Abstract:
A filter for a filter vessel which converts the filter vessel to use disposable filters for removing hazardous particulate matter from an aqueous flow. The filter includes a rigid support housing having an input passage for the aqueous flow, an exit passage for the aqueous flow, an internal sealing surface and a locking seal located adjacent to the input passage to securingly engage the filter vessel for the aqueous flow. The invention also includes a sleeveless disposable filter cartridge. The cartridge includes a flexible filtering medium having first and second ends. A terminal seal is affixed to the first end of the filtering medium for sealing engagement with the filter vessel and a wall seal on the second end of the filtering medium for engagement with the internal sealing surface of the support housing.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates generally to filters and, more particularly, to a disposable filter for removing particulate matter from an aqueous flow, especially radioactive materials entrained in cooling water, which provides an improved cartridge-style filter for use in such installations to reduce the volume and weight of the hazardous waste resulting from the end of life of the filter. 
     (2) Description of the Prior Art 
     Nuclear reactors use water in primary and secondary support systems. Some of the particulate entrained in these systems are radioactive. These radioactive particles must be removed for safe and efficient system operational and maintenance. This is done conventionally by filter elements that are installed for a given period of time to remove the particulates. After a period of time, the filter becomes clogged with removed particulate and must be replaced. 
     Conventional filters for this purpose have a perforated, stainless steel outer cylinder and, in some cases, an inner stainless steel cylinder, and stainless steel end fittings, and a permanently installed interior filter medium. The filtrate flows from inside to outside through the filter medium and the pores of the stainless steel cylinder. The outer stainless steel cylinder and end fittings have been considered a necessity to give the filter the structural strength and integrity to withstand the temperature, pressure and dynamic filtration loads of the forces of the flowing liquid and avoid corrosion. 
     However, when the filter is spent, the outer and inner cylinders and end fittings become a large, strong, corrosion resistant, heavy piece of hazardous, radioactive waste. Requirements for disposal of this type of waste safely are very costly. The steel is difficult to compress to a reduced volume and does not easily shred to smaller pieces. Disposal of the filter, therefore, requires a great deal of cost. 
     One solution to this problem is disclosed in U.S. Pat. Nos. 5,478,469 and 5,678,230, issued to Bryan and Pop. These patents disclose a disposable filter for removing hazardous particulate matter from an aqueous flow. The filter includes a rigid support housing having an input port for the aqueous flow, an exit port for the aqueous flow, a brace to securingly engage a filter vessel for the aqueous flow, an internal seal and an external seal, and a disposable filter cartridge configured similarly to the housing and sized to be substantially entirely received within the housing and sealingly engage the internal seal and having a filter medium that extends across a path from the input port to the exit port when received in the housing, the cartridge having a terminal seal located to sealingly engage the cartridge to the aqueous flow filter vessel outside of the housing when the cartridge sealing engages with the internal seal. The rigid support housing may be installed in a filter vessel for an extended period and held in place by the brace, and repeatedly during the extended period, a disposable cartridge may be installed within the housing to seal the cartridge to the filter vessel, aqueous flow may be directed through the filter medium, and the cartridge may be removed and discarded. These patents are hereby incorporated by reference in their entirety. 
     For all of its advantages, the Bryan and Pop filter did have some drawbacks. Specifically, the brace arrangement was difficult to machine and install in the field. Furthermore, the disposable filter included some hard to dispose of metal parts. Finally, the porous outer sleeve used to add strength to the disposable filter took up critical space that limited the applications which could benefit from the filter. 
     Thus, there remains a need for a new and improved disposable filter which performs well in existing facilities, reduces the cost of disposal of spent filters contaminated with hazardous materials such as radioactive particulate matter while, at the same time, overcomes the problems associated with Bryan and Pop. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a filter for a filter vessel which converts the filter vessel to use disposable filters. The filter includes a rigid support housing having an input passage for the aqueous flow, an exit passage for the aqueous flow, an internal sealing surface and a locking seal located adjacent to the input passage to securingly engage the housing to the filter vessel for the aqueous flow. 
     The invention also includes a disposable filter cartridge. The cartridge includes a flexible filtering medium having first and second ends. A terminal seal is affixed to the first end of the filtering medium for sealing engagement with the filter vessel and filter vessel lid and a wall seal on the second end of the filtering medium for engagement with the internal sealing surface of the support housing. The filtering medium is sized to be substantially entirely received within the support housing and to sealingly engage the internal sealing surface in the support housing with the wall seal and the filter medium extends across a path from the input passages to the exit passages of the support housing when the terminal seal engages with the filter vessel and filter vessel lid. 
     In the preferred embodiment, a lifting point is formed in the disposable filter cartridge adjacent to the terminal seal to permit easy removal of the cartridge either by hand or tooling. 
     The support housing may be installed in a filter vessel for an extended period and held in place by the locking seal, and repeatedly during the extended period, the disposable filter cartridge may be installed within the support housing to seal the disposable filter cartridge to the filter vessel and the support housing, to direct aqueous flow through the filter medium, and the disposable filter cartridge may be removed and discarded. 
     In a preferred embodiment the housing has a cylindrical shape including two ends and inner and outer sidewalls, with an input port at one end of the cylindrical shape and a plurality of exit ports in the form of apertures in the outer sidewall. In the preferred embodiment the cartridge has a cylindrical shape including two ends and a sidewall, the terminal seal being located at one end, the sidewall extending across the path between inlet port and outlet ports of the housing, and the wall seal engaging the internal sealing surface of the housing. 
     Typically, the housing is made of stainless steel. In a preferred embodiment the cartridge includes ends containing seals and a flexible filtering medium. The flexible filtering medium may be of any suitable filtering medium such as polysulfone foam or polypropylene. The seals may be silicone rubber. 
     Accordingly, one aspect of the present invention is to provide a filter for removing particulate matter from an aqueous flow. The filter includes: (a) a rigid support housing having an input passage for the aqueous flow, an exit passage for the aqueous flow, an internal sealing surface and a locking seal located adjacent to the input passage to securingly engage the housing to a filter vessel for the aqueous flow; and (b) a disposable filter cartridge sized to be substantially entirely received within the housing and having a filter medium that extends across a path from the input passage to the exit passage when received in the housing, the cartridge having a terminal seal located to sealingly engage the cartridge to the filter vessel for aqueous flow outside of the filter vessel and the housing when the cartridge sealingly engages with the internal sealing surface of the housing, whereby the support housing may be installed in a filter vessel for an extended period and held in place by the locking seal, and repeatedly used during the extended period, the disposable filter cartridge may be installed within the support housing to seal the disposable filter cartridge to the filter vessel and the support housing, aqueous flow may be directed through the filter medium, and the disposable filter cartridge may be removed and discarded. 
     Another aspect of the present invention is to provide a disposable filter cartridge for removing particulate matter from an aqueous flow and for installation inside a support housing that is installed within an aqueous flow filter vessel and that has an input port at one end and exit ports in a housing sidewall. The disposable filter cartridge includes: (a) a flexible filtering medium having first and second ends; (b) a terminal seal affixed to the first end of the filtering medium for sealing engagement with the filter vessel; and (c) a wall seal on the second end of the filtering medium, the filtering medium sized to be substantially entirely received within the support housing and to sealingly engage the internal sealing surface in the support housing with the wall seal and the filter medium extends across a path from the input passage to the exit passages of the support housing when the terminal seal sealingly engages with the filter vessel, whereby the disposable filter cartridge may be installed within the support housing to seal the disposable filter cartridge to the filter vessel, aqueous flow may be directed through the filter medium, and the disposable filter cartridge may be subsequently removed and discarded. 
     Still another aspect of the present invention is to provide a filter for removing particulate matter from an aqueous flow. The filter includes: (a) a rigid support housing having an input passage for the aqueous flow, an exit passage for the aqueous flow, an internal sealing surface and a locking seal located adjacent to the input passage to securingly engage the housing to a filter vessel for the aqueous flow; (b) a disposable filter cartridge, the cartridge including: (i) a flexible filtering medium having first and second ends; (ii) a terminal seal affixed to the first end of the filtering medium for sealing engagement with the filter vessel; and (iii) a wall seal on the second end of the filtering medium, the filtering medium sized to be substantially entirely received within the support housing and to sealingly engage the internal sealing surface in the support housing with the wall seal and the filter medium extends across a path from the input passage to the exit passages of the support housing when the terminal seal sealingly engages with the filter vessel; and (c) a lifting point formed in the disposable filter cartridge adjacent to the terminal seal, whereby the support housing may be installed in a filter vessel for an extended period and held in place by the locking seal, and repeatedly during the extended period, the disposable filter cartridge may be installed within the support housing to seal the disposable filter cartridge to the filter vessel and the support housing, aqueous flow may be directed through the filter medium, and the disposable filter cartridge may be removed and discarded. 
     These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is cross-sectional view of a filter vessel holding the nested support housing and disposable filter cartridge constructed according to the present invention; 
     FIG. 2 is a cross sectional view of the support housing of the present invention; 
     FIG. 2A is a partial expanded view of the structure and operation of the support housing seal; and 
     FIG. 3 is a cross sectional view of the disposable filter cartridge of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, like reference characters designate like or corresponding parts throughout the several views. Also in the following description, it is to be understood that such terms as “forward”, “rearward”, “left”, “right”, “upwardly”, “downwardly”, and the like are words of convenience and are not to be construed as limiting terms. 
     Referring now to the drawings in general and FIG. 1 in particular, it will be understood that the illustrations are for the purpose of describing a preferred embodiment of the invention and are not intended to limit the invention thereto. As best seen in FIGS. 1-3, the present invention, indicated generally at  100 , includes a support housing  200  and a disposable filter cartridge  300 . Disposable filter cartridge  300  is nested in support housing  200  which in turn is inserted in a high-strength, stainless steel filter vessel  500 . Disposable filter cartridge  300  includes terminal seal  306 , wall seal  308  and flexible media  302  interposed therebetween. Terminal seal provides a sealing engagement with filter vessel  500  (shown in partial sectional view). 
     Preferably, flexible media  302  is comprised of polypropylene or polysulfone. The practice of the present invention includes using other suitable filter media materials as a particular situation may dictate. The structural integrity and filtering ability of flexible media may be enhanced by introducing pleats or corrugations therein. In a preferred embodiment, flexible media  302  filters particles in the range of between about 0.2 and about 100 microns. 
     Each of the seals  306 , 308  may be constructed from a elastomeric material such as a silicone rubber. A desirable material is that designated RTV 664 available from General Electric. Seal  308  has an outer sealing surface sized to create a compressive fit against the internal sealing surface  218  located in the annular seal cavity  216  of adaptor housing  200 . Seal cavity  216  is formed in solid base plate  208 . The term solid as used herein refers to the lack of any flow openings in the side walls of base plate  208 . 
     Disposable filter  300  may also include a lifting aperture  311  to facilitate removal from support housing  200 . In a preferred embodiment, lifting aperture  311  may be shaped or adapted to receive a variety of tools for removing disposable filter  300  from adaptor housing  200 . Preferably, lifting aperture  311  is round or generally cylindrical. For economy of construction lifting aperture  311  and terminal seal  306  may be formed as an integral unit from silicone rubber. 
     Reinforcing member  320  may be included as shown in FIG. 3 to add strength to lifting aperture  311 . Desirably, this element is constructed of a non-metallic material to enhance the ease of volume reduction and increase the number of potential disposal methodologies of spent filter  300 . Suitable materials include polymers such as polyethylene, polypropylene, nylon, cellulosic materials and the like. Ceramics could be used but are not preferred because they may present disposal difficulties. 
     Because some materials may not bond well to silicone rubber, a plurality of anchors may be provided in reinforcing member. In the preferred embodiment shown in FIG. 3, the anchors comprise a series of holes  322  positioned in the circular reinforcing member  320 . It will be readily understood that the silicone rubber will flow into and fill holes  322  during formation of lifting aperture  311 . Other types of anchors may be used as well. For instance, a series of laterally expending projections could be provided around the circumference of reinforcing member  320 . 
     As seen in FIG. 1, the bottom of filter cartridge does not seat on the floor of annular seal cavity. Also the inside diameter of wall seal  308  does not touch inner shroud  204 . Thus, high pressure fluid entering filter vessel  500  will fill the space under filter cartridge  300  and be stopped at sealing surface  218 , as best seen in FIG.  2 . 
     As seen in FIG. 2, support housing  200  includes outer shroud  202 , input passage  210 , annular seal cavity  216  having an internal sealing surface  218 , base  208  and locking seal  400 . Housing  200  also includes an output passage which in this preferred embodiment is a porous member comprised of a plurality of holes  206 . Outer shroud  202  and base  208  are constructed of metal, preferably stainless steel for its resistance to corrosion. 
     Support housing  200  may further include an inner shroud  204  whose function is to protect flexible media  302  from back pressure situations. Back pressure may be created unintentionally if a drain valve is left open and then an outlet valve downstream of filter assembly is opened. Static system pressure may force a backflow through the combined housing  200  and filter  300  unit. Inner shroud  204  protects flexible media  302  from damage in such a situation. There need not be any direct contact between these two elements in order for inner shroud  204  to perform its protective function. In the preferred embodiment, inner shroud  204  is concentric with outer shroud  202  and is also constructed of stainless steel. A lifting point  214  may be provided to facilitate installation and removal of the adaptor housing into or from the filter vessel. As is the case with outer shroud  202 , inner shroud  204  is porous and may include a plurality of holes  212  for fluid flow. 
     Locking seal  400  performs two functions. First, it holds adaptor housing in place so that a spent disposable filter  300  may be removed. Second, it creates a seal against the high-pressure fluid entering though input passage  210  and bypassing wall seal  308 . Locking seal  400  is positioned in a seal recess  207  in base plate  208 . Seal  400  is wedge-shaped in cross section with the point of the shape directed towards the bottom of the adaptor housing  200 . 
     The embodiment depicted in FIG. 2 is referred to as an inside diameter embodiment because locking seal  400  is positioned in the inside diameter of base plate  208 . Locking seal includes protuberance  402  which extends into input passage  210  by a small amount. As support housing  200  is inserted into filter vessel  500  and firmly seated therein, protuberance  402  is radially compressed against the inlet port  502  of filter vessel  500 . Any attempt to remove support housing by pulling upward in the direction of arrow “A” is resisted by the interference fit between inlet port  502  and locking seal  400 . The friction force, illustrated by arrow “F” in FIG. 2A, can be substantial with the proper selection of the compressive forces generated in locking seal  400 . In a preferred embodiment, silicone rubber is used to take advantage of its suitable characteristics for creating the desired interference fit. 
     It has been found that in addition to the friction force caused by the interference fit between the inlet port  502  and locking seal  400  which acts parallel to the central axis of support housing  200 , an additional compressive force acting at an angle to the housing centerline creates an additional friction force as the locking seal  400  is drawn upwardly towards the upper surface of seal recess  207 . It has been found that the friction forces are so great as to require the use of a mechanical puller to remove the support housing from the filter vessel. The advantage of this arrangement is that filter cartridge  300  may be removed from support housing  200  without unintentionally removing support housing  200  from filter vessel. 
     In an alternative embodiment, referred to as the outside diameter embodiment, locking seal  400  may be located in a recess formed around the outside circumference of base plate  208 . The protuberance in this embodiment engages the inside surface of filter vessel to create the compressive fit described above. 
     The structure of the support housing  200  and filter cartridge  300  provide several advantages over prior art designs. First, no separate mechanism is required to hold the support housing firmly in the filter vessel as filter cartridge  300  is removed therefrom. Locking seal  400  performs a dual function of creating a hydraulic seal against the high pressure fluid and locking the support housing  200  in place with only one easy to manufacture part. 
     Second, the axial loading on flexible media  302  when filter vessel  500  is pressurized is reduced by moving the wall seal on the second end from the inside diameter to the outside diameter. Thus a structural reinforcing member for filter cartridge  300  is not required. 
     The combination of locking seal structures of the present invention eliminates the exposed wall seals used in prior art designs. Such an exposed seal is susceptible to deformation and damage during routine handling. 
     Yet another advantage of the present invention is that support housing installation/removal and filter cartridge replacement may be accomplished using simple tools. These features are important as these activities are sometimes done remotely given the high radioactive contamination levels present in the components of the filter vessel  500 . 
     Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. By way of example, in an alternative embodiment, one end of the filter cartridge  300  may be closed and not provided with a terminal seal  306 , 308 . This embodiment would be used for filter vessels  500  not requiring seals at both ends of the filter cartridge. Also, each of the terminal seals  306 , 308  may include embedded structural members and provide different types of sealing surfaces to accommodate aqueous flow from the outside to the inside of the filter. 
     It should be understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the following claims.