|Publication number||CA1052719 A|
|Application number||CA 243072|
|Publication date||17 Apr 1979|
|Filing date||7 Jan 1976|
|Priority date||10 Jan 1975|
|Also published as||CA1052719A1, DE2600438A1, US4008054|
|Publication number||CA 1052719 A, CA 1052719A, CA 243072, CA-A-1052719, CA1052719 A, CA1052719A|
|Inventors||James T. Clancey, Charles H. Rice, Everett Gorin, Eric H. Reichl|
|Applicant||James T. Clancey, Charles H. Rice, Everett Gorin, Eric H. Reichl, Consolidation Coal Company|
|Export Citation||BiBTeX, EndNote, RefMan|
|External Links: CIPO, Espacenet|
BACKGROUND OF THE INVENTION
This invention relates -to a process for converting coal to low-sulfur and low-ash gaseous, liquid and solid fuels, and more particularly, to a process for supplying the energy require-ments of a steel plant from an ash- and sulfur-containing coal.
The primary source of energy for the steel industry continues to be coke for the blast furnace. The conventional method for coke manuf~cture, that is, by slot ovens, requires a blend of high and low volatile coals of proper swelling properties to produce a strong coke without damaging t~le ovens.
Beyond these physical properties, there is a need for desirable chemical properties (i.e. low ash and sulfur content) to permit low-cost production of high quality hot metal. With the continued expansion of the worldls productive capacity for steel, a grow~
ing shortage of good metallurgical coals is developing, particu-larly those having the essential low volatile coal ingredients.
Low-sulfur coals also are ln short supply because the electric utilities now compete for such coals to satisfy environmetal requirements In addition to the energy supplied by coke and coke oven by-products, the steel industry consumes liquid and gaseous fuels for blast furnace injection, soaking pits, reheat furnaces, steam and power generation, etc. Future supplies oE these fuels are also in jeopardy.
There are extensive reserves of coals in the United States, and in other parts of the world as well, suf~icient in fact, to satisfy a substantial part of the energy needs of the world for centuries to come. Unfortunately, these coals in -their indigenous state are not suitable for use either as clean fuel, i.e. low ash- and low sulfur-containing, or as feedstock for coke ; manufacture.
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Accordingly, the primary object of the present invention is to provide a process for converting any coal, by itself, whether it be caking or non-caking, low sulfur or high sulfur, low ash or high ash, low volatile or high volatile, to a desired spectrum of clean gaseous, liquid and solid fuels.
The solid fuel, for purposes of a steel plant, is coke, or formcoke. The term "formcoke" defines coke o~tained by the calcination of preformed or preshaped carbonaceous solids and is used to distinguish from coke obtained as broken pieces of all sizes and shapes from conventional coke ovens.
The prior art is represented by the following patents and publications:
U.S. 1,925,505 - Rose - Aug. 29, 1933 2,166,321 - Pott - July18, 1939 2,664,390 - Revere et al. - Dec.29, 1953 2,686,152 - Franke - Aug~10, 1954
3,018,242 - Gorin - Jan.23, 1962 3,240,566 - Bullough et al. - Mar.15, 1966 3,401,089 - Friedrich et al. - Sept. 10, 1968 203,562,783 - Gorin - Feb.9, 1971 3,748,254 - Gorin - July24, 1973 3,791,956 - Gorin et al. - Feb.12, 1974 German Pat. No. 320,056 - Rutgerswerke AG- Apr. 21, 1920 "Process for the Solvent Extraction of Coal"
Bureau of Mines Informatlon Circular - I.C. 7420 (Oct. 1947) "Pott-Broche Coal-Extraction Process and Plant of Ruhrol G.m.b.~l., bottrop-Welheim, Germally".
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SUr~MARY OF THE INVENTION
The present invention is an improvement ln the process for liquefaction of coal by solvent extraction which comprises, in its broadest aspects, the following essential operations:
.~ (1) Simultaneous solvent extraction and hydrotreatment of the coal in a coal liquefaction zone under hydrodesulfurizing conditions selected -to yield a coal extract having a lower organic sulfur content than the coal;
(2) separation of the liquefaction product into at least two parts, the first part being a low solids-containing product containing said coal extract, and the second part being a high solids~containing product containing said undissolved ash-containing hydrocarbonaceous residue;
(3) treatment of the first part, as follows:
(a) recovery of the major portion of the ; 20 solvent for recycle to the liquefaction zone;
- (b) production of a pelletizable mixture of coal extract and carbonaceous solids;
(c) formation of pellets from the pelletizable mixture; and (d) induration of the pellets, concurrent with, or subsequent to their formation, to form hardened low-ash and low-sulfur pellets;
(4) treatment of the second part, as follows:
(a) distillation of the second part to yield a hydrocarbonaceous ash-containing solid and a hydrocarbonaceous distillate; and (b) reaction of said hydrocarbonaceous ash- -containing solid with steam in a steam-carbon gasification zone to yield a gaseous product and ash-containing inc,rgani~ sulfur;
(5) recovery of a hydrocarbonaceous distillate fraction from said hydrocarbonaceous distillate for use as solvent in the liquefaction zone; and
(6) treatment of the gaseous product from the gasifi-cation zone to yield a methane-rich gas and hydrogen for use in the liquefaction zone.
The advantages of th~ process of the present invention include the following:
` (1) A single coal, whether it be caking or non-caking, high sulfur or low sulfur, high volatile or low ; 20 volatile, high ash or low ash, may be used to satisfy the energy requirements of an ore reduction plant.
(2) The process may be readily operated continuously to yield a spectrum of fuels whose distibution and respective compositions may be regulated in response to conditions maintained in the coal liquefaction zone and the separation zone.
(3) The process permits autogenous maintenance of solvent balance and hydrogen requirements.
,'.~' ' , (4) The process is especially valuable in its appli-cation to high-sulfur and high-ash coals. A
variety of asn-free fuels which are substantially free of inorganic sulfur a~,d much reduced in organic sulfur may be readily obtained as will ,~r be apparent from the following more detailed ; description of the invention in its broadest aspect and in its preferred embodiment.
- DESCRIPTION OF THE DRAWINGS
FIGURE 1 is a schematic flowsheet of the present invention in its broadest aspects; and FIGURE 2 is a schematic flowsheet of the pr~ferred embodiment of the present invention.
(in its broadest aspects) Liquefaction Referring to FIGURE 1, coal and liquefaction solvent are intrcduced into a coal liquefaction zone 10. The coal is introduced through line 11. The liquefaction solvent is introduced through lines 12 and 13.
Any coal may be used in the process of this inven-tion, non-limiting examples of which are lignite, bituminous coal and sub~bituminous coal. The coal may be non-caking, weakly caking or caking. It may be low in sulfur or high j in sulfur, or in between; it may be low in ash or high in ash, or in-between; or it may be low volatile or high volatile, or in-between. The process of the present invention is of - especial value in the case of non-caking or weakly caking coals and high-sulfur coals since normally such coals have only lim,ted utility.
' A sui.table liquefaction solvent is a mixture o:F
polycyclic, aromatic hydrocarbons which is liquid under the conditions of temperature and pressure maintained during coal liquefaction. A suitable boiling range for such a solvent, for example, is within the range 230 to 475C. The solvent may be conveniently derived as a distillate fraction from one or more of the unit operations of the present process.
The selected coal, in a finely divided state, is subjected to simultaneous solvent extraction and hydro-treatment in the liquefacti.on zone 10 under hydrcdesulfurizingconditions. The extraction operation may be any of those used by those skilled in the art, fcr example, continuous, batch, countercurrent or staged extraction. Hydrogen for the hydro-- treatment may be supplied as gaseous hydrogen, or by means of a hydrogen-donor solvent. If gaseous hydrogen is used, the solvent may be any suitable polycyclic aromatic hydrocarbon, or : mixtures of polycyclic aromatic hydrocarbons which are liquid at . the temperature and pressure of extraction. If a hydrogen-donor solvent is required, at least a portion of the polycyclic aromatic hydrocarbons is partially hydrogenated. Such a solvent is rehydrogenated to maintain its effectiveness as a hydrogen donor.
The conditions maintained in the extraction zone are those which are effective in desulfurizing the extract, that is, in reducing the organic sulfur content of the extract. Those conditions are generally known and are typically as follows:
t; Gaseous Hydrogen H-Donor : Temperature,C. 400-450 400-450 Pressure, Kg/cm2 70-200 5- 50 H addition, Wt.~ MAF* coal0.70-2.5 0.70-2.5 Solvent to Coal (wt. ratio)1.5-3.0 1.5-3.0 *MAF is moisture- and ash-Eree coal
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The product consists of an effluent: gas (eontainincj H2S) whieh is rejeeted through a line 14 and an effluent slurry product (containing solvent, extract and undissolved hydrocarbonaceous solids and ash) whieh is conducted by a line 15 to a separation zone 16.
Separation of the Extraction Slurry _ . .
Separation of the effluent slurry from the liquefae-tion zone into at least two parts is effeeted in the separation zone 16 at elevated temperature, generally elose to that of the liquefaction zone. The first part is a low solids-containing produet eontaining eoal extraet and solvent. The second part is a high solids-containing slurry product eontaining eoal extraet, solvent and the major portjon of the undissolved ash-containing hydrocarbonaeeous solids. The separation may be aeeomplished by settling, hydroelones, eentrifugation, filtration or by a eombination of two or more of these unit operations.
Cooling of the extraetion slurry before separation may result in seleetive preeipitation of some of the higher moleeular weight portions of the extract. At times, such cool-ing may be done deliberately to facilitate separation of thesolids from the extract and to improve the quality of the extraet. Seleetive preeipitation of this type may be further intensified, if desired, by addition of a preeipitating solvent, for example a paraffinie or naphthenie hydrocarbon. The manner in which a precipitating solvent may be advantageously used is now well known. An example of its use is fully described in U. 5. Patent No. 3,791,956.
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Treatment of Low-Solids Product from Se~aration Zone The low-solids liquid product issuing from the separation zone 16 is conducted wit:hout intentional cooling by a line 17 to a distillation zone 18. The primary purpose of the distillation zone is to recover the major portion of the solvent along with that part of the extrac-t which boils below or in the boiling range of the solvent. Some distillate may be ]eft in the extract in order to lower the naturally high viscosity of the extract. The temperature of the molten extract (which, in a solvent-free state, is a solid at temperatures below 100C.) should be kept below that at which any coking of the extract might occur.
The distillation zone may be any suitable distillation equipment for flashing off most of the distillables, leaving a bottoms product consisting essentially of non-distillable extract, some solvent and whatever solids are in the feed to the distillation zone. The vaporous products are conducted through a conduit 19 to a fractional distillation zone 20 where they are fractionally distilled to yield a distillate fraction suitable for use as a distillate fuel and a higher boiling distillate fraction which is solventO The distillate fuel fraction is with-drawn through conduit 21 and the solvent is recycled through conduit 12 to the liquefaction zone 10.
The coal extract is then conducted through a conduit 22 to a suitable mixing zone 23 wherein low-ash and low-sulfur carbonaceous solids are added in sufficient quantity to form a high solids-containing product which is pelletizable when hot, in forming zone 25. The amount of carbonaceous solids required for this purpose is a function of the binding properties of the extract and of the solvent, as well as the relative proportions of the extract and retained solvent. Furthermore, binder may g _ : . . ' , .
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be added extraneously to supplement the extract and solvent.
If the conditions maintained in the subsequent forming zone 25 are such as to cause volatilization of the solvent, then the pelletizable mixture may, of course, be richer in solvent. But if the conditions ln the forming zone do no-t cause volatilization of solvent, then the pelletizable mixture must be of the necessary composition for pelletization. In general, the pelletizable composition, excluding any solvent that may be vaporized in the forming zone, is typically as follows:
Carbonaceous solids 35-75 weight percent Extract and solvent 25-65 weight percent where the extract is generally at least 75 weight percent of the extract-solvent mix, and is preferably greater than 90 weight percent. The pellets will have substantially the same composition unless the pelletization is conducted under carbonizing conditions which result in production of some gas and tar.
The carbonaceous solids admixed with the extract in the mixing zone 23 are supplied through a conduit 2~. They are preferably derived from the process itself. However, in its broadest aspects, the process of the present invention may resort to extraneous sources of carbonaceous solids, however derived.
The pelletizable composition, suitably admixed in the mixing zone, is transferred to the forming zone 25. The primary objective of the forming zone is to form pellets out of the pelletizable mass received from the mixing zone. The pellets ma~ be made by any one of the many known pelletizing processes, for e~ample, briquetting, extrusion or agglomeration, ~ 30 under carbonizing or non-carbonizing conditons a-t a temperature above the softening point of the binder. The process selected should be one which is adapted to be used at an elevated .~
temperature at whlch the extract is fluid.
If the pellets are formed in the forming zone 25 under carbonizing conditions, that is at a temperature above 400C., the resulting pellets will be sufficiently hard to permit handling. However, if no carbonization occurs in the forming zone, induration of the pellets subsequent to the forming step is required. In such event, the pellets formed in the forming zone 25 are advanced to an induration zone 26.
Hardening of the pellets in the induration zone 26 may be effected by heating the pellets under carbonizing conditions, that is at a temperature above 4C0C., or by simply cooling them below the softening point of the solution of extract and solvent which is generally above 150C. Carbonization of the pell~ts, whether effected in the course of pellet formation in the forming zone or subsequently in a separate zone, yields a vaporous product which contains a fraction corresponding to the solvent used for the coal extraction which may be recovered for use in the liquefaction zone 10. As will be seen later in the description of the preferred embodimentl mixing, forming and induration need not be performed separately, but in any suitable or appropriate combination of steps.
JA~ Hardened pellets are withdrawn from the induration .. ~
; zone 26 through a conduit 27. Depending upon the forming process selected, the pellets may contain off-size pellets, ~ that is pellets which are not suitable for -the intended use, .: either because they are too small or too large. In such event, the off-size pellets, after suitable size adjustment, may be recycled for use as part or all of the carbonaceous solids . admixed with extract in the mixing zone 23. Such recycle is shown by the lines 24 and 28. Those pellets which are within ':
the desired range may be used as is in certain operations. For ':, ,:
example, -they may serve as part of a coke oven feed, or as solid reductant in certain ore reduction furnaces. Or they may be subjected to a temperature between 800 and 950C. to : yield blast furnace coke.
' ; Treatment of High Solids Prociuct from Separation Zone ~, At least a portion of the high solids product ~- issuing from the separation zone 16 is tranferred through a conduit 29 to a distillation zone 30 which is maintained at a temperature sufficiently high to distill off solvent, leaving a ~ 10 hydrocarbonaceous ash-containing solid. If extract is present, ; as may well be the case unless exhaustive solvent washing has been resorted to, the temperature maintained in the distilla-tion zone 30 should be sufficiently high to carbonize the ` extract to coke or char and vaporous products. A suitable . temperature is in the range of 425 to 760C. The ash-containing ,,.
solids are withdrawn from the zone 30 and conducted by a con-duit 31 to any conventional type steam-carbon gasification zone 32 operated under conditions to yield CH4, CO and H2. The solid gasification residue rlch in inorganic sulfur compounds is discharged from the system through a conduit 33. The gaseous product is conducted by a conduit 34 to a conventional-type gas treatment zone 35 for the recovery of hydrogen. The other principal product CHI, is recovered through a conduit 36 as high Btu gas. The hydrogen is conducted by a conduit 37 to the ` liquefaction zc,ne 10. As pointed out earlier, a portion of the required coal liquefaction solvent is introduced into the ; liquefaction zone by a conduit 13. The solvenl is derived from the distillation zone 30. The vapors issuing from the latter zone are conducted by a conduit 3~ to a fractional distillation zone 39 which is a conventional type. The fraction having the ' :' ' ,:
; desired boiling range for -the solvent is recovered for that purpose, while the balance may be wi-thdrawn through conduit 40 to serve as distillate fuel. Instead of returning solvent directly to the liquefaction zone, the solvent may first be hydrogenated by the hydrogen from conduit 37 to thereby yield a hydrogen-donor solvent which may then be used as the scurce of hydrogen in the liquefaction zone, as is more fully shown in the preferred embodiment of FIGURE 2.
FIGURE 2 shows schematically a coal conversion plant utilizing the preferred embodiment of the present invention. It is directed specifically to the conversion of a high sulfur coal to the low-ash and low-sulfur fuels required in a steel plant, including fcrmcoke suitable for use in a blast furnace.
Feed Coal ;~
A high-sulfur coal is used which has a volatile matter content of at least 20 weight percent. A typical coal suitable for use in this preferred embodiment has the composi-~ tion shown in Table I below:
Proximate analysis: W-t. Percent MF* Coal Volatile matter 41.7 Fixed carbon 45,9 Ash 11.6 Ultimate analysis: Wt. Percent MAF** Coal ~ydrogen 5-34 Carbon 78.97 - Nitrogen 1.60 ; Oxygen 10.47 Sulfur 3.62 *MF means moisture-free.
**MAF means moisture-and-ash-free.
The feed coal is preferably ground to a finely divided state, for example, minus 14 mesh Tyler Slandard screen, and is freed of substa~tially all extraneous water.
(1) Coal Liquefaction Zone The feed coal is introduced into an Extractor 50 via a conduit 510 Hydrogen donor (H-donor) solvent is intro-duced into the Extractor via a conduit 52. The coal and the solvent react therein to yield the desired coal extract in ;; admixture with undissolved solids.
The solvent extraction process is a non-catalytic, continuous, countercurrent process conducted in a vertical cylindrical vessel, at a temperature in the range of 350 to 475C., a pressure in the range of 4 to 50 kg/cm~, and a : solvent-to-coal ratio of 1.5 to 3Ø Under such conditions, the amount of hydrogen transferred is between 0.7 and 2.5 . (weight percent MAF coal).
The solvent is a polycyclic, aromatic hydrocarbon ~ which is liquid at the temperature and pressure of extraction, ;. and contains partially hydrogenated aromatics. It is 20 naturally derived from the hydrogenation of extract or fractions thereof. It usually has a relatively wide distilla-tion range with an initial atmospheric boiling point of about .:; 200C. and a final boiling point of 500C. or even higher.
(2) Separation Zone Following extraction, the effluent mixture of solvent, extract and residue is conducted rapidly from the Extractor 50 so as to avoid excessive cooling of the mixture, through a conduit 53 to a F~ydroclone system 54 consisting of one or more hydroclones adapted to concentrate the solids preferentially ~ 14 -.
in the underflow. While the greater part of the residue is in the product underflow from the Hydroclone system, the exact amount is controlled, firstly to assure that both overflow and underflow products are pumpable, and secondly to maintain the required distribution of lo~-sulfur fuels for the steel plant.
While the organic sulfur has been reduced in the E~tractor, the ~; inorganic sulfur is still left in the solid residue. In this preferred embodiment of the invention, the solids content of the extract (exclufling solvent) recovered from the Hydroclone system overflow may be in the range of 0.05 to 15 weight per-cent, while the solids content of the total underflow from the Hydroclone system may be in the range of 30 to 55 weight percent, but is generally between 40 and 55 weight percent.
' (3) Treatment of the Overflow from the Hydroclone System The overflow from the Hydroclone system is pumped by a pump (not shown) through a conduit 55 to a Still 56 where at least some solvent and any light oil are fractionally distilled.
The light oil is suitably recovered (not shown) for use as distillate fuel, while the spent solvent is witndrawn through a conduit 57. A portion of the spent solvent is sent through a conduit 58 to a Solvent Rehydro unit S9 while the remainder is recycled to the Extractor 50 through a conduit 60 which connects with conduit 52. The portion of the spent solvent which is sent to the Solvent Renydro unit is subjected to the usual conditions for rehydrogenation of hydrogen-donor solvents by means of hydrogen gas introduced by conduit 61. Typical hydrogenation conditions are as follows:
Temperature, C. - 340 Pressure - 70 Kg/cm2 H2 Rate _ 0.9 m3/Kg Catalyst - 5/16 cm. pellets of NiS-MoS2 on Al203 ~h~
The hydrogenation product is fractionated to recover the rehydrogenated solvent which is returned to the Extractor through a conduit 62 and conduit 52. The remainder is with-drawn through a conduit 63 for use as distillate fuel.
The extract-containing portion recovered in the Still 56 is conducted to a Pelletizer 64 through a conduit 65.
The Pelletizer consists essentially of a rotary cylindrical kiln, usually slightly inclined from the horizontal. It serves to mix, form and harden pellets all in the same vessel.
The extract-containing portion contains not only extract~ but also some solvent, and in the case of this preferred embodi-ment, less than about 5 percent by weight of solids. In order to establish a pelletizable mass in the Pelletizer 6~, the feed to the Pelletizer, when admixed in the Pelletizer, should have about the following composition, excluding any solvent that may be vaporized in the Pelletizer:
Weight Percent Solids 60-75 Extract and Solvent25-40 The composition of the pelletizable mass is, to some extent, dependent upon the density of the solids, the higher the density the less binder is required. The reason fcr this is presumably absorption of binder in the pores of the less dense solids.
As previously stated, there is generally less than 5 percent solids in the extract-containing stream to the Pelletizer. Accordingly, it is necessary to provide a sub-stantial amount of solids to raise the weight percent to the required range of 60-75. This may be done in one or both of two ways. ~'irstly, a portion of the extract feedstream is 30 diverted through a conduit 66 to an Extract LTC unit 67 adapted to subject the extract to low temperature carbonization, that is to heat at 425 to 500C. whereby a char product is obtained which is conducted to the Pelletizer through a conduit 68. A vaporous product is also obtained, which is conducted by a conduit 69 to a condenser 70 where the liquefiable portion is condensed and withdrawn through a conduit 71 for use as distillate fuel. The non-liquefiable portion is withdrawn through a conduit 72 for use as low Btu gas.
The other way to raise the solids content of the pelletizable mass to within the desired range is to recycle off-size pellets from the Pelletizer through a conduit 73, a pre-heater 74, and a conduit 75. If the solids content of the extract feedstream is sufficiently greater than 5 percent, as might be the case in certain non-preferred embodiments, then the recycle pelle-ts will provide all the additional solids needed so that carbonization of extract becomes unnecessary.
~ he pelletiz~ble mass of the desired composition is subjected to pelletization under adiabatic low temperature carbon-ization conditions at a temperature above 400C. as is now well known. For example, the operation of the Pelletizer 64 is set forth in UO S. Patent 3,401,089, granted Septemb~r 10, 1968 to R. J. Friedrich et al. The pellets of the desired size consist are withdrawn from a separator 76 located at the end of the rotary kiln and conducted by a conduit 77 to a Calciner 78. The off-size pellets, as previously stated, are recycled with appropriate crushing as may be required to yield the desired size consist for use in the pelletizable mass. The vaporous product from the kiln is withdrawn through a conduit 79 to join conduit 69 leading to the condenser 70.
The Calciner 78 is adapted to heat the pellets of .~:
-; 30 desired size, generally 60 mm x 20 mm, to a temperature between .; 800 and 950C. at a pressure between 0 (1 atmospheric absolute) ' - 17 ~
and 15 kg/cm2. The calcined pellets are withdrawn through a conduit 80 for use as formcoke in a blast furnace.
(4) Treatment of the Underflow from the Hydroclone System The solids-rich underflow from the Hydroclone 54 is pumped through a conduit 81 to a Pelletizer 82 after appropriate adjustment of the composition of the underflow to yield a pelletizable mass in the Pelletizer. The desired composition is generally the same as that set forth for the composition maintained in Pelletizer 64 and is generally establlshed by appropriate removal of solvent in the proper amount. However, the function and operation of Pelletizer 82 are not the same as `~ that of Pelletizer 64. In this instance, the Pelletizer 82 serves to mix and to form pellets in much the same manner as does Pelletizer 64 but under non-carbonizing conditions, i.e.
at temperatures between 300 and 370C., high enough to vaporize the solvent during the formation of the pe~lets. The vaporous sc:lvent may be removed through a conduit 83 fcr condensation and reuse. The formed pellets may need to be water-quenched , (not shown) to harden them for subsequent handling. They are withdrawn from the Pelletizer 82 through a conduit 84 to a Gasifier 85.
`~ The preferred size of pelletc for use in the Gasifier 85 is greater than 14 mesh Tyler Standard screen. If there are any pe:Llets above about 5 cm, then it is desirable to crush them -to less than 5 cm. The portion oE the pellets (including the crushed oversize pellets) which is less than 14 mesh in size is separated and may be recycled to the inlet ; of the Pelletizer 82. In such case, due recognition of this recycle stream of solids must be given in the maintenance of the desired composition. The pellets of desired size are then ` conveyed through the conduit 84 to the Gasifier 85.
The gasifier 85 is preferably of the fixed bed ~ype, requiring a non-caking or weakly caking carbonaceous feed for satisfactory commercial operation. In such a gasifler, a bed of pellets which are relatively stationary with respect to each other moves progressively downwardly first through a carbonization zone 86 and then through a gasification zone 87.
- Steam and oxygen are introduced into the gasification zone and are circulated upwardly through the downwardly moving bed while ash is suitably rejected from the bottom of the cJasifier. The temperatures in the carbonization zone are maintained within the range 500 to 775C. by the hot gases issuing from the gasi-fication zone. The gasification zone is maintained at a temper-ature in the range of 775 to 1050C. The pressure is 20 to 40 kg/cm2. The incoming pellets are carbonized in the carboniza-tion zone, yielding tar vapors which are withdrawn with the effluent gases via a conduit 88. The carbonized pellets move downwardly in reactive contact with the upflowing steam and oxygen to form CO2, CH4, H2, and C~. These pass through the carbonization zone and into conduit 88. The effluent gas, 20 including tar and solvent vapors is passed into a condenser 89 for separate recovery of gas, solvent and tar. Solvent is recovered from the condenser and conducted via a conduit gO to connect with conduit 58 which ]eads to the Solvent Rehydro unit 59. The tar-free gas is conducted by a conduit 91 to a suitable hydrogen recovery system 92 of conventional type from which a hydrogen-enriched gas is recovered. This gas i5 with-drawn through conduit 61 to serve in the rehydrogenation of the solvent. The remaining gas is wi-thdrawn through a conduit 93 to serve as a high Btu gas.
'',^' ' "' The ash and sulfur contents of the spectrum of products shown in FIGURE 2 will naturally depend upon the specific conditions selected for each of the described essential operations. The more severe the conditions of hydrogenation maintained in the Extractor 50, the larger is the amount of organic sulfur that is removed. The more effective the separation of solids, i.e. ash, from the extract in the Hydroclone system 54, the lower will be the ash and hence sulfur content of the solid, liquid and gaseous products since the major part of the inorganic sulfur will be rejected as ash from the Gasifier 85. However, it may be desirable from an economic point of view to accept or tolerate some ash and sulfur, without impairing the usefulness of the product or doing harm to the environment. The process of the present invention permits both flexibility and selectivity in modifying not only the distribution of products, but also their respective compositions.
According to the provisions of the patent statutes, the principle, preferred construction and mode of operation of the invention have been explained and what is considered to represent its best embodiment has been illustrated and described. However, it should be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.
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|International Classification||C10L9/02, C10B53/08, C10G1/04, C10J3/72, C10G1/00, C10G1/06|
|Cooperative Classification||C10B53/08, C10G1/002, C10L9/02, C10G1/065, C10G1/006, C10G1/042, Y10S208/951|