US2888393A - Hydrocarbon coking and hydrogenation process - Google Patents

Description

May 26, 1959 w. P. BALLARD ETAL HYnRooARBoN COKING AND HYDROGENATION PRocEss Filed Feb. 25, 1956 Alll x msg United States Patent O HYDROCARBON COKING AND HYDRO- GENATIGN PROCESS Application February 23, 1956, Serial No. 567,196

Claims. (Cl. 208-58) This invention is directed to a hydrocarbon conversion process. More particularly, it relates to the cracking and coking of hydrocarbon oils in the presence of hydrogen and hydrogenation of the cracked products in contact with a hydrogenation catalyst. According to the process of this invention, a hydrocarbon oil is subjected to cracking and coking temperatures in a reaction zone in contact with coke and added hydrogen under iluidized conditions. Coke is Withdrawn from the reaction zone, subjected to combustion in a burning zone and returned to the said reaction zone. Hydrocarbon vapors and hydrogen are withdrawn from the reaction zone and subjected tol hydrogenation reaction conditions in a hydrogenation-zone in Contact with a hydrogenation catalyst.

Fluid coking is a Well-known process for the conversion of heavy oils, for example, crude oil residuums, cracking residues and asphalt resins, to useful products, such as,

gasoline and gas oil cracking stock. The gasoline fractions from conventional uid coking are of the unsaturated nature and usually require further treatment to produce stable products. We have now found that ,hydrogen may be introduced into a uid colring reaction zone to effect iluidization and improvement in the yield and quality of products obtained in the coking step. The presence of hydrogen in the coking reactor results in the suppression of lpolymer formation and degradation to coke so that greater yields of valuable liquid products lare obtained. Further, bypassing the entire eluent'hydrocarbon vapors and hydrogen from the coking zone to a hydrogenation Zone, gasoline of improved stability is produced as well as gas oils of improved catalytic cracking characteristics.

In the process of this invention, the luid coking zone is operated at a pressure within the range of from about 200 to about 2000 p.s.i.g. so that vapors from the coking zone may flow to the hydrogenation zone without intermediate compression. The pressure of the hydrogenation zone is generally the same as that of the coking zone, i.e., within the range of from about 200 to about 2000 p.s.i.g. allowing for the small drop in pressure which accompanies friction losses through the vessels, transfer lines and auxiliary equipment.` The temperature of the fluid coking zone is usually of the order of 900 to l100 F. The hydrogenation zone is operated at a hydrogenation temperature within the range of'about 600'to 800 F. The eluent from the coking zone may be cooled before introduction into the hydrogenation zone by the injection of cold recycle hydrogen, or, in the alternative, by the injection of an extraneous hydrocarbon oil.` In the latter case, the injected oil passes to the hydrogenation zone with the cracked products and is concomitantly subjected to desulfurizationr and hydrogenation.

IA Hydrogenrecycle gas is introduced into the fluid coking reactorat a rate within the range limited by the minimum rate which is suicient to obtain satisfactory iluidization and thermaximum rate which may be employed without excessivevcarry-over of solids from lthe lluid bed by -entrainment. The foregoing range of reactor vlapor velocities is usually from about 0.5 to about 2.5 feet per sec- 2,888,393 Patented May 26, 1959 ICC ond. The .hydrogen recycle rate will further vary substantially with the pressure of operation. The recycle rate employed might be about 860 standard cubic feet per barrel at a vapor velocity of about 0.5 foot per second and at 200 pounds per square inch and range up to about 159,000 standard cubic feet per barrel at a vapor velocity of 2.5 feet per second and at 2000 pounds per square inch.

Ordinarily the coke burner is operated at a pressure near that of the reactor. Flue gases from the coke burner have a high energy content because of their high temperature and pressure. It is, therefore, desirable to recover the energy in the hot flue gas by passing this stream through turbines or other power recovery equipment.

A11 advantage of the process kof this invention is that the yields of desired products are increased and the quality of products is improved as compared with a conventional fluid coking operation.

Another advantage of the process of this invention is that cracked products may be passed directly to a hydrogenation zone without intermediate separation and reheating of the hydrogenation charge.

Another advantage of the process of this invention is that gasoline of improved stability, middle distillates of improved stability and burningcharacteristics and gas oil of improved catalytic cracking characteristics are produced.

The accompanying drawing diagrammatically illustrates the process of this invention. Although the drawing illustrates one arrangement of apparatus in which the process of this invention may be practiced, it is not intended to limit the invention to the particular apparatus or materials described.

Residual oil charge, from an external source not shown, is introduced through line 1 and charge nozzles 2a, 2b and 2c into a bed of lludized hot coke particles in fluid coking reactor 3. Hydrogen-containing gassin line 4 is introduced into reactor 3 to elfect fluidization of the coke particles therein. The residual oil, when contacted with the hot coke particles, is cracked to produce hydrocarbon vapors and coke deposits on the coke particles. Coke is withdrawn from the dense phase of the coke bed in reactor 3 through standpipe 5 and is transported in a current of air or other oxygen-containing gas from line 6 through a transfer line 7 to coke burner 8 wherein the coke is subjected to combustion under high temperature fluidized conditions. Flue gas is removed through line 9 and is rejected to the atmosphere through power recovery facilities not shown. Highly heated coke is withdrawn from the burner l3 through standpipe 10 into the coke bed in reactor 3. Coke product is withdrawn from burner 8 through line 10a and discharged to external use not shown. Coke product may be advantageously used to produce at least a part of the hydrogen consumed in the process by partial oxidation or by the water gas reaction.

Hydrocarbon vapors and hydrogen are withdrawn from reactor 3 through line 11 and passed to hydrogenation reactor 12. Eluent from the cokiug reactor is cooled to hydrogenation temperature by injection of recycle hydrogen from line 13 into line 11. ln the alternative, cooling may be effected at least in part by the injection of an extraneous cooling oil from an external source not shown through line 14 into line 11.

In the ligure, reactor 12 is indicated as an upllow reactor containing a `lixed bed of catalyst. Obviously the hydrogenation reactor may be modified to employ downward llow or to employ a iluid bed of catalyst. Any

j sulfur resistant, catalysthaving hydrogenation activity may be used in the process of this invention. However, catalysts, such as molybdena-alumina, cobalt molybdate, or ynickel-tungsten sulfide, are particularly suitable. Ef,- lluent from the hydrogenation reactor flows through line 15 and is cooled in cooler 16 and discharged into separator 17. Gas from separator 17 is discharged through line 18 to hydrogen purification facilities diagrammatically indicated as 19. Hydrogen purilication facilities 19 may comprise an absorption or liquefaction system which effects separation of methane and heavier components from the hydrogen, and it may comprise reforming facilities effecting conversion of the gaseous hydrocarbons present to hydrogen. A hydrogen-rich stream is discharged through line 20 and recycled to the coking and hydrogenation reactors by compressor 21 and line 22. Makeup hydrogen from an external source, not shown, is supplied through line 23.

Liquid from separator 17 is withdrawn through line 24 and charged to fractionator 25. Overhead product from fractionator 25 comprising gasoline and light hydrocarbons is discharged through line 26 to further processing or storage not shown. Middle distillate product is withdrawn from the fractionator through line 27 and heavy gas oil through line 28 for discharge to external use or storage not shown. The hydrogen content of the hydrogen recycle gas will, of course, depend upon many factors, for example, the conditions employed in the separation of the recycle gas from the liquid products, the conditions employed in hydrogen puriiication, and the severity of the coking and hydrogenation steps to the extent that diluent hydrocarbons are produced by cracking therein. Under some operating conditions, gas separated in separator 17 may contain effective concentrations of hydrogen and may be recycled Without purification by passing gas in line 18 directly to line 20. In another modication, not indicated in the figure, the hydrogen content of the recycle gas may be maintained at effective levels by the well-known expedient of withdrawing a bleed stream of low hydrogen content and replacing the gas so withdrawn with make-up gas of relatively high hydrogen concentration. We prefer that the mol fraction of hydrogen in the coking reactor be at least about 45 percent. This proportion of hydrogen may be obtained by maintaining at least 50 percent hydrogen in the hydrogen recycle gas. However, higher partial pressures increase the eifectiveness of hydrogen and it may be desirable to maintain a higher recycle hydrogen purity up to the maximum level economically practicable which may be about 95 percent hydrogen. When employing hydrogen recycle gas of about 95 percent hydrogen content, the partial pressure of hydrogen in the reaction zone will be about 90 percent of the total pressure.

In an example, 5000 barrels per day of crude residuum are charged to a uid coker operated at 400 p.s.i.g. and 975 F. 2,650,000 standard cubic feet per hour of hydrogen recycle gas are injected into the uid coking reactor for uidization. Vapor effluent from the coker reactor is admixed with an additional 700,000 standard cubic feet per hour of hydrogen to reduce the temperature to 750 F. The combined coolant and coker reactor eiluent is passed through a hydrogenation reactor operated at 385 p.s.i.g., containing cobalt molybdate catalyst. Gasoline, kerosene, middle distillates and heavy gas oil are separated as products. About 180 tons per hour of coke are withdrawn from the fluid coker reactor and dispersed in about 800,000 standard cubic feet per hour of air. The dispersed coke is passed to a coke burner operated at 1565 F. and 400 p.s.i.g.

Obviously many modiiications and variations of the invention as hereinbefore set forth may be made Without departing from the spirit and scope thereof and only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. In a process for the conversion of hydrocarbon oils wherein a hydrocarbon oil is subjected to cracking and coking in a cracking zone at a temperature within the range of from about 900 to about 1100 F. in contact with a uidized bed of coke particles, the improvement which comprises conducting said cracking and coking in the presence of hydrogen at a partial pressure within the range of about 45 to 90 percent of the total pressure, maintaining the pressure in said cracking zone within the range of 200 to 2000 p.s.i.g., withdrawing hydrocarbon vapors and hydrogen from said cracking zone and subjecting said hydrocarbon vapors and hydrogen at a partial pressure within the range of about 45 to 90 percent of the total pressure to reaction in a hydrogenation zone at a temperature in the range of about 600 to about 800 F. in the presence of a hydrogenation catalyst selected from the group consisting of molybdena-alumina, cobalt molybdate, and nickel-tungsten sulfide substantially at the pressure of said cracking zone.

2. The process of claim 1 in which the hydrocarbon vapors and hydrogen withdrawn from said cracking zone are cooled from the temperature of said cracking zone to a temperature within the range of about 600 to about 800 F. at least in part by injection of hydrogen-containing gas.

3. The process of claim 1 in which the hydrocarbon vapors and hydrogen withdrawn from said cracking zone are cooled from the temperature of said cracking zone to a temperature within the range of about 600 to about 800 F. at least in part by injection of an extraneous oil stream.

4. The process of producing a superior gas oil adapted for catalytic cracking that comprises subjecting a residual petroleum stock to a temperature within the range of about 900 to about 1100 F. and at a pressure within the range of about 200 to about 2000 p.s.i.g. in a reaction zone in contact with coke and added hydrogen under uidized conditions at a hydrogen partial pressure within the range of about 45 to 90 percent of the total pressure, withdrawing coke from the reaction zone and subjecting it to combustion in a burning zone, withdrawing coke from said burning zone and passing coke so withdrawn to said reaction zone, withdrawing a stream comprising hydrocarbon vapors and hydrogen from said reaction zone and subjecting said stream to a temperature within the range of about 600 to about 800 F. and at substantially the pressure of said reaction zone in a hydrogenation zone in contact with a hydrogenation catalyst at a hydrogen partial pressure within the range of about 45 to 90 percent of the total pressure and fractionating evolved vapors from said hydrogenation zone to separate gas oil.

5. In the conversion of hydrocarbon oils the process that comprises subjecting hydrocarbon oil to contact with coke and added hydrogen at a partial pressure within the range of about 45 to 90 percent of the total pressure under uidized conditions at a temperature of about 900 to 1100 F., and a pressure of about 200 to 2000 p.s.i.g., withdrawing coke from the reaction zone and subjecting it to combustion in a burning zone, withdrawing coke from said burning zone and passing coke so withdrawn to said reaction zone, withdrawing a stream comprising hydrocarbon vapors and hydrogen from said reaction zone and contacting said stream with a hydrogenation catalyst at a temperature of about 600 to 800 F. at a hydrogen partial pressure within the range of about 45 to 90 percent of the total pressure and at substantially the pressure of said reaction zone.

References Cited in the tile of this patent UNITED STATES PATENTS 2,330,069 Marshall Sept. 21, 1943 2,619,450 Fleming Nov. 25, 1952 2,700,015 Joyce Jan. 18, 1955 2,727,853 Hennig Dec. 20, 1955 2,731,508 Jahnig et al. Ian. 17, 1956 2,738,307 Beckberger Mar. 13, 1956 2,769,754 Sweetser Nov. 6, 1956

Claims (1)

1. IN A PROCESS FOR THE CONVERSION OF HYDROCARBON OILS WHEREIN A HYDROCARBON OIL IS SUBJECTED TO CRACKING AND COKING IN A CRACKING ZONE AT A TEMPERATURE WITHIN THE RANGE OF FROM ABOUT 900 TO ABOUT 1100*F. IN CONTACT WITH A FLUIDIZED BED OF COKE PARTICLES, THE IMPROVEMENT WHICH COMPRISES CONDUCTING SAID CRACKING AND COKING IN THE PRESENCE OF HYDROGEN AT A PARTICL PRESSURE WITHIN THE RANGE OF ABOUT 45 TO 90 PERCENT OF THE TOTAL PRESSURE, MAINTAINING THE PRESSURE IN SAID CRACKING ZONE WITHIN THE RANGE OF 200 TO 2000 P.S.I.G., WITHDRAWING HYDROCARBON VAPORS AND HYDROGEN FROM SAID CRACKING ZONE AND SUBJECTING SAID

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