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Treatment of a Highly Sour Natural Gas Stream by Hybrid Membrane-Amine Process: Techno-Economic Assessment


 The sweetening of highly sour natural gas streams is challenging. This paper highlights the main findings of a techno-economic study comparing the traditional approach involving only amine (DGA) versus a hybrid membrane-amine treatment process.
 The hybridized membrane-amine process has been compared to the benchmarked classical DGA amine process, being the abundant process for treatment of sour natural gas. The acid gas membrane unit is deployed upstream of the amine process to selectively bypass a substantial part of the acid gas load to the sulfur recovery unit (SRU), thus affecting a substantial reduction in the amine process size and requirements.
 The membrane process separation efficiency has been manipulated at two levels: the performance factors (permeance and selectivity) and by deploying a two-stage configuration. The membrane process is designed to recover about 70% of acid gas load and bypass it to the SRU. This has substantially off-loaded the acid gas reaching the amine process. Consequently, the amine process size and requirements (amine circulation rate, electrical drive power, steam for amine regeneration) is proportionally reduced. The membrane process, however, results in increased hydrocarbons slippage into the feed of SRU. Therefore, manipulating the membrane process separation efficiency has a direct impact on the SRU size and operation. Financially, the membrane process has clear role in altering the contribution of the different elements of the capital investment cost (CAPEX) and the operating cost (OPEX). The two-stage membrane process is more appealing for the reduced hydrocarbons slippage, but more power is needed for inter-stage compression. Enhancing the membrane performance factors leads to a more economically attractive process than the amine stand-alone.