Influence of H2O phase state on system efficiency in O2/H2O combustion power plant

In this work, oxy-fuel combustion with H2O as diluent in natural gas power plant is proposed, and the effect of phases of H2O on the overall system efficiency is investigated. Three different phase states of H2O, liquid water, steam and liquid-steam mixture are investigated, and the corresponding systems GST-L, GT-S and GT-M system are simulated and compared. To overcome the problem that the steam Rankin cycle cannot fully utilize the latent heat of water, the transcritical CO2 (T-CO2) cycle is introduced. The thermal analysis results show that the GT-M system with steam-water mixture as diluent performs the best, and the energy and exergy efficiency is 60.86% and 49.29%, respectively. The GST-L system takes the second place, and the GT-S system shows the lowest efficiency. The results reveal that steam-water mixture is the best phase of H2O recycled to control the combustion temperature, and the integration of gas turbine and T-CO2 cycle can fully utilize the thermal energy of flue gas to generate electricity. Therefore, the high-efficiency power generation with near-zero carbon emissions is achieved.