Design and off-design performance of advanced mixed gas-steam cycle power plants

Mixed gas-steam cycles have been proposed to increase efficiency and specific work of gas turbine engines. These cycles allow recovery of exhaust heat for re-use within the gas turbine plant and are an attractive alternative to combined cycles for small and middle range industrial power plants. Thermodynamic studies about the combined use of water injection, steam injection, recuperation, intercooling and aftercooling have been shown to offer the potential of efficiency and specific power improvement. The aim of this work is to investigate plants obtained by the up-grading of a simple cycle aeroderivative gas turbine engine with additional devices and a limited number of modifications of the base engine. The following plant configurations are considered and compared: recuperative water injected gas turbine (RWI) with aftercooling and economiser to preheat the water to be injected; and steam injected gas turbine (STIG). In the paper the procedure of the devices design for the enhanced cycle is described. Moreover part load behaviour of the plants is considered.