Patent Application
20150290589
The present invention relates generally to reverse-osmosis separator modules, and more particularly to spiral-wound separator elements encapsulated in an outer shell for pressurized liquid-separation processes.
Reverse-osmosis (RO) is a separation technique that is suitable for a wide range of applications. For example, RO membranes are used in water purification processes to remove salts and other effluent from seawater or brackish water solutions. In a typical RO purification process, an RO separator module having an RO membrane is placed in a pressure vessel in which a supply of feed liquid (e.g., seawater) is pressurized against one side of the membrane. The RO membrane rejects the solutes in the feed liquid (e.g., salt and other effluent) to produce a concentrate liquid on the one side, and enables transport of a solute-free permeate liquid (e.g., salt-and-effluent-free water) across the membrane to the other side. The permeate liquid and concentrate liquid are each collected from the RO separator module through separate flow paths.
A common RO membrane configuration in water treatment applications is a spiral-wound RO separator element. In the spiral-wound configuration, a flat sheet membrane construction is wound around a permeate collection tube, in which flow paths are provided in the membrane construction for flow of the liquids. An RO module casing, or shell, is formed around the outer body of the spiral wound membrane construction in order to encapsulate the RO separator element. Current RO module shells are formed by winding fiberglass coated in uncured liquid resin around the spiral-wound RO separator element, which is then cleaned of excess resin and thermally cured. The handling of the fiberglass and liquid resin is not an environmentally or employee-friendly process, and the equipment required to mix and pump the liquid resin, apply the fiberglass, and heat cure the composite adds unnecessary time and costs to the end product. The liquid resin also results in dimensional variation of the shell outer diameter, which causes rejection of parts that are undersized, oversized, or have an unacceptable appearance.
The present invention provides a pre-formed shell housing for a spiral-wound RO separator element, which replaces the process of applying fiberglass and liquid resin to the RO separator element, thus enabling faster processing times and reduced labor costs, reduced material and equipment costs, reduced process variation and improved quality control, and/or an improved environmentally-friendly process. The selection of a suitable material for the pre-formed shell housing may also reduce corrosion or degradation by the feed liquid, may provide chemical inertness for U.S. Department of Agriculture (USDA) and U.S. Food and Drug Administration (FDA) approval, and may provide enhanced lateral strength for withstanding forces exerted on the shell housing.
According to one aspect of the invention, a reverse-osmosis separator module includes a pre-formed shell housing having a longitudinal axis extending between opposite ends and defining an inner chamber. A reverse-osmosis separator element is telescopically disposed in the inner chamber, and includes a permeate tube extending along the longitudinal axis and a membrane construction spirally wound around the permeate tube. An end cap is located at each end of the pre-formed shell housing.
Embodiments of the invention may include one or more of the following additional features. That is, the spiral-wound RO membrane construction may include axial and radial flow paths, and a semi-permeable membrane. The axial flow paths may be provided for enabling the feed liquid to enter the membrane construction at one end of the reverse-osmosis separator element, and the semi-permeable membrane is configured for separating the feed liquid into permeate liquid and concentrate liquid. The axial flow paths may also enable the concentrate liquid to exit the reverse-osmosis separator element at an opposite end, and the radial flow paths may enable the permeate liquid to pass to the permeate tube and exit the reverse-osmosis separator element through the permeate tube at either end.
Further optional features additionally include the spiral-wound membrane construction forming a membrane construction body portion with an outer surface, and the pre-formed shell housing having an interior surface that may be so dimensioned for receiving the RO separator element, such that the outer surface of a membrane construction body portion engages the shell housing interior surface, such as with a slip-fit tolerance, for reducing bypass of the feed liquid and/or reducing interruption of the membrane construction flow paths. The shell housing may be configured as a cylindrical tube having a major body portion with the interior surface forming a uniform inner diameter along the longitudinal axis. The shell housing may also have an outer surface which forms a wall thickness between the inner surface and outer surface, and the wall thickness may be so dimensioned for withstanding forces exerted on the shell housing without failure when the reverse-osmosis separator module is operating under pressure and/or if the reverse-osmosis separator element swells and compresses against the shell housing.
In yet other embodiments of the invention, the pre-formed shell housing may be made from metals, thermoplastics, composites, or other rigid materials capable of withstanding corrosion and degradation by the feed liquid. A suitable material may also be selected for withstanding the forces exerted on the shell housing during operation. For example, the shell housing may be made of polypropylene, which provides chemical inertness and may facilitate FDA approval. The polypropylene shell housing may have a wall thickness between 0.125 inches to 0.250 inches for providing sufficient lateral strength and burst strength when the RO separator module is subjected to forces during pressurized liquid-separation, such as high-pressure seawater desalination.
Still other embodiments of the invention may have the respective end caps of the RO separator module each including an end wall disposed transverse to the longitudinal axis of the shell housing, and the respective end walls may have through-passages for enabling fluid to enter or exit the inner chamber. The through-passages may be configured as a plurality of vanes and/or may also be configured for receiving the permeate tube of the RO separator element. The respective end caps may further include side surfaces having outer annular grooves for securing the RO separator module in a pressure vessel and/or for engaging a seal member, such as a brine seal, in the pressure vessel. The respective end caps may be affixed to the pre-formed shell housing by thermal welding, sonic welding, adhesive bonding, threading, and/or other attachment means. One of the end caps may be integrally formed and unitary with the pre-formed shell housing.
Further in accordance with the invention, a plurality of RO separator modules may be employed in a pressure vessel for the liquid-separation process. As such, at least one of the RO separator module end caps may be configured for operatively connecting in series with an end cap of another similar RO separator module.
In other embodiments, the at least one end cap for the first-mentioned RO separator module may be the same end cap for the other similar RO separator module for interconnecting the respective RO separator modules in series. The end cap interconnecting the RO separator modules may be threaded on both ends, or may have other attachment means for attaching to the respective RO separator modules. The end caps being attachable to the pre-formed shell housing may promote modularity in the liquid-separation system design.
According to another aspect of the invention, a reverse-osmosis separator module for separating feed liquid into permeate liquid and concentrate liquid includes a pre-formed shell housing having a longitudinal axis and an interior surface defining an inner chamber that extends between an inlet end and an outlet end. A reverse-osmosis separator element having a membrane construction body portion extending between the inlet end and the outlet end is disposed in the inner chamber, wherein the membrane construction body portion has an outer surface that engages the interior surface of the shell housing for encapsulating the membrane construction body portion and reducing bypass of the feed liquid. An inlet end cap and an outlet end cap are affixed at respective ends of the shell housing, and each of the end caps have an outer face disposed transverse to the longitudinal axis. The outer face of the inlet end cap has openings for enabling the feed liquid to enter the inner chamber, and the outer face of the outlet end cap has openings for enabling the concentrate liquid to exit the inner chamber. The inlet end cap and/or the outlet end cap may have separate openings for enabling the permeate liquid to exit the inner chamber.
According to yet another aspect of the invention, a method for assembling a reverse-osmosis membrane module is provided, which includes the steps of: obtaining a pre-formed tubular shell housing having a wall thickness and a uniform inner diameter along a longitudinal axis; affixing a first end cap to one end of the pre-formed shell housing; telescopically inserting a spiral-wound reverse-osmosis separator element into the pre-formed shell housing with a slip-fit tolerance using hand pressure; and affixing a second end cap to an opposite end of the pre-formed shell housing.
The following description and the annexed drawings set forth certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features according to aspects of the invention will become apparent from the following detailed description when considered in conjunction with the drawings.
The annexed drawings, which are not necessarily to scale, show various aspects of the invention.
The principles of the present invention have particular application for reverse-osmosis separator modules used in pressurized liquid-separation processes, such as seawater desalination for industrial application, and thus will be described below chiefly in this context. It will of course be appreciated, and also understood, that principles of this invention may be applicable to other liquid-separation processes, such as seawater or brackish water desalination for producing drinking water, or for the concentration of food liquids, such as fruit juices or dairy-products. In addition, the principles of this invention may be used in the production of ultrapure water for the semi-conductor or pharmaceutical industries, for wastewater and waste reuse treatments, or any similar liquid-separation processes.
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The RO separator element 40 may include a variety of separation mediums, such as membrane-based (e.g., spiral-wound or hollow fiber) separation mediums. A suitable type of membrane construction may be selected in a well-known manner for providing the desired flow rate, permeate flux, solute rejection, and other factors. For example, the membrane construction may include a semi-permeable membrane configured for separating a feed liquid into a permeate liquid (which passes through the membrane) and a concentrate liquid (which contains the solutes rejected by the membrane). The semi-permeable membrane may include ultrafiltration membranes or microfiltration membranes of a suitable type, such as thin film composite membranes. Representative semi-permeable membranes include those made from polysulfones, polyether sulfones, polyamides, polyacrylonitrile, polyfluroethylines, cellulose ester, and the like.
In a preferred embodiment, the RO separator element 40 includes a membrane construction 41 spirally wound around a permeate collection tube 43 that extends along the longitudinal axis 21. The spiral-wound membrane construction 41 may include axial flow paths for enabling the feed liquid to enter the membrane construction 41 at one end 47 (e.g., toward an inlet end 27) of the RO separator element 40, and for enabling the concentrate liquid to exit the RO separator element 40 at an opposite end 49 (e.g., toward an outlet end 29). The spiral-wound membrane construction 41 may also include radial flow paths, such as in the radial-spiral direction, which enables the permeate liquid to pass to the permeate tube 43, through permeate tube passages, and then exit the RO separator element 40 toward either end 27, 29.
The membrane construction 41 may be formed as a flat-sheet construction having the semi-permeable membrane layer interposed between a feed channel layer for enabling the axial flow paths and a permeate collection layer for enabling the radial flow paths. The feed channel layer may be formed as a biplanar extruded net, and the permeate collection layer may be formed from a tricot woven fabric, such as polyester. The spiral-wound membrane construction 41 may include one or more spiral wraps around the permeate collection tube 43, thus forming a membrane construction body portion 45 that extends along the longitudinal axis 21 between opposite ends 47, 49, and has an outer surface 46.
The pre-formed shell housing 20 may be made from pre-fabricated piping, tubing, or any pre-formed tubular member with an inner chamber that can be sized for encapsulating the RO separator element 40. In a preferred embodiment the pre-formed shell housing 20 is a cylindrical tube having a major body portion with the interior surface 23 forming a uniform inner diameter along the longitudinal axis 21. In this manner, the inner diameter may be continuously uniform along the entire length of the shell housing 20; or the shell housing 20 may have outwardly or inwardly tapered sections toward respective ends 27, 29, that may facilitate the telescopic insertion and/or containment of the RO separator element 40. The pre-formed shell housing 20 also has an outer surface 25 that may define an outer diameter of the cylindrical shell housing 20. The outer diameter may also be continuously uniform along the major body portion of the shell housing 20.
The distance between the shell housing outer surface 25 and shell housing interior surface 23 defines a shell housing wall thickness, which may also be uniformly thick along the major body portion of the shell housing 20 for enabling even distribution of stresses when the RO separator module 10 is subjected to forces during operation. For example, as described in further detail below, the RO separator module 10 may be placed in a separate pressurized vessel that forces the feed liquid against the semi-permeable membrane for effecting the liquid-separation process. The pressure exerted by the pressure vessel is typically greater than the osmotic pressure of the feed liquid, which may be between 10-600 psi for purification of fresh and brackish waters, or between 600-1200 psi for desalination of seawater. The membrane construction body portion 45 may also exert pressure on the shell housing interior surface 23 as the membrane construction body portion 45 swells in the radial dimensions. The membrane construction body portion 45 may swell when liquids flow through the membrane construction 41 and as pressure is applied to the liquids, or when the membrane construction 41 interacts with certain ions or chemicals.
So as to withstand the forces exerted on the shell housing 20 without failure (e.g. without exceeding the yield strength or causing plastic deformation), the shell housing 20 may be made from suitable materials, such as metals, plastics or composites having sufficient lateral and burst strength. The materials selected for the shell housing 20 may also be capable of withstanding corrosion and degradation by the feed liquid. For example, suitable metals may include stainless steels or copper-alloys; suitable plastics may include polypropylene, polyethylene, ABS, PVC, or similar plastics; and suitable composites may include fiberglass reinforced epoxy, or the like. Other rigid materials (e.g. having a hardness similar to or greater than polypropylene) may also be utilized. In a preferred embodiment, the shell housing may be made of polypropylene, which provides chemical inertness and may facilitate USDA and FDA approval of the purified liquid. The polypropylene shell housing may have a wall thickness between 0.100 inches to 0.300 inches, or more preferably 0.125 inches to 0.250 inches, for providing sufficient strength during pressurized liquid-separation, such as high-pressure seawater desalination.
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The slip-fit tolerance between the shell housing interior surface 23 and the outer surface 46 of the membrane construction body portion 45 may be between 0.001 inches and 0.050 inches, or more particularly between 0.001 inches and 0.020 inches. For example, referencing
The shell housing interior surface 23 may also be so dimensioned for accommodating swelling of the membrane construction body portion 45 during operation, or over the life of the RO separator module 10. For example, the membrane construction body portion 45 may swell in the radial direction between 0.5% to 5%, which may cause the membrane construction body portion 45 to compress against the shell housing interior surface 23, which could interrupt the membrane construction 41 flow paths. As such, the shell housing inner diameter (D2) may be sized between 0.5% to 5% greater, more preferably between 0.5% to 2% greater, than the outer diameter (D3) of the membrane construction body portion 45.
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The end caps 60, 80 may also provide for confining the membrane construction body portion 45 inside of the shell housing 20, and may prevent telescoping (relative axial movement) of the spiral-wound membrane construction 41 sheets. The end cap through passages 63 may be formed between a plurality of vanes having radial cross-members 65 for enabling liquid passage and for confining the membrane construction body portion 45 to inside the shell housing 20. The end caps 60, 80 may also have a side surface 68 transverse to the end face 61. As shown in
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Although the invention has been shown and described with respect to a certain embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
This application claims the benefit of U.S. Provisional Application No. 61/978,211 filed Apr. 11, 2014, which is hereby incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61978211 | Apr 2014 | US |
