Pilot Test of a Nanoporous, Super-hydrophobic Membrane Contactor Process for Post-combustion CO2 Capture

In a project funded by the U.S. Department of Energy and Illinois Clean Coal Institute, a membrane contactor technology for CO₂ capture from flue gases has been developed jointly by Gas Technology Institute and PoroGen Corporation. The objective was to develop cost effective separation technology for CO₂ capture from flue gases based on a novel hollow fiber membrane contactor that will provide a significant reduction in the cost of capturing CO₂ from flue gases. The process combines advantageous features of both absorption and membrane processes to cost-effectively separate and capture CO₂ from emission sources.
The key component of the HFC process is the super-hydrophobic porous hollow fiber, which is made from poly(ether ether ketone) (PEEK). PEEK is an engineering polymer with thermo-mechanical properties and chemical resistance superior to most commercial plastics including typical polymers used in membrane fabrication. The unique characteristics of PEEK allow the HFC device to be utilized successfully in challenging and aggressive chemical environments which are encountered in both absorption and regeneration. These properties, combined with super-hydrophobicity, enable PEEK HFC to overcome pore wetting and chemical durability problems that have plagued prior HFC technologies.
Compared to conventional absorption/desorption technologies, the critical advantage of the HFC process is the high contact surface area provided by the hollow fibers that enable an increased volumetric mass-transfer rate, resulting in compact systems with small footprints. In our study, PEEK HFC has shown exceptionally high CO₂ capture rates due to the high membrane intrinsic CO₂ permeance as well as the structured PEEK hollow fiber module configuration.
High CO₂ capture level (> 90% removal) and high CO₂ product purity (> 95%) have been demonstrated in compact HFC modules in a single-stage process configuration. In a laboratory test, the absorption and desorption steps were integrated into a continuous CO₂ capture process utilizing 2-inch diameter bench-scale modules containing 10 to 20 ft2 of membrane area. The integrated process operation was stable through a 200-hour test, utilizing a simulated flue gas stream, with greater than 90% CO₂ capture and 97% CO₂ product purity achieved throughout the test. The integrated absorption/desorption HFC process has also been testing in the field with actual flue gases at a coal-fired power plant using 4-inch diameter by 5 feet long HFC modules (at Midwest Generation’s Will County Station in Romeoville, IL). The HFC system field tests demonstrated greater than 90% CO₂ removal with 97% CO₂ product purity with aMDEA solvent. The mass transfer coefficient in the absorption step was 1.2 (sec)-1, which is over an order of magnitude greater than that of conventional column contactors.
The PEEK HFC technology is now being scaled from the bench scale to a pilot scale utilizing larger size HFC modules and will be tested at the National Carbon Capture Center (NCCC) at a 0.5 MWe scale. The HFC modules employed measure 8-inches in diameter by 5 feet long with a membrane surface area of about 500 to 1,000 ft2 per module and will be utilized for both CO₂ absorption and solvent regeneration. We have completed the preliminary pilot plant design and obtained the cost of fabrication from several modular system vendors. The HFC pilot system is designed for greater than 90% CO₂ capture from flue gas with greater than 95% CO₂ product purity with aMDEA solvent. The HFC test at NCCC will include parametric testing and a continuous steady-state run of at least two months. Mass and energy balance data will be collected and a techno-economic analysis will be conducted after the pilot test to better define the process efficiency and economic. The HFC process will be ready for further process scale up after this pilot testing at a scale of 10 to 25 MWe.