Thermodynamic matching mechanism and topological evolution for liquid natural gas integrated liquid air energy storage: A dual-stage refrigeration strategy with pre-cooling

The integration of liquefied natural gas (LNG) cold energy with liquid air energy storage (LAES) is regarded as a promising route for reducing air-liquefaction power consumption and improving large-scale energy-storage performance. In existing studies, performance improvement is generally pursued through pressure, temperature, and flow-rate optimization within predefined process topologies, whereas the spatial evolution of the local temperature difference and pinch point is rarely used to guide topology development. In this study, a mechanism-driven optimization framework is established for an LNG-LAES system incorporating an independent nitrogen refrigeration loop, and the thermodynamic model is quantitatively benchmarked against pilot-scale experimental data. By mapping the local temperature-difference distribution, the pinch point of the conventional single-stage configuration is identified in the intermediate-temperature region near −80 °C, where the effective utilization of external nitrogen cooling is restricted. A −80 °C cold-energy cutoff strategy combined with nitrogen-flow modulation is therefore introduced to reshape the composite curves and shift the pinch point toward the deep-cryogenic end. The remaining temperature-profile mismatch in the high-temperature region is subsequently used to guide the introduction of air pre-cooling and a second nitrogen-expansion stage, thereby forming a dual-stage refrigeration topology. At the best-performing condition within the investigated range, corresponding to a liquefaction pressure of 6.1 MPa, a liquid-air storage pressure of 1.6 MPa, and an external-nitrogen temperature of −164 °C, the effective logarithmic mean temperature difference (LMTD) of the main cold box is reduced from 11.95 to 6.48 °C, while the LNG mass-flow ratio is reduced to 0.588, representing a 50% reduction relative to the single-stage baseline. Over the practical LNG-temperature range of −145 to −135 °C, the round-trip efficiency (RTE) is maintained between 75.52% and 78.84%. A mechanism-based design basis is thereby provided for reducing the instantaneous LNG cooling requirement and improving the operational adaptability of LNG-assisted LAES systems.