US2086490A - Conversion of hydrocarbon oils - Google Patents

Description

July 6, 1937.

l.. DE FLOREZ ET AL CONVERSION OF HYDROCARBON OILS Filed June 8, 1951 ZM; a@ l mw MW NVEPMRS ATTORNEY Patented July 6, 1937 'CONVERSION 0F HYDROCARBON OILS Luis de Flores, Pomfret, Conn., and James W.

Gray, Port Arthur, Tex.2 assignors to The Texas Company, New York, N. Y., a corporation of Delaware Application June s, 1931, serial No. 542,914 1 claim: (c1. 19e-4s) This invention relates to the conversion of high boiling hydrocarbons into low boiling products. such as gasoline and has particular reference to a process wherein the conversion of hydrocarbon oils takes place in a plurality of stages.-

5 I'he invention contemplates a multi-stage process in which hydrocarbon oil is passedA successively through a plurality of zones maintained under conversion conditions whereby the oil may be subjected to a series of operations that are l0 regulated to precise conditions for efllcient productionlof the desired product. The invention further contemplates that the zones or Astages of treatment are individually controlled so that the oil may be subjected to separate operations -such as, distillation, heating, cracking, digestion,

fractionation, each stage of operation being controlled independently of vany other stage.

More particularly, the invention, for example, may be carried out in athree stage cracking operation, although the invention is notv so limited. In a three stage treating system we provide a high temperature high pressure zone, a high pressure digesting'zone of slightly lower pressure, and a relatively low pressure low temperature cracking and distilling zone. The

high temperature high pressure zone may conveniently take the form of a'coil or tubular heater whichv is individually controlled by firing; the high pressure digestion zone of slightly low- 80 er pressure mayconsist of an enlarged chamber of-sumcient size to aio'rd al time. factor for the reaction or digestion operation and this zone may be controlled by the 'regulated introduction of a cooling ,medium suchas cool or preheated charg ing stock, clean distillate cycle stock or an extraneous material for reaction or Acombination with the products undergoing digestion; and the relatively low pressure low temperature crack-'- Aing and distilling zone may comprise a tower for yt0 vaporization and fractionating which may be controlled by the degree of pressure reduction or by the amount of reflux condensation therein.

Heretofore, conversion processes of the general type referred to above, have been carried out in a two stage operation, consisting of the first two stages only of those mentioned and the third stage comprising merely a distillation zone. In the conventional two stage operation, control of the reaction chamber may be effected in various ways and for this purpose it has been proposed to use a cooling medium in indirect heat exchange with the oil in the transfer line connecting the heater and reaction chamber. We

are awareaalso that it has been proposed in a two stage process to introduce a cooling me- 'dium directly into the 'oil in the transfer line or into the reaction chamber. However, our invention is distinguished from processes disclosed heretofore in not only providingv a greater 5, number yof stages of cracking than the prior methods but also inthe process of the invention the application of certain prior methods of regulating the temperature would be impractical for various reasons, especially because oi' coke de- 10 posits. In our process, it will be observed that control of the heating stage must be maintained to supply sufllcient heat to the oil and yet lavoid coking the tubes, thatcontrol of the digestion or reaction zone must be maintained to avoid 15 coke deposits from the accumulation of excess heat therein and yet maintain suillcient heat to vpromote the reaction and polymerization with a suitable quantity of heat remaining to be carriedover to the distillation zone, and that control of the distillation zonemust be maintained to produce the desired degree of cracking and to separate the volatile constituents from the residual fraction to serve as cycle stock for further processing.

'I'he result of operating a three stage process isthe production of a highly cracked material in the tubes whichhas anti-knock properties, the polymerization of certain of the cracked materials in the digestion chamber and the formation 3 of the required amount of cycle stock by the cracking in the tower. The advantage of cracking oil in this manner is to conserve heat,`snce each of the two last stages is supplied with heat already put into the oil; to make an improved 35 gasoline, particularly from an anti-knock point of view; and to reduce the gas loss by polymerization in the intermediate or digestion stage. Other advantages will be observed from the following description of the process and the ap- '40 paratus. I 4' For the purposes of illustrating the invention, reference will now be made to the drawing wherein an apparatus is shown for conveniently carrying out the invention and comprising an vem- 45 bodiment thereof.

The reference character i represents diagrammatically aheater for heating the oil to conversion'temperatures.. This heater may be any well-known or preferred type in which Coils or 50 tubes are located within a furnace for conducting a charge of oil therethrough in a constricted stream while heat is applied thereto by suitable burners.

A transfer line 2 conducts hot oil from the coil 55 pressures.

2 or tubes in furnace I to a digester 3. The digester is preferably ,an elongated horizontal drum of large capacity and capable of withstanding high It is to be understood, however, that other shapes or designs of digesters may be used.

A vaporizer 4 is connected to the digester by a line 5 in which is interposed a pressure reducing valve 5. The vaporizer preferably consists of a vertical tower into which the hot oil is introduced near the bottom through theline 5. The vaporizer may be equipped with trays v1 or other convenient means of fractionation so that the evolved vapors may be separated from entralned liquid or high boiling constituents.

The fractionator IU is adapted to receive vapors from the vaporizer 4 through the vapor line II, communicating therebetween. The fractionator may be any of the usual type of fractionating towers, preferably of the bubble tower design, wherein bubble trays I2 are located at spaced intervals therein, to contact the vapors with reflux liquid to separate a vapor fraction of desired boiling range.

A vapor line I5 serves to conduct the fractionated vapors to a condenser coil. I5. A line I1 then conducts the condensate and uncondensed gases to a receiver I8 which is equipped with the usual gas release pipe I9 and a liquid draw-off line 20..

Referring again to the vaporizerl 4.a tarA line 25 serves to withdraw the residual oil or tar from the bottom thereof to atar stripper 23. A line ,21 conductsthe uhvaporized fraction-from the tar stripper to a fuel or residual oil storage tank .28. A vapor line 29 conducts the vapor fraction from the'stripper to a condenser coil 30. A pump' 3| pumps the condensate from the condenser through the line 32'for use as a reux medium.

The line 32 merges with a charge lirie 33, hereinafter referred to, whereby the condensate may be conducted to the vaporizer 4. A by-pass line 35 serves to conduct any or all of the condensatev from the line32, if desired, to the fractionator I0 where it enters by oneV or more branch lines 36 and 31, connected at different elevations to the fractionator.

Referring now to the fractionator I0, a reux line 40, connected to the bottom thereof, serves to withdraw condensate from the body of oilcollecting in the bottomof said fractionator. A pump 4I, interposed in the line 40, pumps any part or all ofthe condensate in the line v4I), under pressure, back to the heater I.

A charge tank 45 serves to hold a supply of oil to be converted. A line 4G, connecting to tank 45, serves to convey the charge to a pump `41 which then forces the charge thr'ough the'line 32 hereinbefore referred to, either alone or mixed withlaI desired quantity of distillate from line 32 to the vaporizer'4.

quantity of cool charge stock, if desired, :to the hot oil in said transfer line. Aline 55, connected to the transfer line 2, serves to conduct an extraneous material for cooling or reaction with,v

the oil such as hydrogen, hydrocarbon gas or oil.

In practicing the invention with an apparatus per square inch or Attention is now directed.' to the means by will be sufficiently high to maintain the desired temperature in the digester.

In the digester 3, the hot oil from the heater I is maintained at a high temperature for sufficient length of time to provide a suitable time factor for conversion while the oil is passing therethrough. The temperature of the oil in the drum 3 is usually dependent on the quantity of heat carried by the oil from the heater I and the heat so transferred to the digester 3 is preferably maintained by heavy insulation of the digester. It is important that the conditions in the digester be qite well regulatedand the temfperature par-- ticularly -be with certain limits in order to. avoid filling the drum with large deposits of coke. The

It is proposed that pressure in the drum 3 is usually about 600 pounds.

above. A satisfactory vternperature has been found to be of the order of 910 F. or thereabouts. n

The products from the drum 3, containing considerable quantity of low boiling oils, are conducted through the line 5 to the vaporizer 4.

A reducednsuperatmospheric pressure near 60 to pounds per square inch, is maintained in the vaporizer by the regulation of the pressure reducing valve 5 in the line 5. The low boiling products quickly vaporize as a result of the rejduced pressure and a vapor fraction and a residual liquid fraction separate in the vaporizer.

-The vapors from the vaporizer 4 containing the 'desired gasoline and heavier constituents suitable for cracking, such as gas oil, pass to the fractionator I0 through line II. In the fractionator the vapors are dephlegmated ,to form a vapor fraction of the desired low boiling constituents,

such as gasoline, and a liquid fraction comprising a lclean distillate recycle' stock. The distillate recycle stock accumulates in a'body in the bottom of the fractionator from where it is continuously drawn by the pump 4I and forced, entirely or in part, to the heater I.

'I'he residual liquid fraction separating in the vaporizer 4 is drawn of! fromthe bottom thereof to a stripper 26. This stripperis preferably operated in the nature oi a flash still, that is, the pressure is preferably reduced. as the oil passes through the line 25. lThe lower boiling products capable of vaporizationy at the prevailing temperatures and pressures immediately ash into vapor form inthe still 26.' A heavy residue or fuel oil is drawn oifthrough theline 21 to a storage tank 28. lI'he vapors consistingchiey of oils l of the nature `of gas ,oil are condensed and pumped either back to the vaporlzer 4 or to the fractionator I0, or both, where -the condensate acts in the nature of a reflux medium. It will i be noted, therefore, that the body of clean distil-l late recycle stock at the bottom ofthe fractiontor may also contain. a distillate from the flash rstill 25. A

The fresh charging stock to the system may be drawn from. a source ofsupply such as 'at tank 45 and pumped into the top of the vaporizer 4. In the `vaporizer, the fresh charge comes in constrippedv of its lower boiling constituents and 'at the same time condenses undesirable constituents in the vapors. A conversion temperature of about 700-850 vI.v and a 'pressure of 50-150 pounds per square inch is preferably maintained in the vaporizer'l and as a result thereof not only.

may conversion 'gester continue, of the fresh charge occur. The unvaporized fresh charge mingles with the hot residual fraction in the vaporizer -and eventually passes to thestripper 26. The pressure in the tower l may be regulated to control the temperature by causing more or less vaporizing which absorbs heat. Furthermore, the temperature in the vaporizer may be regulated by the amount of cooling effected by the reflux liquid and charging stock introduced through the lines 32 and 33.

We will now describe the control Vthe temperature of the oil in the vdigester I. According to one method ofso'peration a regulated portion of the clean distillate recycle stock of the oilpassing from the di- 25' may be, introduced into the hot oil inthe transfer line .2` and for this purpose we have shown the by-pass line 60 line 2.' The recycled stock is relatively cooler than the oil in the transfer line 2, and if extensive oil entering the digester.

'cooling is not required the vresultant cooling will often regulate sumciently the temperature of the In another method of operations. part -of the cool fresh charging stock maybe pumped to the hot oil in the transfer line 2 by passing a regu lated quantity through theby-pass line 52. It will'be observed 'that in the ordinary type of operation more extensive cooling nay be obtained in this way. v ,A

but also substantial conversion.

manner in which we betweenthe-line III and transfer In still another method of operation we may introduce an extraneous material through the line ll.- For this purpose a suitable oil may be introduced which will not only cause cooling but also supply hydrogen for hydrogenation or even free hydrQ'en may be introduced. Furthermore, any of the above methods'may be used separately or any or all of them may be operated simultaneously.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only'such limitations should beimposed as are indicated in the ap- We claim:

'Ihe method of cracking hydrocarbon oil, which comprises subjecting the oil to heat and greater than atmospheric pressure in a cracking zone to crack the oil, vaporizing portions of the thus treated oil under reduced pressure greater than atmospheric pressure. washing tsrryi material from the vapor at said reduced pressure, separately withdrawing the wash liquid containing the tarry material, vaporizing the wash liquid and condensing the vapors whereby the wash liquid is freed fromtarry material, removing the tarry material from the system, reusing the liquid to wash additionah vapor, condensing a relatively heavy fraction of thewashed vapors,

`passing nie condensed heavy fraction to the,

cracking zone to crack the same together with said hydrocarbon oil. and condensing the remaining washed vapors.

LUIS ns FLOREZ.

' JAMES GRAY.

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