Direct Air Capture (DAC) using amine might have same regeneration energy as flue gas CO2 capture when integrated with it
Process modelling predicts that the solvent regeneration energy for direct air capture (DAC) can be similar to that for CO2 capture from flue gases when MEA air absorption for DAC is combined with conventional post-combustion (PCC) capture.?As shown in the diagram above, this is achieved by feeding the solvent from the air absorber to the PCC flue gas absorber, where its rich loading is increased from the relatively low value that can be achieved with air to ‘normal’ values (from ~0.3 maximum to ~0.45 molCO2/molMEA).?The overall regeneration energy for combined DAC and PCC will then remain low, so long as the lean loading is above (just above, for maximum effect) the inflexion point in lean loading beyond which the specific reboiler duty (SRD) rises rapidly.
Based on the presented modelling work (paper now available here https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4283821), this approach allows the specific reboiler duty for air capture to be reduced from 6.65 GJ/tCO2 for a stand-alone MEA DAC plant to the region of 3.5 to 4 GJ/tCO2 of low-grade heat, depending on the configuration, for a combined (Co-DACCS) system.?There is no change required in the lean loadings for the DAC absorber (and hence absorber performance) vs. stand-alone DAC operation and a minimal increase in the total size of the DAC absorber to compensate for less capture in the PCC absorber. The diagram above shows two different integration configurations for the air absorber, split and series, with different CAPEX-OPEX trade-offs.?But further work is obviously needed on the development of amine air absorbers, with the key question being whether capital costs and power requirements for moving the air can be made low enough to support exploitation of the regeneration energy benefits of combined operation.?But, even though the final design for a Co-DACCS installation needs to be developed and the concept tested, low cost measures to make new conventional PCC plants ‘DACCS-ready’ might be worth considering, before their hardware configuration is locked in.
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Further details are available in reporting on the UKCCSRC’s Co-Cap project and there will be an oral presentation at the GHGT-16 conference – please come and see us there (Session 8A - Post Combustion Capture Process Modelling II, Wednesday, October 26, 2022, 11:20 AM - 1:00 PM).
Colleagues working on Co-DACCS: Stavros Michailos, Abby Samson, Mathieu Lucquiaud
Professor of Carbon Capture and Storage at University of Sheffield
2 年And on Jan's comment about the air volume, yes this is an inherent characteristic for all DAC, a lot of air needs to be moved. One approach that is being examined in the field is to use natural air movements as much as possible, included thermally-induced convection. The capital cost of large collectors is also an issue, although the mass required to be transferred is not that high. All work in progress. What we are doing here is to communicate something on regeneration energy that may be of use to the DAC community in various ways, not selling a solution to VCs. Far too much DAC development is taking place in secret!
Professor of Carbon Capture and Storage at University of Sheffield
2 年Good question Guido, but the DAC amine lean loading does not need to be lower than for flue gas capture, we assumed a value of 0.12 molCO2/molMEA in both cases. The VLE for the amine is shown in the slide below from the GHGT presentation. It may seem that this lean loading is unnecessarily low for the flue gas capture but here the temperature increases rapidly due to the greater amount of CO2 and, unless the initial lean loading is quite low, a thermodynamic limit will be reached and mass transfer will stop - see https://internal-journal.frontiersin.org/articles/10.3389/fenrg.2022.866838/full .
CCS business development
2 年Interesting. But is the lean loading for DAC the same as "normal" absorbers? I would expect that the DAC amine loading needs to be lower to comply with the lower concentration of CO2 in air. In other words, doesn't the DAC solvent portion need to be stripped more than the conventional one? meaning more regeration energy for the DAC portion? I wish I was able to attend GHGT this year to discus this in person Jon Gibbins
Vice President Energy Transition Solutions at Green-Plastic-Solar Innovations
2 年DAC costs are still too high for practice
Co-founder & CCO dvlp.energy
2 年Steven Bardey (PhD)