Development of dynamic simulation model of LNG tank and its operational strategy

Abstract

Liquefied natural gas has recently received much attention due to the tightened environmental regulations associated with sulfur oxide and nitrogen oxide. LNG is generally stored in liquid form below its saturation temperature of −162 °C. During the storage process at the floating storage regasification unit, LNG continuously evaporates, and it results in the pressure build-up inside the tank leading to potential hazards unless the pressure is controlled properly. In this study, the variation in the pressure and temperature inside the storage tank was estimated by conducting a dynamic simulation of the mathematical model of a non-equilibrium LNG tank. For this, different initial filling ratios (i.e., 10, 50, and 94 vol%) were applied to the modeling and its analysis. First, the model was divided into three zones to enhance its accuracy: vapor, upper and lower LNG zones. Then, two scenarios (i.e., “sealed tank mode” and “venting mode”) were adopted for simulation. Finally, the evaporation rate of LNG was estimated based on its initial filling ratio. As a result, we could estimate the change of pressure and temperature accurately during the operation of the LNG storage and develop an operating strategy based on the different initial filling ratios.