Experiment and simulation of LNG self-pressurization considering temperature distribution under varying liquid level

Abstract

For LNG-fueled ships, estimating the rate of self-pressurization is critical because the pressure limit of an LNG storage tank and the specifications of the boil-off gas processing system depend on the pressure rise rate. However, estimation using a non-equilibrium model exhibits deviated prediction on the pressure increase when thermal stratification is occurred in LNG. Therefore, in this study, a new numerical model is proposed for estimating the self-pressurization of LNG by considering the nonuniform one-dimensional fluid temperature distribution at varying LNG levels. The suggested model was verified using a pilot-scale experiment with a 150 m3 LNG tank capacity. The results show that the proposed model can explain the limited evaporation at a higher level and the vigorous evaporation at a lower level. Furthermore, the suggested model exhibits that the temperature profile in LNG can be determined by the evaporation at the liquid surface according to different levels and can successfully predict the increasing rate of pressure by excluding the assumption of a homogeneous LNG temperature.