Performance evaluation of a novel integrated two-stage Rankine cycle and carbon dioxide energy storage system for LNG cold energy recovery

This study proposes a novel integrated two-stage Rankine cycle and carbon dioxide energy storage system to further improve the efficiency and economics of the LNG cold energy power generation process. A mathematical model is established to analyze the impact of key parameters on system performance. The economic performance of the system under different charging and discharging time allocation strategies is evaluated. Additionally, the proposed system is compared with the traditional Rankine cycle LNG cold energy power system to evaluate its application potential. The results indicate that with an increase in storage pressure on the high-pressure side, both energy storage density and power generation profit initially rise, then decline. The maximum energy storage density can reach 4.05 kWh/m3, and the maximum daily power generation profit is 12,624 USD. Moreover, as the peak-valley electricity price difference increases by 0.01 USD/kWh, the annual total profit increases by approximately 0.048 million USD, and the net present value increases by approximately 0.835 million USD. Implementing a strategy that charges during valley load periods and discharges during flat and peak load periods yields a levelized cost of electricity of 0.023 USD/kWh and a payback period of 3.03 years. The proposed system exhibits superior investment potential compared to the traditional Rankine cycle LNG cold energy power generation system, with an increased annual total profit of 0.32 million USD.