Numerical Study On The Characteristics Of LNG Rollover In Storage Tank

With the increasing environmental pollution and the growing energy consumption in China,the demand of clean energy the natural gas will increase rapidly in the future.It is expected that the demand of liquefied natural gas(LNG)will reach 60 million tons by2020,and the safe storage of LNG is very important to the development of LNG industry.LNG has strict requirements on the storage environment.During the long-term storage,the unstable storage phenomenon caused by the violent evaporation of the liquid in the storage tank which was called the stratification and rollover.The stratification and rollover of LNG directly threatens the safe storage of LNG.Therefore,the study of the stratification and rollover of LNG in storage tanks is of great significance to the LNG industry.In this paper,the numerical calculation method is adopted.Firstly,the liquid movement characteristics inside the tank after the stratification was completed is analyzed,and then the influence of the stratified density difference on the liquid storage state inside the tank is studied,and then the influence of nitrogen content in LNG on its density is analyzed.Finally,the influence of different filling method performed on the stratification is simulated.This study shows that:(1)The interface of stratification was the place where disturbance first appeared,and the velocity at the liquid surface and the bottom of the tank appear relatively late,and the velocity maximum is relatively small.(2)In this study,the velocity value of 0.083 m/s can be regarded as a basis for judging whether the liquid inside the storage tank is in a secure storage state.When the stratified density difference is small(less than 0.4 kg/m~3),the liquid inside the storage tank is naturally convective and the storage tank is in a safe storage condition.(3)The critical density difference in the vertical 150 m~3 LNG storage tank from stable storage to unstable storage is in the vicinity of 0.4-0.6 kg/m~3.Through theoretical analysis,the correctness of the empirical results of judging the occurrence of stratification in actual projects was verified.(4)The nitrogen containing of LNG has a significant effect on the density,a tiny content of nitrogen can lead to a greater density difference,which is enough to cause the stratification.(5)Reasonable filling methods can reduce the risk of stratification for different densities of LNG.