Two-stage membrane-based process utilizing highly CO2-selective membranes for cost and energy efficient carbon capture from coal flue gas: A process simulation study

Membrane technology for CO2 capture has become an attractive strategy due to its cost and energy efficiency and low materials costs. In the past decade, membrane-based process designs for post-combustion power plant CO2 capture have been developed, utilizing existing highly CO2-permeable membranes with relatively low CO2/N2 selectivity (<50), and have obtained reasonably economic carbon capture. However, few membrane-based process designs were proposed for moderate to highly CO2-selective membranes (CO2/N2 selectivity of 50-300, and >300, respectively), which have vastly emerged in recent years, such as various facilitated transport membranes (FTMs). Herein, we proposed a two-stage membrane-base process design targeting economic carbon capture from coal-fired flue gas. This process design features the utilization of highly CO2-selective membranes for one-stage CO2 enrichment to 95% dry-base purity in the first stage and recycle of the remaining CO2 by a highly CO2-permeable membrane in the second stage, in order to achieve economic CO2 capture with 90% capture rate and >95% CO2 product purity. Through an integration-iteration membrane model and the Aspen Plus process simulation, a sensitivity study of operating pressures (feed and permeate pressures) and membrane properties (CO2 permeance and CO2/N2 selectivity) was conducted. Critical CO2/N2 selectivity of 300-400 was found for the highly CO2-selctive membranes to meet the demand for cost and energy efficient results. The lowest possible membrane area of 4.8 x 105 m2 and fractional energy of 19.3% were obtained, which is comparable to or even more attractive than reported membrane-based process designs. This work provides a new membrane process design option for highly CO2-selective membranes and gives insights on the influence of membrane performance and operation condition.