Abstract:
The present disclosure describes a brine seal for use with a spiral wound membrane element. The brine seal has an elongate body with a flexible wing. The brine seal is wrapped around the spiral membrane element with a space between each turn of the brine seal. The wrapped spiral wound membrane unit is placed inside a pressure housing. Between the wrapped spiral wound membrane element and an inner surface of the pressure housing is an annular space. The brine seal, the spiral wound membrane element and the pressure housing establish a bypass flow channel that spirals around the spiral wound membrane element, through the annular space. Feedstock can enter the bypass flow channel to provide sanitary flushing of the annular space. Some of the feedstock in the bypass flow channel enters the spiral wound membrane to improve the efficiency of the spiral wound membrane element.

Description:
FIELD 
       [0001]    The present disclosure relates generally to spiral wound membrane elements. 
       BACKGROUND 
       [0002]    The following discussion is not an admission that anything discussed below is citable as prior art or common general knowledge. 
         [0003]    Typically, a spiral wound membrane element is made by wrapping one or more membrane leaves around a perforated central tube. One edge of a feed carrier sheet is placed in a fold of a generally rectangular membrane sheet. The fold of the membrane sheet is positioned along a perforated central tube. A permeate carrier sheet is provided between each pair of membrane sheets. Glue lines seal the permeate carrier sheet between adjacent membrane sheets along three edges, forming a membrane leaf. The fourth edge of the leaf is open to the perforated central tube. All of the sheets are wrapped around the perforated central tube. 
         [0004]    In use, the spiral wound membrane element is housed in a pressure housing, also referred to as a pressure tube or a pressure vessel. A pressurized feedstock is delivered at an upstream end of the pressure housing and flows into the spiral wound membrane element. Within the spiral wound membrane element, the pressurized feedstock flows through the feed spacer sheets and across the surface of the membrane sheets. The membrane sheets may have a discriminating layer that is suitably sized for microfiltration, ultrafiltration, reverse osmosis or nanofiltration. A portion of the pressurized feedstock is driven through the discriminating layer by transmembrane pressure to produce a permeate stream. The permeate stream flows along the permeate carrier sheets into the central tube for collection outside the pressure housing. The components of the pressurized feedstock that do not pass through the membrane, also referred to as retentate, continue to move through the feed spacer sheets to be collected at a downstream end of the pressure housing. 
         [0005]    Some specific industries (for example the dairy industry) require sanitary spiral wound membrane elements that meet the requirements of the Sanitary 3A Standards for Crossflow Membrane Modules. Sanitary problems can arise in areas of low flow, also referred to as areas of tight tolerance. In areas of tight tolerance, there is limited fluid access and therefore limited flushing to remove solids or provide sanitization solutions. One region that typically has low flow is between an inner surface of the pressure housing and the outer surface of the spiral wound membrane element, referred to as the annular space. 
         [0006]    In some modules a portion of the feedstock flow is sent through the annular space. This is referred to as bypass flow. Bypass flow improves flushing of the annular space; however, the bypass flow also reduces the volume of feedstock that passes through the spiral wound membrane element to contribute to the production of permeate. 
         [0007]    Various factors affect permeate production including temperature, osmotic pressure gradients, polarization layer, the charge of materials, fouling and the balance of fluid pressures across the membrane sheets, referred to as transmembrane pressure. The pressure of the feedstock within the feed spacer sheets influences the transmembrane pressure. As the permeate volume increases, the pressure and velocity of the feedstock within the feed spacer sheets decreases. Furthermore, the flow of feedstock through the feed spacer sheets is exposed to resistance, which is a source of head loss. Due to the volume loss of the feedstock and the head loss, the pressure and velocity of the feedstock within the feed spacer sheet decreases along the length of the spiral wound membrane element. This decreased feed spacer sheet pressure decreases the transmembrane pressure and decreases overall permeate production. The decreased velocity reduces disruption of the polarization layer at the membrane surface, which further reduces permeate production. 
         [0008]    Typically, more than one spiral wound membrane element is housed in one pressure housing. For example, in the dairy industry between one and ten spiral wound membrane elements can be housed in one pressure housing. The multiple spiral wound membrane elements are connected in series and they typically share a common central tube. A standard dairy feedstock is introduced into the upstream end of the pressure housing at a pressure of about 100 psi. Along the length of a given spiral wound membrane element, the feed spacer sheet pressure may decrease about 5 to 10 psi. This pressure decrease can accumulate when multiple spiral wound membrane elements are used in one pressure housing and decrease the production of permeate within a given pressure housing. 
       SUMMARY 
       [0009]    A sanitary brine seal for use with spiral wound membrane elements is described below. A brine seal extends from the outside of a membrane element to the inside of a pressure vessel thus blocking flow through the annular space. In conventional practice, brine seals are provided as a ring on an end of the membrane element to prevent, or minimize, bypass flow. The brine sanitary seal described in this specification, however, is wrapped in a spiral around a membrane element. The sanitary brine seal does not attempt to close the ends of the annular space, but instead it provides a longer and narrower passage for bypass flow through the annular space. The sanitary brine seal may be shaped such that the bypass flow presses the sanitary brine seal against the inside of the pressure vessel. The sanitary brine seal may also reinforce the element. The bypass flow passage may communicate with feed spacers of the spiral wound membrane element. 
         [0010]    One brine seal has a bottom surface that is adjacent to a portion of an outer layer of the spiral wound membrane element. A first edge faces a downstream end of the spiral wound membrane element. A second edge of the brine seal faces an upstream end of the spiral wound membrane. A protruding part extends away from the spiral wound membrane element. Successive wraps of the brine seal around the spiral wound membrane element maintain a distance between the first edge of one wrap and the second edge of a neighboring wrap. Across this distance, the outer layer of the spiral wound membrane or a porous sleeve or a spacer around the membrane element, is exposed. 
         [0011]    When in use, the spiral wound membrane element is housed inside a pressure housing, either alone or in series with other spiral wound membrane elements. Pressurized feedstock is introduced into a feed end of the pressure housing. A portion of the pressurized feedstock enters the spiral wound membrane element and a portion provides a bypass flow. The bypass flow flushes the annular space between an inner surface of the pressure housing and the spiral wound membrane element. The bypass flow may push against and move the protruding part. For example, the protruding part may be pushed into contact with the inner surface of the pressure housing. This may help create a seal between the brine seal and the pressure vessel, accommodate variations in the outer diameter of the spiral wound membrane element or help centralize the spiral wound membrane element within the pressure housing. 
         [0012]    The brine seal defines a lateral boundary of a bypass flow channel within the annular space. An upper boundary of the bypass flow channel is defined by the inner surface of the pressure housing and a lower boundary is defined by the exposed outer layer of the spiral wound membrane element. The bypass flow channel extends along and around the spiral wound membrane element from the feed end of the pressure housing to an output end. 
         [0013]    In normal operation, the pressure in the feed spacer sheets decreases along the length of the spiral wound membrane element. This pressure drop decreases the transmembrane pressure and decreases the production of permeate. Therefore, a pressure gradient may develop between the feedstock in the bypass flow channel and the feedstock within the feed spacer sheets. Without being bound by theory, this pressure gradient may cause the feedstock within the bypass flow channel to enter the spiral wound membrane element. The flow of feedstock from the bypass flow channel into the spiral wound membrane element increases the flow rate of the feedstock within the feed spacer sheet. The increased flow rate of feedstock within the feed spacer sheet may contribute to increasing the transmembrane pressure, and therefore permeate production may also increase. Optionally, however, the outer surfaces of the membrane element may be impermeable. In this case, the brine seal provides an increased velocity per unit of bypass flow to allow for a more efficient, or effective, flush of the annular space. 
         [0014]    Within the pressure housing, operational pressure and temperature conditions during filtration physically stress the structural integrity of the spiral wound membrane element. For example, the layers of the spiral wound membrane elements may shift along the longitudinal axis and the layers may also expand radially. These structural changes decrease permeate production. The physical stress on the structural stability of the spiral wound membrane element can also increase during high temperature or chemical solvent based sanitization procedures. Optionally, part of the brine seal is sufficiently rigid and optionally pre-stressed to reinforce the structural integrity of the spiral wound membrane element and withstand the physical stresses associated with filtering operations and sanitization procedures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a top-plan view of a brine seal. 
           [0016]      FIG. 2  is a cross-section view taken along line  2 - 2 ′ of  FIG. 1 . 
           [0017]      FIG. 3  is a side view of the brine seal of  FIG. 1  wrapped around a spiral wound membrane element. 
           [0018]      FIG. 4  is a mid-line schematic drawing of the spiral wound membrane element and the brine seal of  FIG. 3  within a pressure housing. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    A brine seal for use with a spiral wound membrane element is described below. At least a part of the brine seal extends from the outside of a spiral wound membrane element into an annular space inside of a pressure housing. The brine seal has an elongate body, longer than the circumference of the spiral wound membrane element, and extends simultaneously around the circumference and along the length of the spiral wound membrane element. A bypass flow is created that is oblique to the length of the spiral wound membrane element. The brine seal may extend across the annular space such that essentially all of the bypass flow is oblique to the length of the spiral wound membrane element. 
         [0020]    The  FIGS. 1 to 4  depict a brine seal  10  for use with a spiral wound membrane element having a preferred but optional cross-sectional shape that accommodates variations in the spiral wound membrane element diameter while encouraging an effective seal with the inside of the pressure vessel. This brine seal has an elongate body comprising a wing and, optionally, a reinforcing member. 
         [0021]    The brine seal  10  is an elongate body comprising a wing  14  and a reinforcement member  16 . The brine seal  10  has a first edge  18 , a second edge  20 , a first end  19 , a second end  21 , a top surface  22  and a bottom surface  24 . Part of the cross-section of the brine seal is angled into the direction of bypass flow. 
         [0022]    As shown in  FIG. 2 , the wing  14  extends away from the top surface  22 , at the first edge  18 . The wing  14  is an integral part of the brine seal  10 . Optionally, the wing  14  can be a separate component that is positioned proximal to, or upon the brine seal  10 . The wing  14  has an upstream surface  26  and a downstream surface  28 . As will be discussed further below, the brine seal  10  is made from materials that allow the wing  14  to move about the first edge  20  so that the upstream surface  26  moves closer or further away from the top surface  22 . This movement changes the angle between the upstream surface  26  and the top surface  22 . The angle is represented by the dotted line Y in  FIG. 2 . 
         [0023]    As described further below, the brine seal  10  is wrapped around a dairy spiral wound membrane element  100  and housed within a pressure housing  150 . Optionally, the brine seal  10  is compressed between the spiral wound membrane element and the pressure housing  150  and this compressive force helps hold the brine seal  10  in the wrapped position. Optionally, the first end  19  and the second end  21  may be clamped in place by a clamp, or other suitable methods (not shown) that holds the brine seal  10  in the wrapped position around the spiral wound membrane  100 . In this case, the brine seal  10  will hold the wrapped position during filtration operations and sanitization procedures. Optionally, the reinforcement member may be shape pre-formed so that it is pre-stressed when the brine seal  10  is installed on the spiral wound membrane element  100 . Two or more of these options may be used together. 
         [0024]      FIG. 2  depicts the optional reinforcement member  16  encapsulated, or housed, within the brine seal  10  between the top surface  22  and the bottom surface  24 . When housed within the brine seal  10 , the reinforcement member  16  can be made of a variety of suitably rigid materials, such as stainless steel, aluminum, copper, titanium, gold, platinum, carbon fibers, glass fibers, thermoplastic fibers and cellulose fibers. The reinforcement member  16  can be a wire or wire-like structure, that is twisted, intermeshed, woven, or not. The reinforcement member  16  can also be other suitable structures, such one or more bands, sheets or a layered fabric. The reinforcement member  16  is sufficiently rigid to help hold the brine seal  10  in a given position during filtering operations and sanitization procedures. 
         [0025]    Optionally, the reinforcement member  16  is a coiled spring that, in the relaxed position, has an inner diameter slightly smaller than the outer diameter of the spiral wound membrane element  100 . In this case, the reinforcement member  16  can be uncoiled to increase the inner diameter sufficiently to allow the brine seal  10  to be positioned along the length of the spiral wound membrane element  100  and released. The release will cause the reinforcement member  16  to return to the relaxed position and help hold the brine seal  10  in the wrapped position during filtration operations and sanitization procedures. 
         [0026]    Optionally, the reinforcement member  16  is external to, and fixed to, the brine seal  10 . In this option, the reinforcement member  16  is composed of rigid materials that meet food contact standards, for example, 300 series stainless steel can be used. When external to the brine seal  10 , the reinforcement member  16  can be any of the suitable structures described above. However, a suitable external structure is limited by the material used and the manner in which the reinforcement member  16  is fixed to brine seal  10 . When external to the brine seal  10 , the reinforcement member  16  can be fixed to any of, or any combination of, the first edge  18 , the second edge  20 , the first end  19 , the second end  21 , the top surface  22  and the bottom surface  24 . The external reinforcement member  16  is fixed to the brine seal  10  by any suitable method or technique that will withstand the stresses associated with standard operational and sanitization procedure conditions. 
         [0027]    The brine seal  10  can be constructed of a number of suitable materials that meet food contact standards. Examples of suitable materials include thermoplastic polymers such as: polypropylene, low density polyethylene, high density polyethylene, ethylene propylene diene monomer, fluroelastomer, polyvinylidene fluoride, polytetrafluroethylene and urethanes. 
         [0028]      FIG. 3  depicts the brine seal  10  wrapped helically, spirally, or generally around and along the longitudinal axis (shown by arrow X) of a spiral wound membrane element  100 . The bottom surface  24  of the brine seal  10  is adjacent to an outer layer  116  of the spiral wound membrane element  100 . The brine seal  10  is oriented with the second edge  20  and the upstream surface  26  facing an upstream end  104  of the spiral wound membrane element  100 . The first edge  22  and the down stream surface  28  face a downstream end  106  of the spiral wound membrane element  100 . The reinforcement member  16  (not shown in  FIG. 3 ) holds the brine seal  10  in the wrapped position. 
         [0029]    The brine seal  10  forms a series of turns  12  around the spiral wound membrane element  100 . The series of turns  12  are shown in  FIG. 3  as individual turns  12   a,    12   b ,  12   c  and  12   d.  An individual turn is considered to extend between points of the same angular position on adjacent wrappings of the second edge  20 . The number of turns  12  in the series can be variable and may depend upon the dimensions of the spiral wound membrane element  100 . Optionally, but preferably, a gap  32  is provided between adjacent turns  12 . The gap  32  defines the width of the bypass channel and may provide fluid communication with the spiral wound membrane element  100 , which may be porous in all, or part of, its outer surface. For example, the gap  32  is shown in  FIG. 3  between the first edge  18  at turn  12   b  and the second edge  20  at turn  12   a.  The width of the gap  32  is substantially constant through the series of turns  12 . Alternatively, the width of the gap  32  may be different between the individual turns. For example, the width of the gap  32  within turn  12   a  may be wider, or narrower, in comparison to the width of the gap  32  within turn  12   d.  Optionally, the gap  32  may get progressively narrower, or wider, towards the downstream end  106  of the spiral wound membrane element  100 . Preferably, the gap  32  get progressively narrower towards the downstream end  106 . Optionally, the brine seal may extend along only a part of the length of the membrane element  100 . 
         [0030]    The spiral wound membrane element  100  has an upstream end  104  and a downstream end  106 . As will be discussed further below, the upstream end  104  receives the pressurized feedstock. The downstream end  106  is the end of the spiral wound membrane element  100  where a permeate flow (not shown) and a retentate flow (not shown) are collected. The brine seal  10  is oriented upon the spiral wound membrane element  100  with the first edge  18  closest to the upstream end  104  and the second edge  20  closest to the downstream end  106 . 
         [0031]    The spiral wound membrane element  100  wraps around the central tube  108 . The spiral wound membrane element  100  comprises a mixed layer  110  of multiple layers of membrane leaves. The mixed layer  110  is formed by wrapping the membrane leaves around the central tube  108  so that each of the membrane sheet, the permeate carrier sheet and the feed spacer sheet have one edge that is close to the central tube  108  and one edge that is distal from the central tube  108 . At the periphery of the mixed layer  110 , distal to the central tube  108 , is an outer layer  116 . The outer layer  116  comprises the distal edges of the membrane leaves. In the outer layer  116 , the distal edges of the feed spacer sheets extend to and optionally past the distal edges of the membrane sheet and permeate carrier sheet of a membrane leaf. The distal edge of one feed spacer sheet can terminate on the feed spacer sheet of another membrane leaf. In that case, the outer layer  116  comprises feed spacer sheets that cover the distal edges of the membrane sheets and permeate carrier sheets and the feed spacer sheets provide fluid communication with the mixed layer  110  below. The feed spacer sheets prevent the distal edges of one membrane leaf from coming in direct contact with another leaf. Direct contact between the distal edges of different membrane leaves can create unsanitary areas of tight tolerance. 
         [0032]    Optionally, the feed spacer sheets do not terminate on other feed spacer sheets, rather each feed spacer sheet terminates before covering the distal edge of a membrane leaf. However, in this case the feed spacer sheets still prevent the distal edges of different membrane leaves from coming in direct contact, while providing fluid communication with the mixed layer  110 . 
         [0033]    Adjacent the outer layer  116  is the brine seal  10 . Optionally, a cage, net or other porous sleeve (not shown) can be positioned between the outer layer  116  and the brine seal  10 . The cage can be made of similar materials as the feed spacer sheets, optionally of larger dimensions. The cage can assist in structurally reinforcing the mixed layer  110  and the outer layer  116 . Optionally, the cage is made from polypropylene or polyethylene, or similar materials. In this option, the first edge  18  and the second edge  20  can be thermally bonded together, for example by ultrasonic welding. Optionally, the brine seal  10  can be bonded to the cage to reinforce the structural stability of the brine seal  10 , the cage and the spiral wound membrane element as a whole. 
         [0034]      FIG. 4  depicts three spiral wound membrane elements  100 ,  100   1 ,  100   11  positioned within a pressure housing  150 . The pressure housing  150  has an upstream end  152  with an inlet pipe  153  and a down stream end  154  with an outlet pipe  155 . The pressure housing  150  is tubular in shape with an inner surface  156  and an outer surface  158 . 
         [0035]    Each spiral wound membrane element  100 ,  100   1 ,  100   11  is wrapped by a brine seal  10 ,  10   1 ,  10   11 . The three spiral wound membrane elements  100 ,  100   1 ,  100   11  are connected in series and share a common central tube  108 . Although only three spiral wound membrane elements  100  are shown in  FIG. 3 , there can be four to eight, or more, spiral wound membrane elements  100  within a given pressure housing  150 . 
         [0036]    The helical wrapping of the brine seal  10  in combination with the spiral wound membrane element  100  and the pressure housing  150  define a bypass flow channel  34  that extends through the annular space  160 . The bypass flow channel  34  is defined by the wing  14 , and the top surface  22  adjacent turns of the brine seal  10 , the inner surface  156  of the pressure housing  150  and the outer surface of the spiral wound membrane element  100  exposed in the gap  32 . As shown in  FIGS. 3 and 4 , the outer layer  116  of the spiral wound membrane  100  is exposed at the gap  32 , which allows fluid communication between the bypass flow channel  34  and the outer layer  116  of the spiral wound membrane element  100 . 
         [0037]    In operation, the inlet pipe  153  introduces a pressurized feedstock (not shown) at the upstream end  152  of the pressure housing  150 . This creates a pressure gradient within the pressure housing  150  that drives the feedstock from the upstream end  152  towards the down stream end  154 , along the longitudinal axis of the pressure housing  150 . At least a portion of the pressurized feedstock enters the first spiral wound membrane element  100  at the upstream end  104 . The portion of pressurized feedstock enters and travels through the feed spacer sheets of the spiral wound membrane element  100 . A portion of the pressurized feedstock leaves the feed spacer sheets and crosses the membrane sheet to form a permeate stream. The permeate stream flows through the permeate carrier sheets of the membrane leaves to be collected in the central tube  108 . The remaining pressurized feedstock within the feed spacer sheets forms the retentate stream, which continues to flow through the feed spacer sheets and exits the first spiral wound membrane element  100  at the downstream end  106 . 
         [0038]    A portion of the retentate will enter the second spiral wound membrane element  100   1  at the upstream end  104   1 . This portion of the retentate stream proceeds through the second spiral wound membrane element  100   1  forming a second permeate stream and a second retentate stream. The second permeate stream is collected in the central tube  108 . The second retentate stream exits the second spiral wound membrane element  100   1  at the down stream end  106   1  and at least a portion of the second retentate stream enters the third spiral wound membrane element  100   11  at the upstream end  104   11 . The third spiral wound membrane element  100   11  forms a third permeate stream and a third retentate stream. The first, second and third permeate streams are collected from the central tube  108  and the third retentate stream exits the down stream end  106   11  and collected by the outlet pipe  155  at the downstream end  154  of the pressure housing  150 . 
         [0039]    The portion of the pressurized feedstock that does not enter the first spiral wound membrane element  100  enters the annular space  160  at the upstream end  152  of the pressure housing  150  to provide bypass flow. Due to the orientation of the brine seal  10  the bypass flow will push or hold a portion of the wing  14  against the inner surface  156  of the pressure housing  150 . 
         [0040]    As the bypass flow proceeds along the helical path of the bypass flow channel  34 , the bypass flow is exposed to the pressure gradient between the annular space  160  and the outer layer  116  that develops along the longitudinal axis of the spiral wound membrane element  100 . A portion of the bypass flow will pass through the gap  32  and enter the outer layer  116 . When inside the outer layer  116 , this portion of the bypass flow will enter the feed spacer sheets and flow into the mixed layer  116 . This increases the fluid volume and pressure within the feed spacer sheets throughout the spiral wound membrane element  100 , which increases the transmembrane pressure and contributes to increase permeate production. 
         [0041]    Along the longitudinal axis of the pressure housing  150 , at the downstream end  106  of the spiral wound membrane element  100 , the bypass flow that does not pass through the gap  32  will mix with the retentate produced in the spiral wound membrane  100 . A portion of this mixture will enter the spiral wound membrane element  100   1  and a portion will enter the annular space  160  to create a bypass flow around the spiral wound membrane element  100   1 . This mixing of bypass flow and retentate flow will occur downstream of each spiral wound membrane element  100 ,  100   1 ,  100   11  within the pressure housing  150 . 
         [0042]    The wing  14  may face the bypass flow with the upstream surface  26  at an initial angle, relative to the top surface  22  (shown as the dotted line Y in  FIG. 2 ), for example 30° to 60°. When pushed by water flowing in the bypass stream, the upstream surface  26  can move to a greater angle, relative to the top surface  22 , for example between 45° and 90°. Alternatively, the upstream surface  26  can be bent downwards to a lower angle relative to the top surface  22 , for example between 5° and 45°. Through this range of movement, the wing  14  can accommodate dimensional differences in the outer diameter of various spiral wound membrane elements  100 , between different parts of a single membrane element  100 , or in the diameter of the inner surface  156  of various pressure housings  150 . When the wing  14  is in contact with the inner surface  156 , the spiral wound membrane element can be centered within the pressure housing  150 . 
         [0043]    Of particular interest to a horizontally arranged pressure housing  150 , the wing  14  may elevate the spiral wound membrane element  100  off the lower inner surface  156  of the pressure housing  150 . 
         [0044]    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.