US2105122A - Art of cracking hydrocarbons - Google Patents

Description

1 1938. T. B. KlMBALL ET AL 2,105,122

ART OF CRACKING HYDROCARBON Filed June 20, 1953 Tar g INVENIOR Mamas B, lnmbal/ 0n GJfaasa ATTORNEYS Patented Jan. 11, 1938 UNITED STATES PATENT, QFFCE ART OF CRACKING HYDROCARBONS Thomas 13.. Kimball, Hammond, and Orin G.

Kaasa, Munster, Ind, assignors to Sinclair Refining Company, New York, N. Y., a corporation of Maine Application June 20, 1933, Serial No. 676,616

10 Claims.

which this invention more particularly relates, a.

stream of oil to be cracked is forced through a heater and heated to a high temperature therein, oil to be coked is reduced to coke in a coking receptacle by direct heat exchange with the stream of heated oil discharged from the heater, and the vapors from the coking receptacle are cooled to separate, in a separating receptacle, a residual tar which is usually introduced into the coking receptacle. The separation of entrained liquid particles from the vapors from the coking receptacle, an unusually persistent form of entrainment, has required special operations, particularly in combined operations involving return to the heater of fractions condensed from vapor mixtures including vapors from the coking receptacle. Scrubbing oi the vapors from the coking receptacle in a liquid oil body including the separated tar is one of the best means of eliminating such entrainment. The maintenance of the substantial liquid bodies necessary to eiiect such scrubbing, however, involves a loss with respect to recovery of liquid distillates because of so-called polymerization reactions which proceed in such oil bodies at the elevated temperatures necessarily involved. Such polymerization reactions are reduced to a minimum by reducing to a minimum the mean time for which the average. molecular group is maintained at these elevated temperatures. This is accomplished by maintaining, in the separating receptacle in which residual tar is separated from the cooled vapors .from the coking receptacle, that minimum volume of liquid tar necessary to maintain liquid discharge from the lowermost part of the separating receptacle. Then, by maintaining a relatively high temperature in the separating receptacle, an improved recovery of liquid distillates is to be had. However, under these conditions, the tar separated in the separating receptacle tends to become progressively more refractory with respect to the coking conditions maintained in the coking receptacle with a consequent tendency to choke the system in which the operation is carried out through the gradual increase in volume of a refractory tar fraction cyclically circulating from the separating receptacle to the coking receptacle and back to the separating receptacle, and so on. This effect is avoided, in the combined operation, by

introducing into the coking receptacle part, but

only part, of the residual tar separated in the separating receptacle, the balance being discharged from the system in which the operation is carried out. The ratio between the part introduced into the coking receptacle and the part discharged from the system is with advantage kept at a maximum short of that value at which such progressive accumulation of a cyclically circulating refractory tar fraction begins. The invention consists essentially in combination, in operations of this general type, of the maintenance of a minimum of liquid tar volumein the separating receptacle with the introduction of part, but only part, of this separated tar into the coking receptacle, the maximum advantage of the invention being. derived when maximum temperatures short of those at which coking begins are maintained in the separating receptacle. In putting this invention into practice, the entrainment diificulties to which. reference has been made are eliminated by improved fractionation of the vapors escaping from the separating receptacle;

Thus, according to this invention, a stream of oil to be cracked is forced through a heater and heated therein to a temperature approximating 1000 -l150 F. and an oil to be coked is reduced to coke, in a coking receptacle, by direct heat exchange with the stream of heated oil discharged from the. heater. The vapors from the coking receptacle are cooled, advantageously to a temperature upwards of 750 F., to separate a residual tar in a separating receptacle, that minimum volume of liquid tar necessary to maintain liquid discharge from the lowermost part of the separating receptacle is maintained therein, liquid tar is discharged from the lowermost part of the separating receptacle and part, but only part, of this discharged tar is introduced into the coking receptacle. The oil to be coked may be introduced into the separating receptacle, that part of such oil remaining unvaporized therein combining with the residual tar separated therein, or it may be introduced directly into the coking receptacle, or it maybe introduced into a iractionating operation to which the Vapors escaping from the separating receptacle are subjected, in direct heat exchange with the vapors, for example. The cooling of the vapors from the coking receptacle may be effected by direct heat exchange with oil to be cracked, in operations in which a fraction condense-d from the vapors escaping from the separating. receptacle is returned to the heater, or with oil to be coked or with a fraction condensed from the vapors escaping from the separating receptacle, and stock so utilized as a cooling medium may be introduced either directly into the separating receptacle or into the vapors passing from the coking receptacle and thus into the separating receptacle.

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

The apparatus illustrated comprises the heating furnace I in which a heating coil 2 is arranged, a coking chamber 3, a separating tower 4, fractionating towers 5 and 6, a condenser I, and a receiver 8. Reflux condensers 9 and II) on tower 4, II and I2 on tower 5, and I3 and I4 on tower 6 are provided for control or supplementary control of the operation of these several towers. Reflux condensers 9, H and I3 are arranged as heat exchangers to permit the recovery of heat abstracted from the vapors passing therethrough in stock to be'supplied to the operation; Coolers I5, I9 and I! are provided for cooling residual or liquid fractions discharged from towers 4, 5 and 5 respectively and coolers I5 and I6 are arranged to permit the cooling or partial cooling of residual or liquid fractions discharged from towers 4 and 5 and returned to the operation. Only one coking chamber is illustrated; usually a group of two, three or more coking chambers is connected between the manifold headers I8, I9, 20 and 53 to avoid interruption of the combined operation while permittingdischarge of accumulated coke from and cleaning of individual coking chambers.

In order to facilitate the maintenance of liquid discharge from the lowermost part of the tower 4 while maintaining the minimum volume of liquid tar therein, this tower is provided with a tar leg 2I, the liquid level of separated tar remaining within the tower normally being maintained within this tar leg. By this expedient it is possible to maintain without unusual difficulty a volume of liquid tar as low as one-half a barrel or even less in the separating tower of the combined apparatus in which the normal charging rate to the heater approximates 200-300 barrels per hour.

In carrying out the invention in the apparatus illustrated: Oil to be cracked, a gas oil or kerosene character stock for example, is forced by means of pump 22 through the heating coil 2 and is heated therein to a temperature, for example, of 11201130 F., and the hot oil products discharged from the heating coil are introduced, through connection 23, into the coking chamber 3. Oil to be coked is introduced into the coking chamber 3 through connection 24, and is reduced to coke therein by direct heat exchange with the hot oil products entering the coking chamber I through connection 23. The coke product accumulates in the coking chamber. The vapors from the coking chamber pass to separating tower 4 through connection 25. A temperature approximating 775 F. is with advantage maintained in the lower part of the separating tower 4. To maintain this temperature, a cooler oil is brought into direct heat exchange with the vapors from the coking chamber, either by in troduction into the separating tower 4 through any of connections 26, 21, 28 and 29 or by in- .troduction into the transfer connection 25 through connection 30 or by combined introduction of cooling oil through two or more of these connections. A residual tar is separated in separating tower 4 and is discharged, as a liquid, through connection 3|, that minimum volume of liquid tar necessary to maintain liquid discharge being maintained in the tar leg 2|. Part of the residual tar discharged through connection 3I is introduced into the coking receptacle 3 through connection 24, either by means of pump 32 through connection 33 or by means of pump 34, after passing through the cooler I5, through connections 35, 36 and 31, and another part of this residual tar is discharged through connection 38. The vapors escaping from the separating tower 4 are subjected to fractionation in the fractionating tower 5, the vapors escaping from the fractionating tower are subjected to fractionation in the fractionating tower 6, and the vapors escaping from this fractionating tower, constituting a gasoline fraction for example, are condensed in the condenser I, the condensed distillate being separated from uncondensed vapors and gases and collected in receiver 8.

The oil to be cracked, supplied to the heating coil 2, may consist, for example, of a distillate fraction separated in the fractionating tower 6, supplied hot to the pump 22 through connection 39, or. of an appropriate fraction supplied to the pump 22 from an extraneous source through connection 40, or a mixture of the two. All or part of the distillate fraction separated in fractionating tower 5 may be discharged through connection 4| after passing through cooler H.

The oil to be coked, at least the higher boiling constituents of which are ultimately introduced .into the coking chamber 3, may, in the first instance, be introduced either into the coking chamber 3 through connection 24, or into the separating tower 4 through connections 25, 27, 28 and 29 or one or more of them, or into the transfer connection 25 through connection 39, or

into the fractionating tower 5 through connections 42 and 43 or one of them, or simultaneously through anytwo or more of these connections. Oil to be coked containing constitutents suitable as components of the distillate collected in receiver B or of the distillate separated in fractionating tower 5, for example, is with advantage introduced either into the fractionating tower 5, through connections 42 and 43 for example, or into the upper part of separating tower 4, through connections 28 and 29 for example. Such oil may be supplied, for example, through connection 44. Oil to be coked which is relatively free from constituents of intermediate boiling range is with advantage introduced either directly into the coking chamber 3 through connection 52 or into the separating tower 4 through connections 26 and 21 or one of them. Such oil may be supplied, for example, through connection 45. For example, crude oil may be introduced through any of connections 29, 28, 43 and 42, reduced crude oil containing a substan tial proportion of constituents of intermediate boiling range may be introduced through any of these connections or through connection 30, reduced crude oil relatively free from constituents of intermediate boiling range or fuel oil of this character may be introduced through any of connections 29, 28, 21, 26, 30 and Z4, and cracked tars and the like may be introduced through any of the connections 26, 30 and 24; The invention is not limited to the foregoing distribution of stocks, but this distribution is given merely to illustrate. i

' The fraction separated in the fractionating tower may be a distillate fraction if, any oils introduced through either connection 42 or connection 43 are distillate fractions or it may include residual constituents'if such oils include residual fractions. This fraction separated in tower 5 maybe either discharged through connection 46 where oil to be coked is not introduced into the fractionating tower 5, or it may be in whole or in part introduced into the separating tower 4 through connection 26 or connection 2'! or into the transfer connection 25 through connections 4'! and by means-of pump 48 as a cooling medium Whether or not oil to be coked is introduced into tower 5, and this either with or without having passed through cooler IE, or it may be introduced in whole. or in part into the coking chamber 3 through connection 24 or into the transfer connection 25 through connection 30 or into the separating tower 4 through connection 26 or connection 2'! where oil to be coked is introduced into tower 5. The use of the fraction or part of the fraction separated in the fractionating tower has a cooling medium in the operation of separating tower 4 is particularly advantageous where this fraction-is condensed, at least in part, by direct, heat exchange with oil to be coked introduced into tower 5. I

The several towers 4, 5 and 6 are controlled either by regulated circulation of a stock to be supplied to the operation through reflux condensers 9, II and i3, appropriate by-pass connections being provided for control of this circulation, or by regulated circulation of a cooling medium through reflux condensers l0, I2 and I4 or by regulated introduction of a vaporizable refluxing medium through the connections .49, 5G and 5!,or by any of these means conjointly.

Oil to be coked containing foreign solids, such as crude oil or reduced crude oil containing substantial proportions of salt, cracked tar containing high proportions of solid or semi-solid materials, and residual stocks including solid or semi-solid reactants or reaction products such as those resulting from the treatment of lubricating oils with caustic alkali, for example, is with advantage introduced directly" into the coking chamber 3 through connection 52. The bulk of such foreign solids is thus precipitated as part of the coke accumulating in the coking chamber and that part of the residual tar discharged through connection 38 is, in this manner, freed from that proportion of the thus precipitated solids which it would otherwise contain if this stock were introduced, for example, into the separating tower 4. The value as a liquid fuel of the residual tar discharged through connection 38, in operations in which such residual oil containing foreign soiids is to be handled, can thus be substantially increased. In one aspect, the invention thus makes possible the recovery of substantial values from residual oils containing foreign solids otherwise useless even as fuel.

The features of operation combined in the process of the invention cooperate to improve the recovery of liquid distillates and to improve the capacity of any particular apparatus in.which the operation is carried out. In one aspect, the concentration of the residual tar separated in the separating receptacle is a measure of the improvement in recovery of liquid distillates.

This invention makes possible the separation of a residual tar in the separating receptacle so concentrated as to have a gravity, corrected to atmospheric temperature, as low as 5 A. P. I. In another aspect, the concentration of the residual tar so separated is a measure of the improvement in capacity of the apparatus in which the operation is carried out. As the concentration of this residual tar is increased, the burden imposed upon the coking operation proper is reduced and the ratio of vapors to liquids discharged from the separating receptacle is increased. In the combined operation of the invention, full realization of this improvement with respect to the coking operation proper is had because of limitation, by means of the invention, of accumulation of any cyclically circulating refractory tar fraction. Further, by the provision of adequate fractionation of the vapors escaping from the separating receptacle, a distillate frac-- tion substantially free from tar constituents and appropriate to be supplied to the heating oper ation is recovered.

We claim:

1. In cracking and coking petroleum oils, the improvement which comprises forcing a stream of oil to be cracked through a heater and heating it therein to a temperature approximating 1000- 1150 F. and reducing. another oil to coke by direct heat exchange with this stream of heated oil in a coking receptacle, cooling the vapors from the coking receptacle to separate a residual tar in a separating receptacle, maintaining that minimum volume of liquid tar in the separating receptacle necessary to maintain liquid discharge from the lowermost part thereof, discharging liquid tar from the lowermost part of the separating receptacle and introducing part but only part of this discharged tar into the coking receptacle.

2. In cracking and coking petroleum oils, the. improvement which comprises forcing a stream of oil to be cracked through a heater and heating it therein to a temperature "approximating 1000-1150 F. and reducing another oil to coke by direct heat exchange with this stream of heated oil in a coking receptacle, cooling the vapors from the coking receptacle to a temperature approximating 775 F. to separate a residual tar in a separating receptacle, maintaining that minimum volume of liquid tar in the separating receptacle necessary to maintain liquid discharge from the lowermost part thereof, discharging liquid tar from the lowermost part of the separating receptacle and introducing part but only part of this discharged tar into the coking receptacle.

3. In cracking and coking petroleum oi1s,'the improvement which comprises forcing a stream of oil to be cracked through a heater and heating it therein to a temperature approximating 1000- 1150 F. and reducing another oil to coke by direct heat exchange with this stream of heated oil in a coking receptacle, cooling the vapors from the coking receptacle to separate a residual tar in a separating receptacle, introducing oil to be coked into the separating receptacle, maintaining that minimum volume of liquid tar in the separating receptacle necessary to maintain liquid discharge from the lowermost part thereof, discharging liquid tar from the lowermost part of the separating receptacle and introducing part but only part of this discharged tar into the coking receptacle.

4. In cracking and cokingpetroleum oils, the improvement which comprises forcing a stream of oil to be cracked through a heater and heating fit it therein to a temperature approximating 1000"- -1150 F. and reducing another oil to coke by direct heat exchange with this stream of heated oil in a coking receptacle, cooling the vapors from the coking receptacle to separate a residual tar in a separating receptacle, maintaining that minimum volume of liquid tar in the separating receptacle necessary to maintain liquid discharge from the lowermost part thereof, discharging liquid tar from the lowermost part of the separating receptacle and introducing part but only part of this discharged tar into the coking receptacle, and introducing oil to be coked into the coking receptacle.

5. In cracking and coking petroleum oils, the improvement which comprises forcing a stream of oil to be cracked through a heater and heating it therein to a temperature approximating l000-1l50 F. and reducing another oil to coke by direct heat exchange with this stream of heated oil in a coking receptacle, cooling the vapors from the coking receptacle by direct heat exchange with oil to be coked to separate a residual tar in a separating receptacle, maintaining that minimum volume of liquid tar in the separating receptacle necessary to maintain liquid discharge from the lowermost part thereof, discharging liquid tar from the lowermost part of the separating receptacle and introducing part but only part of this discharged tar into the coking receptacle.

6. In cracking and coking petroleum oils, the improvement which comprises forcing a stream of oil to be cracked through a heater and heating it therein to a temperature approximating 1000"- 1150 F. and reducing another oil to coke by direct heat exchange with this stream of heated oil in a coking receptacle, cooling the vapors from the coking receptacle by direct heat exchange with another oil to separate a residual tar in a separating receptacle, maintaining that minimum volume of liquid tar in the separating receptacle necessary to maintain liquid discharge 'from the lowermost part thereof, discharging liquid tar from the lowermost part of the separating receptacle and introducing part but only part of this discharged tar into the coking receptacle.

7. In cracking and coking petroleum oils, the improvement which comprises forcing a stream of oil to be cracked through a heater and heating it therein to a temperature approximating 1000-1150 F. and reducing another oil to coke by direct heat exchange with this stream of heated oil in a coking receptacle, cooling the vapors from the coking receptacle to separate a residual tar in a separating receptacle by direct heat exchange with a fraction condensed from the vapors escaping from the separating receptacle, maintaining that minimum volume of liquid tar in the separating receptacle necessary to maintain liquid discharge from the lowermost part thereof, discharging liquid tar from the lowermost part of the separating receptacle and introducing part but only part of this discharged tar into the coking receptacle.

8. In cracking and coking petroleum oils, the improvement which comprises forcing a stream of oil to be cracked through a heater and heating it therein to a temperature approximating 1000-l150 F. and reducing another oil to coke by direct heat exchange with this stream of heated oil in a coking receptacle, cooling the vapors from the coking receptacle to separate a residual tar in a separating receptacle by direct heat exchange with a fraction condensed from the vapors escaping from the separating receptacle, maintaining that minimum volume of liquid tar in the separating receptacle necessary to maintain liquid discharge from the lowermost part thereof, discharging liquid tar from the lowermost part of the separating receptacle and introducing part but only part of this discharged tar into the coking receptacle, and condensing said fraction by direct heat exchange with oil to be coked.

9. In cracking and coking petroleum oils, the improvement which comprises forcing a stream of oil to be cracked through a heater and heating it therein to a temperature approximating l000-1l50 F. and reducing another oil to coke by direct heat exchange with this stream of heated oil in a coking receptacle, cooling the vapors from the coking receptacle to a temperature upwards of 750 F. to separate a residual tar in a separating receptacle, maintaining that minimum volume of liquid tar in the separating receptacle necessary to maintain liquid discharge from the lowermost part thereof, discharging liquid tar from the lowermost part of the separating receptacle and introducing part but only part of this discharged tar into the coking receptacle.

10. In cracking and coking petroleum oils, the improvement which comprises forcing a stream of oil to be cracked through a heater and heating it therein to a temperature approximating l000'1150 F. and reducing another oil to coke by direct heat exchange with this stream of heated oil in a coking receptacle, cooling the vapors from the coking receptacle to separate a residual tar in a separating receptacle, maintaining that minimum volume of liquid tar in the separating receptacle necessary to maintain liquid discharge from the lowermost part thereof, discharging liquid tar from the lowermost part of the separating receptacle and introducing part but only part of this discharged tar into the coking receptacle, and introducing oil to be coked containing foreign solids directly into the coking chamber.

THOMAS B. KIMBALL. ORIN G. KAASA.

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