WO1999011361A1

WO1999011361A1 - Reverse osmosis filter assembly and method of manufacture

Info

Publication number: WO1999011361A1
Application number: PCT/US1998/017193
Authority: WO
Inventors: Robert P. Hallmark
Original assignee: Hydranautics
Priority date: 1997-08-29
Filing date: 1998-08-20
Publication date: 1999-03-11
Also published as: TW422737B

Abstract

A filter assembly and method of manufacture is disclosed for separating particulates from a fluid stream. The filter assembly is made from a core tube (20) with a spirally wound filter membrane (18) of composite polyamide disposed thereon. The filter assembly comprises end caps (14, 16) which include a plurality of ports forming a feed inlet (26), a concentrate outlet (28), and permeate outlets (22, 24). The filter assembly includes an enclosure or shell (12) that encompasses and surrounds the end caps (14, 16) and filter membrane (18) to form a cylindrical chamber. The core tube (20) is disposed coaxially within the chamber.

Description

REVERSE OSMOSIS FILTER ASSEMBLY AND METHOD OF MANUFACTURE

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to filtration systems and, in particular, a reverse osmosis (RO) filter assembly having no pressure vessel that provides higher flux and operates at half the pressure.

2. Discussion of the Prior Art Reverse osmosis is a well known process for the removal of dissolved particulates from a fluid stream such as water. Osmotic filters involve a process whereby fluid flows across a semipermeable membrane barrier thereby forming a salt concentration gradient across the solid/liquid interface so as to allow for the preferential transport of solvent over solute, for example, water over salt ions. Feed water typically is purified by reverse osmosis systems for applications that include agricultural, by-product reclamation, sewage and industrial wastewater treatment, and highly purified water for medical use or electronics manufacturing.

Conventional RO filter devices include a pressure vessel or housing containing a semipermeable membrane which permits water to pass through but is substantially impermeable to certain impurities. A pressure vessel is necessary in conventional RO filter designs because high pressure is applied within the housing to the membrane so as to force unpurified water through the membrane, while impurities are prevented from passing therethrough. While pressure vessels are suitable for numerous RO filtration applications, it is desirable to eliminate the cost and performance limitations of pressure vessels. The present invention overcomes the problems associated with conventional RO filter systems utilizing pressure vessels to provide a reverse osmosis filter apparatus that requires no pressure vessel and achieves increased performance. The present invention provides a filtration assembly that features a filter membrane having improved flux at lower pressures in an FRP enclosure to eliminate costs and a myriad of problems associated with pressure vessels. SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improved filtration device or apparatus for commercial and industrial use.

It is an additional object of the present invention to provide a reverse osmosis RO filtration assembly that does not have a pressure vessel.

It is an object of the present invention to provide a module according to the present invention so as to eliminate the use of the costly and complex pressure housing or vessel used for filter elements of conventional designs.

It is another object of the present invention to provide more efficient and compact RO system for applications having space limitations.

Accordingly, the present invention provides a reverse osmosis filter assembly that includes a hollow, perforated core tube comprising an unobstructed bore and a tapped, spirally wound filter membrane disposed thereon. The filter membrane includes an elongated envelope formed from a pair of semipermeable membrane sheets that surround a permeate carrier sheet. The filter membrane is spirally wound around the core tube with separator means to maintain spacial relationship between convoluted layers of the elongated envelope. The filter assembly comprises end caps disposed adjacent each end of the filter membrane assembly. The end caps include a plurality of ports to form a feed inlet, a concentrate outlet and permeate outlets, whereby the permeate outlets are disposed adjacent to the core tube. The filter assembly includes an enclosure or shell that encompasses and surrounds the end caps and filter membrane to form a cylindrical chamber. The core tube is disposed in coaxial relationship with and within the chamber. The enclosure operates at high pressures without a pressure vessel.

Accordingly, the present invention provides a process of manufacturing a filter assembly, the process comprising the steps of forming a spirally wound filter membrane assembly on a hollow, perforated core tube having an unobstructed bore. The forming step includes forming an elongated envelope from a pair of semipermeable membrane sheets of a polyamide structure and a permeate carrier sheet, whereby the semipermeable membrane sheets surround the permeate carrier sheet and each of the membrane and carrier sheets are spirally wound around the core tube with a separator sheet thereby maintaining spacial relationship between convoluted layers of the elongated envelope. The filter membrane assembly is taped around an outer circumference thereof and each end of the filter membrane assembly is cut to a predetermined length. End caps having a bonding area are added adjacent each end of the filter membrane assembly. Finally, a shell, e.g. made of fiber reinforced plastic (FRP), is formed around the bonding area and filter membrane assembly. In this manner a filter assembly can be made that has improved flux while operating at high pressures without a pressure vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the present invention will become more clearly appreciated from the following description taken in conjunction with the accompanying drawings in which like elements are denoted by like reference numerals, and in which:

FIG. 1 is a schematic cross-section illustrating the RO filtration module according to an embodiment of the present invention;

FIG. 2 is a schematic view illustrating the interior of an end-cap of the present invention;

FIG. 3 is a schematic cross-sectional view, taken along lines 3-3 of FIG. 2, illustrating the end-cap filter of the present invention;

FIG. 4 is a schematic end view illustrating the end cap of the present invention; FIG. 5 is a schematic cross-sectional view, taken along lines 5-5 of FIG. 3, illustrating the annular lands of the end caps; and

FIG. 6 is a schematic view illustrating an additional embodiment of a filter module of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The structure of the filtration assembly or module 10, according to the various embodiments of the present invention, is illustrated in FIGS. 1-6. Referring to FIG. 1, the filtration module 10 generally includes a shell 12 and end caps 14 and 16 for enclosing a filter element or membrane 18 surrounding a permeable core tube 20. The end caps 14 and 16 have permeate ports 22 and 24, respectively, for transporting filtered fluid out of the filtration module 10. The permeate ports 22 and 24 are located at the center of the end caps 14 and 16, and are adapted to connect to the core tube 20. A feed port 26 and a concentrate port 28 are located offset from the center of the end caps 14 and 16, respectively. The feed port 26 is adapted to connect to piping that supplies feed fluid to the filtration module 10. The concentrate port 28 is adapted to connect to piping that carries concentrate fluid out of the filtration module 10. Each of the feed and concentrate ports 26 and 28 are further adapted to interface with the filter element 18. Alternatively, the feed and concentrate ports 26 and 28 can be smaller and disposed around the perimeter of the permeate ports 22 and 24 in the end caps 14 and 16 as is illustrated in FIG. 6. A plug 30 may close off a permeate port 24 when it is necessary to terminate it such as at the end of a series of filtration modules. The shell 12 of the filtration module 10 can formed of fiber reinforced plastic

(FRP) or other composite wound materials or processes. For example, the shell, such as an FRP shell, can be fabricated from any combination of composite materials including fiberglass, carbon fiber and other natural or manmade fibers and combined with polyester, epoxy and other resins. According to an embodiment of the present invention, the shell 12 consists essentially of wrapped fiberglass threads reinforced by polyurethane and dried to form a hard outer shell. Alternatively, the shell 12 can also be made from extruded stock material, of a cylindrical shape, made from polymers, metals or composite materials. Elimination of the pressure vessel has many advantages including the elimination of numerous manufacturing tolerances required for typical filter designs for filtration systems requiring pressure vessels. Such reduced manufacturing tolerances can reduce the cost of manufacturing relative to conventional element designs. The filter module of the present invention is designed to operate normally at pressures up to 400 psi but under failure testing has operated at operating pressures of 1,200 psi of more. The filter module 10 of the present invention also can have applications in high-pressure filtration systems, whereby such module 10 featuring the elimination of a separate pressure vessel is considered an advancement over conventional filter designs.

The end caps 14 and 16 are configured to have the feed, concentrate and permeate ports located on the ends of the end cap so as to facilitate connections to conventional piping. Alternatively, the end caps 14 and 16 can be designed to have side entry ports. The end caps 14 and 16 have threaded feed, concentrate and permeate ports so as to allow connection to any form of coupling such as hydraulic couplings, quick disconnecting fittings, plain and flange fittings, and the like. For example, the module 10 can use a 1/2" threaded opening for the permeate ports 22 and 24, as well as for the feed and concentrate ports 26 and 28, respectively. The end caps 14 and 16 are adapted to have an inner diameter configured to receive the end filtration membrane, thereby disposing the end of the filtration membrane adjacent the end caps 14 and 16. End caps 14 and 16 also are configured to connect permeate ports 22 and 24 directly to the core tube 20 such as by adhesives, bonding or the like, thereby eliminating the need for o-rings. Thus, the filtration module 10 of the present invention advantageously eliminates multiple o-ring seals as are used in conventional pressure vessels, such o-ring seals also are known to be a source of cross contamination such as, for example, leakage during operation which reduces the quality of permeate output (or product) obtained from the separation process.

The filtration module 10 of the present invention is designed for a filter element or membrane 18 of a spirally wound configuration. The filter element can utilize advantageously a membrane providing high salt rejection elements or high performance RO membrane elements. An Energy-Saving Polyamide (ESP A) element manufactured by Hydranautics of Oceanside CA, has the qualities of permeate flow rate in the range of approximately 2,600 to 12,000 gallons per day ("GPD") or a flux rate in the range of approximately 9 to 50 meters cubed/meters squared/per day (m³/m²/d), thereby providing superior salt rejection while reducing water usage, energy consumption and plant downtime. An Energy-Saving Nanofiltration (ESNA) element also manufactured by Hydranautics of Oceanside CA, has qualities of permeate flow rate in the range of approximately 2,600 to 12,000 GPD or a flux rate in the range of approximately 9 to 50 m³/m²/d, thereby providing an ideal membrane for applications requiring the removal of organic particulates, bacteria or viruses and provides a nominal 90% salt rejection. The filtration module 10 can advantageously be used in multiple or single element systems including applications that operate systems using micro-filtration (MF), ultra-filtration (UF), nano-filtration (NF) and reverse osmosis (RO) membranes such as, for example, filtration systems used in car washes and vending machines. Ultra-low-pressure operation provides increased energy savings with significantly lower installation and operating costs. ESP A and ESNA membranes are durable, cleanable and reliable over a wide range of operating conditions. The filtration module 10 also can be referred to as an ESPA-FREE or ESNA-FREE module having low-pressure high flux membrane which is free of pressure vessels, thereby reducing system complexity and cost. Conventional modules utilize a u-packing seal for sealing the void between the filter element and the inner wall of the pressure vessel. The u-packing of conventional filters can be a potential area of by- pass leakage during the operation of the filtration module whereby any leakage reduces the separation efficiency of the filtration module. The filtration module 10 of the present invention has the additional advantage of not needing the u-packing so as to eliminate the u-packing seal as a source of by-pass leakage.

Additionally, the performance of membrane elements operating in a reverse osmosis system is affected by the feed water composition, feed temperature, feed pressure, and permeate recovery ratio. Performance at a given set of system operating parameters can be calculated from nominal membrane performance at reference test conditions. RO filtration systems equipped with spiral wound membrane elements are designed to operate at a constant flux rate, i.e., to produce a constant permeate flow. Over operating time, the feed pressure is adjusted to compensate for fluctuation of feed water temperature, salinity and permeate flux decline due to fouling or compaction of the membrane. The ESPA and ESNA polyamide series of membranes have improved performance characteristics at low pressures when compared to conventional composite membranes. The membrane structure of these two membranes has been enhanced to allow greater water permeability without sacrificing salt rejection, for example, the ESPA and ESNA polyamide series of membranes use about half the feed pressure to produce the same amount of permeate as conventional membranes thereby lowering feed pressures by 50 to 250 psi.

The core tube 20 can be made from stock material having the permeate holes machined therein. The core tube can be extruded from polymers, metals or composite materials, such as polyvinylchloride (PVC). The membrane 18 and spacer material are wound around the core tube 20, which can be wrapped on the outside by taping and the like. When the end caps 14 and 16 are placed adjacent the ends of the membrane 18, the core tube 20 engages the permeate ports 22 and 24 in such as manner as to create a seal. As is illustrated in FIGS. 2-5, each of the end caps 14 and 16 include a bonding area 32 having a plurality of raised lands 34 formed circumferentially around the end caps 14 and 16. For ease of illustration, end cap 14 only is shown. The bonding area 32 and raised lands 34 assist in forming the shell 12. Lands 34 can be formed circumferentially on the outer surface of the end caps 14 and 16. The end cap 14 includes an inner diameter 36 configured to accept the filter membrane 18. The annular lands 34 connect and mate with the shell 12 to retain the end caps 14 and 16 adjacent the end of the filter membrane 18. The end caps 14 and 16 further include segments 38 disposed on portions 40 arranged to form quadrant areas 42. Segments 38 are configured to engage and hold an end of the cylindrical filtration membrane 18, thereby resisting conning or telescoping of a spirally formed filtration membrane 18. The quadrant areas 42, in connection with the segments 38 on portions 40 form voids so as to allow for fluid flow and the efficient forming of a gradient at the ends of the filtration membrane 18. Thus, end caps 14 and 16 of the present invention advantageously are designed to include the features of forming (1) a gradient or distribution of the salts of the liquid between the feed and concentrate ports; (2) a system to resist conning on the telescoping effect of the filter element 18 under pressure because of the holding action of the end caps; (3) an exit port for the permeate integral to the end cap; and (4) a structural housing of the membrane integral to the FRP shell.

Referring to FIG. 6, according to an alternative embodiment of the present invention, a filter module 50 includes end caps 14 and 16 having permeate ports 22 and 24, feed port 52 and concentrate port 54. Feed and concentrate ports 52 and 54, respectively, comprise a plurality of small diameter holes arranged adjacent the permeate ports 22 and 24 respectively. The construction of feed port 52 is adapted to engage a source of fluid so as to supply the filter module 10. Similarly, the concentrate port 54 is adapted to engage an output so as to supply concentrate thereto. In this manner, the filtration module 10 of the present invention also can have applications in filtration systems having and is an advancement over conventional filter designs.

In operation, feed water or liquid is supplied through the feed port 26 which passes through the membrane 18 and is thereby collected in the core tube 20 and exits through the permeate ports 22 and 24. The filtration module 10 separates, e.g. water from salt ions, using a spirally wound ESPA or ESNA membrane. The spirally wound membrane assembly is comprised of semipermeable membrane sheets or leaves, that are affixed at the edges to form an envelope and a spacing material sheet for the passage of permeated solutions. On top of the semipermeable membrane sheet is another spacer material sheet that allows the feed and nonpermeated solution to flow over the surface of the membrane leaves. The membrane envelope, the spacing material sheets for the feed and permeate are spirally wound around the hollow core tube 20 having numerous holes along the length thereof. A feed solution is supplied to the feed port 20 and such feed solution flows from the spiral edges of the membrane envelope parallel to the core tube 20. As the feed solution flows over the membrane surface under pressure a portion of the feed liquid of reduced dissolved solids content is forced through the membrane leaf. As a result of this separation process a reduced solids solution is collected on the permeate side of the membrane (inside) and a concentrated solution forms on the outer surface of the membrane envelope. The permeated solution flows spirally through the permeate spacing material sheet and is discharged into the center of the core tube 20 where the solution can flow out of the central permeate ports 22 and 24 located on either end of the module. The concentrated feed solution flows over the surface of the membrane through the feed spacing material and exits the module via concentrate port 28 on the end of the module opposite feed port 26. In this manner, the RO filter module 10 of the present invention can advantageously operate at low pressures to filter a feed solution.

The filtration module of the present invention can be manufactured according to a process of forming the shell 12 around an assembly formed of the filtration element 18 and end caps 14 and 16. The spirally wound filter membrane assembly 18 can be formed on a hollow, perforated core tube 20 having an unobstructed bore. An elongated envelope is formed from a pair of semipermeable membrane sheets of a polyamide structure and a permeate carrier sheet. The semipermeable membrane sheets are configured to surround the permeate carrier sheet. Once configured each of the membrane and carrier sheets are spirally wound around the core tube 20 along with a separator sheet or web so as to maintain a spacial relationship between convoluted layers of the elongated envelope. The filter membrane assembly can be held together by winding tape or other web around an outer circumference thereof. Each end of the filter membrane assembly is cut or trimmed to a predetermined length, for example, 40 inches, so as to be received by each end cap. The fiber reinforced plastic (FRP) shell is formed by winding the fibers and reinforced material around the bonding area of each end cap and filter membrane assembly. The assembly can be dried by heating or the like.

Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A reverse osmosis filter assembly comprising in combination; a hollow, perforated core tube having a substantially unobstructed bore; a filter membrane assembly including a tapped, spirally wound filter membrane disposed on said core tube, said filter membrane having an elongated envelope including a pair of semipermeable membrane sheets surrounding a permeate carrier sheet and spirally wound around said core tube, and separator means for maintaining spacial relationship between convoluted layers of said elongated envelope, said membrane sheets being made of a polyamide structure; end caps disposed at each end of said filter membrane, said end caps including a plurality of ports forming a feed inlet, a concentrate outlet and permeate outlets, said permeate outlet being disposed adjacent to said core tube; and an enclosure surrounding said end caps and filter membrane assembly forming a cylindrical chamber, said core tube being disposed in coaxial relationship with and within said chamber, wherein the filter assembly operates at high pressure without a pressure vessel.

2. The filter assembly as claimed in claim 1 wherein each of said end caps includes a bonding area formed on an outer surface of said end cap, said bonding area being adapted to engage said enclosure.

3. The filter assembly as claimed in claim 2 wherein said bonding area includes annular lands, said annular lands being adapted to engage fibers of said enclosure.

4. The filter assembly as claimed in claim 3 wherein each of said end caps includes a plurality of segments formed on a portion of an interior surface of said end caps adapted to engage said filter membrane assembly and to prevent the conning thereof.

5. The filter assembly as claimed in claim 4 wherein each of said end caps includes areas formed by said segments and portions on said interior surface adapted to allow for a gradient to form between the feed and concentrate ports to improve fluid flow of said filter membrane assembly.

6. The filter assembly as claimed in claim 1 wherein said filter membrane is made of an Energy-Saving Polyamide (ESPA) having the qualities of superior salt rejection with reduced water usage and energy consumption.

7. The filter assembly as claimed in claim 6 wherein said filter membrane is formed of a composite ESPA membrane having a permeate flow rate in the range of approximately 2,600 to 12,000 GPD.

8. The filter assembly as claimed in claim 7 wherein said filter membrane is formed of a composite polyamide membrane ESPA membrane having a flux rate in the range of approximately 9 to 50 m³/m²/d. 9. The filter assembly as claimed in claim 1 wherein said filter membrane is made of an Energy-Saving Nano filtration (ESNA) element having a 90 % salt rejection ratio for removing organic particulates.

10. The filter assembly as claimed in claim 9 wherein said filter membrane is formed of a composite ESPA membrane having a permeate flow rate in the range of approximately 2,600 to 12,000 GPD.

11. The filter assembly as claimed in claim 10 wherein said filter membrane is formed of a composite polyamide membrane ESPA membrane having a flux rate in the range of approximately 9 to 50 m³/m²/d.

12. A process of manufacturing a filter assembly, the process comprising the steps of: forming a spirally wound filter membrane assembly on a hollow, perforated core tube having an unobstructed bore, said forming including the steps of forming an elongated envelope from a pair of semipermeable membrane sheets of a polyamide structure and a permeate carrier sheet, whereby said semipermeable membrane sheets surround said permeate carrier sheet and each of said membrane and carrier sheets are spirally wound around said core tube and separator means maintaining spacial relationship between convoluted layers of said elongated envelope; taping said filter membrane assembly around an outer circumference thereof; cutting each end of said filter membrane assembly to a predetermined length; adding an end cap having a bonding area adjacent each end of said filter membrane assembly; and forming a fiber reinforced plastic shell around said bonding area and filter membrane assembly.

13. A filter assembly made by the process claimed in claim 12.

AMENDED CLAIMS

[received by the International Bureau on 5 January 1999 (05.01.99); original claims 1, 3, 4, 12 and 13 amended; new claims 14-16 added; remaining claims unchanged (3 pages)]

1. A reverse osmosis filter assembly comprising in combination; a hollow, perforated core tube having a substantially unobstructed bore; a filter membrane assembly including a membrane spirally wound on said core tube, said filter membrane having an elongated envelope including a pair of semipermeable membrane sheets surrounding a permeate carrier sheet, and separator means for maintaining spacial relationship between convoluted layers of said elongated envelope, said membrane sheets being made of a modified polyamide, said modified polyamide comprising a polyamide layer on a porous support , wherein said polyamide layer is formed by first coating an an ύno-containing compound on said porous support and second coating a polyfunctional acid halide-containing compound on said porous support; end caps disposed at each end of said filter membrane, said end caps including a plurality of ports forming a feed inlet, a concentrate outlet and a permeate outlet, said permeate outlet being disposed adjacent to said core tube; and an enclosure surrounding said end caps and filter membrane assembly, said enclosure being constructed of a fiber roving wrapped around said filter assembly, wherein the filter assembly operates at high pressure without a pressure vessel.

3. The filter assembly as claimed in claim 2 wherein said bonding area includes annular lands, said annular lands being adapted to engage fibers contained in said fiber roving of said enclosure. 4. The filter assembly as claimed in claim 3 wherein each of said end caps includes a plurality of segments for ed on a portion of an interior surface of said end caps adapted to engage said filter membrane assembly and to prevent the conning thereof.

AMENDED SHEET (ARTICLE W

8. The filter assembly as claimed in claim 7 wherein said filter membrane is formed of a composite polyamide membrane ESPA membrane having a flux rate in the range of approximately 9 to 50 mVmJd.

9. The filter assembly as clai ed in claim 1 wherein said filter membrane is made of an Energy-Saving Nano filtration ( ESNA) element having a 90 % salt rejection ratio for removing organic particulates.

10. The filter assembly as cl: timed in claim 9 wherein said filter membrane is formed of a composite ESPA membrane having a permeate flow rate in the range of approximately 2,600 to 12,000 GPD.

12. A process of manufacturing a filter assembly, comprising the steps of: forming a spirally wound filter membrane assembly on a hollow, perforated core tube having an unobstructed bore, said forming including the steps of forming an elongated envelope from a pair of semipermeable membrane sheets and a permeate carrier sheet, whereby said semipermeable membrane sheets surround said permeate carrier sheet and each of said membrane and carrier sheets are spirally wound around said core tube and separator means maintaining spacial relationship between convoluted layers of said elongated envelope, wherein said semipermeable membrane sheets comprise modified polyamide, said modified polyamide comprising a polyamide layer on a porous support, wherein said polyamide layer is formed by first coating an amino-containing compound on said porous support and second coating a polyfunctional acid halide-containing compound on said porous support; adding an end cap having a bonding area adjacent each end of said filter membrane assembly; and const cting a fiber reinforced plastic shell around said bonding area and filter membrane assembly, wherein said constructing comprises wrapping a fiber roving around said bonding area and said filter assembly.

13. A filter assembly made by the process of claim 12.

14. The process of claim 12, wherein said fiberglass roving is impregnated with resin.

15. The process of claim 14, wherein said resin is selected from the group consisting of polyester and epoxy.

16. The process of claim 12, wherein said roving is selected from the group consisting of fiberglass and carbon fiber.