Abstract:
A filter holder assembly is provided that utilizes a fail-safe regenerator unit with an annular spacer ring having an extended metal collar for containment and positioning of a compliant ceramic gasket used in the assembly. The filter holder assembly is disclosed for use with advanced composite, filament wound, and metal candle filters.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application relates to a U.S. patent application Ser. No. 09/676,342, filed on Sep. 29, 2000, entitled “FILTER HOLDER GASKET ASSEMBLY FOR ENHANCED SECUREMENT OF CANDLE FILTERS” to Bruck et al. 
    
    
     The Government of the United States of America has rights in this invention pursuant to Contract No. DE-AC21-94MC31147, awarded by the United States Department of Energy. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to hot-gas cleanup systems and more particularly to filter holder and gasket assemblies that provide particulate barrier seals between the body of a candle filter element and the filter holder when coupled to a hot gas cleanup system support plate. 
     BACKGROUND OF THE INVENTION 
     Modern industrial methods have resulted in a need for devices and systems that are capable of efficiently filtering high temperature combustion gases containing particulate material. In combustion turbine applications, for example, a combustion turbine uses energy generated from hot pressurized combustion gases produced by burning natural or propane gas, petroleum distillates or low ash fuel oil. When coal and other solid fuels are burned, particulates carried over from the combustion of such solid fuels can cause turbine blade erosion and fouling. An efficient system for filtering of such hot combustion gases would permit the use of such solid fuels. Examples of such filtering apparatus and systems can be found in U.S. Pat. Nos. 5,433,771 and 5,876,471. 
     Currently, various assemblies of commercially available candle filters are employed for application within hot gas filtration systems. For example, in co-pending application Ser. No. 09/393,561, filed Sep. 10, 1999 (Docket No. 99E7659), entitled “FILTER ASSEMBLY FOR METALLIC AND INTERMETALLIC TUBE FILTERS”, to Alvin, et al., there is taught the use of an integral metal filter failsafe-regenerator assembly; and in co-pending application Ser. No. 09/602,214, filed Jun. 23, 2000 (Docket No. 99E9210), entitled “MULTIPURPOSE SINGLE EXTERNAL SEAL FILTER ASSEMBLY FOR METALLIC AND CERAMIC TUBE FILTERS WITH INTEGRAL LOCKING MEANS”, to Alvin et al, there is taught the use of a single compression fit gasket for integral metal filter faisafe-regenerator assemblies. 
     With the development of advanced materials, the geometry of the candles has varied, particularly in the flange region, requiring modification to the fixturing and sealing arrangements for the individual elements within the filter housing, in order to provide an effective particulate barrier seal during use in high temperature applications for each candle configuration. Employing separate filter holder designs for each candle filter configuration adds considerable expense to such systems and is inefficient. 
     Accordingly, a new filter holder assembly design is desired that will securely mount candle filter elements with a wide variety of variably sized flange geometries, within existing hot gas filtration systems. Furthermore, such an improved filter holder is desired that can be effectively employed in high temperature, high pressure, oxidizing, as well as reducing gas process environments. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a filter holder assembly for holding a candle filter element within a hot gas cleanup system pressure vessel. The filter holder assembly includes a filter housing with a peripheral sidewall defining an interior chamber therein. A generally annular spacer ring is provided in the assembly and is positioned within the interior chamber. The assembly of the present invention further includes at least one top compliant gasket separate and apart from the filter housing. This top compliant gasket is preferably positioned on a candle filter flange end top surface for providing a seal between the spacer ring and the filter flange top surface. In addition, the top gasket is positioned generally adjacent to the collar of the spacer ring. 
     The assembly of the present invention further includes a collar that extends axially from the spacer ring and forms a stepped portion between the collar and the outside diameter of the spacer ring. In the present invention, this stepped portion permits the top gasket to seat against the spacer ring during filtering or back-pulsing, thereby resisting disruption of gasketing that can compromise the filtering effectiveness of the filter holder assembly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal, sectional view of a pressure vessel incorporating a filter assembly in accordance with the present invention; 
     FIG. 2 is a side, elevational view of an array of filter assemblies, including filter elements, coupled to a tube sheet as shown in FIG. 1; 
     FIG. 3 is a sectional view of a filter holder and gasket assembly employing a non-collared annular spacer ring; 
     FIG. 4 is a sectional view of a filter holder and gasket assembly depicting an embodiment in accordance with the present invention; 
     FIG. 5 is an enlarged, sectional view of a portion of the filter holder and gasket assembly of FIG. 4; and 
     FIG. 6 is a sectional view of a portion of a filter holder, candle filter and gasket assembly illustrating an alternate embodiment of this invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     FIG. 1 shows a filtering apparatus  20  for separating particulate matter from a gas stream. This apparatus includes a pressure vessel  22  in which there are mounted a plurality of clusters  24  comprising a plurality of filter element arrays  26 . These filter element arrays  26  include a plurality of filter elements  28 . 
     The pressure vessel  22  has a dome-shaped head  30  and a body  32 . The dome-shaped head  30  terminates in a linear tip  34 , defining an exit opening or nozzle  36  for the filtered gas to be removed from the vessel  22 . While the exit is shown at the top, it may also be at the side of the head  30  for ease of attachment of auxiliary components. The body  32  includes a dirty gas inlet  25 , where gas containing particulates enters at a temperature of from about 1110° F. (600° C.) to about 1830° F. (1000° C.) and also usually contains about 2 vol. % to 25 vol. % water vapor in the form of steam, 200 ppmv to 0.5 vol. % sulfur in the form of SO 3 , SO 2 , H 2 S and other components such as C, chloride, alkali, and the like. The body also contains an upper part  38  having a generally circular cylindrical shape joined by a frustoconical ash hopper  40  for receiving the particulate matter terminating in a linear tip defining an opening or nozzle  42  connected to an ash discharge line. A plurality of ports  44  extend from the dome-shaped head  30 . The ports  44  provide a site for inserting instrumentation and for viewing the interior of the dome-shaped head  30  during shutdown periods. Through each port, tubes  46  for supplying a backpulse burst of gas for cleaning the filters  28  can be placed. 
     Referring to FIG. 2, the pressure vessel includes a tube sheet  48 . The tube sheet  48  supports the plurality of filter element arrays  26 . Each filter element array  26  comprises a manifold plenum consisting of an upper plate  50  and a lower plate  52  and side plate. In accordance with the present invention, each filter element  28  is held by a filter assembly  60  and coupled to the corresponding lower plate  52  of the manifold plenum. The filter assemblies  60  are integrated into a structural unit by plenum support pipes  54 . Each plenum support pipe  54  is secured centrally within the pressure vessel  22 . A dust shed or particle-deflector  56  having a generally frustoconical shape is also shown. 
     Referring now to FIG. 3, a single filter holder and gasket assembly  60  is shown in assembled form. The filter holder and gasket assembly  60  comprises a filter holder  72  having a peripheral sidewall  74  which defines an interior chamber  76 . A fail-safe regenerator device  78  is positioned within the interior chamber  76 , and an annular spacer ring  80  is mounted within the interior chamber  76 . The assembly  60  also includes a sock or sleeve  82 , a top compliant gasket  84 , a middle compliant gasket  86 , an additional compliant primary gasket  85  and a cast clamp  88 . It is noted that the fail-safe regenerator device  78  is preferably, but not necessarily, a part of the assembly. The spacer ring  80  is positioned adjacent to and/or in contact with the compliant primary gasket  85 . 
     Referring again to FIG. 3, in one embodiment of the invention shown, the spacer ring  80  is permanently mounted to the fail-safe regenerator to produce a single unit that is placed within the interior chamber  76  of the filter holder and gasket assembly  60 . While this arrangement makes assembly more convenient, one skilled in the art will readily appreciate that the spacer ring  80  and fail-safe regenerator  78  can be assembled as two separable components. In the embodiment illustrated, the spacer ring  80  may be welded in abutment with the fail-safe regenerator device  78  to provide a means for positioning the fail-safe regenerator unit  78  in the interior chamber  76 . So positioned, the top gasket  84  is compressed between the bottom of the spacer ring  80  and the top surface  81 ′ of a candle filter flange  83 ; and the compliant primary gasket  85  is compressed between the top section of the spacer ring  80 ′ and the stepped section of the interior chamber  76 ′. When assembled with cast clamp  88  and bolt  89  the filter element  28  resists moving and contacting the inner surface of the filter holder  77 , thereby preventing possible damage to the filter element  28 . 
     The fail-safe regenerator device  78  is provided to prevent particulate matter from traveling into the clean gas area of the pressure vessel if a filter element or gasket fails, is damaged or breaks. Additionally, the fail-safe regenerator  78  will heat the backpulse gas, which is generally cooler than the gas stream coming from the combustion or gasification process gas stream, minimizing thermal fatigue, cracking and/or failure of the filter element  28 . 
     Referring again to FIG. 3, the filter holder  72 , annular spacer ring  80 , and fail-safe regenerator device  78  are made of a material that can withstand the relatively high temperatures that are reached in a particular system and possess the strength and durability to support the filtering components, preferably a high temperature metal material, such as 310S stainless steel. 
     Referring again to FIG. 3, the gaskets and cushions  82 ,  84 ,  85  and  86  are individual components that are separate and apart from the filter holder  72 . These components are preferably made from high temperature ceramic fibers that are woven or braided into a desired pattern or shape, such as an annular gasket or circular sleeve. The shape and size of each component must be large enough to be positioned on or around the candle filter  28  to provide an adequate particulate barrier seal to resist gas leakage. More particularly, the sleeve or sock  82  is preferably made of a woven or braided oxide fabric. The top gasket  84  and middle gasket  86  can be made of a braided or woven oxide based fabric that encases an oxide fiber, intermeshed, compliant mat, or of a lapped or rolled woven or braided configuration. 
     Referring again to FIG. 3, the sock or sleeve  82  is positioned around the outer surface of a filter flange  83  of the candle filter element  28  to prevent contact of the filter element  28  and/or filter flange  83  with the interior surface of the metal filter housing  77 . The top compliant gasket  84  is positioned along the top surface  81 ′ of the filter flange  83  to provide a compliant cushion and particulate matter barrier seal between the spacer ring  80  and filter flange top surface  81 ′. The middle compliant gasket  86  is positioned at the base of the filter flange  83  over the sock or sleeve  82 . The middle compliant gasket  86  provides a cushion between the lower section of the filter flange  83 ′, the upper section of the filter body  28 ′ and the cast clamp  88 . The gasket  85  is positioned around the spacer ring. When the gasket  85  is compressed by the cast clamp ring  88 , a primary particulate barrier seal can be formed. The assembled filter holder and gasket assembly  60  can then be coupled to the rest of the combustion assembly. 
     Referring now to FIG. 4, in the form of the present invention shown, there is disclosed an assembly  101  for securing the position of the mat-filled complaint ceramic gasket seals during use of candle filter elements in hot gas filter system applications. This assembly  101  includes an extended metal collar  102  as either an integral or separately connected part of an annular spacer ring  104  that is positioned above a candle filter element  106 . The extended collar  102  is positioned along the inside diameter of the spacer ring  104 . The dimensions of the extended metal collar  102  are provided such that it can extend axially into the inside diameter bore of the candle filter  106 , preferably such extension distance is approximately 10-mm. The extended metal collar  102  is also structured such that an approximately 1-mm gap results between itself and the inside diameter of the candle filter element  106 . Preferably, the annular spacer ring  104  with extended metal collar  102  is joined to the failsafe-regenerator  112 , forming an integral unit to facilitate installation within the filter holder assembly  101 . 
     Referring again to FIG. 4, a top or mat-filled compliant ceramic gasket  110  is positioned along the outer surface of the extended metal collar  102  of the annular spacer ring  104  as shown. The gasket  110  seats against the annular spacer ring  104 , which serves as the base for a fail-safe regenerator unit  112 . In this manner, the extended metal collar  102  protects the top gasket  110  from contact with pulse cleaning gas and dislocation during a filter process operation, as well as during back pulse cleaning. As a result, the top gasket  110  remains properly positioned during operation of the hot gas filter system; maintains alignment of the fail-safe regenerator unit  112  within the filter housing, the primary compliant gasket  111 , the candle filter element  106 , the middle compliant gasket  114 , and a cast metal clamp  116 ; and, resists passage of fines from the process gas stream into the cleaned gas passage of the filter assembly  101 . 
     Referring now to FIG. 5, in the form of the invention shown, the extended metal collar  102  of the annular spacer ring  104  can be represented as having dimensions x and y. A properly selected y dimension, for example, can be effective in providing the annular spacer ring  104  with the capability to secure and retain the position of a gasket such as gasket  110  as shown, along the top surface of the candle filter  106  within the filter assembly. It is important to note that the design of the spacer ring  104  provides a relatively simple geometry that, with respect to manufacturability considerations, does not require extensive machining to form. The substantially L-shaped cross-section of the spacer ring  104 , for example, eliminates the need for forming relatively complex geometries by excessive machining of components. 
     Table 1 provides examples of preferred x and y dimensions for candle filter elements with variably sized flange configurations. 
     
       
         
               
               
               
               
             
           
               
                   
                 TABLE I 
               
               
                   
                   
               
               
                   
                 Candle 
                 x,mm 
                 y,mm 
               
               
                   
                   
               
             
             
               
                   
                 DuPont PRD-66 
                 10 to 12 
                 20.5 
               
               
                   
                 McDermott CFCC 
                 10 to 12 
                 19 
               
               
                   
                 Techniweave CFCC 
                 10 to 12 
                 16.5 
               
               
                   
                   
               
             
          
         
       
     
     It can therefore be appreciated that the appropriate dimensions can be selected for a given candle filter element to promote securement and retention of the top compliant gasket  110 , shown in FIGS. 4 and 5, within the candle filter system. 
     The extended collar of the present invention therefore provides the benefits of: (i) proper positioning and retention of the top compliant gasket  110 , shown in FIGS. 4 and 5, during filter operation; (ii) aligning the candle element properly within the metal filter housing; (iii) resisting passage of fines into the clean gas passage of the filter system; and (iv) mitigating catastrophic failure of the filter elements and release of particulates to a turbine, for example. 
     It can be appreciated that the extended collar of the present invention can also be applied to a broad range of filter elements with variable flange geometries and configurations. It can be further appreciated that the dimensions of the collar can be adjusted to accommodate both commercially available, conventional filter elements as well as “non-standard” or developmental candle filter elements. In a preferred embodiment of the present invention, the outside diameter along the axial extension of the extended collar is dimensioned to provide a gap between this outside diameter and the inside diameter of a given candle filter element flange. 
     The present invention may be embodied in other forms without departing from the spirit or essential attributes thereof. For example the alternate embodiment illustrated in FIG. 6 can be employed, particularly for metal, intermetallic, and superalloy porous filter elements. In this embodiment an annular, axial extension  122  is formed during manufacture of the filter element  120  along the flange surface  124  proximate the bore  126  of the filter element. The raised section  122  thus captures the top compliant gasket  128  between the top surface  124  of the flange  130  and the now recessed annular spacer ring  132 . The arrangements of the primary compliant gasket  134 , fail-safe regenerator  136 , sleeve  138 , middle compliant gasket  140 , cast clamp/bolts (shown in FIG. 4) would all remain as previously described. Accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.