Comparative study on the globally optimal performance of cryogenic energy storage systems with different working media

Cryogenic energy storage (CES) has garnered attention as a large-scale electric energy storage technology for the storage and regulation of intermittent renewable electric energy in power networks. Nitrogen and argon can be found in the air, whereas methane is the primary component of natural gas, an important clean energy resource. Most research on CES focuses on liquid air energy storage (LAES), with its typical round-trip efficiency (RTE) being approximately 50% (theoretical). This study aims to explore the feasibility of using different gases as working media in CES systems, and consequently, to achieve a high system efficiency by constructing four steady-state process models for the CES systems with air, nitrogen, argon, and methane as working media using Aspen HYSYS. A combined single-parameter analysis and multi-parameter global optimization method was used for system optimization. Further, a group of key independent variables were analysed carefully to determine their reasonable ranges to achieve the ideal system performance, that is, RTE and liquefaction ratio through a single-parameter analysis. Consequently, a multi-parameter genetic algorithm was adopted to globally optimize the CES systems with different working media, and the energy and exergy analyses were conducted for the CES systems under their optimal conditions. The results indicated the high cycle efficiency of methane and a low irreversible loss in the liquefaction cycle. Moreover, the Joule-Thomson valve inlet temperature and charging and discharging pressures considerably affected the system performance. However, exergy loss in the CES system occurred primarily in the compressor, turbine, and liquefaction processes. The maximum optimal RTE of 55.84% was achieved in the liquid methane energy storage (LMES) system. Therefore, the LMES system is expected to exhibit potential for application in the CES technology to realize the integration of natural gas pipelines with renewable power grids on a large scale. Moreover, the results of study have important theoretical significance for the innovation of the CES technology.