Accidental release of Liquefied Natural Gas in a processing facility: Effect of equipment congestion level on dispersion behaviour of the flammable vapour

An accidental leakage of Liquefied Natural Gas (LNG) can occur during processes of production, storage and transportation. LNG has a complex dispersion characteristic after release into the atmosphere. This complex behaviour demands a detailed description of the scientific phenomena involved in the dispersion of the released LNG. Moreover, a fugitive LNG leakage may remain undetected in complex geometry usually in semi-confined or confined areas and is prone to fire and explosion events. To identify location of potential fire and/or explosion events, resulting from accidental leakage and dispersion of LNG, a dispersion modelling of leakage is essential. This study proposes a methodology comprising of release scenarios, credible leak size, simulation, comparison of congestion level and mass of flammable vapour for modelling the dispersion of a small leakage of LNG and its vapour in a typical layout using Computational Fluid Dynamics (CFD) approach. The methodology is applied to a case study considering a small leakage of LNG in three levels of equipment congestion. The potential fire and/or explosion hazard of small leaks is assessed considering both time dependent concentration analysis and area-based model. Mass of flammable vapour is estimated in each case and effect of equipment congestion on source terms and dispersion characteristics are analysed. The result demonstrates that the small leak of LNG can create hazardous scenarios for a fire and/or explosion event. It is also revealed that higher degree of equipment congestion increases the retention time of vapour and intensifies the formation of pockets of isolated vapour cloud. This study would help in designing appropriate leak and dispersion detection systems, effective monitoring procedures and risk assessment.