Comparative study of advanced hydrogen liquefaction using triple cascade mixed refrigerant cycles with integrated energy exergy economic and environmental analysis.

Hydrogen, as a clean energy source, is recognized as a pivotal energy carrier in the global transition to sustainable energy systems and serves as a crucial pathway for energy storage and efficient utilization within cryogenic systems. Hydrogen liquefaction is one of the most promising methods for increasing its energy density, enabling more efficient storage, transportation, and utilization in large-scale energy systems. However, substantial challenges persist, particularly regarding the high energy consumption associated with the liquefaction process. This study addresses these challenges by proposing two designs for a triple-cascade mixed refrigerant cycle aimed explicitly at reducing energy consumption for high-density hydrogen storage: 66.7 kg/m3 at - 245 °C (Case 1) and 76 kg/m3 at - 249 °C (Case 2). The proposed systems utilize two mixed refrigerant cycles for the precooling and cryogenic stages. In Case 1, pure nitrogen is employed as the third refrigerant in the precooling stage, whereas Case 2 incorporates a regenerative cryogenic hydrogen cycle as the third refrigerant throughout the entire system, coupled with a carbon dioxide cycle for compressor cooling. Simulations were conducted using Aspen HYSYS, with optimization through the Aspen Optimizer algorithm. The results indicate that Case 1 achieves a specific energy consumption (SEC) of 6.98 kWh/kgH₂, representing a 17.4% reduction from the baseline, while Case 2 reduces SEC to 6.19 kWh/kgH₂, a 14.5% decrease. The exergy analysis of the heat exchangers shows a 37% reduction in exergy destruction in Case 2 compared to Case 1. Additionally, Case 2 demonstrates a 5.8% reduction in capital expenditure and a 22% reduction in carbon footprint (CFP). These findings highlight the potential of the proposed triple-cascade process to enhance energy efficiency, improve both thermodynamic and economic performance, and reduce environmental impact.