Co-DAC – Combined Direct Air Capture and PCC Amine Capture for Reduced Energy and Capital Cost Requirements
Why is this research needed?
Even in optimistic decarbonisation scenarios, there are likely to be residual emissions that will have to be offset. Hence, research on Greenhouse Gas Removal (GGR) technologies, such as DACCS, to identify ways for efficient deployment is necessary and essential for achieving net-zero targets. By 2050, deployment of engineered removals, such as DACCS, at large scale (between 75 and 81 MtCO2 per year), will be needed to help compensate residual emissions . The UK government deems that net-zero scenarios are not likely without the deployment of negative emission technologies.
Currently DACCS cost are high due to high CAPEX and the lack of policy mechanisms that reward negative emissions. Several start-up companies are trying to commercialise DAC using processes based on chemical absorption or adsorption but typically as standalone applications. On the other hand, DAC with conventional amines can, in theory, be efficiently integrated to existing capture plants and hence reduce energy costs.
The proposed project attempts to identify ways to combine DAC technologies with conventional PCC plant; the project is a combination of experimental and modelling campaigns. A small air absorber will be built and tested; the absorber design assumes low-liquid-loading gauze packings that has the potential to avoid excessive heights; and hence the proposed absorber will be easier to transport and install. Preliminary modelling results  suggest a specific reboiler duty of ~6.7 GJ/tCO2 for standalone DAC, but that this can be reduced to ~3.7 GJ/tCO2 for air capture in Co-DAC mode (integration with gas turbine PCC plant), similar to the value for complete capture of the added fossil CO2 in the GT flue gas. Further modelling will explore the energetic performance of several configurations and conditions and potential tradeoffs between CAPEX and OPEX will be investigated.
The research aims to provide useful information for the design of air absorbers and their integration to conventional PCC plants. This synergy can improve the logistics of CO2 transport and potentially reduce the capital charges of CO2 capture by operating the DAC absorber when electricity is not needed.
1. Net zero strategy: build back greener. BEIS, 2021
What is this research investigating?
The overall objective of the research is to obtain information that will underpin further development of the Co-DAC option for DACCS, where DAC is combined with conventional post-combustion capture. The UK is likely to have an intrinsic advantage in deployment of such technology because of our planned cluster-based CCS infrastructure.
More specific objectives for this initial project can be summarised as follows:
1) Build an air absorber with low-liquid-loading gauze packing.
2) Experimental campaigns to test the performance of the absorber. This includes mass transfer measurements and associated fluid flow rates, and calculation of reaction rates.
3) Process modelling of integrating the air absorber with absorber treating flue gas from typical gas turbines. Calculation of relevant KPIs such as specific reboiler duty, solvent flow in the DAC absorber and net negative emissions rate.
4) Dissemination through conference presentations and publication of journal papers.
What does the research hope to achieve?
The research work will inform topics of active interest for policy such as support mechanisms for engineered Greenhouse Gas Removal (GGR) deployment. A critical question for the UK Government, which the applicants have been explicitly asked by officials, is where the UK might have intrinsic advantages in DACCS, because it can just as well be undertaken anywhere in the world; the atmosphere is well-mixed and transports the CO2 ‘for free’. In particular, now, and possibly for some time, the UK has an intrinsic disadvantage with respect to energy costs and it is difficult to see how more established large-scale processes, such as Carbon Engineering’s calcination-based cycle, could advantageously be sited in the UK. But, using this project’s Co-DAC approach, energy costs can be very significantly reduced and also the UK’s planned amine post-combustion capture (PCC) plants on industry, EfW, BECCS and fossil power, plus our cluster-based CO2 transport and storage system, can provide a local and persistent shared-infrastructure advantage for capturing an additional 50-100% of CO2 from the air, compared to stand-alone DACCS in regions without this infrastructure.
Industrial experts can comment on the design of the developed air absorber and its suitability for integration on existing PCC plants. The project will also provide information to industry regarding economic benefits realised by increasing the CO2 capture rate, when for example the power plant is shut, and what modifications are necessary to existing PCC plants to accommodate the DAC technology. Further information on Co-DACCS will allow the UK’s PCC plants to be made ‘DACCS-ready’ (i.e. low- or zero-cost measures that would facilitate future DACCS retrofits, analogous to the UK’s existing ‘capture ready’ regulations) and underpin the engineering development for deployment of the Co-DAC equipment.
A new area of research will be revealed to the CCUS community on topic of high interest – the efficient design and implementation of GGR. In particular, the project will showcase the performance of an amine air absorber using nonproprietary solvents, but many additional improvements on this basic design can be envisaged.
This research is ongoing. Outputs will be shared below as they become available.