Design and modeling of liquid hydrogen cargo transfer system with make-up boil-off gas compression

Abstract

This study proposes and evaluates a compressor-assisted liquid hydrogen (LH2) unloading system that utilizes boil-off gas (BOG) to enable LH2 transfer without a submerged pump. An integrated dynamic simulation of the carrier tank, pipeline, and terminal tank was developed to compare the performance of this proposed system with that of conventional pump-assisted unloading. The analysis was extended to several operational scenarios, including increased make-up BOG injection, the presence of thermal stratification within the carrier tank, and large-scale LH2 unloading operations. The results demonstrate that the proposed system achieves a boil-off mass fraction and sendout BOG quantity comparable to those of the conventional method. Under thermal stratification, the boil-off mass fraction and sendout BOG decreased significantly, by 50 and 38 %, respectively. Moreover, the proposed system reduced energy consumption by 68-76 % relative to the pump-assisted method; however, this reduction was limited to 11 % when substantial make-up BOG was injected. For large-scale unloading, the boil-off mass fraction decreased slightly, from 5.69 to 5.38 % owing to reduced relative heat ingress, whereas the sendout BOG and compressor work increased nearly in proportion to the tank capacity. These findings suggest that proposed compressor-assisted unloading is a technically viable alternative to conventional pump-assisted methods, offering effective LH2 transfer performance and scalability.