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a b s t r a c tA membrane-based pilot plant for carbon dioxide capture from the flue gas of a coal-fired power plant has been installed and operated at the National Carbon Capture Center in Wilsonville, Alabama, USA. The membrane system is sized to treat flue gas containing one ton per day of carbon dioxide. Stable operations for three extended runs conducted over a period of two years have been achieved with both pulverized coal and simulated natural gas flue gas. Carbon capture rates up to and over 90% were achieved with full-scale Polaris™ modules in individual trials that ran up to 1800 h. Both cross-flow and countercurrent sweep spiral-wound modules demonstrated effective and stable carbon capture performance. This paper describes the experimental correlations that were developed, and summarizes the observed performance envelopes resulting from the combination of selected operating process conditions, equipment, and modules.

Two new large scale (200 cm2) composite Pd and Pd–Au membranes were prepared and tested in an actual coal derived, but desulfurized, syngas in order to further quantify permeance loss due to species other than sulfur and to determine the nature of the contaminants. As in our previous work, membranes were tested at the National Carbon Capture Center (NCCC) in Wilsonville, Alabama. Before the syngas test, the Pd and Pd–Au membranes had thicknesses of 7 and 6.6 μm, H2 permeances at 450 °C of 17.7 and 29.2 N m3 m–2 h–1 bar–0.5, and H2/He selectivities higher than 2700 and 160 000, respectively. The two membranes produced H2 at an exceptionally high purity level of 99.8–99.9%. The selectivity of the Pd–Au membrane was stable for over 473 h in an actual syngas atmosphere at 450 °C and 12.6 bar demonstrating the high robustness and suitability of these membranes in industrial environments. However, as seen in our previous study, the two membranes showed a decrease in H2 permeance upon syngas introduction (ranging from 40 to 50%), indicating the presence of a fast surface poisoning process. The XPS analysis of a Pd coupon attached to the Pd membranes, and therefore exposed to the same syngas as the Pd membranes, revealed the presence of Mg, Na, Hg, O, C, and S on its surface. Furthermore, depth profile analysis revealed the presence of C at a concentration level of 4 atom % at a depth of 1.1 μm. Tests in pure H2 atmosphere at 450 °C after syngas exposure resulted in a moderate permeance recoverability for the pure Pd membrane (77%), while an outstanding 100% recoverability was achieved with the new Pd–Au alloy. Compared to our previous study, the Pd–Au membrane had a thicker Au layer on its surface (approximately 0.5 μm instead of 0.2 μm) that was intended to better mitigate surface poisoning by syngas contaminants. The average Au content of the layer with the Au gradient (2.2 μm in thickness) was determined by XRD and equaled 23 atom %.

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This final report describes work conducted for the U.S. Department of Energy National Energy Technology Laboratory (DOE NETL) on development of an efficient membrane process to capture carbon dioxide (CO 2 ) from power plant flue gas (award number DE-NT0005312). The primary goal of this research program was to demonstrate, in a field test, the ability of a membrane process to capture up to 90% of CO 2 in coal-fired flue gas, and to evaluate the potential of a full-scale version of the process to perform this separation with less than a 35% increase in the levelized cost of electricity (LCOE). Membrane Technology and Research (MTR) conducted this project in collaboration with Arizona Public Services (APS), who hosted a membrane field test at their Cholla coal-fired power plant, and the Electric Power Research Institute (EPRI) and WorleyParsons (WP), who performed a comparative cost analysis of the proposed membrane CO 2 capture process.The work conducted for this project included membrane and module development, slipstream testing of commercial-sized modules with natural gas and coal-fired flue gas, process design optimization, and a detailed systems and cost analysis of a membrane retrofit to a commercial power plant.The Polaris™ membrane developed over a number of years by MTR represents a step-change improvement in CO 2 permeance compared to previous commercial CO 2 -selective membranes. During this project, membrane optimization work resulted in a further doubling of the CO 2 permeance of Polaris membrane while maintaining the CO 2 /N 2 selectivity. This is an important accomplishment because increased CO 2 permeance directly impacts the membrane skid cost and footprint: a doubling of CO 2 permeance halves the skid cost and footprint. In addition to providing high CO 2 permeance, flue gas CO 2 capture membranes must be stable in the presence of contaminants including SO 2 . Laboratory tests showed no degradation in Polaris membrane performance during two months of continuous operation in a simulated flue gas environment containing up to 1,000 ppm SO 2 .A successful slipstream field test at the APS Cholla power plant was conducted with commercialsize Polaris modules during this project. This field test is the first demonstration of stable performance by commercial-sized membrane modules treating actual coal-fired power plant flue gas.Process design studies show that selective recycle of CO 2 using a countercurrent membrane module with air as a sweep stream can double the concentration of CO 2 in coal flue gas with little energy input. This pre-concentration of CO 2 by the sweep membrane reduces the minimum energy of CO 2 separation in the capture unit by up to 40% for coal flue gas. Variations of this design may be even more promising for CO 2 capture from NGCC flue gas, in which the CO 2 concentration can be increased from 4% to 20% by selective sweep recycle.EPRI and WP conducted a systems and cost analysis of a base case MTR membrane CO 2 capture system retrofitted to the AEP Conesville Unit 5 boiler. Some o...