US1965075A - Treating hydrocarbon oils - Google Patents

Description

July 3, 1934. J. w. GRAY TREATING- HYDROCARBON OILS Filed .June '7,l 1928v mmro@ lw/ g; @imn /f- Patented .July 3, 193A;

UNITE STATES PATENT OFFIC James W. Gray, Port Arthur, Tex., assigner to The Texas Company, New York, N. Y., a corporation of Delaware Application June 7, 1928, Serial No. 283,486

6 Claims.

This invention relates to the conversion of higher boiling hydrocarbons into lower boiling ones, and relates particularly to cracking processes wherein reflux condensate or backtrap formed in the process is cycled back to the cracking zone.

In cracking processes it is common for the reux condensate which is cycled back to the cracking zone to contain 10 or 15% of even l-Cl larger proportions of gasoline, and it is an object of the present invention to provide methods and means for carrying on a cracking operation in such a manner as to substantially remove the gasoline constituents from the reflux condensate yl` before its introduction into the cracking zone.

- By thus removing these lighter constituents from the reflux condensate which constitutes a part of the charge to the cracking zone, it is possible to reduce the pressure employed in the cracking 20 zone and furthermore affect an increase in the yield of gasoline distillate obtained.

In order to more fully disclose the invention, reference will now be had to the accompanying drawing which is a diagrammatic elevation par- 25' tially in section illustrating a specific embodiment of the invention.

In the example of the invention thus illustrated, a cracking system of the tube and tank or coil and drum type is shown, but it is to be under- 30l stood that the invention is not 'limited to this particular type of cracking system, and may as a matter of fact be employed in any cracking process in which reflux condensate is refluxed or introduced to the cracking Zone. In the type of apparatus thus illustrated a heating coil is shown mounted in a furnace l1 and there is a battery of cracking stills comprising stills 12 and 13 with a transfer line 14 for delivering the heated oil from the coil l0 to the stills. The stills 40 are shown interconnected by vapor equalizing Y lines 15 and liquid level lines 16 and mounted in a furnace or heating chamber 17. The stills are provided with tar or residue draw off lines 18 and with an exit vapor line 19.

The vapor line 19 extends to a dephlegmator 20 which is preferably in the form of a rectifying or fractionating tower such as a bubble tower constructed with bubble trays 21. In the upper part of the tower is shown a coil 22 into which fresh changing stock is introduced for the purpose of supplying a cooling reflux to the tower. As illustrated, a charging pump 23 is provided with a charging line 24 communicating with the coil 10, and branch lines 25u and 25h 55 are provided so that a portion or all of the charging stock may be passed through the coil 22. It is to be understood that if desired other cooling means in lieu of the coil 22 may be employed for furnishing a cooling reflux to the tower 20, thus, for example, the tower may be equipped with a 6.0 separate reflux condenser arranged to condense a portion of the vapor from the tower and vform a reflux condensate for refluxing to the top of the tower. A vapor line 26 is shown extending from the tower 20 to a condenser coil 27 and a receiving drum 28 having a gas outlet 29, and a distillate outlet line 30 is provided for withdrawing the distillate from the coil 27. The dephlegmator or fractionating tower 20 constitutes a primary dephlegmator or fractionating means for treating the evolved vapor from the cracking stills and is normally maintained under a relatively high pressure, preferably being under a pressure approximating that o f the cracking stills.

A secondary dephlegmator or fractionating tower 31 is provided for treating the reflux condensate collected inthe tower 20 at a lower pressure than that obtaining in the tower 20. The tower 31 may consist of any suitable type of rectifying or dephlegmating apparatus and is illustrated as of the bubble tower type, bubble trays 32 being indicated in the drawing. A line 33 is provided for conducting reflux condensate or backtrap from the tower 20 to the tower 31. A pressure reducing valve 34 is shown which is preferably arranged to be operated by suitable iloat mechanism actuated bythe liquid level in the bottom of the tower 20. The pipe 33 is shown communicating with the lower portion of the tower 31 but preferably enters the tower at a point several trays removed from the body of the liquid that collects in the bottom of the tow.- er. The pipe 33 is shown provided with a branch line 35 which extends to a coil 36 which is arf ranged to be either heated or cooled. The coil 36 has an outlet pipe 37 which extends to the tower 31, and thus a portion or all of the reflux condensate removed from the tower 20 may be cooled or heated to such extent as may be desired before its introduction to the tower 31. If desired; instead of reducing the pressure by means of the'valve 34, the pressure maybe reduced at a point beyond the heating or cooling coil 36, as by means of the valve indicated in the line 37. If necessary, a pump may be employed to insure the passage of the reflux condensate from the tower 20 through the coil 36 to the tower 31, but ordinarily the differential in pressure between the towers will be adequate to insure the proper passage of the oil. The bottom of the tower 31 may, if desired, be equipped with a steam coil or other heating means for heating the body of liquid in the bottom of the tower.

5 A line 38 is provided for removing the stripped `f the art.

reflux condensate from the tower 31 and conducting it toa high pressure hot oil pump 39 which operates to force the condensate through a line 40 and thence into the heating coil l0.

In some cases it is desirable to provide a separate chamber or tower arranged to receive the reflux condensate from the bottom of the tower 3l and subject it to a further stripping or fractionating action, and in such case the pump 39 is arranged to draw reiiux condensate from this chamber and a vapor line from this chamber may be connected to the tower 31 at some convenient point above the body of the reflux condensate collected in the bottom thereof. But ordinarily if the tower 31 is of ample volume it is unnecessary to have the additional stripping chamber.

The evolved vapors from the tower 31 are removed by a vapor line 41 to a condenser coil 42 and the condensate is collected in a receiver 43 provided with a gas outlet 44 and a liquid condensate outlet 45. The receiver 43 is also provided with an outlet pipe 46 which extends to a low pressure pump 47 having a discharge line 48 communicating with the upper end of the tower 31 so that distillate collected in the receiver 43 may be pumped to the top of the tower 31 to serve as a cooling medium therefor. An-

y other distillate outlet pipe 49 is shown extending to a high pressure pump 50 provided with a discharge line 51 extending to the tower 20 so that distillate from the receiver 43 may be conducted to the tower 20 to supply added cooling thereto. The pipe 5l is shown provided with several branch lines 52 so that the redux distillate may be admitted at diierent points in the tower.

In practicing the invention with the apparatus thus illustrated the heating coil 10 and cracking stills 12 and 13 are ordinarily maintained under a high super-atmospheric pressure, the exact pressure used varying of course with the particular charging stock employed and with other variable conditions as are well known in Generally speaking the stills 12 and 13 are held under several hundred pounds pressure and the fractionating tower 20 is preferably maintained at a pressure approximating that of the stills, in this way retaining the advantages of carrying on a primary separation or fractionation of the evolved vapors under high pressure as well as the advantage of effecting condensation of the overhead vapor from the tower 20 under relatively high pressure in the condenser 27.

In such a method of operation however the reux condensate collected in the bottom of the tower 20 almost of necessity, contains proportions of gasoline constituents, approximating 10% by volume or sometimes even greater amounts, and in the practice of my invention this reiiux condensate is delivered to the tower 31 maintained under a pressure reduced from that obtaining in the tower 20 so that this condensate may be thus subjected to fractionation or stripping under the reduced pressure to substantially free it of gasoline constituents. The liquid withdrawn from the high pressure fractionating tower is ordinarily at a high temperature, for example of the order of 700 F., and thus the contained heat in the liquid may be utilized to effect vaporization and thus enable fractionation in the low pressure tower 31. The stripped and fractionated reux condensate is drawn off from the secondary tower through the line 38 and forced by the pump 39 into the coil 10 wherein the reux condensate combined with the fresh charging stock introduced by the pump 23 is raised to a cracking temperature for delivery to the cracking stills.

The distillate obtained from the overhead vapor fraction taken oi from the secondary or low pressure tower 31 and collected in the receiver 43 may be removed from the system as a separate cut and the conditions in the tower 31 may be maintained so that this distillate may have substantially the end boiling point of the distillate collected in the receiver 28, or if desired the distillate collected in the receiver 43 may have a higher end point. However, if desired, distillate collected in the receiver 43 may be conducted to the high pressure tower 20 so as to thus subject the distillate received from the low pressure tower to the polymerizing or stabilizing action that may take place in the higher pressure tower. Consequently a desirable method of operation is to employ the low pressure pump 47 in delivering to the tower 31 such quantities of distillate from the receiver 43 as may be necessary to supply the required cooling for the tower 3l, and the remaining portion of the distillate instead of being drawn off as a separate cut through the line 45 is picked up by the high pressure pump 50 and discharged into the high pressure fractionating tower 20 so as to thus supply cooling to the tower 20, and also to bring this distillate into a high pressure zone so that it may thus be subjected to polymerization or stabilization, In this way a single cut of gasoline or light distillate of desired boiling point and color and which is furthermore relatively stable is produced and collected as a distillate in the receiver 28.

The pressure in the tower 3l may be reduced to approximately atmospheric pressure, but it is generally preferable to have some super-atmospheric pressure in the tower 31, since this pressure facilitates the delivery of distillate from the condenser coil 42, and so long as the pressure is not too great permits the proper stripping of the reiiux condensate in the tower 31. A pressure of approximately 25 pounds may be recommended for carrying on the fractionating or stripping operation in the tower 31, although higher pressures may be employed. The temperature in the bottom of the tower 31 is ordi- 130 narily about 500 F. or 600 F.

In one method of operation contemplated by the invention, the stripped or fractionated reflux condensate obtained from the tower 31, instead of being directed into the coil l0, is ad- 135 mitted to another cracking system in which the cracking operation is preferably carried on at pressures and temperatures higher than that obtaining in the cracking stills 12 and 13. In this way the stripped reux condensate obtained 140 from one cracking system operating under a given temperature and pressure is subjected to a second cracking operation carried on at higher pressures and temperatures. If desired, the reilux condensate obtained from the tower 31 instead of being charged to a separate cracking system may be passed through a separate heating coil maintained at a higher temperature than that obtaining in coil 10, after which the oil thus 150 heated is admitted to one or both of the cracking stills 12 and 13.

In a specific example of the invention, a temperature in the transfer line 14 of 845 F. was employed with a temperature of 790 F. in the still 12, and 780D F. in the still 13. The stills 12 and 1B and fractionating tower 20 were held at 305 lbs. pressure, and the pressure was dropped in the fractionating tower 31 to 40 lbs. The temperature in the bottom of the fractionating tower 20 was 740 F., and the temperature in the bottom of tower 3l was 590 F. Samples were withdrawn from the bottom of towers 20 and 31, and it was found that the amount of 400 end point material contained in the reflux condensate in the bottom of tower 20 was 12%, and the amount of 400 end point material contained in the reflux condensate in the bottom of tower 31 was 1.5%. It is of course to be understood that the conditions stated in this specii'ic run represent merely a typical instance of the invention, and that in the practice of the invention conditions may be varied within comparative wide limits.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

What I claim is:

1. In the conversion of higher boiling hydrocarbons into lower boilinU ones, the process that comprises subjecting hydrocarbon oil to cracking distillation Linder superatmospheric pressure, separately withdrawing from said cracking distillation operation unvaporized residual products, separately withdrawing evolved vapors from said cracking distillation operation and subjecting said evolved vapors to dephlegmation while still under said superatmospheric pressure to form a vapor fraction and a reflux condensate, forming a final condensate product from the vapor fraction, delivering said reflux condensate into an intermediate point in a fractionating zone maintained at reduced pressure, subjecting the reux condensate under the reduced pressure to rectication against a refluxing medium therein to form a light vapor fraction and a reflux condensate at the bottom of the Zone substantially free from constituents within the boiling range of said final condensate, conducting the latter reflux condensate to said cracking distillation operation, condensing said vapor fraction and conducting the resultant condensate to the pressure dephlegmator to be redistilled therein whereby said condensate is vaporized and the vapors thereof admix with the aforesaid Vapor fraction formed in said pressure dephlegmator.

2. In the conversion of higher boiling hydrocarbons into lower boiling ones, the process that comprises subjecting hydrocarbon oil to cracking distillation under superatmospheric pressure, subjecting evolved vapors to dephlegmation while still under superatmospheric pressure to form a vapor fraction and a reflux condensate, forming a final condensate from the vapor fraction, withdrawing said reflux condensate from the dephlegmator and dividing the condensate into two streams, one of which is passed directly to a low pressure fractionating tower, and the other stream of which is passed through a cooling coil and thence into said fractionating tower being introduced thereinto at a point above that at which the other stream is introduced, subjecting the liquids thus admitted into the low pressure tower to rectification therein iuider the reduced pressure to form a vapor fraction and a reflux condensate at the bottom of the tower substantially free from constituents within the boiling range of said final condensate and conducting the latter reiiux condensate to the said cracking distillation operation.

3. The method of converting hydrocarbon oils into lower boiling products which comprises heating such oils to a cracking temperature while maintaining them under a substantial superatmospheric pressure, separately withdrawing vaporous and non-vaporous products from said cracking operation while maintaining said vaporous products under superatmospheric pressure extending from the said cracking operation, subjecting said vapors to fractional condensation while maintaining them under said pressure to condense and thereby separate from said vapors undesired higher boiling constituents, withdrawing and condensing the fractionated vapors to form the desired low-boiling distillate product, separately withdrawing the said condensate formed in said fractional condensation operation and discharging it into a fractionating zone maintained under a relatively low-pressure whereby a substantial portion of said condensate including light constituents thereof desired in the final low-boiling distillate product is vaporized, subjecting the latter vapors to fractionation against a reiiuxing medium in said lowpressure fractionating zone to separate as a vaporous cut substantially only the said constituents thereof desired in the low-boiling distillate product, withdrawing and condensing the said desired fractionated vaporous out and introducing the resulting condensate into the said higher pressure fractional condensation operation whereby said condensate is redistilled therein and the vapors thereof admix with the aforementioned fractionated vapors withdrawn therefrom and condensed to form the desired distillate product.

4. The method of converting hydrocarbon oils into lower boiling products which comprises heating such oils to a cracking temperature while maintaining them under a substantial superatmospheric pressure, separately withdrawing vaporous and non-vaporous products from said cracking operation while maintaining said vaporous products under super-atmospheric pressure extending from the said cracking operation, subjecting said vapors to fractional condensation while maintaining them under said pressure to condense and thereby separate from said vapors undesired higher boiling constituents, withdrawing and condensing the fractionated vapors to form the desired low boiling distillate product, separately withdrawing the said condensate formed in said fractional condensation operation and discharging it into a fractionating zone maintained under a relatively low pressure whereby a substantial portion of said condensate including light constituents thereof desired in the nal low boiling distillate product is vaporized, subjecting the latter vapors to fractionation against a refluxing medium in said low pressure fractionating zone to separate as a vaporous cut substantially only the said constituents thereof desired in the low boiling distillate product, and withdrawing and condensing the said desired fractionated vapors.

5. The method of converting hydrocarbon oils into lower boiling products which comprises heating such oils to a cracking temperature while maintaining them under a substantial superatmospheric pressure, separately withdrawing vaporous and non-vaporous products from said cracking operation while maintaining said vaporous products under super-atmospheric pressure extending from the said cracking operation, subjecting said vapors to fractional condensation While maintaining them under said pressure to condense and thereby separate from said vapors undesired higher boiling constituents, withdrawing and condensing the fractionated vapors to form the desired low boiling distillate product, separately withdrawing the said condensate formed in said fractional condensation operation and discharging it into a fractionating Zone maintained under a relatively low pressure whereby a substantial portion of said condensate including light constituents thereof desired in the final low boiling distillate product is vaporized, subjecting the latter vapors to fractionation against a refluxing medium in said low pressure fractionating Zone to separate as a vaporous cut substantially only the said constituents thereof desired in the low boiling distillate product, withdrawing and condensing the said desired fractionated vapors, and withdrawing reux condensate fromthe low pressure fractionating zone and passing the same to the rst mentioned heating zone for further cracking.

6. The method of converting hydrocarbon oils into lower boiling products which comprises heating such oils to a cracking temperature while maintaining them under a substantial superatmospheric pressure, separately withdrawing vaporous and non-Vaporous products from said cracking operation while maintaining said vaporous products under super-atmospheric pressure extending from the said cracking operation, subjecting said vapors to fractional condensation while maintaining them under said pressure to condense and thereby separate from said vapors undesired higher boiling constituents, withdrawing and condensing the fractionated vapors to form the desired low boiling distillate product, separately withdrawing condensate formed in said fractional condensation operation and discharging it into a fractionating zone maintained under a relatively low pressure whereby a substantial portion of said condensate including light constituents thereof desired in the iinal low boiling distillate product is vaporized, subjecting the latter vapors to fractionation against a refluxing medium in said low pressure fractionating Zone to separate as a vaporous cut substantially only the said constituents thereof desired in the low boiling distillate product, and withdrawing and condensing the said desired fractionated vapors.

JAMES W. GRAY.

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