Performance enhancement of hydrogen liquefaction process via absorption refrigeration and organic Rankine cycle-assisted liquid air energy system

Abstract

This study focuses on the design and analysis of a liquid hydrogen production process integrated with an absorption refrigeration system, a liquid air energy storage system, and an organic Rankine cycle for designing an energy-efficient integrated process. The absorption refrigeration system and liquid air energy storage system facilitate hydrogen pre-cooling, whereas the organic Rankine cycle helps to recover the waste heat generated after air combustion. An ammonia/water-based absorption refrigeration system accompanied by liquid air precools the hydrogen to −180 °C, and the vapor compression refrigeration system liquifies the hydrogen. In this study, an energy-efficient process integration scheme was designed to reduce the overall energy consumption and recover waste heat. The net specific energy consumption of the process was 6.71 kWh/kg. The design variables and composite curve analyses indicate that the most energy-intensive part of the process is the liquefaction section. Moreover, exergy analysis indicates that multi-stream heat exchangers primarily contribute towards exergy destruction. The exergy efficiency of the process was 35.7%. Environmental analysis shows that the refrigeration cycles mainly contribute towards carbon dioxide emissions. Furthermore, according to the economic analysis, compressors and multi-stream heat exchangers accounted for 88.5% of the total capital investment. Overall, these analyses report energy efficient integration and indicate the potential for further improvements, particularly in the refrigeration cycle. This study is expected to provide insights into the design of energy-efficient integrated hydrogen liquefaction processes that exploit the benefits of the absorption refrigeration system, liquid air energy storage system, and organic Rankine cycle.