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

摘要

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. H_2O and CO_2 derived from flue gas is used as diluent to moderate the high temperature in oxy-fuel system. N_2 Brayton cycle as the primary subsystem is utilized to generate electricity from GT exhaust heat. Organic Rankine cycle and transcritical CO_2 cycle is used as the secondary subsystem for the low-grade power generation. Accordingly, organic Rankine cycle system and transcritical CO_2 cycle system are established and simulated. The cryogenic LNG provides cold energy for the two-stage power generation subsystems and CO_2 capture to reduce the power consumption of compression. The numerical results show that when 94.8% of CO_2 with 97.2% purity is captured, the power consumption of carbon capture is approximately 0.57 kWh/kg-CO_2 and 0.07 kWh/kg-CO_2 in O_2/CO_2 and O_2/H_2O combustion atmosphere. Transcritical CO_2 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 CO_2 cycle system is 58.78% in O_2/CO_2 atmosphere and 54.87% in O_2/H_2O atmosphere.