ROTARY DIFFUSER FOR PRESSURE RECOVERY TO BE USED IN STEAM COOLING CIRCUIT OF GAS TURBINE

PROBLEM TO BE SOLVED: To improve efficiency of a combined cycle by feeding steam discharged from a steam turbine to a gas turbine to cool rotating parts thereof, and disposing a diffuser in a return pipe to be used for returning used steam from the gas turbine to the steam turbine so as to suppress pressure decrease. SOLUTION: A turbine rotor 10 is composed of rotor wheels 12-18 and has a bore tube assembly including inner and outer tubes 50, 48. The inner and outer tubes 48, 50 define an annular steam cooling passage 52 and a return passage 54 for cooling used steam. In each passage 52, 54, steam flows to an outer rim of the rotor via radial tubes 56, 58. Then steam supplied via the passage 52 and the tube 56 is fed to buckets 12a, 14a as cooling steam. Further a diffuser 70 is connectively provided on the tube 50, which is a return pipe, at a portion rearward from a position adjacent to a plenum 60 where steam is fed. Therefore pressure decrease along the tube 50 is suppressed.