Co-Cap: Collaboration on Commercial Capture (Flexible Funding 2020)

An open-technology and open-access post-combustion capture initiative – Professor Jon Gibbins, Director, UK CCS Research Centre and Professor of CCS, University of Sheffield; and Dr Stavros Michailos, Researcher Co-Investigator, University of Sheffield (now Lecturer, University of Hull)

Post-combustion CO₂ capture (PCC) plants are the basis for the majority of projects in the current wave of UK CCS deployment.  Applications actively being considered include gas-fired and biomass power plants, energy-from-waste plants, refineries and steam-methane reformer retrofits.  PCC plants are also widely applicable globally, particularly for retrofit applications.

This proposal addressed two issues:

1. Knowledge-sharing for cost reduction
2. Residual CO₂ emissions from PCC plants in the context of net-zero

The delivery of the objectives of this project was enhanced by a number of subsequent open-access projects that it facilitated.  The following non-experimental projects are completed:

• UPCC: Ultra-high Post-Combustion CO₂ Capture – a University of Sheffield QR SPF project (Dec 2020 to March 2021) – £18k funding for additional modelling work
• AECOM for BEIS, Start-up and Shut-down times of Power CCUS Facilities – showing solutions for 95% CO₂ capture at all times (Feb-July 2020), Gibbins acted as an academic reviewer. https://www.gov.uk/government/publications/start-up-and-shut-down-times-of-power-carbon-capture-usage-and-storage-ccus-facilities
• BAT Review for New-Build and Retrofit Post-Combustion Carbon Dioxide Capture Using Amine-Based Technologies for Power and CHP Plants Fuelled by Gas and Biomass as an Emerging Technology under the IED for the UK – UKCCSRC review by Gibbins and Lucquiaud https://ukccsrc.ac.uk/best-available-techniques-bat-information-for-ccs/ – 95% capture including start and stop are recommended in the associated guidance https://www.gov.uk/guidance/post-combustion-carbon-dioxide-capture-best-available-techniques-bat

Related experimental projects are still ongoing:

• PCC-CARER – UKCCSRC/industry funding https://ukccsrc.ac.uk/research/flexible-funding/flexible-funding-2021/prof-jon-gibbins-university-of-sheffield/
• FOCUSS – BEIS/industry funding https://www.ssethermal.com/news-and-views/2022/06/carbon-capture-rates-in-focuss-as-sse-thermal-secures-grant-from-beis/

Delivery of the project objectives was started by early workshops, as envisaged in the proposal, and then continued through stakeholder engagement on the BAT review, a number of conference presentations, an open-access journal peer-reviewed paper and updates on the project web page.  A list is given at the end of this blog.  This amounted to more material and engagement than anticipated in the proposal, due to assistance by the unforeseen related projects, and activity was extended over a considerably longer period than originally envisaged.  The project also helped to get a new detailed engineering study for an amine capture plant made available on the UKCCSRC web site https://ukccsrc.ac.uk/open-access-sherman-feed/ and publicised to potential users.

In addition to high levels of CO₂ capture from combustion flue gases, the research outcomes also suggested a way to reduce the regeneration energy penalty for CO₂ capture from air using amines.  This has resulted in a new UKCCSRC project with co-investigator Stavros Michailos as PI, Co-DAC: Low-energy Direct Air Capture potential when combined with a Post Combustion Capture plant, with the concept described in a GHGT-16 presentation/paper https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4283821.  Stavros Michailos has also progressed to a new position as Lecturer at the University of Hull.

As a result of computer modelling in this project, a clear theoretical understanding has been gained of how PCC plant operating parameters can be adjusted to achieve high levels of CO₂ capture and the factors that determine the amount of heat required when doing so.  In general, previous studies have not undertaken an holistic analysis and have therefore concluded that there are greater barriers to achieving high capture levels than, in fact, exist – the problems they encountered being due to pre-selection of operating parameters such as stripper pressure or absorber liquid/gas ratio.

An outline illustration of a PCC plant is shown below.  This project modelled the performance of such a plant using a non-proprietary capture solvent, a solution of 35% w/w monoethanolamine (MEA) in water.

One key finding was that lean solvent loadings of ~0.1 mol CO₂/mol MEA are required to achieve high capture levels (95-99%) in the absorber.  This is not a surprising result as the leaner a solvent is, the more aggressively it will remove CO₂ from a gas mixture.  The problem is how to produce this low lean loading without requiring excessive energy.  Previous studies, using a fixed stripper pressure, have concluded that a lot of energy would be required but we were able to show that, provided the pressure in the stripper/reboiler was high enough, the amount of heat required per tonne of CO₂ captured would not go up.  The high pressure is important to suppress wasteful water vapour production in the reboiler; some water vapour is essential to ‘strip’ the CO₂ from the solvent when it is heated, but a lot of heat is required to produce it.

It was also found that a high rich loading in the solvent leaving the absorber was essential to minimise heat demand in the stripper/reboiler; not doing so means that ‘unused’ solvent is being circulated and heated and also involves more water vapour being emitted from the stripper with the CO₂.  High solvent rich loadings require that enough packing is available in the absorber to transfer enough CO₂ from the flue gas to the solvent.  Up to 24 m of packing height was found necessary to capture the 99% of the CO₂ in the flue gas from a gas turbine that comes from the burnt fuel, leaving only the 1% that came from the air going into it.  But this study emphasised that the solvent flow through the absorber is also critical: too low and it is insufficient to capture the CO₂, too high and the CO₂ is captured but the rich loading will be lower than the optimum value.

Work is now ongoing to test these theoretical findings on the amine capture pilot plant at the University of Sheffield’s Translational Energy Research Centre (www.terc.ac.uk), shown below, at a scale of around 1 tonne of CO₂ capture per day.

Project outputs