Modeling LNG Pool Spreading and Vaporization

Liquefied Natural Gas (LNG) vapor dispersion analysis is heavily influenced by the estimation of the source term: (a) the LNG (liquid) leak rate and duration, and (b) the pool spreading and vaporization. A sophisticated dispersion model will produce the wrong answer if the source term used is in error. This paper discusses the validation of SuperChems™ Expert’s dynamic liquid pool model for simultaneous spreading and vaporization. The model is capable of performing multicomponent analysis to account for differences in LNG composition. LNG spills can be modeled on various surfaces including water. SuperChems™ Expert’s dynamic pool model is shown to accurately reproduce field data for LNG as well as other liquids.

Consequence analysis of LNG hazards requires modeling of liquid spills on land and water surfaces. The liquid spill duration, release rate, and rate of vaporization are important factors for the estimation of safe separation distances for flammable vapor dispersion and thermal radiation from pool fires. Dispersion distances calculated to ½ LFL are required for the siting of LNG facilities. For an LNG spill, NFPA 59A (2001) requires facilities to have impoundments be sited such that the average concentration of methane in air does not exceed 50% of its lower flammability limit (LFL) beyond the property line1. The federal code of regulations for siting LNG facilities in 49 CFR Part 193 allows the use of both DEGADIS and FEM3A2 for dispersion analysis. DEGADIS is a refined box model while FEM3A is a computational fluid dynamics (CFD) model. There is no defined model for calculating the source term. 

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