US3332614A

US3332614A - Centrifugal extractor

Info

Publication number: US3332614A
Application number: US407945A
Authority: US
Inventors: Donald S Webster; Warren E Winsche
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-10-30
Filing date: 1964-10-30
Publication date: 1967-07-25
Anticipated expiration: 1984-07-25

Description

CENTRIFUGAL EXTRACTOR 2 Sheets-Sheet 1 Filed 001:. 30, 1964 E w A M M EEQQQQ w INVENTORS Dana/d S. Webs/er Warren E. W/nsche Attorney y 6 D. s. WEBSTER ETAL 3,332,614

GENTRIFUGAL EXTRACTOR Filed Oct. 50, 1964 2 s-Sheet 2 III/1111111111 INVENTORS Dana/d S. Webster Warren E Wmsc/re BY M 4. W

,dffomey United States Patent 3,332,614 CENTRIFUGAL EXTRACTOR Donald S. Webster, Aiken, S.C., and Warren E. Winsche, Bellport, N.Y., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Oct. 30, 1964, Ser. No. 407,945 3 Claims. (Cl. 233-13) The invention described herein was made in the course of, or under, Contract AT(O7-2)1 with the US. Atomic Energy Commission.

The present invention relates to a centrifugal liquidliquid extractor. More particularly, this invention relates to an improved centrifugal extractor which provides remote regulation for continuous processing of radioactive materials.

Liquid-liquid extractors, having a centrifugal pump mixer, integral centrifugal separator and circular outlet weirs for the continuous separation of liquids having different specific gravities from mixtures thereof have been described in Chemical Processing of Reactor Fuels, chapter VII, Academic Press, Inc., New York, 1961, page 271 and in Chemical Engineering Practice, volume 6, by H. W. Cremer and T. Davies, Academic Press, Inc., New York, 1958, pp. 528-541. The theory and operation of centrifugal separators generally is described in Chemical Engineers Handbook 3rd edition, by J. H. Perry, McGraw- Hill Book Company, Inc., New York, 1950, pages 992- 1001.

Where a solvent extraction process is used in the separation of irradiated uranium, and other valuable nuclear materials, from less valuable or unwanted byproducts, it is known to use mixer-settlers. These devices mix aqueous and organic solutions for mass transfer, then separate the resulting dispersion by gravity in settling tanks. Large settler volumes are needed to obtain complete separation of phases. A substantial reduction in the volume of the settler, and consequently in the overall size, is achieved by using centrifugal force to aid settling in devices known as centrifugal extractors and contactors. The smaller voltime requirement gives centrifugal contactors the advan tages of reduced solvent and aqueous inventory, reduced space requirements, reduced exposure of solvent to radiation (when used to process radioactive fluids), and increased nuclear safety. In the centrifugal separation of imiscible liquids, the heavy phase collects in the outer peripheral region within a rotating bowl and the light phase collects near the central region. For continuous operation, centrifugal, circular, weirs are provided for the heavy and light phases. The weir radii are chosen so that the interface between the liquid phases is at an intermediate radius which results in the heavy phase product containing a minimum amount of entrained light phase and the light phase product containing a minimum amount of entrained heavy phase. The required weir heights are relatively independent of the absolute and relative flow rates of the product streams. However, the Weir heights required to maintain the interface at an intermediate radius vary appreciably with changes in the relative densities of the liquid phases. For some operations, such as liquid-liquid extractions of radioactive solutions, it is highly desirable to provide quick acting remote control of the interface position so that the centrifugal equipment can accommodate changes in process conditions affecting relative densities of phases. Moreover, the equipment should be safe for processing nuclear materials and require minimum maintenance, and maximum reliability for continuous operation.

Accordingly, it is an object of the present invention to provide a centrifugal liquid-liquid extractor suitable for continuous processing of radioactive materials which may be regulated remotely.

It is a further object of the invention to provide a centrifugal extractor using circular weirs with a novel means for remotely controlling the interface between the liquid phases.

It is a still further object of the invention to provide such an extractor having maximum reliability under conditions of minimum maintenance, which is safe for use with nuclear materials, is efficient and has a high capacity and flexibility to cope with variations in liquid densities and flow rates.

The foregoing objects are accomplished by the present invention which is in a centrifugal liquid-liquid extractor comprising a cylindrical centrifuge bowl, means to rotate said bowl about its cylindrical axis, a mixing chamber at the lower end of said bowl, means for feeding process streams into said mixing chamber, impeller means in said chamber for mixing the process streams and pumping them into the bowl, outlets for the heavy and light liquid phases, circular weirs in said bowl for controlling the flow of the heavy and light phases and forming a weir chamber, and means for applying air pressure on the liquid in the weir chamber for controlling the position of the interface between the liquid phases in the bowl.

Various other objects and advantages and the manner in which they may be accomplished will be readily understood upon reading the following detailed description of the invention in conjunction with the attached drawings wherein:

FIG. 1 is a perspective view of a centrifugal extractor assembly incorporating the invention, certain parts being cut away and shown in cross-section for clarity; and

FIG. 2 is a schematic illustration of the weir section in the extractor of the invention.

Referring to FIG. 1, the centrifuge bowl, or rotor assembly, generally indicated by 1 is rotatively mounted within a stationary housing or casing 2. The rotor assembly is essentially a circular hollow cylinder comprising cylindrical bowl wall 3 having upper and lower end plates 4 and 5, respectively, the upper end plate being connected at its center by some conventional means 6 to a drive shaft 7. Drive shaft 7 is driven by a vertically oriented induction motor, not shown, which is fixedly mounted to and supported by the top of the casing in a manner described hereafter. The circular weir section and discharge ports are located in the upper portion of the centrifuge bowl. The weir section comprises a plurality of spaced fiat, circular plates oriented perpendicular to the rotational axis of the centrifuge which function to control the flows of the heavy and light phases leaving the bowl. In the embodiment herein illustrated, the light phase weir is formed by a plate 8 having an OD smaller than the ID. of the bowl wall 13 and which has circular opening 9 at its center. A plurality of spaced radial ducts 10, formed integral with or attached to the top of plate 8, communicate at their inner ends solely with opening 9 and at their outer ends solely with circumferentially spaced outlet slots 11 through wall 3. The ducts 10 are attached at their inner ends to shaft 7 and at their outer ends to wall 3 by some suitable means, such as welding, for example, thereby forming circumferentially spaced openings 54 at the outer edge of plate 8 for the passage of the heavy phase into the heavy phase weir chamber as will be described.

The heavy phase weir is formed by plate 12 attached at its outer periphery to wall 3 and provided with circular opening at its center. A third plate 13 which serves as a baffle is disposed in space relationship above plate 12 and is attached at its center to shaft 7. The outer radius of plate 13 is greater than the inner radius of plate 12 but less than the radius of wall 3. A fourth plate 14, disposed in space relationship between plate 13 and end plate 4, is attached at its outer periphery to Wall 3, and is provided with an opening in its center having a radius equal to that of the central opening in plate 12. A plurality of circumferentially spaced outlet slots 15 are provided through wall 3 between plate 14 and end plate 4. Flat,

radial vanes 55 are provided between the

circular plates

8, 12, 13 and 14 to maintain constant angular velocity of the liquid in the weir section.

The central portion of the bowl contains a plurality of radial vanes 16 attached, as by welding, at their inner edges to shaft 7 and at their outer edges to wall 3. The vanes extend the full length between plate 8 and the lower end plate 5 thus forming pie shaped segments occupying the major portion, called the settling section, of the centrifuge bowl.

Lower end plate 5 has central opening 17 which serves as an inlet for the liquid mixture. Spaced above intake 17 is inlet diversion baflie 18 which is formed by a circular plate attached at its inner circumference to the lower end of shaft 7 and having an outer radius greater than the radius of the bowl inlet 17. The purpose of the inlet diversion bafiie is to prevent injected solutions from spraying up the rotating assembly, thus partially bypassing some of the settling section. A plurality of holes 19 are circumferentially spaced through the inlet diversion baflle to allow entrained air to pass directly to the air space in the settling section.

The rotating assembly is surrounded by a cylindrical casing 2 having a radially enlarged end section, opposite the weirsection of the bowl, in which is located the collection chambers for the light and heavy phases. The casing may be a generally welded construction as illustrated. The collection chambers are formed by outer cylindrical wall 20 having upper and lower flat

annular end plates

21, 22 and intermediate flat annular plate 23. The inner diameters of

plates

22 and 23 are slightly larger than the outer diameter of centrifuge bowl 3 to provide clearance for free rotation of the latter. Short

cylindrical sections

24 and 25 are attached at their lower edges to the top inner edges of

plates

22 and 23, respectively, and extend upwardly therefrom to a position closely adjacent to the lower edges of openings 11 and 15, respectively, in the upper end of wall 3. The lower inner edge of plate 23 is located closely adjacent the top edges of slots 11. The uppermost annular chamber formed by this construction is the collection chamber for the heavy phase and the lower annular chamber is for the light phase.

Exit ports

26 and 27 for the heavy and light phase chambers are provided through wall 20. Conventional connector means 28 and 29 for external conduits not shown are tangentially attached to wall 20 in communication with

ports

26 and 27. As illustrated, these are arranged for clockwise rotation of the rotor.

Flanged motor mount 30 may be bolted as at 50 to the upper face of end plate 21. The induction motor not shown, which drives shaft 7 has its housing attached to motor mount 30 in any convenient manner so that the entire rotor assembly is suspended from and supported solely by the motor and its bearings.

The lower end of casing 2 is flanged at 31 where it is connected to lower end plate 32, as by bolts 51, for example, a suitable sealing gasket 52 being inserted therebetween. End plate 32 contains a mixing chamber 33 formed by cylindrical section 34 and circular plate 35. Plate 35 has a central opening 36 which is connected to T section 37 through which the process liquids enter the separator. The radially innermost portion of the plate 32 has upwardly curved lip section 38 extending through bowl inlet 17 in spaced relation therewith to provide for smooth flow of the mixture into the bowl and to minimize leakage of liquid into the space between the bowl and casing.

The lower end of shaft 7 has attached thereto and coaxially therewith extension 39 passing through curved lip 38 into the mixing chamber where there is attached to its lower end a turbine blade assembly comprised of diametral flat blades 40 attached to the bottom of circular disk 53. A flow direction baffle 41 is formed by a flat circular plate attached at its periphery to cylindrical section 34 in order to provide peripheral openings. Baffie plate 41 has central hole 42 in spaced relationship about shaft extension 39 and has attached to its upper face a plurality of radially extending antivortex vanes 47.

The drive shaft, centrifuge bowl assembly, casing assembly, inlet diversion baffie 18, bowl inlet 17, curved lip 38, baffle plate hole 42, shaft extension 39, and turbine blade assembly, are all coaxial, and all parts of the rotor assembly and weir section are geometrically uniform. A tangential drain connection 43 is provided between the casing and the inlet T to permit return of the liquid which collects in the space between the centrifuge bowl and the casing.

Air pressure is supplied to the weir section by means of axial passage 44 connected at its lower end to radial passages 45 through drive shaft 7. The radial passages enter the weir section between

plates

8 and 13. Air pressure from a source, not shown, is supplied to passage 44 through a rotary seal 46 at the upper end of the drive shaft.

The general operation of this centrifugal extractor will now be described. The flow paths of the liquid phases are shown by the dashed and solid arrows which represent the light and heavy phases respectively. The drive motor through shaft 7 drives the rotor assembly at the desired speed. The feed streams enter the mixing chamber through T 37 and are mixed by turbine 40 which also pumps the dispersion, in the direction of the arrows, through the peripheral openings in baffle plate 41 and between the antivortex vanes 47 through inlet opening 17 into the centrifuge bowl. Upon entering the bowl, the solution impinges upon the inlet dispersion baffle 18 and starts to travel towards the top of the bowl. Holes 19 in inlet diversion bafile allow air entrained within the mixture to pass directly to the air space in the center of the settling section. The centrifugal force within the rotating bowl causes the heavy phase to settle rapidly from the dispersion toward the peripheral region of the bowl. In turn the less-dense, light phase is displaced rapidly toward the central region. As more clearly shown in FIG. 2, at the top of the bowl, the light phase flows over weir 8 through opening 9 into radial ducts 10 where it is thrown outwardly through holes .11 into the light phase collection chamber, from which it leaves the extractor through outlet means 29. v

The heavy phase is forced to the wall of the'bowl where it flows through peripheral openings 54 and is forced radially inward between the light phase radial ducts 10 and over the heavy phase weir at the central opening of plate 12. It then flows under the bafiie plate 13, around the peripheral edge thereof, then radially inwardly under plate 14 and over the inner edge thereof, fromwhere it is thrown outwardly through outlet 15 into the heavy phase collection chamber, leaving through outlet means 28.

The manner in which the air weir of the invention functions will be described'with reference to the schematic illustration of FIG. 2 which shows the upper portion of the centrifuge bowl assembly. In the liquid-liquid centrifugal extractor of this invention, during the time the mixture is passing through the bowl the heavy H and light L phases are continually separating producing therebetween an annular dispersion band, or interface. As flows are increased and residence time is decreased, the width of the dispersion band inside the rotating bowl increases until entrainment occurs in one or both of the end streams. Thus, the interface position has a critical effect upon the performance of the extractor. The interface position in a centrifugal liquid-liquid separator is a function of the radii of the outlet weirs for the light and heavy phases and of the densities of the phases. In addition, for flow rates at which the crest of liquid over the weirs is appreciable, the interface position will vary with the flow rate. In this invention air pressure is supplied through

passages

44 and 45 to the heavy phase weir chamber between

plate members

8 and 13. The weir radii of

plates

8 and 12 are selected so that the interface radius is slightly less than the bowl radius when atmospheric pressure is applied to is now a function of the air pressure in the heavy phase weir chamber, the position of the dispersion can be adjusted by either increasing or decreasing the air pressure until the end streams are free of entrainment. The baflle plate 13 and weir plate 14 act as a seal for the air pressure applied to the heavy phase weir chamber.

The invention will be further illustrated by the following examples:

Example 1 A centrifugal liquid-liquid extractor of the design shown in FIG. 1 was fabricated of stainless steel. The centrifuge bowl 1 had an ID. of inches and a length from the bowl inlet to the light phase outlet weir of 10 inches. The pump and 'mixing chamber had a volume equal to 10% of the volume of the bowl. The turbine pump impeller had four fiat blades one inch wide and six inches in diameter. The light phase weir radius was 2.0 inches and the heavy phase weir radius was 3.2 inches.

The machine was operated at 1800 rpm. and was fed an organic phase comprising 30% tri-n-b-utyl phosphate dissolved in kerosene at 16 g.p.m., and an aqueous phase "comprising 0.5 molar nitric acid at 24 g.p.m. The specific gravities of the light and (heavy phases were 0.83 and 1.01 respectively. The interface within the centrifuge bowl was maintained within the limits imposed by the internal and external diameters of the light phase weir (i.e., effective diameters of the light phase weir and peripheral openings 54) by an air pressure of from 4 to 9 p.s.i.g. applied to the heavy phase weir chamber. At an air pressure of 6 p.s.i.g. and for the above flow rates corresponding to a hold up time in the mixer and separator of about 10 seconds, the entrainment was less than 0.5% in either phase.

Example 2 In this example the apparatus and procedure of Example 1 was duplicated, except that uranyl nitrate was added to the aqueous phase to make a solution containing 10 grams of uranium per liter of solution. The efliciency of extraction of uranium by the organic phase was greater than for a holdup time of 10 seconds, and greater than for a holdup time of 20 seconds, compared to the separation obtained during agitated batch contacting of the same solutions for 20 minutes.

It is not intended that this invention be limited to the specific embodiments described and illustrated in the foregoing specification but only by the scope of the appended claims.

Having thus described our invention, we claim:

1. A centrifugal liquid-liquid extractor comprising a cylindrical centrifuge bowl mounted in a housing for rotation about its cylindrical axis, means at one end of said bowl for feeding process liquids into said bowl, a weir section comprising a plurality of spaced apart flat circular plates extending generally perpendicular to the rotational axis of said bowl at the other end, the first of said plates having central and peripheral openings of respective passage of light and heavy phase liquid therethrough, at least one duct positioned to communicate at its one end with said central opening and at its other end with a light phase outlet from said bowl, a second of said plates having a peripheral opening at a radius greater than said central opening of said second plate, said first and third plates defining a heavy phase weir chamber, means in said bowl for introducing pressurized gas in said weir chamber from an external source, a heavy phase outlet from said bowl beyond said third plate, and means positioned between said third plate and said heavy phase outlet for cooperating with said third plate to seal said pressurized gas in said weir chamber.

2. The centrifugal liquid-liquid extractor of claim 1 wherein said means positioned between said third plate and said heavy phase outlet is a flat circular plate having a central opening having a radius less than said radius of said peripheral opening of said third plate.

3. The centrifugal liquid-liquid extractor of claim 1 wherein said duct positioned to communicate with said central opening of said first plate and said light phase outlet from said bowl is substantially radial.

References Cited UNITED STATES PATENTS 703,630 7/1902 Ten Winkel 23321 736,976 8/1903 Keiper 23328 1,247,473 11/1917 Weston 233-21 2,083,809 6/1937 Asch 233-28 3,081,027 3/1963 COulson 23314 X M. CARY NELSON, Primary Examiner.

H. T. KLINKSIEK, Assistant Examiner.

Claims

1. A CENTRIFUGAL LIQUID-LIQUID EXTRACTOR COMPRISING A CYLINDRICAL CENTRIFUGE BOWL MOUNTED IN A HOUSING FOR ROTATION ABOUT ITS CYLINDRICAL AXIS, MEANS AT ONE END OF SAID BOWL FOR FEEDING PROCESS LIQUIDS INTO SAID BOWL, A WEIR SECTION COMPRISING A PLURALITY OF SPACED APART FLAT CIRCULAR PLATES EXTENDING GENERALLY PERPENDICULAR TO THE ROTATIONAL AXIS OF SAID BOWL AT THE OTHER END, THE FIRST OF SAID PLATES HAVING CENTRAL AND PERIPHERAL OPENINGS OF RESPECTIVE PASSAGE OF LIGHT AND HEAVY PHASE LIQUID THERETHROUGH, AT LEAST ONE DUCT POSITIONED TO COMMUNICATE AT ITS ONE END WITH SAID CENTRAL OPENING AND AT ITS OTHER END WITH A LIGHT PHASE OUTLET FROM SAID BOWL, A SECOND OF SAID PLATES HAVING A PERIPHERAL OPENING AT A RADIUS GREATER THAN SAID CENTRAL OPENING OF SAID SECOND PLATE, SAID FIRST AND THIRD PLATES DEFINING A HEAVY PHASE WEIR CHAMBER, MEANS IN