| As a clean, efficient energy and chemical raw materials, natural gas is gettingmore and more attention and favor from all over the world in recent years. InLNG(Liquefied natural gas) industry, the design and construction of LNG tank is keyfor LNG receiving terminals, which needs a high cost, long period, more professionaland high technical requirements. Therefore LNG tank research has an importantrealistic significance to the development of national LNG industry, worseningenvironmental problems and energy crises.All possible thermal effects for large-scale LNG tank during construction, testing,cool-down, normal and abnormal operation and warming-up shall be considered dueto its low operation temperature. Normally, the inner tank contains LNG, but whenthe LNG leaks from the inner tank and accumulates in the annular space, the outerconcrete tank comes into contact with LNG, which may pose a threat to LNG tanks.Under this accidental case, it is necessary for concrete wall of LNG tank to bechecked and evaluated its mechanical properties in low temperature. In addition, LNGitself has the characteristic of flammability and explosion, which may bringinestimable loss, even lead to serious secondary disasters. So, it is also necessary forLNG tank to be checked and evaluated its hot response process and failure mechanismunder fire.Thermal conduction analysis and thermal stress analysis for service condition,LNG spill condition and fire hazard condition are performed using a2-Dimensionalaxisymmetric finite element model (FEM) through ANSYS. The major work whichhas been carried out on this thesis and the important conclusions are summarized asfollows:1. In case of service condition, thermal protection system is always working at alow temperature environment, which has a high performance requirements to thematerial of insulation. The temperature of the concrete outer tank is similar to theenvironment. Thermal protection system can prevent potential damage to LNG tanksfrom external heat leakage and low temperature liquid.2. In case of leakage of the inner tank, the cooling process of outer wall is slow.Thermal distribution becomes constant after1-week from initial of LNG spill, when the temperature of outer wall is greatly reduced. Cryogenic liquid has almost no effecton the temperature of top ring beam and roof. Thermal corner protection caneffectively reduce the temperature effect on the outer wall.3. In case of leakage of the inner tank, low temperature creates large shrinkagedeformation to the concrete outer wall. The height of compression zone, the averagecompressive streses in compression zone are met the requirements of EN14620-1andBS7777. Stresses in reinforcing bars and prestressing tendon are limited to the yieldstrength. Stresses in roof concrete are small. Therefore, the serviceability requirementand liquid-tightness can be satisfied.4. In case of fire hazard condition, the heating process of concrete roof and wallalong the thickness direction shows obvious lag. The temperature of roof and wallouter surface reach to640°C after two hours, while the inner surface temperature isalmost not changed. Thereby a certain thickness of concrete can effectively preventexternal heat leakage into the tank, which is crucial to the safe operation.5. In case of fire hazard condition, high temperature radiation creates expansiondeformation to the concrete outer tank. The deformation of roof is larger than outerwall. Stresses in reinforcing bars and prestressing tendon are limited to the yieldstrength. The structural integrity of tank can be guaranteed. But some permanentdamage may occur for the high temperature of outer tank surface concrete. |
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