Abstract:
A filtration device having a plurality of membrane modules is provided. Each of the plurality of membrane modules has first and second permeable sheets that are separated by a spacer, a first ring disposed around a perimeter of a first hole in the first permeable sheet, and a second ring disposed around a perimeter of a second hole in the second permeable sheet, the second hole in alignment with the first hole. The first ring of each of the plurality of membrane modules is in abutment with the second ring of a preceding one of each of the plurality of membrane modules so that the plurality of membrane modules are interconnected for communication therebetween. Some embodiments further provide a third sheet that disposed between successively adjacent membrane modules.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is related to and claims the benefit of the filing date of co-pending provisional application U.S. Ser. No. 60/345,296, filed on Jan. 2, 2002, which application is incorporated herein by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention relates generally to the field of filtration and, in particular, to self-manifolding sheet membrane modules.  
         BACKGROUND  
         [0003]    Filtration units are typically employed in liquid, e.g., water, waste, etc., treatment plants for purifying the liquid. This involves filtering particles, e.g., micron, submicron, etc., from the liquid to produce a filtered liquid (or filtrate). Many filtration units use bundles of hollow-fiber membranes, e.g., small diameter tubes having permeable walls, for filtering. In some applications, the bundles are immersed in the liquid to be filtered and filtrate passes through the permeable walls and into the tubes under a pressure gradient. One problem with using bundles of hollow-fiber membranes is that hollow-fiber membranes are expensive.  
           [0004]    Some filtration units use a number of sheet membrane modules for filtering. Typically, each sheet membrane module includes a pair of sheet membranes separated by a flow passage. The sheet membrane modules are usually immersed in the liquid to be filtered and filtrate passes through the pair of sheet membranes of each sheet membrane module and into the flow passage under a pressure gradient. Most of these filtration units are constructed by potting several of sheet membranes within a container using, for example, a liquefied thermoplastic, such as polyurethane. However, this is expensive owing to the large amounts of potting material that is typically required.  
           [0005]    For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for alternative filtration devices.  
         SUMMARY  
         [0006]    One embodiment of the present invention provides a filtration device. The filtration device has a self-supporting membrane module suspendable within a fluid environment. The membrane module includes an envelope having a pair of permeable sheets that form a permeable boundary of the envelope. A spacer is disposed between the pair of permeable sheets. Each of the pair of permeable sheets has a hole passing therethrough. The hole of one of the sheets is aligned with the hole of the other sheet.  
           [0007]    Another embodiment provides a filtration device having a plurality of membrane modules. Each of the plurality of membrane modules has first and second permeable sheets that are separated by a spacer, a first ring disposed around a perimeter of a first hole in the first permeable sheet, and a second ring disposed around a perimeter of a second hole in the second permeable sheet, the second hole in alignment with the first hole. The first ring of each of the plurality of membrane modules is in abutment with the second ring of a preceding one of each of the plurality of membrane modules so that the plurality of membrane modules are interconnected for communication therebetween. Some embodiments further provide a third sheet that disposed between successively adjacent membrane modules. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is a front view of an embodiment of a membrane module according to the teachings of the present invention.  
         [0009]    [0009]FIG. 2 is a view taken along line  2 - 2  of FIG. 1.  
         [0010]    [0010]FIG. 3 is a view taken along line  3 - 3  of FIG. 2.  
         [0011]    [0011]FIG. 4 a  illustrates an embodiment of a filtration apparatus according to the teachings of the present invention.  
         [0012]    [0012]FIG. 4 b  is a cross-sectional view illustrating clamping of the filtration apparatus of FIG. 4 a  according to another embodiment of the present invention.  
         [0013]    [0013]FIG. 4 c  is a view taken along line  4   c - 4   c  of FIG. 4 b.    
         [0014]    [0014]FIG. 5 illustrates another embodiment of a filtration apparatus according to the teachings of the present invention.  
         [0015]    [0015]FIG. 6 illustrates yet another embodiment of a filtration apparatus according to the teachings of the present invention.  
         [0016]    [0016]FIG. 7 illustrates an embodiment of a method for cleaning the filtration apparatus of FIG. 6.  
         [0017]    [0017]FIG. 8 illustrates an embodiment of a method for cleaning a filtration apparatus according to the teachings of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]    In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense.  
         [0019]    FIGS.  1 - 3  illustrate an embodiment of a membrane module  100  according to the teachings of the present invention. Membrane module  100  includes an envelope  102 . Envelope  102  includes a pair of permeable sheets  108 , e.g., sheet membranes, that are substantially parallel to each other and that form a permeable boundary of envelope  102 . A flexible spacer  116  is disposed between permeable sheets  108  and is fixedly attached to each of permeable sheets  108 . However, the present invention is not limited to a flexible spacer. Rather, in some embodiments, a substantially rigid spacer is used in place of flexible spacer  116 . Moreover, the present invention is not limited to a spacer that is fixedly attached to each of permeable sheets  108 . Instead, in one embodiment, the spacer can be movably attached to each of permeable sheets  108  or can be free of any attachment to each of permeable sheets  108 . Each of permeable sheets  108  has a hole  120  passing therethrough, such that hole  120  of one of permeable sheets  108  is aligned with the hole  120  of the other of permeable sheets  108 , as shown in FIG. 2.  
         [0020]    In one embodiment, a single pair of aligned holes  120  are adjacent an edge  119  of membrane module  100 , as shown in FIGS. 1 and 2. A single pair of aligned holes  120  simplifies the manufacture of membrane  100  and thus reduces the cost of membrane  102 . A single pair of aligned holes  120  enables the use of a single manifold for connecting a series of membrane modules  100  together. Advantages of a single manifold are discussed below. However, membrane module  100  is not limited to a single pair of aligned holes  120 , and in other embodiments, membrane module  100  includes multiple pairs of aligned holes  120 , e.g., adjacent an edge  121  membrane module  100 , centered between edges  119  and  121 , etc.  
         [0021]    In one embodiment, a ring  122  is disposed around a perimeter of hole  120  of each of permeable sheets  108 . Rings  122  provide a self-manifolding feature that enables a number of membrane modules  100  to be connected together via rings  122 . This eliminates the need for potting a number of sheet membranes within a container. In other embodiments, a number of membrane modules  100  are connected together without rings  122 . In these embodiments, adjacent membranes are directly attached so that holes  120  of adjacent membranes are aligned. This also provides a self-manifolding feature,  
         [0022]    Disposing flexible spacer  116  between permeable sheets  108  and fixedly attaching flexible spacer  116  to each of permeable sheets  108  enables membrane module  100  to be self-supporting. This enables a pressure gradient to be applied across permeable sheets  108  without substantially deflecting permeable sheets  108 . That is, fixedly attaching flexible spacer  116  to each of permeable sheets  108  causes membrane module  100  to be substantially rigid.  
         [0023]    In one embodiment, permeable sheets  108  are attached to each other at their edges  110  and  112  by a suitable method, such as gluing, hotplate welding, ultrasonic welding, or the like. In another embodiment, permeable sheets  108  are integral. In this embodiment, the integral permeable sheets  108  are folded, e.g., at edge  121 . In other embodiments, ring  122  is secured to an exterior surface  140  of each of permeable sheets  108  by gluing or the like. In some embodiments, permeable sheets  108  are of polysulfone, polyethersulfone, polyethylene, nano-filter membranes, reverse osmosis membranes, or the like. In one embodiment, permeable sheets  108  include both permeable and non-permeable materials.  
         [0024]    Flexible spacer  116  is fixedly attached to each of permeable sheets  108  at an interior surface  118  of each of permeable sheets  108 , e.g., by gluing or the like. To maintain sufficient permeability of permeable sheets  108  for ensuring adequate filtration performance, flexible spacer  116  is adhered to each of permeable sheets  108  at discrete locations of interior surface  118 , e.g., locations  124 . In one embodiment, this is accomplished by applying an adhesive to discrete portions of interior surface  118  of each of permeable sheets  108 , e.g., at random.  
         [0025]    In various embodiments, flexible spacer  116  includes members  132 . In some embodiments, members  132  are of polyester, polypropylene, or any material that is hydrolytically stable, resistant to chlorine oxidation, etc. In one embodiment, members  132  are distributed to provide a mesh having a number of passageways  136  (e.g., interstices of the mesh) between them that collectively define a flow passage between permeable sheets  108  and thus within envelope  102  of membrane module  100 . The mesh supports permeable sheets  108  so as to prevent sheets  108  from being compressed together or pulled apart, for example, by pressures encountered by membrane  100  during operation.  
         [0026]    In operation, membrane module  100  is disposed in a fluid environment, e.g., water, sewage, or the like, so that the fluid wets exterior surface  140  of each of permeable sheets  108 . A pressure gradient is applied across each of permeable sheets  108  such that the pressure within the fluid environment is greater than within envelope  102 , e.g., by pumping up the pressure of the fluid environment or applying suction at either of holes  120 . This causes liquid filtrate, filtered water, sewage or the like, to flow through each of permeable sheets  108  and into envelope  102  of membrane module  100 . The filtrate flows through passageways  136 , in one embodiment, and exits membrane module  100  via one or both of holes  120 . In another embodiment, the pressure gradient is reversed such that the pressure within envelope  102  is greater than the within the fluid environment, causing the fluid within membrane module  100  to flow through each of permeable sheets  108  and into the fluid environment, for example, for backwashing membrane module  100 . In some embodiments, backwashing is performed while cleaning exterior surfaces  140 . In various embodiments, fibers  132  are distributed so that the pressure drop along the length of envelope  102  is small relative to the pressure gradient across each of permeable sheets  108 .  
         [0027]    [0027]FIG. 4 a  illustrates another embodiment of a filtration apparatus  400  according to the teachings of the present invention. Elements of FIG. 4 a  that are common to FIGS.  1 - 3  are numbered as in FIGS.  1 - 3  and are as described above. Filtration apparatus  400  includes a plurality of membrane modules  100   1  to  100   N , such as membrane module  100 . In one embodiment, membrane modules  100   1  to  100   N  are successively adjacent and substantially parallel to each other. Adjacent rings  122  respectively of adjacent membrane modules  100  abut to interconnect adjacent membrane modules  100  for communication therebetween. For example, as shown in FIG. 4 a , adjacent rings  122   2  and  122   3  respectively of adjacent membrane modules  100   1  and  100   2  abut to interconnect adjacent membrane modules  100   1  and  100   2 , adjacent rings  122   4  and  122   5  respectively of adjacent membrane modules  100   2  and  100   3  abut to interconnect adjacent membrane modules  100   2  and  100   3 , etc. This forms a manifold  401  for collecting filtrate that flows within each of envelopes  102  of each of membrane modules  100 , respectively, as indicated by arrows  410 .  
         [0028]    In one embodiment, a single manifold  401  is adjacent edge  119  of each of membrane modules  100  and thus membrane modules  100  are interconnected adjacent edge  119  only. A single manifold  401  simplifies assembly of filtration apparatus  400 , installation of filtration apparatus  400  in fluid containment apparatus, and maintenance procedures, e.g., replacing on or more membrane modules  100 . In another embodiment, a bore  403  passes through flexible spacer  116  of each of membrane modules  100  and interconnects holes  120 , thereby forming a portion of manifold  401 , as shown in FIG. 4. Filtration apparatus  400  is not limited to a single manifold  401 , and for other embodiments, filtration apparatus  400  includes multiple manifolds  401  so that membrane modules  100  are also interconnected at other locations, e.g., adjacent edge  121  membrane modules  100 , centered between edges  119  and  121 , etc.  
         [0029]    For another embodiment, successively adjacent membrane modules  100  are connected together by aligning holes  120  of the adjacent membrane modules  100  and attaching the adjacent membrane modules  100  together directly by attaching the region around the perimeters of the holes  120  of adjacent membranes together, e.g., by gluing or the like. In this embodiment, bore  403  of each membrane module  100  forms manifold  401 . Adding additional membrane modules  100  adds to manifold  401 , and therefore this embodiment is also self-manifolding.  
         [0030]    In one embodiment, adjacent rings  122  respectively of adjacent membrane modules  100  are maintained in abutment by a compressive force applied across the plurality of membrane modules  100 , e.g., by clamping or the like. In other embodiments, the abutment between adjacent rings  122  respectively of adjacent membrane modules  100  is sealed, such as by an “O” ring disposed between the adjacent rings  122 , a seal integral with a face of one of the adjacent rings  122 , or any other suitable sealing arrangement known by those skilled in the art.  
         [0031]    In another embodiment, a clamp  450  applies the compressive force, as shown in FIGS. 4 b  and  4   c . In particular, for one embodiment, clamp  450  includes jaws  452  disposed on a rod  456 , where membrane modules  100  are sandwiched between jaws  452 . For one embodiment, rod  456  passes through manifold  401  and the bore  403  that passes through each of membrane modules  100 . For another embodiment, at least one of jaws  452  is selectively movable relative to rod  456 . FIG. 4 c  shows that during clamping, each of jaws  452  engages manifold  401  so as to provide a flow passage  462  for fluid pass through, as indicated by arrow  460 .  
         [0032]    To remove one or more of membrane modules  100   1  to  100   N  e.g., membrane module  100   2 , from filtration apparatus  400 , the compressive force across membrane modules  100   1  to  100   N  is removed. Rings  122   3  and  122   4  of membrane module  100   2  are respectively separated from rings  122   2  and  122   5  respectively of the adjacent membrane modules  100   1  and  100   3 . This enables membrane module  100   2  to be removed from filtration apparatus  400 . In this manner, any one of the individual membrane modules may be removed from filtration apparatus  400 .  
         [0033]    In one embodiment, hangers  150  are attached to each of membrane modules  100  at corners  152  and  154 , as shown in FIG. 1. In one embodiment, hangers  150  are attached only at comers  152 . Hangers  150  are used, in one embodiment, to suspend each of membrane modules  100  and thus filtration apparatus  400  within a fluid containment apparatus, such as a tank, a flow channel, or the like, from a supportive structure, such as a frame, adjacent or integral to the fluid containment apparatus. Hangers  150  are adapted to be removable from the supportive structure to facilitate the independent removal of each of membrane modules  100  from the supportive structure, e.g., for maintenance, replacement, or the like. In various embodiments, hangers  150  are rendered removable by configuring hangers  150  as clamps that selectively clamp to the supportive structure, hooks, ties, or using other methods known to those skilled in the art.  
         [0034]    To remove membrane module  100   2 , for example, from filtration apparatus  400  for embodiments where filtration apparatus  400  is suspended within the fluid containment apparatus, rings  122   3  and  122   4  of membrane module  100   2  are respectively separated from rings  122   2  and  122   5  while the hangers  150  of membrane module  100   2  suspend membrane module  100   2  within the fluid containment apparatus. Then, the hangers  150  of the membrane module  100   2  are removed from the supportive structure, and membrane module  100   2  is removed from filtration apparatus  400  and the tank, while filtration apparatus  400  less membrane module  100   2  remains suspended within the tank.  
         [0035]    To install membrane module  100   2  in filtration apparatus  400  after removing membrane module  100   2 , as described above, membrane module  100   2  is inserted between membrane modules  100   1  and  100   3 . In one embodiment, membrane module  100   2  is inserted between membrane modules  100   1  and  100   3  while filtration apparatus  400  is suspended in the fluid containment apparatus. In this embodiment, hangers  150  of membrane module  100   2  are attached to the supportive structure to suspend membrane module  100   2  within the fluid containment apparatus. Rings  122   3  and  122   4  of membrane module  100   2  are respectively aligned with rings  122   2  and  122   5  respectively of membrane modules  100   1  and  100   3 . The compressive force is applied across membrane modules  100   1  to  100   N  to respectively abut rings  122   2  and  122   5  against rings  122   3  and  122   4 .  
         [0036]    In operation, filtration apparatus  400  is disposed within a fluid containment apparatus as described above so that a fluid, such as water, sewage, or the like, resides in each of regions  402  between envelopes  102  of adjacent membrane modules  100 , as shown in FIG. 4 a . A pressure gradient is applied across each of permeable sheets  108  of each of envelopes  102 , for example, by pumping up the pressure of the fluid in the fluid containment apparatus or applying suction at an opening  404  of manifold  401  and/or an opening  406  of manifold  401 . This causes liquid filtrate, e.g., filtered water, sewage, or the like, to pass through each of permeable sheets  108  of each of membrane modules  100  and into envelope  102  of each of membrane modules  100 , as illustrated by arrows  408  of FIG. 4 a . The filtrate passes within each of envelopes  102 , as illustrated by arrow  410 , and into manifold  401 . The filtrate exits filtration apparatus  400  via opening  404  and/or opening  406  of manifold  401 . During backwashing, the pressure gradient is reversed, thus causing the direction of arrows  408  and  410  to be reversed.  
         [0037]    [0037]FIG. 5 illustrates another embodiment of a filtration apparatus  500  according to the teachings of the present invention. Elements in FIG. 5 that are common to FIGS.  1 - 4  are numbered as in FIGS.  1 - 4  and are as described above. Resilient spacers  502  are disposed between adjacent hangers  150 , as shown in FIG. 5. Resilient spacers  502  are alternately compressed and released, for example, by alternately applying a compressive force (indicated by arrows  504 ) to hangers  150 . In one embodiment, alternately applying the compressive force to hangers  150  is accomplished using a support structure from which hangers  150  suspend each of membrane modules  100 . Compressing resilient spacers  502  moves adjacent envelopes  102  toward each other, as indicated by arrows  506 , causing the fluid residing in each of regions  402  to flow out of each of regions  402 , as indicated by arrow  508 . Releasing resilient spacers  502  moves adjacent envelopes  102  away from each other and back to their original positions, as indicated by arrow  510 , causing fluid to flow into each of regions  402 , as indicated by arrow  512 . Therefore, alternately compressing and releasing resilient spacers  502  produces an alternating flow into and out of each of regions  402 . This produces flows, e.g., turbulence-induced flows, near exterior surface  140  of each of permeable membranes  108  for reducing membrane fouling and assisting in cleaning surfaces  140 .  
         [0038]    [0038]FIG. 6 illustrates another embodiment of a filtration apparatus  600  according to the teachings of the present invention. Elements in FIG. 6 that are common to FIGS.  1 - 4  are numbered as in FIGS.  1 - 4  and are as described above. A sheet  602 , such as polypropylene monofilament, polyester monofilament, etc., is disposed between each of envelopes  102  of filtration apparatus  600 . In some embodiments, sheet  602  has a mesh.  
         [0039]    For one embodiment, sheet  602  is suspended between each of envelopes  102  by attaching an end  604  of sheet  602  to manifold  401 . In this embodiment, an end  603  of sheet  602  located opposite of end  604  remains free. In other embodiments, sheet  602  is flexibly supported between each of envelopes  102 , e.g., flexibly attached to manifold  401  by a resilient strap, spring, or the like, so that sheet  602  floats between each of envelopes  102 . For these embodiments, sheet  602  can be moved between each of envelopes  102 . This acts to produce turbulence, for one embodiment, that acts to reduce fouling of exterior surfaces  140  and to keep exterior surfaces  140  clean.  
         [0040]    In one embodiment, air bubbles  700 , generated within the fluid in which envelopes  102  are immersed, flow between each of envelopes  102  and move sheets  602  into contact with exterior surfaces  140  of each of permeable membranes  108 , as illustrated in FIG. 7. In this way, sheets  602  impart forces to exterior surfaces  140  for cleaning exterior surfaces  140 . For some embodiments, air bubbles  700  move sheets  602  during backwashing. In another embodiment, sheets  602  are disposed between each of envelopes  102  of filtration apparatus  600  so as to contact exterior surfaces  140 . Filtration apparatus  600  is moved, e.g., vibrated, so as to cause a scrubbing action between monofilament sheets  602  and exterior surfaces  140 . For one embodiment this is performed during backwashing.  
         [0041]    For another embodiment, sheets  602  impede the upward flow of air bubbles  700  and cause air bubbles  700  to change their course as they flow generally upward between envelopes  102 . This acts to produce turbulence in the fluid between successive membranes. The turbulence acts to promote mixing adjacent exterior surfaces  140 . The turbulence acts to reduce the thickness of concentration boundary layers adjacent exterior surfaces  140 . This acts to reduce fouling of exterior surfaces  140  and to keep exterior surfaces  140  clean.  
         [0042]    [0042]FIG. 8 illustrates another embodiment of a filtration apparatus  800  according to the teachings of the present invention. Elements in FIG. 8 that are common to FIGS.  1 - 4  are numbered as in FIGS.  1 - 4  and are as described above. Filtration apparatus  800  is alternately positioned at angles  802  and  804  from the vertical to facilitate cleaning and/or reductions in fouling of surfaces  140 , e.g., surfaces  140   1  and  140   2 , of opposing permeable membranes  108  of each of envelopes  102 . When filtration apparatus  800  is positioned at angle  802 , surface  140   1  faces downward and surface  140   2  faces upward, as shown in FIG. 8. Alternatively, when filtration apparatus  800  is positioned at angle  804 , surface  140   2  faces downward and surface  140   1  faces upward. In operation, air bubbles  806 , generated within the fluid in which envelopes  102  are immersed, flow substantially vertically upward and impinge upon the downward facing surface  140 , e.g., surface  140   1  of FIG. 8, of each of permeable membranes  108  at the angle at which apparatus  800  is positioned from the vertical, e.g., angle  802  of FIG. 8. Bubbles  806  flow along the downward facing surface  140 , e.g., surface  140   1 . This decreases the fouling rate and aids in the cleaning of the downward facing surface  140 . For various embodiments, this cleaning process is performed during backwashing.  
       Conclusion  
       [0043]    Embodiments of the present invention have been described. The embodiments provide membrane modules that eliminate the need for hollow-fiber membranes and sheet membranes that are potted within a container. Moreover, the embodiments provide a self-manifolding feature that enables a number of membrane modules to be connected together. The embodiments also provide for cleaning external surfaces of the membrane modules.  
         [0044]    Although specific embodiments have been illustrated and described in this specification, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. For example, instead of alternately compressing and releasing resilient spacers  502  of FIG. 5 to produce an alternating flow into and out of each of regions  402 , alternately stretching and releasing resilient spacers  502  can respectively produce a flow into and out of each of regions  402 . Moreover, alternately stretching and compressing resilient spacers  502  can respectively produce a flow into and out of each of regions  402 .