Abstract:
A filtration system ( 10 ) operable at elevated temperatures and regenerateable in situ employing microwave energy ( 99 ). In one embodiment, the system includes multiple channels ( 35 ) with means for selectively placing individual ones of the channels on-line for filtration and off-line for regeneration.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a non-provisional application claiming priority based on provisional application Ser. No. 60/378,023, filed May 13, 2002. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   This invention was made with Government support under Subcontract No. 4000000723 funded by the Government. The Government has certain rights in the invention. 

   BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   This invention relates to filters and filter systems which are operable at elevated temperatures and capable of extracting volatilizable particulates from a gas stream. In particular, this invention relates to ceramic fiber-paper based filters which may be regenerated in situ employing microwave energy. 
   2. Background of the Invention 
   Heretofore, it has been known in the art that ceramic fibers may be formed into a ceramic paper. It is also suggested in the prior art that this paper may be corrugated and wound into a cylindrical filter for the capture of volatilizable particulates from a gas stream, and that the filter may be regenerated employing microwaves. 
   However, these prior art filters and/or the systems within which they are employed suffer from problems of premature clogging of the entry ends of the tubular chambers defined by the corrugations, and from inadequate capacity to accommodate the anticipated or actual overall flow of gas streams through the filter, resulting in excessive pressure drop across the filter, at times creating undesirable or even disastrous results, and/or regeneration only during shut-down or diversion of the source of the gas stream, such diversion effectively taking the filtration system offline. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with one aspect of the present invention, there is provided at least one filter module comprising a housing which defines an inlet and an outlet for the passage of a gas stream into and out of the housing. Within the housing there is disposed a pleated ceramic fiber-based filter medium which separates the interior of the housing into at least two filtration chambers, one of which is in fluid communication with the inlet to the housing and a second one of which is in fluid communication with the outlet of the housing. As desired, multiple further filtration chambers may be interposed in fluid flow communication between the “inlet” chamber and the “outlet” chamber. A gas stream entering the inlet chamber passes through the multiple pleats of the filter medium of each chamber wherein particulates are extracted from the gas stream and accumulate on the filter medium. The filtered air stream passes through the outlet chamber and any intervening chamber, and exits the housing through the outlet thereof. As desired, the inlet and/or the inlet to the housing may be in the form of a plenum extending along one side of the housing. 
   In accordance with a further aspect of the invention, there is provided an outlet plenum which extends along the outlet side of the housing (opposite the inlet side). In one embodiment, this plenum serves the dual function of a pathway for conveying away the exhaust gas stream from the filter and as a selectable pathway for the transmission of microwaves into the filter housing. 
   In one embodiment, the overall filter structure comprises at least one, and preferably a plurality of individual housing/pleated filter subassemblies, all aligned in a common plane or parallel planes so that their respective outlet sides are aligned such that they share a common elongated exhaust plenum. Within, and concentrically of, the interior of this exhaust plenum there is provided a rotatable, preferably tubular, member. This member includes a plurality (one for each filter subassembly or grouping of filter subassemblies) of ceramic microwave-permeable segments spaced apart from one another along the length of the wall of the tubular member. The remainder of the tube includes holes of a proper diameter to stop 2.45 GH microwaves while allowing the free passage of exhaust gas therethrough. Thus, each segment is sized and designed to cover a respective one or ones of the outlets of the aligned outlets of the multiple subassemblies to define a transparent window for the admission of microwaves (while preventing the flow of exhaust gas therepast), but stopping exhaust flow, passing along the length of the tubular member, into a respective one or ones of the filter subassemblies when the segment is in register with the outlet from a respective filter subassembly. In this embodiment, each segment also is positioned at a location which is progressively rotated about the outer circumferential wall of the tubular member. In one embodiment, no two filter subassemblies are open to microwaves at any given time. In other embodiments, only a limited number of filter subassemblies are open to microwaves at any given time Thus, through selective rotation of the tubular member about its longitudinal axis, admission of microwaves into a filter subassembly may be restricted to only a single filter subassembly or a selected group of filter subassemblies, at any given time, thereby providing for the regeneration of a single filter subassembly or selected group of filter subassemblies while the remaining filter subassemblies remain available for receiving and filtering of the inlet gas stream flowing through the inlet plenum and exhausting of the cleaned gas stream via the exhaust plenum. This selective regeneration of the filter subassemblies is conducted in situ and provides for sequential regeneration of the multiple subassemblies, thereby preventing any material interruption of the flow of the gas stream through the overall filter system, hence the ability of the overall filter system to accommodate a substantially larger volume of gas flow, and avoiding undesired pressure drop (back pressure) across any one of the multiple filter subassemblies, all without deleterious effects on the normal operation of the generator of the contaminated gas stream, e.g., a diesel engine. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is a representation of one embodiment of a filter system including various features of the present invention, including multiple stacked filter subassemblies; 
       FIG. 2  is a representation of the gas exhaust end of the filter depicted in FIG.  1  and partly cutaway to depict various internal features of the filter; 
       FIG. 3  is a representation, partly cutaway, depicting a filter system including various features of the present invention, including a single filter subassembly; 
       FIG. 4  is representation of an elongated tubular member for rotatable disposition within the exhaust plenum of the filter depicted in  FIG. 1 ; 
       FIG. 5  is a representation of one embodiment of a housing/pleated ceramic fiber paper filter medium module suitable for use in the filter of the present invention; and, 
       FIG. 6  is a exploded view representing a top comb and a bottom comb employed in the disposition of a pleated ceramic-based filter paper within a module of the present system. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring specifically to  FIG. 1 , the depicted embodiment of a filter system  10  of the present invention includes a housing  12 , which in the depicted embodiment is of a generally rectangular cross-section having its opposite short sides  14 , 16  sealed by respective end plates  18 , 20 . Each of the opposite longer sides  22 , 24  of the housing preferably is rounded and partially defines an inlet plenum  26  and an outlet plenum  28 , respectively, for the flow of a gas stream (see arrows) through the filter system. 
   Internally of the housing there is provided at least one, and preferably a plurality of filter modules  25  (see FIG.  5 ), each of which, in the depicted embodiment includes a pleated ceramic filter paper  27  captured between first and second comb elements  29 , 31  (typical), respectively, (see FIGS.  6  and  7 ). As seen in  FIGS. 2 and 5 , the top margins (ribs)  33  of each comb projects above the planar level of the pleated paper, thereby defining multiple gas flow channels  35  (typical, see arrow C)along the length of each module. The bottom of each module is of like construction as the top of the module and includes ribs  36  which define flow channels along the bottom of the module, the channels of both the top and bottom of the module being oriented in like directions from the inlet to the outlet end of the module (see FIG.  2 ). 
   The inlet end  37  of each module is closed by a gas impermeable wall  39  which extends from the bottom edge  41  of the inlet end of the module to a location short of the top portion  43  of each comb rib. The exhaust end  45  of each module includes an end wall  47  which extends from a height equal to the height of the ribs and extends from the rib height to terminate short of the bottom edge  49  of the module (See  FIG. 2 ) thereby leaving an open space  51  at the inlet ends of the top flow channels and closure of the outlet ends of the top flow channels. The top and bottom of each module is overlaid by top and bottom panels  53 , 55 , respectively, of the housing, such panels being overlaid and sealed to the top surfaces of the ribs of the top and bottom of the module, respectively. 
   Referring to  FIG. 6 , one embodiment of a filter module includes a first plurality of top combs  29  whose opposite ends are secured to end walls  39  and  47  and a second plurality of bottom combs  31  which are designed such that the teeth of the bottom combs mesh between the teeth of the top combs to capture therebetween a pleated sheet of ceramic fiber-based filter paper  27 . 
   In  FIG. 2 , there are depicted two stacked modules  25 , 25 ′, the stack being formed by the placement of the bottom  57  of the upper module  25  in overlying relationship to bottom  57 ′ of the lower module  25 ′, with the bottom ribs of the top module abutting respective ones of the ribs of the bottom ribs of the bottom module of the stack, thereby defining a plurality of planar flow channels  41  between the two overlying bottoms of the modules. 
   At the exhaust end of the flow channels  41  of the stacked modules of  FIG. 2 , there are provided first and second obliquely converging elongated panels  61 , 63  which extend along the full dimension of the exhaust ends of the stacked modules. One side  65  of the first panel  61  is secured to the end wall  47  of the top module  25  and one side  67  of the second panel  63  is secured to the end wall  47 ′ of the bottom module  25 ′. The opposite sides  69 , 71  of the converging panels are joined to one another by a porous ceramic microwave permeable wall  73 . This wall, in turn, is mounted within a slot in a tubular wall which extends along the length of the exhaust plenum of the housing. 
   In the depicted embodiment of  FIG. 1 , the filter system further includes an inlet  77  at a first end  32  of the inlet plenum  26 , an outlet  34  at a first end of the outlet plenum  28 , and a hollow tubular microwave barrier  79  disposed internally of, concentric with, and extending along at least substantially the length dimension of the outlet plenum  28  and with a portion  81  thereof projecting beyond a second end  83  of the outlet plenum. This tubular barrier is rotatably mounted within the outlet plenum and is provided at its outboard portion  81  with a first ring gear  85  which encircles the tubular barrier. An indexing motor  87  is mounted to the housing and includes a driven shaft which carries a second ring gear  89  thereon, the teeth of the second ring gear  89  meshing with the teeth of the first ring gear whereby activation of the motor functions to rotate the tubular barrier about its longitudinal axis within the outlet plenum, as desired. 
   As seen in  FIG. 4 , at least one, and most commonly a plurality of cutouts  90  through the wall  92  of the tubular barrier  79  are provided to define one or more outlet ports  95 , 95 ′ for the movement through such cutout(s) of microwaves from within the internal volume of the hollow tubular barrier. 
   Referring specifically to  FIGS. 1 and 2 , microwaves are introduced from a source  99  thereof, into the end of the hollow tubular microwave barrier  79 , and move along the length of the tubular barrier toward the exhaust port. As required, a microwave barrier  101  may be provided adjacent the exhaust port to preclude the passage of microwaves out through the exhaust port. Thus the microwaves are contained within the exhaust plenum except in the instance where a port  95 ,  95 ′ through the wall of the tubular barrier is in register with the ceramic wall  71  adjacent the exhaust ends of the stacked modules. In this latter situation, microwaves move from the exhaust plenum, through the ceramic wall and into the modules. 
   In the operation of filter system of the present invention, a gas stream bearing volatilizable particulates is directed into the filter system via the inlet and into the inlet plenum. This gas stream is distributed by the plenum into the inlet ends of the flow channels of both the top and bottom modules, hence along the exposed surfaces of the multiplicity of pleats of the ceramic-based filter paper. (see arrows in  FIG. 2  indicating gas flow). The gas passes through the filter paper with the particulates in the gas stream being captured on the exposed surfaces of the pleats. The cleaned gas thereupon flows along the exhaust flow channels defined between the overlying bottoms of the modules, through the ceramic wall, thence out through the exhaust port of the exhaust plenum. 
   In a preferred embodiment, as indicated by the dashed lines  103 , 103 ′ of  FIG. 1 , a plurality of stacked modules are ganged together are served by a common inlet plenum and a common exhaust plenum. In this embodiment, the length of the tubular microwave barrier is sufficient to include a cutout through its wall at multiple locations along the length of the barrier, a given cutout being spaced circumferentially apart from adjacent one or ones of others of the cutouts so that only one or a selected number of the cutouts are in register with their respective modules at any given time. (see FIG.  4 ). The registration of the cutouts with their respective modules is accomplished by means of the indexing motor operating through the first and second ring gears. In this manner, as desired, one or more than one of the modules are accessed by microwaves and closed to full exhaust flow at any given time, while during this given time, others of the modules are closed off from the microwaves and open to full exhaust flow. 
   Within those modules which are accessed by the microwaves, the microwaves react with the ceramic-based filter paper to heat the filter paper to the volatilization temperature of the particulate matter captured on the filter paper. The gaseous products from the volatilization of the particulates are swept out the exhaust plenum, thereby regenerating the filter paper in situ. During the time in which one (or more) module is being regenerated, there is no material change in the flow of gas through the others of the ganged modules, hence there is little or no deleterious effect with respect to back pressure, flow capacity, or interruption of the device which is generating the particulate-bearing gas stream.