Integrated hydrogen liquefaction system synergizing liquid air energy storage and LNG cold energy: Flexibility enhancement, comprehensive optimization and sustainability assessment

The cold energy derived from liquefied natural gas (LNG) at coastal receiving terminals and from liquid air energy storage (LAES) presents a promising approach for mitigating the substantial energy consumption and carbon footprint associated with the hydrogen liquefaction process (HLP). However, persistent challenges include the reduced system flexibility caused by the integration of LAES and the insufficient coupling among the involved subsystems. To address these issues, this study proposes an integrated hydrogen liquefaction system that synergistically couples LAES and LNG cold energy, with its electricity supply predominantly sourced from offshore wind power. The proposed system features two operational modes: energy storage and release, strategically switching between modes according to peak and off-peak times. NSGA-III is employed for comprehensive performance optimization, with target metrics determined through the parameter sensitivity and Kendall correlation analysis. Optimization results indicate that the optimized system achieves a specific energy consumption (SEC) of 6.285 kWh/kgLH2, an exergy efficiency of 48.68%, a net present value (NPV) of 5.16 × 108 USD, and a levelized cost of hydrogen (LCOH) of 4.975 USD/kgLH2. The system performance under different operating modes is assessed from thermodynamic, economic, and environmental perspectives, indicating industrial feasibility and superior performance. Additionally, the round-trip efficiency (RTE) of LAES reaches a significant 170.8%, and the capital cost can be recovered in as few as 2.853 years under the lowest electricity prices and a 12-h peak-time scenario. The proposed system provides a highly flexible, low-energy-consumption, and low-emission solution for the application of LAES technology and LNG cold energy to HLP.