Spiral wound filtration membrane cartridge with chevron seal

#This invention relates to a spiral wound filtration cartridge construction utilized in fluid separation processes such as reverse osmosis or ultrafiltration. More particularly, this invention relates to a spiral wound filtration cartridge construction having a chevron seal construction with a partial feed bypass means which prevents fluid stagnation within and around the cartridge during use.

#Prior to the present invention, spiral wound filtration cartridges have been provided comprising a centrally positioned tube about which are wound membrane sheets and suitable permeate spacers and feed spacers. The membrane sheets are V shaped and the feed spacers are positioned within the shaped membrane while the permeate spacers are positioned outside the V shaped membranes. The feed spacers promote passage of feed fluid into the V shaped membrane and the permeate spacers promote permeate flow from outside the V shaped membrane into holes through the walls of the centrally positioned conduit for recovery. The feed passes axially through the spiral wound membrane cartridge and retentate is recovered from the end at which the feed is introduced. The filtration cartridge is held within a cylindrically shaped housing to provide mechanical strength to the cartridge during use.

#It has been proposed to provide a controlled by pass of feed fluid within the space between the housing and the outside surface of the cartridge in order to prevent bacterial growth during use caused by clogging of the cartridge with retentate. U.S. Pat. No. 4,301,013 discloses the use of a tight fitting open mesh within the housing space between the cartridge and the housing to provide the desired by-pass flow. It has also been proposed in U.S. Pat. No. 4,548,714 to wrap the cartridge with a leaf of the feed spacer to provide for fluid flow around the cartridge. It has also been proposed by U.S. Pat. No. 4,906,372 to utilize a seamless porous rigid sleeve within the housing to separate the cartridge from the housing and to provide for feed by-pass. These cartridges are difficult to produce with the requisite tolerance needed to permit their use in the field, particularly when it is desired to change the cartridge within the housing. That is, these cartridge and housing arrangements are difficult to replace in the field since each cartridge-housing arrangement varies in size and shape.

#FIG. 1 is a partial cross sectional view of the cartridge apparatus of this invention without the fluid feed means cartridge.

#FIG. 2 is a cross-sectional view of a filtration cartridge useful in the present invention prior to being spirally wound.

#FIG. 3 is an exploded view of the seal and filtration cartridge of this invention.

#Referring to FIG. 1, the spiral wound apparatus of this invention 10 (excluding the outer housing and fluid feed means) includes a central tube 12 having an exit 14 and an exit 16 for recovering permeate from the apparatus 10. Optionally, one of the exits 14 or 16 can be blocked so that the permeate is recovered only from one exit 14 or 16. The spiral wound filtration cartridge 18 is comprised of the elements shown in FIG. 2 which will be described herein below. The spiral wound portion 18 includes an axial seal 20 which serves to prevent retentate and permeate from mixing. An end plate 24 is sealed to rigid solid outer tube 26 about the periphery 28 and to the periphery of exit 16 at the inner periphery 30 of end plate 24. The end plate 24 is not required for use in this invention. Exit 32 is in fluid communication with central tube 12 and permeate recovery conduit 34. Retentate exits form spiral surface 33 of spiral cartridge 18 through exit holes 36 in end plate 24 and is recovered. The cartridge 18 is enclosed in permeate screen 42 so as to provide a porous spacing between the spiral wound cartridge 18 and outer tube 26. If desired, the cartridge can be enclosed by a feed screen 40 or with any porous sheet such as cylindrical screen. However, it is preferred to utilize the permeate screen 42 to wrap the outside surface of cartridge 18 because the permeate screens 42 typically are denser than the feed screen 40 which reduces flow and therefore waste. Also, the permeate screen 42 are attached to central tube 12 and to the end adhesive 20 which reduces or eliminate screen slippage. The end adhesive 20 prevents feed fluid in screen 40 from mixing with permeate produced within cartridge. A chevron seal 39 having legs 43 and 50 is provided and is retained on outer tube 26 by a flexible ring 41 which positions leg 43 of seal 39 within slot 45. Ring 41 is positioned within slot 47 thereby to retain seal 39 against the outside surface 49 of tube 26. The seal 39 is provided with holes 51 which permit a portion of the feed to by-pass the filtration cartridge 18.

#Referring to FIG. 2, an unwound cartridge 18 is depicted showing the central tube 12 surrounded by a plurality of V shaped membranes 38, feed screens 40 are positioned with in the membranes 38 and permeate screens 42 are positioned outside the membranes 38. The lateral edges of the permeate screens 42 at the end of the cartridge adjacent the fluid feed means are sealed to the adjacent membranes 38 so as to prevent feed fluid from entering the permeate screens 42 such as disclosed in U.S. Pat. No. 3,966,616 which is incorporated herein by reference. The V shaped membranes can be any fluid permeable membrane such as an ultrafiltration, reverse osmosis or a microporous membrane. The membranes 38 and screens 40 and 42 are spirally wound about the central tube 12 with the outside wrapping of the cartridge 18 comprising the elongated permeate screen 42 shown in FIG. 2. However, the outside wrapping can be formed from a plurality of overlapping permeate or feed screens and can be more than one screen in thickness if desired. The permeate screen 42 are attached to central tube 12. The cartridge 18 then is sealed axially by adhesive 20 so as to prevent feed fluid from entering the working portion of the permeate screens 42. The outside wrap of permeate screen 42 provides a means for feed fluid to enter it and to clean the space between the outer surface of the spiral wound cartridge 18 and the inner surface of outer tube 26. The permeate screen 42 typically is made of woven fabric such as polypropylene or polyester or knitted fabric such as Tricot. The feed screen 40 typically is made from polypropylene or polyethylene extruded netting or woven fabric. In use, feed fluid enters the feed screens 40 at one spiral wound surface of cartridge 18. Permeate passes through the membranes 38 into permeate screens 42, through holes 44 and out of tube 12 and through recovery conduit 34. During manufacture, the spiral wound cartridge 18 is inserted into tube 26. The solid tube 26 provides a constant size and shape for the cartridge 18 so that it can be replaced easily within a cylindrical housing.

#Referring to FIGS. 3, 4 and 5, the chevron seal 39 includes a plurality of peripheral holes 51 which provide fluid communication for feed flow into the space 54 between outer tube 26 and housing 56 (see FIG. 5). The central hole 14 provides an outlet for permeate produced within cartridge 18. The size and number of the holes 51 controls the rate of by-pass flow. Flexible ring or gasket 41 is positioned about the periphery of and within the peripheral slot 47 of tube 26. Under the pressure of incoming fluid feed, the leg 50 of chevron seal 39 seals against the inner surface of housing 56 to effect fluid flow into filtration cartridge 18 and to prevent by-pass flow other than that directed through the holes 51. The chevron seal 39 prevents flow other than through the holes 51 so that fluid flow within space 54 is accurately controlled. The fluid flow within space 54 prevents clogging and bacterial growth within the space 54.