Steam turbine, method of cooling steam turbine, and heat insulating method for steam turbine

A steam turbine, comprising:

• a double-structure casing comprising an outer casing and an inner casing;
• a steam inlet pipe disposed to communicate between an inlet portion of the outer casing and an inlet portion of the inner casing;
• a turbine rotor operatively disposed in the inner casing, the turbine rotor is implanted with plural stages of moving blades;
• plural stages of stationary blades circumferentially provided between a diaphragm outer ring and a diaphragm inner ring, the stages of the stationary blades are arranged alternately with the stages of the moving blades, respectively, in the axial direction of the turbine rotor;
• a plurality of protruded portions circumferentially protruded toward an inner radial direction with respect to the turbine rotor, each of the protruded portions respectively corresponds with each of the turbine stationary blades;
• and
• an exhaust passage that guides a working fluid, which has passed through a final stage moving blade, to an outside of the outer casing,
• wherein an upstream side surface of each of the protruded portions contacts with a downstream side surface of each of the diaphragm outer rings, respectively;
• and
• wherein a heat insulating structure is provided at, at least one of the upstream side surface of the protruded portion and the downstream side surface of the diaphragm outer ring.

A method of cooling a steam turbine, comprising:

• a double-structure casing comprising an outer casing and an inner casing;
• a steam inlet pipe disposed to communicate between an inlet portion of the outer casing and an inlet portion of the inner casing;
• a turbine rotor operatively disposed in the inner casing, the turbine rotor is implanted with plural stages of moving blades;
• plural stages of stationary blades circumferentially provided between a diaphragm outer ring and a diaphragm inner ring, the stages of the stationary blades are arranged alternately with the stages of the moving blades, respectively, in the axial direction of the turbine rotor;
• and
• an exhaust passage that guides a working fluid, which has passed through a final stage moving blade, to an outside of the outer casing,
• wherein the inner casing and the diaphragm outer ring are directly cooled by introducing a cooling medium into a cooling medium passage formed between the inner casing and the diaphragm outer ring through a supply pipe.

A heat insulating method for a steam turbine, comprising:

• a double-structure casing comprising an outer casing and an inner casing;
• a steam inlet pipe disposed to communicate between an inlet portion of the outer casing and an inlet portion of the inner casing;
• a turbine rotor operatively disposed in the inner casing, the turbine rotor is implanted with plural stages of moving blades;
• plural stages of stationary blades circumferentially provided between a diaphragm outer ring and a diaphragm inner ring, the stages of the stationary blades are arranged alternately with the stages of the moving blades, respectively, in the axial direction of the turbine rotor;
• a plurality of protruded portions circumferentially protruded toward an inner radial direction with respect to the turbine rotor, each of the protruded portions respectively corresponds with each of the stages of the turbine stationary blades, wherein an upstream side surface of each of the protruded portions contacts with a downstream side surface of each of the diaphragm outer rings, respectively;
• and
• an exhaust passage that guides a working fluid, which has passed through a final stage moving blade, to an outside of the outer casing,
• wherein a heat insulating structure provided at least one of the upstream side surface of the protruded portion and the downstream side surface of the diaphragm outer ring, to block the transfer of heat from the diaphragm outer ring to the protruded portion.