5E analysis and multiple-objective optimizations of LNG cold energy cascade utilization system based on liquid air energy storage and air separation unit integration

Liquefied natural gas (LNG) ships and Floating Storage and Regasification Units (FSRU) have limited storage space and experience significant fluctuations in electricity demand, posing challenges for the efficient utilization of LNG cold energy. Existing systems generally suffer from safety risks, suboptimal economic performance, and a lack of parameter optimization studies. To address these challenges, this paper proposes a novel LNG cold energy cascade utilization system (LNG-ASU-LAES-ORC), integrating liquid air energy storage (LAES), an air separation unit (ASU), a two-stage organic Rankine cycle (ORC), cold storage (CS), and a peak shaving unit. Based on reliable sub-model validation, a comprehensive analysis on 5E analysis (energy, exergy, economic cost, environmental impact, equalization energy performance) is then conducted and discussed. Results indicate that the proposed system utilizes the LNG cold energy by 68.8%, achieving an exergy efficiency of 64.28%. The round-trip efficiency (RTE) of the LAES unit is 68.8%, while the ASU unit has an average energy consumption (AEC) of 0.03216 kWh/Nm³ N₂. Over its operational lifespan, the system's net present value (NPV) is estimated at 8.33 million USD, with a dynamic payback period (DPP) of 12.5 years. Environmental impact analysis reveals that the air separation unit has the most significant impact. The system's sustainability index (SI) is 8.09. Its peak shaving capacity, measured by the Equalization Energy Factor (EF), is 0.66. This study provides a valuable reference for the application of LNG cold energy utilization systems in maritime settings.