Numerical study of mixed working fluid in an original oxy-fuel power plant utilizing liquefied natural gas cold energy

Oxy-fuel combustion is considered one of the most promising technologies for carbon capture and storage (CCS) in power plant. The working fluid, which is composed of CO2 and H2O, is obligatory to moderate the combustion temperature in oxy-fuel systems. The content of H2O in the working fluid has a significant influence on system performance. An original oxy-fuel power plant with the utilization of liquefied natural gas (LNG) cold energy is proposed, and the H2O content in the working fluid is adjustable in the work. The results reveal that when the H2O mass fraction is less than 0.3, the system efficiency increases with the increase of the H2O content in the working fluid. When the H2O mass fraction in the working fluid rises over 0.3, the system efficiency decreases with the increase of H2O content due to the decrease of the recycling heat carried by H2O. The optimum heat transfer effect of the recirculating H2O is obtained when the H2O mass fraction is 0.3, and the optimal thermal efficiency is 58.3%. Compared to dry cycle, the thermal efficiency of the proposed system is increased by 17.3% under the optimum condition.