LNG Technology: The Weathering in Above-Ground Storage Tanks

Liquefied natural gas (LNG) is an energy source with worldwide steady growth: natural gas supply, as gas demand, is expected to grow in the near future. LNG is stored in tanks at pressure slightly higher than the atmospheric value and at its boiling point. Despite the high degree of insulation in the tank walls, it is impossible to avoid a net input heat transfer from the surroundings, so that vaporization is always present. It causes an increase in the pressure of the tank and a consequent boiloff in order to avoid overpressure. The change in composition and density of the liquid phase is called LNG aging or weathering. This phenomenon has been studied in order to obtain a model that can predict the variations that occur in the tank over time. Unlike other previously developed models, the proposed model does not require knowledge of the boiloff rate; instead, it calculates the rate directly from the heat flow to the tank. As a consequence, from a comparison with experimental data, it is proved that a more reliable representation of the phenomenon can be obtained.