Abstract:
A method for potting hollow fiber membranes comprises the steps of forming a bundle of membranes with a layer of adhesive; covering one end of the bundle with a permeate pan, the ends of the membranes protruding upwards into the permeate pan; and flowing a liquid potting material into the permeate pan. The bundle may be tilted to more quickly distribute the liquid potting material. An apparatus for filtering liquid with hollow fiber membranes comprises a bundle of membranes, a layer of adhesive spaced from the end of the bundle, a permeate pan covering the end of the bundle, and a header formed with the membranes, the adhesive and the pan.

Description:
FIELD 
       [0001]    The present invention relates to a method of potting hollow fiber membranes and an apparatus for filtering with hollow fiber membranes. 
       BACKGROUND 
       [0002]    In order to filter a fluid with hollow fiber membranes, the membranes are fixed to a header, alternatively called a potting head or a tube sheet, such that their outer surfaces are sealed to a first face of the header, but their lumens are open to a second face of the header. In an immersed membrane module the header, with the membranes, is then attached to a permeate pan to create a permeate collection space between the second face of the header and the pan. The permeate collection space is connected to a source of suction to create a trans-membrane pressure across the walls of the membranes and to carry the liquid from the ends of the membranes through the permeate collection space. 
         [0003]    In U.S. application Ser. No. 10/167,699, the ends of membranes are potted in a liquid wax to create a fugitive lamina. The wax is allowed to solidify around the ends of the membranes. A thermosetting or thermoplastic synthetic resinous material is then poured over the wax to create a fixing lamina. The wax prevents the ends of the membranes from being plugged with the resinous material. The resinous material is allowed to harden around the membranes into a header. The wax is then removed by, for example, heating or dissolving with a solvent, leaving the ends of the membranes open to a space formerly occupied by the wax. 
         [0004]    In U.S. Pat. No. 6,592,759, ends of membranes are potted in a dense gel. A liquid, less dense than the gel, is poured over the gel and around the membranes. The gel prevents the ends of the membranes from being plugged with the liquid. The liquid is allowed to harden into a header. Once the liquid has hardened, the gel is removed by vibrating to a fluid state, flushing with a solvent, or heating. 
         [0005]    In U.S. Pat. No. 7,393,486, a bundle of hollow fiber membranes are potted by injection molding a hot thermoplastic into a cavity containing the membranes. The cavity is formed between a mold and two spaced-apart layers of adhesive pre-applied to the bundle of membranes. The hot thermoplastic is allowed to harden into a header. 
         [0006]    In U.S. application Ser. No. 12/381,097, ends of membranes are inserted into a spacer and held with open ends protruding upwards from the spacer. The spacer can be a plate with openings to accommodate the membranes or the spacer can be flexible plastic strips. In the case of flexible plastic strips, the strips can be wound up in spiral shape, or segments of plastic strip can be combined to form a multi-layer package. Once the membranes are inserted in the spacer, a liquid is then poured around the membranes and over the top of the spacer. The spacer is non-permeable to the liquid thus preventing the liquid from flowing down the membranes. The liquid is allowed to harden into a header. 
       SUMMARY OF THE INVENTION 
       [0007]    This specification describes a method of potting hollow fiber membranes, and an apparatus for filtering liquid with hollow fiber membranes. 
         [0008]    The method for potting hollow fiber membranes comprises the steps of forming a bundle of membranes with a layer of adhesive, covering the end of the bundle with a permeate pan so that the end of the bundle extends upwards into the pan, and flowing a liquid potting material into the pan to fill the spaces between the membranes and to cover the layer of adhesive. 
         [0009]    Through this method, the steps of potting the ends of the membrane in a fugitive lamina, and removing the fugitive lamina once the header has formed, are avoided. This method also avoids the need to rapidly inject hot thermoplastic into the potting area. A thermosetting resin may solidify more slowly than melted thermoplastic and does not need to be hot to be in liquid form. Using the force of gravity, the liquid resin is allowed to spread across the layer of adhesive without covering the ends of the membranes. The permeate pan is bonded to the membranes as the resin cures. 
         [0010]    An apparatus for filtering liquid with hollow fiber membranes comprises a bundle of membranes held together by a layer of adhesive material; a permeate pan covering the end of the bundle to create a permeate collection space which is in fluid communication with the ends of the membranes; and a header integrally formed with the membranes, the layer of adhesive, and the permeate pan. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Examples of embodiments of the invention or inventions will be described below with reference to the following figures. 
           [0012]      FIG. 1  shows a plan view of two layers of adhesive on a sheet of hollow fiber membranes. 
           [0013]      FIG. 2  shows an isometric view of sheets of fibers of  FIG. 1  assembled into a larger bundle of fibers having two layers of adhesive. 
           [0014]      FIG. 3A  is an isometric view of a plate clamped circumferentially around a bundle of fibers. 
           [0015]      FIG. 3B  is a cross-section view of  FIG. 3A  viewed along the cut line A-A. 
           [0016]      FIG. 4A  is an isometric view of a plate and bundle abuted against a permeate pan. 
           [0017]      FIG. 4B  is a cross-section view of  FIG. 4A  viewed along the cut line B-B. 
           [0018]      FIG. 5  is a cut-out cross-section view of  FIG. 4A  viewed along cut line C-C, with a potting region filled with a liquid resin. 
           [0019]    FIGS.  6 A,B and C are side views showing the use of gravity to more quickly flow a liquid resin across a potting region. 
           [0020]      FIG. 7  is a side view of a bundle fitted into a permeate pan. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  shows a plan view of a sheet  1  of hollow membrane fibers  5  with two layers of adhesive  2  and  3 . Optionally, one layer of adhesive can be used. The sheet of membranes  1  can be formed by laying the membranes  5  on a supporting surface, such as a table, so that the membranes  5  are generally parallel to each other but spaced apart from each other, for example between 0.2 and 2 times their diameter. Optionally, the sheet can be formed by any suitable fabric forming method and have inert fibers running transversely across the membranes to help maintain the membranes in position. Further optionally, the sheet may be formed by winding the membranes onto a drum, preferably though a guide that advances across the face of the drum at a speed relative to the speed of rotation of the drum which lays the fibers in a spiral around the drum at a desired spacing. The membranes may have diameters, for example, between 0.2 and 2.5 mm and there may be, for example, between 10 and 500 membranes in a sheet. The width of the sheet may be, for example, from 200 mm to 1200 mm and the length of the sheet, and its membranes, may be, for example, between 200 mm and 3200 mm. In various Figures, the membranes are shown as cut to a shorter lengths to allow other parts to be shown larger. To form the sheet  1 , a first layer of adhesive  2  is placed over the sheet  1  or forming surface so that it is spaced from one end  4  of the sheet  1 . Optionally, a second layer of adhesive  3  can be placed over the sheet  1 . The second layer of adhesive  3  is at or spaced from the end of the sheet  4 . The second layer  3  optionally does not cover or fill the ends of the membranes  5 . The second layer  3  may be placed close to the ends of the membranes  5 , without closing the ends, to reduce the length of the membranes  5  that will protrude into, and interfere with flows of fluids in, the permeate cavity behind the header. The layers of adhesive  2 , 3  hold the sheet together. The layers of adhesive  2 , 3  also seal the entire outer circumference of the membranes  5 , although a perfect seal does not need to be formed. The adhesive may be thermoplastic and applied by melting it so that it flows over and around the membranes  5 . The adhesive may also be melted after applying it to the membranes  5  and molded or shaped while it is molten to provide a layer of uniform shape or more carefully controlled size. The adhesive may be of a type normally referred to as hot melt glue, which may be a polyethylene or a blend of ethylene vinyl acetate co-polymers. Alternately, the adhesive may be a resin such as polyurethane or epoxy. 
         [0022]      FIG. 2  shows a bundle  11  of membranes  5  made by stacking a number of sheets  1 , for example between 1 and 30 or between 10 and 20 sheets, together. Sheets  1  are stacked so that their adhesive layers  2 , 3  lay on top of each other to generally form a parallelepiped. Optionally, one or more sheets may be rolled up together to generally form a cylinder or made into other shapes. The sheets  1  may be glued, welded, melted or clamped together or simply held together manually or by wrapping a string, wires, band or other wrap around the bundle. A first layer of adhesive  12  is at, or spaced from, one end  14  of the stack of membranes  5 . Optionally, a second layer of adhesive  13  is spaced from and situated between the first layer of adhesive  12  and the end  14  of the membranes  5 , optionally so as to leave the ends of the bundle of membranes  5  uncovered by adhesive. 
         [0023]      FIGS. 3A and 3B  shows a bundle  11  of membranes  5  clamped circumferentially by a plate  101  about a first layer of adhesive  12 .  FIG. 3B  is a cross section of  FIG. 3A  viewed along the cut line A-A. The plate  101  is composed of four metal girder segments: two length girders  102  and two end girders  103 . The length girders  102  are clamped lengthwise along opposite sides of the bundle  11  against the first layer of adhesive  12 . The length girders  102  are preferably just slightly shorter than the length of the bundle  11 . The two length girders  102  are held together by one or more clamps  104  with jaws  105 . The jaws  105  are brought together against the two length girders  102  to compress the first layer of adhesive  12 . This creates a seal between the first adhesive layers  12  of the sheets  1 , as well as a seal between the length girders  102  and the adjacent outermost first layer of adhesive  12  of the bundle  11 . Once the bundle  11  is clamped between the two length girders  102 , the exposed first layer of adhesive  12  at the sides of the bundle  11  are heated with a heat gun, or a similar heating device to glue the sides of the sheets  1  together. Additional adhesive may be added if necessary. The end girders  103  are preferably slightly longer than the width of the bundle  11 . The end girders  103  are then abutted against the first layer of adhesive  12  of the bundle  11 , perpendicular to the length girders  102  to create a rectangular plate  101 . The end girders  103 , like the length girders  102 , are sealed against the outermost first layer of adhesive  12  of the bundle  11 . Once in position, the end girders  103  can be bolted to the length girders  102  with angle brackets  106  at each of the four intersecting corners where the girders meet. The girders do not need to be bolted together, however. The clamps  104  can be left in place, and additional clamps  104  can be added to hold the end girders  103  against the length girders  102  (not shown). If the bundle  11  is cylindrical in shape (not shown), the plate may be a collar. 
         [0024]      FIGS. 4A and 4B  are substantially the same as  FIGS. 3A and 3B , respectively, the difference being that one end of a bundle  11  is covered with a permeate pan  208  to form a potting region  216 . The permeate pan  208  is an inverted bowl. The base of the pan is open to receive the ends of the membranes  5  in a bundle  11 . The base of the permeate pan  208  seals against the top of a plate  101 . The potting region  216  is defined by a space between the plate  101 , a layer of adhesive  12  and the permeate pan  208 .  FIG. 4B  is a cross section of  FIG. 4A  viewed along the cut line B-B. Upon seating the pan  208  on the plate  101 , the pan  208  has a collection space  210  in fluid communication with the ends of the membranes  5 . The plate  101  may have rubber inserts  212  to improve the seal between the plate  101  and the base of the permeate pan  208 . The permeate pan  208  is pressed into the rubber inserts  212  of the plate  101  and held in place with wires  214  wrapped circumferentially around both the permeate pan  208  and the plate  101 . Wires  214  are not required, however: any sort of clamp or vice could apply pressure from the top of the permeate pan  208  and the bottom of the plate  101 . A hole  218 , such as a spigot hole, may be present in the top of the permeate pan  208 . A pipe can be used in flowing a potting liquid into the potting region  216 . An end of a-up pipe  299 , can be inserted through the hole  218 , down through a space between the membranes  5 , and into the potting region  216 . Optionally, multiple pipes  299  can be inserted through one or more holes  218  into the potting region  216 . Pipes  299  could also be inserted up through the bottom of the first layer of adhesive  12  (preferably before clamping) or through a hole made in the side of the permeate pan  208  (not shown). The pipes  299  could extend into the potting region  216  to any depth, but preferably a distance of ⅛th and ⅜ths of the total length of the potting region  216 , from both ends of the potting region  216 . Once filled with a liquid urethane (as described below) or other resin and left to solidify into a header, the header will be formed integrally with the membranes, the sides of the permeate pan  208 , and the top of the layer of adhesive  12 . The plate  101  and pipe(s)  299 , are to be removed preferably before the resin has completely solidified as they do not form part of the header. 
         [0025]      FIG. 5  shows a front cross-section view of a potting region  216  and surrounding area substantially as shown in  FIGS. 4A , viewed along cut lines C-C, filled with liquid resin  222 . The potting region  216  is the space defined by a first layer of adhesive  12 , a plate  101 , and, a permeate pan  208 . A liquid resin  222 , is flowed into the potting region  216  through a pipe  299 , and around the membranes  5 . When a sufficient amount of liquid resin  222  is present to form, when solidified, a header, the flow of liquid resin  222  into the potting region  216  is stopped. The liquid resin  222  does not extend to the very ends of the membranes  5  and does not cover or fill the ends of the membranes  5 . As the liquid resin  222  is left to solidify, it forms meniscuses  226  around the membranes. To avoid forming a meniscus, the resin may be filled to the second layer of adhesive  13 . 
         [0026]    A protector cap  220  is optionally fit into a hole  218  to redirect the pipe  299  downward towards the potting region  216 . The protector cap  220  is to help prevent covering or filling the ends of the membranes  5  with a liquid resin  222  when it is being flowed into the potting region  216 . 
         [0027]      FIGS. 6A ,  6 B, and  6 C show side views of the process of filling a potting region  216  with a liquid resin  222  through a pipe  299 . The end of the pipe  299  is inserted through a hole  218  in a permeate pan  208  down into the potting region  216 .  FIG. 7B  shows the tilting of the potting region  216  to flow the liquid resin  222  throughout the potting region  216  more quickly using the force of gravity. The bundle  11  may be tilted in any direction to flow the liquid resin  222  in that direction more quickly. The liquid resin  222  is not allowed to flow over the ends of the membranes  5  or cover or fill the ends of the membranes  5 . When the liquid resin  222  has reached a pre-defined level  224 , which is below the ends of the membranes  5 , the bundle  11  is tilted back to a position to make the liquid resin  222  level. The flow of liquid resin  222  from the pipe  299  is then stopped. 
         [0028]      FIG. 7  shows a side view of the bundle of membranes  11  fitted into the open base of a permeate pan  208 . A first layer of adhesive material  12  forms an interference fit with the walls of the pan  208 . A perfect seal is not required, however, a good fit around the circumference of the first layer of material  12  will limit the amount of liquid resin that may escape when the liquid resin is flowed into the pan. Liquid resin is flowed into the permeate pan in the same way as described in  FIGS. 4 to 6 . It may be flowed in through a hole  218  in the pan  208 . One or more pipes  299  and one or more protector caps  220  may be used assist with flowing the liquid resin  222  into the pan  208 . The liquid resin  222  is left to harden into a header. Once hardened, the header will be integrally formed with the pan  208  and the bundle of membranes  11 . 
         [0029]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.