Abstract:
An axial seal plate for an air preheater having a single, unitary structure including a sealing portion disposed intermediate first and second end portions extending orthogonally from the sealing portion. The axial seal plate does not including any welds for joining the end portions to the sealing portion.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to the apparatus of a rotary regenerative air preheater. More particularly, the invention relates to axial seal plates of air preheaters.  
           [0002]    A rotary regenerative air preheater transfers sensible heat from the flue gas leaving a boiler to the entering combustion air through regenerative heat transfer surface in a rotor which turns continuously through the gas and air streams. The rotor, which is packed with the heat transfer surface, is divided into compartments by a number of radially extending plates referred to as diaphragms. These compartments are adapted to hold modular baskets in which the heat transfer surface is contained.  
           [0003]    The air preheater is divided into a flue gas side or sector and one or more combustion air sides or sectors by sector plates. In a typical installed rotary regenerative heat exchanger, flexible radial seals mounted on the top and bottom edges of the diaphragms are in close proximity to these sector plates and minimize leakage of gas and air between sectors. Similarly, flexible axial seals mounted on the outboard edge of the diaphragms are in close proximity to axial seal plate assemblies mounted on the inner surface of the housing and minimize leakage therebetween.  
           [0004]    Conventional axial seal plate assemblies include numerous component parts. The axial seal plate generally includes a pair of side plates which are each mounted to the side edges of a curved sealing plate by long seam weld. Multiple support ribs are mounted to the radially outer surface of the axial seal plate to provide pressure stiffening. The support ribs are usually burned to a radius and are welded to the sealing plate. The long length of the weld joining the side plates to the sealing plate leads to various weld distortions, which effect the close tolerances required for the axial seal plate.  
           [0005]    The axial seal plate seal surface it set at its proper position through the use of access doors on each side of the seal plate, which allow access for measuring the critical sealing gaps on each side of the axial seal plate assembly.  
         SUMMARY OF THE INVENTION  
         [0006]    Briefly stated, the invention in a preferred form is an axial seal plate for an air preheater having a single, unitary structure including a sealing portion disposed intermediate first and second end portions extending orthogonally from the sealing portion. The axial seal plate does not including any welds for joining the end portions to the sealing portion.  
           [0007]    Preferably, the axial seal plate also has first and second transition portions disposed between the sealing portion and the first and second end portions, respectively. Each transition portion extends at an angle of 45° from the sealing portion and the respective end portion extends at an angle of 45° from the transition portion.  
           [0008]    The axial seal plate also includes multiple pressure stiffening bars mounted to the sealing portion. Preferably, at least one tab mounts each of the pressure stiffening bars to the sealing portion. The inner edge of each tab is welded to the outer surface of the sealing portion and the outer edge portion of each tab is welded to the pressure stiffening bar to mount the pressure stiffening bars to the seal plate.  
           [0009]    It is an object of the invention to provide an axial seal plate which requires less structural parts and eliminates the need for access doors.  
           [0010]    It is also an object of the invention to provide an axial seal plate which requires less welding during construction.  
           [0011]    It is further an object of the invention to provide an axial seal plate which requires no machining of the seal surface.  
           [0012]    Other objects and advantages of the invention will become apparent from the drawings and specification. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawings in which:  
         [0014]    [0014]FIG. 1 is a general perspective view of a conventional bisector rotary regenerative air preheater which is cut-away to show the upper sector plates.  
         [0015]    [0015]FIG. 2 is a top view of a conventional axial seal plate assembly.  
         [0016]    [0016]FIG. 3 is a front view of the axial seal plate assembly of FIG. 2.  
         [0017]    [0017]FIG. 4 is a perspective view of the radially outer side of the axial seal plate assembly of FIG. 2.  
         [0018]    [0018]FIG. 5 is a top view of an axial seal plate assembly in accordance with the invention.  
         [0019]    [0019]FIG. 6 is a front view of the axial seal plate assembly of FIG. 5.  
         [0020]    [0020]FIG. 7 is a perspective view of the radially outer side of the axial seal plate assembly of FIG. 5. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    [0021]FIG. 1 of the drawings is a partially cut-away perspective view of a typical bi-sector air preheater  10  showing a housing  12  in which the rotor  14  is mounted on a drive shaft or post  16 . The housing is divided by means of the flow impervious sector plates  18  and  20  into a flue gas sector  24  and an air sector  26 . Corresponding sector plates are also located on the bottom of the unit. Mounted on the inside of the housing are axial seal plate assemblies  28  which extend the full height of the rotor.  
         [0022]    The hot flue gases enter the air preheater  10  as indicated by the arrow  30 , flow through the flue gas sector  24  where heat is transferred to the heat transfer surface in the rotor  14 . As this hot heat transfer surface then rotates through the air sector  26 , the heat is transferred to the air flowing through the rotor from the bottom as indicated by the arrow  32 . Consequently, the cold air inlet and the cooled gas outlet define a cold bottom end and the hot gas inlet and the heated air outlet define a hot top end. The rotor  14  has a shell  34  and is divided into a plurality of pie-shaped compartments  36  by the diaphragm plates  38  with each compartment containing a plurality of heat exchange basket modules  40 .  
         [0023]    The axial seal plate  42  of a conventional axial seal plate assembly  28  generally includes a pair of side plates  44  which are each mounted to the side edges  46  of the curved seal plate  42  by long seam weld  48 . The long length of the welds  48  joining the side plates  44  to the seal plate  42  leads to various weld distortions, which effect the close tolerances required for the axial seal plate  42 . Multiple support ribs  50  are mounted to the radially outer surface  52  of the seal plate  42  with multiple stitch welds  54  to provide pressure stiffening. The radially inner edge  56  of the support ribs  50  are usually burned to a radius which matches the curvature at the seal plate  42 .  
         [0024]    The axial seal plate  58  of an axial seal plate assembly  60  in accordance with the present invention is a single, unitary structure, rolled and formed to have a sealing portion  62  disposed intermediate oppositely disposed integral end portions  64 . The use of a unitary axial seal plate  58  eliminates the need for two vertical seam welds to join the end portions  64  to the sealing portion  62 . To facilitate rolling the end portions  64 , a transition portion  66  is formed between the sealing portion  62  and each end portion  64 . The transition portion  66  splits the ninety degree (90°) bend defined by the sealing portion  62  and each end portion  64  into two forty-five degree (45°) bends.  
         [0025]    Multiple pressure stiffening bars  68  are mounted to the radially outer surface  70  of the sealing portion  62  to ensure that the seal plate  58  is sufficiently rigid. The radially inner edge  72  of each stiffening bar  68  is not burned to the radius of the sealing portion  62 , as are conventional support bars  50 . Rather, the stiffening bars  68  have a rectangular shape. Tabs  74  welded to the outer surface  70  of the axial seal plate  58  and the stiffening bars  68  bridge any gaps between the inner edge  72  of the stiffening bars  68  and the outer surface  70  at the sealing portion  62  and thereby mount the stiffening bars  68  to the seal plate  58 .  
         [0026]    Preferably, each tab  74  has a length  76  of 3 inches. As shown in FIG. 8, three tabs  74  generally provide sufficient support to mount each stiffening bar  68  to the seal plate  58 . Although each tab  74  is welded along its full length  76  to the seal plate  58 , the limited number of tabs  74  and the fixed length  76  of the tab  74  reduces the total length of the weld required to mount each bar  68 , compared to conventional seal plate assemblies  28 , reducing weld distortions in the sealing portion  62 . That is, a total weld length of 18 inches is required to mount each stiffening bar  68  of the subject invention to the seal plate  58  while the minimum total weld lengths of 52 inches are generally required in conventional seal plate assemblies  28 . Since the sealing portion  62  has a close tolerance (0.060″ on the radius over 10-12 feet), eliminating weld distortions reduces the assembly time.  
         [0027]    The low distortion axial seal plate assembly  60  also includes four seal plate plugs  78  through which the axial seal plate assembly  60  is set at the proper dimension. This eliminates the requirement for multiple access doors on each side of all axial seal plates common to the current axial seal plate design. L-shaped adjusters  80  mounted to the end portions  64  of the seal plate  58  facilitate positioning the seal plate assembly  60  during installation and removal.  
         [0028]    It should be appreciated that the low distortion axial seal plate assembly  60  requires less structural parts, requires less welding, and eliminates the need for access doors. Consequently, the assembly  60  may be manufactured and installed at a significant cost savings, compared to conventional axial seal plate assemblies  28 .  
         [0029]    While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.