Multi-objective optimization of propane pre-cooled mixed refrigerant (C3MR) LNG process.

Multi-Objective optimization of propane pre-cooled mixed refrigerant (C3MR) LNG process is performed with two objective functions: (a) maximizing the exergy efficiency and (b) minimizing the total cost of the product. The process simulation is developed using Aspen Plus, while the feasible solutions are produced using non-dominated sorting genetic algorithm II (NSGA-II). The results from exergy-based analysis revealed that when the exergetic efficiency is maximized, the total cost of product has increased from 5047$/h to 52776 $/h, with 71% of the investment costs come from precooling heat exchangers and main cryogenic heat exchangers. On the contrary, when the total cost of product is minimized, the total investment cost is reduced by 18% at the expense of exergetic efficiency. At the lowest cost of product, the total exergy destruction has increased to 111.4 MW or 38% higher compared with the case of maximization of exergetic efficiency. The optimization shows the range of Pareto feasible solutions are between 0.557 and 0.613 for exergetic efficiency and between 45600 and 52776 $/h for the total cost of product. This study demonstrates the approach to solve a multi-objective problem and to find Pareto front for an LNG process without imposing any weighted preferences to the objective functions. • Propane pre-cooled mixed refrigerant process are analyzed using exergy-based methods and optimized with genetic algorithm. • Multi-objective optimization is the combination of the exergy-based methods and non-dominated sorting genetic algorithm II. • Over 70% of the investment costs associated with pre-cooling heat exchangers and main cryogenic heat exchanger. • The total product cost minimization: the total investment cost is reduced by 18% while the exergetic efficiency decreased. • Pareto front for the two objective functions is shown at 100th generations. [ABSTRACT FROM AUTHOR]