US2285744A - Method for coalescing foamy oil - Google Patents

Description

E. G. RAGATZ METHOD FOR COALESOING FOAMY OIL hun@ 9, w42.

original Filed Jan."4, 195e fixed Gas Patented June 9, 1942 i 1 METHOD FOR COALESCING FOAMY OIL Edward G. Ragatz, Los Angeles, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation of California 4 Claims.

This invention relates to fractional distillation of oil, and particularly to the vacuum steam distillation of heavy hydrocarbon oils to produce lubricating oil distillates. This application is a division of my co-pending application Serial No. 57,560 for Vacuum steam distillation of heavy oils, led January 4, 1936, now Patent 2,158,425, dated May 16, 1939.

In said co-pending application the invention was directed to an improved distillation system having increased distillation capacity for the extremely heavy or deep cut fractions but without employing the increased or excessive hydrocarbon oil feed temperatures usually associated with such increase in capacity of deep cut distillation and without the undesirable results attendant upon such excessive heating, such as decomposition of the oil resulting in coke deposit in the heater tubes, discoloration of the distillates, loss of the heavy hydrocarbon distillate yields, the production of asphalts of impaired quality and the production of excessive amounts of fixed gases.

This was accomplished by supplying the latent heat of vaporization to the Vaporizable constituents of the feed material to be distilled in the vaporizing Zone of the fractionating system, by withdrawing, reheating and recirculating to the vaporizing Zone a relatively large quantity of unvaporized oil, said oil containing and conveying from the heater to the vaporizing zone sufficient sensible heat to supply a substantial portion of the latent heat of vaporization of the vaporizable constituents of the feed material. The recirculated unvaporized oil is preferably hot residual equilibrium material withdrawn from the flash section of the vaporizing Zone and is substantially unvaporizable under the conditions prevailing therein. This oil thus withdrawn from the flash section of the vaporizing zone for recirculation is usually extremely foamy, containing substantial quantities of gas and cannot be efliciently handled by the circulating pump and which often results in the pump becoming gaslocked and subject to dangerous hammering.

It is an object of this invention to provide such a heavy oil recirculatory system wherein the said recirculated oil may be eiciently handled at high temperatures by the circulatory pumping equipment.

The invention accordingly resides in providing for coalescing and freeing the hot unvaporized oil of gas and foam withdrawn from the ash zone, prior to pumping and recycling through the reheater. This enables more efcient and effective handling of the oil at high temperatures by the pumping equipment.

The accompanying drawing diagrammatically illustrates the preferred apparatus by which the process of this invention may be carried on, in which H is a double section heater provided with two separate sets of heating coils, one set for the fresh hydrocarbon feed to be distilled and the other set for the recirculated unvaporized oil; S is the stripping section; F the fractionating section; V the vaporizing section of the fractionating column; and C is the recirculating oil surge tank and coalescing chamber.

The typical operation of the distillation system may be as follows:

The cold hydrocarbon feed oil to be distilled is forced by means of pump I0 through the feed heater coils II and I2 and thence through lines I3 and I4 at a temperature of approximately 725 F.750 F. into the flash section V of the fractionating column, where it flows across the ash tray I5. The heated feed thus introduced into the flash section of the fractionating column is intimately contacted as it flows across the tray I5 with rising steam and hydrocarbon vapors from the stripping sections S therebelow. Upon thus contacting the said steam and vapors, the heated oil feed is partially flashed into vapors, which in turn pass upward together with the steam and vapors from the stripping section through the fractionating section F of the fractionating column.

The unvaporized portion of the oil passing across the flash tray I5 is totally withdrawn therefrom through pipe I6 and introduced into the coalescing chamber' C near the top where it rst flows over the gas disengaging tray I'I and then drops in a coalesced body into the lower portion thereof. The unvaporized coalesced oil is withdrawn from the bottom of the coalescing chamber C through pipe I8 by means of pump I9. A portion of the unvaporized oil thus withdrawn from the bottom is recirculated through cooler 22 to the top of the coalescing chamber through pipe 20 and allowed to fall in the form of a spray from nozzles 2I upon the oil flowing over the disengaging tray II. The effect of the cool recirculated oil spray impinging upon the oil passing over the disengaging tray I1 is to break the foam and cause its rapid coalescence. The oil collected in the lower portion of the coalescing chamber C is thus rendered relatively gas free, and even though still at a high temperature it can be efficiently handled by means of the pump i9 without the usual difficulties with gas lock and hammering.

The gas disengaged from the unvaporized oil in the coalescing chamber C is returned to the vaporizing section V of the fractionating column through line 35.

The balance of the oil withdrawn from the coalescing chamber C is forced by means of pump I9 through line 25 into the recirculating oil heating tubes 26 in the heater H. From the heating tubes 26 the reheated oil, at a temperature of approximately 725 F.750 F'., flows through pipe 2l and a portion thereof is introduced through cross connection line Ei and valve 33 into the hot feed line lil. The commingled hot feed and the reheated unvaporized recirculated oil thus ow together through line lll into the flash section of the fractionating column as described hereinbefore. Instead of recirculating all of the unvaporized oil Withdrawn from the coalescing chamber C through the heater tubes 26, if desired all or a portion thereof may, by means of cross connection S, be commingled with the cold feed material and heated together therewith in the feed heater tubes ll and I2.

The remaining portion of the reheated recirculated unvaporized oil not commingled with the hot or cold feed is introduced by way of valve 3l and line 32 into the top of the stripping section S. The stripping section S is thus supplied with unvaporized unstripped oil from the flash section of the column which has been reheated and which is at a higher temperature than that which would result in the usual method of operation where the unvaporized material flows directly from the flash tray Without being reheated into the top of the flash section.v

The reheated oil introduced into the top of tne stripping section S passes downward therein in countercurrent contact with steam introduced through line 35 wherein additional heavy lubricating oil fractions are vaporized. The stripped residual oil is withdrawn from the bottom of the stripping section through the bottoms draw-off line 3T.

The combined vapors from the stripping section and the ash tray pass from the vaporizing section V up through the fractionating section F in countercurrent to descending reflux condensate derived from the condensation from the overhead vapors in condenser Gil. Condensate and xed gases are separated in the separating drum 4I and a vacuum may be maintained upon the system by means of a vacuum pump 42. The portion of the condensed overhead vapors not returned through line i5 as reflux to the top of the fractionating column is withdrawn through line 6 to production.

It has been found advantageous to recirculate the heavy unvaporized oil from the flash tray through the heater with sufficient rapidity and in suflicient quantity so that that portion thereof which is commingled by means of valve 353 and cross connection 29 with the hot feed material flowing to the vapcrizing section and flash tray will bear a ratio of from 2 to 5 volumes of recirculated oil to one Volume of introduced feed. In recirculating the said unvaporized heavy oil 'through the heater and in commingling it with the feed material, it is advantageous to withdraw for such recirculation the unvaporized oil from the flash tray which in this case is the top tray l5 in the vaporizing section V. This oil from the flash tray is preferred to column bottoms or other lower residual material for the reason that it approximates the equilibrium liquid of the flash section vapors, or in other words this withdrawn recirculated material is in approximate equilibrium with the vapors leaving the vaporizing section and entering the fractionating section of the column. When this condition obtains, the absorption oil effect of the oil recirculated and commingled with the feed stock is a minimum, permitting the distillation of the net overhead vapor cut at a lower temperature and a greater efficiency than would be possible were column bottoms or other oil less nearly in equilibrium with the vapors employed.

The portion of the recirculated reheated oil introduced into the top of the stripping section S through line 32 constitutes in quality and quantity that remaining portion of the feed not vaporiZed in the vaporizing section of the fractionating column.

The advantages of the hereinabove described process are that since steam and reduced pressure is usually employed for effecting the vaporization of the heavy cuts at the distillation column, and since this vapor-ization heat must be supplied at the vaporizing zone by sensible heat imparted to the oil feed at the heater, and since the temperature plane to which the oil feed can be raised at the heater is definitely limited due to the cracking tendencies of the feed stock, it is highly desirable to increase the heat available for vaporization at the distillation column by conveying the said necessary heat thereto by recirculation through the heater of a relatively large proportion of equilibrium fractions which are comparatively unvaporizable under the conditions prevailing at the ash section of the column. Moreover the return of a portion of the separately reheated unvaporized oil from the flash section of the column directly to the top of the stripping section without remixture with the feed makes possible the operation of the said stripping section at the maximum temperatures permitted in the distillation unit heaters. Difculties heretofore encountered in attempting to recirculate hot oil from a fractionating column where it was necessary to handle such recirculated material by means of pumps is overcome by employing means as illustrated herein to coalesce the oil and eliminate its gas lock tendencies prior to such pumping operations.

The invention, while particularly applicable to the distillation of heavy petroleum is, however, applicable to the distillation of other liquids.

I claim:

l. A process for coalescing hot foamy oil withdrawn from a vaporizer comprising forming the body of said foamy oil into a thin layer of increased area and contacting said thin layer of hot foamy oil with a spray of cool oil.

2. A process for coalescing hot foamy cil withdrawn from a vaporizer comprising forming the body of said foamy oil into a thin layer of increased area and contacting said thin layer of hot foamy oil with a cool spray of previously coalesced oil collecting the coalesced oil and spray and returning it to the said vaporizer.

3. A process for coalescing hot foamy oil from a vaporizer comprising flowing said hot foamy oil in a thin layer over a coalescing tray in a coalescing chamber, cooling a portion of the previously coalesced hot oil withdrawn from said chamber and directly contacting said foamy oil on said tray with a spray of said cooled oil, collecting the commingled coalesced oil and spray in a lower portion of the said coalescing chamber and Withdrawing the coalesced oil from said chamber.

4. A process for coalescing hot foamy oil from a Vaporzer comprising flowing said hot foamy oil in a thin layer over a coalescing tray in a coalescing chamber, cooling a portion of the previously coalesced hot oil withdrawn from said chamber and directly contacting said ioamy oil on said tray with a spray of said cooled oil, co1- lecting the commngled coalesoed oil and spray in a lower portion of the said coalescing chamber, withdrawing the coalesced oil from said chamber and separately venting gases from said coalesced foamy oil from said coalescing chamber.

EDWARD G. RAGATZ.

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