Safety Study On The Storage And Transportation Of LPG And LNG

With the deterioration of global environment and the improvement of people’ living standard requirement,clean energy demand is increasing.As two clean fuels,LPG and LNG have got the fast development in our country.They contribute a great deal to the social progress.However,LPG and LNG bring us hazard along with their benefits.A lot of security incidents have happened in the process of storage and transportation of LPG and LNG since their births and lead to heavy losses of life and property.In order to utilize combustible liquefied gases safely and try our best to avoid the occurrence of disasters,the subject of studying storage and transportation safety of combustible liquefied gases is becoming more important.Under high temperature environment,LPG tanks or tankers will be exposed to high temperature radiation inevitably.The LPG tanks or tankers in the state of high pressure storage or transportation are without the protection of thermal insulation.As a result,the LPG will absorb much heat and the temperature will rise,then the tanks or tankers may be at overpressure state.The physical model of LPG tank under high temperature is established to study the thermal response of the fluid in the tank.Great universal CFD software FLUENT is used to study the change of temperature field,pressure field and velocity field.The temperature contour,pressure contour and velocity vector were obtained after the numerical calculation to the temperature field,pressure field and velocity field.Tankers with different fill level,size and wall temperature were simulated.The changes of pressure and temperature over time under different situations were calculated.The results showed that the higher the fill level was,the quicker the pressure increased.Under the same condition,pressure of the tankers with fill level of 50% and 80% are 65.7% and 136.5% more than that of the tanker with a fill level of 30%.The size of the tanker had a great influence on the safety of transportation.When the tanker was smaller,the pressure and temperature in it increased more quickly.The final pressure of the tanker with sides of 0.2m was seven times that of the tanker 20 m on a side.And the temperature of the former was three higher than that of the latter.Finally,thermodynamic analysis was applied to the system of tanker and fluid,drawing the conclusion that the system was a dissipative structure with external energy and internal energy dissipation.Rollover is a major threat to the storage of LNG.Taking the world famous rollover accident,La Spezia rollover accident,as the background,the paper constructs the three-dimensional geometric model and mathematic model of the tank after simplifying and idealizing the tank state and the various conditions with the software of FLUENT.The heat and mass transfer after stratification is studied.At the same time,the temperature and the density of the both layers is analyzed.The temperature and the density of the upper LNG layer increases abidingly,but the lower layer moves in the opposite direction.The velocity of rising or falling is fast followed by slow.The heat and mass transfer between upper layer and lower layer first rises then falls,which is coincides with the variation of the both layers.The simulated time when rollover happens is 33 hours which is 2 hours more than the actual time.The error is 6%,which shows that the computing model is proper.