Numerical simulation of ice-ring formation in the jointed rock mass around underground LNG storage cavern using thermo-hydraulic model

摘要

A new technology for storing LNG in the underground cavern has been developed by combining the concept of groundwater drainage and an ice-ring with insulation system for LNG carriers and above-ground storage tank. Formation of the ice-ring, which is one of the core technologies forming LNG storage system, can be identified by a complex mechanism undergoing between the thermal characteristics of the rock mass and hydro-geological characteristics of groundwater. The key to the technology of LNG storage system have been well demonstrated through the design, construction and operation of the Pilot Plant existing at Daejeon, Korea. The results obtained from the study with regards to the formation of the ice-ring, showed that the freezing temperature of the water flowing through rock joints is affected by the latent heat during freezing, aperture of joints and the flow rate of groundwater. In the present study, the freezing temperature and the penetration length of groundwater was investigated by a thermo-hydraulic coupled analysis and CFD analysis of the groundwater flow in the joints during formation of the ice-ring. The factors affecting the freezing temperature of groundwater during the ice-ring formation are the rate of rise in groundwater level and the joint aperture. In addition, the numerical modeling studies demonstrated that the two factors were affecting each other prominently. The freezing temperature of groundwater in both narrow and wide aperture of a joint can be applied with a value higher than.3.C, which was assumed as freezing temperature in the past. However, these numerical analyses were conducted in a limited range with several assumed conditions. Therefore, further analysis with several other conditions would be necessary to clarify the freezing temperature of groundwater in the rock joints.