US2102269A - Cracking of hydrocarbon oils - Google Patents

Description

Dec.- 14, 1937.

Original Filed Feb. 26, 1930 2 Sheets-Shed 1 Q 1 (h re/m5 Deb. 14, 1937. 1.. c. HUFF 2,102,269

CRACKING OF HYDROCARBON OILS Original Filed Feb. 26, 1930 2 Sheets-Sheet 2 7' TOR/YEY Patented Dec. 14, .1937

UNITED STATES PATENT OFFICE CRACKING OF HYDROCARBON OILS Application February 26, 1930, Serial No. 431,405 Renewed April 30, 1935 5 Claims.

This invention relates to the art of treating hydrocarbon oils by the method of thermal decomposition known as cracking and has for its object the production of hydrocarbons, within the boiling range of motor fuel, which are of a highly unsaturated nature and are especially desirable for use as fuel in internal combustion engines employing high compression pressures.

With the continually increasing use of high compression internal combustion engines employing a carbureted fuel the demand for suitable fuel which will withstand the high compression pressures employed without appreciable detonation has steadily mounted until such suitable fuel has come to demand considerable premium in the market.

In a cracking process of the liquid-vaporphase type which is in wide commercial use, one of the usual methods of operation is to produce a distillate containing from 60 to 85% more or less, of material falling Within the boiling range of gasoline and which is redistilled to efiect a separation of this gasoline-like component. The residual material commonly termed pressure distillate bottoms, which is left from this redistillation of the pressure distillate is exceptionally suitable for the production of a highly anti-knock motor fuel when processed under high temperature or so called vapor-phase cracking conditions. Inasmuch as these so-called pressure distillate bottoms are a highly refractory cracking stock and would considerably lower the throughput if returned and reprocessed in the liquid vapor-phase system, it would be economical to treat them separately in a system employing conditions most suitable for the conversion of this particular oil.

My process comprises a liquid-vapor-phase, system wherein the pressure distillate vapors are further fractionated in a secondary fractionating tower within the system and wherein the reflux, corresponding to pressure distillate bottoms, from this secondary fractionating' tower is reconverted under vapor phase cracking conditions.

A salient feature of my invention is the optional use of a residuum revaporizing or flash distilling system wherein the residual products from both the liquid-vapor-phase and the vapor-phase systems may be released under reduced pressure and their combined redistillation thereby effected.

My process also provides for the use of reflux from the dephlegmator of the flash system, consisting of reflux condensate combined with preheated and topped raw oil charging stock, as a cooling medium in the vapor-phase dephlegmator or in the liquid-phase dephlegmator, or in both.

The process also provides for the return of reflux from the dephlegmator of the vapor-phase system to the liquid-phase heating element and its reconversion therein.

The attached drawings, Fig. 1 and Fig. 2represent a diagrammatic elevation, not drawn to scale showing one particular construction of an apparatus to which my process is adapted. The raw oil enters the process through line I and is fed by means of pump 2 through line 3 and valve l into dephlegmator 58 of the flash system. Here the oil is stripped of its natural gasoline content, if any, by heat from the vapors arising in the dephelgmator. The preheated and stripped raw oil together with. reflux condensate from the vapors may collect in the bottom of the dephlegmator 58 and pass therefrom through line 5 and 'valve 5 to the hot feed pump 6. From here the oil may be fed through valve 1, line 8 and valve 8 into fractionating tower 42 of the vaporphase system, or through valve 9 and line l into the primary dephlegmator 2! of the liquidvapor-phase system or by proper manipulation of the valves 1 and 9 any portion may be fed in either direction.

The oil thus fed into the vapor-phase fractionating tower 42 assists in cooling and fractionating the vapors arising therein. Its unvaporized portions are collected together with the reflux condensate in the bottom of the tower and pass through line ll, valve ll, heat exchanger or reboiler l2, through line l2 and valve I3 to pump l3 and is then fed by pump l3 through line 68 and valves 69 and 1 into line IS.

The heat exchanger or reboiler l2 serves to strip the reflux liquid from fractionating tower d2 of the low boiling gasoline-like constitutents which may be contained therein by reboiling the reflux liquid by indirect contact with hot vapors from the vapor-phase reaction chamber 39 at the same time partially cooling the cracked vapors. The low boiling constituents or light ends thus separated may pass through line H and valve 4' back into the fractionating tower 42 at a point above the reflux level.

Oil fed into the primary dephlegmator 2|I through line I!) serves the same purpose of assisting cooling and fractionation in this portion of the apparatus, collects with other reflux condensate in the bottom of this fractionating tower 2| and passes through line l5 and valve IE to pump 56. CH from pump I 6 combines in line it with the oil fed from pump l3 through line 58 and the total combined feed from line, I6 is pumped through the liquid-vapor-phase heating element 11.

This liquid-vapor-phase heating element is located in any suitable furnacel8. Theoil passing through the heating'element I1 is heated to the desired temperature under any desired pressure and passes through line 19 and valve l9 into the liquid-vapor-phase reaction chamber 20. Vapors from this reaction chamber pass through line -68 and valve 68 into the primary dephlegmator 2| where they are cooled and fractionated by ,incoming oil from line I as above described.

Dephlegmator 2| may be any'suitable fractionating device employing any'vsuitable fractionating means such as perforated pans orpacking.

' The vapors leaving primary 'dephlegmator'2 twill consist of a small amount :ottfixedl gas ,and the product commonly known as pressure i distillate portions of the pressuredistillate whichcorre- T spond togasoline are separated from the heavier portions. These lighter -portions,may pass as vapor throughline 24,valves 24; and25 into the 7 upper; portion of the vapor-phase fractionating tower 42 or they may pass through line 26 controlled by=valve 21 .through condenser 28, line 28" and valve 29 into receiver29 wherein theliquid products are separated from the fixed gas-the flxed'gas-being released through line- 30 controlled by valve 3i -and the liquid productsbeing withdrawn to storage. or elsewhere through line 32:controlled by valve 33.

Reflux; corresponding to what is commonly known as pressure distillate 'bottoms, from the secondary fractionating- .tower '23 may pass through-line 34, valve =34" and by means of pump 35.may:be fed through valve 35 and'line 36 to the vapor-phase heating element 35'which is locatedinany suitable furnace 31. This material after being subjected to the 'desiredconditions of temperature and pressure in heating element 36 may pass in ,a-substantiall-y; vaporized state through line '38 and'valve :38 and into the vaporphase -reactionchamber 39.-- Vapors from this reaction chamber-may pass through line -and valve -=4l to the heat exchanger ,or reboiler 12 .where they reboilthe bottoms from the fractionating tower 42 and "are thereby-partially cooled 'as above described, and thence continue through line 40 and valve -4I' into the'vapor-phase fractionating 'tower' 42.

Tower 42 .may takethe form'of'any suitable fractionating device'andispreferably a tower of the-packed or'bubble type. Vapors leaving this tower pass-through line 43,'valve 43.,conderiser 44,. line 44jand 'valve45' into receiver 45 where the condensed'liquid produced is separatedfrom -the uncondensed gas. The fixed gas is released throughline 46 2controlled by valve 41' and the ,liquid productis withdrawn to storage or'elsewhere through line '48 controlledby valve 49.

The'liquid residual "product from reaction chamber 20:0f the liquid-vapor-phasesystem may .be-"withdrawn by well known means not shown for use as :fuel in thesystem, or to-storage or elsewhere. Theliquid residual product from the reaction chamber 39 of the vapor-phase system may likewise be separately withdrawn by means not 'LSh'Own or it may be withdrawn through line '50and valve 5| :into' line '52where it may combine, if desired, with the residual liquid withdrawn from reaction chamber 20 through line 53 and valve 54. Either one of these residual products or the two combined in any proportion may pass through line 52 and valve 55, where the pressure is substantially reduced, into flash distilling chamber 56. The lighter portions of the residual liquids are here revaporized by their own latent heat and may *passthrough; line 51 and valve 5? into flash dephlegmator 58.

Flash dephlegmator 58 may be any suitable fractionating device, but is preferably a tower containing perforated pans or similar fractionating means. The flashed vapors are herein fractionated and partially cooled by incoming 'raw' oil and'the lighter portions of the vapors maypass through line 59, valve 59, condenser 60,-,line60' and valve 6| into receiver 6| where the condensed liquid is separated from the uncondensed gas; the gas being released through line .62 controlled by valve #63 :and condensate 1 being withdrawn through; line 64 controlled by valve 65. i 1

The condensed liquid receivers ifl, 45-or. B] may be returned. ;in any products from; any of the desired quantityby wellknownmeans not'shown,

to their respective ,fractionating towers 23," 42

and m assist cooling and: fractionation in the I fractionating towers. The flashedresidual -pr0ductirom flash chamber 56 may be withdrawn throughlinelifi and valve 61 to l'storage 'or elsewhere. I

Any pressure ranging fromsub-atmospheric to high superatmospheric pressures, say ,up "to 2000 pounds persquare inch-more oriless, may be employed throughout the system or differential pressures may be employed between'various portions of the apparatus. Cracking "temperatures ranging from 700 to ,1400'degrees F. more or less,

may be employed .in eithergor both heating elements but preferablytemperaturesemployed in heating .element I! are withinfthe range of what ;iscommonly termed liquid-phase cracking temperatures, say,700 to, -1000 degrees -F., orthereabouts, and temperatures employed'in the heating'element 36 are preferably maintained within the'range of what are commonly termed vaporphase cracking temperatures, e. g. 900 to 1400 I degreesF; more or less. I As a specific'example of one of the many operations possible with my process and 'in the,

apparatus ,just described a 32 :degree A, R I; gravity Mid-Continent gas oil is usedzas charging stock .for the liquid-vapor-phase' process.

The-total charge is fed to the .fractionating zone of-the flash systemand in combination with the reflux condensateffrom this flash dephlegmat'or is vfed in part to theprimary dephlegmator of the liquid-vapor-phase system and in part 'to the fractionating tower of the vapor-phase system. Reflux condensate and preheated raw oil from both of these fractionating zones is subjected in the liquid-vapor-phase heating element to. an outlet temperature of approximately 900 degrees F. under a pressure of approximately 225 pounds persquare inch.

Very little liquid is-maintainecl in the reaction chamber of the liquid-vapor-phase system and consequently little or no coke is depositedin this chamber. Substantially the same pressure is 'maintained in the chamber 20 and tower 2| as that maintained inthe heating element I! but this pressure is reduced inthe secondary fractionatingtower of "the liquid-vapor-phase system to approximately 90 poundsper squareinch;

Reflux condensate corresponding to pressure distillate bottoms from the secondary liquid-vapor-phase fractionating tower comprises the charging stock to the vapor-phase system. This oil is heated in the vapor-phase heating element to a temperature of approximately 1200 degrees F., and a substantially equalized pressure of approximately 80 pounds per square inch is maintained throughout the vapor-phase system.

Residual oil from both the liquid-vapor-phase and the vapor-phase reaction chambers is flash distilled at a reduced pressure at approximately 20 pounds per square inch.

Recovery of the various products from an operation such as outlined may be somewhat as follows:

Approximately 54% of distillate boiling within the range of motor fuel and equivalent in antiknock rating to a blend of approximately benzol with 65% straight run gasoline may be recovered from the liquid-vapor-phase system.

The system in this particular case is so operated that a relatively high percentage. of pressure distillate bottoms are produced and from this oil approximately 22% of gasoline based on the charging stock may be recovered by processing in the vapor-phase system. This vapor-phase gasoline while quite possibly of lower gravity than ordinary cracked or straight run gasoline may still fulfill the boiling range requirements for regular or even premium motor fuel and may show a benzol equivalent of some 60% or thereabouts.

About 10% of a relatively heavy distillate is rerovered from the flash system and a final heavy residual product from the process removed from the flash chamber may represent only 8%, more or less, of the original charging stock. The remaining 6% or thereabouts may represent the coke, gas produced and loss in processing.

I claim as my invention:

1. A hydrocarbon oil cracking process which comprises initially cracking the oil in a primary cracking zone under suflicient pressure to retain a substantial portion thereof in the liquid phase, separating the thus treated oil into vapors and unvaporized oil, simultaneously cracking a condensate separated from said vapors in the vapor phase in a second cracking zone, flash distilling said unvaporized oil by pressure reduction and dephlegmating the resultant flashed vapors independently of the vapor phase cracked vapors rom said second cracking zone and in contact with fresh charging oil for the process thereby forming a mixture of unvaporized charging oil and flash reflux, dephlegmating the vapors from said primary cracking zone and the vapors from said second cracking zone in contact With portions of said mixture, then supplying the charging oil and resultant reflux condensate to the primary cracking zone, and condensing the dephlegmated vapors.

2. A process as defined in claim 1 further characterized in that said condensate comprises a secondary reflux condensate produced by secondary dephlegmation of the vapors from said primary cracking zone.

3. A hydrocarbon oil cracking process which comprises initially cracking the oil in a primary cracking zone under sufl'lcient pressure to retain a substantial portion thereof in the liquid phase, separating the thus treated oil into vapors and unvaporized oil, simultaneously cracking a condensate separated from said vapors in the vapor phase in a second cracking zone, flash distilling said unvaporized oil by pressure reduction and dephlegmating the resultant flashed vapors in contact with. fresh charging oil for the process thereby forming a mixture of unvaporized char ing oil and flash reflux, passing the vapors from said primary and second cracking zones to independent dephlegmating zones, dividing said mixture and introducing a portion thereof into each of said independent dephlegmating zones to serve as a dephlegmating medium therein, supplying unvaporized charging oil and reflux condensate from said dephlegmating zones to the primary cracking zone, and condensing the vapors unconolensed in said dephlegmation.

4. A hydrocarbon oil conversion process which comprises cracking hydrocarbon oil in a primary cracking Zone under suflicient pressure to retain a substantial portion thereof in liquid phase, separately removing vapors and unvaporized oil from said zone, fractionating the Vapors to form a relatively heavy reflux condensate and a lighter reflux condensate, returning such heavy reflux condensate to said zone, cracking the lighter reflux condensate substantially in vapor phasein a second cracking zone maintained at higher temperature than said primary zone, fractionating the resultant vapor phase cracked vapors, reducing the pressure on the unvaporized oil withdrawn from said primary zone and thereby flash distilling the same, fractionating resultant flashed vapors independently of said vapor phase cracked vapors thereby forming flash reflux condensate, introducing such flash condensate into contact with the vaporphase cracked vapors undergoing fractionation and supplying resultant liquid products to the primary cracking zone, and finally condensing the fractionated vapors.

5. A conversion process which comprises cracking hydrocarbon oil in a primary cracking zone under suflicient pressure to retain a substantial portion thereof in liquid phase, simultaneously cracking a lighter oil substantially in vapor phase in a second cracking zone maintained at higher temperature than said primary zone, fractionating resultant vapor phase cracked vapors to condense heavier fractions thereof, removing unvaporized oil from said primary zone and flash distilling the same by pressure reduction, fractionating resultant flashed vapors independently of said vapor phase cracked vapors, introducing flash reflux thus formed into contact with said vapor phase cracked vapors undergoing fractionation and supplying liquid products of this fractionating step to said primary zone, removing vapors from the primary zone and fractionating the same independently of said vaper phase cracked vapors, supplying resultant reflux condensate to the second cracking zone as said lighter oil, and finally condensing the fractionated vapors.

LYMAN C. I-IUFF.

Images