Abstract:
A heat transfer element basket assembly for a rotary regenerative heat exchanger having a basket framework including oppositely disposed first and second side shells, means for holding the side shells in a spaced relationship, and heat absorbent material is disposed within the framework. The inboard end portions of first and second substantially planar flange plates are mounted to the outboard end portions of the first and second side shells, respectively. The outboard end portions of the first and second flange plates are each mounted to an adjacent diaphragm plate to install the basket assembly in the heat exchanger rotor. The first and second side shells of the basket assemblies define an angle therebetween which is substantially equal to the angle of the diaphragm plates. The outboard end portions of the first and second flange plates may be mounted to a diaphragm plate by bolting, welding or a combination where one of the flange plates is bolted and the other flange plate is welded.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to rotary regenerative heat exchangers. More particularly, the present invention relates to heat exchange baskets, which contain heat absorbent material, for rotary regenerative heat exchangers. 
     A rotary heat exchanger is employed to transfer heat from one hot gas stream, such as a flue gas stream, to another cold gas stream, such as combustion air. The rotor contains a mass of heat absorbent material which is first positioned in a passageway for the hot gas stream where heat is absorbed by the heat absorbent material. As the rotor turns, the heated absorbent material enters the passageway for the cold gas stream where the heat is transferred from the absorbent material to the cold gas stream. 
     In a typical rotary heat exchanger, such as a rotary regenerative air preheater, the cylindrical rotor is disposed on a vertical central rotor post and divided into a plurality of sector-shaped compartments by a plurality of radial partitions or diaphragms extending from the rotor post to the outer peripheral shell of the rotor. These sector-shaped compartments are loaded with heat exchange baskets which contain the mass of heat absorbent material commonly comprised of stacked plate-like elements. 
     In many conventional horizontal rotary heat exchangers having full sector heat exchange baskets, the baskets are attached to the rotor by a formed flange. The formed flange is bent to an included angle of less than 90° and has one end portion mounted to the side of the basket and another end portion which is bolted to a shell bar. The flange is subjected to high bending stresses and to fatigue loading as the rotor rotates and is therefore subject to failure later in life. The nature of the formed flange design does not allow for the optimization of frontal area for heat transfer surface. Installation of shell bars for mounting the full sector heat exchange baskets, along with the associated gussets and filler pieces to reduce bypass flow, is very time consuming either in the manufacture of a new rotor, or the modification of an existing rotor. 
     SUMMARY OF THE INVENTION 
     Briefly stated, the invention in a preferred form is a heat transfer element basket assembly for a rotary regenerative heat exchanger which has a plurality of diaphragm plates which divide the rotor into a plurality of sector-shaped compartments. The basket assembly includes heat absorbent material is disposed within a basket framework. The basket framework includes oppositely disposed first and second side shells and means for holding the side shells in a spaced relationship. The inboard end portions of first and second substantially planar flange plates are mounted to the outboard end portions of the first and second side shells, respectively. The outboard end portions of the first and second flange plates are mounted to an adjacent diaphragm plate to install the basket assembly in the rotor. 
     The diaphragm plates are at a selected angle to each other to form a plurality of substantially identical compartments. The first and second side shells of the basket assemblies define an angle therebetween. The angle defined by the first and second side shells is substantially equal to the angle of the diaphragm plates. 
     The inboard end portion of the first and second flange plates are welded to the outboard end portions of the first and second side shells, respectively. The outboard end portions of the first and second flange plates may be mounted to a diaphragm plate in three ways. The outboard end portion of each flange plate and the outboard end portion of each diaphragm plate may each have at least one opening, such that each flange plate is mounted to the adjacent diaphragm plate by at least one bolt and nut. The outboard end portion of each flange plate may mounted to the adjacent diaphragm plate by a weld. One of the flange plates of each basket assembly may be mounted to a diaphragm plate by a nut and bolt while the other flange plate is mounted to a diaphragm plate by a weld. 
     It is an object of the invention to provide a new and improved heat transfer element basket assembly for a rotary regenerative heat exchanger. 
     It is also an object of the invention to provide methods of mounting the inventive heat transfer element basket assembly within the rotor of a rotary regenerative heat exchanger which provide flexibility of installation and removal. 
     Other objects and advantages of the invention will become apparent from the drawings and specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     FIG. 1 is a general perspective view of a horizontal rotary regenerative air preheater. 
     FIG. 2 is a perspective view of a prior art full sector heat exchange basket, with the heat exchange plates removed. 
     FIG. 3 is top view of the outboard portion of a rotor having a pair of the prior art full sector heat exchange baskets of FIG. 2 mounted within adjacent compartments. 
     FIG. 4 is a perspective view of a full sector heat exchange basket, in accordance with the present invention, with the heat exchange plates removed. 
     FIG. 5 is an enlarged top view of the side shell and flange plate of FIG. 4, illustrating the weld connection therebetween. 
     FIGS. 6 a ,  6   b ,  6   c  and  6   d  are top views of sections of the outboard portion of the rotor of FIG. 1 illustrating the installation of heat exchange baskets in accordance with the present invention by bolting. 
     FIGS. 7 a  and  7   b  are top views of sections of the outboard portion of the rotor of FIG. 1 illustrating the installation of heat exchange baskets in accordance with the present invention by welding. 
     FIGS. 8 a  and  8   b  are top views of sections of the outboard portion of the rotor of FIG. 1 illustrating the installation of heat exchange baskets in accordance with the present invention by bolting and welding. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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  22  and an air sector  24 . Corresponding sector plates are also located on the bottom of the unit. The hot flue gases enter the air preheater  10  as indicated by the arrow  26 , flow through the flue gas sector  22  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  24 , the heat is transferred to the air flowing through the rotor from the bottom as indicated by the arrow  28 . 
     The rotor  14  has a shell  30  and is divided into a plurality of pie-shaped compartments  32  by the diaphragm plates  34  with each compartment containing at least one heat exchange basket  36 . As shown in FIG. 1, the diaphragm plates  34  of each compartment define an obtuse angle  38 . 
     FIG. 2 illustrates a single prior art, formed flange, full sector heat transfer element basket  40 , with the heat transfer plates removed. These full sector baskets  40  were developed to reduce the number of baskets required in each compartment. In some instances as many as ten or more baskets were replaced by a single basket. This resulted in tremendous labor savings for basket replacement. 
     Conventional formed flange baskets  40  typically comprise oppositely disposed side shells  42  which are joined at their inboard ends by a basket nose  44  and at their outboard ends by a basket cover  46 . Pressure plates  48  extend laterally across the basket  40  and basket bars  50  extend longitudinally across the basket  40  to provide additional mechanical integrity to the basket,  40 . A formed flange  52  extends longitudinally from the outboard end of each side shell  42 . Heat exchange material  53  is disposed within the basket  40 . 
     With reference to FIG. 3, the baskets  40  are loaded into an empty rotor compartment  32  which is in the 12:00 o&#39;clock position. The basket  40  is lowered into place until the formed flanges  52  rest on shell bar assemblies  54  which are welded to the diaphragm plates  34 . Each of the formed flanges  52  is mounted to a shell bar assembly  54  by a bolt  56  which extends through openings in the formed flange  52  and the shell bar assembly  54  and a spherical washer  58  to engage a nut  60  housed within a nut cage  62 , which is a part of the shell bar assembly. A gusset  64  and a filler piece  66  are welded to the shell bar assembly  54  on each side of the diaphragm plate  34  to reduce the air/gas flow bypass area around the basket  40 . 
     The angle  68  between the longitudinal extension portion  70  of the formed flange  52  and the laterally extending leg  72  of the formed flange  52  can vary between 75° and 86.25°. The length  74  of leg  72  can exceed four (4) inches. This construction causes some very high stresses at the bolted connection due to loading on the leg  72 . 
     The length  74  of leg  72  and angle  68  determine the amount of bypass area which must be blocked by the filler piece. If for example, angle  68  is 86.25° and length  74  is four inches, the total bypass area in each compartment is approximately 244 square inches. Since this bypass area does not contain any heat exchange materials, the size of the bypass area can represent a significant reduction of thermal performance and a significant increase in pressure drop. 
     With reference to FIGS. 4 and 5, a heat exchange basket  36  in accordance with the invention includes oppositely disposed side shells  76  which are joined at their inboard ends by a basket nose  78  and at their outboard ends by a basket cover  80 . Pressure plates  82  extend laterally across the basket  36  and basket bars  83  extend longitudinally across the basket  36  to provide additional mechanical integrity to the basket  36 . A flat, flange plate  84  extends longitudinally from the outboard end of each side shell  76 . 
     The basket  36  is constructed such that the angle  86  defined between the two side shells  76  of the basket  36  is substantially the same as the angle  38  defined between the diaphragm plates  34  forming the compartment  32 , with only a small nominal clearance. The inboard end portion  88  of the flange plate  84  is welded to the side shell  76  with a full penetration weld  90 . The outboard end portion  92  of the flange plate  84  has holes  94  in it which may be used to attach the basket  36  to the rotor  14 . 
     There are three different methods for mounting the heat exchange basket  36  may be attached to the rotor  14 . In the first method, the flange plates  84  are bolted to the rotor  14 , utilizing the holes  94  in the flange plate  84 . In the second method, the flange plates  84  are welded to the rotor  14 . In the third method, one of the flange plates  84  is bolted to the rotor  14  and the other flange plate  84  is welded to the rotor  14 . Of the three methods, the first method requires the longest installation period. However, should the heat exchange baskets  36  ever require removal, the first method requires the shortest removal period. The second method requires the shortest installation period but the longest removal period. As would be expected, the installation period for the third method is shorter than that of the first method and longer than that of the second period and the removal period for the third method is longer than that of the first method and shorter than that of the second method. 
     To install the heat exchange baskets  36  using the first method (bolting), an empty compartment  32  is positioned at the 12:00 o&#39;clock position and the first basket  36  is lowered into place (FIG. 6 a ). A first  96  of the two flange plates  84  is then bolted to the adjacent diaphragm plate  34 , which is shy of the 12:00 o&#39;clock position with a bolt  98 , washers  100 , and nut  102 . It is intended that no shims need to be used between the first flange plate  96  and the diaphragm plate  34 . The second flange plate  104  is then shimmed  106  as necessary and bolted to the adjacent diaphragm plate  34 . 
     The rotor  14  is then rotated  1800  and a second basket  36 ′ is lowered into an empty compartment  32 ′ (FIG. 6 b ). Similar to the first basket  36 , a first  96  of the two flange plates  84  is bolted to the adjacent diaphragm plate  34  without the use of shims. The rotor  14  is then moved such that the adjacent empty compartment  32 ″ is at the 12:00 o&#39;clock position. A third basket  36 ″ is lowered into place, the unbolted second flange plate  104  of the second basket  36 ′ is shimmed  106  as necessary, and the second flange plate  104  of the second basket  36 ′ and the first flange plate  96  of the third basket  36 ″ are bolted to the diaphragm plate  34  disposed therebetween. Similar to the first and second baskets, the first flange plate  96  of the third basket  36 ″ to be mounted to the rotor  14  is mounted without the use of shims. 
     The rotor  14  is again rotated approximately 180° to install two more baskets (not shown) adjacent the first basket  36 . Installing the baskets  36  in this manner helps keep the rotor  14  balanced. This process is continued until all the baskets  36  are installed. It should be understood that during this process some of the bolting will need to be redone as adjacent baskets are installed and it is possible to deviate from the sequence described above. 
     For example, depending on the number of compartments, there will be either one or two empty compartments at the end of the installation process. A single remaining empty compartment  32  (FIG. 6 c ) is positioned at the 12:00 o&#39;clock position and the bolting  98 ,  102  mounting the basket  36 ′,  36 ″ in each adjacent full compartment  32 ′,  32 ″, to the diaphragm plate  34  which is common to the empty compartment  32  is removed. A basket assembly  36  is lowered into the single remaining compartment  32  and the first flange plate  96  of the basket assembly  36  in the single remaining compartment  32  and the second flange plate  104  of the basket assembly  36 ′ in the adjacent full compartment  32 ′ are bolted to the shared common diaphragm plate  34 . One or more shims  106  are inserted between the second flange plate  104  of the basket assembly  36  in the single remaining compartment  32  and the shared common diaphragm plate  34 , if necessary and the second flange plate  104  of the basket assembly  36  in the single remaining compartment  32  and the first flange plate  96  of the basket assembly  36 ″ in the adjacent full compartment  32 ″ are bolted to the shared common diaphragm plate  34 . 
     If two empty compartments remain (FIG. 6 d ), a first  32  of two adjacent empty compartments  32 ,  32 ′ is positioned at the 12:00 o&#39;clock position and the bolting  98 ,  102  mounting the basket  36 ″,  36 ′″ in each adjacent full compartment  32 ″,  32 ′″ to the diaphragm plate  34  which is common to one of the empty compartments  32 ,  32 ′ is removed. A basket assembly  36  is lowered into the first compartment  32 . The first flange plate  96  is bolted to the diaphragm plate  34  of the first compartment  32 ′ if the adjacent compartment  32  is empty. The first flange plate  96  of the basket assembly  36  in the first compartment  32  and the second flange plate  104  of the basket assembly  36 ″ in the adjacent full compartment  32 ″ are bolted  98 ,  102  to the shared common diaphragm plate  34  if the adjacent compartment  32 ″ is full. The rotor  14  is rotated to position the second compartment  32 ′ at the 12:00 o&#39;clock position and a basket assembly  36 ′ is lowered into the second compartment  32 ′. One or more shims  106  is inserted between the second flange plate  104  of the basket assembly  36  in the first compartment  32  and the common diaphragm plate  34 , if necessary and the second flange plate  104  of the basket assembly  36  in the first compartment  32  and the first flange plate  96  of the basket assembly  36 ′ in the second compartment  32 ′ are bolted to the common diaphragm plate  34 . One or more shims  106  are inserted between the second flange plate  104  of the basket assembly  36 ′ in the second compartment  32 ′ and the diaphragm plate  34 , if necessary. The second flange plate  104  is bolted to the diaphragm plate  34  of the second compartment  32  if the adjacent compartment  32 ′ is empty. The second flange plate  104  of the basket assembly  36 ′ in the second compartment  32 ′ and the first flange plate  96  of the basket assembly  36 ′″ in the adjacent full compartment  32 ′″ are bolted to the shared common diaphragm plate  34  if the adjacent compartment  32 ′″ is full. 
     To install the heat exchange baskets  36  using the second method (welded), an empty compartment  32  is positioned at the 12:00 o&#39;clock position and the first basket  36  is lowered into place (FIG. 7 a ). A first  96  of the two flange plates  84  is then welded  108  to the adjacent diaphragm plate  34 , which is shy of the 12:00 o&#39;clock position. It is intended that no shims need to be used between the first flange plate  96  and the diaphragm plate  34 . The second flange plate  104  is then shimmed  106  as necessary and welded  110  to the adjacent diaphragm plate  34 . 
     The rotor  14  is then rotated 180° and a second basket  36 ′ is lowered into an empty compartment  32 ′ (FIG. 7 b ). Similar to the first basket  36 , a first  96  of the two flange plates  84  is welded  112  to the adjacent diaphragm plate  34  without the use of shims and the second  104  of the two flange plates  84  is shimmed  106  as necessary and welded  114  to the adjacent diaphragm plate  34 . The rotor  14  is then moved such that the adjacent empty compartment  32 ″ is at the 12:00 o&#39;clock position. A third basket  36 ″ is lowered into place, a first  96  of the two flange plates  84  is welded  116  to the adjacent diaphragm plate  34  without the use of shims and the second  104  of the two flange plates  84  is shimmed  106  as necessary and welded  118  to the adjacent diaphragm plate  34 . 
     The rotor  14  is again rotated approximately 180° to install two more baskets (not shown) adjacent the first basket  36 . Installing the baskets in this manner helps keep the rotor balanced. This process is continued until all the baskets are installed. Based on rotor size, basket size, and basket configurations in the rotor, it is possible to deviate from the sequence described above. 
     To install the heat exchange baskets  36  using the third method (one flange welded and one flange bolted), an empty compartment  32  is positioned at the 12:00 o&#39;clock position and the first basket  36  is lowered into place. A first  120  of the two flange plates  84  is then welded  122  to the adjacent diaphragm plate  34 , which is shy of the 12:00 o&#39;clock position. It is intended that no shims need to be used between the first flange plate  120  and the diaphragm plate  34 . The rotor  14  is then rotated to the adjacent compartment  32 ′, moving the first basket  36  towards 11:00 o&#39;clock. A second basket  36 &#39; is lowered into place and the first flange plate  124  is welded  125  to the adjacent diaphragm plate  34 , which is towards the 1:00 o&#39;clock position. This leaves the second flange plate  126  of the first basket  36  and the second flange plate  128  of the second basket  36 ′ unfastened. These flange plates  126 ,  128  are fastened to the diaphragm plate  34  disposed between them, using a bolt  130 , a nut  132 , washers  134  and shims  136 . 
     The rotor  14  is rotated 180° and third and fourth baskets 36″  36 ′″ are mounted to the rotor  14  in an identical manner as the first and second baskets  36 ,  36 ′. This process is repeated until all the baskets are installed. Based on rotor size, basket size, and basket configurations in the rotor, it is possible to deviate from the sequence described above. 
     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.