Steam turbine single shell extraction lp casing

Abstract

A single shell extraction casing includes a stepped shell which is formed from a plurality of circumferentially shaped ledge rings located along the axial length of the casing between turbine stages and covered by a casing wrapper. The stepped shell has a simpler construction than the double shell configuration of a conventional turbine extraction casing. Pockets for supporting diaphragms between the multiple stages in the stepped single shell extraction casing are connected directly between ledge rings so they are away from the casing wrapper. This decreases the amount of welding and manufacturing complexity needed to install the diaphragm support pockets.

What is claimed is: 
     
         1 . A single shell turbine casing with stepped structure, the turbine casing comprising:
 a plurality of ledge rings positioned along an axial length of the turbine casing so as to be located between a plurality of stages located within the turbine casing, and   a casing wrapper covering the outer circumferences of the plurality of ledge rings,   the plurality of ledge rings have varying diameters so as to form the stepped structure of the casing.   
     
     
         2 . The turbine casing of  claim 1  further comprising a plurality of diaphragm support pockets extending along an axial length of the turbine casing. 
     
     
         3 . The turbine casing of  claim 2 , wherein the casing is formed from first and second halves joined together along a joint extending along the axial length of the turbine casing, and wherein the plurality of diaphragm support pockets extending along the joint between the first and second halves. 
     
     
         4 . The turbine casing of  claim 2 , wherein each of the plurality of diaphragm support pockets is connected between a corresponding pair of the plurality of ledge rings. 
     
     
         5 . The turbine casing of  claim 2 , wherein each of the plurality of diaphragm support pockets is connected between a corresponding pair of the plurality of ledge rings so as to be mounted away from the casing wrapper. 
     
     
         6 . The turbine casing of  claim 2  further comprising a plurality of steam extraction pipes to which the turbine casing is connected, and through which steam is extracted from the turbine casing. 
     
     
         7 . The turbine casing of  claim 1 , wherein the plurality of ledge rings are each substantially circular in shape. 
     
     
         8 . The turbine casing of  claim 7 , wherein the turbine casing has a dual conical shape formed by the smallest diameters of the varying diameter ledge rings being located substantially in the center of the axial length of casing. 
     
     
         9 . The turbine casing of  claim 8 , wherein the single shell turbine casing is a steam extraction casing for a dual axial flow steam turbine. 
     
     
         10 . The turbine casing of  claim 9  further comprising an inlet pipe through which steam enters the center of the turbine casing and flows in two opposite directions through the turbine casing. 
     
     
         11 . The turbine casing of  claim 10 , wherein the inlet pipe is conical shaped. 
     
     
         12 . The turbine casing of  claim 1 , wherein the casing is formed from first and second halves, and wherein the single shell turbine casing, by reason of its stepped structure, requires a number of bolts to join together the casing's first and second halves that is less than a number of bolts required to join together a dual shell turbine casing that is formed from first and second halves and that is comparable in size to the single shell turbine casing. 
     
     
         13 . The turbine casing of  claim 6  further comprising a plurality of steam extraction pockets through which steam is extracted from an interior of the single shell turbine casing's stepped structure. 
     
     
         14 . The turbine casing of  claim 13  further comprising a plurality of conduit areas connecting the plurality of steam extraction pockets to at least a portion of the plurality of steam extraction pipes. 
     
     
         15 . The turbine casing of  claim 14 , wherein the plurality of connecting conduit areas are located behind the plurality of diaphragm support pockets and between the casing wrapper and an inner wrapper extending between a portion of the plurality of ledge rings. 
     
     
         16 . The turbine casing of  claim 15  further comprising a plurality of openings in the casing wrapper through which steam passes from the plurality of conduit areas into the steam extraction pipes. 
     
     
         17 . The turbine casing of  claim 16  further comprising a second plurality of openings in the casing wrapper through which steam in an interior of the turbine casing passes directly into the steam extraction pipes. 
     
     
         18 . A single shell turbine casing with stepped structure, the turbine casing comprising:
 a plurality of ledge rings positioned along an axial length of the turbine casing so as to be located between a plurality of stages located within the turbine casing, the plurality of ledge rings have varying diameters so as to form the stepped structure of the casing,   a casing wrapper covering the outer circumferences of the plurality of ledge rings,   a plurality of diaphragm support pockets extending along an axial length of the turbine casing, each of the plurality of diaphragm support pockets being connected between a corresponding pair of the plurality of ledge rings, and   a plurality of steam extraction pockets through which steam is extracted from an interior of the single shell turbine casing's stepped structure, the plurality of steam extraction pockets being connected to a plurality of steam extraction pipes to which the turbine casing is connected by a plurality of connecting conduit areas located behind the plurality of diaphragm support pockets and between the casing wrapper and an inner wrapper extending between a portion of the plurality of ledge rings.   
     
     
         19 . The turbine casing of  claim 18 , wherein the turbine casing is formed from first and second halves, and wherein the single shell turbine casing, by reason of its stepped structure, requires a number of bolts to join together the casing's first and second halves that is less than a number of bolts required to join together a dual shell turbine casing that is formed from first and second halves and that is comparable in size to the single shell turbine casing. 
     
     
         20 . A single shell turbine casing with stepped structure, the turbine casing comprising:
 a plurality of ledge rings positioned along an axial length of the turbine casing so as to be located between a plurality of stages located within the turbine casing,   the plurality of ledge rings having varying diameters so as to form the stepped structure of the casing, and   a casing wrapper covering the outer circumferences of the plurality of ledge rings,   the casing being formed from first and second halves joined together, and wherein the single shell turbine casing, by reason of its stepped structure, requires a number of bolts to join together the casing's first and second halves that is less than a number of bolts required to join together a dual shell turbine casing that is formed from first and second halves and that is comparable in size to the single shell turbine casing.