Modeling, analysis, and modifications of different GT cooling techniques for modern commercial combined cycle power plants with reducing the irreversibility of the HRSG

The development of efficient techniques of gas turbine (GT) blade cooling has increased TIT significantly. The mass flow rates of GT cooling fluids increase with increasing TIT and the required flow rate of the cooling steam may exceed the available flow rate as TIT increases beyond 1500 °C for the M501H GT combined cycle, mandating the development of a different GT cooling technique that uses less steam for GT blade cooling. Such a cooling technique (steam/air–air GT cooling) applies steam cooling for the first two stages of turbine blade rings (the stationary components only) and was introduced in the development of the M501J GT combined cycle, developed by Mitsubishi Heavy Industries (MHI). In this paper, the steam-cooled combustor and the expansions in the gas turbines that utilize the cooling techniques for modern commercial combined cycle power plants (107H/109H GT, M501H GT, and M501J GT) are presented, modeled, and analyzed. Modifications that enable the M501H GT combined cycle to be operated using the same cooling technique (steam–steam–air GT cooling) at any given TIT and pressure ratio (rcom) are presented. Techniques to reduce the irreversibility of the HRSG are introduced, leading to significant improvements in both efficiency and power for all cycles.