CONTROL RING

FIELD

[0001] This application claims the benefit of U.S. Application Serial No. 62/636,347, filed February 28, 2018, which is incorporated by reference.

FIELD

[0002] The present disclosure relates generally to spiral wound membrane elements, for example spiral wound membrane elements that can be used in sanitary applications.

BACKGROUND

[0003] The following discussion is not an admission that anything discussed below is citable as prior art or common general knowledge.

[0004] Typically, a spiral wound membrane element is made by wrapping one or more membrane leaves around a perforated central tube. One edge of a feed spacer sheet is placed in a fold of a generally rectangular membrane sheet. The fold of the membrane sheet is positioned along a perforated central tube. A permeate carrier sheet is provided between adjacent membrane sheets. Glue lines seal the permeate carrier sheet between adjacent membrane sheets along three edges, forming a membrane leaf. The fourth edge of the leaf is open to the perforated central tube. All of the sheets are wrapped around the perforated central tube.

[0005] In use, the spiral wound membrane element is housed in a pressure housing, also referred to as a pressure tube or a pressure vessel. A pressurized feedstock is delivered at an upstream end of the pressure housing and flows into the end of the spiral wound membrane element, specifically into the edges of the feed spacer sheets, and in some cases also around the outside of the element as discussed further below. Within the spiral wound membrane element, the pressurized feedstock flows through the feed spacer sheets and across the surface of the membrane sheets. The membrane sheets may have a separation layer that is suitably sized for microfiltration, ultrafiltration, reverse osmosis or nanofiltration. A portion of the pressurized feedstock is driven through the separation layer by transmembrane pressure to produce a permeate stream. The permeate stream flows along the permeate carrier sheets into the central tube, then through the central tube to an outlet at the end of the pressure housing. The components of the pressurized feedstock that do not pass through the membrane, also referred to as retentate, continue to move through the feed spacer sheets to be collected at a downstream end of the pressure housing.

[0006] The outside diameter of the membrane element is typically smaller than the inside diameter of the pressure housing, for example by a few mm. An annular space exists between an inner surface of the pressure housing and the outer surface of the spiral wound membrane element. The annular space is an area of tight tolerance, but a portion of the feedstock can pass through the annular space. This is referred to as bypass flow. In some cases, the membrane element has an impervious outer wrap and a brine seal is provided between the outer wrap and the pressure housing to completely block or enclose the annular space to prevent bypass flow. While preventing bypass flow can improve permeate production by forcing more of the feedstock through the membrane element, feedstock may stagnate in the annular space. The annular space fluid may communicate with the feed channel through portions of the feed spacer being exposed to the annular space.

[0007] Some industries require spiral wound membrane elements that intentionally provide some bypass flow. For example, membrane elements in the dairy industry must meet the requirements of the Sanitary 3A Standards for Crossflow Membrane Modules. Meeting these standards requires some bypass flow to flush out the annular space. Membrane elements used in these industries are referred to as sanitary modules or sanitary elements. Some examples of sanitary elements are described in US Patent Numbers 5,985,146; 7,208,808; 8,668,828; and, 8,940,168. Sanitary modules also typically have a cage around the membrane leaves.

[0008] Typically, more than one spiral wound membrane element is housed in one pressure housing. For example, in the dairy industry five or six spiral wound membrane elements are typically housed in one pressure housing. The central tubes of the membrane elements in a pressure housing are connected in series, and feedstock also passes through the membrane elements in a housing generally in series. In a complete system, there may be many pressure housings. The pressure housings are typically oriented horizontally on racks, which can reach heights of up to 10 m. From time to time, the membrane elements are removed from a pressure housing and replaced with new membrane elements. This is generally done by sliding membrane elements into and out of the pressure housing while the pressure housings remain installed in the racks. However, some brine seals can make it difficult to slide membrane elements into or out of a pressure housing.

SUMMARY

[0009] A spiral wound membrane element with a bypass control ring, a bypass control ring for a spiral wound membrane element, and a method of making a spiral wound membrane element are described herein. The membrane element may be used in sanitary applications, for example to provide fluid separation for the dairy industry.

[0010] A bypass control ring is a ring adapted to fit onto a spiral wound membrane element. The bypass control ring has an inside diameter compatible with the outside diameter the spiral wound membrane element. The outer diameter of the bypass control ring is compatible with the inside diameter of a pressure housing. Optionally, the bypass control ring may have a groove or other feature providing a path traversing the bypass control ring at the inner or outer diameter. The bypass control ring may be made of a thermoplastic material, for example a thermoplastic material having a low coefficient of friction with stainless steel or fiberglass. The outside diameter of the bypass control ring may be adjustable. In use, the bypass control ring at least restricts flow through the annular space between the membrane element and a pressure housing.

[0011] A membrane element has a bypass control ring, for example on one or both ends of the element, for example on the downstream end of the module. The membrane element may have a porous outer wrap upstream of the bypass control ring. The bypass control ring may be fitted on the element in direct contact with feed spacers and/or membrane leaves or the porous outer wrap of the membrane element.

[0012] In an assembly method, a bypass control ring is heated, which causes the ring to expand. The heated bypass control ring is placed over a spiral wound membrane element, for example on an end of the element. The bypass control ring is then cooled to fit more closely to the membrane element, optionally compressing the membrane element. Optionally, the outside diameter of the bypass control ring is modified after it is fit to the membrane element, for example by machining, thermal remolding or compression.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a side view of a first bypass control ring.

[0014] Figure 2 is a side view of a second bypass control ring.

[0015] Figure 3 is a side view of a third bypass control ring.

[0016] Figure 4A is a side view of a fourth bypass control ring.

[0017] Figure 4B is an isometric view of the fourth bypass control ring of Figure 4.

[0018] Figure 5 is an isometric view of a fifth bypass control ring.

[0019] Figure 6 is a side view of the end of a spiral wound membrane element having a bypass control ring installed on it. DETAILED DESCRIPTION

[0020] Figures 1 to 5 show various examples of bypass control rings 10, specifically a first bypass control ring 10A in Figure 1, a second bypass control ring 10B in Figure 2, a third bypass control ring 10C in Figure 3, a fourth bypass control ring 10D in Figures 4A and 4B, and a fifth bypass control ring 10E in Figure 5. Each bypass control ring 10 has an inner portion 12 defining the inner diameter of the bypass control ring 10 and an outer portion 14 defining the outer diameter of the bypass control ring 10. In some cases, the outer portion 14 occupies only part of the width of the bypass control ring 10 and the inner portion 12 is visible in the Figures. The distinction between the inner portion 12 and the outer portion 14 can be notional, for example in the bypass control rings 10 shown which are unitary structures. The inner diameter of the bypass control ring when installed on a spiral wound membrane element is the same as, or similar to, the outer diameter of the spiral wound membrane element. The outer diameter of the bypass control ring when installed in a pressure housing is the same as, or similar to, the inner diameter of a pressure housing. [0021] The bypass flow may be affected, at least in part, by the difference between the inner diameter of the pressure housing and the outer diameter of the bypass control ring. A smaller difference between the two diameters may correspond to a lower bypass flow. For processes where the bypass flow is used keep the spiral wound membrane element sanitary, the inner and outer diameters are considered“similar to” each other when the bypass flow is sufficient to keep the spiral wound membrane element sanitary, but is not so large that an unacceptable amount of energy is required to maintain the desired level of flow and or pressure for a given process.

[0022] The bypass control ring 10 can have one or more ridges on its internal surface that are in contact with a membrane element. The bypass control ring 10 can alternatively have ridges on the exterior surface of the ring, or ridges on both its internal and external surface. A ridge can be, for example, a single ridge that travels around the circumference of the ring in a continuous shape. Optionally, a ridge can be discontinuous, for example because its circumference is interrupted by additional features such as dimples or recessions that allow a flow path across the width of the ring. The ring could also have a continuous or discontinuous ridge that runs around the circumference of the ring but in a spiral shape, in one or multiple turns, optionally with a thread profile that is rounded, V- shaped, square, or acme screw.

[0023] With the first bypass control ring 10 A, the outer portion 14 covers only about half of the width of the first bypass control ring 10A, which can be in a range of about 1.5" to about 2.5". The outer portion 14 is shaped to provide a single, continuous, ridge extending circumferentially though one rotation and extending radially to the outer diameter of the first bypass control ring 10 A. The inside diameter may be in a range of about 7.5" to about 7.7". The outside diameter may be in a range of about 7.90" to 8.05".

[0024] With the second bypass control ring 10B, the outer portion 14 covers only about half of the width of the second bypass control ring 10B, which can be in a range of about 1.5" to about 2.5". The outer portion 14 is shaped to provide a series of discontinuous ridges, extending circumferentially though one rotation and extending radially to the outer diameter of the second bypass control ring 10B. The inside diameter may be in a range of about 7.5" to about 7.7". The outside diameter may be in a range of about 7.90" to about 8.05". [0025] With the third bypass control ring 10C, the outer portion 14 covers most, for example between 75% and 100%, of the width of the third bypass control ring 10C, which can be in a range of about 1.0" to about 2.0". The outer portion 14 is shaped to provide a single continuous ridge, extending circumferentially though one rotation and extending radially to the outer diameter of the third bypass control ring 10C. The inside diameter may be in a range of about 7.5" to about 7.7". The outside diameter may be in a range of about 7.90" to about 8.05".

[0026] With the fourth bypass control ring 10D, the outer portion 14 covers most, for example between 75% and 100%, of the width of the fourth bypass control ring 10D. The inner portion 12 is shaped to provide a single, continuous, ridge extending in a spiral through the width of the fourth bypass control ring 10D and extending radially to the inner diameter of the fourth bypass control ring 10D. The inside diameter may be in a range of about 7.5" to about 7.7". The outside diameter may be in a range of about 7.90" to 8.05".

[0027] With the fifth bypass control ring 10E, the outer portion 14 covers most, for example between 75% and 100%, of the width of the fourth bypass control ring 10E. The outer portion 14 is shaped to provide a single, continuous, ridge extending in a spiral through the width of the fifth bypass control ring 10E and extending radially to the outer diameter of the fifth bypass control ring 10E. The inside diameter may be in a range of about 7.5" to about 7.7". The outside diameter may be in a range of about 7.90" to 8.05".

[0028] The fourth and fifth bypass control rings 10D and 10E each provide a single, continuous, ridge extending in a spiral through the width of the bypass control rings. Reducing the depth of the sprial ridge and increasing the width of the bypass control ring both work, independently and in combination, to reduce the bypass flow. The width of the fourth and fifth bypass control rings can be in a range of about 1.5" to about 10". A bypass control ring having a width of about 8” and having a sprial ridge with a depth up to about 0.25” provides an acceptable bypass flow for some particular applications. If the spiral depth was increased, the ring width may be increased in order to achieve a similarly acceptable bypass flow.

[0029] Figure 6 shows a bypass control ring 10 installed on the downstream end of a spiral wound membrane element 20. The spiral wound membrane element 20 has a plurality of membrane leaves 22 separated by feed spacers 24. A porous outer wrap 26 is provided around the membrane leaves 22 and feed spacers 24. The outer wrap 26 may terminate at the upstream edge of the bypass control ring 10, or upstream of the upstream edge of the bypass control ring 10. Alternatively, a bypass control ring 10 can be installed on the upstream end of a spiral wound membrane element 20. If installed on the upstream end of the spiral wound membrane element 20, the porous outer wrap 26 may terminate at the downstream edge of the bypass control ring 10, or downstream of the downstream edge of the bypass control ring 10. In yet another alternative, a bypass control ring 10 can be installed on the upstream end and the downstream end of a spiral wound membrane element 20. In other alternatives, one or more bypass control rings 10 are installed along the length of a spiral wound membrane element 20, either with or without a bypass control ring 10 on one or both ends of the element 20. In the examples shown, there are no anti-telescoping device (ATD) physically attached to an element 20. However ATDs are provided as separate elements, within one ATD typically provided between the ends of every pair of elements 20 installed in series in a housing. Optionally, an ATD may be incorporated into an element 20, either on an end of the element opposite a bypass control ring 10 or adjacent a bypass control ring 10.

[0030] The outer wrap 26 may be made from a plastic net or mesh, for example as in a plastic mesh typically used in sanitary elements. The outer wrap 26 can assist in structurally reinforcing spiral wound membrane element 20, in particular by resisting unwinding of the membrane leaves 22 and feed spacers 24. Optionally, the outer wrap is made from polypropylene or polyethylene, or another plastic. The outer wrap 26 may be made by wrapping a flat sheet of net or mesh material around the membrane leaves 22 and feed spacers 24 and bonding its edges together, for example by ultrasonic welding.

[0031] Depending on the design of the spiral wound membrane element 20, the membrane leaves 22, the feed spacers 24 or both may be exposed at the outer surface of spiral wound membrane element 20 or to the inside of the outer wrap 26. At a minimum, the feed spacers 24 should extend to the edge of an overlying membrane leaf 22 to prevent the distal edges of one membrane leaf 22 from coming in direct contact with another leaf 22. In this case, even through the feed spacers 24 are not exposed, the edge of the feed spacer 24 is still in communication with feedstock outside of the spiral wound membrane element 20. Typically the edge of a feed spacer 24 is located somewhere beyond the edge of an overlaying membrane leaf 22 and the edge of an underlying membrane leaf 22. In some cases, the feed spacer 24 may extend past the edge of an underlaying membrane leaf 22 to contact an underlying feed spacer 24. In all of these cases, feedstock can flow into the feed spacers 24 from outside of the spiral wound membrane element 20. Accordingly, in use, bypass flow in the annular space around a spiral wound membrane element 20 may communicate with feed spacers 24 of the spiral wound membrane element 20. Placing a bypass control ring 10 only on the downstream end of an element advantageously encourages this communication which can increase permeate production and, in at least some cases, reduce stagnation at the outer periphery of the element 20.

[0032] The bypass control ring 10 may contact the exposed portions of the membrane leaves 22 and/or feed spacers 24. Optionally, as shown in Figure 6, parts of the membrane leaves 22 and/or feed spacers 24 can be cut back at the end of spiral wound membrane element 20 to reduce the diameter of the spiral wound membrane element 20. This can help with fitting the bypass control ring 10 onto the end of the spiral wound membrane element 20 without reducing the diameter of the entire spiral wound membrane element 20. Alternatively, the bypass control ring 10 may contact an outer wrap 26 that extends to the end of the spiral wound membrane element 20.

[0033] A bypass control ring 10 can be made of a plastic or other material. The bypass control ring 10 can be, for example, molded (i.e. injection molded), machined or 3D printed. Examples of suitable materials that are accepted for food contact include thermoplastic polymers such as: polypropylene, polyethylene (PE), low density polyethylene, high density polyethylene, ultra high molecular weight polyethylene (EIHMWPE), polyvinylidene fluoride, polytetrafluroethylene, and thermopastic polyurethanes. Other suitable materials that are accepted for food contact include elastomers, fluroelastomers, and thermosetting polyurethanes. Heat shrink materials, such as Raychem Semi Rigid Modified Polyolefin, are other examples of suitable materials for the bypass control ring 10. A semi-rigid heat shrink material may be molded to form the bypass control ring 10. Optionally, the bypass control ring 10 could be made of a material such as nylon, ABS, polyethersulfone, polyetheretherketone, polyetherimide or stainless steel. The bypass control ring 10 can be made of a low friction material such as PE or UHMWPE, for example material having a low coefficient of friction with stainless steel or fiberglass. The bypass control ring 10 can be made of an elastomer (such as ethylene propylene diene methylene rubber (EPDM), silicone rubber, or nitrile butadine rubber) or a fluoroelastomer (such as a copolymer of at least

hexafluoropropylene (HFP) and vinylidene fluoride (VDF or VF2); a terpolymer of at least tetrafluoroethylene (TFE), vinylidene fluoride (VDF or VF2) and

hexafluoropropylene (HFP); or a copolymer of at least tetrafluoroethylene (TFE) and perfluoromethylvinylether (PMVE)). The fluoroelastomer may have a fluorine content from about 66 to about 70%. The fluoroelastomer may be categorized under the ASTM D1418 and ISO 1629 designation of FKM, and may be sold under the name Viton™. Bypass control rings made of elastomers or fluoroelastomers may have a high coefficient of friction with stainless steel or fiberglass. A lubricant, such as glycerin, may be used to help insert a bypass control ring made of an elastomer or fluoroelastomer. The lubricant may be removed, such as by rinsing the lubricant away, after the bypass control ring is inserted.

[0034] The bypass control ring 10 can be heated to cause it to expand and increase in diameter for installation. The heated bypass control ring is then slipped over the end of the spiral wound membrane element 20 and allowed to cool. As it cools, the bypass control ring 10 shrinks to provide a tight fit onto the spiral wound membrane element 20. Optionally, the bypass control ring 10, when cooled, has a diameter that is smaller than the end of the spiral wound membrane element 20. This helps retain the bypass control ring 10 in place on the spiral wound membrane element 20 and may also compress the spiral wound membrane element 20. Alternatively, the bypass control ring 10 can be stretched without yielding it. In this case, the stretched bypass control ring 10 is placed over the element 20 and then released, allowing the bypass control ring to elastically contract to its original size, which may provide a snug fit against the element 20 or compress the element 20. In another alternative, when the bypass control ring 10 is formed from a heat shrink material, the bypass control ring 10 can be placed over the spiral wound membrane 20, and heated to cause it to shrink. The heat-shrink material and the size of the bypass control ring 10 are selected so that the shrinking provides a tight fit onto the spiral wound membrane element 20. Optionally, the bypass control ring 10, when shrunken, has a diameter that is smaller than the end of the spiral wound membrane element 20. This helps retain the bypass control ring 10 in place on the spiral wound membrane element 20 and may also compress the spiral wound membrane element 20. One example of a heat shrink material that may be used is Raychem Semi Rigid Modified Polyolefin, which has a 250% (min.) ultimate elongation and shrinks at temperatures above 125 °C, such as at temperatures of about 150 °C.

[0035] The bypass control ring 20 may compress the element 20 sufficiently to reduce the circumference of the element 20 by an amount from about 2 to about 4 mm. The bypass control ring 10 may compress against the element 20 with sufficient force to: keep the bypass control ring 10 in place, prevent the feed channel from opening up, prevent the element 20 from telescoping, or any combination thereof, during standard operating conditions, which may include contact with elevated temperature feed streams. For example, the bypass control ring 10 may sufficiently compress the element 20 that the compressive force, in combination with the underlying coefficient of friction and the interference due to the structure of the bypass control ring, is greater than the applied force pushing the bypass control ring 10 downsteam. For a bypass control ring having a cross sectional area of 3.5” squared and facing a pressure drop of 15 psi, the applied force pushing the control ring downstream is about 52.5 lbs.

[0036] The outside diameter of the bypass control ring 10 may be initially slightly more or less than the inside diameter of a pressure housing. If slightly less, the resulting gap can still sufficiently restrict bypass flow. If slightly more, or if the bypass control ring 10 remains stretched when installed on the spiral wound membrane element 20, the outer diameter of the bypass control ring 10 can be reduced after the bypass control ring 10 is installed but before or as the spiral wound membrane element 20 is inserted into a pressure housing. For example, the bypass control ring 10 can be machined or thermally modified (i.e. remolded) to reduce its diameter. In another option, the bypass control ring 10 is compressed as it is placed in the pressure housing, for example in a fixture that the spiral wound membrane element 20 slides through or against the pressure housing itself. Compressing the bypass control ring 10 to match the inside diameter of the pressure housing is easier with designs such as the first bypass control ring 10A and second bypass control ring 10B. It is acceptable for the bypass control ring 10A to completely seal the annular space in the pressure housing because feedstock entering the annular space can flow out of the annular space through the feed spacers 24. In this case the feedstock may also flow through the outer wrap 26 or through a longitudinal gap between the outer wrap 26 and the bypass control ring 10.

[0037] Optionally, one or more additional bypass control rings 10 can be placed at one or more locations along the length of the spiral wound membrane element 10. A bypass control ring 10, being relatively rigid and optionally pre-stressed, can help resist expansion or unwinding of the spiral wound membrane element 20 during filtering operations or sanitization procedures. However, it is expected that one bypass control ring 10 on the downstream end of a spiral wound membrane module 20 will be sufficient.

[0038] In a test, spiral wound membrane elements 20 were fitted as shown in Figure 6 with third bypass control rings 10C 3D printed of nylon and having outside diameters slightly less than the inside diameter of a pressure vessel. One ring 10C was placed on the downstream end of each element 20. The force required to slide six of these elements through a stainless steel housing was compared to the force required to slide six commercially available modules (Dow HYPERSHELL RO8038) having a continuous non-porous shell as in, for example, LIS Patent Number 5,985,146 entitled Sanitary Rigid Shell Spiral Wound Element. The force required for the commercially available modules was about 90 pounds. Although the coefficient of friction of nylon is not particularly low, the force required to move the elements 20 with bypass control rings 10 was about 20-30% less than the force required to move the commercially available modules. The elements 20 with bypass control rings 10 may have forces required to insert them into a housing, slide them in a housing and/or remove them from a housing that is equal to or less than, for example at least 10% less, at least 20% less or at least 30% less, than forces required for existing caged sanitary elements, for example the Dow HYPERHSELL RO8038, and/or shelled sanitary elements, for example the Suez AF8038 sanitary RO module. The elements 20 with bypass control rings 10, in a nominal 8 inch diameter, may have forces required to slide 6 of them in a nominal 8 inch stainless steel housing, that at least 10% less, at least 20% less or at least 30% less, than 90 pounds force. [0039] At least a part of the bypass control ring 10 extends outwards from the outside of a spiral wound membrane element 20 into an annular space inside of a pressure housing. The bypass control ring 10 may inhibit flow through the annular space, yet still allow sufficient bypass flow past the bypass control ring 10 (i.e. between the bypass control ring 10 and the housing, or between the bypass control ring 10 and spiral wound membrane element 20) to provide sanitary conditions. Alternatively, the bypass control ring 10 may completely block the annular space. In this case, particularly with the bypass control ring 10 on the downstream end of an element 20, the bypass control ring 10 causes feedstock to flow from the annular space into, and through, the spiral wound membrane element 20 to provide sanitary conditions. In some cases, feedstock in the annular space may flow in part past the bypass control ring and in part into, and through, the spiral wound membrane element 20.

[0040] Optionally, no non-porous shell or other restriction is present on the outside of the spiral wound membrane element 20 upstream of the bypass control ring 10. Optionally, one or more ridges on the bypass control ring 10 reduce the contact area of the bypass control ring 10 with the inside of the pressure housing, which may improve sanitization or reduce the installation and/or removal force.

[0041] The bypass control ring 10 can be constructed of a material with expansion characteristics that will allow the bypass control ring 10 to thermally expand in use. In this case, the bypass control ring 10 can have an outer diameter less than the inside diameter of a pressure housing to ease installation and/or removal, yet further restricting bypass through the annular space in use.

[0042] The examples described above are sized for nominal 8-inch sanitary membrane elements. However, similar rings 10 with different widths or diameters or both could be applied to elements of differing diameters that are available in the industry. Rings 10 narrower or wider than the examples described above may also be used with 8” or other diameter elements 20. The width of a bypass control ring 10 might be, for example, in a range from about 0.25” to about 90% of the length of a spiral wound membrane element 20. Optionally, a ring 10 is not more than half of the nominal length of the element 20, for example not more than 20” long. Optionally, the width of a bypass control ring is about 1” or more and/or about 8” or less. Optionally, a bypass control ring 10 could be chemically altered after it is molded or by using additives in the thermoplastic resin when the ring is molded. The alteration could be selected to provide anti-fouling or scale resistant properties. Optionally, the ring could have physical features, for example surface properties, to provide anti-fouling or scale resistant properties.

[0043] This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art.