Thermodynamic Analysis of Full Scale Baseload LNG Chain

Abstract

The world’s growing energy demand and the need for low-carbon energy sources are key factors that have made natural gas (NG) an attractive energy source compared to other available fossil fuels (i.e. coal and oil). Being the most feasible NG transportation method over long distances, the liquefied NG (LNG) demand is significantly increasing. The LNG supply chain, consisting of production, liquefaction, shipping, and regasification, is, however, an energy-intensive and thereby emission intensive process. Therefore, the appropriate LNG production with least energy consumption and maximum energy efficiency is of high importance. Thus, optimization of LNG chains is essential from both economic and sustainability point of view. Amongst energy efficiency optimization approaches, exergy analysis, based on the second law of thermodynamics, is a powerful tool that has been widely used to quantify exergy destructions and to determine exergy efficiencies and thereby, identify process improvement opportunities. In this thesis work, rigorous and detailed exergy analysis was performed on an entire baseload LNG chain that was simulated using ProMax® and Aspen Plus® simulation software for the delivery of 439 million standard cubic feet per day (MMSCFD). A comparison of the losses across the various units with and without utilities was performed, and optimization opportunities within the chain were identified. Findings of this study revealed that the LNG chain under consideration is associated with total loss of near 647 MW and 1054 MW during holding and loading operation modes, respectively. The main contributor to the exergy loss was found to be the utility section accounting for 61% of the total exergy loss. Within the LNG process, significant amounts of losses were found to occur in the sulfur recovery units, liquefaction unit, and sweetening processes; accounting for 38%, 30% and 24% of the total exergy loss, respectively. The compressors and their drivers (GTs), stream generators, LNG flashing and storage, columns (absorbers, distillations) and heat exchangers were found to be the main exergy consumers.