Patent Publication Number: US-7914255-B2

Title: Apparatus and method of diaphragm assembly

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to turbines and more particularly to diaphragm assemblies used with steam turbines. 
     At least some known steam turbines include diaphragm assemblies that channel flow downstream to rotating turbine blades. Known diaphragm assemblies are stationary and include a plurality of circumferentially spaced partitions. Each partition extends generally radially between an outer band and an inner band. At least some known bands are formed with openings that extend through the band. A cross-sectional shape of the opening is substantially similar to a cross-sectional profile of the partitions. 
     During assembly of the diaphragm assembly, each partition is aligned with a respective band opening and the partitions are then inserted through the opening such that the partitions are retained in position between the bands. However, because known turbines and diaphragms use advanced aero-shaped partitions, such as bowed partitions, inserting the partitions through the openings may be a difficult task. Specifically, the bowed cross-sectional shape of the partitions may make it difficult to align the partitions with the openings. Such alignment problems, known as fit-up issues, generally increase as the amount of the bow increases and/or as a thickness of a band increases. 
     To facilitate reducing fit-up issues, at least some known turbines use “booted partitions” to reduce the likelihood of interference between the bands and partitions during assembly. More specifically, within such turbines, the overall size of the openings formed in at least one band are increased such that a clearance gap is defined between the partitions and the bands. A boot is coupled around the partitions to close the gap. However, the booted partitions cause a radial step to be defined at the interface between the boot and the band. The radial steps create flow disturbances reducing the overall stage efficiency and generally such partitions require a larger signature footprint within the turbine. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a method of assembling a diaphragm assembly for a steam turbine is provided. The method includes forming at least one opening within a radially outer band and forming at least one opening within a radially inner band. The method also includes coupling at least one partition to at least one opening within the radially outer band including a radially inner surface and a radially outer surface wherein the at least one opening is at least partially defined by a wall that extends obliquely between the outer band radially inner surface and the outer band radially outer surface. The method additionally includes coupling the at least one partition to the at least one opening within the radially inner band wherein the at least one partition extends between the at least one radially outer band opening and the at least one radially inner band opening. 
     In another aspect, a diaphragm assembly for a steam turbine is provided. The diaphragm assembly includes a radially inner band including a radially inner surface, an opposite radially outer surface, and a plurality of openings extending therebetween. The diaphragm assembly also includes a radially outer band including an opposite radially inner surface, a radially outer surface, and a plurality of openings extending therebetween. The diaphragm assembly additionally includes at least one partition extending between the inner band and the outer band wherein at least one of the radially outer band openings is at least partially defined by a wall that extends obliquely between the outer band radially inner surface and the outer band radially outer surface. 
     In a further aspect, a steam turbine is provided. The steam turbine includes an inner carrier, an outer carrier, and a diaphragm assembly for a steam turbine. The diaphragm assembly includes a radially inner band including a radially inner surface, an opposite radially outer surface, and a plurality of openings extending therebetween. The diaphragm assembly also includes a radially outer band including an opposite radially inner surface, a radially outer surface, and a plurality of openings extending therebetween. The diaphragm assembly additionally includes at least one partition extending between the inner band and the outer band wherein at least one of the radially outer band openings is at least partially defined by a wall that extends obliquely between the outer band radially inner surface and the outer band radially outer surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of an exemplary steam turbine; 
         FIG. 2  is an exploded view of an exemplary diaphragm assembly that may be used with the steam turbine shown in  FIG. 1 ; 
         FIG. 3  is a perspective view of a partition used with the diaphragm assembly shown in  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of a portion of the partition (shown in  FIG. 3 ) coupled to an outer band used with the diaphragm assembly shown in  FIG. 2 ; and 
         FIG. 5  is a schematic illustration of a portion of the outer band shown in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a schematic illustration of an exemplary opposed-flow steam turbine  10 . Turbine  10  includes first and second low pressure (LP) sections  12  and  14 . As is known in the art, each turbine section  12  and  14  includes a plurality of stages of diaphragms (not shown in  FIG. 1 ). A rotor shaft  16  extends through sections  12  and  14 . Each LP section  12  and  14  includes a nozzle  18  and  20 . A single outer shell or casing  22  is divided along a horizontal plane and axially into upper and lower half sections  24  and  26 , respectively, and spans both LP sections  12  and  14 . A central section  28  of shell  22  includes a low pressure steam inlet  30 . Within outer shell or casing  22 , LP sections  12  and  14  are arranged in a single bearing span supported by journal bearings  32  and  34 . A flow splitter  40  extends between first and second turbine sections  12  and  14 . 
     It should be noted that although  FIG. 1  illustrates a double flow low pressure turbine, as will be appreciated by one of ordinary skill in the art, the present invention is not limited to being used with low pressure turbines and can be used with any double flow turbine including, but not limited to intermediate pressure (IP) turbines or high pressure (HP) turbines. In addition, the present invention is not limited to being used with double flow turbines, but rather may be used with single flow steam turbines as well, for example. 
     During operation, low pressure steam inlet  30  receives low pressure/intermediate temperature steam  50  from a source, for example, an HP turbine or IP turbine through a cross-over pipe (not shown). The steam  50  is channeled through inlet  30  wherein flow splitter  40  splits the steam flow into two opposite flow paths  52  and  54 . More specifically, the steam  50  is routed through LP sections  12  and  14  wherein work is extracted from the steam to rotate rotor shaft  16 . The steam exits LP sections  12  and  14  and is routed to a condenser, for example. 
       FIG. 2  is an exploded view of a diaphragm assembly  100  that may be used with steam turbine  10  (shown in  FIG. 1 ).  FIG. 3  is a perspective view of a partition  110  used with diaphragm assembly  100 .  FIG. 4  is a cross-sectional view of a portion of partition  110  coupled to an outer band  108  used with diaphragm assembly  100 .  FIG. 5  is a schematic illustration of a portion of outer band  108 . 
     Diaphragm assembly  100  includes an inner carrier  102  and an outer carrier  104 . Diaphragm assembly  100  also includes a radially inner band  106 , radially outer band  108 , and a plurality of circumferentially-spaced partitions  110  that extend generally radially between inner carrier  102  and outer carrier  104 . Radially outer carrier  104  is radially outward from, and adjacent to, radially outer band  108 ,and radially inner carrier  102  is radially inward of, and adjacent to radially inner band  106 . 
     Radially inner band  106  includes a plurality of openings  112  that extend through inner band  106  from a radially inner surface  114  of inner band  106  to a radially outer surface  116  of inner band  106 . Openings  112  are circumferentially-spaced along inner band  106 , and in the exemplary embodiment, openings  112  are each substantially identical. Radially outer band  108  also includes a plurality of openings  118  that extend through outer band  108  from a radially inner surface  120  of outer band  108  to a radially outer surface  122  of outer band  108 . In the exemplary embodiment, surfaces  120  and  122  are substantially parallel to each other. In the exemplary embodiment, openings  118  are each substantially identical. Openings  118  and  112  are aerodynamically shaped and with a contoured shape that is substantially identical to a cross-sectional shape defined by an exterior surface  124  of partitions  110 . As such, openings  112  and  118  are sized to receive partitions  110 . 
     More specifically, in the exemplary embodiment, openings  118  and  112  are each substantially airfoil-shaped. In the exemplary embodiment, each inner band opening  112  is approximately the same size, or is slightly smaller, than each outer band opening  118 . 
     Each opening  118  is defined by a wall  121  that extends between outer surface  122  and inner surface  120  and forms a perimeter  119  that circumscribes opening  118 . Moreover, in the exemplary embodiment, wall  121  includes a ruled surface. Wall  121  is oriented obliquely, with respect to surface  120  or  122 , around a portion of perimeter  119  of at least one opening  118 . Specifically, within a portion of perimeter  119 , wall  121  is oriented at an oblique angle β with respect to outer band  108 . Angle β varies around perimeter  119 . More specifically, along circumferential sides  123  and  125  of opening  118 , angle β is at its largest oblique angle while at leading edge and trailing edge sides  127  and  129  of opening  118 , angle β is at its minimum oblique angle. Accordingly, in the exemplary embodiment, because wall  121  is oriented at least partially around perimeter  119 , a cross-sectional area  150  of each opening  118  adjacent radially outer surface  122  is larger than a cross-sectional area  152  of each opening  118  adjacent radially inner surface  120 . 
     Each partition  110  extends between inner and outer bands  106  and  108 , respectively, and are circumferentially spaced as defined by generally radially openings  112  and  118 . In the exemplary embodiment, partitions  110  each have an aerodynamic cross-sectional shape that is substantially identical to that of openings  118  and  112 . Partitions  110  may have any geometric shape that may be variably selected to facilitate increasing diaphragm assembly  100  performance and/or increasing coupling strength between partitions  110  and inner and outer bands  106  and  108 . In one embodiment, partitions  110  are bowed. 
     In the exemplary embodiment, each partition  110  includes a pair of opposing sidewalls  140  and  142  coupled together at a leading edge  132  and a trailing edge  134 . In the exemplary embodiment, sidewall  140  is a convex surface and sidewall  142  is a concave surface. Each partition  110 , in the exemplary embodiment, includes a flared portion  144  and a blade portion  146 . Flared portion  144  extends across an oblique angle θ from blade portion  146 . Angle θ varies across sidewalls  140  and  142  from leading edge  132  to trailing edge  134  in an orientation that substantially mirrors the orientation of outer band  108  wall angle β. As such, at trailing edge  134  and leading edge  132 , angle θ is at its minimum angle. 
     During assembly, partitions  110  are each aligned such that the partitions  110  are substantially aligned with openings  118 . In the exemplary embodiment, partitions  110  are inserted through outer band  108  from the radially outer surface  122  of outer band  108 . The combination of two flared sidewall portions and the angular orientation of wall  121  facilitates creating a snug fit between an inner surface of each outer band opening  118  and an outer surface of each partition  110 . Similarly, partitions  110  are aligned with openings  112  and inserted through openings  112 . Flared openings  112  and  118  and flared partitions  110  facilitate coupling partition  110  to openings  112  and  118  and provide adequate clearance for partitions  110  to be inserted into openings  112  and  118 . In an alternative embodiment, partitions  110  may be welded to inner and outer bands  106  and  108  around partition perimeters  136 ,  138 . In another embodiment, partitions  110  may be secured to inner and outer bands  106  and  108  with a mechanical joint. After coupling partitions  110  to inner and outer bands  106  and  108 , radially inner and outer bands  106  and  108  are then coupled to radially inner and outer carriers  102  and  104 . 
     During assembly of known diaphragm assemblies, alignment problems, known as fit-up issues, frequently arise. Flared partitions and flared openings reduce fit-up issues without causing a radial step in the diaphragm assembly. Radial steps in known diaphragm assemblies create flow disturbances reducing the overall stage efficiency. Through eliminating the radial step, the engine operates more efficiently. Additionally, a diaphragm assembly with flared openings and partitions reduces the axial space necessary for the assembly, because known partitions, such as bowed partitions, require a large signature footprint within the turbine. Because the flared portion of the above-described diaphragm assembly is shallow near leading and trailing edges of partitions, the outer band maintains sufficient material for adequate axial ligaments and structural integrity between each opening and leading and trailing edges of the outer band. 
     The above-described diaphragm assembly includes an outer band that includes a plurality of contoured openings defined at least partially by an oblique wall. The assembly also includes partitions that extend between the inner and outer bands and that each include a flared sidewall portion. The combination of the oblique openings and flared sidewall portions of the partitions facilitate reducing difficulty in assembling the diaphragm assembly. 
     Exemplary embodiments of a diaphragm assembly are described above in detail. The diaphragm assembly is not limited to use with the specific embodiments described herein, but rather, the diaphragm assembly can be utilized independently and separately from other components described herein. Moreover, the invention is not limited to the embodiments of the diaphragm assembly described above in detail. Rather, other variations of a diaphragm assembly may be utilized within the spirit and scope of the claims. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.