Determining thresholds for CO2 leakage detection (CO2DETECTIVE) (Flexible Funding 2024)

Ceri Vincent, British Geological Survey, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “Determining thresholds for CO2 leakage detection (CO2DETECTIVE)”.

The CO₂Detective project compared the efficacy of established and newly developed sensors and techniques with fixed and mobile deployments.

Setting the scene

In the unlikely event that geological carbon dioxide (CO₂) storage sites leak, surface expression will vary widely both temporally and spatially, so mobile techniques that can quickly and reliably screen large areas for further focused investigation are needed. However, sensitivity is often sacrificed for mobility, reducing the chances of successfully detecting leaks presenting with low CO₂ concentrations. Thus, techniques for point measurement remain a key aspect of leakage detection.

A mobile form of detection would also benefit other near-surface gas monitoring, for example when checking the integrity of subterranean pipelines that transport CO₂ from onshore industrial clusters to storage sites.

Tools for demonstrating the absence of any detectable leakage are important for project operators and for providing assurance and evidence to regulators, local populations, investors, insurers and policymakers.

Objectives of the project

The two objectives of the CO₂Detective project field work were:

• benchmark the efficacy of established and newly-developed near-surface gas sensors and techniques with fixed and mobile deployments (‘near-surface’ in this context is less than around two metres above and below the ground surface)
• assess the scalability of research findings to understand the opportunities, issues and risks to commercial-scale CO₂ transport and storage

Method

The project team created an artificial leak of a known quantity of CO₂ into shallow soil, to benchmark different soil gas detection techniques’ deployability and ability to detect leakage.

Field work was divided between three teams:

• team one set up the leakage experiment
• team two discharged and metered the CO₂ release
• team three consisted of soil-gas monitoring experts who investigated the ‘leak’

Information was not shared between the teams, to create a realistic scenario where leaking CO₂ needed to be found and quantified at a site of suspected of escaping CO₂. The ‘leak area’ (roughly triangular, with sides around 30m each) was determined partly by practical considerations, including enabling CO₂ cylinders to be secured for safe operation.

Figure 1: Team one after setting up the ‘leak’. BGS © UKRI 2026

Figure 2: Team three looking for the ‘leaks’ using the ECCSEL BGS soil-gas facility. An ultraportable off-axis integrated cavity output spectroscopy and soil gas analysers are in the cart. A hand-held gas analyser is being used to analyse a sample drawn via a hollow steel probe driven into the ground. A portable CO2 flux accumulation chamber (analyser in the ‘backpack’) is also being deployed. Soil sample collection for the CO2GeoNet SLINKI project is also being carried out. BGS © UKRI 2026

Field work

Team three deployed sensors on two days during one week in February 2025. On the first day, the weather was calm. Winds were stronger on the second day, making locating leaks with the mobile sensors more challenging as the CO₂ gas quickly dispersed. The team located two main leaks and an intermittent leak using the ECCSEL BGS soil-gas facility.

Benchmarking

The aim of this project was to benchmark techniques rather than specific models, based on the experience of the field team when deploying the techniques, so manufacturer details are not provided here. The following techniques were deployed:

• portable chamber-based CO₂flux
• ultraportable off-axis integrated cavity output spectroscopy (OA-ICOS)
• portable IR- and laser-based field gas meters, drawing soil gas from about 0.5 m below ground level via hollow probes driven into the ground

Deployed sensors were assessed for:

• ease of field deployment
• detection range, reaction and stabilisation times
• ease of use, data retrieval and interpretation
• robustness and service requirements

The portable CO₂ flux analyser scored highly against these criteria. The analyser weighs around 10kg and is supplied in ‘backpack’ format for portability. Acquiring data was easy and rapid; however, good data depends on getting a good seal with the ground surface. There is a risk of missing a leak, since this technique delivers point rather than continuous measurements.

The OA-ICOS also scored highly against these criteria. This technique can cover large areas quickly, reducing the risk of missing a leak signal, but the equipment was the heaviest (about 30kg) of our tested techniques, making field deployment more difficult. It had good sensitivity at near-baseline CO₂ concentrations (for better baseline characterisation and source apportionment) and it coped well with extremely high CO₂ concentrations, even when they exceeded the certified upper measurement range. It also flushed and recovered to background quickly. The OA-ICOS detected CO₂ at the soil surface for all but the lowest rate release during these tests.

Field analysis of CO₂ in soil gas accessed through hollow steel probes scored reasonably against the criteria by being fast, robust and portable. Driving the probe into the ground avoided atmospheric air being measured instead of intended soil gas. Gas samples could also be collected ‘end of probe’ for laboratory analysis, for example isotopic compositions to distinguish leaking stored ‘fossil’ CO₂ from biogenic CO₂ produced within the soil. This method generally produces a point measurement, which means a small area leak could be missed, and sensitivity at low concentrations may be inadequate for attributing CO₂ sources. Additionally, these meters cannot easily be owner-serviced and factory servicing (involving international shipping) can be time-consuming and expensive.

Given that the commercially available techniques benchmarked here can cost tens of thousands of pounds and some have to be sent to the manufacturer for servicing, the project team wanted to develop a lower-cost (a few hundred pounds) sensor in-house. A low-cost sensor could mean that, for a moderate budget, multiple sensors could be deployed to examine a wider area, or be left unattended at a suspected leak to monitor over longer periods and be easily replaced if lost. Our lower-cost sensor was developed using a Raspberry Pi and COZIR CO₂ sensor housed in a pelicase and was tested in the laboratory; improvements are planned for future projects.

Figure 3: The BGS team that developed a low-cost CO2 sensor. BGS © UKRI 2026

Interpretation and upscaling

One of the greatest challenges with potential leaks is finding them, as CO₂ storage sites may cover several square kilometres and buried pipelines could be many kilometres long. Another challenge in monitoring for CO₂ in the near-surface zone is that CO₂ quickly disperses in air, therefore sensors must usually be close to the leak to find and quantify it. Highly mobile and quick-to-deploy surface measurement techniques that draw samples very close to the ground are generally protected from wind turbulence, therefore they are extremely valuable for locating potential leaks.

Another significant challenge for investigating potential leaks is distinguishing leaking CO₂ from CO₂ that is naturally present in soil and air at highly variable concentrations, depending on the season and the time of day, land-use and vegetation, as well as meteorological (especially humidity) and other environmental conditions. Understanding the origin of detected CO₂ requires site-specific knowledge of geology, soil and moisture, weather systems and other natural biotic and abiotic processes; findings need to be set within or account for these influences. Thus, when a leak location is found, following up with a campaign of detailed point measurements and methods, including collecting gas samples for isotopic analysis, is a natural next step.

Each line of evidence helps the CO₂ Detectives build towards a complete picture of site behaviour and sources of CO₂ at the surface. Both mobile and point measurement sensors have a place in CO₂ leakage detection and quantification. Deployability of techniques and being able to rapidly collect reliable data are important monitoring considerations; benchmarking these techniques illustrates the role for each in leakage detection.

Next steps

The OA-ICOS is already becoming one of our default wide-area scan methods, especially where options for mounting lasers on off-road vehicles are limited. For the time being, the OA-ICOS will continue to be deployed alongside benchmarked instruments while we further explore its potential in monitoring CCS.

Following on from the CO₂Detective project, funding is being sought to further develop the low-cost sensor.

Read more on Ceri’s Flexible Funding 2024 project page.

Dr Nejat Rahmanian, University of Bradford, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “Carbon Sequestration in Steel and Cement Industries using Indirect Mineral Carbonation (IMC) Process”.

Introduction

The steel and cement sectors are among the largest industrial contributors to global carbon dioxide (CO₂) emissions, responsible for approximately 7% and 6.5% of total emissions respectively. Current estimates indicate that steel production releases between 1.8 and 2.2 tonnes of CO₂ per tonne of steel, depending on the production technology employed, while cement production emits approximately 0.9 to 1 tonne of CO₂ per tonne of cement. To meet global climate goals, carbon emissions from steel, cement, and concrete must be reduced by over 90% by 2050.

Figure 1 Infographic shows the contribution of the steel and cement sector to CO2 emission (Source Industrial Deep Decarbonization, shorturl.at/tR9SD)

This UKCCSRC-funded project explored a practical route to CO₂ capture and utilisation by converting industrial by-products, i.e. steelmaking slag and cement kiln dust and finally its sequestration and conversion to calcium carbonate. The approach is rooted in indirect aqueous mineral carbonation, with a focus on using commonly available chemicals, minimal energy input, and lab-scale process simplification.

The overall aim was to recover calcium from waste streams using controlled leaching and subsequently convert it into a stable mineral form by reacting it with captured CO₂.

Figure 2: Overall view of CO2 capture and storage in the steel industry

Methodologies

To achieve the aim of the project, the study investigated a novel Indirect Mineral Carbonation (IMC) pathway for CO₂ sequestration, leveraging industrial alkaline wastes from steel and cement plants. The methodology was strategically designed as an integrated four-stage framework: (i) sample characterisation, (ii) acid leaching and process optimisation, (iii) impurity removal and CO₂ capture, and (iv) product synthesis and characterisation. Together, these stages ensured a robust evaluation of technical feasibility to support the project’s four core objectives and deliver reliable data for process feasibility and optimisation.

Calcium extraction from a range of waste materials was investigated. These included BOF slag, blast furnace slag, and ladle slag using different acids under various operating conditions. The experimental design employed a full factorial approach to determine the influence of acid type, leaching temperature, reaction time, and solid-to-liquid ratio on calcium extraction efficiency and selectivity. Following the leaching stage, a pH swing method was applied to selectively precipitate major impurities such as Fe, Al, and Mg, thereby improving the quality of the calcium-enriched filtrate for subsequent carbonation. The purified solution was then carbonated using sodium carbonate, generated in a preceding CO₂ scrubbing step, to precipitate high-purity calcium carbonate under the ambient conditions.

Overall Conclusion and Looking Forward

This study demonstrated a four-stage indirect mineral carbonation process for the valorization of calcium-bearing industrial wastes from steel and cement industries successfully, albeit with the limited time and budget, specifically basic oxygen furnace (BOF) slag for CO₂ capture and permanent storage as solid calcium carbonate (CaCO₃).

The successful indirect mineralization of CO₂ from captured gas via the carbonation process using real industrial waste under low-energy conditions demonstrates the potential of this pathway as a carbon management strategy. By coupling resource recovery with CO₂ utilization, the process delivers dual environmental benefits—reduction in emissions and valorization of waste.

These findings establish a basis for future research aimed at process optimisation, including improving carbonation kinetics, enhancing material conversion efficiency, and evaluating scale-up potential. Further investigation into system integration and lifecycle assessment is also recommended.

Acknowledgment

The PI would like to thank UKCCSRC/EPSRC for providing this funding opportunity. The author welcomes potential industrial collaborators interested in continuing this research project and invites them to get in touch via email.

Read more on Nejat’s Flexible Funding 2024 project page.

Professor Mathieu Lucquiaud, University of Sheffield, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “Transforming Waste Into a Climate Service (TWICS): A Comparative Assessment of Energy-from-Waste with CCS and Waste-derived Sustainable Aviation Fuels”.

Executive Summary

Municipal solid waste (MSW) is emerging as a contested climate mitigation tool, subject to competing claims from sectors pursuing decarbonisation under resource constraints. In the UK, MSW is targeted both for carbon dioxide removal via energy-from-waste (EfW) with carbon capture and storage (CCS) and as a feedstock for producing sustainable aviation fuel (SAF). These pathways are not complementary, each tonne of waste directed to one excludes its use in the other, yet current policy frameworks incentivise them in isolation without internalising the opportunity cost of allocation.

This study compares the climate performance of EfW with CCS and MSW-to-SAF using a consequential life cycle assessment framework aligned with ISO 14044. The aim is to inform climate-optimal waste allocation by quantifying the system-level greenhouse gas (GHG) implications of each route. Both pathways deliver net-negative emissions under baseline assumptions, but the mechanisms and sensitivities differ. EfW with CCS derives its benefit primarily from permanent biogenic carbon removal, while the SAF route relies solely on upstream fossil fuel displacement and material recovery credits.

The analysis shows that EfW with CCS generally provides the greater GHG benefit per tonne of MSW, achieving up to −1215 kg CO2-eq. in the base case and remaining net-negative (−610 kg CO2-eq.) even under conservative assumptions that exclude all credits from avoided burdens. In contrast, SAF delivers a smaller but notable benefit of up to −700 kg CO2-eq.

A sensitivity analysis on the biogenic carbon fraction of waste reveals a break-even point at 5%, below which SAF would become the more climate-effective option, compared to 50-70% biogenic carbon fraction in most post-residual waste feedstock. The findings raise questions about the traditional waste hierarchy, which prioritises material recovery over energy recovery without accounting for the permanence of emissions removal. In a carbon-constrained future, recognising the distinct value of durable carbon dioxide removal (CDR) alongside circular material flows will be essential to coherent and climate-credible waste allocation strategies.

Introduction

The UK faces a strategic challenge in determining how best to utilise residual MSW in pursuit of net-zero climate goals. Historically destined for landfill or incineration, residual waste is now being re-evaluated as a potentially high-leverage resource for carbon mitigation. Its biogenic fraction, arising largely from paper, food, garden, and other organic waste, enables certifiable CDR if captured and permanently stored. This has brought EfW with CCS into sharper focus, particularly as the UK seeks to scale industrial decarbonisation and meet its climate commitments.

Yet EfW is not the only climate-oriented use of residual waste. UK Government policy is actively stimulating the production of waste-derived SAF through the Renewable Transport Fuel Obligation (RTFO). SAF displaces fossil derived aviation fuel, e.g. Jet-A the most common fuel for jet aircraft, in a hard-to-abate sector but emits its carbon at point of use.

Objectives of TWICS

The Transforming Waste Into a Climate Service (TWICS) project seeks to clarify the climate-optimal use of residual municipal solid waste in a policy landscape increasingly characterised by competition, trade-offs, and conflicting incentives. Specifically, the project addresses the unresolved question of whether the UK should prioritise CDR via EfW with CCS, or fossil fuel displacement via the production of waste-derived SAF.

The project objectives are:

• Quantify and compare the global warming potential (GWP), avoided emissions, and CDR potential of two divergent waste-to-energy pathways in the UK context: EfW with CCS and MSW-to-SAF.
• Model both systems using a harmonised approach in terms of: system boundary, LCA typology, and functional unit.
• Assess implications for key policy domains, including: CCUS cluster deployment strategy, SAF mandates and subsidies, and long-term waste resource governance
• Provide evidence to guide decisions on where to direct residual waste.

Research Questions

1. Which pathway delivers greater climate benefit per tonne of residual MSW in the UK context: EfW with CCS or waste-derived SAF?
2. How sensitive are the comparative outcomes to key system parameters and assumptions (e.g. biogenic carbon content)?
3. What could implications be for UK policy in terms of waste allocation, climate strategy, and alignment with the waste hierarchy?

Methodology

To address these questions, TWICS utilises the ISO 14040 and ISO 14044 standards for LCA. The methodology is designed to isolate the net climate implications of diverting waste to either pathway, accounting for both direct and system-level impacts. The study follows the principles and requirements set out in ISO 14040 and ISO 14044, adopting a cradle-to-gate consequential life cycle assessment (LCA) framework to compare two alternative uses of MSW in the UK:

• EfW with CCS
• SAF production via a waste-to-ethanol-to-jet pathway (MSW-to-EtOH-to-SAF)

A consequential LCA approach is necessary to estimate the environmental effects of diverting residual waste to energy-from-waste with CCS versus SAF production and model systemic changes and capturing knock-on impacts across systems such as avoided emissions.

Key Results

Figure 1 – Global Warming Potential of Energy from Waste with CCS, including avoided landfill

Figure 2: Global Warming Potential of Energy from Waste with CCS, excluding avoided landfill

Figure 3 – Global Warming Potential of Municipal Solid Waste-to-Sustainable Aviation Fuel, including avoided landfill

Figure 4 – Global Warming Potential of Municipal Solid Waste-to-Sustainable Aviation Fuel, excluding avoided landfill

Conclusion

A consequential life cycle assessment framework shows that both waste pathways deliver net-negative greenhouse gas emissions but differ substantially in the structure, durability, and sensitivity of their mitigation benefits.

EfW with CCS emerges as the stronger performer in absolute terms, delivering up to −1215 kg CO₂-eq. per tonne MSW with avoided landfill credited, and remaining net-negative (−610 kg CO₂-eq.) even under conservative assumptions excluding all avoided burden credits. Its climate benefit is dominated by permanent carbon dioxide removal from the biogenic fraction of waste. By contrast, the SAF pathway’s benefit is distributed across material and energy displacement, and is inherently more sensitive to system expansion assumptions and upstream burdens.

The TWICS framework highlights the importance of evaluating waste valorisation with careful consideration of climate potential. A coordinated approach is needed for residual MSW, as a strategic climate resource. This approach must evaluate allocation based on system-wide mitigation effectiveness and the permanence of climate benefit.

Read more on Mathieu’s Flexible Funding 2024 project page.

Dr Aliakbar Hassanpouryouzband, University of Edinburgh, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “AssureFlow-CCS: Advanced Strategies for CO2 Flow Assurance”.

Why AssureFlow-CCS is needed

For CCS to work at scale, CO₂ streams must be transported and stored safely under a wide range of conditions. In practice, captured CO₂ often contains impurities, which can affect hydrate formation, salt solubility, and corrosion. These processes directly influence flow assurance and the long-term security of geological storage.

The AssureFlow-CCS project set out to better understand these challenges by combining targeted experiments with improved models, generating the evidence needed to predict how impure CO₂ behaves underground and how to manage associated risks. Alongside this, the project has also explored how CO₂ storage can occur together with hydrogen generation in reactive ultramafic systems, providing a dual pathway for climate mitigation and clean energy production.

Building new capability

A major achievement of the project has been the development of a state-of-the-art high-pressure, high-temperature reaction vessel. This system tracks H₂, H₂S, O₂, pH, Eh, conductivity, pressure, and temperature in real time, allowing researchers to observe rock–fluid reactions as they happen. The device was built with support from UKCCSRC and a University of Edinburgh POT bid.

Figure 1. High-pressure experimental setup developed in AssureFlow-CCS for real-time monitoring of CO₂–rock–fluid reactions

What we found

Figure 2. Presenting AssureFlow-CCS results at a Petrobras event in Rio de Janeiro (2025)

Early results show that CO₂ impurities can significantly alter fluid chemistry and reaction pathways, with consequences for hydrate stability, salt precipitation, and corrosion. At the same time, experiments confirmed that hydrogen generation can proceed alongside CO₂ mineralisation, highlighting the potential of combined storage and energy production. These insights are critical for improving predictions of flow behaviour in storage sites and ensuring the reliability of CCS infrastructure.

The findings have been shared at international events, including the EAGE Annual Meeting (Toulouse 2025), a Petrobras event in Rio de Janeiro, and a summer school in Denmark, all partly supported by UKCCSRC.

Publications supported by AssureFlow-CCS

The project has contributed to two major publications:

Nature Communications (2025): Thermal Marangoni natural convection enables directional transport across immiscible liquids https://www.nature.com/articles/s41467-025-60930-y

Renewable & Sustainable Energy Reviews (2025): Emerging potential unconventional applications of gas hydrate technologies in sustainable and environmental industries https://www.sciencedirect.com/science/article/pii/S1364032125006604

What’s next

The team will extend experiments to longer durations and more complex CO₂ mixtures, providing the data needed to refine models and support large-scale CCS deployment. By tackling the critical issue of CO₂ flow assurance while demonstrating the potential for CO₂ storage with hydrogen generation, AssureFlow-CCS is helping deliver safer, more effective carbon storage and new opportunities for clean energy.

Read more on Ali’s Flexible Funding 2024 project page.

Farshad Jafarizadeh, Heriot-Watt University, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “Minimizing Environmental Impacts of CO2 Storage Projects: Time-Lapse Monitoring of Fault Reactivation for Safe Sequestration”.

Climate change mitigation at the gigatonne scale depends on safe and reliable Carbon Capture and Storage (CCS). One of the key questions is straightforward: how can we be sure that the CO₂ injected deep underground will remain securely trapped? It is not enough to inject and walk away. Achieving safe, large-scale storage requires robust measurement, monitoring, and verification (MMV) strategies that can identify potential risks before they escalate. One important risk is fault reactivation, where increases in reservoir pressure may induce small slips along faults, potentially creating leakage pathways.

In our recent UKCCSRC Flexible Fund project, we investigated how time-lapse (4D) seismic monitoring can be applied not only to track CO₂ plumes, but also to detect these subtle geomechanical events before they threaten containment.

Using 4D Seismic to “Listen” for Fault Movement

Time-lapse (4D) seismic surveys work much like an ultrasound of the Earth. By comparing repeated surveys (a base survey and subsequent monitor surveys), we can detect changes in pressure and fluid saturation caused by CO₂ injection in the subsurface.

Two key types of signals are considered:

• Amplitude changes are primarily sensitive to CO₂ saturation and fluid distribution.

• Time-shift signals are differences in seismic wave arrival times that reflect velocity changes caused by pressure and saturation changes.

For this study, time-shift signals are particularly valuable because they provide a clear geomechanical response in the overburden, unaffected by fluid saturation effects in the reservoir.

Modelling Fault Reactivation and Detectability of Time-Shift Signals

To evaluate the detectability of 4D seismic signals, we applied two analytical approaches to represent the effects of CO₂ injection:

• The Geertsma solution, which links reservoir pressure changes to strain in the reservoir and surrounding rock.

• The Okada solution, which relates fault slip to strain in the fault plane and its surroundings.

From the calculated vertical strain cubes, and by integrating both effects where pressure increase acts as the triggering mechanism for fault slip, we applied a rock physics model to estimate the corresponding time-shift signals for different earthquake magnitudes. We then evaluated the minimum event size (Richter scale) detectable by different monitoring systems. For three common acquisition methods, the minimum time-shift thresholds are as follows: Permanent Reservoir Monitoring (PRM), 0.06 ms; Ocean Bottom Nodes (OBN), 0.07 ms; and Towed Streamers, 0.24 ms. These thresholds show that PRM and OBN can detect seismic events as small as magnitude 2.65 Richter, a value that can be directly linked to maximum injection pressure and injection volume, which are key parameters for ensuring safe CO₂ sequestration (shown in Fig. 1).

Fig. 1: Relationship between moment magnitude and time-shift signals for different fault lengths

North Sea Case Study

We applied our approach to the 2001 Ekofisk K-22 incident in the Norwegian North Sea, where a leaking water injector led to an unexpected pressure build-up of around 20 MPa, triggering a magnitude 4.3 seismic event on the Richter scale. This case was selected because observed data from Towed Streamer were available for validation, and the overburden time-shift signal is unaffected by fluid type, providing a clearer geomechanical response.

Our modelling results indicate that:

• Pressure effects generated a time-shift of approximately +3.3 ms
• Fault slip produced a smaller but still detectable time-shift of 0.25–0.35 ms (Fig.2 shows the modelling workflow for the time-shift signal for a fault-slip event)

These findings demonstrate that 4D seismic monitoring can capture both pressure-induced responses and fault reactivation, even when using typical acquisition methods such as Towed Streamer.

Fig. 2 Workflow for post-stack time-shift estimation using Okada modelling

Conclusion and Future Directions

Our findings show that time-lapse seismic can hear the Earth’s smallest whispers of stress and strain before they grow into larger risks. This offers operators a practical way to ensure safe, long-term CO₂ storage.

The study highlights that:

• 4D seismic is not just for plume tracking; it is also a vital tool for geomechanical safety assurance and monitoring.
• Pressure and tectonic signals often overlap in observed data; however, careful analysis of angle-dependent time-shift data (pre-stack time-shift analysis) and horizontal velocity perturbations can improve their separation. Future research should explore these approaches further.

Read more on Farshad’s Flexible Funding 2024 project page.

Dr Stavros Michailos, University of Hull, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “EfW-UPCC: Techno-Economic Assessment of Ultra-high Post-Combustion Capture in Energy from Waste Plants”.

Introduction

Decarbonising industrial clusters is essential to the UK’s net-zero target by 2050. This commitment has designated Carbon Capture Utilisation and Storage (CCUS) as a necessity and not an option. Post-Combustion Capture (PCC) of CO₂ using amines is expected to dominate, with two out of the three UK government-funded Track-1 CCS Cluster Sequencing capture projects to be amine-based PCC plants¹. PCC offers the advantage of retrofitting existing infrastructure, making it a practical and cost-effective option for multiple industries such as energy from waste, and is also being considered for new-builds².

Background

EfW plants have the potential to replace landfills while generating low carbon electricity and heat. When PCC is added, then the EfW+PCC assembly can be a carbon dioxide removal (CDR) technology and achieve negative emissions since typically up to 50% of the CO₂ contained in the flue gas is biogenic. Obviously, the higher the capture fraction, the higher the chances for carbon removal to account also for upstream emissions.

Up until recently, the conventional wisdom has been – largely because it was a ‘standard’ baseline used in studies comparing costs – that capturing 90% of the CO₂ in a flue gas stream was both good enough and the best that could be done to minimise the cost per tonne of CO₂ captured. But, to help deliver net-zero fossil CO₂ stack operation ( or 100% of the added fuel CO₂ or 100% fossil CO₂ capture), combustion applications fitted with PCC should ideally operate at such a manner that the whole amount of the fossil CO₂ added to the air is captured and hence the vented gas should contain the same amount of CO₂ as the combustion air; this entails gross capture fraction from the EfW flue gas of ~99.7%.

Aim

The main aim of the project is to establish feasible design and operational windows of ultra-high capture fractions up to up to 100% of the fossil-based CO₂ emissions and reveal the true cost of achieving 100% capture and challenge the assumption that such high capture levels are prohibitively expensive.

Novelty

A key innovation in this study is the use of low lean solvent loadings (<0.15 molCO₂/molMEA) and moderately elevated desorber pressures (2.4 bara). This increases the CO₂ mass transfer rate without demanding massive changes to absorber height (main CAPEX) or solvent flow rates and for specific reboiler duties (SRD) that lie well within the range of reported energy penalty for 90–95% capture, i.e. between 3 and 4 GJ/tCO₂^3,4. In essence, it lets existing infrastructure do more with only minor upgrades.

Results

Mass and energy balances have been established (through Aspen Plus modelling) for different absorber heights, i.e. 20 (2 beds x10), 24 (3 beds x8) and 30m (3 bedsx10), and capture fractions of 95% and 100%. All cases, include intercooling at 40°C (in-out). The optimum lean loading for EfW flue gas has been identified at 0.12 molCO₂/molMEA. Figure 1 is the SRD for different capture fraction and absorber heights. Taller absorbers allow for lower L/G ratios and higher rich loading which have appositive impact on the SRD. The increase of SRD from 95% to 100% is 13.5%, 6.7% and 3.6% for 20, 24 and 30m absorber heights.

Figure 1. The SRD for different absorber packing heights and capture fractions

The 24 m absorber is likely to be the industrial standard for PCC. The CAPEX breakdown for this case is presented in Figure 2A. Regeneration costs include stripping and solvent reclaiming with the latter to account for approximately 8% of the regeneration costs. On the other hand, electricity costs—primarily reflecting steam consumption and assuming a coefficient of performance (COP) of approximately 4—represent a significant portion of the operating expenses, i.e., 62%.

Subsequently, the cost of CO₂ capture has been calculated. The increase in the capture cost from 95% to 100& capture is 5.72%, 3.66% and 3.25% for the 20, 24 and 30m absorber, respectively. This is a significant improvement against the consensus that ultra-high capture fractions are related to excessive costs. Further, the marginal cost of capture of transitioning from 95% to 100% fossil CO₂ capture is 175, 141 and 102 £/tCO₂ for the 20, 24 and 30m absorber, respectively; in all cases, these figures are lower than current and projected direct air capture costs.

Figure 2. CAPEX (A) and OPEX (B) breakdown for the 24m absorber and capture fractions of 95% and 100%

Figure 3. The cost of CO2 captured for different absorber packing heights and capture fractions

Conclusions

The path to net-zero will require scalable technologies that can deliver deep decarbonisation at reasonable costs. By showing that 100% fossil CO₂ capture from EfW plants is not only technically achievable but also cost-competitive, this work lays the groundwork for new CCUS strategies, informs UK government policy and boosts investor confidence.

Outputs

• Michailos, M. Lucquiaud, A. D. Benz, D. Mullen, W. Elliott and J. Gibbins. A Performance Modeling Study for Zero Fossil CO2 Stack Operation and Solvent Thermal Reclaiming in Post-Combustion Capture Industrial Applications Industrial & Engineering Chemistry Research 2025 Vol. 64 Issue 13 Pages 7100-7114 https://doi.org/10.1021/acs.iecr.4c04530
• Qurrotin Ayunina, S. Michailos, MF Rojas Michaga, K. Rabea, K. J Hughes, L. Ma, D. Ingham, M. Pourkashanian. Conceptual design and thermodynamic investigation of novel energy and fuel generation systems from municipal waste coupled with carbon capture and storage, Energy Nexus, Volume 18, 2025, 100460, https://doi.org/10.1016/j.nexus.2025.100460

Acknowledgments

SM would like to acknowledge the Engineering and Physical Sciences Research Council (EPSRC) under the United Kingdom CCS Research Centre grant EP/W002841/1 (Flexible Funding 2024).

Read more on Stavros’s Flexible Funding 2024 project page.

Dr Ruiqi Wang, Durham University, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “Environmental Considerations For Large-scale Direct Air Capture With Fuel Cell”.

Our objectives

Direct air capture (DAC) system aims to extract CO₂ directly from the ambient air, and it is generally coupled with permanent geological storage or utilised in the production of fuels, chemicals, and other materials. With the rapidly evolving potential for scaling up engineered removals, DAC has been proposed to be developed and scaled up over next decades, contributing significantly towards achieving the net-zero emissions targets.

Liquid solvent-based DAC (L-DAC) as one of the most advanced and commercial DAC technologies faces its main challenges in high-temperature heat and energy demand for regeneration process. To avoid compromised carbon reduction efficiency of DAC due to use of fossil fuels for generating requisite heat and electricity, solid oxide fuel cell (SOFC) fed by green hydrogen has emerged as a viable option to simultaneously supply high-grade heat and renewable electricity to DAC.

The longer supply chain for L-DAC integrated with green hydrogen fed SOFC introduces indirect environmental impacts from installation of renewable energy sites, and presents additional risks and environmental considerations for energy generation and storage. This research therefore aims to use life cycle assessment (LCA) to thoroughly evaluate the life cycle impacts of an L-DAC system integrated with green hydrogen-fed SOFC, which will highlight key environmental considerations for the large-scale deployment of the proposed system.

Our system

The L-DAC process adopts the potassium-carbonate loop to capture CO₂ from air. The ambient air is first drawn through an air contactor where CO₂ reacts with aqueous potassium hydroxide (KOH) to form potassium carbonate (K₂CO₃). Then the K₂CO₃ is pumped into a pellet reactor where the solution reacts with calcium hydroxide (Ca(OH)₂), further precipitating calcium carbonate (CaCO₃) pellets. The pellets are then calcined at approximately 900 ℃, liberating CO₂ for compression and subsequent sequestration and utilisation.

The SOFC operates on green hydrogen and supplies both power and high-temperature heat to L-DAC unit. At the anode of SOFC, hydrogen is oxidised to water molecule whilst releasing electrons. Oxygen ions (O^2-) formed at the cathode migrate through the electrolyte to complete the electrochemical reaction. The electrons flow between the anode and cathode via an external electrical circuit to generate DC electricity which drives the air contactor fans, pellet reactor, slaker, air separation units, and the CO₂ compression unit. The high-temperature anode exhaust delivers steam and residual fuel to the calciner, and high-temperature vitiated air from cathode exhaust is fed to heat jacker surrounding the calciner, meeting the thermal demand of L-DAC.

The green hydrogen is produced on-site via a high-temperature steam electrolysis (HTSE) unit. It also has a thermal linkage with SOFC by using the exhaust from stacks of fuel cell for the required high-temperature heat, while the electrolyser’s electrical load is met with external power such as grid electricity and renewable electricity.

Figure 1. Schematic view of L-DAC integrated green hydrogen-fed SOFC system

Our findings

Relative to the L-DAC with natural gas-based combined heat and power supplied baseline (0.305 kg CO₂ eq./kg CO₂ captured), coupling the L‑DAC unit to an SOFC fed by hydrogen produced from wind-powered HTSE cuts self‑emitted GHGs by up to 86 %. The results from LCA show that the deployment of SOFC with L-DAC has significantly decreased the impacts in climate change, marine and terrestrial eutrophication, ozone depletion, photochemical ozone formation, and fossil resource use. Producing hydrogen through HTSE is not shown as the best option in several impact categories compared to hydrogen production from steam methane reforming, namely acidification, freshwater ecotoxicity and eutrophication, human toxicity, land use, particulate matter, mineral and metals resource use.

Read more on Ruiqi’s Flexible Funding 2024 project page.

Professor Vahid Niasar, University of Manchester, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “Quantification of capillary suction induced by brine evaporation and salt precipitation during CO2 injection in saline aquifers”.

As countries ramp up efforts to meet net zero targets, geological carbon storage in saline aquifers is emerging as a crucial strategy for long-term CO₂ sequestration. When dry CO₂ is injected into brine-filled porous rocks, salt crystals can form and block the tiny pathways that fluids use to move, a process that can dramatically reduce the injectivity of storage site and long-term performance.

Thanks to support from the UK Carbon Capture and Storage Research Centre (UKCCSRC), our team at the University of Manchester has zoomed in – quite literally – on this phenomenon using microfluidics and high-resolution optical techniques. By watching salt crystals grow in real time under a microscope, we were able to uncover how and why pore-scale salt precipitation happens, and what it means for CO₂ storage.

Why Salt Matters in CO₂ storage

When CO₂ is injected into deep saline aquifers, it displaces brine in the pores of the rock. But not all the water is pushed out. Some gets trapped and starts to evaporate into the dry CO₂ stream, especially near the injection well where the CO₂ is driest. This sets the stage for salt precipitation, especially halite (NaCl), which crystallises once the brine becomes supersaturated. These salt crystals can clog the pore space, reducing permeability and making it difficult for more CO₂ to be injected.

What makes things more complex is the role of capillary suction in porous media that pull liquid back toward drying zones. This capillary-driven backflow can amplify evaporation, accelerating the cycle of brine evaporation and salt growth. But until now, we lacked real data on how these forces work at the pore scale.

What We Did

We conducted microfluidic experiments to simulate brine evaporation and salt precipitation under CO₂ flow using our custom-fabricated glass micromodels. Using a state-of-the-art imaging system including μPIV (micro-Particle Image Velocimetry), we captured the behaviour of residual brine, salt crystals, and tracer particles over time.

Microfluidic chip with porous structure and the dual-field imaging system used for simultaneous brightfield and fluorescence imaging

We tracked:

• The displacement of brine by CO₂
• The fragmentation of brine into isolated clusters
• The onset of salt precipitation
• The motion of tracer particles drawn toward drying zones

We observed that there is often a sustained backflow of brine through thin films along pore walls or around salt crystals, driven by capillary pressure. This creates feedback loops where salt growth boosts capillary suction, which in turn fuels further evaporation and precipitation.

Key Findings

• Evaporation and precipitation are temporally distinct: After the CO₂ displaces most of the brine, evaporation and crystal growth continue over a much longer period.
• Brine clusters break into smaller pockets that evaporate independently, leading to dispersed single- and polycrystalline salt formations.
• Capillary suction increases over time, especially in confined zones, driving water towards the evaporation front.
• Thin-film flows were visualised and confirmed to contribute to additional salt growth from distant sources.
• Most importantly, salt and capillarity are deeply linked. Salt crystals increase the effective surface area for evaporation, which enhances capillary suction—a self-reinforcing cycle.

Brightfield images show salt formation; fluorescent tracer particles reveal capillary-induced fluid motion toward the growing crystals

These insights shed light on why injectivity loss can worsen over time, even after initial brine displacement has stabilised. Understanding this evolution is vital for both predicting long-term performance and designing smarter injection strategies.

What’s Next

The experimental results from this study provide a valuable dataset for validating pore-scale models of salt precipitation, which in turn can inform reservoir-scale simulations. We also evaluated a potential mitigation strategy, which showed promise in reducing localised clogging.

Further work will explore:

• Scaling the findings to heterogeneous or fractured systems
• Integrating pore-scale physics into larger simulation frameworks
• Developing operational guidelines to avoid or reverse salt blockage

Sharing the Science

As part of the UKCCSRC-supported project, the team visited Shell’s Energy Transition Campus in Amsterdam and Delft University of Technology in June 2025. These collaborative visits sparked new conversations around cross-scale modelling, experimental design and field applications. We are grateful to UKCCSRC for enabling these exchanges, which are critical for bridging academic research and real-world deployment.

Visit to Shell’s ETCA and TU Delft

Read more on Vahid’s Flexible Funding 2024 project page.

Dr Wei Li, University of Nottingham, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “Accelerating the Development of Advanced Silica-alkoxylated Polyethyleneimine (APEI) Adsorbents for Direct Air Capture”.

Project Overview

Effective carbon capture and storage (CCS) technologies are urgently needed to limit global warming and mitigate the adverse effects of climate change. Among CCS approaches, Direct Air Capture (DAC) stands out for its flexibility and potential to remove CO₂ directly from the atmosphere. However, current DAC technologies remain costly due to the extremely low atmospheric CO₂ concentration (~0.04%) and the limited development of efficient adsorbents. To enhance the viability of DAC, it is essential to overcome the critical challenge of developing cost-effective and high-performance adsorption materials. The goal of the project was to optimise alkoxylated polyethyleneimine (APEI) for DAC applications by addressing two challenges:

1) Material stability vs. performance – Developing a new evaluation approach and modelling tools to optimise APEIs for DAC conditions using the developed model that balances CO₂ adsorption efficiency with long-term oxidative stability.

2) Silica support optimisation – Selecting and preparing silica supports with suitable pore structures and particle sizes, ensuring the material performs effectively in fixed-bed DAC systems and is scalable for real-world applications.

What We Did

Specifically, our project focused on overcoming the above two major challenges. We aimed to optimise APEI adsorbents by tuning key parameters: alkoxylation degree (AD), molecular weight, and PEI loading on silica, and by modelling their long-term oxidative degradation under realistic DAC conditions. To evaluate and optimise APEIs for DAC, we developed comprehensive adsorbents with varying ADs, PEI loadings, and molecular weights. These materials were tested for CO₂ adsorption performance, followed by long-term oxidation testing for up to 60 days at 50–80 °C. After oxidation, their remaining CO₂ adsorption capacities were measured under both post-combustion capture (PCC) and DAC conditions to assess performance retention.

To track performance evolution over time, periodic CO₂ adsorption measurements were conducted. A range of degradation models was applied to evaluate long-term stability. Among them, Avrami–Arrhenius kinetic models proved most effective, offering accurate predictions of degradation mechanisms and capturing non-linear behaviours. This provided valuable insights into the materials’ long-term reliability. Additionally, we developed a new evaluation metric, cumulative CO₂ uptake (see Figure 1), over the adsorbent’s various service life, moving beyond traditional single-time-point measurements. This approach enabled more meaningful comparisons between APEIs and helped define optimal end-of-life performance thresholds.

We also focused on identifying and validating silica supports suitable for large-scale APEI impregnation, with particular attention to pore structure and particle size, both of which are critical for efficient fixed-bed DAC operation. Up to 10 types of mesoporous silica were screened, and their pore volume, surface area, and particle size were evaluated as factors known to significantly influence APEI loading capacity and mechanical flow properties. Among these, PQ10 silica was selected as the optimal support due to its high pore volume and large particle size.

A 25 kg batch of PQ10 was sieved to isolate particles larger than 300 µm. These retained excellent textural properties post-sieving and were used to produce high-loading silica-APEI adsorbents. To validate performance, larger scale adsorbents (over 2 kg) were prepared and compared against lab-scale samples. The sieved PQ10-based adsorbents performed reliably in both cases, confirming their suitability for scale-up and industrial deployment in DAC applications.

Figure 1. CO2 adsorption capacity at 50 °C after oxidation at 80 °C for 10 days, comparing the performance of FG (PEI) and APEI samples. The shaded area under the FG curve represents the cumulative CO2 adsorption capacity during the 10-day oxidation period. The full cumulative data for other APEI formulations are not shown here but will be provided in our forthcoming publication.

Key Findings

We observed a clear trade-off between oxidative stability and CO₂ adsorption performance as the alkoxylation degree (AD) increased. While a higher AD enhanced oxidative resistance (i.e. prolonged operational life), it also led to a reduction in initial CO₂ capture capacity.

The Avrami–Arrhenius model provided an accurate fitting for the complex degradation behaviour of APEIs. Using cumulative CO₂ uptake as the evaluation metric, we found that medium alkoxylation levels offered the best overall balance between long-term oxidative stability and CO₂ adsorption performance.

PQ10 silica proved to be a practical and scalable support, with a high proportion of large particle sizes. Its structural integrity and adsorption consistency post-sieving confirmed its suitability for industrial-scale DAC applications. Its ability to support high APEI loadings and maintain performance under DAC-relevant conditions highlights its commercial potential.

Conclusion

The optimised APEIs and the selected PQ10 silica support are highly suitable for fixed-bed DAC operation. Combined with the advanced degradation modelling approach and the use of cumulative CO₂ adsorption performance as a robust evaluation metric, this project presents a reliable method for selecting silica-APEIs tailored to specific application conditions, balancing both adsorption capacity and long-term stability.

Read more on Wei’s Flexible Funding 2024 project page.

Dr Aaron Cahill, Heriot-Watt University, was awarded funding in the UKCCSRC’s Flexible Funding 2024 call to look at “Development of a Quantitative Wellbore Leakage Risk Assessment Tool for Screening Storage Projects (Q-WELLRATe)”.

Decommissioned oil and gas wells may pose a hidden risk for safe CO₂ storage. That’s why we developed Q-WellRATE, a fast, physics-based model to help assess legacy well potential leakage and support the UK’s carbon storage ambitions.

Understanding the Challenge

As the UK advances its plans for large-scale carbon capture and storage (CCS), the safe containment of CO₂ underground is essential. A particular challenge for many North Sea storage sites is the presence of thousands of legacy wells, old oil and gas wells drilled and abandoned over previous decades. Even when sealed, these wells can potentially act as pathways for CO₂ leakage if plugs degrade or go undetected, threatening project success and public trust.

Traditional approaches to legacy well risk assessment are often slow and require detailed site-specific data, limiting their usefulness for screening large numbers of wells. Recognising this, our team set out to create a new tool that balances scientific rigour with speed and flexibility.

The Q-WellRATE Solution

Q-WellRATE is a simplified, physics-based model designed for rapid estimation of CO₂ leakage rates along compromised legacy wells. Developed at Heriot-Watt University with support from UKCCSRC, it allows users to:

• Simulate a wide range of geological and engineering scenarios, including different well designs and abandonment practices
• Incorporate depth-dependent temperature, pressure, and fluid properties for realistic non-isothermal flow
• Run thousands of simulations per hour to enable screening and spatial risk mapping across entire regions

The model aims to support both high-level regional studies and targeted analysis of individual wells, helping operators, regulators, and policymakers prioritise resources and interventions.

Key Insights and Results

In applying Q-WellRATE to North Sea scenarios, several important findings emerged:

• Cement plug integrity is critical: even minor defects can significantly increase leakage risk
• Plug length has diminishing returns: after a certain threshold, longer plugs provide little additional benefit, informing cost-effective design
• Site-specific factors matter: geology, temperature, and pressure influence risk, but wellbore condition remains the overriding control
• Fast, transparent assessment: the model’s efficiency allows for rapid “area of review” studies, supporting timely decision-making

Stakeholder Engagement

A key part of the project was collaboration with stakeholders, including the North Sea Transition Authority, Shell, and Storegga. Their technical feedback guided the model’s development, from simulating multi-modal well failures to integrating real-world abandonment designs. Engaging with both regulators and industry has helped Q-WellRATE address practical challenges and better meet potential user needs.

Looking Ahead

Our main technical output, i.e. a draft manuscript prepared for peer-reviewed publication, details the Q-WellRATE methodology, findings, and implications for CCS project safety. Looking forward, we plan to refine the model further, explore more complex scenarios, and share our work with the wider CCS community.

By providing a robust and rapid tool for legacy well risk assessment, Q-WellRATE supports the UK’s journey toward safe, large-scale carbon storage and helps turn old infrastructure from a challenge into an opportunity.

Schematic illustration of a legacy well (left) and CO2 injection well (right) with potential leakage pathways annotated. A: leakage via damaged casing, B: leakage via cement plugs and open hole, C: leakage via damaged annular cement

Read more on Aaron’s Flexible Funding 2024 project page.

The UK Carbon Capture and Storage Research Community (UKCCSRC) is supported by the Engineering and Physical Sciences Research Council (EPSRC) as part of the UK Research and Innovation (UKRI) Energy Programme.

The mission of the UKCCSRC is to ensure that carbon capture and storage (CCS) plays an effective role in helping the UK achieve net-zero greenhouse gas emissions by 2050.

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