US2110495A - Conversion of hydrocarbon oils - Google Patents

Description

March 8, 1938.

c. H. ANGELL CONVERSION oF HYDRocARBoN oILvs Filed Dec. l1, 1935 Patented Mar.. 8, i938 PATENT lori-*ICE coNvaasroN or nynaoclianoN ons Charles H. Angell, Chicagm'll., assignor to Universal Oil Products Company, Chicago, lll., a corporation of DelawareY i Application December 11, 1935, serial Na -saisis 12 anims. (c1. iss- 49) 'I'his invention, particularly refers to an improved process for the conversion of hydrocarbon oils employing two cooperative cracking stages wherein relatively high-boiling oils. comprising intermediate liquid conversion products of the process and any high-boiling fractions of the charging stock. are subjected to relatively mild cracking conditions inthe first stage while relatively low-boiling oils, comprising low-boiling conversion products from the rst stage and any desired low-boiling fractions of the charging stock, are subjected to more severe cracking or reforming conditions in thev second stage, and With'provision for recovering liquid residue from either or both cracking stages orv for reducing residual liquid from either lor both cracking stages to substantially dry coke in a cooperative coking stage of the system. A

One specic embodiment of the invention comprises subjecting an oilof relatively high-boiling characteristics, recovered from within the system, as will be later described. to conversion conditions of cracking temperature and superatmospheric pressure in a heating coil, introducing the heated products into an enlarged chambery wherein separation of vaporous and liquid conversion. products is accomplished,V withdrawing the latter from said chamber, subjecting the vaporous conversion products toy fractionation in commingled state with hydrocarbon oil charging stock forthe process. whereby the Acommingled oilsare separated into selected relatively lowboiling and high-boiling fractions, returning the selected high-boiling fractions `from said fractionating step to the heating coil`for conversion,

recovering any. selected desirable low-boiling fractions from the fractionating step, subjecting other `selected relatively low-boiling fractions from the fractionating step to independently controlled conversion conditionso cracking temperature and superatmcspheric 4pressure in a separate heating coil, cooling the heated products from said separate heating .coil sufliciently to prevent any substantial further conversion thereof, separating the resulting products into vapors' and non-vaporous residue,V removing the latter from the zone of separation, subjecting the vapors to fractionation whereby their insumciently converted components are 'condensed as reiluxA condensate, returning the reilux condensate to'` the first mentioned heating coil for further conversion, subjecting fractionated Vvapors of the desired end-boiling point from the last mentioned fractionating step to condensation and recover- 55. ing the resulting distillate.

Residual liquid recovered from either the relatively light oil vcracking operationor the relatively heavy oil cracking operation, or both, may be removed from the system as a nal residual product thereof or a portion or all of either or 5` A both of these materials may be heated to a relatively high temperature under non-coking conditionsin a separate heating coil and thence introduced into an enlarged coking chamber wherein their high-'boiling components are reduced to l0 substantially dry coke, vaporous products from the coking operation being returned either to the same chamber to which the hot conversion products from the first mentioned heating coil are supplied or to the separating zone to which the 15 partially cooled products from said separate heating coil are supplied or, in part, to both these zones.

The`features and advantages of the 'present process will be readily apparent to those familiar 20 to the cracking art, particularly with reference to the accompanying diagrammatic drawing and the following description thereof. The drawing illustrates one specic form of apparatus embodying the features of the invention and. sev- 25 eral of the various modlcations of theembodtment of the invention above outlined, which are contemplated within thel scope of the invention, are indicated in the ldrawing and-described in conjunction therewith. 30l

Referring to the drawing, charging stock for the process, which may comprise `any desired type -of oil rangingfrom straight-run gasoline,

lnaphtha or other light distillate through the various fractions of crude petroleum to fuel or 35 heavy residual oil and specifically including crude petroleum or other oil of relatively wide lboiling range which may contain straight-run or cracked. motor fuel or motor fuel fractions, ls

supplied through line I and valve 2 to pump 3 40 by'means o which it maybe fed through line 4 and valve Sinto fractionator 6 to commingle therein witlt thehot vaporous conversion products supplied to this zone, as will be later described, whereby the charging stock is subjected 45 to substantial vaporization and to fractionation together with the vaporous conversion products, f

lor, when desired, the charging stock may be diverted from line 4 vand passed, 'all or in part, through line l', valve 5" and line into cham- 50 ber 1 wherein 1t commingles with the hot conversion products supplied to this zone, as *will be .later described, and i s therein subjected to substantial vaporization, its ,vaporized components passing therefrom, as will be later more I4 to subject the Asame to the desired conversion temperature, preferably at a substantial superi atmospheric pressure, and the resulting hot con-- version products are discharged through line I6 and valve I1 into chamber 1.

Chamber 1', which may function as a reaction zone or as a reduced pressure vaporizing chamber., may be operated at any desired pressure ranging from substantially atmospheric to substantially the same pressure as that employed at the outlet from heating coil I4. Separation of the vaporous and non-vaporous components of the conversion products supplied to chamber 1 is accomplished in this zone and when charging stock is supplied thereto its low-boiling components are vaporized and commingle with the.

vaporous conversion products while any highboiling components of the charging stock, similar in boiling range to the residual liquid conversion products separated from the vapors in this zone, commingle with said residual liquid. The residual liquid products are withdrawn from the lower portion of chamber 1 through line I8 and may be directed, all or in part, through line I9 and valve 28 to cooling and storage or elsewhere, as desired or they may be directed, all or v in part, as will be later more fully described, to further treatment within the system. The vaporous conversion productsare withdrawn from the upper portion' of -chamber 1, together with vaporous components of any charging stock supplied to this zone, and directed through line ZI and valve 22 to fractionation in fractionator 6.

The vaporous conversion products thus supplied to fractionator 6 are separated in this zone, together with any charging stock supplied thereto, into selected relatively low-,boiling and high- 4boiling fractions. The high-boiling fractions are withdrawn, aspreviously described, from the lower portion of the fractionator'and supplied to heating coil I4. I

Selected low-boiling fractions are withdrawn vtogether with uncondensable gas from the upper portion of the fractionator and directed through line 23 and valve 24 to condensation and cooling in condenser 25. The resulting distillate and .gas passes through line 28 and valve 21 to vcollection and separation in receiver 28. Un'condensable gases may be released from the receiver through line 29 and valve 38. A portion or all of the distillate may, when desired, be directed from receiver 28 through line 3| and. valve 32 to storage or elsewhere, as desired.

In case the total motor fuel conversion products of this stage of the system and any gasoline or gasoline fractions contained in the charging stock are of satisfactory antiknock value preferably only this material is withdrawn inV vaporous state from the -upper portion of the fractionator,

V Acondensed and recovered, as described, in receiver 28, or, in case only. selected low-boiling components of the motor fuel conversion products and any corresponding fractions of the charging stock are of satisfactory antiknock value, the distillate collected in receiver 28 is preferably limited to such material. On the other hand in case the low-boiling components of the commingled charging stock and vaporous conversion products do not contain any appreciable quantity of materials within the boiling range of motor fuel which are of good antiknock value, the total motor fuel components of the commingled materials, either alone or together with selected somewhat higher boiling fractions thereof such as, for example, naphtha, kerosene or kerosene distillate, light gas oil and the like, are recovered, as described, in receiver 28, in which case all or a regulated portion of this material is directed from receiver 28 through line 33 and valve 34 to pump 35 by means of which it is supplied to further conversion or reforming in heating coil 4I, as will be later more fully described.

In case motor fuel or motor fuel fractions of satisfactory antiknock value are recovered in receiver 28 somewhat higher boiling components of the commingled vaporous conversion products and charging stock, including any motor fuel fractions of inferior antiknock value and also preferably including somewhat higher boiling oils such as naphtha, kerosene, kerosene distillate, light gas oil and the like, are withdrawn as condensate from one or a plurality of suitable intermediate points in the fractionatonprovision be-L ing made in the case here illustrated for supplying such material from the fractionator through line 36 and valve 31 to pump 35, by means of which vit is directed to heating coil 4I for further conversion. y

The relatively low-boiling oil supplied, as described, to pump 35 is directed therefrom through line 38 and may pass therefrom, all or in part,

' through line 38 and valve 48 to heating coil 4I.

. heated to the desired relatively high conversion vtemperature under any desired pressure conditions ranging from substantially atmospheric to 1000 pounds, or more, per square inch superatmospheric pressure. A substantial superlatmospheric pressure of several hundred pounds per square inch is, however, preferred in heating coil 46 particularly in case any substantial quantity of materials of poor antiknock value within the boiling range of motor fuel are supplied to this zone f or reforming. The stream of highly heated products is discharged from heating coil 4I through line 41 and valve 48 and is preferably directed through heat exchanger 43 wherein substantial cooling of the hot conversion products is accomplished. as previously described, the partially cooled products being directed from ,heat exchanger 43 through line 48,

`valve 50 and line 5I into separating chamber 53.

It is, of course, entirely within the scope of the invention to by-pass heat exchanger 43 and/or to employ other means for cooling the 2,110,495 3 y stream of hot conversion products from heating coil 4I. Such other cooling means may comprise, for example, the introduction of a suitable cooling oil into the stream of hot conversion products from heating coil 4I, by well known means not illustrated. Such cooling oil may comprise, for example, selected nal or intermediate liquid products of the process such as distillate from receiver 69, a portion of the total or selected fractions of the reux condensate from fractionator 54 and the like.

Chamber 53, in the case here illustrated, comprises the lower portion of column 52, the yupper portionof which comprises fractionator 54, although separate structures may, of coursebe employed for these two zones, when desired. In

case heating coil 46 is operated at a substantial superatmospheric pressure a substantially reduced pressure is preferably employed in chamber 53, pressure reduction being accomplished either by the regulation of valve,48 in line 41 or valve 50 in line 49, or both. This reduction.

in pressure serves to additionally cool the conversion products supplied to chamber 53 and alsoserves to assist vaporization in this zone. Separation of the vaporous and residual'liquid components of the materials supplied to chamber 53 is accomplished therein, the latter being withdrawn from the lower `portion thereof through line 55 wherefrom they may, when desired,'be directed, all or in part, through line 56 and valve 51 to cooling and storage or elsewhere, as desired, or this material may be d.'- rected, all or in part, to further treatment for its eventual reduction to coke, as will belater more fully described. Vaporous products pass from chamber 53, through a suitable partition 58 into fractionator 54, wherein their components boiling above the range of the desired inal light distillate product of this stage of the process are condensed -as reflux condensate.

The reflux `condensate formed in fractionator 54 is withdrawn from the lower portion thereof, above partition 53, through line 59 and valve 60 to pump 6I by means of which it is supplied through line 62, valve 63 and line I3 to conversion in heating coil I4, in the vmanner previously described.

Fractionatedv vapors lof the desired end-boiling point are withdrawn, together with uncondensable gas, from the upper portion of fractionator 54 and directed through line 64 and valve 65 to condensation and cooling in condenser 6B. The resulting distillate and uncondensed gas passes through line 61 and valve 68 tol collection and separation in receiver 69. Uncondensed gases may be released from the receiver through line 10 and valve 1I. Distillate may be withdrawn from receiver 69 through line 12 and valve 13 to storage or to any desired further treatment.v

When desired, regulated quantities ofthe distillate collected in receiver 69- may loerecirculated by well known means, not illustrated in the drawing, into the upper portionv of fractionator 54 to serve as a reuxing and cooling medium in this zone for assisting fractionation of the vapors and to maintain the desired Vapor outlet temperature therefrom. This same expedient may also be employed, when desired, for cooling and |assisting fractionation of the vapors in fractionator 6 by returning regulated quantities of the distillate from receiver 28 to fractionator 6 by well known means, not illustrated.

It is, of course, also within the scope of the invention, when desired, to separate the reflux I condensate formed in fractionator 54 into selected relatively low-boiling and high-boiling fractions, in which case only the relatively highboiling fractions are supplied from the lower portion of the fractionator to conversion in heating coil I4, in the` manner previously described, while selected lower boiling fractions are withdrawn by well known means, not illustrated, from one or a plurality of suitable intermediate points in the fractionator 'and may, when desired, be returned by well known means, not illustrated, to further conversion in heating coil 4I. 'Ihis method of operation is particularly advantageous in case the vaporous products undergoing fractionation 4in column 52 contained high-boiling motor fuel fractions whichare of unsatisfactory antiknock value and which may, by the method described, be returned to further treatlmerit in heating coil III. It may also be desirable in case the oil supplied to heating coil-4I from receiver 28 lor fractonator 6 contains materials above the lboiling range of motor fuel, in which case materials of similar boiling range may be supplied, in the manner described, from fra-c- .tionator 54 to heating coil 4I.

.li-portion or au of the residual liquid with- .drawn from chamber 1 through line` I8, as previously described, may, when desired, be directed through valve 14 in this line to pump 15 by means of which it is directed through line 16, valve 11 and line 18 to further treatment in heating coil 19. The invention also contemplates further treatment, when desired, of a regulated portion or all 'of the residual liquid from chamber 53 in heating coil 19, ink which case this material may be directed through valve 80 in line 55 to pump 8I by means of `which it is supplied through line 82, valve 83 and line -18 vto heating coil 19.

Heating coll 19 is located within a suitable furnace v84 by means of which the oil supplied to the heating coil is preferably heated to a relatively high conversion temperature without allowing it to remain in this zone-for a suiiicient length of time to permit any substantial formation and deposition of coke in,the heating coil and communicating` lines. The stream of highly heated relatively high-boiling oil is discharged.

from heating coil 19 through line 85 and valve 8S into coking chamber 81 wherein its high-boiling components are reduced to substantiallydry coke by means of heat supplied to the oil passing through heating coil 19.

Chamber 81 may be operated at any desired pressure ranging from substantially atmospheric to a superatmospheric pressure of several hundred pounds per square inch which, however, is

also serve, when desired, as a means of introducing steam, water or other suitable cooling material into the chamber after its `operation is completed and after it has been isolated from the rest of the system in order to hasten cooling and facilitate removal lof the coke. A plurality of coking chambers may, of course, be employed, when desired, although only one is illustrated in the drawing, in which case the chambers preferablyare alternately operated, cleaned and prepared for further operation in order that the coking stage, in common with the rest of the system, may be operated continuously. Vaporous products are withdrawn from the coking chamber through line 9| and maybe directed through line 92, fvalve 93 and line 5i to chamber 53 wherein any high-boiling components of the vapors, including any entrained tars or pitchlike material unsuitable for conversion with the reflux condensate froml fractionator 54, are 'separated therefrom and commingle with the residual liquid withdrawn from chamber 53. In case the coking chamber is operated at a somewhat higher pressure than that employed in chamberyl all or a portion of the vaporous products from the coking chamber may, when desired, be directed through lineV 94 and valve 95 into chamber 1 wherein undesirable high-boiling components of the vapors are collected together with the residual' liquid withdrawn from this zone.

In case chamber 1 is operated at a substantial superatmospheric pressure it may be desirable to subject the residual liquid from this zone to further vaporization for the purpose of recovering desirable low-boiling components therefrom which are suitable for further conversion within the system to produce additional yields of motor fuel; For this purpose provision is made in the case here illustrated for supplying all or a regulated portion of the residual liquid withdrawn from chamber 1 by way of line 16 through line 96 and valve 91 into the reduced pressure vaporizing chamber 53 and this method of operation may be employed regardless of whether the process is operated for the production of liquid residue, coke, or both.

The preferred range of operating conditions which may be employed to accomplish the desired results in an apparatus such as illustrated and above described may be approximately' as follows: The first mentioned or relatively heavy oil heating coil may employ an outlet conversion temperature ranging, for example, from 800 to 950 F. preferably with a superatmospheric pressure at this. point in the system of from 100 to 500 pounds, or more, per square inch. Any desired pressure ranging from substantially atmospheric up to substantially the same pressure as that employed at the outlet from this heating coil may be utilized in the succeeding reaction or vaporizing chamber and this pressure may be substantially equalized or reduced in the succeeding fractionating, condensing and collecting portions of this stage of the system. The relatively light oil heating coil preferably employs an outlet conversion temperature ranging, for

example, from 950 to 1050 F. and the pressure employed in this zone, as measured at the o utlet therefrom, may range from a low superatmospheric pressure of 30 pounds, or thereabouts,

dper square inch to a superatmospheric pressure 75 system. The residue heating coil preceding the coking chamber, when this stage of the process is employed, may utilize an outlet conversion temperature ranging, for example, from 900 to 1000 F. preferably with a superatmospheric Vpressure of from 30 to 300 pounds, or thereabouts, per square inch, and with a relatively short time element in this zone, as previously indicated. 'Ifhe coking chamber may be operated at any desired pressure ranging from substantially the same as that employed at the outletfrom the communicating residue heatingcoil down to substantially atmospheric pressure.

As a specific example of one of the many operations of the process of the inventionas it may be accomplished in an apparatus such as illustrated and above described, the charging stock comprises aY Michigan crude of about 35.5 A. P. I. gravitycontaining approximately 28.5 per cent of 400 F. end-point straightrun gasoline having an octane number of approximately 43 by the motor method. Thecharging stock is supplied to the fractionator of the relatively mild cracking stage of the process from which is removed an overhead distillate product containing all of the straight-run gasoline and the motor fuel produced in the relatively mild cracking stage as well as somewhat higher boiling components of the charging stock and ofsthe conversion products from the relatively mild cracking stage boiling up to approximately 500 F. The higher boiling components of the chargingstock and the total intermediate vliquid conversion products of the process, comprising the reflux condensate formed in the fractionator, are subjected in the heating coil of this stage to an outlet conversion temperature of approximately 920 F. at a superatmospheric pressure of about 400 pounds per square inch and this pressure is substantially equalized. in the succeeding reaction chamber from which vaporous products are supplied to the same fractionator to which the charging stock is supplied while residual liquid products from the reaction chamber are supplied to the vaporizing and separating chamber of the relatively light oil cracking or reforming stage of the system. Said light distillate product recovered from the topping and relatively mild conversion stage is subjected in the 4light oil cracking or reforming coil to an outlet conversion temperature of approximately 980 F. at a superatmospheric pressure of approximately 890 pounds per square inch andthe heated products from this zone are passed .in indirect heat exchange with the distillate supplied thereto and are then introduced into the reduced pressure vaporizing and separating chamber which is operated at a superatmospheric pressure of approximately 50 pounds per square inch. 'I'his pressure is substantially equalized in the fractionating, condensing and collecting equipment of this stage of the system. Residual liquid from the reduced pressure vaporizing and separating chamber is quickly heated in a separate heating coil to an outlet -conversion temperature of approximately 1000 F. at a superatmospheric pressure of about 60 pounds per Square inch and is then introduced into alternately operated coking chambers maintained at substantially the same pressure, wherein their high-boiling components are reduced to coke and from which vaporous products are supplied to said reduced pressure vaporizing and separating chamber. Reflux condensate from the fractionator of the relatively light oil cracking or reforming stage is returned to, the rst mentioned cracking coil. This operation will produce, per barrel of charging stock,

l mainder being chargeable, principally, to uncondensable gas.

I claim as my invention:

1'. In a process for the conversion of hydrocarbon4 oils wherein oils of relatively high-boiling characteristics recovered from within the system are subjected to conversion conditions of cracking temperature and superatmospheric pressure, the resulting vaporousand residual liquid conversion products separated and the vaporous products subjected to fractionation in commingled state with hydrocarbon oil charging stock for the proc- A ess, the improvement Awhich comprises recovering from the. fractionating step any desirable lowooiling components of the commingled charging stock and vaporous conversion products, separating the remaining components of the commingled materials into relativelylow-boiling and highboiling fractions, subjecting the latter to said conversion, separately ysubjecting said relatively low-boiling fractions to independently controlled conversion conditions of cracking temperature and superatmospheric pressure, cooling the resulting heated products sumciently to prevent any substantial further conversion thereof, separatingthe resulting partially cooled materials into vaporous and residual liquid components, subjecting the vapor to fractionation whereby their insufliciently converted components are condensed as reflux condensate, subjecting fractionated vapors of the desired end-boiling point from the last mentioned fractionating step to condensation, recovering the resulting distillate, and subjecting reux condensate recovered from the last mentioned fractionating step to conversion in the first mentioned cracking stage of the system, separately heating residual liquid from the separating stage of the first-mentioned cracking operation to a high conversion temperature under non-coking conditions, introducing the resultant heated products to a coking zone wherein their high-boiling components are reduced to coke, and returning vaporous products from the coking zone to the separating stage of the second-mentioned cracking operation,

2. A process such as claimed in claim 1 wherein residual liquid from the separating stage of the first mentioned cracking operation, prior to the heating thereof to said high conversion temperature, is commingled in the separating stage of the second mentioned cracking operation with the partially cooled conversion products undergoing separation therein.

3. A process such as claimed in claim 1 wherein partial cooling of the heated products in the t second mentioned cracking stage of the system is accomplished by passing the same in indirect heat exchange with at least a portion of said low-boiling fractions supplied to this stage of the system for conversion. I

4.A process for the conversion of hydrocarbon oils which comprises subjecting oils of relatively high-boiling characteristics recovered from within the system to conversion conditions of cracking temperature and superatmospheric pressure in a heating coil, introducing the heated products into an enlarged reaction chamber also maintained at a substantial superatmospheric pressure wherein vaporous and residual liquid conversion products are separated, subjecting vaporous products from said enlarged chamber to fractionation in commingled state with'hydrocarbon oil charging stock for the process, recovering from the fractionating step any desirable vlow-boiling components of the commingled charging stock and vaporous conversion products, separating the remaining components of the commingled materials into selected relatively low-boiling and high-boiling fractions, supplying the latter to the flrst mentioned heating coil for conversion, subjecting selected low-boiling fractions recovered from the fractionating step to independently controlled conversion conditions of cracking temperature and superatmospheric pressure in a separate heating coil, cooling the heated products discharged from saidseparate heating `coil sufficiently to prevent any substantial further conversion thereof, introducing theresulting partially cooled products into a separating chamber 'operated at substantially reduced pressure relative to that employed in the last mentioned heating coil wherein they are separated into vapors and liquid residue, subjecting the vapors from said separating chamber to fractionation whereby their insuillciently converted components are condensed as reflux condensate, subjecting fractionated vapors of the desired endboiling point from the last mentioned fractionating step to condensation, recovering the resulting distillate, returning reflux condensate recovered from the last mentioned fractionating step to conversion in the rst mentioned heating coil, withdrawing residual liquid from the reaction chamber, introducing the same into said reduced pressure vaporizing chamber, withdrawing non-vaporous liquid residue from the reduced pressure vaporizing chamber, heating the same in another separate heating coil to a high conversion temperature under non-coking conditions, introducing the resulting heated products into a coking chamber wherein their high-boiling vcomponents are reduced to coke, and returning vaporous products from the coking chamber to one of the aforementioned separating zones of the system wherein vaporous and residual liquid products are separated.

5. A vprocess such as claimed in claim 4 Wherein said partial cooling of the heated products from the second mentioned heating coil is accomplished, at least in part, by passing the same in indirect heat exchange with at least a portion of said relatively low-boiling fractions supplied thereto.

6. Avprccess such as claimed in claim 4 wherein charging stockfor the process, comprising a hydrocarbon oil of relatively wide boiling range, is supplied to said reaction chamber.

7. A process such as claimed in claim 4 wherein hydrocarbon oil charging stock for the process issupplied to the first mentioned fractionating stage of the system.

8. In a process for the conversion of hydrocarbon oils wherein oils of relatively high-boiling characteristics recovered from within the system are subjected to conversion conditions of cracking temperature and superatmospheric pressure, the resulting vaporous and residual liquid conversion products separated and the vaporous products subjected to fractionation in commingled state with hydrocarbon oil charging stock for the process, the improvement which comprises recovering from the fractionating step any desirable lowboiling components of the commingled charging stock and vaporous conversion products', separating the remaining components of the commingled materials into relatively low-boiling and high- 'boiling fractions, subjecting the latter to said conversion, separately subjecting said relatively low-boilingv fractions to independently controlled conversion conditions of cracking temperature and superatmospheric pressure, cooling the re.- sultlng heating `products suiilciently to prevent any substantial further conversion thereof, separating the resulting partially cooled materials into vaporous and. residual liquid components,

subjecting the vapor to fractionation whereby` their insuiiiciently converted components are condensed as reux condensate, subjecting fractionated vapors of the desired end-boiling point from the last mentioned fractionating step to condensation, recovering the resulting distillate, and subjecting redux condensate recovered from the last mentioned fractionating step to conversion in the rst mentioned cracking stage of the system, separately heating residual liquid from the separating Vstage of the second-mentioned cracking operation to a high conversion temperature under non-coking conditions, introducing the resultant heated products to a coking zone wherein their high-boiling components are reduced to coke, and returning vaporous products from the coking zone to the. separating stage of the second-mentioned cracking operation.

9. The process as deiined in claim 1 further characterized in thatadditional vaporous products from the coking zone are returned to the mst-mentioned cracking operation.

10. The process as defined in claim 8 further characterized lin that additional vaporous products from the coking zone are returned to the first-mentioned cracking operation.

11. A conversion process which comprises heating hydrocarbon oil to cracking temperature under pressure in a heating coil, separating resultant vapors and unvaporized oil, iractionating the heavy stock to said-coil, subjecting said lighter stock to independently controlled cracking conditions of temperature and pressure in a second heating coil and then separating the same into vapors -and residue, fractionating the former and returning resultant reilux condensate to the rst-named coil, heating atleast a portion of said unvaporized oil tohvigh conversion temperature in a third coil and distilling the same to coke in a coking zone, and supplying vaporous products from the coking zone to the separating stage o the mst-mentioned cracking operation. 12. Avconversion process which comprises heating hydrocarbon -oil to cracking temperature under pressure in a heating coil, separating resultant vapors and unvaporized oil, fractionating the -vapors in commingled state with charging oil for the process to form a relatively heavy ycracking stock and a lighter cracking stock, supplying said heavy stock to said coil, subjecting said lighter stock to independently controlled cracking conditions of temperature and pressure in a second heating coil and then separating the same into vapors andresidue, fractionating the former and returning resultant reux condensate to the .firstnamed coil, heating at least a portionof said unvaporized oil to high conversion temperature in a third coil and 'distilling the same to coke in a coking zone, and supplying vaporous products from the coking zone to theseparating stage of the second-mentioned cracking operation.

CHARLES H. ANGELL.

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