US2844524A - Integration of coker with refinery - Google Patents

Description

July 22, 1958 H. ERNST, JR

INTEGRATION OF COKER WITHREFINERY Filed Dec. 18, 1953 0 Lu Lu m m "5 6 E' g g 3 0 1 r i r I I t 2 L" pnooucrs FRACTIONATION O E m i v FLUID ,7, 2 o OOKING l k T A-sFER LINE BURNER 2 VACUUM DISTILLATION 0- I I N n v a In] 4- ATMOSPHERIC FRACTIONATION Henry Ernst, Jr. Inventor United States Patent 2,844,524 INTEGRATION OF COKER WITH'REFINERY Henry Ernst, Jr., Fanwood, N. J., assignor to Esso Research and Engineering Company, a corporation of Delaware Application December 18, 1953, Serial No. 399,036

2 Claims. (Cl. 196--55) This invention relates to the coking of heavy petroleum residua in contact with hot fluidized solids and to a process particularly adapted for such coking.

It recently has been proposed to coke heavy residuum oils by injecting them into a coking vessel containing a fluidized bed of hot finely divided coke and to supply the necessary heat for the coking by circulating a stream of the coke through an external combustion chamber and back to the coking vessel. This offers a great advantage over the delayed coking process in that the operation is continuous. This method of fluidized coking is more fully described in co-pending application, Fluid Coking of Heavy Hydrocarbons and Apparatus Therefor, Serial No. 375,088, filed August 19, 1953, by Pfeifler et al. The development of the fluid coking process, however, has revealed many mechanical, operating and processing difliculties.

Because the gas oil product from fluid coking is usually designated for further processing by catalytic cracking, the gas oil must be relatively free of catalystpoisoning impurities. The fluid coking operation, however, tends to volatilize ash materials, like the compounds of iron, nickel, chromium, and vanadium. Further, some heavy condensed ring aromatics of poor catalytic cracking quality are also passed over with the coker product. For these reasons, it is the prudent practice to fractionate the coker product to remove from the catalytic-feed stock heavy ends which contain these materials. Generally these heavy ends are recycled to the coker in order that all of the available hydrocarbon material in the ends can be converted to lighter, and hence more valuable, products. Because'a fractionation at high temperatures is diflicult from an operability standpoint and is also wasteful of heat, it is normally not 100 percent selective and because a relatively low boiling gas oil cut is made to avoid inclusion of 'ring aromatics and ash, the heavy ends from the separation contain large quantities of desirable' light fractions condensed ,alongwith the ends. Recycling these ends directlyto a cokenresults in: V 1

(1) The necessity for a large coker (approximately 15 to 40% larger) to accommodate the recycled gas oil vapors.

(2) Loss of the lighter gas oil to coke and gas because of repetitious pyrolysis.

(3) Loss of cracking quality by the thermal cracking of the gas oil.

To circumvent these serious economic debits inherent in the above method of recycle operation, the process 7 of this invention was conceived. In normal operation,

the fluid coker receives topped crude that has been processed by atmospheric and vacuum distillation to remove naphthas and gas oils. According to this invention, by recycling the heavy ends from fluid coking operation to the vacuum distillation zone, the gas oils contained in the ends can be substantially removed and sent to catalytic Patented July 22, 1958 processing and in this manner the economic drawbacks to the conventional mode of operation will be avoided. This new process is illustrated in the attached drawing which forms a part of this specification.

Accordingly, it is an object of this invention to provide an improved method for converting topped crude into high yields of napthas and gas oils suitable for further catalyic cracking. Another object is to devise a process for coking residuum oils in such a manner as to reduce the amount of gas oils recycled to the coker. A more specific object of this invention is to increase the efliciency and practicability of the fluid coking process by adroit treatment of fractionated recycled heavy ends from the coker eifluent. pear more clearly as this description proceeds.

Succinctly stated, the inventions objects are attained by processing a crude in the following manner: The crude is first subjected to atmospheric and then to vacuum distillation to secure the virgin naphthas and gas oils for other operations. The reduced crude is then sprayed into a conventional fluid coker. The volatiles issuing from the coker are fractionated to obtain gas oils for catalytic cracking and heavy impurity containing ends. The heavy ends are recycled, not to the coker, but to the vacuumv distillation zone where gasoils are removed from the ends before the ends are again subjected to pyrolysis.

Referring now to the attached drawing, the crude enters the process by a line 1 after being suitably heated to about'600" to 800 F. It is first fractionated in a conventional atmospheric fractionator 10 and separated into light gases, removed by line 2, a naphtha fraction, removed by line 3, a gas oil fraction, removed by line 4, and the topped crude bottoms, removed by line 21. The light gases, naphtha and gas oil are sent to other conventional refining steps not shown. The topped crude, via lines 21 and 5, is transferred to a vacuum distillation chamber 20 j where further amounts of gas oil are separated and removed from the topped crude and passed by line 6 to line 4. The vacuum crude produced is then transferred by line 7 to the fluid coking vessel 30 and sprayed into the dense fluidized bed of coke particles having a particle size of to 500 microns. It is to be understood that the fluidized bed can consist of other finely divided solids such as sand. However, the coking vessel per se is not a part of this invention. As shown, the coker consists of a coking vessel 30 and a solids heating or burning system shown herein as a transfer line burner 70. A conventional fluid bed burner may be substituted for the transfer line burner, if desired, both types being well known. Either is entirely satisfactory for the present application.

The fluid coker is operated at about atmospheric pressure or a, little above, e. g., 0 to '50 p. s. i. g. The vacuum bottoms from 'thecrudeenters the coker 'through'a plurality of nozzles and contacts the hot fluidized coke particles. Coking occurs and the hydrocarbon mixture deposits a carbon residue on the fluidized coke particles of the bed and yields a substantial proportion of lighter hydrocarbons. The gaseous coker products pass upward through the coker and through a gas-solids separator or cyclone 40 where entrained fines are removed and returned to the fluidized bed by line 13. The hot products are then transferred to a fractionation zone 60 through line 14.

Coke is removed from the coker by line 8 in order that the pseudo-liquid level of the particles can be maintained at the desired height and in order to remove the coke particles that have increased beyond a fluidizable size because of the carbon deposition. The coke particles flow down standpipe 8 by gravity and are engaged by a stream of air from line 9, the air being supplied by a source not shown, and are pneumatically conveyed up- Further objects and advantages will apward in the transfer line burner 70. The conveying air supports a partial combustion of the entrained coke particles in the transfer line burner. This burning adds heat to the remaining or unburned coke particles which are thereafter recycled. The coke particles, after their partial combustion, are separated from the flue gas formed during the combustion, in a gas-solids separator 50. The separated solids pass downward to the coker by line 11. The flue gas is removed by line 15 from "the separator and may be utilized for its heat value elsewhere. The coke returned in line 11 to the coker may be in excess of the amount needed and a drawoff can be made of this excess by line 12.

Standard operating conditions are contemplated for the coker in order that large proportions of gas oils may be produced to serve as catalytic cracking stock. Thus the fluidized bed density will be about 20 to 60 lbs. per cu. ft., the superficial fluidizing velocity about 0.5 to 7 ft./sec., the coking temperature about 900 to 1050 F., the hydrocarbon vapor residence time about to 30 seconds, and the operating pressure about or slightly above atmospheric. A fluidizing gas such as steam is added through one or more inlet lines, one of which is shown at 31. The coker efiiuent is separated into the desired products by a fractionator 60. As illustrated, only three fractions are separated but a more selective fractionation can be made. Uncondensed gases are removed from the fractionator by line 16 and passed to line 2 where they are removed from the process. The desired gas oil in cluding some gasoline fractions is removed by line 17 and blended with the gas oil from the initial distillation stage in line 4. The mixture of gas oils then can be sent to catalytic cracking, storage or other operations as desired. Obviously, the coker gas oil can be kept separate from the virgin gas oil and separately treated. The bottoms fraction is removed from the fractionator by line 18 and is passed to line 5 where it enters the vacuum distillation zone as has been before indicated. Although it is not contemplated, a portion of the recycled bottoms can be passed to the coker via lines 19 and 7. This will depend upon specific operating conditions and economics.

For an Elk Basin crude, the following material balance could be expected:

Crude feed 30,000 bbl./day. Air 8,830 s. c. f. 111. Out:

Flue gas 9,600 s. c. 'f. m. Uncondensed gases 2.5 mm. s. c. f./

day.

Virgin naphtha, 375 F. B. Pt 7,000 bbl./ day. Virgin gas oil, 375 to 1,l00 F. B. Pt. (including some 1000 1100 coker material) 19,000 bbL/day. Coker gas oil, 250 to 1,000 F.

B. Pt 2,320 bbL/day.

Coke 162 tons/day.

4 Internal:

Topped crude, boiling above 860' F. (to vac. distillation) 9,000 bbL/day. Recycled bottoms, boiling above 1000 F 1,370 bbL/day. Vacuum crude, boiling above 1100 F. (to coker) 3,800 bbl./day Vacuum crude, boiling above (net virgin).

1100 F. (including recycle bottoms from coker gas oil) 4,300 to 5,000

bbl./day.

While a preferred embodiment of this coking operation has been described and illustrated in simplified form, it will be understood that a complete commercial unit will include a considerable amount of adjunctive equipment such as pumps, heat exchangers, valves, and instruments which are not shown herein. Also, it is to be understood that the invention is not to be limited by this description, butonly by the following claims.

What is claimed is:

l. A process of coking residual oils which comprises admixing a topped crude from an atmospheric distillation Zone with a recycled impurity containing bottoms fraction, separating the resulting mixture in a vacuum distillation zone into a light product fraction substantially free from impurities and a heavy tar boiling above 1050 F. containing the bulk of said impurities, subjecting said heavy tar to conditions of coking of a temperature in the range of 900 to 1050 F. and a vapor residence time of 5 to 30 seconds in a coking zone containing a bed of relatively dense fluidized coke particles to produce hydrocarbon vapors and carbonaceous residue which is deposited on said coke, separating from said hydrocarbon vapors in a fractionation zone a relatively heavy impurity containing bottoms fraction boiling above 1000' F. and recycling and blending this fraction as aforesaid.

2. A process of coking residual oils which comprises admixing a topped crude feed from an atmospheric distillation zone with a recycled impurity containing bottoms fraction, separating the resulting mixture in a vacuum distillation zone into a light product fraction substantially free from impurities and a heavy tar containing the bulk of said impurities, subjecting said heavy tar to conditions of coking of a temperature in the range of above 900 to 1050 F. and a vapor residence time of about 5 to 30 seconds in a coking zone containing a bed of relatively dense fluidized coke particles to produce hydrocarbon vapors and carbonaceous residue which is deposited on said coke, separating from said hydrocarbon vapors in a fractionation zone a relatively heavy impurity containing bottoms fraction boiling above about 1000 F. and recycling and blending this fraction as aforesaid.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. 2. A PROCESS OF COKING RESIDUAL OILS WHICH COMPRISES ADMIXING A TOPPED CRUDE FEED FROM AN ATMOSPHERIC DISTILLATION ZONE WITH A RECYCLED IMPURITY CONTAINING BOTTOMS FRACTION, SEPARATING THE RESULTNG MIXTURE IN A VACUUM DISTILLATION ZONE INTO A LIGHT PRODUCT FRACTION SUBSTANTIALLY FREE FROM IMPURITIES, SUBJECTING SAID HEAVY TAR TO CONDITIONS OF SAID IMPURITIES, SUBJECTING SAID HEAVY TAR TO CONDITIONS OF COKING OF A TEMPERATURE IN THE RANGE OF ABOVE 900* TO 1050*F. AND A VAPOR NRESIDENCE TIME OF ABOUT 5 TO 30 SECONDS IN A COKING ZONE CONTAINING A BED OF RELATIVELY DENSE FLUIDIZED COKE PARTICLES TO PRODUCE HYDROCARBON VAPORS AND CARBONACEOUS RESIDUE WHICH IS DEPOSITED ON SAID COKE, SEPARATING FROM SAID HYDROCARBON VAPORS IN A FRACTIONATION ZONE A RELATIVELY HEAVY IMPURITY CONTAINING BOTTOMS FRACTION BOILING ABOVE ABOUT 1000*F. AND RECYCLING AND BLENDING THIS FRACTION AS AFORESAID.

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