Dynamic simulation study on effect of liquefied natural gas temperature on jetty boil-off gas generation at liquefied natural gas exporting terminals

Abstract

Liquefied Natural Gas (LNG) is obtained by cooling natural gas below -161 °C. The liquefaction reduces volume of natural gas by about 600-fold. The reduction in the volume makes natural gas transportation economical over longer distances. However, the liquefaction process itself requires significant amount of energy. Furthermore, differences between temperatures of ambient and LNG cause heat leak into LNG. This results in constant boiling of LNG, and vapors are generated. In order to maintain the pressure of LNG container within safe limits, the vapors generated, called boil-off gas (BOG), must be relieved. In this work, Aspen Plus and Aspen Plus Dynamics v8.8 process simulation tools are used to quantify BOG generation at LNG exporting terminals, for various LNG temperatures. An LNG ship with four moss type spherical tanks is considered in this study. Typical tank design parameters and insulation schemes are used to simulate heat leak calculations. LNG exporting terminal operations are simulated to calculate BOG generation dynamically with respect to LNG loading time. BOG generated during LNG ship-loading is called Jetty BOG or JBOG. This study will provide valuable information about effect of LNG temperature on JBOG that would help in operating LNG plants at optimum conditions and economically minimizing JBOG generation. Minimizing JBOG at LNG exporting terminals will reduce flaring, and thus reduce wastage of material, energy, and potentially environmental impact.