Abstract
The aim of this work is to evaluate the consequences of Liquefied Natural Gas (LNG) release from the pumps connected to a storage vessel during the loading phase. This phenomenon is relevant for determining the hazardous areas for workers and asset, and in turn for assessing risk on a consequences based methodology. For this purpose, different hazard zones are identified based on different scenarios of accidental events. In particular, when a fire scenario is developed, the hazard area is delimited by the inflammable limits of natural gas in air and by the dimension of the LNG pool. Another important scenario is related to thermal effect. When LNG is released, a liquid pool with very low temperature (around -160°C) is formed and instantly evaporation of this liquid starts. Since Natural Gas cloud is characterized by extremely low temperature, the hazardous area is delimited by the isotherms of the LNG vapour in air. The investigation of the LNG behaviour starts with computing the evaporation case when containment area of pumps is filled with LNG at different wind velocity. In particular, a multi-phase and multi-component incompressible solver based on a Volume Of Fluid (VOF) method is implemented. To perform this investigation, Computational Fluid-Dynamic (CFD) simulations are carried out using the open-source software OpenFOAM®. The methodology introduced in this work allows to evaluate fire scenario and tank structural embrittlement scenario due to low temperatures, as it takes into account the mutual interactions among all the phases present in the system in transient mode, i.e. released Liquified Natural Gas, vapours of LNG and air. As main results, the shape of the LNG vapour flammable limits and isothermal curves are precisely evaluated as a function of wind conditions, determining the evolution of the methane dispersion in the air, which is crucial in the description of the scenario resulting from the consequences analysis.
