US2090859A - Conversion of hydrocarbon oils - Google Patents

Description

Aug. 24, 1937, J, B, BARNE 2,090,859

JONVERSION OF HYDROCARBON OILS Filed April 6, 1935 STABILIZING COLUMN ABSORBER FRACTIONATOR FURNACE 3| FURNACE I INVENTOR JOHN B.BA NES TORNEY Patented Aug. 24, 1937 UNITED STATES CONVERSION OF HYDROCARBON OILS John B. Barnes, Chicago, Ill., assignor to Unlvcrsal Oil Products Company, Chicago, Ill., a corporation of Delaware Application April 6, 1935, Serial No. 15,017

4 Claims.

This invention particularly refers to an improved process for the selective conversion of relatively low boiling and relatively high boiling hydrocarbon oils under independently controlled conversion conditions of elevated temperature and superatmospheric pressure in separate heating coils wherein the liquid conversion products are subjected to vaporization at substantially reduced pressure relative to that at which they are formed, the resulting non-vaporous residual liquid subjected to coking assisted by commingling therewith, in the coking zone, regulated portions of the highly heated products from the light oil heating coil of the system and wherein the light distillate product of the process, preferably comprising materials of high anti-knock value within the boiling range of gasoline, are subjected to stabilization and the normally gaseous products of the process subjected to absorption, hydrocarbon oil charging stock for the process being utilized as an absorption medium for said gases and the enriched charging stock supplied to a fractionator wherein it is subjected, together with the vaporous conversion products of the process, including those from the coking operation, to fractionation for the recovery of fractionated vapors, from which said light distillate and gas are recovered, and for the formation of intermediate liquid conversion products comprising said relatively low boiling and high boiling oils which are subjected to said conversion.

One of the features of the present invention comprises separation of the hydrocarbon oil charging stock for the process and the intermediate liquid conversion products of the process (reflux condensate) recovered by fractionation of the vaporous conversion products into selected relatively low boiling and high boiling fractions and subjecting said relatively low boiling and high boiling fractions each to independently controlled conversion conditions of elevated temperature and superatmospheric pressure each in a separate heating coil of the same cracking system. 7 Another feature of the invention resides in the use of a furnace, for heating of the high boiling fractions of the charging stock and reflux condensate, of what is known as the double-end fired type, wherein, in the presentinvention; two separate substantially equal streams of said relatively high boiling oil are simultaneously subjected to substantially the same heating conditions and thereby each is subjected to substantially identical conversion conditions of elevated temperature, superatmospheric pressure and con- 55 version time, the two highly heated streams issu-v ing from separate similar sections of the heating coil of the furnace being commingled and supplied to subsequent portions .of the system.

Another feature of the invention residesin the use of another furnace of the double-end-fired type wherein the relatively low boiling fractions of the charging stock and reflux condensate are heated to the desired conversion temperature in a centrally located fluid heating section and in one combustion zone of the furnace and then subjected to what is ordinarily termed soaking under independently controlled heating conditions in the other combustion zone of the furnace whereby the oil is maintained at a. substantially constant relatively high conversion temperature for a predetermined time.

Another feature of the invention comprises the use of highly heated products from the light oil heating coil of the system as a means of assisting reduction of the flashed residue from the vaporizing chamber of the cracking-system to substantially dry coke by commingling said residual liquid with regulated quantities of said highly heated products in alternately operated relatively low pressure coking chambers. Any remaining portion of said highly heated products from the light oil heating coil, not required as a heat carrying medium for the coking operation, is supplied to the same high pressure reaction chamber to which the highly heated products from the heavy oil heating coil of the system are supplied and the vaporous products from the coking zone are returned to the same vaporizing chamber to which liquid and vaporous products from the reaction chamber are supplied and from which the non-vaporous residual liquid subjected to said coking is derived.

Another feature of the present invention resides in theuse of regulated quantities of the relatively high'boiling fractions of the charging stock and reflux condensate as a heating medium for reboiling the light distillate product of the process in the stabilization stage of the system. The high boiling fractions of the reflux condensate and charging stock employed in this manner are thereby cooled and, in the preferred embodiment of the present invention, are then returned to the fractionator of the system to serve as a cooling and refluxing medium in this zone.

Another special feature of the invention comprises the use of hydrocarbon oil charging stock for the process as an absorber oil for removing high boiling components, including propane, butane and their hom0logs, as well as any higher boiling materials, from the normally gaseous conversion products of the process, the enriched charging stock ,being supplied from the absorp tion step to the fractionator of the system.

I am aware that many of the features of the present process are not in themselves new with the present invention but the invention is not based upon the individual features per se but depends upon thenovel and advantageous manner inwhich the individual features are combined in a single unified process in which they are interdependent and in which they mutually contribute to produce the desired final results. It will be understood, however, that-the invention is not limited to the use, in combination, of all of the features above mentioned and/ or subsequently described but is limited only as necessitated by the prior art and defined in the appended claims.

In one embodiment, the invention comprises subjecting an oil of relatively high boiling characteristics to conversion conditions of elevated temperature and superatmospheric pressure in a heating coil and communicating reaction chamber, withdrawing both vaporous and liquid conversion products from the reaction chamber in commingled state and introducing the same into a reduced pressure vaporizing chamber wherein subjecting fractionated vapors of the desired end boiling point to condensation, collecting and separating the resulting distillate and uncondensed gases, subjecting said gases to absorption by contacting the same with hydrocarbon oil charging stock for the process, supplying the enriched charging stock from the absorption step to said fractionating step wherein it commingles with the v'aporous conversion products of the process and issubjected to separation together [with the reflux condensate into selected relatively low boiling and high boiling fractions, returning said highboiling fractions of the charging stock and reflux condensate to the heating coil for further conversion, subjecting said low boiling fractions of the charging stock and reflux condensate to independently controlled conversion conditions of elevated temperature and superatmospheric pressure in a separate heating coil, introducing regulated quantities of the highly heated products from the last mentioned heating coil into the coking chamber to supply heat thereto and assist reduction of the residual liquid conversion prod- ,ucts to coke, supplying any, remaining portion of the highly heated products from the last mentioned heating coil to said reaction chamber, subjecting said distillate recovered by condensa- -tion of the fractionated vaporous conversion products to stabilization to substantially free the same of any excessive quantities of undesirable low boiling components and dissolved gases, supplying heat for said stabilization step by indirect heat exchange between the distillate resulting from said stabilization and regulated quantities of said relatively high boiling fractions of the charging stock and reflux condensate from the liractionator' whereby to reboil said distillate, cooling the resulting stabilized and reboiled distillate by indirect heat exchange with the distillate supplied to the stabilization step, whereby to preheat the latter, and removirm said cooled stabilized distillate from the system as the final motor fuel product of the process.

The accompanying diagrammatic drawing illustrates one specific form of apparatus in which the process of the invention may be accomplished.

- Referring to the drawing, furnace l comprises the relatively heavy oil heating zone of the system to which relatively high boiling fractions of the intermediate liquid conversion products (reflux condensate) and charging stock are supplied,

as will be later more fully described, and wherein the oil is heated to the desired conversion temperature. The furnace here illustrated is what is generally known as a double-end-flred type of furnace having separate. combustion and heating zones 2 and 3 and a centrally located fluid heating zonel. Controlled amounts of combustible fuel and air are independently supplied to each of the combustion and heating zones 2 and 3 through suitable firing tunnels indicated at 5 on opposite ends of the furnace and the hot combustion gases from each of the combustion and heating zones 2 and 3 pass over the respective bridge walls 6 and. l, are commingled in the central portion of the furnace and pass downward through fluid heating zone I to flue 8 and thence to a suitable stack (not shown). The fluid conduit through which the relatively high boiling oil supplied to furnace I is passed is divided, in the case here illustrated, into two substantially equal sections, one of which comprises the right hand half of tube bank 9 located within fluid heating zone 4, tube'bank I located adjacent the roof of combustion and heating zone 3 and tube bank H located adjacent the floor Y of combustion and heating zone I while the other section comprises the left hand side of tube bank 9, tube bank l2 located adjacent the roof of combustion and heating zone 2 and tube bank ll located adjacent the floor of combustion and amounts of the relatively heavy oil in two contially equal heatingconditions and the drop in pressure due to friction through the furnace is greatly reduced as compared with that which would result from passing the total oil through. The two streams of her at any desired point in this zone may be employed. 1

Chamber l8 i preferably maintained at a substantial supera mospheric pressure which may be substantially the same or somewhat lower than that employed at the outlet from the heating coil.

- heating zone By maintaining substantially .equal firing conditions in combustion an'd'heating zones 2 and 3 and by passing substantially equal tinuous streams through the two sections of the fluid conduit all of the oil is subjected to substan The reaction chamber is preferably well lulu- 7Q 'from by radiation so that the heated products supplied to thiszone and particularly their vaporous components are subjected therein to appreciable continued conversion. In the case here illustrated, both vaporous and liquid conversion products are withdrawn in commingled state from the lower portion of chamber I8 through line 20 and valve 2| and are introduced into vaporizing chamber 22.

Chamber 22 is preferably maintained at a substantially reduced pressure relative to that employed in the reaction chamber and the liquid conversion products supplied to this zone are subjected therein to further vaporization. Residual liquid conversion products remaining unvaporized in chamber 22 are withdrawnirom the lower portion of this zone through line23 and valve 24 to pump 25 by means oftwhich they are fed through line 25 and are introduced by means of the respective lines 28 and 28'; con trolled respectively by valves 29 and 29', into coking chambers 30 and 30' wherein they are reduced to substantially dry coke.

Furnace 3| comprising the light oil heating zone of the system is also, in the case here.

illustrated, a furnace of the double-end-flred type having independently fired combustion and heating zones 32 and 33 and a centrally located fluid heating zone 34. Controlled amounts of combustible fuel and air are independently supplied to each of 'the combustion and heating zones 32 and 33 by means of suitable firing tunnels indicated at 35 located at opposite ends of the furnace and the combustion gases from both combustion and heating zones 32 and 33 pass over the respective bridge walls 36 and 37 and are directed downward in commingled state through fluid heating zone 34' to flue 38 and thence to a suitable stack (not shown). In the case here illustrated, relatively low boiling oils from within the system are supplied, as will 'be later more fully described, to that portion of the fluid conduit located within fluid heating zone 34 and thence pass successively through tube bank 40" located adjacent the floor of combustion and heating zone 32, tube bank M located adjacent the roof of the furnace and tube bank 42 located 32 and 33. Preferably, the oil'is heated to or near the desired maximum conversion temperature in passing through tube banks 33, to and the left hand portion of tube bank ll and then is maintained for a predetermined time at a substantially constant temperature near that previously attained as it passes through the right hand portion of tube bank 4H and tube bank 62. The highly heated streamof relatively low boiling oil is discharged from tube bank 52 through line 53 and a regulated portion or all of this material is directed through linet l and through the respective lines 35 and t5, controlled, respectively, by valves A16 and 53', into coking chambers 30 and 30' wherein they commingle with the .materials undergoing coking in this zone and serve to assist the coking operation or a portion or all of the highly heated products from,

e products from furnace 3| not required as a heatcarrying medium for assisting the coking operation may be directed from line 43 through line .49 and valve 50 into reaction chamber I8 wherein they are subjected to continued conversion together with the heated products from heating coil l, serving to heat the latter and particularly the vaporous components thereof to a somewhat higher conversion temperature to increase their conversion and being themselves partially cooled by contact with the cooler products from furnace l whereby conversion of the more highly heated products from furnace3l is retarded.

Coking chambers 30 and 30 are similar zones preferably operated at substantially atmospheric or a relatively low superatmospheric pressure which is preferably somewhat higher than that employed in the vaporizing chamber in order to avoid the use of a pump or compressor for returning the vaporous products from the coking chamber to the vaporizing chamber. It will be understood, of course, that one or any desired number of a plurality of coking chambers may beemployed although two are illustrated in the drawing and when a plurality is employed the chambers may be simultaneously operated in parallel or preferably are 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. Chambers 30 and 30' are provided with suitable drain lines 5| and 5|, respectively, con-- trolled by the respective valves 52 and 52' and these lines may also serve as a means of introducing steam, water or any other suitable cooling medium into the chambers after their operation is completed and after they have been isolated from the rest of the system in order to hasten cooling and facilitate the removal of coke therefrom. Vaporous products are withdrawn from coking chambers 30 and 30' through the respective lines 53 and 53', controlled respectively by valves 54 and 54, and are introduced through line 55 into vaporizing chamber 22 wherein any entrained or dissolved tars and similar highboiling materials are removedtherefrom and returned together with the other residual liquid conversion products in this zone to the coking chambers for furthertreatment. Vaporous products supplied to and evolved from the liquid conversion products inchamber 22 are directed therefrom, in the case here illustrated, through line and valve 51 to heat exchanger 58 wherein any entrained particles of heavy liquid and/0r high boiling components of the vapors unsuitable as charging stock for either heating stock and intermediate conversion products of the process, as will be later more fully described. The condensate formed in heat exchanger 58, may be returned therefrom through line 59 and valve 60 tovaporizing chamber 22 and is pref-r erably employed as a refluxing mediumin this zone by being passed over suitable bafiies or fractionating means (not shown), which may be located within the upper portion of the vaporizingchamber. The vaporous products from chamber 22 remaining uncondensed in heat exchanger 58 are directed through line 8| and valve 82 to fractionation in fractionator 83. 1

The components of the vaporous products supplied to fractionator 83 boiling above the range of the desired final light distillate product of the process are condensed in this zone as reflux condensate which is separated by fractional condensation into selected relatively low boiling and high boiling fractions. The high boiling frac- 10 tions are withdrawn from the lower portion of the fractionator through line 84 and valve 85 to .pump 88 by means of which they are fed through line 81 and thence, allor in part, through line 88, line 88, valve 18, heat exchanger 58,

line H, valve I2 back into line 88 and thence to the two similar sections of the heating .coil in furnace I for further conversion. A regulated portion or all of the relatively high boiling oils supplied to furnace I may, when desired, by-

pass heat exchanger 58 by means of valve 13 in line 88.

Selected relatively low boiling fractions of the reflux condensate are withdrawn from a suitable intermediate point in fractionator 83, for example, through line I4 and valve I5 and in the case here illustrated are introduced into stripping column 18 wherein they are substantially freed of dissolved or entrained gases and low boiling components 'within the range of the desired final light distillate product of the process by means of heat supplied to the column in any v desired well known manner such as, for example,

by passing a suitable. heating medium such as steam, hot oil or the like through a closed coil 11 in the lower portion of this zone. Vapors and gases evolved in column I8 are returned through line I8 and valve I8 to fractionator 83. The reboiled side stream is withdrawn from the lower portion of column I8 through line 88 and valve 49 8| to pump 82 by means of which this material is supplied through line 83 and valve 84 to conversion in the relatively light oil heating coil located within furnace 3|, in the manner previously described.

Fractionated vapors of the desired end boiling point are withdrawn together with uncondensable gas produced by the operation from the upper portion of fractionator 83 through line 85 and valve 88 and are subjected to-condensation and cooling in condenser 81. The resulting distillate and gas passes through line 88 and valve 88 to collection and separation in receiver 88.

Regulated quantities of the distillate collected inreceiver 88 may, when desired, be recycled by -5 well known means (not shown) to the upper portion of fractionator 83 to serve as a cooling and refluxing medium in this zone'for assisting fractionation-of the vapors and to maintain the desired vapor outlet temperature from the frac- C0 tionator.

Distillate comprising the "unstabilized motor I fuel product of the process is 'withdrawn from receiver 88 through line 8I and valve 82 to pump 83 by means of which it is fed through line 84,-' '2 valve 85, heat exchanger 88, line 81 and valve will be later more fully described, and the unvaporized distillate collecting in the bottom of column 88 is withdrawn therefrom through line I88 and valve I8I to heat exchanger I82 wherein it is subjected to additional heating and reboiling by indirect heat exchange with a regulated portion of the relatively high boiling oil withdrawn from the lower portion of fractionator 83 and supplied to heat exchanger I82 through line I83 and valve I84 whereby it is partially cooled and from which it is directed throughline I85 and valve I88 back into fractionator 83 at any desired point. or plurality of points in this zone wherein it serves as a cooling and refluxing medium for assisting fractlonlation of the vapors. The vapors evolved in heat-exchanger I82 are directed through line I81 and valve I83 back into stabilizing column 88. The reboiled and stabilized distillate is withdrawn from heat exchanger I82 through line I88 and valve II8 to heat exchanger 88 wherein it is cooled by indirect heat exchange with the distillate supplied from receiver 88 to column 98 and serves to preheat the distillate. The stabilized and partially cooled distillate from heat exchanger 88 may be directed through line I I I and valve II2 to further cooling and storage or to any desired further treatment. The low boiling materials liberated from the distillate in stabilizer 88 are. directed from the upper portion of this zone through line H3 and valve H4 and are subjected to cooling and condensation in condenser I I5 of any suitable form from which the resulting distillate and gas passes through line H8 and valve III to collection and separation in receiver H8. The distillate collected in receiver II8 may be utilized as a cooling and refluxing medium in stabilizer 88 by recirculating the same to the upper portion thereof through line I I8, valve I28, pump I2I, line I22 and valve I23.

The uncondensed gaseous products are released from receiver II3 through line I24 and valve I25 and are introduced into absorber I28. The gases separated-from the unstabilized distillate in receiver 88 are also directed to absorber I28 by means of'line I21 and valve I28. The gaseous products of the process thus'supplied to absorber I28 are intimately commingled in this zone with regulated quantities of the hydrocarbon oil charging stock for the process which is supplied through line I28 andvalve I38 to pump I3l by means of which it is fed'through line I32 and valve I33 into the upper portion of the absorber. The remaining portion, if any, of the charging stock may be directed, for example, through line I34 and valve I35 into the lower portion of absorber I28 or, depending primarily upon its characteristics, may be supplied direct to fractionator 83 or to either heating coil of the system by wellknown means (not shown). The unabsorbed components of the gases are released from the upper portion of absorber I28 and pass through line I38 and valve I31 to storage or elsewhere, as desired. The enriched charging stock containing absorbed high boiling components of the gases including propane, butane and the cor.- responding unsaturated compounds is withdrawn from the lower portion of absorber I28 through line I38 and valve I38 to pump I48 by means of which it is directed through line I, valve I42 and line I85 into fractionator 83, wherein it is subjected to vaporization and to fractionation together with the vaporous conversion products of the process; the low boiling and high boiling fractions of the charging stock combining with the corresponding low boiling and high boiling .fractions of the reflux condensate to form the relatively low boiling and high boiling oils subjected to conversion in the low boiling and high boiling oil heating coils of the system.

The preferred range of operating conditions which may be employed to accomplish the objects of the present invention in an, apparatus of the inch. The light oil heating coil may employ an outlet conversion temperature ranging, for exampie, from 900 to 1050 F., preferably with a super-' atmospheric pressure of from 300 to 800 pounds, or more, per square inch, although lower pressures down to substantially atmospheric may be ably operated at substantially the same pressure employed at the outlet from the light oil heating coil, when desired, particularly in case all of the heated products from this zone are introduced into a low pressure coking zone. The reaction chamber is normally operated at a superatmospheric pressure which may range from 100 to 500 pounds, or more, per square inch, which, however, is no greater than that employed in the communicating heating coil utilizing the lowest pressure, in case heated products from both heating coils are introduced into the reaction chamber. The vaporizing chamber is preferably operated at a substantially reduced pressure relative to that employed in the reaction chamber ranging, for example, from 100 pounds, or thereabouts, per square inch, down to substantially atmospheric pressure. Any desired pressure ranging from substantially atmospheric to 150 pounds or more per square inch may be employed in the coking zone although, as previously mentioned, this zone is preferably operated at a somewhat higher pressure than that employed in the vaporizing chamber. The fractionating, condensing and collecting portions of the cracking system may utilize pressures substantially the same or somewhat lower than the pressure employed in the vaporizing chamber. The stabilizing column maybe operated at any desired pressure ranging from substantially atmospheric to several hundred pounds per square inch superatmospheric pressure, the preferred range being from 125 to 275 pounds per square inch. The absorber is preferas that employed in the receiver and gas separator of the cracking system, the preferred range being from 50 to 150 pounds per square inch although lower or higher pressures may be employed in this zone, when desired.

As a specific example of one of the many possible operations of the process of the present invention as it may be accomplished in an apparatus'of the character illustrated and above described, the charging stock, in this particular case, comprises a gas oil of about 32 A P. I.

gravity which is utilized, in part, as absorber oil in the absorption stage of the system. The enriched absorber oil and the remaining portion of the charging stock is supplied to the fractionator of the system. High boiling components of the reflux condensate and chargingstock, 90% or more of which boils above approximately 570" F. is supplied from the fractionato'r of the system to the heavy oil heating coil through which it flows 15 in two substantially equal streams each of which are uniformly heated to an outlet conversion temperature of approximately 925 F. at a. superatmospheric pressure, measured at the outlet from the heating coil, of approximately 300 pounds per square inch and the heated products are introduced into the reaction chamber of the system which is operated at substantially the same pressure. Both vaporous' and liquid conversion products are withdrawn from the lower portion of the reaction chamberand introduced into the vaporizing chamber which is operated at a superatmospheric pressure of approximately 60 pounds per square inch. Non-vaporous residual liquid from the vaporizing chamber is supplied to alternately operated coking chambers maintained at a'superatmospheric pressure of approximately '75 'pounds per square inch, vaporous products from which are returned to the vaporizing chamber. Low boiling fractions of the reflux condensate and charging stock, 90% or more of which boil within the range of approximately 400 to 600 F, are supplied from the fractionator of the 7 system to the light oil heating coil wherein they are heated to a conversion temperature of approximately 950" F. and then maintained at a substantially constant temperature not exceeding approximately 975 F. being discharged from this zone at a superatmospheric pressure of approximately 750 pounds per square inch. A regulated quantity of the highly heated products from the light oil heating coil sufiicient to effect reduction I of the high boiling materials in the coking zone to substantially dry coke are supplied to the alternately operated coking chambers and the remainder of these products are introduced into the reaction chamber. The stabilizing stage'of the system, which is operated substantially in the manner above descriped and illustrated, employs a superatmospheric pressure in the stabilizing column of approximately 225 pounds square inch and the absorber to which gaseous products from the receiver of the cracking system and from the stabilization stage are supplied and therein contacted. with the charging stock, as above described, is operated at a superatmospheric pressure of approximately 50 pounds per square inch. This operation may produce, per barrel of charging stock, approximately 70% of 400 F. end point motor fuel having an octane number of approximately '70 by the motor method and a Reid vapor pressure of approximately 10 pounds per square inch and about 50 pounds of low volatile coke of good structural strength and uniform quality, the remainder being chargeable, principally, to lean non-condensable gas.

I claim-as my invention:

1. A process for the conversion of hydrocarbon oils which comprises subjecting an oil of relatively high boiling characteristics to conversion conditions of elevated temperature and. superatmospheric pressure in a heating coil and communicating reaction chamber, withdrawing both vaporous and liquid conversion products from the reaction chamber in commingled state and introducing the same into a reduced pressure vaporizing chamber wherein separation of vapors and residual liquid conversion products is accomplished, withdrawing the latter from the vaporizing chamber and introducing the same into a cokingzone wherein their reduction to substantially dry coke is accomplished, simultaneously subjecting another hydrocarbon oil of relatively low boiling characteristics to independently controlled more severe conversion conditions of elevated temperature, superatmospheric pressure and conversion time in a separate heating coil, introducing regulated quantities of the highly heated products from said separate heating coil into the coking zone to assist the coking operation, introducing any remaining portion of the highly heated products from said separate heating coil into the reaction chamber, withdrawing vaporous products from the coking zone and introducing the same into said vaporizing chamber, subjecting vaporous products from the vaporizing chamber to fractionation for the formation of reflux condensate and recovering a light distillate product from the fractionated vapors by condensation,

2. A process of the character defined in claim 1, wherein the reflux condensate formed by said fractionation of the vaporous conversion products is separated into selected relatively low boiling and 'high boiling fractions which are returned respectively to the relatively light oil and relatively heavy oil heating coils for further conversion.

3. A process of the character defined in claim 1, wherein hydrocarbon oil charging stock for the process is commingled with the vaporous conversion products undergoing said fractionation and the resulting reflux condensate is separated into" selected relatively low boiling and high boiling fractions and wherein said relatively low boiling and high boiling fractions are supplied respectively to the relatively light oil and relatively heavy oil heating coils of the system.

4. A conversion process which comprises subjecting a relatively heavy hydrocarbon oil to conversion temperature under pressure in a heating coil and. communicating reaction zone and subsequently separating the same into vapors and unvaporized oil in a separating zone, removing unvaporized oil from the separating zone and introducing the same to a coking zone, simultaneously passing a lighter hydrocarbon oil through a second heating coil and heating the same therein to higher conversion temperature than the oil in the first-named coil, dividing the resultant heated products from said second coil and introducing to the coking zone a suflicient quantity thereof to reduce the unvaporized oil therein to coke, introducing the remaining portion of said heated products from the second coil into said reaction zone, removing vapors from the coking zone and introducing the same to the separating. zone, and fractionating and condensing the vapors from the separatig zone.

' JOHN B. BARNES.

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