Thermodynamic analysis of a dual mixed-refrigerant hydrogen liquefaction process with continuous ortho–para conversion method

Hydrogen liquefaction, essential for storage and transmission in the hydrogen economy, typically consumes one-third of hydrogen's lower heating value, hindering economic viability. This study analyzes a dual mixed refrigerant (DMR) process for efficient hydrogen liquefaction. The configuration employs two stages,precooling and liquefaction, each utilizing two mixed refrigerant cycles. The precooling stage reduces hydrogen temperature from 25 °C to -190 °C, while the liquefaction stage achieves final cooling to -253 °C. The process implements continuous catalytic ortho–para hydrogen conversion throughout, using equilibrium conditions. Process modeling uses UniSim Design with REFPROP database, incorporating equilibrium hydrogen equations. Parametric analysis identifies optimal operating conditions by varying refrigerant cycle pressures while maintaining 0.5 °C minimum pinch temperatures. Energy performance is evaluated through specific energy consumption (SEC). Exergy analysis reveals heat exchangers and compression systems as primary sources of irreversibility. The study establishes relationships and physical insight between operating parameters and system performance, providing a framework for enhancing DMR processes with continuous ortho–para conversion.