Abstract:
A steam turbine exhaust hood includes an exhaust hood section, and a butterfly plate arranged in the exhaust hood section. The butterfly plate includes a complex curvilinear cross-sectional profile having a first section that extends between a first end portion and a middle portion, and a second section that extends between the middle portion and a second end portion. One of the first and second sections is formed from at least two curvilinear segments including at least one curvilinear segment having a positive curvature and at least one curvilinear segment having a negative curvature.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The subject matter disclosed herein relates to the art of steam turbomachines and, more particularly, to a butterfly plate for a steam turbomachine hood. 
         [0002]    Many power generation facilities employ steam turbomachine systems having a low pressure (LP) steam turbine portion coupled to an intermediate pressure (IP) steam turbine portion and a high pressure (HP) steam turbine portion to drive a generator. In general, steam is expanded in the LP steam turbine portion and channeled into an exhaust hood. The exhaust hood separates steam under vacuum from atmospheric conditions, while providing support to rotating and stationary turbomachinery. Generally, stationary components direct steam toward rotating components to facilitate rotor rotation that is employed in power generation. Also, exhaust hoods provide static pressure recovery that allows for additional expansion of gases passing to last stage turbine buckets. 
         [0003]    An exemplary exhaust hood is formed from various complex sheet metal plates that are combined to form a shell assembly. The shell assembly is machined to provide connections for internal and external components. The shell assembly includes upper and lower halves that guide steam downward toward a condenser. The exhaust hood includes a butterfly plate that turns an upper steam flow 180° downward toward the condenser. Existing butterfly plates include both linear and elliptical cross-sectional profiles that are formed to turn the upper steam flow vertically downward. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    According to one aspect of the exemplary embodiment, a butterfly plate for a steam turbine exhaust hood includes a complex curvilinear cross-sectional profile having a first section that extends between a first end portion and a middle portion, and a second section that extends between the middle portion and a second end portion. One of the first and second sections is formed from at least two curvilinear segments including at least one curvilinear segment having a positive curvature and at least one curvilinear segment having a negative curvature. 
         [0005]    According to another aspect of the exemplary embodiment, a steam turbine exhaust hood includes an exhaust hood section, and a butterfly plate arranged in the exhaust hood section. The butterfly plate includes a complex curvilinear cross-sectional profile having a first section that extends between a first end portion and a middle portion, and a second section that extends between the middle portion and a second end portion. One of the first and second sections is formed from at least two curvilinear segments including at least one curvilinear segment having a positive curvature and at least one curvilinear segment having a negative curvature. 
         [0006]    According to yet another aspect of the exemplary embodiment, a steam turbomachine system includes a turbine portion including an inlet section and an exhaust section, and an exhaust hood mounted about the exhaust section. The exhaust hood includes an exhaust hood section, and a butterfly plate arranged in the exhaust hood section. The butterfly plate includes a complex curvilinear cross-sectional profile having a first section that extends between a first end portion and a middle portion, and a second section that extends between the middle portion and a second end portion. One of the first and second sections is formed from at least two curvilinear segments including at least one curvilinear segment having a positive curvature and at least one curvilinear segment having a negative curvature. 
         [0007]    These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0008]    The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
           [0009]      FIG. 1  is a schematic representation of a steam turbomachine system including a low pressure (LP) steam turbine portion having an exhaust hood provided with a butterfly plate formed in accordance with an exemplary embodiment; 
           [0010]      FIG. 2  is an upper plan view of the LP steam turbine portion and exhaust hood in accordance with an exemplary embodiment; 
           [0011]      FIG. 3  is an elevational cross-sectional view of the LP steam turbine portion and exhaust hood of  FIG. 2 ; and 
           [0012]      FIG. 4  is a graph illustrating a partial cross-sectional profile of the butterfly plate in accordance with an exemplary embodiment. 
       
    
    
       [0013]    The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    Referencing  FIG. 1 , a steam turbomachine system in accordance with an exemplary embodiment is indicated generally at  2 . Steam turbomachine system  2  includes a high pressure (HP) steam turbine portion  4  operatively coupled to an intermediate pressure (IP) steam turbine portion  6  which, in turn, is operatively coupled to a low pressure (LP) steam turbine portion  8 . In the exemplary embodiment shown, LP steam turbine portion  8  includes an exhaust hood  11 . Exhaust hood  11  includes a first exhaust hood section  12  joined to a second exhaust hood section  13  about LP steam turbine portion  8 . As each exhaust hood section  12 ,  13  is substantially similar, a detailed description will follow with reference to first exhaust hood section  12  with an understanding that second exhaust hood section  13  includes corresponding structure. 
         [0015]    As best shown in  FIGS. 2-3 , first exhaust hood section  12  includes a main body  14  defined by an upper shell portion  15  and a lower shell portion  16  that are coupled along a horizontal joint  18 . As shown, upper shell portion  15  includes a pressure relief opening  20  (shown in an open configuration) that leads to an interior housing  24  which encloses LP steam turbine portion  8 . Pressure relief opening  20  is generally in a normally closed configuration that opens to alleviate a pressure that may build up within interior housing  24 . LP steam turbine portion  8  is positioned within interior housing  24 . 
         [0016]    In the exemplary embodiment shown, LP steam turbine portion  8  includes an inner casing  30  that houses a first steam turbine section  33  and a second steam turbine section  35 . First steam turbine section  33  includes a first bearing cone  38  that is supported within interior housing  24  by a first Herzog plate  40 . First bearing cone  38  defines a first steam guide  41  having an outlet section  42  that allows steam to pass from first steam turbine section  33  into interior housing  24 . First outlet section  42  includes a first guide member  44  that directs steam from first steam guide  41  into inner casing  30 . Similarly, second steam turbine section  35  includes a second bearing cone  47  that is supported within interior housing  24  by a second Herzog plate  49 . Second bearing cone  47  defines a second steam guide  50  having a second outlet section  51  that allows steam to pass from second steam turbine section  35  into interior housing  24 . Second outlet section  51  includes a second guide member  53  that directs steam from second steam guide  50  into inner casing  30 . As further shown, exhaust hood  11  includes an inlet  58  that guides steam from IP turbine portion  6  into first and second steam turbine sections  33  and  35  of LP steam turbine portion  8 , and an outlet  61  that passes steam from interior housing  24  to a condenser (not shown). 
         [0017]    In accordance with the exemplary embodiment, exhaust hood  11  includes a butterfly plate  70  that guides steam from upper shell portion  15  toward outlet  61 . More specifically, steam exiting first and second outlet sections  42  and  51  above horizontal joint  18  must first flow upward within interior housing  24 . The steam turns 90°, and flows toward butterfly plate  70 . Butterfly plate  70  bends the steam another 90° toward outlet  61 . In order to reduce pressure losses associated with vortices created by the multiple bends in the steam flow, butterfly plate  70  includes a particular cross-sectional profile. 
         [0018]    In accordance with an exemplary embodiment, butterfly plate  70  includes a first end portion  73  that extends to a second end portion  75  through a middle portion  76 . A first section  80  is defined between first end portion  73  and middle portion  76 , and a second section  82  extends between middle portion  76  and second end portion  75 . As first and second sections  80  and  82  are substantially similar, reference will now be made to  FIG. 4  in describing first section  80  with an understanding that second section  82  is a mirror image thereof. 
         [0019]    First section  80  includes a complex curvilinear cross-sectional profile  82  having a first substantially linear segment  84  that leads to a first curvilinear segment  85  that in turn lead to a second substantially linear segment  88 . Second substantially linear segment  88  leads to a second curvilinear segment  90  that extends through middle portion  76 . First curvilinear segment  85  includes a negative curvature while second curvilinear segment  90  includes a positive curvature. The terms “negative” and “positive” are simply used to describe that first curvilinear segment  85  includes a curvature that is the opposite of the curvature of second curvilinear segment  90 . The particular geometry of first section  80  can be described by the formula: Y=0.94 Θ 6 −1.86 Θ 5 −0.86 Θ 4 +2.9 Θ 3 −0.75 Θ 2 +0.5 0+0.6 where Θ is the angle from top dead center of exhaust hood  11 , measured in radian and 0≦Θ≦1.3. Y is a non-dimensional distance from an outer end (not separately labeled) of first steam guide  41  with the constraint of 0&lt;y&lt;0.15 for middle portion  76 . The formula defines the particular points that define the shape of butterfly plate  70 . Actual non-dimensional distance of complex curvilinear cross-sectional profile  82  may lie within ±0.15 of Y. 
         [0020]    Spacing between middle portion  76  and the outer end (not separately labeled) of first steam guide  41  as well as the overall shape of butterfly plate  70  contribute to reducing vortices in the steam flow exiting from LP steam turbine portion  8  above horizontal joint  18  towards outlet  61 . Reducing vortices in the steam flow leads to fewer pressure losses and enhanced exhaust hood recovery. At this point it should be understood that the exemplary embodiments provide a mechanism for guiding steam flow from an upper portion in an exhaust hood toward a condenser. The butterfly plate is sized and shaped so as to reduce the creation of vortices in the steam flow to avoid efficiency loses in the turbomachine system. 
         [0021]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.