Advancements in CO2 Membrane Separation Technologies: Reducing Emissions and Enabling CCS

Abstract To overcome production restraints caused by CO2 and H2S in mature basins, operators require more cost-effective gas treatment to effectively remove these impurities from natural gas. Cellulose triacetate (CTA) based CO2 separation membranes have already been used extensively in acid gas treatment and associated enhanced oil recovery. A new technical challenge was to provide a horizontal membrane element that could easily replace poorly performing existing flat-sheet spiral-wound membranes with minimal operational changes to debottleneck existing hardware capacity, minimize hydrocarbon loss, and reduce membrane replacement frequency. Existing CTA vertical hollow fiber CO2 separation membranes were further developed and modified into the form of 8-in./8.25-in diameter horizontal packaging. Qualification testing was performed at an in-plant gas test loop using full-scale membrane elements. Test programs included varying inlet parameters such as feed gas pressure, temperature, and a wide range of CO2 concentrations. Results showed that the horizontal configuration of the hollow fiber gas separation membrane exhibited superior separation characteristics in terms of gas throughput and hydrocarbon retention in the sales gas, when compared to alternative currently available CO2 removal membrane technologies. The robustness of the membrane polymer was confirmed throughout several startup and shutdown scenarios, with stable gas flux and selectivity observed during rigorous and long-term testing. The membrane elements can be deployed in existing installations as a "drop-in" solution to overcome production constraints, whilst driving down the cost of excessive membrane replacements. In brownfields, more efficient acid gas removal and enhanced hydrocarbon recovery will reduce emissions by lowering gas flaring and limiting the potential release of methane. Upfront capital expenditure and ongoing operational expenses in greenfield projects can be significantly reduced by the greater natural gas treatment capacity per membrane compared to alternative membrane solutions. The high-purity CO2 permeate stream can also support the implementation of carbon capture and sequestration (CCS), thereby helping to reduce the assets carbon footprint and overall emissions. The advancements in horizontal CTA membranes have been proven in operation at several facilities, where they have improved the economics of the assets via reduced hydrocarbon flaring and increased gas throughput. An intelligent, automated digital membrane monitoring tool has been developed and deployed to further optimize membrane operations. Operators have also been able to actively pursue acid gas fields previously considered uneconomical for production. Such greenfield and brownfield case studies will be presented as part of this paper.