US1877987A - Art of distillation under vacuum - Google Patents

Description

BAR OMB TRICL C zvp ENSER p 20, 1932- J. R. SCHONBERG 1,877,987

ART OF DI STILLATION UNDER VACUUM Filed June 12, 1928, 2 Sheets-Sheet l LIGHT COOLER COOLER.

TANK

CONDENSER.

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awueutoz @51 M WW P 1932- J. R. SCHONBERG I 1,377,987

ART OF DISTILLATION UNDER VACUUM Filed June 12, 1928 2 Sheets-Sheet 2 Q %1 Mai tamed gmbemto'c I low vapor velocity,

Patented Sept. 20, v1932 NITED STATES 1: E N i P SPICE JACKSON 3. SCHONBEBG,

DEVELOPMENT COMPANY, A CORPORATION OF DELAWARE ART OF DISTILLATION UNDER VACUUM Application filed June 12, 1928. Serial No. 284,867.

This invention relates generally to an improved method of Vacuum distillation and more particularly to vacuum distillation at high vapor velocities for the manufacture of petroleum lubricating oils.

When a raw oil of dark color, such as reduced crude is subjected to continuous vacuum distillation by flashing the crude at high temperature into a tower, very often trouble is experienced caused by either one of two opposite eflfects: If the distillation is carried out at a high linear velocity of the vapors in the tower, parts of the crude are carried over by splashing and entrainment, impairing the color of the distillate. If, on the other hand, the distillation is carried out at a which, at a constant vaci uum, is equivalent to a low feed rate, the crude through the tower.

remains too long in the heating coils and cracking sets in, injuring the viscosity, flash,

and pour test of the oil.

The object of the present invention is to eliminatevthese two serious draw-backs of vacuum distillation for lubricating oils. In particular, a long series of experiments led me to the discovery, regulated conditions much higher vaporvelocities can be maintained than have heretofore been considered to be practical.

The invention will be fully understood from the following description in connection with. the accompanying somepartsin section, and -Fig. ,2 is an enlarged Referringto Fig. 1, the topped crude. is charged preferably from the last still 1 of a continuous crude battery by pump 2 throughpipe 3 "nto a heating conduit 4. The feed is heated in the latter to a high temperature, say 700 F., and is then discharged through line 5 into the tower 6 which serves both to disengage the vapors and to frac- .-tionally condensethe distillate. The unva- .porized heavy residue drops to the bottom of the tower,--is,dra wn oft throughline 7 by pump 8 and 's discharged through the cooler or heat exchanger 9 into the storage tank 10.

that, under carefully drawings, in which" Fig. 1 is a diagrammatic side elevation of 1 an illustrative form of the apparatus with vertical section.

These bottoms may be worked up for asphalt or may serve as fuel oil.

The heavy lubricating oil condensed by cooling coils 11 and ,caused to flow into pan 12 by the deflector plate 13, flows by gravity through line 14 intq the drum 15, from which it is discharged by pump 16 through lines 17, 19 and cooler 'r heat exchanger 18 into the heavy distillate tank 20. Cooling coils 11 may be of the tsual pancake coil construction, through w ich the cooling liquid such as oil or wate, is circulated. The uncondensed vapors/leave the top of the tower through line 21 and pass into condenser 22 where the light lubricating oils are 0on densed and flow by gravity into drum 23 from which they are removed by pump 24 through lines 25, 27 and cooler.vv 26 into the light lubricating oil tank 28. Steam and permanent gases line 29 and: come into the barometric condenser 30 in which the steam is condensed. The permanent gases are removed through lines 31 and 32 by means of the vacuum pump leave condenser 22 through m 33. Lines 34 and 35 serve to directly cona nect drums 15 and 23 respectively to the vacuum pump. a I

Referrmg to Fig. 2, the hot feed comin from the heating conduit is discharged through line 5 tangentially into the annular bafile 36 provided with a cap 37 at the top and. open at its lower periphery, which is preferably serrated. This baflle serves to separate the heavy, unvaporized residue from the vaporsand to evenly distribute the latter. The va ors are forced to bubble through the liquid seal formed by the heavy residue at the bottom of the tower. The liquid level indicated by the dotted line 38 is held by the liquid level control 39. A manifold with steam spray/s40 serves for introduction of, steam, if so desired, to strip light constituents from the bottoms.

The main feature of the process is the regulation of the vapor velocity. The actual velocity of the vapors in the tower can be computed knowing the gravity, the molecular weight, and the amount of the light and heavy distillate, the tower temperature below pan 12, and the vacuum held. In one run, for instance, 3620 gallons of light and heavy distillate together were obtained per hour. The combined'distillate had a gravity of 23 A.P.I., corresponding to 7.63 lbs./gal.,

and an average molecular weight of 290."

the volume of a gas (or vapor) is directly proportional to the absolute temperature and inversely proportional to the pressure, the

7 volume of the distillate at 1165 Rankine under 0.97" of mercury pressure is semi ts zi' o fe i s z Dividing this volume by the inside cross section of the tower, 7 8.5", the linear vapor velocity is obtained as 2%%l l -3 I%il w i |m feet/second When steam is admitted througn'sprays 40, the volume of the vapors will be correspondingly increased. The velocity increase due to the amount of steam is calculated similarly to the above example and is then added to.

the velocity due to the oil vapors alone.

The prior art employed comparatively low vapor velocities, such as 34 feet/second when distilling. under high vacuum.

I discovered that, keeping the vacuum and the temperature at the various points of the apparatus constant, the feed rate can be increased until unusually high vapor velocities are obtained with the equipment described, without thereby injuring the quality. Working, for instance, at an absolute pressure of-1 the tower. For instance at an absolute tower- 'pressure of 0.5 inches of mercury the optimum vapor velocity ranges between that is between 11.3 and 15.6 feet/second.

Among the principal advantages of such vacuum distillation at high vapor velocity are the following-4) the maximum possible feed rate is maintained, resulting in an increase of the capacity of the unit, 2) the possibilityljof crackin in the heating coils 4 is dimin shed since 1: e time spent by the feed iiig -said- =:heating coils is decreased, 3) distillatest-good color, flash and viscosity is obtainedig v The apparatus in which the distillation is carried out may vary without departing from the scope of this invention. For instance bell-cap plates can be placed inthe tower. The vapor velocity is again calculated as above.

It will be understood that the invention is not limited to the particulars given but it is regarded as limited only in the following claims in which it is my intention to claim all inherent novelty as broadly as the prior art permits. i I

I claim:-

1. In the high vacuum distillation of petroleum lubricating oils, the improvement which comprises vaporizing part at least of the oils under an absolute pressure of less than one inch of mercury, and passing the vapors through a fractionating zone at a linear velocity increased over approximately 8 feet per second in inverse proportion to the square root of the absolute pressure held in the tower while maintaining the vacuum.

2. In the vacuum distillation of petroleum lubricating oils, the improvement which comprises heating a stream of the oil to a temperature at which it tends to vaporize at least in part, expanding the heated oil into an enlarged zone, passing the vapors evolved therein through a linearfractionating zone at a linear velocity between approximately feet per second and feet per secmercury or less equlvalent to 11 inches of mercury or less.

3. In the vacuum distillation of petroleum lubricating oils the improvement which comprises passing the hydrocarbons through a eatingzone of small cross section, then through a fractionating zone in which separation of vapors from unvaporized hydrocarbonstakes place, passing the vapors through said fractionatin'g zone at a linear velocity between approximately feet per I second and feet secondyand maintag-inking the atsolue pressure in said me tionating zone atone inch of mercury or less equivalent to. 12 inches of: mercury or less.

JACKSON R5. SCEEGNBERG.

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