Enhanced cryogenic CO2 capture using dynamically operated low-cost fiber beds

Abstract

Recently Tuiniers et al. (2010) proposed a method for CO2 capture using cryogenically chilled packed beds with spherical packing that served as CO2 de-sublimation sites. The research presented here extends that work using fibrous packing inside the cryogenic columns, which serve to increase the surface area-to-volume ratio of the column by up to an order of magnitude as well as significantly reducing the sweep gas pressure drop through the column. Two types of fiber were chosen to study the effect of surface area on the total amount of CO2 captured within the column: hollow cellulose acetate fibers (325μm OD/125μm ID) with porous walls and monofilament nylon fibers (200μm OD). The pre-chilled cellulose acetate fiber columns were able to capture 191.2kg of CO2/m3 of volume at a pressure drop of 3.9psi/ft (81.0kPa/m) despite very high superficial velocities of simulated flue gas (10% CO2 in N2) through the column (5,700sccm, or 1.33m/s). The nylon monofilament fibers were found to capture up to 185kg of CO2/m3 despite lower surface area than the porous cellulose acetate fibers. The total uptake as a function of surface area within the column was found to reach a maximum, which has been tentatively attributed to the limited amount of specific heat held within the column itself. While in actual operation a pure CO2 sweep may be used to recover the solid CO2 within the column, a N2 sweep was used here to unequivocally demonstrate that the process can be used to generate a pure CO2 product. By performing a two-stage sweep, CO2 purities between 28mol% (1.33m/s sweep) and 99.5mol% (4.4cm/s sweep) were obtained. The findings of this study suggest that these low-cost fibrous materials have the opportunity to reduce the capital expenditures of a world-scale cryogenic CO2 capture system as well as increase the total loading of CO2 captured per chilling cycle while also reducing gas compression costs.