Influence of steam injection and hot gas bypass on the performance and operation of a combined heat and power system using a recuperative cycle gas turbine

The influence of steam injection and hot gas bypass on the performance and operation of a combined heat and power (CHP) system using a recuperative cycle gas turbine was investigated. A full off-design analysis was used to investigate not only the change in performance but also the variation in engine operation caused by steam injection. The performance improvement capability and operating limitations of full steam injection was examined. Selected operations (partial steam injection and underfiring) that secure minimum compressor surge margin were comparatively analyzed. Partial steam injection was found to be a better option than underfiring in all thermodynamic aspects. Under ISO condition, power and efficiency improvements in the partial injection targeted at a 10% surge margin are 27% and 7.4%, respectively. This study also investigated the increase in steam generation brought by the bypass of turbine exhaust gas around the recuperator. This bypass provided high operational flexibility by varying the capacity of thermal energy supply in both the pure CHP operation and the steam-injected operation. In particular, in the steam-injected operation, the capacity of thermal energy supply can be largely increased by the said bypass, while producing a greater power output than the pure CHP system.