High retention spiral wound element with protective features

Abstract

Printed spacer film elements offer the unique advantage of applying any pattern on the film surface to act as a supply spacer material. This is in contrast to conventional supply spacer web materials that are uniform in thickness and density across the web. More open supply spaces can be used but can also result in higher stress concentrations and where the spacer material is in contact with the opposing film leaf. This patent presents the concept for reducing damage on the film leaf by increasing the printed pattern concentration near the center tube where stress concentration is the greatest, orienting the film leaf to minimize damage from slippage during crimping before crimping, moving the fold away from the first feature to minimize leakage at the insertion point.

Description

TECHNICAL FIELD

[0001] The subject invention relates to a membrane system for fluid component separation, and in particular to a spiral wound membrane element. BACKGROUND

[0002] In cross-flow filtration, a feed fluid is flowed through a filter and released at the other end, while a portion of the fluid is removed by filtration through a membrane surface that is parallel to the direction of fluid flow. There are various forms of cross-flow filtration, including plate-and-frame systems, cartridge systems, hollow fiber systems, and spiral wound systems. Plate-and-frame filtration modules, cartridge filtration modules, and spiral wound filtration modules typically rely on stacked membrane layers that provide spacing between adjacent filtration membrane layers. The present invention is primarily directed to spiral wound membrane elements.

[0003] Spiral wound membrane filtration elements known in the art consist of a laminated structure that includes a membrane sheet sealed to or around a porous permeate carrier that creates a path for fluid that passes through the membrane to the central tube to be removed longitudinally relative to the axis of the central tube, while this laminated structure is spirally wound around the central tube and spaced from itself by a porous feed spacer, allowing fluid to flow axially through the element from the feed end to the reject end of the element. Traditionally, a feed spacer mesh is used to allow feed water to flow into the spiral wound element, and to allow waste water to exit the element in a direction that is parallel to the central tube and axial with respect to the element construction, a portion of the feed water will pass through the membrane.

[0004] Improvements to the design of spiral wound elements have been disclosed in Barger et al. U.S. Patent 6,632,357, Bradford et al. U.S. Patent 7,311,831, and Roderick et al. in Australia (2014223490), Japan (6499089), China (CN105163834B), Israel (240883), and Korea (10-2196776) entitled “Improved Spiral Wound Element Construction” which replace feed spacers with islands or protrusions that are printed, deposited, or embossed directly onto the inside or outside surface of the membrane or onto the permeate carrier. Roderick et al. U.S. Patent 11,090,612 entitled “Graded spacers for filtration wound elements” describes the use of highly graded spacer features for varying feed flow characteristics in spiral wound elements. Roderick et al. U.S. Patent Application PCT / US17 / 62424 entitled “Interference Patterns for Spiral Wound Elements” describes patterns in spiral wound elements that keep membrane feed spaces open but also provide support for the membrane envelope region during crimping. Roderick et al. U.S. Patent Application PCT / US18 / 55671 entitled “Bridge Support and Reduced Feed Spacers for Spiral-Wound Elements” describes support features that are applied to the far end of the membrane envelope (the end farthest from the center tube) to provide support during gluing and crimping of the spiral wound element. Herrington et al. U.S. Provisional Application No. 63,051,738 entitled “Variable Velocity Patterns in Cross Flow Filtration” describes support patterns that vary in size from the feed end to the rejection end of the membrane feed space in the feed flow path parallel to the center tube in order to control the velocity of the feed solution as the concentration of the feed solution increases from the feed end to the rejection end of the spiral wound element. Roderick et al. U.S. Patent 11,083,997 entitled describes denser patterns at the feed and rejection ends of the membrane feed space and more open patterns in the middle in order to avoid nesting of printed patterns during element manufacture.The above references can be helpful in understanding the present application and are incorporated herein by reference. SUMMARY

[0005] Embodiments of the present application provide a spiral wound element comprising: (a) a center tube; (b) one or more membranes, each membrane folded upon itself at a fold line, thereby providing a first membrane half and a second membrane half having inner surfaces facing each other, wherein each folded double membrane is spiral wound around the center tube with the fold line proximate to the center tube; (c) each membrane having a plurality of spacing features disposed on the inner surface of the first half; and (d) a fold protection element mounted with the inner surface of the first half and the inner surface of the second half, wherein the fold protection element extends a first distance on the first half from the fold and a second distance on the second half, wherein the second distance is greater than the first distance. In some embodiments, a region of the first half beginning at the fold and extending a third distance has no spacing features, and wherein the second distance is greater than the third distance.

[0006] In some embodiments, the fold protection element comprises the inner surface of the second half and a region of the inner surface of the first half on which is disposed a material identical to that of the spacing features. As used in this context, "identical material" refers to a material having identical relevant properties (e.g., conditions suitable for deposition on the membrane, mechanical properties, etc.). In this application and this context, it does not require identity of properties not relevant to mechanical performance or manufacture.

[0007] In some embodiments, the fold protection element comprises a tape having adhesive on one side only, wherein the adhesive side of the tape is adjacent to the inner surfaces of the first and second halves, wherein the hardness of the tape is sufficient to prevent the spacing features on the opposing half from damaging the half beneath the tape. In some embodiments, the tape is impermeable to prevent fluid flow through the membrane that can be damaged near the fold. In some embodiments, the fold protection element can comprise a UV-cured inkjet material, a hot melt polyolefin, a polyurethane, a decal, or other material that can be deposited on the active membrane surface. The thickness of the deposited fold protection material can be.010 inches thick, but is more preferably.002 inches or less. The material should be flexible to avoid cracking at the fold line creases. In some embodiments, the tape comprises a polyolefin or a polyester.

[0008] Embodiments of the invention provide a spiral wound element comprising: (a) a center tube; (b) one or more membranes each folded upon itself at a fold line to provide a first and second membrane half having inner surfaces facing each other, wherein each folded double membrane is spiral wound around the center tube with the fold line proximate to the center tube; (c) each membrane having a plurality of spacing features disposed on the inner surface of the first half; and (d) an inner wrap support element comprising a plurality of inner wrap support features disposed on the inner surface of the first half, wherein the inner wrap support features are disposed at a density and the spacing features are disposed at a density less than the density of the inner wrap support features.

[0009] In some embodiments, the fold protection spacing features are disposed at a density parallel to the center tube and a density orthogonal to the center tube, wherein the density parallel to the center tube is constant and wherein the density orthogonal to the center tube decreases as a distance from the fold increases.

[0010] Embodiments of the invention provide a method of producing a spiral wound element comprising: (a) providing a center tube; (b) providing one or more membranes each folded upon itself at a fold line to provide a first and second membrane half having inner surfaces facing each other, wherein each folded double membrane is spiral wound around the center tube with the fold line proximate to the center tube, each membrane having a plurality of spacing features disposed on the inner surface of the first half; (c) providing a fold protection element mounted with the inner surface of the first half and the inner surface of the second half, wherein the fold protection element extends a first distance on the first half and a second distance on the second half from the fold, wherein the second distance is greater than the first distance; (d) spiral winding the one or more membranes around the center tube. In some embodiments, the fold 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. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is an exploded view of a spiral wound membrane element.

[0012] Figure 2 is an exploded view of a partially assembled spiral wound membrane element.

[0013] Figure 3 is a view of a membrane observed after operation and inspection showing damage from increased crimp tension near the center tube.

[0014] Figure 4 is a longitudinal cross-sectional view of a spiral wound membrane element.

[0015] Figure 5 is a view of a spiral wound element membrane sheet with denser spacing features near the center tube to provide more support during manufacture.

[0016] Figure 6 is a view of a spiral wound element membrane sheet with denser spacing lines near the center tube to provide more support during manufacture.

[0017] Figure 7 is a view of a spiral wound element membrane sheet with denser spacing dot lines near the center tube to provide more support during manufacture.

[0018] Figure 8 is a view of a spiral wound element membrane sheet with denser spacing features and lines or dot lines near the center tube to provide more support during manufacture.

[0019] Figure 9 is a view of a spiral wound element membrane sheet with fold line supports at the center line.

[0020] Figure 10 is a view of a spiral wound element membrane sheet with fold line supports and support features offset from each other on either side of the center line.

[0021] Figure 11 is a view of the end of a spiral wound element with two membrane leaves before crimping, the spiral wound element having fold protection in the membrane at the apex of the fold and printed features on the membrane sheet adjacent to the center tube.

[0022] Figure 12 is a view of the end of a spiral wound element with two membrane leaves before crimping, the spiral wound element having fold protection in the membrane at the apex of the fold and printed features on the membrane sheet opposite the center tube.

[0023] Figure 13 is an end view of a spiral wound printed spacing element showing a membrane envelope. DETAILED DESCRIPTION

[0024] Supply spacers in spiral wound filter elements are needed to maintain the passage of fluid supply from the supply end to the retentate end of the feed channel, but the spacer design also impacts the local flow rates, turbulence, stagnation zones, and other fluid flow conditions. Extruded mesh supply spacers have traditionally been used in membrane manufacturing due to their ease of integration in the production process, but many of their hydrodynamic properties, depending on the nature of their design, are dependent on the thickness of the spacer. Conventional mesh spacers also provide uniform support characteristics in the supply space from the distal end of the center tube all the way to the proximal end of the membrane sheet near the center tube. Printed supply spacers enable unique design characteristics that cannot be obtained by conventional extruded or woven mesh spacers, as their thickness and geometry can be independently varied to produce a wide range of configurations that can be tailored to the specific application or specific challenges found in spiral wound membrane element construction.

[0025] Cross-flow filtration by its nature relies on a portion of the feed fluid passing through the filter and becoming part of the filtrate, thus creating a situation where the amount of feed fluid is constantly decreasing as the feed fluid passes through the filter. The higher the portion of filtrate produced, the lower the portion of feed / concentrate fluid that remains to flow through the filter. As fluid flows through the element, a portion of the fluid passes through the membrane. Modeling simply, a constant flux through the membrane produces a progressively decreasing feed solution flow rate as the feed solution flows from the supply end to the retentate end of the supply space in the element. In reality, the amount of fluid passing through any location along the feed flow path depends on the local flow conditions and the local concentration of solutes or suspended material, as well as the local pressure, which also depends on any back pressure in the supply space and the local back pressure from the permeate side of the element.

[0026] During the manufacture of a spiral wound element, the permeate carrier material is attached to the center tube by tape or bonding, 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 center tube by a rotating mechanism such as a lathe. The center tube is captured or keyed to the lathe so that the lathe can rotate the center tube and cause the membrane envelope and permeate carrier to wrap around the center tube. The torque on the center tube must be sufficient to curl the envelope until the entire envelope is wrapped around the center tube. Sufficient tension must be maintained in the membrane envelope to ensure that the glue penetrates completely through the permeate carrier and contacts both membrane leaves to ensure that the membrane envelope is completely sealed. As the membrane envelope is wrapped around the center tube, the diameter of the element increases. However, the torque and force on the membrane envelope is greatest at the point where the diameter is smallest at the center tube. During the curling, the greater forces near the center tube create greater forces on the membrane envelope, particularly the feed space. One of the key advantages of the printed spacer technology is that a more open feed spacer channel can be created. However, one aspect of a more open feed space is that the concentration of force applied to the membrane envelope and thus to the feed spacer is that higher forces are applied to the feed spacer element, particularly near the center tube. This can cause the feed spacer support pattern to compress into the membrane layers, causing damage to the active surface of the membrane. This will result in a loss of rejection performance of the finished element, as well as an increase in flux due to damage to the active surface. The present invention provides a means to control the stress concentration in the membrane envelope near the center tube by increasing the density of the feed space support features in the membrane envelope near the center tube. The printed spacer technology is a new field and this increase in support pattern density near the center tube is not anticipated in the prior art (to avoid damage to the active surface of the membrane leaves).

[0027] The feed forming features employed can have any of a variety of shapes, including dots, ovals, bars with rounded ends, bi-convex forms, stretched polygons, lines, or other geometric shapes. Due to the shape of these features and the fact that the fluid must traverse the outside of these features, the fluid flow rate will vary locally in the area between the feed spacer features from the feed end to the rejection end of the membrane element.

[0028] In spiral wound elements, the membrane leaves are folded at a centerline, where prior to crimping the centerline is in contact with the permeate carrier at the center tube. Fold protection is described in the prior art. Fold protection is typically composed of a tape that is applied along the width of the membrane sheet at the location of the fold. The prior art also discusses fold protection applied by printing or otherwise applying a polymer or other resin as a fold protection material. Fold protection is used to protect the membrane leaves at the location where the fold is created when folded to avoid damage from the fold. Damage from the fold in the absence of fold protection can result in both rejection and loss of flux in the finished membrane element. In printed spacer technology, fold protection can be uniquely used by extending the fold protection over the top of the printed spacer features near the center tube to help avoid stress concentrations in the printed spacer features that can damage the active surface of the membrane on the unprinted side of the membrane leaves.

[0029] For printed features, the positioning of the fold relative to the starting location of the printed feature was found to be an important design feature that was not previously appreciated. By placing the fold at a distance greater than the result of the core tube circumference divided by the number of leaves, a narrower membrane leaf can be created that has a reduced tendency to move away from the insertion point that would cause center tube leakage in a traditional contained element web. However, this distance should also be less than 1" to minimize the area of leaves that have reduced feed flow due to the narrower channel height. By keeping the fold within this distance range, improved element construction can be achieved with less insert leakage that was not previously possible.

[0030] Due to the printed feature being on one half of each folded membrane sheet, the inventors found that the incidence of defects observed using a common orientation was reduced where each membrane sheet was oriented with the printed side of the membrane closer to the center tube in the crimped element, resulting in a final membrane element with printed features pointing away from the center tube. During the manufacture of spiral wound elements, there is differential slippage where the side of the folded membrane sheet facing away from the center tube moves relative to the inner sheet. By minimizing the movement of the features (e.g., element 70 in Figure 5 , damage to the opposing membrane sheet can be reduced and improved element performance achieved.

[0031] Figure 1is a schematic of a conventional spiral wound membrane element prior to crimping, showing the important elements of a conventional spiral wound membrane element 100. The permeate collection tube 12 has holes 14 in the collection tube 12 where permeate fluid is collected from the permeate carrier 22. In manufacture, the membrane sheets 36 are a single continuous sheet folded at the centerline 30, including a non-active porous support layer (e.g., polysulfone) on one face 28 and an active polymer membrane layer on the other face 24 bonded or cast to the support layer. In assembly of the element, the active polymer membrane surface 24 is adjacent to the feed spacer web 26 and the non-active 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 web 26. As the feed solution 16 flows through the feed spacer web 26, particles, ions, or chemicals rejected by the membrane are trapped at the active polymer membrane surface 24 and molecules of the permeate fluid (e.g., water molecules) pass through the active polymer membrane surface 24 and into the porous permeate carrier 22. As the feed solution 16 passes along the active polymer membrane surface 24, the concentration of the materials rejected by the membrane increases due to the loss of permeate fluid from the bulk feed solution 16 and this concentrated fluid exits the active polymer membrane sheet 24 at the rejection end as the retentate solution 18. The permeate fluid in the permeate carrier 22 flows from the distal end 34 of the permeate carrier 22 in the direction of the center tube 12 where it passes through the center tube inlet hole 14 into the center tube 12 and exits the center tube 12 as the permeate solution 20. To avoid contamination of the permeate fluid by the feed solution 16, the non-active polymer membrane layer 28 is sealed along the bond line 32 with adhesive through the permeate carrier 22, thereby creating a sealed membrane envelope where the only exit path for the permeate solution 20 is through the center tube 12. Typically, the bond line 32 is 1" to 3" in width after the adhesive has been compressed during the crimping process.

[0032] Figure 2 A partially assembled spiral wound membrane element 200 is shown in FIG. 2. As described in connection with FIG. 1, the membrane envelope 40 includes membrane sheets 36 folded at one end with the permeate carrier 22 disposed between the membrane sheets and sealed along the edges with a suitable adhesive bond line 32 (FIG. 2). Figure 1 As described in connection with FIG. 1, the membrane envelope 40 includes membrane sheets 36 folded at one end with the permeate carrier 22 disposed between the membrane sheets and sealed along the edges with a suitable adhesive bond line 32 (FIG. 2). Figure 1 In a conventional design of a membrane element once crimped, the feed spacer web 26 is placed adjacent to the envelope 40 to allow the feed fluid 16 to flow between the membrane envelope 40 layers and expose all of the active polymer surfaces 24 of the membrane sheets to the feed fluid. The permeate or product fluid is collected in the permeate carrier 22 inside the membrane envelope 40 and spirals down to the center tube 12 where the product or permeate fluid is collected and the retentate stream 18 exits the element. A single spiral wound element can include a single membrane envelope and feed spacer layer or can include multiple membrane envelopes and feed spacer layers stacked and crimped together to form the element.

[0033] Figure 13 The membrane element component of the spiral wound element is further defined using the printed spacer feature 70. The membrane envelope 40 includes a membrane sheet 36a that is the active polymer film surface with the printed spacer feature 70 adhered to it. The membrane sheet 36b is the inactive polymer side of the membrane sheet 36 that does not have the printed spacer feature 70 adhered to it. The membrane sheet 36 is folded at the fold line 30 and has a permeate carrier 22 that is glued on three sides along the adhesive line 32 Figure 1 ) to create the membrane envelope 40 so that the permeate solution 20 Figure 1 ) can be transferred to the center tube 12 and discharged from the center tube 12 as the permeate solution 20. It is important to note that the membrane envelope 40 is joined along the adhesive line 32 and the adhesive is bonded to the inactive side of the membrane sheet 36a and 36b on the non-active film layer 28 Figure 1 ).

[0034] Figure 3 A membrane element is described that is open for inspection. Figure 3 The element includes two membrane envelopes 40. The membrane envelopes 40 are wrapped around the center tube 12 and adhesively joined to the center tube 12 at both ends. The permeate fluid flows in the permeate carrier 22 Figure 2 ) towards the center tube 12 as indicated by the flow direction arrow 56. Inspection reveals damage 58 on the membrane sheet 36 on the membrane envelope 40 due to increased pressure at the center tube 12 from the crimping during the manufacturing process.

[0035] Figure 4 The components of the spiral wound element in the longitudinal cross section are defined. The membrane envelope 40 is wrapped around the center tube 12. The number of wraps of the finished outer diameter of the element is defined by the diameter of the center tube 12 and the number of wraps of the membrane envelope 40 around the center tube. The number of wraps is also defined by the number of membrane envelopes 40 that make up the completed assembly. The equation that defines the pressure P applied to the center tube is given by the following:

[0036]

[0037] Where:

[0038] P is the uniform pressure on the center tube

[0039] T is the tension on the membrane envelope 40 during crimping

[0040] D is the diameter of the center tube

[0041] t is the thickness of the membrane envelope 40

[0042] N is the number of layers of the membrane envelope 40

[0043] i represents the current layer, and 0 represents the first layer.

[0044] In many automated spiral winding element coiling systems, tension is applied to the permeate carrier 22 to ensure uniform winding of the spiral winding element and to ensure sufficient tension is applied when the adhesive must penetrate the permeate carrier 22 and seal to the non-functional surface of the membrane to seal the membrane encapsulation 40, ensuring that the membrane encapsulation 40 is at the adhesive line 32 ( Figure 1 The membrane encapsulation 40 is sealed at the point of contact. It is evident from the equation that the tension on the membrane encapsulation 40 during coiling is a 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 significant compression on the first winding of the membrane encapsulation 40 around the central tube 12, and the greater the amount of winding, the greater the pressure on the central tube 12. Therefore, the first winding of the membrane encapsulation 40 around the central tube 12 affects the spacer element 70 (…). Figure 5 It has the maximum compressive force.

[0045] For example, consider an 1812 spiral wound element. This element has a diameter of 1.8 inches (45.7 mm) and a length of 12 inches (304.8 mm). The calculations of the forces on the first winding, based on the given dimensions and force assumptions, are shown in the table below:

[0046] Table 1 Force on the first winding of the membrane support.

[0047]

[0048]

[0049] As is evident from the table in the example shown above, as winding occurs, the applied tension load (T) on the permeate carrier must be reduced by 9 / 10 (to reduce 39.76 psi to 4.41 psi). This can be programmed into the tensioning mechanism on the automatic winding machine as the winding process occurs. It should be noted that this reduction is non-linear due to the increasing circumference of each winding as winding occurs. In this case, 16 to 17 windings are required to achieve a finished element circumference of 1.8 inches (45.7 mm). A desired winding pressure is required to properly wind the spiral winding element using the printed spacer. Excessive pressure may cause film damage near the center tube 12, and insufficient pressure may prevent the adhesive from penetrating the permeate carrier 22 ( Figure 2), and can also cause the finished diameter of the membrane element to be too small. To avoid damaging the polyamide membrane surface, the pound per square inch concentration on any particular spacing element 70 should be less than 50 psi and preferably less than 25 psi. The optimal crimping pressure will vary for each size of membrane element. The force on any particular spacing element will also be determined by the pitch density and surface area size of the individual spacing elements 70. An example embodiment is shown in the table above for spacing features with a diameter of.020 inches and a pitch between features of.25 inches. The allowable crimping tension will vary for each element size based on the diameter of the center tube, the diameter of the finished element, the support feature pitch, the support feature surface area, and the properties of the adhesive used to seal the membrane envelope 40.

[0050] Figure 5 An example embodiment of the present invention is shown where the supply spacing elements 70 are spaced closer X as they approach the center fold line 30, which is the point of origin around which the center tube 12 ( Figure 1 ) is wrapped during manufacture. The closer pitch of the spacing elements 70 can begin at a distance W from the center line 30 that is equivalent to one third of the length of the printed half of the membrane sheet 36a. The distance W can also begin at a distance from the fold line 30 that is equivalent to one fourth of the full length of the printed half of the membrane sheet 36a, but can also begin at a distance from the fold line 30 that is equivalent to one tenth of the full length of the printed half of the membrane sheet 36a or less. During preliminary manufacture, the supply spacing elements 70 are printed or otherwise attached on only one half of the active surface of the membrane sheet 36a. In alternative embodiments of manufacture, the spacing elements 70 are applied on the back side of the membrane sheet 36a. In the example embodiment, the supply spacing elements 70 are applied to the active surface of the membrane sheet 36a. After the supply spacing elements 70 are attached to the membrane sheet 36a, the membrane sheet 36 is folded at the center line 30 so that the active surfaces of the membrane sheets 36a and 36b face each other. The supply spacing elements 70 provide a pitch between the active surfaces of the membrane sheet 36 so that the supply fluid 16 flows between the active surfaces of the membrane sheet 36 parallel to the center line 30 and exits the supply space as the reject solution 18. By reducing the pitch X of the spacing elements 70 toward the center line 30, there is more support per unit area on the membrane sheet 36 to mitigate damage to the membrane sheet 36 during the manufacturing and crimping processes. The height of the spacing elements 70 can be reduced near the fold line 30 so that they do not exert a significant concentrated force on the opposite unprinted surface of the membrane sheet 36b. The adhesive support features 64 can constitute a denser spacing configuration than the spacing elements 70 so as to provide support along the edge of the membrane sheet 36b while preventing the adhesive from compressing the membrane sheet 36a along the edge and closing the inlet and outlet supply channels.

[0051] Figure 6The example embodiment of the present application shown illustrates a variation of feed spacing support features 72 that provide more support along the feed solution flow path of the feed fluid 16 up to the point where the feed fluid exits the feed space of the membrane sheet 36 as the retentate solution 18. In this case, the support features 72 comprise continuous lines. Because the support features 72 are parallel to the direction of feed solution flow, they do not represent a significant resistance to the flow of the feed fluid.

[0052] Figure 7 The example embodiment of the present application shown illustrates a variation of feed spacing support features 74 that provide more support along the feed solution flow path of the feed fluid 16 up to the point where the feed fluid exits the feed space of the membrane sheet 36 as the retentate solution 18. In this case, the support features 74 comprise dashed lines that can have line segments of various lengths and spacing between the line segments. Because the support features 74 are parallel to the direction of feed solution flow, they do not represent a significant resistance to the flow of the feed fluid.

[0053] Figure 8 The example embodiment of the present application shown in FIG. 6 illustrates a variation of feed spacing support features 76, 78, and 80 that can comprise a combination of line segments that can include continuous lines, dashed lines with narrow spacing, and multiple dashed lines with wider spacing between the line segments. As previously described, because the support features 76, 78, and 80 are parallel to the direction of feed solution flow, they do not represent a significant resistance to the flow of the feed fluid.

[0054] Figure 9 The example embodiment of the present application shown in FIG. 7 illustrates a variation of the fold line support 94 that comprises 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 cross over at the fold line 30 and interfere with each other (i.e., do not nest when folded) so that fluid can flow parallel to the center tube 30 around and between the features of the printed raised patterns 100. In this configuration, the printed raised patterns 100 can be used in conjunction with the spacing features 70 to provide support near the centerline 30.

[0055] In Figure 10 The example embodiment of the present application shown in FIG. 8 illustrates the spacing features 70 on one side of the centerline 30 and the alternating spacing features 96 on the other side of the centerline 30. The spacing features 96 are located near the center tube 12 to provide additional support near the center tube 12. It is undesirable for the spacing features 70 and 96 to interfere during crimping when the membrane sheet is folded at the centerline 30. To avoid interference, the spacing features 70 and 96 are offset from each other by a dimension Y. Additionally, the spacing support features 70 and 96 can be located at a lower height near the centerline 30 to help reduce stress concentrations near the centerline 30.

[0056] Many membrane elements use fold line support features to protect the fold lines from leakage caused by creases or deformation of the membrane leaf's working surface. Fold line protection can take many forms, but is typically a type of tape. The tape protects the membrane at the crease from damage, or, if damaged during folding, seals the membrane leaf to prevent leakage. The use of printed materials as fold line protection materials has also been discussed in the prior art. Figure 11 An end view of the central tube 12 before it is wound into the membrane element is shown, with the permeate carrier 22 wrapped around the central tube 12. Figure 11 Two membrane encapsulations 40 are depicted wrapped around the central tube 12. However, depending on the diameter of the membrane element and the thinness of the membrane encapsulations 40, any number of membrane encapsulations 40 can be wrapped around the central tube 12. In this view, the fluid to be processed enters the supply space 84 and then passes through the membrane 36 and into the permeate carrier 22. The permeate flows within the permeate carrier 22, where it enters the central tube 12 via the fluid orifice 14 and exits from the end of the central tube 12.

[0057] Figure 11 The application of the fold line protection section 82 (tape or printed material) is represented by a fold line protection section that begins at the end of the printed half of the diaphragm 36 near the center tube 12, adjacent to the support feature 70, continues along the fold line 30, and then extends to the unprinted opposing surface of the diaphragm 36 and extends an appropriate distance (typically 1 inch or less) on top of the support feature 70 to reduce force concentration at the top of the support feature 70 where the support feature impacts the unprinted surface of the diaphragm 36. The optimal distance of the fold line 30 from the starting position of the support feature 70 can also be defined as the outer diameter of the center tube 12 divided by the diameter of the spirally wound film element 200. Figure 2 ) of film encapsulation 40 ( Figure 2 The distance is determined by a fixed quantity. The optimal distance is also preferably less than 1", because distances greater than this optimal distance increase the area with altered flow characteristics due to the reduced channel height. As previously mentioned, the height of the support features 70 can be relatively small near the central tube 12. Additionally, the support features 70 can be spaced 0 inches to a length Y, which may be a distance smaller than the diameter of the central tube 12. In this configuration, the folded protective portion 82 can extend to cover the section at the top of the support features 70. Figure 11 In the illustrated embodiment, support features 70 are applied or otherwise incorporated into the half of the membrane 36 that will be adjacent to the central tube 12 after manufacturing. In this embodiment, the support features 70 will be geometrically open at the top, which will open the flow path between the support features 70 and help reduce fluid pressure loss from the supply end to the choke end of the finished membrane element near the central tube 12. Figure 12In the illustrated embodiment, support features 70 can be applied to the membrane sheet 36b opposite the unprinted membrane sheet 36a that is glued across the permeate carrier 22 that is rolled and glued to the center tube 12 near the center tube 12. In Figure 10 In the illustrated embodiment, support features 70 can be printed on both active surfaces of the membrane sheets 36 (36a and 36b), but the patterns 96 can be offset to ensure that they do not interfere with each other as they slide past each other during rolling.

[0058] During the rolling operation, a pressure bar 90 is typically used to hold the membrane envelope 40 Figure 2 ) against the center tube 12 to help maintain uniform rolling of the membrane envelope to ensure that the membrane envelope does not develop wrinkles or creases during rolling. The pressure bar 90 can be free to rotate on bearings and rely on friction with the membrane element to rotate during rolling. If the pressure bar pressure 92 is too great, it can damage the membrane sheets 36. For printed spacer elements, the desired pressure bar pressure to avoid damage to the membrane sheets during rolling should be as light as possible to avoid exerting additional force concentrations on the support features 70. In any case, the force exerted by the pressure bar 70 on a 40 inch long element should be best at 16-18 pounds, but less than 25 pounds for printed spacer elements. To minimize the load concentration on the support features 70, the diameter of the pressure bar 90 should be as large as possible for a given size element, or multiple pressure bars can be used to share the load.

[0059] The fold protection element can also be constructed by applying a polyurethane or epoxy based adhesive on the second surface of the fold region. The polyurethane or epoxy based adhesive used should be selected to have the appropriate viscosity and wicking properties to penetrate into the second surface to prevent flow through the area penetrated by the polyurethane or epoxy based adhesive. An optional step of using a squeegee or roller to flatten the adhesive can also be performed that can also assist the penetration of the adhesive into the second surface. To simplify the handling, stacking and storage of the membrane sheets while the adhesive is still tacky, a tape can be applied to cover the adhesive and can remain in the assembled membrane element.

[0060] The application has been described in conjunction with the various example embodiments. It should be understood that the foregoing description is merely illustrative of the application and the scope of the application should be determined with reference to the claims as considered in light of the specification. Other variations and modifications of the application will be apparent to those of ordinary skill and can be made without departing from the scope of the application.

Claims

1. A spiral wound element, the spiral wound element comprising: (a) a center tube; (b) one or more membranes, each membrane folded on itself at a fold line, thereby providing a first membrane half and a second membrane half having inner surfaces facing each other, wherein each folded double membrane is spiral wound around the center tube with the fold line close to the center tube; (c) each membrane having a plurality of spacing features disposed on the inner surface of the first membrane half; and (d) a fold protection element mounted with the inner surface of the first membrane half and the inner surface of the second membrane half, wherein the fold protection element extends a first distance on the first membrane half from the fold line and a second distance on the second membrane half beyond a top of at least some of the plurality of spacing features, wherein the second distance is greater than the first distance.

2. The spiral-wound element of claim 1, wherein, The fold protection element comprises a region of the inner surface of the second membrane half and the inner surface of the first membrane half on which a material is disposed that is the same material as the spacing features.

3. The spiral-wound element of claim 1 wherein, The fold protection element comprises a tape having adhesive on one side only, wherein the adhesive side of the tape is adjacent to the inner surfaces of the first membrane half and the second membrane half, wherein the tape is impermeable.

4. The spiral-wound element of claim 3 wherein, The tape comprises a polyolefin or a polyester.

5. The spiral-wound element of claim 1 wherein, A region of the first membrane half beginning at the fold line and extending a third distance has no spacing features, and wherein the second distance is greater than the third distance.

6. A method of producing a spiral wound element, the method comprising: (a) providing a center tube; (b) providing one or more membranes, each membrane folded on itself at a fold line, thereby providing a first membrane half and a second membrane half having inner surfaces facing each other, wherein each folded double membrane is spiral wound around the center tube with the fold line close to the center tube, each membrane having a plurality of spacing features disposed on the inner surface of the first membrane half; (c) providing a fold protection element mounted with the inner surface of the first membrane half and the inner surface of the second membrane half, wherein the fold protection element extends a first distance on the first membrane half from the fold line and a second distance on the second membrane half beyond a top of at least some of the plurality of spacing features, wherein the second distance is greater than the first distance; (d) spiral winding the one or more membranes around the center tube.

7. The method of claim 6, wherein, A region of the first membrane half beginning at the fold line and extending a third distance has no spacing features, and wherein the second distance is greater than the third distance.

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