Analysis of a Boil-Off Gas Recovery System for Liquid Hydrogen Vessel Shipping with Cryogenic Compressed Hydrogen Storage

During the marine transport of liquid hydrogen, heat ingress leads to the generation of boil-off gas (BOG), which increases the pressure in the liquid hydrogen storage tanks. Effective BOG management is therefore essential to ensure tank safety and minimize hydrogen loss. This study develops a cryogenic compression recovery and storage system for BOG generated during the marine transport of 160,000 m3 liquid hydrogen. The core process involves compressing a portion of the BOG and subsequently utilizing the BOG’s inherent cold energy to cool the compressed hydrogen, ultimately enabling the storage of the final cryogenic compressed hydrogen product. ASPEN-PLUS software was employed to analyze the proposed system’s specific energy consumption (SEC) and ψ (hydrogen density/SEC) for producing cryogenic compressed hydrogen (CcH2) across a temperature range of 53 to 110 K and a pressure range of 40 to 100 MPa. Seven optimal sets of state parameters were identified for the cryogenic compressed hydrogen product. Based on a specified optimal parameter set of 80 K and 50 MPa, a simulation of the proposed system’s performance yielded a SEC of 2.25 kWh/kg CcH2 and an exergy efficiency of 87.88% with BOG feed at 53 K and 0.1 MPa, along with the exergy loss and exergy efficiency for each component. Compared to a BOG re-liquefaction system and a MRJT CcH2 system under identical conditions, the proposed system achieves 31.81% and 64.9% reduction, respectively, in SEC and 17.32% and 94.6% improvement, respectively, in exergy efficiency. Furthermore, the effects of feed temperature and cryogenic compressed hydrogen product mass flow rate on the proposed system’s SEC and exergy efficiency were investigated.