US2319750A - Distillation process - Google Patents

Description

y 1943- J. R. SCHONBERG, EI'AL 2,319,750

DISTILLATION PROCESS Filed Aug. 12, 1939 C ON-DENSE FLASH ZONE STEAM -457- .S TR P NC ZONE Wigwam Patented May 18, 1943 DISTILLATION PROCESS Jackson R. Schonberg and James B. Maxwell,

Westfield, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application August 12, 1939, Serial No. 289,762

6 Claims.

boiling range and for the production of low penetration asphalts. In accordance with the present process, a small portion of the oil from' a plate above the flash zone is withdrawn and recirculated with the fresh feed through the heating coil while the temperature of the oil in the stripping section is maintained substantially equivalent to or above the temperature of the entering feed to the flash zone by removing oil from the stripping section, reheating and returning the same.

Recirculation of relatively high boiling stock with the fresh feed is known in flash distillation operations. However, the recirculated high boiling stock is usually withdrawn from the distillation tower at a point below the point of introduction of fresh feed. These recirculation operations are conducted primarily to effect a better flash distillation operation by preventing an excessive drop in temperature of the unvaporized portions from the flash zone. An excessive temperature drop is undesirable below the flash zone since further vaporization of the oil is materially decreased-and relatively large quantities of steam are necessary in order to vaporize the desired amount of the oil from the liquid bottoms. Thus, the added portion of high boiling oil recirculated through the furnace or heating coil with the fresh feed and to the flash zone serves as an added heat reservoir from which sensible heat may be secured to supply suflicient latent heat in order to effect the desired vaporization without causing an excessive temperature drop of the unvaporized oil.

In operations of this character it is necessary to recirculate a relatively large amount of oil in order to supply an ample reservoir of sensible heat so that an excessive temperature drop will not occur due to the amount of latent heat removed in securing the desired vaporization. Re-

circulation of a large volume of oil is not desirable since it dilutes the oil which is to be flashed with relatively high boiling fractions and thus offsets, to a large extent,.the benefits of preventing a substantial temperature drop in the flash zone. Recirculation of a relatively large volume of oil is also undesirable in that increasingly larger equipment is needed in order to secure the desired capacity.

It is also known in flash distillation operations to remove oil fractions not vaporized in the flash zone by means of open steam in a stripping section. In these operations it has been found that the vaporization of the fractions to be removed occurs principally on the upper plates of the stripping section. The latent heat of vaporization required on these plates to secure the desired vaporization materially lowers the temperatures. This is undesirable since steam stripping on the plates below the flash zone becomes increasingly less'efiective as the temperatures of the respective'plates are lowered.

We have now discovered a process by which it is possible to secure an optimum separation between the overhead products and the bottoms product in a distillation operation and to effect material economies in the distillation of oils. In accordance with our process, a relatively small amount of oil' is withdrawn from a plate above the flash zone and recirculated through the heating coil with the fresh feed and reintroduced into the flash zone, while the temperature in the stripping section is maintained substantially equivalent to or above the temperature of the entering feed to the flash zone by simultaneously withdrawing oil from the stripping section, reheating and returning the oil to the stripping section. We have discovered that when the distillation operation is conducted in this manner it is possible to secure high yields of high vi..- cosity lube fractions boiling in the range immediately above the asphalt boiling range and to simultaneously produce low penetration asphalt/s as determined by the A. S. T. M. test.

- Our process may be readily understood by ref erence to the attached drawing illustrating one modification of the same. Fresh feed oil is introduced into furnace l by means of feed line 2. This oil flows through the radiant and convection sections of furnace l and is withdrawn by means of line 3 and introduced into flash zone 4 of distillation tower 5. Steam may be introduced into the feed oil in furnace l by means of steam line 6. Temperature and pressure conditions are maintained in distillation tower 5 adapted to secure a flash operation and to remove overhead the desired amount of the fresh feed without causing appreciable decomposition of, the same. The vaporized portions of the oil flashed in flash zone 4 pass upwardly through a fractionating section I of distillation tower 5. Section I contains a suitable number of bubble cap plates or their equivalent. The unvaporized portions of the oil pass downwardly from flash zone 4 into stripping zone 8. Stripping section 8 contains a suitable number of bubble cap trays or their equivalent. Steam is introduced below the stripping zone by means of line IS in order to assist in the removal of the desired amount of vapors from the unvaporized oil. Heavy unvaporized bottoms are withdrawn from distillation tower by means of line 9. A side stream of intermediate boiling range may be withdrawn from distillation tower 5 by means of line Ill. The overhead vaporized portion is withdrawn from distillation tower 5 by means of line H, condensed in condenser I2, and passed to distillate drum [3. Reflux is returned to tower 5 by means of line H. Uncondensed vapors are removed from distillate drum I3 by means of line 20, while the condensed distillate product is removed by means of line 2!. An oil cut is withdrawn from the plate in the fractionating section immediately above the flash zone by means of line l5, recirculated with the fresh feed through furnace I into flash zone 4. Another oil cut is simultaneously withdrawn from a plate in the stripping section below the upper plate by means of line I6, reheated in a separate coil in coil furnace l and then reintroduced into the stripping section on the plate from which it was withdrawn or on a plate immediately below the point of withdrawal by means of lines I! and 22. Steam may be introduced into the oil being reheated by means of line l8.

The process of the present invention may be widely varied. The invention is readily applicable in the distillation of any oil and is especially desirable in the flash distillation of oils boiling in the range above about 550 F. In accordance with the preferred modification of the present invention, conditions are adapted in the distillation operation to remove overhead from 50% to 95% of the fresh feed. In general, it is preferred to recirculate with the fresh feed a relatively small critical quantity of oil which includes the highest boiling fractions of the overhead products and the lowest boiling fractions of the bottoms products, The quantity of oil recirculated with the fresh feed should preferably be below i 10% and not over based upon the total quantity of fresh feed.

It is quite important that the relatively small quantity of recirculated oil should contain the relatively low boiling constituents of the bottoms and the relatively high boiling constituents of the overhead and that the temperature of the stripping section be maintained by withdrawing, reheating, and returning relatively higher boiling fractions from the stripping section. The amount of oil withdrawn, reheated and returned to the stripping section will be adjusted to maintain the temperature in the stripping section substantially equivalent to or above the temperature of the entering feed to the flash zone. In certain operations a reheating operation may be desirable, in which case the entire quantity of oil is withdrawn from an upper plate, preferably from the first or second plate adjacent the flash zone, reheated and returned to a plate immediately below the plate from which it was withdrawn. In other operations it is desirable to recirculate a quantity of oil which may be either greater or less than the quantity of oil flowing down the stripping section. If the latter opera- These results are secured since the removal and recirculation with the fresh feed of a relatively small portion of oil from the flash section enhances the efliciency of the stripping section, while the reheating of the oil in the stripping section substantially improves the efiective value and results secured by recirculating the oil with the fresh feed.

The present invention is not to be limited in any manner whatsoever, but only in and by the following claims in which it is desired to claim all novelty insofar as the prior art permits.

We claim:

1. Process for the flash distillation of oil for the production of maximum yields of high viscosity oils boiling immediately above the asphalt boiling range and for the production of low penetration asphalts comprising heating a feed oil by passing the same through a heating coil, withdrawing and introducing the heatedfeed oil into a distillation tower under conditions to secure flash vaporization of a substantial amount of the oil, passing vaporized portions upwardly through the tower into a fractionating section, withdrawing a portion of the oil from a plate in the fractionating section immediately above the flash zone and recirculating the same in the absence of added recycled higher boiling oils through said heating coil into the flash zone with the fresh feed, passing unvaporized portions of the oil downwardly from the flash zone into a stripping section, withdrawing oil from an upper plate in said stripping section, reheating and returning the same to a plate in said stripping section under conditions adapted to secure in said stripping section a temperature at least substantially as high as the temperature of the entering feed into said flash zone.

2. Process in accordance with claim 1 in which said oil withdrawn and returned to said stripping section is reheated under conditions adapted to secure in said stripping section a higher temperature than the temperature of the fresh feed entering into said flash zone.

3. Process in accordance with claim 1 in which conditions of said distillation tower are adapted to secure 50% to flash vaporization of the feed oil in said flash zone and stripping section.

4. Process for the flash distillation of oils for the production of maximum yields of high viscosity oils boiling immediately above the asphalt boiling range and for the production of low penetration asphalts comprising heating a petroleum oil by passing the same through a heating zone, introducing said oil into a flash zone of a distillation tower under conditions to secure substantial vaporization of the oil, passing vaporized portions of the oil upwardly through a fractionating section, withdrawing from a plate immediately above said flash zone an oil containing relatively low boiling constituents of the bottoms and relatively high boiling constituents of the the amount of said recirculated oil is less than 10%, based upon the fresh feed.

6. Process in accordance with claim 4 in which the temperature in said stripping section is maintained at least equivalent to the temperature of the fresh feed oil by withdrawing the oil from the plate immediately below the flash zone, re-

heating the same, and returning the withdrawn oil to the same plate.

JACKSON R. SCHONBERG. JAMES B. MAXWELL.

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