Patent Publication Number: US-11655733-B2

Title: Turbine stator, steam turbine, and partition plate

Description:
TECHNICAL FIELD 
     The present invention relates to a turbine stator, a steam turbine, and a partition plate. 
     Priority is claimed on Japanese Patent Application No. 2018-183138, filed Sep. 28, 2018, the content of which is incorporated herein by reference. 
     BACKGROUND ART 
     A steam turbine includes a rotor that rotates centered on an axis and a casing that covers the rotor. The rotor has a rotor shaft extending in an axial direction centered on the axis, and a plurality of rotor blades disposed around the rotor shaft. In a casing, a partition plate having a plurality of nozzles (stator blades) disposed around the rotor is fixed to an upstream side of each rotor blade. 
     Patent Literature 1 discloses a nozzle diaphragm (partition plate) in which a nozzle diaphragm outer ring (outer ring) is provided on an outer side of the nozzle in a radial direction, and a nozzle diaphragm inner ring (inner ring) is provided on an inner side of the nozzle. The nozzle diagram is formed in an annular shape by vertically combining semi-annular members. Such a nozzle diaphragm accommodates the turbine rotor inside in a rotatable state. A plurality of nozzle diaphragms are arranged in the casing. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1 
     Japanese Unexamined Patent Application, First Publication No. 2017-150386 
     SUMMARY OF INVENTION 
     Technical Problem 
     By the way, in the steam turbine, the steam flowing inside causes a pressure difference between an upstream side and a downstream side of the partition plate in the axial direction. Due to the pressure difference, a load is generated on the partition plate so that the inner side in the radial direction bends toward the downstream side in the axial direction. In order to suppress the deformation of the partition plate due to such a load, the strength of the partition plate is maintained by ensuring a constant thickness in the axial direction. On the other hand, in a case where the partition plate is thick, there is a concern that the size of the steam turbine will increase significantly as the number of stages increases. Therefore, it is desired that deformation of the partition plate is suppressed while reducing the thickness in the axial direction. 
     The present invention provides a turbine stator, a steam turbine, and a partition plate capable of suppressing deformation while reducing the thickness in the axial direction. 
     Solution to Problem 
     A turbine stator according to a first aspect of the present invention includes a partition plate including an inner ring that extends along a circumferential direction around an axis, an outer ring that is disposed on an outer side with respect to the inner ring in a radial direction with respect to the axis, and extends in the circumferential direction, a plurality of nozzles that are disposed between the inner ring and the outer ring in the circumferential direction, and are configured to guide a fluid from an upstream side toward a downstream side in an axial direction in which the axis extends, and an annular protruding portion, protrudes from the outer ring to the downstream side in the axial direction, and extends along the outer ring in the circumferential direction, and a casing surrounding the partition plate front the outer side in the radial direction, and having a contact support surface that is in contact with the annular protruding portion from the downstream side in the axial direction. 
     According to such a configuration, by the annular protruding portion and protrudes from the outer ring, the partition plate has a shape in which a region on the outer side in the radial direction protrudes to the downstream side so as to have an arch shape when viewed front the radial direction. Further, the partition plate is supported by the casing in a state where the annular protruding portion is in contact with the contact support surface. As a result, a compressive force acts on a region of the partition plate on the inner side in the radial direction. Even in a case where a load is generated by the differential pressure between the upstream side and the downstream side of the partition plate, the compressive force resists the load, so that in the partition plate, deformation such that the region on the inner side in the radial direction is directed to the downstream side, in the axial direction is suppressed. In this way, the rigidity of the partition plate with respect to the differential pressure can be ensured without increasing the thickness of the region on the inner side in the radial direction. 
     In the turbine stator according to a second aspect of the present invention, the annular protruding portion may protrude to the outer side in the radial direction from an outer circumferential surface of the outer ring facing the outer side in the radial direction. 
     According to such a configuration, the annular protruding portion the partition plate contacts with the casing earlier than the outer ring and serves as a guide for the casing. As a result, the position of the annular protruding portion with respect to the casing can be determined with high accuracy. Accordingly, the annular protruding portion can be reliably brought into contact with the contact support surface, and the deformation of the partition plate can be suppressed with higher accuracy. 
     In the turbine stator according to a third aspect of the present invention, the annular protruding portion may have a tapered surface formed at a corner that is formed by a protruding portion outer circumferential surface facing the outer side in the radial direction and a protruding portion upstream surface facing the upstream side in the axial direction. 
     According to such a configuration, in a case where the upper half casing is assembled to the partition plate, it is possible to prevent the inner circumferential surface of the casing from being placed on the corner and making it difficult for the annular protruding portion to fit. As a result, it is possible to suppress the assemblability from being deteriorated such that the partition plate and the casing do not fit. 
     In the turbine stator according to a fourth aspect of the present invention, the partition plate may include an upper half partition plate having a semi-annular shape, and upper half partition plate dividing surfaces, which are horizontal surfaces facing a lower side in a vertical direction, at both ends in the circumferential direction, a lower half partition plate having a semi-annular shape, and lower half partition plate dividing surfaces, which are configured to contact with the upper half partition plate dividing surfaces, at both ends in the circumferential direction, and a fixing unit fixing the upper half partition plate and the lower half partition plate to be immovable at a position closer to the nozzle than at least one of the outer circumferential surface of the outer ring and the outer circumferential surface of the annular protruding portion in the radial direction. 
     According to such a configuration, it is possible to improve the assemblability of the partition plate by having the vertically divided structure. Further, the upper half partition plate and the lower half partition plate are fixed at the position closer to the nozzle than at least one of the outer circumferential surface of the outer ring or the outer circumferential surface of the annular protruding portion in the radial direction. As a result, in a case where a load is generated on the partition plate, it is possible to make it difficult to open the region on the inner side in the radial direction, which is particularly easy to open, of the upper half partition plate dividing surface and the lower half partition plate dividing surface. Accordingly, the amount of deformation of the partition plate can be suppressed. 
     In the turbine stator according to a fifth aspect of the present invention, a fin may be disposed on a surface of the annular protruding portion, which faces an inner side in the radial direction. 
     According to such a configuration, the annular protruding portion itself can serve as a flow guide. 
     A steam turbine according to a sixth aspect of the present invention includes the turbine stator, and a rotor that is configured to rotate around the axis in the turbine stator. 
     According to such a configuration, the thickness of the partition plate is reduced, so that the size can be reduced. Further, even in a case where the number of stages is increased to improve efficiency, the increase in size can be suppressed. 
     A partition plate according to a seventh aspect of the present invention includes an inner ring that extends along a circumferential direction around an axis, an outer ring that is disposed on an outer side with respect to the inner ring in a radial direction with respect to the axis, and extends in the circumferential direction, a plurality of nozzles that are disposed between the inner ring and the outer ring in the circumferential direction, and are configured to guide a fluid from an upstream side toward a downstream side in an axial direction in which the axis extends, and a annular protruding portion, protrudes from the cuter ring to the downstream side in the axial direction, and extends along the outer ring in the circumferential direction, in which the annular protruding portion protrudes to the outer side in the radial direction from an outer circumferential surface of the outer ring facing the outer side in the radial direction. 
     Advantageous Effects of Invention 
     According to the present invention, it is possible to suppress deformation while reducing the thickness in the axial direction. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a cross-sectional view of a steam turbine according to an embodiment of the resent invention. 
         FIG.  2    is a cross-sectional view showing a cross section of a main part inside the steam turbine according to the present embodiment. 
         FIG.  3    is a cross-sectional view showing a cross section of a main part inside a partition plate according to the present embodiment. 
         FIG.  4    is a schematic view of the partition plate according to present embodiment as viewed from the axial direction. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a strain turbine according to an embodiment of the present invention will be described in detail with reference to the drawings. 
     As shown in  FIG.  1   , the steam turbine  1  includes a rotor  2  and a turbine stator  10 . 
     The rotor  2  is rotatable around an axis Ar. The rotor  2  has a rotor shaft  21  extending in an axial direction Da around the axis Ar, and a plurality of rotor blades  22  fixed to the rotor shaft  21  along a circumferential direction Dc with respect to the rotor shaft  21 . 
     In the following, the direction in which the axis Ar extends is referred to as the axial direction Da. The radial direction with respect to the axis Ar as a reference is simply referred to as a radial direction Dr. In the radial direction Dr, the vertical direction of the paper surface in  FIG.  1    is defined as a vertical direction Dv. Further, the right and left direction of  FIG.  1    and the right and left direction of  FIG.  4    are defined as a horizontal direction Dh orthogonal to the vertical direction Dv. Further, the direction around the rotor  2  centered on the axis Ar is defined as the circumferential direction Dc. 
     The turbine stator  10  accommodates the rotor  2  inside in a state of being rotatable centered on the axis Ar. The turbine stator  10  has a partition plate  3  and a casing  4 . 
     The partition plate  3  is disposed on the outer circumferential side of the rotor  2 . The partition plate  3  has an annular shape centered on the axis Ar. The partition plate  3  that has an annular shape has a plurality of nozzles (stator blades)  8  arranged in the circumferential direction Dc at a position near the middle of the partition plate  3  in the radial direction Dr and on the upstream side in the axial direction Da from the rotor blade  22  of the rotor  2 . In the steam turbine  1 , a cylindrical space on the outer circumferential side of the rotor shaft  21  and near the middle of the partition plate  3  that has an annular shape, that is, the space where the rotor blade  22  and a nozzle  8  are disposed is a steam flow path through which steam of working fluid flows. The details of the shape of the partition plate  3  will be described below. 
     The casing  4  is disposed on the outer circumferential side of the partition plate  3 . The casing  4  has a cylindrical shape centered on the axis Ar. The casing  4  surrounds the partition plate  3  from the outer side in the radial direction Dr. The casing  4  that has a cylindrical shape includes an upper half casing  41  on the upper portion and a lower half casing  42  on the lower portion with the axis Ar of the rotor  2  as a reference. 
     The upper half casing  41  extends in the circumferential direction Dc. The cross section of the upper half casing  41  orthogonal to the axis Ar forms a semi-annular shape centered on the axis Ar. The upper half casing  41  opens to face a lower side in the vertical direction Dv so as to be capable of accommodating the rotor  2  and the partition plate  3 . 
     The lower half casing  42  extends in the circumferential direction Dc. The cross section of the lower half casing  42  orthogonal to the axis Ar forms a semi-annular shape centered on the axis Ar. An inner diameter of the lower half casing  42  is formed to be the same as an inner diameter of the upper half casing  41 . The lower half casing  42  opens to face the upper side in the vertical direction Dv so as to be capable of accommodating the rotor  2  and the partition plate  3 . The upper half casing  41  is placed on the lower half casing  42  on the upper side in the vertical direction Dv and is fixed by a fastening member such as a bolt  331  (not shown) in a state where the dividing surfaces are in contact with each other. As a result, the casing  4  is formed. 
     As shown in  FIGS.  2  to  4   , the partition plate  3  has an inner ring  6 , an outer ring  7 , the nozzle  8 , and an annular protruding portion  9 . The inner ring  6 , the outer ring  7 , the nozzle  8 , and the annular protruding portion  9  are integrally formed or welded and joined to form a single member. 
     The inner ring extends in the circumferential direction Dc around axis Ar. The nozzle  8  is fixed to an inner ring outer circumferential surface  61 , which is a surface (outer circumferential surface) of the inner ring  6  facing the outer side in the radial direction Dr. Specifically, an inner ring nozzle fixing groove  62  into which part of the nozzle  8  is fitted is formed on the inner ring outer circumferential surface  61 . The inner ring nozzle fixing groove  62  is a groove formed so as to be recessed to the inner side in the radial direction Dr from the inner ring outer circumferential surface  61 . On the other hand, a seal support groove  64  supports a labyrinth seal  65  is formed on an inner ring inner circumferential surface  63 , which is a surface (inner circumferential surface) of the inner ring  6  facing the inner side of the radial direction Dr. The seal support groove  64  is a groove formed so as to be recessed to the outer side in the radial direction Dr from the inner ring inner circumferential surface  63 . That is, the seal support groove  64  opens to the inner side in the radial direction Dr. The labyrinth seal  65  is a seal member made of, for example, an alloy containing copper. The labyrinth seal  65  seals between the rotor shaft  21  and the outer circumferential surface. 
     The outer  7  is provided on the outer side of the inner ring  6  in the radial direction Dr such than the nozzle  8  is interposed. The outer ring  7  extends in the circumferential direction Dc centered on the axis Ar. The nozzle  8  is fixed to an outer ring inner circumferential surface  71 , which is a surface (inner circumferential surface) of the outer ring  7  facing the inner side in the radial direction Dr. Specifically, an outer ring nozzle fixing groove  72  into which part of the nozzle  8  is fitted is formed on the outer ring inner circumferential surface  71 . The outer ring nozzle fixing groove  72  is a groove formed so as to be recessed to the outer side in the radial direction Dr from the outer ring inner circumferential surface  71 . 
     The nozzle  8  is capable of guiding the fluid toward the rotor blade  22  from the upstream side to the downstream side in the axial direction Da. A plurality of the nozzles  8  are provided in the circumferential direction Dc in a state of being interposed between the inner ring and the outer ring  7  in the radial direction Dr. The nozzle  8  according to the present embodiment has an inner shroud ring  81 , a blade  82 , and an outer shroud ring  83 . 
     As shown in  FIG.  2   , the inner shroud ring  81  fixes the blade  82  to the inner ring  6 . An inner protrusion  811  that fits into the inner ring nozzle fixing groove  62  is formed on the surface (inner circumferential surface) of the inner shroud ring  81  facing the inner side in the radial direction Dr. As shown in  FIG.  3   , in a state where the inner protrusion  811  is fitted into the inner ring nozzle fixing groove  62 , a welding portion  50  is formed by performing welding between the inner shroud ring  81  and the inner ring  6  and is integrally joined. 
     As shown in  FIG.  2   , the outer shroud ring  83  fixes the blade  82  to the outer ring  7 . The surface (inner circumferential surface) of the outer shroud ring  83  facing the inner side in the radial direction Dr is integrated with an end portion of the blade  82  on the outer side in the radial direction Dr. An outer protrusion  831  that fits into the outer ring nozzle fixing groove  72  is formed on the surface (outer circumferential surface) of the outer shroud ring  83  facing the outer side in the radial direction Dr. As shown in  FIG.  3   , in a state where the outer protrusion  831  is fitted into the outer ring nozzle fixing groove  72 , the welding portion  50  is formed by performing welding between the outer shroud ring  83  and the outer ring  7 , and is integrally joined. 
     As shown in  FIG.  2   , the blade  82  extends between the inner shroud ring  81  and the outer shroud ring  83  in the radial direction Dr. The blade  8  is a member having a wing shape in cross-sectional shape as viewed from the radial direction Dr. The blade and the rotor blade  22  overlap each other as viewed from the axial direction Da. As shown  FIG.  4   , a plurality of the blades  82  are disposed at intervals in the circumferential direction Dc. 
     The annular protruding portion  9  extends in the circumferential direction Dc along the outer ring  7 . As shown in  FIG.  2   , the annular protruding portion  9  protrudes from the outer ring  7  to the downstream side in the axial direction Da such that the position of the axial direction Da overlap the rotor blade  22  disposed on the downstream side of the nozzle  8  in a state where the partition plate  3  is accommodated in the casing  4 . The annular protruding portion  9  is formed as an integral part with the outer ring  7 . The annular protruding portion  9  according to the present embodiment protrudes to the outer side in the radial direction Dr from the outer ring outer circumferential surface  73  of the outer ring  7  in addition to the downstream side in the axial direction Da. The outer ring outer circumferential surface  73  is the surface (outer circumferential surface) of the outer ring  7  facing the outer side in the radial direction Dr. Further, the annular protruding portion  9  also protrudes to the inner side in the radial direction Dr from the outer ring inner circumferential surface  71 . The annular protruding portion  9  protrudes to the position where the inner position in the radial direction Dr overlaps the outer shroud ring  83  and does not overlap the blade  82  as viewed from the axial direction Da. Therefore, the annular protruding portion  9  is formed in a size that covers the outer ring  7  as viewed from the downstream side in the axial direction Da. The annular protruding portion  9  has a protruding portion outer circumferential surface  91 , a protruding portion upstream surface  92 , a protruding portion downstream surface  93 , and a protruding portion inner circumferential surface  94 . 
     The protruding portion outer circumferential surface  91  is a curved surface of the annular protruding portion  9  facing the outer side in the radial direction Dr. The protruding portion outer circumferential surface  91  is formed on the outer side in the radial direction Dr from the outer ring outer circumferential surface  73 . 
     The protruding portion upstream surface  92  is a plane facing the upstream side in the axial direction Da on the outer side in the radial direction Dr from the outer ring outer circumferential surface  73 . The protruding portion upstream surface  92  is formed the upstream side of the protruding portion outer circumferential surface  91  in the axial direction Da. In the present embodiment, a tapered surface  921  is formed on a corner formed by the protruding portion outer circumferential surface  91  and the protruding portion upstream surface  92 . The tapered surface  921  is inclined so as to face the upstream side in the axial direction Da and the outer side in the radial direction Dr. 
     The protruding portion downstream surface  93  is a plane of the annular protruding portion  9  facing the downstream side in the axial direction Da. The protruding portion downstream surface  93  is connected to an end portion of the protruding portion outer circumferential surface  91  on the downstream side in the axial direction Da. The protruding portion downstream surface  93  is a surface parallel to the protruding portion upstream surface  92  and facing the opposite side in the axial direction Da from the protruding portion upstream surface  92 . 
     The protruding portion inner circumferential surface  94  is a curved surface of the annular protruding portion  9  facing the inner side in the radial direction Dr. The end portion of the protruding portion inner circumferential surface  94  on the downstream side in the axial direction Da is connected to the inner side of the protruding portion downstream surface  93  in the radial direction Dr. The protruding portion inner circumferential surface  94  is formed at a position at a distance from the end surface formed at the tip of the rotor blade  22 . A plurality of fins  941  are provided on the protruding portion inner circumferential surface  94 . Therefore, the protruding portion inner circumferential surface  94  faces the outer end surface of the rotor blade  22  in the radial direction Dr with a slight gap through the fins  941 . As a result, the annular protruding portion  9  also serves as a flow guide that guides the direction in which steam flows. 
     As shown in  FIG.  4   , the partition plate  3  that has an annular shape includes an upper half partition plate  31  on the upper portion in the vertical direction Dv and a lower half partition plate  32  on the lower portion with the axis Ar of the rotor  2  as a reference, and a fixing unit  33  that fixes the upper half partition plate  31  and the lower half partition plate  32 . The upper half partition plate  31  and the lower half partition plate  32  each have the inner ring  6 , the outer ring  7 , the nozzle  8 , and the annular protruding portion  9 . 
     The cross section of the upper half partition plate  31  orthogonal to the axis Ar forms a semi-annular shape centered on is Ar. The upper half partition plate  31  opens to face the lower side in the vertical direction Dv such that the rotor  2  fits. The upper half partition plate  31  has upper half partition plate dividing surfaces  311  at both ends in the circumferential direction Dc. The upper half partition plate dividing surface  311  is a horizontal surface facing the lower side in the vertical direction Dv. 
     The lower half partition plate  32  extends in the circumferential direction Dc. The lower half partition plate  32  is fixed to the lower half casing  42  in a state of being accommodated inner side the lower half casing  42 . The cross section of the lower half partition plate  32  orthogonal to the axis Ar forms a semi-annular shape centered on the axis Ar. The lower half partition plate  32  opens to face the upper side in the vertical direction Dv such that the rotor  2  fits. The lower half partition plate  32  has lower half partition plate dividing surfaces  321  at both ends in the circumferential direction Dc. The lower half partition plate dividing surface  321  is a horizontal surface facing the upper side in the vertical direction Dv. The upper half partition plate  31  is fixed by the fixing unit  33  in a state of being placed on the lower half partition plate  32  on the upper side in the vertical direction Dv. As a result, the partition plate  3  is formed. 
     The fixing units  33  are provided at two locations separated from each other in the horizontal direction Dh. Here, the fixing unit  33  provided on one side of the horizontal direction Dh on the right side of the paper surface in  FIG.  4    will be described as an example. The fixing unit  33  on the other side of the horizontal direction Dh, for which description is omitted, also has the same configuration. 
     The fixing unit  33  fixes the upper half partition plate  31  and the lower half partition plate  32  in a state where the upper half partition plate dividing surface  311  and the lower half partition plate dividing surface  321  are in contact with each other. Specifically, the fixing unit  33  fixes the annular protruding portion  9  of the upper half partition plate  31  and the annular protruding portion  9  of the lower half partition plate  32  immovably at a position closer the nozzle  8  than the protruding portion outer circumferential surface  91  in the radial direction Dr. The fixing unit  33  according to the present embodiment includes the bolt  331 , a bolt insertion recess  332  formed in the upper half partition plate  31 , and a bolt fixing unit  333  formed in the lower half partition plate  32 . 
     The bolt insertion recess  332  is recessed in the vertical direction Dv so as to be toward the upper half partition plate dividing surface  311  from the outer circumferential surface (outer ring outer circumferential surface  73 ) of the upper half partition plate  31 . The bolt insertion recess  332  forms a bolt contact surface  332   a  that is in contact with a head portion of the bolt  331 . The bolt contact surface  332   a  is formed at a position separated from the upper half partition plate dividing surface  311  in the vertical direction Dv. The bolt contact surface  332   a  is a plane parallel to the upper half partition plate dividing surface  311 . A bolt insertion hole  332   b  in which a screw portion of the bolt  331  can be inserted is formed in the bolt contact surface  332   a . The bolt insertion hole  332   b  penetrates the upper half partition plate  31  from the bolt contact surface  332   a  to upper half partition plate dividing surface  311 . 
     The bolt fixing unit  333  is a screw hole recessed from the lower half partition plate dividing surface  321 . The bolt fixing unit  333  is capable of fixing the bolt  331  by inserting the screw portion of the bolt  331 . The bolt fixing unit  333  is provided at a position closer to the outer circumferential surface of the outer shroud ring  83  than the protruding portion outer circumferential surface  91  in the radial direction Dr. The bolt fixing unit  333  is formed such that the position of in the radial direction Dr and the axial direction Da coincides with the bolt insertion hole  332   b.    
     As shown in  FIG.  2   , a plurality of casing positioning recesses  45  recessed over the entire circumference are formed in the inner circumferential surface of the casing  4 . The annular protruding portion  9  can be inserted into the casing positioning recess  45 . As a result, the casing positioning recess  45  determines the position of the partition plate  3  in the axial direction Da with respect to the casing  4 . The casing positioning recess  15  has a recess separation surface  451 , a recess bottom surface  452 , and a contact support surface  453 . 
     The recess separation surface  451  extends vertically from the inner circumferential surface of the casing  4 . The recess separation surface  451  is a plane facing the protruding portion upstream surface  92 . The recess separation surface  451  is formed at a position spaced apart from the protruding portion upstream surface  92  in a state where the partition plate  3  is accommodated in the casing  4 . 
     The recess bottom surface  452  is a surface forming a bottom portion of the recess. The recess bottom surface  452  faces the inner side in the radial direction Dr. The recess bottom surface  452  is a surface parallel to the inner circumferential surface of the casing  4 . The recess bottom surface  452  extends vertically from the end portion of the recess separation surface  451  on the outer side in the radial direction Dr. The recess bottom surface  452  is a surface facing the protruding portion outer circumferential surface  91 . The recess bottom surface  452  is formed at a position spaced apart from the protruding portion outer circumferential surface  91  in a state where the partition plate  3  is accommodated in the casing  4 . 
     The contact support surface  453  extends vertically from the inner circumferential surface of the casing  4 . The contact support surface  453  connects the inner circumferential surface of the casing  4  and the end portion of the recess bottom surface  452  on the downstream side in the axial direction Da. In the casing positioning recess  45 , the contact support surface  453  faces the recess separation surface  451 . The contact support surface  453  is a plane parallel to the recess separation surface  451 . The contact support surface  453  faces the protruding portion downstream surface  93 . The contact support surface  453  is formed at a position being in contact with the protruding portion downstream surface  93  in a state where the partition plate  3  is accommodated in the casing  4 . That is, the contact support surface  453  is in contact with the annular protruding portion  9  from the downstream side in the axial direction Da. 
     According to the turbine stator  10  described above, the annular protruding portion  9  is formed integrally with the outer ring  7  and protrudes to the downstream side in the axial direction Da from the outer ring  7 . As a result, the partition plate  3  has a shape in which the region on the outer side in the radial direction Dr protrudes to the downstream side in the axial direction Da from the region on the inner side in the radial direction Dr where the nozzle  8  or the inner ring  6  is disposed so as to have an arch shape when viewed from the radial direction Dr. Here, in the steam turbine  1 , due to the influence of the steam flowing inside, the pressure with respect to the partition plate  3  on the downstream side in the axial direction Da is lower than the pressure on the upstream side. Due to the differential pressure between the upstream side and the downstream side of the partition plate  3 , a load is generated on the partition plate  3  such that the region on the inner side in the radial direction Dr is curved toward the downstream side in the axial direction Da. However, in the partition plate  3  according to the present embodiment, the region on the outer side in the radial direction Dr protrudes to the downstream side in the axial direction Da. Further, the partition plate  3  is supported by the casing  4  in a state where the protruding portion downstream surface  93  is in contact with the contact support surface  453 . As a result, a compressive force acts on the region of the partition plate  3  on the inner side in the radial direction Dr. Even in a case where a load is generated by the differential pressure between the upstream side and the downstream side of the partition plate  3 , the compressive force resists the load, so that in the partition plate  3 , deformation such that the region on the inner side in the radial direction Dr is directed to the downstream side in the axial direction Da is suppressed. As a result, the rigidity of the partition plate  3  with respect to the differential pressure can be ensured without increasing the thickness of the region on the inner side in the radial direction Dr. Therefore, it is possible to suppress the deformation of the partition plate  3  while reducing the thickness of the partition plate  3  in the axial direction Da. 
     Also, the annular protruding portion  9  protrudes to the outer side of the outer ring  7  in the radial direction Dr in addition to the axial direction Da. Therefore, in a case where the upper half casing  41  is assembled to the partition plate  3  accommodated in the lower half casing  42 , the annular protruding portion  9  first contacts with the upper half casing  41  in the partition plate  3 , and becomes a guide with respect to the upper half casing  41 . As a result, the position of the annular protruding portion  9  with respect to the casing  4  can be determined with high accuracy. Accordingly, the annular protruding portion  9  can be reliably brought into contact with the contact support surface  453 , and the deformation of the partition plate  3  can be suppressed with higher accuracy. 
     Further, the tapered surface  921  is formed on the corner formed by the protruding portion upstream surface  92  and the protruding portion outer circumferential surface  91 . Therefore, in a case where the upper half casing  41  is assembled to the partition plate  3 , it is possible to prevent the inner circumferential surface of the casing  4  from being placed on the corner and making it difficult for the annular protruding portion  9  to be inserted into the casing positioning recess  45 . Therefore, the annular protruding portion  9  can be smoothly inserted into the casing positioning recess  45 . As a result, it is possible to suppress the assemblability from being deteriorated such that the partition plate  3  and the casing  4  do not fit. 
     Further, the annular protruding portion  9  also protrudes to the inner side of the outer ring  7  in the radial direction Dr. Further, the fins  941  that are sliding contact with the tip of the rotor blade  22  are provided on the protruding portion inner circumferential surface  94 . Therefore, the annular protruding portion  9  itself can serve as a flow guide. 
     Also, since the partition plate  3  has the vertically divided structure, it is possible to improve the assemblability of the partition plate  3 . On the other hand, in a case where a load is generated on the partition plate  3  due to the vertically divided structure, the upper half partition plate  31  and the lower half partition plate  32  are easily deformed so as to be open between the upper half partition plate dividing surface  311  and the lower half partition plate dividing surface  321 . However, the bolt fixing unit  333  is formed at a position closer to the outer circumferential surface of the outer shroud ring  83  than the protruding portion outer circumferential surface  91  in the radial direction Dr. Therefore, the upper half partition plate  31  and the lower half partition plate  32  are fixed at positions close to the nozzle  8 . As a result, in a case where a load is generated on the partition plate  3 , it is possible to make it difficult to open the region on the inner side in the radial direction Dr, which is particularly easy to open, of the upper half partition plate dividing surface  311  and the lower half partition plate dividing surface  321 . Accordingly, the amount of deformation of the partition plate  3  can be suppressed. 
     Further, by using the partition plate  3  having the annular protruding portion  9 , the thickness of the partition plate  3  is reduced. Therefore, the casing  4  can be made smaller than the ease where the partition plate  3  having no annular protruding portion  9  is used. In particular, in the present embodiment, the position of the annular protruding portion  9  in the axial direction Da overlaps the position of the rotor blade  22 . Therefore, the annular protruding portion  9  is formed by utilizing the space located on the outer side of the rotor blade  22  in the radial direction Dr. As a result, in the partition plate  3 , the thickness of the region on the inner side in the radial direction Dr (the region adjacent to the motor blade  22  in the axial direction Da) where the nozzle  8  or the inner ring  6  is formed can be prevented from increasing. As a result, the steam turbine  1  as a whole can be made compact. Further, even in a case where the number of stages is increased to improve efficiency of the steam turbine  1 , the increase in size of the steam turbine  1  as a whole can be prevented. 
     Modification Example Other than Embodiment 
     Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations thereof in the respective embodiments are examples, and the configurations are added, omitted, replaced, and changed within a range not deviating from the gist of the present invention. Further, the present invention is not limited to the embodiment, but only to the scope of claims. 
     For example, the annular protruding portion  9  is not limited to being formed integrally with the outer ring  7 . The annular protruding portion  9  need only have a structure in which the protruding portion downstream surface  93  is in contact with the casing  4  while protruding to the downstream side in the axial direction Da from the outer ring  7 . Therefore, the annular protruding portion  9  may be joined to the outer ring  7  by welding or the like after being formed by a member different from the outer ring  7 . 
     Further, the annular protruding portion  9  is not limited to have a structure in which the fins  941  are provided on the protruding portion inner circumferential surface  94 . For example, the annular protruding portion  9  has a structure that does not protrude to the inner side in the radial direction Dr from the outer ring  7 , and a flow guide provided with the fins separately from the annular protruding portion  9  may be disposed between the annular protruding portion  9  and the rotor blade  22  in the radial direction Dr. 
     Also, the fixing unit  33  is not limited to have a structure of immovably fixing the annular protruding portion  9  of the upper half partition plate  31  and the annular protruding portion  9  of the lower half partition plate  32  at a position closer to the nozzle  8  than the protruding portion outer circumferential surface  91  in the radial direction Dr. For example, in the case of the structure in which the annular protruding portion  9  does not protrude to the outer side of the outer ring  7  in the radial direction Dr, the fixing unit  33  may fix the upper half partition plate  31  and the lower half partition plate  32  at a position closer to the nozzle  8  than the outer circumferential surface of the outer ring  7  in the radial direction Dr. Further, the fixing unit  33  is not limited to have a structure of fixing the annular protruding portion  9  of the upper half partition plate  31  and the annular protruding portion  9  of the lower half partition plate  32 . The fixing unit  33  may fix the outer ring  7  of the upper half partition plate  31  and the outer ring  7  of the lower half partition plate. 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, it is possible to suppress deformation while reducing the thickness in the axial direction. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  steam turbine 
               2  rotor 
               21  rotor shaft 
               22  rotor blade 
             Ar axis 
             Da axial direction 
             Dr radial direction 
             Dv vertical direction 
             Dh horizontal direction 
             Dc circumferential direction 
               10  turbine stator 
               3  partition plate 
               6  inner ring 
               61  inner ring outer circumferential surface 
               62  inner ring nozzle fixing groove 
               63  inner ring inner circumferential surface 
               64  seal support groove 
               65  labyrinth seal 
               7  outer 
               71  outer ring inner circumferential surface 
               72  outer ring nozzle fixing groove 
               73  outer ring outer circumferential surface 
               8  nozzle 
               81  inner shroud ring 
               811  inner protrusion 
               82  blade 
               83  outer shroud ring 
               831  outer protrusion 
               50  welding portion 
               9  annular protruding portion 
               91  protruding portion outer circumferential surface 
               92  protruding portion upstream surface 
               921  tapered surface 
               93  protruding portion downstream surface 
               94  protruding portion inner circumferential surface 
               941  fin 
               31  upper half partition plate 
               311  upper half partition plate dividing surface 
               32  lower half partition plate 
               321  lower half partition plate dividing surface 
               33  fixing unit 
               331  bolt 
               332  bolt insertion recess 
               332   a  bolt contact surface 
               332   b  bolt insertion hole 
               333  bolt fixing unit 
               4  casing 
               41  upper half casing 
               42  lower half casing 
               45  casing positioning recess 
               451  recess separation surface 
               452  recess bottom surface 
               453  contact support surface