Abstract:
A bag house filter bag is suspended vertically from a separable hanger. The filter bag has a closure at the top, which is constructed by a series of tucks and folds. The closure also provides a support loop for engagement with the hanger. The filter bag is constructed mainly of woven fabric formed into a cylinder. The folding and stitching pattern of the fabric at the top end enables the bag to transition from linear at the site of the support loop to cylindrical with an even distribution of stress on the fabric. The hanger includes a cross member and a surrounding tube to reduce specific stress on the fabric. The hanger has a removable joint opening clasp at one end of the cross member to enable rapid insertion and removal of the hanger from within the suspension tube without contact, removal or other disturbance of the filter bag.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. application Ser. No. 14/627,949 filed Feb. 20, 2015 entitled Suspendable Filter Bag System, which is a non-provisional of U.S. provisional application No. 61/942,445 filed on Feb. 20, 2014 entitled “Filter Bag Suspension System,” priority from both of which priority is hereby claimed. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to flue gas filtration at power generating facilities. More specifically, this invention relates to “dry” or “semi-dry” flue-gas desulfurization (“FGD”) systems that include a “reverse air” type fabric filter to remove particulate matter from the flue gas prior to atmospheric emission. 
       BACKGROUND OF THE INVENTION 
       [0003]    Compliance with environmental regulations at facilities equipped with dry or semi-dry FGD processes requires removal of particulate matter from the flue gas at a location between the FGD process and emission point. The particulate matter entrained in the flue gas at this location typically consists of solid by-products of the combustion and FGD process including fly ash, partially-burned fuel, and various compounds of sulfur, chlorine, calcium and sodium. 
         [0004]    Many dry or semi-dry FGD systems include “reverse air” type fabric filters to remove particulate matter. Reverse air type fabric filters typically utilize multiple cylindrical filter bag assemblies, each comprised of a fine mesh filter fabric with an integral metal filter cap. The metal filter cap encloses the top end of the filter bag, thereby enabling the assembly to be suspended vertically within the bag house compartment. In the prior art, corrosion and subsequent failure of the filter cap typically causes irreparable filter bag damage, excessive particulate matter emission, unplanned decreases in power plant output, and excessive maintenance costs. Moreover, replacement of the integral filter cap (as a preventive maintenance action) typically necessitates replacement of the entire filter bag assembly, thereby adding to corrective maintenance costs. 
         [0005]    Therefore, there is a need in the art for an alternative suspendable filter bag device that is corrosion resistant and replaceable independently of the filter bag. There is also a need for a filter bag and suspension system which is durable, economical and requires less maintenance. 
       SUMMARY OF THE INVENTION 
       [0006]    In order to meet the need in the art as explained above, a suspendable filter bag system has been devised that replaces the integral metal filter cap with a novel releasable hanger depicted in the following figures of drawing. Generally speaking, the filter bag is composed of woven fabric and has a top, sides and a bottom including an opening at the bottom for receiving unfiltered flue gas. The air filter bag is substantially cylindrical, formed in part by a longitudinal seam which joins side edges of the bag fabric. A closure at the top of the bag is comprised of a lateral fold of gathered fabric. Before folding, pleats are added to reduce fabric stress concentration and to reduce its length. The pleats are then folded and stitched at the ends to form a series of tucks along a more or less linear top edge of gathered fabric. The gathered top edge is then folded over and stitched to the remainder of the bag along a lateral seam below the fold. This construction forms a single, elongate, laterally extending loop of fabric, which is open at the ends and approximately equal in length to the diameter of the cylindrical portion of the bag. The cylindrical shape of the remainder of the bag below is maintained by a series of vertically spaced rigid rings connected along the inside wall of the bag. 
         [0007]    The bag is suspended from the loop by a hanger, which connects the loop to a bag house hook above it. The hanger has a cross member that passes through the loop. The hanger is substantially triangular including an apex at the top and two side arms which terminate at ends of the cross member at the bottom. Two hooks, one at the end of one of the arms and another at the end of the connecting cross member, form a releasable hook and catch joint,which can be opened to accept the cross member into the bag loop and then reclosed to secure the bag to the hanger. Conversely the hooks can be disengaged to allow the removal of the hanger from the bag. Both hooks are integral with the hanger, which is formed by shaping a unitary length of heavy gauge metal wire. The hooks are preferably oriented perpendicular to one another. Stress between the loop fabric and the cross member is reduced by a tube placed over the cross member that spreads the weight of the bag across a larger area of greater radius. The tube is preferably at least as long as the fabric loop. 
         [0008]    In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application or to the details of construction in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being carried out in various ways. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a left, top, front perspective view of an apparatus in accordance with one embodiment of the invention; 
           [0010]      FIG. 2  is a front elevation of the apparatus of  FIG. 1  schematically shown installed in a bag house; 
           [0011]      FIG. 3  is a side elevation of the apparatus of  FIG. 1  schematically shown installed in a bag house; 
           [0012]      FIGS. 4 a  and 4 b    are a front elevational view and a top plan view, respectively, of the filtration bag of  FIG. 1  in an initial condition in accordance with the method of manufacturing by folding and stitching of one embodiment of the present invention; 
           [0013]      FIGS. 5 a  and 5 b    are a front elevational view and a top plan view, respectively, of the filtration bag of  FIG. 1  in an intermediate condition in accordance with the method of manufacturing by folding and stitching of one embodiment of the present invention; 
           [0014]      FIGS. 6 a  and 6 b    are a front elevational view and a top plan view, respectively, of the filtration bag of  FIG. 1  in a final condition in accordance with the method of manufacturing by folding and stitching of one embodiment of the present invention; 
           [0015]      FIGS. 7 a  and 7 b    are a side elevational view and a front elevational view, respectively, of the suspension hanger of  FIG. 1 ; 
           [0016]      FIG. 8  is a pattern layout showing the fold lines and stitching lines on the filtration bag in accordance with the method of manufacturing by folding and stitching of one embodiment of the present invention; 
           [0017]      FIGS. 9 a  and 9 b    are plan views which illustrate the formation of tucks on the filtration bag by pleating and folding in accordance with the method of manufacturing of one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0018]    A suspendable filtration device in accordance with an embodiment of the invention is illustrated in  FIG. 1  and is designated generally be reference numeral  12 . The device  12  generally comprises a filter bag  1  and a suspension hangar  14 . In the embodiment shown in  FIG. 1-3 , the filtration device is shown suspended from the ceiling  20  of a bag house by a ceiling hook  7 . 
         [0019]    The suspension hanger  14  comprises an elongate rigid member  5 , which is formed into a triangular shape having two side arms  5   a  and a cross member  5   b.  As best seen in  FIG. 7 , the side arms  5   a  are integrally connected at an upper vertex  24 . The cross member  5   b  is integrally formed with one side member at a lower vertex  26  and is oriented generally parallel to the plane of the bag house ceiling  20  when properly suspended. 
         [0020]    The hangar  5  is not integrally formed at the third vertex. Instead, the hangar  5  includes a releasable joint  8 , which releasably connects the free ends of the rigid member  5 . In this embodiment, a releasable joint  8  comprises a u-shaped hook  8   a  formed at one end of the rigid member  5  and a u-shaped catch  8   b  formed at the other end of the rigid member  5 . The hook  8   a  and catch  8   b  are oriented in opposite directions so as to enable releasable interconnection as best seen in  FIGS. 1 and 7 . When the joint  8  is disconnected, the cross member  5   b  can be inserted through or released from a tube  4 , which supports the filter bag  1 . When the joint is connected, the filtration bag and tube are securely suspended from the hangar  14 . 
         [0021]    The tube  4  passes through a loop  10  formed at the top of the filter bag  1  for suspending the filtration bag  1 . The loop  10  also forms a filter bag closure, which is formed, as described in more detail below, by folding over gathered fabric at the top of the bag and stitching it to the remainder of the bag along lateral seam  9  below the fold. 
         [0022]    Referring to  FIGS. 2 and 3 , the filtration device  12  is constructed and arranged to be suspended and contained within a bag house or similar enclosure through which flue gas is induced to flow by fan, draft or other pressure differential means. The filtration device  12  is arranged vertically such that unfiltered flue gas enters the filter bag  1  interior in a vertically upward direction as indicated by the lower, vertically-upwardly projecting fluid flow lines of  FIGS. 2 and 3 , and exits the filter bag through the side walls as indicated by the upper horizontally and/or horizontally-upwardly projecting fluid flow lines. The filter fabric and surface area of the filter bag  1  are selected to separate particulate matter from the flue gas stream with a separation efficiency, particle size classification and pressure differential suited to the specific application. 
         [0023]    The filter bag  1  is constructed principally of an elongate strip of woven filter fabric. The elongate edges of the fabric are overlapped and stitched along a longitudinal seam  2  to form a cylinder or tube having the requisite circumferential strength. Circular former ring(s)  3  are sewn into external pockets at regular intervals along the length of filter bag  1 . The interval between each circular former ring  3  is selected to prevent substantial deformation of the filter fabric cylindrical shape during operation. The filter bag  1  is suspended by the hangar  5  on the bag house ceiling hook  20 . 
         [0024]    The region of the filter bag  1  above the uppermost former ring  3   a  is folded and stitched in an important manner and serves several functions including: (1) transitioning the bag cross-sectional shape from circular to linear; (2) enclosing fully the uppermost end; and, (3) permitting insertion of a suspension apparatus such as the suspension tube  4  and hanger  5 . The construction of the filter bag  1  in the region above the uppermost former ring  3  is further optimized to minimize stress throughout the entire filter bag  1 , and most particularly in the region above the uppermost former ring  3  at which the cross-sectional shape transitions from circular to linear. Important construction parameters include the quantity and arrangement of the tucks and the tuck dimensions. The dimensions are selected so that the sum of the exterior angle beta (β) and adjacent interior angle delta (δ) is 180 degrees. 
         [0025]    Referring to  FIGS. 4-6 , the construction of filter bag  1  in the region above a reference line (located near and above the uppermost former ring  3   a  of  FIG. 1 ) is shown in three sequential steps with the filter fabric laid flat. In a first step shown in  FIGS. 4 a  and 4 b   , the filter fabric is folded and stitched along a longitudinal seam  2  in a “French fell” or similar pattern. The seam  2  is preferably located along the longitudinal centerline of the filter bag  1 . 
         [0026]    In an intermediate step shown in  FIGS. 5 a  and 5 b   , a collar of gathered fabric is formed proximate the end. In a preferred embodiment, the gathered fabric is formed by folding and stitching four tucks in the fabric along the fold and stitch lines, respectively, designate thereon. The longitudinal length of the tucks, and intermediate length of the collar, is identified by reference letter “A”. The radial or widthwise dimension of the tucks is identified by reference letter “B”. The width of the collar is identified by reference letter “C”. Preferably, the width of the tucks “B” is chosen so that the width of the collar “C” approximates the diameter of the filter bag  1  when the filter bag expands from its flat shape shown in  FIGS. 4-6  to a cylindrical shape by hanging in the bag house (the “installed diameter”). The tucks are preferably arranged generally as shown in  FIG. 5 a    in which all tucks and corresponding stitch lines are parallel with the longitudinal seam  2 , all tucks are positioned within the bag interior at approximately equal spacing intervals, and two tucks are laterally opposed with the corresponding stitch lines approximately coincident with longitudinal seam  2 . Excluding hem allowance, the longitudinal dimension “A” of the stitched tucks  3  is selected to be approximately two (2) times the length of the overlap “D”, described below. 
         [0027]    In a final step, show in  FIGS. 6 a  and 6 b   , the fabric loop  10  is formed in the collar by folding the filter material along a lateral (perpendicular to the longitudinal seam  2 ) and stitching the fabric to itself along a lateral seam  4 , which is approximately bifurcated by the longitudinal seam  2 . After the final step, the longitudinal length of the collar is reduced to a final dimension D chosen such that the sum of the interior and exterior angles beta (β) and delta (δ) shown in  FIG. 2  is approximately 180 degrees. 
         [0028]    Referring concurrently to  FIGS. 1 and 7 , the suspension tube  4  and hanger  5  are constructed of a metallic, composite or thermoplastic material selected for superior resistance to corrosion, deflection and deterioration in flue gas containing the solid, liquid and gaseous by-products of the combustion and FGD process. Such by-products include fly ash, partially burned fuel and various compounds of sulfur, chlorine, calcium, sodium and oxygen. The diameter of the suspension tube  4  is selected to minimize stress concentration in the fabric and stitching of filter bag  1 . The tube  4  accepts the cross member  5   b  of the hanger  5  which includes side arms  5   a  and  5   b.  The length “E” of suspension tube  4  is selected to approximate the installed diameter of filter bag  1 . 
         [0029]    The hanger  5  is constructed and arranged to minimize stress concentration within suspension tube  4 . The hanger  5  is also constructed and arranged to be rapidly inserted or removed from within the suspension tube  4  without contact, removal or other disturbance of filter bag  1 . To facilitate this latter function, the cross member  5   b  of the hangar  5  can be easily inserted and removed from the tube  10  by opening and closing the releasable joint  8 . Since the hook  8   a  and catch  8   b  are integrally formed from the hangar, which is made from a heavy gauge metal wire, the construction of the releasable joint is very simple and strong. One of the unique advantages of this construction is that a damaged or corroded hanger can be easily and quickly replaced with another hangar by passing the replacement hanger through the suspension tube prior to removing the corroded hangar. The weight of the filter bag  1  can then be supported by the replacement hanger before the corroded hanger is removed. This design feature avoids the need for taking down the bag as required by the suspension systems of the prior art. 
         [0030]    A fold and stitch pattern in accordance with a preferred embodiment of the invention is shown in  FIG. 8  and can be used to manufacture the filter bag  1  shown in  FIGS. 1-7 and 9 . Construction of the bag according to this pattern or its equivalent is important to the optimal distribution of forces through the fabric as the geometry of the construction transitions from circular to linearly diametric. The legend included on this drawing identifies the stitch center lines and both interior and exterior fold lines. 
         [0031]      FIG. 9 a    illustrates a plurality of preliminary pleats formed in the filter fabric that are necessary to form the tucks described above. With the filter fabric held more or less along a straight line, the filter fabric is first gathered into opposite facing center pleats  11  and  13  and end pleats  14  and  16 . The end pleats  14  and  16  are rotated (as shown by rotational direction arrows) into a configuration abutting one another and are sewn together forming end tucks  6 . The center pleats are then rotated (as shown by rotational direction arrows) into a configuration abutting the rest of the filter fabric and then sewn to form opposite facing center tucks  12 . Once sewn together, the preliminary collar has the cross sectional configuration shown in  FIG. 9 b   , which is an enlarged cross-sectional view of  FIG. 5   a.    
         [0032]    Therefore, the foregoing is considered as illustrative only of the principles of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.