Research On Anti-rolling Technology For Large LNG Storage Tank Filling

As a clean and efficient energy source,liquefied natural gas(LNG)has obvious advantages in environmental protection and economy of energy utilization.The import volume and demand of LNG in China have increased rapidly,and the number of completed LNG receiving stations has increased year by year.Large LNG storage tanks are the core equipment of LNG receiving stations and the main equipment for storing LNG.The study of large LNG storage tanks is of great significance for the transportation and storage of LNG.When LNG is stored in the tank,it is easy to cause problems such as evaporation,stratification and tumbling due to aging or filling with new LNG,which seriously affects the safe operation of LNG storage tanks.Therefore,the safe storage of LNG has become an important issue in the natural gas industrial chain.Based on the review of relevant literature at home and abroad,this paper analyzes the stratification and rollover phenomenon and its mechanism in LNG storage and transportation process,establishes the mathematical model of LNG stratification and tumbling,and uses the Fluent software to carry out LNG stratification and rollover model.Solving and analyzing the simulation results show four stages of LNG layered rolling:the tumbling stage at the tank wall,the interface tumbling transfer stage,the tumbling leveling stage and the new stratification forming stage.The LNG layering and rolling model is used to analyze the different factors affecting the LNG layering and rolling process.The numerical simulation study on the rolling process of large LNG storage tanks under different working conditions was carried out,and the effects of different layer numbers,stratification height and delamination density on the tumbling density field velocity field of large LNG storage tanks were obtained.The occurrence time,intensity and duration of the LNG are similar to those of the same diameter and the same density difference.The LNG rollover occurs earlier,lasts longer,and the tumbling is more severe.The higher the stratification height,the later the LNG roll occurs.The more severe;the greater the density difference,the earlier the aging of the LNG tumbling occurs,and the longer the duration.Establish a three-dimensional filling model of 16×10~4m~3large LNG storage tanks,improve the previous method of filling the upper and lower injection ports with stratified and simultaneous filling method,and apply dynamic mesh technology to simulate the LNG in the tank during the filling process of large LNG storage tanks.The stratification process was carried out to study the effects of factors such as height,density difference,deflection angle and filling method on LNG stratification during LNG filling with different temperature and specific gravity.The results show that the low-temperature heavy fluid filling should be filled with the upper filling or layered nozzle simultaneously;the high-temperature light fluid should be filled in the bottom layer,and the lower the filling port,the better the mixing effect;when the deflection angle is 15-20°,When the stratification is simultaneously filled,the LNG in the tank can be automatically cycled and mixed,and the density difference of LNG in the tank is the smallest after the filling.