Non-equilibrium thermodynamic model for liquefied natural gas storage tanks

Abstract

A thermodynamic non-equilibrium model is introduced to evaluate the thermal performance of vertical and horizontal liquefied natural gas (LNG) storage tanks in refueling stations. This model incorporates a resistance-capacitance network to reduce the required computation time to several hours compared with the computational fluid dynamics (CFD) method which requires several days or weeks to run under high-performance computing. The accuracy of the non-equilibrium model is validated with two sets of experimental data, and thermodynamic equilibrium and CFD models, respectively. Our results indicate that the non-equilibrium and equilibrium models have a similar accuracy to predict the pressure and temperature changes in vertical and horizontal LNG storage tanks under stationary conditions. However, the equilibrium model fails to predict the tank performance under sudden pressure changes such as those produced via vapor return from heavy-duty trucks duringre fueling. In contrast, the non-equilibrium model accurately predicts the pressure of LNG storage tank under dynamic conditions. Our results also indicate that, compared to vertical tanks and under dynamic operating conditions, horizontal storage tanks can hold LNG for longer periods without methane release to the atmosphere.