Performance of humid air turbine with exhaust gas expanded to below ambient pressure based on microturbine

A new type of HAT cycle comprising HAT and Inverted Brayton cycles, named BAHAT in this paper, is proposed to enhance the microturbine’s performance. By adding an exhaust compressor after flue gas condenser, the gas expander expands to a pressure lower than ambient. Simulation and parameter optimization results show that the electricity efficiency and specific work of BAHAT are about 2 percentage points and 20% higher than that of HAT cycle respectively when turbine inlet temperature is 950 °C. The working pressure of aftercooler, humidifier and turbine hot section is only about 0.4 MPa though the optimal total pressure ratio is about 9–10. The drops of compression work and outlet water temperature of humidifier are considered the main factors to enhance BAHAT’s efficiency. In addition, the exhaust compressor inlet gas temperature affects BAHAT’s efficiency and water recovery ratio apparently. It is also shown that it is easy to achieve water self-support for BAHAT, mixing makeup water to the water loop before entering economizer shows the best thermodynamic performance, and air leakage to the bottom cycle influences both efficiency and water recovery ratio of BAHAT.