Thermo-economic and advanced exergy analysis of liquid carbon dioxide energy storage system integrated with LNG cold energy recovery use

Aiming at the problem of wind and solar power curtailment caused by high-proportion integration of wind power and photovoltaic power into the grid, this paper proposes a liquid carbon dioxide energy storage system coupled with liquefied natural gascold energy recovery. The cascaded cold energy during LNG regasification is used to drive the Organic Rankine Cycle (ORC) for power generation and assist in CO2 condensation. The results show that the system achieves a round-trip efficiency of 103.50%, an exergy efficiency of 22.25%, an energy storage density of 16.97 kWh/m3 and the levelized cost of electricity is 0.0271 $/kWh under the designed system parameters. Compressor1and expander3 contribute the most to the efficiency improvement. There exists an optimal matching of charging and discharging pressures to minimize the cost of electricity. Although reducing the pressure of the low-pressure storage tank increases the energy storage density, it raises the cost of electricity. Exergy analysis reveals that the LNG cold energy power generationsubsystem accounts for 79.05% of the total exergy destruction, among which the ORC condenser and evaporator are the main contributors. Advanced exergy analysis identifies ORC Expander 2, ORC Expander 4, ORC immersed evaporator 3, ORC Expander 1 and Heat Exchanger 6 as the primary optimization objectives, whose endogenous avoidable exergy destruction accounts for 76.26% of the total avoidable exergy destruction. Integrated with ORC, this liquid CO2 energy storage system achieves cascade utilization of LNG high-grade cold energy, boosts system efficiency and verifies its feasibility for practical engineering.