Gas/steam cycles with open-circuit steam cooling of gas turbine blades

This paper addresses the impact of gas turbine blade steam cooling on the thermodynamic performances of Combined (CC) and steam injected (STIG) cycles. The investigation is restricted to open configurations whereby, after exchanging heat inside the blade, steam is discharged into the mainstream gas and is ultimately lost at the stack. The calculation method includes a cooled expansion model capable of accounting for variations of coolant thermophysical properties, and therefore applicable to both air and steam cooling. Results show that, compared to air cooling, steam gives significant reductions of cooling flows and higher specific work; however, for the same turbine inlet temperature (TIT) cycle efficiency remains nearly constant for STIG and decreases for CC. The use of steam acquires more luster by regarding it as a means to reach TIT's which would be unattainable with air cooling, thus producing interesting gains both in efficiency and specific work