This study presents the engineering design and optimization of a compact 3 t/day hydrogen liquefaction system, specifically targeting reduced specific energy consumption (SEC) and ensuring the para-hydrogen mole fraction in the liquefied hydrogen product meets the industrial standard of ≥95%. The primary thermodynamic contribution of this work is the systematic design of a three-stage ortho-para hydrogen conversion system, which is meticulously guided by the enthalpy release profile of the ortho-para conversion reaction. This design strategically employs one isothermal and two adiabatic converters to achieve a final para-hydrogen mole fraction of 99% in the liquid hydrogen product, while minimizing the required number of conversion stages. Correspondingly, the heat exchanger network is streamlined to only five stages, reducing system complexity compared to conventional designs. The adopted refrigeration scheme integrates liquid nitrogen precooling with a single-stage helium reverse Brayton cycle. Process simulation and sensitivity analyses were performed using Aspen HYSYS V14 software to optimize key operational parameters, including hydrogen pressure and the helium cycle pressures. Under optimized conditions (hydrogen pressure of 15 bar, helium low pressure of 2 bar, helium high pressure of 7.1 bar), the system achieves an SEC of 15.69 kWh/kg, demonstrating competitive efficiency with a structurally simplified and thermodynamically efficient design suitable for distributed applications.
Sun et al. (Thu,) studied this question.