Turbine with a shroud ring around rotor blades and method of limiting leakage of working fluid in a turbine

A turbine, comprising:

• a rotor comprising a shaft and rotor blades fixed to the shaft;
• a shroud ring circumscribing the shaft and surrounding the rotor blades;
• a stator comprising an annular shell disposed radially outside of and circumscribing the shroud ring;
• and
• locations circumferentially apart from one another about the shaft at which the shroud ring and the annular shell are coupled to each other,
• wherein each of the locations comprises:
• a pair of radially-extending surfaces that are axially spaced apart from one another and offset radially so that the top of one of the radially-extending surfaces is at or below the bottom of the other of the radially-extending surfaces;
• and
• a key residing between the surfaces and extending into the annular shell and the shroud ring,
• wherein the key allows the annular shell to thermally expand and contract thereby varying a radial distance between the annular shell and the shroud ring during operation of the turbine, and
• wherein the key fixes a relative axial position between the shroud ring and the annular shell during operation of the turbine.

A method, comprising:

• on a turbine comprising a rotor wheel with rotor blades and a stator comprising an annular shell circumscribing the rotor blades,
• arranging a portion of a shroud ring adjacent a first radially-extending surface on the annular shell so that the shroud ring fits concentrically about the rotor wheel and between the rotor blades and the annular shell,
• locating an annular washer adjacent a second radially-extending surface on the annular shell so that the annular washer fits concentrically around part of the shroud ring;
• and
• using a key disposed between the first radially-extending surface and the second radially-extending surface to couple the annular shell to the shroud ring,
• wherein the key is removeable from the shroud ring and is disposed entirely between the shroud ring and the annular shell,
• wherein the key mechanically couples the shroud ring to the annular shell to allow thermal expansion and contraction of the annular shell and to fix a relative position between the shroud ring and the annular shell during operation of the turbine, and
• wherein at working temperature of turbine, tip regions of the rotor blades are in proximity to an inner region of the shroud ring.