Post-combustion CO2 capture technology typically uses chemicals that extract CO2 from flue gases in power plant chimney pipes. The gases are passed through a liquid chemical solution (solvent) that extracts the CO2, while regenerating (recovering) the solvent for re-use by adding heat. But the process requires significant heat, which is costly and leads to an ‘efficiency penalty’ – a decrease in power efficiency.

Other limitations to today’s technologies include their size and high capital costs, as well as the sulphur dioxide (SO2) present in these flue gases, which is harmful to both the environment and human health.

New solvents and ultra-efficient membranes

The team behind the EU-funded iCAP project developed a prototype absorption system that uses third-generation liquid solvents. These require less heat for CO2 capture and a lower temperature for solvent regeneration, making the entire process more energy-efficient and cost effective. One of the project’s industrial partners is planning to develop one of the solvents for commercialisation.

The project’s new, ultra-efficient membrane materials with improved permeability have also been particularly successful – one has already been patented. The membranes act as walls – they allow CO2 to pass through them easily, while separating CO2 from the other gases present.

For combined CO2 and SO2 removal, two systems – one amine and one ammonia-based – were tested in various projects with positive results. This simultaneous removal has the potential to streamline power plant processes and reduce capital costs. 

The team also assessed existing and new power production cycles with carbon capture, by varying temperatures and recycling gases for use at a later stage. Three novel natural gas-based power cycles show promise and could eventually lead to more efficient fossil fuel based power production.

“Our findings could help cut CCS operating costs by between 30 to 40%, while the energy penalty linked to CO2 capture could fall by up to 5 percentage points,” says iCAP project coordinator Hallvard Fjøsne Svendsen of the Norwegian University of Science and Technology in Trondheim, Norway.

Beyond power plants

While primarily developed for carbon capture in power plants, these new solvents and membranes could also prove a useful capture technology in the cement, steel and aluminium industries.

Moreover, the project’s combined CO2 and SO2 capture research would be particularly relevant to countries such as Australia and China, where power plants don’t tend to remove the harmful SO2. Research teams from both countries were involved in the project.