Design and Optimization of a Process Based on Extractive Distillation for the Sweetening Natural Gas

Abstract

For the sweetening natural gas process, the most used scheme at industrial field is the chemical absorption by alcohol amines. Recently, Lastari et al., (2010) proposed a design using the cryogenic extractive distillation by employing like entrainer the same hydrocarbon liquefied fractions of the process. In this work, it was used the Aspen Plus One 7.0 ®?simulator, considering non-equilibrium trays to model these schemes, coupled to a multi-objective stochastic optimization procedure, using Differential Evolution (DE) as main algorithm. The optimization is focused on minimizing the Total Annual Costs (TAC) and maximizing the acid gas removal interpreting the information with Pareto fronts. Finally a post-optimization analysis was performed considering a dynamic study by singular value decomposition (SVD) technique, thermodynamic efficiency and greenhouse gases generation studies for several representative spots for each Pareto. The process performance was focused on breaking the CO2- ethane azeotrope, following the next procedure: assessment of pure different entrainers (propane, n-butane, n-pentane and n-hexane) on three arrangements with and without thermally coupled. We compare the performance of these sequences with the conventional system using chemical absorption by mono-ethanol amine (MEA) like benchmark problem. A comparison between Pareto fronts analysis showed that cryogenic extractive distillations reached out bigger CO2 removals with lower TACs than chemical absorption.