Strategies To Improve the Performance of Hydrogen Storage Systems by Liquefaction Methods: A Comprehensive Review

The main challenges of liquid hydrogen (H2) storage as one of the most promising techniques for large-scale transport and long-term storage include its high specific energy consumption (SEC), low exergy efficiency, high total expenses, and boil-off gas losses. This article reviews different approaches to improving H2 liquefaction methods, including the implementation of absorption cooling cycles (ACCs), ejector cooling units, liquid nitrogen/liquid natural gas (LNG)/liquid air cold energy recovery, cascade liquefaction processes, mixed refrigerant systems, integration with other structures, optimization algorithms, combined with renewable energy sources, and the pinch strategy. This review discusses the economic, safety, and environmental aspects of various improvement techniques for H2 liquefaction systems in more detail. Standards and codes for H2 liquefaction technologies are presented, and the current status and future potentials of H2 liquefaction processes are investigated. The cost-efficient H2 liquefaction systems are those with higher production rates (>100 tonne/day), higher efficiency (>40%), lower SEC (<6 kWh/kgLH2), and lower investment costs (1-2 $/kgLH2). Increasing the stages in the conversion of ortho- to para-H2 lowers the SEC and increases the investment costs. Moreover, using low-temperature waste heat from various industries and renewable energy in the ACC for precooling is significantly more efficient than electricity generation in power generation cycles to be utilized in H2 liquefaction cycles. In addition, the substitution of LNG cold recovery for the precooling cycle is associated with the lower SEC and cost compared to its combination with the precooling cycle.