US2037380A - Art of cracking hydrocarbons - Google Patents

Description

April M, w36. E, C HERTHEL 2,037,380

ART OF CRACKING HYDROCARBONS Filed June 29, 1929 n sa/fhe vZ3 :NVNTOR Eagan@ C #erf/1rd ATTORNEYS Patented Apr. 14, 1936 UNITED STATES PATENT OFFICE Eugene C. Herthel, Chicago, Ill., assignor to Sinclair Refining Company, New York, N. Y., a

corporation of Maine Application June 29, 1929, Serial No. 374,859

2 Claims. (Cl. 196-58) pump 53, vapors are taken off from the bulk This invention relates to improvements in the cracking of higher boiling hydrocarbon oils such as gas oil to produce therefrom lower boiling hydrocarbon oils such as gasoline; more particularly the invention provides an improved operation for cracking higher boiling hydrocarbon oils such as gas oil in which residual tar or reduced residual tar discharged from a pressure distillation cracking operation is utilized to control the cracking operation and at the same time subjected itself to a further cracking operation and to an operation for the separation therefrom of a distillate fraction suitable to be supplied to the cracking operation.

According to this invention, a high boiling oil such as gas oil is forced through a heating Zone under superatmospheric pressure and thence into an expansion chamber, this oil is heated to a relatively high cracking temperature in the heating zone, a residual tar from a pressure clistillation cracking operation is introduced into the oil passing from the heating zone to the eXpansion chamber reducing the temperature of the hot oil discharged-from the heating Zone prior to separation of vapors from the oil mixture in the expansion chamber, the pressure on the oil passing from the heating Zone to the expansion chamber is reduced before it enters the expansion chamber but either before or after the introduction of the residual tar, vapors including vapors of the desired lower boiling hydrocarbon oils and vapors separated from the introduced residual tar are taken off from the expansion chamber and residue is discharged from the expansion chamber. The vapors taken off from the expansion chamber are, with advantage, subjected to a refluxing operation from which reflux co-ndensate including condensed components separated from the introduced residual tar in the expansion chamber is returned to the heating operation.

The invention will be further described in connection with the accompanying drawing which illustrates one form of apparatus `adapted for carrying out the invention. It will be understood that the accompanying drawing is largely diagrammatic and conventional; the apparatus is shown generally in elevation, partly in section and with parts broken away.

The invention is generally useful in conjunction with pressure distillation cracking operations. The pressure still system illustrated is of the general type described in Letters Patent No. 1,285,200, issued to Sinclair Rening Company, November 19, 1918, on the application of Edward W. Isom. In the operation of the system illus-- trated, a charge of oil is circulated from the bulk supply drum 5U upwardly through the heating tubes 5| arranged in the heating furnace 52 and back to the bulk supply drum by means of supply drum under superatmospheric pressure and subjected to a reuxing operation in the reflux tower 54 from which refluxcondensate is returned to the circulating charge, and vapors remaining uncondensed escape from the reflux tower 54 to the condenser 55 arranged to discharge into receiver 56 from which the condensed cracked distillate product is discharged through connection 5l and uncondensed vapors and gases through connection 58, pressure in the system being maintained and regulated by means of Valve 59 or by means of appropriate valves arranged beyond the condenser or receiver. 'Residual tar is discharged from the bulk supply f drum 59' during operation through connection 60. The operation of the system may be carried out, for example, as described in Letters Patent No. 1,598,136, issued to Sinclair Rening Company, August 3l, 1926, on my application. 'I'he pressure still system illustrated may be, and usually is, one of a battery of several such systems; manifold connections to such a battery are indicated at 6I and 62. As further eX- amples, the invention is also useful in conjunction with pressure still systems operated as described in my application filed January 12, 1928, Serial No. 246,262, or in conjunction with pressure still systems in which a single pass heater discharges into a vaporizing Zone from which vapors are taken off under superatmospheric pressure and from which residual tar is discharged.

In the pressure still system illustrated, the operation of the reilux tower 54 is controlled by the regulated introduction of stock to be cracked through connection 63, or this control may be supplemented by the regulated introduction of a part of the distillate product or some similar fraction through connection 64, or the operation is controlled by the regulated introduction of part of the distillate product .or some similar fraction through connection 64.

The cracking operation of the present invention isl carried out, in the apparatus illustrated, in the heating coils 9, lil and Il, expansion chamber l2 and fractionating tower I6. nace in which the heating coils 9, ID, and il are arranged comprises a series of heating ues, a rebox and a stack flue connected so that the heating gases from the rebox l pass successively through the heating flues 2, 5 and i to the stack flue 5. Ducts, including suitable forcing means, are provided to permit recirculation of a part of the heating gases escaping from flue 3 to flue 4 through ues 2 and 3 as shown at 6 and to permit recirculation of a part 0f the heating gases escaping through the stack flue 5 through ues 3 and 4 as shown at l. The heating coils 9, Ill and l I comprise banks of heating tubes connected to The heating fur-A form three single continuous coils. A high boiling oil such as gas oil is forced by means of pump 8 through preheating coil 9, cracking coil Il] and cracking coil II in succession and then into expansion chamber I2 through pressure regulating and reducing valve I3. Residue such as fuel oil is discharged from expansion chamber I2 through connection I4. Vapors are discharged from expansion chamber i 2 through connection I5 into the lower end of fractionating tower I6. This fractionating tower may be'oi any conventional type, a bubble tower, for example. The fractionating tower I6 and the expansion chamber I2 are with advantage thoroughly lagged or thermally insulated. In the fractionating tower I6 those components of the vapor mixture heavier than suitable as components of the desired product are condensed. The operation of this tower may be controlled by the regulated introduction of stock to be cracked through connection I 1, or this control may be supplemented by the regulated introduction of a part of the distillate product or some similar fraction through connection I8, or the operation may be controlled by regulated introduction of a part of the distillate product or some similar fraction through connection I8. Vapors remaining uncondensed escape from the upper end of tower I6 through connection 2U to condenser 2I arranged to discharge into receiver 22 from which the condensed cracked distillate product is discharged through connection 23 and uncondensed vapors and gases through connection 25.

In carrying out the present invention, the high boiling oil or oil mixture supplied thereto is heated to a relatively high cracking temperature in the cracking coils I0 and I I and as this hot oil passes from the cracking coil I I to the expansion chamber I2 through connection 81 residual tar or reduced residual tar discharged from the pressure distillation cracking operation through connection 60 is introduced through connections 3| and 88 by means of pump 32 reducing the temperature of the hot oil discharged from the cracking coil II prior to separation of vapors from the resulting oil mixture in the expansion chamber I2. The pressure regulating and reducing valve I3 is shown positioned to reduce the pressure on the hot oil discharged from the cracking coil I I prior to the introduction of the residual tar through connection 88. This is usually the more advan- K tageous arrangement, although this pressure regulating and reducing valve may be positioned beyond the junction of connections 81 and 88.

The high boiling oil supplied to the cracking coil I!) may comprise raw gas oil supplied through connections 26, 21 and I9 by means of pump 24, or reflux condensate supplied from the lower part of fractionating tower I6 through connections 28, 29 and I9 by means of pump 8, or reflux condensate supplied from an intermediate part of iractionating tower I6 through connections 30, 33, 29 and I9 by means of pump 34, either of which reiiux condensates may include components of raw oil introduced as a refluxing medium into the fractionating tower I6, or mixtures of such reflux condensates and raw oil supplied through connection 26, for example.

The residual tar from the pressure distillation cracking operation may be introduced into the hot oil passing from the heating zone to the expansion chamber, through connections 3| and 88 in the apparatus illustrated, as discharged from the pressure distillation cracking operation, or

oil components of this tar may be evaporated therefrom, as described in Letters Patent No. 1,677,773, issued to Sinclair Rening Company, July 17, 1928, on the application of Thomas de Colon Tifft and myself, for example. In the apparatus illustrated, the residual tar from the pressure still system may be discharged directly through connections 69, 35 and 36 to pump 32, supplying this residual tar through connection V3l to the cracking operation of this invention, or

residual tar from the pressure still system may be discharged through connections 68 and 31 into an evaporator 38 in which a pressure lower than that prevailing in the pressure still system is maintained and in which part of the residual tar is vaporized to escape as vapor through connection 39 to tower 40, the remaining reduced residual tar being discharged through connections 4I and 36 to pump 32. All or part of this residual tar may, in some cases, be passed through cooler 9I. The vapors entering tower 40' through connection 39 may be condensed or may be separated into higher and lower boiling fractions therein. Condensate is discharged from tower. 40 through connection 42. Uncondensed vapors escape therefrom through connection 43 to condenser 44 arranged to discharge into receiver 45 from which condensate is discharged through connection 46 and uncondensed vapors and gases through connection 41. Pressure in the evaporator 38, or in the evaporator 38 and the tower 40, may be maintained and regulated by means of valve 48 or valve 49 or by means of appropriate valves arranged beyond the condenser or receiver. The operation of tower 40 is controlled by the regulated introduction of stock to be cracked through connection 65, or this control may be supplemented by the regulated introduction of a part of the distillate product or some similar fraction through connection 66, or the operation may be controlled by the regulated introduction of a part of the distillate product or some similar fraction through connection 66. In carrying out this invention, the operation of the evaporator 38 may be controlled by regulated introduction of a cooling medium,

such as gas oil or reduced crude oil, through connection 89, for example, to avoid too high concentration of pitch constituents in the residual tar discharged through connection 4I. To increase the concentration of pitch constituents,

steam may be supplied through connection 90.

Pumps 61 and 68 are provided for supplying .part of any one or more of the several distillate products collected in the receivers 22, 56 and 45 to any one or more of the towers I6, 4I! and 54 as refluxing media through connections 69, 10, 1I and 12 or such of these connections as may be required.

The total condensate separated in tower I6 may be supplied to the cracking coils I0 and II, or a higher boiling condensate and a lower boiling condensate may be separated in this tower and the lower boiling condensate supplied to the cracking coils I0 and II and the higher boiling condensate supplied to the pressure distillation Acracking operation, connections 14 and 15 being provided for this purpose. Condensate separated in tower 40 may be supplied, or in part supplied, to cracking coils Ill and I I through connections 42, 16, 29 and I9 by means of pump 11 or may be supplied or in part supplied to the pressure distillation cracking operation through connections 42, 18 and 15 by means of pump 11. A single raw stock, gas oil for example, may be supplied or in part supplied to tower I6 as a reiiuxing medium through connections 26, 'I9 and I'I, or supplied or in part supplied to tower 40 as a reiiuxing medium through connections 26, 19, 80 and 65, or supplied or in part supplied to tower 54 as a refluxing medium through connections 26, 19, 80 and 63. Or, a lower boiling raw stock may be supplied or in part supplied to tower I6 as a reuxing medium through connections 26, 'I9 and I'I and a higher boiling raw stock supplied or in part supplied to tower 40 or to tower 5ft as a refluxing medium through connections SI, 82 and 30 and either or both of connections 63 and 65 by means of pump 83. Where a lower boiling raw stock is so supplied to tower I6, the total higher boiling raw stock may be supplied to tower 40 through connections 3|, 82, 80 and 65 and the total condensate mixture from tower 40 supplied to tower 54, that is to the pressure still system, through connections 42, '18,15 and $3.

If excess heat is available in the expansion chamber I2, a crude stock, for example, a crude oil or a reduced crude oil, may be supplied together with the residual tar from the pressure distillation cracking operation through connection 88, the crude stock being supplied through connections 8A and 85 by means of pump 85. Such crude stock may thus be utilized to supplement control of the cracking operation by introduction of the residual tar and at the same time lmay be separated, in the expansion chamber I2, into a vaporized fraction escaping to the fractionating tower EE and a residual stock mixing with the residue collecting in and discharged from the expansion chamber. Raw stocks, of gas oil character for example, may be so separated from such crude stocks and supplied to 'the cracking operation of the invention or to the associated pressure distillation cracking operations as condensates from fractionating tower I6, for example.

In carrying out the invention in the apparatus illustrated, the discharge pressure from the cracking coils I and II may be in the neighborhood of 40G-800 pounds per square inch and the pressure in the expansion chamber I2 may approximate atmospheric pressure, or the expansion chamber I2 may be operated under superatmospheric pressures, for example, 20-25 pounds per square inch, lower however than the discharge pressure from the cracking coils. Fractionating tower I6 may be operated under substantially the same pressure as the expansion chamber I2, or when the expansion chamber I2 is operated under superatmospheric pressure the fractionating tower IS may be operated under a pressure lower than that prevailing in the expansion chamber I2. Raw oil supplied through connection i9 may enter the preheating coil 9 at a temperature approximating 60-80" F. or, where condensates are supplied hot from either or both oi the towers I6 or Ml, the oil supplied through connection I9 may be at a temperature as high as 300 F. or higher. Oil passing from the preheating coil 9 to the cracking coil I0 may be at a temperature approximating 550-750" F. and the oil may be heated in the cracking coils I0 and II to a temperature, as discharged, approximating 900-l000 F. Residual tar introduced into the hot oil passing from the cracking coils I0 and II to the expansion chamber I2 may be supplied through connection 88 at a temperature in the range of S50-650 F., or at a lower temperature where this residual tar is admixed in connection 83 with a raw crude stock supplied through connection 65. The resulting oil mixture may be discharged into the expansion chamber I?. at a temperature approximating '700-900o F. when the fractionating tower I is operated under substantially atmospheric pressure, the temperature of the escaping vapors may be in the neighborhood of SOO-600 F. It will be understood that the foregoing temperatures and pressures are given to assist in the iilustration of the invention and that the invention is not limited thereto. The precise conditions of operation of the pressure still system or systemsA from which residual tar is supplied to the cracking operation of this invention are not given because they are not essential with respect to the present invention, varying widely with the different types of pressure distillation cracking operations.

I claim:

1. In cracking higher boiling hydrocarbon oils to produce lower boiling hydrocarbon oils, the improvement which comprises forcing high boiling oil through a heating Zone under superatmospheric pressure and thence directly into an expansion chamber, heating the oil to a cracking temperature in the heating Zone, introducing a concentrated residual tar from a pressure distillation cracking operation into the oil passing from the heating zone to the expansion chamber and thereby reducing the temperature of the hot oil discharged from the heating zone prior to separation of vapors from the oil mixture, reducing the pressure on the oil passing from the heating Zone to the expansion chamber, taking off vapors including vapors of the desired lower boiling hydrocarbon oils and vapors separated from the introduced residual tar from the expansion chamber and discharging residue from -the expansion chamber.

2. In cracking higher boiling hydrocarbon oils to produce lower boiling hydrocarbon oils, the improvement which comprises forcing high boiling oil through a heating zone under superatmospheric pressure and thence directly into an expansion chamber, heating the oil to a cracking temperature in the heating zone, introducing a concentrated residual tar from a pressure distillation cracking operation into the oil passing from the heating zone to the expansion chamber and thereby reducing the temperature of the hot oil discharged from the heating zone prior to separation of vapors from the oil mixture, reducing the pressure on the oil passing from the heating zone to the'expansion chamber, taking off vapors including vapors of the desired lower boiling hydrocarbon oils and vapors separated from the introduced residual tar from the expansion chamber and subjecting them to a reluxing operation, supplying reiiux condensate including condensed components separated from the introduced resid-ual tar in the expansion chamber from the refluxing operation to the heating operation, taking off vapors including vapors of the desired lower boiling hydrocarbon oils from the reluxing operation and discharging residue from the expansion chamber.

EUGENE C. HERTHEL.

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