Rotating diffuser for pressure recovery in a steam cooling circuit of a gas turbine

The present invention generally relates to a steam-cooling circuit in a gas turbine and particularly relates to pressure recovery in a spent cooling steam return passage in the steam-cooling circuit of a gas turbine for improving cooling system efficiency. The present invention also relates to pressure recovery in the spent cooling steam return passage of a gas turbine employed in a combined cycle system for improving the performance of the system. The buckets of a gas turbine are steam-cooled via a bore tube assembly having concentric supply and spent cooling steam return passages rotating with the rotor. A diffuser is provided in the return passage to reduce the pressure drop. In a combined cycle system, the spent return cooling steam with reduced pressure drop is combined with reheat steam from a heat recovery steam generator for flow to the intermediate pressure turbine. The exhaust steam from the high pressure turbine of the combined cycle unit supplies cooling steam to the supply conduit of the gas turbine.