The Potential of a New Distillation Process for the Upgrading of Acid Gas

Abstract

Abstract In this work, the potential of a new low-temperature distillation process for natural gas sweetening has been investigated. The proposed technology consists of a dual pressure distillation scheme, developed to bypass the SLV locus of the system CH4-CO2 in order to avoid the formation of a solid phase in all the parts of the process, while still being able to fulfill the required natural gas purity specifications. The performances of the new low-temperature distillation process have been assessed for different case studies, considering gas feeds with a CO2 content and with a H2S content in the range 5-65 mol% and 0-15 mol%, respectively. The profitability of the proposed solution has been determined in terms of energy expenses when compared to the more traditional MDEA gas sweetening process. The work has been performed coupling the use of a commercial process simulator (Aspen HYSYS® V7.3) with in-house Fortran routines for the thermodynamic modeling also accounting for the presence of a solid phase. The new solution has been studied and optimized in terms of energy savings related to the cooling duty consumptions. Results of the analysis have shown that the relative trade-off between the two technologies depends on the contents of the acidic compounds in the natural gas stream and on the geographic area where the gas field is located. The new low-temperature technology has shown higher performances and economic profitability when compared to the more traditional gas sweetening processes (such as absorption with alkanolamine solutions) when the CO2 and/or H2S content in the natural gas feed is high, thus possibly enabling the exploitation of extremely acid and sour gas fields. The obtained results have been used for the design of both an industrial unit and a pilot plant that is going to be used to test the process on a lab-scale. The increasing energy demand compels industry to design new solutions for the profitable exploitation of natural gas reservoirs with high CO2 and/or H2S content. Low-temperature distillation technologies represent a cost-effective alternative when sweetening natural gas containing a high amount of acidic components. The new process exploits a different and simpler approach from the ones known in the literature, being able to offer the competitive advantages of low-temperature technologies while avoiding CO2 solidification and solvent addition.