US2734852A

US2734852A - moser

Info

Publication number: US2734852A
Authority: US
Publication date: 1956-02-14
Anticipated expiration: 1973-02-14

Description

Feb. 14, 1956 J. F. MOSER, JR

ELUTRIATING-BURNER IN FLUID COKING PROCESSES Filed Sept. 27. 1954 f LIGHT GASES FLU E GASES NET COKE PRODUCT AIR CONVEYING GAS VACUUM RESIDUUM u NAPHTHA U HEATlNG U OILS "7 I GAS OILS Inventor: John F. Moser Jr. By K a I Attorney United States Patent ELUTRIATINGPBURNER IN COKING PROCESSES John F. Moser, Jr., Baton Rouge,.La., assignor toEsso Research-and Engineering Company, .acorporation of Delaware- Application September-27, 1954,,Serial-No. 458,370' 5 (Elaims. (Cl. 201-144) This; invention relatesto a, process for treating hydro: carbons and more particularly'relates to the coking of heavy residual oils to produce lower boiling hydrocarbons and coke. More particularly, the present invention pertains to an improved hydrocarbon oil. fluid coking processwherein seed coke is conserved through the use of anelutriator-burner of special design.

The hydrocarbon oil which is to be coked according to the present process is preferably a-high boiling hydrocarbon oil which cannot be vaporized at ordinarypressures without cracking the high boiling constituents; The residual oil may be that produced by distilling crude petroleumoil at ordinary atmospheric pressure or-under subatmospheric pressure such as vacuum distillation. Broadly, however, the presentprocess may also be used for pyrolytieallyupgrading or coking charging; stocks comprising shale oils, synthetic oils, pitches, tars, coal "tars, asphalts, cycle stocks, extracts, whole crudes, distillate or residual fractions therefrom, or mixtures thereof.-

Processes are known in the prior art for cracking'orcoking residual oils in the presence of finely divided catalytically inert or substantially cat-alytically inert solids maintained as a fluidized bed.

In the present process, a dense fluidized bed' of finely divided catalytically inert refractory solids such'as sand,

metal beds, ete., but especially particulate coke produced:

by theprocess, is used and the preheated residual oil is introduced into the dense fluidizedbed of the finely divided solids maintained at a coking temperature; Vaporous products of cokingare taken overheadand further treated as desired to recover lower boiling hydrocarbon fractions. During the. coking, coke is formed and deposited on the fluidized solids. A'net coke product of improved properties is withdrawn from the process to maintain the weight. inventory of the solids constant. Coke particles from the.

coking zone or reactor are stripped'toremove volatile hy drocarbons therefrom and are passed to an. elutriator burner of special, design wherein they are preferablymain:

tained in a fluidized condition and. contacted with air OI other oxygen-containing gas to. burn some of the coke.- particlesand to heat .thecoke particles. The heated coke. partielesare then returned to the coking zone .to supplyheat thereto. The net coke product of the process is with drawnvfrom the elutriatonburner andpreferentially comprises relatively coarse coke. This coke-product has improved. properties because .01? an oxidation treatment as.

will-more clearly appear hereinafter.

O e the Problems in the-fluid cokingp esidu l r other heavyoil feeds is the control of the particle size of the coke particles in the circulatingcoke-stream. The most desirable particle size range for cireulation in the system is that from about ,40 to400 microns, although some of it, may be of a size up to 1000 microns. or so;., There is a gradual increase in size of the particles beingeirculated because coke is made from the oil teed and de posited'unifomily on the particles regardlessof size. As. the circulating coke particles become coarser, fluidization 2,734,852 Eatented Feb. 14,- 1956 2-. becomespoor, eirculationbecomes more erratic and contacting 'efii'ciencydecreases.

It has been'found that the amount of coke produced by a fluid coking system is related to the Conradson carbon of the feed For feed stocks ranging-from about 5 to 30 weight. percent 'Conradson carbon, e. g-., 20 weight percent, about 6 to 34 weight percent, e. 2 2 weight percent, based*onfeed, ofcok'ewill be producedand; anywhere from 0 to of this will be burnt'to supply heat, the remainder being withdrawn as product. Notmally-about 7%' coke-on feed or-theequivalentmust be burnt to supply heat. Of the coke in the system, about 0.05 to 0.5"lbs;/lb. of lfeed, e: g 0.2 lbs;/lb., has to be reduced in size in some manner to form seed coke in order to maintain the size and size'dis'tribution of 'the coke particles in. the system substantially constant.

As the weightrate'ofcokecombustion is a function primarily of surface area, the above condition of particle size accretion is aggravated bythe combustion step in the burner because the small coke particles, Weight torweight, have a relativelylargersurface than the larger particles andwill therefore, be preferentially burntby the. free oxygen-eontaininggas in the-"burner. It is desirable in order to conserve growth nuclei of the proper size to remove coke particles coarserthan the pre terredsize range as netproduct coke; and the sarnetoh'en it would be most desirable-if the-bulk'ofthe heat released for the cokingprocess by-coke combustion were obtained from this undesirable coarse particle, sizerange.

Previous cokingprocesses, irrorder to maintain the weight'inventory, numerical inventory, and size distrihu tion of the particulate coke relatively constant have required withdrawing coarse coke particles from the unit, grinding them and returning the ground particles to the unit as seed coke or'growth nuclei. Ihepresent invention a y d c o e minat e nece ty o uch grinding of withdrawn coarse cokepartieles to produce seed coke.

I y of 'e' osarb n il fluid o inspros s e p i y pr p s d; i as een a ma y to e t a o t rw s cl s fy he mat ri l w thdrawn s e oke Product This ons e he growth uclei n he-syst m and decreasesconsiderably the coke o i most o t es hemes, an ex ran us elu i tns ga a 'be n requi e o acc mpli is c a ifi t o an is results in a onsi e abl nd need ess xpenselso. a he part cu at flu i o pr duc y a hyd ocarbon. oil fluidcoking, process isextremely hard and smooth, there has existeda need {on-an inexpensive and pra cal ethod for impro n it P op In gh f he. above. a pr me 'o iect (t the-Present invention is to present to the art an improvedhydrocarbon oil fluid coking Process. A more particular objfict is to devise a vfluid coking process wherein provision: is made for the withdrawal of .thenet lcoke product of the process preferentially s relatively coarse material without the use of extraneous elutriating gases.= Another object of thisinventionis. to-devise an elutriatorrcombustion vessel for supplying heated coke to hydrocarbon oil fluid duces greatly or eliminates the necessity of supplying seedcoke .orgrowth melerto; said process.

According-to the present invention; the/burner used to gen at he o h Pyrolysis s segmented to con ain n ut nz ne. The p icul te coke from he fl id co er t be rehea d is in oduse intohis elu iati n zone. the con eyin gas ed er nspo tthe coke to the burner-elutriator being used to' augment e mmi u i n costs- 2:73 m A A the elutriating gas. A free oxygen-containing gas, e. g., air, is admitted to the base of the elutriating zone and serves to preferentially burn coarse coke particles therein. The gaseous products of combustion then serve to elutriate fines from the mass of coke contained in the elutriation zone. The size of some of the coarse particles is decreased during this burning by burning or spalling into smaller coke particles which are then carried by the upflowing gas into the upper portion of the burner zone and are not consumed further. These smaller coke particles then act as seed coke in the process and also improve fluidization characterization and mobility of the circulating stream of coke particles. The net coke product of the coking process is removed from the lower portion of the elutriation zone and comprises relatively coarse coke.

In a preferred embodiment of the invention, as much combustion as possible is accomplished in the elutriation zone consistent with suitable elutriating gas velocities. By consuming over 3 weight percent of the coke particles removed as product from the base of the elutriation zone, the properties of the coke are greatly improved, particularly the friability, density, surface area, and hydrodesulfurization characteristics of the coke. The heat released in the combustion is recovered from the elutriated fines and the combustion gases in the main fluid bed of the burner-elutriator. Sufficient additional burning is accomplished in the main fluid bed of the elutriator-burner to maintain the temperature of the reheated coke particles 100 to 300 F. or more above the coking temperature.

This preferential burning of the coarse particles greatly increases their friability and, consequently, the natural attrition occurring between the fluidized particles in the elutriation zone accounts for a substantial production of fines or seed coke particles. This attriting efliect can be increased by introducing the elutriating gas into the zone as high velocity jets.

The attached drawing, forming a part of this specification, depicts one form of apparatus and mode of operation thereof adapted for carrying out the present invention but this showing is for purposes of illustration only and the invention is not to be restricted thereto.

Referring now to the drawing, the reference character designates a reactor or coking zone combined with a superposed product quench and fractionization system. The coking zone contains a fluidized dense bed 12 of finely divided inert particles, preferably particulate coke. The dense bed 12 has a level indicated at 14 with dilute or disperse phase thereabove. The inert solids of the fluidized bed 12 have a particle size between about and 1000 microns, preferably between about and 400 microns. The fluidized bed 12 is maintained at a temperature between about 850 and 1600 F., preferably about 900 to 1100 F.

When coking to produce gas oils for catalytic cracking, temperatures in the lower range of about 850 to about 1050 P. will be used; when coking to produce motor fuels and heating oil the coking temperature will be about 1050 to 1200 F., and when coking at extremely high temperatures to produce chemicals such as unsaturated hydrocarbon gases and aromatic hydrocarbons. temperatures in the higher range of about 1200 F. to about 1600 F., preferably about l250 to 1450" F., will be used.

The preheated oil feed to be converted is introduced directly into the dense fluidized highly turbulent bed 12 in the reactor at a plurality of points via line 1. The oil feed is preferably preheated in any suitable manner as by heat exchange with product streams, etc., to a temperature between about 600 and 800 F. before being introduced into the reactor 10. The oil feed comprises. preferably, a residual petroleum oil such as tar, pitch, crude residuum, heavy bottoms or other similar hydrocarbon stocks having an API gravity between about -10 and 20, a Conradson carbon between about 5 and cooled and refluxed through the tower.

the naphtha product may be cooled in heat exchanger weight percent and an initial boiling point between about 850 and 1200 F. Steam or other substantially inert gas may be introduced at one or more points 24 to strip the coke of adhering hydrocarbons before it is circulated to be reheated and to assist in maintaining the bed in a fluidized condition. the invention, a portion of the product naphtha is recycled to the coking vessel via line 2. This naphtha vaporizes readily and supplies fiuidizing gas to the coker, thereby reducing steam requirements, and the naphtha is advantageously reformed.

The fluidized bed 12 is maintained as such by the upflowing hydrocarbon gases and vapors formed by the coking of the oil feed and by the steam added to the process. The superficial velocity of the gases and vapors. passing upwardly through the bed 12 is between about 0.5 and 4 ft./sec. when using finely divided coke of about 40 to 400 microns, and at a superficial velocity of about 1 to 2 feet per second, the density of the fluidized bed will be about 40 lbs. per cu. ft. but may vary between about 15 and 60 lbs. per cu. ft. depending on the gas velocity selected and the particular particle size range.

Vaporous products of coking leave the bed 12 and pass overhead through a cyclone system 28 arranged at the top interior of the reactor 10. The Vaporous reaction products leaving the coking zone contain entrained solids and the cyclone 28 or other gas-solids separating device is used to separate or recover the entrained solids and return them to the dense fluidized bed through dipleg 32. More than one cyclone in stages may be used and the cyclone may be arranged externally of the reactor 10. The vapors continue upwardly into the combination tower wherein they are initially quenched to a temperature in the range of 600 to 900 F. by a cool reflux stream. This quenching removes the heavy ends containing catalyst contaminants and refractory constituents from the coker efiluent. These heavy ends are withdrawn by line 16 as product. A portion of these ends is recycled byline 17 for further treatment and another portion is cooled by a heat exchanger 18 and returned to the tower by line 19 to serve as a quench medium. The vapors continue upwardly through the tower wherein intermediate boiling range fractions are condensed. Thus, gas oils are removed by liue 20, heating oils by line 21 and naphthas by line 22. The remaining uncondensed light gases are removed from the tower by line 23. To effect staged heat removal, portions of the product streams may be Thus, some of 25 and recycled by line 26.

A preferred mode of operation is to recycle a major portion of the naphtha product to the coker via line27. This recycled naphtha may be suitably reheated as by heat exchange with the heavy ends in heat exchanger 18. By recycling the naphtha, it is thermally reformed in the coking zone and its octane number is substantially in creased with no appreciable increase in total unsaturation or appreciable decrease in yield of the naphtha. It is known that vapor phase thermal reforming of the coker naphtha substantially decreases its aniline point, thus improving its octane. However, the bromine number of the naphtha remains substantially constant which indicates that there is no appreciable increase in unsaturation. As

dense bed 12 into stripping zone or vessel 36 which is In a preferred embodiment of shown as havinga smaller diameterthan reactor 'and whichex-tends down from reactor-10'as anintegralstructure. Otherformsof strippers may be used. Steam or other stripping gas is introduced through line or lines 24 into the bottom portion of the stripping zone 36 to remove volatile hydrocarbons from the coke in the stripping zone and then pass upwardly into the dense fluidized bed 12 -in-reactor 10. The temperature in the stripping zone is between about-800 and 1600- F; and the velocity of the upflowing gas in the stripper may be between about 0.4 and 3.0-feet per second to maintain a dense fluidized mixture; Baflles can be placed in the stripping zone to increase the contact efliciency.

Stripped coke particles are removed from the bottom ofthe stripper through line 3 to which conveying gas is added through one or more lines 4 as is known by the art. This conveying gas will amount toabout .05 to 0.2 cu; ft. (atthe conditions of-the conduit) per lb. of coke circulated; This conveying gas subsequently serves as elutn'ating gas 'inthe burner-elutriator.

According to one methodof operation of the present invention and in order to reduce or remove the coarse coke particles in the circulating stream which are formed by successive layers or deposits of coke on the particles during the coking process, the coke particles in line 3 are passed to the upper portion of an elutriation zone 5 in anelutriator-burner 6 of special design. As above pointed'ounthe coke particles increase in, size because of the formation and deposition of more cokejon the coke particles than is consumed to supply heat to the proc-- ess and coarse particles having a particle size bigger than about 500 to 1000 microns must be removed or somehow reduced in size if they are to remain in the unit. According to the present invention, coarse particles are segregated and burnt to make smaller particles within the desired range of 40 to 400 microns, and to obtain relaitively'coarse product coke of improved properties.

As illustrated-the elutriator-burner is segmented by vertical baffle 37to contain an'elutriation zone and a combustion zone. The upper portion of the zone formed by the bathe in this example is of reduced cross-sectional area to increase the efiiciency of separation and to reduce elutriation gas requirements, although in some cases. it may have the same area as the lower portion. The upper portions of the elutriation and combustion zones. are in fluid communication with a commonsolids gas disengag-.

ing space and contain in their lower portions fluidized beds of coke. A free oxygen-containing gas .is admitted to each of the zones by lines 7 and 9 to maintain thefluidity of the beds therein and. to burn the solids.

The relatively cool coke circulating from the coker via line 3 is admitted to the upper portion of the elutriation zone. zone alongwith the conveying gas elutriate the finer portions of the circulated coke overhead into the solids gas disengaging space. Additional elutriating. gas, e. g., steam, can be admitted to the elutriation zone by line 13; The coarser fractions of the coke amounting to about 1 to 10 weight percent. of the cokecirculated 'from the coker settle downwardly into the fluid bed in the elutriation zone. This coarser coke contacts the air admitted to the zone and is preferentially burnt, consuming the oxygen in the air. The net coke product of the process is removed from the lower portion of this zone byline 29. Thisproduct coke may be suitably quenched or otherwise cooled before it is sent to storage.

The air introduced to the combustion zone by line 9 is regulated either in quantity or quality so' as to. burn a sufficient amount of coke to supply the remaining,

amount of heat necessary to the coking process not generated in the elutriation zone. Normally, about 80 to 95 percent oftheheat required for the pyrolysis will be generated in the combustion zone. In cases where it is desired to maximize the net coke product produced by the cokingproccss, extraneous liquid gases orsolids fuels may Ascending combustion gases from the base of the- 6 be admitted'to the combustionzone byline Band-pretenentia-l-lyburnt therein.- The -velocityofthe ascending gases in the combustion-zone-are maintained vvithin the range ofl to 4'fti/ sec.

The combustion gases or flue-gasesemerge from the fluidized beds and pass through-cyclone system 30 01: other solids separating device wherein; entrained solids are removedand returned to the bed by dipleg 31. These flue gases are then vented'to the atmosphere-byline 33. Before venting, the heatcontentof the gases maybe suit; ably extracted as -by heat exchange with-feed streams to the process.

Reheated coke at at-temperature of to 3t l( )-'F above the coking temperature overflows into standpipe34 and is circulated to the eoking-vessel-10.-

Air or other oxygen-containing gas is introduced through line 7-into the bottom-pertion'of the elutriating consumed and disappear rapidly and very little-oxygen containing gas will-reach the upper levelsof the elutriatorburner where the fine particles are present; Most ofthe oxygen will be consumed in the first few feet of travel, e. g., 1 to 10 feet, through-the coke bed-inthe -zone in cases where the temperature is between about 1000 and 1700" F.

It is preferred to introduce this oxidizing air into the elu'triation zone as high velocity jets to causesattrition. among the particles, e. g., at velocities in therangetof 500 to.3000 ft./se c. The oxidizing gas is, preferably, airbut. other free oxygen-containing gases may be used such as air-steam mixtures, oxygen-enriched flne gases, oxygenenrichcd air, etc.

In the elutriating zone 5, the superficial velocity of the gases including conveying gas. from, line 3 flowing up through zone 5 "is selected to be between about 2:0 and 20 ft./sec. so that middle-sized coke ,particles of about 75 to 400 microns are preferentially clutriated overhead without substantial combustion. of thesepar-ticles. The

du d in siz an become fin nough to be movcdupintn:

h lu ph se oftheelutriator-bumer. forrecycle .tothc. coking zone. During burning, some of the oarse coke spall, attrite or otherwise break down into smaller pieces.

Because the amount: of coke circulated -from -the fluid coker to the elutriating zone will be in excess of -that removed as net product coke and that elutriated an over-flow aperture 38 .is provided- 'inthewall: partitioningthe primary combustion zone from theelutriationzone- The excess fluidized coke in the elutriating zone which-is not elutriated overhead passes through this opening.

It. is preferred -to admit a sufficient amount of air through line 7 so that at least l fweight'percenhpreferably 3 to 5 weight percent. of: the coke'partic'les removedas product byline '7 is consumed. This controlled-oxidation greatly .improvestheproperties of th'e product coke. surface area, real: density, and

fited. This extent of oxidation is to be compared 'tonormal coking operations wherein only about -0.'3'=-to 1% of the coke .;is :burned per pass. Such a situation obtains when about 5 weight percent coke based on fresh. -fc'ed is burned in the burner and-=a coke/oil-cireulatiomratio 'offrom 5 to 15 isemployed;

As a specific example, about=23,000 barrels per'dayof' residual oil 'having'an API gravit-y'of; '45 and a-Cpnrad' son'carbon -of- 24"weig'ht percentand an initial "boiling point of about 1000 F., and about 13,000 lbs. per hour of steam are added to thedense bed 12 in reactor 10. In this example, naphtha is not recycled to the coker. The oil feed is preheated to about 600 F. The solids to feed oil ratio by weight to the reactor is about 8 to l. The temperature in the reactor is about 950 F., in the elutriating zone is about 975 F., and in the combustion zone 11 is about 1150 F. About 35,000 s. c. f./min. of air is admitted to the combustion zone by line 9, and about 5,000 5. c. f./min. is admitted to the elutriating zone by line 7. About 2300 s. c. f./rnin. of steam is admitted to line 3 by line 4 and 4,600 5. c. f./min. of additional elutriating steam is admitted to the elutriating zone by line 13.

The circulating solid is coke formed in the process having a particle size of about 50 to 800 microns with the majority of the particles being between about 150 and 300 microns. The superficial velocity of the gas in the reactor is about 1 ft./sec. and the density of the dense fluidized bed 12 is about 40 lbs./ cu. ft. The superficial velocity of the gas in the burner 6 is about 3 ft./sec. and the density of the dense fluidized bed 11 is about 35 lbs./ cu. ft.

The overhead products leaving cyclone separator 28 are at a temperature of about 950 F. and are quenched to a temperature of about 800 F.

The yields obtained as percent of fresh feed are as follows:

C3 weight percent" 9.9 C4 volurne percent 3.6 C5430 F do 20.5 430-1050 F do.. 51.1 Gross coke -weight percent 27.0

NOTE.ThB 1050" F.+ material is recycled to extinction.

The gross coke made is 87,500 lbs./ hr. of which 69,900 lbs. are removed as net coke product. The size distribution of the circulating coke and of the coke products is as follows:

Weight percent on given mesh 1 By screen analysis.

With the present invention it is possible in many cases to maintain the proper size of coke particles in the circulating coke stream without the necessity of withdrawing coarse coke particles, grinding them and then returning the ground particles to the circulating coke stream.

From this description it will be readily apparent that the present invention provides for an improved hydrocarbon oil fluid coking process wherein a burneoelutriator vessel of special design permits the withdrawal of a relatively coarse coke product of improved properties and minimizes seed coke requirements of the coking process by selectively retaining coke of seed size within the system.

Having described the invention, what is sought to be protected by Letters Patent is succinctly set forth in the following claims.

What is claimed is:

1. An improved method of coking hydrocarbon oils including heavy residual petroleum oils which contain constituents unvaporizable at ordinary pressures without cracking, comprising contacting a hydrocarbon oil with a fluidized bed of finely divided coke in a coking zone maintained at a coking temperature above about 850 F. to produce lower boiling hydrocarbons while depositing coke on the fluidized particles, removing coke from said coking zone andrpassing it to an elutriation-combustion zone, segmented to contain an elutriation portion and a combustion portion containing fluidized solids, elutriating coke fines from said fluidized solids in said elutriation zone, fluidizing and combusting the remaining relatively coarse coke with a free oxygen-containing gas in said elutriation portion, withdrawing relatively coarse net coke product of improved properties from the lower end of said elutriation portion, overflowing excess coke particles from said elutriation portion into said combustion portion, combusting further amounts of the coke in said combustion zone to raise the temperature of the solids'therein to 300 F. above said coking temperature, returning solids from said combustion portion to said coking zone to supply heat thereto, and removing a stream of vapor ous reaction products overhead from saidcoking zone.

2. In a hydrocarbon oil fluid coking process wherein an oil is pyrolytically converted by contact with particulate solids maintained at a coking temperature in a coking zone, said oil depositing carbonaceous residue on said solids causing the solids to accretein size, wherein said solids are circulated to an external fluid combustion zone and back to maintain saidcoking temperature, and wherein solids are withdrawn from said process as net product to maintain the weight inventory of the solids substantially constant; a method for preferentially withdrawing said net product as relatively coarse material, which comprises segmenting said fluid combustion zone to obtain an elutriation zone, said elutriation zone containing fluidized solids in the lower portion and extending upwardiy into the solids disengaging space of said fluid combustion zone, introducing solids circulated from said coking zone into said elutriation zone, passing a free oxygen-containin gas upwardly through said elutriation zone, maintaining the velocity of ascending gases in said elutriation zone within the range of 2 to 20 ft./sec whereby relatively coarse solids gravitate to the lower portion of said elutriation zone, some of which are preferentially burnt by said gas, withdrawing said net product from the lower portion of said elutriation zone, and overflowing excess solids, not elutriated from or withdrawn said elutriation zone, into said combustion zone.

3. The method of claim 2 wherein the rate of flow, o

and the concentration of oxygen in said free oxygencontaining gas is maintained to obtain a burning of at least 3 weight percent of the solid particles withdrawn as product whereby a coke product of improved properties is obtained.

4. A method for supplying heated coke to a hydrocarbon oil fluid coking process and for selectively withdrawing relatively coarse coke from said process, comprising circulating relatively cool coke from said process to the elutriation portion of an elutriator-combustion zone containing an elutriation portion and a combustion portion, said portions being in fluid communication at their upper extremities with a common solids-gas disengaging space and containing fluidized coke particles, injecting an oxidizing gas into said portions to fluidize, burn and heat the coke therein, maintaining the velocity of the ascending gas in said elutriation portion to cause relatively coarse coke to settle in the lower portion thereof and to be preferentially burnt therein, withdrawing net coke product of said process from the lower end of said elutriation portion, overflowing excess coke from said elutriation portion to said combustion portion, and circulating coke from said combustion portion to said process to supply heat thereto.

5. The method of claim 4 wherein an extraneous fuel 7 is admitted to and burnt in said combustion portion whereby the net coke product of said process is increased.

References Cited in the file of this patent UNITED STATES PATENTS Matheson et al June 21, l955.-

Claims

1. AN IMPRVED METHD OF COKING HYDROCARBON OILS INCLUDING HEAVY RESIDUAL PETROLEUM OILS WHICH CONTAIN CONSTITUENTS UNVAPORIZABLE AT ORDINARY PRESSURES WITHOUT CRACKING, COMPRISING CONTACTING A HYDROCARBON OIL WITH A FLUIDIZED BED OF FINELY DIVIDED COKE IN A COKING ZONE MAINTAINED AT A COKING TEMPERATURE ABOVE ABOUT 850* F. TO PRODUCE LOWER BOILING HYDROCARBONS WHILE DEPOSITING COKE ON THE FLUIDIZED PARTICLES, REMOVING COKE FROM SAID COKING ZONE AND PASSING IT TO AN ELUTRIATION-COMBUSTION ZONE, SEGMENTED TO CONTAINING AN ELUTRIATION PORTION AND A COMBUSTION PORTION CONTAINING FLUIDIZED SOLIDS, ELUTRIATION COKE FINES FROM SAID FLUIDIZED SOLIDS IN SAID ELUTRATION ZONE, FLUIDIZING AND COMBUSTING AND REMAINING RELATIVELY COARSE COKE WITH A FREE OXYGEN-CONTAINING GAS IN SAID ELUTRIATION PORTION, WITHDRAWING RELATIVELY COARSE NET COKE PRODUCT OF IMPROVED PROPERTIES FROM THE LOWER END OF SAID ELUTRIATION PORTION, OVERFLOWING EXCESS COKE PARTICLES FROM SAID ELUTRIATION INTO SAID COMBUSTION PORTION COMBUSTING FURTHER AMOUNTS OF THE COKE IN SAID COMBUSTION ZONE TO RAISE THE TEMPERATURE OF THE SOLIDS THEREIN