Abstract:
A bypass seal for a rotary regenerative air preheater includes primary and secondary seal leaves that are joined at a single position longitudinally intermediate their first and second sends. The first end portion of the primary seal leaf extends longitudinally beyond the first end of the secondary seal leaf and the second end portion of the secondary seal leaf extends longitudinally beyond the second end of the primary seal leaf. When installed in the air preheater, the first end portion of the primary seal leaf of each bypass seal in one of the seal rings overlaps the second end portion of the secondary seal leaf of an adjacent bypass seal in the seal ring.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to rotary regenerative air preheater and more particularly to bypass seals for rotary regenerative 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 is supported in a housing and 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. In the normal arrangement, circumferential bypass seals are provided between the rotor and the housing to prevent the air and gas from flowing around the outside of the rotor.  
           [0003]    In conventional air preheaters, the bypass seals have two, separate, overlapping leaves, a base leaf and a second, overlapping leaf which covers leakage paths through the base leaf. Each of the leaves is typically thirty six (36) inches long and there is fifty percent (50%) overlap between the leaves, providing a combined bypass seal length of fifty four (54) inches. The bypass seals are installed in the field, requiring the installer to hold the two seal leaves in place during the installation process.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention involves an improved design of bypass seals for a rotary regenerative air preheater. The invention involves the use of primary and secondary seal leaves that are joined at a single position longitudinally intermediate their first and second ends to form a bypass seal. The first end portion of the primary seal leaf extends longitudinally beyond the first end of the secondary seal leaf and the second end portion of the secondary seal leaf extends longitudinally beyond the second end of the primary seal leaf such that the first end of the primary seal leaf defines the first end of the bypass seal and the second end of the secondary seal leaf defines the second end of the bypass seal. When installed in the air preheater, the first end portion of the primary seal leaf of each bypass seal in one of the seal rings overlaps the second end portion of the secondary seal leaf of an adjacent bypass seal in the seal ring.  
           [0005]    Each of the seal leaves includes a base portion and a sealing portion extending from the base portion to a sealing edge. The sealing portion has a plurality of tabs separated by equidistantly spaced slots extending laterally from the sealing edge. The slots provide additional flexibility to the bypass seal and facilitate bending the bypass seal into an arcuate form during installation. One of the tabs of each seal leaf overlaps each of the slots of the other seal leaf to prevent leakage through the slot.  
           [0006]    The base portions of each of the seal leaves define a plurality of complimentary equidistantly, longitudinally spaced mounting slots. The first of the mounting slots is positioned at a distance D 1  from the first end of the bypass seal and the last of the mounting slots is positioned at the distance D 1  from the second end of the bypass seal. The first mounting slot of the primary seal leaf is positioned at the distance D 1  from the first end of the primary seal leaf, the last mounting slot of the primary seal leaf is positioned at a distance D 2  from the second end of the primary seal leaf, the first mounting slot of the secondary seal leaf is positioned at a distance D 2  from the first end of the secondary seal leaf, and the last mounting slot of the secondary seal leaf is positioned at the distance D 1  from the second end of the secondary seal leaf, where D 2 &gt;D 1 . 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a general perspective view of a rotary regenerative air preheater.  
         [0008]    [0008]FIG. 2 is a cross-section side view of a portion of a rotary regenerative air preheater illustrating the bypass seals of the present invention.  
         [0009]    [0009]FIG. 3 is an exploded view of the bypass seal of FIG. 2.  
         [0010]    [0010]FIG. 4 is a front view of the assembled bypass seal of FIG. 2.  
         [0011]    [0011]FIG. 5 is an enlarged and more detailed view of Area  5  of FIG. 2.  
         [0012]    [0012]FIG. 6 is an enlarged and more detailed view of Area  6  of FIG. 2. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    [0013]FIG. 1 of the drawings is a perspective view of a rotary regenerative air preheater  10  of the type to which the present invention applies. Forming the base of the unit is the cold end center section  12  which is constructed in the conventional manner known in the art and comprises structural steel support beams and the associated support members (not shown in detail) to form the support frame. The rotor of the air preheater (not shown in FIG. 1) is rotatably supported on this cold end center section  12 . The upper end of the rotor is supported by the hot end center section  14 .  
         [0014]    Mounted on the sides of the cold end center section  12  are the cold end connecting plate duct assemblies  16  and  18 . These form the connections and the transition between the duct work of the steam generator and the generally circular housing  24  of the air preheater. Mounted on the sides of the hot end center section  14  are the hot end connecting plate duct assemblies  20  and  22 . Like the cold end connecting plate duct assemblies  16  and  18 , these form the connections and transition between the duct work and the air preheater housing  24 . Attached to and extending between the hot and cold connecting plate duct assemblies is the rotor housing  24 .  
         [0015]    With reference to FIG. 2, the cold end center section  12  and the hot end center section  14  are shown in cross-section in a simplified form, excluding all the internal structural details. Attached to the sides of the cold end center section  12  are the cold end connecting plate duct assemblies  16  and  18  and the hot end connecting plate duct assemblies  20  and  22  are attached to the sides of the hot end center section  14 . The rotor  26  is rotatably mounted between the cold and hot end center sections.  
         [0016]    [0016]FIG. 2 illustrates the rotor housing arrangement wherein the housing  24  rests on the horizontal housing support flange  28  which is installed around the periphery of the cold end connecting plate duct assemblies  16  and  18 . Mounted to the flange  28  are a series of vertical alignment bars  30  which extend upwardly from the flange  28  all around the periphery. The housing  24  and the alignment bars  30  are welded to a cold end circumferential connecting plate flange  32 . The hot end connecting duct assemblies  20  and  22  also have a horizontal flange plate  34  around the periphery similar to flange  28 . The alignment bars  36  are welded to and extend downwardly from this flange  34 . The upper end of the housing  24  and these alignment bars  34  are mounted to the hot end connecting plate flange  38 .  
         [0017]    With reference to FIGS. 2, 5, and  6 , annular “T-bar” sealing members  40 ,  42  are attached around the periphery of the top and bottom end portions  44 ,  46  of the rotor  26 . Extending inwardly from the inside of the housing  24 , generally near both the top and bottom ends  48 ,  50  of the rotor  26 , are the connecting plate flanges  32 ,  38  which each form a generally annular-shaped flange all around the rotor  26 . Attached to the flanges  32 ,  38  are the bypass seal brackets  52 ,  54  which likewise collectively extend all the way around the rotor  26 . Attached to the brackets  52 ,  54  are the actual bypass seals  56 .  
         [0018]    With reference to FIGS. 3 and 4, a primary seal leaf  58  is mounted to a secondary seal leaf  60  to form each bypass seal  56 . Each seal leaf  58 ,  60  includes a base portion  62  and a sealing portion  64  which extends at an obtuse angle α from the base portion  62  of the leaf. The seal leaves  58 ,  60  are manufactured from conventional material, such that the assembled bypass seal  56  is a flexible member. The sealing portion  64  of each seal leaf  58 ,  60  is divided into a plurality of tabs  66  by slots  68  which extend from the sealing edge  70 , to provide additional flexibility to the bypass seal  56 . The slots  68  are longitudinally, equidistantly spaced, providing tabs  66  that have substantially the same width W. When the primary and secondary seal leaves  58 ,  60  are assembled to form the bypass seal  56 , the slots  68  in each leaf  58 ,  60  is positioned adjacent to a tab  66  of the other leaf  60 ,  58 , such that the tabs  66  of one leaf  58 ,  60  block leakage through the slots  68  of the other leaf  60 ,  58 .  
         [0019]    Each seal leaf  58 ,  60  has a plurality of equidistantly longitudinally spaced mounting slots  72 , preferably four such slots  72 , which are patterned non-symmetrically on the leaf  58 ,  60 . That is, the first slot  74  in the primary seal leaf  58  is positioned at a distance D 1  from the right side edge  76  of the seal leaf  58 , the last slot  78  in the primary seal leaf  58  is positioned at a distance D 2  from the left side edge  80  of the seal leaf  58 , the first slot  82  in the secondary seal leaf  60  is positioned at a distance D 2  from the right side edge  84  of the seal leaf  60 , and the last slot  86  is positioned at a distance D 1  from the left side edge  88  of the seal leaf  60 , where D 2 &gt;D 1 . Consequently, when the mounting slots  72  of the primary seal leaf  58  are aligned with the mounting slots  72  of the secondary seal leaf  60 , the left end segment  90  of the primary seal leaf  58  is not overlapped by the secondary seal leaf  60  and the opposite, right end segment  92  of the secondary seal leaf  60  is not overlapped by the primary seal leaf  58 . When the bypass seals  56  are installed in the air preheater  10 , the bypass seals  56  are positioned such that the left end segment  90  of the primary seal leaf  58  of each bypass seal  56  overlaps with the right end segment  92  of the secondary seal leaf  60  of an adjacent bypass seal  56 , thereby preventing leakage between adjacent bypass seals  56 . It should be appreciated that the subject invention also includes a bypass seal  56  having D 2 &lt;D 1 , so long as the mounting slots  72  of the seal leaves  58 ,  60  all of the bypass seals  56  to be installed in a single air preheater  10  have the same relationship.  
         [0020]    In a preferred embodiment, multiple spot welds  94  located on the longitudinal centerline  96  of the bypass seal  56  mount the primary seal leaf  58  to the secondary seal leaf  60 . It should be appreciated that other conventional means for mounting the two seal leaves  58 ,  60  together, for example a single spot weld, a seam weld, rivets, etc., may also be used. It should also be appreciated that the two seal leaves  58 ,  60  may be mounted together at a longitudinal position other than the centerline  96 . When the bypass seal  56  is installed, it is bent to conform to the curvature of the housing  24  and rotor  26 . Such bending results in a small amount of relative movement between the two seal leaves  58 ,  60  of the bypass seal  56 . If the seal leaves  58 ,  60  are mounted together at two or more longitudinally spaced positions, the spot welds  94  (or other means for mounting the two seal leaves together) will constrain the relative movement between the two seal leaves  58 ,  60 . Such constraint can result in deformation of the bypass seal  56  which could negatively impact its performance. If the two seal leaves  58 ,  60  are mounted together at only one longitudinal position, relative motion on either side of the weld position is not constrained. Small variations in the longitudinal positions of the individual spot welds  94  in a bypass seal  56  are generally acceptable, so long as such variation does not result in substantial deformation of the bypass seal  56  during installation.  
         [0021]    The assembled bypass seal  56  is mounted to the bypass seal bracket  52 ,  54  in the field by a plurality of nuts  98  and bolts  100 , where the threaded shaft of each bolt  100  is inserted through an opening  102  in the bypass seal bracket  52 ,  54  and a mounting slot  72  of the bypass seal  56  to be engaged within the threaded opening of the nut  98 . The lateral length L of the mounting slot  72  allows for proper positioning of the bypass seal  56 . The lateral length L of the mounting slot  72  and the obtuse angle α of the sealing portion  64  of the bypass seal  56  also allow the sealing edge  70  of the bypass seal  56  to be biased against the sealing surface  104  of the “T-bar”  40 ,  42 . This provides a better seal and ensures that the sealing edge  70  maintains intimate contact with sealing surface  104  as the material of the sealing edge  70  is worn during use.  
         [0022]    When the air preheater  10  is assembled, the bypass seals  56  form circumferential bypass seal rings  106 ,  108  positioned between the bottom and top ends  50 ,  48  of the rotor  26  and the bottom and top flanges  28 ,  34 , respectively, and between the rotor  26  and the housing  24 , to prevent the bypass of air and gas around the rotor in the gap  110  between the rotor  26  and the housing  24 . When installed, the bypass seals  56  are flexible, circumferential members which are biased against the sealing surfaces  104  to form a gas and air tight seal.  
         [0023]    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.