Abstract:
A precoat filtration element for a condensate polisher system that yields high weld strength in the form of a septa having a core with a plurality of perforations and wound filter elements, the wound filter elements wound around said core, and the septa including an extension flange at one end; and an end fitting having a solid base and a threaded post, the end fitting being slideably engaged within the extension flange such that an outside wall of the solid base is in mechanical contact with an inside wall of said extension flange, and upon insertion, the threaded post is coaxial with the septa center axis, and extends longitudinally outwards away from said septa. Spot welding the end fitting solid base to the extension flange provides high tensile strength over prior art designs.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to precoat-type filter elements or septa, and to a filtration system based on solid particulate filtration media, particularly, but not limited to, ion-exchange particulate filter media, and the like, supported on a septum. Such filtration systems, often known as “precoat filters” are widely used in a variety of applications. More specifically, the present invention relates to an end plug attachable to a septum&#39;s cylindrical body at each end. 
         [0003]    2. Description of Related Art 
         [0004]    Precoat filter units may be used in the chemical and refinery processing industry, the treatment of industrial waste, and the treatment of condensate boiler feed-water in fossil and nuclear steam generating systems. In particular, these filters are used where, after treatment, the liquid product must be very high in purity and closely adhere to specified standards of particulate, deionization, or chemical composition. Precoat-type filters are used, for example, in condensate polishing in fossil nuclear, and concentrated solar power plants. Precoat filtration systems, such as powdered precoat demineralizer systems, have been successfully used in condensate polishing technology for removing dissolved and suspended impurities from fluid streams in fossil and nuclear power generating facilities. 
         [0005]    A precoat filter is a type of filter in which a slurry is applied as a cake, called a precoat, to the exterior of a porous support structure called a septum. After the precoat is applied to the septum, a fluid to be filtered is then directed through the precoat and the septum where the precoat serves to filter the fluid. 
         [0006]    Precoat filtration uses a fine dispersion of a filter medium such as cellulose, carbon, or diatomite or powdered resin, which is deposited in a thin layer on a coarser carrier. A precoat filter element is a device designed to filter solid particles from a liquid-solid slurry after a precoat of built up solid material (filter aid or filtered solid) has been applied to the inner surface of the filter medium, 
         [0007]    The predominant force keeping the precoat material on the element is flow, though rough, irregular surfaces help keep precoat material in place on the element surface. A continuously wound precoat element design ensures consistent differential pressures and, in turn, uniform precoats. 
         [0008]    Currently, wound filter elements are constructed of polypropylene, nylon or carbon fiber yarn wound around a stainless steel core with stainless steel end fittings. Resins, such as Powdex®, are used with the filter. Powdex® is a powdered, strong acid or strongly basic hydroxide form of ion exchange resins. They may be used individually or as a mixture of both types. To ensure product consistency the elements are typically manufactured with computer controlled winding machines. These elements are available in a variety of end fittings for Powdex® systems, such as flanged doubled open ended, Sealfast™, or Ecoloc™ designs. 
         [0009]    The wound Powdex® filter elements are available with suitable cores and end fittings. 
         [0010]    The resin may be precoated on Aegis® wound and DualGuard® precoat septa in precoat filtration systems, by Graver Technologies LLC, which in some instances have been referred to as Powdex® filter demineralizers. 
         [0011]    A particular example of water treatment requiring stringent quality control, and in which the use of precoated filters is common, is the polishing of condensed boiler steam in fossil or nuclear power plants. Two principal types of nuclear power plants are boiling water reactors (BWR) and pressurized water reactors (PWR). Though they use different processes for generating steam to drive turbines in producing electricity and require different water chemistry, both employ similar water purification systems commonly referred to as condensate polishers. 
         [0012]    In boiling water reactors, should particles pass through the feedwater system and into the reactor, they may cause degradation and become radioactive. Should radioactive particles be created, they pose a costly disposal problem and may well present a threat of exposing personnel to radioactive materials. The presence of particulate contaminants in pressurized water reactors can cause stress cracks in heat exchanger tubes. 
         [0013]    A condensate polisher, such as Powdex®, is a system used to remove impurities from turbine condensate before it is re-used for boiler feedwater. It combines the mechanical process of filtration with the chemical process of ion exchange to remove most impurities from turbine condensate. This filter element is typically a tubular string wound septum, coated with Powdex® ion exchange resin to remove impurities from a fluid stream. 
         [0014]    Precoating is a process of applying a coating of material (precoat) to the outside of a septum so that the coating traps the impurities from a fluid stream instead of the septum. Once the filtration is performed over a period of time, the system is backwashed (cleaned) by reversing the fluid flow to remove impurities. 
         [0015]    Unlike filter cartridges, where particle entrapment must be effected throughout the depth of the yarn winding filter medium, it is essential in precoat septum applications that no particle entrapment be effected within the body of the yarn winding. That is to say, in a cartridge filter, the cartridge is normally utilized until it becomes plugged or nearly plugged, and then it is discarded. Therefore, particle entrapment throughout the entire depth of the filter medium is essential to optimize the filter&#39;s usefulness. In the case of the precoat septa, however, backflushing is an essential requirement so that the device can be cleaned and reused over and over again. Ideally, therefore, particle entrapment within the depths of the winding is not desired, since particles entrapped within the depth do not flush out effectively. Accordingly, the yarn winding on a precoat septum is preferably wound to assure a tighter pore size, particularly on the surface of the winding, to prevent particulate matter from entering the depth of the yarn winding. 
         [0016]    Filter/Demineralizer systems have the capabilities of removing both dissolved and suspended impurities. This is usually achieved by the processes of filtration and ion exchange, but can also combine the processes of adsorption and absorption. 
         [0017]    Precoat filter demineralizers combine superior filtration, compared to deep bed polishers, with kinetically superior ion exchange by using finely ground, highly regenerated resins precoated onto septa in pressure vessels that are specially designed to provide uniform precoat application and process flow distribution. 
         [0018]    The standard of performance required in such highly demanding environments has come to indicate the use of a finely divided ion-exchange resin filtration system wherein the particulate filter medium is supported on a septum where it is intended to be retained by the flow stream of the liquid to be filtered. 
         [0019]    A septa provides for strong, durable support for enhanced resin precoating/flow distribution and efficient, aggressive backwashing. Typically, septa are manufactured of stainless steel. Advanced, stainless steel backwashable precoat septa have been used for reactor water cleanup (RWCU), fuel pool, and other specialty applications in nuclear power generation. For example, Aegis® PowerGuard elements incorporate an advanced sintered metal design that allows for precise control of porosity (from 2 to 200 microns). Key features include low pressure drop; virtual elimination of contaminant leakage; high strength; excellent resistance to corrosion and fatigue; collapse strengths over 400 psid; low carbon 316L, stainless steel construction; operating temperatures up to 1000° F.; and excellent cleaning and precoating characteristics. 
         [0020]    The septa include end plugs for attachment. Currently, manufacture of the septa, including the end plug, and the subsequent attachment of the end plug to the septa, uses a labor and tooling intensive multistage process. Problems in the prior art with attachment of the end plug include lower than acceptable weld strength during spot welding. This affects the overall attachment strength, durability, and longevity of the end plug/septa combination. 
         [0021]    Attempts to provide a stronger spot weld to attach an end plug to the septa cylindrical body have included introducing different weld recipes to the prior art end plug design; however, these iterations failed to achieve the high strength, easy, manufacturability, and extended durability desired. 
         [0022]    Although it is counter-intuitive to implement an end plug having a solid base, especially for enhancing a welded joint, the advantage realized by the present invention of having a stronger precoat filtration element connection end plug allows for an extended life for a filter element constantly subjected to contaminants, and numerous backflushing forces. 
       SUMMARY OF THE INVENTION 
       [0023]    Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an end plug for a precoat filtration element that provides for a more secure attachment to a septa, and a stronger weld junction. 
         [0024]    It is another object of the present invention to provide an end plug for a precoat filtration element that facilitates an improved spot welding attachment scheme. 
         [0025]    The above and other objects, which will be apparent to those skilled in the art, are achieved in the present invention which is directed to a precoat filtration element comprising: a septa having a core with a plurality of perforations and wound filter elements, the wound filter elements wound around the core, the septa including an extension flange at one end; and an end fitting comprising a solid base and a threaded post, the end fitting slideably engaged with the extension flange of the septa such that an outside wall of the solid base is in mechanical contact with an inside wall of the extension flange, and upon insertion, the threaded post is coaxial with the septa center axis, and extends longitudinally outwards away from the septa. 
         [0026]    The septa may cylindrical in cross-section and the solid base of the end fitting comprises a cylindrical block. The solid base is preferably spot welded to the extension flange. 
         [0027]    The wound filter elements include polypropylene, nylon, carbon, polyester, or glass fiber yarn wound around the septa. The septa and the end fitting may comprise stainless steel. 
         [0028]    A fine dispersion of a filter medium of cellulose, diatomite, or powdered resin may be deposited in a thin layer on the wound filter elements. The wound filter elements are wound to realize a tighter pore size on an outside surface to prevent particulate matter from entering the depth of the wound filter element winding. The fine dispersion of the filter medium may include divided ion-exchange resin. 
         [0029]    A median maximum load of a welded end fitting/septa combination between the solid base and the extension flange is preferably greater than 2000 foot-pounds. A median extension of the welded end fitting/septa combination is preferably about less than 0.30 inches. 
         [0030]    The extension flange may be cylindrical with a diameter greater than the end fitting solid base diameter. 
         [0031]    The solid base and the threaded post may be machined from a single block and are integral with one another. 
         [0032]    In a second aspect, the present invention is directed to an end plug for a precoat filtration element comprising a solid cylindrical base having an outside diameter and a center axis, and a threaded post coaxial with the solid cylindrical base center axis. 
         [0033]    In a third aspect, the present invention is directed to a method of making a precoat filtration element comprising: providing a cylindrical, perforated septa having an extension flange at one end; winding the septa with a wound filter element; treating the filter media with a fine dispersion of a filter medium of cellulose, diatomite, or powdered resin deposited in a thin layer on the wound filter element; inserting a solid cylindrical base of an end plug within the extension flange; and spot welding the solid cylindrical base of the end plug to the extension flange, such that a median maximum load of the spot welded end plug/septa combination between the end plug solid base and the extension flange is greater than 2000 foot-pounds. 
         [0034]    In a fourth aspect, the present invention is directed to a condensate polisher system for removing impurities from a turbine condensate before re-use for boiler feedwater, including: a steam generator in fluid communication with a turbine at one communication point and a filter/demineralizer element at a second communication point, the filter/demineralizer element including a plurality of precoat filter elements in fluid communication with a condensate pump, a condenser, and a hotwell, each of the filter/demineralizer elements comprising: a septa having a core with a plurality of perforations and wound filter elements, the wound filter elements wound around the core, the septa including an extension flange at one end; and an end fitting comprising a solid base and a threaded post, the end fitting slideably engaged with the extension flange of the septa such that an outside wall of the solid base is in mechanical contact with an inside wall of the extension flange, and upon insertion, the threaded post is coaxial with the septa center axis, and extends longitudinally outwards away from the septa; wherein the condensate polisher system combines a mechanical process of filtration with a chemical process of ion exchange to remove impurities from the turbine condensate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0035]    The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
           [0036]      FIG. 1  depicts a partial cross-sectional view of a precoat filter element having a perforated septa core terminated by an attachment end plug; 
           [0037]      FIG. 2  depicts a cross-sectional view of the end plug of  FIG. 1 ; 
           [0038]      FIG. 3  depicts a top view of end plug of  FIG. 1  with a centered threaded post; 
           [0039]      FIG. 4  depicts a standard spot weld arrangement; 
           [0040]      FIG. 5  depicts a cross-sectional diagram of a spot weld apparatus welding the cup-shaped end plug of  FIG. 3  to cylindrical flanges of a septa; 
           [0041]      FIG. 6  depicts a graph of tensile data for a spot welded cup-shaped top fitting end plug for a precoat filtration element; 
           [0042]      FIG. 7  depicts an embodiment of the end plug of the present invention; 
           [0043]      FIG. 8  depicts a partial cross-sectional view of the end plug of  FIG. 7  attached to a septa; 
           [0044]      FIG. 9  depicts a graph of tensile data for a spot welded top fitting end plug of the present invention for a precoat filtration element. 
           [0045]      FIG. 10  depicts a cross-sectional diagram of a spot weld apparatus welding end plug to a septa, and more specifically to a flange extension of the septa; and 
           [0046]      FIG. 11  depicts a filter/demineralizer configuration for condensate polishing utilizing a precoat filtration element having the end plug of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0047]    In describing the preferred embodiment of the present invention, reference will be made herein to  FIGS. 1-11  of the drawings in which like numerals refer to like features of the invention. 
         [0048]      FIG. 1  depicts a partial cross-sectional view of precoat filter  10  having a perforated septa core  12  terminated by an attachment end plug  14  of the prior art. End plug  14  is inserted within an extended cylindrical flange  16 , which extends longitudinally from the cylindrical body of septa core  12 , and spot welded in place. 
         [0049]    Resistive spot welding (RSW) is a process in which contacting metal surfaces are joined by the heat obtained from resistance to electric current. Work-pieces are held together under pressure exerted by electrodes. Typically the sheets are in the 0.5 to 3 mm (0.020 to 0.118 in) thickness range. The process generally requires two shaped copper alloy electrodes to concentrate welding current into a small “spot” and to simultaneously clamp the sheets together. Forcing a large current through the spot will melt the metal and form the weld. Additional weld material may also be placed at the spot welding point. The attractive feature of spot welding is that a lot of energy can be delivered to the spot in a very short time (approximately 10-100 milliseconds). That permits the welding to occur without excessive heating of the remainder of the sheet. 
         [0050]    The amount of heat (energy) delivered to the spot is determined by the resistance between the electrodes and the magnitude and duration of the current. The amount of energy is chosen to match the sheet&#39;s material properties, its thickness, and type of electrodes. 
         [0051]      FIG. 2  depicts a cross-sectional view of the prior art end plug  14  of  FIG. 1 . Referring to  FIG. 2 , end plug  14  comprises a body portion  18  that defines a hollow, cup-shaped, cylindrical body forming a void  20  facing (for the purposes of directionality only) downwards. Upon attachment to septa  12 , body portion  18  is axially aligned, such that body portion  18  is centered about septa  12 . The outside wall of body portion  18  aligns longitudinally with the cylindrical body of septa core  12 . Body portion  18  is designed to have an outside diameter that is less than the inside diameter of extended cylindrical flange  16 , such that end plug  14  may be insertably attached to extended cylindrical flange  16  by weld, thread, friction fit, or the like. Currently, it is advantageous from the standpoint of strength and reliability to weld end plug  14  to the extended cylindrical flange  16  of septa core  12  by a spot welding technique. The present invention enhances the strength of the weld, and facilitates manufacturability of the connection. 
         [0052]    Extending from the base of body portion  18  is a threaded post  22  used to attach the precoat filter to other segments of the filtration system. Threaded post  22  is radially centered about the base of body portion  18 , and extends in a direction opposite the open end of body portion  18 . 
         [0053]      FIG. 3  depicts a top view of end plug  14  with centered threaded post  22 . 
         [0054]    Initially, to manufacture an end plug, wound rolls of stainless are fed into a stamping press over custom tooling to blank the body of the component. In this manner, the stamped end plug is “cup shaped” forming body portion  18  and void  20 . A second step and fixture are used to provide a hole for threaded post  22 . Threaded post  22  is then inserted within the hole, and resistance welded in a third fixture, forming the final end plug depicted in  FIG. 2 . 
         [0055]    The final component is a stamped, down-facing cup that in certain applications preferably has an outer diameter of approximately 1.085 inches, a wall height of approximately 0.50 inches, and a wall thickness of about 0.050 inches, with a ¼-20 threaded post  22  sticking out of the top surface of the cup. The longitudinal axis of threaded post  22  is perpendicular to the top surface  24  of body portion  18 . 
         [0056]    The end plug is then spot welded to the cylindrical flanges  16  of septa  12 . 
         [0057]      FIG. 4  depicts a standard spot weld arrangement. Spot welding typically sandwiches two pieces of material  40 ,  42  between two electrodes  44 ,  46  having electrode tips  44   a ,  46   a  respectively. Spot welding usually requires current flow through a certain number of layers, and does not utilize a center plug, which reduces resistance—the key ingredient to a spot weld. 
         [0058]      FIG. 5  depicts a cross-sectional diagram of a spot weld apparatus welding the cup-shaped end plug  14  to septa cylindrical flanges  16 . Electrodes  44 ,  46  and electrode tips  44   a ,  46   a  contact diametrically opposed points on cylindrical flanges  16  once end plug  14  is slideably inserted within flanges  16 . A weld point  48  is formed at each point aligned with electrode tips  44   a ,  46   a , respectively. 
         [0059]      FIG. 6  depicts a graph of tensile data for a spot welded cup-shaped top fitting end plug for a precoat filtration element. Each curve 1-12 represents a different specimen. The load in foot-pounds denoted by the ordinate (Y-) axis is graphed against the measured extension in inches, denoted by the abscissa (X-) axis. Maximum loads and maximum extensions are recorded in Table 1. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE I 
               
               
                   
               
               
                   
                   
                 Maximum  
                 Extension at  
               
               
                   
                 Specimen  
                 Load 
                 Maximum Load 
               
               
                   
                 label 
                 [lbf] 
                 [in] 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 A 
                 1349.2 
                 0.23 
               
               
                 2 
                 B 
                 739.9 
                 0.10 
               
               
                 3 
                 C 
                 1366.2 
                 0.22 
               
               
                 4 
                 D 
                 1113.3 
                 0.16 
               
               
                 5 
                 E 
                 1383.8 
                 0.23 
               
               
                 6 
                 F 
                 1372.6 
                 0.22 
               
               
                 7 
                 G 
                 1490.8 
                 0.14 
               
               
                 8 
                 H 
                 1398.5 
                 0.16 
               
               
                 9 
                 J 
                 1334.5 
                 0.18 
               
               
                 10 
                 K 
                 1003.9 
                 0.15 
               
               
                 Maximum 
                   
                 1490.8 
                 0.34 
               
               
                 Minimum 
                   
                 739.3 
                 0.20 
               
               
                 Median 
                   
                 1244.9 
                 0.20 
               
               
                   
               
             
          
         
       
     
         [0060]    As shown, the maximum load recorded was 1490.8 foot-pounds, and the corresponding extension at maximum load was 0.34 inches. On average, the median maximum load of the twelve specimens was 1244.9 foot-pounds, and the median extension recorded was 0.20 inches. 
         [0061]    In order to enhance the strength of the welded junction, the proposed new generation end plug is machined from round stock in the form of a monolithic one piece solid cylinder, having an outer diameter, for example, of 1.085 inches, a height of approximately 0.5 inches, with a ¼-20 threaded post, which is preferably integral to the solid cylinder from which it is made. 
         [0062]      FIG. 7  depicts end plug  70  of the present invention. End plug  70  comprises a solid base in the form of a cylindrical block  72  having chamfered edges  74 . This design adds weight to the end precoat filtration element, and presents a larger heat sink to the welding process, thus making for a counter-intuitive design enhancement; however, the weight gain is offset considerably by the advantages realized in facilitating a spot weld attachment, and the resultant increased weld strength. 
         [0063]    Threaded post  76  is preferably a ¼-20 threaded post, axially centered about solid cylindrical block  72 . In one embodiment, post  76  is machined from the same round stock that formed solid cylindrical block. In an alternative embodiment, threaded post  76  is attached to cylindrical block  72  by weld, threads, friction fit, or other attachment schemes known in the art suited for the adverse environments to which the precoat filtration element is exposed. 
         [0064]      FIG. 8  depicts a partial cross-sectional view of end plug  70  of  FIG. 7  attached to septa  78 . Referring to  FIG. 8 , end plug  70  comprises cylindrical block  72  that defines a solid cylindrical body having a planar face  80  facing (for the purposes of directionality only) downwards. Upon attachment to septa  78 , cylindrical block  72  is axially aligned with, and is centered about, and coaxial with, septa  78 . The outside wall of cylindrical block  72  may either be the same diameter as the outside diameter as the septa, or may extend slightly beyond the longitudinal cylindrical walls of septa  78 ; that is, cylindrical block  72  may have a larger diameter than septa  78  or be the same diameter as septa  78 . Septa  78  includes a flange extension  82  at its end. Flange extension  82  may be completely circular about septa  78 , having a slightly larger diameter than the diameter of septa  78  to receive cylindrical block  72 , or may be segmented extensions (not completely circumferential). Flange extension  82  extends parallel to the cylindrical walls of septa  78  in the longitudinal or axial direction and forms a larger diameter than the septa cylindrical walls to receive cylindrical block  72 . 
         [0065]    End plug  70  is insertably attached to flange extension  82  preferably by spot weld, but may also be attached by complementary threads, friction fit, or other attachment schemes known in the art. Currently, it is advantageous from the standpoint of strength and reliability to weld end plug  70  to flange extension  82  of septa  78  by a spot welding technique, and the present invention is designed to strengthen the welded joint by allowing for a more robust weld attachment. 
         [0066]      FIG. 9  depicts a graph of tensile data for a spot welded top fitting end plug of the present invention for a precoat filtration element. Each curve 1-5 represents a different specimen. The load in foot-pounds denoted by the ordinate (Y-) axis is graphed against the measured extension in inches, denoted by the abscissa (X-) axis. Maximum loads and maximum extensions are recorded in Table 2. 
         [0000]    
       
         
               
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                 Maximum  
                 Extension at  
               
               
                   
                 Specimen  
                 Load 
                 Maximum Load 
               
               
                   
                 label 
                 [lbf] 
                 [in] 
               
               
                   
               
             
             
               
                 1 
                 1 
                 1604.3 
                 0.16 
               
               
                 2 
                 2 
                 2180.3 
                 0.25 
               
               
                 3 
                 3 
                 2065.8 
                 0.28 
               
               
                 4 
                 4 
                 2273.2 
                 0.31 
               
               
                 5 
                 5 
                 2217.7 
                 0.29 
               
               
                 Maximum 
                   
                 2273.2 
                 0.31 
               
               
                 Minimum 
                   
                 1604.3 
                 0.16 
               
               
                 Median 
                   
                 2180.3 
                 0.28 
               
               
                   
               
             
          
         
       
     
         [0067]    As shown, the maximum load recorded was 2273.2 foot-pounds, almost 800 foot-pounds greater than that realized by a cup-shaped end plug under the same spot welding conditions. The corresponding extension at maximum load was 0.31 inches. On average, the median maximum load of the five specimens was 2180.3 foot-pounds (an 800 foot-pound difference over the prior art), and the median extension recorded was 0.28 inches (only 8/100 ths  of an inch greater than the prior art). 
         [0068]    The minimum weld strength of the new generation end plug of the present invention was measured to be 6 to 8.5 times greater than that of the prior art. This comes at a cost of weight and weld current/time; however, given the remote location of these devices in a system, and the difficulty (and hazard) of replacing or repairing them, the benefits of using an end plug of the present invention in many instances outweigh the detriments of weight, cost, and weld time. 
         [0069]      FIG. 10  depicts a cross-sectional diagram of a spot weld apparatus welding end plug  70  to septa  78  (of which only the septa&#39;s flange extension is shown), and more specifically to flange extension  82 . Electrodes  86 ,  88  and electrode tips  86   a ,  88   a  respectively, contact diametrically opposed points on flange extension  82  once end plug  70  is slideably inserted within flange extension  82 . A weld point  90  is formed at each point aligned with electrode tips  86   a ,  88   a , respectively. 
         [0070]    A precoat filtration element of the present invention is utilized in a condensate polisher system to remove impurities from, for example, a turbine condensate before it is re-used for boiler feedwater. 
         [0071]      FIG. 11  depicts a filter/demineralizer configuration for condensate polishing. In this example, a steam generator  92  is in fluid communication with a turbine  94  at one communication point, and a filter/demineralizer configuration  96  at a second communication point. Filter/Demineralizer configuration  96  includes a plurality of precoat filter elements  98 , which are in fluid communication with condensate pump  100 , condenser  102 , and hotwell  104 . This condensate polisher combines the mechanical process of filtration with the chemical process of ion exchange to remove most impurities from the turbine condensate. Given the placement of the precoat filter elements, removal or repair would be costly, timely, and impractical. Consequently, it is advantageous for the design of the precoat filter element to be robust. Although contrary to prior art designs, and counter-intuitive to designs for simplifying welded joints in particular, the present invention&#39;s introduction of a solid, monolithic cylindrical block end plug presents a stronger welded bond that is far greater than that presented by prior art designs. 
         [0072]    While the present invention has been particularly described, in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.