US2339932A - Chemical process - Google Patents

Description

Jan. 25, 1944. KUHL 2,339,932

CHEMICAL PROCESS Filed April 10, 1941 VAPOR- LIIV C'OK/IVC .D HUM conlvzyon STEAM INA ET F221) INLET Patented Jan. 25, 1944 CHEMICAL PROCESS Paul E. Kohl, Madison, N. J., assignor to Stand. and Oil Development Company, a corporation of Delaware Application April 10, 1941, Serial No. 387,857

5 Claims. (01. 202-23) The present invention relates to improvements in the art of treating hydrocarbons, and more particularly it relates to the thermal treatment of relatively heavy petroleum oil stocks such as topped crudes, for the purpose of converting them, among other things, into substantial quantities of hydrocarbon oils boiling within the gas oil and gasoline range.

Prior to the present invention, a great deal of research had been directed by the petroleum oil industry toward treating reduced or topped crudes thermally, for the purpose of increasing the amount of gas oil which may be recovered from a given quantity of original crude. There are two general methods of accomplishing this result, namely, the viscosity reducing of the topped or reduced crude, and the coking of the said reduced crude. Both of these processes lead, as indicated, to increased quantities of gas oil which maybe used as a feed stock for a thermal or catalytic cracking operation to produce cracked gasoline, or the gas oil may be treated to produce a domestic heating oil.

Most of the coking and viscosity reducing operations hitherto developed have been of the intermittent type, that is to say, the operation may be carried out for two or three days, whereupon the same must be discontinued to remove the coke which deposits in the coking drum. The decoking of a drum is an expensive and timeconsuming operation and any process which would procur the coke in such a form that it could be continuously removed from the drum without substantial .deposit therein would constitute an improvement in the art, both in the way of labor saving and equipment reduction. The broad object of the present invention is to operate the coking of heavy petroleum oils continuously.

Another aspect .of the present invention involves preheating a heavy oil to coking temperatures, discharging the preheated oil into a drum or case where it contacts granular coke which is present in said drum, and continuously withdrawing the added coke, together with the formed coke, from the coking zone thus obviating the necessity of frequent shutdowns to remove coke which has deposited within the drum. Another object of my invention is to maintain in the coking drum a substantially constant amount of added coke, and this is accomplished by recycling to the coking drum suflicient coke for this purpose.

Other and further objects of the present invention will be apparent from the following description and claims, reference being had to the accompanying drawing. 4

The accompanying drawing shows diagrammatically and in partial section an apparatus in which the present invention may be carried into efiect.

Referring in detail to the drawing, a topped crude, such as an East Texas reduced crude having an A. P. I. gravity of 18, is introduced into the system through line I carrying pump 3 and is thereafter discharged into a heating coil 5 where the oil is heated to a temperature within the range of from 850 F. to 1100 F. The crude oil should be heated as rapidly as possible in the heating coil 5 in order to prevent any appreciable amount of coke formation. If desired, 10% to 20% (mol) of steam may be discharged into line I through line 6, the steam'operating to prevent excessive amounts of coke formation in the heating coil. The preheated crude oil is withdrawn from heating coil 5 through line It and is then discharged into the bottom of a coking drum l2.

In carrying out my present operation, I introduce into the drum, together with the oil, a quantity of granular petroleum coke. having an average particle size below 20 mesh, preferably, although somewhat larger particle size coke may be used. This coke is discharged from-a hopper 15, in communication with a screw conveyor I6, onto a screen or perforated member l'l. Coking drum I2 which is shown in vertical section, carries a partition wall M for the purpose which will bl, presently explained. Partition wall I 4 is disposed, as shown, at about the geometrical center of drum l2, and preferably it is braced by rods l9 and 20. The oil discharged through line l0 into the drum I 2 passes upwardly, and the screen I! serves to distribute the oil uniformly into the mass of coke discharged on screen ll. of 800 F. to 1200 F. is also discharged into the lowermost portion of drum l2 through line IS. The coke which is discharged into the drum I2 is preferably at an elevated temperature, say at a temperature of from 900 F. to 1200" F., the said coke being obtained from the process preferably and being dried and hardened before delivery to hopper l5, as will more fully appear hereinafter. The process is preferably so manipulated that the sensible heat of the hot coke recovered from the process is used inthe coking ofthe oil. Since the coking operation is an endothermic reaction, the hot coke will serve to supply at least a portion of the heat superheated steam, say at a temperature is introduced into the drum through line-l is forced upwardly into the mass of the coke. The screen or perforated member I! serves, as previously stated, to eilect a substantially uniform distribution of the oil through the coke. The steam also passes upwardly with the coke and oil and serves mainly to assist in the volatilization of vaporizable constituents of the charging oil.

The reaction vessel is constructed of such proportions that the velocity of rising steam and oil vapors in section A is such as to maintain the coke in a semi-suspended fluid turbulent mass. This insures that unvaporized oil will be distributed uniformly andin small masses over the entire coke mass.

It will be observed that the coke and oil discharged into the coking drum l2 pass upwardly through the said drum and to the left of partition wall H. When the coke has attained the elevation C it, together with the coke formed as a result of the coking operation, spills over into section B at the right of partition wall ll. The coke gravitates through section B and is withdrawn through outlet conduit 22, which preferably carries a star feeder 24. Preferably superheated steam at a temperature of from 800 F. to 1000" F. or 1100 F. is discharged into section B through line 26, this steam serving to dry and harden the coke and to assist in purging it of volatilizable hydrocarbons. The coke withdrawn through conduit 22 which, as indicated, consists of the coke added to the drum, as well as the coke formed therein, may be dried, hardened and treated with air to partially oxidize or burn the same, thus producing a friable mass which is non-adherent. If, as is indicated, the lumps of coke are too large, they may be ground to the desired size before recycling to the coking drum, The coke withdrawn from line 22 may be delivered in part to a grinder 28 where it is ground to the desired size and then conveyed by suitable means, such as a, Redler conveyor, 32 to hopper i! for further use in the process. The remainder of the coke may be withdrawn from the system through line 3| and delivered to storage.

The hydrocarbon vapors and steam are withdrawn from coking drum l2 overhead through line 30, and these gases may be delivered to condensing and fractionating equipment to recover gasoline, gas oil, normally gaseous hydrocarbons, and the like, in apparatus which is not shown.

As previously indicated, the amount of coke maintained in drum I2 is preferably substantially constant, and this is accomplished by regulating the amount of coke fed from hopper l5 into the drum; that is to say, the discharge of coke into the drum by means of conveyor l8 and its withdrawal through star feeder 24 may be regulated so as to maintain the coke in the drum at some predetermined quantity which, in must instances, is a desideratum.

It is pointed out that many modifications of my invention may be made by those familiar with this art without departing from the spirit thereof; for example, instead of introducing the oil into the bottom of the drum as shown in the drawing, the said oil may be discharged into the top of the, drum. The continuous motion 'of the coke in section A tends to prevent the accumulation oftar' or coke on the walls of the drum since the motion has a scouring 5 action on the inner walls of the drum.

Attention is directed to the fact that air may be introduced through line 35 into section B of the drum for the purpose of causing partial combustion of the coke. Obviously the amount of air thus introduced should be limited. The combustion of the coke, of course, not only dries and hardens the latter but serves to further heat the coke so that it may be recycled to hopper at a temperature up to say 1200 F. or 5 higher. Coke at this temperature discharged into the drum will, as stated, serve to supply a portion of the heat necessary in the coking reaction.

In the foregoing description, a screw conveyor was included as the means for discharging the coke into the drum. It is pointed out that instead of using a screw conveyor for feeding the coke to the drum, other feeding means may be employed. For example, the coke may be forced 5 into the drum by means of a ram motivated hydraulically or otherwise. Furthermore, the coke may be dispersed in superheated steam, CO2, flue gas, and the like and discharged into the bottom of the drum, whereupon the preheated oil would be sprayed on the coke and thereafter the operation carried out as hereinbefore described.

By way of summation, the present invention relates primarily to a coking operation which may be operated continuously and is charac- 5 teriz'ed by the feature that the oil undergoing coking is in contact with a moving mass of added coke in granular form, the coke moving upward through the coking zone and serving to provide the oil undergoing coking with a large surface 40 and, further, to absorb heavy adherent oils resulting from the preliminary phases of the coking operation, thus preventing their adherence to the walls of the coking drum until such time as said adherent material has been sufliciently dried and hardened and therefore rendered substantially non-adhesive.

The precise details particularly as regards the specific gravity of the oil charged to the coking zone, the temperatures and other details set forth hereinbefore are purely for purposes of illustrating my invention.

The temperature and pressure conditions prevailing in section A of drum I2 may be those pre viously employed by others in coking heavy hydrocarbon oils. Also the residence time of the oil in section A is conventional and per se does not form the gist .of my present invention and those familiar with the art will appreciate that depending on the nature of the stock the resident time will vary. Ordinarily, the cold oil may be passed through coil 5 at a rate of 4 to 6 volumes of oil per volume of coil per hour and the preheated oil remains in drum l2 for from about 20 to. 100 seconds with about 50 seconds resident time in section A of drum l 2 giving good results.

What I claim is:

1. The method of coking a heavy residual hydrocarbon oil which comprises providing two contiguous vertical zones, discharging a granular petroleum coke into one of said zones at near the lower portion thereof, forcing the coke upwardly through said zone, discharging superheated steam in the lowermost portion 'of the said zone to maintain the coke in a semi-suspended fluid turbulent mass as it passes upwardly through the said zone, discharging a preheated heavy residual hydrocarbon oil upwardly in the lower portion of said zone onto the coke moving upwardly I in said zone, permitting contact between thepreheated oil and the coke for a suflicient period of time while temperatures are from about 850 F.

superheated steam is discharged into the flrstnamed zone.

a. The process set forth in claim 1 in which the coke gravitating through the second-named zone is subjected to a partial combustion tor the purpose oi drying and hardening the coke and raising its temperature where the coke is maintained in a fluid turbulent state by aeriiormed fluids and thereafter returning the hot coke to the firstnamed zone where itserves to supplyatleaata portion or the heat necessary in the coking operation.

4. The method of coking heavy residual hydrocarbon oils which comprises lowinga mass of petroleum coke upwardly through a coking zone where the coke is maintained in a fluidized turbulent mass of gasesforced therethrough, contacting a heavy preheated hydrocarbon oil with the coke moving upwardly through the coking zone, the preheated oil being introduced into the mass of coke at near the bottom thereof, pennitting contact between coke-and oil for a suiiicient period of time to efiect the desired conversion, forcing the coke from the coking zone into a contiguous zone at a point elevated from the bottom of said zone, gravitating the coke through 16 the second-named zone, subjecting the coke in the second-named zone to the influence of superheated steam for the purpose of removing volatilizable hydrocarbons therefrom, recovering added coke and coke formed in the process from the 20 bottom of the second zone and recovering hydrocarbon vapors produced in the process from the coking zone.

5. The process set forth in claim t in which the coke recovered from the second zone is rellturncdsubstantiallytotheflrstzone.

PAULE. KUHL.

Images