US3673080A

US3673080A - Manufacture of petroleum coke

Info

Publication number: US3673080A
Application number: US831548A
Authority: US
Inventors: Warren G Schlinger; Harold C Kaufman
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1969-06-09
Filing date: 1969-06-09
Publication date: 1972-06-27
Anticipated expiration: 1989-06-27

Abstract

Clusters of petroleum coke pellets are made by the steps of dispersing particulate carbon seed particles in a high boiling petroleum oil, heating the seeded oil in a coking heater under conditions of controlled cracking, and introducing the effluent from the heater into a coke drum where the seed particles serve as nucleating agents in the formation of clusters of petroleum coke pellets.

Description

United States Patent Schlinger et al.

[ June 27, 1972 MANUFACTURE OF PETROLEUM COKE Inventors: Warren G. Schlinger, Pasadena, Calif.;

Harold C. Kaufman, Houston, Tex.

Assignee: Texaco Inc., New York, NY.

Filed: June 9, 1969 Appl. No.: 831,548

US. Cl ..208/l31, 44/10, 44/20,

23/2092 Int. Cl ..C10g 9/14 Field of Search ..208/46, 50, 106, 131;

References Cited UNITED STATES PATENTS 9/1944 Hemminger Bogart et al. .::.20s/s0 2,717,865 Kimberlin et al. ..208/1 31 2,775,549 12/1956 Shea ..208/l31 X 3,022,246 2/1962 Moser.. ..208/127 3,116,231 12/1963 Adee ....208/46 3,338,817 8/1967 Zrinscak et al. ....208/46 3,460,907 8/1969 Winsett.... ....23/209.1 3,524,806 8/1970 Case ..208/46 Primary Examiner-Edward J. Meros Attorney-K. E. Kavanagh, Thomas H. \Vhaley and Carl G. Ries [5 7] ABSTRACT 3 Claims, 1 Drawing Figure MANUFACTURE OF PETROLEUM COKE BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to an improvement in the manufacture of petroleum coke. More specifically it relates to producing clusters of petroleum coke pellets by an improved delayed coking process.

2. Description of the Prior Art Regular petroleum coke as made by the well known delayed coking process consists of dehydrogenated and condensed hydrocarbons of high molecular weight in the form of a uniform unsubdivided matrix of considerable physical extent containing dispersed throughout petroleum based aliphaticlike compounds.

In the regular delayed coking process, oil is charged into a fractionating tower. The bottoms from the fractionating tower are heated and introduced into a coke drum where coke is formed. Coke made by the regular delayed coking process is amorphous and generally soft. Further, the density of such material is low, its porosity is high, and it is weak in compression. Accordingly, such coke may be unsatisfactory for use in metallurgical processes, such as for example in a blast furnace where coke beds must support without crushing the weight of upper beds containing iron ore and limestone.

SUMMARY This invention pertains to a process for manufacturing clusters of petroleum coke pellets which are characterized by unusually high compressive strength, high density, and low porosity. More particularly, the invention relates to the discovery that fused clusters of petroleum coke pellets from about one thirty-second to one-fourth diameter may be formed by heating in a coking heater under controlled thermal cracking conditions a high boiling liquid petroleum feedstock containing dispersed throughout minute seed particles such as particulate carbon soot or a combination of particulate carbon soot and catalyst fines. The partically cracked effluent from said coking heater is introduced into a coke drum where petroleum coke pellets are produced and are consolidated, forming clusters of coke pellets and balls ranging in diameter from about 1 to 6 inches.

The principal object of this invention is to produce clusters of spheroidal shaped solid petroleum coke pellets of improved compressive strength by cracking and polymerizing a high boiling liquid petroleum feedstock containing seed particles, e.g., carbon soot or particulate carbon plus catalyst fines.

This and other objects will be obvious to those skilled in the art from the following disclosure.

DESCRIPTION OF THE INVENTION Feedstream According to the process of the present invention a conventional coking heater may be charged with a feedstream of high boiling liquid petroleum feed taken from the bottoms of a vacuum tower or a fractionator; for example, the bottoms from a distillation column fed with petroleum liquids such as virgin crude, reduced crude, heavy slops and naphthas, residual fuel oil, decanted oil from a catalytic cracker, heavy fuel oil slurry, heavy gas oils, and mixtures thereof. Included in said feedstream to the coking heater is about 0.01 to about 0.5 weight percent or higher particulate carbon. Amounts above 0.5 weight percent do not materially enhance the process. The particulate carbon may be added to the high boiling liquid feedstream as dry particulate carbon soot; or it may be part of a residue slurry of particulate carbon in fuel oil which is supplied to said fractionator as part of the feed.

Such a fuel oil-particulate carbon slurry may be prepared by the carbon recovery process described in US. Pat. No. 2,992,906 issued to Frank E. Guptill, Jr. In said process, very fine carbon particles entrained in the gaseous products of reaction of fossil fuels and oxygen are separated from the product gas by scrubbing the gaseous products with water,

forming a particulate carbon-water slurry. This particulate carbon-water slurry is contacted with alight liquid hydrocarbon, forming a slurry of particulate carbon in light liquid hydrocarbon. A heavy liquid hydrocarbon e.g., fuel oil, is then mixed with said light liquid hydrocarbon carbon slurry and then the light liquid hydrocarbon is distilled off leaving said slurry residue of particulate carbon soot in heavy fuel oil. Altemately, the particulate carbon-light liquid hydrocarbon slurry may be fed to the fractionator.

Electron micrographs of the carbon soot particles show that they resemble small spheres of sponge like" texture that may range in size from about 0.01 to 0.5 microns but which are usually about 70 millirnicrons in'diameter. Because of this structure the carbon has a tremendously high surface area, for example from about 300 to 1,000 square meters per gram. Particulate carbon soot is both oleophilic and hydrophilic. 1 gram of soot will absorb about 2 to 3 cc. of oil. A typical analysis of the particulate carbon soot comprises in weight percent: carbon 92 to 94, hydrogen 0.4 to 1.1, sulfur 0.3 to 0.6, and ash 3.4 to 4.7.

In another embodiment of this invention the feedstream to the coking heater may contain about 0.003 weight percent or more of catalyst fines in addition to the aforesaid particulate carbon. The catalyst fines may be added to and mixed with the high boiling liquid feedstream to the coking heater; or the catalyst fines may be part of the decanted oil which is supplied to said fractionator as part of the fresh feed. For example, fresh feed to the fractionator may contain up to about 30 weight percent of fluid cracked heavy cycle gas oil from a catalytic cracker regenerator, also known as FCHCGO (Decanted Oil). About 0.04 to 0.40 pounds or more of catalyst fines may be present in each gallon of FCHCGO oil charged. The bulk of the fines have a particulate size range of about 1 to microns. Composition of the catalyst may be approximately 50 percent aluminum oxide (Al- O )-with the bulk of the remainder being silicon dioxide.

The effluent from off the top of the coke drum comprising essentially hydrocarbon vapors and optionally a comparatively small amount of water vapor is also charged into the fractionator.

Fractionator The fractionator for producing the high boiling liquid petroleum feed is operated at a pressure in the range of 7 to 12 psig and a temperature in the range of 275 to 750 F. Pressure gas oil yields from the fractionator amount to about 60 to 65 weight percent, basis fresh feed to fractionator, and include light, intermediate, and heavy gas oils varying individually with end point specifications. Other products from the fractionator include: propylene and butylene feedstocks (about 1 to 3.5-weight percent), light and heavy naphthas (about 10 to 18 weight percent), and fuel gas (about 1 to 5 weight percent).

Feedstreams to the fractionator which have a high salt content may be desalted by conventional desalting techniques in order to prevent the fouling of heat exchange surfaces and the plugging of heater tubes. For example, the crude feedstock may be intimately mixed with water, caustic, and a demulsifying agent to dissolve salt and bottoms sediment. Water is then electrostatically separated from the oil, carrying along the inorganic impurities. The caustic and demulsifant aid in the separation.

Vacuum Tower The bottoms from the fractionator containing essentially all of the aforesaid carbon soot and catalyst fines may be introduced directly into a coking heater or preferably into a conventional vacuum distillation tower where under a vacuum of about 19 to 30 mm of mercury further separation of the lighter components from the charge stock is effected. With the vacuum tower on-stream, the total gas oil yield (pressure gas oil vacuum gas oil) will be greater than the gas-oil yield without a vacuum tower in the line.

Besides maximizing the gas-oil yield, the vacuum tower alters the composition of the feed to the coking heater in the next step, e.g., increases specific gravity, viscosity, ash content and concentration of seed particles. The effect of operating with the vacuum tower in the line as compared to operating without the vacuum tower and discharging the bottoms from thedistillation tower directly into the coking heater is shown in Table 1. Most of the properties of the charge stock to the coking heater increase when the vacuum tower is in the line. Further, the effect on the product is beneficial as the coke pellets appear finer and unite better in a cluster.

TABLE I [Effect of vacuum tower operation on charge stock to coking heater] High boiling High boiling petroleum petroleum oil made oil made without vacwith vacuum uum tower tower operin line (fracating (vactionator uum tower Property bottoms) bottoms) Gravity, API 8. -12. 0 3. 0-7.0 Sp. gr. at 60 F 0. 086-1. 014 1. 022-1. 052 Sulfur, wt. percent 1. 2-1. 1. 5-2. 0 Basic N p.p.m 3, GOO-4,000 5, 000-6, 000 Viscosity, SFS at 210 F 200-600 500-1, 000 Salt content, grams/bbl. -20 -40 Ash, wt. percent 0. 03-0. 07 0. 05-0. 10 Conradson carbon, wt. percent 11. 0-14. 0 17. 0-22. 0 Metals, p.p.m.:

Ni 45-65 60-80 V 60-75 75-100 F 70-85 90-120 Free carbon soot content, wt. percent..- 0 04-0. 10 0. 12-0. 28 Catalyst content, ll)./gal 0 003-0. 04 0. 006-0. 06 Watson characterization factor, K,. 10. 0-10. 8 10. 4-10. 7 Hydrogen to carbon weight ratio, min- 0 11-0. 110 0. 10-0. 108 Boiling point at 10 mm., 10% overhead,

Optionally present (equal parts by weight of A110; and SiOr).

Coking Heater The coking heater serves as a thermal cracking reactor. The charge to the coking heater may be the seeded hot heavy residuum from the bottom of the vacuum tower or from the, bottom of the fractionator. The coking heater charge in weight percent (basis fresh feed charged to the fractionator) is in the range of about 53 to 66 with the vacuum tower on and about 74 to 94 with the vacuum tower down. High boiling residuums having the desired composition may be also introduced into the process at this point.

The coking heater may comprise an externally fired heating coil of such design as to effect a rapid heating of the oil to a predetermined temperature and a minimum soaking time, thereby controlling the cracking of the oil while it is in the coil. In the cracking reaction, large molecules are split into two or more smaller molecules. Thermal cracking starts at a temperature of about 750 F. and the rate of reaction doubles for every F. increase in reaction temperature. Polymerization and condensation reaction wherein two molecules combine to form a larger molecule are prevented from proceeding in the coil to the point where coke is formed. Rather, such solid forming reactions are delayed until the effluent from the coking heater is charged into the coke drum.

The coking heater may be one of conventional design wherein the feed is heated from an inlet temperature in the range of about 650 to 720 F. to a sufficiently high temperature so that thermal cracking occurs at a rapid rate. However, residence time is controlled and kept to a minimum so that only about percent of the thermal cracking is completed in the coil.

The coking heater outlet temperature is controlled at a temperature in the range of 900 to 930 F. Higher temperatures may cause rapid coking in the coking heater and shorten on stream time. Lower temperatures produce soft coke with a high VCM (volatile combustible matter) content.

The residence time in the tubular heater must be long enough to bring the oil up to the desired temperature. However, excess time in the tubular heater may cause coking and result in clogging the heater coil. Thus, the residence time in the tubular coil is maintained at about 1 to 3 minutes (preferably less than 2 minutes) while at the previously. mentioned conditions of temperature and pressure.

One method for controlling the velocity, and residence time in the heating coil is by injecting a relatively small amount of liquid water into the high boiling petroleum oil feed entering the heating coil. Water injection is controlled at a rate sufficient to maintain the oil velocity in the heating coil high enough to prevent coke from forming and depositing in the heater coil. For example, the amount of liquid water injected into the high boiling liquid petroleum feed may vary from about 0.3 to 4.0 weight percent (basis oil charged to the coking heater).

Coke Drums The hot efiluent from the coking heater may comprise high boiling liquid petroleum and cracked compounds of said high boiling liquid petroleum, hydrocarbon vapors, and a comparatively small amount of water vapor. The effluent is introduced into a coke drum at a temperature in the range of 880 to 895 F. and a pressure in the range of about 40 to 60 psig. The coke drum is stationary and consists of a vertical elongated cylinder having a truncated cone-shaped section at the lower end. The charge is fed to the coke drum axially at the bottom and passes through a deflector assembly mounted on the bottom head inside the coke drum. The deflector assembly consists of a short cylinder with a closed top and with eight elongated vertical slots equally spaced around the walls. These slots divide the charge into eight separate streams. Each stream emerges radially from a slot and then swirls upwardly as directed by the conical shaped sides which form the end section of the vessel.

As the charge fills the coke drum, petroleum coke pellets form and combine in clusters, in a manner to be further described. Hydrocarbon vapors at a temperature in the range of 810 to 820 F. and a pressure in the range of about 20 to 45 psig leave from the top of the coke drum and flow into the fractionator, along with a comparatively small amount of water vapor, if any.

While the exact mechanism by which the petroleum coke pellets are formed and clustered is unknown, it may be postulated that in the coke drum the particulate carbon soot dispersed in the substantially liquid charge may serve as seeds or nucleating agents on which the hydrocarbons condense, polymerize, and crosslink. Under time-temperature conditions in the coking zone the resulting deposit on the surface of a seed particle or on a growing coke particle undergoes dehydrogenation and the formation of a layer of coke. Repetition of this coking cycle causes successive layers of coke to build-up on the growing particle.

Initially, the particulate carbon soot seed and the growing particles will be in suspension in the upwardly swirling feedstream within the coke drum. However, at some point, pellet sized particles will settle out by gravity and deposit on and fuse with other coke pellets at the bottom of the coke drum, forming a cluster of petroleum coke pellets. The pellets harden and the level of the coke bed raised until a batch of clustered petroleum coke pellets fills the coke drum.

In appearance, the petroleum coke pellet clusters may take on several forms. For example, in a preferred embodiment of the invention with the vacuum tower in the line, the subdivided spheroidal shaped petroleum coke pellets about onethirty-second to one-fourth inches in diameter are fused to contiguous pellets to form a cluster. In another form, the petroleum coke pellets are partially fused to contiguous pellets and partially bonded to each other by means of from about 2 to 30 weight percent of a solid asphaltic-like material as produced along with the pellets during the coking of said high boiling petroleum oil. A variation of this last form consists of spheroidal shaped clusters of said fused and bonded petroleum coke pellets wherein the diameter of the spheroid is about 1 to 6 inches and the outer surface is smooth.

When a coke drum has been filled with a batch of hardened coke clusters to a desired level, it is taken out of service and decoked. First, superheated steam is put into the coke drum at the bottom, to displace hydrocarbon vapors and to remove high boiling point hydrocarbons remaining on the coke. Then, after the coke drum has been steamed for a sufficient length of time, e.g., about 1 to 3 hours to produce specification VCM coke, the coke drum is filled with water and cooled. The water is then drained from the cooled coke drum, and the top and bottom heads are removed. An axially aligned hole is cut vertically through the coke bed to permit the introduction of high pressure jet streams of water. By this means, the batch of petroleum coke is broken up into lumps and removed from the bottom of the drum.

The coke yield, basis weight percent of coking heater charge is in the range of 20 to 26 with the vacuum tower on and from about 17 to 21 with the vacuum tower down.

The petroleum coke produced by the process of our discovery is characterized by the properties shown in Table 11. When tested by means of a Chatillion light spring tester, a oneeighth inch diameter pellet will withstand a compressive load of 17 pounds average and about 14 pounds minimum. In comparison, a comparable sized piece of regular petroleum coke will fail at a compressive load of 8 pounds average and about 6 pounds minimum. Further, the petroleum coke does not degrade during handling; that is, there is no increase in fines nor other sizing changes during movement and stockpiling.

Undersirable adulterating products may be removed from the petroleum coke by calcining the coke in a rotary kiln at a temperature in the range of about l,000 to l,500 C.

TABLE ll Properties of Spheroidal Petroleum Coke Clusters DESCRIPTION OF THE DRAWING A more complete understanding of the invention may be had by reference to the accompanying schematic drawing which shows the previously described process in detail. Although the drawing illustrates a preferred embodiment of the process of this invention, it is not intended to limit the invention to the particular apparatus or materials described.

With reference to the drawing, fresh feed consisting of heavy slops and naphtha in line 1, a mixture of crude oils, fuel oil, and if present decanter oil from a catalytic cracker containing catalyst fines in line 2, and slurry oil containing particulate carbon from a synthesis gas carbon recovery system in line 3 are introduced into fractionator 4. Coke drum vapor and optionally a comparatively small amount of steam from coke drums 5 and 6 are also introduced into fractionator 4 by way of line 7.

Over a temperature range of about 275 to 750 F. and a pressure range of about to 25 psig the aforesaid feed is separated into various product streams. For example, the following streams are taken from the fractionating tower: light, intermediate and heavy gas oils through

lines

8, 9 and 10 respectively. Overhead products such as the following are removed through overhead line 11: propylene and butylene feedstock, light and heavy naphtha, water, and fuel gas.

In a'preferred embodiment, with valve 12 closed and valve 13 opens the bottoms from fractionator 4 at a temperature in the range of about 710 to 725 F. and a pressure of about 12 psig are passed through

line

14, 15 and 16 into vacuum tower l7. Vacuum gas oil is removed from the vacuum tower through lines 18 to 21. Vacuum residuum, at a pressure of about 30 mm of mercury and a temperature in the range of about 600 to 690 F. is removed from the bottom of vacuum tower 17 through lines 22 to 24 and valve 25.

By means of pump 26, line pressure is increased to about 300 to 600 psig and the vacuum residuum is passed through lines 27 and 28 and into coking heater 29. Liquid water maybe injected into the high boiling petroleum oil in line 27 by way of

lines

30 and 31. Metering valve 32 controls the rate of water injection.

From line 33 at the exit of coking heater 29, the hot effluent at an exit temperature in the range of about 900 to 930 F.

and a pressure in the range of about 40 to 60 psig is passed into coke drum 5 by way of lines 34 to 36, and control valve 37. While coke drum 5 is being filled, valve 38 is closed and coke drum 6 is being decoked. After coke drum 5 has been filled, valve 37 is closed, valve 38 is opened, and coke drum 6 is filled by way of

lines

33, 39, 40 and 41 while drum 5 is being decoked.

The efiluent from coking heater 29 enters at the bottom of coke drum 5, emerging through eight vertical slots, for

exampic

42 and 43, in the side wall of deflector assembly 44. Similarly, during the filling of coke drum 6, the effluent from coking heater 29 emerges through eight vertical slots, for example, 45 and 46, in the side walls of deflector assembly 47.

During the filling of coke drum 5, overhead valves 48 and 49 are closed and valve 50 is opened. Hydrocarbon effluent vapors and perhaps a comparatively minor quantity of steam are removed from the top of coke drum 5 and are introduced into fractionator 4 as previously described, by way of lines 51 to 53 and line 7. Similarly, while coke drum 6 is being filled valves 50 and 54 are closed, valve 49 is opened, and overhead effluent vapors from coke drum 6 are sent to the fractionator by way of lines 55 to 57, and line 7.

Steaming of the coke to control its VCM is accomplished at a temperature of about 910 F. Steam in line 58 may be introduced into the bottom of coke drum 5 through

lines

59 and 36 by opening valve 60 and closing valve 37. Overhead valve 50 is closed and valve 48 is opened to permit the steam and hydrocarbon vapors from coke drum 5 to pass through lines 51, 61 and 62 and into a unit, not shown, for separating sour water from intermediate gas oil. In a similar manner, by closing

valves

38 and 49, and opening

valves

63 and 54, steam in line 64 may be passed through

lines

65, 41, coke drum 6, and

lines

55, 66, 67, and into an oil-water separating unit.

Cooling water enters at the top of the coke drum through lines not shown and discharges from the bottom. After the top and bottom covers are removed from a coke drum, the petroleum coke inside is broken up by high impact water jet and is removed through lines 68 and 69 at the bottom of coke drums 5 and 6 respectively. Lumps of petroleum coke clusters are sent to storage through line 70.

Altemately, when it is desirable to use the bottoms from the fractionating tower as the high boiling petroleum feed to the coking heater, vacuum tower 17 may be removed from the line by closing

valves

13 and 25 and opening valve 12. Fractionator bottoms are then introduced directly into coking heater 29 by way of

lines

14, 71, 72, 24, 27, and 28.

EXAMPLE OF THE PREFERRED EMBODIMENTM M The following is ofiered in a better understanding TABLE IV [Composition of charge stock to fractionator] Fluid cracked California Heavy- Fuel oilheav c cle San Ardo California reduced slops and carbon gas oil ith v crude crude crude naphthas slurry catalyst g n itigty 0. 976-0. 983 0. 904-0. 947 0973-0. 993 0. 904-0. 986 0. 994-1. 034 0. 973-1. 037

rscos y:

ssU t; F 15. GOO-22,000 500-3, 000 IOU-1,500 200-400 Table IV Continued TABLE IV [Composition of charge stock to fractlonator] C H H F l l Flgid crackeld a l' or m eavy ue oi eav c e e San Ardo California reduced slops and carbon gas o i l vzith crude crude crude naphthas slurry catalyst HSU at 210 l" HFHal. 122 F... Gravity, A1l Ash, wt. percent.

v Sulfur, wt. percent Conradson: carbon, wt. percent Carbon: soot, wt. percent Catalyst content, lbs/gal- Characterization factor, K..- 11. 3-11 7 11. -11. 9 Salt content, crams bbl. 10-50 Usual volume range, percent 12-72 0-23 "Equal parts by weight 01 A120; and S102.

of the present invention, but the invention is not to be construed as limited thereto.

With reference to the process shown in the drawing, a fresh feedstream of about 60,300 BPSD* (*BPSD means barrels (42 gallons per barrel) per standard operating day (24hours).) of mixed petroleum feedstocks as shown in Table 111 and having the properties as shown in Table IV is introduced into a fractionator. In addition, about 26,180 BPSD of hydrocarbon effluent vapor (basis feed to coke drum) and about 274 BPSD of steam are fed into the fractionator.

TABLE 111 Fresh Feed To Fractionatorw About 47,000 BPSD of high boiling petroleum oil of about 12API from the bottom of the fractionator at a temperature of about 730 F. anda pressure of about 12 psig are introduced into a vacuum tower. Other streams removed from the fractionator include: about 10,000 BPSD of intermediate gas oil of about 28AP1 at a temperature of about 520 F.; about 12,000 BPSD of heavy gas oil of about 23AP1 and a temperature of about 690 F; about 11,000 BPSD of light gas oil of about 34AP1 and a temperature of about 415 F.; and about 7,214 BPSD of miscellaneous and overhead products including propylene and butylene feedstocks, light and heavy naphtha, H 0, and fuel gas.

About 12,000 BPSD of vacuum gas oil are removed from the vacuum tower at a temperature of about 550 F. and a pressure of about 22 mm of mercury. Another stream of about 500 BPSD of vacuum gas oil is removed from the tower at a temperature of about 175 F. and a pressure of about 17 mm of mercury. These two streams are combined yielding 12,500 BPSD of vacuum gas oil of about 17AP1.

34,000 BPSD of vacuum tower bottoms of about 3 to 7AP1, at a temperature of about 690 F. and a pressure of about 30 mm of mercury are removed from the bottom of the vacuum tower and pumped at a pressure of about 55 psig to the coking heater. Along the way about 274 BPSD of liquid water are injected into the high boiling petroleum oil. The

coking heater is a 4 coil externally fired tubular heater. Each coil has an inside diameter of 3% inches and is about 3,000 feet long. The vacuum tower bottoms feed stream is divided into four equal streams, one to each coil. A pressure differential of about 250 psig across the coil is required to send the high boiling petroleum oil through the heating coil at a velocity of about 10 feet per second at the inlet and about feet per second at the outlet.

The effluent from the heater at a temperature of about 907 F. is introduced into one of a pair of coke drums at a temperature of about 885 F. and a pressure of about 45 psig. While one coke drum is being filled, the other is being decoked. The tum-around time for each coke drum is about 28 hours. During the coking reaction about 26,180 BPSD of effluent vapors (basis feed to coking heater) and a relatively small amount of water vapor (about 274 BPSD) are removed from the top of the coke drum and passed to the fractionator as previously described.

After a coke drum is filled with coke to a desired level, it is taken out of service and decoked. About 15,000 pounds per hour of superheated steam is flowed then upwardly through the coke drum to displace residual hydrocarbon vapors and to remove any high boiling point hydrocarbons remaining on the coke. The coke is steamed for about three hours or until the Volatile Combustible Matter (VCM) in weight percent is in the range of 8.0 to 29.5 and preferably in the range of 9.5 to l 1.0.

About 100,000 lbs/hr. of water are then flowed through the coke pit. Chunks of petroleum coke clusters are then separated from the water, removed from the coke pit, and transported by conveyor to the coke storage area.

The coke pellet clusters may be broken into small lumps and used as is for metallurgical purposes. Or, by calcining at a temperature of about 1,000 to 1,500 C., the density of the coke may be increased and certain impurities removed.

A visual examination of the product petroleum coke shows it to be composed of subdivided solid carbon spheroidal pellets about one-thirty-second to one-fourth inch diameter loosely fused together in a cluster. A fraction of the clusters are ball-shaped with smooth polished surfaces. Such balls may range in diameter from about 1 inch to 6 inches-and are randomly dispersed throughout the coke drum.

The process of the invention has been described generally and by examples with reference to various compositions of high boiling petroleum oils, seed particles and nucleating agents, and various other materials of particular composition for purposes of clarity and illustration only. From the foregoing it would be apparent to those skilled in the art that the various modifications of the process, the materials, and the amounts of the materials disclosed herein can be made without departure from the spirit of the invention.

We claim:

1. In the delayed coking process for producing petroleum coke, the improvement for producing clusters of petroleum coke pellets which comprises: charging a distillation zone with petroleum oil and a slurry of liquid hydrocarbon and particulate carbon soot providing a minimum of 0.01 weight percent of particulate carbon, recovering the liquid bottoms product from said distillation zone at a temperature above 690 F., injecting 0.3 to 4.0 weight percent of liquid water into said liquid bottoms product and heating said mixture in a heating zone at a temperature in the range of about 650 to 930 F. for a limited time to effect controlled cracking, and introducing the efiluent from said heating zone into a coking zone where at a temperature in the range of about 800 to 895 F. and a pressure in the range of about 20 to 60 psig uncondensed hydrocarbon effluent vapor and steam are removed overhead, and where over a period of time with said particulate carbon soot acting as nucleating agents, petroleum coke pellets form and fuse together to form a cluster.

2. The process of claim 1 wherein the petroleum oil charged into the distillation zone contains at least about 0.003 pounds of catalyst fines comprising aluminum oxide and silicon dioxide per gallon of petroleum oil.

3. The process of claim 1 wherein said liquid bottoms product from the distillation zone is a hydrocarbon oil fraction from vacuum distillation having a 10 percent point at 10 mm Hg of at least 800 F.

050 v UNITED STAS PATE P 9) @FFECE CE TIFECA'E @F @QRQ'MfiN Patent No. 3, 73, I Dated 79 97 Inventor) Warren G. Schlinger, Harold C. Kaufman and Carr It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

l. Add the name of Carroll L. Crewley es e co-inventor. *3

2. Column 3, line 19 chan e "N to N Column 5, line 38 00035-09045 should be re:-

errenged to line 37 in the column headed by Range 5. Column 6, line 2 Change "opens" to open 7. Column 7, Table IV Under Sen Ardo Crude "60 80" should read 60-80 8. Column 7, line 38 Change '02, O3, O4" to Signed and sealed this 6th day of March 1973.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. Q ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents

Claims

2. The process of claim 1 wherein the petroleum oil charged into the distillation zone contains at least about 0.003 pounds of catalyst fines comprising aluminum oxide and silicon dioxide per gallon of petroleum oil.
3. The process of claim 1 wherein said liquid bottoms product from the distillation zone is a hydrocarbon oil fraction from vacuum distillation having a 10 percent point at 10 mm Hg of at least 800* F.