Keys to modeling LNG spills on water

Although no LNG ship has experienced a loss of containment in over 40 years of shipping, it is important for risk management planning to understand the predicted consequences of a spill. A key parameter in assessing the impact of an LNG spill is the pool size. LNG spills onto water generally result in. larger pools than land spills because they are unconfined. Modeling of LNG spills onto water is much more difficult than for land spills because the phenomena are more complex and the experimental basis is more limited. The most prevalent practice in predicting pool sizes is to treat the release as instantaneous or constant-rate, and to calculate the pool size using an empirical evaporation or burn rate. The evaporation or burn rate is particularly difficult to estimate for LNG spills on water, because the available data are so limited, scattered, and difficult to extrapolate to the large releases of interest. A more effective modeling of possible spills of LNG onto water calculates, rather than estimating, the evaporation or burn rate. The keys to this approach are to: center dot Use rigorous multicomponent physical properties. center dot Use a time-varying analysis of spill and evaporation. center dot Use a material and energy balance approach. center dot Estimate the heat transfer from water to LNG in a way that reflects the turbulence. These keys are explained and demonstrated by predictions of a model that incorporates these features. The major challenges are describing the effects of the LNG-water turbulence and the heat transfer from the pool fire to the underlying LNG pool. The model includes a fundamentally based framework for these terms, and the current formulation is based on some of the largest tests to-date. The heat transfer coefficient between the water and LNG is obtained by applying a "turbulence factor" to the value from correlations for quiescent film and transition boiling. The turbulence factor is based on two of the largest unignited tests on water to-date. The heat transfer from the fire to the pool is based on the burning rate for the largest pool fire test on land to-date. (c) 2006 Elsevier B.V. All rights reserved.