US3443746A - Counter-current wash for centrifugal separator - Google Patents

Description

y 3, 1969 R. H. HALBACH Y 3,443,746

COUNTER-CURRENT WASH FOR CENTRIFUGAL SEPARATOR Filed Jan. 19. 1967 Sheet or-s FIG. 1

IN VENTOR.

R2LPH H. HALBACH B GENT.

May 13, 1969 R. H. HALBACH 3,443,746 COUNTER-CURRENT WASH FOR CENTRIFUGAL SEPARATOR Filed Jan. 19. 1967 Sheet 3 of 5 i I I FIG. 2 FIG. 3

m 70 I04 s2 5i us 4 46 r 26 I3O I 32 [3'50 1 ll I36 ll 2 I32 3 5g V INVENTOR.

RALPH H. HALBACH y 3, 1969 R. H. HALBACH 3,443,746

COUNTER-CURRENT WASH FOR CENTRIFUGAL SEPARATOR Sheet 4 of5 Filed Jan. 19, 1967 FIG.

INVENTOR.

RALPH H. HALBACH y 1969 R. H. HALBAH 3,443,746

COUNTER-CURRENT WASH FOR CENTRIFUGAL SEPARATOR Filed Jan. 19, 1967 Sheet f of 5 FIG.

INVENTOR. RA PH H. HALBACH AGENT.

United States Patent 3,443,746 COUNTER-CURRENT WASH FOR CENTRIFUGAL SEPARATOR Ralph H. Halbach, Westport, Conn., assignor to Dorr- Oliver Incorporated, Stamford, Conn., a corporation of Delaware Filed Jan. 19, 1967, Ser. No. 610,418 Int. Cl. B04b 15/12 US. Cl. 233-15 16 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a centrifugal separator having a wash zone wherein a plurality of wash liquids counter-currently wash the underflow before it is discharged from the rotor. Each of the wash liquids is individually channeled to the Wash zone through its own system of conduits and individually discharged into the wash zone.

One of the major problems in the continuous centrifugal separation of multiphase feed materials, where purity of the discharged product is essential, is the reduction in the concentration of solubles in the underflow discharged product. Solubles may be defined as organic and inorganic salts in solution in the mother liquor. The application of centrifugal separating forces does not, in and of itself, separate or concentrate the solubles into one of the separated fractions. Therefore, solubles will be present in both the overflow and underflow discharges in proportion to the amount of mother liquor from the feed that is present in each of the discharges.

Experimentation has shown that the concentration of solubles in the underflow can be reduced by the controlled introduction of a wash liquid into the rotor. The wash liquid displaces the mother liquor as the carrier of the underflow and will thus reduce the soluble concen tration in the underflow discharge in relation to the amount of mother liquor that is replaced. To take advantage of this concept various nozzle centrifuges have been designed to introduce a controlled amount of Wash liquid in conjunction with a recycling of part of the underflow back into the rotor. The returned underflow controls the location of the centrifugal separating zone, maintains the operating balance between overflow and underflow, and retains the desired concentration level of the underflow discharge. Actual experience, however, has shown that when these machines are used for feeds such as starch slurries, where purity is imperative, there is a practical limit to the effectiveness with which the solubles can be displaced from the underflow discharge. The problem is that the discharge tubes for the return underflow and wash liquid are not positioned close enough to the countercurrent washing gap to prevent the build-up of eddy-currents and turbulence in the wash zone which is created by the difference in the circumferential velocities of the wash fluid flowing into the separating chamber of the rotor and the concentrated slurry flowing out of the separating chamber of the rotor. The average washing eificiency of these machines has been found to be about 66% with the best obtainable under standard operating conditions being a reduction in the concentration of the solubles in the underflow from approximately .962% to 54%. With such substantial amounts of these contaminants still remaining in the underflow product the only way for these machines to produce acceptable results has been to use a series of them in tandem with the underflow from one machine being the feed in the next machine and so on. The increased investment in capitalization and service costs has thus severely limited the in- 3,443,746 Patented May 13, 1969 dustrial application of these machines in the starch and allied fields.

Patent Number 3,111,490, to applicant, recognized this problem and the improved washing arrangement it teaches has been able to substantially reduce turbulence in the wash zone and correspondingly increase the washing efliciency. This is accomplished by placing the wash fluid discharge tubes in a zone contiguous to the countercurrent washing gap so that both the wash fluid and the discharging slurry will have the same velocity in the counter-current washing orifice. Theoretically, it should be possible for this machine to reach 100% solubles removal from the underflow. Again, however, practical application of the machine has proven otherwise. The orifice through which the solubles pass outwardly while soluble-free wash water moves inwardly for the countercurrent displacement of mother liquor by wash liquid cannot be sufficiently reduced in size and still pass solids having the desired physical dimensions. In order to maintain the desired height in the orifice, vis-a-vis the particle sizes and the flow characteristics of the concentration of solids through the orifice, the average solubles removal will range between -93%, depending upon the particle size and composition of the starch slurry. It is, therefore, still necessary, in order to obtain the desired degree of purity, which starch production requires, to use two centrifugal separators in series with the underflow from the first providing the feed material to the second.

Thus, to an extent, the problem of reducing the soluble concentration in the underflow discharge to acceptable levels in a single centrifugal separator still existed. The instant invention is also based upon the principle of controlled introduction of wash liquid to reduce the solubles concentration in the underflow discharge, but because of the unique features disclosed hereinafter the theoretical limit of solubles removal in a single centrifugal separator is a practical reality. The washing arrangement disclosed herein overcomes the inherent difliculties in both Patent Number 3,111,490 and other prior art centrifugal separators by providing a series of Washing stages, using variable and different washing fluids, in a single centrifugal separator. Discharging solids are thus counter-currently washed and the solubles laden mother liquor correspondingly stripped by each individual wash stage to incrementally increase purity until the solubles concentration in the underflow discharge has been reduced to the desired parameter. The washes are each individually discharged in a zone contiguous to a counter-current washing orifice so as to reduce turbulence and induce a laminar flow for maximum wash liquid-mother liquor exchange.

It is, therefore, an object of the present invention to effectively eliminate solubles from the underflow discharge of a nozzle-type centrifuge.

It is another object of the present invention to provide a series of wash stages in a single centrifugal separator to counter-currently wash the underflow before it is discharged from the centrifuge.

It is a further object of the present invention to provide means to feed a plurality of wash liquids to a single wash zone.

It is still another object of the present invention to recycle at least part of the underflow into at least one of the wash stages.

The subject matter which applicant regards as his invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, as to its organization and method of operation together with further objects and advantages thereof will best be understood by reference to the following description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is an elevational view in section of acentrifugal apparatus incorporating the instant invention;

FIGURE 2 is an enlarged elevational view in section with parts removed for clarity of showing of the left side of the axis of rotation of the centrifugal apparatus of FIGURE 1;

FIGURE 3 is an enlarged elevational view in section with parts removed for clarity of showing of the right side of the axis of rotation of the centrifugal apparatus of FIGURE 1;

FIGURE 4 schematically depicts the inter-relationship of FIGURES 2 and 3;

FIGURE 5 is an enlarged detailed plan view partly in section of the discharge nozzles for the underflow of the centrifugal apparatus of FIGURE 1;

FIGURE6 is an enlarged detailed partial plan view with parts broken away for clarity of showing of the novel feed impeller of the centrifugal apparatus of FIGURE 1;

FIGURE 7 is an elevational view partly in section taken along the line 7-7 of FIGURE 6; and

FIGURE 8 is a partial view taken along the line 88 of FIGURE 7.

Referring to the drawings, a centrifuge 10 is shown to illustrate an exemplary application of the present invention. However, it should be understood that the present invention is not limited in its application to the particular centrifuge disclosed. It should also be understood that while only two washing stages are disclosed in the exemplary application of the present invention, additional washing stages are within the scope of the invention.

Referring now to FIGURES 1-5 the centrifuge 10 has a rotor 12 which comprises a frustoconical bowl 14 and a matching rotor cover 16 held together by a clamp ring 18. The rotor 12 has an inner separating chamber 20 and is carried by a vertical rotatable shaft 22. A tapered generally cylindrical shell 24 surrounds shaft 22 and together with a conically shaped rotor hub 26 forms a feedwell 28 for the material to be separated. A series of cylindrical feed inlets 27, 29 concentric with shaft 22 discharge the mixture to be centrifugally separated into the feedwell 28. The rotor hub 26 is rigidly connected to shaft 22 by means of'a key 30 and hub nut 32 on threaded portion 34. The rotor hub is also rigidly connected to the lower end of the rotor bowl by means of threaded attachment 36.

An annular impeller 38 (see FIGURES 6 and 7) extends outward from cylindrical shell 24 and has a feed material portion 40 lying in a plane substantially parallel to the rotor hub 26 and a wash feed poriton 42 which extends outward from feed material portion 40 substantially parallel to rotor bowl 14. The feed material portion 40 has a plurality of equally spaced radially extending wedge shaped vanes 44 which together with the rotor hub 26 and the lower portion of the impeller form a series of passageways 46 for the feed material as it travels from the feedwell 28 to the separating chamber 20. The feed material portion 40 of the impeller 38 is suitably sealed with the cylindrical shell 24 by O-ring seal 48, and is connected to the rotor hub 26 by means of spaced bolts 50. The lower portion of the feedwell 28 has a plurality of equally spaced vanes 52 which serve to impart rotary motion to the material to be separated as it is fed to passageway 46.

The separating chamber 20 of the rotor is provided with a stack of nested discs 54, overlying the feed portion 40 of impeller 38, to separate the feed mixture into the light and heavy phases. Suitable means, such as circumferentially spaced vertical feed tubes 56 are provided for distributing the feed material onto the separating discs. The vertical feed tubes 56 enter into passageway 46 at the vortex end of the vanes 44 to receive the feed material. The tubes 56 then extend axially through the disc stack and have vertical inboard and outboard slots all along their length to discharge the feed material onto the individual discs.

The disc stack 54 because of its nested closely spaced relationship, enhances the separation of the feed mixture into the light and heavy phases by forcing the mixture and the separated phases into an even, non-turbulent laminar flow. The heavy phase is caused to move outward by centrifugal force while the lighter phase moves inward due to the inward velocity of the mother liquor. The lighter phase wends its way to the inner end of the disc stack 54 where it is discharged into annular chamber 58 between the disc stack and cylindrical shell 24. The chamber 58 has a plurality of equally spaced vanes 60 which transport the lighter phase axially until it is dis charged as overflow past power reactor 62 (see Patent Number 3,080,109) into collection chamber 64.

The heavy phase, now in the form of a concentrated slurry, is discharged from the disc stack 54 and collects along the inner surfaces of the rotor cover 16 and the wash feed portion 42 of the impeller. The heavy phase is then washed, as will be explained in greater detail below, and subsequently discharged from the rotor as the underflow. The annular peripheral portion 66 of the bowl 14 has a plurality of spaced underflow discharge nozzles 68, which can be of any suitable type. An annular raceway 70 is provided at the inner end of the nozzles and is, as was disclosed in Patent Number 3,111,490, divided into a plurality of hopper-like chambers 72, with one such chamber for each discharge nozzle (see FIGURE 5 The hopper-like chambers 72 are formed by wedgeshaped filler blocks 74 held in position by any suitable means such as bolts 76.

Wash system A wash fluid impeller having a plurality of wash fluid receiving chambers, corresponding to the number of wash stages in the wash system, is fixedly attached to the rotor hub 26 by means such as bolts 82. Since in this particular exemplary application of the present invention only two washing stages are disclosed there are only two wash fluid chambers, but, as stated in the introduction to this specification, additional washing stages and therefore additional wash fluid systems are intended to be within the purview of this invention.

The primary wash fluid, which is in this particular exemplary application, preferably formulated of recycled underflow with a controlled amount of wash liquid, enters the centrifuge through inlet 84 and is discharged through nozzle 86 into primary wash fluid chamber 88. The return underflow is ejected from nozzle 68 into volute 69 and from there through conduit 90 to the inlet 84. A portion of the underflow is discharged from the centrifugal system by means of conduit 92 having control valve 94. A wash liquid inlet 95 feeds a controlled amount of wash liquid into conduit 90 just before conduit 90 discharges into inlet 84. A second wash fluid, in this exemplary application solubles-free' wash liquid, is fed into secondary wash fluid chamber 96 through inlet pipe 98. Inlet pipe 98 has an enlarged tapered feed end 100 which prevents any of the primary wash fluid from being sprayed from nozzle 86 into the secondary wash fluid chamber 96. Each of the wash fluid chambers has a plurality of radially spaced vanes 102 in chamber 96, and 103 in chamber 88, which impart rotary motion to the respective wash fluids to bring them up to speed and pump them to the individual wash stages.

The annular wash feed portion 42 of the impeller 38 extends outwardly from the feed material portion 40, in a plane substantially parallel to the rotor bowl 14, with its upper end 104 terminating in a plane substantially coincident with the center line plane. Rotor cover 16 has a pheripheral portion 105 terminating in an annular fiat surface 111 which together with upper end 104 of the wash feed portion 42 forms the counter-current washing orifice 113. The wash feed portion 42 of the impeller provides the wash feed channels to transport the wash fluid from the wash fluid chambers 88 and 96 to the washing zone. Each of the individual wash fluids is transported from its wash fluid chamber to the washing zone in its own series of channels within the wash feed portion of the impeller. Since, in this particular exemplary application, the wash system has only two washing stages, the wash feed portion 42 of the impeller has only two such layers 108 and 110 of wash feed channels. It should again be understood that if additional washing stages are to be used, it is within the purview of this invention for the feed portion of the impeller to have additional layers of channels to supply the wash fluid to the wash zone. As can be seen in FIGURES 2 and 6 primary wash fluid layer 108 is made up of a series of equally spaced radially extending channels 112 out into the inner surface of wash feed impeller portion 42 and interspersed between support ribs 114. A cover member 116 overlies the channels 112 and is connected to the support ribs 114 by any suitable means such as welding. The primary wash fluid is discharged from channels 112 into the counter-current washing orifice 113 through outlets 115 at the upper end of the wash feed portion 42 of the impeller. Layer 110' (FIG- URES 2 and 8) is comprised of a series of channels 118 out into the outer surface of wash feed impeller portion 42 and interspersed with support ribs 120- which abut against the rotor bowl 14. Secondary wash fluid flows between ribs 120 and is discharged from channels 118 through outlets 122 contiguous to the counter-current washing orifice 113 at the upper end of the impeller.

An annular ring 130 which seats on the rotor hub 26 and is connected thereto by bolts 50 serves to separate the flow channels (to be described below) from the wash fluid chambers 80 and 96. Primary wash fluid from chamber 88 is pumped by vanes 103 through a flow channel comprising passages and raceways 132, 133, 134, 135 to the channels 112. Secondary wash fluid is pumped from chamber 96 through flow channel 136 to channels 118. The raceways serve to increase the manufacturing tolerances between mating conduits by having the corresponding outlet and inlet ends of the conduits discharge and receive the wash fluid from a larger cross sectional area.

Operation In accordance with the present invention a feed mixture is discharged into feedwell 28 through inlets 27 and 29. Radial vanes 52 in the lower end of the feedwell bring the mixture up to speed and pump it through passageway 46 between the impeller portion 40 and the rotor hub 26. The feed mixture then rises through vertical feed tubes 56 and is discharged into the separating disc stack 54. The separated lighter phase continues along the disc stack and is discharged out of the rotor as the overflow through chamber 58 and over power reactor 62. The heavier phase leaves the disc stack and begins to collect as a concentrated slurry along the inner surfaces of the rotor cover 16 and the impeller portion 42. Continued buildup of the heavy phase in conjunction with the action of centrifugal forces causes the heavy phase to bleed through the counter-current washing orifice 113 where it is subjected to a series of washing stages. In this particular exemplary application, there are two washing stages. The washing fluid in the primary washing stage comprising recycled underflow with a controlled amount of wash liquid. The wash fluid in the secondary washing stage comprising solubles-free wash liquid. Both wash fluids are separately discharged into the counter-current washing orifice with the primary washing fluid being the first to contact the outwardly moving heavy phase. In the washing orifice 113 part of the washing liquid separates from the returned and washed underflow and moves inwardly toward the separating chamber while the heavy phase and the rest of the washing liquid moves outward toward the discharge nozzles 68. In this manner the washing liquid counter-currently displaces the mother liquor as the carrying liquid for the heavy phase to eliminate any solubles which may have been carried in the heavy phase. By incorporating two separate wash stages in the same centrifugal separator the mother liquor and the solubles in solution therewith are effectively blocked and the desired degree of purity can be easily and readily attained.

The washed heavy phase is then discharged through nozzles 68 and collected in volute 69 for discharge into recycling conduit 90. A portion of the underflow is drawn out of the centrifugal system through conduit 92. Wash liquid from conduit may then be mixed with the underflow and the mixture is then pumped into the centrifuge through inlet 84 into wash fluid receiving chamber 88. The primary wash fluid is brought up to speed by vanes 103 and pumped through passageways 132, 133, 134, and into channels 112 in the impeller portion 42 and from there discharged into the counter-current washing orifice 113 through outlet 115. The secondary washing fluid is pumped into chamber 96 through inlet pipe 98 and from there forced by vanes 102 through conduit 136 and channels 118 in impeller portion 42, for final discharge through outlets 122 contiguous to the counter-current washing orifice 113.

Since it is within the purview of this invention to have more than the two wash stages discussed above in a particular wash system, it is also within the scope of this invention to vary the wash fluids in each of the individual wash stages according to the demands of the slurry being washed. Thus, for example, the percent solubles content of the wash liquid combined with the return underflow is adjustable as is the number of wash stages that will use a wash fluid comprised of a mixture of return underflow and wash liquid. The number of wash stages that will use either solubles free wash liquid or wash liquid of fixed solubles content alone can also be made responsive to the demands of the system. It should also be understood that if need be the wash liquid itself may be varied from one wash stage to the next, using, for example, a heavier immiscible liquid.

As this invention may be embodied in several forms without departing from the spirit or essential character thereof, the present embodiment is illustrative and not restrictive. The scope of the invention is defined by the the appended claims rather than by the description preceding them, and all embodiments which fall within the meaning and range of equivalency of the claims are, therefore, intended to be embraced by those claims.

I claim:

1. A centrifugal apparatus having a rotor, a separating chamber in said rotor, means to feed a multiphase feed material to the separated into component fractions into said chamber, at least one overflow to discharge a separated fraction from said rotor, at least one underflow to discharge a separated fraction from said rotor, means cooperating with the walls of said separating chamber to form a restricted opening opposite said underflow discharge, means to introduce a plurality of wash fluids into said rotor, and means individually discharging the plurality of wash fluids into a zone contiguous to said restricted opening so as to counter-currently wash the flow of separated feed material from said separating chamber to said underflow discharge.

2. A centrifugal apparatus as defined in claim 1 wherein said last mentioned means comprises an impeller having therein a plurality of conduit layers, each of said layers being transversely spaced apart from each other within said impeller and each layer having at least one channel.

3. A centrifugal apparatus as defined in claim 2 wherein at least one of said layers discharges wash fluid directly into said restricted opening.

4. A centrifugal separator as defined in claim 2 further including a plurality of wash fluid receiving means in said rotor, said means receiving the wash fluid as it is fed into the rotor.

5. A centrifugal separator as defined in claim 4 furtheir including means to return at least a part of the underflow discharged from said rotor to at least one of said receiving means.

6. A centrifugal separator as defined in claim 4 further including a plurality of individual wash liquid flow channels in said rotor between said wash fluid receiving means and said impeller, each of said flow channels connecting a wash fluid receiving with a corresponding layer in said impeller.

7. A rotor for a centrifugal separator comprising a feedwell, means to introduce a multiphase feed material to be separated into said feedwell, a separating chamber, at least one overflow discharge from said rotor, at least one underflow discharge from said rotor, an impeller in said separating chamber having means thereon to transfer feed material from said feedwell to said separating chamber, said impeller having a portion thereof which cooperates with the inner wall of said rotor to form a washing passage for the underflow as it passes from the separating chamber to the underflow discharge, means to introduce Wash fluid into said rotor, and at least one means within said impeller to channel the wash fluid to a zone contiguous to said washing passage.

8. Apparatus as defined in claim 7 wherein said lastmentioned means comprises at least two transversely spaced apart layers of wash feed channels within said impeller.

9. Apparatus as defined in claim 8 further including a plurality of wash fluid receiving means in said rotor to receive the wash fluid as it is fed into the rotor and pump it to the impeller.

10. Apparatus as defined in claim 9 including means interconnecting said underflow discharge and at least one of said wash fluid receiving means to recycle at least part of the underflow back into said rotor,

11. Apparatus as defined in claim 9 wherein there is provided one wash fluid receiving means for each layer of channels within said impeller and conduit means within said rotor interconnecting each of said wash fluid receiving means with its corresponding layer of channels.

12. Apparatus as defined in claim 11 wherein at least one layer of said channels in said impeller discharges directly into the wash passage.

13. Apparatus as defined in claim 11 further including means intermediate said impeller and said wash fluid receiving means to separate said conduit means into individual flow channels, with one such channel for each wash liquid.

14. An impeller for a centrifugal separator having a first portion and a second portion, said first portion having a plurality of spaced apart vanes thereon, said second portion having at least two transversely spaced apart layers of channels therein, each of said channels being separated from the others.

15. A centrifugal separator comprising a rotor having a hub, a feedwell in said rotor, means to feed a multiphase feed material to be separated into said feedwell, a separating chamber in said rotor to ceutrifugally separate the feed material, at least one overflow discharge and at least one underflow discharge from said rotor, an annular impeller in said rotor, said impeller having a first portion spaced apart from and substantially parallel to said hub with a plurality of equally spaced radial vanes extending from said impeller between said impeller and said hub, said vanes serving to pump feed material from said feedwell to said separating chamber, said impeller having a second portion which cooperates with the walls of said rotor to form a restricted passage directly opposite said underflow discharge, a plurality of chambers in said rotor, means to inject Wash fluid into said chambers, said impeller having a plurality of spaced layers of Wash feed channels within said second portion corresponding to the number of wash fluid chambers in said rotor, said channels discharging into a zone contiguous to said restricted opening, conduit means interconnecting each layer of channels within said impeller with its corresponding wash fluid chamber, means in said wash fluid chambers to pump the wash fluid from said chambers through said wash feed channels in said impeller into said restricted opening, and means interconnecting said underflow discharge and at least one of said wash fluid chambers to return at least part of said underflow to said rotor. 16. A centrifugal apparatus having a rotor, a separatmg chamber in said rotor, means to feed a multiphase feed material to be separated into component fractions into said chamber, at least one overflow to discharge a separated fraction from said rotor, at least one underflow to discharge a separated fraction from said rotor, a wash zone adjacent said underflow discharge, the underflow passing through said wash zone before it enters said underflow discharge, and means to introduce a plurality of wash liquids to said wash zone, the wash liquids passing through said wash zone counter-currently to the flow of the underflow.

References Cited UNITED STATES PATENTS 2,917,230 12/1959 Kaldewey 233-14 3,011,647 12/1961 Elsken 233-14 X 3,111,490 11/1963 Halbach 233-14 ROBERT W. JENKINS, Primary Examiner.

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