US2194692A

US2194692A - Process of treating hydrocarbon oil

Info

Publication number: US2194692A
Application number: US148269A
Authority: US
Inventors: Sturgis W Darling
Original assignee: Texaco Development Corp
Current assignee: Texaco Development Corp
Priority date: 1937-06-15
Filing date: 1937-06-15
Publication date: 1940-03-26
Anticipated expiration: 1957-03-26

Description

March 26, 1940. s. w. DARLING PROCESS OF TREATING HYDROCARBON OIL NNN.

Patented Mar. 26, 1940 PATENT [OFFICE f 2,194,692. raocass or TREATING HrDnocARBoN oIL l Sturgis W. Darling, Houston, Tex., assignor, by mesme assignments, to Texaco Development Corporation, New York, N. Y., a corporation of Delaware `ipplication June 15, 1937, Serial No.` 148,269

14 Claims.

This invention relates to the art of producing gasoline-like 4products or relatively low-boiling hydrocarbons from relatively high-boiling hydrocarbons.

According to this invention a relatively clean oil stock, preferably a condensate oil obtained by fractionation of vapors in a bubble tower, is passed through the first portion of a cracking zone which preferably extends through the radiant section of a furnace wherein the oil is maintained under high-temperature` and high-pressure conditions to eifect part or all of the desired conversionthereof.r 'I'he heated oil, after passing through this portion of the cracking zone, is divided into two streams, one stream being passed to a coking zone, such as an enlarged coke still to supply the heat required to decompose heavy oil introduced into the coking zonev to a solid coke-like mass.V The other stream is mixed with a heavy oil containing reflux condensate and unvaporized constituents of a relatively heavy oil, such as, a reduced crude oil charge, and the combined stream is passed through the latter portion of the cracking zone which preferably extends `through the convection section of the furnace to eifect viscosity-A breaking of the heavy oil `and further cracking of the clean oil. `'I'he stream of combined cracked products leaving the cracking zone is passed into a separating zone orevaporator to separate vapors and unvaporized oil, the latter being passed to a flash orvaporizing Zone preferably maintained under reduced 'pressure to vaporize volatile constituents therefrom. All orp'artr of the remaining unvaporized oil or tar residue is passed to the coke still where it is reduced to coke by the heat derived from the stream of oil from the cracking zone in the radiant section of the furnace, as above mentioned. Fresh charging oil forfthe process, such as .reduced crude oil, preheated in any suitable manner, is contacted with the hot vapors from the flash zone and evaporator to form the heavy oilabove` mentioned which contains reflux condensate and unvaporized constituents of the vcrude oil. The vapors remaining uncondensed after being contacted with fresh oil are` fractionated to separate light motor fuels,such as gasoline, from insufciently cracked products, such as reflux condensate which is subjected to cracking con-v ditions. d, y

Other advantages and features of the invention will be hereinafter given in the detailed de- I scrption of the invention in connection with the (or 19e-,48) n paratus adapted for practicing? the methods of this invention. I

`Referring, now to the drawing, the reference character Iil designates a furnace or heater housing a cracking zone in the form of a coilrl2. 5 d The cracking zone I2 extends, for example, through the radiant section I4 and the hottest part of convection section I6 of the furnace I0. Clean oil, such as reflux condensate obtained in the process as later described, is passed through line I8 by the pump 20 into the `preheating coil 22/ positioned inthe cooler portion `of `the convection section I6 of the furnace` I0. The pre- Y heated cleanoil then passes through line24 and temperature and high-pressure conditions to bring about the desired conversion. The oil stream leaving the rst part of the cracking zone is subdivided into two streams, one stream being passed through'a line 26 having a pressurereducing valve 2l intothe coke still28 in order to supplythe heat required therein to crack the tar residue within the coke still to a coke-like mass. The other stream is passed through line 3E! and is mixed with a heavy oil which contains `relatively heavy reflux condensate and. heavyy unvaporizedv liquid constituents of the charge introduced into the process,as will be 30 later described, passing through line 32 by means of pump 33. The

lines

26 and 30 are provided with valves to permit controlling the amountsof cracked products being passed through the lines. The combined stream is passed through the` 35 latter portion of thecracking zone I2 which is positioned in or which extends through the conoil stream leaving the iirstpart` of the cracking zone through line 30 andadmixed therewithfis subjected to further cracking.

The stream of cracked products leaving the 45 latter portion ofthe cracking zone I2 is passed through line Shaving a pressure-reducing valve 3G into the evaporator or separating zone 38 fof the combined evaporator andfractionating tower Ml. Before passing the stream of cracked products into the evaporator 38, a quench oil may be introduced into liney 34 as at 4`2`, if desired. Due to the reduction in pressure on the heated oil, there is a separation into vapors-Which pass upwardly in the evaporator, and a` cracked resil tower 58.

due which is collected in the bottom of the evaporator 38. The cracked residue is passed through line 46 having a pressure-reducing valve 48 into the lflash zone 48 of the combined fractionator and crude flash tower 50 maintained at a lower pressure than the evaporator 38. Due to the reduction in pressure, there is a further vaporization of the unvaporized liquid or residue withdrawn from the evaporator 38, and the vapors pass upwardly in the flash zone 49 of the combined fractionator and crude ash tower 50. The remaining unvaporized cracked residue or tar is collected in the bottom of the flash zone 49. All or a portion of the cracked tar residue may be passed through line into the coke still 28 where the tar residue is subjected to further cracking by mixture with a portion of the stream of cracked products leavingvthe first portion of the cracking zone I2 through line 26, as hereinbefore described. If the coke drum 28 is maintained atrabout' the same or higher pressure as the tower 5I), a pump 52 is used to force the cracked residue into the drum 28.

Preferably, the cracked tar residue from the flashzone 59 is mixed with the stream of cracked products'in line 25 before such stream is introduced into the coke still or drum 28 in order to raise" the'temperature of the cracked residue to a cracking temperature prior to entering the coke drum to thereby facilitate vaporization of the lighter constituents and decomposition of the tar residue to coke thereby obtaining an increase in the "yield of light products from the cracked residue However, the cracked tar residue from flash Zone i9 may be passed directly to the coke still 28, or a part of the cracked tar residue may be passed directly Yinto the coke still and another `portion mixed with the stream in line 26 before passing to the coke still 28. Two or more coke stills may be provided so that one still can be in use" while another still is being cleaned.

' The vapors from the top of the coke still 28 are passed through line 53 into the lower portion of the fractionating section 54 of the combined fractionator and crude flash tower 50. Fresh charging stock for the process, such as reduced crude oil; preferably preheated, is passed through line 58`by means of pump 68 and is introduced into the lupper portion of the fractionating section 54 of the combined` fractionator and crude flash The reduced crude oil charge flows downwardly in the fractionating section 54 countercurrent tothe hot vapors rising from the flash zone 49 and the hot vapors passing through line 53 from the coke still 28, as hereinbefore described. In this way intimate contact between vapors and liquid oil takes place resulting in condensation of heavier constituents of the vapors and vaporization of lighter constituents contained in the charge oil.` The vapors leaving the combined fractionator andcrude flash tower 50 arel passed through line 62. The heavy reflux condensate yand unvaporized reduced crude oil are collected as liquid at the bottom of the fractionating section 54 inthe trap-out tray 66 provided with a hood 68. The liquid collected on the trapout'tray 65 is passed through line 10 and is forced into the upper portion of the fractionating section '16 ofthe combined evaporator and fractionating tower L18 by means of pump 12. In the fractionating section i6 the heavy reflux condensate and unvaporized reduced crude oil are intimately contacted'jwith vthe hot cracked vapors rising from the evaporatorlor.separating zone 38, and in this waythere is a partial condensation of heavy constituents contained in the vapors and additional vaporization of some of the unvaporized reduced crude oil. The reflux condensate and unvaporized reduced crude oil are collected at the bottom of the :fractionating section 16 on trap-out tray 18 provided with a hood 80. This liquid which collects on the trap-out tray 'I8 is the heavy oil above mentioned which is pumped through line 32 and mixed with one portion of the sub-divided stream leaving the first portion of the cracking zone I2 through line 38, the mixture being passed through the latter portion of the cracking zone |2 extending through the convection section of the furnace.

The vapors leaving the top of the combined evaporator and fractionating tower 40 are passed through line 84 into the bottom portion of a secondary fractionating zone, such as a bubble tower 86. The vapors introduced into the secondary fractionating Zone 86 through line 84 pass upwardly therein and are fractionated to condense insufficiently cracked products as reflux condensate which collects in the bottom of the secondary fractionating zone 86 and forms the clean oil which is passed through line I8 into the cracking zone or coil I2 extending through the radiant section I4 of the furnace I0. A cooling coil 81 in the upper part of the secondary fractionating zone 86 and other methods of reuxing may be used as will be laterv explained. The vapors of the desired end point pass' from the secondary fractionating zone 86 through line 88 and then through a condenser 98, the distillate being collected in a reservoir or collecting drum 92 having a gas outlet 94 and a liquid outlet 96. The distillate which is drawn oi through line 96 is a motor fuel of the nature of gasoline. A part of the gasoline collected in the collecting drum 92 may be passed through line 98 by pump |88 into the upper portion of the secondary fractionating zone 86 to act as reux liquid.

The vapors leaving the top of the combined fractionator and crude flash tower 50 through line 62 may be fractionated in tower 85, but they are preferably separately fractionated and a part thereof used as reflux in the secondary fractionating zone 86. The vapors are passed through line |04 into about the middle portion of a gas oil-naphtha fractionating tower |86 to separate naphtha vapors from insuiiiciently cracked products as reflux condensate. As the vapors pass upwardly in the fractionating tower |86 they are fractionated to condense insufficiently cracked products and the desired naphtha vapors pass through line |88 and condenser IIB wherein they are condensed. The thus obtained condensed naphtha and lighter gaseous hydrocarbons are pumped by means of pump II 2 into the lower portion of the secondary fractionating zone 86 where the naphtha is mixed with and retained to some extent by the gas oil or reilux condensate and then passed through the cracking zone I2, By mixing the naphtha with the recycle condensate and passing the mixture through the cracking zone I2 reforming of the naphtha is accomplished along with cracking of the gas oil. The gas oilcollecting at the bottom of the fractionating tower |06 is forced through line I I6 and cooler ||8 by pump |26, and a part thereof may bepassed through line |22 into the upper portion of the secondary fractionating zone 86 to act as reflux liquid, and the rest of the cooled liquid may be passed through line |24 into the top of the fractionating tower |06 to act as reflux liquid therein. Valves are provided in lines |84 and |08 to permit by-passing of the fractionating tower i I 06 through line` I2iV wherebythe vapors are condensed in condenser IIO and the condensed oil is passed to the bottom of fractionator 86 by pump II2.

In a typical operation contemplated by thi invention a reduced crude oil stock or similar heavy oil stock preferably preheated to about q 400 to 475 F. in any suitable Way is introduced into the fractionating section 54 of the combined fractionator andcrude flash tower 59. The pressure in the combined fractionator and crude flash tower 50 is maintained at about 25 to 125 pounds per square inch. 'I'he introduced hot reduced crude oil is contacted in the fractionating section 54 with hot vapors rising from the flash zone 49 and with hot vapors coming from thecoke still 28 through line 53. In this way some of the vapors in the fractionating section 54 are condensed to form heavy reflux condensate, and the lighter constituents of the reduced crude oil are vaporized. A mixture of unvaporized crude oil stock and heavy reflux condensate is collected in the trap-out trayy 66 at the bottom of the fractionating section 54, and this mixture is Withdrawn at a temperature of 'about 650,-700 F., preferably, about 675 F. and forced into the fractionating section 'l0 of the combined evaporator and fractionating zone by means of the pump 72. The combined evaporator and fractionating rone 4I] is maintained at a pressure of about 100 to 400 pounds per square inch.

The mixture introduced into the fractionating section 'i0 comes incontact with hot vapors rising from the evaporator or separating zone 38 of the combined evaporator and fractionating zone 40 to cause vaporization of some of the liquid mixture. At the same time some of the vapors rising from the evaporator or separating Zone 3B are condensed. The vapors leaving the combined evaporator and fractionating zone or tower 40 are passed through line 811 into the bottom of the secondary fractionating zone 86 wherein they are fractionated. The light products having the desired end pointV aretaken off through line 88, condensed and collected in drum 92. During fractionation reflux condensate containing insufficiently cracked products collects at the bottom of the bubble tower or secondaryfractionating zone 8S, and this condensate is the clean oil or recycle gas oil stock which is passed through line i8 and through the cracking zone I 2.

The condensate from the bottom of the secondary fractionating Zone 86 may be preheated by` passing it through a preheater coil 22 extending through the cooler portion of the convection section I6 of the furnace I0. The preheated oil is then passed through the first portion of the cracking zone E2 extending through the radiant section M of the furnace where it is subjected to a cracking temperature of` about 900 to 11.00`

F., preferably about 990 F., and a pressure between `about 200 and 1000 pounds per square inch.

The cracked products leaving the rst portion of the cracking zone i2 are subdivided into Vtwo streams, one stream being passed through line 26 to the coke still 28, while the .other stream is passed through line 30 and mixed with the heavy oil passing through line 32. The unvaporized crude oil and reflux condensate collecting at the' zone or coil I2 extending through the convection section I6 of the furnace I0. 'Ihe heavy oil is at a temperature of about 770860 F. preferably about 840 F.

Before passing this heavy oil through the cracke ing zone I2, it is mixed with a portion of the cracked products leaving the iirst part of the cracking zone through line 30 as above mentioned, and by this admixture and with heat applied exteriorly to the cracking zone I2, the ternperature of the heavy oil is raised to a cracking temperature of about 800.to y975 F.preferably about 900 F., while under a pressure between about 200 and 1000A pounds per square inch to effect a mild cracking of the heavy oil. After the y heavy oil is mixed with the divided stream passing through line 30 the combined stream is passed through the latter portion of the cracking zone I2 extending through the convection section I 6 of the furnace I0 where further cracking of the clean oiltakes place, and the hydrocarbons are converted into low-,boiling hydrocarbons within the gasoline-boiling range having an excellent anti-knock quality. During its passage through the latter portion of the cracking zone I2 the heavy oil in the combined stream is subjected to a mild cracking or viscosity-breaking operation thereby forming lower boiling products most of which are recovered as reflux condensate to be subjected to cracking.

The cracked residue from the evaporator or separating Zone 38 in the combined evaporator andfractionating tower 40 at a temperature of about '770 to 860 F., preferably about 840 is passed into the flash zone 49 of the combined fractionator and crude iiash tower which is under less pressure than the combined evaporator and `fractionating tower 40', and some flash distillation or vaporization is obtained. The not vapors which are released in the evaporator or is at a temperature of about 700 F. or above. All

or only a portion of the cracked tar residue is passed to the coke' still 28 through line 5I; A part of the cracked tar residue may be withdrawn from the bottom of the flash `zone i9 andused as fuel oil. tom o f flash Zone 49 passing through line 5I is preferably mixed with a stream of cracked products leaving the first portion of the cracking zone `I2 through line 25 before it is introduced into the coke still 28, but the tar residue may be introduced directly into the coke still 28 or a part thereof may be mixed with the stream of cracked products passing through line25 and the` rest passed directly into the coke still. This stream of cracked products is at a high temperature about 900-l100 F., preferably about 990 F., and is utilized to raise the tar residue to a coking temperature and to furthercrack the tar residue to obtain an increased yield of gasoline or other light hydrocarbon products. The temperature of the coke still 23 is maintained at about SSW-900 F., preferably about 880 F. l

The pressure in the coke still 28 preferably is lower Vthan the pressure in the cracking Zone I2, and, thereforepsome flash distillation or vaporization of the cracked products is obtainedyin the coke still. A part of the tar residue 'from The cracked tar residue from the bot- 1 iii? the ash zone 49 may be used as fuel oil, or all cracked products from the first portion of the cracking zone I2 was diverted'to the coke still 28 through line 26 before the heavy oil was injected into the latter portion of the cracking zone 2 through line 32 so as to obtain a stream of cracked'products having a high temperature for cracking the tar residue.

The vapors from the coke still 28 are passed through line 53 into the lower portion of the fractionating section 54 of the combined fractionator and crude flash tower E below the point of .introduction of the hot reduced crude oil charge which is introduced through line 58 into the fractionating section 5d of the combined fractionating and flash tower 50. These vapors from the coke still contain cracked naphtha vapors which are combined with the gas oil for reforming as will be presently described. Some of the vapors are fractionated in the fractionating section 5l! and the vapors passing overhead through line G2 `are condensed and the condensate is introduced by pump H2 or through line |22 into the secondary fractionating zone 86 to be added to the gas oil condensate for recycling through cracking Zone i2 and reforming of the cracked naphtha.

The vapors from the top of the combined fractionator and crude ash tow-er 5@ may be condensed to recover a hydrocarbon product, or they may be passed to the gas-oil naphtha fractionating tower. E05. The liquid from the bottom of the fractionating tower H35 may be cooled and passed through line |22 to the top of the secondary fractionating Zone 66 as gas oil reflux, or a part of the liquid may be passed through line IM and used as reflux liquid for the fractionating tower m6. The vapors coming from the top of the fractionating tower H155 are, preferably, condensed and passed to the lower portion of the secondary fractionating zone 86 to be added to the condensate oil therein. The vapors leaving the top of the fractionating tower l contain naphtha constituents. These vapors are condensed by passing through condenser Ii and the condensate is added to the gas oil or condensate oil in the bottom of the secondary fractionating zone 8% for reforming the naphtha constituents when the condensate oil is recycled through line i8 and passed through the cracking zone i2.

The vapors from the secondary fractionating zone 86 may be condensed and the liquid collected and treated in the usual manner to produce gasoline or the like.

l/Vhile the primary and secondary fractionating zones have been shown in the drawing in separate towers, it is to be clearly understood that these zones can be located in a single tower; also the evaporator and flash zone, while shown in the drawing as parts of a combined fractionator and crude flash tower, and a combined evaporator and fractionating tower, respectively, can be constructed and used as separate apparatus as will be apparent to one skilled in the art.

While a particular embodiment of the invention has been described it is to be expressly understood that the invention is not restricted thereto, and various modifications and adaptations thereof may be made without departing from the spirit of the invention. Y

I claim: l

1. In a process for converting higher-boiling hydrocarbons into lower-boiling ones, in which oil is passed through a cracking Zone and then into a separating zone to separate vapors from the cracked residue, the vapors being passed through primary and secondary fractionating zones and the cracked residue being passed to a ash zone to produce further vaporization thereof, the vapors leaving said second fractionating zone being condensed and collected as a hydrocarbon product having the desired boiling range, the steps which comprise passing condensate oil from the secondary fractionating Zone to the cracking Zone wherein it is maintained under high-temperature and high-pressure conditions to produce conversion of the condensate oil, contacting a relatively heavy oil stock with the hot vapors from the flash zone to Vaporize some of the lighter constituents of the heavy oil and to condense some of the vapors to form reflux condensate and collecting reux condensate and unvaporized constituents of the heavy oil and passing them to the primary fractionating zone where further contact with hot vapors occurs, collecting reflux condensate and unvaporized liquid constituents of the heavy oil in the primary fractionating zone and admixing such reflux condensate and unvaporized heavy oil with the cracked products passing through the latter part of the cracking Zone to raise the temperature of the admixed condensate and unvaporized heavy oil to a cracking temperature, passing such admixture through the latter part of the cracking zone to effect conversion thereof and then passing such mixture to the separating zone to separate hot vapors which are passed to the primary fractionating zone.

2. A process for converting higher boiling hydrocarbons into lower boiling hydrocarbons, which comprises contacting reduced crude oil stock with hot hydrocarbon vapors to vaporize some of the reduced crude oil stock and to condense soine of the hot vapors as heavy reflux condensate, collecting the heavy reiluX condensate and unvaporized crude oil and passing them to a primary fractionating zone wherein they flow downwardly and contact hot vapors therein, passing the vapors from the primary fractionating Zone to asecondary fractionating Zone wherein they are fractionated to separate condensate oil from a hydrocarbon product containing lower boiling hydrocarbons, collecting the condensate oil from the secondary fractionating zone and passing it as a stream through the first portion of a cracking Zone in the radiant section of a furnace, collecting reflux condensate and unvaporized crude fraction in the primary fractionating zone and admiXing such condensate and unvaporized crude fraction with the first-mentioned stream leaving the cracking zone in the radiant section of the furnace to form a combined stream and passing the combined stream through the latter portion of the cracking Zone in the convection section of the furnace, passing the treated and cracked products from thecracking zone to a separating zone to obtain separation of vapors from cracked residue, passing the vapors to said primary fractionating Zone, passing the cracked residue to a flash zone maintained at a lower pressure to obtain fiash distillation into vapors and tar residue, passing the tar residue from the flash Zone to a coking Zone and diverting a portion of the stream of cracked products from the cracking zone in the radiant section of the furnace to the coking zone to obtain further cracking of the tar residue therein, the stream being diverted before the introduction of the reux condensate and liquid from the primary fractionating zone, and passing the vapors from the coking zone into contact with the reduced` crude'v ing fraction, subjecting the condensed heavy conj,

stituents to elevated temperature and superat mospheric pressure to eiect conversion thereof into lower boiling products, dividing the products of conversion into at least two portions, admixing the unvaporized heavy oil with one of the divided portions to supply heat to the heavy oil and to effect cracking of the heavy oil, separating the products of conversion from the admixed stream into hot vapors and unvaporized liquid constituents, using the last-mentioned hot vapors as the I vapors for contacting the .relatively heavy charging oil stock, passing the unvaporized liquid constituents to anenlarged zone wherein they are subjected to further conversion, passing another of the divided portions into the enlarged zone to Supply heat to the unvaporized liquid constituents in the enlargedzone to subject them to further conversion.

4. A process for converting higher-boiling hydrocarbons intolower-boiling hydrocarbons which comprises passing oil through a cracking zone wherein it is maintained under high-tern-` perature and high-pressure conditions to effect the desired cracking, passing a portion of the stream of cracked products into a separating Zone to separate hot vapors from a cracked residue,

passing cracked residue `thus obtained to aV flash zone under a lower pressure for further separation into hot vapors and a tar residue, withdrawing the tar residue and passing itto a coking zone, contacting relatively heavy hydrocarbon oil with the hot vvapors from the ash zone to vaporize part of the heavy oil, collecting the unvaporized portions Aof the heavy oil and contacting them with the hot vapors from the separating zone to vaporize` the lighter constituents thereof and condense some of the heavy constituents from the vapors, andi fur ther treating the separated lighter constituents to separate a relatively light hydrocarbon fraction therefrom, collecting and admixing the unvaporized portions ofthe heavy oil with the portion ofv the stream of cracked products passing to the sep; arating zone to thereby raise the heavy oil'v to cracking temperature and eect cracking thereof, and passing another portion of the stream of` hot cracked products from the cracking zone to the coking zone to effect cracking of the tar resi' due introduced into the coking zone.

5. A` process for converting higher boiling hy'- drocarbons into lower boiling hydrocarbons, which comprises contacting relatively heavy oil stock with hot vapors in a fractionating zone to vaporize some of the heavy oil andv condense some of the vapors as heavy reflux condensate, collect-y ing the heavy reiiux condensate and unvaporized of the heavy oil stock and to condense some of i the h'otvapors, passing the vapors from the. pri--4 constituents of the heavy oil stock and passingv tionating zone whereinthey are fractionated to separate condensate oil from lighter hydrocarbon vapors which are condensed and the distillate separated as a desired product, collecting the condensate oil from the secondary fractionating zone and passing it through a portion of a cracking zone whereinl it is maintained under high temperature and high pressure conditions to effect the desired conversion, collecting refiux` condensate and unvaporized constituents of the4 heavy oil in the primary fractionating zone and passing them through another portion of the cracking zone after the reiiux condensate and unvaporized constituents of the heavy oil rare commingled with cracked products coming from the first mentioned portion of the cracking zone, and passing the commingled treated and cracked products from the cracking Zone toa separating zone to separate hot vapors from cracked residue and passing such hot vapors into the primary fractionating zone tofsupply hot vapors thereto, directing cracked residue from said separating Zone to a flash zone wherein separation of vapors from tar residue takes place under a lower pressure and passing resultant separatedvapors to the first-mentioned fractionating zone, passing the vapors from said first mentioned fractionating zone to a fractionating tower to obtain gasoil and naphtha fractions, introducing the naphtha fraction into the bottom portion of the secondary fractionating Zone 4and introducing the gas-oil fraction into the top portion of the secondary fractionating zone toeifect condensation l of heavy constituents of the vapors therein which are addedto the condensate oil in the secondary fractionating zone.

6. A process as defined in claim 5 wherein tar residue from the flash Zone is passed to a `coking zone and at least a portion of the cracked products from the first mentioned portion of said cracking zone is diverted to said coking zone to crack the tar residue.

7. A process for converting higher boiling hydrocarbons into llower boiling hydrocarbons, which comprises introducing relatively heavy oil stock into the fractionating section of a hash tower `in contact with hot vapors therein to vaporize some of the -heavy oil and condense some of the vapors as heavy reflux condensate, collecting the heavy reflux condensate and unvaporized constituents of such heavy oil stock and passing them to a primary fractionating zone in contact with hotvapors therein to vaporize some of the heavy reflux condensate and unvaporized constituents of the heavy oil stock and to condense some ofthe hot vapors, passing the vapors from the primary fractionating zone to a secondary fractionatingk zone kwherein they are fractionatedl to separate condensate oil from a light hydrocarbon product adapted for use as a motor fuel, collecting the condensate oil from the secondary fractionating Zone and passing it through a cracking zone wherein it is `maintained under hightemperature `and high pressure conditions to `effect the desired conversion, collecting the reflux condensate and unvaporizedi constituents v of the heavy oil' in the primary fractionating zone and miiclngthem with cracked products coming from said cracking Zone to raise the temperature of the introduced reux condensate and unvaporized constituents of the heavy oil to a cracking temperature and effect cracking thereof, and passing the commingled treated and cracked products to` a separating zone to separate hot `mary fractionating zone to a secondary frachot vapors into the primary fractionating zone to supply hot vapors thereto, directing cracked residue from said separating zone to the aforesaid flash tower wherein separation of vapors from tar residue takes place under a lower pressure and the separated vapors pass into the fractionating section thereof into contact with the introduced heavy oil stock, passing the vapors from said fractionating section to a fractionating tower to obtain gas-oil and naphtha fractions, introducing the naphtha fraction into the bottom portion of the secondary fractionating zone and introducing the gas-oil fraction into the top portion of the secondary fractionating zone to effect condensation of heavy constituents of the vapors therein which are added to the condensate oil in the secondary fractionating Zone.

8. A process as defined in claim 7 wherein tar residue from the flash tower is passed to a coking Zone and at least a portion of the cracked products from` said cracking Zone is diverted to said coking Zone, the cracked products being diverted before admixture therewithl of the reflux condensate and unvaporized constituents of the heavy oil.

9. A process for converting higher boiling hy-` drocarbons into lower boiling hydrocarbons which comprises passing oil as a stream through a primary cracking zone wherein it is maintained under high temperature and high pressure conditions to effect the desired extent of cracking, passing a portion of the stream of resultant cracked products through a secondary cracking zone thence into a separating zone to separate hot vapors from a cracked residue, fractionating the vapors to separate lower boiling hydrocarbons as a product, passing cracked residue thus obtained to a flash zone under a lower pressure for further separation of hot vapors and a tar residue, withdrawing the tar residue and passing it to a coking zone, contacting relatively heavy hydrocarbon oil with cracked vapors from said separating zone to vaporize some of the heavy hydrocarbon oil, admixing unvaporized portions of the heavy yoil with the portion of cracked products passing tothe secondary cracking zone to thereby raise the unvaporized portions of the heavy oil to cracking temperature, supplying additional heat to the secondary cracking zone to effect cracking of the unvaporized portions of the heavy oil, and passing another portion of the stream of hot cracked products from the primary cracking zone to the coking zone to eect coking of the tar residue introduced into said coking zone.

10. A process for converting higher boiling hydrocarbons into lower boiling hydrocarbonswhich comprises passing oil as a stream through a cracking zone wherein it is maintained under high temperature and high pressure conditions to effect the desired cracking, passing a portion of the stream of cracked products into a separating zone to separate hot vapors from a cracked residue, passing cracked residue thus obtained to a ash zone under a lower pressure 4for further separation vinto hot vapors and a tar residue, withdrawing the tar residue and passing it to an enlarged Zone, contacting relatively heavy hydrocarbon oil with the hot vapors from the flash zone to vaporize part of the heavy oil, collecting the unvaporized portions of the heavy oil and contacting them with the hot vapors from the separating zone to vaporize the lighter constituents thereof and condense some of the heavier constituents of theV vapors and separating the remaining vapors vapors from cracked residue and passing suchas a" lower boiling hydrocarbon fraction, collecting and admixing the unvaporized portions ofthe heavy oil with the portion of the stream of cracked products passing to the separating zone to thereby raise the heavy oil portions to cracking temperature, supplying additional heat to the admixture to effect cracking of the heavy oil portions, and passing another portion of the stream of hot cracked products from the cracking zone to said enlarged zone to effect cracking of the tar residue introduced into said enlarged Zone.

i1. A process for converting high boiling hydrooarbons into low boiling hydrocarbons which comprises introducing relatively heavy charging stock into contact with hot vapors in a primary fractionating zone, passing vapors from the primary fractionating zone to a secondary fractionating zone wherein fractionation takes place to separate a reflux condensate from lighter fractions, subjecting reflux condensate from the secondary fractionating zone to cracking conditions of temperature and pressure to eiect conversion into lower boiling products, dividing the products of conversion into at least two portions, admixing resultant `reflux condensate and unvaporized charging stock from the primary iractionating zone with one of the divided portions to supply heat to the heavy oil and to effect cracking thereof, passing resultant products of conversion into a separating zone wherein separation or" vapors from residual constituents takes place, passing resultant separated vapors to said primary fractionating zone, subjecting residual constituents derived from said separating zone to further cracking by contacting such residual constituents with the other of the divided portions of the aforesaid products of conversion.

12. A process for converting high boiling hydrocarbons into low boiling hydrocarbons which comprises introducing relatively heavy charging stock into contact with hot vapors in a primary fractionating Zone, passing vapors from the primary fractionating zone to a secondary fractionating zone wherein fractionation takes place to separate a reflux condensate from lighter fractions, subjecting rei-lux condensate from the secondary fractionating zone to cracking conditions of temperature and pressure to effect conversion into lower boiling products, dividing the products of conversion into at least two portions, admixing resultant reflux condensate and unvaporized charging stock from the primary fractionating zone with one of the divided portions to supply heat to the heavy oil and to effect cracking thereof, passing resultant products of conversion into a separating zone wherein separation of vapors from residual constitutents takes place, passing resultant separated vapors to said primary fractionating zone, directing resultant liquid residue to a ashing zone wherein the residue is subjected'to ash distillation, passing residue from said flashing zone to a coking zone and subjecting the residue therein to coking by contacting it with the other portion of aforesaid products of conversion.

13. A process for converting higher boiling hydrocarbons into lower boiling hydrocarbons which comprises introducing relatively heavy charging stock into a fractionating Zone receiving vapors from the flashing zone hereinafter specified, withdrawing resultant reflux condensate and unvaporized charging stock'and directing the oil so withdrawn to a primary fractionating zone of the separating zone hereinafter specified, passing vapors from said primary fractionat- 75 ing Zone to a secondary fractionating zonewherein fractionation takes place to separate reflux condensate from lighter fractions, passing resultant reflux condensate from said secondary fractionating zone through a primary cracking zone subject such mixture to' cracking, passing the i resultant treated and cracked products to a separating zone wherein vapors separate from cracked residue, passing resultant separated vapors intosaid primary fractionating zone, directing resultant cracked residue from the separating zone to the aforesaid dashing zone wherein separation of vapors from residue takes place and from. which the vapors pass to the aforesaid fractionat-v ing zone of the flashing Zone, passing resultant residue from the flash zone to a coking zone and diverting a portion of the high temperature cracked products from the cracking zone to the coking zone to effect coking of the cracked residue introduced thereto, the cracked products being diverted before the introduction into the cracking zone of the reflux condensate and unvaporized charging stock from the primary fractionating Zone. i

14. A process `for converting high boiling vhydrocarbons `into lower boiling hydrocarbons which comprises introducing relativelyl heavy charging stock into a fractionating zone receiving vapors from the ashing zone hereinafter specified, withdrawing resultant reflux condensate and unvaporized charging stock and directing the oil so withdrawn to a primary fractionating zone of the separating zone hereinafter specied, passing uncondensed vapors from said primary fractionating zone to a secondary fractionating Zone wherein fractionation takes place to separate a reux condensate from lower boiling fractions, passing resultant reflux condensate from said secondary fractionating zone through a portion of a cracking zone in a radiant section of a furnace wherein the condensate oil is maintained under cracking conditions of temperature and pressure to effect the desired conversion into lower boiling oils, withdrawing resultant reuX condensate and unvaporized charging stock from said primary 'fractionating zone and combining such reflux condensate and unvaporized charging stock with cracked `products from said radiant section andl passing the mixture through another portion' of the cracking zone in a convection section of the furnace, directing the resultant cornmingled and cracked products to a separating Zone wherein vapors separate from cracked residue, passing resultant separated vapors into said `primary fractionating zone, directing resultant cracked residue from the separating zone to the aforesaid hashing rzone wherein separation of vapors from residue takes place and from which the vapors pass to the aforesaid fractionating i Zone of the ashing Zone, passing vapors from the oil fraction into an upper portion of said secondary fractionating zone to effect condensation of constituents therein which are added to the reux condensate in the secondary fractionating zone.

' STURGIS W. DARLING.