US2789942A - Fluid coking process - Google Patents

Description

April 1957 w. M. COOPER, JR., EIAL 2,789,942

FLUID coxmc PROCESS 2 Shee'ts-Sheet 1 Filed Aug. 15, 1955 H MKDOE m w GENES I INVENTORS T William M. Cooper, Jr

Edward F U rch Bernard L. Schulman Walter 6. May BY ATTORNEY April 1957' w. M. COOPER, JR., EI'AL 2,789,942

FLUID coxmc PROCESS Filed Aug. 15, 1955 2 Sheets-Sheet 2 VENT COKE FROM 82 FINE 'coKE GRINDER PRODUCT ELUTRIATION sAs FIRST STAGE ELUTRIATOR I 75 9!, 9o

. as as, as '92 T 11 a J 63 as 84 SECOND STAGE 28 85 ELUTRIATOR PROCESS FIGURE 1H E ELUTRIATION GRINDER WALL 3 v GAS '2 WEAR PLATE 22 2s 4 C'I'O0A%%N82'I$E STEAL 25 NOZZLE 24 WI'INVENTORS i iam M. Cooper, Jr iii-Bil Edward E Upchurch Bernard L. Schulman Walter G. May

04.. ATTORNEY United States Patent FLUID COKING PROCESS William M. Cooper, In, and Edward F. Upchurch, Roselle, N. .F., Bernard L. Schulman, Edgewood, Md., and Walter G. May, Union, N. J., assignors to Esso Research and Engineering Company, a corporation of,

The present invention relates to an improved fluid coking process. It is more particularly concerned with a method and means of comminuting and classifying coke produced by a hydrocarbon oil fluid process to secure a coke product therefrom of boiler fuel size.

In brief compass, this invention proposes combination of a jet grinding zone and an elutriation zone, integral with the fluid coking process. Coke produced by the coking reaction is reduced in size by the action of supersonic velocity gas jets in the grinding zone. The attrited coke is then transferred to an elutriation zone wherein fines are separated and removed from the comminuted material as product of the process. The coarser coke particles remaining from the elutriation are recycled to the grinding zone for further comminution. Through a particular design and. advantageous arrangement of apparatus, and by operating in accordance with this design and arrangement, the efficiency of the cok ing process is greatly improved.

The fluid coking process is directed to the pyrolytic upgrading of heavy residual oils. In this fluid coking process an oil is converted to lighter compounds such as naphthas and gas oils through contact with a fluid bed of particulate solids, preferably coke particles produced by the process, maintained at a. coking temperature by circulation through an external heating zone, e. g. a burner. Coke or carbonaceous residue is produced in the coking zone and is deposited on the contact solids becoming a part thereof and causing them to grow in size. I

Charging stocks customarily used in fluid coking operations comprise principally petroleum derived residua characterized by Conradson carbon contents of from 5 to 50 wt. percent, gravities of to 20 API, and initial boiling points above 600 F., but may include cycle stocks, lube oil extracts and similar high boiling, low value heavy oils containing constituents non-vaporizable Without thermal cracking. Other types of oils such as asphalts, shale oils, coal tars, and synthetic oils through a 200 mesh screen, i. e., be less than 74 microns in diameter. Because of the relative hardness and non: friability of this coke, comminuting of this coke has presented problems.

Another problem in the operation of a fluid coking process is the supplying of seed coke or fresh growth nuclei to the process. Because of the deposition of coke on the solids, they continue to grow in size and means must be taken to compensatefor this growth. As the circulating coke particles become coarser, fluidization becomes poorer, circulation more erratic and contacting efiiciency decreases. It has been customary in the past to reduce in size the particles in some manner, as by crushing a portion of the coke withdrawn from the system, to produce the requisite amount of seed coke. The most desirable particle size range for circulation in the coking process is from about to 400 microns, although some of the material may range in size from about 20 to 1000 microns or more. The seed coke as produced is desirably of a size within the range of 75 to microns. Below this range, particles agglomerate readily or are blown from the system, and above this range the circulated in the system, about 0.05 to 0.5 lb./lb. feed, has to be reduced in size in some manner to form seed coke in order to maintain the number, size and size distribution of the particles in the system substantially constant.

It is a purpose of this invention to devise an improved fluid coking process with provision for production of a coke product of boiler fuel size and with provision for supplying requisite seed coke to the coking reactor. Other more particular features of this invention will appear as this description proceeds during which the attached drawings, forming a part of the specification,

are discussed in detail.

Figure l of the drawings illustrates one preferred embodiment of the improved fluid coking process of this invention. The main items of equipment shown are a coking vessel, burning vessel, grinder and elutriator.

Figure 11 illustrates in more detail a nozzle design for introducing a gas stream at supersonic velocities into the grinder to aflect size reduction of the fluid coke.

Figure III illustrates an alternative two-stage method;

of classifying the coke in the process and another specific embodiment of an elutriation vessel.

In its general aspects this invention is concerned with a process of comminuting particulate solids. The process comprises the steps of maintaining a dense, turbulent, fluid bed of particulate solids in a grinding zone and injecting a plurality of gas streams at high velocities into the fluid bed, thereby reducing in size the particulate;

solids by attrition and collision between the particles.

Charge solids are continuously introduced into the fluid bed. Spent gases are withdrawn overhead and entrained solids are recovered therefrom. The recovered entrainedv solids and a portion of the bed are introduced into the disperse phase of a disperse phase elutriatiou'zone by means of a standpipe and riser conveying system. An

Patented Apr. 23, 1957,

3 elutriation gas, e. g. steam, is flowed upwardly through the elutriation zone at a velocity sufllcient to entrain :most of the relatively fine particles (below about 74 microns in size) while permitting coarser particles to fall to the base of the elutriation zone. A second fluid bed is formed in the lower portion of the elutriation zone and relatively coarse solids are withdrawn therefrom and returned to the grinding zone for further treatment. The elutriated finer particles are withdrawn overhead and separated from the elutriation gas to recover a fine solids product.

This invention is particularly concerned with an improved hydrocarbon oil fluid coking process. The improved process comprises the steps of converting an oil in a coking zone by contact with a fluid coking bed of coke particles maintained at a coking temperature to produce vaporous conversion products and carbonaceous residue which is deposited on the coke particles becoming a part thereof, recovering overhead the vaporous conversion products, circulating a portion of the coke particles to an external combustion zone, partially burning coke particles in the combustion zone to raise the temperature thereof 100 to 400 F. above the coking temperature, returning heated coke particles from the combustion zone to the coking zone to maintain the coking temperature, circulating another portion of the coke particles to a grinding zone, maintaining a fluid grinding bed of coke particles therein, injecting an attrition gas as a plurality of supersonic velocity gas jets in opposed relationship therein thereby comminuting an appreciable portion of the particles in the fluid grinding bed, withdrawing spent gases overhead from the grinding zone and recovering entrained solids therefrom, circulating the entrained solids so recovered and a portion of the fluid grinding bed to the disperse phase of a disperse phase elutriation zone, introducing an elutriation gas into the lower portion of the elutriation zone in amounts suflicient to entrain relatively fine coke particles while permitting relatively coarse par ticles to fall, maintaining a fluid elutriation bed of relatively coarse coke particles in the lower portion of the elutriation zone, withdrawing elutriation gases carrying entrained solids overhead from the elutriation zone, recovering therefrom a fine coke product, recycling a portion of the fluid elutriation bed to the grinding zone for further comminuting and circulating a portion of the fluid grinding bed to the coking zone to supply requisite seed coke thereto.

The invention is also concerned with a novel apparatus for comminuting and classifying particulate coke. The apparatus comprises in combination: a grinding vessel having an upper portion of an enlarged cross-sectional area; a fluid bed of particulate coke therein extending into the upper portion; a plurality of high velocity gas jet nozzles extending through the grinding vessel into the lower portion in horizontal opposed relation; means for withdrawing spent gas overhead from the grinding vessel and for recovering entrained solids therefrom; a vertically disposed disperse phase elutriation vessel; a fluid bed of relatively coarse coke particles in the lower portion thereof; means for admitting an elutriation gas into the lower portion of said elutriation vessel; and a standpipe and riser conduit system for conveying solids, including solids separated from the spent gases and solids from the fluid bed in the grinding vessel, to the disperse phase of the elutriation zone and for conveying relatively. coarse solids from the lower portion of the elutriation zone to the grinding zone.

In its more particular aspects the invention proposes an elutriation vessel of particular design and a particular mode of operation thereof whereby more efiicient use is made of the elutriation gas. Also, a two-stage elutriation method, particularly eflicacious for securing seed coke for the coking process besides a boiler fuel sized product is proposed. There is also developed a unique method of superheating and supplying steam to the jet attrition nozzle's in the grinding vessel.

Referring now to Figure I, there is shown diagrammatically a coking process incorporating the teachings of this invention. Heavy oil to be converted, such as vacuum residuum, is introduced into a coking vessel 1 by manifold injection system 2 at a rate in the range of 0.25 to 2.0 lbs./hr./ lb. of coke contained therein. The coking vessel has a lower stripping section 1a and a superposed vapor quench and product separation system or scrubberfractionator 1!). A fluid bed of particulate fluid coke of a density in the range of 30 to 60 lbs/cu. ft. is maintained in the vessel at a temperature in the range of 900 to 1600 F. A dilute or disperse solids phase exists above the fluid coking bed wherein entrained solids tend to settle out.

Upon contact with the high temperature particles of the fluid bed, the injected oil undergoes pyrolysis evolving substantial quantities of vaporous conversion products and depositing coke or carbonaceous residue on the solids. Normally 65 to vol. percent of the oil is converted to products boiling below 1000" F. The vapors are removed overhead through a cyclone system 5 wherein entrained solids are separated and removed. More than one cyclone can be used, arranged in series or parallel, and it may be located externally of the reactor.

The vapors arising from the fluid bed are at or near their dew point and have a propensity for condensing and forming coke deposits on contiguous surfaces. To inhibit or prevent the formation of such coke deposits, a diluent gas such as steam is injected into the disperse phase and/ or into each of the successive cyclone inlets to lower the dew point of the vapors and/ or to preheat the vapors thereby preventing condensation. This is particularly efficacious when operating with the coker on a oncethrough basis, more fully explained below, where several cyclones in series must be used to assure substantially complete removal of entrained solids.

The vapors issuing from the cyclone are met with a recycled scrubbing or quench oil suitably dispersed as by baffles and are thereby cooled to below incipient cracking temperatures, i. e., below about 750 F. This condenses from the vapors heavier ends containing coke forming constituents and catalyst poisons such as organic metal salts. The vapors then pass upwardly to fractionation section 1b of the vessel and are separated into the various product fractions desired. For example, a gas oil of catalytic cracking quality boiling below about 1015 F. is separated and removed by line 6 and a heating oil is removed by line 7 as product. The remaining vapors comprising naphtha and lighter compounds are then withdrawn overhead by line 8 andare subjected to further conventional processing.

The heavier ends initially condensed from the vapors collect in the lower portion of the scrubber section and are removed by line 3. A portion of these heavy ends amounting to about 20 to 40 wt. percent on fresh feed, are cooled to about 450 to 800 F. and recycled by line 4 to serve as a scrubbing oil. The remaining portion is removed as product or is recycled to the coking zone for further treatment. By recycling this material less efiicient operation of cyclone 5 is permitted as fines carried through the cyclones will be entrapped in the condensed material and returned to the reactor with the recycle.

In many cases, however, it is desirable to operate the coker on a once-through basis at limited conversions so as to produce a residual fuel oil to meet market demands. It is usually necessary in this case to provide more stages of cyclones to secure a better removal of the entrained particles. It the residual oil removed as product still contains fine solids, the solids can be removed by filtering or thickening as in a Dorr thickener. The residual oil product can also be thermally cracked in a cracking coil to secure further amounts of lighter products. The coke fines exert a beneficial scouring action in the crackof occluded hydrocarbons in the stripping section and then passes upwardly fluidizing the main coking bed at superficial gas velocities in the range of 0.5 to ft./ sec.

This fluidizing gas or a portion thereof can be admitted as high velocity jets, if desired, to secure some attrition and size reduction in this part of the system to meet seed coke requirements. If so introduced, the gas may conveniently be highly superheated, as indicated here inafter, to reduce the amount of gas required.

To maintain the coking temperature a portion of the coke is continuously circulated from the stripping zone In via line it) to an external heating zone, e. g., a fluid bed burner 11. Conduit may comprise a conventional standpipe and riser system known in the art whereby proper pressure balance and circulation rates are maintained. Gas, e. g. steam, is injected into the base of riser by line 10a to effect circulation. The heating zone preferably comprises a fluid bed burner but may also comprise a gravitating bed burner or transfer line burner, also known in the art. Although the coke may be heated indirectly or extraneous fuel may be burnt to supply heat to the coke to meet the heat requirements of the process, it is preferred to burn a portion of the coke laid down on the particles in the coking zone.

As shown, the coke in the fluid bed burner 11 is maintained as a fluid bed by air or other free oxygen-containing gas introduced into the base of the vessel via line 12. By partial combustion the coke is raised to a temperature 100 to 400 F. above the coking temperature. Reheated coke is circulated to the coking vessel 1. via standoioe and riser system 13 at a rate of 2 to 20 lbs/lb. of 'resh oil feed to maintain the coking temperature. Line 13a admits a conveying gas, e. g. steam, to conduit 13. Flue gases are withdrawn overhead through cyclone system 14 wherein entrained solids are removed and then are vented from the burner by line 15.

The coke to be comminuted may be withdrawn from any point in the coke circulation system between the burner and the coking vessel. As shown, it is with drawn via standpipe 15 and introduced into a feed hopper 17 in an amount sulficient to meet the net coke product and seed coke requirements of the coking process. This feed hopper is not essential and may be dispensed with if desired. Gases may be admitted to the feed hopper to maintain the mobility of the solids therein and gases are vented from the top of the vessel by line 18 as'necessary.

Fluid coke is transferred from the feed hopper by standpipe 19 and conduit system 20 to grinding vessel 21. Gas, e. g. steam is injected into the base of the riser by line 26a in controlled amounts to effect circulation. It is preferred to construct the terminal portion of line 20 as shown. The method of construction permits eflicient introduction of solids into the disperse phase of a fluidized solids vessel, such as grinding vessel 21, although a downwardly curved line, such as shown with vessel 30, may also be used. Line 20 terminates in a horizontal pipe located about 6 feet above the level of the fluid bed. The end of the horizontal pipe is closed, and a bottom opening section is cut in the pipe which permits the solids to be uniformly and evenly discharged.

The upper portion of grinding vessel 21 is enlarged to an area 1.25 to 4 times the cross-sectional area of the lower portion to permit solids to de-entrain. A fluid bedof solids, having a fluidized density of to 60 lbs./cu.ft., is maintained in the lower portion of the ome grinding vessel. Disposed about the lower portion of the vessel are a plurality ofgrinding nozzles 22 for introducing gas jets at above sonic velocities into the fluid bed to cause breakage and attrition of the particles. The nozzles are supplied with an attrition gas, e. g., superheated steam, by line 23. Grinding energy requirements are in the range of 75 to H. P.- hr./ton of through 200 mesh material produced. The nozzles are disposed concentrically about the vessel in opposed relation, whereby the force of the jets is directed to the center of the vessel and wear of the walls of the vessel is substantially avoided. For example, 8 opposed nozzles in two. levels with 4 on each level are used with a vessel diameter at the nozzle level of 8 ft. 6 in.

It is much preferred to introduce the attrition gas into the vessel as supersonic velocity jets as in this manner more efiicient grinding is attained. Supersonic velocity is a velocity above the velocity of sound in the gas under the exit conditions of the gas. Lower velocities may be used, however, if desired.

Figure II illustrates one nozzle design for securing supersonic velocities. As shown, the nozzle is contained by conduit 22 which extends through the grinder vessel wall 21a and through a metallic wear plate 24 designed to prolong the life of the vessel in that area. A second movable or adjustable conduit 25 extends within conduit 22 and terminates in a converging-diverging nozzle 26 which efficiently accelerates the gas and converts its potential energy into kinetic energy. Other designs and arrangements of attritor nozzles will occur to those skilled in the art.

Returning to Figure I, a constant inventory of coke is maintained in the grinding vessel by an automatic controller. This comprises a conventional level indicator 27 which sends impulses such as pneumatic pressure impulses to a motor-driven valve 28, e. g., an air operated piston slide valve, in the coke withdrawal line 29.

Most of the ground coke is withdrawn from the bottom of the grinding vessel via line 29 and passed to an elutriator vessel 30. Theremainder of the coke is carried overhead by the spent grinding gas via line 31 to a separation system, e. g., a cyclone 32, wherein the entrained finer particles are separated from the gas. The separation system may comprise, of course, several cyclones in series or parallel. Gas is vented from the cyclone by line 33 and separated fines are circulated to the elutriator via lines 34 and 29. The material separated in cyclone 32 is relatively fine and may be withdrawn as product via line 37. Usually, however, the separated particles contain enough oversized material sufiicient to justify further classification. The back pressure on the grinding system is regulated by a control valve 35 in line 33 responding to pressure measuring means 36 located in the top of grinder 21. As the pressure of the gas in line 33 may be greater than the pressure at which the elutriator is operated, it may be convenient to pass a portion or all of this gas to the elutriator to serve as elutriation gas therein. Thus the grinding gas would further serve as an elutriation gas.

Solids fro-m the grinder are introduced downwardly.

into the disperse phase of the elutriator by line 29. They are distributed within the disperse phase by suitable baffling means 38 which may comprise, for example, perforated screens, distributing weirs, distributing bars, perforated plates or equivalent means. An elutriation gas, e. g., steam, is admitted to the base of the vessel by line 39. The gas serves first to fluidize relatively coarse particles collected in the base of the vessel and then passes upwardly stripping fine particles from the descending solids. Superficial gas velocities used in this type of straight walled elutriation vessel lie in the range of 1.0 to 5.0 ft./sec. 4.5 to 30 actual cu. ft. of gas/lb. of coke introduced into the elutriator are used to affect the classification. In some applications it is preferred to introduce only part of the elutriation gas at the base of vessel 30, sufiicient were to obtain proper 'fluidizatiori of the bed, and'to introduce the rest needed for elutriation into the disperse phase above the fluid bed. The outage of thevessel, i. e., the distance from the fluid bed level L to the upper outlet, normally is about to ft. and may be varied "to regulate-the degree of classification, besides regulating the coke feed rate and the eluti-iation gas fate. Normally, however, the level of the fluid bed is maintained substantially constant by level control means which coinprises a level indicator from which control impulses are transmitted to a motor-driven valve 41 in the outlet line 20 of the elutriator. v

Elutria'tion gas carrying entrained fines in amounts in the range of 0.02 to 0.4 lb./cu. ft. is removed overhead by line 42 and passed to a separating means, e. g., a cyclone system 43. Entraine-d solids are separated from the gases and are removed as product by line 44. The gases, substantially free of solids, are vented by line 45. Coarse solids are removed from the fluid bed in the lower portion elutriator and are recycled to the grinding vessel by line 20 for further comminuting. 7

It will be appreciated by those skilled in the art that this particular combination of apparatus and operation of the same has advantages over other fluid coking processes in that there are no moving parts in the coke grinding devices and thus less maintenance is required. Also with the nozzle arrangement shown in Figure 11, replacement or adjustment of the nozzles can be effected while the grinder is in operation.

Instead of using an independent source of steam for the grinding nozzles, it is desirable in some cases to supply superheated steam to the nozzles in the following manner. Steam or water can be conveniently superheated or vaporized in a heating coil 46 placed within the fluid bed of burner vessel 11, as shown. This steam can then be transferred by line 47 to the grinder nozzles. The nozzles may, of course, be supplied with steam from an independent source by line 48, if desired. Some of the steam from heating coil 46 may be conveniently used elsewhere in the process. Thus a portion or all of the steam may be transferred via line 49 to line 9 of the coking vessel and serve as fluidizing gas therein.

Certain advantages are obtained by superheating the steam used in the grinding vessel. The amount of grinding which a given amount of steam can accomplish at supersonic velocities is a function of the enthapy change of the steam across the nozzles. Thus it is possible that the available energy of a given steam supply may result in higher grinding steam rates than is economically desirable. This can be offset by increasing the energy level of the grinding steam by superheating it instead of merely increasing the pressure.

The fine material recovered from the process by line 44 is usually too fine to be used as seed coke. If admitted to the coking vessel, it readily agglomerates or adheres together with other particles, or is rapidly lost from the system by entrainment. It has been found that there seldom exists particles below about 50-74 microns in size in the coking reactor. To meet the seed coke reuirements of the process, some of the comminuted material from the grinder can be transferred to the coking zone. This seed coke may be supplied either from the solids from cyclone 32 and/or the solids withdrawn from the base of the grinding vessel. As shown, solids are transferred from line 34 by line 50 to riser 13 and are thence introduced into the vessel. Conveying gas is admitted by line 51 to line 50 to transport the solids.

The following Table I presents a specific example of pertinent operating conditions applicable to the present process. The example is for a process as depicted in Figure I. To further illustrate this invention, Table II is presented. This Table illustrates the size and the size distribution of the coke in various parts of the system ah'dis to be 're'ad'i'n conjunction'with Table l.

TABLE I C king Burn- Feed Elutrl- Grind- Vessel lng Hopper ation ing Vessel Vessel Vessel Fluid Bod Temperature, F. 950 1, 350 300 300 Pressure in Disperse Phase,

p.s.i.g 6.0 6.0 0 2.3 1.0 Coke Holdup, Tons 275 13 Average Fluidizcd Density,

lbs/cu. ft 40 40 40 35 35 Gas Velocity at Bed Level,

fLJS'Q-C s 3.5 2.5 2.0 2.0 2.0 Outrage, ft. (distance from bed to vessel outlet) 17 17 5 12 12 Overhead Entrainment,

Tons/hr 189 0 34 5 42.5 Coke Circulation to Vessel,

Tons/min 22.3 23 0 0.57 1 3 l 3 Iluidiring stcsm, wt. percent on feed Air, Std, cu. ft./min Elutriation Gas, St

ltJmin Total Grinding Steam, lbs./hr. (Initially 750 F. at 600 p. s. i. g. max. velocity of 3,820 lt./sec.) 31,000

Feed-Hawkins residuum:

11 2 API 840 F. boiling point. 24 wt. percent C nradson carbon. 4.5 wt. percent sulfur. 2 ,300 bbL/day fresh feed rate. 73 V02. percent conversion to 1,000 F. minus products in cokcr,

excluding coke.

1 With 8 opposed grinding nozzles on two levels:

Coke halancc- Tons/day Coke make Coke burning rate" 220 C ke grinding rate el w crons) 1,016 Fine c ke products (90 percent less than 74 microns)... 828 Losses in flue gases, etc 2.0

TABLE II Coke particle size Wt. percent Smaller than:

800 microns 99.5 99.9 99.9

20 microns" Median sizc microns 190 58 75 40 Column No.:

1. Fluid bed in coker.

2. Circulatcd from burner to elutriator.

3. Coke overhead from grinder.

4. Coke circulated to elutriator from grinder.

5. Coke circulated from clutriator to grinder.

0. Coke product from elutriator.

1. There is a long stripping section in the lower portion of at least 10 diameters which enters into an enlarged upper portion. This permits gas velocities in the lower portion 1.5 to 2.5 times those in the top section.

2. The coke fed into the elutriator is introduced into the top section and dispersed upwardly.

3. A shallow, dense bed of relatively coarse coke of a depth of /2 to 1 diameter is maintained in the bottom section supported by a glid. Solids are overflowed from this fluid bed through a standpipe. The maintenance of this bed allows a very high entrainment rate of coke which is necessary to strip out fines from the bed.

4. Auxiliary elutriation gas is injected downwardly into the narrow stripping section to break up streamers of falling coke.

5. Coke fines are recycled to the enlarged upper portion to scrub out coarse particles from the entrained fines.

This particular combination of features permits increased feed rates without loss of fines in the coarse bottom product from the elutriator or the appearance of coarse particles in the overhead product.

In operation, coke from the grinder is introduced upwardly into the upper portion of the first stage of elutriator 75 via line 77. Fines are entrained from the injected solids and are removed overhead by line 78. The fines are recovered in a cyclone system 79 and the gases are vented overhead via line 80. The recovered fines are removed as product by line 81 and have a size under about 200 microns. A portion of this fine material is transferred by line 82 to the upper portion of the first stage elutriator as reflux. This amounts to about to Wt. percent on the coke feed supplied by line 77.

Coarse solids fall down to the base of the elutriation zone through an elongated stripping section wherein complete removal of the fines is attained. The coarse solids settle in the base and form a fluid bed 83 supported by grid 84. The bed is fluidized by elutriation gas admitted to the base of the vessel by line 85.

For both elutriators superficial gas velocities will normally range from 2 to 8 ft./ sec. in the lower section and from 1.0 to 3.0 ft./sec. in the enlarged portion. Slightly higher velocities in this range are used in the second stage handling the coarser material. Normally, 4.5 to 9 actual cu. ft. of gas will be passed through the elutriator per pound of coke classified, though this depends on the percentage of material carried overhead, and may vary wide- 1y. To break up streamers of coke falling through the vessel a portion of the elutriation gas is injected by a plurality of line 86 downwardly into the stripping section of the elutriator as shown. This may be done at more than one level, if desired. Relatively coarse solids containing some finer particles are overfiowed from the fluid bed into conduit 97 and transferred to and injected upwardly into the upper portion of the second stage elutriator 76. The second stage elutriator operates in the same manner as the first stage. The finer particles are removed overhead via line 87, recovered in cyclone system 88, and removed by line 89. This fraction is substantially coarser than the material recovered by line 81 from the first stage. The separated gases may be vented from the cyclone by line 90 but preferably the gases are transferred by line 91 to the first stage to secure economy in Operation. The first stage may, however, be independently supplied with elutriation gas by line 92, if desired.

As before, the relatively coarse material gravitates to the lower portion of the second stage elutriator and forms a fluid bed 93 therein. Elutriation gas is supplied to the vessel by line 94 and by downwardly injected jets 95. Coarse solids substantially free and relatively sharply separated from finer material are removed from the vessel by overflow standpipe 96. This material is recycled to the grinder for further treatment.

The intermediate size material in line 89 serves as seed coke in the coking process and the fine material secured by line 81 is of suitable size for burning in a conventional pulverized fuel burner. A higher velocity will be used in the second stage which will result in the carryover of some coarse material in the fines but because this intermediate size fraction is used as seed coke, no detriment occurs.

An example illustrating typical operating conditions for this two-stage elutriating process is presented in Table III.

TABLE III Size ranges:

Coke to Residue Residue Wt. percent Larger Coke to First Boiler From Seed From than Grinder Elutricoke 1st Coke 2nd ator Elutri- Elutriator ator 20 .1 Median Size.

This method of staging the elutriation has the follow ing advantages over a single straight-sided elutriation vessel.

1. The classification in the first elutriation is more selective, i. e., less coarse residue has to be recycled for a given amount of fine overhead material meeting fixed specifications.

2. The seed coke contains less lines (under 50 microns). Because solids under about 50 microns in size are all lost (by agglomeration) when it is supplied to the coker, a large amount present in the seed coke fraction creates an added load on the grinder.

Having described this invention and preferred embodiments thereof, What is sought to be protected by Letters Patent is succinctly set forth in the following claims.

What is claimed is:

I. An improved hydrocarbon oil fluid coking process which comprises converting an oil in a coking zone by contact with a fluid coking bed of coke particles maintained at a coking temperature to produce vaporous conversion products and carbonaceous residue which is deposited on said coke particles becoming a part thereof, recovering overhead said vaporous conversion products, circulating a portion of said coke particles to an external combustion zone, partially burning coke particles in said combustion zone to raise the temperature thereof to 400 F. above said coking temperature, returning heated coke particles from said combustion zone to said coking zone to maintain said coking temperature, circulating another portion of said coke particle to a grinding zone, maintaining a fluid grinding bed of coke particles therein, injecting an attrition gas as a plurality of supersonic velocity gas jets in opposed relationship therein thereby comminuting an appreciable portion of the particles in said fluid grinding bed, withdrawing spent gases overhead from said grinding zone and recovering entrained solids therefrom, circulating the entrained solids so recovered and a portion of said fluid grinding bed to the disperse phase of a disperse phase elutriation zone, introducing an elutriation gas into the lower portion of said elutriation zone in amounts sufiicient to entrain relatively fine coke particles of boiler fuel size While permitting coarser particles to fall, maintaining a fluid elutriation bed of relatively coarse coke particles in the lower portion of said elutriation zone, withdrawing elutriation gases carrying entrained solids overhead from said elutriation zone, recovering therefrom a fine coke product, recycling 2. portion of said fluid elutriation bed to said grinding Zone for further comminuting, and circulating a portion of said fluid grinding bed to said coking zone to supply requiste seed coke thereto.

2. The process of claim 1 wherein said attrition gas comprises steam and the steam is superheated by indirect heat exchange in said external combustion zone.

3. Apparatus for comminuting and classifying particulate fluid coke which comprises, in combination, a grinding vessel having an upper portion of enlarged crosssectional area, said enlarged upper portion having a cross-sectional area 1.2 to 4.0 times as great as the lower portion of said vessel, a fluid bed of particulate coke therein extending into said upper portion, a plurality of high velocity gas jet nozzles extending through said grinding, vessel in the lower portion thereof in horizontal opposed relation, means for withdrawing spent gases from said grinding vessel and for recovering entrained solids therefrom, a vertically disposed disperse phase elutriation vessel, a fluid bed of relatively coarse coke particles in the lower portion thereof, means for admitting an elutriation gas into said last mentioned fluid bed, means for removing gases overhead from said elutriation vessel and for recovering elutriated solids therefrom, a staudpipe and riser conduit system for conveying solids from said grinding vessel and introducing said solids into the dis perse phase of said elutriation zone, and another standpipe and riser conduit system for conveying relatively coarse solids from the lower portion of said elutriation zone to said grinding zone.

4. The apparatus of claim 3 comprising in addition thereto a second vertically disposed disperse phase elutria tion vessel, means for transferring coarse solids from said last mentioned fluid bed to said second elutriation vessel, means for admitting elutriation gas to the lower portion thereof and for removing gases with entrained solid from the upper portion thereof as an intermediate size product, and means for conveying solids from the lower portion of said second elutriation vessel to said grinding vessel.

5. The apparatus of claim 3 wherein said elutriation vessel has an elongated narrow lower portion above diameters in length, an enlarged upper portion into which the solids from said grinding vessel are introduced, and conduit means for recycling solids recovered from said overhead gases to the upper portion of said elutriation vessel.

6. A process of comminuting particulate solids which comprises the steps of maintaining a fluid bed of particulate solids in a grinding zone, introducing charge solids averaging in size from 75' to 250 microns into said fluid bed, injecting a plurality of attrition gas streams at supersonic velocity into said fluid bed thereby reducingin size said particulate solids, removing spent gases overhead from said fluid bed and recovering entrained solids therefrom, withdrawing and introducing a portion of said bed and the entrained solids so recovered into the disperse phase of a disperse phase elutriation zone, the average size of the solids introduced into said disperse zone ranging between and 150 microns flowing an elutriation gas upwardly through said zone at a velocity sufiicient to entrain relatively fine particles While permitting relatively coarse particles to fall, forming a second fluid bed in the lower portion of said elutriation zone, withdrawing overhead from said elutriation zone fine product solids less than microns in diameter, and recycling relatively coarse solids averaging about 75 to microns in size from said second bed to said grinding zone for further treatment.

7. The process of claim 6 wherein said disperse phase elutriation zone comprises two elutriation stages in series and. solids of intermediate size are withdrawn as product between stages.

8. The process of claim 6 wherein the upper portion of said elutriation zone is of enlarged cross-sectional area, wherein additional amounts of elutriation gases are downwardly injected into the disperse phase of the narrow lower portion, wherein said solids are upwardly injected into said upper portion and where a portion of said fine product solids is recycled to said disperse phase.

References Cited in the file of this patent UNITED STATES PATENTS Stephanofr Apr. 24, 1951

Claims (2)

1. AN IMPROVED HYDROCARBON OIL FLUID COKING PROCESS WHICH COMPRISES CONVERTING AN OIL IN A COKING ZONE BY CONTACT WITH A FLUID COKING BED OF COKE PARTICLES MAINTAINED AT A COKING TEMPERATURE TO PRODUCE VAPOROUS CONVERSION PRODUCTS AND CARBONACEOUS RESIDUE WHICH IS DEPOSITED ON SAID COKE PARTICLES BECOMING A PART THEREOF, RECOVERING OVERHEAD SAID VAPOROUS CONVERSION PRODUCTS, CIRCULATING A PORTION OF SAID COKE PARTICLES TO AN EXTERNAL COMBUSTION ZONE, PARTIALLY BURNING COKE PARTICLES IN SAID COMBUSTION ZONE TO RAISE THE TEMPEATURE THEREOF 100* TO 400*F. ABOVE SAID COKING TEMPERATURE, RETURNING HEATED COKE PARTICLES FROM SAID COMBUSTION ZONE TO SAID COKING ZONE TO MAINTAIN SAID COKING TEMPERATURE, CIRCULATING ANOTHER PORTION OF SAID COKE PARTICLES TO A GRINDING ZONE, MAINTAINING A FLUID GRINDING BED OF COKE PARTICLES THEREINL INJECTING AN ATTRITION GAS AS A PLURALITY OF SUPERSONIC VELOCITY GAS JETS IN OPPOSED RELATIONSHIP THEREIN THEREBY COMMINUTING AN APPRECIABLE PORTION OF THE PARTICLES IN SAID FLUID GRINDING BED, WITHDRAWING SPENT GASES OVERHEAD FROM SAID GRINDING ZONE AND RECOVERING ENTRAINED SOLIDS THEREFROM, CIRCULATING THE ENTRAINED SOLIDS SO RECOVERED AND A PORTION OF SAID FLUID GRINDING BED TO THE DISPERSE PHASE OF A DISPERSE PHASE ELUTRIATION ZONE, INTRODUCING AN ELUTRIATION GAS INTO THE LOWER PORTION OF SAID ELUTRIATION ZONE IN AMOUNTS SUFFICIENT TO ENTRAIN RELATIVELY FINE COKE PARTICLES OF BOILER FUEL SIZE WHILE PERMITTING COARSER PARTICLES TO FALL, MAINTAINING A FLUID ELUTRIATION BED OF RELATIVELY COARSE COKE PARTICLES IN THE LOWER PORTION OF SAID ELUTRIATION ZONE, WITHDRAWING ELUTRIATION GASES CARRYING ENTRAINED SOLIDS OVERHEAD FROM SAID ELUTRIATION ZONE, RECOVERING THEREFROM A FINE COKE PRODUCT, RECYCLING A PORTION OF SAID FLUID ELUTRICATION BED TO SAID GRINDING ZOND FOR FURTHER COMMINUTING, AND CIRCULATING A PORTION OF SAID FLUID GRINDING BED TO SAID COKING ZONE TO SUPPLY REQUISITE SEED COKE THERETO.

3. APPARATUS FOR COMMINUTING AND CLASSIFYING PARTICULATE FLUID COKE WHICH COMPRISES, IN COMBINATION, A GRINDING VESSEL HAVING AN UPPER PORTION OF ENLARGED CROSSSECTIONAL AREA, SAID ENLARGED UPPER PORTION HAVING A CROSS-SECTION AREA 1.2 TO 4.0 TIMES AS GREAT AS THE LOWER PORTION OF SAID VESSEL, A FLUID BED OF PARTICULATE COKE THEREIN EXTENDING INTO SAID UPPER PORTION, A PLURALITY OF HIGH VELOCITY GAS JET NOZZLES EXTENDING THROUGH SAID GRINDING VESSEL IN THE LOWER PORTION THEREOF IN HORIZONTAL OPPOSED RELATION, MEANS FOR WITHDRAWING SPENT GASES FROM SAID GRINDING VESSEL AND FOR RECOVERING ENTRAINED SOLIDS THEREFROM, A VERTICALLY DISPOSED DISPERSED PHASE ELUTRIATION VESSEL, A FLUID BED OF RELATIVELY COARSE COKE PARTICLES IN THE LOWER PORTION THEREOF, MEANS FOR ADMITTING AN ELUTRIATION GAS INTO SAID LAST MENTIONED FLUID BED, MEANS FOR REMOVING GASES OVERHEAD FROM SAID ELUTRIATION VESSEL AND FOR RECOVERING ELUTRIATED SOLIDS THEREFROM, A STANDPIPE AND RISER CONDUIT SYSTEM FOR CONVEYING SOLIDS FROM SAID GRINDING VESSEL AND INTRODUCING SAID SOLIDS INTO THE DISPERSE PHASE OF SAID ELUTRIATION ZONE, AND ANOTHER STANDPIPE AND RISER CONDUIT SYSTEM FOR CONVEYING RELATIVELY COARSE SOLIDS FROM THE LOWER PORTION OF SAID ELUTRIATION ZONE TO SAID GRINDING ZONE.

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