US1981914A - Art of cracking hydrocarbons - Google Patents

Description

Nov. 27, 1934. 'E c. HERTHEL 1,981,914 ART OF CRACKING HYDROGARBONS Filed June 29', 1929 Gasol/ne ATTORNEYS Patented- Nov'. 27, 19 34 UNITED STATES 'PATENIWOFFICE 1,981,914 7 ART OF CRACKING HYDROCARBONS Eugene 0,. Herthel, Chicago, 111., assignor to- Sinclair Refining Company, New York, N. Ya, a

corporation of Maine Application June 29, 1929, Serial No. 374,860

2 Claims.

in the methods of operation described in an appli- V cation filed May 26, 1928, Serial No. 283,021, and in an application filed April 12, 1929, Serial No. 354,450. Y 10 In carrying out the invention, as in the method of operation described in the application first mentioned above, oil, gas oil for example, is forced successively through primary and secondary stages in a heating zone under superatmospheric pressure and thence into an expansion chamber maintained under a pressure lower than that prevailing in the heating zone and from which vapors are taken oil and residue is discharged, the oil is heated to a high cracking temperature in the primary stage in the heatin zone, a relatively 0001 oil is introduced into the oil passing from the primary to the secondary stage in the heating zone lowering the oil temperature and the oil mixture is discharged from the secondary stage in the heating zone at a temperature lower than that at which the oil is discharged from the primary stage in the heating Zk 1e. The high boiling oil supplied to the primary stage in the heating zone is thus subjected to severe cracking conditions and to maintained cracking conditions while overcracking is avoided by limiting the time at which this oil is at the extreme high temperature. The secondary stage in the heating zone may be sub-divided and relat-ively cool oil introduced at a number of points through the secondary stage. oil is with advantage preheated, for example, to an incipient cracking temperature, before introduction into the primary stage in the heating zone. This preheating 'may be accomplished. for example, by heat exchange with heating gases escaping from the major heating operations.

The vapors taken off from the expansion chamher may be condensed in toto to form a. composite I'produ'ct which may then be fractionated in any convenient manner for the separation of a gasoline product, a gas oil fraction or fractions and any higher boiling fraction or fractions. These vapors, however, with advantage are subjected to direct fractionation for the separation of such several fractions.

In carrying out the present invention, however,

instead of introducing a relatively low-boiling relatively refractory cool oil into the oil passing The high boiling from the primary to the secondary stage in the heating zone, as in the method of operation described in the application first mentioned above, a residual tar or reduced residual tar discharged from a pressure distillation cracking operation is introduced into the oil passing from the primary to the secondary stage in the heating zone lowering the oil temperature and the oil mixture is discharged from the secondary stage in the heating zone at a temperature lower than, that at which the oil is discharged from the primary stage in the heating zone; Such residual tar is thus utilized to control the cracking of the lower boiling raw oil and at the same time is subjected to a further cracking. operation and to an opration for the separation therefrom of a fraction or fractions suitable to be supplied to the primary stage in the heating zone or to' be otherwise cracked.

The invention will be further described in con- 76 nection 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 80 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 Refining Company, November 19 1918-, on the application of Edward W. Isom. In the operation of the system illustrated, a charge of oil is circulated from the bulk supply drumv 50 upwardly through the heating tubes 51 arranged in the heating furnace 52 and back to the bulk supply drum 50 by means of pump 53, vapors are taken off from the bulk supply drum under superatmospheric pressure and subjected to a refluxing operation in r the reflux tower 54 from which reflux condensate 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 57 and uncondensed vapors and gases through connection 58,-pressure. in the system being maintained and regulated by means of valve59 or by means of appropriate valves arranged .beyond the condenser or. receiver. Residual tar is discharged from the bulk supply drum 50 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 Refining Company, August 31, 1926, on my application. The 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 61 and 62. As further examples, 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 reflux 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 is carried out, in the apparatus illustrated, in the heating coils 9, 10 and 11, expansion cham ber 12 and fractionating tower 16. The heating furnace in which the heating coils 9, 10 and 11 are arranged comprises a series of heating flues, a firebox and a stack flue connected so that the heating gases from the firebox 1 pass successively through the heating flues 2, 3 and 4 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 flues 2 and 3 as shown at 6 and to permit recirculation of a part of the heating gases escaping through the stack flue 5 through flues 3 and 4 as shown at 7. The heating coils 9, 10 and 11 comprise banks of heating tubes connected to formthree single continuous coils. A high boiling oil such as gas oil is forced by means of pump 8 through preheating coil9, cracking coil 10 and cracking coil 11 in succession and then into expansion chamber 12 through pressure regulating and reducing valve 13. Residue such as fuel oil is discharged from expansion chamber 12 through connection 14. Va

pors are discharged from expansion chamber 12 through connection 15 into the lower end of fractionating tower 16. This fractionating tower may be of any conventional type, a bubble tower, for example. The fractionating tower 16 and the expansion chamber .12 are with advantage thoroughly lagged or thermally insulated. In the fractionating tower 16 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 17, or this control may be supplemented by the regulated introduction of a part of the distillate product or some similar fraction through connection 18, or the operation may be controlled by regulated introduction of a part of the distillate product or some similar fraction through connection 18. Vapors remaining uncondensed escape from the upper end of tower 16 through connection 20 to condenser 21 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 high cracking temperature in the cracking coil 10, the primary stage, and as this hot oil passes from the cracking coil 10 to the cracking coil 11, the secondary stage,-residual tar or reduced residual tar discharged, from the pressure distillation cracking operation through connection 60 is introduced through connection 31 by means of pump 32.

The high boiling oil supplied to the cracking coil 10 may comprise raw gas oil supplied through connections 26, 27 and 19 by means of pump 24, or reflux condensate supplied from the lower part of fractionating tower 16 through connections 28, 29 and 19 by means of pump 8, or reflux condensate supplied from an intermediate part of fractionating tower 16 through connections 30,

33, 29 and 19 by means of pump 34, either of which reflux condensates may include components of raw oil introduced as a refluxing medium sued to Sinclair Refining 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 60, 35 and 36 to pump 32, supplying this residual tar through connection 31 to the cracking operation of this invention, or residual tar from the pressure still system may be discharged through connections 60 and 37 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 vapors through connection 39 to tower 40, the remaining reduced residual tar being discharged through connections 41 and 36 to pump 32. All or part of this residual tar may, in some cases, be passed through cooler 91. 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 47. 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 connections 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 41. To increase the concentration of pitch constituents, steam may be supplied through connection 90.

- Pumps 67 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, 16, 40 and 54 as refluxing media through connections 69, 70, '71 and 72 or such of these connections as may be required. 3

The total condensate separated in tower 16 may be supplied to the cracking coil 10, or a higher boiling condensate and a lower boiling condensate may be separated in this tower and the lower boiling condensate supplied to the crackin coil 10 and the higher boiling condensate supplied to the pressure distillation cracking operation, connections 74 and '75 being provided'for this purpose. Condensate separated in tower 40 may be '40 as a refluxing medium through connections 26, .79, 80 and 65, or supplied or in part supplied to tower 54 as a refluxing medium through connec-- tions 26, 79, 80 and 63. Or, a lower boiling raw stock may be supplied or in part supplied to tower 16 as a refluxing medium through connections 26, '79 and 1'1 and a higher boiling raw stock supplied "or in part supplied to tower 40 or to tower 54 as a refluxing medium through connections 81, 82 and 80 anddaither or both of connections 63 and by means of pump 83. Where a lower boiling raw stock is so upplied to tower 16, the total higher boiling ra stock may be supplied to tower 40 through connections 81, 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, 78, and 63.

If excess heat is available in the expansion chamber 12, a crude stock, for example, a crude oil or a reduced crude oil, may be supplied thereto through connections 84 and 85 by means of pump 86 and separated therein into a vaporized fraction escaping to the fractionating tower 16 and a residual stock mixing with the residue collecting in and discharged from the expansion chamber 12. 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 16, for example.

In carrying out the invention in the apparatus illustrated, the discharge pressure from the heating coil 11 may be in the neighborhood of 400- 700 pounds per square inch and the pressure in the expansion chamber 12 may approximate atmospheric pressure, or the expansion chamber 12 may be operated under superatmospheric pressures, for example 20-25 pounds per square inch, lower however than the discharge pressure from the heating coil 11. Fractionatlng tower 16 may be operated under substantially the same pressure as the expansion chamber 12, or when the expansion chamber 12 is operated under superatmospheric pressure the fractionating tower 16 may be operated under a pressure lower than that prevailing in the expansion chamber 12; Raw oil supplied through connection 19 may enter the preheating coil 9 at a temperature approximating 60-80. F. or, where condensates are supplied hot from either or both of the towers '16 or 40, the oil supplied through connection 19 may be at a temperature as high as 300 F. or higher. Oil passing from the preheating coil 9 to the cracking coil 10 may be at a temperature approximating 550-750 F. and the oil may be heated in the cracking coil 10 to a temperature, as discharged, approximating 875-950 F. Residual tar introduced into the hot oil passing from the cracking coil 10 to the cracking coil 11 may be supplied through connection 31 at a temperature in the range of 350-650 F., and the resulting oil mixture may enter the cracking. coil 11 at-a temperature in the neighborhood of 600-800 F. This oil mixture may be heatedin the cracking coil 11 to a temperature, as discharged approximating 700-950 F. When the fractionating tower 16 is operated under substantially atmospheric pressure, the temperature of the escaping vapors may be in the neighborhood of 300-600 F. It will be understood that the foregoing temperatures and pressures are given to assist in the illustration oi. the invention and that the invention is not limited thereto. The precise conditions of operation of the pressure still system or systems from which residual tar is supplied to the cracking operation of this invention are not given because they are not w 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 a high boiling distillate oil successively through primary and secondary stages in a heating zone under superatmospheric pressure and thence into an expansion chamber, heating the distillate oil to a cracking temperature as discharged in the primary stage, introducing a*concentrated residual tar from a pressure distillation cracking operation into the oil passing from the primary stage to the secondary stage in the heating zone, heating the oil in the secondary stage to a temperature as discharged from the secondary stage lower than the temperature as discharged from the primary stage, reducing the pressure on the oil passing from the secondary stage in the heating zone to the expansion chamber, taking 011 vapors including vapors or the desired lower boiling hydrocarbon oils 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 a high boiling distillate oil successively through primary and secondary stages in a heating zone under superatmospheric pressure and thence into an expansion chamber, heating the distillate oil to a cracking temperature as discharged in the primary stage, introducing a concentrated residual tar-from a pressure distillation cracking operaoil passing from the primary stage to the secondary stage from the refluxing operation to the primary stage in the heating/zone, taking off vapors including vapors of the desired lower boiling hydrocarbon oils from the refluxing operation and discharging residue from the expansion chamber.

EUGENE C. HERTHEL.

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