Construction and optimization of cryo-compressed hydrogen storage system coupled with multiple ortho-para conversion methods

Cryo-compressed hydrogen represents an advanced high-density physical hydrogen storage method. Considering the significant impact of different ortho-para hydrogen conversion methods on the cooling load, an in-depth examination of three different forms of ortho-para conversion in CcH2 systems is conducted in this study. In this system, the feed hydrogen is firstly compressed to 40 MPa by several stages of compressors with interstage coolers and then cooled to -173.15 oC in stepped cooling system. Cryogenic hydrogen eventually converts to equilibrium state (38.62% of parahydrogen at -173.15 oC) through various methods, including adiabatic conversion, isothermal conversion and continuous conversion, before being stored in cryogenic tanks at a density of 58.38 kg/m 3. A comparative group process with non-conversion and parallel processes with varied conversion methods are set for horizontal contrast, and all the processes are simulated in Aspen HYSYS and optimized by genetic algorithm with minimum specific energy consumption (SEC) set as the objective function. The research results show that the process integrated with isothermal conversion shows the best performance of 4.40 kWh/kgH2 by SEC while the others are 4.43 kWh/kgH2 (Continuous conversion) and 4.47 kWh/kgH2 (adiabatic conversion), leading the way among fellow CcH2 systems already in existence. Besides, the figure of merit (FOM) and exergy efficiency (EXE) of the isothermal-conversion system are 17.1% and 59.6%. Comprehensive energy analysis, heat transfer analysis, and exergy analysis are conducted based on optimized system parameters, yielding insights crucial for the development of medium and large-scale supercritical hydrogen storage systems.