Hydrogen enrichment by CO2 anti-sublimation integrated with triple mixed refrigerant-based liquid hydrogen production process

Hydrogen has attracted significant global attention as a source of clean energy. With the increasing focus on utilizing hydrogen as a clean fuel, large-scale storage and transportation have emerged as essential parts of the hydrogen supply chain. Liquid hydrogen (LH2) is the most suitable alternative in this regard; additionally, LH2 ensures the purest form of hydrogen. Since hydrogen is primarily produced from fossil-based fuels, its purification is a critical step during LH2 production. Conventionally, pressure swing adsorption is adopted as a purification technique for this purpose. In contrast, cryogenic techniques have the limitations of low purity and recovery. In this study, a unique cryogenic approach with dual advantages, viz. hydrogen enrichment through CO2 solidification and precooling of hydrogen, is adopted. This is the first simulation study conducted on the removal of CO2 from a mixture of H-2 and CO2 using anti-sublimation. The proposed process was simulated using Aspen Hysys (R) V11. The anti-sublimation process was performed in a specially designed chamber equipped with a refrigeration cycle. The anti-sublimation conditions were verified based on the phase behaviors of the H-2/CO2 mixture and pure CO2. The purified and precooled hydrogen was liquified using three refrigeration cycles. The overall specific energy consumption of the proposed process is 9.62 kWh/kg, which is lower than those of commercial LH2 production processes. Moreover, the high exergy efficiency (31.5%) favors this unique approach of hydrogen enrichment and liquefaction. The economic analysis of the proposed process revealed a total acquisition cost (TAC) of 52.8 mil $/y. The results of this study will assist engineers to develop a sustainable green economy by enhancing the competitiveness of large-scale hydrogen storage and transportation.