Coupled hydro-thermal modeling of ice ring formation around a pilot LNG cavern in rock

Abstract

A new method of storing LNG (Liquefied Natural Gas) in a lined, hard rock cavern has been developed and verified by the construction and operation of a pilot plant in Korea. Creation of an ice ring is one of the core techniques in LNG storage in a lined rock cavern. The ice ring serves not only as a primary barrier against the intrusion of groundwater into an LNG cavern, but also as a secondary protection in case of leakage of LNG. Dry conditions within an ice ring protect a containment system against cracking due to the freezing of groundwater. Therefore, it is crucial to estimate and control the thickness and location of the ice ring when designing and operating an underground LNG storage cavern. In order to find suitable numerical scheme that simulates field results, the behavior of the ice ring around the pilot LNG cavern is investigated by hydro-thermal-coupled analyses. Through coupled analyses composed of three cases (CASE_1: constant thermal properties, CASE_2: temperature-dependent thermal properties, and CASE_3: phase change consideration in addition to CASE_2), the position and thickness of the ice ring, the temperature distributions and the groundwater level around the cavern are estimated and compared with measured data obtained from the pilot LNG cavern. The results show that the temperature distribution and groundwater level around the LNG cavern can be estimated reliably within an error of less than 4 °C and 1.0 m, respectively. The accuracy of numerical modeling is increased when the temperature-dependent properties are taken into account. The effect of phase change during freezing and thawing of groundwater is relatively small due to the dryness inside the ice ring and low porosity of the rock mass. These results imply that the adopted numerical method can be applied to full-scale underground LNG caverns for the control of the ice ring.