Accidental release in the bunkering of LNG: Phenomenological aspects and safety zone

The continuous increase in consciousness on properties and models characterizing cryogenic fuels has opened a new era for the supply of alternative sources of energy, especially in the naval sector. However, practical insights providing comprehensive indications for the development of safe and optimized procedures are still missing or lacking. In this perspective, a preliminary investigation on the commonly adopted procedure was integrated with a 3-dimensional representation of a typical port area in computational fluid dynamics (CFD) simulations implementing sub-models suitable for cryogenic conditions. At first, different scenarios were selected as representative for possible release conditions: Unloading Operation (UO), Shore to Ship (STS), and Truck to Ship (TTS) bunkering operations. This study indicates that TTS can be the most critical scenario because of the simultaneity of bunkering and disembarking procedures. The numerical analysis was devoted to the quantification of the safety distance in the case of the absence of an ignition source. The area where skin and eyes' frostbite are possible is assessed, as well, based on the combination of estimated temperature and local wind speed. The resulting safety distances were compared against estimations deriving by discrete and integral models without obstacles, demonstrating that neglect obstacles lead to non-conservative results. Indeed, a local increase in mixing effectiveness, limiting the flammable area within the channel between quayside and ship, was identified and characterized in this work. Besides, it was found that only under certain circumstances for TTS operations a flammable cloud can potentially reach passengers. Hence, the installation of barriers and mitigation systems (e.g., water curtains) is strongly recommended.