Amine-membrane hybrid process economics for natural gas sweetening

In this study, natural gas sweetening using the amine-membrane hybrid process was investigated by economic evaluation. The Amine-membrane hybrid system consists of a membrane section applied to reduce the bulk flow acid gases followed by the amine section to enhance gas quality. Membrane feed pretreatment operation is also considered to approach the real membrane unit. The hybrid system is economically optimized by considering both single and two-stage membrane sections applying different methane and membrane prices, feed flow rates, membrane type and presence of other impurities (N-2). Economic evaluations show that the two-stage cellulose acetate (CA) membrane section, in the hybrid system, is unsuitable and a single-stage membrane hybrid system for feed with high acid gas content (about 20mol%) is competitive with the amine sweetening unit due to the decrease in Total Operating Cost (TOC) with a small increase in Total Capital Investment (TCI). The product price increases rapidly by scale-down in the unit capacity below 100 MMSCFD feed rate. Economic assessment indicates that application of higher selective membranes than CA reduces the TOC but at the same time enhances the TCI. It seems, therefore, that the use of a semi selective membrane such as CA is beneficial.