Gas turbine installation, cooling air supplying method and method of modifying a gas turbine installation

1. A gas turbine installation comprising:

a compressor for compressing intake air;

a combustor for burning compressed air introduced from said compressor;

a turbine for producing torque of a turbine rotor by combustion gas introduced from said combustor;

an exhaust casing connected to the downstream side of said turbine and made up of an outer casing and an inner casing;

an exhaust diffuser connected to a combustion gas outlet of said turbine and made up of an outer diffuser and an inner diffuser, which are disposed between said outer casing and said inner casing, said exhaust diffuser acting to restore static pressure of the combustion gas introduced from said turbine;

a strut for coupling said outer casing and said inner casing to each other;

a strut cover for coupling said outer diffuser and said inner diffuser to each other in a covering relation to said strut;

a first cooling system for taking in cooling air extracted from said compressor to a space between said outer casing and said outer diffuser, and introducing the cooling air to the inner peripheral side of said inner diffuser via a space between said strut and said strut cover; and

a second cooling system partitioned from said first cooling system and introducing, as cooling air for cooling said inner casing, the atmosphere from the inner peripheral side of said inner diffuser.

2. A gas turbine installation comprising:

an exhaust plenum comprising an exhaust casing connected to the downstream side of a turbine and made up of an outer casing and an inner casing, and an exhaust diffuser connected to a combustion gas outlet of said turbine and made up of an outer diffuser and an inner diffuser, which are disposed between said outer casing and said inner casing, said exhaust diffuser acting to restore static pressure of combustion gas introduced from said turbine;

a first cooling system for introducing, from the outer peripheral side of said outer diffuser, cooling air for cooling said exhaust plenum; and

a second cooling system for introducing, from the inner peripheral side of said inner diffuser, cooling air for cooling said exhaust plenum,

wherein at least one of said first and second cooling systems is connected to a final stage wheel space of said turbine or a gas path of said turbine.

3. A gas turbine installation comprising:

an exhaust plenum comprising an exhaust casing connected to the downstream side of a turbine and made up of an outer casing and an inner casing, and an exhaust diffuser connected to a combustion gas outlet of said turbine and made up of an outer diffuser and an inner diffuser, which are disposed between said outer casing and said inner casing, said exhaust diffuser acting to restore static pressure of combustion gas introduced from said turbine;

a first cooling system for introducing, from the outer peripheral side of said outer diffuser, cooling air for cooling said exhaust plenum; and

a second cooling system for introducing, from the inner peripheral side of said inner diffuser, cooling air for cooling said exhaust plenum, wherein said first and second cooling systems merge with each other; and

wherein check means for preventing backflow of the cooling air is disposed in said first cooling system at a position upstream of a merging point between said first and second cooling systems.

4. A gas turbine installation comprising:

an exhaust plenum comprising an exhaust casing connected to the downstream side of a turbine and made up of an outer casing and an inner casing, and an exhaust diffuser connected to a combustion gas outlet of said turbine and made up of an outer diffuser and an inner diffuser, which are disposed between said outer casing and said inner casing, said exhaust diffuser acting to restore static pressure of combustion gas introduced from said turbine;

a first cooling system for introducing, from the outer peripheral side of said outer diffuser, cooling air for cooling said exhaust plenum; and

a second cooling system for introducing, from the inner peripheral side of said inner diffuser, cooling air for cooling said exhaust plenum,

wherein a partition wall for partitioning said first and second cooling systems from each other is disposed between said inner diffuser and said inner casing.

5. A gas turbine installation according to claim 4 , wherein a downstream end of said partition wall in a direction of flow of the cooling air is fixed to said inner casing and sealed off.

6. A gas turbine installation comprising:

an exhaust plenum comprising an exhaust casing connected to the downstream side of a turbine and made up of an outer casing and an inner casing, and an exhaust diffuser connected to a combustion gas outlet of said turbine and made up of an outer diffuser and an inner diffuser, which are disposed between said outer casing and said inner casing, said exhaust diffuser acting to restore static pressure of combustion gas introduced from said turbine;

a first cooling system for introducing, from the outer peripheral side of said outer diffuser, cooling air for cooling said exhaust plenum; and

a second cooling system for introducing, from the inner peripheral side of said inner diffuser, cooling air for cooling said exhaust plenum,

wherein a partition plate for defining said second cooling system between said partition plate and said inner casing is disposed on the inner peripheral side of said inner casing.