US2074120A - Process and apparatus for pressure distillation - Google Patents

Description

March 16, 1937. 2,374,120

' PROCESS AND APPARATUS FOR PRESSURE DISTILLATION D. G. BRANDT Filed July 25. .1926

QWxSQk WEDGO Patented Mar. 16, 1937 UNITED STATES PROCESS AND APPARATUS FOR PRESSURE DISTILLATION David G. Brandt, Westfield, N. J., assignor to Doherty Research Company, New York, N. Y., a corporation of Delaware HHSSU] Application July 23, 1926, 'Serial. No. 124,320

4' Claims.

The present invention relates to the cracking of heavier hydrocarbons to obtain lighter hydrocarbons therefrom' and more particularly to obtain from gas oil or like material a finished motor spirit or gasoline. The invention of the present application is an improvement upon my prior pending applications Ser. No. 710,996 and Ser. No. 654,532, filed May 5, 1924 and July 30, 1923, respectively the last of which has matured into Patent No. 1,872,879, Aug. 23, 1932. I

In my saidprior applications, I have disclosed a process and apparatus for the pressure distillation of relatively heavy hydrocarbons to obtain pressure benzine therefrom, said prior applications disclosing passing charging stock of the character ofgas oil, or the like into a cracking chamber. A mixture of hydrocarbons is then withdrawn from the cracking chamber and forced through a pipe still or heating coil where the mixture is heated to cracking temperature. From the pipe still the heated oil is discharged into a separating chamber wherein the-liquids and vapors separate and both the liquids and vapors are taken from said separator into a vertical cracking chamber in which the vapors are passed in countercurrentrelation to the liquids while still at cracking temperature and under pressure to complete the cracking reaction. Vapors from said cracking chamber are passed through a dephlegmator, the reflux from which is run back into the cracking chamber and uncondensed gases and vapors from which are passed through 'a pressure controlling and reducing valve and thence to a condenser. My prior application Ser.

No. 532,954 filed Jan. 31, 1922, which has matured into Patent No. 1,784,087, Dec. 9, 1930, discloses also drawing off heavy liquid from the bottom or lower portions of said cracking chamber and relieving pressure thereon to permit the'heat contained in the liquid so drawn off to drive over a pressure distillate'which is condensed, the residuum liquid resulting after the passing off of said distillate being used for fuel or other purposes.

Certain objects of the present invention are improving the results obtained from my said prior processes and apparatus by controlling the circulation of the liquids in said vertical cracking chamber to prevent the mixing of the feed with the liquid from the separator within the cracking chamber proper; to obtain a finished gasoline from a cracking'plant; andto conserve and return to the process part of the heat formerly lost in the residuum drawoff.

The novel features of the present inventionare pointed out with particularity in the appended claims. The invention itself, however, together with further objects and advantages, will best be understood from the following description taken in connection with the accompanying drawing in which The figure is an elevational view,'partly diagrammatic in character, of an apparatus adapted to operate in accordance with the method or process of the present invention and including the novel features hereinafter described and claimed.

In the apparatus illustrated in the drawing, raw charging stock, preferably gas oil, is brought in through pipe 2 to the feed pump 4 and thence forced through pipes 6 and 8 to the upper portion of a tower I0 combining the functions of a heat exchanger, a bubble cap tower and a dephlegmator. The pipe 8 enters a chamber I2 at the top of the tower I0 and the oil thereupon passes through a coil or heat exchanger I4 within chamber I2 and thence through coils Ida, I 4b, I40, and I4d in the chambers I 2a, 1211, I 2c, and

. I2d arranged below the chamber I2 in the tower I0 and in theorder mentioned in going from the top to the bottom of the tower. The chambers I2, I2a, I21), I20, and I2d inclusive, and if desired others of like character not illustrated, comprise the bubble-cap or tray section of the tower I0 through whichrefiux passes downwardly from one chamber tothe other and vapors pass upwardly as indicated by arrows in counterflow to the reflux in a well-known manner, this type of apparatus being so well-known that the details of the bubble caps are omitted from the drawing. It will be seen that the bubble cap section of the tower I0 according to the present invention differs from the standard bubble cap apparatus primarilyin that the chambers of the individual trays of the bubble cap section of tower I 0 include coils I4, I la, Mb, I40, it; in contact with the vapors in the chambers and through which the ingoing charging stock passes in series, these coils thereby acting as heat exchangers, heating the ingoing stock at the same time that they condense a portion of the rising and outgoing vapors to increase the reflux condensate normally formed in such apparatus. Below the chamber I2d, tower I0 comprises two or more dephlegmating chambers I6, to which vapors pass in series on their way to the bubble cap section of the tower I0. Owingtothe character of chamber IG-the bottom I5of chamber I2d is not of the bubblecap type but is perforated substantially uniformly to act as distributor for reflux liquid passing down thru it. ChambersIB are partly filled with fragments I8 of glass, coke or other inert material to increase the dephlegmating effect. The lumps or fragments l8 rest on horizontal perforated partitions supported within tower I0 at the lower-ends of the chambers I 6. Lower chamber I6 contains also coil 20 through which the charging stock passes after leaving the coil I4b previously mentioned, coil 20 having the same function as the coils I4, I4w, etc. in the upper portion of toWerI 0. Directly below the lower chamber I6 is a chamber lSa in which is mounted a coil a similar to and connected in series with the coil 20. The stock being charged into the apparatus through coils l4, etc.'20 and 20a is discharged into the chamber lfia. where it is mixed with reflux flowing down into chamber lBa from upper chambers in thetower lll as well as with that formed in chamber I611. The bottom of the chamber lBa is formed of two perforated plates spaced apart, the space being filled with fragmentary material 18 of the type referred to above. This arrangement causes intimate contact over an extended area, of the vapors entering and the liquids leaving the tower l0.

The dephlegmating tower l6 preferably is set on top of a heat insulated cracking chamber 24, there being a frustro-conical plate 26 at the bottom of tower l0 and separating the tower from the cracking chamber 24.- The plate or partition has a central aperture 28 through which reflux condensate from the tower discharges into the cracking chamber. Charging stock after passing through the coil 20a. and mixing with reflux in chamber ifia is discharged downward centrally through the opening 28 into the cracking chamber along With the reflux condensate. The cracking chamber 24 contains a considerable body of material which has been either cracked previously or is undergoing cracking and, according to the present invention, it is desired to prevent the reflux from tower l0 and the charging stock from mixingimmediately with such materialin chamber 24 until the material in the chamber has substantially completed the cracking action obtainable without reheating. According to the present invention therefore, a central conduit of large dimension is set vertically beneath the aperture 28 to receive the reflux and charging stock coming down through the aperture. Preferably conduit 30 carries at its upper end funnel-shaped mouth 32 for receiving the reflux and charging stock and guiding it into the conduit 30. Below the chamber 24 and spaced therefrom by a diaphragm 34 is a mixing chamber 35 and conduit 30 extends through the diaphragm34 so as to conduct the mixed reflux and charging stock through chamber 24 and into the mixing chamber 36 before the charging stock and reflux can mix with the material from chamber 24. Material which has undergone cracking in chamber 24 passes from the lower end of said chamber into the mixing chamber 35 through pipes 38, ,38. The mixture of reflux, charging stock and previously cracked material, in the proportions of about 60% previously cracked stock to 20% fresh stock and 20% reflux, is taken out of chamber 36 through pipe 40, returned to the system and'forced by pump 42 through pipe 44 to a pipe still or heating coil 46 contained in the furnace 48. Any gas oil obtained as described below by separating it from liquid taken out of chamber 24 is .included in the 20% fresh stock just mentioned. Ordinarily, the liquid passing through coils. Ma, l4b etc. in tower ID is only 10%. of the liquid entering pipestill from pump 42 andis seldom more than 20%. In most aspects however, the present invention is independent of the ratio, between the liquid flowing through coils I411, I423, etc. and that pumped into pipe-still 46. Inthe coil 46, the oil is heated to between 750 and 900 F. under considerable pressure and discharged through'pipe 59 to the upper portion of the separator 52. Vapors from separator 52 pass out of the top of the separator through pipe 54 which passes through the side of the cracking chamber 24 and discharges into a distributor 56 near the bottom of the cracking chamber. Lid;- uids entering the separator 52 pass to the lower portion of the separator through the interior of conduit 58 and the majority of these liquids leave the separator through a pipe 60 which passes through the side of the chamber 24 somewhat above the mid-level of the liquids therein and discharges directly into the chamber. The liquid discharged from pipe 60 thereupon works its way downwardly through the chamber 24 while undergoing further cracking and in a general way countercurrent to the vapors and gases discharged from the distributor 56. The majority of the liquids flowing downwardly in the chamber 24 as just mentionedand remaining unvaporized passes through the pipes 38, 38 into the mixing chamber 35. p

It has been found that the cracking reaction is one requiring an appreciable amount of time in which to complete itself. If the cracking reaction initiated by a given heating of the oil has not been permitted to complete itself before the oil is returned to the cracking coil, the oil which has not completed its cracking from a previous heating is almost sure to crack in the pipe still when returned thereto. The excessive cracking of the oil in the pipe still is undesirable, not only because of the carbon which may thereby be deposited in the pipe still, but because of poor utilization of the heat imparted to the 021 if the cracking has not been completed in the chamber 24. The capacity of the separator chamber 52 is preferably made such that the oil is held in chamber 52 until it is conditioned, or about to crack, before being transferred to chamber 24. The oil as introduced into chamber 24 being about to crack, the contact of the hot oil with the hot gases coming from the top of separator 52 and distributed through the oil in chamber 24 by the distributor 56 produces a rapid cracking action in the chamber 24. Moreover, the distributor 56 being adjacent the outlet from chamber 24 any oil leaving this chamber must come into contact with the hottest gases, thus insuring that any molecule of the oil which has absorbed enough heat in coil 46 to be chemically unstable will crack before leaving chamber 24. The heat delivered to the oil in the pipe still is therefore effectively utilized in chambers 52 and 24 and very high firing rates can be applied to the pipe still Without depositing an objectionable amount of carbon in the coil 45. The capacity of the apparatus is therefore very high for a given area of heating surface in the coil 45. In addition to the advantages just discussed, the gases and vapors delivered to the lower part of chamber 24 by the distributor 55 and rising through the liquid in the chamber strip out of the liquid undergoing cracking in the chamber substantially all of the gasoline-like material in this chamber. The formation of gasoline-like material in the oil heated in pipe still 425 is therefore promoted to a maximum degree owing to the substantial absence of any. gasoline-like material in the feed to the still. In this-connection, experience has shown that a partial pressure of gasoline in material being heated to cracking temperature correspondingly reduces the amount of gasoline formed by a given heating.

It is necessary that a certain amount of liquid be withdrawn from the cracking still, not only to prevent the liquid level in the apparatus from becoming too high but also to maintain the proper "is not to be taken to mean that no carbonforms in chamber 24, as the metal surfaces within this chamber which are exposed to the hotoil accumulate a layer of crystalline carbon, the metal seemingly catalyzing the separation of carbon from the liquid undergoing cracking: Nevertheless the liquid itself within the chamber 24, under the. conditions "desired according tothe'present invention, contains practicallyno free carbon.

In order to maintain the desired condition of the liquid as to free carbon which has just been mentioned, the shell of chamber 24 moreover is tapped slightly above diaphragm 34 and an outlet pipe 62 connected into the shell at this level through which residuum maybe drawn off at the rate desired from the chamber 24, the flow of liquid through pipe 62 being regulated by valve 64.

It is observed, moreover, in order to maintain the optimum operating conditions in the cracking circuit that some of the heavy residuum. should be withdrawn from the bottom of the separator 52. For this purpose, the valved pipe 63 is led out of the bottom of separator 52, pipe. 63 connected with the pipe 62 throughwhich residuum is taken from chamber 24. Y 2

While, according tothe present invention, it is desired to prevent the formation of free carbon mixed with the liquid in the chamber 24, the presence of a small amount of free carbon in the liquid taken out of the bottom of separator 52 through pipe 63 is not harmful. As a general rule, the oil passing through pipe 62 to the concentrator is made up of about 60% of material taken from the bottom of the cracking chamber 24 and about 40% of material from the separator 52 although all of itmay be withdrawn from 24 or 52. 4

Pipe 62 delivers liquid into chamber 66 in the bottom of a concentrator 68. The pressure in concentrator 68 is substantially reduced as compared to that in the chamber 24 and gasoline and gas oil contained in the liquid entering chamber 56 are thereby permitted to evaporate under the reduced pressure and .due to the heat contained in the incoming liquid itself.

For instance, if chamber 24 is at 250 lbs. gage pressure, concentrator 68 is operated at about lbs. gage to give a certain gravity to the residuum withdrawn from chamber 66. The proper pressure to hold in chamber 56, therefore, varieswith the pressure and temperature in chamber 24 as well as with the grade of residuum or fuel oil desired. Moreover, when a fuel oil is desired of a gravity heavier than that readily obtainable merely by reduction of pressure under the conditions prevailing at a given time, steamer gas may be introduced into the lower part of chamber to assist vaporizing liquid in this chamber.

, Vaporsformed in chamber'iiii pass out of the chamber through the opening H1 in the j diaphragm l2 which forms the top of the chamber 6?. The vapors from opening it; pass into a bubble cap tower comprising chambers 14,;14a, 14b, and 740 in the upper part ofthe concentrator 68. The bubble capportion of the concentrator comprises bubble cap sections or trays which maybe of standard or other preferred design and the details of which are not illustrated' It will beunderstood, however, that the vapors pass up through chambers I4, 14a, 14b, and 140, the heavy vapors being condensed and flowing as a reflux back into chamber 14. v formation of reflux and to prevent any vapors heavier than gasoline from passing out of concentrator 68, a cooling coil Iii is placed in the top of the I chamber 140. Gasoline vapors passing, the coil l6 are taken out of the top of the concentrator 63 through pipe 78 and passed thence through condenser 89 to suitable storage tanks. Reflux condensate, however, formed in bubble cap sections '14, 74a, 14b and 140 is not permitted to flowback into chamber 66 at the bottom of the 4 concentrator 68 but,'owing' to the form given" the diaphragm 12, and the 'outlet 70 therethrough; is trapped in the lower portion of the chamber 74 from which the condensate, consisting principally of gas oil may be drawn out through pipe 82 and forced by pump 84 back through pipe 86 into'the mixing chamber 36 mentioned above. By the arrangement and method just described, much of the heat of the residuum drawnfrom the bottoms of chamber 24 and 52 may be returned to i the cracking circuit with the gas oil or the like from concentrator B8. The gas oil from chamber l4 may, of course, be stored and mixed with or used in place. of gas oil from other sources. On the other hand the portion of the liquid from the lower part of chamber 24 which enters the chamber 65 and which does not vaporize'at the pressure and temperature in chamber 66 is taken out of the lower part of this chamber through pipe 88 and passes through a cooler 90 from which it is taken to suitable storage. This liquid isa fuel oil. I

In the operation of valve 64 and the valve'in pipe 63 to admit liquid into chamber 66 from the cracking chamber 24, and the separating chamber 52, it is preferred that the valves be opened to their fullest extent whenever liquid is tobe passed through them and closed tight again as soon as the desired amount of liquid has been withdrawn through them. I have found that this way sticking of valve 64 and of the valve in pipe 63 is avoided. When these valves are only cracked open to permit the desired amount of liquid to flow through them continuously, the valves soon become inoperative due to gum and carbon adhering to them and to their seats.

Gases and vapors liberated from the surface of the oil in chamber 24 pass through the aperture 28 and into the dephlegmator Ill. Here the vapors are dephlegmated, the d ephlegmating action due to the outer surface of tower Hl being assisted both by the cooling of the vapors by the coils M, Ma, 1411, I40, Md, 2!! and 2% previously mentioned and by pumping a volatile liquid such as gasoline into the chamber E2 of tower it. The design and arrangement of the coils I4, Ma, 5412, Md, 2!}, and 29a is such that the dephlegmating action is least in the section of tower Iii in which the vapor temperature is highest and is. increased by steps to the section or chamber of the tower H! in which the vapor temperature is lowest. It will be seen, moreover, that the increase in dephlegmating effect in the directionof decreasing temperatures in tower H], in other words, in the directionof flow of the vapors being dephlege mated, is as specifically disclosed,'a product of three factors; namely, the increasing area of the liquid injected into the uppermost chamber I2 of tower I0. By thus graduating the dephlegmating effect and increasing it in the direction of flow of the gases, the temperature at the lower or hotter 5 end of tower I0 may be at a maximum temperature, with minimum of reflux at this point, thus producing optimum conditions for the escape of gasoline from the cracking chamber 24 both as to temperature and as to reduction of mechanical entanglement of gasoline vapors in the reflux. The temperature at the upper end of tower I0 is, however, maintained such that no vapors heavier than those of commercial gasoline pass out of tower I0, and I am thus enabled to produce coml5 mercial or end-point gasoline direct from the vapors of a cracking chamber without rerunning the distillate to eliminate heavy ends as is now the practice.

Of course it is impossible to maintain an absolutely constant rate of cracking in chamber 24.

The dephlegmating effect of tower I0 must therefore be varied to produce the desired end point gasoline. The variation of the cooling effect in tower I0 required by variations in the rate of cracking in the chamber 24 is obtained by varying the amount of gasoline pumped back into the chamber I2.

It has been found possible to attain the desired results as to the temperature in the tower I0 and particularly in the upper end thereof by automatically controlling the speed of the pump I06 which returns gasoline to the tower in accordance with the temperature of the vapors passing from the tower to the condenser. A satisfactory method and arrangement for operating pump I06 in accordance with the temperature of the vapors in tower I0 is disclosed in my prior application No. 654,532, filed July 30, 1923. However, I do not limit myself to automatic control of pump I06 as this pump may be controlled by hand within the present invention. These vapors pass through an offtake pipe 92, containing a pressure-maintaining valve I00, valve I00 preferably being in duplicate so that one may be used if the other is out of order. It has been found moreover according to the present invention, that maintaining the temperature in the top of the tower I0 at the point producing by condensation a given end point gasoline from the vapors which have passed therefrom, also automatically maintains the pressure in the dephlegmator I0 substantially constant and avoids the necessity of adjusting the valve I00 during the normal operation of the apparatus. Maintaining a constant pressure in tower I0 also of course automatically maintains substantially constant pressures throughout the other parts of the apparatus.

Vapors not condensed in dephlegmator I0 pass out of the top thereof through pipe 92 to condensers 94, 96, and 90 through which the vapors pass in series. Intermediate tower I0 and condenser 94, the pressure is reduced by controlling valve I00 previously mentioned. Condenser 94 is the first condenser through which vapors from pipe 92 pass. Gasoline condensed in condenser 94 passes through pipe I02 to a container I04. Vapors uncondensed in the condenser 94 then pass through the condenser 96 and finally through condenser 98. Condensate from condenser 96 7 passes through pipe I09 to container H0 and vapors, condensate and gases from condenser 98 pass through pipe II2 to container IIO. Uncondensed gases and vapors pass off from the receiving tank or container IIO through pipe H4. Gas 75 or vapors from container I04 also may pass through pipe II6 into the top of container I I0 and thence ofi through pipe II4. Pipe II4 may lead to burners or to other means for utilizing the gas and uncondensed vapors. Preferably the gas in pipe H4 is scrubbed for gasoline before being utilized. Gasoline from tank H0 is run to gasoline storage through pipe IIB, the flow through pipe H8 being conveniently regulated by an automatic valve I20 operated by a float in chamber I22.

As mentioned above, the satisfactory control of the dephlegmating effect in tower I0 and more particularly the control of the dephlegmating effect in the top chamber of the dephlegmator has been found to be best achieved by introducing into chamber I2 a varying amount of gasoline of the end point it is desired to make in the apparatus. For this purpose a pump I06 is provided whose intake is connected by pipe I23 with the tank I04. Pump I06 forces gasoline received by it from pipe I23 into chamber I2 through pipe I08 to maintain a constant end point on the gasoline formed from the vapors leaving chamber I2. The necessary variations in the amount of gasoline pumped to dephlegmator I0 to compensate for changes in the vapor flow therethrough are readily produced by thermostatic control of the speed of pump I06, a thermostat (not shown) for this purpose being connected into the vapor line 92.

Liquid gasoline from the condenser has a cooling effect when introduced into tower I0 due both to its temperature and to its vaporization at the temperatures in the tower. The gasoline from tank I04 moreover, is preferably introduced into chamber I2 in suflicient quantity so that a considerable portion of it does not Va porize in chamber I2 when pumped thereinto, but runs down into chambers below chamber i2 before vaporizing. Advantage is therefore taken in the design of dephlegmator or tower I0 of the cooling effect of the heavy gasoline from condenser 94 when pumped back into the chamber I2 by correspondingly reducing the size of the cooling coils in the chambers below the top tray.

All the gasoline from condenser 94, however, is not required to be put back into chamber I2 and gasoline from tank I04 not used by pump I06 flows through valve I26 in pipe I24 to pipe H8 and thence to storage. Similarly, gasoline from condensers 96 and 98 collects in tank H0 and flows from this tank to storage through pipe II8. A valve I20 in pipe IIB is controlled by a float in float tank I22 connected to tank IIO, so as to maintain a substantially constant level of gasoline in tank I I0.

In addition to the pipe connections previously mentioned as used in the operation of the apparatus and process according to the present invention, there are illustrated in the drawing certain pipe connections used only on particular occasions. For instance, the vapor line 54 leading from the top of the separator chamber 52 to the cracking chamber 24 has a branch pipe I2Bconnected thereto and leading into the chamber 24 above the normal liquid level in chamber 24 and whereby the pressure above the liquid in chambers 24 and 52 may be equalized when it is desired to draw out the liquid in the chambers when for any reason the apparatus is shut down. A valve I29 is provided in the pipe I28 normally preventing passage of vapors through the pipe. Moreover, the feed line 6 for the raw oil has a pipe connection I30 passing these through the side of the chamber 24 above the conduit 30 and arranged to deliver more or less of the feed into the upper end of the conduit 30 whenever for any reason it is not desired that the entire feed pass through the cooling coils I4, Ma and I411; etc. and tower I0. Also, special draw-offs areprovided from chambers 36 and 52 for taking out liquid from the lower ends of chambers whenever it is desired to drain the liquid from these chambers. For this purpose valved pipe I32 leads from the bottom of chamber 36 connecting with the pipe 62 and valves by-pass I34 connects the pipe 82 with pipe I8 for permitting reflux collecting in chamber I4 to pass into a recycle gas oil tank. Similarly a valved pipe I36 is connected into the lower end of chamber 52 and arranged to deliver to pipe 62. Another way of discharging oil from chambers 36 and 52 is provided by a pipe I38 connected at one end to a pipe 08 and coil 90, connection being provided from the coil 90 to a relief tank. Whendesired, liquid may be discharged from chambers 36 and 52 into pipe I38 and thence into the relief tank through valved pipe connections I40 and I42 respectively. Moreover, provision is made whereby, when desired, some or all of the liquid going through the pump. 42 may be circulated through the chambers 52, 24, and 36 without passing through the pipe coil 46. The arrangement for this purpose comprises a connection between the pipes I38 and 44 including a valve I44. By opening the valve I44and the valves in pipes I40 and I42, when flow from pipe I38 to pipe 88 is cut ed the pump 42 may be kept in operation while little or no cracking is being carried out. It is preferred, moreover, that the valves in pipes I32 and I36, as well as other valves which may be used to draw oiT partially cracked material from chambers 24 and 52 during the normal operation of the apparatus shall be operated like valve 64 so as to be open to the fullest extent when it is desired to draw olT liquid and to close them tight at other times.

While an apparatus according to the present invention and adapted to operate in accordance with the process of the present invention is illustrated in the accompanying drawing and described herein in detail it should be understood that such detailed disclosure is illustrative only and is not intended as limiting the scope of the appended claims.

The separator and cracking chamber have been shown as being insulated. The usual practice for cracking stills is to insulate all equipment including pipe lines which handle hot oil. This insulation is not illustrated in the drawing for the sake of clearness.

Having thus described my invention, I claim:

1. In an apparatus of the class described, a cracking chamber, a mixing chamber connected to the lower end of said cracking chamber, a dephlegmator set over said cracking chamber and receiving vapors therefrom, a central con-. duit in said cracking chamber, the upper end of which stands above the normal level of liquid in the chamber and the lower end of which connects directly with said mixing chamber, and means whereby reflux from said dephlegmator and fresh stock charging liquid passdirectly into said conduit.

-2. The method of treating a relatively heavy hydrocarbon oil to produce a relatively light drocarbon therefrom comprising heating said relatively heavy hydrocarbon to cracking temperature while under pressure, removing said heated hydrocarbon from the heating conditions and permitting it to crack under insulating conditions from'heat previously stored therein, distilling a portion of said cracked hydrocarbon to produce a gas oil and a fuel oil, dephlegmating vapors produced by said cracking reaction, preheating oil by said vapors, withdrawing residual hydrocarbon from that undergoing cracking and mixing it with additional hydrocarbon for heating to continue the process, the mixtures so formed comprising of stock preheated by the vapors undergoing dephlegmation, 20% of liquid reflux obtained by dephlegmating said vapors, and 10% of said gas oil derived by distillation from previously cracked material.

3. The process of cracking high boiling point hydrocarbons to produce relatively low boiling point constituents of the nature of gasoline, which comprises maintaining a body of high boiling point hydrocarbons in a cracking zone under cracking conditions of temperature and pressure, subjecting the vapors evolved from the hydrocarbons in said zone to reflux condensing conditons to separate high boiling point constituents from relatively lower boiling point constituents, passing the reflux condensate produced into a charge mixing zone, withdrawing heavy liquid hydrocarbon material from said cracking zone into a single vaporizing zone and vaporizing substantial portions thereof under a bon oil to cracking temperature under pressure,

in Which relatively high-boiling oil constituents previously subjected to cracking conditions are admixed with fresh stock and the resulting mixture circulated in a closed cycle including a heating zone maintained under cracking conditions of temperature and superatmospheric pressure, the improvement which comprises withdrawing a portion of said mixture being circulated into a single vaporizing zone and substantially reducing the pressure thereon to permit the heat contained therein to vaporize all of the constituents desired to be separated from said withdrawn mixture, dephlegmating the vapors formed to permit separation of gasoline vapors from the remainder of the vaporized material by reflux condensation, and passing the refluxed condensate from such dephlegmation step free of the resulting unvaporized residue in said vaporizing zone to said circulating mixture.

DAVID G. BRANDT.

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