Abstract:
In a first membrane filtration module comprises a membrane module comprising a plurality of permeable hollow membranes; a fluid distribution device adapted to removably surround at least a portion of the membranes of the membrane module, the fluid distribution device comprising a plurality of through-hole openings for distributing a fluid, and the fluid distribution device adapted to distribute a flow of fluid along a surface of the permeable hollow membranes. In a second membrane filtration device comprises a membrane module comprising a plurality of permeable hollow membranes, each of the permeable hollow membranes having a surface; and a gas distribution device: adapted to distribute gas bubbles to the surface of the permeable hollow membrane, adapted to removably surround at least a portion of the plurality of permeable hollow membranes, and defining a plurality of through openings for distributing the gas bubbles to the membranes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit, under 35 U.S.C. §120(a), of Australian Provisional Application Serial No. 2010901864, filed 30 Apr. 2010, the entire contents and substance of which are hereby incorporated by reference as if fully set forth below. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    Embodiments of the present invention relate to membrane filtration systems and, more particularly, to an improved cleaning method and apparatus for such systems. 
         [0004]    2. Description of Related Art 
         [0005]    The use of membrane filtration systems is rapidly growing. The success of such systems largely depends on employing effective and efficient membrane cleaning methods. Commonly used physical cleaning methods include backwash (e.g., back pulse, back flush) using liquid permeate or a gas, and membrane scrubbing or scouring using a gas in the form of bubbles in a liquid. Examples of this second type of method are generally described in U.S. Pat. No. 5,192,456 to Ishida et al.; U.S. Pat. No. 5,248,424 to Cote et al.; U.S. Pat. No. 5,639,373 to Henshaw et al.; U.S. Pat. No. 5,783,083 to Henshaw et al.; and International Patent Application Publication Nos. WO98/28066 and WO00/18498 (assigned to the Applicant). 
         [0006]    These conventional methods use a variety of techniques to introduce gas bubbles into the membrane arrays to produce effective and efficient surface cleaning Effective cleaning can be achieved by introducing bubbles into the array in a uniform manner—as much as possible to produce efficient cleaning of the membrane surfaces. 
         [0007]    Some filtration systems include a bundle of fibre membranes mounted in a generally vertical orientation between spaced upper and lower headers with bubbles flowing from below the lower header or formed by flowing gas or a gas/liquid mixture through openings in the lower header. A filtration system of this variety is illustrated in  FIG. 1 . 
         [0008]    The use of openings in the lower header complicates the potting process of fibres in the lower header and can lead to breakage of the fibres in the region of the openings, as well as limitations on the packing density of the fibres within the header. 
       SUMMARY 
       [0009]    Briefly described, embodiments of the present invention relate to an improved method and apparatus for flowing fluid to or from a membrane module that overcomes, or at least ameliorates, one or more of the disadvantages of the prior art or at least provides a useful alternative. 
         [0010]    According to a first aspect, embodiments of the present invention provide a membrane filtration module comprising a fluid distribution device for distributing a flow of fluid along the surfaces of permeable hollow membranes located in the membrane module. The fluid distribution device can be adapted to removably surround at least a portion of the membranes, and define a number of through openings for distributing the fluid. 
         [0011]    According to another aspect, embodiments of the present invention provide a membrane filtration device comprising a gas distribution device for distributing gas in the form of bubbles to the surfaces of permeable hollow membranes located in the membrane module. The gas distribution device can be adapted to removably surround at least a portion of the membranes, and define a number of through openings for distributing the gas bubbles to the membranes. 
         [0012]    According to yet another aspect, embodiments of the present invention provide a method of distributing a fluid flowing along the surfaces of permeable hollow membranes located in the membrane module. The fluid flow can be distributed by a fluid distribution device adapted to removably surround at least a portion of the membranes and define a number of through openings for distributing the fluid. 
         [0013]    According to another aspect, embodiments of the present invention provide a filtration system for removing fine solids from a liquid suspension comprising: a vessel for containing the liquid suspension; a plurality of permeable, hollow membranes positioned within the vessel; means for providing a pressure differential across walls of the membranes, such that some of the liquid suspension can pass through the walls of the membranes to be drawn off as permeate; means for withdrawing permeate from the membranes; and a fluid distribution device for distributing a flow of fluid along the surfaces of the permeable, hollow membranes, wherein the fluid distribution device is adapted to removably surround at least a portion of the membranes and is provided with a number of through openings for distributing the fluid. 
         [0014]    According to another aspect, embodiments of the present invention provide a filtration system for removing fine solids from a liquid suspension comprising: a vessel for containing the liquid suspension; a plurality of permeable, hollow membranes positioned within the vessel; means for providing a pressure differential across walls of the membranes, such that some of the liquid suspension can pass through the walls of the membranes to be drawn off as permeate; means for withdrawing permeate from the membranes; and a gas distribution device for distributing gas in the form of bubbles to the surfaces of the permeable hollow membranes, wherein the gas distribution device is adapted to removably surround at least a portion of the membranes, the device being provided with a number of through openings for distributing the gas bubbles to the membranes. 
         [0015]    In some embodiments, the permeable hollow membranes can be arranged in an elongate bundle and the fluid distribution device extends circumferentially around a portion of the bundle. For example and not limitation, the bundle of membranes extends between approximately vertical spaced upper and lower headers and the fluid distribution device extends around a portion of the bundle at or adjacent the lower header. In some embodiments, the membranes are hollow fibre membranes. 
         [0016]    The fluid distribution device can have a ring-like configuration and the defined through openings can be evenly spaced along the circumference of the ring. In some embodiments, the fluid distribution device can be formed from two or more detachable interengaging components. For example, the fluid distribution device is formed of a pair of semicircular components. The fluid distribution device can be a clip. 
         [0017]    According to another aspect, embodiments of the present invention provide a membrane filtration module including a number of membranes extending between spaced headers. The headers can be retained in respective first and second end housings. The end housings can incorporate means that are adapted to allow anchoring of the first and second end housings against longitudinal movement along the longitudinal axis of the module. The means can be adapted to allow anchoring comprising first and second spaced apart ridges encircling the periphery of the end housings engageable against respective opposed shoulders of an encircling clip. In addition, a first of the opposed shoulders can be mechanically supported against a sleeve member, which is mechanically supported on a header member. Also, a second of the opposed shoulders can be mechanically urged against a first end of a slidable cup member, which is sealingly slidable over the end housings and is urged into sealing engagement with the header member, wherein the clip forms a fluid distribution device with a number of through openings arranged to provide an uniform distribution of fluid flow through the device. 
         [0018]    Further features of embodiments of the present invention, and the advantages offered thereby, are explained in greater detail hereinafter with reference to specific embodiments illustrated in the accompanying drawings, wherein like elements are indicated by like reference designators. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  illustrates a simplified schematic side elevation view of a prior art module using aeration through the lower header. 
           [0020]      FIG. 2  illustrates a simplified schematic side elevation view similar to that of  FIG. 1  illustrating a side aeration method, in accordance with an exemplary embodiment of the present invention. 
           [0021]      FIG. 3  illustrates a simplified schematic side elevation view of a feed manifold arrangement, in accordance with an exemplary embodiment of the present invention. 
           [0022]      FIG. 4  illustrates an perspective view of a base portion of a pressurized module and a clip arrangement used therein to support the module, in accordance with an exemplary embodiment of the present invention. 
           [0023]      FIG. 5A  illustrates an isometric view of a portion of the clip, in accordance with an exemplary embodiment of the present invention. 
           [0024]      FIG. 5B  illustrates a plan view of the clip of  FIG. 5A , in accordance with an exemplary embodiment of the present invention. 
           [0025]      FIG. 5C  illustrates a cross-sectional view taken along lines A-A of  FIG. 5B , in accordance with an exemplary embodiment of the present invention. 
           [0026]      FIG. 6  illustrates a graphical representation of a transmembrane pressure profile for bottom entry aeration configuration of the module and the side aeration configuration of the module, in accordance with an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    To facilitate an understanding of the principles and features of embodiments of the invention, they are explained hereinafter with reference to their implementation in an illustrative embodiment. In particular, embodiments of the present invention are described in the context of being membrane filtration systems. More particularly, embodiments of the present invention are described in the context of an improved cleaning method and apparatus for such systems. 
         [0028]    Embodiments of the present invention, however, are not limited to its use as a membrane filtration system. Rather, embodiments of the invention can be used wherever a filtration system is needed or desired. Thus, the membrane filtration system described hereinafter for use to filter media in a fluid, such as water, can also find utility for filtering other items. 
         [0029]    Additionally, the materials and components described hereinafter as making up the various elements of the protection system are intended to be illustrative and not restrictive. Many suitable materials and components that would perform the same or a similar function as the materials and components described herein are intended to be embraced within the scope of the invention. Such other materials and components not described herein can include, but are not limited to, materials and/or components that are developed after the time of the development of embodiments of the present invention, for example. 
         [0030]    Referring now in detail to the figures, wherein like reference numerals represent like parts throughout the several views,  FIG. 1  illustrates a conventional aeration method. 
         [0031]    As shown in  FIG. 1 , a module  10  comprises a lower header  12 , where one end of the membrane fibres forming the module  10  is potted. The fibres are typically arranged in a bundle  14  when potted. The lower header  12  can have a number of evenly distributed through-holes  16  extending therethrough from its base  18  to its upper surface  20  for provision of gas, for example air, into the base of the fibre bundle  14 . The lower header  12  is in fluid communication and connected to a manifold  22 , which supplies the gas to the lower openings of through-holes  16 . In use, the module  10  can be immersed in feed liquid contained in a feed vessel  24  and the gas flows into the manifold  22  and upwardly through the holes  16  to form gas bubbles within the fibre bundle  14  to scour and clean the surfaces of the membranes. 
         [0032]    This conventional aeration method—while efficient in providing a desired flow of bubbles within the fibre bundle—has a number of disadvantages. The need to define holes in the lower header complicates the potting process by requiring the formation of the holes and distribution of the fibres between the holes. Further, the holes make the use of double ended withdrawal of permeate from the membranes difficult. Also, once formed, the size and configuration of the holes cannot be easily changed without replacing the entire module. The holes also occupy space within the lower header leading to a reduction in the available possible packing density of fibres. 
         [0033]      FIG. 2  shows a simplified diagram of an exemplary embodiment of the present invention. A module  100  is similar in design to that shown  FIG. 1 , but, in this case, the scouring gas is distributed along the sides of the fibre bundle  104  by an externally mounted aeration distribution device  106  that can be positioned near or at the base of the module  100 . In an exemplary embodiment, this distribution device  106  comprises a clip  108 , which may be formed in two parts to fit around the fibre bundle  104 , although other configurations of the aeration distribution device  106  may be used, including those having a single part or number of parts. In this embodiment, a gas or a gas bubble liquid mixture can be provided below the distribution device  106  and the distribution device  106  can direct the gas or mixture of gas bubbles and liquid evenly around or about the sides of the membrane bundle  104  to provide cleaning of the membrane surfaces. 
         [0034]    The gas distribution method and device of embodiments of the present invention may be employed in both pressurized and submerged (non-pressurized) membrane filtration systems. 
         [0035]    An exemplary embodiment of the present invention employed in a pressurized filtration system will now be described.  FIGS. 3-4  illustrate an exemplary arrangement of the distribution device. In this exemplary embodiment, the device used for gas distribution may also be used to support the module  100  within the pressurised vessel casing. 
         [0036]    As shown in  FIG. 3 , the module  100  can include a lower permeate collection chamber  120  that is in fluid communication with the membrane ends potted in the lower header  110 . The module  100  is located within a pressure housing  130  that can be fluidly connected to a feed supply manifold  140 . The base of the housing  130  defines openings  132  to allow flow of feed liquid into the housing  130  and around the membranes in the bundle  104 . The aeration distribution device  106  is located near the base  131  of the membrane bundle  104  and fits between the bundle  104  and the inner wall of the housing  130 . Scouring or cleaning gas can be supplied into the feed supply manifold through a gas supply tube  150 . The gas is supplied through openings in the tube  150  into the feed liquid to form bubbles that flow upwardly through the supply manifold  140  and through openings  132  into the housing  130 . The bubbles can then continue upwardly through the distribution device  106  and along the outer surface of the membrane bundle  104 , so as to remove accumulated solids from the surface of the membranes by scouring and agitating the membranes within the bundle  104 . 
         [0037]    Further detail of the configuration and mounting of the aeration distribution device is illustrated in the perspective view of  FIG. 4 . In some embodiments, the membrane bundle  104  is adapted to be replaced by a sideways movement of the filter cartridge containing the bundle  104  and its associated enclosing assembly, whereby the upper and lower header assemblies need not be disturbed or dismantled. 
         [0038]    The components of the filtration module illustrated in the embodiment of  FIG. 4  are a bundle of microporous hollow fibres  104  terminating in opposing ends  202 . One end of the bundle is potted in the lower header  110 . The lower header  110  can be encased in an end piece or cap  204  that serves as a former for the header during manufacturing and serves to provide external working surfaces that are used to support the fibre bundle  104  in use, so that it can resist both the extending forces encountered during normal filtration and the compressive forces encountered during backwash. 
         [0039]    The end piece or cap  204  defines a pair of grooves  206 ,  208  for receiving O-rings that can form a slidable seal against an inner surface of connecting flange  214  of filtrate cup or housing  220 . The structure of the connecting flange  214  can be such that the filtrate cup  220  can slide upwardly onto the end piece  204 —when annular clip  106  forming the aeration distribution device is removed—to the extent that the upper end of the filtrate cup  220  clears (e.g., it entirely clears) internal skirt or flange of the manifold  222 . 
         [0040]    A connecting sleeve  230  further includes shoulder portions  232 ,  234  located on an inner surface. The shoulder portions  232 ,  234  are adapted to engage the circular clip  106  forming the aeration distribution device, whereby supporting pressure is applied by means of the clip  106  to one of an opposed shoulders  240  defining the groove  242  in the cap  204  when the connecting sleeve  230  is in sealed, mating relationship with the manifold  222 . As a result, the cap  204  can be mechanically supported against motion along the longitudinal axis of the membrane bundle in a first direction, while the other of the opposed shoulders  244  defining the groove  242  in the cap  204  is mechanically supported against an opposed surface of the clip  106  that, in turn, is mechanically urged against a lower rim portion of the slideable cap  204  thereby urging the slideable cap  204  to an extended position with respect to the bundle  104 . 
         [0041]    As with the operation of the arrangement shown in  FIG. 3 , in use, feed liquid can flow through the feed supply manifold  140  and upwardly through the distribution device  106  and along the sides of the membrane bundle  104  contained within the pressure housing  130 . Permeate can be withdrawn through the lower header  110  and collected in the filtrate cup  220 . When gas scouring or cleaning is desired, gas can be fed into the feed supply manifold  140  and the gas bubbles formed flow upwardly through and are uniformly distributed around the membrane bundle  104  by the distribution device  106 . 
         [0042]    In an exemplary embodiment, a method of removing the clip  106  includes disengaging and sliding downwardly the outer sleeve  230  to the extent that the sleeve  230  is drawn below the level of the clip  106 . The clip  106  can comprise two halves permitting the clip  106  to be disengaged from the groove  242  in the end piece  204  in which it normally resides, thereby allowing the filtrate cup  220  to be drawn downwardly, as described above. 
         [0043]    When these clearing actions are performed on the filtrate cup  220 , the clip  106  and the outer sleeve  230  located at both ends of the module  100 , then the entire module  100  complete with casing and sleeves can slide sideways with respect to its longitudinal axis, so as to be lifted clear of the header assemblies without disturbing the header assemblies. A reverse process can be followed to replace the filter module and filter module assembly. 
         [0044]    While this arrangement can be used with single ended filter cartridges it may be more useful with the double ended opposed header arrangements shown, where it is commonly more difficult, or in some cases not possible, to remove the filter cartridge without disturbing the header assemblies without compacting the filter cartridge and filter cartridge assembly in some manner along their longitudinal axes. 
         [0045]    As best shown in  FIG. 5A-5C , the aeration distribution device can comprise a pair of semi-circular clip portions  106   a.  Each free end of the clip portion  106   a  is provided with a respective locking protrusion  300  and  302  extending in the plane of the inner circumferential surface  304  of the clip portion  106   a.  One locking protrusion  300  extends in the plane of the upper surface of the clip portion  106   a,  while other protrusion  302  extends in the plane of the lower surface of the clip portion  106   a  with each protrusion having a width approximately half the width of the clip portion  106   a.  In use, a pair of the clip portions  106   a  can be fitted together with overlapping engagement of the associated locking portions  300  and  302  to form a circular clip  106  when located with the groove  242  of the end cap  204 . 
         [0046]    Each clip portion  106   a,  as probably best shown in  FIG. 5C , can include a series of circumferentially spaced reduced width regions  306  provided generally equidistant along the length of the clip portion  106   a.  In some embodiments, the reduced width regions can be generally rectangular in shape, when viewed in plan, and separated from each other by a radially extending ridge  308 . Each of these reduced width portions  306  defines a through opening or hole  310  formed in its base portion  312 . Still referring to  FIG. 5C , the base portion  312  can be centrally located between the upper and lower edges of the clip portion  106   a.  The number and size of the holes  310  can vary, as it may be determined by the required gas distribution and flow needed to provide efficient and uniform cleaning of the membranes in the module. 
         [0047]    Conventional systems without an aeration distribution device where gas is provided below the module tend to produce a flow of bubbles that have a distribution favoring the path of least resistance. In other words, the bubbles tend to flow directly upward from the source of gas, unless some form of distribution device is provided to distribute and equalize the flow around the periphery of the membrane bundle to provide a uniform flow of bubbles to the whole surface of the membrane bundle. 
         [0048]    This problem with conventional systems is further exacerbated in arrangements where a number of membrane modules are aerated from a common source of gas. In such cases, when one module becomes fouled before another, the gas flow can favor the less fouled module leading to reduced bubble flow in the fouled module and thus further increased fouling. 
         [0049]    Embodiments of the present invention overcome this problem of conventional systems, and others, by equalizing the flow of gas between and around the modules. 
         [0050]    The use of a removable aeration distribution device enables older style systems, where appropriate, to be retrofitted with embodiments of the present invention, while also allowing easy adjustment and optimization of the gas distribution profile of any particular module installation. In other words, aeration distribution devices having varying hole sizes and positions may be used to optimize the operation of the cleaning process for a particular module configuration. 
         [0051]    The use of the distribution device with openings that restrict and distribute fluid flow therethrough has also been found to provide a further advantage when draining the module following a backwash or cleaning process. Typically, the liquid containing the solids dislodged during a backwashing and/or scouring process is periodically removed by a drain down of the feed vessel or module. As this drain down impinges on the filtration process time of the system, it is desirable to minimize the time taken for a drain down. Accordingly, the drain down usually results in a rapid flow of liquid from the module. A rapid and unevenly distributed liquid flow can result in undue stress being placed on the membrane portions located near the discharge region for the waste flow. The use of a distribution device according to embodiments of the invention ameliorates this problem by restricting and distributing the flow evenly amongst the membranes resulting in the less chance of damage to the membranes. 
         [0052]    The use of the distribution device according to embodiments of the invention may result in a decrease in the aeration discharge backpressure. The backpressure experienced in the side aeration method described above is the static head of liquid level present during the scouring or cleaning process; with a bottom aeration configuration, however, where gas is supplied through holes in the lower header, the aeration must overcome both the static head pressure of the liquid level as well as the backpressure resulting from the fibres in the lower header hindering the gas flow from the holes. 
         [0053]    The arrangement described also provides support for the end cap  204  in both an upward and a downward longitudinal direction whereby the end cap  204  (and hence the opposed ends  202 ) of the fibre bundle resist the compressive forces exerted during backwash and extensive forces exerted during normal filtration. This support is provided without the necessity of using any form of internal stiffening integral to the membrane module itself. Rather the mechanical support is provided by reliance on the module casing and associated header assemblies. 
         [0054]      FIG. 6  illustrates a graphical representation comparing the performance of different aeration entry configurations by comparison of transmembrane pressure (TMP) profiles. While it is clear that the use of aeration within the fibre bundle provides a lower overall TMP profile, each profile shows a stable and comparable performance over time. Accordingly, embodiments of the present invention provide adequate performance while ameliorating a number of the disadvantages of the aeration configuration using aeration entry through the lower header. 
         [0055]    It will be appreciated by those skilled in the art that the aeration distribution device according to the invention is not limited to the particular configurations described above and a number of variations in shape, size and construction are possible. 
         [0056]    It will also be appreciated that further embodiments and exemplifications of the invention are possible without departing from the scope or spirit of the invention described.