US2091118A - Art of cracking - Google Patents

Description

Allg- 24, 1937. E. c. HERTHEL ET AL' 2,091,113

l ART OF CRACKING- Filed April 1, 193s l VEN ORS (br/fon 62' mia/ gd ene C', #erf/fel fw QW ,w 1 aww Patented Aug. 24, 1937 UNITED STATES PATENT OFFICE ART OF CRACKING Eugene C. Herthel, Flossmoor, Ill., and Carlton L. Schmidt, Hammond, Ind., assignors to Sinclair Rening Company, New York, N. Y., a

corporation of Maine Application April 1, 1933, Serial No. 663,954

2 Claims.

5 of 925 F. for example, under superatmospheric pressure, upwards of 200 lbs. per square inch for example, and then discharged, with reduction of pressure, into a separating receptacle in which a vapor fraction is separated from. tar. The improvements of this invention make possible a reduction in the proportion of tar made and, at the same time, the production of a cleaner tar or, in another aspect, an increase in the recovery of liquid products other than tar conjointly with the production of a tar of improved quality.

The tar separated in the separating receptacle in operations of this character includes tar constituents produced by cracking and may include tar lconstituents of stocks supplie-d to the operation as well as varying proportions of oil constituents. Normally the tar is the least valuable of the products of such operations and consequently the oil content of the tar made represents a double loss to the extent that such oil might be recovered as a part of the more valuable liquid products other than tar in that it represents at the same time an increase in the proportion of tar made and a decrease in the proportion of liquid products other than tar made. The obvious economic necessity for minimizing the proportion of tar made has provoked various proposals intended to'accomplish this end. Excepting those involving ultimate reduction of the tar made to coke, these proposals have been characterize-d by the production of dirtier and consequently less valuable tars. This invention makes possible a reduction in the proportion of tar made Without involving this disadvantage.

According to the present invention, a stream of high boiling oil is heated to a cracking temperature under superatmospheric pressure, the presu sure on the hot oil products of this heating operation is reduced and they are then introduced into a separating receptacle in which the hot oil products are cooled by the introduction, into the separating receptacle, of a liquid oil fraction vaporizing substantially completely under the conditions prevailing in the separating receptacle and which is substantially free from those constituents of the expanded hot `oil products of boiling range next lower than, that is abutting, that of the tar to be separated in the separating receptacle, that minimum volume of separated liquid tar necessary to maintain liquid discharge therefrom is maintained within the separating receptacle and a vapor fraction and a liquid tar are separately discharged from the separating receptacle. By utilizing an oil fraction of the specied characteristics as the cooling medium in the separating receptacle an unusually complete stripping of oil constituents from the separated liquid tar is effected, the absence from the coolingmedium of those constituents of the hot oil products discharged into the separating receptacle from the heating operation of boiling range abutting that of the tar rendering this cooling medium a highly effective distillation medium,v

upon vaporization, by reducing the partial pressure of the highest boiling of the oil constituents separated as vapors in the separating receptacle. At the same time, further cracking or polymerization of constituents of the liquid tar separated in the separating receptacle is minimized bythe maintenance of a minimum volumeof separated liquid tar within the separating receptacle thus enabling, in conjunction with the improved stripping of oil constituents from the tar, the production of a more concentrated and at the 1 The invention will be further described in con.-r

nection with the accompanying drawing which illustrates,` diagrammatically and conventionally, in `elevation and partly in section with parts broken away, one form of apparatus appropriate for practice of the invention.

The apparatus illustrated comprises a heating furnace l, a separating tower 2, a fractionating tower 3, a condenser 4 and a receiver 5. High boiling oil to be cracked, stock supplied from an extraneous source through connection tor the higher boiling fraction or part of the higher boiling fraction separated as a condensate/in. fractionating tower 3 suppliedthrough connections 1 and 8 or a mixture of the two, is forced, by means of pump 9, through the heating coil I0,

arranged in the heating furnace I, and thence through the pressure reducing valve Il in transfer connection l2, into the separating tower 2. High boiling oil supplied through connection v6 can be supplied tothe heating coil l0 directly through connection 3l, or, when condensate is supplied from the lower part of tower 3 to the heating coil IG, through connection 32. The stream of oil fiowing through the heating coil I is heated to a temperature, for example, of 945-975 F. under a superatmospheric pressure, for example, of 30G-600 lbs. per square inch as discharged therefrom. VThe pressure on the hot oil products discharged from the heating coil I0 is reduced as they pass through valves II and they are then introduced into the separating tower 2 maintained under a pressure, for example, of 25-'75 lbs. per square inch. A cooling medium is introduced into the separating tower 2, or into the transfer connection I2 and thence into the separating tower 2, through any one or more of the connections I3, I4, I5, and I at a rate regulated to maintain a temperature, for example, of 725-'7'75 F. in the lower part of this tower. Separated liquid tar is discharged from the lower part of this tower through connection I'I and the separated vapor fraction is discharged from the upper part of this tower, to be introduced into the fractionating tower 3, through connection I8. In the fractionating tower 3, two high boiling condensates are Separated, the higher boiling of these being discharged through connection I and the lower boiling being discharged through connection I9. The fractionating tower 3 is controlled, for example, to produce as an overhead product a gasoline fraction of desired boiling range, condensed and collected in the condenser 4 and the receiver 5, this control being effected by regulated circulation of a cooling medium through the reflux condenser 20 or regulated introduction of a refluxing medium through connection 2| or by these means conjointly. A part of the distillate product may be supplied as a refiuxing medium by means of connection 22 or a corresponding stock from an extraneous source may be supplied through connection 23, for example. The distillate product is discharged from receiver 5 through connection 24 and uncondensed vapors and gases through connection 25. The higher boiling condensate separated in the fractionating tower 3, or part of it, may be supplied to the heating coil I0 through connections 'I and 8 or this higher boiling condensate or any remaining part of it may be discharged through cooler 26. The lower boiling of the two condensates separated in the fractionating tower 3 may, in whole or in part, be supplied to the pump 21 or discharged through cooler 28. A stock to be used as a cooling medium in the separating tower 2 may be supplied to pump 21 through connection 29.

In carrying out the invention in the apparatus illustrated, for example: 'I'he lower boiling of the two condensates separated in the fractionating tower 3 or a corresponding stock is supplied to the separating tower 2 as a cooling medium, by means of pump 21, and that minimum volume of separated liquid tar necessary to maintain liquid discharge through connection I'I is maintained in the lower part of separating tower 2. Usually it is advantageous to introduce that proportion,

usually a small proportion, of this fraction necessary to maintain slight reiluxing into the separating tower 2 `through connection I6 and to introduce the balance of the total proportion required to maintain the desired temperature in the lower part of the separating tower 2 into the transfer connection I2 through connection I3. The condensate separated as an intermediate fraction in the kfractionating tower 3, discharged therefrom through connection I9, is substantially free from those constituents of the expanded hot oil products discharged into the separating tower 2 of boiling range next lower than, or abutting that of the tar -discharged through connection II, these higher boiling constituents being separated as the higher boiling condensate separated in the fractionating tower 3 and discharged therefrom through connection 'I. The absence of these intermediate constituents from the stock introduced into the separating tower 2 as a cooling medium effects the unusually complete stripping of the liquid tar separated in the separating tower 2 to which general reference has previously been made. Stocks of boiling range corresponding to that of this intermediate fraction are as a class appropriate to be used as the cooling medium introduced into` the separating receptacle in accordance with this invention. The provision of a tar leg of cross sectional area substantially less than that of the separating receptacle proper, such as the tar leg 30 in the apparatus illustrated, materially facilitates the maintenance of a vminimum volume of separated liquid tar in the separating receptacle. By maintaining the liquid level of separated liquid tar within the tar leg 30, in apparatus such as that illustrated, it is comparatively easy to maintain liquid discharge through connection II while maintaining a volume of separated liquid tar in the separating tower 2 not exceeding 1/2 barrel in operations in which the charging rate to the heating coil IIJ exceeds 200 barrels per hour.

We claim:

1. In cracking higher boiling petroleum oils to produce gasoline, the improvement which comprises heating a stream of high boiling oil to a cracking temperature under superatmospheric pressure, reducing the pressure on the hot oil products of this heating operation and then introducing them into a separating receptacle, cooling the expanded hot oil products by introducing continuously into this receptacle a liquid oil fraction vaporizing substantially completely therein and substantially free from those constituents of the expanded hot oil products of boiling range abutting that of the tar to be separated in the receptacle, takingoff vapors from said separating receptacle and subjecting them to a condensing operation thereby forming a condensate including those constituents of the expanded hot oil products of boiling range abutting that of the tar to be separated in said separating receptacle, preventing direct return of the last-mentioned condensate to said separating receptacle, maintaining within the receptacle that minimum volume of separated liquid tar necessary to maintain liquid discharge therefrom, and separately discharging a vapor fraction and a, liquid tar from the separating receptacle.

2. In cracking higher boiling petroleum oils to produce gasoline, the improvement which comprises heating a stream of high boiling oil to a cracking temperature under superatmospheric pressure, reducing the pressure on the hot oil products of this heating operation and thenintroducing them directly into a separating receptacle, cooling the expanded hot oil products by introducing continuously into this receptacle a liquid oil fraction vaporizing substantially completely therein and substantially free from those constituents of the expanded hot oil products of boiling range abutting that of the tar tobe separated in the receptacle, taking off vapors from said separating receptacle and subjecting them t0 l a condensing operation thereby forming a condensate including those constituents of the expanded hot oil products of boiling range abutting that of the tar to be separated in said separating receptacle, preventing direct return of the lastmentioned condensate to said separating receptacle, maintaining within the receptacle that minimum volume of separated liquid tar necessary to maintain liquid discharge therefrom, and Separately discharging a vapor fraction and a. liquid tar from the separating receptacle.

EUGENE C. HERTHEL. CARLTON L. SCHMIDT.

Images