Performance analysis of a liquid carbon dioxide energy storage system integrated with a coal-fired power plant

The intermittency and fluctuation of renewable energy pose a great threat to the stability of power systems. This adverse effect can be mitigated by using energy storage systems to perform the flexibility transformation of coalfired power plants (CFPP). In this work, a novel liquid carbon dioxide energy storage (LCES) system integrated with CFPP is proposed. Rather than adopting heat storage tanks, the condensation water from CFPP is drawn to directly retrieve the compression heat during charge, while the high-pressure CO2 at the expander inlet is preheated by the extraction steam during discharge, enabling the LCES system to be thermally decoupled. The thermodynamic models are established, and integration schemes are investigated to obtain better system performance. Thermodynamic analysis reveals that the LCES system can achieve an electricity storage efficiency of 55.04 %, an increase of 8.04 % over the pre-integration level. Meanwhile, the round-trip efficiency, exergy efficiency and energy density of the system are 45.68 %, 57.63 % and 16.01 kWh/m3, respectively. Cold storage and preheaters are the most crucial components for enhancing system performance, according to a detailed exergy analysis. Subsequently, the parametric analysis is conducted to study the effect of some key parameters on the system performance. The variable CFPP load simulation among them shows that CFPP operates more efficiently when it works at low load during charge and at high load during discharge.