Numerical study on an original oxy-fuel combustion power plant with efficient utilization of flue gas waste heat

In this work, an original oxy-fuel combustion natural gas power plant with two-stage power generation subsystems is proposed to realize the high-efficiency power generation with low-cost carbon capture. H2O and CO2 derived from flue gas is used as diluent to moderate the high temperature in oxy-fuel system. N2 Brayton cycle as the primary subsystem is utilized to generate electricity from GT exhaust heat. Organic Rankine cycle and transcritical CO2 cycle is used as the secondary subsystem for the low-grade power generation. Accordingly, organic Rankine cycle system and transcritical CO2 cycle system are established and simulated. The cryogenic LNG provides cold energy for the two-stage power generation subsystems and CO2 capture to reduce the power consumption of compression. The numerical results show that when 94.8% of CO2 with 97.2% purity is captured, the power consumption of carbon capture is approximately 0.57 kWh/kg-CO2 and 0.07 kWh/kg-CO2 in O2/CO2 and O2/H2O combustion atmosphere. Transcritical CO2 cycle is revealed to be more efficient for the utilization of flue gas waste heat (including the latent heat of flue gas) than organic Rankine cycle. The net power generation efficiency of transcritical CO2 cycle system is 58.78% in O2/CO2 atmosphere and 54.87% in O2/H2O atmosphere.