The Reheat Gas Turbine With Steam-Blade Cooling—A Means of Increasing Reheat Pressure, Output, and Combined Cycle Efficiency

The reheat (RH) pressure can be appreciably increased by applying steam cooling to the gas-generator (GG) turbine blading which in turn allows a higher RH firing temperature for a fixed exhaust temperature. These factors increase gas turbine output and raise combined-cycle efficiency. The GG turbine blading will approach “uncooled expansion efficiency”. Eliminating cooling air increases the gas turbine RH pressure by 10.6 percent. When steam is used (injected) as the blade coolant, additional GG work is also developed which further increases the RH pressure by another 12.0 percent to yield a total increase of approximately 22.6 percent. The 38-cycle pressure ratio 2400° F (1316° C) TIT GG studied produces a respectable 6.5 power turbine expansion ratio. The higher pressure also noticeably reduces the physical size of the RH combustor. This paper presents an analysis of the RH pressure rise when applying steam to blade cooling.