(481f) Hollow-Fiber-Based Adsorbent System for CO2 Capture from Flue Gas | AIChE

(481f) Hollow-Fiber-Based Adsorbent System for CO2 Capture from Flue Gas


Deckman, H. W. - Presenter, ExxonMobil Research and Engineering
Kelley, B. T. - Presenter, ExxonMobil Upstream Research Company

We describe a rapid temperature swing adsorption (RTSA) system based on hollow polymer fibers impregnated with CO2 sorbents and designed for the capture of CO2 from the flue gas streams of coal-fired power generation facilities. This post-combustion capture system relies on a two-bed configuration, each bed being composed of hollow fibers with sorbent particles dispersed in the porous polymer matrix. The system takes advantage of the hollow fiber morphology by passing cooling water through the bores during sorption to maximize sorption capacities, and steam through the bores during desorption to release CO2 to the collection system. The thin walled hollow fibers offer the advantage of rapid heat and mass transport , with less than 1 second response times expected for both under anticipated operating conditions. To ensure that the heating and cooling agent only thermally interacts with the fiber walls, a dense lumen layer is required on the interior of the fiber wall and must provide high resistance to molecular transport between the fiber sheath and the core. To probe the latter, nitrogen gas permeation experiments have been conducted. Incorporation of a fiber lumen layer composed of poly-vinylidene chloride yields a substantial reduction in N2 transport through the fiber wall, from about 8 x 10-8 mol/m2-s-Pa uncoated to about 6 x 10-13 mol/m2-s-Pa coated. Further reductions are anticipated with optimization of the composition and structure of the lumen layer. Rapid cycling is also critical for the technical and economic viability of the system. Gravimetric sorption experiments on the fiber sorbents yield a CO2 sorption halftime of about 7 seconds at a CO2 partial pressure of 7 psia. Subsequent sorption measurements and modeling show that much more rapid equilibration should occur in actual practice with the thermally moderated fibers having cooling water flowing in the bore. To explore the economic viability of this system and provide research guidance, an economic analysis of the system is being conducted, including capital expenditures, operating costs, and compression to a sequestration-ready stream. The flue gas stream is assumed to be received at ~1 atm and 40°C, and the additional 0.35 atm bed pressure drop is assumed to be supplied by additional draft fans. The cycle time is taken to be 25 seconds, which is much longer than the observed halftime for sorption, as well as the expected timescale for heat transfer in the fiber. Greater than 95% of the effluent CO2 is captured. The CO2-rich capture stream is pressurized to 2300 psia for underground sequestration. Though the details of the economic analysis are being continually refined, it is clear that the system has the potential for a carbon cost on CO2-avoided basis that is significantly less than systems based on liquid sorbents. This potential is enabled in part by the low pressure drop across the bed and rapid cycles, both of which are made possible by the thin fiber sorbents. Our current estimate for the parasitic load on a 400MW power station is about 120MW, with about half being consumed for CO2 compression. This hollow-fiber-based adsorbent system has many potential advantages over conventional and competing technologies, including low cost, no waste products, and applicability to retrofit scenarios. The system should also be applicable to many pre-combustion CO2 capture scenarios.