ABSTRACT:

In order to secure large LNG (liquefied natural gas) storage facilities and to stabilize the LNG supply on a long term basis, a new system of storing LNG in a lined rock cavern has been developed. The concept consists of protecting the host rock against the extremely low temperature by using a containment system with a gas tight steel liner and insulation panels. Moreover, the moderated and controlled frost development in the surrounded rock mass contributes to create an ice ring, acting as a secondary barrier against any possible leakage. Therefore, the location and thickness of the ice ring are important factors for the stability of the underground LNG storage in a lined rock cavern. This paper describes the results of the numerical modeling performed to investigate the impact of ice ring formation and propagation on the ground water flow, where the ice ring is formed by the phase change of groundwater due to the cooling-down in the rock mass around the cavern. The results of the numerical simulation showed that the process of ice ring formation was similar to the one evaluated by the interpretation from the geophysical survey data during the pilot operation.

1. INTRODUCTION

Many attempts have been made to store LNG in unlined rock caverns but were not successful. The failures were due to thermal stresses generating cracks in the host rock and the thermal cracks contributed to deteriorating the operational efficiency of the cavern because of induced gas leakage and increased heat flux between ground and storage [1, 2]. To provide a safe and cost-effective solution, a new concept of storing LNG in a lined hard rock cavern has been developed and tested for several years [3]. The concept consists of protecting the host rock against the extremely low temperature by using a containment system with a gas tight steel liner and insulation panels. Moreover, the moderated and controlled frost development in the surrounded rock mass contributes to create an ice ring, acting as a secondary barrier against any possible leakage (Fig. 1). Therefore, the location and thickness of the ice ring are important factors for the stability of the underground LNG storage in a lined rock cavern. In order to verify the technical feasibility of such storage concept, a pilot plant was constructed in the Daejeon Science Complex in 2003. From January through August 2004, a pilot test has been performed using LN2 (liquid nitrogen) instead of LNG for safety and practical reasons [4].

Fig. 1. Concept of LNG storage in a lined rock cavern. (available in full paper)

The main purpose of this paper is to understand mechanism related with ice ring formation during the stop period of the drainage system in rock mass around the pilot cavern after six months of cooling-down. So behavior of rock mass and structures associated with heat transfer, groundwater flow and ice ring formation is simulated with a CFD code, FLOW3D.

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