US2717866A - Hydrocarbon conversion of reduced crudes in the presence of coke particles - Google Patents

Description

Sept. 13, 1955 F. F. DOERING, JR. ET AL 2,717,366

HYDROCARBON CONVERSION OF REDUCED CRUDES IN THE PRESENCE OF COKE PARTICLES Filed June 27, 1951 Glexzis voor'higs, J srzvenoors Qbborneg United States Patent CONVERSION OF REDUCED THE PRESENCE 0F COKE HY DRO CARBON CRUDES 1N PARTICLES Application June 27, 1951, Serial No. 233,896 1 Claim. (Cl. 196-55) The present invention relates to a method of treating hydrocarbon oils. More particularly, the invention pertains to an improved process of converting crude oil into valuable distillate oils and coke while eliminating the production of heavy liquid residues of marginal value. In brief compass, the invention involves the combination of crude distillation with a liquid phase coke-producing thermal treatment of heavy distillation residue and the return of the liquid product of the thermal treating stage to the crude distillation stage, the liquid phase thermal treatment being carried out at conditions adapted to prevent coke deposition on equipment walls.

In refining crude oil it is standard practice first to subject the crude to distillation or topping to produce various distillate fractions, such as naphtha, heating oil and gas oil cuts boiling up to about 800950 F., or, in modern vacuum stills, up to about 10001050 F. Most of these distillate fractions are normally converted into high quality gasoline range motor fuels by such conventional treatments as thermal and/or catalytic reforming and cracking, or similar operations.

The residue from the crude distillation may be processed to yield valuable high molecular weight materials including lubricating oils, waxes, resins, fuel oils, asphalt, etc., depending on the origin and character of the crude. More recently, however, the demand for motor fuels has increased so greatly that it has become extremely difficult to satisfy the motor fuel market by merely processing crude distillates in the manner indicated above. This situation has prompted considerable research and development work directed toward an efficient conversion of crude residua into additional quantities of motor fuels. One of the most common methods used for this purpose in current practice is coking of reduced crude, which is a drastic heat treatment usually carried out at temperatures of, say, about 800l000 F. It results in the direct production of gasoline in addition to gas oil and hydrocarbon gases together with solid coke.

In the past, residues from atmospheric or vacuum crude distilation have been coked in intermittent processes wherein the feed stock is heated to coking temperatures and discharged in liquid phase into a heat insulated soaking drum to remain therein at coking conditions for a sufficient length of time to effect the desired conversion into lower boiling products. In the course of this heat treatment, large quantities of hard adherent coke are formed which is deposited on the walls of the heating coils and soaking drum. At frequent intervals the process must be interrupted to remove coke deposits and thus to prevent plugging and overheating of the equipment.

Various proposals have been made to cope with coke formation in a manner permitting continuous operation of the coking process. Most of these methods involve the addition of a finely divided solid, such as sawdust, coke, sand, or the like, to the oil feed with the result that the coke formed is deposited on the added solids to form coked particles of relatively uniform size and shape 2,717,866 Patented Sept. 13, 1955 which may be more readily removed in continuous operation and which simultaneously serve as a scouring agent to remove loosely adhering coke deposits from the equipment walls. Best results are obtained by diluting the heavy residual oil feed with a light distillate oil and coking the diluted feed in the presence of subdivided solids while maintaining turbulence in the liquid phase undergoing coking, as it is disclosed and claimed in the copending Kimberlin and Gray application Serial No. 226,893 filed May 17, 1951. The present invention involves an improvement useful in operations of this and similar types.

Low temperature liquid phase coking of the character referred to above has for its principal purpose the production of hydrocarbon oils of suitable boiling range and quality to be converted into high octane motor fuels by subsequent catalytic cracking. Prior to the present invention it has been proposed to subject the efliuent of the coking stage to fractionation in a separate distillation stage to recover, in addition to small proportions of gas, gasoline and heating oils, substantial yields of gas oils suitable for catalytic cracking, and coke-carrying bottoms which may be further treated for product coke recovery and seed coke return to the coking stage. In many cases, a simpler and less expensive procedure is desirable for working up the coker efiiuent. Also, the further conversion of liquid phase coking products boiling above the gas oil range into valuable gasoline and additional gas oil is of considerable interest. The present invention provides a procedure suitable for these purposes.

It is, therefore, the principal object of the present invention to provide improved means for the complete conversion of crude oil into distillate oils and coke by distillation of the crude oil and a liquid phase coke-forming thermal treatment of heavy distillation residues. Other and more specific objects and advantages will appear from the following description of the invention wherein reference will be made to the accompanying drawing, the single figure of which is semi-diagrammatical illustration of a system adapted to carry out a preferred embodiment of the invention.

In accordance with the present invention, crude oil is distilled to produce various distillate fractions andra heavy residue which is subjected to a liquid phase cokeforming thermal treatment, such as liquid phase coking, in the presence of subdivided solids, particularly in the presence of product coke, and at conditions adapted to prevent coke deposition on equipment walls. The effluent of the coking stage is separated into coke and liquid free of solids, the liquid being returned to the crude distillation stage to be distilled therein together with the crude oil into distillate oils and heavy residue. A portion of the coke produced is returned to the coking stage as seed coke, the remainder being recovered as product coke, if desired after suitable drying and calcination.

When operating in this manner, crude distillation and liquid phase coking are combined into an integrated process permitting complete conversion of the crude into highly valuable distillate products and coke. The distillate products consist of gas oils suitable as catalytic cracking feed, heating oils, gasoline and gases, all of which are of greatest value. The product coke may be used for electrode manufacture since it is produced under long time, low temperature coking conditions. in addition, the process is fully continuous. Coke deposition on equipment Walls and resulting expensive coke removal steps are avoided, and a separate distillation stage for the coking product is eliminated.

The process of the invention is applicable to all types of crude oils and similar materials including heavy cracked oils, shale oil, coal tar, synthetic oils, etc. The

first stage of the process may be any conventional atmospheric and/ or vacuum crude distillation procedure adapted to produce a heavy hydrocarbonaceous residue in addition to distillate oils of the motor fuel, heating oil and gas oil boiling ranges. In accordance with a preferred embodiment of the invention, combined atmospheric and vacuum crude distillation is employed wherein the crude oil is first distilled at atmospheric pressure to produce various distillate fractions and a reduced or topped crude boiling above about 600 F., preferably above about 800 F. This reduced crude is flashed. into a vacuum still operated at about 13-150 mm. Hg presrure to produce a gas oil boiling between about 600 and 1100 F. and a heavy pitch, the latter forming the feed for the second stage of the process.

The second stage may be any liquid phase heatsoaking treatment adapted to produce substantial proportions of gas oil range and lower boiling hydrocarbon fractions and coke from the heavy feed stock. Conditions suitable for this purpose include temperatures of about 7501000 F., preferably 750-850 F., pressures of about atmospheric to 3000 p. s. i. g. or higher, preferably about 1000-2500 p. s. i. g. and residence times varying from a few seconds to one or two hours,

or more, all properly correlated to obtain the desired degree of thermal cracking.

In accordance with the preferred embodiment of the invention, the second process stage comprises a liquid stage delayed coking step of the type described in the above-mentioned copending Kimberlin et al application. Briefly, this preferred procedure involves dilution of the heavy oil feed with about 20-120 vol. percent of naphtha and coking of the diluted feed at temperatures of about 750-850 F., pressures of about 1000-3000 p. s. i. g., and residence times of about 2-180 minutes (depending on the temperature employed and the degree of conversion desired), in the presence of about 15-100 lbs. of added finely divided coke per bbl. of total oil feed to the coking stage, in a system comprising a heating coil followed by an agitated soaking zone.

The total product of the coking stage in the form of a slurry of coke in oil is passed to a separating stage wherein the coke is separated from the oil. Conventional continuous filtering or settling devices such as a rotary filter, a slurry thickener, or the like may be used for this purpose. Clarified oil is returned to the crude distillation stage to be worked up therein together with the crude oil, heavy coked residue being recycled from the distillation stage to the coking stage together with virgin pitch. A portion of the separated coke may be recovered as product coke. The remainder is returned to the coking stage as seed coke, if necessary after grinding to a suitable size of, say, about 5-250 microns diameter and preferably in the form of a slurry of coke in naphtha serving as diluent in the coking stage.

Having set forth its objects and general nature, the invention will be best understood from the following more detailed description wherein reference will be made to the drawing.

Referring now to the drawing, the system illustrated therein essentially comprises an atmospheric crude fractionation still 9, a vacuum flash tower 23, a liquid phase coking stage 37, 41 and a separating stage 45, 50. The functions and coaction of these elements will be explained hereinafter using the conversion of a petroleum crude as an example. It should be understood, however, that the system may be applied to the conversion of other heavy hydrocarbonaceous materials in a substantially analogous manner.

In operation, a crude oil, such as a typical West Texas crude, is supplied through line 1 and mixed therein with about 8-30 vol. percent on fresh crude of liquid coking product supplied from line 3 as will appear more clearly hereinafter. The mixed feed is passed to coil furnace 5, heated therein to, say, about 500800 F. and then supplied through line 7 to crude still 9 operated at substantially atmospheric pressure. The feed may be fractionated in still 9 into several fractions comprising an overhead of hydrocarbon gases amounting to about 1-2 wt. percent (based on crude) withdrawn through line 10; a light naphtha having an end boiling point of about 250-300 F. (about 17-27 vol. percent on crude) withdrawn through line 1.11; a heavy naphtha having a boiling range of about 250 or 300 to 430 F. (11-32 vol. percent on crude) withdrawn through line 13; a light gas oil or heating oil boiling between about 430 and 620 F. (about 20-32 vol. percent on crude) recovered through line 15; a heavy gas oil of about 620-800 F. boiling range (12 to 22 vol. percent on crude) withdrawn via line 17; and a reduced crude containing all liquid products boiling above about 800 F. (about 23-41 vol. percent on crude) withdrawn through line 19.

The reduced crude in line 19 may be passed to a conventional vacuum flash tower 23 preferably after heating in coil furnace 21 to about 600-800 F. Tower 23 may be operated under a vacuum of about 8-150 mm. Hg so as to operate the reduced crude into a vacuum gas oil of about 800-1100 F. boiling range (about 14-25 vol. percent on crude) recovered through line 25 and vacuum pitch boiling above about 1100 F. (about 9-17 vol. percent on crude) withdrawn through line 27.

The pitch in line 27 which may have a gravity of about 5-17 API and a Conradson carbon of about 10-25%, is supplied by pump 29 to line 31 at a pressure of about 1000-3000 p. s. i. g. Fresh seed coke having a particle size of about 5-250 microns may be fed to line 31 from lock hopper 33 or the like to start up the operation, and at certain intervals, as required. Aeration taps t may be provided to maintain the coke in a free-flowing condition. However, in normal operation seed coke is preferably supplied from line 35 as a slurry of product coke in heavy product naphtha as will appear more clearly hereinafter. After the addition of this coke slurry the contents of line 31 may consist of about 45-85 vol. percent of pitch, 15-55 vol. percent of heavy naphtha and about 15-100 lbs. of seed coke of 5-250 microns particle size per bbl. of liquid.

This slurry is passed through fired coil 37 to be heated therein to about 780-820 F. at a pressure of, say, about 2000 p. s. i. g. Coke deposition on the coil walls is avoided by maintaining high turbulence in coil 37. For this purpose, coil 37 may be designed for a relatively high liquid flow velocity of about 4-10 ft. per second. The effluent of coil 37 is passed through line 39 to soaker 41 wherein it is soaked substantially at the temperature and pressure of coil 37 and in a highly turbulent state for a time sufficient to convert about 50-90% of the pitch into distillate oils and coke. Any suitable means such as an agitator 42 may be used to maintain turbulence in soaker 41. Total residence times of the feed in coil 37 and soaker 41 may be about 1-3 hours depending on the temperature employed and the amount of conversion desired. Residence time should be the longer the lower the temperature and the higher the desired conversion, within the ranges specified.

The total coking product is passed from soaker 41 through line 43 provided with pressure reducing valve 44, to a liquid-vapor separation stage such as flash drum 45. Pressure is lowered by valve 44 from the coking pressure to a lower range of from about 50-1000 p. s. i. g. to permit vaporization of the gaseous and some of the lighter liquid coking products in flash drum 45. This vaporization causes cooling of the liquid product to a temperature of about 600-750 F., which is below coking temperature and thus prevents further coking and fouling of the flash drum with coke where no agitation is provided. Gaseous and light liquid coking products are removed from flash drum 45 by line 46 provided with pressure release valve 47, and return to still 9. The liquid coking products are withdrawn from flash drum 45 by line 48 provided with pressure release valve 49 to a liquid-solid separation stage such as a conventional rotary filter 50. The coking products in line 48 may be further cooled to about 200450 F. by introduction of cooled coke-free oil via line 51. For this purpose, a part of the coke-free filtrate may be withdrawn from line 52 via line 51, passed through cooler 53, and reintroduced into line 48 to provide the desired cooling for the coked oil feed to filter 50.

Liquid filtrate and product vapors are Withdrawn from the interior of filter 50 through line 52 into butter tank 54 under the influence of vacuum pump 55. Liquid oil is withdrawn from tank 54 and returned via lines 57 and 3 to line 1 and coil furnace in the amounts described above. Vapors removed from tank 54 via line 59 by means of pump 55 may be either recovered through line 61 or returned to still 9 via line 63 for further fractionation together with the liquid coking product and virgin oils.

Of the overall distillate oils the fraction recovered via lines and 11 may be treated by stabilization, absorption, etc. to recover light naphtha and gases which may be further converted into valuable products by alkylation, polymerization, isomerization, etc. Heavy naphtha recovered through line 13 may be subjected to reforming, hydroforming, aromatization, etc. to produce high octane gasoline. The heating oil fraction recovered through line may be finished in a conventional manner and passed to storage. The heavy gas oils removed via lines 17 and 25 represent suitable feed stocks for the production of high octane gasoline by catalytic cracking.

Returning now to rotary filter 50, a filter cake of wet coke removed from the surface of filter 50 by a suitable scraper 64 may be passed through line 65 to a drying and/or calcining device, such as a retort or rotary kiln 67 operated at a temperature of about 800-1200 F. Vaporized oil may be recovered from kiln 67 via line 69 and mixed with the filtrate from filter 50 in line 52. The dry coke is withdrawn through line 71. Product coke may be recovered through line 73 in amounts of about 1020 wt. percent of pitch fed to line 31. The remainder of the dry coke is passed to line 35 in which it is slurried with heavy product naphtha branched off line 13 via line '75 to produce the slurry of seed coke in naphtha diluent to be supplied to line 31 as described above.

The system described with reference to the drawing permits of various modifications. If desired, all or any portion of the Wet coke in line 65 may be by-passcd through line '77 around kiln 67 to line 71 to be returned directly to line 35, and/ or to line 73 to be recovered. Any desired portion of the seed coke in line 35 may be passed continuously or at suitable intervals through a conventional disintegrating device, such as a ball or rod mill 79, wherein the coke may be ground to a suitable particle size of less than 250 microns, if required. In place of rotary filter 50 conventional slurry settlers may be used, for example a slurry thickener of the Door Thickener type substantially as described in such texts as Riegel, Industrial Chemistry, 1937, 3rd edition, page 708. Other subdivided solids, such as kieselguhr, clay, coal ashes, etc., may be used in place of coke to start up the process. If desired, the vacuum distillation tower may be omitted and the atmospheric residuum in line 19 introduced into line 3.1 for coking. Other modifications Within the spirit of the invention may appear to those skilled in the art.

The invention will be further illustrated by the following specific example.

EXAMPLE A mixed crude oil, from fields of Louisiana, Mississippi and West Texas, having a gravity of about 33 API and a crude assay by distillation as shown in column I of Table I below is mixed with about 25 vol. percent of coked residuum and recycled naphtha.

Table I I II III Crude Distilla- Products, Percentages 0n Assay, tion of Net Prod- Crude Distilla- Crude nets of tion of Pius Combined Crude Coker Process Only Products Gas, Wt. Percent 0. 2 1. 5 1. 5 Light Naphtha, 300 F. E. P.,

V 01. Percent 16.9 17.6 17. 6 Heavy Naphtha, 300/430 F.,

V Percent; 13.7 28.5 14.5 Heating Oil, 430/620 F., Vol.

Percent 25. 4 28. 5 28. 5 Atmospheric Gas Oil, 620l800 F., V01. Percent 16. 8 19.1 19. 1 Vacuum Gas Oil, Vol. Percent. 14. 7 17.3 17.3 Vacuum Bottoms, Vol. Percen 12.2 13.2 0.0 Coke, Wt. Percent 0. 0 0.0 2. 6

The mixture is subjected to atmospheric and vacuum distillation to give various fractions in the amounts shown in column II of Table I, all percentage figures being based on the original crude oil feed. Of the 28.5 volume percent of heavy naphtha shown in column II, 14% represents a recycle stream and 14.5% represents net production; also the 13.2% of vacuum bottoms are consumed in the process and do not represent a net product. The 13.2% vacuum bottoms shown in column II are blended with the 14.0% of recycle heavy naphtha and to each barrel of this blend is added about 55 lbs. of 200 mesh coke from a previous operation. The added coke amounts to about 4.6 wt. percent on crude fed. This mixture is heated with agitation to about 800 F. under a pressure of about 2100 p. s. i. g., the total time of residence above about 775 F. being about minutes. The coked product is cooled and filtered and the coke removed from the filter is heated in a retort to about 1000 F. to distill ofi adhering oil which is added to the filtrate. The dry coke removed from the retort amounts to about 86 lbs. including the 55 lbs. of seed coke added and about 31 lbs. of product coke per barrel of feed to the coking zone. This amounts to about 2.6 wt. percent net production of coke based on crude oil feed as shown in column III of Table I. The combined coker product filtrate and distillate from the retort are mixed with more crude oil, in the proportions indicated above, for distillation and a repetition of the process as just described.

The above description and exemplary operations have served to illustrate specific embodiments of the invention. It will be understood that the invention embraces such other variations and modifications as come Within the spirit and scope thereof.

What is claimed is:

The continuous process of converting hydrocarbon mixture containing distillable and non-distillable hydrocarbonaceous constituents into distillate oils and coke, which comprises subjecting said mixtures to distillation in an atmospheric distillation zone followed by further distillation in a vacuum zone to produce naphtha, gas oils and a heavy hydrocarbonaceous distillation residue, subjecting said residue to a liquid phase thermal treatment in the presence of subdivided seed coke having a particle size under 250 microns and a naphtha diluent boiling in the range of 250-450" P., at least a portion of said naphtha diluent being obtained from the atmospheric distillation step, said thermal treatment being carried out in a treating zone composed of a narrowly confined elongated path followed by an expanded soaking zone, maintaining sufficient turbulence during said thermal treatment to prevent coke deposition on the confines of said treating zone and maintaining during said thermal treatment conditions of temperature between 750 and 850 F., pressure between 1000 and 3000 p. s. i. g. and residence time of 2 7 to 180 minutes so as to obtain formation of coke and sub- References Cited in'the file of this patent stantialproportions of distillate oils, Withdrawing from UNITED STATES PATENTS said treating zone a slurry of coke in liquid product, flashing said slurry into a flashing zone to produce product 1243' 221/75 Potts y 30, 1946 vapors and a cooled slurry, returning said product vapors 5 2,128,220 Cooke Allg- 1938 to said atmospheric distillation zone, separating coke a d 2,236,447 Thomas June 16, 1942 liquid from said cooled slurry, returning at'least a o ti 2,599,112 Houdry at 26, 1943 of said separated liquid to said atmospheric distillation 2,316,931 Brandt p 19 3 2,336,126 Read Dec. 7, 1943 zone to be subjected therein to said distillation, reslurrying at least a portion of said separated coke after 10 2 RPllman 14, 1943 it has been reduced to a particle size of ie than 259 -;3?2 Pier et a1 Jan. 19 microns in a portion of said naphtha fraction boiling 2,34%94 Myers 1744 within the range of 250 to 450 F. and feeding said re- 2'358573 Hemmmger Sept 1944 slurried coke and naphtha to said distillation residue to 2338380 Barron 91 1946 supply at least a portion of said naphtha diluent and seed 15 214 Alveson June 221 1948 com 2,453,641 Reed Nov. 9, 1948

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