US1958959A - Treating hydrocarbon oils - Google Patents

Description

May 15, 1934. w. MfSTRATFORD TREATING HYDROCARBON OILS Filed Nov. 28, 1928 2 Sheets-Sheet l May 15, 1934. w. M. STRATFORD TREATING HYDROCARBON OILS Filed Nov. 28, 1928 2 Sheets-Sheet 2 J. R m w w W 8 om @553 xfi M W mN u #8 QEQQI 3 W a g m 5 0M o o 9 3E cu N 3&38 5,35%

Patented May 15, 1934 PATENT OFFICE 1,958,953 TREATING HYDROCARBON OILS-7' William M. Stratford, New York, N. Y., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application November 28, 1928, Serial No. 322,310

7 Claims.

This invention relates to the cracking of hydrocarbon oils for the production of lower boiling products such as gasoline or naphtha distillates.

My invention contemplates subjecting the origd inal charging stock to be treated to a primary cracking operation accompanied with removal of evolved vapors, the dephlegmation of these vapors to obtain the light distillate desired and to form also a higher boiling fraction and finally the treatin meat of this higher boiling fraction at higher temperatures and pressures than obtain in the primary cracking zone or the subjection of this fraction to a cracking operation which is not accompanied with the separate removal of vapor from the secondary cracking zone during the operation.

In one method of operation contemplated by the invention the evolved vapors from the primary cracking zone are subjected toa dephlegmating or fractionating action so as to form the light distillate desired and a higher boiling fraction containing constituents the critical temperatures of which are below the temperature of the primary cracking zone. There is a disadvantage in returning these constituents to the same cracking zone from which they have come due to the fact that their presence tends to' increase the pressure that it is required to carry in such cracking zone and, due to the volatility of these constituents under the conditions obtaining in the cracking zone, it is difficult to maintain these constituents within a zone of sufficient temperature for suflicient time to effect the desired degree of cracking.

' The fraction containing these constituents is therefore, instead of being returned to the original cracking zone, conducted to a secondary c'facking zone which may be maintained under conditions better suited for the conversion of these constituents. Thus the fraction may be conducted to a cracking zone maintained at higher 40 temperatures and pressures than obtain in the primary cracking zone. Furthermore, the invention contemplates that this fraction containing constituents the critical temperatures of which are below the temperatures obtaining in the primary cracking zone may be treated in a cracking zone without removal of vapor during the operation. In this way an original charging stock, comprising constituents from which a good yield of light distillate can be obtained in a cracking operation carried on with distillation under pressure during the operation, is treated in this way and the digestion without distillation or the separate removal of vapor during the operation is applied to the more refractory fraction that is obtained from the evolved vapors of the primary cracking operation.

In a preferred embodiment of the invention the original charging stock is heated to a cracking temperature and subjected to cracking accompanied with separate removal of vapor in a primary cracking zone, the evolved vapors are passed to a fractionating column from which an overhead gasoline or naphtha distillate is obtained and also a reflux condensate which is withdrawn from the tower and forced through a conduit of restricted cross section wherein the oil is heated to a higher temperature than obtains in the fractionating column and preferably to a higher temperature than is employed in the primary cracking zone. The oil thus heated is then discharged into an enlarged reaction chamber which is maintained at the desired cracking temperature and pressure for a sumcient period of time to effect the desired cracking. The reaction chamber is in the form of a closed converter or autoclave from which there is no separate removal of vapor and the liquid contents of the converter, including such commingled vapors as may be present, are

directed into the primary cracking and vaporizing zone for distilling oh the lower boiling products formed in the reaction chamber.

, In order to more fully disclose the invention reference will now be had to the accompanying drawings wherein Figure 1 is a diagrammatic sectional elevation of an apparatus constituting one example and a preferred embodiment of the invention.

Figure 2 is a diagrammatic view illustrating a modification of the invention.

Figure 3 is a partial sectional elevation showing another modificationof the invention.

The apparatus thus illustrated includes as elements of the primary cracking zone a charging pump 10, a heating coil 11 and a pressure still 12. The charging pump 10 is adapted to draw charging stock from a suitable source and introduce it through a charging line 13 to the -coil 11 which is positioned in a furnace 14. A transfer line 15 is provided for conducting the heated oil from the coil 11 to the still 12. A valve 16 is indicated in the transfer line so that if desired the pressure in the still 12 may be lower than that obtaining in the coil 11. It is to be understood, however, that suflicient pressure is maintained in the still 12 to insure that the desired cracking will take place therein and if desired the pressure in the still may be substantially the same as that in the coil 11. The still is either insulated to prevent loss of heat or is positioned in a furnace adapted to maintain the desired cracking temperature. In some 'cases a battery or plurality of stills may be used in lieu of the single still shown in the drawings.

The still is equipped with a residue or tar drawoff line 17 and with a vapor line 18 which communicates with a dephlegmator or fractionating column 19. A vapor line 20 conducts vapors from the fractionating column to a condenser coil 21 and a receiving drum 22 having a valved gas outlet line 23 and a valved condensate draw-off line 24 is provided for receiving the pressure distillate. The tower 19 may be a packed tower or a bubble tower or of any suitable design to effect the fractionation or rectification of the vapors evolved from the still 12. Part of the condensate from the receiver 22 may be pumped back to the top of the tower to serve as a cooling reflux therefor or the tower may be equipped with cooling coils or a separate reflux condenser or any other suitable means for cooling. If desired, the vapor line 18 may be equipped with a valve as illustrated so that the fractionation in the tower 19 may be carried on at a lower pressure thanthat of the still 12, or the valve may be omitted and the fractionation conducted under substantially the pressure of the still.

The line 25 is provided for conducting reflux condensate from the tower 1.9 to the hot oil pump 26 which operates to conduct the reflux condensate through a line 27 into a coil 28 positioned in a furnace 29, and a transfer line 30 is provided to conduct the oil thus heated into a reaction or digestion chamber 31. A line 32 is shown having a valve 33 for conducting oil from the reaction chamber 31 into the still 12.

' In practicing the invention the charging stock to the primary cracking zone may constitute any distillate or residuum adapted for treatment for conversion into lower boiling point products. The charge is preferably a virgin stock, that is, an oil which has not been subjected'to any material cracking operation and thus the charge may comprise a. gas oil distillate as obtained from the crude stills and which has not been subjected to an essential cracking operation. Although a cycle stock, that is, an oil which has been subjected to a prior cracking operation and which has not been converted into the boiling point product desired, may be introduced into the primary cracking zone, it is preferable to use as the charging stock to the primary cracking zone a virgin stock or mixtures of virgin and cycle stocks. Cycle stock may be admitted directlyto the secondary cracking zone by the charging line 34 and pump 35.

In carrying out the process with the apparatus thus illustrated the virgin gas oil or other charging stock that it is desired to treat is raised to the desired cracking temperature in the coil 11 and passed thence into the cracking and vaporizing chamber 12. The temperature of the oil as delivered to the transfer line 15 is ordinarily about 800 to 900 F., preferably about 850 to 875 F. A body of cracking and vaporizing oil is maintained in the still 12 under pressures of about 200 to 500 pounds pressure, preferably about 400 pounds pressure at temperatures of about 750 to 850 F., preferably approximating 825 F. Tar or residue is withdrawn from the still 12 either continuously or by shots as may be desired and the evolved vapors pass through the vapor line 18 to the fractionating column 19 wherein they are subjected to fractionation so 'as to form a vapor fraction which is removed through the line 20 and which is collected in the receiver 22 as a condensate constituting the gasoline or naphtha distillate desired. The reflux condensate which collects in the bottom of the tower 19 and which contains constituents the critical temperatures of which are below the cracking temperature maintained in the still 12 is forced by the hot oil pump 26 through the heating coil 28.

The reflux condensate which collects in the bottom of the tower 19 is at an elevated terriperature, usually at a temperature approximating 700 to 750 F. or higher and this hot oil is further heated in the coil 28, preferably to a higher temperature than the temperature maintained in the still 12. Thus the oil delivered to the transfer line 30 may approximate 875 to 1000 F. The heated oil is delivered by the transfer line 30 into the reaction chamber 31 wherein a body of oil is maintained, preferably at higher temperatures an pressures than obtain in the still 12. This reaction chamber or secondary cracking zone is ordinarily held at pressures ranging from 600 to 1000 pounds and at a temperature ordinarily only slightly below that maintained in the transfer line 30. In some cases, if desired, the reaction chamber 31 may be equipped with a line (not shown) adapted for drawing off a certain amount of tar or residue from the bottom in order to thus prevent any excessive deposition of carbon in the chamber but there is no distillation carried on in this chamber, that is, no separate removal of vapor as distinct from residual products effected and the contents of the chamber 31 that have been subjected to the cracking operation are directed into the line 32 and passed thence through the pressure reducing valve 33 into the still 12. Although .these products thus discharged from the reaction chamber or secondary cracking zone may be subjected to fur- 115 ther cracking in the primary cracking and vaporizing zone it may be stated that ordinarily the reaction chamber of the secondary cracking zone is held at higher temperatures and pressures than the primary cracking zone so that the discharge 120 of constituents from the secondary cracking zone into the first is primarily to accomplish distillation of the products thus discharged rather than to effect further cracking.

One method of operation contemplated by the 125 invention includes, as has been stated, the introduction of cycle stock or oil that has already been subjected to a cracking operation directly into the secondary cracking zone. In this method of operation a virgin stock or a mixture of virgin 130 and cycle stock may be introduced by the pump 10 to the primary cracking zone and a cycle stock introduced by the pump 35 to the secondary cracking zone, the reflux condensate obtained'from the dephlegmation of vapors from the primary cracking zone being also passed to the secondary cracking zone.

In one modification of the invention the evolved vapors from the primary cracking zone are fractionated into two cuts or fractions besides that of the gasoline or naphtha distillate, the lighter of these two cuts comprising essentially constituents the critical temperatures of which are below the temperature obtaining in the primary cracking zone and this cut is 'conducted to the H5 secondary cracking zone for cracking at higher temperatures and pressures and without separate removal of vapor during the operation, while the heavier of these two cuts is returned to the primary cracking zone. Thus in lieu of the single fractionating tower 19, shown in Figure 1, two towers may be used, as indicated in" Figure 2, the vapor line 18 communicating with the first tower 19a and a vapor line 36 extending from the tower 19a to the second tower 19b to which is connected the vapor line 20. The heavier condensate obtained in the first tower is withdrawn through the line 25a and pumped by means of a pump 38 back to the coil 11 for passage with the original charging stock into the still 12 and the intermediate fraction drawn from the bottom of the second tower and consisting essentially of constituents the critical temperatures of which are below the temperature in the primary cracking zone, is drawn oif through the line 25b to the pump 26 and forced into the heating coil 28 and thence into the reaction chamber 31.

In another modification of the invention, instead of passing cracked products from the reaction chamber 31 into the cracking still 12 these products are directed into a dephlegmator or fractionating tower which receives the vapors from the cracking still 12. Two fractionating towers, such as shown in Figure 2, may be provided in this method of operation, the vapors from the cracking still 12 passing through line 18, and the products from the reaction chamber 31 passing through line 32 and branch line 321;, to the lower part of the first fractionating tower 19a. The vapors from the tower 19a pass to the second tower 19b and the overhead vapor fraction taken off the tower'19b constitutes the gasoline or naphtha distillate desired while the reflux condensate or bottoms obtained in this tower constitute ,the charge to the secondary cracking zone including the heating coil 28 and reaction chamber 31. The residual oil obtained in the bottom of the tower 19a is preferably withdrawn from the system, as through a line 37. If desired, instead of having two towers a single tower may be employed, as indicated in Figure 3, the vapors from the cracking still 12 or primary cracking zone being delivered through the vapor line 18 into a tower 190 at a point above the point of entry of line 32a which delivers products from the reaction chamber 31 or secondary cracking zone. The charge to the secondary reaction zone may be drawn off through the line 25b from a pocket 38 in the tower 190 at a point above the point of entry of line 32a which introduces products from the secondary cracking zone.

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.

I claim:

1. In the conversion of higher boiling hydrocarbon oils into lower boiling oils, the process that comprises passing fresh clean charging oil through a heating zone of restricted cross section wherein it is raised to a cracking temperature under a pressure of at least 200 pounds per square inch, subjecting the resulting hot oil in a primary cracking zone to cracking temperatures at a superatmospheric pressure of at least 200 pounds per square inch to effect cracking and vaporization, subjecting evolved vapors to fractionation to form a vapor fraction of requisite boiling point for the light distillate desired and a higher boiling point condensate containing constituents the critical temperatures of which are below the cracking temperatures obtaining in the primary cracking zone, withdrawing this condensate from the fractionating zone, passing condensate .so withdrawn through a zone of re-- and upwards but without concomitant and sep-' arate removal of vapor to thereby effect cracking anddigestion, expanding the cracked products from said enlarged zone into the primary cracking zone for distillation and preventing residual products of cracking from entering said heating zone.

-2. In the conversion of higher boiling hydrocarbon oils intqlower boiling oils, the process that comprises passing the oil under superatmospheric' pressure through a zone of restricted cross section to thereby raise the oil to a cracking temperature, directing the heated oil into a distilling zone wherein a body of oil is maintained at cracking temperatures under a superatmospheric pressure of at least 200 pounds per square inch, passing evolved vapors from the distilling zone to a fractionating zone and subjecting the vapors therein to fractionation to thereby form avapor fraction of requisite boiling point for the light distillate desired and a higher boiling condensate containing constituents the critical temperatures of which are below the temperature maintained in the distilling zone, withdrawing condensate from the fractionating zone in a heated condition and passing it through a zone of restricted cross section to thereby raise the temperature of the oil to a higher temperature than that obtaining in said distilling zone, said higher temperature being from 875 F. to 1000 F., directing the oil thus heated into an enlarged digestion zone wherein a body of oil is maintained at a substancomitant and separate removal of vapor, ex-

panding the cracked products from said enlarged zone into said distilling zone for distillation and preventing residual products of cracking from drawn from said primary cracking zone and isolated from the process.

4. In the conversion of higher boiling hydrocarbon oils into lower boiling oils, the process that comprises passing fresh clean charging oil through a heating zone of restricted cross section wherein it is raised to a cracking temperature under superatmospheric pressure, maintaining a body of the resulting hotoil in a primary cracking zone at a temperature of not more than 900 and under a pressure of from 200 to 500 pounds per square inch to effect cracking and vaporization, subjecting evolved vapors to fractionation to form a vapor fraction of requisite boiling point for the light distillate desired and a higher boiling point condensate containing constituents the critical temperatures of which are below the cracking temperatures obtaining in the primary cracking zone, withdrawing this condensate from the fractionating zone, passing condensate so withdrawn through a zone of restricted cross section to thereby heat the oil to a cracking temperature higher than that obtaining in the primary cracking zone, said higher temperature being from 875 F. to 1000 F., directing the oil thus heated into an enlarged digestion zone and maintaining the oil therein at a substantially constant temperature higher than that obtaining in the primary cracking zone and under higher pressures of the order of 600 pounds and upwards but without concomitant and separate removal of vapor to thereby effect cracking and digestion, expanding the cracked products from said enlarged zone into the primary zone for distillation and preventing residual products of cracking from entering said heating zone.

5. In the conversion of higher boiling hydrocarbon oils into lower boiling oils, the process that comprises passing fresh clean charging oil through a heating zone of restricted crosssection wherein it is raised to a cracking temperature under superatrnospheric pressure, maintaining a body of the resulting hot oil in a primary cracking zone at a temperature of not more than 900 and under a pressure of from 200 to 500 pounds per square inch to efiect cracking and vaporization, subjecting evolved vapors to fractionation to form a vapor fraction of requisite boiling point for the light distillate desired and a higher boiling point condensate containing constituents the critical temperatures of which are below the cracking temperatures obtaining in the primary cracking zone, withdrawing this condensate from the fractionating zone, passing condensate so withdrawn through a zone of restricted cross section to thereby heat the oil to a cracking temperature higher than that obtaining in'the primary cracking zone, said higher temperature being from 875 F. to 1000 F., directing the oil thus heated into an enlarged digestion zone and maintaining the oil therein at a substantially constant temperature higher than that obtaining in the primary cracking zone, and under higher pressures of the order of 600 pounds and upwards but without concomitant and separate removal of vapor to thereby efiect cracking and digestion, fractionating combined cracked products derived from said body and from said condensate to form a final desired product and preventing residual products of cracking from enter ing said heating zone.

6. In the conversion of higher boiling hydrocarbon oils into lower boiling oils, the process that comprises subjecting oil in a primary cracking zone to cracking temperatures at superatmospheric pressure to efiect cracking and vaporization, subjecting oil in a secondary cracking zone to cracking at higher temperature and pressure than obtains in the primary cracking zone, passing vapors evolved in the primary cracking zone to a fractionating zone, directing products from the secondary cracking zone into said fractionating zone at a point below the point of entry of the vapors from the primary cracking zone, withdrawing a condensate from the fractionating zone at a point above that of the introduction of the products from the secondary cracking zone and conducting this condensate as charging stock to the secondary cracking zone.

7. In the conversion of higher boiling hydrocarbon oils into lower boiling oils, the process that comprises subjecting oil in a primary cracking zone to cracking temperatures at superatmospheric pressure to' effect cracking and vaporization, subjecting oil in a secondary cracking zone to cracking at higher temperature and pressure than obtains in the primary cracking zone, passing vapors evolved in the primary cracking zone to a fractionating zone, expanding products from the secondary cracking zone into said fractionating zone, subjecting the commingled products therein to fractionation to form a residual product comprising unvaporized constituents of the expanded products from the secondary cracking zone admixed with condensate formed in the fractionating zone, an intermediate condensate formed of vapors condensed in the fractionating zone and free from residual constitucuts of said expanded products from the secondary cracking zone and a lighter distillate of requisite boiling point for the final light distillate desired and directing said intermediate condensate as charging stock into the secondary cracking zone.

WILLIAM M. STRATFORD.

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