Thermal grade regulation of cascaded packed-bed thermal storage for liquid air energy storage coupled with coal-fired power plants

Liquid air energy storage (cryogenic Carnot battery) coupled with coal-fired power plants is a potential approach to improve operational flexibility and support deep peak shaving. In this coupled system, the thermal storage unit plays an important role in recovering compression heat and providing stable heat during the discharging process. To improve the heat release stability, this study numerically investigates a cascaded packed-bed thermal storage system under constant-power operating conditions. The charging power and heat extraction power are fixed at 15 MW and 10 MW, respectively. A two-stage simulation scheme is adopted. First, nine packed-bed configurations composed of high-temperature phase change material (PCM), rock and low-temperature PCM are compared under the same boundary conditions. Then, the effects of particle size, inlet mass flow rate and initial state of charge are analyzed based on the selected configuration. The results demonstrate that the arrangement of filling materials plays a critical role in thermal grade regulation by controlling thermal front evolution, outlet temperature stability, and PCM utilization. Although PCM-rich configurations exhibit higher theoretical storage capacity, their heat release performance is limited by poor temperature matching and rapid thermal attenuation. The proposed H-R-L configuration achieves an improved balance between heat storage capacity, thermal stability, and useful heat extraction, providing a more effective solution for cascaded thermal storage in LAES applications. Under the studied conditions, the H-R-L configuration reaches a theoretical capacity of approximately 114 MWh, a charging efficiency of about 90%, and maintains a useful heat release period of approximately 6.5 h above 240 °C. Further analyses indicate that particle size, mass flow rate, and initial SOC can regulate the trade-off between heat transfer enhancement, pressure loss, and thermal utilization. The results can provide a reference for the design and operation of packed-bed thermal storage in Liquid air energy storage systems coupled with coal-fired power plants.