US3841991A

US3841991A - Coal conversion process

Info

Publication number: US3841991A
Application number: US00348397A
Authority: US
Inventors: S Cohen; J Hochman
Original assignee: Exxon Research and Engineering Co
Current assignee: ExxonMobil Technology and Engineering Co
Priority date: 1973-04-05
Filing date: 1973-04-05
Publication date: 1974-10-15
Anticipated expiration: 1991-10-15

Abstract

1. A PROCESS FOR THE PREPARATION OF LIQUID PRODUCTS FROM COAL WHICH COMPRISES: (A) PREPARING A SLURRY OF FINELY DIVIDED COAL PARTICLES IN A HYDROGENATED AROMATIC HYDROGEN-DONOR SOLVENT HAVING A BOILING POINT IN THE RANGE BETWEEN ABOUT 350*F. AND ABOUT 800*F. IN A SLURRY PREPARATION ZONE; (B) INTRODUCING SAID SLURRY FROM SAID SLURRY PREPARATION ZONE INTO A FLUIDIZED BED COKING UNIT REACTION ZONE; (C) WITHDRAWING OVERHEAD PRODUCTS FROM SAID FLUIDIZED BED COKING UNIT REACTION ZONE AND RECOVERING AN INTERMEDIATE FRACTION BOILING IN THE RANGE BETWEEN ABOUT 350*F. AND ABOUT 800*F. (D) HYDROGENATING SAID INTERMEDIATE FRACTION AND INTRODUCING AT LEAST PART OF THE HYDROGENATED PRODUCT INTO SAID SLURRY PREPARATION ZONE; (E) TRANSFERRING SOLIDS FROM SAID FLUIDIZED BED COKING UNIT TO A BURNER AND BURNING A PORTION OF THE SOLIDS TO PROVIDE HEAT FOR THE PROCESSL AND (F) RECYCLING HOT SOLIDS FROM SAID BURNER TO SAID FLUIDIZED BED COKING UNIT REACTION ZONE.

Description

- S. J- COHEN` TAL COAL CONVERSION PROCESS Ost. 15. 1974 United States Patent O 3,841,991 COAL CONVERSION PROCESS Saul J. Cohen, Chester, NJ., and Jack M. Hoehman, Cobham, England, assignors to Esso Research and Engineering Company Filed Apr. 5, 1973, Ser. No. 348,397 Int. Cl. Cg 1/04 U.S. Cl. 208-8 10 Claims ABSTRACT OF THE DISCLOSURE A process for the preparation of liquid products from coal wherein nely-divided coal particles are slurried in a hydrogen-rich liquid hydrocarbon solvent at low temperature and substantially atmospheric pressure and the resulting slurry is passed into a fluid bed coking unit Where conversion of the coal, solids separation, and thermal cracking of a heavy product take place simultaneously. An intermediate fraction taken overhead from the coking unit is hydrogenated and a portion of the product is recycled for use as coal solvent. The remaining overhead streams are sent to conventional downstream refining units and solids derived from the coal are withdrawn as char.

BACKGROUND OF THE INVENTION (1) Field of the Invention This invention relates to the manufacture of liquid hydrocarbons from coal and is particularly concerned With an improved coal conversion process wherein conversion of coal, separation of solvent, and thermal cracking of heavy products are carried out simultaneously in a fluidized coking unit.

(2) Description of the Prior Art There is substantial interest in the development of processes for the manufacture of synthetic crude oils and liquid hydrocarbons from coal. Among the more promising processes of this type are those based upon the solvent extraction of liquid constituents from the coal with an aromatic solvent. Such processes require that the coal be digested at elevated temperature and pressure with a hydrogen-donor solvent, generally in the presence of added hydrogen gas. The hydrogen contributed by the solvent and gas increases the amount of extract recovered and upgrades the liquid products. Following this solvent treatment, the products are separated to yield a high boiling extract containing liquid hydrocarbons derived from the coal and a solid phase composed of insoluble coal residues. The extract is then subjected to catalytic cracking or other rening processes for conversion of the high boiling material into lower boiling hydrocarbons. The solids separated from the extract are generally subjected to a low temperature carbonization treatment for the production of additional liquid products and char useful as fuel. Although processes of this type have advantages over some of the other coal conversion methods suggested in the past, they generally require a large plant investment and are expensive to operate. Efforts to improve the economics of such processes have to date been only partially successful.

SUMMARY OF THE INVENTION This invention provides an improved process for the manufacture of liquid hydrocarbons from coal which at least in part overcomes the disadvantages of earlier processes and permits conversion of the coal at relatively low cost. The improved process of the invention involves the rice preparation at low temperature and substantially atmospheric pressure of a slurry of finely-divided coal particles in a hydrogenated aromatic solvent derived from coal and the subsequent introduction of this slurry into a fluidized bed coking unit operating at a temperature in the range between about 900 and about 1l00 F. Liquefaction and hydrogenation of the coal, separation of the solids, and thermal cracking of the heavy liquid products take place in the coking unit in the presence of the hydrogen-rich solvent, increasing the yield of low boiling liquid products and decreasing the yield of char. The products taken overhead from the coking unit reaction zone are fractionated and an intermediate liquid stream boiling within the range of about 400 -F. and about 700 F. is passed to a catalytic hydrogenation unit. A portion of the resulting hydrogenated aromatic solvent produced in the hydrogenation zone is recycled for use in preparing the coalsolvent slurry. The remaining liquid products obtained by fractionation of the overhead stream from the coking unit reaction zone are sent to conventional downstream refining units for further processing. Solids produced in the coking unit reactor are transferred to a burner where a portion of the hydrocarbon solids are burned to generate heat for the process. A portion of the unburned solids are recycled to the reaction zone and the rest are withdrawn as product char.

The process of the invention has numerous advantages over conventional coal liquefaction processes in that coal conversion, solids separation, and thermal cracking of heavy liquids produced from the coal all take place within the coking unit reactor and hence separable liquefaction, solids separation and coking or carbonization units are not required. This permits savings in plant investment and operating costs. It also results in much better heat integration than can be obtained in conventional processes, permits generation of all of the process heat from coal without the use of complex coal-red furnaces, eliminates the need for slurry-handling heat exchangers and other equipment which normally poses severe design, operation and maintenance problems in conventional processes, obviates the necessity for handling slurries at the high pressures required in prior art processes, and permits significant reductions in pumping and compression costs. Moreover, it has been found that the yields obtained in the process of the invention compare favorably with those obtained in other coal conversion processes which require extraction of the coal with an aromatic solvent and that the molecular hydrogen which is generally needed to provide reasonable conversion levels in the liquefaction zone of conventional processes is not necessary. These and other advantages, coupled with the savings in plant investment and operating costs, make the economics of the process appear attractive.

BRIEF DESCRIPTION OF THE DRAWING The single figure in the drawing is a .schematic flow sheet of a preferred embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the process depicted in the drawing, raw coal from a coal preparation plant or storage is introduced into the system through line 10 and fed through hopper 11 and a screw conveyor or similar device 12 into a slurry preparation vessel 13. The coal introduced will generally be in a finely-divided state and will normally consist of particles between about 1A inch and about 325 mesh on the U.S. Sieve Series Scale in size. 'The use 0f particles of about 8 mesh or smaller is generally preferred. The coal may be bituminous, sub-bituminous or lignite. Special drying and other coal pretreatment steps are not normally necessary but may be used if desired. A typical inspection vof a coal suitable for purposes of the invention is as follows:

TABLE I Typical Coal Inspections Wt. percent Moisture, saturated 13.0 Ash, dry 10.6 Mineral matter, dry 12.8 Volatile matter, DMF 1 45.1 Fixed carbon, DMF 54.9 Carbon, DMF 79.1 Hydrogen, DMF 5.6 Oxygen, DMF 10.6

Nitrogen, DMF 1.2 Sulfur, total, dry 4.7 Sulfur, pyritic, dry 1.7 Sulfur, organic, DMF 3.4 B.t.u./lb., dry 12,610 B.t.u./lb., DMF 14.360

1 Dry, mineral-free.

An aromatic hydrogen-donor solvent is introduced into slurry preparation vessel 13 through line 14 simultaneously with the coal. The solvent employed will normally be a coal-derived liquid produced by the hydrogenation of an intermediate overhead stream boiling between 350 F. and about 800 F., preferably between about 400 F. and about 700 F. This stream is made up predominantly of hydrogenated aromatics, naphthenic hydrocarbons, phenolic materiais, and similar compounds and will normally contain at least 30 percent by weight, preferably at least 50 percent by weight, of compounds which are known to be hydrogen donors under the temperature and pressure conditions employed in the uidized coking reaction zone. Other hydrogen-rich solvents may be used in lieu of or in addition to such a coal-derived liquid, particularly on initial start-up of the process. Suitable aromatic hydrogen-donor solvents include hydrogenated creosote oil, hydrogenated intermediate product streams from the catalytic cracking of petroleum feedstocks, and other coal-derived liquids which are rich in indane, C to C12 Tetralin, Decalin, biphenyl, methylnaphthalene, dimethylnaphthalene, C12 and C13 acenaphthenes, di, tetraand octahydroanthracene, tetrahydroacenaphthene and similar donor compounds.

A typical hydrogenated, coal-derived liquid boiling between about 350" F. and about 800 F. which is rich in hydrogen-donor compounds and is therefore suitable for use as an aromatic hydrogen-donor solvent in the process of the invention is described in Table 1I below.

TABLE II.-TYPICAL HYDROGEN-DONOR SOLVENT A. Distillation Cumulative wt. Sp. gr., percent over- Tenp., F. at 760 mm.:

Total B. Mass speetro analysis Element analysis, nngs wt. percent Typical compound CnHz n n alkylbenzene C Han-s tetralin C Harm indene CnH2n12 naphthalene l .sulfur Total CnHzn-M acenaphthene CHzn-ie acenaphthylcne C Hh-i5 phenanthrene CnHrn-ze cholanthrenes OUH; -25 benzopyrenes co @com It will be understood, of course, that the composition of the recycle solvent obtained by the hydrogenation of an intermediate fraction of the coal-derived liquids will depend in part upon the particular coal employed, the coking conditions used, the start-up solvent selected, the boiling range of the intermediate fraction selected, the hydrogenation conditions employed, and the likeand that the composition of the recycle stream may therefore differ somewhat from that set forth above.

The coal introduced into the slurry preparation vessel 13 by means of conveyor 12 and the hydrogen-rich solvent introduced through line 14 are combined in the preparation vessel in a ratio of from about 0.5 to about 5 parts of solvent per part of coal by weight. The ratio selected for a particular preparation will depend in part on the particle size of the coal introduced into the process, the moisture content of the coal, the temperature and the viscosity of the solvent employed, the degree of agitation provided by stirrer or similar mixing device 1S, and other considerations. In general it is preferred to employ from about 1.5 to about 3 parts of solvent per part of coal by weight. The slurry will normally be prepared continuously as indicated in the drawing. In some cases, however, a batch slurry preparation technique may be used.

The slurry prepared in vessel 13 is discharged from the vessel through line 16. The slurry temperature will depend primarily upon the temperature of the solvent introduced through line 14 and the solvent-to-coal ratio. In general, the slurry temperature will range between ambient and about 200 F. Little or no reaction takes place between the coal and solvent in the preparation vessel and hence the temperature and residence time in vessel 13 are not critical.

The solvent-coal slurry prepared as described above is mixed with a high boiling bottoms stream introduced through line 17 and passed from line 16 into

injection lines

18, 19 and 20. From here the feed slurry is injected into the reactor Vessel 21 of a fluidized coking unit of conventional design. Reactor vessel 21 contains a bed of coal and char particles which is maintained in a uidid state by means of saturated stream introduced near the bottom of the vessel through line 22. The bed temperature is maintained between about 900 F. and about 1100" F. by means of hot char which is introduced into the upper part of the reactor vessel through riser 23. The pressure -within the reactor will normally range between about 10 and about 30 pounds per square inch guage.

The coal-solvent slurry introduced into reactor 21 is sprayed onto the surfaces of the downwardly moving char particles in the uidized bed and rapidly heated to bed temperatures. Hydrocarbons present in the coal are hydrogenated and liquefied in the presence of the hot solvent. As the temperature increases, the coal-derived liquids and solvent are vaporized and heavier constituents undergo thermal cracking reactions. The vaporized products, steam, and entrained liquids move upwardly through the bed, pass through cyclone separator 24 where char particles present in the uid stream are rejected, and move into scrubber 25. The char particles and unreacted coal residue and other solids move downwardly in the uidized bed and are withdrawn from the bottom of reactor 21 to standpipe 26 containing slide valve 27.

The uid stream passing overhead from reactor 21 into fractionator 25 is cooled to condense out a heavy bottoms fraction boiling in excess of about 1000 F. and scrubbed to remove the remaining solids. The heavy bottoms product containing the solids recovered in the fractionation operation is recycled through line 17 for reintroduction into the reactor with the slurry of coal and solvent. In the upper part of the fractionator tower, the lighter constituents are fractionated. A heavy gas oil boiling up to about 1000 F. is withdrawn through line 28 and sent to downstream rening units not shown in the drawing for further processing. An intermediate stream boiling in the range between about 350 F. and about 800 F., preferably between about 400 F. and about 700 F., is withdrawn through line 29 and a portion of this stream is cooled in heat exchanger 30 and recycled to the upper part of the tower. The rest of the intermediate stream is passed to a catalytic hydrogenation zone 31. Lighter constituents are taken overhead from the scrubber through line 32 to a condenser 33 from which naphtha is recovered through line 34 and noncondensable gases are taken olf through line 35. 'Ihe naphtha and gas streams may be further processed in the conventional manner.

The char withdrawn from the bottom of reactor 21 through standpipe 26 and slide valve 27 passes into riser 36 where steam is added through line 37 to aid in moving the solids. The slide valve serves to control the bed level in reactor 21 so that the depth of the bed will normally range between about 30 and about 50 feet. 'I'he bed velocity generally ranges from about l to about 3 feed per second. The reactor holding time is preferably between about and about 30 seconds.

The char particles in riser 36 are carried upwardly into burner 38. Air is introduced into the bottom of the burner through line 39 to aid in maintaining the char particles in the uidized state and support the combustion of a part of the char. The burner temperature is maintained in the range between about 1100 F. and about 1200 F. by regulating the amount of air admitted. The pressure in the burner vessel will normally be similar to that in the reactor, between about 10 and about 30 pounds per square inch guage. Hot char particles are withdrawn from the burner by means of standpipe 40 containing slide valve 41 and recycled with steam added at line 42 through riser 23 to the reactor 21. The larger char particles are taken olf through line 43 containing slide valve 44 and passed to quenching zone 45 where water is added by means of line 46 to cool the char. Fine solids present in the char product are carried overhead with the steam formed in the quenching vessel and are recycled to the burner through line 47. The cooled char product is withdrawn from the bottom of the quenching vessel through line 48 containing slide valve 49 and sent to storage for use as a high grade fuel or the generation of synthesis gas to be used in the manufacture of hydrogen. Air may be added through line 50 to assist in handling the char product. The combustion gases formed in the burner are taken over head, passed through cyclone separators 5l and 52, and discharged as stack gases through valve 53 and line 54. The bed velocity in the burner will normally range between about 2 and about 3 feet per second and the depth of the bed is generally controlled at between about l0 and about feet.

The intermediate boiling fractiontaken overhead from the coking unit scrubber and passed to hydrogenation zone 30 as described earlier is heated to the hydrogenation temperature of from about 500 F. to about 1000 F. in furnace 55 before being introduced into the hydrogenation zone. Here the hot fluid is contacted with hydrogen introduced through line 56 at a pressure between about 200 and about 5000 pounds per square inch in the presence of a sulfur-resistant hydrogenation catalyst such as Cobalt molybdate, cobalt molybdate on alumina, nickel tungsten, molybdena on alumina or the like. Hydrogenation temperatures in the range between about 600 and about 750 F. and pressures between about 500 and about 3000 pounds per square inch guage are normally preferred. Hydrogen treating levels in the range from about 200 to about 4000 standard cubic feet per barrel of feed will normally be used. The hydrogenated aromatic product is withdrawn from hydrogenation zone 31 through line 57 and passed to a condenser and separator 58 from which gases are taken overhead through line 59 and liquids are removed through line 60. The gases from the condenser and separator are scrubbed in recycle scrubber 61 and then recycled through line 62 to the input hydrogen stream to hydrogenation vessel 31. The bottoms product from the condenser separator is introduced into stripper 63 where gases containing hydrogen sulde, nitrogen compounds and the like are taken overhead through line 64. The hydrogenated aromatics product from the stripper is withdrawn through line 65. A portion of this product is recycled through

lines

66 and 14 for use as solvent in the slurry preparation vessel 13. The remaining hydrogenated aromatic material is recovered and sent to downstream refining units or storage.

The nature and advantages of the process of the invention are further illustrated by the results obtained in pilot plant tests carried out in a small scale fluidized coking unit. Sub-bituminous Wyodak coal having a moisture content of approximately 30% was crushed and screened to obtain a mesh product. This material was mixed with a hydrogen-donor solvent to form a slurry containing 2 parts of oil per part of wet coal by weight. The solvent employed was one prepared by the hydrogenation of a coal-derived aromatic oil having a boiling range prior to hydrogenation of from about 400 to about 700 F. This solvent contained 8.68 weight percent hydrogen, had a hydroaromatic index of 83.3, and had a specilic gravity of 1.0182. The coal-solvent slurry was fed to a uidized coking unit operated at a reactor temperature of 1000 F. and a pressure of 13 pounds per square inch guage. The steam dilution rate was 2l weight percent, based on the slurry, and the reactor holding time was 14.6 seconds. Gases were taken otf overhead from the reaction vessel, liquids were condensed and collected, and the coke formed was recovered at the end of the run. The products obtained, based on diy coal fed to the process, included 20.3 weight percent gases, 20.9 weight percent liquids, 51.0 weight percent char and 7.8 weight percent water. The composition of the gases and the material balance for the run are shown in Table III below.

Following the run referred to above, a second run was made under essentially the same conditions except that a nonhydrogenated coal-derived oil having a 400 to 700 F. boiling range was used in lieu of the hydrogendonor solvent employed earlier. This material contained 6.57 weight percent hydrogen and had a specic gravity of 1.0616. A Fischer assay was also run on a sample of the coal. The results obtained in the three tests referred to above are set forth in Table III.

TABLE IIL-COKING F WYODAK COAL SLURRIES [Minus 100 mesh coal of approximately Ili, mailture-content, 2:1 slurry oil/wet eo Hydrogen- Fischer donor Raw assay solvent 1 oil 2 Wyodak slurry slurry coal Coking conditions:

Temperature, F 1,000 1, 000 1,010 Pressure, p.s.i.g 13 13 (e) Steam dilution, wt. percent of slurry 5 21. 0 18. 0 N one Reactor holding time, seconds 14. 6 15. 3

Yields, wt. percent on dry coal; gas:

Hg 1. 45 0. 61 0. 06 3. 90 2. 50 1. 81 0. 75 0. 33 0. 34 1. 72 0. 81 0. 59 0. 72 0. 45 0` 25 0. 59 0. 30 0. 18 0. 03 0. O2 0. 0l 0. 62 0. 42 0. 24 0. 32 0. 80 0. 51 1. 50 1. 04 1. 75 8. 40 8. 51 5. 85 0. 21 0. 11 0. 1l

20. 9 12. (l 12. (i 51.0 63. 7 64. 5 7. 8 6. 9 l0. 3

Run material balance 100. 0 99. 5 99. 1

Cg- Gas 'eld (includin CO, CO2,

II. 10.3 15.7 11.0 Cri' Liquid Yield 21. 9 5 13. 2 13. 3

1 Coal-derived 40G-700 F. solvent, 8.68 wt. percent hydrogen, 83.3 hydroaromatic index, 1.0192 sp. gr.

2 40G-700 F. cut, 6.57 wt.. percent hydrogen, 1.0616 sp. gr.

3 Includes moisture in the coal, expressed as wt. percent on wet slurry fed.

4 Not adjusted to close material balance. Does not include (31+ yield. 5 Estimated. Atmospheric.

It can be seen from the above table that the yield of char obtained with the hydrogen-donor solvent was signicantly lower than that obtained with the nonhydrogenated oil and that obtained in the Fischer assay. This lower char yield indicates that a significant quantity of the coal was hydrogenated and lique-ed in the coking unit. The liquid yield obtained with the hydrogen-donor solvent was more than 160% of the Fischer assay yield and compares favorably with that obtained in conventional coal liquefaction processes. As pointed out earlier, the conventional processes normally require the addition of molecular hydrogen if acceptable yields are to be obtained and hence the results obtained in accordance with the invention Without adding hydrogen are surprising. It should be noted that the liquid yield in the run carried out with the nonhydrogenated oil was estimated because of a small leak in the coking reactor during the second run. The values shown in the table appear to be approximately correct, however, and are supported by ythe Fischer assay values. It will be recognized, of course, that some of the char and gases obtained were contributed by the slurry oils. Based upon results obtained in coking oils in the absence of coal, it is estimated that the char yield on 4coal alone, after backing out the predicted char yield from the oil, was about 55% for the nonhydrogenated oil and about 46% for the hydrogenated slurry oil. Similarly, the gas yield from the coal alone is estimated to have been about 12% for the hydrogenated oil and about 16% for the nonhydrogenatcd oil. These values show that the uidizcd coking of coal in the presence of a hydrogen-donor solvent as disclosed above has substantial advantages -over conventional coal liquefaction processes and coking processes carried out without such a solvent.

The advantages of the process of the invention are further illustrated by the results of tests in which the product from a low severity coal liquefactlon operation and a slurry of coal in a hydrogen-donor solvent were sepa- Iately Coked in a fluid bed coking uni-t. The coal liquefaction product was obtained by the liquefactlon of an Illinois coal in the presence of a heart cut hydrogenatcd creosote oil and added molecular hydrogen at a temperature of about 800 F. and a pressure of 350 pound-s per square inch gauge. This liquefaction product was ed to a small scale lluidized bed coking unit oper-ated at a temperature of l000 F. and a pressure of 13 pounds per square inch gauge. The steam dilution rate was 11.4v weight percent based on iced, and the reactor holding time was 26.6 seconds. The coking operation resulted in the production of 2.9 Weight percent gas, 69.0 Weight percent liquids, and 28.1 Weight percent char. The char yield, based on the coal liquefied, was 48%. The Cokin-g run in which a slurry of coal and solvent was used was carried out by irst crushing and screening a sample Of the Illinois coal to less than 200 mesh. This coal was then added to the same heart cut hydrogenated creosote oil used in the earlier run to produce a slurry having a s01- vent-to-coal ratio of 4.5 to l. The coking unit feed pump and nozzle design precluded the use of a more concentrated slurry. During coking of the slurry, a steam dilution rate somewhat higher than that employed in the earlier run was used to avoid plugging of the nozzle in the colring unit and hence the reactor holding time was lower than in the earlier run. The char yield on coal was 44.4 weight percent. The results of these two runs are set forth in Table IV below.

TABLE Tf-COKIN G TESTS 1 Liquid yields were adjusted slightly to close material balance.

The data set forth in the above table show that the direct coking of a slurry of coal in a hydrogen-donor solvent in accordance with the invention resulted in a char yield of only 44.4 weight percent based on coal, compared t0 a yield of about 48% where the coal was rst liqueed and the liquefaction product was recovered and coked. The gas yield in the process of the invention was only 11.5 Weight percent on coal, compared to a yield of about 8 weight percent in the l'iquefaction step and about 5 weight percent in the coking of the liqueaction product. Although these differences may in part be due to the shorter reactor holding time employed in the direct coking operation, the results demonstrate that the process of the invention permits relatively high yields of liquid products without the addition of molecular hydrogen and that these yields compare lfavorably with those obtained in conventional operations involving separate liquefaction, solids separation, and coking steps.

The carrying out of the liquefaction, solids separation, and coking steps simultaneously in a iluidized bed coking unit in accordance with the invention eliminates the investment, operating and maintenance costs required if separate liquefaction and solids separation equipment is used; provides much better heat integration and thermal eiciency than can be obtained in conventional processes; permits generation of all of the required process heat from coal Without the usc of complex and expensive coal-fired furnaces and auxiliary equipment; alleviates the need for heat exchangers and other equipment for handling high temperature slurries which normally poses severe design, operating and maintenance problems in conventional operations; permits signicant reductions in pumping and maintenance costs; and has other advantages over processes suggested in the past. These engineering and economic advantages, the favorable yields of liquid products, and the ability to secure such yields without the addition of molecular hydrogen make the process of the invention attractive in a variety of different applications.

What is claimed is:

1. A process for the preparation of liquid products from coal which comprises:

(a) preparing a slurry of finely divided coal particles in a hydrogenated aromatic hydrogen-donor solvent having a boiling point in the range between about 350 F. and about 800 F. in a slurry preparation zone;

(b) introducing said slurry from said slurry preparation zone into a uidized bed coking unit reaction zone;

(c) withdrawing overhead products from said uidized bed coking unit reaction zone and recovering an intermediate fraction boiling in the range between about 350 F. and about 800 F.;

(d) hydrogenating said intermediate fraction and introducing at least part of the hydrogenated product into said slurry preparation zone;

(e) transferring solids from said uidized bed coking unit to a burner and burning a portion of the solids to provide heat for the process; and

(f) recycling hot solids from said burner to said fluidized bed coking unit reaction zone.

2. A process as defined by claim 1 wherein said fluidized bed coking unit reaction zone is maintained at a temperature between about 900 F. and about 1100 F. and at a pressure in the range between about and about 30 pounds per square inch gauge.

3. A process as defined by claim 1 wherein said slurry zone at a temperature between ambient and about 200 F.

4. A process as defined by claim 1 wherein said slurry is prepared with from about 0.5 to about 5 parts of solvent per part of coal by weight.

5. A process as defined by claim 1 wherein said intermediate fractionl has a boiling range between about 400 F. and about 700 F.

6. A process as defined by claim 1 wherein said hydrogenated aromatic hydrogen-donor solvent contains at least 30 percent by weight of compounds known to be hydrogen donors under the temperature and pressure conditions in said fluidized bed coking unit reaction zone.

7. A process as dened by claim 1 wherein said slurry is introduced into said uidized bed coking unit reaction zone in the substantial absence of added molecular hydrogen.

8. A process as defined by claim 1 wherein said intermediate fraction is hydrogenated at a temperature in the range between about 500 F. and about 1000 F. and at a pressure in the range between about 200 and about 5000 pounds per square inch in the presence of a sulfurresistant hydrogenation catalyst.

9. A process as dened by claim 1 wherein said coal particles have a particle size between about 1A inch and about 325 mesh on the U.S. Sieve Series Scale.

10. A process as defined by claim 1 wherein said coal is a subdbituminous coal.

References Cited UNITED STATES PATENTS 2,624,696 11/ 1953 Schutte 208-165 2,982,701 5/1961 Scott 20S-l1 3,505,201 4/ 1970 Hodgson et al. 208-8 3,523,886 8/1970 Gorin et al 208-8 3,565,766 2,/1971 Eddinger et al. 201-23 3,617,513 '1l/1971 Wilson 208-8 3,503,864 '3/ 1970 Nelson 208-10 VERONICA OKEEFE, Primary Examiner U.S. Cl. X.R. 201-23; 208-10