US2719114A

US2719114A - Cracking and coking of heavy hydrocarbon oils in the presence of subdivided material

Info

Publication number: US2719114A
Application number: US146287A
Authority: US
Inventors: Frederick W Leffer
Original assignee: Universal Oil Products Co
Current assignee: Universal Oil Products Co
Priority date: 1950-02-25
Filing date: 1950-02-25
Publication date: 1955-09-27
Anticipated expiration: 1972-09-27

Description

Sept. 27, 1955 F W L EFFER 2,719,114

CRACKING AND COKNG 'OF HEAVY HYDROCARBON OILS IN THE PRESENCE OF SUBDIVIDED MATERIAL Filed Feb. 25, 1950 United States Patent O CRACKING AND COKING OF HEAVY HYDRO- CARBON OILS IN THE PRESENCE OF SUB- DIVIDED MATERIAL Frederick W. Leifer, Riverside, lll., assignor to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application February 25, 1950, Serial No. 146,287 8 Claims. (Cl. 19655)` This invention relates to an improved method and means for effecting the cracking and coking of hydrocarbon oils in the presence-of subdivided solid material, particularly coke, to produce more desirable lighter hydrocarbon fractions and net useable coke. More. particularly, the present improved process provides for the cracking and coking of heavy residual petroleum oils and tars in a manner utilizing a moving or fluidized bed of coke particles, with heat being supplied to the conversion zone by a continuous stream of heated particles and a highly heated distillate stream, which in turn is preferably a recycle stream recovered by fractionation of the vaporous products of the process.

Recent methods of converting and coking heavy petroleums in the presence of subdivided solid material have brought about considerable improvement over the more conventional methods of forming coke as a deposit on the wall of a chamber, however, there have been certain difficulties of economical and mechanical nature. For example, the method of contacting a material undergoing coking with a gaseous heat carrying medium of suflicient heat content to effect the coking reaction, re sults in the dilution of the vaporous conversion products by large amounts of gaseous material which in turn necessitate a fractionation system of elaborate design, or excessively large dimensions, for the recovery of normally liquid reaction products. Also, the supply of heat by hot gaseous combustion products which are generated within the coking zone itself, or in a cornbustion Zone communicating with the coking zone, gives rise to the contamination of the condensable conversion products by undesired oxygenated impurities. A coking method which relies on the supply of heat to a coking zone essentially by the introduction thereto of a highly heated coked particle stream, produces a tendency toward agglomeration of particles by the cementing action of unvaporized components of the heavy oil charge, with the result that heat fails to penetrate sufciently rapidly tothe core of such aggregates and the latter reach the point of discharge from the coking zone before they have become converted into a dry coke of sufficiently small particle size to permit an undisturbed continuous tlow of coke from one zone to another. Further, a coking method requiring a high temperature level for successful separation of the desired components and production of dry residual particles, such as coking at temperatures of the order of 1350 to l800 F., results in the decomposition of valuable hydrocarbon components which at lower temperatures would be recoverable as normally liquid products, but which at the higher temperatures are converted into excessively large yields of normally gaseous products.

It is a principal object of the present invention to obtain an improved net yield of valuable distillates from heavy hydrocarbon charge stocks and the production of distillates which are substantially free from oxygenated impurities, with heat being supplied-to a cracking and coking zone by means of a continuous stream of-.nely

divided heated coke particles and a high temperature distillate oil stream.

It is also an object of the present invention to provide a continuous cracking and coking operation for heavy residual hydrocarbon charge streams, with conversion carried out in the presence of finely divided coke particles and recycled distillate oil in order to provide more valuable distillates and net coke, such that fractionation is required of substantially only the vapor,- ous conversion products formed by the conversion re actions of the oil fractions.

`It is a further object of the present invention to carry out the cracking and coking of heavy charge streams in the presence of subdivided contact material in a manner which permits continuous withdrawal of freely 'flowing substantially asphalt-free or non-baking coke material from the conversion zone while continuously returning a stream of finely divided coke particles as nuclei for the formation of additional coke in the conversion zone.

It is a still further object of the improved operation of this invention to carry out a separation of coke particles within a heating zone adapted and arranged for effecting combustion and heating of at least a portion of the coked material in a iludized bed and under conditions which assure `a segregation of iine from coarse coke particles.v

In a broad aspect, the improved method of this invention for the conversion of a heavy normally liquid or readily fuseable hydrocarbonaceous charge such as heavy oils, reduced crudes, cracked residual oils, tars and the like, into more valuable lower boiling products'and coke in a Ycontinuous operation, comprises, maintaining a descending bed of coke particles in a cracking and coking zone, continuously supplying a stream of heated coke particles to the upper portion of the bed, continuously introducing a distillate oil stream at a temperature above the average bed temperature in the coking zone to the lower portion of the bed therein, introducing the heavy hydrocarbonaceous charge stream at a lower temperature than the average bed temperature in the coking zone into an elevated portion of the bed therein and effecting the conversion and coking of the charge stream upon its dispersion within the bed of coked particles, the 'conversion of the heavy charge stream and the production of a residue in the form of substantially asphalt-free coke particles being accomplished by the combined heating effects of the stream of heated particles being introduced into the upper portion of the bed and the high temperature distillate oil stream, continuously discharging vaporous conversion products from the coking Zone and passing them to a fractionating Zone, continuously withdrawing coke particles from the lower portion of the bed in the coking zone, and subsequently heating and returning at least a portion of the withdrawn coke particles as the stream of heated coke particles being passed to the upper portion of the bed.

In effecting this type of coking operation, some of the coke newly formed within the coking zone is deposited as a layer of additional coke on coke nuclei which are present in the bed, while at the same time new coke nuclei or particles may be formed, In an ideal operation, a

complete segregation of the coke being withdrawn from the coking Zone to provide fine and coarse particles is desirable, so that only the tine particles may be returned to the coking zone as nuclei for the production of coarser particles, and the coarse particles may be discharged as net coke production from the system. An exacting separation of tine from coarse particles, however, would require auxiliary operating steps which would impair the economy of the operation. Therefore, from a practical standpoint, effecting a rough separation of coke into a portion having a relatively high content of fine particles and a portion having a lower content of fine particles is preferred, as carried out by the present operation. The rough separation is readily accomplished with the aid of a fluidized bed type of contact operation wherein the linear velocity of the fluidizing medium passing through the bed is regulated or controlled to bring about the desired separation by gravitational segregation. Also, it is particularly advantageous and desirable to effect simultaneously with the rough separation of particles, the hardening or devolatilization of the coke production, both for the fine particles being returned to the coking zone and the larger particles being withdrawn as net coke from the system. Accordingly, the present invention provides for discharging a coke stream from the conversion zone into a separate heating zone, therein heating the coke particles while they are maintained in a fluidized dense phase hed therein, and simultaneously separating the coke particles in this heating zone by gravitational segregation into a portion of largely coarse particles to be recovered as net coke production of the process and into a portion of largely liner coke particles to be introduced as the heated coke stream into the conversion zone.

In a particular embodiment of applying the gravitational segregation, the present improved method comprises, maintaining a descending bed of coke particles in a cracking and coking zone, supplying a stream of heated coke particles to the upper portion of the bed in the coking zone, introducing a heated distillate oil stream at a temperature above the average bed temperature into the lower portion of this bed, introducing a heavy hydrocarbon charge stream at a temperature below the average bed temperature into an elevated portion of the descending bed, effecting the cracking and coking of the heavy hydrocarbon charge and the production of residue in the form of substantially asphalt-free coke particles by the combined heating effects of the stream of heated coke particles and the high temperature distillate oil stream, continuously withdrawing vaporous products from the coking zone and separately therefrom discharging a stream of coke particles from the lower portion of the bed in the coking zone into a separate confined combustion zone, maintaining a uidized bed of coke particles in the combustion Zone and burning a portion of the coke in the uidized bed by passing free oxygen-containing gas upwardly therethrough, reducing the linear velocity of the upowing combustion gases in an elevated portion of the fluidized bed in the combustion zone, effecting thereby the settling of the relatively heavy and coarse particles within the elevated portion of the uidized bed of particles, withdrawing a particulated coke stream having a high proportion of relatively coarse particles at a low point of said elevated portion and discharging it from the combustion zone as net coke production of the process, disengaging the combustion gases upwardly from the uidized bed and discharging them from the combustion zone, and continuously withdrawing a stream of hot subdivided coke having a high proportion of relatively fine particles from the upper portion of the fluidized bed of the combustion zone and introducing the same as the stream of heated coke particles to the upper portion of the descending bed of particles in the cracking and coking zone.

In the operation of the coke heating step of the present process the oxygen-containing gas stream may be air in admixture with combustion gases or other relatively inert medium, preferably a portion of the hot combustion gases issuing from the combustion and heating zone, and the oxygen content of the stream is regulated to eliect the burning of such a portion of the coke as will supply the heat needed to effect the devolatilization or hardening of the coke particles and the heating of the tine particles which in turn are being returned to the coking zone to supply at least a portion of the heat for conversion of the heavy charge stream. Moreover, thc quantity and rate of liow of the fluidizing medium containing the oxygen or air stream, is regulated and controlled to provide the desired segregation of the particles within the upper portion of the combustion zone, as hereinbefore described.

The descending bed of coke particles within the cracking and coking zone may be maintained as a relatively compact moving bed, or in an alternative operation the bed of particles is fluidized in order to provide a complete and uniform contacting of the particles with the charge streams. When operating with a relatively compact descending bed, the heated distillate oil stream is supplied countercurrently upwardly through the descending bed of particles at a relatively moderate temperature and at a low rate of flow or velocity which does not fluidize the bed of particles. In the fluidized operation, the distillate oil stream is supplied at a relatively higher temperature and a higher rate of velocity, although, it is preferable not to effect violent uidization but to maintain a fairly quiescent tluidization of the coke in the contacting zone in order to assure a substantially countercurrent contact of the residue particles with the hot distillate oil stream. The iiuidized bed operation and the various modes of moving bed operations are not exactly equivalent and the choice between them depends on various factors, including particularly the coke-forming tendency and coke yield of the heavy hydrocarbon charge stream and the extent to which it is desired to effect the cracking of this stream and the distillate oil stream, as will become more apparent from the further description.

It is a particular feature of the invention to provide a selective cracking step which utilizes a clean distillate type of refractory oil, preferably in the form of reflux recycle from the fractionation stage of the process and preferably boiling below the heavy hydrocarbon charge. This distillate oil is heated to a substantially higher temperature than the heavy oil charge being introduced into the bed of particles within the coking zone, and preferably to a temperature substantially above the average temperature of the descending bed within this zone, and the heated light oil stream is passed upwardly countercurrently to the descending bed of particles. The heavy oil stream is supplied at a temperature at which the transfer line and distributing means for dispersing the heavy stream within the descending bed remains substantially clean and unobstructed from the formation of coke, While the ascending more highly heated recycle oil Stream precludes agglomeration of coke particles and aids in the coking of the heavy or asphalt-like oil portions being adsorbed on the descending coke particles. Thus, there is assured that only substantially dried or asphalt-free coke material reaches the bottom portion of the fluidized bed for subsequent withdrawal therefrom and transfer' to the combustion and heating zone. At the same time, the highly heated recycle undergoes a substantial amount of cracking upon being reheated and introduced into the coking and conversion zone.

It may also be seen that a particular advantage of the present operation accrues from the use of the highly heated distillate oil stream in that the tendency for temperature decrease of the solid particles as they descend in the coking bed is effectively counteracted by a heatcarrying medium which is compatible with, or of the same general chemical character as, thevaporous cracked products being formed from the heavy hydrocarbon charge during its initial contact with the continuous stream of heated finely divided coke particles being introduced to the upper portion of the bed in the coking zone. The highly heated distillate oil or recycle stream being introduced continuously to the lower portion of the bed thus permits to preclude contamination of the vaporous cracked products by substantial amounts of gases from an external source and/or by oxygenated products (such as would result from the generation of heat by partial combustion of carbonaceous or hydrocarbonaceous material in the coking zone) while it permits atthe same time fraterna@ Lto 4maintain' theJhighestf-temperature-^ level iin@V the flowest -portion of the' coke bed inthe cokingzone;l lthatf-isrtovsay in that-part-ofthe coking-'zoneinfwhich'it isfea'sible to rapidlyfconvert the `heaviest,unvaporizable components or cracked products `offthe` heavy hydrocarbon r charge into substantially asphalt-free lcoke f and vaporous prod- Auctswithout impairing the 1 distillate yyield obtained "by the initial `cracking ofi-thel heavy .hydrocarbon charge (normally at a 4somewhat 'lower temperature) in the .upper lportion of the-coke -'bed in 'they cracking land. coking zzone.

:Heat `is dissipated-.from theHdi-stillateoil or. recycle `stream duringhits :ascent-.infathe cokebedhastanresult of charge streamV inethe..upper=portion.'of thersamefbed while the resultant vaporous productsrobtained.inzthelowerbed .portion are either subjectedzto. further contactflwithimore elevated. portions of .fthercokekbedor are rwithdrawn from an intermediate'. leveltof1 the l:descending l.cokerbed fto the fractionation =step foflfthewprocess.

Thus, in onextypicalimode of. operation, :the vaporous products `of` 1the..distillate;foil .stream :afterzthey ahave attained a somewhatalower .temperature by-:the `passage through the lowerportion :ofthe descendingtcoke bed in the` conversion .zoneaas described'above,1may;he` passed upwardly through the remaining heightzof ithe .descending bed and comminglediftherein:withstheuheavy hydrocarbon charge.and/ortthe:crackediproducts=derivedfrom l the latter,zthereby permitting '.utiliza'tionofra further portion of the `heat .content ofthetxdistillatecoilistreamuin the cracking of 'the heavythydrocarbon. charge. 'i zrFurthermore, in this modeof operationhthe;upowingtvaporous products of the `distillateoilstream :may .be utilized in ymaintaining the descending :bediin a denseiluidized phase `while the heavy .'hydrocarhonicharge is ,introduced tat. a

substantial distance :belowthe upper-.level of` the ibed, and

i the; resultant commingled vaporousnproducts :formed lby the conversion ,of :bothuhe eheavyzrhydrocarbon .charge stream and the light distillatezoil` streamarerwithdrawn from the top portion of the cracking and coking zoneiat a point substantially above thefiuidized coke bedtherein. While this uidiz'ed dense phase bed operationmay be utilized in the conversionrof all ofthe heavyrhydrocarbon charging stocks contemplated herein, it is,:ap'plicablewith particular advantages ',:toz: the :conversion of-` heavy hydrocarbon charges having .a,\low;A. P. Legravityv and. a high average boiling point rand yielding lcopiousamounts ,of coke, that is to say, heavy oil fcharges havingfan-A. P. I. gravity of less-than 1-5,;.a..U.\-0. Pfcharacterization factor of less than i about 11.5 ;andI yielding ,coke lin-l an;amount of about 40 percent;or;-rnore .by weight-of the rheavy oil charge.

Alternative1y,`.thezftypical Vmode of operation just described may be modiedby operating it'with .a relatively compact moving bedpintrodueing the heavy hydrocarbon charge at a suitabledistance belowithe'top of the descending bed into this bed,.and-withdrawing.therresultant commingled vaporous `conversionnproducts fof fthe yheavy hydrocarbon charge and :distillate oil ,continuouslyfrom .the top portion ofthe crackingzand.cokingrzone, preferably at a point above the moving bed therein. "This .moving bed operation `rnayfbes-applied more :particularly-to the conversion of heavy 4hydrocarbon charges'v having an A. P. I. gravity within lthe approximate lrange offrom l2 to 22, a U. VO. P. characterization factor-offrom about l1` to yabout 11:8'and-yielding coke in an amount of from about 25 -to "about "40 percentby weight ofthe t heavy oil charge.

f1 In lbothnthefuidized -dense vphase bed :operation fand ifthe moving bedoperation as :described above, itzis to :be

understood that the point or level :of introduction of the @heavy hydrocarbon charge may be adjusted upwardly or lw-.downwardly, depending on whether a 'lesser or greater :extendof cracking of the components lof-this .charge .va-

`fporisable without substantial cracking is `desired,.and the @total height of the descending bed `is such that-the .dis-

y:tillate oil stream is allowed suicient time in they portion of-thedescending bed below the-level of introdnctionof Athe heavy hydrocarbon :charge to-assure.that.-only:dried or-.substantially asphalt-free coke reaches the Vcokeloutlet at l.the .bottom portonfof theconversionzone.

In another typical mode of operation, `.wherein the ...yaporous'products.of the distillate oil ystreamare `withf-drawn from an intermediate pointor-levelof-thedescend- .ing coke bed, the heated stream vof `coke particles vand vthe heavy hydrocarbon charge streamare both introduced .into the vtop portion of vthe conversionzoneandthe hydrocarbon charge stream is subjected tocracking .by `the .heat supplied in the .heated-coke particleestream .while this :hydrocarbon charge travels concurrently with the descending coke bed. The vaporous conversion products formed from Athe heavy hydrocarbon charge 4are Vwithdrawn froman intermediate point or level of the descending bed, preferably in commingledfstate-withthe vaporous products formed during the upward ,passageof the distillate oil stream through ,the lower `portion of -the -bed,

CAS

-and the distillate oil stream is introduced with asufti- ,cient heat content to the bottom portion of the.descend ing bed ,to assure the discharge from the latter 4of sub- .stantially asphalt-free coke particles. This kmode of operation is preferable for converting heavy hydrocarbon charging stocks of relatively high A. P I. gravity and relatively low coke yields, more particularly those Ahav- `ing.an AJP. I. gravity ofabout 19 or more and a U.O. P. characterization factor of about 11.8 or'higher and yielding coke in an amount of .less than about 25. percent by weight of the heavy hydrocarbon charge.

"The operation and further advantages of the improved `cracking and cokingprocess as vprovided-by this inven- -fportionof the combustion'chamber, as indicated by line 2-2 in Figure 1 of the drawing.

Figures 3 and 4 indicate alternative arrangements for the cracking and coking zone.

Referring now to Figures 1 and 2 of the drawing, there is indicated line 1 having control valve 2 and a pump 3 suitable to pass a'heavy oil charge stream to the lower portion of a fractionator 4. As hereinbefore noted, the charge stream may be a heavy residual petroleum such as reduced crude, topped crude, VBunker C fuel, or the like, lwhich does not ordinarily provide a good charging `stock to a catalytic cracking unit. By way of example, a -residual oil obtained from a thermal petroleum oil cracking operation and having an A. P. I. gravity of 8.6 and a U. O. P. characterization factor of 10.8 and yielding 50.5% by weight of hard coke, may be lcharged in-'this manner. A heavy combined feed stream is then withdrawn from the lower portion of the fractionator 4 by way of line 5, control valve 6, pump 7, andk through line"8 to a heating coil 9 within a suitable'heater 10, whereby the feed stream may be rapidly raised'to an elevated temperature of the order of 750 to 850 F., 4for example 780 F., in a manner as hereinbefore noted, to preclude coking in the transfer line and with'little or no cracking taking place in the heater. The-preheated streammay then be passed by way of line 11 and control l-valve 12 yto a suitable distributing means 13, which -in troduction of the preheated charge into a descending bed of subdivided coke particles passing continuously through the lower portion of the coking chamber.

In accordance with the embodiment of the improved operation of the invention preferred for the conversion of particularly heavy charging stocks, a iluidized bed of coke particles is maintained in a continuously descending manner through the coke chamber 14, with the upper extremity of the bed being indicated by the broken line 15, and the subdivided coke particles being introduced to the upper portion of the bed by way of a suitable transfer line 16 and control valve 17. A heated stream of the coked particles is passed through the line 16 from a suitable combustion and heating chamber 1S. Also, a heated distillate stream is introduced upwardly through the lower portion of the coking and conversion chamber 14 by way of line 19 and valve 20, in order to assure the discharge of substantially asphalt-free coke particles from the coking zone and to supply a vaporous fluidizing medium for the maintenance of the continuously descending tluidized bed of particles in that zone. Preferably, the distillate stream is a recycle stream of hydrocarbon oil which is recovered in the fractionation section of the conversion unit, as will be described hereinafter in more detail. The light distillate recycle stream may be supplied to the conversion chamber 14 at a temperature of the order of 950 to ll00 F., for example 1025J F., whereby to aid in supplying heat for conversion within the coking zone and maintain an average bed temperature therein of the order of 925965 F., for example 945 F. The heated coke particles being introduced to the upper portion of the bed may be supplied at a temperature of the order of 1000 F. to ll00 F., for

example l0l5 F. Thus, the entire reaction heat required for the conversion and coking is supplied to the coking zone through the two independent streams introduced, respectively, to the top portion and the bottom portion of the descending bed.

This method of heating is particularly advantageous. As the heavy charge stream is introduced into an elevated section of the descending bed, the high temperature coke particles continuously introduced to the upper portion of the descending bed raise the temperature of the heavy charge almost instantaneously to an effective coking temperature and at the same time furnish both the heat of vaporization for such portions of the heavy charge as reach the bed in the liquid phase and are vaporizable at the pressure and conversion temperature in the elevated portion of the bed and the heat of reaction for at least a substantial portion the cracking and coking occurring in the conversion zone. Thereby, the descending coke particles are rapidly cooled to the relatively moderate temperature which is desired for the production of high yields of distillates boiling lower than the charge, namely to a temperature in the approximate range of from 925 to 965 F. Upon further descent of the coke particles to the lower section of the conversion zone without further heat supply thereto, however, their heat content or temperature would be too low for securing complete conversion of residual components of the charge and intermediate conversion products into dry coke and vapors. imparting also this heat requirement to the heated coke particles to be introduced into the top portion of the descending bed would cause excessive cracking of the hydrocarbons in the upper bed section into copious proportions of normally gaseous products. Such a disadvantageous effect is avoided by imparting the heat requirement for the final coking to the lower section of the descending bed by the introduction thereto of the highly heated distillate oil or recycle stream which at the same time precludes agglomeration of those coke particles not yet substantially free from asphalt-like constituents and, moreover, in the particular operation described with reference to Figure l of the drawing, is supplied at a rate assuring the maintenance of the descending bed in the fluidized dense phase. Thus, the overall heat distribution within the coking and conversion zone is such as to permit the maintenance of a relatively low average bed temperature throughout the major portion of the descending or iluidized bed within the coking zone and a somewhat higher dry-distillation temperature in the lowermost portion of this zone whereby the formation of normally liquid cracked products without excessive decomposition into normally gaseous conversion products is favored and the dilution of the vaporous cracked products by substantial amounts of gases from extraneous sources is precluded.

The resulting contacted and newly formed coke material, reaching the lower end of the conversion chamber 14 is substantially asphalt-free state, is passed through an elongated stripping section 21 and standpipe 22 having control valve 23. Suitable high temperature stripping steam or other substantially inert gaseous stripping material, is introduced into the lower end of the stripping leg 21 by way of line 24 and valve 25 in order to countercurrently contact the descending particles and strip entrained vaporous hydrocarbons therefrom. An air stream is introduced by way of line 26, valve 27 and blower 28 to a riser line 29, which receives the coke particles from standpipe 22 and transfers them to the lower end of combustion chamber 18. Also, in accordance with the present invention, the air stream preferably contacts the coke particles in a luidized phase within the combustion and burning chamber 18, in a manner to effect elutriation of the particles and at least a rough separation or segregation into relatively fine and relatively heavy or coarse particle portions.

In accordance with the construction and arrangement of the combustion chamber of the present embodiment, illustrated in both Figures l and 2 of the drawing, the upper portion of chamber 18 is of enlarged diameter with baling means in an elevated portion thereof to provide for the separation of fine and coarse particle portions and separate withdrawal of these portions. An extended semi-cylindrical baille section 30 and a still higher semi-cylindrical baille section 31 together with partitioning plates or bailles 32, form semi-annular sections for the collection of particles within the enlarged upper portion of the chamber. The semi-annular section 33, adjacent the lower baille 30 provides a collecting well for thc reavier or coarser coke particles which will fall into that zone by virtue of the elutriating effect of the iluidizing and aerating stream contacting the coke within the chamber. The semi-annular section 34 adjacent the extended semi-cylindrical wall 31 provides means for collecting the ner or less coarse particles carried to the upper level of the lluidized bed in the combustion chamber i8 by Virtue of the controlled tluidization and separation operation within the combustion chamber 18. Suflicient air or oxygen is of course admitted to the riser line 29 and into the combustion chamber to effect the burning of a portion of the coke material, or coke deposition, to effect the desired heating of the particles which are returned to the cracking and coking chamber 14. Resulting combustion and ilue gases are removed from the upper portion of the chamber 18 by way of particle separator 3S and outlet line 36, while as indicated, the recovered lines from separator 35 are returned by way of a dip leg to the collecting well 34, in order that the tine particles may pass from the chamber with the roughly separated tinc particles by way of the transfer line 16 to the coking chamber 14.

Suitable stripping of the coke particles may of course be accomplished within each of the collecting

zones

33 and 34 respectively. Thus, steam or other suitable stripping medium may be introduced to the collecting zone 33 by way of line 37 and control valve 38, while steam or the like may be introduced to the collecting zone 34 by way of line 39 and control valve 40. As hereinbefore agr-19u44 Iperature which is above the average bed temperature of the coking zone, for example at about 1025" F.

The heavier coke particles that are collected within zone 33 of the combustion chamber, are withdrawn there- `-rom by way of line 41 and control valve 42, and subsequently introduced into a suitable quenching chamber 43 to lbe contacted by a suitable fluid cooling medium,

preferably an aqueous stream such as water or lowtemperature steam, so that the coke may be Withdrawn as Inet useable coke material. High temperature steamwhich is produced within the quenching chamber 43l-may be `passed by Way of'line 44 and control valve 45 to a particleseparator 46 which permits the discharge of substantially particle free steam by way of outlet line 47 and control valve v48, while recovered coke fines may be `returned to the cracking and coking chamber `14 by way of line-49 and control valve 50, or they may be returned from the separator 46, by means not shown in the `drawfing, tothe well 34. Water is indicated as being charged tothe lower end of the quenching tower 43 through line v51-and control'valve 52 in order to countercurrently con- Y tact the descending stream or bed of particles therein. An outlet line 53 and valve 54 provide means forwith- -`drawing coke slurry from the 'lower end of the tower 43. The amount of net coke which is produced in the fgiven operation willof course vary with the-type of heavy charge stream and the control of the operation within the cracking and coking chamber which results in the coke formation or deposition on nuclei particles. The elutril'ation within combustion chamber 18 is of course controlled and regulated to return vline-material to the coking zoneat a suicient rate to maintain a descending vor lluidized particle bed of substantially uniform depth -ffor contacting the heavy oil charge and electing the de- -=sired conversion.

It is also a feature of the present embodiment to utilize the hot lluegas stream,` passing byway of conduit 36 from combustion chamber 18,V to AsupplyL heat to the heat exchanger or heater 10, which in turn provides for the preheating of the charge streams to the cracking and conversion zone. The heater is indicated as having two cells, accommodating the heating coils 9 and 55 which in turn are provided for heating, respectively, the heavy oil and recycle distillate streams. The line gas from conduit 36 is indicated as being split into two paths through separate portions ofthe heater, .as provided by the control valve 56 and control valve 57 in line 58. Suitable outlet conduits 59 and 60 provide means for discharging the substantially cooled combustion gases from the heater 10 to a .suitable stack or to other heat exchange apparatus. An auxiliary burner 61 or other heat supplying means may of course be. connected with heater 10 in order4 to supply heat thereto, where llue gas heating is insufficient, or .for starting up purposes.

The resulting vaporous conversion products which pass through the upper portion of. the cracking and coking chamber 14 are withdrawn through a suitable particle separator 62 and subsequently passed by .way of line 63 and control valve 64 to the fractionating .chamber 4. Recovered coke particles from the separatory .62 .are vof `coursereturned to the luidized bed maintained. in the lower portion of `the contacting chamberby Way .of a suitable dip leg. The fractionatorf4 andthe entire lfractionating system indicated .diagrammaticallyfmay be` of conventional design .and is not limiting -to the present -improved cracking and coking operation. -A Iside cut stream is indicated as being withdrawn trom `the rin- -termediate portion `ofthe fractionator 4 by way of line 165 .and.control valve :66 and passed to `a 'suitable reflux accumulator 67. Uncondensed gases and vapors are lreturned frornthe vupperfportion of theaccumulator 67 by way of an .overhead 'liner68 and control valve 69,

while-a condensed distillate stream is Withdrawn from the `lowerportion of the accumulator 67 by way of line 470, vcontrol valve 71 and pump 72. This distillate stream is directed from pump' 72 by way of lline 73 to the heating coil'SS within heater 10, to pass as hereinbefore described tothelower end of the descending or lluidized .bed maintained within the cracking and coking chamber 14. Also it is noted, the distillate stream is preheated rto a high temperature above the average temperature -of the uidized-bed of particles in the conversion chamber. The highly heated recycle .distillate stream `will v undergo la substantial amount of cracking while providing the desired heating and drying of coke `within the lower portion of the liuidized bed maintained within the conversion chamber 14.

The uncondensed vapors from the fractionator 4 are indicated as being withdrawn through line 74 and control val-ve 75, passing by Way of condenser 76 to line "77 and control valve 78, with the latter line connecting with a suitable receiver 79. Uncondensed gas is withdra-wn from the receiver 79 by way of line 80 and control valve281, while thelight distillate is withdrawn from the lower end of the receiver by way of line 82 and control valve '83 and pump 84. A portion of the light cracked distillate may be returned to the upper portion of the `fractionator by way of line and control valve `86 to provide reflux to the top of the column 4, while line 87 and valve 88 provide means for withdrawing light cracked distillate from the fractionating system.

The embodiment of the present drawing provides that the combustion chamber 18 be somewhat elevated above the cracking and coking chamber in order that a stream fof `the collected fine coke particles may be passed by gravity flow to the upper portion of the descending uidized :bed maintained within the coking and conversion chamber '14. If it is so desired, the combustion chamlber may be directly `superimposed over or on top of the coking and conversion chamber 14, with suitable -conduit means providing for the substantially vertical straight line flow-ofnely -divided and heated coke particlesl-downwardly from -the combustion chamber into the conversion chamber and upper portion of the uidized bed, the upper level of which is indicated by the broken line 15. Still further, the contacted coke particles from the lower end of the chamber 14 and stripping zone 21 may be transferred in a fluidized manner in a substantially vertical upward flow from the stripping chamber 21 to the lower end of the combustion chamber and the uidized bed maintained therein.

'The construction of the upper portion of the combustion chamber 18, as shown, provides an economical and desirable way for electing an elutriation which in turn separatesthe `coke particles into a portion largely consisting of relatively line particles and a portion which consists of substantially coarser particles. The diameter ofthe upper and large portion of the combustion chamber 18 is suicientlylarge to provide a substantial increase in cross-sectional area immediately above the upper extremity of the semi-cylindrical-bafe member 30, preferably-about '50% to 85% increase in cross-sectional area over that within the lower portion of the combustion chamber, such that the resulting reduction in velocity brings about a settling of a major portion ofthe heavier or larger coked particles into the collecting .zone 33.

'The increased cross-sectional area immediately above the vupper extremity of the bafes '31 and 32, as provided tion of the relatively tine coke particles into the collecting Well 34, such that the'stream comprising a predominately ilarge portion of -lineparticles may be transferred to the coking and cracking zone of the chamber 14,

Without departing from the principal features of the improved method herein provided, the operation described with reference to Figures l and 2 may be modified in the manner hereinbefore indicated by maintaining a descending relatively compact moving bed in the conversion zone and withdrawing the vaporous cracked products from the uppermost portion or above the descending bed; a suitable reactor arrangement for preforming this modification is illustrated in Figure 3 of the drawing. Or, alternatively, this operation may be modified in the manner also hereinbefore indicated by maintaining a descending relatively compact moving bed in the conversion zone and withdrawing the vaporous cracked products from an intermediate point or level of the descending bed, that is to say, intermediate the points of introduction of the heavy hydrocarbon charge to the uppermost portieri and of the highly heated distillate oil or light recycle stream to the lowermost portion of the descending bed; a suitable reactor arrangement for practicing this latter modification is illustrated in Figure 4 of the drawing.

Referring to Figure 3 of the drawing, the reaction and coking chamber 89 is provided to take the place of the coking chamber 14 in the apparatus and operation described with reference to Figures l and 2. The stream of heated relatively tine coke particles is supplied through line 16 and valve 17 to an elevated portion of the chamber 89 onto the top of a compact moving bed of coke particles descending therein. The highly heated distillate oil or light recycle stream is introduced through line 19 and valve 20 into the bottom portion of the descending bed to pass upwardly through the latter and commingle in the more elevated portions of the bed with the heavy hydrocarbon charge which is supplied through line 11 and valve 12 and dispersed in the descending bed by means of the distributing head 13, and with the conversion products of this heavy charge. As in the operation with a iuidized dense phase bed, the vaporous products resulting from the cracking and coking reactions are disengaged from the top of the descending bed in commingled state and are withdrawn from the chamber 89 through

lines

63 and 64 to a suitable fractionation system such as the fractionator 4 of Figure 1. Asphalt-free coke is withdrawn from the chamber 89 through the stripping leg 21 and through line 22 and valve 23 to be further processed as already described with reference to Figures l and 2. As hereinbefore noted, this moving bed type of operation may be utilized with particular advantages in the conversion of heavy charging stocks yielding approximately from 25 to 40% by weight of coke. A typical charge of this type is a Smackover topped crude having an A. P. I. gravity of 17.9 and a U. O. P. characterization factor of 11.45 and yielding 27.5% by weight of hard coke of low volatility.

Figure 4 of the drawing illustrates an arrangement wherein the cracking and coking chamber 90 takes the place of the coking chamber 14 of Figure l to permit a descending compact moving bed type of operation wherein the heavy hydrocarbon charge and the distillate oil streams receive a more Selective treatment than in the embodiments described with reference to Figures 1 and 3 and which is of greatest advantage when converting heavy charging stocks of relatively high gravity and low coke yields. The stream of heated relatively tine coke particles is supplied through line 16 and valve 17 to the top portion of the chamber 90 to maintain the latter substantially filled with a descending fairly compact moving bed of particles. The highly heated distillate oil or light recycle stream is supplied through line 11 and Valve 12 to the uppermost portion of the descending bed and is dispersed therein by means of the distributing head 13. The large amounts of vaporous products forming during the concurrent iiow contact of the heated coke particles with the heavy hydrocarbon charge of relatively high A. P. I. gravity preclude agglomeration of the coke particles in the portion of the descending bed above the vapor withdrawal header 91 and the unvaporized or insuiiiciently coked components of the charge and intermediate products passing further down with the coke particles are prevented from causing any material cementing of particles by the vaporous products which form in the lower portion of the descending bed from the highly heated distillate or light recycle stream introduced to the bottom portion of the bed through line 19 and valve 20, and which assure completion of the conversion of the unvaporized entrainment on the coke particles into asphaltfree coke and vaporous products. The resultant dry coke particles are withdrawn from chamber 94) through the stripping leg 21 and through line 22 and valve 23 to be further processed as already described with reference to Figures 1 and 2. The vaporous cracked products resulting from the conversion of both the heavy hydrocarbon charge stream and the distillate oil or light recycle stream are withdrawn in commingled state from the descending coke bed through the vapor collecting header 91 and through line 63 and valve 64 to fractionation such as described with reference to Figure 1. A typical heavy charging stock advantageously convertible in this descending bed type of operation is, for example, an East Texas fuel oil having an A. P. I. gravity of 25.0 and a U. O. P. characterization factor of 11.95 and yielding a hard granular coke of low volatility in an amount of 18.5% by weight.

The cracking and coking operation as described above may be carried out under suitable pressure conditions, ranging from about atmospheric pressure to 300 pounds or more. The preferred average pressure maintained in the cracking and coking zone (

chamber

14, 89 or 90) is within the range of from l5 to 125 pounds per square inch, for example 45 pounds per square inch, and the pressure in the heating or combustion and particle segregating zone (chamber 13) is substantially equalized with that in the coking zone in such manner that a substantially gravitational flow of heated tine coke particles from the former to the latter is assured throughout the continuous operation.

I claim as my invention:

1. An improved method for cracking and coking a heavy hydrocarbon. charge stream in the presence of heated subdivided solid material, which comprises, main-- taining a descending bed of coke particles within a cracking and coking zone, supplying a stream of heated coke particles at a temperature above the average coke bed temperature to the upper portion of said bed, introducing a distillate oil stream at a temperature above the average coke bed temperature to the lower portion of said bed, introducing said heavy charge stream at a lower temperature than said average bed temperature into an elevated portion of said bed intermediate the points of introduction of said heated particles and said distillate stream, effecting the cracking and coking of said heavy charge stream in said descending bed and the production of a residue in the form of substantially asphalt-free coke particles by the combined heating effects of said heated coke particles and of the high temperature distillate oil stream, continuously discharging resulting vaporous conversion products from said cracking and coking zone and passing them to a fractionating zone, continuously withdrawing coke particles from the lower portion of said bed and passing at least a portion of the withdrawn coke particles to a separate heating zone wherein they are heated to a higher temperature than said average bed temperature and returning at least a portion of the resulting heated subdivided coke from Said heating zone as the aforesaid stream of heated coke particles to the upper portion of the bed in said coking zone.

2. The method of claim l further characterized in that said distillate oil stream is a recycle stream of distillate recovered from said fractionating zone.

3. The method of claim l further characterized in that the particles supplied from said coking zone to said heating zone are subjected therein to segregation as well as heating and a portion comprising predominantly the finer coke particles is returned a-s said heated stream of coke particles to the upper portion of the bed maintained in said coking zone.

4. The method of claim l further characterized in that said distillate oil stream is a recycle stream of distillate recovered from said fractionating zone and boiling below said heavy hydrocarbon charge stream and said recycle stream is introduced at a suicient temperature to said descending bed to maintain in the lower portion thereof a higher temperature than the temperature conditions prevailing in said bed at and above the supply of said heavy hydrocarbon charge thereto.

5. The method of claim 1 further characterized in that the particles supplied from said coking zone to said heating zone are subjected therein to segregation as well as heating and a portion comprising predominantly finer coke particles is returned as said heated stream of coke particles to the upper portion of the bed maintained in said cokng zone while the remaining portion comprising largely coarser coke particles is separately withdrawn from said heating zone as net coke product of the operation.

6. An improved method for cracking and coking a heavy hydrocarbon charge stream in the presence of subdivided solid material, which comprises maintaining a descending bed of finely divided coke particles in a cracking and coking zone, supplying a stream of heated coke particles at a temperature above the average coke bed temperature to the upper portion of said bed, continuously introducing said heavy charge stream at a temperature below the average bed temperature into an intermediate point in the height of said bed, continuously introducing a distillate oil -stream at a temperature above the average bed temperature into the lower portion of said bed, effecting the conversion of said charge stream into lower boiling cracked products and particulated coke substantially free from asphalt by the combined heating eifects of said distillate oil stream and said heated coke particles, discharging resulting vaporous conversion products from said cracking and coking zone and passing them to a fractionating zone, continuously withdrawing resulting coke particles from the lower portion of the bed in said coking zone and passing them into a separate combustion zone, maintaining a uidized bed of said withdrawn coke particles within said combustion zone, passing a gas stream containing free oxygen upwardly through y said bed and effecting the fluidization of said bed and the burning of at least a portion of the coke therein and the resultant heating of the particles within said bed, reducing the linear velocity of the up-owing resulting combustion gases within the upper portion of said combustion zone suiciently to bring about the settling of relatively heavy and large coke particles and a segregation permitting the carrying of the smaller and less heavy coke particles to a higher elevation in said combustion zone, withdrawing a particulated coke stream having a high proportion of relatively coarse particles at a low point of said elevated portion of said combustion zone as net coke production, di-sengaging the resulting combustion gases from the iiner coke particles in the upper portion of said combustion zone and discharging said combustion gases therefrom, withdrawing a stream of resulting heated particulated coke having a high proportion of relatively line particles from said upper portion of the uidized bed in said cornbustion zone, and transferring `said iine particles as said stream of heated coke particles to the upper portion of the descending bed in said coking zone.

7. The method of claim 6 further characterized in that a stream of said hot combustion gases discharged from the upper portion of said combustion zone is passed in indirect heat exchange relationship with the heavy hydrocarbon charge stream, and the latter is heated to an elevated temperature precluding coking prior to its introduction into the descending bed in said coking zone.

8. The method of claim 6 further characterized in that said distillate oil stream being introduced into the lower portion of the descending bed in said coking zone is a side cut distillate recovered from said fractionating zone and boiling below said heavy hydrocarbon charge, and said distillate stream is heated by passing the same in heat exchange relationship with a stream of hot combustion gases discharged from -said combustion zone before said distillate stream is introduced into the descending bed in said coking zone.

References Cited in the le of this patent UNITED STATES PATENTS 654,290 Stebbins July 24, 1900 2,027,552 Roberts, Jr. Ian. 14, 1936 2,340,974 Myers Feb. 8, 1944 2,362,270 Hemminger Nov. 7, 1944 2,419,517 Eastwood Apr. 22, 1947 2,460,404 Ward Feb. 1, 1949 2,500,870 Robinson Mar. 14, 1950 2,527,575 Roetheli Oct. 3l, 1950 2,530,645 Beckman Nov. 21, 1950 2,548,026 Kaasa Apr, l0, 1951 2,661,324 Letler Dec. 1, 1953 FOREIGN PATENTS 574,892 Great Britain Jan. 24, 1946

Claims

1. AN IMPROVED METHOD FOR CRACKING AND COKING A HEAVY HYDROCARBON CHARGE STREAM IN THE PRESENCE OF HEATED SUBDIVIDED SOLID MATERIAL, WHICH COMPRISES, MAINTAINING A DESCENDING BED OF COKE PARTICLES WITHIN A CRACKING AND COKING ZONE, SUPPLYING A STREAM OF HEATED COKE PARTICLES AT A TEMPERATURE ABOVE THE AVERAGE COKE BED TEMPERATURE TO THE UPPER PORTION OF SAID BED, INTRODUCING A DISTILLATE OIL STREAM AT A TEMPERATURE ABOVE THE AVERAGE COKE BED TEMPERATURE TO THE LOWER PORTION OF SAID BED, INTRODUCING SAID HEAVY CHARGE STREAM AT A LOWER TEMPERATURE THAN SAID AVERAGE BED TEMPERATURE INTO AN ELEVATED PORTION OF SAID BED INTERMEDIATE THE POINTS OF INTRODUCTION OF SAID HEATED PARTICLES AND SAID DISTILLATE STREAM, EFFECTING THE CRACKING AND COKING OF SAID HEAVY CHARGE STREAM IN SAID DESCENDING BED AND THE PRODUCTION OF A