Modelling large LNG pool fires on water

PresentationThere has been a rising demand for natural gas across the World. In many countries, this demand is being satisfied through an increasing number of marine LNG Carrier (LNGC) deliveries and hence there is a safety requirement to understand the consequences of significant accidents that could lead to the catastrophic failure resulting in a large spill of LNG in a harbor. The impact of thermal radiation on LNGCs, terminal facilities and the public outside the site fence-line from an LNG pool fire on water could extend a long distance according to current empirical models. The Phoenix pool fire experiments were conducted by Sandia laboratories to validate these models for large LNG spills on water. It was observed that the pool fire did not extend across the entire area of an 80 m diameter LNG pool. In addition, the flame height was greater than expected and there was very little smoke obscuration compared to the 35 m tests at Montoir. This combination of physical phenomena made it difficult to use existing models to predict the consequences of thermal radiation, especially when extrapolating to different and potentially larger spill sizes. A recent study using empirical analysis and CFD demonstrated that the thermal updraft of a large fire will drive an inward flow of air and natural gas from the non-burning region with a velocity greater than the burning velocity of the outwardly spreading pool fire. Medium scale tests using a 4 x 1 m LNG pool in a fire tunnel confirmed that an artificially generated air-flow of 2.8 m/s was sufficient to stop the flame spread across the pool and confirmed the previous analysis. This paper describes an empirical model that has been developed based upon this analysis to account for the reduced pool fire size and successfully model the larger flame height that was observed during the Phoenix test. An analysis of large spills using this model showed that the calculated flame view factor was significantly reduced compared to pool fire models that predict that the fire will extend across the whole spill surface. The paper will also discuss the effect of water on combustion and hence provide an explanation for the reduced smoke obscuration that was seen during the Phoenix tests