Coking Of Heavy Feedstocks

Abstract

The formation of char in fluid coking is inhibited by the presence of hydrogen-donor compounds in the fluid coking zone, increasing the yield of desirable liquid products. A hydrogen-donor solvent is admixed with a heavy fluid coker feedstock in amounts sufficient to provide at least 10 weight percent of hydrogen-donor compounds, based on total feed to the fluid coker. Preferable compounds for use as hydrogen donors are the partially saturated hydroaromatic compounds such as indane, C.sub.10 -C.sub.12 tetralins, C.sub.12 and C.sub.13 acenaphthenes, di-, tetra-, and octahydroanthracene, and tetrahydroacenaphthene. The process is particularly useful in the production of liquid hydrocarbon products from solid coal wherein the coal is subjected to solvent liquefaction and the resulting liquid slurry is fed into a fluid-coking zone. Where hydrogen-donor solvent is used for the liquefaction step, and it does not become completely hydrogen-depleted, no additional solvent need be added prior to fluid coking. However, additional hydrogen-donor solvent may be added (and if not nondonor solvent was used in liquefaction, must be added) prior to such coking. The use of additional hydrogen-donor solvent further enhances the yield of liquid products and inhibits char yield. Preferably, the fluid-coking step will be used in conjunction with an external burner, and a portion of the product coke will be removed for use in generating hydrogen by contact with steam, with such hydrogen being used to satisfy at least in part the demands for hydrogen in the hydrogenation of the recycle solvent.

Description

DISCUSSION OF PRIOR ART

The search for a commercially attractive process for making liquid products from coal began long ago. The coking (pyrolysis) of coal has long been a well-established industry, with liquid byproducts being recovered along with the primary product, coke. Solvation of coal, with or without the addition of molecular hydrogen, has also long been known as a feasible but not an economically attractive process for obtaining liquid products from coal (as exemplified by U.S. Pat. No. 1,342,790 ). The Pott-Broche process (e.g., U.S. Pat. No. 1,881,927), with modifications, was capable of producing high-cost gasoline from coal. During World War II Germany produced large quantities of synthetic fuels using coal as a feedstock, but at a prohibitively high cost. After the cessation of hostilities, when crude oil again became available to Germany, the more economical process of refining petroleum supplanted synthetic fuels production.

With the possible dwindling of supplies of crude oils, however, the search for an economically attractive coal liquefaction process has continued. Gorin has suggested several process schemes utilizing a hydrogen-donor solvent in the liquefaction zone, and limiting the conversion so as to selectively liquefy only those materials most susceptible to hydrotreating. In this scheme, however, the need for separating undissolved solids from the liquid extract phase adds greatly to investment and operating costs. (See U.S. Pat. Nos. 3,018,241 and 3,117,921, for example). Johnson (Re. 25,770) and Schuman et al. (U.S. Pat. No. 3,321,393) have suggested the hydrogenation of coal in a three-phase system utilizing a liquid-fluidized bed of hydrogenation catalyst. This scheme also is burdened with the need for high-temperature solids-liquid separation. The present invention avoids the need for a mechanical means of solids-liquid separation at high temperatures by charging the entire liquid-solids slurry from a liquefaction zone into a fluidized coker. The lighter material readily vaporizes leaving the heavier liquid components to crack and volatilize in the presence of hydrogen-donor solvent, producing additional lighter components and resulting in a reduced char yield.

Many patents have suggested the use of coking as a part of a coal liquefaction process. Gorin's patents (U.S. Pat. Nos. 3,018,241 and 3,018,242) suggest the "carbonization" of the solid residue remaining after solids-liquid separation. Pevere et al. (U.S. Pat. No. 2,664,390) suggest carbonization of a mixture of liquids and solids, but "oversize solid particles" must be removed, apparently to avoid plugging the nozzles of the atomizer which is employed. Pevere et al. do not use a hydrogen-donor solvent or fluid coking. Frese et al. (U.S. Pat. No. 2,738,311) suggest the coking of heavy oil and residue, but first flash off all lighter components (including all possible hydrogen-donor solvents) and do not contemplate fluid coking at all.

As can be seen by the foregoing discussion, the prior art has not contemplated the combination of hydrogen-donor liquefaction and fluid coking which forms the basis of the present invention.

DISCUSSION OF THE INVENTION

The present invention is directed to a process for converting coal into liquid products. Basically, the invention depends upon the combination of a hydrogen-donor liquefaction step with a succeeding fluid coking of the liquid products from the liquefaction zone in the presence of unconsumed hydrogen-donor solvent. As a modification, however, it should be understood that any type of coal liquefaction (e.g., nonhydrogen-donor solvation) can be carried out and a hydrogen-donor solvent added to the liquid products from the liquefaction zone, with or without first having flashed off a substantial amount of the lighter materials.

In order better to understand the present invention, each of the sections of the complete overall process scheme will be separately discussed. It should be clearly understood, however, that the overall scheme, which envisions the production of hydrogen from withdrawn coke from the burner, is exemplary only and that the production of hydrogen need not be carried out in order to enjoy the benefits of the present invention.

Mixer

Solid Feed. The basic feedstock to the process of the present invention is a solid, particulate carbonaceous material, such as bituminous coal, subbituminous coal, lignite, brown coal, etc. Although it is desirable to grind the coal to a particle size distribution from about 8-mesh and finer, it has been found that the solvation reaction will result in a size reduction even if particles as large as one-fourth inch on the major dimension have been introduced into the liquefaction zone. Thus, it is possible to charge large chunks of coal rather than the preferred finely divided coal. A typical inspection of the feed coal thus far experimented with is given in table I, below. --------------------------------------------------------------------------- TABLE I

Typical Feed Coal Inspections

Moisture, saturated 13.0 Ash, Dry 10.6 Mineral matter, dry 12.8 Vol. Matter, DMF* 45.1 Fixed Carbon, DMF 54.9 Carbon, DMF 79.1 Hydrogen, DMF 5.59 Oxygen, DMF 10.6 Nitrogen, DMF 1.24 Sulfur, Total, dry 4.70 Sulfur, Pyritic, dry 1.71 Sulfur, Organic, DMF 3.42 B.t.u./lb., Dry 12,610 B.t.u./lb., DMF 14,360 --------------------------------------------------------------------------- *dry, mineral-free.

The carbonaceous material preferably is dried to remove excess water, although it is feasible to charge the "wet" coal if the liquefaction facilities have been sized to allow the withdrawal of evolved steam. The coal can be dried by conventional techniques prior to introduction into the mixer used to establish the slurry feed for liquefaction. Preferably, however, the wet coal is mixed with hot hydrogen-donor oil which is charged tO the mixer and water is volatilized in the mixer, thereby reducing the feed slurry moisture content to less than about 2 weight percent. Thus, the mixer also serves the function of a drier.

Hydrogen-Donor Solvent.

In the mixer, the coal feedstock at ambient temperature is admixed with a liquid solvent, preferably a hydrogen-donor solvent, which is at a temperature from 500.degree. to 700.degree. F. The solvent/coal weight ratio is within the range from 1/1 to 2/1, resulting in a slurry temperature within the range from 300.degree. to 350.degree. F. A mechanical propeller or other agitating device may suitably be provided in the mixing zone so as to obtain a uniform slurry concentration.

The solvent stream will boil within the range from 350.degree. to 900.degree. F. (preferably from about 375.degree. to about 800.degree. F.) so as to remain in the liquid phase after the slurry has been formed. Preferably, the solvent will contain at least 30 weight percent (preferably at least 50 weight percent) of compounds which are known to be hydrogen donors under the liquefaction conditions and (as has now been discovered) under coking conditions.

Hydrocarbon streams containing one or more of the hydrogen-donor compounds, in admixture with nondonor compounds or with each other, will be suitable. Compounds such as indane, C.sub.10 to C.sub.12 tetralins, C.sub.12 and C.sub.13 acenaphthenes, di-, tetra-, and octahydroanthracene, and tetrahydroacenaphthene are preferred as hydrogen-donor compounds, as are other derivatives of the partially saturated hydroaromatic compounds.

Where the solvent stream is a hydrogenated recycle solvent fraction (as is preferred), the composition of the equilibrium solvent will vary somewhat, depending upon the source of the coal used as a feedstock to the system and the operating conditions in the liquefaction, coking and solvent hydrogenating sections. However, a typical description of the hydrogenated recycle solvent fraction will be similar to that shown in table II. ##SPC1##

Liquefaction Zone

The slurry of coal in solvent is passed into a liquefaction zone, where the convertible portion of the coal is allowed to dissolve and depolymerize to form free radicals. At the temperature maintained within the liquefaction zone (e.g., about 750.degree. F.), the coal softens almost instantaneously and the expanding gases trapped within the coal particles cause vesiculation and swelling of the particles. Where, as is preferred, the slurry is preheated in a furnace-type heater before introduction into the liquefaction zone, the softening begins while the coal particles are in the furnace-type heater. Within approximately 5 minutes, the coal particles disintegrate to produce some low molecular weight, benzene-soluble materials. Little hydrogen transfer is involved in this disintegration phase, even if donor-type solvents are used, but nondonor solvents such as dodecane do not disperse the fragments of coal as well as do tetralin and naphthalene. The dispersed fragments (not necessarily liquefied) are cracked to produce free radicals which can recombine to form material which is not soluble even in pyridine. If a hydrogen-donor solvent is present, however, the tendency to recombine is substantially inhibited, both in the liquefaction zone and in the coking zone. Since the depolymerized (cracked) coal molecules can either recombine with each other or be stabilized by accepting hydrogen from the donor solvent, the degree of inhibition will depend on the amount of donor solvent which is present. Where the donor solvent contains about 50 weight percent of hydrogen-donor constituents, and the solvent/coal ratio is from 1/1 to 2/1, the concentration of hydrogen-donor constituents in the liquefaction zone can be seen to range initially from 25 weight percent to 331/3 weight percent and will be depleted by the liquefaction reaction. However, molecular hydrogen can be added to the liquefaction zone to partially replenish the hydrogen-donor solvent by in situ hydrogenation of the depleted molecules (e.g., naphthalenes may be hydrogenated to tetralins).

Liquefaction conditions which are suitable may include a temperature from 650.degree. to 1,000.degree. F., a pressure from 300 p.s.i.g. to 3,000 p.s.i.g., a solvent/coal weight ratio from 1/1 to 2/1, a molecular hydrogen input rate from zero to 4 weight percent (based on m.a.f. coal charged into the liquefaction zone in the slurry), and an oil residence time of 5 to 60 minutes, all so combined as to obtain a MEK conversion in the range from 60 to 90 weight percent, preferably about 85 weight percent. The conversion is expressed as the percent of moisture and ash free (m.a.f.) coal that is converted to materials which are soluble in methylethyl ketone (MEK). It is calculated by the equation:

wherein

a=percent ash in the moisture-free coal feedstock,

S.sub.f =percent solids in the feed slurry,

S.sub.p =percent solids in the product slurry.

Before measuring S.sub.p, MEK is added to the product slurry as a solvent, in the ratio of 1 volume of MEK for each volume of product slurry. The results so obtained are referred to as "MEK conversion."

As aforesaid, in the liquefaction zone the hydrogen-donor solvent reacts with the free radicals resulting from depolymerization. As a result, even though hydrogen may be charged into the liquefaction zone to replenish the donor solvent, a portion of the hydrogen-donor solvent becomes hydrogen-depleted. The degree of depletion is a function of the specific solvent and of the conditions employed. A typical recycle solvent will contain about 50 weight percent of compounds which will donate hydrogen and, during about 1 hour within the liquefaction zone with molecular hydrogen being added, will be depleted to the extent that only 25 weight percent of the solvent is made up of hydrogen-donor compounds.

A gaseous phase product is removed from the liquefaction zone as well as the liquid slurry. Exemplary compositions of the gas product and liquid product (without separation from solids in the slurry) are given below in table III. --------------------------------------------------------------------------- TABLE III

Exemplary Gas and Liquid Products

Gas Product Liquid Product Comp. Wt. % Temp. .degree.F. Cum. Wt. % Sp.Gr. 60/60.degree. F. __________________________________________________________________________ Co 1.2 337 IBP CO.sub.2 21.8 437 7.4 0.9014 H.sub.2 S 17.7 485 14.7 0.9496 CH.sub.3 SH 5.2 549 22.6 0.9667 H.sub.2 4.7 596 31.4 1.0089 C.sub.1 20.1 658 40.2 1.0370 C.sub.2 15.8 732 49.0 1.0560 C.sub.2 .sup. 0.4 786 53.4 1.0791 C.sub.3 7.3 835 59.1 Solid C.sub.3 .sup. 0.5 [Btms 30.9] Solid C.sub.4 2.9 100.0 C.sub.4 .sup. 1.1 C.sub.5 1.3 100.0 __________________________________________________________________________

operating conditions in the liquefaction zone are shown in table IV in comparison with operating conditions in the other zones.

Since the amount of hydrogen-donor components in hydrogen-donor solvents is substantially reduced by the liquefaction step, it may be desirable to add more of such components to the slurry effluent from the liquefaction zone. This is easily accomplished by adding hydrogenated recycle solvent to the slurry before it is introduced into the coking zone. Suitably, the slurry may first be passed through a flash zone to partially remove the lower boiling materials, including the materials boiling in the range of the solvent. Thus, at least a portion of the partially hydrogen-depleted donor solvent is removed, to be replaced by fresh hydrogenated recycle solvent. If such a flash zone is used, the slurry (at a temperature of about 800.degree. F. and a pressure of about 350 p.s.i.g.) is dropped to a pressure of about 100 p.s.i.g., and the liquid volume reduced by flashing (e.g., to about one-half the original volume). Additional recycle solvent may be added in amounts from one-half the volume of the removed solvent (which would effectively replace the donor constituents removed by flashing) to twice the volume (or more) of the removed solvent. As shown later, the donor solvent is not substantially cracked in the coking zone, so the additional volume is limited only by the heat load required to vaporize the solvent in the coker. The addition of fresh hydrogen-donor solvent reduces char make in the coker.

Coking

Preferably, a fluid coking zone is employed, whereby volatile matter is driven off and heavier materials are cracked to produce distillable products. A fluid coking zone is operated at elevated temperatures which promote the further depolymerization and cracking of the coal (as well as of liquefied components thereof which are in the slurry). As aforesaid, the cracking and depolymerization reactions form free radicals which may recombine and polymerize, resulting in the production of char. However, by providing a substantial amount of hydrogen-donor compounds as part of the coker feedstock, the tendency toward polymerization is inhibited and char yield is reduced, with a concomitant increase in the yield of liquid products.

In the fluidized coking zone, a bed of heated coke particles is maintained in the fluid state. The slurry feed is directed into the bed of coke for vaporization and cracking. The vaporous and gaseous products are removed overhead as a coker distillate stream and fractionally distilled. The heavier components may be recycled to the coking zone while the lighter products may be separated into a recycle solvent stream and at least one product stream (boiling at temperatures lower than the boiling range of the recycle solvent.

Heat for the coking reactions is supplied by removing a portion of the coke in the coking zone and burning a part thereof, whereby the remaining removed coke is highly heated before being returned to the coking zone as the source of heat. A suitable fluid coker will have a coke holdup of 1,522 tons and a coke circulation rate of 68 tons/minute. Steam diluent may be added at the rate of 260,000 lb./hr.

The coking reaction can also be accomplished in a delayed coker or by other processes well known in the refining arts. The fluid coking process is preferred for use with the present invention, and is carried out in the manner well known to those skilled. in the art, since the presence of the hydrogen-donor solvent does not deleteriously affect operation of the coking unit.

Coke Burner

In the coke burner, a recirculating stream of coke from the coker is contacted with air in order to burn off a part of the coke and generate heat to support the coking reactions and vaporization taking place within the fluidized coker. The coke burner will operate generally under conditions including a temperature from 1,000.degree. to 1,500.degree. F., a pressure from zero to 30 p.s.i.g., a superficial gas velocity of 0.5 to 4.0 ft./sec., an air rate sufficient to provide the amount of heat required for the coking zone and/or hydrogen production zone, and an average coke residence time from 5 to 10 minutes. If withdrawn excess coke is to be used for the generation of hydrogen, a hydrogen generator will be placed downstream of the coke burner. For most efficient operation, a second burner will be provided for the hydrogen generator. This second burner would operate at a higher temperature (e.g., 2,000.degree. F.) in order to provide heat for the high-temperature hydrogen production zone. Where only one burner is employed, air or oxygen must be introduced into the hydrogen generator to burn additional coke and raise the temperature to the desired level.

Hydrogen Generator

The hydrogen generator receives hot coke from the burner and contacts it with steam in order to carry out the water-gas reaction:

C+H.sub.2 O CO +H.sub.2

Unreacted steam is carried from the hydrogen generator along with the carbon monoxide and hydrogen and is suitably contacted in a shift reactor with further steam and a shift catalyst in order to obtain more hydrogen, following the shift reaction:

CO+H.sub.2 O CO.sub.2 +H.sub.2

Suitable catalysts for use in the shift reaction are well known, including the old iron oxide catalysts and the newer catalysts such as copper/zinc oxide combinations. A two-stage shift reaction utilizing a high-temperature catalyst in the first stage and a low-temperature catalyst in the second stage may be employed, if desired.

The hydrogen generator operates with a fluid bed of coke, as does the burner and the coker. The coke is maintained in a fluid bed by the injection of the reactant steam. Air or oxygen may be introduce to react with coke in the bed and evolve heat, there raising the temperature of the coke to the desired level. Alternatively, a second burner may be used, as aforesaid, which is operated at a higher temperature (e.g., 2,000.degree. F.) in order to maintain the 1,600.degree.-1,800.degree. F. temperature required in the hydrogen generator. Operating conditions in the hydrogen generator include a steam rate of 0.1 to 1.0 pound per hour per pound of coke in inventory, a temperature from 1,600.degree. to 1,800.degree. F., a pressure form zero to 250 p.s.i.g., and average coke residence time of 0.5 to 2 hours, a bed depth of 10 to 15 feet, and a superficial gas velocity of 0.5 to 4.0 feet/second.

All of the operating conditions for the various reaction zones are shown in table IV.

Solvent Hydrogenation Zone

The solvent hydrogenator receives the recycle solvent (boiling generally within the range from 350.degree. to 800.degree. F.) from the coker fractionator. It is contacted in the solvent hydrogenation zone with hydrogen in presence of a hydrogenation catalyst such as cobalt molybdate, and under hydrogenation conditions such as a temperature from 650.degree. to 850.degree. F., a pressure from 650 to 2,000 p.s.i.g., and a space velocity from one to six weights of liquid per hour per weight of catalyst. The hydrogenated oil is then fractionated to the desired boiling point range in a stripping tower before being sent back to the mixer. Table II shows the analysis of a typical hydrogenated solvent. --------------------------------------------------------------------------- TABLE IV

Operating Conditions

Liquefaction Zone Minimum Maximum Preferred __________________________________________________________________________ Temperature, .degree.F. 700 1,000 800 Pressure, p.s.i.g. 350 3,000 1,000 Solvent/coal wt. ratio 1/1 2/1 1.2/1 Wt. % H.sub.2 (on MAF coal) 0 4 2 Oil residence time, min 5 60 30 MEK Conversion, wt. % 60 90 85

Fluid Coker Temperature, .degree.F. 900 1,300 1,100 Pressure, p.s.i.g. 0 30 12 Superficial gas velocity, ft./sec. 0.5 4 2 Coke particle size, microns 10 1,000 20-500 Bed Density, 1b./cu.ft. 15 60 40 Space velocity, w./hr./w. 0.1 1.0 0.3

Coke Burner Temperature, .degree.F. 1,000 1,500 1,200 Pressure p.s.i.g. 0 30 15 Superficial Gas Velocity, ft./sec. 0.5 4 3.0

Hydrogen Generator Temperature, .degree.F. 1,700 1,900 1,800 Pressure, p.s.i.g. 20 300 150 Superficial gas velocity, ft./sec. 0.5 4.0 2.5 % Coke gasified/hr. 20 40 30 Ash concentration, wt. % 50 70 60 Steam conversion, wt. % 40 80 60

Solvent Hydrogenation Temperature, .degree.F. 650 850 700 Pressure, p.s.i.g. 650 2,000 1,350 Space Velocity, w./hr./w. 1 6 2 SCF H.sub.2 /bbl. feed 1,000 10,000 5,000 __________________________________________________________________________

EXAMPLES

The following examples show the effect of hydrogen-donor solvent on char yield in various coking operations. All char yields are weight percent, based on coal feed.

Example 1

A nondonor solvent oil (boiling at 450.degree. to 750.degree. F.) was mixed with finely divided coal at a solvent/coal weight ratio of 2/1. The mixture was subjected to a temperature of 1,100.degree. F. at ambient pressure to coke the mixture (equivalent to delayed coking). The char yield was 61.0 weight percent, not quite as high as the char yield obtained by coking coal at 1,100.degree. F. in the absence of a solvent (78 weight percent).

Example2

Finely divided coal was well dispersed in naphthalene (a nondonor oil) at a solvent/coal ratio of 2/1 and subjected to liquefaction conditions of 750.degree. F. for 20 minutes. From an analysis of benzene insoluble materials in liquid product, correlations indicated that a char yield of 77 weight percent would have been obtained if the product had been coked.

Example 3

Example 2 was repeated with the coal dispersed in dodecane (a nondonor solvent at a solvent/coal ratio of 2/1, and subjected to liquefaction at 750.degree. F. for 43 minutes. Correlations indicated a char yield of 77 weight percent.

Example 4

Illinois coal, ground to a particle size distribution of about 100-mesh and finer was first dried and then contacted in a mixer with a hydrogen-donor solvent similar to that described in table II at a solvent/coal weight ratio of 1.2/1. The the resultant admixture was passed through a liquefaction zone at 775.degree. F. and a pressure of 350 p.s.i.g. for a residence time of about 60 minutes, and the total liquid slurry effluent from the liquefaction zone was charged to a fluid coker at a temperature of 1,000.degree. F. and a pressure of 10 p.s.i.g. The car yield was 45.4 weight percent.

Example 5

Example 4 was repeated with a solvent/coal ratio of 2/1 and under liquefaction conditions of 850.degree. F. and 980 p.s.i.g. Char yield was 35.0 weight percent, showing a reduction in char yield due to additional donor solvent in the coker feed.

Example 6

Example 4 was repeated except that the slurry effluent from the liquefaction zone was centrifuged to obtain a residual solids product which contained about 50 weight percent solids and 50 weight percent liquid. This residual solids product was slurried in fresh hydrogen-donor solvent to a solids concentration of about 25 weight percent before being charged to the coking zone. The char yield was only 18.1 weight percent, showing a further reduction in char yield due to the further increase in additional donor solvent in the coker feed.

Example 7

Depleted donor solvent was charged to the coker at 1,000.degree. F. and 10 p.s.i.g. Only 1.2 weight percent was degraded to gas and 0.2 weight percent to char, with 98.4 weight percent being recovered undegraded. This establishes the fact that solvent losses due to passage through the coking zone are quite low and are almost negligible. It has been found by mass spectographic analysis that five-sixths of the hydrogen transferred in the coker from donor solvents was donated to the liquid products and only one-sixth to molecular hydrogen. This indicates that only slight degradation of the donor solvent is suffered in the coking zone, and only minor amounts of the hydrogen transferred was lost as molecular hydrogen.

a preferred specific application of the present invention is shown in the drawing, which represents a schematic diagram of a coal liquefaction scheme utilizing a fluidized coker for processing the effluent from the coal liquefaction zone.

Referring now to the drawing, it is seen that particulate coal is introduced by way of line 100 into a mixer 102, wherein it is combined with a recycle oil stream introduced by way of line 104 to form a paste. The solvent/coal ratio in the mixer may suitably be about 1.2 parts of solvent per part of coal (by weight). The slurry from the mixer 102 is conducted by way of line 106 into a liquefaction zone 108 which is maintained under liquefaction conditions including a temperature of about 800.degree. F. and a pressure of about 1,000 p.s.i.g. Hydrogen also may be introduced (2 weight percent, based on m.a.f. coal feed) in the gaseous form by way of line 110 if desired, although it is not necessary for the basic H.sub.2 donor process. Within the liquefaction zone 108, hydrogen is transferred from the hydrogen-donor solvent to the coal, causing a depolymerization of the coal along with the solvation effect of the solvent. Thus, within the liquefaction zone 108 is produced a mixture of undepleted hydrogen-donor solvent, depleted hydrogen-donor solvent, dissolved coal, undissolved coal, and mineral matter. This mixture remains in the liquid phase, and a vapor phase of lighter hydrocarbons and gases is maintained above the liquid phase.

The liquid mixture is removed by way of line 111 and is transported into a fluid coker 114. The flash vessel 112 may be employed, if desired, as will be hereinafter discussed. The fluid coker is operated to maintain a dense phase bed 115 of coke particles within the lower portion thereof. The bed is maintained in the fluidized state by steam introduced through line 116 and by the evolution of vapors from volatilization and cracking of the feed stream being introduced by way of line 117.

Within the coker 114, the liquid hydrocarbons undergo thermal cracking and, because of the presence of undepleted hydrogen-donor solvent, hydrogen donation does occur so as to enhance the depolymerization and cracking of the coal molecules thereby maximizing the production of vaporous products and minimizing the amount of char which is produced and laid down on the bed of coke.

A portion of the coke in the coker 114 is withdrawn by way of line 118 and is carried through the line 120 by an entraining gas stream such as steam introduced by way of line 122 and is introduced into a fluidized bed 124 in the burner 126. The fluidized bed of coke 124 is maintained in the fluidized state by air which is introduced by way of line 128 as well as fluidizing steam which may also be introduced. It is also partially maintained by the evolution of combustion products from the reaction of air with the carbon and hydrogen which make up the coke particles. A flue gas is removed by way of line 130, while hot coke particles are removed by way of line 132 and are entrained in a carrying steam stream introduced by way of line 134 for passage through line 136 and reintroduction into the coker 114.

The vaporous products from the coker 114 pass upwardly through a cyclone separator 140 and are therein separated from entrained coke particles which are returned through the dip leg 142 beneath the level of the fluidized bed. The vaporous products are fractionated in a distillation tower (suitably mounted directly above the coker vessel, as indicated) and a bottoms product such as hydrocarbons boiling above 1,000.degree. F. are removed from the tower and recycled by way of line 144 into the coke bed for further conversion.

The fractionator also may be operated to produce a heavy gas-oil stream boiling within the range from 700.degree. to 1,000.degree. F. as indicated by line 146, a naphtha stream boiling up to about 400.degree. F. which is removed by way of line 148 and a gas stream which is removed by way of line 150. A recycle solvent stream boiling within the range from about 400.degree. to about 700.degree. F. is removed by way of line 152 and at least a portion thereof is recycled for use as hydrogen-donor solvent by way of branch line 154. If desired, a portion of this stream may be removed for further treatment and disposition by way of product line 156.

The recycle solvent is contacted in the hydrogenation zone 160 with hydrogen which is introduced by way of line 162, in the presence of a hydrogenation catalyst such as cobalt molybdate and under hydrogenation conditions such as a temperature of about 700.degree. F., a pressure of about 1,350 p.s.i.g., and a space velocity of about 2 weights of liquid per hour per weight of catalyst. The hydrogenated oil is removed by way of line 164 and may be passed through a flash separation zone 166, for the removal of hydrogen and light ends through line 168, if desired. The liquid from this flash zone passes through line 167 into a stripping zone 190 where the naphtha is removed through line 191. The solvent leaves the stripping zone through line 193 and is optionally split into two separate streams. Stream 194 can be used to enrich the coker feed with fresh H.sub.2 donor oil and the other portion of the hydrogenated liquid passed by way of line 104 into the mixer 102 as discussed above. The stream 194 is best used in conjunction with flash zone 112, wherein the liquid volume of the slurry may be reduced by 50 percent and the volume reconstituted by addition of fresh solvent.

If desired, the gaseous products from the liquefaction zone 108 may be removed by way of line 170, passed through a separator 172, and a gas stream removed by way of line 174. Light hydrocarbons in the gaseous stream may be removed by way of line 176 and introduced into the fractionating tower 145, for distillation along with the products of the coker.

In order to provide a balanced unit, wherein hydrogen may be manufactured from a portion of the coke from the coker 114, a portion of the hot coke may be removed from the burner 126 by way of line 180, entrained in steam introduced by way of line 182 and passed by way of line 184 into a hydrogen production zone 186. In the hydrogen production zone 186, the hot char is maintained in the fluidized state with superheated steam introduced by way of line 188 and the transfer steam introduced by way of line 184.

In the hydrogen generator 186 the carbon in the char is converted to carbon monoxide by reaction with the steam, with a net production of hydrogen. The gaseous product, comprising a mixture of carbon monoxide, hydrogen and water is removed by way of line 190 for further treatment such as reaction in a shift reactor to convert the carbon monoxide into carbon dioxide by reaction with steam, with a net production of more hydrogen. The product char is removed from the hydrogen generator through a line (not shown). Ultimately, the hydrogen may be purified by well-known processes and returned for use as the hydrogen in the hydrogen-donor solvent hydrogenation zone and for introduction into the liquefaction zone if desired.

Thus, it is seen that the present invention does provide an improved way of carrying out the liquefaction of coal and the production of vaporous hydrocarbon products therefrom, wherein the mechanical separation of solid particles from the extract from the liquefaction zone is avoided and the formation of char in the coking zone is minimized by the presence of the undepleted hydrogen-donor solvent.

While the present invention has been discussed in connection with the coking of coal extracts, it is equally applicable to the coking of any heavy (e.g., 1,000.degree. F.+) hydrocarbon stream, such as petroleum residua, where the production of liquid products should be maximized and coke yield minimized.

Having disclosed our invention, what is to be protected by Letters Patent should be limited only by the appended claims, and not by the specific examples herein given.

Claims

We claim:

1. In the fluid coking of an admixture of liquids and solids obtained by solvent liquefaction of coal containing less than 5 weight percent of compounds capable of hydrogen-transfer donation under coking conditions,

the improvement of concurrently coking in admixture with said feedstock a hydrogen-donor solvent boiling within the range from 300.degree. F. to 900.degree. F. and containing hydrogen-donor compounds chosen from the group consisting of C.sub.10 to C.sub.12 tetralins, indane, C.sub.12 and C.sub.13 acenaphthenes, di-, tetra-, and octahydroanthracene and tetrahydroacenaphthene, and mixtures of two or more thereof,

said hydrogen-donor compounds constituting at least 30 weight percent of said solvent and at least 10 weight percent of the admixture of liquid, solids, and solvent.

2. A process in accordance with claim 1 wherein by solvent liquefaction of coal, and the hydrogen-donor solvent is at least in part supplied by unreacted solvent from said liquefaction.

3. A process in accordance with claim 2 wherein fluid coking conditions include

a temperature from about 1,000.degree. F. to about 1,500.degree. F. and

a pressure from about zero p.s.i.g. to about 30 p.s.i.g.

4. A process for obtaining liquid hydrocarbon products from solid coal which comprises

1. in a liquefaction zone contacting said coal with a hydrogen-donor solvent under liquefaction conditions chosen to obtain a liquefaction zone slurry product containing partially hydrogen-depleted donor solvent, liquefied coal, undissolved coal and mineral matter,

said partially hydrogen-depleted donor solvent retaining sufficient hydrogen-donor constituents so that such constituents constitute at least 10 weight percent of the total slurry product,

2. coking the entire slurry product in a fluid coking zone under coking conditions including a temperature within the range from 1,000 to 1,500.degree. F.,

whereby a coker distillate stream and a coke stream are obtained,

3. separating said coker distillate stream into at least a recycle solvent fraction and another fraction,

said recycle solvent fraction boiling within the range from 350.degree. F. to 900.degree. F.,

4. hydrogenating said recycle solvent fraction, and

5. using at least a portion of said hydrogenated recycle solvent fraction as the hydrogen-donor solvent in step (1).

5. A process in accordance with claim 4 further comprising the steps of:

6. burning at least a portion of the coke stream in a burning zone to generate heat for the coking reaction and to obtain a recycle coke stream and a product coke stream,

7. contacting at least a portion of said product coke stream with steam under hydrogen-producing conditions, and

8. returning said recycle coke stream to said coking zone.

6. A process in accordance with claim 4 wherein the liquefaction conditions include

a temperature from 700.degree. F. to 1,000.degree. F.,

a pressure from 350 p.s.i.g. to 3,000 p.s.i.g., and

an average oil residence time from 5 to 60 minutes, and

wherein the coal particle size range is about 8-mesh and smaller.

7. A process in accordance with claim 6 wherein the recycle solvent contains at least about 50 weight percent hydrogen-donor compounds, and has a boiling range from about 372.degree. F. (at about 8.4 percent over) to about 785.degree. F. (at about 94.4 percent over), and where the solvent-to-coal ratio is about 1.2/1, by weight.

8. A process for obtaining liquid hydrocarbon products from solid coal which comprises

1. in a liquefaction zone contacting said coal with a hydrogen-donor solvent under liquefaction conditions chosen to obtain a liquefaction zone slurry product containing partially hydrogen-depleted donor solvent, liquefied coal, undissolved coal and mineral matter,

said partially hydrogen-depleted donor solvent retaining sufficient hydrogen-donor constituents so that such constituents constitute at least 10 weight percent of the total slurry product,

2. adding to said slurry product fresh hydrogen-donor solvent,

3. coking the mixture of slurry and fresh hydrogen-donor solvent under fluid coking conditions including a temperature within the range from 1,000.degree. F. to 1,500.degree. F.,

whereby a coker distillate stream and a coke steam are obtained, and the yield of coke is reduced.

9. A process in accordance with claim 8 wherein at least a portion of the liquid portion of the slurry is removed prior to addition of fresh hydrogen-donor solvent.

10. A process in accordance with claim 9 wherein at least 50 weight percent of the liquid feed to the coker is fresh hydrogen-donor solvent and at least 30 weight percent of the fresh hydrogen-donor solvent is constituted of hydrogen-donor compounds.