Abstract:
The present disclosure describes an axial bypass sleeve for use with a spiral wound membrane element. The axial bypass sleeve has a protrusion and an opening that defines a flow path to provide fluid flow communication through the axial bypass sleeve. In use, the axial bypass sleeve is wrapped around a spiral wound membrane element and both are placed in a pressure housing. A pressurized feedstock is introduced into the pressure housing. A portion of the pressurized feedstock flows through the spiral wound membrane element to produce a permeate stream and a retentate stream. A portion of the pressurized feed stock flows around the spiral wound membrane element, called bypass flow. The protrusion extends into the annular space to restrict the bypass flow. A portion of the bypass flow passes through the opening and enters into the spiral wound membrane element to increase permeate production.

Description:
[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 tight tolerance 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]    A common solution to low flow in the annular space is to direct a portion of the feedstock flow into 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]    An axial bypass sleeve for use with spiral wound membrane elements are disclosed in the detailed description below. Part of the axial bypass sleeve protrudes away from the axial bypass sleeve. Another part of the axial bypass sleeve allows fluid communication through the axial bypass sleeve. 
         [0010]    The axial bypass sleeve has a top surface and a bottom surface. The axial bypass sleeve can be wrapped around a spiral wound membrane element with the bottom surface in proximity to the spiral wound membrane element. The axial bypass sleeve comprises a protrusion and one or more holes that define a flow path. The protrusion can be integral with the axial bypass controls sleeve or the protrusion can be a second component. The holes allow fluid communication between the top surface and the bottom surface of the axial bypass sleeve. 
         [0011]    In operation, the axial bypass sleeve is wrapped around a spiral wound membrane element. The spiral wound membrane element and axial bypass sleeve are placed 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 will contribute to a pressurized stream of bypass flow through an annular space between the inner surface of the pressure housing and the outer surface of the spiral wound membrane element. The protrusion restricts the bypass flow at a downstream location within the annular space, which modifies the pressure of the bypass flow. 
         [0012]    Due to the pressure decrease along the length of the feed spacer sheets, a pressure gradient can develop between the annular space and within the feed spacer sheets. Without being bound by theory, this pressure gradient may cause pressurized feedstock within the bypass flow to flow through the flow path and into the feed spacer sheets of the spiral wound membrane element. This 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 permeate production may increase along the length of the spiral wound membrane element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1A  is a top-plan view of an axial bypass sleeve. 
           [0014]      FIG. 1B  is a partial cut-away, side view schematic drawing of an axial bypass sleeve wrapped around a spiral wound membrane element. 
           [0015]      FIG. 2A  a top-plan view of a second axial bypass sleeve. 
           [0016]      FIG. 2B  is a partial cut-away, side view schematic drawing of the second axial bypass sleeve wrapped around a spiral wound membrane element. 
           [0017]      FIG. 3  is a top-plan view of a third axial bypass sleeve. 
           [0018]      FIG. 4  is a schematic cut away drawing of three spiral wound membrane elements located within a pressure housing, each spiral wound membrane wrapped by the second axial bypass sleeve. 
           [0019]      FIG. 5  cross-sectional view taken along line  5 - 5   1  of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    An axial bypass sleeve for use with a spiral wound membrane element is described below. The axial bypass sleeve has a top or outside surface and a bottom or inside surface. A part of the sleeve protrudes away from the top surface of the axial bypass sleeve and another part of the sleeve is open between the top and bottom surfaces. A protrusion can be integral with the axial bypass sleeve. Alternatively, the protrusion can be a separate component that is positioned proximal, upon or below the rest of the axial bypass sleeve. 
         [0021]    The  FIGS. 1 to 5  depict an axial bypass sleeve for use with spiral wound membrane elements, as further described below. The axial bypass sleeve comprises a protrusion and at least one opening to allow fluid communication through the axial bypass sleeve. 
         [0022]      FIG. 1A  depicts an axial bypass sleeve  10 . The axial bypass sleeve  10  is generally planar and comprises a protrusion  14  and at least one access port  16 . As will be described below, the planar axial bypass sleeve  10  can be wrapped around a spiral wound membrane element  100  and can form a cylinder-like body. The axial bypass sleeve  10  has a first edge  18 , a second edge  20 , a first side  22  and a second side  24 . The protrusion  14  is shown as a region that begins at the dotted line in  FIG. 1 , and ends at, or near, the second edge  20 . The access ports  16  are shown as a series of perforations through the axial bypass sleeve  10  and positioned between the first edge  18  and the protrusion  14 . The access ports  16  can be any shape or design that permits fluid communication through the axial bypass sleeve  10 . Optionally, there can be a greater density of access ports  16  proximal to the protrusion  14 . 
         [0023]      FIG. 1B  shows the axial bypass sleeve  10  wrapped around a spiral wound membrane element  100 . The protrusion  14  is shown as a region of gradually increased thickness. A variety of different approaches can be used to increase the thickness of the protrusion  14 . For example, during the manufacture of the axial bypass sleeve  10 , more materials can be incorporated to form a protrusion  14  that is integral with the axial bypass sleeve  10  with a predetermined thickness. The final thickness of the protrusion  14  can be decreased, if desired, by cutting away material from the protrusion  14  so the protrusion  14  has a desired thickness. Optionally, the protrusion  14  can be added to the axial bypass sleeve  10  after manufacture by one or more additional parts, for example, a ring inserted upon, or below the axial bypass sleeve  10  to form the protrusion  14 . 
         [0024]    The cut away section of  FIG. 1B  depicts the spiral wound membrane element  100  underneath the axial bypass sleeve  10 . The axial bypass sleeve  10  is wrapped by fixing the first side  22  and the second side  24  together. The first side  22  and the second side  24  can be fixed together by suitable fixation methods that may include, thermal bonding, ultrasonic welding, adhesives and the like. The axial bypass sleeve  10  may be tension wrapped around the spiral membrane element  100  and the fixing of the first side  22  and the second side  24  maintains that tension. The tension wrapping of the axial bypass sleeve  10  may prevent or decrease telescopic unraveling or compression of the spiral wound membrane element  100 , as is known to occur under standard operational conditions. 
         [0025]    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 axial bypass sleeve  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 . 
         [0026]    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. 
         [0027]    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 . 
         [0028]    Adjacent the outer layer  116  is the axial bypass sleeve  10 . Optionally, a cage (not shown) can be positioned between the outer layer  116  and the axial bypass sleeve  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 . 
         [0029]      FIG. 2A  depicts a second axial bypass sleeve  210 . The second axial bypass sleeve  210  is generally planar and comprises a protrusion in the form of tabs  214 , and access ports  216  that are associated with each tab  214  (as shown in  FIG. 2B ). As described further below, the access ports  216  are formed by the cutting of the tabs  214  from the second axial bypass sleeve  210 . Optionally, the access ports  216  are holes that are cut through the axial bypass sleeve  210  and the tabs  214  are fixed to the axial bypass sleeve  210 . 
         [0030]    The second axial bypass sleeve  210  comprises a first edge  218 , a second edge  220 , a first side  222  and a second side  224 . In  FIG. 2 , the tabs  214  are shown as generally rectangular in shape but other shapes may also be used. 
         [0031]    The tabs  214  can be formed by two cut lines  226  of equal length through the axial bypass sleeve  210 . The two cut lines  226  each have a first end  228  and a second end  230 . The two cut lines  226  are cut parallel to the first and second sides  222 ,  224 . An upstream cut line  232  is cut perpendicular to the two cut lines  226  and forms provides an edgewise connection, also referred to as the upstream edge, between the two first ends  228 . The upstream cut line  232  is parallel to the first and second edges  218 ,  220  and the upstream cut line  232  is closest to the first edge  218  of the axial bypass sleeve  210 . The tabs  214  also have a joined side  234  that is integral with the axial bypass sleeve  210  and opposite and parallel to the third cut line  220 . The joined side  234  is closest to the second edge  220 . The joined side  234  provides a pivot point that allows the tabs  214  to move to an extended position. Optionally, the joined side  234  may be indented or creased to facilitate pivoting. 
         [0032]    For the purposes of this disclosure, in the extended position, the tab  214  is not aligned with the planar surface of the axial bypass sleeve  210  and an upstream edge of the tab  214 , formed by the upstream cut line  232 , extends away from the planar surface. In the extended position, the tabs  214  open the access ports  216  and allow fluid communication through the access ports  216 . The pivotal connection affords the tab  214  a wide range of positions, as indicated by an angle ranging from about 1° to about 180° relative to the planar body of the axial bypass sleeve  210 . Optionally, while in the extended position the tab  214  is at an angle ranging from about 1° to about 90°, or from about 1° to about 45°, or from about 1° to about 30°. All of these degree ranges are relative to the planar body of the axial bypass sleeve  210 . When the tabs  214  are in the extended position, the associated access ports  216  are open to provide fluid communication across the planar body. 
         [0033]      FIG. 2B  depicts the second axial bypass sleeve  210  wrapped around a spiral wound membrane element  100 . The tabs  214  are shown in the extended position. 
         [0034]      FIG. 3  depicts a third axial bypass sleeve  310 . The third axial bypass sleeve  310  is very similar to the axial bypass sleeve  210 , described above. The third axial bypass sleeve  310  is generally planar and comprises tabs  314  and access ports  316 . The third axial bypass sleeve  310  has a first edge  318 , a second edge  320 , a first side  322  and a second side  324 . The tabs  314  are made by a combination of cut lines and holes made through the third axial bypass sleeve  310 . Optionally, the access ports  316  are holes that are cut through the axial bypass sleeve  310  and the tabs  314  are fixed to the axial bypass sleeve  310 . 
         [0035]    The tab  314  has two primary holes  328  cut through the third axial bypass sleeve  310 . 
         [0036]    An upstream cut line  332  connects the two primary holes  328 . The primary holes  328  have an upstream side  338  that is closest to the first edge  318  and a downstream side  340  that is closest to the second edge  320 . Each primary hole  328  has a first lateral side  342  closest to the first side  322  and a second lateral side  344  closest to the second side  324 . The upstream cut line  332  connects the upstream sides  338  of the two primary holes  328 . Between the two primary holes  328  and closer to the second edge  320 , two secondary holes  330  are cut through the third axial bypass sleeve  310 . A secondary cut line  336  joins the downstream side  340  of each primary hole  328  with the secondary holes  330 . 
         [0037]    Between the two secondary holes  330  is a joined side  334  that provides a pivot point that allows the tabs  314  to move through a range of the extended position. In the extended position, the primary holes  328  and the secondary holes  330  contribute to the access port  316 , which provides fluid communication through the planar body of the third axial bypass control sleeve  310 . 
         [0038]    In comparison to the tabs  214 , the tabs  314  generally have a more curvilinear shape with fewer corners, creases and edges, which are a source of tight tolerance. Optionally, a variety of other methods may be used to create a similar curvilinear shape, or other shapes of the tabs  314  that do not act as a source of tight tolerance. 
         [0039]    Optionally, the axial bypass sleeves  10 ,  210 ,  310  can be cylindrical, such as a heat shrink tube or other forms of deformable sleeves that can be positioned around the spiral wound membrane element  100 , as described below. 
         [0040]    The axial bypass sleeves  10 ,  210 ,  310  can be constructed of a number of suitable materials that preferably meet food contact standards. Examples of suitable materials include polypropylene, low-density polyethylene, high-density polyethylene and porous plastics. Optionally, the axial bypass sleeves  10 ,  210 ,  310  can be constructed of metal or alloys, such as  300  series stainless steel. Further, the axial bypass sleeves  10 ,  210 ,  310  can also be constructed of metal or alloys that are encapsulated within another suitable material, for example, aluminum encapsulated in polypropylene. 
         [0041]    The number of tabs  214 ,  314  can vary depending upon the size of the axial bypass sleeve  210 ,  310 , which may depend upon the size of the spiral wound membrane element  100  used in a given application. Further, there may be a longitudinal distribution of tabs  214 ,  314  such that a smaller number, or a greater number, of tabs  214 ,  314  are positioned towards the first edge  218 ,  318  in comparison to the second edge  220 ,  320 . Preferably, a greater number of tabs  214 ,  314  are positioned towards the second edge  220 ,  320 . 
         [0042]      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 upstream end  152  and the downstream end  154  define a longitudinal axis of the pressure housing  150 , shown as line X in  FIG. 4 . The pressure housing  150  is tubular in shape with an inner surface  156  and an outer surface  158 . 
         [0043]    Each spiral wound membrane element  100 ,  100   1 ,  100   11  is shown wrapped by a second axial bypass sleeve  210 ,  210   1 ,  210   11 . Any of the axial bypass sleeves  10 ,  210  and  310  are suitable to be positioned around a spiral wound membrane element  100 . The three spiral wound membrane elements  100 ,  100   1 ,  100   11  may be connected in series and share a common central tube  108 . Although only three spiral wound membrane elements  100  are shown in  FIG. 4 , there can be four to eight, or more, spiral wound membrane elements  100  within a given pressure housing  150 . 
         [0044]      FIG. 4  shows the tabs  214  in an extended position and extending through the annular space  160  in contact with the inner surface  156  of the pressure housing  150 .  FIG. 5  depicts the cross-sectional area of the annular space  160  through which bypass flow is restricted by the tabs  214 . For clarity,  FIG. 5  only shows the next set of tabs  214  seen through the section of line  5 - 5   1 . 
         [0045]    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 crosses the membrane sheet to form a permeate stream. The permeate stream flows through the permeate carrier sheets 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 . 
         [0046]    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 . 
         [0047]    A portion of the pressurized feedstock 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 axial bypass sleeve  10 ,  210 ,  310  the bypass flow is restricted by the protrusion  14  or the tabs  214 ,  314 . The restriction helps to maintain the pressure of the bypass flow through the annular space  160 . With specific reference to the second and third axial bypass sleeves  210 ,  310  the bypass flow pushes, and holds, the tabs  214 ,  314  in the extended position. While in the extended position, a fluid path is created between the annular space  160 , through the access ports  216 ,  316  and into the outer layer  116  of the spiral wound membrane element  100 . Based upon the pressure gradient between the annular space  160  and the outer layer  116 , a portion of the bypass flow will pass through the access ports  16 ,  216 ,  316  and enter the outer layer  116 . When inside the outer layer  116 , the bypass flow will enter the feed spacer sheets and flow into the mixed layer  110 . This increases the flow rate and pressure within the feed spacer sheets through out the spiral wound membrane element  100 , which increases the transmembrane pressure and contributes to increase the permeate production. 
         [0048]    Along the longitudinal axis of the pressure housing  150 , at or past the downstream end  106  of the spiral wound membrane element  100 , the bypass flow that does not pass through the access ports  16 ,  216 ,  316  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 . 
         [0049]    Optionally, the tabs  214 ,  316  can be in the extended position prior to loading the spiral wound membrane element  100  into the pressure housing  150 . For example, the tabs  214 ,  314  may be opened to an approximate 45° angle relative to the planar body of the axial bypass sleeve  210 ,  310 . Of particular interest to a horizontally oriented pressure housing  150 , the tabs  214 ,  314  that are positioned on the bottom of the spiral wound membrane element  100  may elevate the spiral wound membrane element  100  off the lower inner surface  156  of the pressure housing  150 . The elevation of the spiral wound membrane element  100  may ease the loading of the spiral wound membrane element  100 . 
         [0050]    The pressurized bypass flow may push the tabs  214 ,  314  into contact with the inner surface  158  of the pressure housing  150 . This contact may assist in the centering of the spiral wound membrane element and cause a more even distribution of bypass flow around the entire circumference of the spiral wound membrane element  100 , independent of the orientation of the pressure housing  150 . 
         [0051]    The range of movement through the extended position allows the tabs  214 ,  314  to accommodate dimensional differences between the outer diameter of various spiral wound membrane elements  100  and diameters of the inner surface  156  of various pressure housings  150 . 
         [0052]    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.