CA2264932A1 - Shear localized filtration system - Google Patents

Abstract

A filtration apparatus is provided, of the type that includes a stack of rapidly rotating membrane packs (32) and a stack of stationary separator elements (36A, 36B) interleaved with the membrane packs to leave thin gaps (40A, 40B) between them, which obtains the advantages of both series-connected and parallel-connected systems. A feed conduit (82) connects the radially outer ends (110) of the gaps, to carry feed fluid into and out of each gap.
The rapidly rotating membrane packs cause radially outward flow near their surfaces, which causes radially inward flow (102) near the surfaces of the stationary elements, to cause fluid flow radially inwardly and then outwardly through each gap. The stationary elements have apertures (131-138) to equalize the pressure on opposite sides thereof and to promote fluid shear at the membrane surfaces. An accumulator (140) is coupled to the feed inlet (12) to maintain feed fluid pressure during an abnormal loss of feed fluid pressure, for the time required to stop rotation of the stack of membrane packs.

Description

10152025CA 02264932 1999-03-04WO 98/09720 PCT/U S96/ 14352SHEAR LOCALIZED FILTRATION SYSTEMBACKGROUND OF THE INVENTION:A feed fluid such as waste water, can be separated into permeate, suchas pure water which passes through a membrane, and concentrate whichincludes water with a high concentration of particles. Such separation can beaccomplished by the use of a stack of membrane packs lying within a container.Fouling of the membrane packs, by the buildup of particles at the surface whichblock pores of the membranes, can be reduced by rapidly rotating themembrane packs. as described in U.S. Patent Number 4,025,425 by Croopnick.Fouling can be further reduced by placing stationary separator elementsbetween pairs of membrane packs, to create turbulence in the gap between therotating surface of the membrane pack and the stationary surface of theseparating element. It is noted that when a membrane pack has large pores(many microns wide), it may be referred to as a filter pack, but applicant usesthe term membrane pack herein for both.The turbu|ence—enhancing separator elements lying between membranepacks should be relatively thin to take up little space, but must not touch theIt would bedesirable if the separator elements could be designed for maximum strengthrapidly rotating membrane packs or they will be destroyed.against deflection while minimizing conditions that could cause their deflection.A common filtration construction directs the feed fluid in series throughthe gaps. For example, if there is a stack of fifty membrane packs andcorresponding stationary elements to produce one hundred gaps, the fluid mayflow in a series serpentine path through the one hundred gaps. Such serialflow has the advantage that the feed fluid moves along a long path in contactwith the surfaces of the membrane packs, to remove a considerable portion ofSUBSTITUTE SHEET (RULE 26)10152025CA 02264932 1999-03-04WO 98/09720 PCT/US96/14352the filtrate. However, such serial flow has a disadvantage that the feed fluid isnot homogeneous, in that the concentration of particles in the feed fluid mayincrease by many times between the upstream and downstream ends of thefeed fluid path. Also, there can be a large pressure drop along the long path,due to friction applied to the moving feed fluid, especially for more viscousliquids. Such large pressure drop can result in the feed fluid pressure beingoptimum (for maximum permeate flow through the membranes while minimizingfouling) at only a small portion of the total feed fluid path. The flow of the feedfluid in parallel through all of the gaps is seldom used, because the short pathlength requires repeated return of the fluid for reflow, resulting in large pressurelosses. A filtration system which allowed the feed fluid to flow along a longpath in contact with the membrane surfaces while maintaining the feed fluidlargely homogeneous in pressure and particle concentration, would be of valuein the filtration of a wide variety of fluids.SUMMARY OF THE INVENTIONIn accordance with one embodiment of the present invention, a filtrationsystem is provided, of the type wherein a stack of rotatable membrane packsis spaced by separator elements to leave gaps through which feed fluid moves,which produces enhanced filtration. A filtration system is operated so the feedfluid is flowed into a conduit that connects the radially outer edges of the gapsthat separate the rotating membrane packs from the substantially stationaryseparator elements. Portions of the feed fluid flow largely radially inwardlyalong inward paths that lie adjacent to the stationary elements, and flow largelyradially outwardly along outward paths that lie adjacent to the rotatingmembrane packs, to produce a largely circulating flow along each gap.Portions of the fluid that have moved radially inwardly and outwardly along aSUBSTITUTE SHEET (RULE 26)10152025CA 02264932 1999-03-04W0 98l09720 PCT/US96l14352path, pass into the feed conduit to move to another gap, while other portionsmove back into the same gap along the inward paths. The feed fluid movesalong a long path in moving into and out of each of the gaps and flowingradially inwardly and outwardly along each gap, and yet a substantiallyhomogenous feed fluid is maintained because fluid in each gap is constantlymixed with fluid from other gaps by way of the feed conduit.As the feed fluid moves through the gaps. permeate of the feed fluidpasses through membranes of the membrane packs and moves out of theapparatus. The centrifugal force and large shear (difference in fluid velocitynear the pack surfaces) minimizes the buildup of particles at the membranesurface which would clog its pores. The stationary separator elements haveapertures to leave spokes, which helps create shear and which equalizespressure on opposite faces of the elements. An accumulator is preferablyconnected to the feed conduit, as at the feed inlet. Such accumulator assuresthat the feed fluid pressure can only gradually decrease, to prevent blowout ofthe membranes as the membrane packs stop rotating in the event of loss offeed fluid pressure.The novel features of the invention are set forth with particularity in theappended claims. The invention will be best understood from the followingdescription when read in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGSFig. 1 is an isometric view of a rotary filtration apparatus constructed inaccordance with one embodiment of the present invention.Fig. 2 is a sectional side view of the apparatus of Fig. 1.Fig. 3 is a view taken on the line 3 - 3 of Fig. 2.Fig. 4 is a sectional view of a portion of the apparatus of Fig. 2, taken onSUBSTITUTE SHEET (RULE 26)10152025CA 02264932 1999-03-04wo 9s/09720 PCT/US96/14352the line 4 — 4 of Fig. 3.Fig. 5 is an enlarged view of a portion of the apparatus of Fig. 4.Fig. 6 is an enlarged view of a portion of the apparatus of Fig. 5.Fig. 7 is a view taken on the line 7 — 7 of Fig. 3, but with the axialdimension exaggerated, and with pluses (+) indicating flow into the paper andcircles indicating flow out of the paper.Fig. 8 is a partial sectional side view of a rotary filtration apparatusconstructed in accordance with another embodiment of the invention.DESCRIPTION OF THE PREFERRED EMBODlMENTSFig. 1 illustrates a rotary filtration apparatus 10 which has a feed fluidinlet 12 for receiving feed fluid. The feed fluid generally includes a liquid, andparticles in the liquid which are of micron size (average diameter less than tenmicrons) or submicron size. The apparatus separates the feed fluid into filtrate,or permeate which flows out of permeate outlets 14, 16, and concentrate whichflows out of an outlet 20 (or out of an inlet 12 in the case of batch processing).Concentrate comprises liquid with a high concentration of particles, and is leftafter much of the permeate in the original feed fluid has been removed. Theapparatus includes a rotor 22 which lies within a sealed container 24. A motor26 is coupled to the rotor to rapidly rotate it about an axis 28.As shown in Fig. 2, the rotor 22 includes a stack 30 of axially-spaced (indirection X that is parallel to the axis) membrane packs 32 that lie within thecontainer. The apparatus also includes a stack 34 of plate—like separatorelements 36. The separator elements 36 are stationary, and positioned so aseparator element 36 lies between each pair of membrane packs 32. Thisleaves gaps 40 between each surface of the membrane pack and adjacentsurfaces of separator elements. The gaps extend radially (parallel to radialSUBSTITUTE SHEET (RULE 26)10152025WO 98/09720CA 02264932 1999-03-04PCT/US96/14352directions Y), in that they have large radial dimensions Y and short axialdimensions X. In particular, Fig. 2 shows first and second membrane packs32A, 32B and shows separator elements 36A and 36B and shows first andsecond gaps 40A, 40B on opposite sides of the first membrane pack 32A.Fig. 2 shows that the membrane packs 32 are mounted at their axialmiddles on a shaft 50 which is hollow to form a permeate conduit 52. Thepermeate conduit extends through the entire length of the shaft, to form thepermeate outlets 14, 16 at the shaft opposite ends. The shaft is rotatablymounted on bearing 54. 56, 58, with a stand indicated at 59 to support thelower bearings, and with the upper bearing supported on the container 24. Itis possible to rotatably support the rotor on a bearing assembly that includesa single bearing.The membrane packs 32 have radially inner and outer ends 60, 62. Theinner ends 60 are mounted on the shaft, while the outer ends 62 are free andtherefore unsupported. The separator elements 36 have radially inner andouter ends 64, 66. The outer ends 66 are mounted on a group of tie rods 70,and are spaced apart by spacers 72. The radially inner ends 64 of theseparator element are free and therefore unsupported.As shown in Fig. 3, each of the separator elements 36 has throughapertures 131 — 138 that leave spokes 141 - 148. The apertures extend radially(away from axis 28) further than the peripheries 150 of the membrane packs.This leaves spaces 152 at the radially outer portions of the apertures, alongwhich feed fluid can move. Also, the radially outer ends 66 of the separatorelements are radially spaced from the sidewalls 80 of the container 24. Thisleaves additional space 154 along which feed fluid can move. The spaces 152,154 form a teed conduit 82, the conduit 82 being of largely toroidal shape (withthe peripheries of the spacer element lying in it).SUBSTITUTE SHEET (RULE 26)10152025CA 02264932 1999-03-04WO 98/09720 PCT/U S96] 14352As shown in Fig. 4, the cross sectional area of the feed conduit 82, asseen in the sectional view of Fig. 4, is much greater than that of any of thegaps 40. As a result, the feed fluid tends to be substantially homogenousthroughout the filtration apparatus, in that there is a substantially uniformpressure of the feed fluid and a substantially uniform concentration of solids inthe liquid of the feed fluid. It is noted that the radially inner ends 60 of themembrane packs are spaced apart by seal spacers 84. Permeate flows radiallyinwardly along each membrane pack, and through holes 86 in the rotor shaftand along the permeate conduit 52 of the shaft.Fig. 5 illustrates the flow of fluids in the gaps such as 40A and 40B andalong the feed conduit 82. Before the membrane packs such as 32A begin torotate, feed fluid 90 fills the feed conduit 82 and the gaps such as 40A, 40B.When the membrane pack 32A is rapidly rotated, fluid lying adjacent to themembrane pack surface 92 rotates with the membrane pack. Such rotationresults in centrifugal force which causes feed fluid lying adjacent to the surface92 to move radially outwardly along an outward path 94 (which also includescircumferential components in the direction of membrane pack rotation). Theradially outward flow along outward paths 94 results in a lower pressure at theradially inward end 100 of the gap, and this causes a radially inward flow offeed fluid along inward paths 102. The result is that there is a circulating flowof feed fluid along each gap. This circulating flow causes fresh feed fluid fromthe feed conduit 82 to repeatedly flow across the membrane pack surface 92.Permeate of the feed fluid moves along membrane—crossing paths 104 througha membrane 105 or other filtering element into porous backup sheets 106 ofthe membrane packs, and in inward directions at 108 to the centers of the packfrom which the permeate is removed.It should be noted that the membrane or filtering element may be aSUBSTITUTE SHEET (RULE 26)10152025CA 02264932 1999-03-04WO 98/09720 PCT/US96/ 14352polymeric membrane, a screen (woven or matt or etched), a porous ceramic.a sintered metal, or other construction that passes only small particles ormolecules. Applicant uses the term "membrane pack" for all of such elements.Common processes include dialysis, electrodialysis, reverse osmosis, andvarious size filtration. Applicant's system is especially useful for microfiltrationand is useful for ultrafiltration, although it possibly can be used for nanofiltrationand even possibly for reverse osmosis.At the radially outer ends 110 of the gaps, fluid moving along the outwardpaths 94 is mixed with the feed fluid, and some of the fluid (at least onepercent) that has moved along the outward paths 94 is returned as indicatedby path 112, while some of it (at least one percent) is moved into the feedconduit as indicated by path 114. The fluid that is not recirculated within thesame gap 40A, can move along the feed conduit 82 and into another gap suchas 408. At the gap inner end 100, much of the fluid passes in a loop indicatedat 120 back along the gap. Some of the fluid passes in paths 122 betweenadjacent gaps such as 40A and 40C, but since there is substantially the samepressure at the radially inner ends of both gaps 40A, 40C, there is little flow inthe directions 122.Fig. 6 indicates the velocity profile, in a circumferential direction, (theradial velocity component is not shown) of feed fluid passing along a gap 40,by the length of the arrows. The circumferential direction is perpendicular tothe radial direction and is parallel to the membrane pack surface motion. Thepath at 93A is very close to the membrane pack surface 92, and the fluidmoves at almost the same speed as the rotating surface 92. The velocity atpath 93 is much less than the velocity at 93A, and the difference componentSUBSTITUTE SHEET (RULE 26)10152025CA 02264932 1999-03-04WO 98/09720 PCT/U S96/ 1435293D tends to sweep away particles 111 from the surface 92 of the membranepack. This phenomenon can be referred to as the localized shear that tendsto sweep particles from the surface. The magnitude of such shear, for a givenvelocity of the surface 92 with respect to the stationary separator elementsurface 113 of the separator element, depends upon the thickness 116 of thegap. The smaller the thickness 116, the greater the localized shear effect, orratio of velocity difference 93D with distance 118 along the gap.Applicant prefers to make the gap 116 as small as possible, but mustprevent the surfaces 92, 113 from touching since this could cause damage tothe membrane pack. Applicant is able to obtain a gap thickness 116 of abouttwo millimeters without causing membrane pack damage in a stack of manytens of membrane packs. In addition to the velocity differential per unitdistance, the small gap results in large turbulence at the surfaces, and suchturbulence near surface 92 also tends to sweep away particles that mightotherwise block the pores of the membrane. if is noted that the largecircumferential fluid movement at 93A and 93 results in fluid near themembrane pack flowing radially outwardly.Thus, by applicant connecting a feed conduit to the radially outer endsof the gaps between membrane packs and separator elements, applicantcauses a recirculating flow through each of the gaps. wherein feed fluid movesradially inwardly near the surface of the separator member and radiallyoutwardly near the surface of the filter packs. Feed fluid moving largely radiallyoutwardly near the outward ends of the gaps, flows into the feed conduit andalso recirculates. With fluid circulating, perhaps several times, through manygaps, applicant obtains the advantages of a serial connection of the gaps ofhaving each quantity of fluid move along many membrane pack surfaces toremove a large proportion of the filtrate from the feed fluid. Applicant avoidsSUBSTITUTE SHEET (RULE 26)10152025CA 02264932 1999-03-04WO 98/09720 PCT/U S96/ 14352disadvantages of a serial connection, because the present system results in asubstantially homogenous fluid throughout the apparatus, in that the pressureis about the same everywhere and the mixing of fluid near the outer ends of thegaps results in the feed fluid everywhere having about the same concentrationof solids.As discussed above, the substantially uniform pressure in the systemallows applicant to apply an optimum pressure to the feed fluid. For example,in one situation, a pressure of 40psi will produce a high flow of permeate intothe membrane packs while obtaining minimal fouling of the membrane packs,while a pressure of 80psi could cause fouling and a pressure of 20psi couldresult in a low permeate flow rate. The optimum pressure depends upon theconcentration of solids. Applicant can adjust the rate at which concentrate isdrawn off, based on the permeate flow, to vary the concentration of solids soas to minimize membrane fouling while still obtaining a considerable permeateflow.As shown in Fig. 3, applicant prefers to construct each separator element36 with apertures 131 - 138, to leave spokes 141 - 148 that form wall portionson circumferentially (perpendicular to a radial line) opposite sides of eachaperture. One advantage of the apertures is that they result in the samepressure on opposite faces 160, 162 of the element. Applicant prefers that themembrane packs have a small thickness such as 8mm, and that the spacerelements have a small thickness such as 6mm, with the gaps each having athickness such as 3mm, for a system using membrane packs of 410mmdiameter. The small thickness of a spacer element would allow locations on itto be axially deflected, when there was a small pressure difference between itsopposite faces. Any such axial deflection which results in direct contact of aspacer element with a rapidly rotating membrane pack, would cause destructionSUBSTITUTE SHEET (RUL:E 26)10152025CA 02264932 1999-03-04WO 98/09720PCT/US96/14352-10..of that membrane pack. By providing at least one aperture in each imaginary90° sector 164 of a separator element, and with the apertures occupying atleast 10% of the area of each spacer element and of each sector and separatorwalls (e.g. spokes) lying in each sector, applicant avoids such a pressuredifference.When the membrane packs rotate so portions shown in Fig. 7 move inthe circumferential directions of arrows 170, feed fluid at 172 lying adjacent tothe pack face 92 also moves circumferenti ally. Applicant constructs each spokesuch as 144, 145 with a leading edge 174 that is designed to interfere withcircumferential fluid movement. The result is a large change in fluid velocityover a short distance near the membrane pack face, which helps sweep awayparticles.The flow near the membrane packs is usually turbulent, and theseparators can be referred to as "turbulators". Of course, in the absence of aseparator, the fluid between a pair of membrane packs would soon rotate withthe packs. With the separators, most of the fluid is static or only slowly rotating,which results in a rapid change in velocity near the membrane packs. Thecross section of each spoke such as 144 in Fig. 7 (in which the thickness isexaggerated) is selected so the spoke is self-centering. That is, if the spokeapproaches the face 93 of one membrane pack, the reaction of the spoke withfluid moving in the circumferential direction 170 is to move the spoke away fromthe membrane pack surface 93.Applicant has experimented with spacer elements having differentnumbers of spokes. It was found that an element such as shown in Fig. 3,which has eight spokes, was best in the tests. An element with four spokesoperated almost, but not quite, as well. The number of spokes is preferablyat least four but not more than sixteen. The radially inner ends of the spokesSUBSTITUTE SHEET (RULE 26)10152025CA 02264932 1999-03-04WO 98/09720 PCT/US96/14352-11..are tied together by a 360° continuous hub 180. The radially outer ends of thespokes are preferably tied together by a continuous rim 182, although this is notabsolutely necessary. The apertures and spokes can be angled from a radialdirection.The membrane packs are rotated rapidly enough that large centrifugalforces and large shear is created to avoid membrane fouling. Membrane packsof 410mm diameter, are rotated at at least 200rpm, and usually at about760rpm to 1000rpm. At 200rpm, the average surface velocity (at a point fourinches from the axis) is about 2 meters per second. Thus, the system operateswith an average membrane pack velocity of at least 2 meters per second, anda velocity at the pack periphery of at least 4 meters per second. The mosteffective rotational speeds for membrane packs usually create centrifugal forcesthat increase pressure by at least 20 psi (140 kPa)The rotary filtration apparatus 10 (Fig. 1) can be operated in a batch orcontinuous process, or in a combination. in a batch process, feed fluid with apredetermined concentration of solids, such as 200ppm (parts per million) ispumped into the container. Inlet and outlet valves 220, 221 are closed. Apump 222 may be connected to a recirculation conduit 230 to maintain a moreuniform concentration of particles, although this can be accomplished within thecontainer 24 (e.g. by dividing the toroidal feed conduit 82 of Fig. 3 into twoparts and pumping fluid up in one part and down in the other). The inlet andoutlet 12, 20 form axially spaced locations of the feed conduit, and therecirculation conduit 230 lies outside of the feed conduit. A sensor 224 isconnected to the container to sense the concentration of particles. The motor26 is energized so the rotor 22 rotates at a predetermined speed, and permeateis constantly drawn from the feed fluid, while the concentration of particles inthe feed fluid increases. The sensor 224 senses this, and can control the pumpSUBSTITUTE SHEET (RULE 26)10152025CA 02264932 1999-03-04W0 98/09720 PCT/US96I14352-12-222 to change the pressure of the feed fluid, and also control the motor 26 tochange the speed of rotation of the rotor, for optimum conditions (largepermeate flow into the membrane pack and low fouling of the membrane packsurfaces). In a continuous process, feed fluid can flow from a source 232continually, though at a slow rate, into the feed fluid inlet 12. Concentrate flowsout of the outlet 20, for use or for further processing.It is noted that in some prior art filtration systems, particles of concentratewere allowed to mechanically build up to a large thickness (a plurality ofparticles thick) on the filter or membrane surface. in the present invention only"fouling" which is a chemical phenomenon, rather than "buildup" which is amechanical phenomenon occurs. In fouling, solutes (particles) are absorpedor adsorped to the membrane by chemical attraction, to the point wherepermeate flow through the membrane is significantly reduced. Fouling occursboth at the surface and below it. For example, very small particles can clingto the walls of membrane pores until the particles close the pores, causingpermeate flow to stop and fouling to occur. The thickness of particles foulinga membrane will be less than one-tenth the gap width, when cleaning muststart.The present invention can prevent any build up, and also reduces therate of fouling. Selection of the proper membrane material for a particularapplication is of great importance in reducing the rate of fouling. Once foulingoccurs, the membrane can be cleaned as by the use of chemicals to dissolveor loosen particles that have adhered to the interstices of the membrane.Measurement of the permeate flow rate enables a determination of the degreeof fouling and indicates when cleaning is needed.Applicant prefers to connect an accumulator 240 (FIG. 1) to the feedconduit 80 at all times. The accumulator assures that the pressure of feed fluidSUBSTITUTE SHEET (RULE 26)10152025CA 02264932 1999-03-04WO 98/09720 PCT/U S96/ 14352-13..will change only slowly, despite a possible interruption of supply or otherphenomenon that might rapidly decrease teed fluid pressure. If the feed fluidpressure should suddenly fall, but the pressure of permeate in the membranepacks falls only slowly, then the larger pressure of permeate in the membranepacks could cause the thin membranes to burst. The accumulator 240 is of acommon type, which include a membrane, bellows, or piston divider member242 lying in a container 244. and separating the container into an air chamber246 that contains air under pressure, and a liquid chamber 248 that containsliquid under the same pressure. Any other means for maintaining feed fluidpressure, such as a valve connected to a high pressure liquid source such asa city water main, and opened only when a rapid pressure drop is sensed, canbe used. When the accumulator must pump fluid for more than a very shorttime, as when it is almost empty after being full, the motor is preferablyautomatically deenergized. The rotor will substantially stop from perhaps 700rpm, in a period such as eight seconds, and the fluid pressure should bemaintained during perhaps six of those seconds.Fig. 2 shows that permeate exits the apparatus in opposite directions A,B through opposite ends of the shaft at 14 and 16. Where there is a largefiltrate flow, this allows for the use of a smaller shaft and bearings 54, 56, 58and seals such as 59’, which reduces cost.Fig. 4 indicates that holes 250 can be formed in the radially inner endsof the membrane packs to allow feed fluid to flow largely axially from one gapto another at their inner ends. However, there would be only small flow throughsuch a hole. and providing such a hole can increase the cost of the membranepack because of the need to seal against the migration of feed fluid into thepermeate.Fig. 8 illustrates a portion of another rotary filtration apparatus 260 whichSUBSTITUTE SHEET (RULE 26)10152025WO 98/09720CA 02264932 1999-03-04PCT/US96/14352_]_4..is similar to that of Figs. 1 - 6, except that the separator elements 262 whichlie between adjacent rotating membrane pack 264A, 2648, also form membranepacks. That is, each separator member 262 has membrane sheets 266 andflow sheets 268 for removing permeate. Permeate passing through amembrane pack separator member 262 passes through a hole 270 in a hollowtying member 272 which is comparable to the tying members 70 of Fig. 2, toremove the permeate.In one system that applicant has designed, the membrane packs haddiameters of 16 inches (40cm), and the gaps 40 were 3mm thick, with the otherdimensions being relative to the diameter, as shown in Fig. 2. In oneapplication, aluminum oxide particles (originally used for dyes) of a size of 0.5microns and up, were to be removed from a waste stream of salt water anddissolved solids. The aluminum oxide particles were to be concentrated fromfour percent to twenty percent of the volume of the stream, by removing the saltwater and dissolved solids which constitute the permeate of the waste stream.Larger particles had been previously removed by settling and screening, so thelargest particles were no more than about 10 microns in diameter. The feedfluid is initially maintained at a pressure of 40psi (270 kPa) and the membranepacks are rotated at 800rpm. As the concentration increases, the pressure canbe maintained constant, or can be increased slightly. Thus, after theconcentration increases, the speed is increased to 1,000rpm and the pressureis increased to 50psi (340 kPa)Thus, the invention provides a filtration system wherein feed fluid movesthrough axially thin gaps between membrane packs and separator elements.The system obtains advantages of a serial connection of the gaps, of a longflow path along the membrane surfaces, while avoiding disadvantages of widelyvarying pressure and particle concentration. The system includes a feedSUBSTITUTE SHEET (RULE 26)CA 02264932 1999-03-04WO 98/09720 PCT/US96/14352_ 1 5 -conduit that connects to the radially outer ends of the gaps, to allow fluid to flowin a loop through each gap, and to promote homogeneous fluid throughout thesystem. The separator elements preferably have through apertures to leavespokes.Although particular embodiments of the invention have been describedand illustrated herein, it is recognized that modifications and variations mayreadily occur to those skilled in the art, and consequently, it is intended that theclaims be interpreted to cover such modifications and equivalents.SUBSTITUTE SHEET (RULE 26)

Claims (14)

IN THE CLAIMS:

1. Filtration apparatus which includes a container (24), a shaft (50) lying on an axis (28) and extending into said container and a bearing apparatus (54, 56, 58) that rotatably supports said shaft in rotation with respect to saidcontainer, a stack (30) of spaced membrane packs (32) mounted on said shaft and lying in said container with each pack having an inside for carrying filtered fluid, an outlet (52) coupled to the insides of said packs for carrying away filtered fluid, a stack (34) of substantially stationary separator elements (36)lying in said container with each element lying between a pair of said membrane packs to leave a gap (40) between them that forms radially inner and outer gap ends (100, 110), a motor (26) connected to said shaft to rotate it and said stack of membrane packs about said axis, and a feed inlet (12) coupled to the inside of said container to flow feed fluid therein, characterized by:
a feed conduit (82) formed in said container and connected to said feed inlet (12) and to said radially outer ends (110) of said gaps, said feed conduitextending around said outer ends of said gaps to connect said radially outer ends of substantially all of said gaps together so said feed fluid can flow fromlocations of said feed conduit into said gaps and from said gaps back into said feed conduit locations.

2. The filtration apparatus described in claim 1 wherein:
said separator elements include at least one middle separator element (40A) that lies between first and second (32A, 32B) of said membrane packs, said middle separator element having first and second opposite faces (160, 162) respectively facing said first and second membrane packs, said middle separator element having a plurality of through apertures (131-138) which connect its faces;
said middle separator element and a plurality of said apertures therein, each extend radially beyond a periphery (150) of said first and second membrane packs, to facilitate the flow of feed fluid between said feed conduit and said gaps, with said separator element being in the form of a plate with a hub extending around said axis and with said apertures being formed in said plate and with said apertures lying over at least 10% of the area of said first and second membrane packs.

3. The filtration apparatus described in claim 1 wherein:
said rotor includes a shaft (50) that has a permeate conduit (52), with said filter packs each being connected to said permeate conduit to flow permeate of said feed fluid thereto;
said shaft has axially opposite end portions (14, 16) projecting from axially opposite ends of said container, and said permeate conduit extends through both of said shaft end portions, to flow permeate out through both ends of said shaft.

4. The filtration apparatus described in claim 1 wherein:
at least some of said elements are membrane pack elements, with each of said membrane pack elements including a membrane sheet (105) facing a corresponding gap and also including a flow sheet (106) that backs the membrane sheet and that forms a permeate passage.

5. The filtration apparatus described in claim 1 wherein:

said gaps have radially inner portions (100), and said gap radially inner portions are connected together but are blocked from the outflow of fluid from said container except along paths extending radially outwardly along said gaps.

6. Filtration apparatus which includes a container (24), a shaft (50) lying on an axis (28) and extending into said container, a stack (30) of spaced membrane packs (32) mounted on said shaft and lying in said container, a stack (34) of substantially stationary separator elements (36) lying in said container with each element lying between a pair of said membrane packs to leave a gap (40) between them, a motor (26) connected to said shaft to rotate it and said stack of membrane packs about said axis, and a feed inlet (12) coupled to the inside of said container to flow feed fluid therein, wherein:
at least one of said separator elements (36) is in the form of a plate with a hub lying around said axis and with a plurality of through apertures (131-138)which occupy at least 10% of the area of the separator element and has a plurality of wall portions (141-148) including wall portions on opposite sides of each aperture, to equalize fluid pressure at opposite faces of said predetermined separator element, whereby to avoid pressure-caused deflection of said separator element.

7. The filtration apparatus described in claim 6 wherein:
said predetermined separator element has four imaginary sectors (164), each subtending an angle of 90° about said axis, and has separator walls (141, 142, 143) in each of said sectors, and said plurality of apertures includes an aperture (131, 132) in each of said sectors, which occupies at least 10% of the area of the sector.

8. The filtration apparatus described in claim 6 wherein:
said predetermined separator element includes a plurality of largely radially-extending spokes (141-148) formed between said apertures, and includes a 360° continuous hub (180) near the radial center of said element and a continuous rim (182) near the radial periphery of said element, to supporteach of said spokes.

9. The filtration apparatus described in claim 6 wherein:
said motor is constructed to rapidly rotate said shaft so the velocity of the periphery of said membrane packs with respect to adjacent portions of said separator elements is at least 4 meters per second;
said predetermined separator element lies between first and second (32A, 32B) of said membrane packs;
said plurality of apertures in said particular separator element extend largely radially to form spokes (141-148) between said apertures, and said spokes are constructed to aerodynamically center themselves between said first and second membrane packs in a stream of said feed fluid that rapidly moves past said spokes as said membrane packs rapidly rotate.

10. The filtration apparatus described in claim 6 wherein:
said apertures comprise between 4 and 16 largely radially-extending apertures (131-138) extending along most of the radius of said predetermined separator element, to leave between 4 and 16 spokes (141-148) between said apertures.

11. Filtration apparatus which includes a container (24), a shaft (50) lying on an axis (28) and extending into said container, a stack (30) of spaced membrane packs (32) mounted on said shaft and lying in said container, a stack (34) of substantially stationary separator elements (36) lying in said container with each element lying between a pair of said membrane packs to leave a gap (40) between them, a motor (26) connected to said shaft to rotate it and said stack of membrane packs about said axis, and a feed inlet (12) coupled to the inside of said container to flow feed fluid therein, characterized by:
each of a plurality of said separator elements includes a plurality of spokes (141-148) extending largely radially, with radially outer ends coupled tosaid container and with radially inner ends, and a hub portion (180) that connects said radially inner ends of said spokes to each other.

12. A method for operating a rotary filtration apparatus which includes rotating about an axis (28), a stack (30) of membrane packs (32) that have rotating pack surfaces (92) and that lie within a container (24), while maintaining a stack (34) of substantially stationary separator elements (36) so each of said separator elements lies between a pair of said membrane packs, and with each element having element surfaces (113), with said packs and elements leaving gaps (40) between said rotating pack surfaces and said element surfaces, including a first gap between a first rotating pack surface ofa first of said membrane packs and a first element surface of a first of said elements, and feeding a feed fluid (90) that is to be separated into permeate and concentrate into said container to lie in said gaps, comprising:
flowing some of said feed fluid at least partially radially inwardly along inward paths (102) that lie in said first gap and that lie adjacent to locations on said first element, with substantially all of the feed fluid that lies adjacent to said first element and in said first gap flowing with a radially inward directional component rather than radially outwardly;
flowing some of said feed fluid at least partially radially outwardly along outward paths (94) that lie in said first gap and that lie adjacent to said rotating pack surface of said first membrane pack, with substantially all of the feed fluid that lies adjacent to said rotating pack surface and in said first gap flowing with a radially outwardly directional component rather than radially inwardly, while flowing some of the permeate from said feed fluid into said first membrane pack and from it into a permeate conduit (52), where at least some of said inward and outward paths lie at substantially the same locations over said first element;
and flowing a portion of said feed fluid that has flowed both radially inwardly and radially outwardly along said inward and outward paths within said first gap, into a feed conduit (82) that connects to a plurality of said gaps.

13. The method described in claim 12 wherein:
said feed conduit (82) lies within said vessel, extends at least partially in an axial direction, and lies radially outward of said stack of membrane packs; and including flowing said feed fluid at least partially axially along said feed conduit, and flowing feed fluid both from said feed conduit into each of said plurality of gaps and from each of said plurality of gaps into said feed conduit.

14. The method described in claim 12 including:
commencing a process to clean said membrane packs of said stack;
allowing particles of said feed fluid to build up on said rotating pack surfaces, but only to a thickness that is less than one-tenth the thickness (116) of the gap between each of said rotating pack surfaces and the adjacent one of said element surfaces, before said step of commencing a process to clean said membrane packs of said stack.