US2178834A - Process of treating hydrocarbon oils - Google Patents

Description

Nov. 7, 1939. J. w. GRAY ErAL PROCESS OF TREATING HYDRCARBON 01?;

Filed Aug. 19, 1937 Patented Nov. 7, 1939 UNITED STATES PATENT OFFICE PROCESS F TREATING HYDROC'ARBON ILS poration of Delaware Application August 19,

11 Claims.

This invention relates to an improvement in the art of cracking hydrocarbons to produce lowboiling hydrocarbons from high-boiling hydrocarbons.

In the treatment of hydrocarbons to produce cracking thereof, it is known to mix hot heavy oil such as topped or reduced crude oil containing heavy constituents with a hot, partially cracked clean oil and then to further crack this mixture.

These processes sometimes result in coking in the coils because there seems to be a limit to the temperature to which the mixed hot heavy oils and cracked clean oils can be further heated without coking. The objectionable coking seems to result because the hot heavy oils and extremely hot clean oils do not apparently mix instantly and uniformly apparently causing overheating of some of the heavy oils by contact with the high-temperature clean oils to cause the formation of coke.

We have overcome the above-mentioned objection by mixing all of the hot heavy oil charge with only a part of the highly heated clean oil or gas oil coming for example from the rst portion of a cracking zone in the radiant section of a furnace and passing this mixture for example through either the latter portion of the cracking zone in the convection section of the furnace or through an insulated section situated outside of the furnace, with the remainder or part of the remainder of the highly heated clean oil or recycle gas oil coming from the rst portion of the cracking zone being injected at a subsequent point or points in the combined stream. If desired, part of the highly heated clean oil from the radiant section of the furnace may be passed through the latter portion of the cracking Zone in the convection section of the furnace and the remainder passed through an insulated section situated outside of the furnace. In this way the temperature of the combined stream is maintained or progressively raised, and the cracking rate is correspondingly increased thus resulting in efiicient viscosity-breaking of the heavy oil. The stream or charge of highly heated clean oil or recycle gas oil coming from the first portion of the cracking zone may be subdivided as much as desired and injected into the latter portion of the cracking zone at a plurality of selected points. Our method is especially advantageous in cases where the temperature of the cracked clean oil or recycle gas oil is exceptionally high, such as when the clean oil is subjected to socalled vapor phase cracking.

Other advantages will be apparent` from the 1937, Serial N0. 159,866

detailed description of our invention hereinafter contained taken in connection with the drawing which shows a diagrammatic iiow sheet of apparatus adapted for practicing our invention.

Referring now to the drawing, the reference 5 character Il) designates a heater or furnace having a continuous heating coil I2 Where theoil to be converted is maintained under superatmospheric pressure and high-temperature conditions for a desired length of time to obtain the desired 10 cracking or conversion. The rst portion I3 of the cracking coil extends through the radiant section I4 of the furnace and the latter portion I5 of the cracking coil extends through the convection section I6. The oil to be cracked is prei- 15 erably a clean oil, such as gas-oil condensate or heavy naphtha, and this clean oil is passed through line 20 by means of pump 22 through the radiant coil section I3 of the cracking coil I2 and is maintained under high-temperature and 20 high-pressure conditions during its passage therethrough to effect conversion into lower boiling products. The stream of high-temperature cracked products leaves the first portion I3 of the cracking coil I2 through line 24 and is sub- 2l'- divided into two portions for passage of a separate portion through each of lines 2B and 23. A heavy oil containing unvaporized liquid constituents of a reduced crude oil and heavy reux condensate, obtained as later described, is passed 30 through line 3U by means of pump 32 and is injected into or admixed with that portion of the cracked products passing through the line 26. In this way the heat of a part of cracked products is utilized to materially increase the tem- 35 perature of the heavy oil, preferably to a cracking temperature.

The combined stream at cracking temperature is passed through the latter portion I5 of the cracking coil I 2 extending through the convec- 40 tion section I 6 of the furnace II) and is therein subjected to additional heating by the furnace gases. The other portion of the stream'of the high-temperature cracked products passing through line 28 may be passed through line` 34 45 and admixed With the combined stream under- .f going cracking at an intermediate point in the coil section I5 extending through the convection section IB of the furnace I ll, or only a part of the stream may be so injected and the rest, passing 50 through line 36, may be injected into the stream of cracked products leaving the coil section l5 through line 4D. v When a part of the high-temperature stream is injected into the combined stream, as for example through line 34, the tem- 55 perature of the combined stream at this point is raised and the cracking rate increased. If desired, the combined stream may be passed through a reaction chamber wherein further cracking may be effected..

The stream of cracked. products after the deaired conversion thereof has been completed is passed through line 09 preferably having a reducing valve 42 into the evaporator or separating Zone 44 of the combined evaporator and fractionating tower 46 having a fractionating section 48. Suitable quenching stock such as gas-oil or lighter may be introduced through line 4,9 into the stream passing through line 453 to cool the cracked products suddenly and prevent overcracking thereof. The evaporator section 44 and the fractionating section 48 of the combined evaporator and fractionating tower 15G are separated by a trap-out tray having a hood 52. In the evaporator the pressure is preferably lower than in the cracking Zone and the stream of cracked products passing into the evaporator 4.4 is separated into hot vapors and a cracked residue. The hot vapors pass upwardly into the fractionating section 48.

The cracked residue is withdrawn from the bottom of the evaporator 44 through line 55 having a pressure reducing valve 58 and passed into the flash zone E8 of the combined fractionating and flash tower 62 having a fractionating section 66. The flash zone 80 and fractionating section 66 of the combined fractionating and ash tower 62 are separated by a trap-out tray 68 provided with a hood 10. The flash Zone 60 is under less pressure than the evaporator 44 so that a flash distillation or vaporization is obtained and a further separation into hot vapors and a cracked residue takes place in the flash zone 60. The cracked residue is suitable for use as fuel oil and may be withdrawn through line 'I2 and further treated if desired. The hot vapors released in the ash zone E0 pass upwardly into the fractionating section 66 of the combined fractionating and flash tower 52 where r they come in contact with downwardly flowing reduced crude oil, or other fresh heavy oil, preferably preheated. The reduced crude oil charge or heavy oil is passed through line 'l5 by means of pump 18 into the upper portion of fractionating section 68 where it cornes in contact with the hot vapors released from the flash Zone 60 and some of the crude oil is vaporized and some of the vapors in the fractionating section 6E are condensed to form reflux condensate. The vapors may be withdrawn through line i9 and may be separately treated as desired, but are preferably forced into a secondary fractionating zone, later to be described, for further treatment.

The heavy reflux condensate and unvaporized reduced crude oil are collected on trap-out tray 58 at the bottom of the fractionating section G6. The reflux condensate and unvaporzed reduced crude oil are passed through line 80 by means of pump 82 into the upper portion of fractionating section 48 of the combined evaporator and fractionating tower 45S where they come in contact with hot vapors released from the evaporator 44. Some of the liquid constituents are vaporized and the combined vapors are fractionated in the fractionating section 48 of the combined evaporator and fractionating tower 45 wherein some of the vapors are condensed to form heavy reflux condensate. The heavy reflux condensate and unvaporized reduced crude oil are collected in trap-out tray 50 at the bottom of the fractionating section 48 and form the heavy oil charge which is passed through line 30 into the coil section l5 or latter portions of the cracking coil |2 extending through the convection section I6 of the furnace I0.

The vapors leaving the top of the combined evaporator and fractionating tower 46 are passed through line 84 into the bottom portion of the secondary fractionating Zone 86 which, prefer ably, is of bubble tower construction. As the vapors pass upwardly in the secondary fractionating zone 8S they are fractionated into lighter and heavier constituents, the lighter constituents passing over as vapors and the heavier constituents being condensed and collected at the bottom of the secondary fractionating zone 86 as condensate oil. This condensate oil is a gas-oil which contains insucently cracked products and is the clean oil which is passed through line 20 and coil section I3 extending through the radiant section I4 of the furnace l0 to be converted.

The vapors of the desired end point leaving the top of the secondary fractionating zone 86 are passed through line 88, cooled and condensed by passing through condenser 90 and the liquid is collected in a suitable receiver or drum 92. The receiver or drum 82 has a valved gas outlet 84 and a valved liquid outlet 9E. The liquid which is collected on the bottom of receiver or ,f

drum 92 comprises a motor fuel product such as gasoline which may be further treated as desired. The vapors leaving the top of the combined fractionating and flash tower 62 are passed through line 1S as above mentioned and may be separatei ly treated as desired, but they are preferably forced into line 84 in any suitable manner and passed to the secondary fractionating Zone 86 along with the vapors passing through line 84.

Some of the liquid collecting on the bottom of the receiver or drum 92 is preferably passed through line |00 by means of pump |52 into the upper portion of the secondary fractionating zone 88 to act as reflux liquid. If desired, a cooling coil |04 may be mounted in the upper part of the secondary fractionating zone 86 to provide additional cooling for the upper portion of the secondary fractionating Zone 86.

If desired, a portion of the heavy oil leaving the bottom of the fractionating section 48 of the combined evaporator and fractionating tower 4G may be passed through line |06 and then through a heating coil |08 in order to preheat the heavy oil or subject it to a relatively mild viscositybreaking treatment. The heated heavy oil leaving the heating coil |08 may then be4 passed through line H0 and into the line 30 'leading to the latter portions of the coil section I5 as described.

Instead of passing all the reduced crude oil into the fractionating section 5t of the combined fractionating and flash tower 62, a part of the reduced crude oil may be passed through lines H6 and ||8 and then through the heating coil |08 in order to preheat it or subject it to a mild viscosity-breaking treatment. The heated oil leaving the heating coil |88 is then passed through line |I0 for admixture with heavy oil withdrawn through line 30 for passage through the latter portion of the coil section I5 as described.

We have found that by injecting the heavy oil passing through line 30 into a part of the highly heated stream of cracked products coming from the first portion or section of the cracking 'Sie zone l2, we avoid objectionable coking. obtained when all of the heavy oil and the high-temperature clean oil are mixed together. The clean oil and the heavy oil apparently do not'mix instantly and uniformly when all of the cracked clean oil is mixed, and some of the heavy oil may become overheated by contact with the hightemperature clean oil and cause the formation of coke. By dividing the high-temperature clean oil into two or more streams and injecting the heavy oil into one of the streams and then cracking such mixture we overcome the objections heretofore noted.

When the temperature necessary to crack the clean oil passing through the rst portion of the cracking zone l2 is extremely high, it will be desirable to use a plurality of injection points into the combined stream passing through the latter portion or section l5 of the cracking Zone I2.

The vapors from the top of the combined fractionating and iiash tower S2 containing both gasoline and gas-oil constituents may be completely condensed and mixed with the condensate being passed through the cracking zone i2 to effect cracking of the gas-oil and reforming of the naphtha contained therein.

An example of a typical operation will now be given, but we are not to be restricted thereto as various changes and modications may be made. A reduced crude oil stock or other relatively heavy charging stock preferably preheated in any suitable manner is introduced into the fractionating section 65 of the combined fractionating and iiash tower 52, maintained at apres-- sure of between atmospheric and 50 pounds' per square inch, where it contacts hot vapors passing upwardly from the ash zone 50 and thus vaporizes some of the light constituents from the reduced crude oil or heavy oil charge. At the same time some of the heavier constituents of the hot vapors are condensed to form heavy reflux condensate. The heavy reflux condensate and unvaporized liquid are collected at the bottom of the fractionating section as, for example, in trap-out tray t8 and are then passed through line St by pump S2 to the fractionating section d8 of the combined evaporator and fractionating tower maintained at a pressure of between about 50 and 100 pounds per square inch, where some of the liquid is vaporized and fractionated by contacting the hot vapors from the evaporator or separating zone le of the combined evaporator and fractionating tower fit. Some of the heavy constituents of the vapors condense to form reflux condensate.

The unvaporized heavy constituents and reiiuX condensate are collected at the bottom of the fractionating section "i8 in trap-out tray 5t. The vapors leave the top of the combined evaporator and fractionating tower d3 at a temperature of about 650750 F. and pass through line 8f3 into the bottom of the secondary fractionating tower 86 to be fractionated therein. The vapors leaving the secondary fractionating zone 0G through line 88 are at a temperature of about SOW-400 F. and are condensed and collected in receiver 02 as low-boiling hydrocarbons suitable for motor fuel, such as gasoline, after further usual treatment.

The gas-oil condensate from the bottom of the secondary fractionating zone 86 containing insufliciently cracked products comprises the clean oil or recycle gas-oil which is passed 'through line 20 and into the rst portion i3 of the cracking zone l2 extending through the radiant section I4', of the furnace l0. This clean oil enters the cracking zone at a temperature of about 550 to 700 F. and leaves the cracking zone at a temperature of about 925 to i100" F. and during its iiow therethrough is subjected to cracking; This highly heated stream of cracked products passes through line 2li and is then subdivided into two streams. One stream passing through line 26 is combined with the heavy oil passing through line 30 from the trap-out tray 50 in the combined evaporator and fractionating tower d6, the heavy oil being at a temperature of about 600 to 900 F. After the injection of the heavy oil into the stream of the high-temperature cracked clean oil passing through line 26, the combined stream is at a temperature of about 850 to 925 F., and this combined stream is then passed through the latter portion l5 of the cracking zone l 2 extending through the convection section i6 wherein further cracking of the clean oil and viscositybreaking of the heavy oil takes place. The combined stream leaves the cracking zone at about 850 to 950 In the cracking zone the pressure is maintained at about 300 to 1000 pounds per square inch.

The other portion of high-temperature cracked clean oil passing through line 28 may be injected at a subsequent point through line 34, for eX- ample, into the combined stream passing through the latter portion l5 of the crackingvcoil i2 extending 'through the convection section lli of the furnace i0 to raise the temperature of the combined stream and increase the cracking rate; or this portion may be passed through line 36 to by-pass the latter portion it of the cracln'ng zone i2 and be injected into the stream of cracked products leaving the latter portion of the cracking zone through line t0.

The stream of cracked products leaving the latter portion of the cracking zone l2 through line Iltis passed into the evaporator or separating zone Sii. The separating zone dit is maintained at a pressure of about 50 to 350 pounds per square inch and a separation of the cracked products into hot vapors and a cracked residue occurs. The hot vapors are fractionated in the fractionating section S of the combined evaporator and fractionating tower l5 and this fractionation is assisted by contact with hot liquid introduced into the tower it through line 80 from the combined fractionating and flash tower t2. lighter constituents of the liquid are vaporized and some of the heavier vapors are condensed to form reflux condensate.

The vapors leave the top of the combined evaporator and fractionating tower it at a temperature of about 650 to '750 F. and pass through line Sfiinto the bottom portion of the secondary fractionating zone The vapors passing upwardly in the secondary fractionating zone' are therein fractionated to condense insuiciently cracked products as refiux condensate and the remaining vapors of lower-boiling hydrocarbons, that is, the desired gasoline, are condensed and collected in receiver 92.' rIhe condensate collected in the bottom of secondary fractionating zone 86 forms the clean recycle gas oil which is recycled through the cracking zone i2 through line 20.

In the fractionating section d8 some of the The crackedl residue from the separating Zone M in the bottom of the combined evaporator and fractionating zone d is passed through line 56 having reducing valve 58 and into the ash zone 60 in the bottom of the combined fractionating and ash tower 62 maintained at a lower pressure than separating Zone 44. A flash distillation takes place in flash zone- 44 and the hot vapors and cracked residue are Separated. The hot vapors from the ash zone 60 pass upwardly and contact the hot reduced crude oil charge or other heavy oil introduced into the fraotionating section 66 ofthe combined fractionating and ash tower 62. Vaporization of some of the lighter constituents of the crude oil and condensation of some of the heavier constituents from the hot vapors are effected in the fractionating section 66. The vapors leaving the top of the combined fractionating and flash tower 62 through line 19 may be passed to the fractionating zone 8G with insumciently cracked products therefrom being added to the reflux condensate therein for passage through the cracking Zone I2 for cracking. The cracked residue from the bottoml of flash zone El] may be drawn off through line 12 and used as iuel oil.

It is within the contemplation of our invention to omit the combined fractionating and ash tower 62, in which event the reduced crude oil charge or other relatively heavy oil charge would be introduced into the fractionating section 48 of the combined evaporator and fractionating tower 46; and the unvaporized liquid or cracked residue separated from the stream of cracked products introduced into the evaporator or separating zone 44 would be withdrawn from the bottom of the evaporator 44. The unvaporized heavy oil and heavy reflux condensate collecting on trap-out tray 5i) would be passed through line as hereinbefore described.

While we have described a particular embodiment of our invention, it is to be expressly understood that our invention is not restricted thereto, and various modications and adaptations thereof may be made without departing from the spirit of the invention.

We claim:

1. A process for treating high-boiling hydrocarbons to produce low-boiling hydrocarbons, which comprises contacting vapors in a primary fractionating zone With a relatively heavy oil and collecting unvaporized heavy oil therein, thereafter subjecting vapors from the primary fractionating Zone to further fractionation in a secondary fractionating Zone to separate relatively high boiling oil therefrom as reiiux condensate, passing reux condensate thus obtained as a stream through the first portion of a cracking zone maintained under high-temperature and high-pressure conditions to produce conversion of such reux condensate into lower boiling products, injecting unvaporized heavy oil from said primary fractionating zone into a portion of the stream of high-temperature cracked products leaving the rst portio-n of the cracking Zone, passing such combined stream through the latter portion of the cracking zone maintained at cracking temperature, injecting another portion of the stream of high-temperature cracked products into the latter portion of the cracking zone at a point subsequent to the injection of such heavy oil to raise the temperature thereof and effect further cracking of the heavy oil, passing the resulting stream of cracked products leaving the latter portion of the cracking zone to a separating zone wherein vapors and cracked residue are separated, and passing such vapors into the primary fractionating zone.

2. A process for treating high-boiling hydrocarbons to produce `low-boiling hydrocarbons,

which comprises contacting vapo-rs in a primary fractionating Zone with a relatively heavy oil and collecting unvaporized heavy oil therein, thereafter subjecting vapors from the primary fractionating zone to further fractionation in a secondary fractionating zone to separate relatively high-boiling oil therefrom as reflux condensate, passing reflux condensate thus obtained through the rst portion of a cracking zone maintained under high-temperature and highpressure conditions to produce conversion of such reflux condensate into lower-boiling products, then subdividing such stream of cracked products into two portions and injecting the unvaporized heavy oil from said primary fractionating zone into one portion of the stream of cracked products and passing such combined stream through the latter portion of the cracking zone maintained at cracking temperature, and injecting the other portion of the stream of cracked products into the combined stream leaving the latter portion of the cracking zone, and passing this newly formed stream of cracked products to a separating zone wherein vapors and. a cracked residue are separated, and passing the vapors into the primary ractionating Zone.

3. A process for treating high-boiling hydrocarbons to produce low-boiling hydrocarbons, which comprises contacting a reduced crude oil with hot vapors to vapo-rize some of the crude oil and condense some of the heavy constituents of the vapors as relatively heavy reflux condensate, passing remaining vapors to a fractionating Zone to therein separate high-boiling oil as reux condensate, collecting the unvaporized reduced crude constituents and relatively heavy reux condensate, passing reflux condensate thus obtained as a stream through the rst portion of a cracking zone maintained under relatively high-temperature and high-pressure conditions to produce conversion thereof into lower-boiling products, injecting the unvaporized reduced crude constituents and relatively heavy condensate into one portion of the stream of high-temperature cracked products from the rst portion of the cracking zone, passing sucht combined stream through the latter portion of the cracking zone maintained at a cracking temperature, injecting another portion of the stream of high-temperature cracked products from the first portion of the cracking zone into the latter portion o-f the cracking zone at a point subsequent to the injection of the unvaporized reduced crude constituents and relatively heavy condensate to raise the temperature and effect further cracking of the introduced reduced crude constituents and relatively heavy condensate, passing the resulting stream of cracked products to a separating zone wherein hot vapors and cracked residue are separated, and using such hot vapors to contact the hot reduced crude oil to be treated.

4. A process for converting higher-boiling hydrocarbons into lower-boiling hydrocarbons, which comprises passing relatively heavy oil to a fractionating zone to contact hot vapors therein and vaporize some of the lighter constituents of the heavy oil and to condense some of the hot vapors therein to form heavy reflux condensate, passing the remaining vapors to a secondary fractionating zone to produce light products and a gas-oil condensate, passing such gas-oil condensate into the first portion of a cracking zone maintained under high-temperature and highpressure conditions to produce conversion of the gas-oil condensate into cracked products, injecting the heavy reflux condensate and unvaporized heavy oil from the irst-mentioned iractionating zone into one portion of the stream of high-temperature cracked products passing through the latter portion of the cracking zone, passing such comb-ined stream through the latter portion of the cracking zone, injecting another portion of the stream of high-temperature cracked products into the latter portion of the cracking Zone at a point subsequent to the injection ofthe heavy reflux condensate and unvaporized heavy oil, injecting the rest of the stream of high-temperature cracked products into the stream of converted products leaving the latter portion of the cracking Zone, passing such newly formed stream of cracked products to a separating zone wherein hot vapors and cracked residue are separated, and passing such hot vapors into the first-mentioned fractionating zone for contact with the heavy oil introduced thereinto.

5. In a process for converting higher-boiling hydrocarbons into lower-boiling hydrocarbons wherein a stream of cracked products from a cracking zone is separated into vapors and cracked residue and the vapors are fractionated in primary and secondary fractionating Zones and condensate oil containing insufficiently cracked products is collected in the secondary fractionating zone, the steps comprisingy passing the condensate oil through a portion of the cracking zone maintained under high-temperature and high-pressure conditions to convert the condensate o-il into lower-boiling hydrocarbons, injecting a preheated heavy oil into a portion of the stream of high-temperature cracked products and passing such combined stream at cracking temperature through another portion of the cracking Zone, and then injecting another portion of the stream of high-temperature cracked products into the combined stream passing through the cracking zone, passing the cracked products from the cracking Zone to a separating zone to obtain the aforementioned vapors and cracked residue.

6. A process of converting higher-boiling oils into lower-boiling ones which comprises, subjecting a relatively clean oil in a stream oi restricted cross-sectional area to elevated conditions of temperature and pressure to eect conversion thereof into lower-boiling hydrocarbons, thereafter dividing said stream into at least two portions, admixing a relatively heavy hydrocarbon oil with one of said portions, passing said mixture through a heating zone and subjecting the mixture therein to elevated conditions of temperature and pressure to effect conversion of said heavy oil, and, thereafter admixing another portion of said divided stream with said admixed stream to raise the temperature of the admixed stream.

7. A process of converting higher-boiling oils into lower-boiling ones which comprises, subjecting [a relatively clean oil in a stream of restricted cross-sectional area to elevated conditions of temperature and pressure to eiect conversion thereorn into lower-boiling hydrocarbons, thereater dividing said stream into at least two portions, adlnixing a relatively heavy hydrocarbon oil with one of said portions and heating said mixture to subject it to elevated conditions of temperature and pressure to effect conversion of said heavy oil, combining said admixed stream with the other portion of said divided stream and subjecting the resultant combined proding the primary section of thepassageway to I,.-

maintain the stream iiowing therein at cracking temperature, diverting a portion of the heated stream from the primary section of the passageway while the remaining portion iiows to the intermediate section, introducing aI heavyfoil stock into sai-d remaining portion of the stream for passage through said intermediate section, heating said intermediate section of the passageway and maintaining the resultant stream mixture at cracking temperature, uniting said diverted portion of the stream with the heated stream mixture for passage through the subsequent section of the passageway, heating said subsequent section and maintaining the composite stream flowing therein at cracking temperature.

9. A process for converting higher boiling hydrocarbons into lower boiling hydrocarbons that comprises passing the hydrocarbons in a continuous stream undergoing conversion successively through a primary section, an intermediate section and a subsequent section of a passageway of restricted cross-sectional area, heating the primary section of the passageway to maintain the stream flowing therein at cracking temperature, diverting a portion of the heated stream from the primary section oi the passageway while the remaining portion flows to the intermediate section, introducing a heavy oil stock into said remaining portion of the stream for passage through said intermediate section, heating said intermediate section of the passageway and maintaining the resultant stream mixture at cracking temperature, uniting the diverted portion of the stream with the heated stream mixture to thereby raise the temperature of the stream flowing in the subsequent section of the passageway.

10. A process for converting higher boiling hydrocarbons into lower boiling hydrocarbons that comprises passing the hydrocarbons in a continuous stream undergoing conversion suc-u cessively through a primary section, an intermediate section and a subsequent section of a passageway of restricted cross-sectional area, heating the primarysection of the passageway to maintain the stream owing therein at cracking temperature, diverting a portion of the heated stream from the primary section of the passageway while the remaining portion flows to the intermediate section, passing av heavy oil stock through a separate heating zone wherein the oil is heated to a cracking temperature and subjected to viscosity breaking, introducing resultant viscosity broken products into said remaining portion of the stream for passage through said intermediate section of said passageway, heating said intermediate section of the passageway and maintaining the resultant stream mixture at cracking temperature, uniting at least a part of said diverted portion of the stream with the heated stream mixture `for passage through the subsequent seotion of the passageway, heating said subsequent section and maintaining the composite stream owing therein at cracking temperature.

11. In a process for converting higher boiling hydrocarbons into lower boiling hydrocarbons wherein the hydrocarbons are passed in a continuous stream undergoing conversion successively through a primary section, an intermediate section and a final section of a passageway of restricted cross-sectional area thence into a separating Zone, the method that comprises heating the primary section of the passageway to maintain the stream flowing therein at cracking temperature, diverting a portion of the heated stream from the primary section of the passage- Way while the remaining portion flows to the intermediate section, introducing a heavy oil stock into said remaining portion of the stream for passage through said intermediate section, heating said intermediate seation of the passage- Way'and maintaining the resultant stream mixture at cracking temperature, uniting a part of said diverted portion of the stream with the heated stream mixture for passage through the nal section of the passageway, heating said nal section and maintaining the' composite stream o-wing therein at cracking temperature, and combining another part of said diverted portion of the stream with the composite products owing from the final section of the passage- Way for passage to said separating zone.

JAMES W. GRAY. JESSE S. WALTON.

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