US2118605A - Process for cracking hydrocarbon oils - Google Patents

Description

May 24, 1938. L. c. HUFF PROCESS FOR CRACKING HYDROCARBONOILS Original Filed Nov. 13, 1950 m F HHHH ll l 1 Ir:

Emmi-LU mm ZEDJOU h MOIEEUHIRMO Mm KOL-(EUMATEMQ INVENTOR LYMAN C. HUFF ATTORNEY Patented May 24, 1938 UNITED STATES PATENT OFFlCE Lyman O. Huff, Chicago, 111., assignor, by mesne assignments, to Universal Oil Products Company, Chicago, 111., a corporation of Delaware Application November 13, 1930-, Serial No. 495,394 Renewed November 2, 1934 1 Claim.

This invention relates to the cracking or thermal decomposition of hydrocarbon oils, and more particularly refers to the treatment of relatively heavy hydrocarbon oils under cracking conditions to produce maximum quantities of more valuable products.

Primarily, the present invention comprises subjecting intermediate products from a liquid-vapor phase or relatively low temperature cracking system to reconversion in a vapor phase or rela tively high temperature cracking system and returning intermediate products from said relatively high temperature system to the heating element of the relatively low temperature system for reconversion.

In its specific embodiment, the process of the invention comprises subjecting an oil to liquid vapor phase or relatively low temperature cracking conditions in a primary heating element, introducing the heated materials into an enlarged reaction zone, subjecting vapors from said reaction zone to fractionation in a primary dephlegmator, from which the heavier portion of the vapors is returned as reflux condensate to the primary heating element for reconversion, and light uncondensed vapors from which are subjected to further fractionation in the secondary fractionating column, subjecting the light uncondensed portion of the vapors from the secondary fractionating column to condensation, cooling and collection, returning the heavier condensed portion of the vapors from the secondary fractlonating column to retreatment under vaporphase or relatively high temperature cracking conditions in a secondary or vapor phase heating element, introducing heated products from said secondary heating element into a separate, enlarged reaction zone, vapors from which are subjected to fractionation in a vapor phase dephlegmator and their lighter constituents separately condensed and collected and returning the heavier condensed portion of the vapors from the vapor phase dephlegmator to the primary or liquid vapor phase heating element for reconversion.

As a feature of the present invention, I provide for the introduction of an extraneous oil into the stream of reconverted oil discharging from the secondary or vapor phase heating element to partially cool the stream of heated oil and prevent excessive formation of coke and gas. Extraneous oil of any desirable characteristics from any source may be employed for this purpose, but preferably I utilize an oil similar in characteristics to the reflux condensate, commonly termed pressure distillate bottoms,

from the secondary fractionating column of the primary or relatively low temperature cracking system. Oil of this character may, for example, be obtained from another cracking system using a secondary dephlegmator, or from the re- 5 distillation of pressure distillate. A portion of this same oil, or similar product, may, if desired, be fed directly into the heating element of the vapor phase or relatively high temperature cracking system, thereby increasing the total charge 10 fed to the system. This oil may also be employed to assist fractionation of the vapors in the dephlegmator of the secondary or vapor phase system.

The accompanying drawing illustrates diagrammatically, and not to scale, one specific form which the apparatus of the present invention will assume. Other features of the invention will be apparent with reference to this drawing. Raw oil charging stock supplied through line l and Valve 2 to pump 3 may be fed through lines 4 and 5 and through valve 6 into dephlegmator l where it assists fractionation and cooling of the vapors in this zone by direct contact therewith, and may pass together with the insufficiently converted portion of the vapors which are condensed in dephlegmator 1, through line 8 and valve 9, back into line t and thence to pump 1. A portion or all of the raw oil charging stock, instead of passing overhead to dephlegmator I, may pass directly through valve H in line 4 to pump 16. Pump l0 supplies the charging stock and reflux condensate from dephlegmator '1 through line I2 and valve 13 to heating element 14. Heating element It is located in a suitable form of furnace i5 and the oil passing therethrough is brought to the desired conversion temperature and passes through line 16, and valve ll into reaction chamber l8.

Separation of vapors and liquid is permitted 40 in chamber 18, the latter being withdrawn from the system or to further treatment through line i9, controlled by valve 20, or, if desired, conditions may be so maintained in chamber l8 such that the residual product remaining therein is 5 reduced to substantially dry coke, in which case no liquid residue is withdrawn during the operation, and the coke produced may be removed at the end of the run. Vapors from reaction chamber l8 pass through line 2i and valve 22 into dephlegmator l, where they are subjected to fractionation, their heavier, condensed portion returning, as already described, to heating element 14 for reconversion, and their lighter, uncondensed portion passing through line 23 and valve 24 to fractionating column 25. The vapors are subjected to further fractionation in column 25, their lighter, uncondensed portion comprising preferably material boiling within the range of motor fuel withdrawn through line 26 and valve 21, is subjected to condensation and cooling in condenser 28, thereafter passing through line 29 and valve 30 into receiver 3|, where it is collected as distillate and uncondensable gas. Distillate may be withdrawn from receiver 3| through line 32 and valve 33. Gas is released from the receiver through line 34, controlled by valve 35.

Reflux condensate formed in fractionating column 25, which in most cases will correspond in characteristics to what is commonly termed pressure distillate bottoms, is withdrawn from this zone through line 36 and valve 3'! and fed by means of pump 38 through line 39, valve 40 and line 4| into heating element 42. An extraneous oil or secondary charging stock, preferably similar in characteristics to the reflux condensate from fractionating column 25, and supplied from any desirable source, for example, another cracking system, through line 43 and valve 44, may be fed by means of pump 45, through valve 46 in line 4| into heating element 42.

Heating element 42 is located in a suitable furnace setting 41 and the oils passing through this heating element are raised to a conversion temperature, preferably higher than that employed in heating element l4, and are discharged through line 48 and valves 49 and 50 into reaction chamber 5|. Provision is made for the introduction of a portion or all of the extraneous oil or secondary charging stock from pump 45 into the stream of heated and reconverted material from heating element 42. This is accomplished by diverting the oil from line 4|, through line 52 and valve 53 into line 48. This feature is provided for the purpose of cooling the stream of heated fluid from heating element 42 to a point where undesirable secondary cracking reactions will not occur, thus eliminating or materially reducing the excessive coke and gas losses characteristic to vapor phase cracking reactions.

Separation of the liquid and vapor is permitted in reaction chamber 5|. The liquid withdrawn through line 54 and valve 55 to pump 56 may, all or in part, be discharged from the system through line 51 and valve 58, or may be fed through line 59 and valve 60 into line |2 and thence to heating element l4 for reconversion. Vapors from re action chamber 5| pass through line 6| and valve 62 into dephlegmator 63, where they are subjected to fractionation, assisted, if desired, by a portion of the extraneous oil or secondary charging stock from line 43, supplied through pump 45, line 64 and valve 65 to dephlegmator 63 into direct contact with the vapors in this zone. The lighter portions of the vapors from dephlegmator 63, preferably comprising material boiling Within the range of motor fuel, are withdrawn through line 66 and valve 61, subjected to condensation and cooling in condenser 68 and thence passed through line 69 and valve 10 to be collected in receiver 1|, distillate from which is withdrawn through line 12 and valve 13, and uncondensable gas from which may be released through line 14, controlled by valve 15.

Reflux condensate from dephlegmator 63, comprising the heavier or insufiiciently converted portion of the vapors from the vapor phase or relatively high temperature cracking reaction, are withdrawn from dephlegmator 63 through line 16 and valve 11 to pump 18 and fed therefrom through line 19 and valve 80 into line l2, and thence to heating element M for reconversion. It will be understood that if extraneous oil or secondary charging stock is fed through line 64 to dephlegmator 63, as described, the major portion of this material thus fed will also be supplied, together with a reflux condensate from dephlegmator 63, to heating element 54.

It will also be understood that the usual expedients such as returning a portion of the final distillate from the system to the zone in which it is produced may be employed to assist fractionation and to maintain the desired outlet temperatures from the various fractionating zones, thus assisting in controlling the quality of the finished product. In this particular case, distillate from receivers 3| and/or 1| may be returned to any or all of the dephlegmators l, 25, and 63 by well-known means, not shown.

Pressures employed within the system may range for subatmospheric to high superatmospheric pressures of 1500 pounds or more per square inch. The primary and secondary cracking system may be operated under substantially the same or under different pressures, and equalized or differential pressures may be maintained between the various elements of each system. Cracking temperatures employed may range from about 750 to some 1200" F. more or less. Preferably, milder cracking conditions are employed in heating element l4 than in heating element 42.

As a specific example of the operation of the process, such as above described, two charging stocks are supplied to the system, one, a fuel oil of about 26 A. P. I. gravity, being the charging stock to the primary or relatively low temperature system, represents about 70% of the total charge, while the secondary charging stock, fed in part direct to the secondary or relatively high temperature heating element and in part into the stream of heated products discharging from this same heating element, represents about 30% of the total charge and corresponds in characteristics to the additional material supplied to this heating element from the secondary fractionating column of the primary system. Reflux condensate from the dephlegmator of the primary system is returned to the heating element of the same system for reconversion, and reflux condensate from the dephlegmator of the secondary system is also returned to the primary heating element. A temperature of approximately 925 F., and a pressure of about 230 pounds per square inch is maintained in the heating element of the primary system. This pressure is substantially equalized throughout the reaction chamber and primary dephlegmator. It is reduced to about 60 pounds per square inch in the secondary fractionating column and in succeeding parts of the primary system. A temperature of approximately 1100 F. is maintained at the outlet from the secondary heating element, but this temperature is reduced to approximately 875" F. in the reaction chamber of the secondary system by the introduction of secondary charging stock into the stream of heated material entering this chamber from the heating element. A pressure of about 150 pounds per square inch is maintained throughout the secondary cracking system. In an operation such as above outlined, a yield of approximately 65% of finished motor fuel having anti-knock value equivalent to a blend of 50% benzol with 50% straight run Pennsylvania gasoline may be produced. Based on the total charging stock, about 17% of substantially dry coke is produced in the primary reaction chamber and about 6% of residual oil is recovered from the reaction chamber of the secondary system. This latter may, if desired, be returned to the primary heating element, and when the process is so operated the gasoline yield may be increased by a little less than 4%, with a slight increase in coke and gas formation. 7

Having thus described my invention, what I claim is:

The process of treating hydrocarbon oils that comprises subjecting hydrocarbon oil in a first cracking zone to a substantially liquid phase cracking temperature to efiect conversion of the high boiling hydrocarbon oils into lower boiling hydrocarbon oils, vaporizing the lower boiling hydrocarbons of the cracked products, withdrawing the unvaporized oil from the system, fractionating the evolved vapors in a first fractionating zone to form a gasoline-like vapor fraction, a lighter reflux condensate and a heavier reflux condensate, returning the heavier condensate to said liquid phase cracking operation, subjecting said lighter condensate to a vapor phase cracking temperature in a second cracking zone, contacting relatively heavy fresh charging stock with the resulting vapors from the vapor phase cracking operation to thereby vaporize a portion of the fresh charging stock, withdrawing the unvaporized portion of the charging stock from the system, dephlegmating the combined vapors from the vapor phase cracking operation and the va pors from the fresh charging stock in a second fractionating zone to produce a vapor fraction suitable for the production of gasoline and a reflux condensate suitable as a clean cracking stock and charging said clean cracking stock to the liquid phase cracking operation.

LYMAN C. HUF'F.

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