US2103977A - Treatment of hydrocarbon oils - Google Patents

Description

Dec. 28,1937. l G; ARMlsTEAD, JR

I TREATMENT 0F HYDROCARBON OILS Filed Nov. 9, 1953 SVI 14...

llll llll ATTORNEY INVENTOR GEORGE ARMISTEADJR Patented Dec. 28, 1937 Y i i 1 Y UNITED STAT Ev-S- PAT OFFICE i l l 2,103,91-7il TREATMENT F HYDROCARBON OILS George' Armistead, Jr., Scarsdale, Y.; assgnor` to Gasoline Products Company, Inc.,k Newartt, N.l J1., a corporation. of Delaware Application Novembere, 1933, serial Nacen/272..

9 Claims. (Gl. 196'48`-) o o This. invention yrelates toy the treatment of hyentsfmay even undergo severecrackingtreatment. drocarbon oils and has particular. reference to a. n V`One ofy the salient objects of the.. present intreatment in which the oil is ultimately converted Ven-tion. is to. i-edu-cefV the proportionate amount of into products consisting principally of gasoline residual material passing directly tothe cokingv j and a solid or semi-solid residue such as coke or zone. y f pitch.y The invention isr especially applicable to A` further salient object of the invention is to: processes in which hot vaporousf. products from provide a.. method for more effectively controlling the cracking zoney are subjected to fractionation the: cracking tennieraturesl and` coke. or residueinV a plurality cf independent zones in: which proforming` temperatures. in; the: respective cracking.

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vremoved from the' cracked vapors and in` which A further objectot the inventionI isy to remove the intermediatecleaner fraction or fractions from., the.y residual materialbefore passing the. such as gas oil andk kerosene, having mini-mumv same to the coke or residue-forming. zone, contendency to coke,s used' to make up theY crack:- stituents which lend.themselvestocracking withing stock which is passed through the cracking* out formingsubstantial amounts of coke, with l5 zone. Y Y the result that the capacity-cf. the operation is.Y In such processes, in some instances, it has materially increased. and. at the same time lowY been a practice to subject the heavier condensed boiling products; of the desired qualityv are proiraction, from theini-tia-L fractionating zone to a duced.`

gressively lighter fractions aref condensed and andfcoke or residue-forming, zones.- l0f im coking operation in which theycondensate is con- Additional obgects and advantages will be 20 verted intoV vaporized products and. a solid or apparent from the more detailed description. of semisolidA residue of coke-i or pitch. the invention. i

It has also beenthe practice in someinstances Inr accordance with the: present. invention a te utilize the initial fractionating zone or zones ,residuum' trom the? initial fractionating zone or for topping or stripping fresh` preheated oil of its zones which may comprise the initiallv condensate lighterr cor-istituents in which case the residual from. the cracked vaporsI or a. mixture ofv such products Withdrawn rfrom the initialfractionatcondensate and topped, or. stripped.V crude is. first ing zone contain the topped or reduced crude subjected to an additional disti-lling operation, from the stripping operation as Well as the initial preferably under reducedpressure, the: residual :t3 condensate from the cracked vapors. materialv fronrthe. distilli-ng operationbei-ng sub- 30 lIhese residual. and condensate products from sequent/ly passed directly` to the coking zone-and the initial iractionating zone contain substantheVevo-lved vapors from the distillation'v treattial quantities of coke and coke-forming conment after bei-ng. fractionatedand condensed stituents such as barry material and polymerized are given. a. preliminary heat .treatment before:

if? material from the cracking. operation which passing tothe cokingzzone.1 f

render these products'l unsuitable for high tern- In the.. preferred. modincation the, evolved vaperature treatment iny tubular heating; systems. pors frena` the. distilling operation previously re- Consequentl-y it hasy been a practice to perform ferred to are divided into Va. heavier and lighter the coking operation i-n a. coking zone in which fraction, the` lighter fraction bei-ng `combined di) the heat necessary to eect the coking ob- *with the'recyclel stock` passing to the cracking 40 tained by contacting! the.` products to be coked zone and the heavier fraction subiectedtoa rela-A with hot products from the cracking zone. It tively. milder heat.treatment.preferablyinatubm will befrnanifest that insuchprocedure the prodlar heating unitlbefore passingl tothe coking or ucts subjected to the cracking operation must be residue-forming zone. A f1.7 givenn sufcient`V hea-.t not .only to attain the de- For a better understanding of theV invention sired crackingqtemperatures but must be supreference` is.7 now made to vthe accompanying plied with sufficient additional heat units to drawing which illustratesiin accnventional` manmaintain the co'king drum at the desired coking ner asuitablel apparatus., for carrying,v outv the temperature i .present invention.. Y v '30 Ithasrbeen' discovered that the products With- In the drawing' the. referenceA character VVIl) 50 drawn: fro-mfthe initial fractionating zone ordidesignates a furnace setting having: suitableV narily contain substantial quantites. of constituheating; elements such'. asa burner vI-I for main- `entsvvhic-h if separated from the coke or coking taining the furnace at.l theYdesi-redtemperature. material` are suitable for treatmentintubular Mounted inthehotter portion. of the furnace heating systems andY thatsome of these constituis. av tubular heating coi-l i2 havingk thellends: of 4455 Cil the tubes interconnected to form a serpentine path for the passage of fluid therethrough. The inlet end I3 of the coil I2 is connected to a source of hydrocarbons to be subjected to cracking treatment such as, for example, a clean condensate stock of the gas-oil and/ or the kerosene type from the fractionating zone.

The oil after passing through the heating coil I2, wherein it is subjected to pyrolytic conditions under relatively high superatmospheric pressure is conveyed through line Id. to a coking drum I5. As illustrated, the line i4 is provided with manifold outlet lines i6, I 'I and I8 leadingV into the coking d rum` I5 and provided with valves I9, 25 and 2l respectively so that the hot products from the cracking coil I2 may selectively pass to the coking drum through any one or more of manifold lines as conditions may dictate.

Leading from the upper end of the coking drum I5 is a vapor line 22 for conducting vapors evolved in the coking drum I5 to a primary fractionating tower 23- provided with suitable fractionating elements 24 for cooling and fractionating the evolved vapors.

If desired fresh charging oil may be introduced into the primary fractionating tower through line 25 having-manifold outlets 26 and 2l provided with valves' 28 and 29 forselectively discharging the oil in to differentV vertical zones of the fractionating tower. -As shown a'preheating coil 3U,r mounted inthe cooler or economizer section of the furnace setting Iii, is interconnected with chargi'ng'line4 25 through lines 3i and 32 so that by properly regulating valves 33,l 3d and 35 in llines 25, 3| and 32 respectively a portion or all of the charging oil may be preheated before passingto the fractionating tower 23. In lieu of providing preheating coil 3E,- other convenient sources of heat may be utilized for preheating thel oil. The desirability of preheating the oil and the extent of such preheating will be determined largely by the character of the oil to -be treated andthe temperature conditions desired to be maintained within the fractionating tower 23. i

-The charging line 25 is `provided with a pump 36 for-subjecting the oil to suicient pressure to discharge it against the pressure maintained within the fractionating tower 23 which, together with heating coil I2 and coking drum I5, is ordinarily `maintained under relatively high superatmospheric pressure. The fresh oil in fractionating tower 23 coming in contact with the hot products from the coking drum I5 serves to cool the hot vapor products and iny turn becomes heatedso that the lighter constituents ar-e vaporized leaving a topped or reduced crude residuum. f

The rractionating tower 23 is'connected to a vapor outlet line 3l leading to a secondary fractionating tower 35 provided with suitable frac- `tionating elements 3B for further cooling and 'fractionating thevapors from tionating tower 23.

Uncondensed vapors from the secondary frac- -tionating tower 38 are removed through vapor outlet line 20, conducted through a suitable condenser 4I wherein vapors having the" desired end point for motor fuel are condensed, and thence passed to a collecting tank 42 having a gas outlet line 3 for removing the permanent and uncondensed gases and a liquid withdrawal 'linelll for removing the desired fraction to suitable storage receptacles (not shown). Y

Thecondensa'te from Vthe second fractionatthe primary fracthrough line vided with a pump 49.

The hot unvaporized constituents in the bottom of fractionating tower 23, which may cornprise the heavier initial pressure condensate removed from the cracked products or a mixture of such condensate and topped or stripped residual products from the fresh charge injected through line 25, 'is withdrawn from-the bottom of yfractionating tower 23 through line 55 having a pressure-reducing valve 5i and the withdrawn oil is introduced into a stripping chamber 52 which is normally maintained at a pressure materially below that existing'in the fractionating tower 23. l

The reduction inpressure within the chamber 52 liberates, in vapor form, lighter constituents from the residual material. The upper zone of the stripping chamber 52 is provided with fractionating elements 53 for condensing all but th vapors having the desired end point.

l As illustrated, I also prefer to separatea condensate `fromthe vapors evolved in the stripping chamber and to this end the upper zone of the tower 52 is provided vwith an'annular trough 54 forming a central vapor passage 55 having an angular deiiecting plate 55 for diverting condensate formed in the upper zone into the annular trough.

The condensate collected in the pan 54 is ordinarily not' su'lciently free from coke-forming constituents as to be entirely suitable for subjection to severe cracking temperatures within the cracking coil I2 and consequently I prefer to subject this condensate to a milder heat treatment in a separate tubular heating coil. Accordingly Vthe condensate is `withdrawn from the annular trough through line 5l' provided with a pump 58 which forces the oil through heating coil 59 mounted in the furnace setting Iii. The

condensate after passing through the heating coil 59, wherein it is subjected to a mild heat treatment, which may be just below, or in the range of incipient cracking or a substantial degree of cracking, preferably in the liquid phase,

is discharged through line SIB into the transfer lineleading from the cracking coil to the coking drum and in which it admixes with the cracked products from the coil I2. If desired the line 6G may discharge directly into the coking drum I5.

The uncondensed vapors from the stripping tower 52 are withdrawn through line 5I leading to a condenser 52 in which the desired constituents are condensed after which they are passed to a collecting tank 63 having a gas outlet 64 and a liquid withdrawal line 55 provided with a valve 66.

The liquid withdrawn from collecting tank 63 lis ordinarily suitable for cracking treatment and may consequently be introduced into line 45 leading to the cracking coil i2. If desired, however,

all or part of this fraction may be withdrawn from the system through line 5l and subjected Vto Afurther treatment such as a reforming treatment or all or part of it vmay .be introduced 68 into the line 5l leading to the heatingA coil'59. As shown suitable Valves are Yrto ber 52 ,under sub-atmospheric pressure, in which f case conventional operating means may be employedin line 6I or in connection with drum 63 to maintain the required degree of vacuum.,

Under these circumstances it may be advantageous to condense substantiallyI all of the evolved vapors in the upper fractionatingsection of vessel 52, providingan additional drawoff pan for the lighter condensate above the pan 54,' this lighter condensate being returned to line l5 leadl f ducive" to the mostv effective conversion of lthe,

. products withoutregard to the temperature conditions lde'siredto be-maintained in thecoking ing to crack-coil I2, while that from-theV lower pan 54 is handled through heatingcoil 59 'as previously'described.r The vapors leaving through v,line 6I( may becondensed yby direct contact with cooled condensate from the'baseof` fractionator 38 and the composite subsequently passed to one j orthe other `of the towers yfor reflux cooling. o

` Instead of ldepending'upon the reduction in pressure4 to effect distillation of the bottoms passed from the primary tower 23 to the distilling or stripping tower 52, the lower end of the tower 52 may be heated by suitable means and/or steam or other suitable gas may be introduced thereinto to effect the desired distillation or stripping of the said bottoms.

The residual material from the bottom of the stripping tower 52 is withdrawn through line 69 having an oil pump 10 for forcing the oil into the coking drum through line 'Il having manifold discharge outlets '12, 13 and 14 so that the residual Amaterial may be introduced into the coking drum `at any one or more vertical Zones in the drum. The point of introduction of the various `materials into the coking drum will depend largely vupon the conditions desired to be maintainedl within the drum which in turn will be determined Aprincipally by the end products desired. Forex- Aample it has been found that priming; that isl to say, the carrying over of entrained coke and pitch into the vapor lines, can be `largely avoided vby properly distributing the point of introduction of the oil streams into the coking drum.

Better results areordinarly secured, however,

by passing the residual materials from pump 1|] Y into the combined discharge line 8D from Vthe two 'sections of the heater, through line 8| to commingle withthese hotternoilsbciore entering the coking drum.

` Y The coking drum YI5 is shown provided with a bottom manway for the purpose'of coke removal when running to coke and a well 16 is.

shown adapted to contain suitable coke boring apparatus. When ruiming to a semi-solid re- Asiduum such as pitch, thehot residue while still in liquid form may be withdrawn through line 11. In the latter case'the resulting pitch will solidify upon cooling and may be pulverized for use aspowdered fuel or otherwise utilized.

When running to coke it is preferable to provide a plurality of coking drums l5 arranged in parallel so that any oneV or more of theV drums may be disconnected from the remainder of the unit without interrupting operation of the unit and lthe coke removed Y'rom the disconnected drum after which the cleaned drum may be placed back in service and another drum or drums disconnected and cleaned in a like manner. If desired the line 45 leading to the cracking coil I2' and the line 51 leading to the heating coil 59 may be interconnected by a line 18 provided with a valve 19 so that in event an insuicient supply oi condensate from the stripping tower 52 is available` a'porti'on ofv the oil from line 45 may be overheating of the tubes.

bottom of the primary fractionating tower in the manner hereinbefore described, whereinv the lighter constituentsare removed prior to passing the same to thecoking drum and wherein a desired fraction of the residual material from the fractionating tower is given a preliminary independent heattreatment-before being passed to passed through vheating coil 59 and thus preventA By treating the residual material from the the coking drum,` makes it possible to maintain temperature conditions inthe cracking zone condrumland` conversely, the coke drum 'may .be maintained under desired temperature conditions conducive to most effectively convert thecontents ofthe coke drum to thewdesired end products without adversely affecting the temperature conditions'desired to Ybe maintained in the cracking zone.

For a better understanding of the invention the following moreA specific example, of temperature and pressure conditions suitable for carrying out the method, maybe helpful, it being understood .i thatthe invention is not limited or dependent tially or entirely of reflux condensate from the I fraotionating tower 38, may be heated to a temperature ranging from 800 to 1000 F. while passing throughthe cracking coil l2 during which time it may be subjected to an outlet pressure ranging, for example, between 200 and rZ 'pounds per square inch. The cracked products, from coil I2, introduced into the coking drum I5 and coming into contact with the residual and Y fractionated productsfrom the stripping cham- ,ber Y52 may be permitted to come to an equiordinarily desirable to maintain these pressures in excess of 100 pounds per square inch in order that pressure of the gas at the outlet of the receiver 42 may be suiliciently high to be introduced into the gas lines. The-pressures in these chambers may, however, be maintained considerably in excess ofV 100 pounds if desired and mayV be of the order of 400 or 500 pounds or even more.

The vapors, from the coking drum, introduced into the fractionating chamber 23', may be at a temperature approximating 750 to,90()k F. and the uncondensed vapors in fractionating tower 23 may be cooled to a temperature ranging from.

650 to 750 F. before being introduced into the second fractionating tower 38. The vapors in fractionating tower 38 are cooled sufciently to produce the desired end product such as, for exv ample, in the neighborhood of 300 F.

The residual products from fractionating tower 23 may be introduced into the stripping chamber 52 at a temperature ranging from 700 to 800 F. as hereinbefore described the pressure conditions within the stripping zone will depend upon the kind and extent of stripping action desired. In cases where the stripping is to be effected by reduction in pressure the pressure will be materially lower than that existing in fractionating Vchamber 23 and may, for example, be at a pressure below 25 pounds per square inch down to pressure approaching a vacuum. In cases where it is desired to effect the stripping action partially or entirely by additional heat or by steam the pressure may be maintained at or below the pressure maintained in the fractionating chamber 2S such as, for example, from 50 to 100 or more pounds. The condensate from the stripping zone passing through coil 59 may be heated to a temperature ranging from 600 to 800 F., for example, so that the oil will be brought to a temperature below cracking if desired or substantial cracking may be effected as desired.

The residual products from the stripping tower 52 may be introduced directly into colring drum i5 at a temperature approximating from 600 to '700 F. and the condensate from tower 38 may be introduced to the inlet ofthe cracking coil i2 at a temperature approximating from 550 F. to 650 F.

In cases where it is desired to introduce fresh oil such as raw or reduced crude, for example, into the fractionating tower 23 the oil may be preheated by passing through coil 30 to a temperature approximating from 300 to 500 F. or it may be passed to the fractionating tower without previous preheating. Y

While the preferred embodiment of the invention has been described, and a specific example given for illustrative purposes, it is understood that the invention embraces such modifications and variations as come within the scope and spirit thereof and that the invention is not to be limited except as necessary to distinguish from prior art.

What I claim is:

1. In the treatment of hydrocarbon oils, wherein the oil is converted into ultimate products consisting principally of a motor fuel and a solid or semi-solid residue, the process which comprises heating an oil containing higher boiling hydrocarbons to a temperature and for a period of time suflicient to convert higher boiling hydrocarbons into lower boiling ones, while maintaining said hydrocarbons under a pressure materially above atmospheric, fractionating vapors evolved during said conversion treatment in a plurality of independent fractionating zo-nes, contacting the hot products from said conversion treatment with fresh oil in the rst of said fractionating zones to thereby heat said oil and vaporize lighter constituents therefrom, distilling residual products from said first fractionating zone under a pressure materially lower than that existing in said first fractionating zone to thereby vaporize lighter constituents therefrom, passing the residual products from said distillation to a residueforming zone, heating the distillate resulting from said distillation, passing the heated distillate and products undergoing conversion into said residue-forming zone in direct contact with the residue products resulting from said distillation, whereby heat from said distillate and products undergoing conversion is utilized to form an ultimate product substantially solid at normal room temperatures, withdrawing vapors from another of said fractionating zones and condensing a desired gasoline fraction therefrom.

2. In the treatment of hydrocarbon oils, wherein the oil is converted into ultimate products consisting principally of a motor fuel and a solid or Ysemi-solid residue, the process which comprises heating an oil containing higher boiling hydrocarbons to a temperature and for a period of time sumcient to convert higher boiling hydrocarbons into lower boiling ones, while maintaining said hydrocarbons under a pressure materially above.atmospheric, fractionating vapors evolved during said conversion treatment in a plurality of independent fractionating zones, contacting the Vhot products from said conversion treatment with fresh oil in the first of said fractionating zones to thereby heat said oil and vaporize lighter constituents,therefrom, distilling residual products from said first fractionating zone to thereu v by vaporize lighter constituents therefrom, passing the residual products from said distillation to a residue-forming zone, heating distillate resuit-ing from said distillation, passing the heated distillate and products undergoing conversion into said residue-forming zone in direct contact with the residue products resulting from said distillation, whereby heat from said distillate and products undergoing conversion is utilized to form anY ultimate product substantially solid at normal room` temperatures, withdrawing vapors from another of said fractionating zones and condensing a desired gasoline fraction therefrom.

3. In the treatment of hydrocarbon oils wherein the oil is converted into ultimate products consisting principally of a motor fuel and a solid or semi-solid residue, the process which compris-es heating an oil containing higher boiling hydrocarbons to a temperature and for a period of time sufficient to convert higher boiling hydrocarbons into lower boiling hydrocarbons: while maintaining said hydrocarbons under a pressure materially above atmospheric, fractionating vapors resulting from said conversion treatment in a plurality of independent fractionating zones, distilling heavier condensate from the rst of said fractionating zones under a pressure materially lower than that existing in said first fractionating zone to thereby vaporize lighter constituents therefrom, fractionating said lighter constituents to form a lighter and heavier fraction, subjecting said lighter fraction to conversion treatment, separately heating said heavier fraction and passing said heavier fraction into a residue-forming zone, passing products undergoing conversion into said residue forming zone, passing residual products resulting from said distillation to said residue-forming zone in direct contact with products introduced thereinto to thereby utilize the heat of said products to form an ultimate product which is substantially solid at normal room temperature, withdrawing vapors from the last of said fraction'ating zones and condensing a desired gasoline fraction therefrom.

4. In the treatment of hydrocarbon oils wherein the Y oil is converted into ultimate products consisting chiefly of motor fuel and a solid or semi-solid residue, the process which comprises heating an oil containing higher boiling hydrocarbons to a temperature and for a period sufficient to convert higher boiling hydrocarbons into lower boiling ones while maintaining said hydrocarbons under a pressure materially above atmospheric, fractionating vapors resulting from said conversion treatment in a plurality of independent fraccondensate to said-enlarged,zone-wherein vapor-- Y ous and residual constituents are separated.l il

tionatingzones, contactingthe hot products from said conversion treatment from freshoil in the iirstrof said fractionating Zones to thereby heat said oil and vaporize lighter constituents there- ,fromr distilling residual products from said Vfirst fractionating Zone under a pressure materially lower than that existing in said fractionating Zone to thereby vaporize lighter `constituents therefrom, fractionating the evolved vapors resulting from said distillation and separating aA lighter and heavier fraction from said distilled vapors, subjecting said lighter fraction to said conversion treatment, separately heating said heavier fraction, passing said heated heavier fraction to a residue-forming zone, passing products undergoing conversion to said residue forming Zone, contacting residual'products resulting from said distillation with products introduced into said residue-forming Zone to thereby utilize heat from said products in forming an ultimate product substantially solid at normal room temperature, removing vapors from the last of said fractionating zone and condensing a desired gasoline fraction therefrom.

5. In the treatment of hydrocarbon oils wherein the hydrocarbons are converted into ultimate.

Y pressure to convert higher boiling hydrocarbons nam-ed heated condensate and the products resulting from said rst mentioned pyro-lytic treatc ment in an enlarged zone to thereby convert residual material into a product substantially Vsolid Y at normal temperatures. y

6. In the art of converting higher boiling hydrocarbon oils into lower boiling ones whereinoil is heated to a cracking temperature under superatmospheric pressure and thereafter passed to an Y enlarged zone wherein vaporous and residual constituents, heating said condensate-to an elevated stituents of the heated oil are separated, the vaporous constituents being thereafter subjected to fractionation in a plurality' of fractionating Zones, and fresh charging oil introduced into the rst of said fractionating zones, the improvement that comprises distilling residual products of said fresh oil and condensate from the first of said fractionating zones at lower pressure than that obtaining in thev first fractionating zone to thereby vaporize lighterconstituentstherefrom,passing residual products resulting from said distillation directly tosaid enlarged zone wherein vaporous and residual constituents' are separated, recovering a condensate from said vaporized lighter contemperature separately from said oil heated to a cracking temperature and passing the thus heated 7. In vthe art of converting fhigher boiling hydrocarbon oilsjinto lower-boiling ones wherein oil is heated to a cracking temperature under-superatmospheric pressure and thereafter passed to Ian enlarged zone wherein vaporous and residual constituents of the heated oil are separated, the vaporous constituents being thereafter subjected to fractionation in a plurality of fractionating zones, and fresh charging oil introduced into the first of said fractionating zones, the improvement that comprises distilling residual products of said Yresh oil and condensate from the first of said .fractionating Zones at lower pressure than that obtaining in the rst fractionating Zone to there- `by vaporize lighter constituents therefrom, passing residual products resulting from said distillation directly to said enlarged zone wherein vaporous and residual constituents are separated and withdrawing condensate from a subsequent one of said fractionating zones and passing the samerto said cracking operation as distillate charging stock therefor.

8. The method of converting hydrocarbon oils into lighter and heavier products which comprises subjecting a stream of distillate charging stock to Y cracking and discharging the stream of cracked products into an enlarged conversion chamber, separately withdrawing vapors from said conversion chamber and passing them. through a plurality of fractionating zones arranged in series, introducing heavy charging oil intothe-frst of said series of fractionating zonesy whereby said charging oil intimately contacts the vapors there-Y in and light constituents are distilled therefrom, separately withdrawing from said first fractionating zone residues of said charging oil and passing the same to an independent distilling zone wherein vaporizable constituents are distilled therefrom, forming a condensate from the latter distilled constituents and heating said condensate to a high temperature while flowing it in an independent restricted stream, thereafter discharging the stream of heated condensate into said conversion chamber, separately withdrawing from said independent distilling Zone unvaporized residue and passing the same into said enlarged conversion Chamber wherein it is additionally distilled and converted by contact with the aforementioned streams of highly heated products discharged thereinto, and withdrawing reflux condensate from a subsequent one of said series of fractionating zones `and passing the same to said cracking operation as distillate charging stock therefor.

9. In a method of processing hydrocarbon oil wherein a clean condensate stock is passed through a heating coil and raised to a cracking temperature while under superatmospheric pressure adequate to form a substantially solid residue by the heat imparted to; said stock during its passage through the heating coil, the products from the heating coil transferred to an enlarged coking zone wherein residue is converted tol coke by the contained heat thereof and the vapors liberated within the coking zone separately withdrawn therefrom; the improvement which comprises fractionally condensing said vapors in a fractionating Zone in contact with fresh oil containing constituents unvaporizable under conditions there obtainingto condense at least part of the insufliprocess, withdrawing a mixture of unvaporized form a condensate, heating said condensate to a fresh oil and reux condensate from said fraccracking temperature, thereafter discharging the tionating zone, subjecting said mixture to distillaproducts thus heated into said coking zone and ion ata lower pressure than that obtaining in said passing residual constituents resulting from said 5 fractionating zone to Vaporize a lower-boiling distillation directly to said enlarged coking zone. 5

raction therefrom, fractionating said vapors to GEORGE ARMISTEAD, JR.

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