Computational models challenge assumption about limits of carbon capture

The researchers, who are based at Imperial College’s Department of Chemical Engineering and Centre for Environmental Policy, used computational models to demonstrate that post-combustion carbon capture using amine absorption could capture up to 99 per cent of carbon at the source while remaining cost effective.

There has been a long-held assumption that 90 per cent carbon capture is the upper limit for carbon capture technologies, becoming ubiquitous across literature and leading to doubts around the feasibility of capturing more.

“In recent years, this 90 per cent assumption is being challenged as we begin or transition towards net-zero emissions,” the researchers explained. “Our findings show that there are no technical or economic barriers in capturing 99 per cent of CO2 from both power and industrial processes. This is highly significant in development of policy around the net-zero transition.”

Carbon capture and storage technologies have an important part to play in meeting decarbonisation targets in line with the Paris Agreement, given that between most global energy consumption still relies on fossil fuels and some industries are unlikely to be able to end their carbon emissions for decades to come. Given the limited availability of carbon removal technologies – which are less technologically mature and potentially more expensive – maximising carbon captured at the source (post-combustion) is particularly important.

“In the context of a net-zero economy, any uncaptured CO2 that is emitted from different sectors would need to be offset though the removal of CO2 from the atmosphere using options such as afforestation, or direct air capture,” the study authors told E&T.

“However, there is currently some uncertainty around the costs and potential scale of technology options for CO2 removal from air. Thus, the ability to maximise the CO2 capture from power and industry in a cost-effective manner is highly valuable as it would reduce the burden on atmospheric CO2 removal.”

Post-combustion carbon capture involves directly separating CO2 from combustion flue gases: the gaseous mixture produced by burning fuel and other materials. The most mature technology employed for this application is amine absorption, which uses a solvent derived from ammonia to form weak chemical bonds with CO2. As much is already understood about how to design, construct, and operate amine-based carbon capture plants, this approach to CCS potentially provides “a quicker and cost-effective pathway to net-zero emissions”.

The Imperial College researchers used a computational model to assess the opportunities of amine absorption. They considered a very wide range of flue gas characteristics, reflecting the range of applications to which amine-based carbon capture could be applied.

They found that in most cases, increasing the capture rate from 90 to 95 per cent has a negligible impact on capture cost, thereby reducing CO2 emissions at “virtually no additional cost”. In the context of power and industrial applications, capture cost at 99 per cent capture rate are not disproportionately higher compared to 90 per cent capture; in most cases, 10 per cent additional CO2 can be captured for less than 10 per cent increased cost per ton of CO2.

“In a net-zero emission context, we expect the additional costs are still beneficial when compared to the cost of negative emission offsets […] the disadvantage of higher capture rates is the increased up-front capital,” the researchers wrote in their Environmental Science & Technology report.

The researchers focused their analysis on a common amine solution (monoethanolamine) for the carbon capture process: one used in many other carbon capture studies. However, it is expected that more advanced solvents could result in lower energy requirements and reduced costs. Moving forwards, they hope to perform detailed case studies using these advanced solvents to assess their effectiveness.

Co-lead author Dr Mai Bui commented: “This work is important for net zero because maximising CO2 capture at the source is more effective than atmospheric CO2 removal when the whole system is considered. We hope our findings will improve the design of future CCS plants.”