US1781390A - Cracking of oils - Google Patents

Description

NOV. 1 1, 1930. E HERTHEL ET AL 4 CRACKING OF OILS 'Filed Jan. 7

. 1925 2 Sheets-Sheet l mw Iv t@ EN Al h,

MKGKN NS @www Nov. "11, 1930.

CRACKING 0F OILS Filed Jan. 7' 1925 E. C. HERTHEL ET AL 2 Sheets-Sheet 2 L I7 /A INVENTORS Eugene f//er/el Edward/#kom such as gasoline orpressure distillate.

Pau-aaa Nov. 11, leso '-uNITEDsTATEs PATENT OFFICE EUGENE C. HERTHEL, OF CHICAGO, ILLINOS, AND EDWARD W. ISOM, OF LOCUST VALLEY, NEW YORK, ASSIGNORS TO ILLINOIS, A CORPORATION OF MAINE" SINCLAIR REFINING COMPANY, OF CHICAGO,

, CRACKING or oILs Application led January This invention relates to an improved method and apparatus for cracking heavier hydrocarbon oils for the production of lighter and lower boiling hydrocarbon oils, More particularly, the invention relates to an improved method of operating circulatory pressure stills provided With retiux'towers. The invention includes an improved method of distilling hydrocarbon oils under pressure and an improved apparatus for use in ing'out such pressure distillation.

When heavy hydrocarbon oils are distilled under pressure, they are cracked with the production of lighter oils.` The products of the cracking reaction also include incondensible gases, and carbon or coke, or heavy tar. In the commercial operation of a pressure' still, some definite product or group of products, e. g. gasoline or pressure distillate, is usually desired, but the vaporsy escaping from the pressure still itself may include heavier` constituents in addition to the constituents desired in thepressure distillate; and, in some cases, particularly in the distillation of lighter charging stocks, the escaping vapors may include vaporized concarryr stituents from the charging stock in their original condition. To the extent that such constituents, heavier than are desired in the pressure distillate, can be decomposed in the pressure still With further production of desired pressure distillate constituents, it is desirable to return such heavier vaporized constituents to the pressure-still for further treatment therein.

In cracking gas oil character charging stock, for example, for the production' of gasoline by distillation under pressure, the vapors escaping from the still may include,

in addition to thedesired gasoline constituents, heavier kerosene vapors or vaporized constituents of a light gas oil character. lf returned to the pressure still, such heavier constituents may be subjected' to further cracking treatment with the production ot additional quantities of the desired gasoline constituent, Whereas if they are condensed with the gasoline constituents, further fractionation treatment ot the pressure distillate 7, 1925. Serial No. 966,

is required to separate the desired gasoline product. In cracking a light gas oil, or charging stock including kerosene character constituents, for the production of gasoline, lighter constituents of the charging stock may be vaporized before they are cracked, and these vapors may also escape With the desired gasoline constituents from the pressure still.

According to the process of the present invention, such constituents of an intermediat-e character as are not desired in the pressure distillate and asv can advantageouslybe subjected to further treatment in the pressure still are returned to the pressure still for further treatment therein by an improved method of operation. The invention also includes an improved arrangement of apparatus for retluxingand returning such intermediate character constituents for further treatment in circulatory pressure stills.

According to this invention, vapors from the pressure still are subjected to a refluxing operation, and the reflux is positively returned to the circulating stream of oil in the still in a manner to insure its subjection to the cracking conditions maintained in the still before any ot' the constituents of the returned reflux can again escape as a vapor.

According to one embodiment of the invention, the vapors from the pressure still may be subjected to al refluxing operation in direct contact With fresh charging stock, and the reflux and admixed charging stockl positively returned to the still in a manner to insure the subjection of the reflux and admixed charging stock to the cracking conditions maintained in the still before any of the constituents ofthel reflux and admixed charging stock can again escape as vapor.

In cracking gas oil character stock, for example, for the production of gasoline, according to the present invention, the vapors escaping from the pressure still itself may be subjected toa retluxing operation whereby heavier constituents, such as kerosene vapors or heavier vapors, are separated, and the separated reflux is positively reintroduced into the circulating stream of oilv undergoing distillation in the vpressure still.

Such refluxed constituents are rapidly revaporized under the conditions prevailing in the still, and, having been subjected to the cracking conditions maintained in the still, are relatively refractbry. According to the present invention, however, they are reintroduced into the body of oil undergoing cracking in a manner such that they are subjected to the cracking conditions maintained in the still before they can again escape as a vapor. v

In subjecting charging stock containing lighter constituents which are. rapidly vaporized in the pressure still to the process of the present invention, the charging stock may also be introduced into the circulating stream of oil undergoing distillation in a manner such that it is subjected to the cracking conditions maintained in the still before any of the lighter constituents can escape as vapors. Where fresh charging stock is introduced during the progress of the cracking operation, it may be introduced into direct Contact 'with the vapors in the reflux tower and returned to the pressure still in admixture with the reflux.

rllhe refluxing operation' may be carried out at substantially the pressure prevailing in the pressure still, or the refluxing operation may be carried out at atmospheric pressure or at an intermediate pressure'lower than that prevailing in the pressure still...

lVhere the refluxing operation is carried out under reduced pressure, a better separation of the heavier vapors may the return of lighter constituents, desirable in the pressure distillate, which might otherwise be subjected to objectionable overcracking, may be'avoided or reduced while at the same `time an increased amount of the heavier constituents which are not desired in the pressure distillate may be returned to the still. For example, in the production of gasoline, the pressure distillate may include a lesser amount of constituents heavier than the desired gasoline product' and the amount of gasoline constituents returned and. subjected to further cracking may be reduced. Overcracking, whiclrtends to produce additional quantities of incondensible gases and alsotends to increase the unsaturation of the pressure distillate to an objectionable degree, is thus avoided or greatly reduced. Both the quality and the yield of the desired product may thus be increased.

rl`he invention is of special value and application' in connection with circulatory pressure stills in whichthe oil. in the still is circulated from a bulk supply tank, in which the vaporized constituents are liberated, through a heater in which the oil is heated to the cracking temperature, and back to the bulk supply tank, and especially in circulatory pressure stills of this general type in which however,

be effected, and..

the circulation is maintained or assisted by a forcing means such as a pump. y

ln such a circulatory cracking still, if reflux is returned directly to the body of oil in the bulk supply tank from which' the distilled vapors are liberated, as in processes heretofore proposed, all ora large part Aof the reflux may be again vaporized and escape with the vapors from the still without further cracking, thereby increasing the load on the still Without producing any useful result. Mreover, if the reflux is returned to the circulating stream of oil by gravity, the tendency of the reflux to vaporize may even interfere to some extent w'ith the circulation.

In the process of the present invention, suchobjections are avoided 'or largely minimized. In carrying out thev present invention in connection with circulatory pressure stills of this type, the reflux is positively introduced into the stream of oil circulating to theheater whereby it is positively forced through the heater and subjectedto cracking conditions therein before it can again escape as a vapor.

Furthermore, according to this invention, the reflux reintroduced into .the pressure still may be employed to assist in maintaining the circulation therein. y

The invention will be further described in connection with the accompanying drawings illustrating several embodiments of the apparatus of the invention, adapted for, the practice of the process of the invention, it will be understood that the invention is illustrated thereby but not limited thereto.

. In the accompanying drawings:

Fig. 1 represents, diagrammatically and partly in eleva-tion and partly insertion, a pressure still system embodying and illustrating the invention.

' Fig. 2 is a fragmentary view lshowing a modified arrangement of the heating element of the still illustrated inFig. 1` and Y Fig. 3 isa view similar tovFigfl showing a modified construction and arrangement.

The invention is of particular advantage in connection with circulatory tubular cracking stills of -the character illustrated. This cracking still is of the general construction illusoil from the bulk supply tank upwardly from the bulk supply tank but K through the vertical tubes and back to the bulk supply tank. Y

Arranged above the bulk supply tank is the reflux towe'r 7 having a series of bafiles therein'. Thereflux tower is connected with the vapor dome of the bulk supply tank through the vaporl line 8. The vapors from the top of the reflux tower escapes through the vapor line 9 to the condenser 10. The condenser discharges into the receiver 11 from which the uncondensed vapors and gases are drawn ofi' through the Valved outlet 12 and the liquid condensatethrough the valved outlet 13. A connection for withdrawing tar during the pro ress of the crackmg operation is shown at 1 Connection 15 is provided for forcing cool oil into the circulating stream of oil through the bea-rings of the circulating pump. pumping out and charging the still is shown at 16.

The pressure may be .controlled and reduced by means of a regulatingr valve 2i between the reflux tower yand the condenser or by valves 12 and 13 located beyond the receiver. ln the latter case, a satisfactory procedure is to withdraw the condensate from time to time or continuously as it collects and to regulate and control the pressure by regu lating the escape of uncondensed vapors and gases from the receiver.

A reflux return pump 17 is arranged to receive reflux from the lower end of the reflux 'overcracking ofthe body of oil tower through connection 18 and to force it through connection 19 into the circulating stream of oil between the circulating pump 6 and the heating tubes. The reflux returned through connection 19 is thus compelled to flow, together with the circulating oil from the bulk supply tank, through the heating tubes wlierc it is heated and subjected to cracking conditions before it can again escape as a vapor from the bulk supply tank, to the reflux tower. The returned re ux may, to a greater or less extent vaporize in the heater, or beforeit enters the heater' as it is admixed with the hot circulating oil, but whether in liquid'or `'vapor phase, it is subjectedto the cracking temperature in the heating tubes 2. 'lhe reflux thus forced into the heating tubes absorbs heat and also assists in preventing Y circulating within vthe still. 'l`he constituents of the reflux which are va porized in the heating tubes also assist in maintaining the upward flow of oil therethrough and the circulation of the oil within the still.

Byreturning the reflux to the lower part of the circulating system, particulary between the circulating pump and the lower end of the heater where a circulating pump is employed, any vaporization of the returned reflux, on contact with the hot circulating oil or in the heater, is employed to maxium acl- A connection for kerosene-character. constitucnts-- connection 20 may be. employed as a safeguard to prevent reflux, and admixed feed, building up to a level sufficient to choke offA the vapor line 8, in case the pump 17 does not take the reflux, and admixed feed, lfrom the lower part of the reflux tower at a sufficient rate.

After the pressure still has been raised to the cracking conditions of temperature and pressure, the vapors escaping from the still through connection 8 rise in the reflux tower 7 where they come in direction contact with fresh charging stock introduced through the line 22 to the top of the tower. The heavier constituents in the vapors from the still are thus refluxed, and the reflux and admixed fresh stock are returned from the bottom of the tower by the pump 17 to the circulating streani of oil entering the heating tubes in the still.

In operating the pressure still in this way, the circulating oil in the still is circulated from a vaporizing zone, i. e., the bulk supply tank, through a heating zone, i. e. the heating tubes, and back to the vaporizing zone; and reflux from the reflux tower is forced into the circulating oil which is circulating from the vaporizing zone to the heating zone and is compelled. to pass through the heating zone in admixt'ure with the circulating body of oil before any vaporized constituents can escape from the vaporyizmg zone. i

ln cracking a heavy gas oil charging stock for the production of gasoline, for example, the vapors entering the reflux tower 7 through the vapor line 8 may include, in addition to gasoline constituents, constitu-l ents of a light gas oil `character as well as The heav ier constituents. are refluxed by direct con` tact with the fresh gas oil charging stock introduced at the-top of the tower through connection 22 and the refluxed constituents and admixed feed collect in the bottoni of' the tower, and are circulated through the heating tubes by .thc reflux return pump 17. In the heating tubes, the kerosene character constituents may be vaporized and in part cracked and the heavier constituents are in part cracked into lighter produrts which are'vaporized. The vapors liberated in the bulk supply tank thus include cracked prode ucts from the fresh charging stock and cracked products from further treatment of the reflux as well as some lighter constituable construction may be employed.

bulk supply ents revaporized without vfurther cracking. The vapors enter the reflux tower from the tank and the cycle of the process is repeated. The pressure distillate, including the gasoline character constituents,- is withdrawn from the' reflux tower as a vapor through the vapor lineA 2. I

the pressure still. The vapors menace 19a to the circulating connection 4 between the circulating pump and the heating tubes in from the reflux tower escape through the vapor line 9a to the condenser l()a which discharges into the receiver 11 from which uncondensed vapors and `gases are withdrawn through connection In the modified` arrangement i1lustrated`-12a and liquid condensate through connection in Fig. 2, the returned reflux, and any admixed charging stock, is introduced upwardly into the lower ends of the heating tubes through which the-.oil in the pressure still is circulating upwardly. The oil from the bulk supply tank is circulated through the connection 4 and upwardly through the heatingtubes 2', and the oil from the reflux return pump is forced through connection 19' into the lower ends of .the heating tubes 2 through a series of nozzles 23 projecting upwardly into the lower ends of the heating tubes. The'oil introduced through the connections 23', including the reflux, vaporizes and is cracked to a greater or less extent in the heating tubes and the resulting vapors assist the circulation. This arrangement of the apparatus is particularly-advantageousv where no circulating pump or other mechanical circulation is'employed and where thermosiphonic circulation is relied u on.

ln the apparatus illustrated in ig. 3, the same or corresponding parts are indicated by the same reference numerals with letter' a appended thereto. ln this apparatus, however, instead of operating the reflux tower at substantially the pressure prevailing in the pressure still, the still pressure is reduced by the pressure control valve 25a in the vapor line 8" leading from the pressure still, and the vapors are discharged into the reflux tower 7 at atmospheric pressure or at a predetermined pressure above atmospheric and lower than the still pressure. l rlhe reflux tower 7 1 `is shown as of helical construction such that the .vapors ow upwardly between the turns of the helical baille, while the redux and any fresh feed flow downwardly over the helical baille. Such a construction permits prolonged contact and heat exchange between the vapors and liquid, both bydirect contact of the vapors and liquid and b indirect contact ofthe vapors with the liqui dowing down over the next higher' turn of the helix. 'lhis towery is of the general construction and operation described and illustrated in.an application of John E. Bell filed April 1, 1924, Serial No. 703,338. It will be apparent that reflux towers of other suit- A. connection 22a is provided for introducing fresh oil into direct contact with the vapors in the upper/end of the tower 7a. The condensed vapors /and unvaporized feed oilcollect at the bottom of the tower in the reux reservoir 26a from which they are pumped by the reflux return pump 22'a through the line 13a'. Where the reflux tower is operated at an intermediate pressure higher than atmospheric pressure, the pressuremay be reduced and regulated between the reflux tower and condenser by regulating valve 24, or the pressure in the condenser may be controlled by valves located beyond the receiver.

The temperatureand pressure employed in carrying out the process and in operating the apparatus can be varied with diderent characters of charging stock. Where ordinary l gas oil is employed as the principal charging stock, still pressures in the neighborhood of 90 to 125 lbs. per square inch may be employed; while with sene for example, higher pressures may be used, for example, up to 300 to 325 lbs. per square inch or even higher. The reflux tower may be operated at the same' pressure as that prevailing in the pressure still, or it may be operated at atmospheric pressure or at an intermediate pressure, for example, 25 to 30 lbs. per square inch.

We, claim:

l. The improved method of cracking hydrocarbon oils, which comprises maintaining a body of the oil in a bulk supply tank, withdrawing oil therefrom and mechanically forcing the oil so withdrawn through a heater located away from the bulk supply tank and back to the bulk supply tank, maintaining the oil at a cracking temperature throughout the cycle, passing the vapors escaping from the bulk supply tank through a reux tower, and pumping the reflux from the reflux tower, into the oil circulating from the bulk supply tank to the heater'between the mechanical forcing means and the heater.

2. The improved method of cracking hydrocarbon oils, which compirses maintaining a body of the oil in a bulk supply tpnk, withdrawing oil therefrom and mechanically forcing the oil so withdrawn through a heater located' away from the bulk supply tank and back to the bulk supply tank, maintaining the oil ata cracking temperature throughout the cycle, subjecting the vapors escaping from the bulk supply tank to a refluxing operation in direct contact with fresh charging stock to the still and mechanically forcing the reflux and adniixed charging stock from the refiuxing operation -into the oil circulating from the bulk supply tank 4to the heater between the first mentioned mechanical forcing means and the heater.

3. The improvement in the operationpoi circulatory pressure stills for cracking hydrocarbon oils, which comprises pumping the oil from a bulk supply `tank upwardly through a vertically arran ed tubular heater and back to the bulk supp y tank, maintain- 5 ing the oil at a crackin temperaturel throughout thl cycle, subjectlng'the vapors escaping from the bulk supply tank to a reuxing operation and mechanically forcing the reflux from the `reluxing operation up-y w wardly into theoil circulating from the hulk supply tank through the heater in the lower part of the heater to assist circulation.

In an apparatus for distilling hydrocarbon oils under pressure, a pressure still 15 comprising a bulk supply tank and a vertically. arranged heater, a connection from the. upper part of the heater to the bulk supply tank, and connections including mechanical circulating means ,between the bulk supply 2'0 tank and the lower part of the heater whe by oil may be circulated from the bulk sup- Ely tank upwardly through the heater and ack to the bulk supply tank, a reflux tower, and connections for conductin vapors from 25 the bulk supply tankjto the re ux tower, and connections including a pump for necting reflux from the reflux tower upwardly into the lower end of the heater.

In testimony whereof we ax our sig- 30 natures.

EUGENE C. HERTHEL.

EDWARD W; ISOM.

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