Highly corrosion-resistant fixed blade assembly for a steam turbine, in particular a geothermal impulse turbine

Abstract

A highly corrosion-resistant fixed blade assembly ( 20 ) for a steam turbine, in particular a geothermal impulse turbine, is formed by an array ( 11 ) of stator blades ( 12 ), supported at their respective longitudinally opposite ends ( 27, 28 ) by an outer ( 21 ) and an inner ring ( 22 ). Each blade ( 12 ), made with a nickel-based metal alloy, for example, an alloy of the Hastelloy® family or a similar material, is integrally connected to the rings ( 21, 22 ) and is supported by the rings via respective mechanical joints ( 31, 32 ) devoid of structural welds, so as to be removable from the rings without breaking the rings.

1 . A highly corrosion-resistant fixed blade assembly ( 20 ) for a steam turbine, in particular a geothermal impulse turbine, comprising an array ( 11 ) of stator blades ( 12 ) substantially arranged in a radial pattern around an axis (A) and supported at respective longitudinally opposite ends ( 27 ,  28 ) by an outer support ring ( 21 ) and an inner support ring ( 22 ); wherein each blade ( 12 ) of the assembly ( 20 ) is firmly connected to the rings ( 21 ,  22 ) and is supported by the rings via respective mechanical joints ( 31 ,  32 ) devoid of structural welds, so as to be removable from the rings without breaking the rings. 
   
   
       2 . An assembly according to  claim 1 , wherein the blades ( 12 ) are made of a nickel-based metal alloy. 
   
   
       3 . An assembly according to  claim 1 , wherein each blade ( 12 ) is integrally connected to the rings ( 21 ,  22 ) and is supported by the rings ( 21 ,  22 ) via mechanical joint members ( 35 ) arranged at the ends ( 27 ,  28 ) of the blade. 
   
   
       4 . An assembly according to  claim 3 , wherein each blade ( 12 ) is supported by the rings ( 21 ,  22 ) exclusively via the joint members ( 35 ). 
   
   
       5 . An assembly according to  claim 3 , wherein the joint members ( 35 ) comprise a pair of male elements ( 36 ) that engage with respective female elements ( 37 ) having a shape matching the shape of the male elements ( 36 ). 
   
   
       6 . An assembly according to  claim 5 , wherein the male elements ( 36 ) are inserted in the respective female elements ( 37 ) with clearances that are eliminated by wedges or shims. 
   
   
       7 . An assembly according to  claim 5 , wherein each blade ( 12 ) carries a male element ( 36 ) and a female element ( 37 ) arranged at the respective ends ( 27  and  28 ) of the blade. 
   
   
       8 . An assembly according to  claim 1 , wherein each blade ( 12 ) has two connection portions ( 29 ,  30 ) arranged at the ends ( 27 ,  28 ) of the blade and which project transversally from the ends of the blade. 
   
   
       9 . An assembly according to  claim 8 , wherein the connection portions ( 29  and  30 ) respectively carry a male element ( 36 ) that engages a female element ( 37 ) formed in a first ring ( 21 ), and a female element ( 37 ) that is engaged by a male element ( 36 ) carried b a second ring ( 22 ). 
   
   
       10 . An assembly according to  claim 8 , wherein the connection portions ( 29  and  30 ) are made as an integral part of the blades ( 12 ) in the same material as the blades. 
   
   
       11 . An assembly according to  claim 1 , wherein the blades ( 12 ) are made h casting with a nickel-based metal alloy containing chromium, molybdenum, tungsten and iron. 
   
   
       12 . An assembly according to  claim 1 , wherein the blades ( 12 ) are made with a metal alloy of the CX2MW type according, to ASTM A494 or another alloy of similar characteristics. 
   
   
       13 . An assembly according to  claim 1 , wherein the blades ( 12 ) are made by casting with a nickel-based metal alloy of the Hastelloy® family or a similar material. 
   
   
       14 . A steam turbine ( 1 ), in particular a geothermal impulse turbine, including a stator ( 5 ) and a rotor disc ( 6 ) integrally connected to a shaft ( 7 ) rotating around an axis (A) of rotation, wherein, the stator ( 5 ) of the turbine ( 1 ) includes a fixed blade assembly ( 20 ) according to  claim 1 .