US2395081A - Cracking and coking hydrocarbon oils - Google Patents

Description

Filed Dec. 31, 194C) I+ m l, ff j mm wm E f IIIW rl J v 8 m IMJOOO f ov k L v al' H .wmol VV O DO-lme mv E mv L ,w 1 nu M N A N1 @.Hwwu' N MNHN@ v Al 1 IINAH mq 'f O- HIIIHIAIIhL/J M g ON E I Q A N xm a mm 11....: y ou 025m: E Y A Nm .ll N

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TOM WILLIAMSON NED A.ScARo|No INI/ENTORS BY l THE/R ATTORNEY Patented Feb. 19, 1946 CRACKING AND CIILIISWG HYDROCARBON Tom Williamson, Port Arthur, Tex., and Ned A.

Scardino, Lockport, Ill., assgnors, by mesne assignmcnts, to The Texas Company, New York, N. Y., a corporation of Delaware Application December 31, 1940, Serial No. 372,510

(Cl. ISG- 48) 7 Claims.

This invention relates to the cracking and coking of hydrocarbon oils and contemplates a process in which the oil is heated to a cracking tem- Eperature and directed into a reaction zone wherein the oil is subjected to cracking conditions of temperature and pressure and wherein separation of vapors from liquid residue takes place and in which the liquid residue together with a portion of the vapors suicient to effect coking is flash distilled to a. -coke residue, while the remaining vapors are separately withdrawn from the reaction zone and directed to a zone separate and apart from the coking zone. The invention is particularly adapted for the treatment of heavy stocks. such as topped or reduced crudes, and in accordance with the invention the heavy stock is combined with a stream of highly heated condensate stock for cracking in a cracking chamber and a mixtureA of residue and vapors is passed to the coking zone to accomplish reduction to a coke residue without priming in the coking zone.

The invention has particular reference to that type of pressure cracking and coking process in which a cycle condensate is passed through a heatingcoil wherein it is heated to a cracking temperature, the resultant heated stream combined witha heavy stock, such as a crude residual stock. and conversion of the commingled products carried on, and in which the residual products Yfrom the cracking operation are passed to a ook-r ing zone for conversion into coke. It has been found that when the total products from the reaction chamber, that is, all of the liquid and vaporous constituents. are delivered to. the coking drum, that conversion to a coke residue may be accomplished, but such operation necessitates the maintenance of relatively low charging and recycling rates in order to avoid priming in the coking drum. The coking operation is usually carried on with a plurality of coke drums, one being on stream while the others are down for the coke drum. When separation of vapors fromv liquid residue takes place in the cracking reaction chamber and when only the residue is passed to the ooking chamber the autogeneous heat of the residue is insuillcient to eiect coking. Even cleaning, and the priming operation is particulari when withdrawing the products from the reaction chamber at temperatures as high as 910 F. it has been found that the contained heat of the residue is insuicient to eiect Vcoking for the production of marketable coke. To-overcome the heat deciency in the residue resort has been had to the by-passing of a portion of the heated stream from the condensate heating coil into the coking drum, but this operation is disadvanta geous because the reduction in the quantity of the heated stream for combining with the heavy stock or black oil has necessitated that Asuch heavy stock or black oil be passed through a heating coil before combining with the cycle condensate stream.

We have found that by retaining only a portion of the vapors in the residue withdrawn from the reaction chamber that autogenous coking may readily be accomplished while avoiding priming in the coking drum. 'l In accordance with our in vention the heavy stock or black oil, such as topped or reduced crude, may b'e employed indephlegmating the vapors from both the coking drum and the cracking reaction chamber, the resultant mixture of residual constituents and condensate is combined with the heated stream from the cycle condensate heating coil for cracking in a reaction chamber in which separation of vapors from liouid Vresidue takes place and the residue is Withdrawn together with sumcient va- Dors to maintain the desired cokingr4 temperature in the coking drum for conversion to a coke residue, while the remaining vapors are passed toa zone separate from the coking zone.

The practice of our invention. in which only that portion of the vapors which is required for cokina is passed with the cracked residue to the looking zone, makes it possible to very materially increase the recycling rate Without coke drum priming. The increase in the rate of cycle condensate passed to the heating coil is accompanied with certain important technical effects. By decreasing the time factor in the-heating lcoil a higher %'distillation point and higher color can be maintained on the cycle condensate without coking difliculties; the increased recycling rate permits increased reaction chamber temperatures for the same soaking volume factor and coking limitation: increased reaction lchamber temperatures result in a higher ratio of vapor passing to the dephlegmator in relation to the black oil being passed from the dephlegmator to the reaction chamber; 'and the resultant highv reaction chamber temperature makes itpossib1e to obtain suincient heat for coking without drawing excessive amounts of vapor along with the liquid to the coking drum.

The invention contemplates further the distribution of the vapors from the reaction charnberl and coking drum in such a way as to inhibit coking in the dephlegmating or fractionating portions of the system while at the Sametime making possible the production cfa heavy fuel'oii product. In running to coke and fuel oil, in accordance with the invention, the vapors from the coking drum are subjected to primaryffractiona- I tion or dephlegmation to produce a tarry con-- densate adapted for fuel oil,thev uncondensed.

vapors passed to a fractionating4 zone into which.

liquid residue together with sufiicient' vaporv for coking is passed to the' COkingdrum.

In running to coke' only, in accordance with the invention, the vapors from the coking vdrum are subjected to primary fractionation or de phlegma'tlon, the uncondensed vapors' combined with Separated vapors from the reactionchamber and subjectedto dephle'g'mation with the chareing stock', the resultant mixtureof reflux condensate and unvaporized charging'stock is then passed to the primary dephlegmating zone'to de phlegrnate the vapors therein and theV nnal mixture of reflux condensate andunvaporized charg- -ing stock isy combined with thehighly heated stream from' the condensate heating` coi1 for reaction in the reaction chamber.

For` the purpose of more fully explaining the invention reference is nowhad. to the accompanying drawing which is a diagrammatic sectionalfelevation of. an apparatus adapted. for the practice of the invention.

In practicing the invention cycle condensate from. a sourcehereinafter explained'is heated to a.. cracking. temperature in a heating coil In mounted in a suitable furnace I I and the heated products pass through a' transfer line I2 to a reaction chamber. I3' which is' suitably heat fnsulated and wherein separation of vapors from liquid residue takes place'. Liquid is prevented from accumulating in the reaction chamber I3 by the rapid withdrawal of all the liquid together with a portion of thevapors'. The mixture is passed through line I4 and pressure reducing valve 5, thence to coking chamber I6 wherein the residue is converted vto coke by Vmeans of its contained heat. In practice a plurality of coke drums are employed so that while one is on stream the other or others may be down for cleaning' and thus continuity in the complete process is maintained.

In accordance with the invention the separated vapors from the reaction chamber and from the coking chamber are admitted to different points' in the fractionating' or dephleg'mating portion of the system so as to avoid coking difliculties' which would beo'ccasioned bythe concentration of these yhighly' heated vapors at one point. As shown in the drawing a dephlegm'a'tor or fractionator l'l, is

provided having an upper section I8 and a lower section I9 separated by a condensate tray 29. Vapors from the coking drum I6 pass through a line 2|, in which may be positioned a valve 22, to the dephlegmating section I9 which is conveniently supplied with bailies such as disc and doughnut elements 23. The separated vapors from the reaction chamber I3 pass through a line 24 and pressure reducing valve 25 to the fractionating section I8 which may also be equipped. with suitable disc and doughnut trays 26. A valved run back line 4| may be provided for conductingV liquid from the trapout tray 2o tothe. dephlegmating section I9 for refiuxing therein.

.Charging stock is introduced by a pump 2l through a line 28 to the fractionating section I8 being preferably admitted to the upper portion ofthe tower I l. The charging stock serves to dephlegmate the vapors from the reaction chamberas well as the'uncondensed coke still vapors from section I9. The commingled reflux'condensate and unvaporized charge is withdrawn from the tray 20 through a line 29 and is directed by a pump 30 through a line 3| to the transfer line I2 or to the reaction chamber I3.

When running to coke and distillate fuel oil the valve in the run back line 4| is closed and al1 the liquid collecting on the tray 20 may be directed by the pump 30 to the heater transfer line I2 or reaction chamber I3 while the fuel oil is withdrawn through a line 40. When running to' coke only the valve in run-back line 4| is open so that the mixture of reflux condensate and unvaporized charging stock may flowv intoV dephlegmator I9 to dephlegmate the vaporsr therein and form a final mixture of reflux condensate and unvaporized charging stock which may be passed through a line 49 and a by-pass line 42 to the line 29 and thence through pump 39 and line 3| to the heater transfer line I2 or reaction chamber I3. In the coke only operation the trapcut tray 29 is unnecessary but in such operation it is desirable to introduce the vapors from the coking drum to a lower portion of the tower Il and subject the vapors toi dephlegma'tion and then combine theV dephlegmated vapors with the separatedvapors fromv the reaction chamber I3 for dephlegmation.

Uncondensed vapors from the tower I'Iv pass through a vapor line 32 to a fractionating tower 33 which is conveniently equipped with bubble trays 34 and which may be supplied with conventional cooling or refluxing means not shown.

Reflux. condensate is drawn from the tower 33 lby a pump 35 and directed through a line 36 to the heating coil I 0. The uncondensed vapors pass from the tower 33-.to a condenser 31 which discharges into a distillate receiver or gas separator 38 wherein the distillate product is collected. A portion of the reflux condensate from tower 33 may be passed through a cooler 43and directed by a pump 44 through aline 45 to the dephlegmating section I9 to provide reflux therefor.

When running to coke and fuel oil the tarry condensate which collects in the dephlegmating section I9 may be withdrawn as a fuel oil product through the line 40. This product may be flash distilled to produce a final fuel product of any desired gravity or flash test, while the flashed distillate may be refluxed in the fractionators. In the. drawing the cracking chamber |3 is shownv as an up-flow chamber, although a downflow chamber may' also be employed. in the practhe black oil Vstream there is a 'tendencyfor the separate vapor stream to contain `quantiti'es'I/,of entrained'tarr-y material. In fanothermeth'od of operation contemplated the products'fromtransfer line I2 including the constituentsifrom line *31 Vare adrriitted into a `down'il'ow reaction chamber in whichliquidis prevented `fromfaccumulat- 1ing Vand the products from lwhich pass Ato a 1succeeding upflow chamber, the separate stream of `vaporsbeing taken off 'from the top 'of the'upiiow chamber to the fractionating section I8 and the mixture o liquid residue and 'vapors'being withdrawn from the bottom 'of the upflow reaction chamber and passed to the coking drum IB.

` When operating with the upflow chamber, as illustrated, it is advantageous to spray the wall of the chamber with a portion of the relluxcondensate from tower'I'I.

In practicing the invention the superclean cycle condensate from lfractionator 33 is subjected `Ito hcracking 'at temperatures ofthe order of 1,000

to 1050" F. preferably'under reasonably high pres- :sures `such as 400-800 lbs. in the heating coil I rand upon being commingled with the black oil `stream .is subjected to 'cracking in the Vreaction `chamber Vat'temperaturesin excess of 900 F. under superatmospheric pressures such as 30D-600 lbs. Liquid is prevented :from accumulating in `the reaction chamber, the mixture of liquid and vapors being rapidly withdrawn "and passed to the coking chamber while the separate vapor stream is passed to the fractionating portion of the system. .A temperature approximating 910 F. is recommended for the mixture of vapors and .residue `in the `line I4, with the temperature `in 'the reaction `chamber being somewhat higher.

Atlhough the pressure is reduced in the coking Y drum it is recommended that superatmospheric pressures of `approximately 100 lbs. orhigher be `maintained therein; with pressures of 350 to 400 .lbs. in the reaction chamber pressures of about 150-175 lbs. are very satisfactory in the coking drum. The major portion of the vapors from the reaction chamber flows through the vapor line while only a minimum proportion ofthe vapors `is needed for admixture with the residue to accomplish the coking thereof. The quantity of vapors required to be included in the residue being withdrawn to 'accomplish coking is dependent upon the temperature in the reaction chamber and it is desirable to maintain las high a temperature as possible in the reaction chamber to keep the quantity of vapor withdrawn with the `residue at a minimum. Ordinarily, a quantity of vapor of the order of 10%-20% of the amount of vapors V:flowing .from .the reaction chamber will be found `adequate to 4accomplish coking without pri-ming. The .amount required can readily be controlled by .observing the temperature in the transfer line to the coking drum or inthe coking drum itself. The temperature .required .for coking will lvary with :the pressure `.used .in .the coking operation and :somewhat with the character V'of thestock. vThe temperature will 'generally be in excess of 825 F. and normally will be `approxi-- mately within a range vof about 840 F. to 885 F. A temperature of 850 F. under 150-175 lbs. pressure has been found very satisfactory. Under the conditions outlined coking is readily vaccomplished to yield a marketable coke while'avoiding bergit is desirable to maintain 'a temperature in the bottom of the dephlegmating section I9 as high as practicable withoutcoking therein. Temperatures as/high as V810-820" F. in the bottom 'of section I9 have been successfully employed.

When running to coke and fuel oil; i. e., when withdrawing from the system the .bottoms vfrom dephlegmator I9 and directing the liquid from tray 20 to the reaction chamber it is generally necessary to maintain somewhat lower temperatures in dephlegmator I9, such as '790 F.-800 F. It is ordinarily desirable to introduce a cooling reflux, such as a portion of the cycle condensate conducted through line 45, into the upper portion of the dephlegmating section I9 in order to prevent coking as Well as to remove tarry entrained material in the vapors.

The charging stock which is most advanta geously a topped or 'reduced crude, after such preheating as may be desired, is introduced into the dephlegmating section I3 to dephlegmate the coke still vapors flowing upwardly from section i9 and the vapors from the reaction chamber en tering through line 24. Gas oil constituents contained in the crude are distilled over into the tower 35. The unvaporized residual constituents together with the reflux condensate formed in section I8 are collected in tray 20 at temperatures of the order of 800 llt-815 F. for passage to the reaction chamber for cracking therein. The practice of the invention is particularly adapted for the treatment of crude stocks containing maximum quantities of gas oil. For the lighter stocks containing large proportions of gas oil such for example as 26-28 A. P, I. gravity topped crudes pressure approximating 400 lbs.'are recommended for the reaction chamber while with heavier stocks such as a 20 A. P. I. gravity reduced crude the pressure should preferably be lowered to about 200 lbs.

The vapors pass overhead from the tower Il' at temperatures approximating 710 lit-730 F. to the tower 33 lwhich may be maintained at approximately the same pressure as that of the tower I l, although somewhat lower pressures may be satisfactorily employed; thus, for example, with a pressure of 150 lbs. in the tower il the tower 33 may be held under a pressure of 135 lbs. The temperature in the bottom of the tower 33 ap y proximates 660 F.680" F. The top temperature in the tower is controlled to take off the distillate of the end point desired; thusa temperature of 390 F. under 135 lbs. pressure may be employed in taking off a 400 end point gasoline distillate.

In a typical example of the invention a 25.0 gravity A. P. I. paraiiin base reduced crude was charged to the fractionator i8 at a rate of 192 barrels per hour, cycle condensate was delivered from fractionator 33 to the cracking coil .I0 at a rate of 477 barrels per hour andthe black oil was passed from thetray-Z to the reaction chamber at the rate of 280 barrels per hour. The outlet temperature of the cracking coil was 1035 F. An upfiow reaction chamber was employed with a pressure of 400 lbs., with a top temperature of 909 F. and a bottom temperature of 915 F. The coking drum was held at 842 F. under 150 lbs. pressure. A distillate fuel oil product Was Withdrawn from the dephlegmator I9.

In a second example of the invention with a 26.2 gravity A. P. I. reduced crude a downflow reaction chamber was employed, the charge was introduced at a rate of 166 barrels per hour, the recycle rate to the cracking coil was 479 barrels per hour, and the black oil recycle rate was 235 barrels per hour. The temperature of the cracking coil outlet was 1015 F. The reaction chamber was under 400 lbs. pressure and the mixture of vapors and residue Was withdrawn from the reaction chamber at a temperature of 910 F. The coke drum was under 175 lbs. pressure and at a temperature of 843 F. A distillate fuel product was withdrawn from the primary dephlegmator.

In a third example of the invention a reduced crude of the same gravity was reduced to coke with no distillate fuel product being made. The charge was introduced at a rate of 124 barrels per hour, the recycle rate to the cracking coil was 446 barrels per hour, and the black oil was passed from dephlegmator I9 to the reaction chamber at a rate of 210 barrels per hour. The cracking coil outlet was at a temperature of 1010" F. Ay downflow reaction chamber was employed being maintained under 400 lbs. pressure and the mixture of vapors and residue was withdrawn from the ree action chamber at a temperature of 909 F. The coke drum was under 175 lbs. pressure and at a temperature of 845 F.

In these runs a yield of about 55%-59% of gasoline having an octane value of 74-77 C. F. R. R. 'was obtained. In the rst and second runs a yield of about of distillate fuel oil was produced.

Prior to applicants invention it had not been possible to operate to coke and distillate fuel oil simultaneously without having to heat the black oil in a separate furnace coil. The practice of the invention has made it possible to run to coke and distillate fuel oil simultaneously with charging rates of the order of 180-200 barrels per hour. The practice of the invention has made it possible when running to coke only to raise the charging rate from about 80 barrels per hour up to 125 barrels per hour, effecting an increase in capacity of 55% without any reduction in gasoline yield, and in fact, on some units the invention has made it possible to increase the charging rate to 140 barrels per hour, effecting an increase of 75% in capacity, also without reduction in gasoline yield.

In accordance with the invention, it is possible to include suicient vapor with the residue withdrawn from the reaction chamber to furnish sufcient heat for coking and yet have the total coking drum input well below the priming point even at capacities of 200% or more over the previous capacity. Previously, for example, when operating on topped paraiiin base crude at recycle rates, that is, the rates of cycle condensate passed to the heating coil, above about 280 barrels per hour priming occurred in the coke drum which limited the charging rate to about 85 barrels per hour. Prior to applicants invention the limits on the recycling rate, that is, the rate of cycle condensate passed to the heating coil were found to be with various stocks approximately within the range of 230 to 280 barrels per hour. The practice of the invention enables the increasing of the recycle rate up to high rates approximating 400-500 barrels per hour. In View of the high recycle rate made possible by the invention it is particularly adapted for the processing of light topped crudes containing large proportions of gas oil.

Although a preferred embodiment of the invention has been described herein, it will be understood that various changes and modifications may be made therein, while securing to a greater or less extent some or all of the benefits of the invention, without departing from the spirit and scope thereof.

We claim:

1. In th'e conversion of higher boiling hydrocarbon oils into lower boiling ones, the process that comprises passing cycle condensate through a heating zonehwherein it is heated to a cracking temperature, combining the resultant heated products with a residual stock for cracking in a reaction zone wherein separation of vapors from liquid residue takes place, maintaining cracking temperatures of the order of upwards of 900 F. under superatmospheric pressure in the reaction zone, preventing the accumulation of liquid residue therein, withdrawing the liquid residue from the reaction zone together with a portion of the vapors sufficient to support autogenous coking and amounting to a proportion of the order of 10-20% of the vapors flowing from the reaction zone, delivering the mixture 0f liquid residue and vapors to a lower pressure coking zone to thereby effect coking solely by the contained heat of the mixture, separately withdrawing separated vapors from said reaction zone, separately dephlegmating the evolved vapors from the coking zone to form a tarry condensate subjecting the dephlegmated vapors and the vapors separately withdrawn from said reaction zone to fractionation to separate reflux condensate from lower boiling products and directing resultant reflux condensate to the aforesaid heating zone.

2. In the conversion of higher boiling hydrocarbon oils into lower boiling ones, the process that comprises passing cycle condensate through' va heating zone wherein it is heated to a cracking temperature, combining the resultant heated products with oil for cracking in a reaction zone wherein separation of vapors from liquid residue takes place, maintaining cracking temperatures of the order of upwards of 900 F. under superatmospheric pressure in the reaction zone, preventing accumulation of-liquid residue therein, withdrawing the liquid residue from the reaction zone together witha portion of the vapors suflicient to support autogenous coking and amounting to a proportion of the order of 10-20% of the vapors flowing from the reaction zone, delivering the mixture of liquid residue and vapors to a lower pressure coking zone to thereby effect coking solely by the contained heat of the mixture, separately withdrawing separated vapors from said reaction zone, primarily dephlegmating th'e evolved vapors from the coking zone to form a tarry condensate, passing the uncondensed vapors to a subsequent dephlegmating zone, introducing the separately withdrawn vapors from said reaction zone directly to said subsequent dephlegmating zone, introducing charging stock into said subsequent dephlegmating zone, withdrawing the resultant mixture of condensate and unvaporized charging stock from said subsequent aso-acer dephlegmating zone and utilizing the mixture as the oil-combined with the heated products from the heatingzone for-cracking in the reaction chamber as aforesaid, subjecting vapors uncondensed in said subsequentdephlegmating zone to further fractionation to separate a distillate product from a. higher Vboiling reflux condensate and directing said reflux condensate to the aforesaid heating zone.

3. In the conversion of higher boiling hydrocarbon oils into lower boiling ones, the process that comprises passing cycle condensate through a heating zone wherein it is heated to a cracking temperature, combining resultant heated products with oil for cracking in a Yreaction zone wherein separation of vapors from liquid residue takes place, maintaining cracking temperatures of the order of upwards of 900 F. under superatmosph'eric pressure in the reaction zone, preventing accumulation of liquid residue therein, withdrawing the liquid residue from the reaction zone together with a portion of the vapors sufficient to support autogenous coking and amounting to a proportion of the order of 20% of the vapors flowing from the reaction zone, de-

livering the mixture of liquid residue and vapors to a lower pressure coking zone to thereby eect coking solely by the contained heat of the mixture, separately withdrawing separated vapors from said reaction zone, dephlegmating separated vapors from thev coking zone and reaction zone with charging stock, utilizing the resultant mixture of reflux condensate and unvaporized charging stock as the oi1 combined with the heated products from the heating zone for cracking in said reaction zone. subjecting the uncondensed vapors to further fractionation to separate a distillate product from higher boiling reflux condensate and directing said reflux condensate to the aforesaid heating zone.

1. In the conversion of higher boiling hydrocarbon oils into lower boiling ones, the process that comprises passing cycle condensate through a heating zone wherein it is heated to a cracking temperature, combining resultant heated products with oil for cracking in a reaction zone wherein separation of vapors from liquid residue takes place, maintaining cracking temperatures of the order of upwards of 900 F. under superatmospheric pressure in the reaction zone, preventing accumulation of liquid residue therein, withdrawing the liquid residue from the reaction zone together with a portion of the vapors sufficient to support autogenous coking and amounting to a proportion of the order of lll-% of the vapors flowing from the reaction zone, delivering the mixture of liquid residue and vapors to a lower pressure coking zone to thereby effect coking solely by the contained heat of the mixture, separately withdrawing separated vapors from said reaction zone, subjecting th'e evolved vapors from the coking zone to dephlegmation in a primary dephlegmating zone, passing the uncondensed vapors from the primary dephlegmating zone to a secondary dephlegmating zone, introducing the separately withdrawn vapors from said reaction zone directly to said secondary dephlegmating zone, introducing charging stock into said secondary dephlegmating zone, passing the resultant mixture of reflux condensate and unvaporized charging stock from said secondary dephlegmating zone to said primary dephlegmating zone to dephlegmate vapors therein, utilizing the resultant mixture of reflux condensate and unvaporized charging stock formed in the primary dephlegmating zone as the olcoznbined withV the heated products from -theheating zone for cracking in said reaction chamber, subjecting vapors uncondensed in said secondary dephlegmating zoneto further. fractionation to separate a distillate product from va higher boiling densate to the aforesaid heating zone.

5. In the conversion of higher boiling hydrocarbon oils into lower boiling oils, the process that comprises passing a condensate stock through a heating zone wherein it is heated to a cracking temperature, combining resultant heated products with a residual stock for cracking in a reaction zone wherein separation into vapors and liquid residue takes place, maintaining cracking temperatures of the order of upwards of 900 F. under superatmospheric pressure in the reaction zone, separately withdrawing vapors from said reaction zone and subjecting them to fractionation, preventing the accumulation of liquid residue in said i reaction zone, withdrawing the liquid residue from the reaction zone together with a portion of the vapors sufficient to support autogenous coking and amounting to a proportion of the order of 10-20% of the vapors flowing from the reaction zone, delivering the mixture of liquid residue and vapors to a lower pressure coking zone to thereby eect coking solely by the contained heat of the mixture, and separately dephlegmating the vapors from the coking zone to form a tarry condensate adapted for fuel oil and withdrawing said condensate as a product of the process.

` 6. In the conversion of higher boiling hydrocarbon oils into lower boiling ones, the process that comprises separately heating a residual stock and a condensate stock and combining the heated stocks at a cracking temperature for cracking in a reaction zone wherein Separation of vapors from liquid residue takes place, maintaining cracking temperatures of the order of upwards of 900 F. under superatmospheric pressure in the reaction zone, preventing the accumulation of liquid residue in said reaction Zone, withdrawing the liquid residue from the reaction zone together with a portion of the vapors sufiicient to support autogenous coking and amounting to a proportion of the order of lll-20% of the vapors flowing from the reaction zone, delivering the mixture of liquid residue and vapors to a lower pressure coking zone to thereby eiect coking solely by the contained heat of the mixure, separately dephlegmating the evolved vapors from the coking zone to form a tarry condensate, and subjecting the dephlegmated vapors and the vapors separately withdrawn from said reaction zone to fractionation to separate higher boiling condensate from lower boiling products.

7. In the conversion of hydrocarbon oils, the process that comprises passing cycle condensate to a heating zone wherein it is subjected to cracking conditions of temperature and pressure, delivering resultant heated products to a reaction zone maintained under cracking conditions of temperature and pressure and wherein separation of vapors from liquid residue takes place, preventing the accumulation of liquid residue therein by rapidly withdrawing the liquid together with a portion of the vapors, passing the separated vapors to a primary fractionating zone, directing the withdrawn mixture of liquid and vapors to a separating zone wherein separation of vapors from residue takes place, dephlegmating the separated vapors, passing the dephlegmated vapors to said primary fractionating zone, introducing reiiux condensate anddirecting said reflux-con- 6 www primary fractionating vzone fto a secon'daiv ffiactionati'ng zone wherein the vapors are fractionated to separate Elighter products vfrom vhigher boiling reux condensate and directing said -re- 5 flux cdndensate to the aforesaid 'heating'zone TOM WLLLrAMsoN. NED A. sc-ARDINo.

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