US1741357A - Art of cracking hydrocarbons - Google Patents

Description

Dec. 31, 1929. BELL 1,741,357

' ART OF CRACKING HYDROCARBONS Filed July 9. 1924 3 SheetsSheet 1 I M /4 Z l fl/ 1 I A5 INVENTOR John E.Bell

BY [2M1] M, MMM

' ATTORNEYS Dem-31 1929. J. E. BELL ART OF CRACKING HYDROC'ARBONS 3 Sheets-Sheet 2 Filed July 9, 1924 \m m NW bzuuum $26 mz ssotumi Q @Q A?! Hun c X INVENTOR V JOhnEBeH F BY 5W1, A M

ATTORNEYS Dec. 31, 1929. J. E. BELL ART OF CRACKING HYDROCARBONS Filed July 9, 1,924

3 Sheets-Sheet 5 QM m Rm x mm INVENTOR John E. Bell BY PM WWW M I ATTORNEYS Patented Dec. 31, 1929 UNITED STATES PATENT oFFmE JOHN'E. BELL, OF BROOKLYN, NEW YORK, ASSIGNOR TO SINCLAIR REFINING COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF MAINE ART OF CRACKING HYDROGARBONS Application filed July 9, 1924. Serial No. 724,957.

This invention relates to an improved nethod of operating pressure stills, and inwlves an improved method of fractionally ondensing the vapors from pressure stills Q'hereby accurate fractionation is obtained lirectly and improved heat economy is The invention relates particularly to imovements in processes of pressure distillaion for cracking hydrocarbon oils of higher boiling point such as gas oils and the like to form more volatile or lighter l1ydrocarbon ails such as those which constitute commercial gasoline or pressure distillate.

In cracking hydrocarbon oils by distillation under pressure, the crude pressure distillate from the pressure still contains in addition to the lighter hydrocarbons suitable as components of gasoline, hydrocarbons of the i9 kerosene group and others even heavier. It has heretofore been necessary to subject the crude condensate from the pressure still to redistillation to fractionate it into merchant able products and to separate out the heavier hydrocarbons.

One of the objects of the present invention is to partially or entirely dispense with this red-istil lation by fractionally condensing the vapors as they come from the pressure still,

' separating the heavier components from the lighter components and separately condensing them, while employing the heat of the vapors undergoing condensation in the cracking operation.

In my prior application filed March 24:, 1924-, Serial No. 701,396 there is described an improved method of fractionating the vapor-s from .a pressure still by passing them successively through a series af separate vapor condensing chambers maintained at progressively lower temperatures and returning a regulated part of the condensate from conlensing chambers of lower temperature into condensing chambers of higher temperature. According to the improved method there described, the accuracy of the fractionation is also promoted by main aining a low temperature differential between the condensing surfaces and the vapors undergoing condensation thereon, for example less than about 25 F. or even less than about 10 F. The fractionation is also improved and controlled by condensation effected by the reg ulated return of cooler condensate, and con densate so returned is also subjected to a refractionation.

The present invention, in certain aspects, relates to further improvements in the methoddescribed in said application, and the method of the present invention likewise involves passing the vapors from a pressure still successively through a series of separate vapor condensing chambers maintained at progressively lower temperatures and returning a regulated part of the condensate from condensing chambers of lower temperature to condensing chambers of higher temperature.

According to the present invention all or a part of the charging stock introduced into the pressure still, during the pressure distillation, is employed in cooling and condensing the vapors undergoing fractionation, and that part of the charging stock so employed is thereby preheated.

According to the present invention, the vapors from the pressure still are passed successively through a series of condensing chambers maintained at progressively lower temperatures and fresh charging stock is passed to the still through the vapor condensing chambers in indirect heat exchangingrelation with the vapors undergoing fractionation therein, and a regulated part of condensate is returned from condensing chambers of lower temperature to vapor condensing chambers of higher temperature.

By directly fractionating the vapors from the pressure still, heat employed in redistilling condensed pressure distillate is saved. Even where the fractions directly separated are subjected to further fractionation heat is conserved to the extent of the direct initial separation. By preheating the feed to the still, the burden of raising the charging stock to the temperature prevailing in the pressure still is removed from the pressure still heating surfaces to an extent corresponding to the temperature to which the feed is preheated; and by employing the latent heat of .100

the distilled vapors in preheating the feed oil, the heat lost in condensing pressure distillate in the ordinary way is returned to the pressure still Where it may be employed in the cracking operation, while the cooling effect of the fresh oil is employed to assist the fractionation.

In the combine-d operation of the present invention, the efficiency of the cracking operation and the capacity of the pressure still is increased by increasing the relative amount of heat actually employed in the conversion of high boiling point oils to lighter or more volatile oils. The improved method of the present invent-ion may be so regulated that substantially all of the heat supplied to the pressure still after the still is initially brought to operating conditions, excepting losses such as those due to rediation and in flue gases, is employed in the useful part of the cracking process. Heat losses due to the latent heat of vaporization of the pressure distillate, usually carried off in the cooling fluid employed in condensing the vapors from the pressure still, are minimized or largely eliminated, and this heat is employed in the cracking process and in fractionating the pressure distillate.

In carrying out the improved process of the present invention, the charging stock employed in cooling and condensing the vapors from the pressure still may be disposed of in various ways after indirect heat exchange with the vapors from the pressure still. Where the condensate collecting in any of the chambers of the series through which the vapors from the still are successively passed is returned to the pressure still, the charging stock employed for cooling and condensing the vapors may be introduced into one or more of these chambers, in whole or in part, effecting a further condensation of the vapors therein and being returned to the pressure still with the condensate therefrom. Where the feed oil employed for cooling and condensing the vapors from the pressure still contains light constituents, it may be introduced into one or more of the condensing chambers to vaporize the lighter constituents and to effect a fractionation of the oil before introduction of the oil into the pressure still, and Where light oil is so directly introduced into the condensing chambers and is in part vaporized by heat exchange with the vapors therein, a further condensation is effected due to thevaporization of the lighter constituents as well as due to the absorption of sensible heat by the fresh oil.

In carrying out the process of the invention in connection with circulatory pressure stills, the charging stock employed in cooling and condensing the vapors from the pressure still may be introduced into the circulating stream of oil. Where the process of the invention is carried out in pressure stills in which the stock undergoing cracking is passed but once through the heating element, the fresh charging stock employed in cooling and condensing the vapors may be passed through the heating element admixed with oth r feed or with reflux condensate; or it may be introduced into the heating element at a separate point, for example, the preheated charging stock may be introduced into the heating element at one point and reflux condensate may be introduced into the heating element at a subsequent point in the passage of the oil therethrough.

In carrying out the improved process of the invention, the fractionation of the pres sure still vapors effected may be controlled by regulating the flow of fresh cooling oil passing through the condensing chambers in indirect heat exchanging relation with the vapors therein and by regulation of the" amount of oil, either condensate from a cooler chamber or part of the oil circulated through the chambers in heat exchanging relation with the vapors therein, directly in troduced into the condensing chambers. The amount of fresh charging stock employed for cooling and condensing the vapors from the pressure still may be suitably varied to effect the desired fractination and any additional charging stock required in the cracking operation may be introduced into the pressure still at some other point.' WVhere the cooling oil is passed successively through the series of condensing chambers, a part of the cooling oil may be by-passed around any one or more of the condensing chambers to further assist in regulating the fractionation, and refluxed condensate from a chamber of lower temper ature may be introduced into the chamber of next higher temperature in the series or into any subsequent condensing chamber.

The series of separate condensing chambers in which the vapors are fractionally condensed may be arranged in vertically superposed position in the form of a tower, the vapors undergoing fractional condensation entering the bottom of the tower and leaving from the top. The condensing surfaces may constitute tubes disposed within the condensing chambers and through which the fresh charging stock flows. That regulated part of the condensate returned from chambers of lower temperature to chambers of higher temperature may be returned by gravity. I

lVhere the vapors from apressure still are directly introduced into such a fractionating tower, one or more of the chambers of relatively higher temperature may be employed for separating the heavier vapors and returning or refluxing them to the still for further cracking, and the vapors constituting the desired fraction or fractions may be condensed in one or more of the sections in the tower, or, after the fractionation is efl ected in'the tower, the vapors comprising the desired final fraction may be conducted to a separate condenser. In cracking hydrocarbon oils for the production of gasoline,

the final condensation oi": the gasoline fraction may be effected in the uppermost section of the tower, "or the gasoline vapors may be conducted from the top of the fractionating tower to a separate condenser, and by suit-- able regulation. of the operation, a gasoline fraction can be directly obtained.

The process of the present invention also provides advantageous methods of treating two or more charging stocks of different characteristics in a single operation. For 6X- ample, heavier charging stock may be circulated through the fractionating tower on its way to the pressure still for indirectly cooling and condensing the vapors therein and lighter charging stock may be directly introduced into the cracking zone; or, in the treatment of heavier oil for the production of gasoline, charging stock containing lighter constituents of a gasoline character may be. em-

ployed in the fractionating tower for indirectly cooling and condensing the vapors therein and may be directly introduced into one or more of the condensing chambers after passing through the tower to efi'ect a vaporization of the lighter gasoline character con- 'stituents and heavier feed oil may be intro- 'duced into the pressure still at some other point.

The invention will be further described in connection with a pressure still of the general type described and illustrated in Patent No. 1,285,200 granted to the Sinclair Refining Company, November 19, 1918 on the application of Edward W. Isom but it will be understood that the invention is of more general application, although it is of particular value in connection with a pressure cracking still of this type.

In the accompanying drawings I have shown certain forms of apparatus in which the process of the invention can be practised and the invention will be further described in connection therewith. It is to be understood, however, that these specific illustrations and descriptions are for the purpose of exemplification and that the scope of the invention is defined in the following claims, in

[which I have endeavored to distinguish it from the prior art, without, however, relinquishing or abandoning any portion or feature thereof.

In the accompanying drawings:

Fig. 1 is an elevation partly in section of a fractionating tower adapted for the practice of the process of the invention,

Fig. 2 represents in elevation and partly in section a fractionating tower of the type shown in Fig. 1 in conjunction with a pressure still, and

Fig. 3 is a modified arrangement of a preserence character wherever it occurs in theseparate figures.

The fractionating tower shown in the drawings is of general type described and illustrated in Patent 1,489,420 granted to the Sinclair Refining Company April 8, 1924, on

my application.

Referring to the drawings, the fractionating tower comprises a cylindrical shell 4 closed by end plates 5, each of which is provided with a hand hole fitting 6. The hand:

holes are normally closed by plates 7 and 8. Slightly separated from the end plate 5 at each end of the tower are header sheets 9 and 10, said sheets forming with the adjacent end plates, inlet and outlet chambers, 11 and 12, for the cooling oil as will presently appear. The space between the header sheets is divided into a plurality of vapor condensing chambers 13, shown as .t'our in number although the number may be varied and is dependent upon the number of cuts desired. Between adjacent vapor condensing chambers are chambers it for the cooling oil, formed by header sheets 15 on opposite sides thereof and the wall of the cylindrical tower.

The header sheets are successively connected by batteries of tubes 16 extending through,

.the respective vapor condensing chambers whereby the cooling oil may flow the length of the tower through the successive sets of tubes. The vapor chambers are provided with suitable baifie plates 17, fitting loosely about the cooling tubes, to provide a circuitous circulation for the vapors therethrough in order that they may be more thoroughly brought in contact in heat exchang ing relation with the cooling tubes.

The lowermost of the vapor condensing chambers is provided with an inlet port 18 for the entrance of the vapors and the up permost. condensing chamber with a vapor outlet 19. Connections 20 are provided to conduct the vapors, or such portion thereof as remains uncondensed, from each vapor chamber, except the topmost, to the vapor condensing chamber next above, arranged to connect'the adjacent condensing chambers about the intermediate chambers for the cooling oil, the point of connection to the upper vapor condensing chamber being sutiiciently above the header sheets forming the bottom of that chamber to allow for the collection of liquid condensate therein. In order to supplement control of the "fractionation effected in the separate vapor condensing chambers, connections are provided for controlling and distributing the flow of cooling oil passingthrough the tubes on its way to the pressure still through the respective batteries of tubes in the separate vapor condensing chambers. For this purpose, each of the intermediate cooling fluid chambers 14 is provided with an outlet 31, these outlets being connected to a common bypass pipe .32, the various connections being provided with valves at appropriate points as illustrated.

Each condensing chamber near its bottom and below the level of the vapor connection thereto has a drawoff pipe 23 which is provided at 36 with a guage glass toindicate the level of the condensate in the chamber and a valve 37 for shutting off the drawott and controlling the passage of condensate therethrough. A pipe 38 connected to the gauge glass receptacle extends to a cooler or storage tank. A branch connection 39 leads from the drawofi' 23 of each condensing chamber, except the lowermost to the top of the next lower condensing chamber at 40, a trap being formed in said pipe at 41 and a valve located therein at 42. A regulated part of the condensate from each con- (lensing chamber may be returned through this connection to the next lower and hotter condensing chamber where it is revaporized and returned for further treatment, the amount of reflux so introduced into the next lower and hotter chamber being controlled by valve 42. A stream of condensate entering the top of each condensing chamber from pipe 40 spreads over the topmost bafiie therein, and, the holes in bafiie through which the cooling tubes extend being somewhat larger than the latter, forms films on the tubes until vaporized being thus effectively subjected to the temperature of the tubes. Refluxed condensate is thus in effect redistilled and refractionated securing a more definite out while at the same time effecting a re ulated condensation of the vapors in the chamber into which it is introduced.

The pressure still illustrated in Figs. 2 and 3 is made up of the bulk supply tank 43 located away from the heating furnace 44, the vertical heating tubes 45 arranged in the heating flue 46 of the furnace, and circulating pipes 47, 4S and 49 connecting the lower and upper ends of the vertical tubes with the bulk supply tank, and a circulating pump 50 for circulating the oil from the bulk supply tank through the vertical tubes and back to the bulk supply tank. Arranged above the bulk supply tank is the fractionating tower 51, the lowermost vapor condensing chamber of which is connected with the vapor dome of the bulk supply tank through the vapor line 52. A return reflux line 53 having a check valve therein to prevent flow into the fractionating tower is provided for the return of condensate to the pressure still.

The vapors from the top condensing chamber in the fractionating tower escape through the vapor line 54 to the condenser 55 where the vapors are subjected to condensation. The

- condenser discharges into the receiver 56 from which the uncondensed vapors and gases are drawn oil through the connection 57 and the liquid condensate through the connection 58. A continuous tar drawofi is shown at 60 and a pumping out line for discharging the still is shown at 61.

In carrying out the process of the invention in conjunction with the pressure distillation of relatively heavy hydrocarbon oils for the production of gasoline, the gasoline traction may be condensed in a separate condenser, as illustrated, or the gasoline fraction may be condensed in one or more of the upper sections of the fractionating tower, and a separate condenser may be dispensed with. Where a separate condenser is not employed, the gases and any vapors escaping from the tower may be cooled or subjected to absorption or scrubbing treatment or to other suitable treatment for the further separation and recovery of liquefiable or otherwise valuable constituents.

That part of the charging stock employed for cooling and condensing the vapors in the tractionating tower is circulated through the tubes 16 in the fractionating tower and then introduced into the pressure still. The hot vapors from the pressure still enter the hottest and lowermost vapor condensing chamber through connection 52 and pass upward- 1y through the successive vapor condensing chambers maintained at progressively lower temperature undergoing partial condensation in each condensing chamber. The uncondenscd vapors and gases from the uppermost and coolest vapor condensing chamber in the tower escape to the final condenser through connection 54. The heaviest vapors are condensed in the lowermost and hottest chamber 13 the nextheaviest vapors in the next chamber 13 and the progressively lighter vapors in the successive chambers 13 and 13 the condensate in each chamber being separately collected in the lower part of that chamber. The liquid condensate collecting in the lowermost chamber 13 is returned to the pressure still through connection 53. A regulated part of the condensate collecting in each of the chambers 13, 13 and 13, is returned to the next lower and next hotter chamber through the connections 41 41 and 41 respectively, the amount of condensate so returned being controlled in each case by the valve in the communicating connection. That part of the condensate collecting in each chamber which is not returned to the preceding chamber is withdrawn through the rec eptacles 36 and may be introduced into another chamber in the tower, separately introduced into the pressure still for further treatment, or otherwise disposed of. Where one or more of the condensates collected in the various sections of the tower are withdrawn from the apparatus, particularly where the tower is operated under sui in peratmospheric pressure, the condensates so withdrawn may be cooled as withdrawn, and before the pressure thereon is reduced.

The pressure may be regulated and reduced by means of a regulating valve 59 between the fi-aetionating tower and the condenser, or by valves in the connections 57 and 58 located beyond the receiver; or the fractionating tower may be operated at a pressure lower than that prevailing in the pressure still and the pressure may be reduced and regulated by a regulating valve 62 in the vapor connection between the pressure still and the fractionati tower. Where the fractionating tower is operated at substantially the pressure prevailing-in the pressure still, reflux may be returned to the still from the tower by gravity through connection 63. Where the fractionating tower is operated at a pressure materially lower thanthatprevailin in the still, a pump 64 is provided for returning reflux to the pressure still through either connection 63 or connections 65, 72 and 68. 1

Fresh charging stock to the pressure still i is circulated to the tower through connection 66 by means of pump 67 and isforcedthrough the batteries of cooling tubes 16 in the -several vapor condensing chambers in the tower, the fresh oil cooling and condensing the vapors and being in turn preheated. After passingthrough the cooling tubes, the fresh oil is introduced into the pressure still. The preheated oil may be introduced into the still directly through the connection 63 or into the circulating line of the still through the connections 72 and 68 or it may be introduced in whole or in part, directly into one or more or the condensing chambers in the towers, through connection69 and valved inlets 7 0 into. the condensing chambers.

Where the fresh charging stock circulated through the cooling tubes in the vapor condensing chambers in the tower contains lighter constituents, these constituents may in part be vaporized and, particularly where the flow of fresh oil is downwardly.through the cooling tubes,'may interfere somewhat with the circulation of the fresh oil and the cooling and condensing of the vapors in the cons densing chambers. The return of circulation of the fresh oil through the cooling tubes may be increased to prevent any substantial vaporization. of such lighter constituents which it may contain, or an increase-d pressure may be maintained upon the fresh charging' stock within the cooling tubes and con necting compartments in the tower to inhibit or prevent such vaporization. Or the fresh oil may be circulated upwardly through the cooling tubes, and any vapors liberated may be trapped off at the upper end of the tower and introduced into the still or into the tower at some appropriate point. In general, the charging stock subjected to the pressure distillation does not contain any large amount of constituents which vaporize under the pressure maintained in the treatment until cracking of the charging stock into lighter hydrocarbons takes place, and the pressure required to force the charging stock through the cooling elements in the tower and into the pressure still is usually sufficient to prevent objectionable vaporization.

Pump 71 is provided for introducing additional feed oil into the pressure still, either into the circulating line of the still through connection 68 or through connections 72, 65 and 63. The pumps 67 and 71 may be arranged to draw charging stock from a single source of supply or they may be arranged to handle charging stock of different charac ter from several sources and to make the appropriate disposition of the particular charging stocks in the cracking system.

In the apparatus illustrated in Fig. 2, the fresh oil for cooling and condensing the vapors in the fractionating tower is circulated downwardly through the tower in countercurrent flow to the vapors from the pressure still, entering the tower through the upper connection 28 and escaping from the lower end of the tower through connection 25. This lower connection is provided with a check valve to prevent circulation upwardly through the cooling tubes of any reflux condensate being returned to the still through connection 65.

In the apparatus illustrated in Fig. 3, the fresh oil employed for cooling and condensing the vapors in the fractionating tower is circulated through the cooling tubes in the tower in concurrent flow with the vapors from the pressure still, entering the tower through the lower connection 25 and escaping through the upper connection 28, which is also provided with a check valve to prevent reverse flow through the cooling tubes in the tower.

In carrying out the process of the invention in apparatus of the type illustrated, fresh charging stock may be introduced into the still in a number of ways. Where the total amount of charging stock is insufficient to effect the cooling desired in the fractionating tower, an additional amount of the charging stock may be circulated through the fractionating tower and returned to the supply, a part only of the oil passing through the cooling tubes being introduced into the pressure still. WVhere too great a cooling effect would be produced if all of the fresh charging stock were introduced through the tower, a part of the fresh feed may be introduced into the circulating line or into the bulk supply tank. An additional cooling effect may also be secured by introducing part of the fresh feed after it has passed through the cooling tubes directly into one or more of the condensing chambers inthe tower. The direct introduction of feed in this way is of particular value in promoting the cooling effect produced where the feed contains light constituents which are vaporized in the condensing chambers. l v here part of the feed is so directly introduced, the unvaporized constituents may be returned to the pressure still with the condensate collecting in the condensing chamber into which it is introduced.

The heavier fractions collected in the tower, or such of them as are adapted to further treatment in the pressure still employed in conjunction with the tower, may be returned to the pressure still, either to the bulk supply tank or to the circulating line. All or a part of the heavier condensates may be returned to the pressure still or they be withdrawn, in whole or in part and subjected to further cracking treatment or oth erwise employed. The fractionation effected in the tower is close and the heavier fractions as well as the lighter fra ctions are susceptible to close control. The process of the invention may thus be employed for effecting an improved fractionation of the heavier cuts of the pressure distillate as well as of the lighter cuts eliminating or reducing redistillation of these fractions. f

The process of the invention also includes improved methods of treating different charging stocks where several different charging stocks are treated in the same pressure still. Where the fresh oil circulated through the cooling tubes in the tower for cooling and condensing the vapors from the pressure still contains light constituents heavier than any desired fraction, the oil after passing through the cooling tubes in the tower may be introduced directly into the heater, to subject all of the charging stock to the cracking conditions maintained in the heating tubes before it escapes as vapors from the still.

In carrying out the process of the invention for the production of gasoline, where the charging stock employed for cooling and condensing the vapors contains gasoline character constituents, all or part of the feed through the cooling tubes in the tower may be introduced directly into the condensing chambers to effect a vaporization of the gasoline character constituents which then pass off with the vapors from the pressure still and are condensed with vapors of a similar character. If a large part of the total feed to the pressure still contains gasoline character constituents, this part of the feed may be employed for cooling and condensing the vapors in the fractionating tower and heavier feed, or feed substantially free from such lighter constituents, may be introduced into the pressure still at some other point. Where only a relatively smaller part of the total feed includes gasoline character constituents, it may be circulated through the cooling tubes and the cooling effect of this feed may be supplemented by circulation of additional amounts of heavier charging stock through the cooling tubes in admixture with it. Where a part of the charging stock contains lighter constitu ents, which, however, are not of a gasoline character, the lighter feed may be introduced into the circulating line and heavier feed circulated through the cooling tubes, or if the heavier feed is insuflicient in amount to effect the desired cooling, the lighter feed may be circulated through the cooling tubes either aloneor in admixture with part or all of the heavier feed, and then introduced into the circulating line.

Higher pressures may be employed with advantage where the charging stock includes relatively large amounts of lighter material, or where charging stock including such lighter constituents which are however heavier than the desired gasoline fraction is introduced directly into one or more of the condensing chambers, the condensate collecting in these chambers may be withdrawn and subjected to cracking treatment appropriate to the character of the fraction, for example,

in another pressure still operated at higher 7 pressure. The intermediate fractions collecting in the intermediate condensing chambers of the series may be withdrawn and separately treated, or they may be condensate formed in a lower chamber for return to the pressure still with the condensate from that chamber, or they may be withdrawn and introduced directly into the cracking zone.

The process of the present invention may be combined with a pressure distillation where tar is drawn off from the pressure still during the progress of the operation, and particularly where during the latter part of a pressure distillation tar is withdrawn in relatively large amount, and where fresh oil is introduced, to maintain the concentration of tarry constituents below an objectionable point during the progress of the operation. In such a combined operation, fresh charging stock, in an amount corresponding to the condensed fractions, and any vapors, withdrawn from the fractionating tower, may be introduced into the pressure still through the cooling tubes in the tower for cooling and condensing the vapors therein, and additional feed for maintaining the still charge approximately constant as tar is withdrawn may be introduced into the circulating line.

Where the process of the present invention is carried out for the production of a gasoline character fraction, and where the desired gasoline fraction is condensed in the uppermost condensing chamber in the fractionating tower, very close regulation. of the fraction obtained can be secured by the return to the next condensing chamber of condensate from the uppermost chamber at a point adjacent the outlet through which the vapors escape to the final chamber. The gasoline character fraction so returned is vaporized and in vaporizing promotes the condensation in the chamber into which it is introduced and substantially reduces the amount, if any, of vapors escaping to the final condensing chamber of a substantially heavier character than the refluxed gasoline fraction. The pressure still and fractionating tower can be operated in this way for the direct production of a marketable gasoline fraction without redistillation of the pressure distillate. WVhere a separate condenser for the final gasoline fraction is employed, a similar effect can be secured by returning to one or more of the upper condensing chambers in the fractionating tower a part of the final gasoline fraction collecting in the separate condenser.

It will thus be seen that this invention provides an improved method of operating pressure stills and fractionating and condens ing the vapors from pressure stills, whereby the vapors from the pressure still can be accurately divided into such cuts or fractions as are desired while dispensing in whole or in part with the operation of redistillation, and in which the heat usually lost in condensing and redistilling the pressure distillate is conserved by employing fresh charging stock on its way to the pressure still for cooling and condensing the vapors undergoing fractionation and by employing the hot vapors undergoing fractionation for preheating the fresh charging stock so employed before introduction into the still.

One of the important advantages of the improved process of the present invention is that it enables the direct production in a single operation of a gasoline character frac-' tion. Another important advantage of the process of the present invention is the heat economy which it effects in utilizing the heat of condensation of the vapors from the pressure still in preheating feed to the pressure still while at the same time employing the fresh feed for cooling and condensing the vapors and in effecting an accurate fractionation thereof.

I claim:

1. The improvement in the operation of pressure stills which comprises subjecting the vapors therefrom to a refluxing operation by indirect heat interchange With raw charging stock to the still, returning the reflux to the still, subjecting the remaining vapors to a further refluxing operatiomand returning a regulated amount of the condensate formed in.said further refluxing operation to said first refluxing operation.

2. The improvement in the operation of pressure stills, which comprises passing the vapors therefrom through a series of separate condensing chambers, passing raw charging stock to the still through the condensing chambers in indirect heat exchanging relation with the vapors therein, separately col pressure stills,

lecting the condensate in each of the chambers, and controlling the condensation in the condensing chambers by returning a regulated part of the condensate from the chambers of lower temperature to the chambers of higher temperature.

3. The improvement in the operation of which comprises passing the vapors therefrom through a series of separate condensing chambers, passing raw charging stock to the still through the condensing chambers in indirect heat exchanging rela tion with the vapors therein, separately conlecting the condensate in each of the chambers, controlling the condensation in the condensing chambers by returningaregulated part of the condensate from the chambers of lower temperature to the chambers of higher temperature, and refluxing the condensate from the chamber of highest temperature to the pressure still.

4. The improvement in the operation of pressure stills, which comprises passing the vapors therefrom through a series of separate condensin chambers, passing raw charging stock to :ne still through the condensing chambers in indirect heat exchanging relation with the vapors therein, separately collecting the condensate in each of the chambers, controlling the condensation in the condensing chambers by returning a regulated part of the condensate from the chambers of lower temperature to the chambers of higher temperature. and supplementing this control of the condensation in the chambers by bypassing regulatedproportions of the raw charging stock around the condensing chambers.

5. The improvement in the operation of pressure stills, which comprises passing the vapors therefrom through a series of separate condensing chambers, passing raw charging stock to the still through the condensing chambers in indirect heat exchanging relation withthe vapors therein, separately collecting the condensate in each of the chamers, controlling the condensation in the condensing chambers by returning a regulated part of the condensate from the chambers of? lower temperature to the chambers of higl temperature, and separately collecting and condensing the vapors from the chamber of lowest temperature.

6. The improvement in the operation of pressure stills, which comprises passing the vapors therefrom through a series of separate condensing chambers, passing raw charging stock to the still through the condensing chambers in conntercurrent flow to the vapors and in indirect heat exchanging relation with the vapors therein, separately collecting the condensate in each of the chambers, and con trolling the condensation in the condensing chambers by returning a regulated part of the condensate from the chambers of lower temperature to the chambers of higher temperature.

7. The improvement in the operation of pressure stills, which comprises passing the vapors therefrom through a series of separate condensing chambers, passing raw charging stock to the still through the condensing chambers in indirect heat exchanging relation with the vapors therein, separately collecting the condensate in each of the chambers and controlling the condensation in the condensing chambers by returning a regulated part of the condensatefrom the chambers of lower temperature to the chambers of higher temperature, and introducing raw charging stock which has passed in indirect heat exchanging relation with the vapors in the condensing chambers into the condensing chambers in direct contact with the vapors therein.

8. The improvement in the operation of pressure stills for the production of a gasoline character fraction, which comprises passing the vapors from the still through a series of separate condensing chambers and separating a gasoline fraction and at least one fraction heavier than gasoline therein, passing raw cha ,ing stock to the still through the con- (lensing chambers in indirect heat exchanging relation with the vapors therein, controlling the condensation in the condensing chambers by returning a regulated part of the condensate from the chambers of low r temperature to the chambers of high r temperature and directly collecting the gasoline fraction.

9. Theimprovement in the operation of circulatory pressure stills for the distillation of hydrocarbon oils, which comprises passing the vapors therefrom through a series of separate condensing chambers, passing ccol oil through the condensing chambers in indirect heat exchanging relation with the vapors therein, separately collecting the condensate in each of the chambers, controlling the condensation in the condensing chambers by returning a regulated part of the condensate from the chambers of lower temperature to the chambers of higher temperature. intro ducing condensate from chambers of higher temperature into the pressure still at one point and introducing oil passed through the condensing chambers in indirect heat exchanging relation with the vapors therein into the still at another point.

10. The improvement in the operation of pressure stills, which comprises passing the vapors therefrom through a series of separate condensing chambers maintained under substantially the pressure prevailing in the still,

passing raw charging stock to the still through the condensing chambers in indirect heat exchanging relation With the vapors therein, separately collecting the condensate in each of the chambers, and controlling the condensation in the condensing chambers by returning a regulated part of the condensate from the chambers of lowertemperatureto the chambers of higher temperature.

11. The improvement in the operation of pressure stills, which comprises passing the vapors therefrom through a series of separate condensing chambers maintained under substantially the pressure prevailing in the still, passing raw charging stock to the still through the condensing chambers in indirect heat exchanging relation with the vapors therein, separately collecting the condensate in each of the chambers, controlling the condensation in the condensing chambers by returning a regulated part of the condensate from the chambers of lower temperature the chambers of higher temperature, and returning heavier condensate from chambers of higher temperature to the still.

12. The improvement in the operation of pressure stills for the distillation of hydrocarbon oils, which comprises passing the va pors therefrom through a series of separate condensing chambers, withdrawing tar from the still during the progress of the cracking operation and feeding raw oil to the still through the condensing chambers in indirect heat exchanging relation with the vapors therein, separately collecting the condensate in each of the chambers, and controlling the condensation in the condensing chambers by returning a regulated part of the condensate from the chambers of lower temperature to the chambers of higher temperature.

13. The improvement in the operation of pressure stills for the distillation of hydrocarbon oils, which comprises passing the vapors therefrom through a series of separate condensing chambers. withdrawing tar during the progress of the distillation and introducing raw oil into the still through the condensing chambers in indirect heat exchanging relation with the vapors therein, separately collecting the condensate in each of the chambers, controlling the condensation in the condensing chaml ers by returning a regulated part of the condensate from the chambers of lower temperature to the chambers of higher temperature, and introducing additional raw oil directly into the still.

In testimony whereof I ailix my signature.

JOHN E. BELL.

CERTIFICATE OF CoRRECTIoN.

Patent No, 1,741,357. Granted December 31, 1929, to

JOHN E. BELL.

It is hereby certified that errorappears in the printed specification of the above numbered patent requiring correction as follows: Page 1, line 39, for the misspelled word "af" read "of"; page 2, line 19, for "rediation" read "radiation", and line 94, for "tractination" read "fractionation"; page 3, line 102, for "baffie" read "baffle"; page 6, lines 95 and 96, for "condensate formed in" read returned to"; page 8, line 82, claim 11, after the word "temperature" insert the word "to"; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 21st day of January, A. D. 1930.

M. J. Moore, (Seal) Acting Commissioner of Patents.

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