Mozambique has one of the best and most innovative projects of exploration of natural gas in the world, the Liquefied Natural Gas (LNG) projects in Cabo Delgado. The LNG supply chains increased the relevance in the energy market during the last 20 years, and economic projections indicate it will continue to grow.

The transportation of natural gas can be through pipelines as gas in high pressure or liquifing it and transport as LNG; liquefying the natural gas and transporting it as LNG carries high energy density, due to the ability for carrying the same amount of energy about 600 times more than gaseous form. In the LNG storage tank, due to the heat leak, the LNG evaporates and consequently the total pressure increases, to maintain the pressure constant, the boil-off gas formed is removed, resulting in the remaining LNG being richer in heavier components.

The research conducted in this dissertation was to develop a model to predict the weathering process in a full containment tank of LNG in a small-scale LNG supply chain. The developed isothermal model integrates a vapour-liquid equilibrium model, and a heat transfer model. It allowed to determine the quantities of BOG formed along the storage time, and identify the effect of various factors, such as the impurities content, the initial LNG inventory, ambient temperature, and initial composition on the generation of the BOG.

The model allowed to access one of the main results of this work, the BOG generation, 3.26% of the initial inventory after 90 days of operation. For the sensitive analysis done with ambient temperatures of 20, 22, 24 and 26 ^oC, it gives the lowest BOG fraction the temperature of 20 ^oC and for a change of 2 ^oC change in the ambient temperature it leads to a change in BOG of 0.01 %. The sensitive analysis caried out for the initial LNG inventory reveals that the evaporation occurs fast for a low filling ratio (10% of the initial inventory), compared to the case of other filling ratios (50, 80 and 90% of the initial inventory), and has the worst energy content based on the LNG composition, as it has the lowest content of methane.

Keywords: LNG, BOG, Isothermal model, Weathering process.