(185c) A CFD Study of LNG Boil-Off Consider Both Heat Leakage and Vibration Effect

Liquefied natural gas (LNG) is becoming an increasingly important clean energy source and is used and transported worldwide. However, its low boiling point makes LNG very easy to evaporate and generate boil-off gas (BOG). The BOG generation not only causes the loss of cold energy but also builds up the pressure of storage tank, which could cause the tank damage or even explosion. Thus, BOG should be minimized at any economic possibilities during its translations. Many studies have been focusing on the BOG generation caused by heat leakage. However, few works based on our literature survey have quantitatively studied the factor of mechanical vibration that can also contribute to BOG generation.

In this study, the BOG generation of an LNG truck caused by both factors of heat leakage and transport vibration has been quantitatively studied by coupling computational fluid dynamics (CFD) and process simulations together. The commercial CFD software, ANSYS Fluent V 18, has been employed to develop the multiphase mixture model for modeling the vibration effect caused by LNG truck transportation, where a user-defined function (UDF) has been programmed with the dynamic mesh algorithm. Energy generated by mechanical vibration were identified through CFD simulation and exported to process simulation, in which a single tank with pressure outlet was modeled to quantify the amount of BOG generated during transportation. This study for the first time addressed two major root causes for BOG generation, which could benefit deeper understanding of BOG generation mechanism and BOG minimization measures during LNG truck transportations.