Performance improvement potential of harnessing LNG regasification for hydrogen liquefaction process: Energy and exergy perspectives

Hydrogen serves as an energy vector; however, its storage and bulk transport are challenging because of its low energy content per unit volume. Similar to liquefied natural gas (LNG), pure hydrogen is liquefied prior to transportation-particularly for transportation over long distances. Liquid nitrogen is widely used as a refrigerant in the precooling phase of the liquefaction; however, considering the scale of the predicted hydrogen energy network, alternative sources must be considered. LNG is a promising candidate because the cold energy obtained during the regasification process of LNG is conventionally released in seawater. In the present study, a simple integrated scheme is proposed, wherein LNG cold energy is used to facilitate hydrogen liquefaction by eliminating the precooling refrigeration cycle. The proposed integrated process was designed and analyzed using the well-known commercial simulator Aspen Hysys (R) v10. The design of the proposed process was optimized via the modified coordinate descent methodology. The results indicated that the overall refrigerant quantity was reduced by approximately 50%, which resulted in a reduction of approximately 40% in the specific energy consumption, i.e., it was reduced to 7.64 kWh/kg(LH2). The exergy efficiency of the proposed process was 42.25%, which is significantly higher than that reported for commercial plants (21%). The coefficient of performance of the proposed process was 40.2% higher than those of previously reported processes. The figure of merit of the proposed process was 0.422. The proposed process is expected to change the value chain dynamics of LNG and hydrogen liquefaction, promoting a shift toward a hydrogen economy.