Non-nesting, non-deformation pattern for spiral wound elements

Abstract

Embodiments of the invention provide for the deposition of spacer elements for helically wound elements that prevent nesting of adjacent spacer layers and clogging of the feed space during element winding.

Description

[0001] This application is a divisional application of the invention patent application with the application date of April 12, 2018, application number 201880025621.1, and invention name “Non-nested, non-deformed pattern for spirally wound elements”. Technical Field

[0002] The subject invention relates to a permeable membrane system for separation of fluid components, and in particular to a spirally wound permeable membrane element. Background Art

[0003] Spiral wound membrane filter elements known in the art include a laminate structure comprising a membrane sheet sealed to or surrounding a porous permeate carrier that creates a path for fluid removal through the membrane to a central tube, while the laminate is spirally wound around the central tube and separated from itself by a porous feed spacer, thereby allowing fluid to flow axially through the element. While this feed spacer must maintain open and uniform axial flow between the laminate, the feed spacer is also a source of flow restriction and pressure drop within the axial flow channel and also presents a flow restriction area and contact with the membrane that is significantly susceptible to membrane fouling due to biological growth, scaling, and particle capture.

[0004] Improvements to the design of spiral wound elements have been disclosed by Barger et al. and Bradford et al. that replace the feed spacers with islands or protrusions deposited or embossed directly onto the outside or active surface of the membrane. This configuration is advantageous in that it maintains spacing for axial flow through the element while minimizing obstruction within the flow channel. The configuration also eliminates the porous feed spacer as a separate component, thereby simplifying the manufacture of the element. Patent publication number US 2016-0008763-A1, entitled "Improved Spiral Wound Element Construction," teaches applying a printed pattern on the back side of the active surface of the membrane or directly on the surface of the permeate carrier.

[0005] The following references (each of which is incorporated herein by reference) may be helpful in understanding the present invention: US3962096; US4476022; US4756835; US4834881; US4855058; US4902417; US4861487; US6632357; and US application 2016-0008763-A1. Summary of the invention

[0006] Embodiments of the present invention provide a membrane for use in a spirally wound permeable membrane system, the system comprising a membrane having spacing features arranged on its surface, wherein the spacing features are configured such that when spirally wound, the spacing features prevent nesting of spacers. The spacing features may be arranged such that the spacing features overlap when the membrane is spirally wound.

[0007] In some embodiments, the spacing features may include a plurality of substantially parallel line segments spaced apart from one another at uneven spacing distances. A first subset of the plurality of line segments may be spaced apart from one another at uneven spacing distances to form a pattern, and wherein other subsets of the plurality of line segments include repetitions of the pattern. The first subset may extend over at least 6 inches measured from a first line segment to a last line segment. The first subset may extend over at least 12 inches measured from a first line segment to a last line segment. The variation in spacing may be less than 15% of an average distance between adjacent spacing features.

[0008] In some embodiments, the spaced features may include a plurality of line segments that are spaced apart from one another and oriented non-parallel to one another at non-uniform angles. A first subset of the plurality of line segments may be oriented at non-uniform angles relative to one another to form a pattern, and wherein other subsets of the plurality of line segments include repetitions of the pattern. The pattern may extend to at least 6 inches measured from a first line segment to a last line segment. The pattern may extend to at least 12 inches measured from a first line segment to a last line segment. The variation in angle may be less than 15% of the average angle of the features relative to the pattern.

[0009] In some embodiments, the spacing features may include a first plurality of line segments that are parallel to each other and arranged in a first grid on the surface, and a second plurality of line segments that are parallel to each other and arranged in a second grid on the surface, wherein line segments in the first plurality of line segments do not intersect line segments in the second plurality of line segments, and wherein line segments in the first plurality of line segments are arranged at angles other than zero degrees with line segments in the second plurality of line segments. The angle may be at least 1 degree but not more than 45 degrees. The angle may be 45 degrees. Each spacing feature in the first plurality of line segments may be separated from an adjacent spacing feature in the first plurality of line segments by no more than a quarter inch. Each spacing feature in the first plurality of line segments may be separated from an adjacent spacing feature in the first plurality of line segments by no more than a tenth of an inch.

[0010] In some embodiments, the spacing features may include a plurality of curvilinear segments spaced apart from one another by non-uniform spacing distances as measured along at least one path traversing the spacing features.

[0011] In some embodiments, the spacing features can be configured such that when the membrane is fabricated into the permeable membrane system, the spacing features at least partially support those on an adjacent layer.

[0012] In some embodiments, the spacing features may be disposed adjacent to an edge of the film.

[0013] In some embodiments, the spacing features may be disposed over the entire surface of the film.

[0014] In some embodiments, the spacing features are more closely spaced near the edge of the film than in the portion of the film away from the edges. The edge of the film can be defined as an area within three inches of the edge of the film. The edge of the film can be defined as an area within one inch of the edge of the film.

[0015] In some embodiments, the spacing features may be made from one or more of thermoplastics, reactive polymers, waxes, or resins; deposited directly onto the film surface.

[0016] In some embodiments, the spacing features may be made of one or more of high temperature thermoplastics, metals, or ceramics; formed separate from the film surface, and then adhered to the film surface.

[0017] An embodiment of the present invention provides a permeable membrane system comprising a membrane as described herein.

[0018] An embodiment of the present invention provides a water treatment device comprising one or more permeable membrane systems as described herein.

[0019] An embodiment of the present invention provides a method for treating water, the method comprising providing a permeable membrane system as described herein, and passing water to be treated through the permeable membrane system.

[0020]

[0013] Embodiments of the present invention provide a method of making a permeable membrane system, the method comprising providing a membrane as described herein, and spirally winding the membrane. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is an illustration of an array of parallel line segments with varying spacing to prevent nesting during winding of a spirally wound element.

[0022] Figure 2 is an illustration of an array of wire segments at various angles to prevent nesting during winding of a spirally wound element.

[0023] Figure 3 A. Figure 3 B. Figure 3C includes illustrations of several configurations of closely spaced patterns designed to prevent nesting during winding of the spirally wound element.

[0024] Figure 4 A. Figure 4 B. Figure 4 C. Figure 4 D includes illustrations of additional example feature embodiments. DETAILED DESCRIPTION

[0025] Compared to the supply spacing mesh, embossing or depositing features onto the surface of the membrane, or onto the permeate carrier sheet of the spiral wound element, or into the permeate carrier sheet to provide spacing between adjacent membranes can provide several advantages, including more open flow channels, lower pressure drop, reduced scaling, and the ability to produce thinner supply spaces than is practical using a mesh. The membrane itself can be made of a polypropylene porous layer, bonded to a polysulfone porous layer, wherein the membrane polymer material is cast onto the polysulfone layer. Various other materials and methods can be used to make the membrane. Membranes that provide different degrees of removal efficiency can be made. Microfiltration membranes can typically remove materials as small as about 0.1 microns, typically bacteria and protozoa, or other contaminants of this size in industrial applications. Ultrafiltration membranes can have pore sizes as small as about 0.01 microns, and can, for example, remove viruses from a fluid source. Nanofiltration membranes can have pore sizes small enough to remove divalent ions, but will allow monovalent ions to pass, such as sodium and chloride. An example of an application of nanofiltration is water softening, for example to remove calcium carbonate. Reverse osmosis is typically the smallest pore size and is sufficient to remove monovalent salts typically used in desalination applications. Various configurations of these spacer features have been disclosed by Barrier et al. and Bradford et al., and PCT / US14 / 18813 (incorporated herein by reference) discloses various methods and materials suitable for depositing spacer features on membranes. These methods and materials can be used to implement embodiments of the present invention.

[0026] Compared to conventional mesh feed spacers, spacer features that are embossed or deposited directly on the membrane surface present a difference during the manufacture of spiral wound elements. Spacer features can be made from a wider variety of shapes and patterns than can be achieved using extruded or woven mesh materials, and their spacing and orientation can likewise vary widely. During typical manufacture of a spiral wound filter element using embossed or deposited features, a membrane sheet with features on one half of the sheet is folded into a leaf, with one side containing the features and the other side blank; the two faces (now facing each other) are the active membrane surfaces. The spacers allow the feed solution to flow between the active membrane surfaces so that all of the active surface of the membrane is available for filtration. Interleaved on the outside of the two membrane sheets are permeate carrier sheets. Fluid flowing through the active membrane sheets comes into contact with the permeate carrier, and the fluid in the permeate carrier is transported to the center tube. An adhesive is applied before rolling up around the center tube to form the finished element. A line of adhesive is deposited from one end of the central tube onto the back (inactive) side of the folded membrane sheet or onto the permeate carrier web above the sheet, around three sides of the perimeter of the sheet, and back into contact with the central tube. The line of glue serves to seal the permeate carrier and isolate it from the feed / exhaust streams. This process is repeated on each sheet used to form the element.

[0027] The printed features are particularly important in the inlet and outlet regions of the spiral wound element, where the areas between these features form spaces through which feed water flows into the element and through which discharge water flows out of the element, and where they must resist the forces generated by compression of the viscous adhesive lines during element rolling. If the printed features were simply a regularly spaced, repeating pattern of lines, line segments, or columns, they could allow adjacent membrane sheets to deform into the feed space and block the flow path during rolling due to the forces on the adhesive. Similarly, some patterns and spacings of features can allow entire adjacent layers of membrane, permeate carrier, and adhesive to deform to nest between the features.

[0028] Exemplary embodiments of the present invention can prevent clogging of the feed channel during spiral wound element manufacturing by providing feature spacing and patterns that prevent collapse and deformation of the membrane and adjacent layers. Additionally, by providing additional support to the membrane during rolling and preventing nesting, exemplary embodiments of the present invention can prevent clogging of the feed channel without requiring changes to the standard process for rolling spiral wound elements.

[0029] An advantage of embodiments of the present invention is that reducing blockage of the feed space between layers of a spiral wound element reduces resistance to flow and therefore reduces pressure drop from the inlet to the outlet of the element, which improves filtration efficiency and reduces energy requirements.

[0030] Exemplary embodiments of the present invention may also provide the advantage of promoting more uniform flow throughout the element and preventing potential fouling due to non-uniform flow. If certain sections of the feed space are unevenly blocked (which may be caused by the nesting of adjacent layers between conventional features), then non-uniform flow may occur within the element. It is well known that non-uniform flow can form stagnation points that allow biofouling and scale deposition.

[0031] refer to Figure 1 In one exemplary embodiment of the invention, rather than being uniformly spaced between adjacent features, the spacing between adjacent features varies slightly in a direction perpendicular to the cross flow in the element. Such varying spacing may be periodic, wherein the varying spacing is set to occur regularly, wherein longer periods generally produce less opportunity for nesting. In some spirally wound element configurations, it is preferred that the period before the pattern repeats is at least six inches (6"), and more preferably, the period is at least twelve inches (12"). In some spirally wound element configurations, it is preferred that the variation in spacing is less than 15% of the average distance between adjacent features so as to not significantly affect the flow characteristics through the element. Variations in feature spacing reduce the likelihood of pattern nesting between successive layers in a spirally wound element.

[0032] refer to Figure 2 In another exemplary embodiment of the invention, an array of line segments of spacer features are provided such that their angles vary slightly from mutual parallelism relative to each other. This variation in angle can be periodic, wherein the set varying angles occur regularly, wherein longer periods generally produce less opportunity for nesting. In some spirally wound element configurations, it is preferred that the period before the pattern repeats is at least six inches (6"), and more preferably, the period is at least twelve inches (12"). In some spirally wound element configurations, it is preferred that the variation in angle is less than 15% of the average angle of the entire array of spacer features so as to not significantly affect the flow characteristics through the element. Variations in feature angles reduce the likelihood of pattern nesting between successive layers in a spirally wound element.

[0033] Similarly, the features or changes in relative angles may be implemented in other shapes, such as curved lines, or the features of a zigzag pattern may be arranged at periodically varying angles to prevent nesting of successive layers. Figure 4 An example of this change is shown in: Figure 4 a is an illustration of a zigzag pattern with varying internal angles between features; Figure 4 B is an illustration of sawtooth-like elements that are arranged non-parallel to each other. Figure 4 C is a graphical representation of a curvilinear feature with varying curve shapes between features; Figure 4D is an illustration of curvilinear features that have similar shapes but are not arranged parallel to each other. Figure 4 The spacing between features in is shown to be consistent, but similar to Figure 1 The features in the layers may also be arranged with varying spacing between the features. The present invention contemplates a variety of such feature shapes and configurations, each of which provides features such that when the element is rolled and bonded, the features at least partially support those features on the adjacent layers.

[0034] Spiral wound elements using conventional extruded mesh spacers do not typically have problems with nesting of adjacent layers because the mesh filaments are so closely spaced that the filaments do not allow the film or entire membrane layer, permeate carrier and adhesive to deform and plug the feed space. Typically, the maximum mesh spacing is eight per inch, with ten to twelve per inch being more common for larger elements, and even denser spacing for smaller elements. Thus, the problem solved by the present invention does not become apparent until the unconventional deposition spacing features are deployed.

[0035] refer to Figure 3 Further exemplary embodiments of the present invention employ patterns of embossed or deposited features that are spaced similarly to conventional mesh feed spacers and arranged in a pattern that minimally obstructs feed flow. These features can be regular arrays of shapes, such as circular or polygonal columns, herringbones, curved segments, or other shapes, and can include arrays of line segments that are offset from one another and set at two different angles to the direction of fluid crossflow. These angles can be equal but opposite, such as +45° and -45° ( Figure 3 A), and can be any angle from + / -1° to + / -45° ( Figure 3 A. Figure 3 B). In some spirally wound element configurations, preferably the maximum spacing of any portion of the features to the nearest adjacent feature is less than or equal to one quarter inch (0.25"), and more preferably less than or equal to one tenth inch (0.10"). In another embodiment, the features comprise an array of offset and opposed angled segments with circular posts spaced ( Figure 3 C) Such closely spaced features may be advantageous because the features and the film surrounding them become substantially less susceptible to deformation during the rolling process where the adhesive comes into contact with the film, and thus it may be advantageous to have these closely spaced patterns along the perimeter of the film where the adhesive is applied to reduce restriction to flow even when less closely spaced patterns are employed elsewhere on the film.

[0036] In each exemplary embodiment, the features may be embossed or deposited in a continuous manner over the entire printed surface of the membrane sheet; embossed or deposited only along the inlet and outlet edge segments of the membrane (e.g., at a width of one to three inches) to support areas where adhesive is applied; or embossed or deposited only along the inlet and outlet edge segments and end segments of the membrane (e.g., at a width of one to three inches) to support areas where adhesive is applied in all areas.

[0037] These features can include various materials compatible with the separated fluid and the permeate carrier, including but not limited to thermoplastics, reactive polymers, waxes, or resins. Additionally, materials compatible with the separated fluid but not compatible with direct deposition to the permeate carrier (including but not limited to high temperature thermoplastics, metals, or ceramics) can be preformed, cast, or cut to size and adhered to the surface of the permeate carrier using an adhesive compatible with the permeate carrier.

[0038] The present invention has been described in conjunction with various exemplary embodiments. It should be understood that the above description is only intended to illustrate the application of the principles of the present invention, and the scope of the present invention will be determined by the claims with reference to the specification. Other variations and modifications of the present invention will be apparent to those skilled in the art.

Claims

1. A membrane for use in a spiral wound permeable membrane system, the system comprising a membrane having spacing features arranged across a surface of the membrane, in, The spacing features are configured such that they prevent nesting of spacers when spirally wound, the spacing features are configured such that they at least partially support those on adjacent layers, wherein the spacing features include a plurality of line segments that are spaced apart from one another and oriented non-parallel to one another at uneven angles, the spacing features are more closely spaced near the edges of the membrane than in portions of the membrane away from the edges, the spacing features are deposited directly onto the membrane surface, or the spacing features are formed apart from the membrane surface and then adhered to the membrane surface, Wherein a first subset of the plurality of line segments are oriented at non-uniform angles relative to one another to form a pattern, and wherein other subsets of the plurality of line segments comprise repetitions of the pattern.

2. The film according to claim 1, in, The pattern extends for at least 6 inches measured from the first line segment to the last line segment.

3. The film according to claim 2, in, The pattern extends for at least 12 inches measured from the first line segment to the last line segment.

4. The film according to claim 1, in, The variation in angle is less than 15% of the average angle of the features relative to the pattern.

5. A membrane for use in a spiral wound permeable membrane system, the system comprising a membrane having spacing features arranged across a surface of the membrane, in, The spacing features are configured such that they prevent nesting of spacers when spirally wound, the spacing features are configured such that they at least partially support those on adjacent layers, wherein the spacing features include a plurality of curved segments spaced apart from one another by measured non-uniform spacing distances as determined along at least one path traversing the spacing features, the spacing features are more closely spaced near the edges of the membrane than in portions of the membrane away from the edges, the spacing features are deposited directly onto the membrane surface, or the spacing features are formed apart from the membrane surface and then adhered to the membrane surface.

6. A membrane for use in a spiral wound permeable membrane system, the system comprising a membrane having spacing features arranged across a surface of the membrane, in, The spacing features are configured so that they prevent nesting of spacers when spirally wound, the spacing features are configured so that they at least partially support those on adjacent layers, the spacing features are more closely spaced near the edges of the membrane than in portions of the membrane away from the edges, the spacing features are deposited directly onto the membrane surface, or the spacing features are formed apart from the membrane surface and then adhered to the membrane surface.

7. A membrane for use in a spiral wound permeable membrane system, the system comprising a membrane having spacing features arranged across a surface of the membrane, in, The spacing features are configured such that they prevent nesting of spacers when spirally wound, the spacing features are configured such that they at least partially support those on adjacent layers, the spacing features include a plurality of substantially parallel line segments that are spaced apart from each other at non-uniform spacing distances, the spacing features are more closely spaced near the edges of the membrane than in portions of the membrane away from the edges, the spacing features are deposited directly onto the membrane surface, or the spacing features are formed apart from the membrane surface and then adhered to the membrane surface, Wherein a first subset of the plurality of line segments are spaced apart from one another at non-uniform spacing distances to form a pattern, and wherein other subsets of the plurality of line segments comprise repetitions of the pattern.

8. The film according to claim 7, in, The first subset extends over at least 6 inches measured from the first line segment to the last line segment.

9. The film according to claim 8, in, The first subset extends over at least 12 inches measured from the first line segment to the last line segment.

10. The film according to claim 7, in, The variation in spacing is less than 15% of the average distance between adjacent spacing features.

11. The film according to any one of claims 1 to 10, in, The edge of the film is defined as the area within three inches of the edge of the film.

12. The film according to claim 11, in, The edge of the film is defined as the area within one inch of the edge of the film.

13. The film according to any one of claims 1 to 10, in, The spacing features are made of one or more of thermoplastics, reactive polymers, waxes, or resins; deposited directly onto the film surface.

14. The film according to any one of claims 1 to 10, in, The spacing features are made of one or more of high temperature thermoplastics, metals, or ceramics; formed spaced apart from the membrane surface, and then adhered to the membrane surface.

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