Patent Application
20130161253
The present disclosure relates generally to spiral wound membrane elements and modules.
The following discussion is not an admission that anything discussed below is citable as prior art or common general knowledge.
Typically, a spiral wound membrane element is made by wrapping one or more membrane leaves around a perforated central tube. Each membrane leaf has one edge of a feed carrier sheet placed in a fold of a generally rectangular membrane sheet so that the membrane sheet encompasses the feed spacer sheet on both sides. The fold of the membrane sheet is positioned along a perforated central tube. A permeate carrier sheet is connected at one edge to the perforated central tube and a glue line seals each permeate carrier sheet to an adjacent membrane sheet along three edges, leaving a fourth edge open to the perforated central tube. All of the sheets are wrapped around the perforated central tube.
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 spiral wound membrane element. Within the spiral wound membrane element, the pressurized feedstock flows through the feed spacer sheets and along the surface of the membrane envelopes. The driving pressures associated with normal operational conditions can stress the structural integrity of the spiral wound membrane element. When the structural integrity is compromised the spiral wound membrane element may axially telescope, or radially expand, which can result in operational inefficiencies or irreparable damage. One structural reinforcement solution is to wrap the spiral wound membrane element in a cage. The cage is often formed of polypropylene netting that is tension wrapped around the spiral wound membrane element. The cage is then fixed to itself, for example by thermal bonding. The cage compresses the spiral wound membrane element, which provides structural support.
Other structural reinforcement solutions include pre-formed cylindrical cages, fiber glass covered elements, heat shrink encased elements and tape-covered elements.
Some specific industries (for example the dairy industry) require sanitary spiral wound membrane elements that meet the requirements of the Sanitary 3A Standards for Crossflow Membrane Modules. Sanitary problems can arise in areas of low flow, also referred to as areas of tight tolerance. One region that typically has tight tolerance is between an inner surface of the pressure housing and the outer surface of the spiral wound membrane element, referred to as the annular space.
Areas of tight tolerance have limited fluid access and, therefore, limited flushing to remove solids or provide sanitization solutions. Sanitization solutions are often high temperature fluids, high pH fluids, low pH fluids, enzyme-based fluids, oxidizing fluids or combinations of these sanitization solutions. The sanitization solutions flush and clean the pressure housing and spiral wound membrane elements therein. However, the sanitization solutions can soften, or degrade, the materials of the various structural reinforcement solutions described above. When the soft, or degraded, materials are exposed to the pressures within the pressure housing, the materials deform, which can reduce the structural support provided to the spiral wound membrane element and the physical integrity of the spiral wound membrane element can be compromised.
A reinforcement element for use in spiral wound membrane elements is disclosed in the detailed description below. The reinforcement element is wrapped around an outer layer of a spiral wound membrane element to structurally reinforce the spiral wound membrane element during filtration operations. The reinforcement element comprises a wire. The wire provides a compressive force that structurally reinforces the spiral wound membrane element. The wire is made from materials that are rigid enough to develop or maintain the compressive force during filtration operations without excessive deformation and the materials will not soften or deform by the increased temperature and chemical conditions associated with sanitization procedures. The reinforcement element structurally reinforces the spiral wound membrane element before, during and after sanitization procedures. Further, the reinforcement element may allow for sanitization procedures with higher temperatures, higher pressures and/or stronger chemicals. Higher temperatures, higher pressures and/or stronger chemicals may result in more efficient sanitization procedures, which may increase the operational life of the spiral wound membrane element and decrease the downtime associated with the sanitization procedures.
The reinforcement element comprises a wire 20 and, optionally, an outer wrap 50. The wire 20 can be a wire, a filament, cord, rope, yarn, braid, extruded body or the like that has a first end 22, an intermediate region 24 and a second end 26. As shown in
The wire 20 can be wrapped in either a clockwise or counter-clockwise manner. During wrapping, the first end 22 can be held at a first edge 104 of the spiral wound membrane element 100, adjacent the outer layer 112. For example, the first end 22 may be attached to an anti-telescoping device, a clamp around the end of the spiral wound membrane element 100, to the central tube 108, or wrapped in a ring around the spiral wound membrane element 100 before beginning to extend along the length of the spiral wound membrane element 100. The intermediate region 24 is then successively wrapped around the longitudinal axis of the spiral wound membrane 100 in a first direction until reaching the second edge 106 of the spiral wound membrane element 100. At this point, the wrapping of the intermediate region 24 changes to a second direction, which is in the opposite direction to the first direction (shown by the dotted line in
Optionally, the wire 20 is wrapped so that the successive wraps in the first direction are parallel to each other and the successive wraps of the wire 20 in the second direction are parallel to each other. A gap 30 can be maintained between parallel wraps of the wire 20 (the gap 30 is shown as a double sided arrow in
Wrapping of the wire 20 in both the first and second directions creates a number of intersections 28 where the wire 20 crosses over itself. The wire 20 wrapped in the first direction is wrapped at an angle to the second direction. The angle minimizes the contact area between the wire 20 wrapped in the first and second direction, which can increase sanitization fluid access to intersections 28. The angle may be oblique or acute.
Alternatively, the wire 20 is a series of independent rings that are positioned around the outer layer 112, or the cage, below the wire 20. In this case, the independent rings of the wire 20 can be fixed in position by tension, friction, ultrasonic welding, thermal welding or adhesives or combinations thereof. The independent rings can be distanced apart by the gap 30 that is at least equal to, or greater than the diameter of the wire 20. The independent rings avoid the creation of the intersections 28 and may have less areas of tight tolerance in comparison to the wire 20 that is wrapped in both the first and second direction.
The wire 20 can be made from a variety of suitable materials. For example, the material for the wire 20 may meet food contact standards. Additionally, the material may allow the wire 20 to hold the wrapped position around the spiral wound membrane element 100 without plastically deforming, or otherwise deforming excessively, during filtration operations or when exposed to high temperatures and chemicals during cleaning. The material preferably does not soften or degrade during high temperature and/or other chemical-based sanitization procedures. Chemical-based sanitary procedures include treatment with a high pH solution, a low pH solution, an enzyme solution or an oxidant solution. An example of a suitable material is stainless steel, including 300 series stainless steel.
The outer wrap 50 may be made from one or more of a variety of deformable materials that meet food contact standards, for example plastic tubes. When the reinforcement member is positioned around the spiral wound membrane element 100, the first edge 52 of the outer wrap 50 may be adjacent to the first edge 104 and the second edge 54 is adjacent the second edge 106. The outer wrap 50 preferably has an outer surface 60 that does not create substantial areas of tight tolerance and provides fluid communication with the wire 20 below. For example, the outer wrap 50 can be a shell, open netting, or a cage made of a micro porous plastic, a micro-porous bonded fiber, or a urethane foam. Optionally, the outer wrap 50 is made from a material that is both deformable and allows fluid passage across the outer wrap 50 to the wire 20 below.
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.
