Post-combustion Capture refers to capturing carbon dioxide from flue gas after the fossil fuel (e.g., coal, natural gas, or oil) has been burned. Of the 4 trillion kilowatt hours of electricity generated in the U.S. in 2015, about 33% was from coal (2016, EIA). In conventional coal-fired power plants, coal is burned with air in a boiler producing steam to rotate a turbine generator and produce electricity.
The biggest challenge in post-combustion capture is separating CO2 generated during combustion from the large amounts of nitrogen (from air) found in the flue gas. In this area, the R&D effort is focused on advanced solvents, solid sorbents, and membrane systems. In addition, novel concepts, for instance hybrid technologies that efficiently combine attributes from multiple key technologies (e.g., solvents and membranes) are being investigated.
Solvent-based CO2 capture involves chemical or physical absorption of CO2 from flue gas into a liquid carrier. The absorption liquid is regenerated by increasing its temperature or reducing its pressure to break the absorbent-CO2 bond. High levels of CO2 capture are possible with commercially-available chemical solvent-based systems; however, these systems require significant amounts of energy for regeneration. R&D objectives include advanced solvents that have a lower regeneration energy requirement than existing amine systems, and that are also resistant to flue gas impurities.
Sorbents are being explored for post-combustion CO2 capture and potentially offer advantages over conventional aqueous solvent based processes (e.g., such as lower regeneration energy requirements due to the heat capacity for solids being significantly lower than that of water). R&D objectives include low-cost durable sorbents that have high selectivity for CO2, high CO2 adsorption capacity, and can withstand multiple regeneration cycles.
Membrane-based CO2 capture uses permeable or semi-permeable materials that allow for the selective transport and separation of CO2 from flue gas. R&D objectives include development of low-cost, durable membranes that have improved permeability and selectivity, thermal and physical stability, and tolerance to contaminants in combustion flue gas.
Novel Concepts for CO2 Capture include hybrid systems that combine attributes from multiple technologies, novel process conditions (e.g., systems that operate at subambient temperatures), and nanomaterials.