The growing public concern over potential terror threats to LNG carriers and the expected increase in LNG shipping traffic led to several recent LNG safety studies. All of these studies addressed the consequences of LNG spills on water; however, none of these recent reports satisfactorily addressed the LNG rapid phase transition phenomenon. Although rapid phase transitions are well researched, the literature published so far does not explicitly quantify the RPT phenomenon. The objective of this paper is to provide a clear understanding of how rapid phase transitions develop and how overpressure is generated.
We present a thermodynamic treatment of rapid phase transitions and discuss the estimation of hazard potential based on the superheat limit. Process Safety Office® SuperChems® software is used to model multi-component LNG spills and to illustrate how LNG composition influences the development of rapid phase transitions and overpressure generation.
A rapid phase transition is the very rapid (near spontaneous) generation of vapor as the cold LNG is vaporized from heat gained from the underlying spill surface or from large volumes of water contacting LNG in a storage tank. Because the vapor is evolved very rapidly, localized overpressure is created. This is also sometimes described as a physical explosion.
Following a release of liquefied natural gas (LNG) from a ship or storage tank, a liquid pool forms and spreads on the surrounding spill surface. Rapid phase transitions have been shown to occur during or following an LNG spill. The hazard potential of rapid phase transitions can be severe, but is highly localized within or in the immediate vicinity of the spill area.
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