 141 1 Blending of coal still distillate is limited so that the total aromatic content is less than 50 percent of the product gasoline.
The hot solid materials fed off gyratory shelf 16 4fall through the partial combustion zone C. In the partial combustion zone D, the falling hot char is contacted with oxygen and air in a controlled proportion to react the carbon to carbon monoxide in the space below zone 56. Additional oxygen admitted through lines e0 oxydizes the carbon monoxide to carbon dioxide and the carbon dioxide passes out through ue :58 into flue gas knockout` chamber 194. By controlling the amount of air and oxygen inlet, the percentage of the Isensible heat of combustion of carbon and oxygen to that contained as sensible heat of carbon dioxide exiting about 3000" F. would be 23% of the total heat of reaction of carbon plus oxygen to carbon dioxide. rIhe combustion chamber arrangement retains as much as 75% of the total heat of reaction as sensible heat of the partially burned solid fuel. Furthermore, the sensible heat can be varied from as little as 23% of the carbon burned to well over 75% of the heat of reaction through the dilution of the oxygen admitted through inlet 62 with nitrogen (compressed air) or other non-reacting gas. As mentioned above, the particular details and construction of the combustion chamber per se are not part of this invention, but are fully disclosed and covered by the claims of my copending application, Serial No. 186,920 filed April l2, 1962.
Heat transfer and methane cracking zone D serves the two stated purposes. The thermal carrier gas is heated by absorbing most of the heat of the hot char carried on and fed downwards by gyratory shelf unit 18 and, at the same time whatever methane is fed through inlet 120 is dissociated into hydrogen and colloidal carbon. Then the hydrogen, which is substantially all of the thermal carrier gas, is bypassed through line 122, knockout drum 126 and line 52 around the combustion zone C, so that none of the products of combustion is entrained in the thermal carrier gas. In this way, the mixing of the products of combustion with the raw matter evolved in the distillation zone B is further avoided.
Methane originates from two sources in this invention. It constitutes about half the volume of gas evolved in the destructive distillation of coal7 and methane is also generated in the dealkylation of the alkylated aroma-tics. In this invention, however, no hydrogen need be wasted in the formation of permanent hydrocarbon gases and none need be provided from outside sources. In order that no hydrogen leaves the system in the form of low-priced hydrocarbon gas when hydrogen gas is salable, all methane can be recycled and thermally cracked.
The enthalphy of disassociation of methane is a rather times Ithe enthalphy of disassociation is the sensible heat remaining in the thermally cracked products. This systen automatically recovers and uses nearly 60% of ithe total heat necessary to crack methane into hydrogen and carbon black and, furthermore, accomplishes the cracking by contacting methane with a very hot annular cascade to produce all of the hydrogen necessary in the system and have the hydrogen available at system pressure without the necessity for compressing it.
The disassociation of methane into two volumes of hydrogen and elemental carbon begins `slowly at 1700 F. but as the temperature is raised to 2500 F. and above the disassociation is extremely rapid. For example, the rate of disassociation of methane about doubles for each F. of temperature rises between 1800 F. and 2000 F. At any temperature the decomposition of methane is proportionate to the time. Although pressure has an effect on the equilibrium of hydrogen and methane, at 2500o F. and above 20 atmospheres it has little measurable effect on the kinetics up to 95% disassociation. In the present system, a residence time of 'three to tive seconds finishing above 2500" F. (the temperature of the hot char y entering zone D) will disassociate approximate 95 to 98% of the methane which is recycled into zone D.
As the cold methane and hydrogen llow countercurrently against the cascading spent char, the char will be cooled down to a temperature leavin-g the system of approximately 300 F.
The char entering the heat transfer and methane cracking zone D, being fed off the periphery of gyratory shelf unit 18 can be heated to approximately 2800 F. and, therefore, heat recovery to the thermal carrier gas is effected as noted above by passing recycled hydrogen or hydrogen and methane countercurrently lthrough -the cascade of very hot char. The methane and whatever C2 and C3 hydrocarbon gases will be dissociated into hydrogen and carbon as they are heated to the temperature of the incandescent char, i.e., above l800 F. Thus the heat transfer zone also functions as a hydrogen generator as noted above.
In order to provide the necessary heat for the system as sensible heat of the char leaving zone C, either the partial combustion and heat exchange function of zones C and D must be repeated or additional solid fuel must be recycled through these zones when the yield of char is much less than of the weight of the MAF. Coal 0r when a large proportion of the methane is to be cracked. In the present invention, the preferred method of accomplishing this is by recycling, as it would appear to be less expensive from the apparatus involved. Referring 4to FIG. 1, char trap or collector 68 at the lower end of zone D collects that char required for recycle so that it may be selectively metered from the bottom of trap 68 by means of star valve 98. Excess char spills over onto the hopper 70 below and is removed from the system. The required amount of char per pound of raw coal to be recycled is metered by gas valve 9S and falls to juncture 100 which in eect is a -gas lift boot. Line 108 is somewhat smaller diameter at the lower end than at the upper end for allowing chunks too coarse to become gas entrained to drop out of the circulating gas stream into a coarse removal chamber through line 102 occasionally emptied by valve 104.
The axial flow fan 106 causes continuous circulation of entraining gas at system pressure upward through duct 108 and into separator 110. The gas then passes through separating cone 112 and returns through line 114. Whatever line char is metered out by star valve 98 through trap 68 is entrained in the continuous gas stream and it is pneumatically conveyed to separator 110 where it falls through line 54 back into the separating bed on top of gyratory shelf 16 after it has been separated from the gas stream. The entrance of recycled char inlet line 54 is below the entrance of thermal carrier 4gas 52 so that no heat is absorbed by recycled char from the thermal carrier.
Thus, the sensible heat capacity of the solid fuel cascade through zones C and D may be increased any required amount, and regulation of this amount of recycle is controlled by suitable controls of starl valve 98.
The char discharge lock 80 may be pressurized by flue gas from a takeoff of liuc 86 and thus pressurizing is controlled by an inlet valve 88 and outlet valve 92 as well as by solid materials entrance and exit bell valves 78 and 84. Upon attaining system pressure in the discharge lock, valve 78 may be opened to allow the passage of char or ash into the discharge lock. Valves 78 and 84 lare then closed and the lock is de-pressurized by opening valve 92 to the atmosphere. When the discharge lock 80 has been de-pressurized, the bell valve 84 can be opened and the char and ash can be discharged into an ash bin or char bin 94. Buffer bin 74 is proportioned such that the material accumulatingin bin 74 is somewhat less than enough to lill the discharge lock 80 so that the valve 78 may operate freely. In order to close -valve 78 and insure its seating free of solid materials, the valve 72 may be momentarily closed.
As a further illustrative but non-limiting example of the thermal analysis of the described process utilizing a Kentucky Elk Horn coal:
The coal of the present example from the East Kentuckly Elkhorn No. 3 bed and the MAF (moisture and ash-free) analysis is identical to the Bureau of Mines sample No. 3-66286.
This coal has been subjected to destructive distillation at 932 F. and the results of the modified Fischer carbonization assay are listed on page 37 of the Bureau of Mines Bulletin 57.
The ultimate analysis of the coal sample is, in pounds per hundred pounds of MAF coal:
Pounds Hydrogen 5.5 Carbon 85.0 Nitrogen 1.5 Oxygen 7.5 Sulfur 0.5
Coal Moisture 7.28 Coal Ash 7.7
The caloritic value is- 15,130 B.t.u. per pound of MAF coal.
The yield of tar and light oil, when carbonized at 932 F. by the Fischer-Schrader method described on pages 3-6 of USBM Bulletin 571, is 42 gallons per short ton of MAF coal. Thermal solution and hydrogen transfer to active sites formed on the coal molecule during destructive distillation, is expected to increase the Fischer Assay volume of condensables by some fty percent. Moreover, the bulk density of the catalyzed condensable matter is about l5 percent less than tar and the total volumetric yield may approach gallons of neutral distillate per MAF ton of Elkhorn coal.
The following heat balance is drawn upon this system as shown in drawing.
This present method of carbonization provides for the hydrogen entrainment and prompt removal of volatile matter as it is distilled from the coal below 950 F. Following the distillation of all condensable matter from the coal, the resulting high volatile char is progressively heated to a temperature at which secondary distillation occurs and substantial devolatilization is effected. Therefore, the following heat balance is neither strictly that of low nor of high temperature carbonization because the volatile matter, entrained in the hydrogen thermal carrier, leaves the carbonizing system at about 900 F. while the char is heated to at least 1600 F. to insure adequate hydrogen recovery.
Further, in the following heat balance, no methane is cracked because an excess of free hydrogen is produced from the secondary distillation of the high volatile char. However, if the market for hydrogen should justify the additional expense, the product methane can be thermally cracked in the system to elemental hydrogen at a direct cost of about eleven cents a thousand standard cubic feet.
SUMMARY AND RECAPITULATION In the following tabulations, heat is expressed in B.t.u. (British thermal units) per pounds of moisture and ash-free coal.
Coal still function A Drying and Preheating Coal to 650 F.
NoTn: Minus sign before a heat quantity denotes that which leaves the zone or is otherwise expended.
Summary of low temperature carbonization functon'B Distilling of the coals condensable matter and heating the coal completely through its plastic range.
B.t.u. per 100 pounds Item (B-l): MAF coal Low temperature carbonization, raising the dried coal and all volatiles from 650 F. through 900 F., including heat of decomposition and of vaporization 21,000
Summary 0f high temperature carbonization function T Raising the high volatile char with secondary volatiles 29 from 900 F. through 1600 F. and contact coking of recycled heavy bottoms.
Summary of coal still function C The heating of char to incandescence by its partial combustion to carbon dioxide.
B.t.u. per 100 pounds Item (C-l): MAF coal Adjusted heat losses to water and to the surroundings Credit Item (C-Z) Sensible heat of the combustion oxygen entering system about 50" F. (Zero pre-v heat) Credit Item (C-3):
Sensible heat of the combustion air entering the system above 50 F. (Zero preheat) Credit Item (C-4):
Sensible heat of the char above 5 0 F. cascading ofr" shelf 41 and entering the combustion zone at 1600 F. +32,500
Item (C-S) Combustion of fuel to CO2, H2O and SO2:
5.4 pounds C 14,100 B.t.u./
76,000 0.04 pounds H 51,300 B.t.u./ 45
lb. 2,060 0.1 pounds S CID 4,050 B.t.u./
Total heat generated by combustion per 100 pounds MAF coal +78,465 Item (FG-l):
Sensible heat in flue gas between 50 and 300 F 43,800 Item (SF-1): 55
Sensible heat in the carbon above 50 leaving zone D over shelf 100 65,500
Summary of coal still function D B.t.u. per pounds Item (TC-l) or (iD-1): MAF coal Item (TC-1) or (D-1):
Heating 1133 SCF of hydrogen from 50 70 to 2700 F. (See Item C-4) 56,400
Item (D-2) Residual heat above 50 F. in 69.05 pounds of char including 7.7 pounds of ash, leaving the system at 300 F 4,600 75 Item (D-3):
Estimated losses to cooling water and to the surroundings Item (SF 1):
Sub-total: Required sensible heat of 69.05 pounds of char available between 50 F. and 3000 F. +65,500
RECAPITULATION OF THE COAL STILL Zonal zent requirement Zone A: B.t.u.
Sensible heat in 53.05 pounds of combustion Zone D flue gas above 50 F. 43,800 Zones B-i-C:
Sensible heat in 1133 SCF (6.0 pounds) of thermal carrier hydrogen above 50 F. 56,400 Zone E:
Residual heat in existing char plus losses 10,700 Combustion Zone D:
Generated by combustion of 5.54 pounds of MAF char +78,400 Sensible heat in char entering Zone D at NOTE: The materials balance on this coal is set out above.
While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.
1. In a process for continuous thermal treatment of coal for the recovery of values therefrom by introducing crushed coal into a vertical retort having a series of gas isolated zones and operable -at substantial pressures, distilling primary volatile matter from the coal in a distillation zone of said retort while utilizing hydrogen at high temperature and system pressure as a thermal carrier iiuid for accomplishing said distillati-on, feeding the coal to a lower gas separated zone of said retort and partially oxidizing the char remaining from said distillation step while preventing the combustion products of said oxidation step from entering the distillation zone, feeding the oxidized hot char to a lower gas separated zone of said retort and passing methane through the partially oxidized hot char to disassociate the methane into hydrogen and carbon, and passing the hot hydrogen so produced at systern pressure into the distillation zone to be utilized as the thermal carrier gas, the improvement that comprises; repeating the steps of partial oxidation of char and feeding the hot char to a lowergas separated zone with a portion of the char by recycling a portion of the char from the lower portion of the lowest recited zone up to the upper portion of the zone for accomplishing partial combustion.
2. A process for the continuous thermal treatment of coal as ydeiined in claim 1 further comprising accomplishing the recycling of a portion of the char by a gas lift, and removing heavy char particles from the portion of the char recycled.
3. A process for the continuous thermal treatment of coal for the recovery of values therefrom, comprising: yintroducing crushed coal into a vertical retort having a series ofgas isolated zones and operable at substantial pressures, distill'ing primary volatile matter `from the coal in a distillation zone of said retort while utilizing hydrogen at high temperature and system pressure as a thermal carrier huid for accomplishing said distillation, yfeeding the coal to a lower gas separated zone of said retort and parti-ally oxidizing the char remaining from said distillation ystep While preventing the combustion products of said oxidation `step from entering the distillation zone, feeding the oxidized hot char to a lower gas separated zone `of said 4retort and passing methane through the partially oxidized Ihot char to disassociate the methane int-o hydrogen and carbon, passing the hot hydrogen so produced at system pressure in-to the distillation zone to be utilized as the thermal carrier gas, passing the admixture of thermal carrier hydrogen and distilled volatile matter of the coal from the distillation zone to a catalytic `treatment zone for contact with a catalyst, fractionating the products of such catalytic treatment in a fractionating zone, and the improvement that comprises selectively recycling certain boiling range constituents from the fractionating zone and re-introducing said constituents back into the distillation zone at selected predetermined horizons to accomplish further thermal treatment of -said recycled constituents.
4. A method for the continuous distillation of coal as defined in claim 3 wherein the recycled selected boiling range constituents are primarily liquid and spraying said liquids at selected horizons into the freely falling coal which is incandesent, -and introducing -those constituents requiring the least thermal `treatment lat a higher horizon than those requiring a more severe thermal exposure which are introduced Iat a lower horizon into the dis-tillation zone. t
5. A method for the continuous distillation of coal as defined in claim 4 further comprising introducing ground coal into at least one of the recycled liquid constituents requiring severe thermal exposure and recycling the stream containing said ground coal into the distallation zone.
6. The process of claim 3 including the step of removing the tar from the admixture of thermal carrier hydrogen 'and distilled volatile matter prior to its introduction into the catalytic treatment zone.
7. A process for the continuous thermal theatment of coal for the recovery of values therefrom, comprising:
introducing crushed coal into a vertical retort having a series of gas isolated zones and operable at substantial pressures, distilling primary volatile matter from the coal in a distillation zone of said retort while utilizing hydrogen at high temperature and system pressure as a thermal carrier iiu-id for accomplishing said distillation,
feeding the coal to a lower gas separated zone of saidv retort and partially oxidizing the char remaining from said distillation step while prevent-ing the combustion products of said oxidation step from entering the distillation zone, feeding the oxidized hot char to `a =lower gas separated zone of said retort, passing methane through the partially oxidized hot char to disassociate the methlane into hydrogen and carbon, passing the hot hydrogen so produced at system pressure in-to the distillation zone to be utilized as the thermal carrier gas -and the improvement comprising removing the products of distillation and thermal carrier hydrogen to a plurality of separate catalytic zones and performing vapor phase catalysis on said products of distillation with different catalytic materials in each of the separate catalytic zones.
8. A method for the continuous distillation of coal as defined in claim 7 wherein one of the several separate catalytic treatment zones is `for the purpose of removing oxygen and sulfur and saturating the oleiins by contacting the products of distillation and the thermal carrier hydrogen with a suitable catalyst.
9. A method for continuous distillation of coal as detned in claim 7 wherein one of the separate catalytic zones accomplishes reforming for removing hydrogen from naphthenes to leave aromatic compounds.
10. A method for the continuous distillation of coal as detined in claim 7 wherein one of the separate catalytic zones is for the purpose of causing an alkylation shift.
111. A process for the continuous thermal treatment of coal for the recovery of values therefrom, comprising: introducing crushed coal into a vertical retort having a series of gas isolated zones and operable at substantial pressures, distilling primary volatile matter from the coal in a distillation zone of said ret-ort while utilizing hydrogen at high temperature and sys-tem pressure as a thermal carrier fluid for accomplishing said distillation, feeding the coial to a lower gas separated zone of said retort and partially oxidizing the char remaining from said distillation step while preventing the combustion products of said oxidation step `from entering the distillation zone, feeding the oxidized hot char to a lower gas separated zone of said retort and passing methane through the partially oxidized hot char to disassociate the methane into hydrogen and carbon, passing .the hot hydrogen so produced at system pressure into the distillation zone to be utilized as the thermal carrier gas, passing the admixture of -thermal carrier hydrogen and distilled volatile matter from the distillation zone to a catalytic zone for catalytic treatment, fractionating the results of the catalytic treatment, recycling selected boiling range constitu-tents of said fractionation to the distillation zone for further thermal treatment, and treating the free talling coal by a hydrogen transfer agent.
12. A method for the continuous distillation of coal ias dened in claim 11 wherein the coal is pretreated by a hydrogen tranfer agent consisting essentially of phenanthrene.
13. A method for the continuous distillation of coal as defined in claim 8, wherein the catalyst for removing oxygen and sulphur and saturating the oletins is cobalt molyibdate.
14. A process for the continuous thermal treatment of coal for the recovery of values ytherefrom comprising; feeding crushed coal vertically downward in a vertical retort having a series of gas isolated zones and operable at substantial pressures, passing inert products of comibustion concurrently downward with the falling coal to raise the temperature of the coal to about 600 F. thereby preheating the coal to expel water andcarbon oxides, distilling primary Volatile matter from the coal in a distillation zone of said retort while utilizing hydrogen at high temperature and system pressure as the thermal carrier Huid for accomplishing said distillation, feeding the coal to a lower gas separated zone of said retort and partially oxidizing the char remaining from said distillation step while preventing the combustion products of said oxidation step from entering the distillation zone, using the combustion products of said oxidation step for said preheating, feeding the Ioxidized hot char to a lower gas separated zone of ysaid retort and passing methane through the oxidized hot char to disassociate the methane into hydrogen and carbon, passing the hot hydrogen so produced at system pressure into the distillation zone to be utilized as the thermal carrier gas, catalytically treating in a plurality of separate catalytic zones the products of said distillation in the environment of lsaid thermal carrier fluid, fractionating the results of said catalysis `and recycling selected boiling range components to predetermined selected horizons of the distillation zone.
References Cited by the Examiner UNITED STATES PATENTS 1,960,972 5/'1934 Grimm et al. 208-8 1,972,944 9/1934 Morrell 208-8 2,115,336 4/1938 Krauch et al. 208-10 2,194,186 3/1940 Pier et al. 208-10 2,657,124 10/1953 Gaucher 48-197 2,658,861 -11/1953 Pevere et al. 208-8 2,662,005 12/19153 Evans 208-169 2,664,390 12/1953 Pevere et al 208-8 3,075,912 1/1963 Eastman et al. 208-8 3,107,985 -10/ 1963 Huntington 208-10 3,132,083 5/1964 Kirk 20S-l5 3,150,071 9/1964 Ciapetta et al. 208-15 DELBERT E. GANTZ, Primary Examiner.
ALPHONSO D. SULLIVAN, Examiner.
H. LEVINE, Assistant Examiner.
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|US4900429 *||Jun 13, 1986||Feb 13, 1990||Richardson Reginald D||Process utilizing pyrolyzation and gasification for the synergistic co-processing of a combined feedstock of coal and heavy oil to produce a synthetic crude oil|
|US4931171 *||Aug 3, 1982||Jun 5, 1990||Phillips Petroleum Company||Pyrolysis of carbonaceous materials|
|U.S. Classification||208/408, 208/418, 208/412, 208/951, 208/169, 208/403, 48/197.00R, 208/431, 208/427|
|Cooperative Classification||Y10S208/951, C10B49/06|