In liquefied natural gas (LNG) processes, the gas feed is cooled to very low temperatures (−160° C). The presence of traces of heavy hydrocarbon components may therefore result in crystallization, and thus equipment plugging. The present work investigates the solid–liquid–vapor equilibria and proposes a way to predict the risks of crystallization.

In the first section, the phase diagrams that may be encountered with natural gas mixtures at these very low temperatures are presented. A literature review shows that few data are available for operating conditions of LNG processes.

In the second section, the crystallization model based on a cubic equation of state, coupled with a Huron–Vidal mixing rule and combined with a solid-phase model is presented. This model requires the crystallization heat capacity of pure components, which must be determined using the few data points available. Nevertheless, it appears that the resulting model is rather predictive when compared to data that were not used in the regression.

Finally, the model is applied in different zones of the LIQUEFIN process, commercialized by AXENS. The results have been used to improve the design of this LNG plant. © 2005 American Institute of Chemical Engineers Process Saf Prog, 2005