LNG 탱크에서 천연가스 유출시 얕은 기초 주변 지반거동의 수치해석적 분석

Numerical Analysis of Behavior of Ground Near LNG Tank Foundation Under Scenario of LNG Leakage

Abstract

최근 천연가스에 대한 수요가 높아지면서 이를 저장하기 위한 LNG 탱크의 건설이 증가하고 있다. LNG는 효율적인 저장을 위해 극저온의 유체로 액화되므로, LNG 탱크의 결함으로 인한 LNG 유출은 막대한 피해를 야기할 수 있다. 많은 연구자들이 다양한 LNG 유출 상황에 대하여 발생가능 한 피해 영향을 평가하였으나, 극저온의 LNG 유체가 유출될 경우 LNG 탱크를 지지하고 있는 지반에 미치는 영향에 대한 연구는 제한적이다. 따라서 본 논문에서는 LNG 탱크 및 지반의 다양한 조건을 고려하여 LNG 유출에 따른 동결 지반의 역학적, 열적 거동 변화에 대한 연구를 수행하였다. 유출 시나리오의 구현을 위해 수치해석을 수행하였으며, 상재하중, 온도 경계조건, 흙의 동결 민감성 변화에 따른 지반과 기초구조물 거동을 조사하고자 하였다. 이를 통해 LNG 유출 이후 지반의 단기 및 장기 온도변화를 평가하였으며, 지반 동결에 따른 간극 및 연직변위 변화를 분석하였다.

Recently, the use of natural gas has steadily increased due to its economical advantage and increased demand of clean energy uses. Accordingly, construction of LNG storage tanks is also increased. Secure of the stability of LNG tanks storage requires high technology as natural gas is stored in a liquid state for efficiency of storage. When a cryogenic LNG fluid leaks on ground due to a defect in LNG tank, damage is expected to be significant. Many researchers evaluated the critical and negative effects of LNG leakage, but there is limited research on the effect of cryogenic fluid leakage on the ground supporting LNG tanks. Therefore, in this study, the freezing expansion of the ground during cryogenic LNG fluid leakage was evaluated considering various outflow situations and ground conditions. The LNG leakage scenarios were simulated based on numerical analyses results varying the surcharge load, temperature boundary conditions, and soil types including freeze-sensitive soil. Consequently, short and long term ground temperature variations after LNG leakage were evaluated and the resulting ground behavior including vertical displacement behavior and porosity were analyzed.

Fig. 1. Freezing mechanism of ground [modified after Taber (1930)]

Fig. 2. Porosity rate function [modified after Michalowski (1993)]

Fig. 3. Standardized small or medium modular LNG storage tank

Fig. 4. Modeling of LNG leakage scenario

Fig. 5. Temperature change with LNG leakage time: (a) 14 days, (b) 90 days

Fig. 6. Modified modeling for LNG leakage scenarios

Fig. 7. Distribution of vertical displacement at after (a) 7 days, (b) 28 days which load is 100 kPa and (c) 7 days, (d) 28 days which load is 35 kPa

Fig. 8. Distribution of vertical displacement with changing of temperature boundary condition at after (a) 7 days and (b) 28 days

Fig. 9. Distribution of (a) temperature, (b) unit volume ratio of ice and (c) porosity at after 28 days with changing of temperature boundary condition

Fig. 10. Distribution of temperature in (a) silt soil and (b) clay soil

Fig. 11. Distribution of vertical displacement in (a) silt soil and (b) clay soil

Fig. 12. Distribution of porosity in (a) silt soil and (b) clay soil

Table 1. Thermal properties of numerical analysis

Table 2. Thermal and mechanical properties used numerical analysis

Table 3. Input parameter for porosity rate function

Table 4. Input parameter for function of unfrozen water content