(398f) CFD Based Dynamic Boil-Off Gas Study during LNG Laden Voyage

Liquified Natural Gas (LNG) is an increasingly important clean energy source, a widely used alternative fuel and is transported all over the world. Currently, the boil-off gas (BOG) generation, minimization, and utilization during LNG storage and shipping are still major concerns for the industry. To address these concerns, the first and also the most important step is to accurately quantity BOG generation amount with consideration of all aspects of root causes. Generally, during the long-distance marine transportation of LNG, two important factors for BOG generations have to be accounted: heat leakage and vibration impact. Many studies have been reported on heat leakage impact on BOG generation. But quite few addresses the impact of LNG tanker vibrates induced by sea waves during the LNG laden voyage. Our previous study on LNG road tanker has indicated that LNG moving caused by mechanical vibrations can also contribute to some extent for the BOG generation. Compared with road transportation, marine transportation will experience stronger vibration and sloshing of fluid inside storage tanks. Thus, the vibration effect on BOG generation during LNG marine transportation cannot be neglected.

In this study, the dynamic BOG generation caused by both vibration and heat leakage during its marine transportation has been investigated quantitively with the power of both computational fluid dynamics (CFD) and process dynamic simulation, the commercial CFD code ANSYS Fluent was V18.1 was applied to develop a multiphase mixture model and simulated fluid displacement caused by vibration and sloshing during laden voyage, where a user-defined function (UDF) was compiled to model the fluid moving inside the tank, energy generated by vibration and sloshing was exported and coupled with heat leakage modeling via process dynamic simulation to quantify the amount of the total dynamic BOG generation. This study could lay a solid foundation for further study on BOG generation minimization or utilization during LNG marine transportations.