US2115794A - Conversion of hydrocarbon oils - Google Patents

Description

May 3, 1938 K. swAR'rwooD 2,115,794

CONVERSION OF' HYDROCARBON OILS Filed Aug. l0, 1936 Frac z o rra Patented May 3, 1938 UNITED STATES PATENT OFFICE CONVERSION OF HYDROCARBON OILS Application August 10, 1936, Serial No. 95,167

2 Claims.

This invention particularly refers to an improvedfprocem for the fractional distillation of hydrocarbon oils of relatively wide boiling range accompanied by the selective pyrolytic conversion of selected relatively low-boiling and higher boiling fractions thereof as well as intermediate liquid conversion products of the process. The invention contemplates the production of high yields of high antiknock gasoline ywith minor yields of either liquid residue or relatively dry coke and fixed gases.

One specific embodiment of the invention cornprises heating charging stock, comprising an oil which contains a substantial quantity of materials within the boiling range of gasoline, naphtha or the like and higher boiling fractions, to a suffciently high temperatuie to effect vaporization of selected low-boiling fractions thereof, including the gasoline, by means of heat recovered from Within the system as later described, subjecting the heated charging stock to fractional distillation, subjecting selected low-boiling fractions of the charging stock recovered from the distilling step to conditions of cracking temperature, substantial superatmospheric pressure and conversion time regulated to effect the production therefrom of high yields of high antiknock gasoline, introducing the resulting products into an enlarged chamber wherein separation of vapors and non-vaporous residue is accomplished, passing said vapors in indirect heat exchange with the charging stock whereby to heat the latter to the desired temperature, as previously described, removing selected higher boiling fractions of the charging stock from the distilling step and commingling the same with said vapors, returning non-vaporous components of the commingled materials directly to said enlarged chamber, subjecting vaporous components of the commingled materials to fractionation for the formation of reflux condensate, subjecting reiiux condensate formed by said fractionation of the vapors to independently controlled conversion conditions of cracking temperature and superatmospheric pressure, introducing the resulting heated products into said enlarged chamber, subjecting fractionated vapors of the desired end-boiling point to condensation and recovering and separating the resulting distillate and gas.

In case the charging stock contains desirable low-boiling fractions, such as materials of satisfactory antiknock value within the boiling range of gasoline, these may be recovered from the fractional distilling step of the process without subjecting the same to cracking, in which case somewhat higher boiling selective fractions of the charging stock, including anyvhigh-boiling gasoline fractions of unsatisfactory antiknock value, are separately recovered from the distilling Zone and subjected to the desired cracking or 5 reforming conditions.

On the other hand, when the charging stock does not contain any appreciable quantity of de sirable low-boiling fractions, such as gasoline of satisfactory antiknock value, its total selected low-boiling components, comprising any gasoline or gasoline fractions of the charging stock as well as, when desired, higher boiling distillates such as naphtha, kerosene, and the like, may be subjected to the desired cracking or reforming conditions separate from the selected high-boiling fractions of the charging stock.

A special feature of the invention is the advantageous manner in which the charging stock is subjected to fractional distillation by means of heat recovered from within the system, which is ordinarily Wasted in a conventional cracking operation. This is accomplished in two stages, the first of which comprises passing the charging stock in indirect heat exchange withl Ythe hot vaporous conversion products, prior to their fractionation for the formation of reflux condensate, while in the second stage the components of the charging stock which remain unvaporized in the distilling zone following the first heating of the charging stock are directly commingled with the hot vaporous conversion products, prior to their fractionation for the formation of lreflux condensate, whereby said remaining non-vaporous components of the charging stock are subjected to further vaporization. These two stages of heat exchange between the charging stock and the hot vaporous conversion products of the process may be accomplished in the same or in sepa rate zones and in case separate zones arey employed the charging stock may pass in indirect and in direct heat exchange with the vapors in any desired sequence.

The method and means provided for heating and eecting fractional distillation of the charging stock has a definite advantage in cooperation with the selective cracking steps of the process and provides an advantageous method and means of Y removing from the vaporous conversion products high-boiling components which are desirable for commingling with the non-vaporous components of the charging stock subjected to further treatment Within the system under less severe conditions than those employed for the reflux condensate vformed by subsequent fractionation of the remaining vaporous components of the charging stock fractions and vaporous conversion products.

The accompanying diagrammatic drawing illustrates one specific form of apparatus embodying the features of the invention and in which the operation of the process may be accomplished. The advantages and features of the invention will be more readily apparent with reference to the drawing and the following description thereof. Various alternative but non-equivalent methods of operation, not previously described, are also shown in the drawing and embodied in the following description.

Intermediate liquids recovered from within the system and supplied, as will be later described, to heating coil I, is subjected therein to the desired conversion temperature preferably at a substantial superatmospheric pressure. Heat for the cracking reaction is supplied to coil i by means of furnace 2. The heated products are discharged from coil I through line 3 and valve 4 into chamber 5.

Chamber 5 may function as a reaction zone wherein the heated products supplied thereto are subjected to appreciable continued cracking, in which case it is preferably operated at a superatmospheric pressure substantially the same or somewhat lower than that employed at the outlet from coil l. On the other hand, chamber 5 may function primarily as a zone wherein separation of vaporous and non-vaporous conversion products is accomplished and, by employing a substantially reduced pressure in this Zone relative to that employed in heating coil I, appreciable further vaporization of the liquids supplied to this zone is accomplished. Chamber 5 may be operated for the production of either liquid residue or substantially dry coke. For the production of liquid residue this zone is preferably operated at relatively low pressure although, when desired, relatively high superatmospheric pressure may be employed in chamber 5 and the liquid products therefrom supplied to a reduced pressure vaporizing zone for the recovery therefrom of desirable low-boiling components which may be supplied to heat exchanger I0 although, for the sake of simplicity, this equipment is not illustrated in the drawing. Coke may be produced in chamber 5 either at relatively low or at a substantial superatmospheric pressure, lowpressure operation normally being preferred. When liquid residue is produced in chamber 5 it may be withdrawn from the lower portion thereof through line Ii and valve 'I to cooling and storage or to a reduced pressure vaporizing chamber, not illustrated, or elsewhere, as desired. When coke is produced in chamber 5 it may be allowed to accumulate in this Zone and be removed therefrom in any suitable well known manner, not illustrated, after the chamber is substantially filled with coke or after its operation is completed for any other reason. The invention also contemplates the use of a multiplicity of coking chambers, although not illustrated, which may be simultaneously or alternately operated.

It is also within the scope of the invention to reduce the liquid products withdrawn from chamber 5 to substantially dry coke in any desired well known type of coking equipment, not illustrated, such as, for example, a separate heating coil and communicating coking chamber, an externally heated coking chamber or oven, a coking Zone to which a heat carrying medium, such as highly heated conversion products from within the system, are supplied, or the like and such coking equipment, when employed, may be operated in conjunction and in cooperative relation with the rest of the system, the vaporous products from the coking Zone preferably being supplied to heat exchanger I or to distilling and fractionating column 45.

Vaporous products are removed from the upper portion of chamber 5 and directed through line 8 and valve 9 to heat exchanger I0 wherein they are partially coo-led and subjected to partial condensation, as will be later more fully described, by indirect heat exchange with the charging stock for the process and by direct contact with high-boiling components of the charging stock.

The high-boiling components condensed from the vapors in heat exchanger I0 are withdrawn from the lower portion of this zone, together with non-vaporous components of the high-boiling fractions of the charging stock supplied to this Zone,l and the commingled high-boiling oils are directed through line II and valve I2 to pump I3 by means of which they are fed thro-ugh line I4 and may be returned, all or in part, through line I5 and valve I5 to chamber 5, wherein they commingle with the heated products supplied to this Zone from the two cracking` coils of the system and are subjected to further treatment therewith, or these high-boiling oils may be otherwise utilized, as will be later described, or may, when desired, be withdrawn, all or in part, from the system through line I'I and valve I8 to cooling and storage or elsewhere, as desired.

Vapors remaining uncondensed in heat exchanger ID, including the uncondensed compo-l nents of the vaporous products from chamber 5 and Vaporous components of the high-boiling fractions of the charging stock supplied to heat exchanger I0, are removed from the upper portion of this zone and directed through line I9 and valve 2E) to fractionation in fractionator 2|.

The components of the vapors supplied to fractionator 2I boiling above the range of the desired final light distillate product of this stage of the process are condensed in this zone as reflux condensate. The total reflux condensate removed from the vapors in fractionator 2I may be withdrawn from the lower portion of this zone through line 22 and valve 23 to pump 24 by means of which it is supplied through line 25 and. valve 26 to cracking in heating coil I. On the other hand, when desired, although not illustrated in the drawing, the reiiux condensate removed from the vapors in fractionator 2l may be separated into selected relatively low-boiling and high-boiling f fractions, in which case either the relatively lowboiling or the relatively high-boiling fractions may be subjected to cracking in heating coil I while the other fraction is removed from the system or subjected to independently controlled cracking conditions in a separate heating coil, not illustrated, or the high-boiling fractions may be supplied to heating coil I and the low-boiling fractions subjected to cracking in heating coil 51, together with selected low-boiling fractions of the charging stock which are supplied to this zone, as will be later described.

Fractionated vapors of the ydesired end-boiling point preferably comprising materials of good antiknock value within the boiling range of gasoline are withdrawn, together with gaseous prod.- ucts of the process, from the upper portion of fractionator 2| and directed through line 21 and valve 28 to condenser 29 wherein they are subjected to condensation and cooling. The resulting distillate and uncondensed gases pass through line and valve 3| to collection and separation in receiver 32. Uncondensed gases may be released from receiver 32 through line 33 and valve 34. Distillate may be withdrawn from receiver 32 through line 35 and valve 35 to storage or toany desired further treatment.

When desired, regulated quantities of the distillate collected in receiver 32 may be recirculated by well known means, not illustrated in the drawing, to the upper portion of fractionator 2l to serve as a refluxing and cooling medium in this zone for assisting fractionation of the vapors and to maintain the desired vapor outlet temperature therefrom.

Charging stock for the processywhich preferably comprises a hydrocarbon oil of relatively wide boiling range, is supplied from any suitable source through line 3l and valve 38 to pump 39 by means of which it is supplied through line lili and Valve 4l to heat exchanger l?. It passes in indirect heat exchange in this zone with the relatively hot vaporous products supplied thereto from chamber 5. A closed coil 52 is provided in the particular case here illustrated, in heat exchanger l5, through which coil the charging stock is passed. The resulting preheated charging stock, after recovering sufficient heat in heat exchanger l5 to effect vaporization of the desired low-boiling components thereof, is directed from ,coil 42 through line 43 and valve @d into distilling and fractionating column 55.

Preferably column 45 is operated at substantially atmospheric or relatively low superatmospheric pressure in order to assist vaporization of the preheated charging stock supplied thereto. The components of the charging stock which remain unvaporized'in column d5, as well as those which are condensed as reflux condensate therein, are withdrawn from the lower portion of the fractionator through line 45 and valve 5l to pump 4S by means cf which they are returned through line i9 and valve 55 to heat exchanger lil.

The unvaporized high-boiling components of the charging stock supplied from column 45 to heat exchanger l@ are directly commingled in the latter` zone with the relatively hot vaporous products therein, serving to assist cooling and partial condensation of the vapors and being thereby subjected to further vaporization. In the case here illustrated, baffles 5! are provided in heat exchanger il) for establishing and maintaining contact between the vapors in this Zone and high-boiling fractions of the charging stock supplied thereto. Any other suitable means of accomplishing this, although not illustrated, may be employed, when desired.

Selected low-boiling components of the charging stock are removed as fractionated vapors from the upper portion of column 45 and are directed through line 52 and valve 53 to condensation and cooling in condenser 5d. The resulting distillate and uncondensed gas passes through line 55 and valve 56 to collection and separation in receiver 5l. Uncondensecl gases may be released from the receiver through line 55 and valve 59. A regulated portion or all of the distillate collected in receiver 51 may, when desired, be withdrawn therefrom through line 55 and valve 5l to storage 01 to any desired further treatment. When desired, regulated quantities of the distillate collected in receiver 5l may be recirculated by well known means, not illustrated in the drawing, to the upper portion of fractionator 45 to serve as ,a refluxing and cooling medium-in this zone for assisting fractionation of the vapors vand to maintain the desired vapor outlet temperature therefrom.

In case the charging stock supplied to column 45 contains no gasoline, or in case the gasoline components of the charging stock are of unsatisfactory motor fuel characteristics, particularly with respect to their antiknock value, the selected low-boiling fractions of the charging stock collected in receiver 5l are preferably withdrawn, all or in part, therefrom through line 62 and Valve 63 to pump 64 by means of which they are supplied through line 65 and valve 66 tocracking or reforming in heating coil 61. This material, in addition to any unsatisfactory motor fuel components of the charging stock, may also include, when desired, somewhat higher boiling oils such as naphtha, kerosene, and the like.

In case the charging stock supplied to column 45 contains any substantial quantity of materials Within the boiling range of gasoline which are of satisfactory antiknock value, such materials are preferably recovered as the overhead distillate product from column 45 inreceiver 51, in the manner previously described. In such cases higher boiling components of the charging stock, comprising any unsatisfactory gasoline fractionsand also including, when desired, higher boiling oils such as naphtha, kerosene, and the like, aare separately recovered from column 45 and supplied therefrom to heating coil 61 for cracking or reforming. In the case here illustrated, provision is made for removing selected intermediate fractions of the charging stock from a suitable intermediate point from column 55 through line 68 and valve 59 to pump 64 by means of which they are supplied, in the manner previously described, to heating coil 61.

The relatively low-boiling oils supplied to heating coil 61 are subjected therein to relatively high cracking temperature preferably at substantial superatmospheric pressure by means of heat supplied from a furnace TB and in case motor fuel or motor fuel fractions are supplied to this zone the cracking conditions of temperature, pressure and time maintained therein are regulated to effect a substantial improvement in their antiknock characteristics without excessively altering their boiling range. Such reforming conditions may also be maintained within the range suitable for cracking any higher boiling oils supplied to this zone to effect the production therefrom of high yields ofgood quality motor fuel.

The highly heated products are discharged from heating coil 5l through line 'll and areintroduced, with or without prior` cooling, Ainto chamber 5 at any desired point or plurality `of points in this zone. Provision is made, in the case here illustrated, for passing products from heating coil 6l through Valve 'l2 in line 'll into line 3, wherein they commingle with the heated products from heating coil and are thence supplied to chamber 5. Provision is also made for introducing a regulated portion or all of the products from heating coil El into the lower portion of chamber 5 by means of line 'i3 and valve 14.

The highly heated products' discharged from heating coil 6l may, when desired, be cooled sufficiently to arrest or appreciably retard their further conversion, prior to their introduction into chamber 5. This may be accomplished by indirect heat exchange between the heated products and any suitable cooling medium in any Well known manner not illustrated, or by introducing a suitable cooling oilinto line 1|. Provision is 75- made, in the case here illustrated, for supplying a regulating portion or all of the high-boiling liquids withdrawn from heat exchanger I0 to line H by passing the same from line I4 either through line 14 and valve 'l5 into line 1| or they may first be passed, all or in part, through line 16, valve Tl and cooler 18, wherein they are cooled to any desired temperature, and thence introduced through line 'I9 and valve 80 into line 1l.

This heat exchange, although it serves to appreciably cool the highly heated products from heating coil El, may add suicient heat to the high-boiling oils from heat exchanger l0 to subject the same to relatively mild cracking.

Preferably, in case it is desired to produce coke as the residual product in chamber 5, the heated products from heating coil 61, or regulated quantities thereof, are introduced into the lower portion of chamber 5, as previously described, wherein they commingle with and supply additional heat to the materials undergoing coking in this zone. In such cases the products from heating coil S1 thus supplied to chamber 5 are preferably not cooled to a temperature below approximately 800 to 950 F. and may, when desired, be supplied to this Zone with little or no cooling and at a higher temperature ranging, for example, from 900 to 1050 F.

The preferred range of other operating conditions which may be employed to accomplish the desired results in an apparatus such as illustrated and above described are approximately as follows: 'I'he heating coil to which reflux condensate from the fractionator of the cracking stage is supplied may employ an outlet conversion temperature ranging, for example, from 900 to 1000D F., preferably with a superatrnospheric pressure at this point in the system of from 100 to 500 pounds, or more, per square inch. The other cracking or reforming coil to which selected lowboiling fractions of the charging stock are supplied preferably employs an outlet conversion temperature of from 925 to 1050 F. and a superr atmospheric pressure of from 200 to 1000 pounds or thereabouts, per square inch as measured at the outlet from this zone. The reaction or coking chamber to which heated products from the two cracking coils are supplied may employ any desired pressure ranging from substantially atmospheric up to substantially the same superatmospheric pressure as that maintained at the outlet from the heating coil utilizing the lowest pressure. When utilized as a reaction chamber the pressure employed in this zone is preferably within the range of 100 to 500 pounds, or thereabouts, per square inch. The succeeding separating fractionating, condensing and collecting portions of the cracking stage of the system preferably employ pressures ranging from substantially atmospheric up to 150 pounds, or thereabouts, per square inch superatmospheric pressure although they may employ higher pressures up to Substantially the same as that employed in the reaction or coking chamber. Substantially atmospheric or relatively low superatmospheric pressure up to 100 pounds, or thereabouts, per square inch is preferred in the distilling and fractionating stage of the system to which the heated charging stock is supplied.

As a specific example of the operation of the process, a charging stock which comprises a California crude or" about 28 A. P. I. gravity is passed in indirect heat exchange with hot vaporous products from the reaction chamber whereby it is heated sufficiently to vaporize and fractionate its low-boiling fractions boiling up to approximately 450 F. and comprising approximately 32-33% of the charging stock. The heated charging stock is introduced into a distilling and fractionating column operated at substantially atmospheric pressure Wherefrom said low-boiling fractions are recovered as the overhead distillate product, which material is supplied to a reforming coil and therein subjected to a cracking temperature of approximately 980 F. at a superatmospheric pressure of about 800 pounds per square inch as measured at the outlet from the reforming coil. The remaining higher boiling fractions of the charging stock are withdrawn from the distilling and fractionating coil and introduced into a vaporizing and separating zone wherein they are directly commingled With hot vaporous products from the reaction chamber whereby their low-boiling fractions amounting to approximately 35 per cent of the charging stock are vaporized. The components of the charging stock remaining unvaporized in this zone are returned to the reaction chamber, together with heavy components condensed from the vaporous conversion products, by their indirect heat exchange with the charging stock and by commingling with the bottoms from the distilling and fractionating column. These highboiling oils commingle in the reaction chamber with the heated products from both heating coils of the system and are subjected in this Zone to the cracking conditions maintained therein. The vaporized components of said high-boiling fractions of the charging stock and the commingled uncondensed components of the vaporous conversion products are subjected to fractionation at a superatmospheric pressure of approximately 50 pounds per square inch and the resulting reflux condensate is supplied to the other cracking coil of the system. The reflux condensate is subjected in this coil to an outlet conversion temperature of approximately 950 F. at a superatmospheric pressure of about 350 pounds per square inch as measured at the outlet from the heating coil and the heated products are introduced into the reaction chamber. The final motor fuel product of the process is recovered by condensation of the vaporous products from the last mentioned fractionating zone. The products from this operation comprise approximately 62 per cent of gasoline having an octane number by the motor method of approximately 70 and about 29 per cent of good quality liquid residue, the remainder being chargeable, principally, to uncondensable gas.

In an operation similar to that above described except that a longer time factor is employed in both heating coils, the succeeding chamber operated at a superatmospheric pressure of about 30 pounds per square inch which is substantially equalized in the succeeding portions of the system and the residual liquid reduced in this chamber to substantially dry coke, the yield of 70 octane gasoline is increased to approximately 68 per cent, based on the charging stock, the gas yield is somewhat increased and approximately 63 pounds of low volatile petroleum coke of good structural strength is recovered as the nal residual product.

I claim as my invention:

l. A hydrocarbon oil conversion process which comprises fractionating cracked vapors in a fractionating zone to condense heavier fractions thereof, independently fractionating charging oil for the process in a second fractionating zone t0 form a distillate cracking stock and residual charging oil, subjecting reiiux condensate from the first-named fractionating Zone and said distillate stock to independently controlled cracking conditions of temperature and pressure in separate heating coils and introducing the resultant products into a common separating chamber wherein vapors are separated from residue, removing the vapors from the chamber and separating high-boiling fractions thereof by passing the removed vapors in indirect heat exchange with the charging oil prior to introduction of the latter to said second zone and by direct contact of the removed vapors with said residual charging oil from the second Zone, returning such separated high-boiling fractions of the vapors to the chamber together with unvaporized portions of the charging oil from the contacting step, in-

characterized in that the vapors removed from 10 the separating chamber are ,simultaneously passed in indirect heat exchange with the fresh charging oil and in direct contact With said residual charging oil.

ImNNETI-I SWARTWOOD. 15

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