Tapping the energy and exergy benefits of channeling liquid air energy system in the hydrogen liquefaction process

Hydrogen's low volumetric energy density challenges its role as an energy vector, especially from bulk storage and transportation viewpoint. Similar to natural gas, hydrogen liquefaction is considered the solution and way forward. The energy-intensive process typically uses liquid nitrogen as a refrigerant in the precooling cycle; however, alternative candidates have also been studied. Liquid air, which has already drawn attention as a standalone cryogenic energy-storage system, can also be a potential candidate. The discharge half-cycle of a liquid-air energy storage system is integrated as the refrigerant stream in the precooling section of the hydrogen liquefaction process. The studied scenario is part of a larger integral scheme involving multiple processes. Aspen HYSYS® v12.1 was used for the design and performance analysis of this unique concept. A process-knowledge-inspired approach was employed to optimize the design variables and realize the maximum potential benefits of the proposed integration. As a result, the total refrigerant requirement was reduced by approximately 46 % compared with the base process. Furthermore, the flexibility brought about by using equilibrium reactors helped optimize the cycle temperatures and pressures. Consequently, 42.1 % (7.88 kWh/kg_LH2) less energy was consumed in the liquefaction process. The high exergy efficiency of 84.29 % indicated excellent integration and optimization. Cryogenic heat exchangers were identified as the primary sources of exergy destruction, and the coefficient of performance of the integrated process was 0.155. The concept presented and the approach adopted in this study are expected to have far-reaching outcomes and benefit the hydrogen energy network and hydrogen economy perspectives.