US2170333A - Conversion of hydrocarbon oils - Google Patents

Description

Aug. 22, 1939. B KRAMER 2,170,333

CONVERSION OF HYDROiARBON OILS Filed June 30, 1937 27. gewi? Fpacumbop Vqp orznrg.

(lwmzben Patented Aug. 22, 1939 UNITED STATES PATENTv OFFICE CONVERSION OF HYDROCARBON OILS Ill., a corporation of Delaware Application June 30, 1937, Serial No. 151,126

3 Claims.

This invention relates to processes for convertinghigher boiling hydrocarbon oils into lower boiling hydrocarbon oils and, more particularly, to a method and means of improvingr the thermal 5&4. .efliciency of modern cracking systems by a related and interdependent combination of heat exchange steps whereby what would otherwise be waste heat is transferred to various Zones of the systemwherein it may be advantageously utilized.

The invention is specifically directed to the general type of process known in the art as sel lective cracking and, more particularly, to a selectivel cracking system wherein reflux condensate-formed by fractionation of the vaporous conversion products is separated into selected relatively low-boiling and high-boiling fractions which are cracked in separate heating coils under independently controlled temperature and pressure conditions. v

In selective crackingsystems of the type above mentioned; it has been found advantageous to remove a substantial quantity of heat from the conversionv products'after they have undergone ythe desired degree of cracking, whereby to control the cracking time and prevent excessive continued conversion which would result in the formation of excessive quantities of coke and/or fixed gases to the detriment o-f loptimum yields of good quality gasoline and residual liquid. In the present invention this is accomplished Yby transferring excess heat from the hot conversion products to the cracking. stock being supplied to the light oil heating coil of the system. By this Vmethod of operation, I not only accomplish the desired cooling of the hot conversion products and control of the crackingtime but, in addition,

by thus preheating the light oil cracking stock,

I materially reduce the load imposed upon the light oil heating coil and furnace so as to conserve fuel and improve the thermal efficiency of the process and also increase the useful life of the high temperature crackingv equipment. As a further feature of the invention, which is cooperative with that above mentioned, I provide for preheating al1 or a portion of the fresh-oil charging stock for the process by passing the same in indirect or direct heat exchange, or both, with the vaporous conversion products'undergoing fractionation, whereby to improve the efficiency of the fractionating step and decrease the required size of the fractionating equipmentand further improve the thermal efficiency of the process by transferring excess: heat from vthe vaporous conversion products to the charging stock and thereby decreasing the heat which must be imparted thereto for cracking in the heating coil or coils of the system.

Thefpresent invention does not reside in any particular single feature of the process herein described and illustrated but rather in the cooperative andV interdependent combina-tion of heat'exchange steps whereby heat is transferred from certain' Zones of the system wherein it is not required or actually detrimental to other zones wherein it serves a useful and advantageous purpose.

One specic embodiment of the invention comprises heating an oil of relatively high-boiling characteristics to cracking temperature at superatmospheric pressure in a heating coil, simultaneously heating an oil of relatively low-boiling characteristics to an independently controlled higher cracking temperature at superatmospheric pressure in a separate heating coil, passing resulting heated products from both heating coils through substantially the entire length of an enlarged insulated" reaction chamber, transferring both vaporous and liquidv conversion products from said reaction chamber'to a reduced pressure Vapor'ming and separating chamber wherein said' liquid products are further vaporized, separating vapors and residual liquid conversion productsin'said Vaporizing chamber and vseparately removing the same therefrom, subjecting said vapors to fractionation for the formation of reflux condensate, subjecting fractionated vapors of the` desired end-boiling point to condensation, recovering the resulting distillate, and passing 'at` least a portion of the fresh hydrocarbon oil charging stock foi` the process in indirect vheat rexchange with the vapors undergoing saidy fractionation, separating said ref flux condensate into selected relatively low-boiling and high-boiling fractions, commingling the preheated charging stock with high-boiling fractions of the reiiux condensate and supplying the commingled"materialsv to the rst mentioned heating coil, passing at least a portion of vsaid selected low-boiling fractions of the reflux condensate first in indirect heat exchange with said vapors in the vaporizing and separating cham# ber, thencegin indirect heat exchange with the hot conversion products in said reaction lchamber at a point therein adjacent their point of removal from this Zone and supplyingv the thus preheated low-boiling reflux condensate to the second mentioned heating coil.

The above mentioned and further objects and advantages of this invention and the manner of attaining them will be explained more fully in conjunction with the following description of the accompanying diagrammatic drawing, which illustrates one specific form of apparatus in which a process of the invention may be conducted.

Referring to the drawing, charging oil for the process is supplied through line I and valve 2 to pump 3 whereby it may be fed through line 4 and valve 5 and coil 6, which is disposed within fractionator 22. The charging stock is preheated' in coil S by indirect heat exchange with the vapors undergoing fractionation in fractionator 22 and thence directed through line I and valve 8 into line 9, wherefrom it is supplied to heating coil l0. By this method a relatively cool charging oil is preheated before being supplied to the heating zone for conversion, and at the same time serves as a means of assisting cooling and fractionation of the vapors in fractionator 22. When desired a portion or all of the fresh charging oil may be supplied from line 4, through line 23 and valve 24 directly into the fractionator or preheated charging stock from coil 6 may be introduced into the fractionator from line 'I through line 25 and valve 26.

Heating coil lll is located in furnace Il of any suitable form by means of which the oil is heated to the desired cracking temperature, preferably at superatmospheric pressure, and the heated products are directed from the heating coil through line I2 and valve I3 into the upper portion of reaction chamber I4.

Chamber I4 is preferably insulated to conserve heat and preferably maintained at cracking temperature and superatmospheric pressure, whereby the heated products supplied thereto undergo further conversion in their descent through substantially the entire length of this zone, excessive cracking being prevented by partially cooling the products at `a point adjacent their point of removal from the reaction chamber. This controlled cooling is accomplished by passing the conversion products in indirect heat exchange with low-boiling reflux condensate from fractionator 22, which low-boiling reflux condensate is passed through coil 50, as will be later described.

Vaporous and liquid conversion products are withdrawn in commingled state from the lower portion of reaction chamber I4 and directed through line I 5 and valve I 6 to Vaporizing chamber Il. It is also within the scope of the invention to omit reaction chamber I4 from one or both cracking steps of the system, when desired, in which case the vaporous` and liquid conversion products from one or both of the heating coils i0 and 44 may be supplied directly therefrom to separating chamber Il, by well known means, not shown.

Vaporizing and separating chamber I1 is preferably operated at a substantially reduced pressure relative to that utilized in reaction chamber I4, when the reaction chamber is employed, and, in any case chamber I'I is preferably operated at lowerrpressure than the heating coils. Separation of the heavy conversion products, which remain unvaporized in chamber Il, from the vaporous conversion products is accomplished in chamber Il, The vapors are partially cooled and the desired separation of heavy materials therefrom is assisted by passing the same in indirect heat exchange in chamber Il with low-boiling reflux condensate from fractionator 22, said lowboiling reflux condensate being passed, as will be later described, through coil 4I in the upper portion of chamber I'I. When desired, any well known fractionating means such as perforated pans, bubble trays, packing or the like, not shown, may be provided in the upper portion of chamber I1 to assist in separation of the desired products therein. The residual liquid may be withdrawn from the lower portion of chamber I'I through line I 8 and valve I9 or, when desired, may be reduced to substantially dry coke therein by any well known means, not illustrated. The vaporous conversion products are directed from the upper portion of chamber II through line 20 and Valve 2| to fractionator 22.

The vaporous conversion products supplied to fractionator 22 are fractionated therein by any well known fractionating means, such as perforated pans, bubble trays, or the like, not shown, and the ascending vapors are cooled by indirect and/or direct heat exchange with charging stock supplied directly thereto and/or passed, as previously described, through coil 6. The heavier components of the vapors are thereby condensed as reflux condensate which is further treated within the system, as will be later described. Further coo-ling of the vapors to maintain the desired vapor outlet temperature from the fractionator may be accomplished, when required, by circulating any suitable cooling medium through coil 21, in the upper portion of the fractionator, or by the direct introduction of a suitable light cooling oil, by well known means, not shown.

The oils supplied to'fractionator 22 are separated by fractionation therein into a vaporous productV of the desired end-boiling point, a selected relatively low-boiling reflux condensate and a selected relatively high-boiling reflux condensate. The fractionated vapors are withdrawn from the upper'portion of fractionator 22 through line 58 and valve 5l' to condenser 58 wherefrom the resulting distillate and uncondensed gases pass through line 59 and'valve 6D tocollection and separation in receiver 6l. Distillate is withdrawn from receiver 6I through line 64 and valve 65 to storageor to any desired further treatment and the uncondensed gases are released from the receiver through line 62 and valve 63.

The relatively high-boiling reflux condensate formed in fractionator 22 is withdrawn from the lower portionk of this zone through line V3Ii and valve 3l to pump 32 whereby it is fed through line'33 and valve 34 into line 9 and thence to further cracking in heating coil I0 together with a portion or all of the preheated charging oil.

The relatively low-boiling reflux condensate formed infractionator 22 is withdrawn from a suitable line 35 and valve 36 to pump 3l whereby it may be fed all or in part through line 38, line 39, valve 40 into and through closed coil 4I, positioned in the upper portion of chamber I1, passing therefrom through line 42 and valve 43 into line 38, wherefrom it may be supplied to heating coil 44 through valve 55, valve 54 in line 38 being totally or partially closed.

Heating -coil 44 is located in furnace 45, of any suitable form, by means of which oil is heated to the desired conversion temperature preferably at superatmospheric pressure and passed therefrom through line 46 and valve 4l to reaction chamber I4 or, when desired, it may be supplied directly from coil 44 to vaporizing chamber I1 by any Vwell known means, not shown.

When desired, all ora portion of the highboiling reflux condensate Vfrom fractionator 22 into and through closed coil 50 positioned in the lower portion of reaction chamber I4, passing therefrom through line 5I and valve 56 into line 38 and thence to heating coil 44, valve 55 in line 38 being either totally or partially closed.

The heated conversion products entering reaction chamber I4 from heating coil I0 and heating coil 44 are cooled through indirect contact with the low-boiling reflux condensate introduced through coil 50, thereby preventing excessive continued cracking of these conversion products and substantially preventing the formation of coke therein as well as reducing the vformation of gas and improving the yield of the desired final products. The combined vaporous and liquid conversion products are withdrawn from reaction chamber I4 and supplied to chamber I'I as previously described, wherein the ascending vapors are further cooled and fractionated by their indirect contact with low-boiling reux condensate introduced through coil 4I. Vaporous products are supplied from chamber II to fractionator 22 wherein they undergo cooling and fractionation as previously described.

Line 52 and valve 53 are provided for use particularly in starting up the process when it is desired to fill the equipment with oil and at any time during an emergency in operation when it is necessary to supply oil direct to heating coil in order to avoid excessive temperatures therein.

rIernperature and pressure conditions in the heating coils and the various other portions of the equipment will vary depending upon the type of charging stock being processed and the desired results. The temperature employed in heating coil IB as measured at the outlet thereof, may vary, for example, from 825 to 975 F., or thereabouts, with any desired superatmospheric pressure ranging, for example, from 10D-500 pounds, or thereabouts, per square inch. The temperature employed in heating coil 44, as measured at the outlet thereof, may vary, for example, from 900-1050 F., or more, with any desired superatmospheric pressure which may range, for example, from 20G-800 pounds, or thereabouts, per square inch. The pressure utilized in the reaction chamber, when such a zone is employed, may be substantially equalized with that employed in the communicating heating coil utilizing the lowest pressure. The separating chamber and succeeding fractionating, condensing and collecting portions of the system are preferably operated at reduced pressure relative to that employed in the reaction chamber or in the heating coils and may range from 150 pounds, or thereabouts, per square inch, superatmospheric, do-wn to substantially atmospheric pressure.

As a specic example of one type of operation which may be conducted in accordance with the features of the present invention in an apparatus such as illustrated and above described; the charging oil for the system is a Mid-Continent topped crude of approximately 25 A. P. I. gravity and is supplied at a temperature of approximately 100 F. to coil 6 and preheated therein by indirect heat exchange with the vaporous conversion products undergoing fractionation, to approximately 250 F. It is then admixed with the relatively high-boiling reflux condensate which is withdrawn from the lower portion of fractionator 22 at a temperature of approximately 700 F. and the' commingled oils supplied to heating coil I8 at a temperature of approximately 575 F. wherein they are heated to a conversion temperature of approximately 925 F. atl a superatmospheric pressure of about 300 pounds per squareinch. A relatively low-boiling fraction of the reflux condensate is withdrawn from fractionator 22 at a temperature of approximately 500 F. and is heated in coil 4I, positioned in the upper portion of vaporizing chamber I'I to approximately 650 F. and further heated in coil 50, positioned in the lowerV portion of reaction chamber I4, to approximately 760 F. and is thence supplied to heating coil 44 wherein it is heated to a conversion temperature of approximately 975 F. at a superatmospheric pressure of about 400 pounds per square inch and supplied therefrom to reaction chamber I4. Reaction chamber I4 is maintained at a superatmospheric pressure of approximately 250l pounds per square inch, which pressure is reduced to approximately 50 pounds per square inch in the separating chamber and is substantially equalized in the succeeding fractionating, condensing and collecting portions of the system. This operation will produce per barrel of charging stock, approximately 55% of good antiknock gasoline and about 38% of good quality liquid residue, the remainder being chargeable principally to uncondensable gas.

I claim as my invention:

l. In a process for the cracking of hydrocarbon oils wherein an oil of relatively high-boiling characteristics is heated to cracking temperature at superatmospheric pressure in a heating coil, an oil of relatively low-boiling characteristics simultaneously heated to an independently controlled higher cracking temperature at superatmospheric pressure in a separate heating coil, resulting heated products from both heatingl coils passed through substantially the entire length of an enlarged insulated reaction chamber,

also maintained at superatmospheric pressure,v

wherein they are subjected to continued cracking, the resulting vaporous and liquid conversion products withdrawn from the reaction chamber and introduced into a reduced pressure vaporizing and separating chamber wherein vaporous and residual liquid conversion products are separated and wherefro-m they are separately removed, said vaporous. conversion products subjected to fractionation for the formation of relatively high-boiling and relatively low-boiling reflux ccndensates which are returned, respectively, tothe first mentioned and second mentioned heating coils for further cracking, frac:- tionated vapors of the desired end-boiling point subjected to condensation and the resulting distillate recovered, the improvement which comprises passing fresh charging oil for the process in indirect heat exchange with vaporous products undergoing said fractionation, commingling the thus preheated charging stock with said highboiling reflux condensate, supplying the commingled materials to the first mentioned heating coil and passing said low-boiling reflux condensate, prior to its introduction into the second mentioned heating coil, rst, in indirect heat exchange with the vaporous conversion products in said vaporizing chamber and then in indirect heat exchange with said vaporous and liquid conversion products prior to their introduction into said vaporizing and separating chamber.

2. In a process for the crackingof hydrocarbon oils wherein an oil of relatively high-boiling characteristics is heated to cracking temperature at superatmospheric pressure in a heating coil,

an oil of relatively low-boiling characteristics simultaneously heated to an independently controlled higher cracking temperature at superatmospheric pressure in a separate heating coil, resulting heated products from both heating coils passed through substantially the entire length of an enlarged insiLlated reaction chamber, also maintained at superatmospheric: pressure, wherein they are subjected to continued cracking, the resulting vaporous and liquid conversion products withdrawn from the reaction chamber and introduced into a reduced pressure vaporizing and separating chamber wherein vaporous andresidual liquid conversion products are separated and wherefrom they are separately removed', said vaporous conversion products subjected to fractionation for the formation of relatively high-boiling and relatively low-boiling reiiux condensates which are returned, respectively, to the first mentioned and second mentio-ned heating coils for further cracking, fractionated vapors of the desired end-boiling point subjected to condensation and the resulting distillate recovered, the improvement which comprises passing fresh charging oil for the process Y Y in indirect heat exchange with vaporous products undergoing said fractionation, commingling the thus preheated charging stock with said highboiling reux condensate, supplying the commingled materials to the first mentioned heating coil and passing said low-boiling reflux cori= densate, prior to its introduction into the second mentioned heating coil, first, in indirect heat exchange with the vaporous products in said vaporizing and separating chamber and then in indirect heat exchange with the hot conversion products in the reaction chamber at a point in this zone relatively close to that of their removal therefrom.

3. A conversion process. which comprises heating hydrocarbon oil to cracking temperature under pressure in a heating coil and passing resultant vaporous and liquid conversion products downwardly through a vertical reaction chamber maintained under cracking conditions of temperature and pressure, removing the vaporous and liquid conversion products as a mixture from the lower portion of the chamber and separating the same into vapors and residue in a reduced pressure separating chamber, passing hydrocarbon oil to be cracked in indirect heat exchange with the vapors in the upper portion of said separating chamber and then in indirect heat exchange with the Vaporous and liquid conversion products in the lower portion of said reaction chamber, and supplying the thus preheated oil to said heating coil.

BERNARD L. KRAMER.

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