Numerical simulation and safety control strategy of LNG storage tank and pipeline pre-cooling process

For the LNG storage and distribution system, a high-precision 3D model of the LNG storage tanks and pipelines is established. Based on thorough consideration of the vaporization phase change of cryogenic liquids, the temperature field and stress field distribution during the pre-cooling process of the storage and distribution system are simulated and analyzed. Areas with significant shrinkage and stress concentration are optimized in advance to reduce thermal displacement and stress effects. According to software modeling and thermal balance relationships, the impact of refrigerant inlet flow rate on the temperature drop rate of the storage and distribution system is studied, and an optimized pre-cooling operation plan is proposed. The study shows that the overall trend of pre-cooling temperature for the storage tanks and pipelines is initially rapid and then gradually stabilizes. The maximum temperature drop rate occurs within the first hour of pre-cooling, and the flow rate should be controlled at 0.2 m/s or less during the initial stage. The maximum equivalent stress in the storage tank appears near the lower edge of the tank wall close to the inlet, while the maximum equivalent stress in the pipeline system occurs at the intersection of straight pipe sections and elbows. These areas should be prioritized as critical zones for weld seam stress monitoring. The maximum total strain in the storage tank is located at the vertical center of the tank wall, where reinforcement measures should be taken. After 7 hours of pre-cooling at flow rates of 0.5 m/s and 1 m/s, the frequency of monitoring tank wall displacement should be increased, and the inlet velocity of the cryogenic fluid should be adjusted appropriately. The pre-cooling patterns for straight pipes and elbows are similar; for elbows, the distance between adjacent fixed points should be reduced, and fixed supports should be installed at the intersection of straight pipe sections and elbows to prevent cracks from forming in weak areas.