US 3075695 A
Description (OCR text may contain errors)
A. U- AYRES IMPROVEMENT IN CENTRIFUGE ROTORS Original Filed Feb.- 27, 1958 Jan. 29, 1963 3 Sheets-Sheet 1 ms mm 2 N Mu M3 m 5 B N Q w m 4 i O A I M. 2 M M B \\v ATTORNEY A. U. AYRES Jan. 29, 1963 INVENTOR. ARTHUR u. AYRES BY U a s ATTORNE Jan. 29, 1963' A. u. AYRES 3,075 5 IMPROVEMENT IN CENTRIFUGE ROTORS Original Filed Feb. 27, 1958 3 Sheets-Sheet 3 W I 0 36 f INVENTOR. ARTHUR U. AYRES ATTORNEY United States Patent 3,075,65 IRZFRQVEWiENT EN (JEN'ERHFUGE RGTGRS Arthur U. Ayres, Philadelphia, Pa, assignor to The fihwples Qorporation, a corporation of Delaware Griginal application Feb. 27, 1953, her. No. 718,634, new
Patent No. spaaasa, dated Get. 20, 1961. Divided and this application Mar. 6. 1959, fier. No. 797,792
2 Qiaims. (Cl. 233-- i-6) This application is a division of my co-pending application now Patent No. 3,004,050, issued October 10, 1961.
This invention pertains to a centrifuge rotor for the refining of fatty oils (e.g. glyceride oils), and more particularly to a centrifuge rotor for the refining of vegetable and animal oils, such as cottonseed oil, soya bean oil, peanut oil, corn oil, sunflower seed oil, sesame oil, rape seed oil, cocoanut oil, babassu oil, palm oil, palm kernel oil, linseed oil, tallow, lard, grease, fish oil, whale oil, etc.
Fatty oils are ordinarily refined by treating the same with an aqueous alkaline reagent, such as sodium carbonate and/or sodium hydroxide. This is followed by the separation of the refined oil from the aqueous phase, the latter containing reaction products and/or impurities such as soapstock, gums, and/or color bodies. The purpose of such refining is to neutralize and remove free fatty acids, to remove gums, to remove color bodies and/or to otherwise improve the quality of the oil.
Such refining, particularly when the purpose is to remove free fatty acids, is frequently followed by a second refining known in the art as rerefining. The purpose of rerefining is to further improve the quality of the oil, largely by way of removal of color bodies, for which a reagent comprised of aqueous caustic soda is well suited.
The use of a rerefining step is generally accepted practice when aqueous sodium carbonate is employed as the reagent for neutralizing free fatty acids in the initial refining, for sodium carbonate is rather deficient as a reagent for removing color bodies. The use of a rerefining step is also beneficial in many instances, depending on the source and/ or type of the crude oil, when the initial refining is conducted with stoichiometric or near stoichiometric proportions, based on free fatty acid present, of caustic soda as the refining reagent.
In any event, the residue of free fatty acids remaining in the fatty oil alter initial refining with an alkaline reagent to remove free fatty acids is very low, e.g. below 25%. Fatty oils so refined also are low in materials commonly referred to as gums, e.g. phosphatides, proteinsceous materials, resins, etc. Fatty oils which have been degummed otherwise than by treatment with a reagent to remove free fatty acids also are low in gum-s. Also certain fatty oils are initially low in free fatty acids, e.g. below 1%.
In the treatment of such fatty oils which are low in free fatty acids and/or gums, whether in such state naturally or as a result of prior processing, it is common practice to employ a reagent, such as aqueous caustic soda, to improve the quality of the oil, e.g. by reduction in free fatty acids and/or col-or or otherwise. In such practic a small amount of soapstock is usually formed, whether by reduction in free fatty acids, or by saponification of a small amount of neutral oil, or both, and the aqueous caustic soda reagent solutions employed are freqaently of such concentration as to cause the soapstock 3,75,fid5 Patented Jan. 29, 1963 formed to be salted out from the aqueous reagent phase, or to otherwise appear in whole or in part in the form of a third phase separate from the oil and the aqueous reagent phase. The result is that the soapstock, being of a density intermediate that of the fatty oil and that of the aqueous phase, tends to be discharged from the centrifuge along with the fatty oil. This is because the aqueous phase, being of a density greater than that of the soapstock phase, forms a layer in the bowl in a position radially outwardly from the soapstock layer, and thus interferes with the proper discharge of the soapstock layer from the bowl as a heavier phase. As a result, at least a part of the soapstock is forced to discharge from the bowl as a lighter phase, ie along with the oil, thus defeating the purpose of the operation, which is to separate both soapstock and aqueous reagent phase from the oil.
This condition may be alleviated, at least to some extent, by the separate feed of water into the peripheral zone of the bowl to reduce the concentration of caustic soda in the aqueous phase, with consequent reduction in its density, ideally to a point where the density of the aqueous phase becomes the same as that of the soapstock phase. Under ideal or near ideal conditions, both phases then are discharged from the bowl together, and separately from the oil. The dilution of the aqueous phase, however, results in the formation of a certain amount of oil-containing aqueous emulsion which is discharged from the bowl along with the soapstock and aqueous phases, with consequent loss in oil.
Another source of difficulty resides in the fact that the capacity of the soapstock phase to retain aqueous reagent phase, either by solution or entrainment, varies not only between different oils, but also for any given individual oil depending in large measure on its gum content. Even during a given run there may be Variations to the extent that a separate aqueous layer may form only sporadically, or may disappear sporadically. In any event, it is difiicult to continuously centrifugally separate by liquid balance an aqueous reagent phase as a layer separate from the soapstocl; layer, and to continuously discharge the same from the bowl, e.g. over a weir.
Af er extensive experimentation, I have discovered and perfected a centrifuge rotor or bowl for the refining of fatty oils wherein the aqueous phase, if, when and to the extent occurring as a layer separate from the soapstock layer, is separated and separately discharged from the centrifugal bowl, while leaving the oil and soapstock layers in desired hydrostatic balance.
Furter features of the invention will become apparent to persons skilled in the art upon becoming familiar herewith, and as the specification proceeds, and upon reference to the drawings in which:
FIGURE 1 is a vertical section, shown broken, illustrating apparatus embodying and useful in the practice of the invention;
FIGURE 2 is a section taken generally on line 2--2 of FEGURE l, with portions removed for better illustration; and
FIGURE 3 is an enlargement of a portion of FIG- URE 1.
Referring now more particularly to the drawings, the centrifuge rotor lib is shown provided with an inlet feed boss 11 which is surrounded by a guide bushing assemably or drag 12. The guide bushing assembly 12 is se- 3, cured in position on a base 13 which also carries a feed nozzle 1 through which the reaction mass is continuously fed into the centrifuge rotor 10.
In the apparatus as illustrated, an auxiliary feed nozzle 15 also is secured to the base 13, and surrounds the feed nozzle 14, and feed nozzle 14 is shown provided with a circumferential head 16, the purpose of which is to deflect outwardly against the inner wall of boss 11 any liquid fed into the bowl through the nozzle 15 in the practice of a modification of the inventionv to be hereinafter more particularly described.
The lower end 17 of rotor is provided with a cylindrical flange 18 positionedfinteriorly of the rotor. The upper .end of flange 18 forms a. seat for a flange 20 of a feed directing member 19 shown with a conical base portion. Member 19 may be secured in position on flange 18 by any suitable means, such as welding, Flange 18 is provided with a plurality of circumferentially spaced slots illustrated at 21, in order to aiford outlets from the space between thernember 19 and the inner peripheral bottom, portion of the rotor .for liquid fed into and passing upwardly and outwardly through such space.
I Member 19, asrshown,v is provided on its inner conical surface with a plurality of circumferentially spaced radially extending vanes or fins 28, and similarly on its outer conical surface with a plurality of circumferentiallyspaced radially .extendingvanes or line 36. The fins 28 'extend'inwardly toward feed opening 29 in the lowermost part of the member 19. Pins 30 extend from the'outer surface of the membcr19 to the inner surface of the lower end 17 ofthe rotor.
The construction so far particularly described may be regarded as more or less conventional, and well-known.
Referring now to the upper part of rotor 10, at 31 is showna rotor top which threadedly engages the upper interior of rotor 10 as illustrated at 32. Rotor top 31 includes an upwardly extending center portion 33 shown provided with'threads' 34 for-engagement by a nut on an overhead driving spindle, not shown.
An annular member 35 threadedly'engages rotor top 31 as illustrated at 36, and is provided with an upwardly extending cylindricalportion 37 which is threadedly engaged by a, ring darn nut SSIas illustrated at 39, ring dam 42' being secured in position between cylindricalportion 37 and ring dam nut 38.
Member 35 also is provided with an annular recessed.
portion 43 in which is positioned an annular resilient valve member 44- shown, associated with a plurality of circumferentiallyspaced vertical outlet channels 45 milled intothe interiorwall of rotor 10.
In the operation or" the apparatus shown in the drawings, a stream of the reaction mass is projected through nozzle l l up into rotor 16' through feed opening 29, and is brought up to rotational speed with the assistance of fins723, and circumferentially spaced radially extending vanes 27.' By virtue of centrifugal'force, the reaction.mass is separatedinto layers arranged in order of decreasing density in a radially inward direction from the interior peripheral wall of rotor 10.
In the following particular description which is by way oi" example, it will beassumed that the reaction mixture is comprised of fatty oil, 'soapstock' and aqueous caustic soda having a density greater than that of the soapstock.
Undcr the influence of centrifugal force, the aqueous electrolyte phase, being the heaviest phase, builds up on the interiorwall of rotor 10, and flows toward annular recess 43, through a plurality of circumferentially spaced channels 49 in rotor top 31.
Annular valve member 44 is so chosen as to have a density intermediate that of the soapstock phase and the aqueous electrolyte phase, and may beef any'suitable resilient material, such as rubber, natural or synthetic; capable of" increasing and decreasing in diameter,
i.e. in radial distance from the axis of rotation,,under the applied conditions present.
Valve member 44 is conveniently, though not necessarily, circular in cross section, and its density may be varied to suit requirements by any means known in the art, e.g. ranging all the way from being made hollow to being loaded with various powdered substances, including metals, which may be incorporated in the rubber itself, or placed in a hollow interior, or built in as a core, as will be readily understood by persons skilled in the art.
it will be understood that when rotor 10 is empty, or when the aqueous electrolyte phase does not form a layer separate from the soapstock, annular valve member 44 is expanded in radius, i.e. increased in circumference, by;
the applied centrifugal force so as to close vertical outlet channels 45, for the density of member 44 is so chosen as to be greaterthan that of the soapstock layer.
Upon the appearance, however, of a third layer comprised of aqueous electrolyte which, under the conditions assumed above, is of greater density than the valve member 44, such aqueous electrolyte layer will flow upwardly along the-interior wall of rotor 10 into annular recess 43, whereupon annular valve member 44 will decrease in radius (i.e. in circumference) by virtue of floating in, or, in other words, being displaced inwardly by, the heavier aqueous electrolyte layer which escapes from the bowl through outlet channels 45.
Thus as long as an aqueous electrolyte layer is present in the rotor, it will be discharged from the rotor through channels 45; Soapstock, on the other hand, will not be discharged through channels 45, for when an aqueous ei'ectrolyte layer is not present, channels 45 are closed by virtue of the radial expansion of circumferential valve member 44 due tocentrifugal force, such expansion being possible in the presence of soapstock only, for valve member 44 is of greater density than the soapstoclc.
From the foregoing it will be seen that when an aqueous; electrolyte layer is present in rotor 19, irrespective of the'manner in which it may occur, e.g. intermittently and/or varying in volume, it-is'carried oif from the rotor 19' Without interfering with the separation of soapstock from oil;
. Oil and soapstock are separated from each other in rotor--10, and are discharged therefrom, in any desired manner;
As illustrated,'rotor top 31 is provided with a conventional dividing-disc 45,- around the inner circumferential edge 47 of'which the separated oil escapes upwardly, and around the outer-cir cumferential edge 48 of which the soapstock escapes upwardly.
' The oil flows upwardly through a plurality of circumfcrentially spaced circular channels 49 in rotor top 31, and into a plurality of-circumferentially spaced channels 52 formed between longitudinal grooves 53 in portion 33' and-a sleeve-54'surrounding portion 33. The oil escapes overupper edge 55- of sleeve 54, and is collected in any convenient manner such as by use of a rotor cover, not shown. Sleeve 54 may be attached to'rotor top 31 in any desired manner, such asby welding.
' Separated soapstock escapes upwardly around'the circumferential edge- 48 of disc 4-6, and passesupwardly through circumferentially spaced channels 56, area 57,
I and over the inner circumferential edge of ring dam 42,
escaping outwardly through a plurality of circumferentially spaced outlet ports 53. As shown, the soapstock, on escaping from ports 53, is deflected downwardly by hood 59, and may be collected along with aqueous electrolyte escaping through channels 45, in any suitable manner such as by the use of a rotor cover, not shown. On the other hand, soapstock and aqueous electrolyte may be collected separately, if desired, as will be obvious. From the foregoing particular description it will be seen that, in the practice of the invention, disturbances in the separation ot'soapstock from the oil'due to the forma tion of a third layer comprised of aqueous electrolyte, are eliminated, for if, when and as such aqueous electrolyte layer forms, it is automatically and selectively removed from the zone of centrifugal separation through outlets separate from those for the discharge of oil and soapstock, thus permitting the separation of soapstock from the oil to proceed in a normal Way.
Priming of the centrifuge bowl upon start-up may be efiected in any desired or customary manner, in the present instance, preferably with a liquid of lower density than valve member 44, so as to keep channels 45 closed during priming and to cause priming liquid to discharge over ring dam l2, as will be well understood by persons skilled in the art. Any suitable priming liquid may be employed, e.g. water, or an aqueous solution of electrolyte, such as of caustic soda or sodium carbonate.
As is well known in the art, the ease with which soapstocl; may be discharged from a centrifugal rotor may vary widely from oil to oil and with the conditions under which the oil is refined. Certain conditions of refining, for instance, may reduce the fluidity of the soapstock quite materially. Moreover, the tendency of soapstock to stick to the rotor wall also may vary from oil to oil and with the conditions of refining. In overcoming such difficulties, the present invention lends itself ideally to the floating of the soapstock layer through the rotor on the surface of a heavier aqueous electrolyte layer, without interfering with the separation of the soapstock from the oil by liquid balance under the conditions employed in the zone of centrifugation, or the discharge of the separated oil and soapstock layers from the rotor. Such floating of the soapstock layer on a heaviest aqueous electrolyte layer takes place in the practice of the invention whenever such heaviest layer appears.
To assist in such discharge of soapstock from the rotor, a suitable auxiliary liquid of higher density than the soapstock, such as aqueous electrolyte, may be passed upward- 1y through the annular space afforded between the nozzle 15 and the nozzle 14 shown in FIGURE 1 of the drawings. This liquid impinges against the head 16 formed on the nozzle 14 and is deflected into contact with the inner wall of the boss 11 of the rotor 14 The centrifugal force generated by the rotation of the rotor causes the liquid to cling to this surface and to flow upwardly into the space occupied by the radially extending fins 3%. Pins 36 bring the liquid up to the speed of the rotor, and the liquid is impelled outwardly through openings 22 under the influence of centrifugal force. Liquid impelled through the openings 21 fiows upwardly along the inner wall of the rotor 16*, thus forming a continuously moving liquid layer upon which the soapstock floats as it passes upwardly through the rotor. Sticking of the soapstocl; to the interior wall of the bowl and/ or packing of the soapstock thereon are thus avoided.
The flotation liquid, being of higher density than the soapstock, is discharged from the rotor through channels 45, the same as the aqueous electrolyte layer is discharged when formed in the rotor as above particularly described. Rubber ring or valve member 44 is, of course, chosen as to density to permit the discharge of the flotation liquid, but not of soapstock.
Vhen the refining or rerefining is under conditions, e.g. including the source of the oil, such that a third layer comprised of aqueous electrolyte is formed, or is likely to form, in the rotor, such as intermittently or continuously, the flotation liquid, if employed, is preferably though not necessarily of the same or similar density as such aqueous electrolyte layer, and preferably though not necessaril also is miscible therewith.
However, it is conceivable that, even though water has a density slightly less than that of the usual soapstock, it might be fed into the rotor as a flotation liquid when the formation of a separate layer of aqueous electrolyte phase is assured, whereupon the water may mere- 1y mix with the latter layer to increase its volume with some decrease in density, but preferably not closely approaching that of the soapstock, in order that valve member 44 may function in its intended manner.
On the other hand, aqueous caustic soda and/ or aqueous solutions of its salts, such as of sodium carbonate or of sodium sulfate, or aqueous solutions of any other suitable electrolyte, may be employed as the flotation liquid, if of higher density than soapstock, or if capable of mixing with separated aqueous electrolyte to form a final flotation liquid of higher density than the soapstock, so as to make possible its selective discharge from the rotor through the channels 4-5.
The following examples are given by way of illustration and not of limitation.
Example 1 Degummed soya bean oil having a free fatty content of 0.25% by weight was continuously mixed at a rate of 2500 pounds per hour with 1.42% of its volume of aqueous caustic soda of 14' Be. at a temperature of 8-0" F. The stream of mixed oil and aqueous caustic soda was then heated to 140 F. and the stream was then centrifugally separated in a centrifuge having a rotor of the type shown in the drawings. A separate layer of aqueous caustic soda began to form immediately in the rotor, and it was discharged peripherally therefrom, that is through channels similar to the channels 453. The soapstock was discharged over a ring dam corresponding to ring dam 42. A composite sample of the soapstoclt upon analysis showed that it was of very low oil content, namely 2.04% by weight on a dry basis. The separated oil was bright throughout the run showing that it was extremely low in soap content.
Example 2 Degummed soya bean oil having a free fatty acid content of 0.45% by weight was continuously mixed at a rate of 2500 pounds per hour with 2.68% of its volume of aqueous caustic soda of 12 as. at a temperature of F. The stream of mixed oil and aqueous caustic soda was then heated to P1, and the stream was then subjected to centrifugal separation in a centrifuge having a rotor similar to the rotor shown in the drawings, but with valve member 44 and channels 45 omitted. There was no discharge of separated heavy component for about 20 minutes, whereupon soapstock (a composite heavy layer) began to be discharged. The separated oil was bright initially and relatively soap free, but gradually became more and more muddy with entrained soap. In about 35 minutes after the run started there was a sudden heavy discharge of soapstock, whereupon the discharged oil cleared up and becarne bright again. A number of such surges or sudden heavy discharges of soapstock occurred with similar variations in the character of the separated oil. A composite sample of the soapstock was analyzed, and showed an oil content of 10.6% by weight on a dry basis. A composite sample of the refined oil showed that it was relatively high in soap content.
Example 3 In an effort to rectify the unsatisfactory refining conditions exemplified in Example 2, degummed soya bean oil having a free fatty acid content of 9.66% by weight was continuously mixed at a rate of 2503 pounds per hour with 0.72% of its volume of aqueous caustic soda of 22 Be. at a temperature of 80 F. The stream of mixed oil and reagent was then heated to 140 F., and the stream was then continuously separated in a centrifuge having a rotor similar to the rotor shown in the drawings, except that the valve member 34 and the channels were omitted. 7.5% by volume of water, based on the total volume of'the reaction mass, was fed into the rotor of the centrifuge through a feed nozzle having a construction and arrangement similar to that disclosed at 15 in FIGURE 1 of the drawings, the water being continuously deposited on however, showed that it contained 29.4% of oil on a dry basis, which represents a rather high loss in oil.
From the foregoing description it will be seen that the annular edge 47 operates as a weir over which the lightest layer, e.g. refined vegetable oil, is discharged. It alsowill be seen that annular edge 47 controls the depth of liquid in the bowl,'for it is not possible for liquid to build up in the bowl between the axis ofrotation'and the annular edge 47.
The annular inner edge of ring dam 42 also operates as a weir over which the next heavier layer, i.e. the layer of intermediate specific gravity or density, e.g. soapstock, is discharged from the bowl. The radial distance from the axis of rotation to the annular inner edge of ringdam 42 controls the radial position of the dividing line or interface in the bowls separatory space between the lightest layer and the next heavier layer. The radial position of such interface is made adjustable by making ring dam 42 interchangeable, and providing a variety of ring dams with annular inner edges of dilferent radial distances from I the axis of rotation. In any event, such interface is made to fall between annular edge 4-7 and annular edge 48 when the bowl is in operation. For any given sizeof ring dam 4-2, the radial position of the interface or dividing line between the lightest layer and the next heavier layer is dependent upon their relative specific, gravities.
In the case of the refining or rerefining of fatty oils, it is customary to select a ring dam 42 with the radial distance from the axis of rotation to its inner operative edge such as to bring the interface or dividing line between the lightest and next heavier layers as close to annular edge 48 as is practicable, without possible loss of oil over weir 48 due to possible variations in conditions within the bowl. a volume of oil in the bowl as is reasonably possible during separation, thus increasing the resident time during which any portion of the oil is undergoing treatment for the separation of reaction products and reagent therefrom. The dividing line or interface, however, may occupy any other position between annular edges 47 and 48, as desired.
It is the disturbance of the hydrostatic balance between the lighter and next heavier layers due to the appearance of a third layer, whether intermittent or continual, that has heretofore presented a major problem in the refiningof fatty oils, and particularly fatty oils of low free fatty acid and/or gum content, whether previously refined or not.
It is the removal of the heaviest layer from the bowl, as, if and when it appears, that produces the new and unexpected results which fiow from the practice of the invention, for it is by effecting such removal of the heaviest layer that the desired hydrostatic balance between the lighter and the next heavier layers is maintained in undisturbed condition. Since the heaviest layer may appear only intermittently, and may vary considerably in volume, or if appearing continuously, may still vary in volume during the separation, it is by the discharge of this heaviest layerfro-rn the periphery of the bowl under control of difference in densities, that makes possible the desired high efiicient separation of refined oil from reaction products and reagent. The terms light, heavy, and intermediate may obviously respectively replace lighter, heaviest, and next heavier as referring to the layers herein.
While the invention has been described more partie ular-ly in connection with the rerefining of fatty oils, it is to be understood that it is applicable to the initial refining of fatty oils under conditions such that a third layer of The purpose is to keep as large aqueous-electrolyte is likely to appear. Also while the appearance of a third layer comprised of aqueous electrolyte' occurs more often when caustic soda is employed as the alkaline refining agent, the same situation is capable of occurring when other alkaline refining reagents, such as sodium carbonate, are employed in excess.
In the practice of the invention, the concentration of alkaline refining reagent in the aqueous solution employed employed vary widely from plant to plant and are such as to causethe appearance of a third layer in the bowl, if the aqueous reagent solution is employed in sufficient excess to create this condition. It may be expected, however, that with the same percentage excess of aqueous refining solution over that required to neutralize free fatty acids, the appearance during the separation of a third layer is more likely to occur with aqueous solutions of higher Baum. Generally-speaking, such third layer does not appear when the alkaline refining agent is substantially depleted during the treatment,e.g. in the case of aqueous causticsoda, to below a specific gravity equivalentto that of 12 B.
The temperatureat which the process is practiced also. is not critical, forthe invention isoperable irrespective.
it will be understood thatthe invention provides a,
safety measure guarding against disturbingthe hydrostatic balance between the fatty oil and soapstock or other reaction products bythepossible appearance .of a third layer comprised of aqueous electrolyte.
While the .valve member 44 has been more particularly described as arubber ring, this is by way of illustration, for valve member 44 may be of any other suitable material of appropriate specific gravity intermediate that of the heavier and heaviest layers.
Moreover, while the centrifugal bowl has been illustrated for convenience in the drawings as being of tubular shape, and as having wings. serving as an acceleratingdeceleratingdevice, it is to be understood that the centrifuge bowl may have any other configuration and con-. struction without departing from the spirit of the invention. Thus the invention is equally adaptable to what is known as the disc-type bowl, and to bowls of any other type.
Having described my invention, it is to be understood that this isby way of illustration, and that changes, omissions, additions, substitutions and/or other modifications,
may be made without departing from the spirit thereof. Accordingly it is intended-that the patent shall cover by suitable expression in the claims the. various features of patentable novelty that reside in the invention.
-1. In a centrifuge rotor for the separationof immiscible components adapted to stratify into light, heavy and intermediate layers, respectively, the rotor having a weir spaced inward from .the outermost portion of the rotor and over which such light layer may be discharged, having a second weir outward-from the first weir and over which such intermediate layer may be discharged, and having an opening through the wall of the rotor at its periphery to the outside thereof; the improvement of a valve element comprising an annulus disposed about the inside of the rotor adjacent its periphery'and substantially in the same radial plane as said opening and being selected of resilient material of density intermediate that of such heavy and intermediate layers to be pressed outward under centrifugal force to cover the opening in the absence of such heavy layer and to float inward on such heavy layer against substantially the same degree of centrifugal force when such heavy layer is in the rotor to permit escape through the opening of such heavy layer only and tothereby avoid 9 10 disturbance by such heavy layer of. the hydostatic balance 1,232,104 Sharples July 3, 1917 between the light and the intermediate layers. 1,373,743 Jones Apr. 5, 1921 2.. The centrifuge rotor of claim 1 having an inlet lead- 1,534,604 Ter Meer Apr. 21, 1925 ing to the inner periphery of the rotor for the feed of an 1,981,800 Calkins Nov. 20, 1934 auxiliary liquid into said rotor. 5 2,138,468 Ayres Nov. 29, 1938 2,209,554 Bath July 30, 1940 References Cited In the file of this patent 2,577,326 Harstick et a1 Dec. 4, 1951 UNITED STATES PATENTS 2,628,021 Staafi Feb. 10, 1953 1,201,558 Cobb Oct. 17, 1916 2.712.896 Boldrin July 12, 1955