Numerical Analysis Of Stratification And Rolloverin LNG Storage Tank

LNG is a kind of natural gas which can be extracted from the natural gas in the gas field after pretreatment,cooling,liquefaction and throttling expansion.During the storage of LNG,a rolling phenomenon is easy to occur.LNG boiling point at atmospheric pressure is about-162?,LNGclose to the tank wall during storage is easily influenced by the environment of heat leakage,the layered LNG in tank formnatural convection circulation independent inthe delamination area respectively,and through between the layers of liquid-liquid interface conductmass transfer and heat transfer,so the density of differentLNG in the tank is changing,the LNG strongly mixingwhen the density is approximately equal in the tank,a large amount ofliquid in a short time releases a large number of evaporation gas,this phenomenon is called "rolling".The phenomenon of rolling is easy to form explosive mixed cloud around the tank,or it can lead to the boiling liquid expanding vapor explosion(BLEVE),which can seriously affect the safety of LNG storage and transportation.The ICEM CFD software is used to establish the physical model of the stratified rolling of LNG storage tanks in this paper,and the two dimensional transient method is used to simulate the process of real storage tank from stratification to rolling.Using VOF model of ANSYS FLUENT software simulate process,and rolling process of the tank wall and the bottom in different heat leakage intensity and different initial density difference of LNG in the tank were simulated,and draw the curve ofvelocity and density at different height and gas-liquid interface in thethe LNG storage tank.And analyze the roll process under different conditions.The numerical simulation results show that the time of rolling in LNG storage tank is different under different working conditions.The same wall and bottom of the tank to increase heat leakage intensity,the rollover phenomenonwillhappen in advance;under the sameheat leakageintensity and different initial density inLLNG storage tank,density difference is small,the more easy to roll,and need less time.By observing the variation of the density and velocity of LNG in the tank at different heights,it is found that the natural convection caused by the heat leakage is the direct driving force of the rolling phenomenon.Through the simulation and analysis of the rolling phenomenon under different working conditions in the LNG storage tank,to provide some theoretical suggestions for the safe storage and transportation of LNG,and to prevent the occurrence of unsafe incidents during LNG storage.