Dynamic characteristics of gas-liquid type compressed CO2 energy storage system with focus on high-pressure liquid energy release process

The gas-liquid type compressed CO2 energy storage system (GL-CCES) is gaining widespread attention for its compact design, flexible layout, and high energy storage density. However, the release of high-pressure liquid fluids involves complex throttling and phase change dynamics, exacerbating the impact of intermittent storage approach on the system performance, but there exists a lack of reliable dynamic modeling to describe the release process. This study proposes a homogeneous non-equilibrium liquid storage tank model for GL-CCES. Based on this model, 1 MW GL-CCES dynamic model is built employing modularity principles. The dynamic response curve of the liquid/gas storage tank's discharge process is analyzed to obtain crucial CO2 parameters and each device's dynamic response characteristic. Results indicate that the discharge of liquid CO2 from the tank passes through the subcooled state, saturated state and then in the two-phase flow state, with the kinetic process of the transition from subcritical to critical flow occurring at a specific pressure difference. CO2 exhibits a more drastic dynamic response to the initially inflowing components and decreases as the number of stages increases. These dynamic characteristics offer significant insights into the system design and safe operation control of GL-CCES.