(449bq) Simulation-Based Analysis for Highly Sour Natural Gas Sweetening Using Membranes/Amines Hybrid Systems

To meet increasing natural gas demands, producers have been compelled to develop unconventionally high sour gas fields. Formerly, most of these fields were considered economically unattractive given its associated technical challenges. Nevertheless, late technological advances in sour gas processing combined with demand pressures have accelerated the development of these type of resources. The most widely employed sweetening gas scheme combines chemical absorption by solvents (typically an alkanolamine) for acid gases (H₂S and CO₂) removal, and Claus technology for H₂S conversion into elemental sulfur. While this sour natural gas processing scheme is both well-known and proven, its application for tapping highly sour gas resources can be operationally challenging, costly, and wasteful. This because the operating costs, which constitute the majority of the costs involved in sour gas sweetening, depend on the feed natural gas sulfur content. In addition, large volumes of elemental sulfur are generated as by-product; which have to be stockpile in ever-larger sulfur mountains. As a result, presently there is a need for more sustainable gas sweetening schemes.

New polymeric membranes have been applied for bulk H₂S removal from natural gas, including at very high H₂S concentrations and operating pressures. Recent developments on this area may contribute to the development of unconventionally high sour gas resources or retrofitting existing plants. For instance, in a primary stage the membrane system could be used to reduce the bulk concentration of H₂S and CO₂ in the feed gas. The permeate acid gases from the membrane system could preferably be reinjected underground, instead of being converted into elemental sulfur and stockpiled onsite. Sequentially, the final sweet gas product specifications could be met by means of an amine-based system. As a result, this type of hybrid scheme for sour gas sweetening present potential for capital and operating cost deductions, as well as saves in sulfur treatment expenditures.

In this study, the effects of the following factors were examined: membrane area, type of amine for the gas absorption unit, cost of lost methane, membrane replacement costs, and the operating/utility costs of the amine unit. To the authors’ knowledge, there is currently a limited availability of studies in this area; particularly, for highly sour gas processing since it is a newly ongoing development. The present study will examine the sweetening of sour gas with around 15% H₂S (i.e., over 20% of H₂S and CO₂ combined) applying a simulation-based analysis approach. The proposed hybrid process was simulated using ProMax^® v3.2. Although the principles for sweetening highly sour gas is not new; analyses where the H₂S concentration is much higher than that of CO₂ are not common. This because gas resources featuring this characteristic are uncommon on a global scale; however, they can be found recurrently in the Middle East region. The simulation results show that the operating expenditures of the sweetening process can be reduced using a hybrid system (instead of a stand-alone amine system). Additionally, the membrane system can be easily coupled to existing gas plants (i.e., retrofitting). This may allow the membrane system to act as a buffer removing the bulk of acid gases upstream; while maintaining the operation of the amine unit (downstream) relatively stable at feedstock of acid gases with varying concentrations.