US2827171A - Thermal diffusion method and apparatus - Google Patents

Description

March 15, 195s Filed June 20, 1956 D. FRAzlER 2,827,171

THERMAL DIFFUSION METHOD AND APPARATUS 2 Sheets-Sheet 1 FEED RATE cc/mn.

INVENTOR. DAVID FRAZlER his A TORNEY March 18, 1958 D. FRAZIER 2,827,171

THERMAL' DIFFUSION METHOD AND APPARATUS Filed Junezm 195e 2 sheets-sheet 2 IN VEN TOR. DAVID FRAZIER 5 ATTORNEY :United States Patent O THERPAL D11? FUSN METHOD AND APPARATUS David Frazier, Cleveland Heights, Ohio, assignor to I1 he Standard @il Company, Cleveland, Ohio, a corporation of ho Application .lune 20, 1956, Serial No. 592,662

6 Claims. (Cl. 210-72) This invention relates to a continuous method and apparatus for separating uid mixtures into fractions enriched with dissimilar components.

lt has been ltnown for some time that it is possible to separate, by thermal diffusion, liquids and gases that are incapable of separation by any other known method, or that are separated by other methods with great difficulty. It was at first believed that thermal diffusion could be carried out only in a discontinuous, i. e., batchwise, manner. More recently, it has been discovered that it is possible to carry out thermal diffusion separation in a continuous manner.

The process of separation by thermal diffusion consists in essence of confining a fluid mixture, a term intended herein to include mixtures that are liquid or gaseous under the conditions of operation, in a narrow chamber and imposing across the chamber a temperature gradient. When the opposed walls defining such a chamber are non-horizontal, thermal circulation of the contents of the chamber is set up by virtue of the differences in density adjacent the relatively heated and cooled walls, referred to herein for convenience as the hot and cold Walls. This thermal circulation is relied upon to separate the components of the mixture that preferentially accumulate adjacent the hot wall from those components that preferentially accumulate adjacent the cold wall.

It has been found that in order to obtain satisfactory rates of separation by thermal diffusion, the opposed thermal diffussion chamber-forming surfaces of the hot and cold walls should be spaced apart no more than about one-half inch, spacings of the order of 0.2 to 0.3 inch being preferred for separation of gaseous mixtures and smaller spacings of the order of 0.15 inch or less, preferably about 0.02 to 0.06 inch, being most effective for separation of liquid mixtures. In view of the small spacings involved, considerable diiculties have been encountered in taking advantage of the separation actually, obtained within a thermal diffusion separation chamber from the point of view of separately withdrawing the dissimilarl fractions formed within the very narrow chamber and also inA replacing these fractions with fresh luid Without undue turbulence and remixing of the separated fractions.

lt has now been found that surprisingly good yields of dissimilar fractions are obtainable, particularly at relatively high feed rates, with thermal diffusion separation chambers formed by non-horizontal, equidistantly-spaced wall members, e. g., substantially vertical, concentric tubes. These excellent results are obtainable by providing upper and lower reservoirs communicating with the upper and lower ends of the chamber and having Sullicient volume to permit mixing of fresh feed with fluids entering the reservoirs from the chamber and also to avoid a turnabout of the fluid within the separation chamber before it reaches the reservoir. Generally, these effects are obtained when the reservoirs are at least about twice as Wide and twice as high or deep as the spacing between the walls forming the separation chamber,

By feeding the fresh fluid into the reservoirs, the separation chamber is lled with the fluid mixture which, by thermal diffusion, is separated into an ascending fraction containing a higher than initial concentration of one of the dissimilar components and a descending fraction containing a higher than initial concentration of another of the dissimilar components. The entering uid mixture is admixed in the reservoirs with these ascending and descending fractions and continuously withdrawn therefrom.

The apparatus and method of the invention land the surprisingly good results obtainable therewith are described in greater detail by reference to the accompanying drawing wherein:

Figure 1 is a schematic illustration, in elevation, of a prferred embodiment of the apparatus of the invention; `an

Figures 2 and 3 are graphs illustrative of the results obtainable wit-h the method and apparatus of this invention as compared with those obtainable under com"arable conditions with apparatus in which the entire feed of fluid mixture enters the chamber midway between the upper and lower ends.

The apparatus illustrated in Figure l comprises an annular thermal diffusion separation chamber 10 formed by the outer surface of an inner tube 11 and the inner surface of an outer tube 12. The upper end of the annular chamber is provided with a reservoir 14 having an inlet connection 16 and an outlet connection 17. The lower end of the chamber is similarly provided with a reservoir 19 having an inlet connection 20 and an outlet connection 21. Suitable means not forming part of this invention are provided for relatively heating and cooling the chamber-forming walls. Thus, for example, the inner tube 11 may be relatively heated by passing steam through it, and the outer tube 12 may be relatively cooled by circulating water through la cooling jacket 22.

In operation, fresh liquid is continously introduced into upper and lower reservoirs 14 and 19 by way of inlet connections 16 and 20 and a temperature gradient is imposed across the separation chamber 10 by relatively heating one of the inner and outer tubes and relatively cooling the other. The feed entering the reservoirs fills the thermal diffusion chamber 10 and While therein is resolved into a first fraction accumulating preferentially adjacent the hot wall ascending to the upper reservoir 14 and a second fraction accumulating preferentially adjacent the cold wall and descending to the lower reservoir 19. Thus, for example, if the inner tube 11 is relatively heated and the `outer tube 12 is relatively cooled, the ascending fraction containing a higher than initial concentration of one of the dissimilar components in the liquid mixture ascends along the outer surface of the inner tube 11 and the other fraction containing a higher than initial concentration of another of the dissimilar components descends along the inner surface of the outer tube 12 into the lower reservoir 19. The fresh liquid mixture entering the reservoirs is admixed with these dissimilar fractions, a portion of the liquid enters the separation chamber 10 to replace the fractions entering the reservoirs and the remainder, enriched with the components in the dissimilar fractions, is separately withdrawn by way of withdrawal ports 17 and 21.

A solvent extract neutral oil obtained by furfural extraction of an oil from a Mid-Continent crude and having a viscosity of SUS at 100 F. and a refractive index of 1.4730 was subjected to separation by thermal diusion at varying rates of feed in an annular separation chamber such as that illustrated in Figure 1 having a height of 6 feet, a mean diameter of one inch and a slit Patented Mar. 18, 1958 having a width and height greater than the distance between said opposed walls, imposing a temperature gradient across the fluid in the chamber, whereby dissimilar fractions are formed, one of which contains a higher than initial concentration of one component and ascends to enter the upper reservoir and another of which contains a higher than initial concentration of another component and descends to enter the lower reservoir, continuously feeding fresh fluid into the upper and lower reservoirs for admixture with the dissimilar fractions from said thermal diffusion separation chamber, directing portions of the admixed iluid in the respective reservoirs into the upper and lower ends of the thermal diffusion separation chamber, and continuously and separately withdrawing dissimilar fractions from the upper and lower reservoirs.

4. Thermal diffusion method which comprises confining a liquid mixture in a vertical thermal diiusion separation chamber comprising opposed walls and terminating in reservoirs at its upper and lower ends, said reservoirs having a width and height greater than the distance between said opposed walls, imposing a tempreature gradi- .ent across the liquid in the chamber, whereby dissimilar fractions are formed, one of which contains a higher than initial concentration of one component and ascends to enter the upper reservoir and another of which contains a higher than initial concentration of another component and descends to enter the lower reservoir, continuously feeding fresh liquid into the upper and lower reservoirs for admiXture with the dissimiiar fractions from said thermal diffusion separation chamber, directing portions of the admixed liquid in the respective reservoirs into the upper and lower ends of the thermal diffusion separation chamber, and continuously and separately withdrawing dissimilar fractions from the upper and lower reservors.

5. Method for continuously separating a fluid mixture into fractions enriched with dissimilar components which comprises imposing a temperature gradient across an annular separation chamber defined by the opposed 4 Walls of substantially vertical concentric tubes and communicating with upper and lower reservoirs at its upper and lower ends; said reservoirs having a width and height at least about twice the distance between the opposed walls, continuously feeding fresh fluid into said reservoirs, whereby the separation chamber is lled with huid mixture for separation into an ascending fraction containing a higher than initial concentration of one of the dissimilar components and a descending fraction containing a higher than initial concentration of another of the dissimilar components and the entering fluid mixture is admixed in said reservoirs with the ascending and descending fractions; and continuously and separately withdrawing, from the upper and lower reservoirs, fractions enriched with dissimilar components by admixture with the ascending and descending fractions.

6. Method for continuously separating a liquid mixture into fractions enriched with dissimilar components which comprises imposing a temperature gradient across an annular separation chamber defined by the opposed walls of substantially vertical concentric tubes and communicating with upper and lower reservoirs at its upper and lower ends; said reservoirs having a width and height at least about twice the distance between the opposed walls, continuously feeding fresh liquid into said reservoirs, whereby the separation chamber is lled with liquid mixture for separation into an ascending fraction containing a higher than initial concentration of one of the dissimilar components and a descending fraction containing a higher than initial concentration of another of the dissimilar components and the entering liquid ture is admixed in said reservoirs with the ascending and descending fractions; and continuously and separately withdrawing, from the upper and lower reservoirs, fractions enriched with disimilar components by adminture with the ascending and descending fractions.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. 3. THERMAL DIFFUSILON METHOD WHICH COMPRISES CONFINING A FLUID MIXTURE IN A VERTICAL THERMAL DIFFUSION SEPARATION CHAMBER COMPRISING OPPOSED WALLS AND TERMINATING IN RESERVOIRS AT ITS UPPER AND LOWER ENDS, SAID RESERVOIRS HAVING A WILDTH AND HEIGHT GREATER THAN THE DISTANCE BETWEEN SAID OPPOSED WALLS, IMPOSING A TEMPERATURE GRADIENT ACROSS THE FLUID IN THE CHAMBER, WHEREBY DISSIMILAR FRACTIONS ARE FORMED, ONE OF WHICH CONTAINS A HIGHER THAN INITIAL CONCENTRATION OF ONE COMPONENT AND ASCENDS, TO ENTER THE UPPER RESERVOIR AND ANOTHER OF WHICH CONTAINS A HIGHER THAN INITIAL CONCENTRATION OF ANOTHER COMPONENT AND DESCENDS TO ENTER THE LOWER RESERVOIR, CONTINUOUSLY FEEDING FRESH FLUID INTO THE UPPER AND LOWER RESERVOIRS FOR ADMIXTURE WITH THE DISSIMILAR FRACTIONS FROM SAID THERMAL DIFFUSION SEPARATION CHAMBER, DIRECTING PORTIONS OF THE ADMIXED FLUID IN THE RESPECTIVE RESERVOIRS INTO THE UPPER AND LOWER ENDS OF THE THERMAL DIFFUSION SEPARATION CHAMBER, AND CONTINUOUSLY AND SEPARATELY WITHDRAWING DISSIMILAR FRACTIONS FROM THE UPPER AND LOWER RESERVOIRS.

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