US2032892A - Cracking hydrocarbon oils - Google Patents

Description

March 3, 1936. 1 D SEGUY CRACKING HYDROCARBON olLs Filed Jan. 3l, 1930 c/ /N'A/STO/Q edn .6719/ BY Moray Patented Mar. 3, 1936 UNITED STATES PATENT OFFICE CRACKING HYDRO CARBON OILS Jean Delattre Seguy, Chicago, Ill., assignor, by mesne assignments, to Universal Oil Products Company, Chicago, Ill., a corporation of Dela- Ware Application January 31, 1930, Serial No. 424,754

1 Claim.

This invention relates to the art of cracking hydrocarbon oils, and more specifically comprises a system in which hydrocarbon oils of relatively high boiling points are converted into products of lower boiling points and greater commercial value.

'I'he invention Which I am about to disclose comprises a combination of several Well known methods of converting and treating hydrocarbon oils into a unit system arranged and operated in such a way as to utilize certain advantages accruing from a combination of these systems, in the manner described.

My process comprises a system in which the oil is first treated under temperature conditions which will cause Vaporization of a substantial portion thereof and this portion of the system may also be maintained at a sufficiently high temperature under the required pressure such as will cause decomposition or cracking of the hydrocarbons in the so-termed liquid-phase. This liquid-phase cracking may be of a mild nature or the temperature, pressure and time in this heating element may be extended to effect substantial cracking in this Zone. Products from this liquid-phase heating element may then pass to an enlarged or reaction Zone also maintained at super-atmospheric pressure in Which a separation of the vaporized and unvaporized products may be effected. Vapors from this enlarged reaction zone vmay be then subjected to further cracking at either reduced or increased pressure or at substantially the same pressure as that maintained in the vaporizing zone. Liquid products from the enlarged or reaction zone may be subjected to conditions which will promote further vaporization of these products. This is accomplished in another vaporizing or flash chamber normally maintained at a pressure reduced sufficiently to liberate sensible heat contained Within the residual oil thereby causing vaporization 0f the lighter portions of said residual oil. This vaporization or flash distillation may be augmented, if desired, by introducing into the body of the liquid in the flash chamber a portion of, or all, the hot vapors from the vapor-phase heating element.

The introduction of these hot vapors into the relatively cool residual oil may also serve the purpose of cooling or quenching said vapors to such an extent as to not only retard the reaction and prevent excessive cracking and the consequent formation of undesirable products, but also to cause the removal of coke or any heavy products of polymerization, such as tarry and,

pitchy matter which may already exist in the cracked vapors. Such heavy products as may be already formed, of course, separate in the flash chamber and are evacuated from the system together with the flashed residuum. Vapors from the flash distillation, together with the vapors from the succeeding liquid-phase and vaporphase reactions, may be collectively subjected to fractionation in a common fractionating zone. This fractionation may be assisted by introducing raw oil charging stock for the process into said fractionating zone in indirect heat exchangev relationship with the products therein. Further cooling may be accomplished in this fractionating zone by introducing straight-run gasoline-that is, gasoline produced by the atmospheric distillation of crude petroleum, or similar light straight run distillate, into the fractionating zone in direct contact with the products therein. Vapors remaining after fractionation may be condensed and collected as the final light product from the system, or before condensation they may be subjected to further treatment by passing them through an absorbent material in such a manner as to remove any unstable product in the cracked vapors, thus obviating or greatly simplifying the treatment of the condensed products usually required in their preparation for commercial use.

From the foregoing, certain novel features of my invention will be apparent, but for the sake of clearness, I will enumerate a few of the more salient features.

. One feature of my invention comprises fractionating the combined vapors from the liquidphase and succeeding vapor-phase treatments and from the ash distillation of the residuum of the other stages of the process.

Another comprises cooling Vapors resulting from the successive liquid-phase and vapor-phase treatments by introducing said vapors into the body .of residuum oil in the vaporizing or flash distillation zone. Another feature consists in assisting the vaporization of the relatively lighter products in the residual oil subjected to flash distillation by introducing thereinto vapors resulting from the successive liquid-phase and vaporphase treatments.

' Another important feature of my invention comprises cooling the vapors in the fractionating tower, handling products from successive liquid phase and vapor-phase treatments and from the flashing operation, by means of introducing into saidtower straight-run gasoline or light Y heating elementA 6V is maintained under ysuperatdistillate in direct contact with said products therein.

Another feature consists in cooling the vapors resulting from the successive liquid-phase and vapor-phase reactions and from the flashing operation, by means of charging stock for the process introduced into said fractionating tower in indirect heat exchange relationship with said products. A combination of the two cooling rneans just described may be used.

' In a system wherein the vapors in the fractionating tower are composed, wholly or in part, of vapors which have been subjected to conversion at the high temperatures which are'characteristic of vapor-phrase cracking it is especially desirable to fractionate and cool thesel products with a cooling agent of more stable nature than the cracked vapors. The commonly used method is to cool the vapors in the fractionating zone with portions of the condensed finished product from this same zone. In the case 4of the vaporphase cracking system this method has the disadvantage of continually subjecting this recirculated cooling medium to revaporizatlon and, said cooling medium being of a relatively unstable nature, its repeated revaporization may cause some of Vits most unstable constituents to break down into products which form gums and other resinous solids in the finished Product and products which may discolor the finished gasoline. Provision is made in my'process for avoid.- ing such revaporization of the cracked product by assisting fractionation and cooling in the fractionating zone with a more stable product such as straight run gasoline or light distillate.

The above and other features of this invention will be apparent upon reference to the attached single ligure, which isa diagrammatic side elevation in no sense to scale of one particular'conception of my process. Other forms of apparatus may be used without departing from the scope of my process.

Raw oil vis vintroduced through line I Yand by means of pump 2 may be charged through line 3 and' valves 4 and 5 directly into the heating element 6. Any portion or all of the raw oil vmay be diverted from line 3 through valve 1 and line 8 and may be circulated through the closed coil 9 located in fractionating tower 26 where it mayV assist cooling and fractionation of 'the vapors in said tower and is returned through line Aitl and valve II back into charging line 3 from where it may pass as preheated raw oil to the heating element 6. Heating element 6 is located'in 'any Vsuitable furnace 6. The oil undergoing treatment in mospheric pressure and is heated therein to the desired outlet temperature, which temperature may be sufficient to cause substantial conversion under a pressure suflicient to maintain the oil substantially in a liquid state or the temperature may be only suiiicient to cause mild conversion and to effect substantial vaporization. In either case the oil is discharged from heating element 6 through line I2 and valve I3 intoV the enlarged reaction chamber I4 Awhich -chamber may be maintained under substantially the same pressure as that maintained in the heating element 6 or under a lower pressure. The vapors which separate from the liquid products in the chamber I4 may pass through line I5 `and valve I6 into the vapor-phase heating element I1 located in a suitable furnace setting I8. The pressure maintained in' this vapor-phase heating element I1V may be substantially the same as that maintained in chamber I4 or may be reduced. In either case the temperature maintained around the vapor-phase heating element I1 is suflicient to cause substantial reco'nversion of the vapors passing there-V through. Liquid products separated from the vapors in chamber I4 may be withdrawn through line I9, valve 20 and valve 2l into the residuum vaporizing or flash chamber 22 wherein the pressure on the residual oil may or may not be reduced below the pressure maintained in the vaporphase heating element, but is preferably reduced sufficiently below the pressure carried in the vaporizing and separating chamber to cause the vaporization of light portions of said residual oil in the flash chamber. Reconverted vapors leaving vapor-phase heating element I1 may pass through line 23, valve 24 and valve 25 directly in the fractionating tower 26. Any desired portion or all of these reconverted vapors may, however, be diverted from line 23 through line 21 and valve 28 and thusV are introduced into the body of residual oil in flash chamber 22 where the twofold purpose of partially cooling the reconverted vapors to effect a separation of the heaviest products therein and that of assisting the `further vaporization of light portions of .the residual oil may be accomplished. The heavy residual products remaining unvaporized in the iiash chamber 22 may be withdrawn from the process through line 29, controlled by valve 3l). The total vapors from the iiash chamber 22 consisting of vaporized light portions of the residual oil together with the uncondensed reconverted vapors which may have been introduced through line 21, pass through line 3l controlled by valve 32, thence combining with and cooling any reconverted vapors entering the fractionating tower 26 through line 23 and valves 24 and 25. Fractionating tower 26 may be any form of suitable fractionating device and is preferably maintained at substantially the same or slightly lower pressure than that maintained in flash chamber 22. Aside from the auxiliary cooling accomplished as already Vdescribed by circulating raw oil through the coil 9 in fractio-nating tower 26, straight run gasoline may be introduced into the fractionating zone in direct contact with the vapors therein through line 33 controlled by valve 34, thereby further cooling and assisting fractionation.k Products condensed in fractionating zone 26 collect as liquid'in the bottom thereof and may pass through line 35 and valve 36 and by means of pump 31 may be introduced intoi the charging line 3 through line 38 and valve 39 and thus may be recycled through the heating element 6. Vapors remaining after fractionation may pass from fractionating tower 26 through line 40, valve 4I and condenser 42 and are collected as liquid and fixed gas in the receiver 43. The condensed liquid products may be withdrawn from Vreceiver 43 through line 44, controlled by valve 45, and the fixed gas may be withdrawn through line 46, controlled by valve 41. Vapors from fractionating tower 26 may, however, before they are `subsequently cooled and condensed, be diverted from line 40 through valve 48 and line 49 and may pass through the vapor treater 50. This vapor treater 50 may consist of a tower or tank partially filled with an absorbent filtering material through which the Vapors must pass in either an` upward or downward direction. In this'particular case the iiow of vapors shown is downward through the filtering material and the treated vapors are removed through line 5I and valve 52 and :are

finally condensed in condenser 42 and collected in receiver 43 as above described.

As an example of the possible operation of my process, which must not, however, be construed as limiting the invention to the conditions outlined, a 28 A. P. I. gravity gas oil may be charged to the heating element 6, having been first preheated in passing through coil 9. This preheated raw oil combined with reflux condensate from tower 26 may enter the heating element 6 at a temperature of approximately 650-700 F. and may attain in said heating element a nal temperature of 800 F. Heating element 6 and chamber I4 may both be maintained at a pressure of approximately 200 pounds per square inch. Vapors from chamber I 4 may be subjected to further decomposition at atemperature of, say 1050 F. and a pressure of 100 pounds per square inch. Liquid withdrawn from chamber I 4 may enter the residuum vaporizing or flash chamber 22 at approximately 650 F. and the pressure on the flash chamber in this case may be maintained at pounds per square inch, or thereabouts. A sufficient quantity of vapors from the vapor-phase heating element I1 may be introduced into the residual liquid in the flash chamber to increase the temperature of said liquid to approximately 750 F., which temperature, at the reduced pressure will cause extensive vaporization and some small additional decomposition of the residual oil. Valve 25 may be so controlled as to hold the pressure of the combined cracked and flashed vapors entering fractionating tower 26 at approximately 60 pounds per square inch. A suicient quantity of straight-run gasoline may be fed into the fractionating tower so that, with the aid of raw oil circulated through the coil 9, the temperature of vapor leaving the tower may be about 380 F. These vapors, having a boiling range and end-point comparable with nished gasoline and thus requiring no redistillation, may however, contain small portions of unstable products which are not conducive to av sweet, water white and stable condensed product without further treating either before or after condensation. In this case the vapors may be passed through the treater 50, where polymerization and separation of their unstable constitutents may occur, thereafter being condensed and collected.

An operation such as above outlined may yield as much as 57% of light material meeting motor process.

fuel specifications as to boiling range, color, stability and requiring only minor chemical treatment such as caustic and plumbite Washes to render it suitable for sale as a premium motor fuel. This product as collected in the receiver will, of course, contain the straight run gasoline used for cooling as well as the distillate produced in the 'I'his blended product, although heavier in gravity than the straight-run gasoline may show a pronounced increase in anti-knock value having, for example, a knock rating equivalent to a -30 blend of straight-run gasoline and benzol. While a higher gas loss than that ordinarily experienced in the so-called liquid-phase processes may be expected from the processdescribed the overall coke, gas and loss gure may be no higher due to the small amount of coke formed by the proper operation of my process.

The above examples are illustrative only and are not to be construed as limitations upon the process.

I claim as my invention:

A process for cracking hydrocarbon oil comprising passing the oil through an elongated heating coil wherein it is raised to cracking temperature, thence delivering the oil to a. separating chamber, separating the oil into liquid and vapors in said chamber, separately removing the liquid and vapors from said chamber, passing the liquid to a flashing still maintained at a substantially lower pressure than the pressure maintained in said separating chamber, passing the vapors removed from said separating chamber through a second elongated heating coil wherein said vapors are subjected to Vapor phase cracking conditions, separating the vapor phase cracked vapors issuing from said second heating coil into two portions, introducing one portion thereof into the bottom of said flash still to pass countercurrent to the liquid oil undergoing flash distillation therein, taking off vapors from the top of said flash still, and combining said vapors directly with the second portion of the vapors issuing from said second heating coil, passing the thus combined Vapors to a fractionating column, condensing therein fractions heavier than the desired distillation product as reflux condensate, and returning said reflux condensate together with charging oil to said rst heating coil.

JEAN DELATIRE SEGUY.

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