Evaluating crystallization risks in liquefied-natural-gas (LNG) production

Liquefied natural gas (LNG) is anticipated to dominate world energy trade and fill the gap between production and energy demands in a few years, especially in the US. LNG is the liquefied version of dry natural gases at ultralow temperatures (approximately -160°C or -260°F at atmospheric pressure), which aims at minimizing storage volume requirements needed for overseas transportation. Within this context, it is clear that technology must continue to be developed to optimize the thermodynamic processes involved in the compression, liquefaction, and revaporization of LNG and associated operational challenges. One key challenge during the production of LNG is the presence of trace amounts of heavy components in the gas feed composition is known to induce the precipitation of a solid phase during the cooling process, which presents the risk of equipment plugging and associated hazards. However, there are very few general thermodynamic tools available for the prediction of solid-liquid equilibrium for very low-temperature conditions (<-200°F). In this study, available thermodynamic predictive tools are evaluated for the determination of LNG crystallization conditions. Previously presented crystallization prediction models are examined, and potential pitfalls identified. The results from this study are expected to provide a better understanding of the thermodynamics of LNG processes and provide a framework for subsequent work in the analysis of LNG refrigeration and liquefaction processes-typically considered the key elements of any LNG project.