Abstract:
Spacers for filter modules which have the advantages of open-channel technology and which at the same time allow high packing densities, similar to those achieved with conventional spiral wound-type modules, are disclosed wherein the spacer is disposed between two layers of a filter material and comprises a sheet material having a gridlike structure, and having upper and lower surfaces defining an upper and lower bearing face for the layers of filter material, the sheet material consisting of a large number of webs interconnected at junction points, of which webs a first portion is disposed parallel to a first preferred direction and a second portion is disposed parallel to a second preferred direction intersecting the first preferred direction, and at least some of the webs have first web regions, which extend to the upper and/or lower bearing face(s), and at least a further portion of the webs has second web regions which are spaced from the upper and lower bearing faces, the second web regions extending over substantially the entire length of those webs.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of international application number PCT/EP2005/003482, filed on Apr. 2, 2005, that claims the benefit of German patent application number 10 2004 017 796.1, filed on Apr. 5, 2004, both of which are incorporated herein by reference in their entireties. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The invention relates to a spacer for use in filter modules comprising two or more layers of a filter material, with a spacer layer being disposed between two successive layers of filter material.  
         [0003]     Filter modules of this type are used, in the form of spiral wound-type modules or stacked modules, for a wide range of filtration tasks, for example for the treatment of industrial waste water, the treatment of industrial process water, the treatment of leachate from landfills or for desalination of seawater.  
         [0004]     Hitherto, dimensionally stable plastic disks with a multiplicity of punctiform elevations or webs, on which filter cushions come to bear, on their surface have been used as spacers in stacked modules. A volume is then available between the surface of the disks and a filter cushion for the flow over the filter material. The disks have apertures, so that the medium flowing over them can flow over a plurality of filter cushions in series. These stacked modules operate on the basis of the principle of open-passage technology, i.e. the medium supplied can flow onto substantially the entire surface area of the filter material, and there are no or only minimal flow obstacles in the direction of flow. The open-passage technology means that stacked modules are not susceptible to fouling, but they do have a relatively low packing density, with the result that the module costs based on the filter area available are higher than in the case of spiral wound-type modules, for example.  
         [0005]     Unlike stacked modules, spiral wound-type modules have hitherto been constructed in such a way that the spacer is constructed as a flexible grid or mesh structure. The spacers are formed in such a manner that webs which are in contact with the filter material form obstacles in the direction of flow, at which obstacles spaces where the through-flow is reduced and deposits accumulate are formed. The deposits of constituents of the medium that form are referred to as fouling. Furthermore, in conventional modules the webs form barriers which restrict the extent to which the modules can be cleaned, since sediment removed during cleaning cannot be discharged from the module on account of the obstacles. Furthermore, the surface area of the filter material is not fully utilized, since no filtration takes place at the bearing locations. On the other hand, spiral wound-type modules have a relatively high packing density and are less expensive than stacked modules, based on the filter area available.  
         [0006]     Spacers for spiral wound-type modules are described, for example, in DE 100 51 168 A1.  
       BRIEF SUMMARY OF THE INVENTION  
       [0007]     It is an object of the present invention to propose spacers for filter modules which have the advantages of open-passage technology and at the same time allow high packing densities, similar to those achieved with conventional spiral wound-type modules. According to the invention, this object is achieved by a spacer as described in claim  1 .  
         [0008]     To avoid fouling at the spacer, it is crucial that spaces through which the flow is reduced and in which deposits can accumulate be avoided as far as possible. As seen in the direction of flow of the medium being filtered, the spacer layer should substantially not have any points of contact with the surface of the filter material, so that the tendency to fouling is minimized. This is made possible by the structure of the spacers in accordance with the invention. The spacers according to the invention can be used for the production of both stacked and spiral wound-type modules.  
         [0009]     The advantages achieved according to the invention in detail are as follows: 
        the substantial to complete absence of dead zones minimizes the susceptibility to fouling;     the unimpeded flow through the feed passage improves the cleanability of the filter module, since it is possible to discharge sediment;     it is possible to treat water carrying relatively high levels of solids which it has not hitherto been possible to treat using spiral wound-type modules;     it is possible to reduce pressure losses by using optimized incoming flow conditions;     the promotion of turbulence makes it possible to reduce the concentration polarization;     it is possible to configure filter modules with an increased packing density compared to standard stacked-plate modules.        
 
       DETAILED DESCRIPTION OF THE INVENTION  
       [0016]     It is preferable for the web regions which are responsible for supporting the filter material on the spacer to be configured in the form of straight fins. In this case, it is generally possible to provide for the fins to extend over the entire length or the entire extent of the filter material, in particular the membrane, in particular if the webs are disposed substantially parallel to the direction of flow of the fluid being filtered.  
         [0017]     The fins may be provided on the same web regions on the upper and lower sides of the spacer layer, so as to form a multiplicity of parallel flow passages.  
         [0018]     One alternative consists in configuring the web regions which bear against the surface of the filter material in the form of punctiform or substantially punctiform regions, i.e. with a small area compared to the extent of the grid or mesh structure.  
         [0019]     By way of example, it is possible to provide for the punctiform supporting regions of the webs to be formed at junction points of the webs.  
         [0020]     All other regions of the grid structure then do not lead to contact with the surface regions of the filter materials and allow the fluid to flow through substantially unimpeded. This minimizes volumes with reduced flow through them as far as possible.  
         [0021]     In a further alternative, the filter material layers are supported on the upper side of the spacer layer at one web region and on the lower side of the spacer layer at another web region. This allows flow onto the spacer layer even with web regions that are continuous in form, with the direction of flow forming an acute angle with the preferred directions.  
         [0022]     In a further preferred embodiment, substantially all the webs are formed parallel to the preferred directions if they comprise web regions which serve to bear against the surfaces of the filter materials.  
         [0023]     One of the preferred directions is preferably oriented substantially parallel to the direction of flow of the fluid being filtered.  
         [0024]     Depending on the particular application, a more or less turbulent flow may be desired in the filter module. By way of example, turbulence is in some cases undesirable in applications in the food industry in which the concentrate represents the product, in order thereby to maintain the quality of the product.  
         [0025]     On the other hand, in waste water applications, it is often desirable for the flow over the membrane to be as turbulent as possible, in order to further reduce the risk of fouling and scaling.  
         [0026]     Webs or web regions which do not bear against the surface of the filter material and are kept at a distance therefrom are in certain applications preferably noncircular in cross section, i.e. in particular of an oblate shape, so that they form a minimal resistance to the incoming flow of the fluid.  
         [0027]     For other applications, these or other web regions may preferably be disposed and/or formed in such a way that they produce regions of turbulence, thereby disrupting laminar flows at the membrane surface, with the result that fouling on the surface of the filter material can be avoided and concentration polarization at the surface of the filter material can also be broken up or avoided.  
         [0028]     Concentration polarization is the regional increase in the concentration of substances in the region of the membrane surface, caused by the solvent being transported through the membrane.  
         [0029]     Overall, the webs are preferably connected to one another and configured in such a way that they form flow channels whose cross section substantially approaches the shape of rectangles. The bearing surface of the web regions which bear against the surfaces of the filter materials will be as small as possible, in order to cover the minimum possible amounts of the filter material surface area available.  
         [0030]     However, the bearing surface as a whole must not be too small, to avoid damage to the filter material surface, which could otherwise be caused by loads resulting from pressure fluctuations during the filtration operation. A cross section through the flow passages which is as far as possible rectangular ensures that the flow velocity is substantially uniform, as seen over the cross section of the passages, so that as much as possible of the available filter material surface area can be utilized uniformly and volumes with a reduced flow through them are avoided. 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0031]     These and further advantages of the invention are explained in more detail below with reference to the drawing, in which, in detail:  
         [0032]      FIG. 1  shows a sectional view through a first embodiment of the filter module of the present invention;  
         [0033]      FIG. 2  shows a plan view of the spacer according to the invention of the filter module shown in  FIG. 1 ;  
         [0034]      FIG. 3  shows an enlarged sectional view of a detail from  FIG. 2 ;  
         [0035]      FIG. 4  shows a sectional view through a further embodiment of the filter module according to the invention;  
         [0036]      FIG. 5  shows a plan view of the spacer according to the invention of the filter module shown in  FIG. 3 ;  
         [0037]      FIG. 6  shows an enlarged sectional view of a detail from  FIG. 5 ;  
         [0038]      FIG. 7  shows a sectional view through a further embodiment of a filter module of the present invention;  
         [0039]      FIG. 8  shows a plan view of the spacer according to the invention of the filter module shown in  FIG. 7 ;  
         [0040]      FIG. 9  shows an enlarged sectional view through a detail from  FIG. 8 ;  
         [0041]      FIG. 10  shows a sectional illustration through a further embodiment of the filter module according to the invention;  
         [0042]      FIG. 11  shows a plan view of the spacer according to the invention from  FIG. 10 ; and  
         [0043]      FIG. 12  shows an enlarged sectional view of a detail from  FIG. 11 . 
     
    
       [0044]      FIG. 1  shows a filter module, which is denoted overall by reference numeral  10  and comprises a first layer  12  of a filter material and a second layer  14  of the filter material, which are held spaced apart from one another by a spacer  16  disposed between them. The filter material layers  12  and  14  may consist of different filter materials, and may in particular also be in the form of membranes.  
         [0045]     A filter cushion can be constructed from two layers of filter material with a spacer between them for discharging permeate. The three layers are welded or adhesively bonded to one another at the outer edges. The cushion shape and the number of joined sides depend on the desired filter module shape.  
         [0046]     The spacer  16  (also referred to below as a spacer layer) is substantially assembled from webs to form a gridlike structure, with the webs disposed in two directions and connected to one another via junction points. In particular, in this case there are webs  18  which are disposed parallel to the direction of flow of a fluid being treated and which are held spaced apart from one another and connected to one another by means of transverse webs  20 . On their surfaces facing upward and downward, the webs  18  have fins  22  and  24 , which serve on the one hand to support the filter material layer  12  and on the other hand to support the filter material layer  14 . They therefore include first web regions which define the bearing surfaces for the filter materials.  
         [0047]     The transverse webs  20 , by contrast, maintain a spacing both from the surface of the filter material layer  12  and from the surface of the filter material layer  14  and thereby avoid zones through which the flow is reduced, allowing the fluid being filtered to flow through substantially unimpeded. These represent the second web regions.  
         [0048]      FIG. 2  provides a further, more detailed illustration of the mesh structure of the spacer layer  16 , providing a clear and detailed illustration of the rectangular grid structure of the spacer layer  16 . The webs  18 , which continue endlessly, carry the abovementioned fins  22 , which form a narrow bearing surface for the filter material layer  12 , on their upper side. The transverse webs  20  hold the webs  18  spaced apart from one another and are in each case set back from the plane formed by the bearing surfaces of the fins  22 .  
         [0049]     A view from below is not shown here, since such a view would be substantially identical to the top view illustrated here.  
         [0050]     Finally,  FIG. 3  shows, in the form of a detail view, a number of variants a, b, c and d of a possible cross section through the webs  20 ; if noncircular webs  20  are used, depending on the particular application, the disposition of the webs opposite to the direction of flow of the fluid being filtered is selected in such a way that the area facing the incoming flow is as small as possible, or is selected in such a way that regions of turbulence are produced in the flow of the fluid. In the former case, the resistance to incoming flow is minimized, whereas in the latter case possible concentration polarization is inhibited.  
         [0051]     In the latter case, the noncircular webs  20  will be disposed in such a way (cf. in particular variants a) and d)) that the liquid is diverted in one direction or the other by the webs  20 , so that laminar flows at the filter material surfaces are broken up. This allows deposits on the surface of the filter material to be reduced or even avoided altogether and also makes it possible to counteract or avoid concentration polarization at the surface of the filter material.  
         [0052]     A further variant of a filter module according to the invention is illustrated in  FIG. 4 . The filter module  30  illustrated in  FIG. 4  is of similar construction to the filter module  10  shown in  FIG. 1 . In this module, a first filter material layer  32  and a second filter material layer  34  are held spaced apart from and substantially parallel to one another by a spacer layer  36 . The grid or mesh structure of the spacer layer  36  is once again constructed from longitudinal and transverse webs  38  and  40 , respectively, resulting in a rectangular structure.  
         [0053]     First web regions  42 , which above and below the plane formed by the webs  38  and  40  carry studs  44  and  46 , against which one or other filter material layer  32  or  34  then comes to bear, are provided at the junction points of the longitudinal and transverse webs  38 ,  40 .  
         [0054]     It can be seen from the plan view of the spacer layer  36  presented in  FIG. 5  that the bearing points of the studs  44  (and this also applies to the downwardly facing studs  46 ) are relatively small, so that a maximum clear surface area of the filter material layers  32  and  34 , respectively, results. Therefore, substantially almost all the web regions count as second web regions, which maintain a spacing from the filter material layers  32  and  34 .  
         [0055]     Once again, various possibilities are available for the configuration of the transverse webs  40 , and these possibilities are illustrated as variants a, b, c and d in  FIG. 6 . The statements which have been made in connection with the filter module  10  apply once again with regard to the selection of the geometry of the cross section of the transverse webs  40  and the orientation thereof.  
         [0056]     The remaining form of the longitudinal webs  38  is substantially independent of the shape of the transverse webs  40 , in particular including in cross section. In this case too, as can be seen for example from  FIG. 4 , it is possible to provide an elliptical cross section, so that on the one hand the stability of the grid structure is maintained, but on the other hand the maximum possible spacing of these webs too from the surfaces of the filter material layers  32  and  34  is maintained. This ensures that even in the surface regions of the filter material layers  32  and  34 , between which the longitudinal webs  38  are disposed, there are no small volumes in which deposits could occur, associated with subsequent fouling.  
         [0057]     FIGS.  7  to  9  describe a further variant of the present invention, the basic structure of which is similar to the embodiment shown in FIGS.  1  to  3 .  
         [0058]     The embodiment shown here relates to a filter module  50  in which a first filter material layer  52  and a second filter material layer  54  are held parallel to and at a spacing from one another by a spacer layer  56  disposed between them. The spacer layer  56  is once again formed by longitudinal webs  58  and transverse webs  60 .  
         [0059]     As in the embodiment shown in FIGS.  1  to  3 , in the embodiment of a filter module shown here, the spacer  56  is constructed from continuous longitudinal webs  58 , which are lined up rectilinearly next to one another and carry fins  62 ,  64  at their upper and lower sides, as can be seen most easily from  FIG. 8 . They represent first web regions which define the bearing surfaces for the filter materials. In the filter module shown here in FIGS.  7  to  9 , the transverse webs  60  of the spacer are disposed differently compared to the embodiment of the filter module shown in FIGS.  1  to  3 . These transverse webs  60  do not run substantially parallel to the surfaces of the filter material layers  52  and  54 , but rather are disposed running at an angle to these surfaces and connect two longitudinal webs  58  disposed parallel to one another, linking to a fin  64  located at the bottom and ending in a fin  62  located at the top, of the adjacent longitudinal web  58 , or in the reverse orientation. The transverse web  60  located downstream as seen in the direction of flow will preferably have precisely the reverse form of linking between the two longitudinal webs  58  running next to one another, so that in the view illustrated in  FIG. 7  the transverse webs as it were cross one another. This results in a particularly effective disruption, so that deposits or concentration polarization can be avoided at the surface of the filter material layers. In this exemplary embodiment, the transverse webs form the second web regions.  
         [0060]      FIG. 9  once again shows possible modifications a, b, c and d of the cross sections of the transverse webs  60 , and the comments made with regard to these different cross sections correspond to what has already been stated in connection with  FIG. 3 .  
         [0061]     Finally, FIGS.  10  to  12  show a further embodiment of the present invention, with a structure similar to that shown in FIGS.  4  to  6 .  
         [0062]     The filter module  70  illustrated once again comprises two filter material layers  72  and  74 , which are held parallel to and spaced apart from one another by a spacer layer  76 . Similarly to the embodiment shown in FIGS.  4  to  6 , both the longitudinal webs and the transverse webs maintain a spacing from the surfaces of the filter material layers  72  and  74 . The longitudinal webs  78  and the transverse webs  80  (second web regions) are connected to one another via junction points  82 , at which studs  84  and  86  for punctiform support of the filter material layers  72  and  74  (first web regions) are formed on the upper and lower sides of the spacer layer. As in the embodiment shown in FIGS.  6  to  9 , the transverse webs  80  run obliquely from the bottom upward, i.e. they connect a stud  86  at a junction point of a longitudinal web  78  to a stud  84  located above it of an adjacent longitudinal web  78  or vice versa, so that in the plan view shown in  FIG. 10  the transverse webs  80  located behind one another as it were cross one another.  
         [0063]      FIG. 12  once again shows possible variants of the cross section of the transverse webs  80 , comprising variants a, b, c and d, which have already been discussed in detail in connection with  FIG. 3 .  
       Exemplary Embodiment  
       [0064]     When the spacers according to the invention are used in membrane technology for the treatment of industrial process water, the main problem is often a high risk of fouling and scaling on the membrane as a result of organic and inorganic constituents of the water. In this context, it is an essential condition for use of a membrane filter that the module can be cleaned. Consequently, the use of spiral wound-type modules according to the prior art is eminently conceivable for relatively unpolluted water. The cleanability of the membrane is improved when using a spacer according to the invention, for example as shown in  FIG. 1 . Moreover, the transverse web configuration shown in  FIG. 3   a  realizes flow guidance which reduces the concentration polarization and therefore the risk of blockages. A thickness of the spacer or the spacing of the bearing surfaces, which is defined by the spacer, of from 1 to 2 mm combined with a ratio of the heights of the second and first web regions, measured in the direction of the spacing, of from 1:2 to 1:4 is conceivable here depending on the degree of contamination of the untreated water.