US2144826A - Conversion of hydrocarbon oils - Google Patents

Description

Jan. 24, 1939. c. H. ANGELL CONVERSION OF HYDROCARBON OILS Filed May 20, 1935 INVENTOR CHARLES H. ANGELL TTORNEY Patented Jan. 24, 1939 UNITEDg STATES PATENT OFFICE versal Oil Products Company, Chicago, Ill., a corporation of Delaware Application May 20,

2 Claims.

This invention particularly refers to an improved process ior the selective conversion of relatively low-boiling and relatively high-boiling hydrocarbon oils to produce substantial yields of gasoline therefrom.

The invention specifically provides an improved process wherein low-boiling products resulting from the relatively mild conversion of relatively high-boiling hydrocarbon oils are subjected to independently controlled more severe conversion conditions at a higher temperature in a separate cracking stage of the same system, the highboiling components of the intermediate liquid conversion products recoveredfrom the second cracking stage being returned to the rst cracking stage for further conversion while lower boiling components of the intermediate liquid conversion products from said separate cracking stage are returned for further conversion to the same stage wherein they are produced, fractionated vapors of the desired end-boiling point from the last conversion stage being subjected to condensation for the recovery of desirable low-boiling distillate such as motor fuel of high antiknock value.

The process of the invention may be operated for the treatment of any desired type of charging stock, ranging from light distillate, such as straight-run gasoline or other motor fuel or motor fuel fractions of inferior antiknock value, through the various fractions of crude petroleum down to heavy residual oils and specifically includes the use of charging stocks of relatively wide boiling range such as i crude petroleum, topped crude and the like. The charging stock is supplied to an intermediate point in the primary or relatively low-temperature cracking stage of the system wherein it is subjected'to vaporization by direct and intimate Contact with the hot vaporous conversion products of this stage. By this method of operation any high-boiling point components of the charging stock of a heavy residual nature are commingled with the residual conversion products recovered from the primary cracking stage while its lower boiling components are subjected to fractionation, together with the vaporous conversion products from this stage, for the formation of reflux condensate, which is returned to the heating coil of the primary cracking stage for further conversion, any low-boiling components of the charging stock corresponding in boiling characteristics to the fractionated vaporousV conversion products of this stage of the process being subjected to further conversion therewith.

One of the advantages of the invention resides in the elimination of relatively high-pressure chambers, such as the reaction chamber common to most modern cracking systems, since the selective conversion of relatively low-boiling and high- 1935, Serial No. 22,288

boiling oils provided by the invention permits confining practically the total conversion reactions to the heating coils of the system without the danger of excessive conversion and the consequent excessive production of coke and/or gas.

Another feature of the invention resides inthe provision for cooling the highly heated products from the Second or relatively high-temperature cracking stage of the system sufficiently to pre'- vent any substantial further conversion thereof, thereby controlling the time factor as well as the temperature and pressure conditions in this stage. This is accomplished by indirect heat exchange between the relatively low-boiling intermediate liquid .conversion products supplied to the heating coil of the second or relatively high-temperature cracking stage and the highly heated conversion products from this zone and this heat exchange serves the additional purpose of substantially vaporizing said relatively low-boiling intermediate liquid conversion products, prior to their introduction into the heating coil, thereby avoiding substantial mixed phase conditions in this zone which are particularly undesirable when relatively high conversion temperatures are employed.

In one embodiment, the invention comprises subjecting an oil of relatively high-boiling characteristics to relatively mild conversion conditions of elevated temperature and superatmospheric pressure in a heating coil, commingling the resulting heated products with hydrocarbon oil charging stock for the process, separating the resulting vaporous and liquid products, recovering the latter, subjecting the vapors to fractionation where- .by their relatively high-boiling components are condensed as reflux condensate, returning the reux condensate to said heating coil, subjecting the fractionated vapors to further conversion under independently controlled more severe conversion conditions in a separate heating coil, cooling the resulting heated products sufficiently to prevent any appreciable further conversion thereof, separating the resulting vaporous and liquid conversion products, recovering the latter, subjecting the vapors to fractionation whereby their insuiciently converted components are condensed as reflux condensate, subjecting fractionated vapors of the desired end-boiling point to condensation, recovering the resulting distillate, separating the reux condensate formed in the last mentioned fractionating stage into selected relatively low-boiling and high-boiling fractions, returning the latter to the rst mentioned heating coil for further conversion, passing the lowboiling fractions in indirect heat exchange with the heated products from said separate heating coil whereby to cool the latter and eifect substantial vaporization of said low-boiling fractions and then introducing the same into said separate heating coil for further conversion.

The accompanying diagrammatic drawing illustrates one specific form of apparatus in which the process of the invention may be accomplished. It will be understood, however, that the invention is not limited to the specic form of apparatus illustrated since various modifications thereof maybe employed without departing from the scope of the invention.

Referring to the drawing, oil of relatively high-boiling characteristics, which is supplied to heating coil I in the manner to be later more fully described, is subjected therein to the desired conversion temperature, preferably at a substantial superatmospheric pressure, by means of heat supplied from a furnace 2 of any suitable form and the heated products are discharged from the heating coil through line 3 and valve 4 into separating chamber 5.

Separating chamber 5, in the case here illustrated, comprises the lower portion of column 6, the upper portion of which comprises fractionator 1, the two portions being separated by a suitable partition of deck 3, although it is, of course, entirely within the scope of the invention to employ separate structures for the separating and fractionating Zones. Chamber 5 may be operated at any desired pressure ranging from substantially the same as that employed at the outlet from heating coil I down to substantially atmospheric pressure although the pressure employed in this Zone and in fractionator 1 is preferably sufficient to cause the flow of fractionated vapors from column 1 through heating coil 21 under the pressure conditions maintained in this heating coil without resorting to the use of a pump or compressor. However, the use of a pump or compressor for this purpose is entirely within the scope of the invention, although such means are not illustrated.

Hydrocarbon oil charging stock for the process, which, as previously mentioned, may comprise any desired type of oil, is supplied through line 9 and valve IB to pump II wherefrom it is fed through line I2 and may be directed, all or in part, through line I3 and valve I4 into chamber 5 and/or through line I5 and valve I6 into line 3. This method of supplying charging stock to the system serves to partially cool the hot conversion products with which the relatively cool charging stock is directly comminged either in line 3 or in chamber 5, or in both, thereby retarding or arresting further conversion of the heated products, and this heat exchange also serves to accomplish .appreciable vaporization of the charging stock in chamber 5. It will be understood, of course, that the charging stock may be preheated, when desired, by any suitable well known means, not illustrated, to any desired temperature below that required for its appreciable conversion, prior to being commingled with the heated products from heating coil I and, by controlling the pressure employed in chamber 5 relative to that at the outlet from the heating coil, as well as the quantity and temperature of the charging stock, conditions in chamber 5 may be controlled to secure the desired degree of conversion in this zone or to prevent any appreciable conversion therein as well as to secure the desired degree of Vaporization for the charging stock and the desired separation of vaporous and liquid products in this zone.

Any high-boiling components of the charging stock of a heavy residual nature which remain unvaporized in chamber 5 are commingled in this zone with the residual liquid components of the conversion products from heating coil I and the resulting residual liquid may be removed from the lower portion of chamber 5 through line I1 and valve I8 to cooling and storage or elsewhere, as desired, and, in case no appreciable reduction in pressure is employed in chamber 5 relative to that employed at the outlet from heating coil I, further vaporization or flash distillation of the residual liquids withdrawn from chamber 5 may be accomplished by supplying the same, by well known means not shown, to reduced pressure vaporizing chamber 34, wherein their non-vaporous components may commingle with the residual liquid products from the second conversion stage of the system.

Suitable baiiies or other rough fractionating means, indicated, for example, at I9, may be employed in the upper portion of chamber 5 to insure the removal of entrained heavy liquid particles from the vaporous products which pass from this zone through partition 8 to fractionation in fractionator 1, thus preventing the inclusion of heavy liquids of a high coke-forming nature in the reflux condensate formed in fractionator 1, which might cause excessive coke formation in the heating coil to which this material is supplied.

Fractionation of the vaporous products supplied to fractionator 1 serves to separate the same into selected relatively low-boiling and high-boiling fractions. The latter, which are condensed in this zone as reflux condensate, are withdrawn from the lower portion of fractionating zone 1 above partition or deck 8 through line 20 and valve 2I to pump 22 by means of which they are returned through line 23, valve 24 and line 53 to further conversion in heating coil I. The lower boiling fractions, preferably including the conversion products boiling within the range of motor fuel as well as any motor fuel components of the charging stock and also including, when desired, somewhat higher boiling materials such as, for example, naphtha, kerosene, kerosene distillate and the like, are removed as fractionated vapors from the upper portion of fractionator 1 and are directed through line 25 and valve 26 to heating coil 21 for further conversion.

In order to assist fractionation of the vaporous products in fractionator 1 and to control the relative boiling point characteristics of the lowboiling and high-boiling fractions separated in thisl zone a relatively cool oil, preferably of lowboiling characteristics, from any suitable source, may be supplied in regulated quantities to fractionator 1. This material may comprise, for example, regulated quantities of the relatively lowboiling reflux condensate withdrawn from fractionator 36 of the second cracking stage of the system and supplied, as will be later more fully described, preferably after being cooled to the desired degree, to fractionator 1, or, in case the charging stock is an oil of relatively low-boiling characteristics, containing no high-boiling fraction unsuitable for conversion in heating coil I, regulated quantities thereof may be supplied to fractionator 1 by well known means, not illustrated.

Heating coil 21 is located within a furnace 28 of any suitable form by means of which suflicient heat is imparted to the vaporous products supplied to this zone to subject the same to a relatively high conversion temperature under the desired pressure conditions, which may range from substantially atmospheric pressure to several hundred pounds per square inch superatmospheric pressure. Preferably, although heating coil 21 is illustrated in a conventional manner in the drawing, it is designed to permit the desired time factor so that the desired degree of conversion is accomplished substantially entirely within the heating coil. The highly heated products are discharged from heating coil 21. through line 29 and valve 30 and are directed through heat exchanger 3| and thence through line 32 and valve 33 into vaporizing and separating chamber 34. In case a substantial superatmospheric pressure is employed at the outlet from heating coil 21 substantial pressure reduction is preferably accomplished as the heated products pass through valve 30 in line 29 or valve 33 in line 32 in order to effect partial cooling thereof. In any case, however, cooling of the highly heated products in heat exchanger 3|, either alone or in conjunction with the reduction of pressure, is sufficient to prevent any substantial further conversion in chamber 34 so as to definitely control the time to which the vaporous products are subjected to conversion and to substantially limit such conversion to heating coil 21. The means of cooling the heated products from heating coil 21 in heat exchanger 3| will be later more fully described.

Separation of vaporous and liquid conversion products is accomplished in chamber 34 which, in the particular case here illustrated, comprises the lower portion of column 35, the upper portion of which comprises fractionator 3'6 and, as previously mentioned, the residual liquid from chamber 5 may be supplied, when desired, to chamber 34 for further vaporization, particularly in case chamber 34 is operated at a lower pressure than chamber 5. The non-vaporous liquid residue is Withdrawn from the lower portion of chamber 34 through line 31 and valve 38 to cooling and storage or elsewhere, as desired. The vaporous products pass from the upper portion of chambei 34 through partition or deck 39into fractionator 36 and, when desired, suitable fractionating means or baffles, not illustrated, may be employed in the upper portion of chamber 34 to serve the same purpose, previously described, as bailles I9 in chamber 5.

The vaporous products supplied to fractionator 36 boiling above the range of the desired final light distillate product of the process are condensed in this zone as reflux condensate and are separated into selected relatively low-boiling and high-boiling fractions, which are subjected to selected further conversion within the same system, as will be later more fully described. Fractionated vapors of the desired end-boiling point are withdrawn, together with uncondensable gas, from the upper portion of fractionator 36 and are directed through line 40 and valve 4| to condensation and cooling in condenser 42. The resulting distillate and gas passes through line 43 and valve 44 to collection and separation in receiver 45. Uncondensable gas may be released from the receiver through line 46 and valve 41 to storage or elsewhere, as desired. The distillate collected in receiver may be withdrawn therefrom through line 48 and valve 49 to storage or to any desired further treatment. When desired, regulated quantities of the distillate collected in receiver 45 may be recirculated by well known means, not shown in the drawing, to the upper portion of fractionator 36 to serve as a cooling and refluxing medium in this zone for assisting fractionation of the vapors and to maintain the desired vapor outlet temperature from the fractionator.

The relatively high-boiling fractions of the reflux condensate formed in fractionator 36 may be withdrawn from the lower portion of this zone above partition or deck 39 through line 50 and valve 5| to pump 52 by means of which this material is supplied through line 53 and valve 54 to heating coil for further conversion.

The selected relatively low-boiling fractions of the reflux condensate formed in fractionator 36 may be withdrawn from any suitable intermediate point or plurality of points in the fractionator and, in the case here illustrated, are directed through line 55 and valve 56 to pump 51 wherefrom this material is fed through line 58 and may be directed, all or in part, through line 59, line 60, valve 6|, heat exchanger 3|, line 62, and valve 63 back into line 59 and thence through line 25 to heating coil 21 for further conversion. The light reflux condensate fed through heat exchanger 3| is preferably heated suiciently to eifect substantial vaporization thereof and serves to cool the heated products from heating coil 21 to the desired degree. Regulated quantities of the lowboiling reflux condensate may, when desired, bypass heat exchanger 3| by means of valve 64 in line 59 in order to control the degree of cooling in heat exchanger 3|.

As previously mentioned, regulated portions of the relatively low-boiling reflux condensate from fractionato-r 36 may, when desired, be utilized as a cooling and fractionating medium in fractionator 1. This may be accomplished by passing regulated quantities of through valve in line 58 and through cooler '66, wherein it is cooled to the desired temperature and from which it is directed through line 61 and valve 68 into fractionator 1. A portion or all of the light reflux condensate supplied to fractionator 1 may, when desired, by-pass cooler 66 by means of line 69 and valve 10.

The preferred range of operating conditions which may be employed to accomplish the objects of the present invention in an apparatus such as illustrated and above described may be approximately as follows: The heating coil of the first cracking stage may employ an outlet conversion temperature ranging, for example, from 800 to 950 F., preferably with a superatmospheric pressure measured at the outlet from the heating coil of from to 500 pounds, or more, per square inch. The pressure employed in separating chamber may range from substantially the same as that employed at the outlet from the heating coil down to substantially `atmospheric pressure and this pressure may be substantially equalized in the succeeding fractionating stage of this portion of the system. The temperature employed in the heating coil of the second cracking stage may range, for example, from 950 to 1l00 F., preferably with a relatively low superatmospheric pressure of the order of pounds per square inch down to substantially atmospheric pressure at the outlet from this zone, although higher pressure up to 1000 pounds, or thereabouts, Der square inch may be employed, when desired. The heated products from-the heating coil of the second cracking stage are preferably cooled to a temperature of the order of 650 to 800 F., prior to their introduction into the succeeding vaporizing and separating chamber and this zone is preferably operated at a relatively low pressure of the order of 100 pounds, or

335 the light reiiux condensate thereabouts, per square inch, superatmospheric pressure, down to substantially atmospheric pressure. The pressure employed in the vaporizing and separating chamber of the second cracking stage may be substantially equalized or somewhat reduced in the succeeding fractionating, condensing and collecting portions of the system.r

The following is a specific example of one of the many possible operations of the process of the invention as it may be accomplished in an apparatus of the character illustrated and above described, utilizing as charging stock a mixed base California crude of about 35 A. P. I. gravity containing approximately 35 percent of 400 F. endpoint gasoline, which charging stock is supplied to the vaporizing and separating chamber of the first cracking stage. The components of the charging stock and reflux condensate from the fractionator of the rst cracking stage having a boiling range of approximately 550 to 750 F. are supplied to the heating coil of this stage of the system, together with reflux condensate from the fractionator of the second cracking stage of approximately the same boiling range, wherein they are heated to an outlet conversion temperature of approximately 940 F., at a superatmospheric pressure of about 300 pounds per square inch. This pressure is substantially equalized in the separating and fractionating portions of this stage of the system and residual liquid from the separating chamber is supplied to the Vaporizing and separating chamber of the second cracking stage. Fractionated vapors having an endboiling point of approximately 550 F., from the fractionator of the rst cracking stage are subjected, together with light reflux condensate'from the fractionator of the second cracking stage having a boiling range of approximately 350 to 550 F., to an outlet conversion temperature of approximately 1000o F. in the heating coil of the second cracking stage and the pressure in this Zone is substantially equalized with that in the fractionator of the rst cracking stage (approximately 300 pounds per square inch) The highly heated products from the last mentioned heating coil are cooled by indirect heat exchange with the light reflux condensate supplied to this zone and by pressure reduction, to a temperature of approximately '780 F., the pressure employed in the succeeding vaporizing and separating chamber being approximately 50 pounds per square inch. Residual liquid is recovered from the vaporizing and separating chamber of the second cracking stage and fractionated vapors having an end-boiling point of approximately 400 F. from the fractionator of this stage are subjected to condensation for the recovery of motor fuel. This operation will produce, per barrel of charging stock, approximately 65 percent of 400 F. endpoint motor fuel having an octane number of approximately 78 and about 12 percent of heavy residual liquid suitable for use as fuel, the remainder being chargeable, principally, to uncondensable gas.

I claim as my invention:

1. A process for the conversion of hydrocarbon oils to produce motor fuel therefrom, which comprises subjecting an oil of relatively high boiling point to conversion conditions of cracking temperature and superatmospheric pressure in a heating coil, commingling relatively cool hydrocarbon oil charging stock for the process with the cracked oil and separating the commingled materials into vapors and non-vaporous residue, subjecting vapors to fractionation for the removal therefrom of selected relatively high-boiling components, returning the latter to the heating coil for further conversion, subjecting the remaining fractionated vapors to independently controlled conditions of further conversion in a separate heating coil at a higher temperature than that employed in the rst mentioned heating coil, cooling the resulting heated products sufficiently to prevent any substantial further conversion thereof and separating the resulting partially cooled products into vapors and nonvaporous residue, subjecting the vapors to fractionation to form a relatively heavy reflux condensate and a lighter reux condensate, returning the heavy reflux condensate to the first mentioned heating coil for further conversion, passing the lighter reflux condensate in indirect heat exchange with the highly heated products from the last mentioned heating coil and then introducing the same into said separate heating coil, subjecting fractionated vapors of the desired endboiling point from the last mentioned fractionating stage to condensation and recovering the resulting distillate.

2. A process for the conversion of hydrocarbon oils to produce motor fuel therefrom, Which comprises subjecting an oil of relatively high boiling point to relatively mild conversion conditions of cracking temperature and superatmospheric pressure in a heating coil, introducing the cracked oil into a reduced pressure vaporizing and sepa- 'rating chamber, introducing relatively cool hydrocarbon oil charging stock for the process into said separating chamber wherein it commingles with the hot conversion products, serving to partially cool the same, and is thereby subjected to vaporization, separating the resulting commingled materials into vapors and non-vaporous residual liquid, recovering the latter, subjecting the vaporous material from the vaporizing chamber to fractionation whereby to remove therefrom selected relatively high-boiling components, returning the latter to the heating coil for further conversion, subjecting the remaining fractionated vapors to independently controlled conversion conditions in a separate heating coil at a higher temperature than that employed in the first mentioned heating coil, cooling the resulting heated products sufficiently to prevent their substantial further conversion, introducing the resulting partially cooled products into a separate vaporizing and separating chamber wherein vaporous and non-vaporous residual liquid products are separated, recovering the latter, subjecting the vapors to fractionation in a separate fractionating zone to form a relatively heavy reflux condensate and a lighter reflux condensate, returning the heavy reflux condensate to the rst mentioned heating coil for further conversion, passing the lighter reflux condensate in indirect heat exchange with the highly heated products from said separate heating coil whereby to effect said partial cooling of the hot conversion products and to subject the lighter reflux condensate to vaporization, then introducing said lighter reflux condensate into said separate heating coil, subjecting fractionated vapors of the desired end-boiling point from the last mentioned fractionating Zone to condensation and recovering the resulting distillate.

CHARLES H. ANGELL.

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