Patent Publication Number: US-2011049034-A1

Title: Modular cross-flow filtration system

Description:
FIELD OF THE INVENTION 
     This invention relates to filtration membrane systems and, in particular, but not exclusively, to modular filtration membrane systems. 
     BACKGROUND TO THE INVENTION 
     Many systems have been developed for water filtration including, for example, media bed filtration; microfiltration and ultrafiltration membrane filtration; and reverse osmosis and nanofiltration membrane filtration. Each system typically involves feeding water through the filtration system in order to remove particulates and/or reduce the concentration of ions in the feed, thereby producing a concentrate product output and a permeate product output. Systems may also comprise a number of filtration stages. 
     However, there are a number of drawbacks associated with existing filtration systems. 
     For example, existing systems typically involve a complex system of interconnected filtration vessels, this requiring significant numbers of connection pipes and hoses. As such, the systems have a large footprint and can be of significant weight. This is of concern, for example, in the oil and gas industry, and in particular offshore applications, where space and weight capacity may be limited. 
     In addition, it will be recognised that the footprint and mass of a filtration system will be influenced by the efficiency of the filtration vessel or vessels in the system. For example, it has been found that the performance of filtration vessels may be degraded by leakage of a seal, typically one or more o-ring, provided between the feed flow and the permeate flow through the filtration membrane, thereby contaminating the permeate flow. 
     Leakage may be caused by a number of factors. For example, the seal may have been incorrectly installed resulting in the seal being cut, nipped, or twisted. Alternatively, the seal may have been omitted or the incorrect size or sealing material may have been used. Often, seal leakage is the result of wear caused by movement or deformation of the components within the vessel. For example, during start up and shutdown/rundown of the filtration membrane trains, a degree of wear can occur due to compression and decompression of the membranes, though as this process is carried out in a controlled manner, the possibility of damage or wear to the membranes can be limited. However, during plant trip conditions, that is, where an unexpected shutdown occurs, the risk of damage to the membranes is greater. During normal operation the filtration membranes encounter a degree of wear and tear, this process being accelerated during cleaning operations. For example, it will be recognised that where the membranes are subject to higher fouling conditions, the membranes require more frequent cleaning and the membrane working life may be reduced. 
     Clearances between the system components may be created, for example, by longitudinal movement of the components, tolerances in the dimensions of the vessel components and the like. Furthermore, wear may be incurred due to hydraulic vibration during operation and during filtration element replacement and removal. 
     In order to reduce wear, a number of spacers, or shims, are often used to pack the components in the vessel. A vessel end plate is then push fit into the end of the vessel and locked into place using a locking ring and a spring coil or the like. However, it has been found that this arrangement can be inaccurate and problematic. 
     As described above, fouling of the filtration membranes acts to reduce system performance. For example, particulate matter may accumulate over time, resulting in blockage of the pores of the filtration membrane. In order to overcome this, microfiltration and/or ultrafiltration membranes may be subjected to a reverse flow, known as backwashing, which assists in removing the accumulated particulates from the membrane. Reverse osmosis and/or nanofiltration membranes may be cleaned by forward flushing. 
     Alternatively, or in addition, cleaning agents may be introduced to assist in cleaning the membranes. The most common chemical used for disinfection of microfiltration and/or ultrafiltration membranes is chlorine, which acts as an oxidant. The cleaning flow is used to clean primary stage membranes. However, as oxidants are detrimental to some membrane types, including nanofiltration and/or reverse osmosis membranes, it is crucial that the cleaning chemicals are kept separate from those membranes during the cleaning/disinfection process. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention there is provided a support assembly for a filtration system, the support assembly comprising: 
     support portions for engaging upper and lower portions of a filtration vessel, the support portions adapted to be coupled together to secure the vessel between the portions. 
     The support assembly of the present invention assists in simplifying the arrangement and installation of the filtration vessels and reduces or eliminates the requirement for heavy, intricate and complex steel framework and interconnecting pipe work that may otherwise be required. 
     The support assembly may be modular. For example, the support portions may comprise a first portion adapted to engage a lower portion of the filtration vessel and a second portion adapted to engage an upper portion of the filtration vessel. Each mounting portion may be adapted to engage a single filtration vessel. Alternatively, each mounting portion may be adapted to engage a plurality of filtration vessels. 
     The assembly may further comprise a locking member adapted to secure the mounting portion together. In particular embodiments, the support portions may be adapted to be coupled together by a cap screw, pin, bolt or the like. 
     The support portions may be adapted for coupling together. For example, at least one of the support portions may comprise a male connection member adapted to engage a female connector portion on the other mounting portion. 
     The assembly may further comprise a locking plate adapted to engage a portion of at least two upper support portions to secure said support portions together. The locking plate may be constructed from any suitable material and, in particular embodiments, the locking plate may comprise a metallic material. Alternatively, the locking plate may comprise a plastic material. Beneficially, the use of a plastic material facilitates use of the locking plate in harsh, marine environments and may assist in reducing the mass of the assembly. 
     The vessels may be adapted to be coupled together in an array. Beneficially, the provision of a modular filtration system according to embodiments of the present invention facilitates the construction of a vessel array of any number and arrangement. For example, the vessels may be coupled together in a three-by-three array, three-by-four array, four-by-four array or any other suitable arrangement. 
     The support portions may be constructed from any suitable material. In preferred embodiments, the support portions may be constructed from a plastic material. 
     The support portions may be of any suitable size and colour. For example, the support portions may be coloured to designate, for example, the type of filtration vessel supported thereon; the size of filtration element or other selected parameter. 
     The assembly may be configured to permit one or more of the vessels to be removed from the assembly. Beneficially, this may permit removal of a selected vessel for replacement or repair without having to disassemble the assembly. 
     According to another aspect of the present invention there is provided a securement system for a filtration vessel adapted to receive at least one internal component, the securement system comprising: 
     a clamp member coupled to the vessel, the clamp member adapted to exert a compressive force on the vessel component to facilitate securing the component in the vessel. 
     The securement system of the present invention facilitates accurate location and securement of the components of the vessel, thereby assisting in minimising wear that may otherwise result in leakage. For example, the clamp member may be adapted to be secured to the vessel in order to apply a compressive force to the vessel components, including for example, at least one of a filtration element, thrust ring, vessel end plate, feed inlet component or any other vessel component. 
     The clamp member may comprise an external threaded surface for engaging an interior threaded surface of the vessel. 
     The clamp member may comprise an interior surface configuration adapted to facilitate coupling of the clamp member to the vessel. Any suitable configuration may be used to facilitate location of the clamp member and, in particular embodiments, the interior surface may be castellated. The clamp member may be of any suitable form. For example, where the vessel is substantially circular, the clamp member may be substantially circular. 
     The clamp member may be hollow. In particular embodiments, the clamp member may comprise an annular ring or the like. 
     The clamp member may be adapted to engage a tool for facilitating turning of the clamp member. For example, the tool may be configured to engage the castellations of the clamp member to facilitate rotation of the clamp member. 
     According to another aspect of the present invention there is provided a filtration system having at least two vessels adapted to be coupled together, each vessel comprising: 
     a housing adapted to receive a filtration element for filtering a fluid feed; 
     an outlet port for directing concentrate produced by the filtration element from the vessel; 
     a chamber adapted to receive permeate produced by the filtration element of the vessel and the filtration element of at least one other vessel; and 
     an outlet port for directing permeate received in the chamber from the vessel. 
     According to another aspect of the present invention there is provided a vessel for use in a filtration system having at least two vessels, the vessel comprising: 
     a housing adapted to receive a filtration element for filtering a fluid feed; 
     an outlet port for directing concentrate produced by the filtration element from the vessel; 
     a chamber adapted to receive permeate produced by the filtration element of the vessel and the filtration element of at least one other vessel; and 
     an outlet port for directing permeate received in the chamber from the vessel. 
     The vessels may be adapted to be directly coupled together. For example, at least one of vessel ports may be directly coupled to a port of another vessel. 
     A filtration system is provided by an assembly which is relatively compact and which is capable of occupying a small footprint. This is particularly beneficial where space is limited such as on an oil platform, a vessel or the like. Where previously a permeate pipe or hose connection would be required from each vessel, this may no longer be required, thereby reducing the number of components for transport and assembly and assisting in reducing the volume/mass of the system. Furthermore, the provision of a permeate header to connect each vessel is no longer required such that the vessels may be stacked closer together and the end clearance distances for access to the vessels can be reduced, further reducing the footprint of the system. 
     The, or each, vessel may further comprise a chamber adapted to receive concentrate produced by the filtration element of the vessel and the filtration element of at least one other vessel. Thus, concentrate flow from each vessel can be integrated into a single concentrate outlet or directed to the filtration element of at least one other vessel as required. 
     The, or each, vessel may further comprise a conduit for directing permeate from the vessel to the chamber. The conduit is adapted to isolate the permeate produced by the filtration element from concentrate produced by the filtration element. 
     The, or each, vessel may further comprise a sampling port adapted to facilitate permeate testing. The sampling port may be adapted to facilitate testing of permeate from a single vessel. Alternatively, the sampling port may be adapted to facilitate testing of permeate from the at least two vessels, for example, permeate received in the permeate chamber. In particular embodiments, the sampling port comprises a valve or the like. The valve may comprise a valve member or quill which is adapted to move relative to the vessel to permit testing of the permeate. In particular embodiments, the quill may be adapted to enter the conduit to facilitate testing of permeate from a single vessel. The quill may also be adapted to enter the chamber to permit testing of permeate in the chamber. 
     The vessels may be coupled together in any suitable configuration. For example, the vessels may be coupled together in a parallel arrangement, series arrangement or a combination of parallel and series arrangements. The vessel may comprise at least one connection port for coupling the vessel to at least one other vessel. In particular embodiments, the vessels may be directly connected together via the connection ports. Advantageously, this permits interconnection between the vessels in a parallel arrangement without the requirement for additional piping or hoses. 
     The ports may be provided at any suitable location on the vessel. In particular embodiments, the permeate outlet port may be located at the side of the vessel. The vessel arrangement provides for simplified construction and operation of the filtration system. 
     The, or each, vessel may comprise a plurality of filtration elements. The filtration elements may be of any suitable size or shape. In particular embodiments, the filtration elements may be of circular cross-sectional shape. 
     The filtration elements may be of any suitable form and, in particular embodiments, the elements may comprise filtration membranes. For example, at least one of the filtration elements may comprise an eight inch (203.2 mm) filtration membrane. Alternatively, or in addition, at least one of the filtration elements may comprise a sixteen inch (406.4 mm) membrane. Alternatively, or in addition, at least one of the filtration elements may comprise an eighteen inch (457.2 mm) membrane. 
     One or more of the filtration elements may comprise at least one of a reverse osmosis membrane and a nanofiltration membrane. At least one of the filtration elements may comprise at least one of a microfiltration membrane and an ultrafiltration membrane. 
     The vessel may be adapted to house at least two filtration elements, the filtration elements comprising at least a primary stage filtration element and a secondary stage filtration element. In particular embodiments, a plurality of filtration elements are provided in each of the primary and secondary stages. 
     The vessel may comprise or define a connection device for location between the at least one primary stage filtration element and the at least one secondary stage filtration element. The device may be coupled to at least one of the filtration elements, thereby facilitating interconnection between the filtration elements. Alternatively, or in addition, the device may form a spacer between the filtration elements. The device may define a chamber or void between the filtration elements, the device permitting fluid access to the connection ports. 
     The system may be adapted to split the fluid feed between the at least two filtration elements. Thus, the system may be adapted to provide a direct fluid feed to the at least two filtration elements. The system may be adapted to split the fluid feed in substantially opposing directions along the vessel. Accordingly, permeate output from a primary stage element in one vessel may be directed to either of the primary stage or second stage element in another vessel. Beneficially, this facilitates improved performance across the system as flow may be directed preferentially to the filtration elements having spare capacity. This may also facilitate cleaning or backwashing of the membrane of vessels using flow from at least one other vessel. 
     The vessel may further comprise a flow control device for directing fluid flow between the primary stage filtration element and the secondary stage filtration element. The flow control device may comprise any suitable device and, in particular embodiments, the flow control device may comprise a barrier member, valve or the like. 
     The system may be configured to permit testing of one or more selected filtration elements within a particular vessel and, in particular embodiments, the sampling port may be adapted to facilitate testing of permeate from one or more selected filtration element within a particular vessel. 
     The system may further comprise a securement system for securing the components within the, or each, vessel. The securement system may comprise a clamping member coupled to the vessel, the clamping member adapted to apply a compressive force to the vessel components. 
     The system may utilise flow pulsation to assist in removing particulate matter from at least one of the filtration elements. The flow pulsation may be achieved by any suitable means. For example, the system may comprise a rotary flow pulsation device adapted for location in a system fluid conduit, the device adapted to rotate in response to fluid flow over the device to produces fluid pulses. In particular embodiments, the device may be adapted for location in a backwash fluid conduit. 
     Alternatively, or in addition, the system may comprise an ultrasonic pulsation device adapted to produce ultrasonic excitation of particulate matter to assist in removing particulates from at least one of the filtration elements. 
     In a further alternative or additional embodiment, the system may comprise a valve adapted to produce flow pulses. For example, the valve may be adapted for repeated opening and closing to produce pulses in the fluid flow travelling through the valve. 
     The system may further comprise a support assembly for securing the filtration vessels together. The support assembly may comprise support portions for engaging upper and lower portions of a filtration vessel, the support portions adapted to be coupled together to secure the vessel between the support portions. 
     According to another aspect of the present invention there is provided a flow control device for location in a filtration system vessel, the device comprising: 
     a first chamber adapted to receive fluid from at least one of a first filtration element and a fluid inlet; and 
     a second chamber adapted to receive fluid from the first filtration element, the device arranged to direct fluid from the second chamber to at least one of a fluid outlet and a second filtration element. 
     In particular embodiments, the device may be arranged such that the first chamber is located adjacent to the first filtration element and the second chamber is located downstream from the first filtration element. In alternative embodiments, the device may be arranged such that the first chamber is located downstream from the filtration element and the second chamber is located adjacent to the first filtration element. 
     The first chamber may be adapted to receive permeate from the first filtration element. Alternatively, the first chamber may be adapted to receive concentrate from the first filtration element. 
     The flow control device may comprise any suitable device and, in particular embodiments, the flow control device may comprise a barrier member, valve or the like. 
     The flow control device may be constructed from any suitable material. For example, the flow control device may be constructed from a plastic, metal, ceramic, glass or other suitable material. In particular embodiments, the flow control device may be constructed from a plastic material and, in particular, a plastic which is resistant to cleaning agents, e.g. chlorine, and/or seawater/brine used in filtration systems. 
     The flow control device may be manufactured by any suitable process. For example, but not exclusively, the device may be constructed by an injection moulding process. The arrangement of the flow control device may be selected according to a selected system parameter, including for example, the degree of system fouling. 
     The flow control device may be constructed from a single component. Beneficially, the provision of a single piece device facilitates use of a low cost device. Alternatively, the device may be constructed from a plurality of components adapted to be coupled together. In particular embodiments, the device may be constructed from two parts. 
     Other aspects of the present invention relate to the use of a flow pulsation device for use in a filtration system. 
     Flow pulsation may advantageously be used to assist in the loosening of material in a filtration element, thereby mitigating or overcome blocking of the filtration element. Flow pulsation may also be used to assist in loosening material during cleaning of the membrane or backwash flow. 
     Flow pulsation may be achieved by any suitable arrangement, including for example, mechanical stimulation, ultrasonic stimulation or the like. 
     For example, in one embodiment, the flow pulsation device may, for example, comprise a rotor adapted for location in a backwash flow conduit. The rotor may be secured within the conduit by any suitable arrangement. In use, the rotor is adapted to rotate in response to backwash fluid flow over the rotor. 
     The device may further comprise at least one barrier member located in the fluid flow path. The barrier member may comprise at least one orifice for permitting fluid flow through the barrier member. In use, the orifice and rotor may be adapted to produce pulses in the fluid flow which assist in removing particulate matter from the filtration element. 
     In an alternative embodiment, flow pulsation may be achieved by rapid oscillation of a control valve. 
     In a further alternative embodiment, flow pulsation may be achieved by an ultrasonic transducer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a perspective view of an assembled filtration system according to an embodiment of the present invention; 
         FIG. 2  is a longitudinal sectional view of a filtration vessel of the filtration system of  FIG. 1 ; 
         FIG. 3  is an enlarged diagrammatic view of an end section of the filtration vessel of  FIG. 2 ; 
         FIG. 4  is a perspective view of a bank of filtration vessels according to another embodiment of the present invention; 
         FIG. 5  is a side view of the bank of filtration vessels of  FIG. 4 ; 
         FIG. 6  is an enlarged diagrammatic view of an end section of the bank of filtration vessels of  FIGS. 4 and 5 ; 
         FIG. 7  is an enlarged longitudinal sectional view of part of the filtration vessel of  FIG. 2  during normal operation; 
         FIG. 8  is a flow diagram of the filtration system during normal operation; 
         FIG. 9  is an enlarged longitudinal sectional view of part of the filtration vessel during a backwash operation; 
         FIG. 10  is a flow diagram of the filtration system during a backwash operation; 
         FIG. 11  is an enlarged longitudinal sectional view of part of the filtration vessel during a cleaning operation; 
         FIG. 12  is a flow diagram of the filtration system during primary stage membrane cleaning; 
         FIG. 13  is a flow diagram of the filtration system during secondary stage membrane cleaning; 
         FIG. 14  is a perspective view of a flow control device according to an embodiment of the present invention; 
         FIG. 15  is a perspective cross-sectional view of an upstream portion of the flow control device of  FIG. 14 ; 
         FIG. 16  is a perspective cross-sectional view of a downstream portion of the flow control device of  FIGS. 14 and 15 ; 
         FIG. 17  is an enlarged longitudinal sectional view of part of the filtration vessel of  FIG. 2  with the flow control device of  FIGS. 14 to 16  during normal operation; 
         FIG. 18  is a flow diagram of the filtration system with the flow control device of  FIGS. 14 to 16  during normal operation; 
         FIG. 19  is an enlarged longitudinal sectional view of part of the filtration vessel of  FIG. 2  with the flow control device of  FIGS. 14 to 16  during a backwash operation; 
         FIG. 20  is a flow diagram of the filtration system with the flow control device of  FIGS. 14 to 16  during a backwash operation; 
         FIG. 21  is an enlarged longitudinal sectional view of part of the filtration vessel of  FIG. 2  with the flow control device of  FIGS. 14 to 16  during a cleaning operation; 
         FIG. 22  is a flow diagram of the filtration system with the flow control device of  FIGS. 14 to 16  during primary stage membrane cleaning; 
         FIG. 23  is a flow diagram of the filtration system with the flow control device of  FIGS. 14 to 16  during secondary stage membrane cleaning; 
         FIG. 24  is a perspective view of a filtration system according to another embodiment of the present invention; 
         FIG. 25  is a perspective view of a flow control device for use in the filtration system of  FIG. 24 ; 
         FIG. 26  is a partial longitudinal sectional view of the flow control device of  FIG. 25 ; 
         FIG. 27  is an enlarged longitudinal sectional view of part of the filtration vessel of  FIG. 2  with the flow control device of  FIGS. 25 and 26  during normal operation; 
         FIG. 28  is a flow diagram of the filtration system of  FIG. 24  with the flow control device of  FIGS. 25 and 26  during normal operation; 
         FIG. 29  is an enlarged longitudinal sectional view of part of the filtration vessel of  FIG. 2  with the flow control device of  FIGS. 25 and 26  during a forward flush operation; 
         FIG. 30  is a flow diagram of the filtration system of  FIG. 24  with the flow control device of  FIGS. 25 and 26  during a forward flush operation; 
         FIG. 31  is a longitudinal sectional view of part of the filtration vessel of  FIG. 2  with the flow control device of  FIGS. 25 and 26  during a primary membrane forward cleaning operation; 
         FIG. 32  is a flow diagram of the filtration system of  FIG. 24  with the flow control device of  FIGS. 25 and 26  during a primary membrane forward cleaning operation; 
         FIG. 33  is an enlarged longitudinal sectional view of part of the filtration vessel of  FIG. 2  with the flow control device of  FIGS. 25 and 26  during a primary membrane reverse cleaning operation; 
         FIG. 34  is a flow diagram of the filtration system of  FIG. 24  with the flow control device of  FIGS. 25 and 26  during a primary membrane reverse cleaning operation; 
         FIG. 35  is an enlarged longitudinal sectional view of part of the filtration vessel of  FIG. 2  during a secondary membrane forward cleaning operation; 
         FIG. 36  is a flow diagram of the filtration system of  FIG. 24  during a secondary membrane forward cleaning operation; 
         FIG. 37  is a perspective view of an assembled securement system for the filtration system according to an embodiment of the present invention; 
         FIG. 38  is an exploded perspective view of the securement system of  FIG. 37 ; 
         FIG. 39  is an enlarged longitudinal sectional view of the assembled securement system of  FIGS. 37 and 38 ; 
         FIG. 40  is a schematic diagram of a filtration system having a rotary pulsation device; 
         FIG. 41  is a diagrammatic view of the rotary pulsation device of  FIG. 40 ; 
         FIG. 42  is a schematic diagram of a filtration system having an ultrasonic pulsation device; 
         FIG. 43  is a schematic diagram of a filtration system having a valve operated pulsation device; 
         FIG. 44  is a perspective view of an assembled support assembly for a filtration system according to an embodiment of the present invention; 
         FIG. 45  is a perspective view of a pair of support portions of the support assembly of  FIG. 44 ; 
         FIG. 46  is a perspective view of a locking plate for use in the support assembly of  FIGS. 44 and 45 ; and 
         FIG. 47  is a perspective view of an alternative locking plate for use in the support assembly of  FIGS. 44 and 45 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In reference initially to  FIG. 1  of the drawings, there is shown a perspective view of a modular filtration system  10  according to an embodiment of the present invention. The system  10  comprises an array of filtration vessels  12  mounted on three mounting assemblies  14 . In the embodiment shown in  FIG. 1 , the vessels  12  are arranged in a three-by-three array, though it will be understood that any suitable arrangement may be used where appropriate. 
     Referring to  FIG. 2  of the drawings, there is shown a longitudinal sectional view of one of the filtration vessels  12  for use in the filtration system  10 . The vessel  12  has a first section  15  housing a number of primary stage filtration elements  16  in the form of microfiltration and/or ultrafiltration membranes. As shown in  FIG. 2 , the membranes  16  are arranged in series. The vessel  12  also has a second section  17  housing a plurality of secondary stage filtration elements  18  in the form of nanofiltration and/or reverse osmosis filtration membranes arranged in series. It will be understood that while the embodiment shown in  FIG. 2  shows a plurality of primary stage and secondary stage membranes  16 , 18 , each membrane stage may comprise a single membrane  16 ,  18  where appropriate. A centrally located connection device in the form of coupler  19  is located in the vessel  12  and the membranes  16 ,  18  are secured to the coupler  19 . 
     As shown in  FIGS. 2 and 3 , the vessel  12  is multi-ported, the vessel  12  having a side-mounted inlet port  20  for directing a fluid feed, such as seawater, through the filtration membranes  16 , 18 . It will be recognised that while the inlet port is shown side-mounted, the inlet port  20  may be located at any suitable location, including for example, end mounted (as shown for example in  FIGS. 4 ,  5  and  6 ). The vessel  12  further comprises a central conduit  22  for receiving permeate produced by the filtration membranes  16 ,  18 . 
     As shown most clearly in  FIG. 3 , which shows an enlarged diagrammatic view of an end section of the vessel  12 , concentrate, e.g. brine, from the final secondary stage membrane  18  is collected in a concentrate chamber  24  and is removed from the vessel  12  via one or more concentrate outlet port  26 . 
     The vessel  12  further comprises a permeate chamber  28  for receiving permeate from the membranes  18  and from the membranes of at least one other vessel  12 . An outlet port  30  directs permeate from the chamber  28 . The vessel  12  further comprises a permeate connector  31  providing a conduit from the central conduit  22  to the permeate chamber  28  while ensuring that the permeate is isolated from the concentrate in the system  10 . 
     Each vessel  12  further comprises a sampling valve  32  located at an end of the vessel  12 . The sampling valve  32  comprises a quill  34  which is adapted to enter the mouth of the permeate connector  31 , thereby facilitating sampling of the permeate output from the vessel  12 . The quill  34  is retractable to facilitate sampling of the permeate output from the permeate chamber  28 . 
     In reference now also to  FIGS. 4 ,  5  and  6 , the system  10  comprises four vessels  12  connected together. Any suitable arrangement may be used and, in the embodiment shown in  FIGS. 4 ,  5  and  6 , the four vessels  12  are directly coupled together in parallel. Specifically, each vessel  12  comprises one or more substantially centrally located connection port  36  adapted to couple the vessel  12  to at least one other vessel  12 , the connection ports  36  arranged for fluid communication with the coupler  19 . The connection ports  36  can be used to feed fluid output from the primary stage membranes  16  of one vessel  12  to the secondary stage membranes  18  of another vessel or vessels  12 . Alternatively, or in addition, the connection port  36  may be used to feed fluid output to the primary stage membrane  16  of another vessel  12  in order to facilitate backwashing of the respective primary stage membrane  16 . The connection port  36  is also used to permit cleaning agents to be introduced to assist in cleaning the primary stage  16  and/or secondary stage membranes  18 . 
     It will be recognised that the membranes may not foul at exactly the same rate with membranes subject to higher fouling having greater resistance to flow. In use, the connection ports  36  are adapted to permit preferential flow through the filtration system  10 , thereby allowing balancing of membrane flux, that is, the flow per unit area through the membranes, across the vessels  12 , even where some primary stage membranes  16  are offline for backwashing or cleaning. 
     The vessel  12  is adapted for use with multiple operating pressures, which could be up to 100 barg (10 MPa gauge pressure/10.1 MPa absolute pressure) or higher. 
     As shown most clearly in  FIGS. 5 and 6 , the permeate outlet ports  30  and the permeate chambers  28  of the vessels  12  are also interconnected, thereby creating a common permeate outlet/chamber. 
     The improved modular layout and arrangement of the filtration system  10  is simplified by utilising an integral permeate chamber  28 , this arrangement removing the requirement to have a permeate pipe or hose connection connecting each vessel  12 . In addition, the number of separate components in the system  10  is reduced such that system assembly time and, where required, disassembly time can be reduced. In addition, a separate permeate header connecting the permeate outlets  30  from each vessel  12  is no longer required, enabling the vessels  12  to be stacked closely together, resulting in a smaller overall footprint for the filtration system  10 . Furthermore, the end clearance for passage access can be reduced, in turn resulting in a more compact footprint for the filtration system  10 . 
     As shown in  FIG. 6 , the concentrate outlet ports  26  are also interconnected such that concentrate may be transferred to another vessel  12  or to a drain or dump (not shown) as required. 
     Thus, the inlet, connection and outlet ports are arranged to facilitate assembly and operation of the filtration system  10  and to assist in reducing the footprint, mass and complexity of the system  10 . 
     In reference now also to  FIG. 7  of the drawings, which shows an enlarged longitudinal sectional view of part of the filtration vessel  12 , the vessel further comprises a chamber  38  located between the primary stage membranes  16  and the secondary stage membranes  18 . The chamber  38  provides for fluid transfer between the membrane stages within the vessel  12  and between the vessels  12  via the connection ports  36 . For example, the chamber  38  permits the transfer of forward fluid flow from the operating primary stage membranes  16  to the downstream secondary stage membranes  18  within each vessel  12 , ensuring that a suitable feed to each stage is maintained during normal operation ( FIGS. 7 and 8 ), during backwashing operations ( FIGS. 9 and 10 ) or during cleaning operations ( FIGS. 11 ,  12  and  13 ). 
     Operation of the system  10  will now be described with reference to  FIGS. 7 to 13  of the drawings. In this arrangement, the primary stage membranes  16  comprise microfiltration and/or ultrafiltration membranes and are arranged to operate in dead-end mode, that is, all water entering the membrane exits as permeate product, with solids retained on the membrane surface. The primary membranes  16  are also of an in-to-out membrane type, that is, the membrane consists of hollow fibres, with water travelling through the lumen of the fibre and filtering through the fibre wall. The secondary stage membranes  18  comprise reverse osmosis membranes and/or nanofiltration membranes. The vessels  12  are directly connected via the connection ports  36 . 
       FIGS. 7 and 8  show the filtration system  10  during normal operation. In use, valve  40  (shown white in  FIG. 8  to represent “valve open”) is opened to permit fluid feed, in the form of seawater, to enter the primary stage membranes  16  of each vessel  12 . Particulates are retained within the membranes  16 , the primary stage membranes  16  acting as a pre-treatment for filtering particulate matter from the fluid feed. Produced permeate passes through the membranes  16  into the central collection conduit  22  and into the central chamber  38 . The permeate is then passed through the secondary stage membranes  18  for further treatment. As shown in  FIG. 7 , the vessel  12  further comprises a sealed cap  42  for preventing permeate travelling directly into the central permeate conduit  22  of the secondary stage membranes  18 . The secondary stage membranes  16  are more suitable for removing smaller particulates and are capable of reducing the concentration of ions in the fluid feed, for example, in order to reduce the concentration of salt ions in seawater. 
     On passing through the secondary stage membranes  18 , permeate is collected in the interconnected permeate chambers  28  ( FIG. 6 ) and a permeate outlet valve  44  ( FIG. 8 ) is opened to permit removal of the permeate from the filtration system  10 . Concentrate is collected in the concentrate chambers  26  ( FIG. 6 ) and a concentrate outlet valve  45  ( FIG. 8 ) is opened to permit removal of the concentrate to a drain, dump or the like (not shown). 
     A portion of the permeate may also be directed to one or more of the other vessels  12  via the connection ports  36 . The degree of transfer between the vessels  12  will depend on a number of factors, including the fouling state of the secondary stage membranes  18  and the capacity of the other vessels  12  in the system. This flow may be used, for example, in a backflow operation to assist in removing accumulated particulates from the primary stage membranes of another vessel  12  as will be described below with reference to  FIGS. 9 and 10 . 
     In this operation, the fluid feed to the vessel  12  to be backwashed is shut off by moving directional control valve  46 . Fluid flow is reversed such that backwash fluid is directed into the central chamber  38  via the connection port  36  of one or more of the operating vessels  12 . Backwash fluid from the connection port  36  comprises permeate from the primary stage membranes  16  of one or more other vessel  12  and a portion of the fluid provides a pre-filtered flow forwards through the secondary stage membranes  18  of the vessel  12  to maintain operation even during backwashing operations. 
     Another portion of the backwash fluid travels in the reverse direction through the primary stage membranes  16  to dislodge or otherwise assist in removing accumulated particulate matter from the primary membranes  16 . An outlet line/conduit  48  on the feed side of the primary membranes  16  is fitted with an orifice plate, control valve or other pressure-reducing device (not shown) in order to maintain a differential pressure across the primary membranes  16  and to ensure sufficient flow for the backwashing operation. Where backwashing is in operation, a backwash control valve  49  is open to provide direction of removed particulates to a drain, dump or the like (not shown). 
     Another portion of the backwash fluid may traverse the chamber  38  and travel into another vessel  12  via connection port  36  as required. 
     Cleaning operations will now be described with reference to  FIGS. 11 ,  12  and  13  of the drawings. In this operation, feed inlet valve  40 , concentrate outlet valve  45  and permeate outlet valve  44  are closed. A chemical supply valve  50  is opened to permit a cleaning agent into the system  10 . The cleaning agent is directed into the central chamber  38  via the connection port  36 . The cleaning agent travels in the reverse direction through the primary stage membranes  16  in order to clean the membranes  16 . 
     Another portion of the cleaning agent may traverse the central chamber  38  and pass to another vessel  12  to facilitate cleaning of the other vessel or vessels  12  as required. Depending on the degree of cleaning required and/or the type of chemical used, the remaining cleaning agent may be re-circulated to the cleaning system or directed to a drain or dump. 
     In order to further improve the performance of the filtration system  10 , the system  10  further comprises a flow control device adapted for location in the central chamber  38 . Different flow control devices may be selected for use in different operating conditions, including for example, the degree of membrane fouling. Flow control devices may be used in particular in medium or heavy fouling conditions as will be described. The flow control devices may be used with the filtration system  10  or alternatively the flow control devices may be used with other and/or existing filtration systems. 
     In reference initially to  FIG. 14  of the drawings, there is shown a perspective view of a flow control device in the form of a barrier plate  52 . The barrier plate  52  is adapted for location in the central chamber  38  of the filtration vessel  12 , thereby providing a discrete flow path between the primary stage membranes  16  and secondary stage membranes  18 . 
     As shown in  FIGS. 15 and 16 , which show cross-sectional views of an upstream portion ( FIG. 15 ) and a downstream portion ( FIG. 16 ) of the barrier plate  52 , and to  FIG. 17  which shows an enlarged longitudinal sectional view of the barrier plate  52  in situ, the barrier plate  52  is provided with a central annulus  54  which provides a fluid flow path between the connection ports  36  of the vessel  12 . The barrier plate  52  forms two chambers  56  and  58  within the plate  52 . 
     With reference to  FIG. 15 , the barrier plate  52  comprises a number of holes defining bores  60  for providing a fluid flow path between the annulus  54  and the primary stage membranes  16 . The bores  60  form the flow path from and to the vessel  12  via the connection ports  36 , facilitating passage of balancing feed flow, cross flow, cleaning flow through the barrier plate  52 . 
     As shown in  FIGS. 15 and 16 , the barrier plate  52  further comprises a number of holes defining bores  62  that extend through the barrier plate  52 . The bores  62  provide a flow path from the primary stage membranes  16  to the secondary stage membranes  18 , the bores  62  providing a longer flow path that will minimize or substantially eliminate the flow of cleaning agents to the downstream secondary stage membranes  18 . 
     The barrier plate  52  is manufactured in two portions, fastened together and incorporating integral seals. External seals  64  between the barrier plate  52  and the vessel  12  may be used depending on the fit, overall length of the plate  52  and the sealing requirements of the system  10 . The external connections on the barrier plate  52  are made oversize to allow for longitudinal dimensional variances of the vessel components and to allow for shimming, where required (e.g. in filtration systems not employing the securement system as described below in reference to  FIGS. 37 to 39 ). 
       FIGS. 17 and 18  show the filtration system  10  comprising the barrier plate  52  during normal operation. In this arrangement, the primary stage membranes  16  comprise microfiltration and/or ultrafiltration membranes and are arranged to operate in dead-end mode. The primary membranes  16  are also adapted for operation in an out-to-in mode that is, the membrane consists of hollow fibres, with water travelling through the fibre wall into the lumen. The secondary stage membranes  18  comprise reverse osmosis membranes and/or nanofiltration membranes. 
     Feed flow is directed into each of the vessels  12 , the feed passing through the primary stage membranes  16 , filtering into the lumen of the hollow fibres and into the upstream chamber  56 . The feed flow passes via through the bores  62  into the downstream chamber  58  and then into the secondary stage membranes  18  for further treatment. A portion of the flow from the upstream chamber  56  will pass to the other vessels  12  via the connection ports  36  to facilitate balanced production from the vessels  12  and/or to permit backwashing. 
       FIGS. 19 and 20  show the filtration system  10  having the barrier plate  52  during a backwash operation of the primary membrane  16 . The inlet to the vessel  12  to be backwashed is closed. A portion of the backwash feed from the connection port  36  enters the upstream chamber  56  of the barrier plate  52  and passes backwards through the primary stage membranes  16  to the drain, dump or the like (not shown). 
     Another portion of the backwash fluid continues to flow forwards to the downstream chamber  58  and then into the secondary stage membranes  18  for further treatment. The overall permeate output from the system  10  is thus shared across the vessels  12 . 
     Another portion of the backwash flow is directed around the annulus  54  to one or more of the other vessels via the connection ports  36 . 
       FIGS. 21 ,  22  and  23  show the filtration system  10  comprising the barrier plate  52  during cleaning operations. During disinfection with an oxidant, cleaning is conducted on all primary stage membranes  16  within the vessels  12  simultaneously. In use, the cleaning agent inlet valve  50  is opened to permit the cleaning agent to enter the barrier plate  52  via the connection port  36 . A portion of the chemical agent is then directed to the upstream chamber  56  where it passes back through the primary stage membranes  16  and re-circulates to the cleaning system via the cleaning return line or to a drain or dump. 
     The remaining cleaning flow traverses the barrier plate  52  and feeds the other vessels  12 , thus avoiding any unwanted direct contact with the secondary stage membranes  18 . The plate  52  provides a longer passage to the secondary stage membranes  18 , the secondary stage membrane flow being held stagnant by the closure of the permeate and concentrate outlet valves. Thus, the low pressure differential across the primary stage membranes  16  prevents forward flow of cleaning agent through the secondary membranes  18 . In addition, performing a low pressure forward flush before production commences will assist in preventing any slippage of chemical, resulting from eddies, turbulence or leakage around the plate  52 . 
     As shown in  FIG. 23 , when it is desired to clean the secondary stage membranes  18 , e.g. by an acidic or alkaline solution, the concentrate and permeate outlet valves  45 ,  44  are opened to permit flow of the cleaning agent through the secondary stage membranes  18 . 
     In reference now to  FIG. 24  of the drawings, there is shown a filtration system according to another embodiment of the present invention. In this embodiment, the primary stage membranes  16  comprise ultrafiltration membranes and are adapted for operation in cross flow mode, that is where water passes both across and through the membrane allowing filtration and removal of the retained particles to the drain. In addition, in this embodiment, the vessels  12  are connected by external piping  65 . 
     In this embodiment, an alternative flow control device in the form of a barrier plate  66  is provided. As shown in  FIGS. 25 and 26 , which show perspective and cross-sectional views respectively of the barrier plate  66  and  FIG. 27  which shows a cross-sectional view of the barrier plate  66  in situ, the barrier plate  66  is arranged to separate the primary membrane flow from the secondary membrane feed flow. 
     On the secondary stage membrane feed side, the plate is also provided with a tap  67  to allow free flow between the vessels  12  via the connection port  36 , thereby permitting the feed to each set of secondary stage membranes  18  within the bank of vessels to be balanced. 
     Normal operation of the system will now be described with reference to  FIGS. 24 ,  27  and  28 . Fluid feed is passed to the vessels  12  via the feed inlet isolation valve (i). The flow rate and pressure is monitored using the flow meter  68  and pressure sensor  70 . The manually actuated primary stage membrane cleaning feed valve (ii) is closed. The fluid feed passes through the primary stage membranes  16  filtering into the central collection conduit  22  and is directed through the barrier plate  66  to the secondary stage membranes  18  for further treatment. A dead-end portion of the flow through the primary stage membranes  16  is collected in a collection chamber  72 . The connection port  36  is sealed by the actuated flush, valve (x) and the closed cleaning valve (ix). 
     A portion of the flow from the primary stage membranes  16  will pass to, or be received from, one or more other vessel  12  via the connection port  36 . The port  36  acts as a balance pipe where the membrane flux varies across the vessels  12 . 
     During normal operation it is expected that there will be a build up of particulates within the primary stage membranes  16 . Thus, in order to facilitate removal of particulates, and with reference to  FIGS. 24 ,  29  and  30 , the actuated flush valve (x) will open. The vessel selection valve (iii) will select each vessel  12  in turn. In parallel to the normal operation described above, flow will pass via the collection chamber  72  and out of the connecting connection port  36  to the drain. Operation of the system may be controlled to facilitate flushing cycles at pre-determined times and for pre-determined duration. Alternatively, or in addition, the system can be manually flushed as necessary. During this operation, flow from the non-flushing primary stage membranes  16  will be received from other pressure vessels  12  via the connection port  36 . 
     However, some fouling conditions within the primary stage membranes  16  require a more aggressive clean. As shown with reference to  FIGS. 24 ,  31  and  32 , for example, cleaning is carried out with the vessels off-line, cleaning enacted from a separate cleaning feed. Following the flushing of the vessels  12  with potable water, chemicals are fed to the primary stage membranes  16  via the feed inlet ( FIG. 32 ). With the feed inlet isolation valve (i) closed and the manually actuated primary membrane cleaning feed valve (ii) open, chemicals are pumped via the primary stage membranes  16  into the collection chamber  72  and out of the connecting connection port  36 . With the actuated flush valve (x) closed and the valve (ix) open, the chemicals are returned back to the cleaning feed for recycling. During this cycle, the vessel selection valve (iii) will select each vessel  12  in turn resulting in periods of high velocity flow and periods of soaking for each of the vessels  12 . 
     During cleaning of the primary stage membranes  16 , the concentrate outlet control valve (v), concentrate outlet return valve (iv), permeate dump/retain valve (viii) and permeate CIP return valve (vii) are all closed so as to prevent flow into the secondary stage membranes  18 . Depending on the type of chemical used, the valve (vi) connection can be open or closed. This allows chemical passage through the hollow fibres to be selected as required. 
     As shown in  FIGS. 33 and 34 , forward flow can also be sent via connection port  36 , and valve (vi) across the primary stage membranes  16  if required. 
     In addition, and in reference to  FIGS. 24 ,  35  and  36 , to clean the secondary stage membranes  18 , the valve (v), valve (viii), valve (i) and the valve (ii) are closed. The valve (iv), valve (vii) and valve (vi) are open. Flow from the cleaning feed is passed via the connection port  36  to the inlet chamber  58  for the secondary stage membranes  18 . The chemical passes through and across the secondary stage membranes  18  and is returned back to the cleaning feed for recycling. 
     Accordingly, the provision of flow control devices such as the barrier plates  52  and  66  provide for system operation in relatively high fouling applications, the barrier plates  52 ,  66  facilitating distinct flow paths for feed flows, cleaning and backwash flows while reducing the risks of damage to the respective membranes. 
     In reference now to  FIGS. 37 to 39 , there is shown a securement system  74  for use in a filtration system vessel  12 , the vessel  12  adapted to contain a number of components including for example, at least one of a filtration membrane, feed inlet  76 , thrust ring  78 , seal plate  80 , vessel end plate  82  or any other vessel component. 
     The securement system  74  comprises a clamp member in the form of a metallic nut  84  with an external coarse thread  86 . The internal diameter of the external thread  86  is less than or equal to the vessel internal diameter and, on location in the vessel  12 , the thread  86  is adapted to engage a corresponding internal thread portion  88  on the vessel  12 . The nut  84  is annular and has internal castellations  90  adapted to permit turning the nut  84  to engage the threaded portions  86 ,  88 . For example, a tool (not shown) having two or more lugs may be adapted to engage with the castellations  90  to turn the nut  84 . The nut  84  may also be locked into place by a grub screw, locking wire, locking pin or the like (not shown). 
     In use, the nut  84  is engaged with the vessel  12  to apply a compressive force to the vessel components, thereby facilitating accurate location and securement of the vessel components to assist in minimising wear that may otherwise result in leakage. The provision of a securement system  74  also obviates the requirement for large tolerances in component design and the use of shimming as has previously been used. 
     The securement system  74  may be used with the filtration systems described above and/or retrofit to existing filtration systems as required. 
       FIGS. 40 to 43  show a number of arrangements for providing flow pulsation in order provide a source of flow variation and attrition to assist micro stimulation of primary stage membranes during backwashing operations. Pulsation acts to loosen material in the membranes and assists with cleaning and/or backwashing operations. During normal forward operation, the backwash line is isolated and no pulsing is encountered. 
       FIG. 40  shows a schematic diagram of an arrangement for flow pulsation using a flow driven rotary pulsation device  92 . An example of a pulsation device  92  is shown in  FIG. 41 , the device  92  comprising a rotor  94  mounted on a shaft  95  which is located in the backwash outlet line, the size, number and angle of the rotor blades  96  being determined by the severity and frequency of the pulse required. The rotor  94  is located between two mounting plates  98 , or stators, each plate  98  comprising one or more orifice  100 . In use, the plates  98  act as fixed orifice plates, the blades  96  adapted to selectively block flow through the orifices  100  to create a fluid flow pulse. 
       FIG. 42  shows a further alternative arrangement for flow pulsation. In this embodiment, flow pulsation may be achieved by an ultrasonic transducer  102 . The primary stage filtration membranes  16  are subjected to ultrasonic pulses by providing a source of ultrasonic vibration adjacent to or onto the membrane  16 , the transducer  102  activated during backwashing to loosen material accumulated on the membrane  16 . 
       FIG. 43  shows an alternative arrangement for flow pulsation. In this embodiment, flow pulsation may be achieved by rapid oscillation of a control valve  104 . In the embodiment shown in the Figure, pulsation is provided by a rapid oscillation of the backwash control valve  104  or alternatively by a valve provided specifically for this purpose. In use, the valve oscillation is achieved by rapidly fluctuating the valve  104  between two positions for the duration of the backwash or for set intervals during the backwash. An exemplary sequence of operation for the valve  104  is described below: 
     1. Backwash is initiated. 
     2. The backwash control valve opens and controls the flow to the backwash set point. 
     3. At this stage the backwash valve modulates between two positions to create a pulse in the system that assists with cleaning of the primary membranes. 
     4. The backwash valve can be modulated to create the pulse for the entire duration of the backwash or for intermittent intervals. 
     5. When complete the backwash valve is closed and the vessel returned to service. 
     In reference now to  FIGS. 1 and 44  to  47  of the drawings, there is shown a vessel support assembly  14  (three assemblies  14  are shown in  FIG. 1 ) for use in supporting the filtration system  10 . The support assembly  14  is adapted to improve and simplify the arrangement and installation of the membrane vessels  12  without the requirement for an intricate steel framework and complex interconnecting pipe work as is typically required. 
     As shown in  FIGS. 1 and 45 , the assembly  14  comprises two interconnecting mounting parts  106 ,  108  which are clamped together around the vessel  12 . The mounting parts are constructed from plastic material, assisting in reducing the mass of the system, though it will understood that any suitable material may be used as envisaged by the person skilled in the art. A plurality of mounted parts  106 ,  108  may be provided along the length of the vessel  12 . 
     Each part  106 ,  108  comprises inter-engaging male projections  110  and female portions  112  for assisting in stacking the mounting parts together to facilitate assembly of an array of filtration vessels (as shown in  FIG. 1 ). Alternatively, the parts  106 ,  108  can be bonded directly to, or formed integrally with, the vessel  12 . The parts  106 ,  108  are secured together by cap screws  114  such that the vessels  12  can be stacked in a self supporting structure, the provision of the support assembly  14  substantially eliminating the need for supporting steelwork. 
     As shown in  FIGS. 44 ,  46  and  47 , the top mounting parks  106  are secured together by a locking plate  116 . 
       FIG. 46  shows a first embodiment of the locking plate  116 , the plate  116  consisting of a strip of material, typically metal, having holes  118  adapted for location over the male projections  110  and a slot  120  adapted for location over the side portions  122  of the mounting parts  106 . The locking plate  116  of  FIG. 46  is dimensioned such that two stacks can be secured together. In an alternative embodiment, as shown in  FIG. 47 , a locking plate  120  may comprise a plurality of holes  118  and slots  120  and the plate  120  is dimensioned in order to secure a number of stacks together, for example, as shown in  FIGS. 1 and 44 . 
     It should be understood that the embodiments described are merely exemplary of the present invention and that various modifications may be made without departing from the scope of the invention. 
     For example, it will be understood that the filtration systems described above may be provided as a kit of parts and the features and components described above may be used in any suitable combination as required by the operational requirements of the system. 
     In some embodiments, the assembly can be configured to permit one or more vessel to be removed from the assembly, this permitting removal of a selected vessel for replacement or repair without having to interfere with or disassemble the assembly. In one arrangement, the locking plate is removed and the mounting parts coupled to the vessel to be removed are separated, for example, by lifting or jacking the upper mounting part, thereby permitting the vessel to be removed. In an alternative arrangement, the coupling between the mounting parts and the vessel may be configured to permit the vessel to be unsecured from the mounting parts, for example by a threaded connection, bayonet-type fitting or the like, thereby permitting removal of the vessel.