Model validation and dynamic simulation of post-combustion carbon dioxide separation with membranes

This work presents a finite-element numerical model for N2–O2–CO2 separation by hollow fiber membranes, scaled-up to treat the combustion gases coming for a medium-size coal-based power unit. The equation set has been expanded to include, beyond the membranes, also compressors and condensers. Two process layouts have been evaluated: one open loop allowing for high purification level, and a recirculating scheme yielding superior enrichments. The resulting simulation, valid from pilot to full-plant scale, takes then into account the interplay of both active and passive process units besides the active membranes, and is fully dynamic in definition and scope. The results show that the degree of purification is mainly affected by the enrichment-side pressure, while the CO2 concentration depends largely on the CO2:N2 selectivity. Even when this latter value is relatively low, a proper scale-up of series/parallel modules can overcome the limitation without exceeding 7–8 bar pressurisation. Simulating the impact of pressure and flow transients on the plant outflows, the recovery procedure and timescales are identified.