Steam turbine

Abstract

A steam turbine 10 in an embodiment includes: an inner casing 21 surrounding a turbine rotor; an outer casing 20 composed of an upper half side outer casing 20 a and a lower half side outer casing 20 b; and an annular diffuser 50 through which steam passed through a turbine stage is discharged radially outward. A vertical distance H from a axis of a turbine rotor 23 to an inner wall of the upper half side outer casing 20 a, an outermost diameter D of final stage rotor blades 22 a, a blade height B of the final stage rotor blade 22 a, and a distance W between inner walls in vertical and horizontal directions to the axis of the turbine rotor 23, at a bottom portion of the lower half side outer casing 20 b forming a discharge port 60, satisfy (H−D/2)/B≦1.7 and (W−D)/2B≧2.

What is claimed is: 
     
         1 . A steam turbine having a path to guide steam having passed through a final turbine stage to a condenser provided below, the steam turbine, comprising:
 an inner casing surrounding a turbine rotor and composed of an upper half side inner casing and a lower half side inner casing;   an outer casing surrounding the inner casing and composed of an upper half side outer casing and a lower half side outer casing; and   an annular diffuser that is provided on a downstream side of the final turbine stage and through which the steam having passed through the final turbine stage is discharged radially outward, wherein   a vertical distance H from a center axis of the turbine rotor to an inner wall of the upper half side outer casing, an outermost diameter D of final stage rotor blades forming the final turbine stage, a blade height B of the final stage rotor blade, and a distance W between inner walls in vertical and horizontal directions to the center axis of the turbine rotor, at a bottom portion of the lower half side outer casing forming a discharge port through which the steam is discharged to the condenser, satisfy the following expression (1) and expression (2).
   ( H−D/ 2)/ B≦ 1.7   Expression (1)
 
   ( W−D )/2 B≧ 2   Expression (2)
 
   
     
     
         2 . A steam turbine having a path to guide steam having passed through a final turbine stage to a condenser provided below, the steam turbine, comprising:
 an inner casing surrounding a turbine rotor and composed of an upper half side inner casing and a lower half side inner casing;   an outer casing surrounding the inner casing and composed of an upper half side outer casing and a lower half side outer casing; and   an annular diffuser that is provided on a downstream side of the final turbine stage and is formed by a steam guide and a bearing cone inside the steam guide and through which the steam having passed through the final turbine stage is discharged radially outward,   wherein a vertical distance H from a center axis of the turbine rotor to an inner wall of the upper half side outer casing, an outermost diameter C at an endmost portion of the steam guide forming an outlet of the annular diffuser, a blade height B of a final stage rotor blade forming the final turbine stage, and a distance W between inner walls in vertical and horizontal directions to the center axis of the turbine rotor, at a bottom portion of the lower half side outer casing forming a discharge port through which the steam is discharged to the condenser, satisfy the following expression (3) and expression (4).
   0.2≦( H−C/ 2)/ B≦ 0.85   Expression (3)
 
   1.1≦( W−C )/2 B≦ 1.8   Expression (4)