A novel liquid CO2 energy storage system incorporating supplementary oxy-fuel combustion

With the large-scale deployment of renewable energy and the growing complexity of power grids, energy storage systems faced increasing demands for capacity, site flexibility, and peak-shaving capability. This study proposed a novel liquid carbon dioxide energy storage (LCES) system incorporating supplementary oxy-fuel combustion. The addition of oxy-fuel combustion elevated the working fluid temperature, thereby enhancing the specific work output and increasing the energy storage density (ESD) relative to conventional compressed gas energy storage technologies. Furthermore, as methane combustion solely produced water and CO2, water was separated from the cycle and CO2 was reused and stored, forming a zero-carbon emission cycle. The balances of mass and energy, the matching of temperature and pressure, and the reduction of exergy destruction were firstly determined. Then, a sensitivity analysis of system parameters was conducted, followed by multi-objective optimization using the NSGA-II algorithm to identify optimal key parameters. Improved configurations based on split recompression and split expansion were proposed, which further enhanced energy efficiency, equivalent round-trip efficiency (ERTE), and ESD. Results indicated that under the initial configuration, a significant heat transfer mismatch in HE5 led to substantial exergy destruction in the first-stage thermal storage unit. With the compressor and the turbine 1 discharge pressure set at 17.9 MPa and 7.6 MPa respectively, the system reached an optimal equilibrium between ESD and efficiency. In the split expansion configuration, this pressure setting achieved an energy efficiency of 54.3 %, an ERTE of 68.9 %, and an ESD of 49.5 kWh/m3.