US2221172A - Conversion of hydrocarbon oils - Google Patents

Description

Nov` 12, 1940. c; w. WATSON E14-AL .CONVERSION 0F HYDROCARBON OILS Filed DeC`. 11, 1937 Patented Nov. 12, 1940 UNITED STATES PATENT oFFicE CONVERSION F HYDROCARBON OILS poration of Delaware Application December 1,1, 1937, Serial No. 179,228

2 Claims.

This invention relates to the conversion .of hydrocarbon oils and has to do particularly with the conversion of heavy hydrocarbon charging stocks using the principle of gas reversion, wherein the oils are converted in the presence of normally gaseous hydrocarbons.

The invention contemplates the conversion of a heavy cracking stock which normally can not be heated to the desired conversion temperatures because of coking diiiculties and is dependent for conversion on temperatures derived primarily from heating a clean recycle stock, which recycle stock is normally insuincient to supply the necessary heat and volume to balance the operation. Heretofore when cracking such heavy charging stocks, it has been necessary, in order to balance out the operation, to supply a refractory oil from an extraneous source to make up for the deficiency in the clean recycle stock produced in the system. It has been found that in such a type of operation the deficiency in' heat and volume of clean recycle stock can be compensated by recirculating normally gaseous. hydrocarbons produced in the system, which are thereby converted into desirable motor fuel.

The invention is particularly applicable to a clean recirculation type of operation in which a clean recycle stock isseparately heated to conversion temperatures and the hot products commingled with a black oil or heavy recycle stock and the mixture subjected to reaction to effect conversion into lower boiling products.

, In the clean oil circulation type of operationy as herein described, the clean recycle gas oil is subjected to temperature, pressure and time of contact conditions which approach those found desirable for conversion of normally gaseous hydrocarbons, such as the C3 and C4 hydrocarbons, and by recirculating these hydrocarbons along with the recycle gas oil, the important dual advantage of supplying the requisite quantity of heat and volume of recycle stock, and at the same time, an advantageous method of converting the gaseous hydrocarbons to motor fuel, `is obtained.

In accordance with the invention, a heavy charging stock, such as a fuel residuum, is combined with a clean recycle stock which has been previously heated to conversion temperatures and the mixture subjected to asoaking operation in a coil or drum soaking zone. The products of reaction are separated into vapors and residuum, The vapors are fractionated to produce a clean recycle stock which is charged to the heater. The vapors are further fractionated to separate a gasoline -fraction, and a normally gaseous hydrocarbon fraction which is also heated to conversion temperatures and charged to the soaking Zone. It is intended that the charging stock be of such character that it could not normally bercracked in a unitary or self-contained process without the recycle of the normally gaseous hydrocarbon fraction to augment the clean recycle stock.

One method of operation is to contact the heavy charging stock with the cracked vapors from the soaking operation, thereby partially condensing the vapors and producing a black oil comprising unvaporized charging stock and heavy reflux condensate. This black oil may be separately heated to a mild cracking temperature in a separate coil or charged directly to the soaking drum. A clean recycle stock is separated from 'the uncondensed vapors and charged to a separate heater wherein it is heated to cracking temperatures and then commingled with the black oil and the mixture reacted in the soaking zone. A normally gaseous hydrocarbon fraction, preferably containing hydrocarbons between 2 and 5 carbon atoms per molecule is added to the clean recycle stock, in suflicient amount to balance such operation.

The invention will be more fully understood from the following description taken in connection with the accompanying drawing which shows a diagrammatic sketch of one form of apparatus suitable for carrying out the process of the invention.

Referring to the drawing, a charging stock, which may be a fuel residuum, a heavy reduced crude, crude bottoms or any other heavy hydrocarbon stock which normally can not be heated to a suciently high cracking temperature without coking and which normally produces insufficient recycle stockto provide a balanced operation, is introduced from a suitable source of supply, not shown, through the line I and forced by the pump 2 through line 3 into primary fractionator 5. In this fractionator, the charging stock contacts cracked vapors thereby condensing the heavy components of the vapors and at the same time vaporizing any low boiling materials of the charge. The mixture of unvaporized charge and heavy reux condensate is collected in the bottom of the fractionator 5 and withdrawn therefrom through the line and pump 1. The uncondensed vapors are conducted from the fractionator 5 through the line 9 to a secondary fractionator I0. In `the latter fractionator, components heavier than gasoline are condensed and collect in the bottom of the fractionator as a clean condensate recycle stock. This clean recycle stock is withdrawn from the bottom of the fractionator by the pump II and forced through the line I2 to a heating coil I4 located. in a heater or furnace I5. In the heating coil the clean recycle stock is raised to cracking temperatures. The conditions maintained in the coil may be temperatures of about 900-ll F. and pressures of about 200-1000 pounds.

The ho-t products from the coil I4 are discharged into the transfer line I5 wherein they are commingled with the black oil from line 6, referred to heretofore, and the lmixture introduced into a soaking drum IS. While no means are shown for heating the black oil introduced from the'line 5, it is .to be understood that this product may be heated to a mild temperature, if desired, in a separate heating coil prior to the commingling thereof with the hot products from coil I4. In the drawing, .two soaking drums are shown, but a single soaking drum or any number may be used. The products pass downwardly through the soaking drum I8, thence through the connecting line I9 to soaking drum 20. The unvaporized products collect in the bottom of the soaking drum 20 and are continuously drawn off through the residuum line 22. It is intended that no substantial amount of liquid is allowed to remain for any appreciable period of time in the bottom of the soaking drum 20 and this is accomplished by means of automatic regulation of the valve '23. Vapors separating in the soaking drum are transferred through the vapor line 25 to the'fractionator 5, referred to heretofore. The conditions maintained in the soaking drums I8 and 20 may be pressures of aboutI 200-1000 pounds and temperatures of about S50-950 F. The residuum drawn olf from the bottom of the soaking drum 20 through the line 22 is introduced into a tar stripper 2l. The tar stripper is maintained under reduced pressure whereby the residuum is flash distilled. The unvaporized cycle fuel residuum is withdrawn from the bottom of the `tar stripper through the valved draw-off line 2B. The vapors are withdrawn from the top of the tar stripper 2l through the Vapor line 30, condenser SI and run-down line 32 to the accumulator 34. In this accumulator a tar stripper gas oil is collected and all or a portion thereof is forced by the pump 35 through the line 35 to the secondary fractionator Ill.

The uncondensed vapors in the fractionator I0 are withdravm from the upper portion thereof .through the vapor line 30 communicating with the condenser 30. In the condenser, gasoline or naphtha is condensed and collected in the accumulator 40. This accumulator is provided with l a gas release line 4I through which fnied gases, such as methane and hydrogen, and all or a portion of the C2 hydrocarbons may be released. The condensate is withdrawn from the accumulator 5I] and forced by the pump 42, through line 43, to a stabilizer 45. In the stabilizer a stabilized gasoline is produced which is withdrawn from the bottom of the stabilizer through valve controlled line 45. The normally gaseous hydrocarbons, such as all those of lower molecular weight than Ces and all or a portion of the Cie are withdrawn from the top of the stabilizer through the vapor line 48 to a condenser 49. In the condenser the C4 and C3 hydrocarbons are condensed and the condensate passed through the run-down line 50 to receiver 52. vUncondensed gases, such as any of those lighter than C3, which may be present and all or a portion of the C3, may be released from the receiver 52 through the Valve controlled line 54. The condensate comprising mainly C4 and C3 hydrocarbons is withdrawn from the receiver 52 by the pump 55 and forced .through the line 56 which communicates with the line I2. A portion of the condensate in receiver 52 may be withdrawn through the line 58 and used as a reflux to the stabilizer 45 or otherwise disposed of, as desired.

In case insun'cient light condensate is produced from the normally gaseous hydrocarbons evolved in the system, additional light charge, such as natural gasoline, light condensate from crude or cracking stills, etc. may be introduced in desired amounts through the line E0. This charge is forced by the pump 5I through line 62 into the stabilizer 45 wherein it commingles with the vapors therein and is fractionated. The lighter portions thereof pass overhead through the line 48 and eventually are collected in receiver 52. The heavier fractions, if any, are collected in .the lower portion of the stabilizer and drawn off through the line 46 with the stabilized gasoline.

As an example of the operation of the inventionu, a fuel residuum from North Texas crude of 16.3 A. P. I. gravity was charged into a primary fractionator, receiving cracked vapors from a reaction chamber and from which a black oil was withdrawn having a temperature of around 750 F. This black oil was preheated to a temperature of about 850 F. and discharged into the reaction chamber. A clean recycle stock was separated from the Uncondensed vapors, which had been contacted with the charging stock in a secondary fractionator, and this clean recycle stock was separately heated to a temperature of about 960 F. and discharged into Ithe reaction chamber. The vapors from the secondary fractionator were condensed to form an unstabilized distillate which was subjected to stabilization to form a stabilized gasoline and a normally gaseous hydrocarbon fraction comprising about r70% C4 hydrocarbons and 30% C3 hydrocarbons. This normally gaseous hydrocarbon fraction in an amount equal to about 60% by weight, based on the fresh feed, was commingled with the clean recycle stock passing to the heater. A temperature of about 900 F. was maintained in the reaction chamber and a pressure of about 200 pounds. The process operated continuously without the introduction of any extraneous refractory stock. About 45% of 400 end point, 9.5 lb. Reid vapor pressure naphtha, and about 50% cycle fuel oil of about 51/2 A. P. I. gravity and about 300 viscosity at 210 Furol were obtained. The naphtha had an octane number of about 68. The process was able to be operated for a long period of time, whereas attempts to carry out the same operation without the recirculation of the normally gaseous hydrocarbon fraction were unsuccessful.

The conditions setl forth in the above example may va-ry considerably. For exam-ple, the pressure may be higher than 200 pounds, such as 400 or 600 or above, and the temperatures may be somewhat higher, 4particularly on the clean recycle heater wheren temperatures of 970 F. to 1040 F. or higher may be used. Also the proportion of the gas recycled may vary considerably and we may -use about 15-75%, preferably around 20-60%. Also the composition of the recycle gas may vary. We may use 50-100% C4 hydrocarbons in the recycle gas and prefer to use as large an amount of C4 hydrocarbons as possible.

While the invention has been described in connection with an apparatus and type of operation using a single coil gas reversion, it is to be understood that the invention is applicable to any well known or preferred type of gas -reversi-on system. It is to be understood that a two coil type operation may be used, wherein the normally gaseous hydrocarbons are subjected to conversion condi-` tions of around 900 to 1250 F. in a separate coil to produce olens and, if desired, partial conversion into normally liquid products; and then all or a portion of the reaction products utilized in the gas reversion operation. In many instances the latter type of operation is the one preferred.

Obviously many modications `and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit-l and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. A process for the conversion of heavy hydrocarbon oils into gasoline, which comprises contacting hot vapors from an enlarged cracking zone with charging stock in a distillation and fractionation tower, thereby dephleg'mating the vapors and partially vaporizing the charging stock, withdrawing from said tower unvaporlzed oil and an overhead Vapor fraction, fractionating the overhead vapor fraction to yform a light distillate containing gasoline and a clean gas oil condensate, passing said gas oil condensate through a heating coil wherein the condensate is raised to a high cracking temperature, combining the unvaporized oil `from the distillation and fractionation tower with the highly heated products from the heating coil, transferring the mixtu-re into an unheated enlarged reaction Zone maintained under cracking conditions of temperature and pressure, wherein cracking and separation of vapors and .liquids occur, withdrawing the liquids from said zone, passing the separated vapors to said distillation and fractionation tower, charging to said distillation and fractionation tower as the charging stock first mentioned a heavy oil which produces an insucient volume of said clean gas oil condensate to maintain 'oper-k ating conditions for the production of a substan- -tiailly 400 end point commercial gasoline, and

mixing with said clean gas oil condensate charged to the heating coil normally gaseous hydrocarbons in suilicient amount to maintain operating conditions for the production of said gasoline.

2. A process according to claim 1 in which the normally gaseous hydrocarbons added to the clean gas are recycled gases predominating in hydrocarbons heavier thank C2 hydrocarbons.

CLAUDE W. WATSON.' DU BOIS EASTMAN.

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