Numerical simulation of LNG dispersion in harbours: a comparison of flammable and visible cloud

The current trends in environmental impact reduction have promoted natural gas and hydrogen either as short- or long-term solutions. In both cases, liquid transportation in cryogenic form is associated with new concerns in terms of safety aspects. So far, infrastructures based on utilizing the liquefied natural gas (LNG) in port areas have been developed and realized worldwide. However, a uniform guideline and set of monitoring criteria are missing because of the lack of knowledge of the phenomenological aspects. This work deals with the numerical characterization of the visible cloud boundaries in the case of an unintentional release during bunkering operations and its comparison with the standard value for the flammability of cloud, based on the lower flammability limit. To this aim, real-scale computational fluid dynamics (CFD) simulations were performed. Results showed that both flammable and visible clouds were dramatically sensitive to the heat transfer with the substrate in an unconfined environment. Besides, turbulence seems to affect the flammable cloud expansion rather than the visible cloud. Eventually, results indicate that the flammable cloud can be up to 50% larger than the visible for confined and 20% large for unconfined environments, conservatively, on the safe side. These values can be adopted for design and emergency purposes.