High Rejection Spiral Wound Element with Protective Features - Patent application

Abstract

Printed spacer membrane elements have the unique advantage of being able to apply any pattern to the membrane surface to act as a feed spacer material. This is in contrast to conventional feed spacer mesh materials, which are uniform in thickness and density throughout the mesh. A more open feed space can be utilized, but the stress concentration is higher and the spacer material may come into contact with the opposing membrane leaf. This patent presents the concept of reducing damage to the membrane leaf by increasing the concentration of the printed pattern near the center tube where the stress concentration on the membrane leaf is greatest, orienting the membrane sheet prior to rolling to minimize damage from slippage during rolling, and moving the fold away from the first feature to minimize leakage at the insertion point.

Description

[Technical field]

[0001] Technical Field The present invention relates to membrane systems utilized in the separation of fluid components, and in particular to spiral wound membrane elements. [Background technology]

[0002] Background technology In cross-flow filtration, the feed fluid flows through the filter and is discharged at the other end, while a portion of the fluid is removed by filtration through the membrane surface parallel to the direction of fluid flow. Cross-flow filtration comes in a variety of forms, including plate-and-frame, cassette, hollow fiber, and spiral wound systems. Filtration modules in plate-and-frame, cassette, and spiral wound systems often rely on stacked membrane layers to provide spacing between adjacent filtration membrane layers, and this invention is primarily concerned with spiral wound membrane elements.

[0003] Spiral wound membrane filtration elements are known in the art that consist of a laminate structure made up of a membrane sheet sealed to or around a porous permeate carrier that forms a path for removal of fluid through the membrane to a central tube, longitudinally relative to the axis of the central tube, which laminate structure is spirally wrapped around the central tube and spaced from itself by a porous feed spacer to allow axial flow of fluid through the element from the feed end to the reject end of the element. Conventionally, a feed spacer mesh is used to allow the flow of feed water (a portion of which passes through the membrane) into the spiral wound element and to allow reject water to exit the element in a direction parallel to the central tube and axially along the element structure.

[0004] Improvements to spiral wound element designs are disclosed in U.S. Patent No. 6,632,357 to Barger et al., U.S. Patent No. 7,311,831 to Bradford et al., and in Australian (Patent No. 2014223490), Japanese (Patent No. 6499089), Chinese (CN No. 105163834B), Israeli (Patent No. 240883), and Korean (Patent No. 10-2196776) patents entitled "Improved Spiral Wound Element Construction" to Roderick et al., which replace the feed spacers with islands or protrusions printed, deposited, or embossed directly onto the inner or outer surface of the membrane or onto the permeate carrier. U.S. Patent No. 11,090,612 to Roderick et al. entitled "Graded spacers for filtration wound elements" describes the use of height graded spacer features used to modify the feed flow characteristics in spiral wound elements. U.S. patent application PCT / US17 / 62424 to Roderick et al., entitled "Interference Patterns for Spiral Wound Elements," describes patterns of spiral wound elements that keep the membrane feed space open but provide support for the membrane envelope bond area during winding. U.S. patent application PCT / US18 / 55671 to Roderick et al., entitled "Bridge Support and Reduced Feed Spacers for Spiral-Wound Elements," describes support features applied to the distal end (end furthest from the central tube) of the membrane envelope to provide support during bonding and winding of the spiral wound elements.U.S. Provisional Patent Application No. 63,051,738 to Herrington et al., entitled "Variable Velocity Patterns in Cross Flow Filtration," describes a support pattern that varies in size from the feed end to the reject end of the membrane feed space in a feed flow passage parallel to a central tube to control the velocity of the feed solution as the concentration of the feed solution increases from the feed end to the reject end of the spiral wound element. U.S. Patent No. 11,083,997 to Roderick et al. describes providing denser patterns at the feed and reject ends of the membrane feed space and more open patterns in the middle to avoid nesting of printed patterns during element manufacture. The above references may facilitate an understanding of the present invention and are incorporated herein by reference. Summary of the Invention [Means for solving the problem]

[0005] Summary of the Invention

[0006] An embodiment of the invention provides a spiral wound element that includes: (a) a central tube; (b) one or more membrane sheets, each membrane sheet folded upon itself at a fold line providing first and second membrane halves with inner surfaces facing each other, each folded bi-membrane sheet spirally wound around the central tube with the fold line proximal to the central tube; (c) each membrane sheet having a plurality of spacing features disposed on an inner surface of the first half; and (d) a crease protection element attached to an inner surface of the first half and an inner surface of the second half, the crease protection element extending from the crease a first distance on the first half and a second distance on the second half, the second distance being greater than the first distance. In some embodiments, a region of the first half beginning at the crease and extending a third distance does not have a spacing feature, and the second distance is greater than the third distance.

[0006] In some embodiments, the crease protection element includes an area of ​​the inner surface of the second half and the inner surface of the first half on which the same material as the material of the spacing feature is disposed. As used in this context, "the same material" means a material having the same relevant properties, such as suitable conditions for deposition on the membrane, mechanical properties, etc. It does not require identity in mechanical performance and properties not related to manufacturing in this application and context.

[0007] In some embodiments, the crease protection element comprises a tape having an adhesive on only one side, the adhesive side of the tape adjacent the inner surface of the first and second halves, and the tape has sufficient rigidity to prevent the spacing features on the opposing halves from damaging the halves underneath the tape. In some embodiments, the tape is impermeable to prevent the flow of fluids through the membrane that may cause damage near the crease. In some embodiments, the crease protection element may comprise a UV cured inkjet material, a hot melt polyolefin, a urethane, a decal, or other material that can be deposited on the active membrane surface. The thickness of the deposited crease protection material can be 0.010 inches, but more preferably is 0.002 inches or less. The material should be flexible to avoid cracking at the fold line of the crease. In some embodiments, the tape comprises a polyolefin or a polyester.

[0008] An embodiment of the invention provides a spiral wound element including: (a) a central tube; (b) one or more membrane sheets, each membrane sheet folded upon itself at a fold line providing first and second membrane halves with inner surfaces facing each other, each folded bi-membrane sheet spirally wound around the central tube with the fold line proximal to the central tube; (c) each membrane sheet having a plurality of spacing features disposed on an inner surface of the first half; and (d) an inner wound support element including a plurality of inner wound support features disposed on an inner surface of the first half, the inner wound support features being arranged at a density and the spacing features being arranged at a density lower than the density of the inner wound support features.

[0009] In some embodiments, the crease protection spacing features are arranged with a density parallel to the central tube and a density perpendicular to the central tube, where the density parallel to the central tube is constant and the density perpendicular to the central tube decreases with increasing distance from the crease.

[0010] An embodiment of the invention provides a method of manufacturing a spiral wound element, comprising: (a) providing a central tube; (b) providing one or more membrane sheets, each membrane sheet folded upon itself at a fold line providing first and second membrane halves with inner surfaces facing each other, each folded bi-membrane sheet spirally wound around the central tube with the fold line proximal to the central tube, each membrane sheet having a plurality of spacing features disposed on an inner surface of the first half; (c) providing a crease protection element attached to an inner surface of the first half and an inner surface of the second half, the crease protection element extending from the crease a first distance on the first half and a second distance on the second half, the second distance being greater than the first distance; (d) spiraling the one or more membrane sheets around the central tube. In some embodiments, the crease protection element comprises a polyurethane or epoxy-based adhesive disposed on the second surfaces of the first and second membrane halves and penetrating through the second surfaces into the corresponding membrane sheets. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is an exploded view of a spiral-wound membrane element. [Diagram 2] FIG. 2 is an exploded view of a partially assembled spiral wound membrane element. [Diagram 3] FIG. 11 is a view of the membrane sheet after operation and post-mortem showing damage due to increased winding tension near the central tube. [Figure 4] FIG. 2 is a longitudinal cross-sectional view of a spiral-wound membrane element. [Diagram 5]FIG. 13 is a diagram of a spiral wound element membrane sheet having a higher density of spacing features near the center tube to provide more support during manufacturing. [Figure 6] FIG. 13 is a diagram of a spiral wound element membrane sheet having a higher density of spacer wires near the center tube to provide more support during manufacturing. [Figure 7] FIG. 13 is a diagram of a spiral wound element membrane sheet with a higher density of spacer dots or dashes near the center tube to provide more support during manufacturing. [Figure 8] FIG. 13 is a diagram of a spiral wound element membrane sheet having a higher density of spacer features and lines or dashed or dotted lines near the center tube to provide more support during manufacturing. [Figure 9] FIG. 13 is a diagram of a spiral wound element membrane sheet with fold line support at the centerline. [Figure 10] FIG. 13 is a diagram of a spiral wound element membrane sheet having fold line support and support features on either side of the centerline that are offset from one another. [Figure 11] FIG. 13 is an end view of a spiral wound element having two membrane leaves prior to rolling, with fold protection at the apex of the membrane fold and with printed features on the membrane sheet adjacent to the central tube. [Figure 12] FIG. 13 is an end view of a spiral wound element with two membrane leaves before rolling, with fold protection at the apex of the membrane folds and with printed features on the membrane sheets on opposite sides of the central tube. [Figure 13] FIG. 1 is an end view of a spiral wound printed spacer element showing components of the film envelope. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] MODE FOR CARRYING OUT THEINVENTION AND INDUSTRIAL APPLICABILITY Feed spacers in spiral wound filtration elements are necessary to maintain a channel through which fluid can flow from the feed end to the reject end of the feed channel, but the design of the spacer also affects local flow rates, turbulence, stagnation zones, and other fluid flow conditions. Extruded mesh feed spacers have traditionally been used in membrane manufacturing due to their ease of integration in the manufacturing process, but by the nature of their design, many of the hydrodynamic properties depend on the thickness of the spacer. Traditional mesh spacers also provide uniform support properties in the feed space from the distal end of the central tube to the proximal end of the membrane sheet adjacent the central tube. Printed feed spacers allow for unique design properties not available with traditional extruded or woven mesh spacers. Their thickness and shape can be independently varied, resulting in a wide range of configurations that can be tailored to specific applications or the specific challenges found in building spiral wound membrane elements.

[0013] Cross-flow filtration, by its very nature, relies on a portion of the feed fluid passing through the filter to become part of the filtrate, thus creating a situation where the amount of feed fluid is constantly decreasing as it passes through the filter. The greater the portion of filtrate that is produced, the smaller the portion of the feed / concentrate fluid that continues to flow through the filter. As the fluid passes through the element, a portion of the fluid passes through the membrane. A simple modelling would be that if the flux through the membrane is constant, the flow of the feed solution will gradually decrease as it flows through the element from the feed end of the feed space to the reject end. In reality, the amount of fluid passing at any point along the feed flow path depends on the local flow conditions, the local concentration of solutes or suspended matter, and the local pressure, which in turn depends on the back pressure in the feed space as well as locally from the permeate side of the element.

[0014] During the manufacture of a spiral wound element, the permeate carrier material is attached to the central tube by tape or adhesive, the membrane envelope is placed adjacent to the permeate carrier, the flat sheet assembly is glued (to seal the permeate carrier envelope), and rotated around the central tube by a rotating mechanism such as a lathe. The central tube is captured or keyed to a lathe so that the lathe can rotate the central tube and wrap the membrane envelope and permeate carrier around the central tube. The torque on the central tube must be sufficient to wind the envelope until the entire envelope is wrapped around the central tube. Sufficient tension must be maintained on the membrane envelope so that the glue penetrates completely through the permeate carrier and contacts both membrane leaves to completely seal the membrane envelope. As the membrane envelope is wrapped around the central tube, the diameter of the element increases. However, the torque and force on the membrane envelope is greatest at the central tube, which has the smallest diameter. Higher forces proximal to the central tube result in higher forces on the membrane envelope, especially the feed space, during winding. One important advantage of the printed spacer technology is the ability to create more open feed spacer channels. However, one aspect of a more open feed space is the concentration of forces applied to the membrane envelope and thus the feed spacer, especially the feed spacer elements near the central tube. This can result in compression of the support pattern of the feed spacer into the membrane layer, causing damage to the active surface of the membrane. This results in loss of rejection performance of the finished element as well as increased flux due to active surface damage. The present invention provides a means to control stress concentration in the membrane envelope near the central tube by increasing the density of the feed space support features of the membrane envelope proximate to the central tube. Printed spacer technology is a new field, and increasing the support pattern density near the central tube to avoid damage to the active surface of the membrane was not anticipated in the prior art.

[0015] The feed shaping features employed can be any of a number of shapes including rounded dots, ellipses, rounded rods, lenticular shapes, elongated polygons, lines or other geometric shapes. Due to the shape of the features and the fact that the fluid must move around the outside of the features, the flow rate of the fluid will vary locally in the areas between the feed spacing features from the feed end to the reject end of the membrane element.

[0016] In spiral wound elements, the membrane leaf is folded at the centerline, which contacts the permeate carrier at the center tube before rolling. Crease protection has been described in the prior art. Crease protection typically consists of a tape applied along the width of the membrane sheet where it is folded. The prior art also discusses crease protection applied by printing or otherwise applying a polymer or other resin as the crease protection material. Crease protection is used to protect the membrane leaf where the crease line will be when folded to avoid damage from the crease line. Damage to the crease line without crease protection can result in rejection and flux loss of the finished membrane element. Crease protection can be uniquely utilized in printed spacer technology by extending the crease protection to the tops of the printed spacer features near the center tube to help avoid stress concentrations of the printed spacer features from damaging the active surface of the membrane on the unprinted side of the membrane leaf.

[0017] For printed features, the location of the fold line relative to the beginning of the printed feature turns out to be a key design feature that was not previously recognized. By placing the fold at a distance above the circumference of the core tube divided by the number of leaves, narrower membrane leaves can be created that have a reduced tendency to move away from the insertion point that leads to central tube leakage in elements that include conventional mesh. However, this distance must also be less than 1 inch to minimize leaf area where feed flow may be reduced due to narrowing of the channel height. By keeping the fold within this distance, improved element structures can be achieved with fewer insertion leaks that were not previously possible.

[0018] The inventors have found that using a common orientation where the printed features on one half of each folded membrane sheet orient each sheet with the side of the membrane containing the printed features closer to the central tube of the wound element, such that the final membrane element has the printed features facing away from the central tube, reduced defect generation is observed. During the manufacture of spiral wound elements, differential slip occurs where the side of the folded membrane sheet away from the central tube moves relative to the inner sheet. By minimizing the movement of features (e.g., element 70 in FIG. 5), damage to the opposing membrane sheets can be reduced and improved performance of the element can be achieved.

[0019] FIG. 1 is a schematic diagram of a conventional spiral wound membrane element prior to wrapping, showing the key elements of a conventional spiral wound membrane element 100. The permeate collection tube 12 has holes 14 therein through which permeate is collected from the permeate carrier 22. In manufacture, the membrane sheet 36 is a single continuous sheet that is folded about the centerline 30 and is composed of an inactive porous support layer, e.g., polysulfone, on one side 28 and an active polymer membrane layer on the other side 24 that is adhered or cast onto the support layer. In the assembled element, the active polymer membrane surface 24 is adjacent to the feed spacer mesh 26 and the inactive support layer 28 is adjacent to the permeate carrier 22. The feed solution 16 enters between the active polymer membrane surfaces 24 and flows through the open spaces in the feed spacer mesh 26. As the feed solution 16 flows through the feed spacer mesh 26, particles, ions, or species rejected by the membrane are rejected at the activated polymer membrane surface 24, and permeate molecules, e.g., water molecules, pass through the activated polymer membrane surface 24 and enter the porous permeate carrier 22. As the feed solution 16 moves along the activated polymer membrane surface 24, the concentration of substances rejected by the membrane increases due to loss of permeate in the bulk feed solution 16, and this concentrated liquid exits the reject end of the activated polymer membrane sheet 24 as rejected liquid 18. The permeate in the permeate carrier 22 flows from the distal end 34 of the permeate carrier 22 in the direction of the central tube 12, where the permeate enters the central tube 12 through the central tube inlet hole 14 and exits the central tube 12 as permeate 20. To avoid contamination of the permeate with the feed solution 16, the non-activated polymeric membrane layer 28 is adhesively sealed along a bond line 32 through the permeate carrier 22, thereby forming a sealed membrane envelope in which the only exit path for the permeate 20 is through the central tube 12. Typically, the width of the bond line 32 is 1-3 inches after the adhesive is compressed during the wrapping process.

[0020] In the existing art, a partially assembled spiral wound membrane element 200 is shown in FIG. 2. The membrane envelope 40 comprises a membrane sheet 36 folded at one end as described in connection with FIG. 1, and a permeate carrier 22 is placed between the membrane sheets and sealed along the edges with a suitable bond line 32 (FIG. 1). In the conventional design of the membrane element once wound, a feed spacer mesh 26 is placed adjacent to the envelope 40 so that the flow of the feed solution 16 flows between the layers of the membrane envelope 40, exposing all of the active polymer surfaces 24 of the membrane sheet to the feed solution. The permeate, or product, fluid is collected on the permeate carrier 22 within the membrane envelope 40 and spirals up to the central tube 12 where the product, or permeate, fluid is collected while the reject stream 18 exits the element. A single spiral wound element may comprise a single membrane envelope and feed spacer layer, or may comprise multiple membrane envelopes and feed spacer layers stacked and wound together to form the element.

[0021] FIG. 13 further defines the membrane element components of a spiral wound element utilizing printed spacer features 70. Membrane envelope 40 includes membrane sheet 36a, which is the active polymer membrane surface to which printed spacer features 70 are adhered. Membrane sheet 36b is the active polymer side of membrane sheet 36 to which printed spacer features 70 are not adhered. Membrane sheet 36 is folded at fold lines 30 and permeate carrier 22 is glued on three sides along adhesive lines 32 (FIG. 1) to form membrane envelope 40, thereby allowing permeate solution 20 (FIG. 1) to migrate to and exit central tube 12 as permeate solution 20. It is important that membrane envelope 40 is attached along adhesive lines 32 and that the adhesive is attached to the inactive sides of membrane sheets 36a and 36b on inactive membrane layer 28 (FIG. 1).

[0022] Figure 3 depicts the membrane element opened for inspection. The element in Figure 3 includes two membrane envelopes 40. The membrane envelopes 40 are wrapped around a central tube 12 and are adhesively attached at both ends to the central tube 12. Permeate fluid flows within the permeate carrier 22 (Figure 2) toward the central tube 12, as indicated by flow direction arrows 56. Autopsy reveals damage 58 to the membrane sheet 36 on the membrane envelopes 40 due to pressure buildup in the central tube 12 from wrapping during the manufacturing process.

[0023] Figure 4 defines the components of a spiral wound element in longitudinal cross section. The membrane envelope 40 is wound around the central tube 12. The number of turns for the finished outer diameter of the element is clearly defined by the diameter of the central tube 12 and the number of turns of the membrane envelope 40 around the central tube. The number of turns is also defined by the number of membrane envelopes 40 that make up the finished assembly. The equation defining the pressure P on the central tube is given by:

number

[0024] In many automated spiral wound element winding systems, tension is applied to the permeate carrier 22 to ensure uniform winding of the spiral wound element and to ensure that the appropriate tension is applied to ensure that the membrane envelope 40 is sealed at the bond line 32 (FIG. 1) when the glue needs to penetrate the permeate carrier 22 and form a seal against the non-active surface of the membrane sheet to seal the membrane envelope 40. As is evident from the equation, the tension on the membrane envelope 40 during winding is the major component of the pressure on the central tube 12, and the smaller the diameter of the central tube 12, the greater the pressure on the central tube 12. It is also evident that there is more compression in the first winding of the membrane envelope 40 around the central tube 12, and the greater the amount of winding, the greater the pressure on the central tube 12. As a result, the first winding of the membrane envelope 40 around the central tube 12 experiences the greatest compression force at the spacer element 70 (FIG. 5).

[0025] As an example, consider an 1812 spiral wound element. This element is 1.8 inches (45.7 mm) in diameter and 12 inches (304.8 mm) long. Calculation of the forces on the first turn is shown in the following chart, given the dimensions and force assumptions:

[0026] [Table 1]

[0027] As is evident from the example chart shown above, the tension load (T) applied to the permeate carrier must be decreased 10 to 1 as the winding occurs (to reduce 39.76 pounds to 4.41 pounds). This can be programmed into the tensioning mechanism of the automatic winding machine as the winding process occurs. Note that this is a non-linear decrease because the circumference of each turn increases as the winding occurs. In this example, 16 to 17 turns are required to achieve a finished element circumference of 1.8 inches (45.7 mm). To properly wind a spiral wound element with printed spacers, there is a desired winding pressure. Too much pressure can damage the membrane near the center tube 12, while too little pressure can prevent the glue from penetrating the permeate carrier 22 (Figure 2) and cause the finished diameter of the membrane element to be too small. To avoid damage to the polyamide membrane surface, the pounds per square inch concentration of a particular spacer element 70 should be less than 50 psi, preferably less than 25 psi. The optimum winding pressure varies for each size membrane element. Additionally, the force exerted on a particular spacer element is determined by the spacing density and surface area size of the individual spacer elements 70. An exemplary embodiment with 0.020 inch diameter spacing features spaced at 0.25 inch feature spacing is shown in the table above. Allowable winding tension will vary for each element size based on center tube diameter, finished element diameter, support feature spacing, support feature surface area, and the properties of the adhesive used to seal the membrane envelope 40.

[0028] FIG. 5 illustrates an exemplary embodiment of the invention whereby the feed spacer elements 70 are spaced closer together X as they approach the central fold line 30, which is the starting point for wrapping around the central tube 12 (FIG. 1) during manufacturing. The closer spacing of the spacer elements 70 can begin at a distance W from the center line 30 that is one-third the length of the printed half of the membrane sheet 36a. The distance W can also begin at a distance of one-quarter the distance from the fold line 30 to the full length of the printed half of the membrane sheet 36a, but can also begin at a distance of one-tenth or less from the fold line 30 to the full length of the printed half of the membrane sheet 36a. In preparation for manufacturing, the feed spacer elements 70 are printed or otherwise attached to only half of the active surface of the membrane sheet 36a. In an alternative embodiment of manufacturing, the spacer elements 70 are applied to the back side of the membrane sheet 36a. In an exemplary embodiment, the feed spacer elements 70 are applied to the active surface of the membrane sheet 36a. Following attachment of the feed spacer elements 70 to the membrane sheet 36a, the membrane sheet 36 is folded at the centerline 30 so that the active surfaces of the membrane sheets 36a and 36b face each other. The feed spacer elements 70 provide spacing between the active surfaces of the membrane sheets 36 to allow the feed fluid 16 to flow parallel to the centerline 30 between the active surfaces of the membrane sheets 36 and exit the feed space as reject solution 18. Reducing the spacing X of the spacer elements 70 toward the centerline 30 provides more support per unit area of ​​the membrane sheet 36 and can reduce damage to the membrane sheet 36 during the manufacturing and rolling process. The height of the spacer elements 70 can be reduced near the fold line 30, thereby avoiding a large concentrated force on the opposing unprinted surface of the membrane sheet 36b. The adhesive support features 64 can include a denser spacing configuration than the spacer elements 70, thereby providing support along the edges of the membrane sheet 36b from the adhesive that compresses the membrane sheet 36a along its edges and closes off the inlet and outlet feed channels.

[0029] 6 illustrates a variation of the feed spacing support feature 72 that provides more support along the feed solution flow path from the feed fluid 16 until it exits the feed space of the membrane sheet 36 as the reject solution 18. In this example, the support feature 72 comprises a continuous line. Because the support feature 72 is parallel to the feed solution flow direction, it does not present much resistance to the flow of the feed fluid.

[0030] 7 shows a variation of the feed spacing support feature 74 that provides more support along the feed solution flow path from the feed fluid 16 until it exits the feed space of the membrane sheet 36 as reject fluid 18. In this example, the support feature 74 includes dashed lines that may vary in segment length and spacing between segments. Because the support feature 74 is parallel to the feed solution flow direction, it does not present a significant resistance to the flow of the feed fluid.

[0031] An exemplary embodiment of the invention is shown in Figure 8. Feed spacing support features 76, 78, and 80 may include a combination of line segments which may include continuous lines, closely spaced dashed lines, and multiple dashed lines with widely spaced segments within the line. As previously mentioned, support features 76, 78, and 80 are parallel to the feed solution flow direction and therefore do not present significant resistance to the flow of the feed fluid.

[0032] An exemplary embodiment of the invention is shown in Figure 9 where the fold line support 94 includes printed raised patterns 100 that provide separation support when the membrane sheet 36 is folded at the centerline 30. In this configuration, the printed raised patterns 100 intersect at the fold line 30 and interfere with each other (meaning they do not nest when folded) to allow fluid to flow over and around the features of the printed raised patterns 100 parallel to the central tube 30. In this configuration, the printed raised patterns 100 can be used in combination with spacing features 70 to provide support proximal to the centerline 30.

[0033] In an exemplary embodiment of the invention shown in FIG. 10, spacer features 70 are on one side of centerline 30 and alternating spacer features 96 are on the other side of centerline 30. Spacing features 96 are proximal to central tube 12 and provide additional support near central tube 12. When the membrane sheet is folded at centerline 30, it is undesirable for spacing features 70 and 96 to interfere during rolling. To avoid interference, spacing features 70 and 96 are offset from one another by dimension Y. Additionally, spacing features 70 and 96 may be reduced in height near centerline 30 to help reduce stress concentrations proximal to centerline 30.

[0034] Many membrane elements use fold line support features to protect the fold lines from leakage caused by fold lines or deformation of the active surface of the membrane leaf. The fold line protection can take various forms, but is typically some form of adhesive tape. The tape protects the membrane sheet at the fold line from damage, or seals the membrane leaf from leakage if damaged during folding. The prior art also considers the use of printed materials as fold line protection materials. FIG. 11 shows an end view of the central tube 12 wrapped around the central tube 12 before the permeate carrier 22 is rolled into the membrane element. FIG. 11 depicts two membrane envelopes 40 wrapped around the central tube 12. However, any number of membrane envelopes 40 can be wrapped around the central tube 12 depending on the size of the diameter of the membrane element and the thinness of the membrane envelopes 40. In this illustration, the fluid to be treated enters the feed space 84, passes through the membrane sheet 36, and enters the permeate carrier 22. The permeate fluid flows through the permeate carrier 22 where it enters the central tube 12 through the fluid holes 14 and exits at the end of the central tube 12 .

[0035] FIG. 11 depicts the application of a fold line protection 82, either tape or printed material, starting adjacent to the support feature 70 at the end of the printed half of the membrane sheet 36 proximal to the central tube 12, continuing along the fold line 30 at the fold line, then extending onto the opposing unprinted surface of the membrane sheet 36 and over the top of the support feature 70 for an appropriate distance, typically 1 inch or less, to mitigate the concentration of force of the top of the support feature 70 impinging on the unprinted surface of the membrane sheet 36. The optimal distance of the fold line 30 from the beginning of the support feature 70 can also be defined as the distance determined by the outer diameter of the central tube 12 divided by the number of membrane envelopes 40 (FIG. 2) that make up the spiral wound membrane element 200 (FIG. 2). The optimal distance is also preferably less than 1 inch, since distances greater than this increase the area with altered flow characteristics due to the reduced channel height. As previously mentioned, the support features 70 can be reduced in height near the central tube 12. Additionally, the support features 70 can be spaced apart from 0 inches to a length Y that can be a distance less than the diameter of the central tube 12. In this configuration, the crease protection 82 can extend in length to cover a segment of the top of the support feature 70. In the embodiment shown in FIG. 11, the support feature 70 is applied or otherwise attached to the half of the membrane sheet 36 adjacent to the central tube 12 after manufacture. In this embodiment, the support feature 70 is geometrically open at the top of the support feature 70, which opens the flow path between the support features 70 and helps reduce fluid pressure loss near the central tube 12 from the feed end to the reject end of the completed membrane element. In the embodiment shown in FIG. 12, the support feature 70 can be applied to the membrane sheet 36b opposite the unprinted membrane sheet 36a that is wrapped adjacent to the central tube 12 and glued via the permeate carrier 22 that is glued to the central tube 12. In the embodiment shown in FIG. 10, support features 70 can be printed on both active surfaces (36a and 36b) of the membrane sheet 36, but the patterns 96 can be offset so that they do not interfere during rolling so that they pass each other.

[0036] During the winding operation, pressure bars 90 are often used to hold the membrane envelope 40 (FIG. 2) against the central tube 12 and to help maintain an even winding of the membrane envelope and to keep the membrane envelope free of wrinkles and creases during winding. The pressure bars 90 rotate freely on bearings and are rotated by friction with the membrane element during winding. Too much pressure bar pressure 92 can cause damage to the membrane sheet 36. For printed spacer elements, the pressure bar pressure desired to avoid damage to the membrane during winding should be as light as possible to avoid additional force concentration on the support features 70. In any event, the force exerted by the pressure bar 70 for a printed spacer element on a 40 inch long element should optimally be 16-18 pounds, but less than 25 pounds. To minimize load concentration on the support features 70, the pressure bar 90 should be as large a diameter as possible for a given size element, or multiple pressure bars can be utilized to distribute the load.

[0037] The crease protection element can also be constructed by applying a polyurethane or epoxy-based adhesive to the second surface in the crease area. The polyurethane or epoxy-based adhesive used should be selected to have the appropriate viscosity and wicking properties to penetrate the second surface and prevent flow through the penetrated area. An optional step of using a scraper or roller to smooth the adhesive can also be performed, which can also assist in the penetration of the adhesive into the second surface. Tape may be applied to cover the adhesive while the adhesive is still tacky and may remain on the assembled membrane element to simplify handling, stacking, and storage of the membrane sheets.

[0038] The present invention has been described in connection with various exemplary embodiments. It is to be understood that the above description is merely illustrative of the application of the principles of the invention, the scope of which is determined by the claims viewed in light of the specification. Other variations and modifications of the present invention will be apparent to those skilled in the art.

Claims

1. A spiral wound element, (a) a central tube; (b) one or more membrane sheets, each membrane sheet folded upon itself at a fold line providing first and second membrane halves with inner faces facing each other, each folded bi-membrane sheet spirally wound around the central tube with the fold line proximal to the central tube; (c) each membrane sheet having a plurality of spacing features disposed on the inner surface of the first half; (d) a crease protection element attached to the inner surface of the first half and the inner surface of the second half, the crease protection element extending from the crease a first distance on the first half and a second distance on the second half, the second distance being greater than the first distance; A spiral element containing

2. The element of claim 1 , wherein the crease protection element includes an area of ​​the inner surface of the second half and the inner surface of the first half having disposed thereon a material that is the same as a material of the spacing feature.

3. 2. The element of claim 1, wherein the crease protection element comprises a tape having adhesive on only one side, the adhesive side of the tape adjacent the inner surfaces of the first and second halves, and the tape is impermeable.

4. A spiral wound element, (a) a central tube; (b) one or more membrane sheets, each membrane sheet folded upon itself at a fold line providing first and second membrane halves with inner faces facing each other, each folded bi-membrane sheet spirally wound around the central tube with the fold line proximal to the central tube; (c) each membrane sheet having a plurality of spacing features disposed on the inner surface of the first half; (d) an inner turning support element including a plurality of inner turning support features disposed on the inner surface of the first half, the inner turning support features being arranged at a first density and the spacing features being arranged at a second density less than the first density; and A spiral element containing

5. 5. The element of claim 4, wherein the inner wrapping support features are arranged at a density parallel to the central tube and a density perpendicular to the central tube, the density parallel to the central tube being constant and the density perpendicular to the central tube decreasing with increasing distance from the fold.

6. 1. A method for manufacturing a spiral wound element, comprising the steps of: (a) providing a central tube; (b) providing one or more membrane sheets, each membrane sheet folded upon itself at a fold line providing first and second membrane halves with inner faces facing each other, each folded bi-membrane sheet spirally wound around the central tube with the fold line proximal to the central tube, each membrane sheet having a plurality of spacing features disposed on the inner surface of the first half; (c) providing a crease protection element attached to the inner surface of the first half and the inner surface of the second half, the crease protection element extending from the crease a first distance on the first half and a second distance on the second half, the second distance being greater than the first distance; (d) winding the one or more membrane sheets around the central tube; The method includes:

7. The element of claim 3 , wherein the tape comprises a polyolefin or a polyester.

8. The element of claim 1 , wherein a region of the first half beginning at the fold and extending a third distance is free of spacing features, and the second distance is greater than the third distance.

9. The method of claim 6 , wherein a region of the first half beginning at the fold and extending a third distance is free of spacing features, and the second distance is greater than the third distance.

10. The element of claim 1 , wherein the crease protection element comprises a polyurethane or epoxy based adhesive disposed on a second surface of the first and second membrane halves and penetrating through the second surface into the corresponding membrane sheet.

11. A spiral wound element, (a) a central tube; (b) one or more membrane sheets, each membrane sheet folded upon itself at a fold line providing first and second membrane halves with inner faces facing each other, each folded bi-membrane sheet spirally wound around the central tube with the fold line proximal to the central tube; (c) each membrane sheet having a plurality of spacing features disposed on the inner surface of the first half; (d) an inner turning support element including a plurality of inner turning support features disposed on the inner surface of the first half, the inner turning support features being arranged at a first density and the spacing features being arranged at a second density greater than the first density; and A spiral element containing

Images