Research On The Effect Of Tank Slosh On LNG Safety Storage And Transportation In Tank

As a clean, efficient, convenient and safe energy, Liquefied natural gas (LNG) with the merits of high thermal value, environmental protection, convenient storage and transportation has been becoming the high-quality energy in modern human society. Especially in recent years, as the global LNG production and trade has become increasingly active, liquefied natural gas industry is becoming one of the fastest growing energy businesses in the global. A number of energy countries pay more and more attention to the introduction of LNG and focus on the construction of LNG ships for LNG transportation in LNG trade chain. However, some technical problems are discovered in the process of LNG ships'construction, and the sloshing of liquid cargo is one of the problems to be solved. Liquid cargo sloshing in the tank can cause severe damage of cargo containments; at the same time, because of LNG's flammability and low temperature, the consequences caused by the event of leakage are very serious.Based on the computational fluid dynamics (CFD) method, the membrane tanks which types are now commonly used are studied in this paper. The sloshing sensitivity of liquid cargo has been studied through the volume of fluid method (VOF) to establish sloshing numerical model. It is found that the impact strength of liquid cargo is mainly influenced by external excitation patterns, liquid filling rate and excitation period and so on. In these factors, the external excitation period is dominant; and once the excitation period is close to the resonance excitation period of liquid cargo, the impact force is the largest, and the wave motion is the highest, which cause the great threat on the safe storage of liquid cargo. Therefore, it is needed to avoid the excitation period close to the liquid resonance excitation period in the actual designing and operating process. According to the problems above, the sloshing sensitivity of the filling rate in membrane tank was analyzed and it is found that the best filling rate is less than 10% or lager than 70% which range is the least sensitivity of sloshing. At the same time, the sloshing extent of liquid cargo in the three main tank types involved of membrane-type, sphere-type and SPB-type are determined by force analysis. It showed by comparison that SPB-type tank have a good anti-sloshing characteristic, while membrane-type is on the contrary.Because of limited pressure-bearing capacity in LNG tank, which is commonly at atmospheric pressure in the process of LNG transportation accompanied by liquid evaporation, there are strict requirements for insulation properties of the containments. Considering the problem of pressure rise in tanks, the insulation of the structure, tank volume, the external environment temperature and filling rate were respectively simulated and the influence effect of the pressure variation were identified. In a word this study provides some references for design and manufacture of LNG ships.