US2130363A - Conversion of hydrocarbon oils - Google Patents

Description

Sept. 20, 1938. E. F. NELSON 2,339,363

CONVERSION OF HYDROCARBON OILS Original Filed Sept. 2, 1933 FRACTIONATOR\ VAPORIZING CHAMBER SEPARATING CHAMBER QONDEN SER 3 V J FURNACE |s l Patented Sept. 20, 1938 UNITED SATES ATENT OFFlCE CONVERSION OF HYDROC'ARBON OILS Application September 2, 1933, Serial No. 687,948 Renewed September 4, 1936 12 Claims.

This invention relates to improvements in the type of cracking process and apparatus wherein liquid conversion products of the process are subjected to vaporization at substantially reduced pressure relative to that at which they are formed and the vaporous conversion products subjected to fractionation for the formation of reflux condensate, comprising their insufficiently converted components, which is returned to a heating coil of the system for further conversion; said improvements comp-rising a novel and effective method and means for preventing the entrainment of heavy residual material in the reflux condensate in order to prevent excessive coke formation in the heating coil.

In modern cracking processes of the type wherein both vaporous and liquid conversion products of the process are withdrawn from a high pressure reaction zone and introduced at substantially reduced pressure into a vaporizing chamber wherein substantial further vaporization of the liquid is accomplished, coking difficulties are often experienced in the heating coil, due to the entrainment of heavy liquid particles in the vapors passing from the vaporizing chamber to the fractionator of the system; the heavy, high coke-forming particles being returned from the fractionator, together with reflux condensate from this zone, to the heating coil.

Fractionating means have heretofore been employed in the upper portion of the vaporizing chamber for the purpose of removing the entrained high coke-forming material from the vapors, prior to their introduction into the fractionator wherein the reflux condensate is formed, but due to the large volume of vapors, relative to the entrained material, rough fractionating means such as baiiles and the like have not proven entirely successful for this purpose. On the other hand, when more efiicientfractionating means such as bubble trays, packing or the like are employed the quantity of heavy residual material present in the vapors is usually sufiicient to cause coking and stoppage or restriction in the fractionating means before the operation of the processhas been completed.

The present invention overcomes the difficulties heretofore encountered in processes of the general character above described by effecting separation of the vaporous and residual liquid conversion products, and, when desired, further vaporization of the liquid, in successive stages. The first stage of separation is preferably accomplished at a sufficiently high pressure to preclude extensive further vaporization of the liquid, which further vaporization is accomplished in a succeeding stage in the presence of a controlled quantity of vapors in order to reduce entrainment.

This method also permits the use of more eflicient fractionating means in the vaporizing chamber and the cumulative result is the substantial elimination of entrained high-boiling liquids in the vaporous products supplied to the fractionator and the formation in the fractionator and return to the heating coil of a clean reflux condensate which is substantially free of high coke-forming residual liquid components. This permits the use of higher conversion temperatures in the heating coil without excessive coke formation in this zone, the ultimate result of which is longer operating periods for the process and the producton of motor fuel of improved anti-knock value.

While the volume of residual liquid produced in a process employing the features of the present invention is usually not appreciably increased its quality is ordinarily improved somewhat, due to the inclusion in the residue of materials which, while relatively heavy with respect to the vapors, are relatively light with respect to the main body of residue. In operations wherein this material is not included in the residue but is returned with the reflux to the heating coil its excessive further conversion in this zone serves to further depreciate the quality of the residual product of the process.

One specific embodiment of the present invention may comprise subjecting a hydrocarbon oil to conversion temperature at superatmospheric pressure in a heating coil and communicating reaction chamber, withdrawing both vaporous and liquid conversion products from the reaction chamber in commingled state and introducing the same into a separating chamber, preferably maintained at a somewhat reduced superatmospheric pressure relative to that employed in the reaction chamber, quickly withdrawing the non-vaporous liquid products, together with a regulated portion of the vapors from the separating chamber and introducing the same into a vaporizing chamber, preferably maintained at substantially reduced pressure relative to that employed in the separating chamber, wherein further vaporization of the liquid conversion products and final separation of the vapors and non-vaporous residue is accomplished, separately withdrawing the remaining vapors from said separating chamber and introducing the same into said vaporizing chamher, subjecting the vapors to a limited degree of fractionation in the vaporizing chamber and then introducing them into a fractionator wherein their further fractionation for the formation of reflux condensate is accomplished, returning the reflux condensate, which comprises the insuificiently converted intermediate products of the process, to the heating coil for further conversion, subjecting fractionated vapors of the desired end boiling point to condensation and collecting the resulting products.

The accompanying diagrammatic drawing illustrates one specific form of apparatus embodying the features of the present invention and a more detailed description of the operation of the process, as it may be practiced in the apparatus illustrated, is included in the following description of the drawing.

Raw oil charging stock for the process is supplied through line i and valve 2 to pump 3 by means of which it is fed through line 4 and may pass either through line 5 and valve 6 into fractionatcr l or through line 8, valve 9 and line Iii direct to heating coil i l, or regulated portions of the raw oil may be supplied both to fractionator 7 and direct to heating coil ii, in the manner described. That portion, if any, of the charging stock supplied to the fractionator is preheated by direct contact with the vaporous products undergoing fractionation in this zone, serving to assist their fractionation and being collected in the lower portion of the fractionator, together with the reflux condensate formed in this zone. The reflux condensate or reflux condensate and preheated raw oil, as the case may be, is withdrawn from the lower portion of fractionator through line I2 and valve !3 to pump i by means of which it is fed through line it] and valve IE to conversion in heating coil l I. It will be understood that the raw oil charging stock may, when desired, be preheated in any other well known manner not illustrated in the drawing, prior to its introduction into the heating coil such as, for example, by indirect contact with hot vaporous and/or liquid products of the process.

Heating coil H is disposed in a furnace l6, of any suitable form, by means of which the required heat is supplied to the oil passing through the heating coil to bring it to the desired conversion temperature, preferably at a substantial superatmospheric pressure and the heated oil is discharged through line IT and valve l8 into reaction chamber l9.

Chamber I9 is also preferably maintained at a substantial superatmospheric pressure and, although not illustrated in the drawing, this zone is preferably well insulated in any well known manner in order to prevent the excessive loss of heat by radiation so that conversion of the heated products from the heating coil and, more particularly, their vaporous components is continued for a predetermined time in chamber 59. In the case here illustrated, both vaporous and liquid conversion products are' withdrawn from the lower portion of chamber IS in commingled state through line 26 and valve 2i and are discharged therefrom into separating chamber 22.

Chamber 22 is preferably operated at a somewhat reduced superatmospheric pressure relative to that employed in chamber l9 in order to assist separation of the vaporous and liquid conversion products in this zone. No appreciable volume of liquid is allowed to remain within chamber 22 but is quickly withdrawn, preferably together with a regulated portion of the vapors,

from the lower portion of chamber 22 through line 23 and valve 24 into vaporizing chamber 25. A major portion, at least, of the vapors separated from the liquid conversion products in chamber 22 pass from the upper portion of this zone through line 26 and valve 21 into vaporizing chamber 25. Control over the proportion of vaporous products withdrawn from chamber 22 through lines 23 and 26 is accomplished, in the case here illustrated, by the manipulation of valves Hand 2? in the respective lines. If de sired, substantially all of the vaporous products separated from the liquid in chamber 22 may be withdrawn from this zone through line 26 and Valve 22 to chamber 25 although it will, in most cases, be desirable to allow a minor portion of the vapors to commingle with the liquid withdrawn from the lower portion of chamber 22 as this insures rapid removal of the liquid from the chamber without allowing any appreciable quantity of such material to accumulate in this zone and the vapors supplied to chamber 25 together with the liquid conversion products from chamber 22 serve to assist further vaporization of the liquid in the vaporizing chamber. The degree of such further vaporization of the liquid conversion products in chamber 25 varies in proportion to the volume of vapors supplied therewith to this zone and by control of the volume of vapors separately withdrawn from chamber 22 a means of controlling vaporization of the liquid conversion products in chamber 25 is afforded. Other factors, such as the pressure employed in chamber 25, of course, also affect the degree of vaporization in this zone, but control of the vapors supplied thereto offers an additional means of regulating the final degree of vaporization of the residue.

Chamber 25 is preferably operated at a substantially reduced pressure relative to that employed in chamber 22 although when a substantial reduction in pressure is employed between chambers l9 and 22 substantially the same pressure may be employed, if desired, in chambers 22 and 25. Fractionating means are preferably employed in the upper portion of chamber 25 and in the case here illustrated rough fractionating means, such as bafiles, indicated at 28, comprise the lowermost fractionating means in this zone and are followed by more eflicient fractionating means, such as bubble trays, for example, indicated at 29. In the case here illustrated, the vaporous products separated from chamber 22 enter chamber 25 at a point immediately below the bubble trays 29 while the liquid products enter chamber 25 beneath baiiles 28. It is to be understood that, if desired, the vaporous products from chamber 22 may also enter the lower portion of chamber 25 but preferably direct commingling of the two streams withdrawn from chamber 22 in the lower portion of chamber 25 is avoided. It will be understood that fractionating means of any suitable type may be employed in the upper portion of chamber 22, although they are not shown in the drawing.

A suitable cooling and refluxing medium such as, for example, a regulated portion of the raw oil charging stock, a regulated portion of the reflux condensate or the combined feed (reflux condensate and raw oil), a regulated portion of the residual oil withdrawn from chamber 25 suitable oil from an external source or a mixture of any such materials or selected fractions thereof may be supplied to the upper portion of chamber 25 at any desired point, for example, through line 30 and valve 3!.

Non-vaporous residue comprising the residual liquid product of the process may be withdrawn from the lower portion of chamber 25 through line 32 and valve 33 to cooling and storage or to any desired further treatment. Vaporous products substantially freed of entrained heavy liquids are withdrawn from the upper portion of chamber 25 and pass through line 36 and valve 35 to fractionation in fractionator '3.

Components of the vaporous products supplied to fractionator I boiling above the end-boiling point of the desired final light distillate product of the process are condensed in this zone as reflux condensate and returned, as already described, to heating coil I I for further conversion. Fractionated vapors of the desired end-boiling point pass, together with uncondensable gas produced by the process, from the upper portion of fractionator I through line 36 and valve 31 to be subjected to condensation and cooling in condenser 38. The resulting distillate and gas passes through line 39 and valve M! to collection and separation in receiver 4!. Unco-ndensable gas may be released from the receiver through line 42 and valve 43. The distillate may be withdrawn from this zone through line 44 and valve 45 to storage or to any desired further treatment. If desired, a regulated portion of the distillate collected in receiver 4! may be recirculated, by Well known means (not shown) to the upper portion of fractionator l as a cooling and refluxing medium to assist fractionation of the vapors and to maintain the desired vapor outlet temperature from the fractionator.

A wide range of operating conditions may be successfully employed in a process such as illustrated and above described, depending primarily upon the type of charging stock employed and the desired results. The range of operating conditions applicable to most charging stocksmay be approximately as follows: A temperature of from 850 to 1000 F. may be employed at the outlet from the heating coil, preferably with a superatmospheric pressure measured at this point in the system of from 200 to 800 pounds, or thereabouts, per square inch. Substantially the same pressure is preferred in the reaction chamber although a somewhat reduced pressure relative to that employed in the heating coil may be utilized in the reaction chamber, if desired. The separating chamber may be operated at substantially the same pressure as that employed in the reaction chamber although ordinarily a somewhat reduced superatmospheric pressure is preferred in this zone. Ordinarily a minimum pressure of from to pounds, or thereabouts, per square inch is preferred in the separating chamber. A substantially reduced pressure relative to that employed in the reaction chamber,

which may be either substantially the same or somewhat reduced relative to the pressure employed in theseparating chamber, ispreferred in the vaporizing chamber. The range of pressures preferred in this zone is from pounds, or thereabouts, per square inch to substantially atmospheric pressure. The pressures employed in the fractionating, condensing and collecting portions of the system may be substantially equalized with the pressure employed in the vaporizing chamber or may be somewhat reduced relative thereto.

It will be understood that the invention is not limited to use in the particular form of apparatus ber.

superatmospheric pressure of approximately 50.

illustrated and above described nor to the exact process described. The features of the invention may be ,utilized to advantage in any type of cracking system of the general character wherein liquid conversion products produced at superatmospheric pressure are subjected to further vaporization at reduced pressure and wherein it is desirable, for any reason, to maintain a clean reflux condensate, substantially free of high boiling residual material of a pitchy, asphaltic or high coke-forming nature.

As an example of one of the many possible modifications of the system illustrated and described which are within the scope of the present invention, the total reflux condensate or a se-,;-

lected low-boiling fraction of the reflux condensate may be supplied for further conversion to a'heating coil separate from that to which the raw oil charging stock is supplied, the highly heated products from both heating coils being;v introduced, for example, into the reaction chamber.

It is also specifically within the scope of the present invention, although not illustrated in the drawing, to supply a relatively heavy oil, such.

as all or a regulated portion of the raw oil charging stock for the process, high-boiling fractions of the reflux condensate or the like, to an intermediate point in the cracking system such as the transfer line between the heating coil and the.

reaction chamber or to any desired point in the reaction chamber.

The adaptability of the features of the present invention to other cracking systems and other modifications 0f the system illustrated will be;-

mately 350 pounds per square inch. This pressure is substantially equalized in the reaction chamber and is reduced to approximately 200 pounds per square inch in the separating cham- The vaporizing chamber is operated at a pounds per square inch. About 15% of the vapors separated from the liquid conversion products in the separating chamber are withdrawn therefrom with the liquid and supplied therewith to the vaporizing chamber. by bubble trays are employed as fractionating means in the upper portion of the vaporizing chamber and a portion of the reflux condensate is recirculated over the bubble trays as a refluxing medium. A superatmospheric pressure of,

approximately 50 pounds per square inch is also maintained in the fractionating, condensing and collecting portions of the system. This operation may produce, per barrel of charging stock, about 55% of 400 end-point motor fuel having an anti:

bon oil wherein said oil is subjected to conversion temperatures at superatmospheric pressure in a heating coil and communicating reaction chamber, resulting vaporous and non-vaporous products subsequently separated at substantially reduced pressure and the vaporous products subjected to fractionation whereby their insufliciently converted components are condensed as reflux condensate, the improvement which comprises withdrawing both vaporous and non-vaporous products from the reaction chamber in commingled state, introducing them intoa zone of primary separation wherein a major portion of the vaporous products are separated from the non-vaporous products, withdrawing the latter, still in commingled state with a minor portion of the vaporous products, to a zone of final separation wherein substantially all of the remaining desirable vaporous products are separated from the non-vaporous residue and subjecting the vaporous products from both stages of separation to preliminary fractionation, for the removal therefrom of entrained high boiling liquids, prior to said fractionation for the recovery or reflux condensate.

2. A process of the character defined in claim 1, wherein the zone of primary separation is maintained at substantially the same pressure as that employed in the reaction chamber and the zone of final separation is maintained at a substantially reduced pressure.

3. A process of the character defined in claim 1, wherein the zone of primary separation is maintained at a reduced superatmospheric pressure relative to that employed in the reaction chamber and the zone of final separation is maintained at a further reduction in pressure.

4. A process of the character defined in claim 1, wherein the zone of primary separation is maintained at a substantially reduced pressure relative to that employed in the reaction chamber and the zone of final separation is maintained at substantially the same pressure as that employed in the zone of primary separation.

5. A process of the character defined in claim 1, wherein the reflux condensate is subjected to further conversion in the same cracking system.

6. A process of the character defined in claim 1, wherein the reflux condensate is returned to the heating coil for further conversion.

7. A process of the character defined in claim 1, wherein the reflux condensate is subjected to further conversion in a separate heating coil of the same cracking system.

8. A conversion process which comprises heating hydrocarbon oil to cracking temperature under pressure while flowing in a restricted stream through a heating zone, discharging the heated oil into anenlarged reaction zone maintained under cracking conditions of temperature and superatmospheric pressure, removing vapors and unvaporized oil as a mixture from the reaction zone and introducing the same to a separating zone maintained under superatmospheric pressure, separating a portion of the vapors from said mixture in the separating zone, removing the unvaporized oil and the remaining portion of the vapors as a mixture from the separating zone and introducing the same to a second separating zone maintained under lower pressure than the reaction zone, separating vapors from residue in the second separating zone, fractionating the vapors separated in said separating zones and retreating resultant reflux condensate under cracking conditions in the process, and finally condensing the fractionated vapors.

9. The process as defined in claim 8 further characteried in that the first-named separating zone is maintained under substantially the same pressure as the reaction zone.

10. A conversion process which comprises heating hydrocarbon oil to cracking temperature under pressure while flowing in a restricted stream through a heating zone, discharging the heated oil into an enlarged reaction zone maintained under cracking conditions of temperature and superatmospheric pressure, removing vapors and unvaporized oil as a mixture from the reaction zone and introducing the same to a separating zone maintained under superatmospheric pressure, separating a portion of the vapors from said mixture in the separating zone, removing the unvaporized oil and the remaining portion of the vapors as a mixture from the separating zone and introducing the same to a second separating zone maintained under lower pressure than the reaction zone, separating vapors from residue in the second separating zone, introducing the vapors separated in the first-named separating zone into -Saidsec0nd separating zone to commingle with the vapors separated from the residue in this zone, effecting a preliminary fractionation of the commingled vapors in the upper portion of the second separating zone to separate coke-forming constituents therefrom, then further fractionating the commingled vapors and retreating resultant reflux condensate under cracking conditions in the process, and finally condensing the fractionated vapors.

11. A conversion process which comprises heating hydrocarbon oil to cracking temperature under pressure while flowing in a restricted stream through a heating zone, discharging the heated oil into an enlarged reaction zone maintained under cracking conditions of temperature and superatmospheric pressure, removing vapors and unvaporized oil as a mixture from the reaction zone and introducing the same to a separating zone maintained under lower superatmospheric pressure than the reaction zone, separating a portion of the vapors from said mixture in the separating zone, removing the unvaporized oil and the remaining portion of the vapors as a mixture from the separating zone and introducing the same to a flashing zone maintained under lower pressure than the separating zone, flash distilling the unvaporized oil in the flashing zone by pressure reduction and separating vapors from residue therein, fractionating the vapors separated in said separating and flashing zones and retreating resultant reflux condensate under cracking conditions in the process, and finally condensing the fractionated vapors.

12. A conversion process which comprises heating hydrocarbon oil to cracking temperature under pressure while flowing in a restricted stream through a heating zone, discharging the heated oil into an enlarged reaction zone, maintained under cracking conditions of temperature and superatmospheric pressure, removing vapors and unvaporized oil as a mixture from the reaction zone and introducing the same to a separating zone maintained under lower superatmospheric pressure than the reaction zone, separating vapors from unvaporized oil in the separating zone and flash distilling the latter in a flashing zone maintained under lower pressure than the separating zone, introducing the vapors separated in the separating zone into the flashing zone to commingle with the flashed vapors therein, efiecting a preliminary fractionation of the commingled vapors in the vupper portion of the flashing zone to separate coke-forming constituents therefrom, then further fractionating the commingled vapors and retreating resultant reflux condensate under cracking conditions in the process, and finally condensing the fractionated

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