High-rejection spiral wound element with protective features

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, a feed fluid flows through the filter and is discharged at the other end, while a portion of the fluid is removed by filtration through membrane surfaces parallel to the direction of fluid flow. Cross-flow filtration comes in various forms, including plate-and-frame systems, cassette systems, hollow fiber systems, 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, consisting of a laminate structure constructed of a membrane sheet sealed to or around a porous permeate carrier that forms a path for fluid removal through the membrane to a central tube, longitudinally relative to the axis of the central tube, the laminate structure 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 design 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 (2014223490), Japanese (6499089), Chinese (CN 105163834B), Israeli (240883), and Korean (10-2196776) patents to Roderick et al. entitled "Improved Spiral Wound Element Construction," which replace feed spacers with islands or protrusions printed, deposited, or embossed directly onto the inner or outer membrane surface 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 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 for spiral wound elements that keep membrane feed spaces open but provide support for the membrane envelope adhesive 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 farthest from the central tube) of the membrane envelope to provide support during adhesive and winding of the spiral wound element.U.S. Provisional Patent Application No. 63,051,738 to Herrington et al., entitled "Variable Velocity Patterns in Cross Flow Filtration," describes support patterns that vary in size from the feed end to the reject end of a membrane feed space within a feed flow channel parallel to a central tube to control the velocity of the feed solution as its concentration increases from the feed end to the reject end of a 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 a membrane feed space and more open patterns in the middle to avoid nesting of printed patterns during element fabrication. 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] Embodiments of the present invention provide 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 to provide first and second membrane halves with inner surfaces facing each other, each folded double 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 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. In some embodiments, a region of the first half beginning at the crease and extending a third distance is free of spacing features, and the second distance is greater than the third distance.

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

[0007] In some embodiments, the crease protection element comprises a tape having adhesive on only one side, the adhesive side of the tape adjacent the inner surface of the first and second halves, and the tape is sufficiently rigid to prevent spacing features on the opposing half from damaging the half underneath the tape. In some embodiments, the tape is impermeable to prevent fluid flow through the membrane, which could cause damage near the crease. In some embodiments, the crease protection element may comprise a UV-curable 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 is more preferably 0.002 inches or less. The material should be flexible to prevent cracking at the fold line. In some embodiments, the tape comprises polyolefin or polyester.

[0008] An embodiment of the present 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 to provide first and second membrane halves with inner surfaces facing each other, and each folded double 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; and (d) an inner wound support element including a plurality of inner wound support features disposed on the inner surface of the first half, wherein the inner wound support features are arranged at a density and the spacing features are arranged at a density lower than the density of the inner wound support features.

[0009] In some embodiments, the fold protection spacing features are arranged at 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 fold.

[0010] An embodiment of the present invention provides a method for manufacturing a spiral wound element, including: (a) providing a central tube; (b) providing one or more membrane sheets, each membrane sheet folded upon itself at a fold line to provide first and second membrane halves with inner surfaces facing each other, each folded double 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 fold protection element attached to the inner surface of the first half and the inner surface of the second half, the fold protection element extending from the fold 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) spirally winding 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 explanation of the drawings]

[0011] [Figure 1] FIG. 2 is an exploded view of a spiral-wound membrane element. [Figure 2] FIG. 2 is an exploded view of a partially assembled spiral wound membrane element. [Figure 3] FIG. 11 is a view of the membrane sheet after operation and post-mortem examination 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. [Figure 5]FIG. 10 is a diagram of a spiral wound element membrane sheet with a higher density of spacing features near the center tube to provide more support during manufacturing. [Figure 6] FIG. 10 is a diagram of a spiral wound element membrane sheet with a higher density of spacer wires near the center tube to provide more support during manufacturing. [Figure 7] FIG. 10 is a diagram of a spiral wound element membrane sheet with a higher density of spacer dotted or dashed lines near the center tube to provide more support during manufacturing. [Figure 8] FIG. 10 is a diagram of a spiral wound element membrane sheet with 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. 10 is a diagram of a spiral wound element membrane sheet with fold line support at the centerline. [Figure 10] FIG. 10 is a diagram of a spiral wound element membrane sheet with fold line support and support features on either side of the centerline that are offset from one another. [Figure 11] FIG. 10 is an end view of a spiral wound element with two membrane leaves before 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. 10 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. 10 is an end view of a spiral wound printed spacer element showing components of the film envelope. DETAILED DESCRIPTION OF THE INVENTION

[0012] MODES FOR CARRYING OUT THE INVENTION AND INDUSTRIAL APPLICABILITY Feed spacers in spiral-wound filtration elements are necessary to maintain a fluid flow channel from the feed end to the reject end of the feed channel, but the spacer design also affects local flow velocity, 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 into the manufacturing process, but by the nature of their design, many of their hydrodynamic properties depend on the spacer's thickness. Traditional mesh spacers also provide uniform support 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 offer unique design features 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 encountered in constructing spiral-wound membrane elements.

[0013] Crossflow filtration, by its very nature, relies on a portion of the feed fluid passing through the filter to become part of the filtrate, creating a situation in which 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 feed / concentrate fluid that continues through the filter. As fluid passes through the element, a portion of the fluid passes through the membrane. A simple model suggests that for a constant flux through the membrane, 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 practice, 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 solids, and the local pressure, which in turn depends on the backpressure within the feed space and locally on the permeate side of the element.

[0014] During the manufacture of spiral-wound elements, the permeate carrier material is attached to the central tube by tape or adhesive, the membrane envelope is placed adjacent to the permeate carrier, and 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 into a lathe so that the lathe can rotate the central tube and wrap the membrane envelope and permeate carrier around it. The torque on the central tube must be sufficient to wrap 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, completely sealing 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 are greatest at the smallest diameter central tube. Higher forces near the central tube result in higher forces being applied to the membrane envelope, particularly the feed space, during winding. One significant advantage of 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, particularly to the feed spacer elements near the central tube. This can result in compression of the feed spacer support pattern into the membrane layer, potentially causing damage to the membrane's active surface. This can lead to a loss of rejection performance in the finished element, as well as increased flux due to active surface damage. The present invention provides a means to control stress concentrations in the membrane envelope near the central tube by increasing the density of the feed space support features in the membrane envelope near 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 membrane's active surface 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 travel around the outside of the features, the fluid flow rate will vary locally in the regions between the feed spacing features from the feed end to the reject end of the membrane element.

[0016] In spiral-wound elements, the membrane leaves are folded at their centerlines, which contact the permeate carrier at the central tube before winding. Crease protection has been described in the prior art. Crease protection typically consists of 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 a crease protection material. Crease protection is used to protect the membrane leaves at the crease line when folded to avoid damage from the crease. Without crease protection, damage to the crease line could result in rejection or flux loss in 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 central tube to help prevent stress concentrations from 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 has been found to be a previously unrecognized important design feature. By placing the fold at a distance greater than 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, which leads to central tube leaks in elements containing conventional mesh. However, this distance also needs to be less than 1 inch to minimize leaf area where feed flow could be reduced due to a narrowing of the channel height. By keeping the fold within this distance, improved element structures with fewer insertion leaks can be achieved that were previously not possible.

[0018] The inventors have found that using a common orientation in which printed features on one half of each folded membrane sheet orient each sheet with the side of the membrane containing the printed features closest to the central tube of the wound element, resulting in a final membrane element with printed features facing away from the central tube, reduces the observed occurrence of defects. 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. Minimizing the movement of features (e.g., element 70 in FIG. 5) can reduce damage to the opposing membrane sheet and improve element performance.

[0019] FIG. 1 is a schematic diagram of a conventional spiral-wound membrane element before 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 folded about the centerline 30 and is composed of an inactive porous support layer, such as polysulfone, on one side 28 and an active polymer membrane layer on the other side 24, 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 chemical 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 the 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 within the permeate carrier 22 flows from the distal end 34 of the permeate carrier 22 toward the central tube 12, where the permeate enters the central tube 12 through the central tube inlet holes 14 and exits the central tube 12 as permeate 20. To avoid contamination of the permeate with the feed solution 16, the inactive polymer membrane layer 28 is adhesively sealed along a bond line 32 through the permeate carrier 22, thereby forming a sealed membrane envelope whose only exit path for the permeate 20 is through the central tube 12. Typically, the width of the bond line 32 is 1 to 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. Membrane envelopes 40 comprise membrane sheets 36 folded at one end, as described in connection with FIG. 1, with permeate carriers 22 positioned between the membrane sheets and sealed along the edges with appropriate adhesive lines 32 (FIG. 1). In conventional designs of once-wound membrane elements, a feed spacer mesh 26 is positioned adjacent to the envelopes 40, allowing the flow of feed solution 16 to flow between the membrane envelopes 40 and expose all of the active polymer surfaces 24 of the membrane sheets to the feed solution. The permeate, or product, fluid is collected on the permeate carriers 22 within the membrane envelopes 40 and spirals 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 into and exit central tube 12 as permeate solution 20. It is important that membrane envelope 40 is attached along adhesive lines 32, with the adhesive being attached to the inactive sides of membrane sheets 36a and 36b on inactive membrane layer 28 (FIG. 1).

[0022] Figure 3 depicts a 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, to which both ends are adhesively attached. Permeate fluid flows within the permeate carrier 22 (Figure 2) toward the central tube 12, as indicated by flow direction arrow 56. Inspection revealed damage 58 to the membrane sheet 36 on the membrane envelopes 40 due to pressure buildup in the central tube 12 caused by 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 sealing of the membrane envelope 40 at the bond line 32 (FIG. 1) when the glue must penetrate the permeate carrier 22 to 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 applied to the membrane envelope 40 during winding is a major component of the pressure exerted on the central tube 12; the smaller the diameter of the central tube 12, the greater the pressure exerted on the central tube 12. It is also evident that there is more compression in the first wrap of the membrane envelope 40 around the central tube 12, and the greater the amount of winding, the greater the pressure exerted on the central tube 12. As a result, the first wrap of the membrane envelope 40 around the central tube 12 experiences the greatest compressive 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. Calculating the force 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 reduced 10 to 1 as the winding proceeds (from 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 nonlinear reduction because the circumference of each wrap increases as the winding proceeds. In this example, 16 to 17 wraps 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), resulting in a membrane element with a finished diameter that is too small. To avoid damage to the polyamide membrane surface, the pounds per square inch (T) 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 is shown in the table above for spacing features of 0.020 inch diameter spaced at 0.25 inch feature spacing. The allowable winding tension varies for each element size based on the 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 present invention, whereby the feed spacer elements 70 are spaced closer together X as they approach the center 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 centerline 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 one-quarter the way from the fold line 30 relative to the entire length of the printed half of the membrane sheet 36a, but can also begin at a distance one-tenth or less from the fold line 30 relative to the entire length of the printed half of the membrane sheet 36a. During 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 backside of the membrane sheet 36a. In the 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 about 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, reducing damage to the membrane sheet 36 during the manufacturing and winding processes. The height of the spacer elements 70 can be reduced near the fold line 30 to avoid exerting 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 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 reject solution 18. In this example, the support feature 72 comprises a continuous line. Because the support feature 72 is parallel to the direction of feed solution flow, it does not present significant resistance to the flow of the feed fluid.

[0030] The exemplary embodiment of the invention shown in Figure 7 illustrates 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 liquid 18. In this example, the support feature 74 comprises dashed lines that can vary in segment length and spacing between segments. Because the support feature 74 is parallel to the direction of feed solution flow, it does not present 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 that 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 direction of feed solution flow and therefore do not present significant resistance to feed fluid flow.

[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 centerline 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 the exemplary embodiment of the invention shown in FIG. 10 , spacer features 70 are present on one side of centerline 30 and alternating spacer features 96 are present 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 have a reduced 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 leaks caused by fold lines or deformation of the active surface of the membrane leaves. The fold line protection can take various forms but is typically some form of adhesive tape. The tape protects the membrane sheets from damage at the fold lines or seals the membrane leaves from leaks if damaged during folding. The prior art also considers the use of printed materials as fold line protection materials. Figure 11 shows an end view of the central tube 12 with the permeate carrier 22 wrapped around it before being wrapped into the membrane element. Figure 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 diameter of the membrane element and the thickness 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 the end of the central tube 12 .

[0035] FIG. 11 depicts the application of fold line protection 82, either tape or printed material, at the end of the printed half of the membrane sheet 36 proximal to the central tube 12, starting adjacent to the support feature 70, continuing along the fold line 30 at the fold line, and then extending onto the opposing unprinted surface of the membrane sheet 36, extending 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 ) comprising the spiral wound membrane element 200 ( FIG. 2 ). The optimal distance is also preferably less than 1 inch, because 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, which can be a distance less than the diameter of the central tube 12. In this configuration, the fold 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 features 70 are applied or otherwise attached to the half of the membrane sheet 36 adjacent to the central tube 12 after fabrication. In this embodiment, the support features 70 are geometrically open at the top of the support features 70, which opens up flow paths 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 features 70 can be applied to the membrane sheet 36b opposite the unprinted membrane sheet 36a, which is wrapped adjacent to the central tube 12 and glued to the central tube 12 via the permeate carrier 22. 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 pass through each other and do not interfere during rolling.

[0036] During the winding process, a pressure bar 90 is often used to hold the membrane envelope 40 (FIG. 2) against the central tube 12, helping to maintain an even winding of the membrane envelope and preventing wrinkles and creases in the membrane envelope during winding. The pressure bar 90 rotates freely on bearings and is 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 desired pressure bar pressure 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 case, the force exerted by the pressure bar 70 for 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 in 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 appropriate viscosity and wicking properties so that it penetrates the second surface and prevents 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. While the adhesive is still tacky, tape can be applied to cover the adhesive and left 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 foregoing description is merely illustrative of the application of the principles of the invention, the scope of which is to be 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 canal; (b) one or more membrane sheets, each membrane sheet folded at a fold line to provide first and second membrane halves with inner surfaces facing each other, each folded membrane sheet spirally wound around the central tube with the fold line at the central tube, each membrane sheet having a plurality of spacing features disposed on the inner surface of the first membrane half; (c) a crease protection element attached to the inner surface of the first membrane half and the inner surface of the second membrane half, the crease protection element extending from the crease a first distance on the first membrane half and a second distance on the second membrane 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 comprises an area of ​​the inner surface of the second membrane half and the inner surface of the first membrane half.

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 being adjacent to the inner surfaces of the first and second membrane halves, and the tape being impermeable to prevent the flow of fluids.

4. 1. 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 at a fold line to provide first and second membrane halves with inner surfaces facing each other, each folded membrane sheet spirally wound around the central tube with the fold line at the central tube, each membrane sheet having a plurality of spacing features disposed on the inner surface of the first membrane half; (c) providing a crease protection element attached to the inner surface of the first membrane half and the inner surface of the second membrane half, the crease protection element extending from the crease a first distance on the first membrane half and a second distance on the second membrane half, the second distance being greater than the first distance; (d) spirally winding the one or more membrane sheets around the central tube; A method comprising:

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

6. 2. The element of claim 1, wherein a region of the first membrane half beginning at the fold and extending a third distance does not have spacing features, and the second distance is greater than the third distance.

7. 5. The method of claim 4, wherein a region of the first membrane half beginning at the fold and extending a third distance does not have spacing features, and the second distance is greater than the third distance.

8. The element of claim 1 , wherein 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.

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