US1992616A - Art of cracking hydrocarbons - Google Patents

Description

Feb. 26, 1935. E? w. ISOM ART OF CRACKING HYDROCARBONS Filed April 12, 1929 w gw m a INVENTOR Edward/[1mm BY ATTORN EY5 Patented Feb. 26, 1935 UNITED STATES ART OF CRACKING HYDROCARBONS Edward W. Isom, Scarsdale, N. Y., assignor to Sinclair RefiningCompany, New York, N. Y.; a corporation of Maine Application April 12, 1929, Serial No. 354,451

3 Claims.

This invention relates to improvements in the manufacture of lower boiling hydrocarbon oils,

such as gasoline, from higher boiling hydrocarbon oils, such as gas oil and the like, by crack- 5 ing operations.

The cracking reaction is progressive; the reaction rate increases as the temperature increases and the products of the initial reaction in turn undergo progressive decomposition. The character of the lower boiling products of the reaction also depends, in some respects, upon the temperature range within which the reaction is effected. High cracking temperatures, upwards of 900-950" F., are advantageous for the production of motor fuel gasoline of high critical compression. At such high cracking temperatures, however, the reaction proceeds very rapidly and this with further decomposition of the initial reaction products tends to involve excessive production of gas and carbon. This invention provides an improved method of controlling the cracking reaction when initiated by heating to a high cracking temperature.

According to the present invention, a flowing stream of the higher boiling oil to be cracked is heated to a high cracking temperature, to a temperature in the range of 900-1200 F. for example, and, when the cracking reaction has proceeded to the desired point, the heated oil is suddenly cooled, to check the cracking reaction, by discharging the stream of heated. oil into a bath of fused caustic alkali maintained by cooling at a temperature lower than thatat which the heated oil is discharged from .the heating operation. The cooling of the hot oil products from the heating operation is thus effectedby direct heat exchange with the fused caustic alkali and, in this manner, can be effected in a time interval much shorter than is possible, practically, with indirect heat exchange. The fused caustic alkali, moreover, is not itself subjected to decomposition involving the production, for example, of carbon although it may act as a condensing agent with respect to more reactive components of the hot oil products discharged from the heating operation. The heating operation is with advantage carried out under superatmospheric pressure and this pressure is with advantage reduced as the heated oil is discharged into the bath of fused caustic alkali. The bath of fused caustic alkali may be cooled by indirect heat exchange with any suitable cooling medium; the time interval is not so important with respect to this heat exchange. The oil flowing to the heating operation is with advantage used as a cooling medium for cooling the bath of fused caustic alkali.

The bath of fused caustic alkali may comprise caustic-soda, or for operation at higher temperatures caustic potash, or for operation at lower temperatures a mixture of caustic soda and caustic potash.

The invention will be further described in connection with the accompanying drawing which illustrates, diagrammatically and conventionally in elevation and partly in section and with parts broken away, one. form of apparatus adapted for carrying out the invention.

The raw oil to be cracked, gas oil for example, is supplied through connection 1 to the series connected heating tubes in the heating furnace 2 by means of pump 3. This oil, or part of it, is supplied to the series connected heating tubes through connections 4 and 5, the cooling coil 6 in the upper end of drum 7 and the cooling coil 8 in the lower end of drum 7 and through connections 9 and 10. A part of this oil may be supplied directly through by-pas's connection 11 and connection 10. The heated oil discharged from the series connected heating tubes in the heating furnace 2 is discharged into the lower end of drum 7 through connection 12. A bath of fused caustic alkali is maintained in the lower end of drum 7, the surface of the bath being maintained at a level between the upper edge of the annular bafile 15 and the outlet to connection 13. The lower end of drum 7 is arranged within a heating furnace 16 for bringing the caustic alkali bath to operating temperature in initiating the operation; except for initiating the op- ,eration or for temporary use in case the temperature of the caustic alkali bath falls 'too low, this heating furnace is not used during the operation proper. A hemispherical baflle 17 is arranged opposite the discharge end of connec-' tion 12 in the lower end of drum 7. In operation, the discharge of the hot oil products from the heating operation, in conjunction with the action of the bafiies 15 and 17, acts to maintain circulation of the bathof fused caustic alkali upwardly through the central space within the baflie 15 and downwardly through the annular space between the baflle 15 and the drum-7. The cooling coil 8 is arranged in the path of circulation of the caustic alkali bathin the annular space between the baffle 15 and the drum 7. In the upper end of the drum 7, above the surface of the bath of fused caustic alkali, vaporized components and unvaporized components of the hot oil products discharged from the heating operation separate, the vapors escaping through connection 18 and the residual oil being discharged through either connection 13 or connection 14 and connection 19. vaporization within the drum 7 is controlled in part by the cooling action of the bath of fused caustic alkali and. in part by the cooling action of oil circulated through cooling coil 6. This control may be supplemented by regulation of the pressure maintained within the drum 7, increasing the pressure to decrease vaporization, or by direct introduction of a cooling medium, a gas oil stock or a crude oil stock for example, through connection 20 by means of pump 21. In general, it is advantageous to avoid the direct introduction of a cooling medium. That control of the vaporization within the drum '7 dependent upon the action of the cooling coils 6 and 8 is regulated by passing of part of the oil supplied to the heating operation through connection 11. The vapors escaping through connection 18 may be subjected to any conventional condensing or fractionating and condensing operations.

In the apparatus illustrated in the drawing, the vapors escaping through connection 18 are discharged into the lower end of a fractionating tower 22. This fractionating tower may be of conventional bubble tower construction, for example. The operation of this fractionating tower may be controlled by circulating a regulated part of the oil flowing through connection 4 through the cooling coil 23 in the upper end of the tower or by directly introducing a regulated part of the final condensate, or some similar fraction, into the upper end of the tower through connection 24 by means of pump 25 or by both of these means conjointly. The condensate separted in the fractionating tower 22 may be discharged, or in part discharged, through connection 26 or, by means of pump 27, supplied to the heating operation together with raw oil, either through connections 28 and 5, cooling coils 6 and 8 and connections 9 and 10 or through connections 29, 11 and 10. The vapors remaining uncondensed escape from the upper end of fractionating tower 22 through connection 30 to condenser 31. This condenser is arranged to discharge into receiver 32 from which the condensed product, gasoline, is discharged through connection 33, uncondensed vapors and gases being discharged through connection 34. The pressure in the condenser 31, the fractionating tower 32 and the drum 7 may be controlled by regulating suitable valves arranged in the discharge connections from the receiver 32.

Connection 12, between the heating furnace 2 and the drum 7, drum '7, outside of the heating furnace 16, connection 18 and fractionating tower 22, as well as connections 9 and 10, are with advantage lagged or thermally insulated.

The heating furnace illustrated comprises a series of heating flues in which are arranged banks of heating tubes connected to form three single continuous coils, a firebox and a stack flue, all connected so that the heating gases from the firebox 36 pass successively through the heating flues 3'7, 38 and 39 to'the stack flue 40. Ducts, including suitable forcing means, are provided to permit recirculation of a part of the heating gases escaping from flue 38 to flue 39 through flues 37 and 38 and to permit recirculation of a part of the heating gases escaping through the stack flue 40 through flues 38 and 39.

In carrying out the invention in the apparatus illustrated, a bath of fused caustic alkali is maintained in the lower end of drum '7, this bath comprising a mixture of 95% caustic soda and 5% caustic potash, for example, melting at a tem-.

perature short of 600 F. Raw high boiling oil, together with any returned condensate, may be supplied to the heating operation under a pressure just suflicient to force the oil through the heater and to efiect the discharge of the hot oil products from the heater through the bath of fused caustic alkali in the drum 7, the vapor space in the drum 7 being maintained under atmospheric pressure or a low superatmospheric pressure, 3-30 pounds per square inch for example, or a higher pressure may be maintained on the 'heater discharge, 400-800 pounds per square inch for example, and this pressure reduced, by means of valve 35, to a pressure just suflicient to effect the discharge of the hot oil products through the bath of fused caustic alkali in the drum 7. In the heater, the oil is heated, for example, to a temperature of 950-1150 F. and in,the drum 7 the hot oil products discharged from the heater are cooled, by passage through the bath of fused caustic alkali, for example, to a temperature of 700-850" F., the bath of fused caustic alkali being maintained approximately at the temperature to which the hot oil products are to be cooled by regulated circulation of cooling oil through the cooling coil8.

Where the hot oil products are dis charged from the heating operation at a temperature upwards of 950-1000 F., the invention has a special advantage in that it provides a method for cooling such hot oil products over that range of temperature, 1000-1100 F. to 700-750" F., within which diffi'culties due to deposition of pitchy or cokey material on cooling are unusually severe, minimizing these difliculties.

I claim:

1. In cracking higher boiling hydrocarbon oils to produce lower boiling hydrocarbon oils, the improvement which comprises heating a flowing stream of the oil to'a high cracking temperature upwards of 900 F. and suddenly cooling the heated oil by discharging the stream at a high cracking temperature into a bath of fused caustic alkali while cooling the bath of fused caustic alkali by passing a stream of cooling fluid through said bath in indirect heat exchanging relation therewith.

2. In cracking higher boiling hydrocarbon oils to produce lower boiling hydrocarbon oils, the improvement which comprises heating a flowing stream of the oil to a high cracking temperature upwards of 900 F. under superatmospheric pressure and suddenly cooling the heated oil by reducing the pressure on the entire stream and discharging the stream of hot oil products under reduced pressure into a bath of fused caustic alkali while cooling the bath of fused caustic alkali by passing a stream of cooling fluid through said bath in indirect heat exchanging relation therewith.

3. In cracking higher boiling hydrocarbon oils to produce lower boiling hydrocarbon oils, the improvement which comprises heating a flowing stream of the oil to a high cracking temperature

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