Simulation on the influence of temperature drop rate on the pre-cooling of LNG storage tanks

A series of debugging work should be carried out before an LNG tank is put into operation, in which the pre-cooling of LNG tank is the most important part. In this paper, the pre-cooling model of 16×10⁴ m³ ground full-containment LNG storage tank was established by MATLAB, to study the changing rules of LNG spray flow, BOG emission flow, tank pressure and LNG vaporization rate in the process of pre-cooling and the influence of the temperature drop rate on the pre-cooing of LNG storage tank. It is indicated that in the process of pre-cooling, the LNG spray flow increases gradually, the BOG emission flow and the tank pressure increase firstly and then decrease, and the LNG vaporization rate only decreases in the late stage of pre-cooling. As the temperature drop rate increases, the LNG vaporization rate only increases in the late stage of pre-cooling, and the LNG spray flow, the BOG emission flow and the tank pressure increase, but the total amounts of LNG spray and BOG emission decrease. When the temperature drop rate exceeds 3 K/h, its effect on the pre-cooling of LNG storage tank is smaller. Solar radiation shall not be neglected in the analysis on the pre-cooling of LNG storage tank. In order to ensure the smooth commissioning of LNG storage tank, it is recommended to control the temperature drop rate less than 1 K/h in the early stage of pre-cooling, and to increase the temperate drop rate and keep the average temperature drop rate 2-3 K/h in the late stage to increase the utilization rate of LNG cold energy. It is verified by actual case that the simulation error of the pre-cooling model of LNG storage tank is less than 10%, which satisfies the engineering application requirements. The research results can be used as the reference for actual pre-cooling process, pre-cooling plan design and pre-cooling parameter optimization of LNG storage tanks.