Impact of Steam Injection and Turbine Exhaust Gas Bypass in the Recuperative Cycle Gas Turbine CHP System

The capability of modulating power and heat productions by steam injection in a recuperative cycle gas turbine was investigated. A combined heat and power system using a current state-of-the-art recuperative cycle gas turbine was modeled. Variations in engine performance characteristics due to steam injection were examined. A full off-design analysis was carried out to investigate not only the performance change but also the variation in engine operation caused by the steam injection. Impact of injecting steam at different locations (recuperator and combustor) was investigated. A special attention was given to the change in the compressor surge margin, and a couple of operations that secures a minimum surge margin were comparatively analyzed. Bypass of turbine exhaust gas around the recuperator to increase steam generation was simulated and its usefulness in controlling heat to power ratio was demonstrated. Variations in electric power and thermal energy productions in response to the modulations of injection ratio and gas bypass were presented for a wide ambient temperature range.