Towards net-zero emissions: Hybrid amine-membrane CO2 capture combining CCS and DAC strategies

The study presents an analysis of a hybrid CO2 capture system integrating a combined cycle gas turbine (CCGT) with two separation technologies: amine-based CO2 capture from flue gas (CCS) and membrane direct air capture (m-DAC). The novelty lies in combining both methods in a single system to reduce energy intensity and increase operational flexibility. Different operating configurations were analyzed, including the flue gas split between the amine and membrane units and the ratio of air supplied to the m-DAC unit relative to the flue gas stream (ϕ). The best results were obtained when the entire flue gas stream was directed to the absorption column (ZF1c=0%) and the cleaned gas was mixed with air and supplied to the m-DAC module. This increased the CO2 concentration at the m-DAC inlet, with energy intensity ranging from 1.70 to 9.03 GJ/t CO2 and captured CO2 flow from 4819 kg/h to 5742 kg/h, depending on ϕ. The ϕ ratio also determines the system's mode of operation: at low values, it functions as a classical CCS unit improving CCGT emissions, while at high values, it operates as a direct air capture unit. The CO2 recovery rate (R′), calculated relative to CO2 produced from methane combustion in the CCGT, exceeded 100% in all scenarios, indicating a net-negative CO2 balance within the plant boundary. The system allows for high-purity CO2 capture: >95% for the amine unit and >85% for the m-DAC module. The results confirm that hybrid CCS/DAC systems represent an energy-efficient and flexible solution for future CO2 capture technologies.