(144e) Effect of LNG Chemical Composition on Consequence Assessment

Over the last ten years, LNG has become a popular fuel and its demand has been keeping the increasing trend. This leads to the construction of new LNG facilities around the world for import, storage and re-gasification. The formation of a vapor cloud following the LNG accidental spill presents potentially significant flammable hazards to both the facility and the surrounding communities.

Correctly predicted exclusion zones during the risk assessment process are critical to effectively mitigate the consequence of a LNG spill and protect the public from the flammable vapors. The accuracy of every step of consequence modeling, including LNG spilling, spreading, vaporization and vapor dispersion, influence the precision of exclusion zone estimation. Numerous publications have advanced mechanisms of the above mentioned steps to obtain a certain level of confidence, including comprehensive Computational Fluid Dynamics models to describe complex geometry and turbulence. Nevertheless, most of the available studies assume pure methane as the analog of LNG. This assumption may not be correct, since the vaporization process of mixture as LNG may be significantly different from the pure methane liquid. As a matter of fact, the methane fraction of LNG can vary from 83 to 99% mol, and neglecting this factor may lead to the inaccuracy of all the following steps. In 2007, the US Government Accountability Office had reported: the Public safety consequences of a liquefied natural gas spill need clarification (Report 07-633T, March 21^st 2007). Under this report, the expert panel evaluated several research areas, one of which is evaluation of the effects of LNG composition on vaporization rate, thermal radiation from fire and explosive behavior.

This paper has investigated the influence of multi-component factor on the vaporization rate as well as vapor dispersion modeling. The studied mixtures involve five components: nitrogen, methane, ethane, propane and butane. Suitable equations of state and vapor-liquid equilibrium of LNG have been adopted to predict the vaporization rate, followed by the vapor dispersion modeling. The behavior of pure methane liquid and several different LNG compositions are compared. The results confirmed the significant impact of composition, which has emphasized the necessity of this factor to be involved in LNG consequence assessment process.