Integration of membrane-based atmospheric CO2 capture with a combined cycle power plant: A novel hybrid CCS/DAC process concept

The study proposes and analyzes the integration of a membrane-based direct air capture system (m-DAC) with CO2 capture from a combined cycle (CC) system. Research was conducted for various ratios of air and flue gas streams supplied to the capture installation. Both single-stage and multi-stage membrane systems were analyzed. The impact of the number of separation stages on system performance characteristics was evaluated, including CO2 recovery rate, permeate purity, and energy intensity. Analyses were also performed for different permeate pressure values. As a reference case, a multi-stage membrane separation process was assumed, targeting 99 % product purity and a pre-industrial CO2 concentration in the retentate stream. The results showed that a standalone m-DAC system is not a competitive alternative to developing chemical DAC technologies due to its high energy intensity exceeding 30 GJ/tCO2. However, its integration with a CC system fueled by 100 % CH4 significantly improved performance across all analyzed scenarios. The lowest energy intensity of 2.22 GJ/tCO2 was achieved when 10 % of the feed stream to the capture installation consisted of atmospheric air. The captured atmospheric CO2 stream remains relatively low compared to CO2 originating from flue gas. The power capacity of the CC system is not constrained by the separation process, facilitating scalability. The integrated system can show a surplus of electricity generated. The study also highlights the necessity of accounting for atmospheric CO2 in the combustion chamber inlet balance, which, in all analyzed cases, enabled the CC system to operate with either negative or at least net-zero emissions.