COMPASsCO2 Newsletter - Ninth Issue

APRIL 30, 2025 Issue 1 NEWSLETTER COMPASsCO2 Contents Main Accomplishments Project Management & Coordination Communication, Dissemination & Exploitation Activities How to Access COMPASsCO2 Outcomes This project has received funding from the European Union’s Horizon 2020 Research and Innovation Action (RIA) under grant agreement No. 958418. Issue : IX Main Accomplishments COMPASsCO2 Scientific Outcomes & Achievements WP 1 (Materials operation conditions and their feasibility studies): This WP focused on defining system parameters and evaluating the feasibility of materials and technologies for a supercritical CO₂ (sCO₂) solar power system. Ten different sCO₂ Brayton cycle configurations were assessed, leading to the selection of optimal process conditions—including a 700°C turbine inlet temperature at 260 Bars and particle/sCO₂ heat exchange parameters— towards a maximized efficiency of approx. 49%. Based on these conditions, candidate materials for both heat exchanger components and heattransfer particles were pre-selected for their ability to perform under extreme thermal and mechanical stress. WP1 also investigated both lowand high-pressure heat exchanger designs, performing thermo-mechanical stress analyses to validate material choices, and ultimately finalized a modular industrial-scale heat exchanger design capable of transferring over 200 MWth with 15 MWth per module. A comprehensive techno-economic analysis was carried out, evaluating the production costs of novel particles and estimating heat exchanger costs using experimental and commercial benchmarks. Five concentrated solar power (CSP) plant configurations were analyzed in terms of cost, efficiency, and levelized cost of electricity (LCOE). Additionally, novel Cr-based alloys and coatings from WP3 were assessed, confirming the economic feasibility of coatings such as Cr/Si slurry (~750 €/m²), while bulk Cr alloys face ductility limitations. The work also included market studies targeting the Mediterranean and MENA regions, identifying broader applications for the developed materials, such as Cr-Si coating for gas turbine blades and industrial process heat at high temperature and harsh environment. WP2 (Development and Testing of Particles): It focused on the development, testing, and optimization of novel heat-transfer particles for use in high-temperature solar applications. State-of-the-art particles do not maintain a constant solar absorptance after thermal testing, making them suboptimal for use in Concentrated Solar Power (CSP) applications. Novel particles developed by Saint-Gobain offer significant performance improvements, including stable solar absorptance, better mechanical stress distribution, and can be produced at a similar cost. Among these, FerOx particles were selected as the best option due to their increased hardness compared to other granulated particle generations, despite having relatively lower solar absorptance. To enhance solar absorptance, three coatings with different compositions and application techniques were Research focus: New particles, metal alloys and heat exchanger Duration: 1 November 2020 – 30 April 2025 Team: 12 partners from 7 countries developed by CIEMAT, DLR, and DFI. Environmental and thermal testing have shown that the coatings maintain stable optical properties. After thermal tests, DFI coatings exhibited the highest solar absorptance, while CIEMAT coatings experienced the lowest decay. Notably, DLR coatings slightly improved solar absorptance after testing, indicating that the heat treatment applied after deposition was insufficient to fully complete the curing process. In terms of abrasion resistance, all three coatings performed similarly at ambient temperatures. However, during abrasion testing at operational temperatures, the DFI coating experienced the greatest loss in solar absorptance, while the DLR coating showed the lowest absorptance loss. The highest solar absorptance at the end of the test was achieved by the CIEMAT coating. WP3 (Development of Metals): This WP focused on the development of advanced chromium-based materials for hightemperature, corrosive environments typical of particle-to-sCO₂ heat exchangers. The team designed and synthesized Cr-NiAl bccsuperalloys 1 and Cr-Si alloys 2 that demonstrated excellent thermal stability up to 1000°C, high strength, and superior oxidation and corrosion resistance, all at a lower material cost than conventional nickel-based superalloys. However, their application as structural materials was limited by their brittleness, due to high ductile-to-brittle transition temperatures (above 600–700°C). To address this, WP3 also developed and patented an innovative Cr/Si slurry diffusion coating process, which was successfully applied to commercial steel and nickel alloys such as Inconel 740 and Rene 80. These coatings exhibited outstanding oxidation resistance, showed no catastrophic corrosion even under long-term and cyclic conditions, and proved highly effective against hot corrosion in sodium sulfate environments. Mechanical and environmental tests, including small punch and creep experiments, confirmed high strength but also brittleness in the bulk alloys. In contrast, coated materials performed well under erosion and oxidation, with TEM and EPMA analysis 1 https://doi.org/10.1016/j.actamat.2023.119183 revealing the formation of stable SiO₂ and Al₂O₃ subscales. To support material design, machine learning and thermodynamic modeling were used to screen alloy compositions, identifying eight promising candidates—five of which matched the desired BCC-B2 microstructure upon experimental validation. Atomistic simulations further refined predictions related to ductility and phase stability. WP4 (Evaluation and Modelling of Metal/Medium Interaction): It evaluated the performance and degradation behavior of heat exchanger materials under realistic hightemperature and high-pressure environments. The erosion behavior of materials is influenced by particle type, particularly hardness, and velocity, with Cr-Si coatings showing a beneficial effect in mitigating erosion. In terms of creep behavior, the observed data aligns with literature values, with minimum creep rates under all selected loads being less than 10^-6 s^-1. Sanicro 25 showed higher creep rates in CO2, while IN-617B displayed similar behavior, and there were some deviations observed among the superalloys. Overall, the atmosphere had very little impact on the creep behavior, and the load had a minimal effect on surface degradation. Demonstrator tests conducted at 700°C and 120 bar required developments in sealing, pumps, and sensors. For state-of-theart (SOTA) alloys, formed layered oxide scales were observed, with IN740 showing the lowest oxidation. Novel alloys exhibited similar behavior to SOTA alloys, although some grain boundary oxidation was noted. In the field of modeling, experimental data was successfully implemented, revealing that fractures are likely to initiate due to impacts at surface oxide asperities. Lifetime modeling was completed by estimating the wear rate and depth for HEX materials. WP5 (Technology Validation): This WP focused on the design, testing, and validation of a high-performance particle/sCO₂ heat exchanger (HEX) for concentrated solar power applications. A HEX mock-up was designed, manufactured and tested, incorporating insights from WP1 through WP4 to select optimal 2 https://doi.org/10.1007/s11085-024-10257-8 materials—such as coated steels and Cr-based alloys—and configure the heat exchanger geometry. Key design challenges, including pressure drop, mechanical stress, particle flow, and manufacturability, were systematically addressed. Initial cold loop testing evaluated particle flow behavior, helping to determine the ideal tube pitch and arrangement for balancing thermal efficiency and particle flow pattern. Subsequent hot-loop testing was conducted using a lab-scale rig operating at ~750°C, where the abrasion resistance of state-of-the-art materials, as well as the WP3 Cr-based materials and coatings, was evaluated. In addition, the impact resistance of various ceramic materials was assessed. These tests provided insight into wear durability and coating stability under cyclic operation. In the final phase, a mock-up particle/sCO2 heat exchanger was manufactured and tested, integrating actual particle flow and a functioning sCO₂ loop. The testing confirmed thermal performance under representative conditions, achieving Technology Readiness Level 5 (TRL 5). Finally, experimental data from WP5 fed back into techno-economic assessments from WP1, refining industrial HEX design, improving performance forecasts, and enhancing cost models for commercial-scale CSP deployment. WP5 Final test rig – integrated particle/sCO2 heat exchanger mock-up Project Management & Coordination Regular project meetings, quarterly phone calls, and monthly WP meetings ensured smooth coordination across the COMPASsCO2 consortium, allowing partners to align on technical progress, challenges, and next steps. These interactions fostered effective collaboration, kept the project on track, and helped maintain a high standard of scientific and technical excellence. In addition, three review meetings with an external expert were held to present project findings, and get an evaluation of the work conducted (see below). Project Meetings Eight Project Meetings (General Assembly – GA) were organized to discuss the overall progress, in terms of milestones, deliverables, technical progress achieved, risk/deviations and corrective actions, etc. While the Kick-off meeting had to be organized online because of the Covid19 pandemic, three physical meetings were held in 2022, 2023 and 2024. Fourth GA Meeting at Plataforma Solar de Almeria (PSA), Tabernas, Spain, 30 November - 1 December 2022 Fifth GA Meeting at FZJ, Jülich, Germany, 6-7 June 2023 Sixth GA Meeting at SGCREE, Cavaillon, France 31 January – 1 February 2024 Review Meetings Throughout the COMPASsCO2 project, 3 Review Meetings with the European Commission and an independent expert were held to assess progress, share key results, and align on future activities. These meetings provided valuable feedback, ensuring that technical achievements, dissemination efforts, and project management remained on track. Each review confirmed the quality of the work performed and highlighted COMPASsCO2’s strong contribution to material research, sCO₂ processes and CSP technologies. First Review Meeting at JCR, Seraing, Belgium, 7 April 2022 Second Review Meeting, Online, 21 March 2024 Third Review Meeting at CVR, Husinec u Řeže, Czech Republic, 25 April 2025 Communication, Dissemination & Exploitation Activities The COMPASsCO2 project has effectively shared its findings through a variety of prestigious international and interdisciplinary platforms. These include published papers in renowned scientific journals, engaging presentations at conferences and workshops, informative papers, workshops and webinars. The project's impact was also extended through digital platforms (e.g. website, Zenodo, social media) and other outreach efforts, ensuring widespread dissemination of research outcomes. Papers Produced by COMPASsCO2 Team The COMPASsCO₂ project has generated a wide range of impactful scientific publications in peer-reviewed journals (13 in total) addressing major challenges in concentrating solar power (CSP) technologies and hightemperature materials. In the field of particle development and coatings, a technical guideline was published on the SolarPACES website in May 2022, standardizing methods for evaluating the optical properties of solar absorber particles. Further research published in May and November 2022 demonstrated significant performance improvements through the use of black oxide and aluminum-incorporated deep black pigment coatings. Additional work on soiling characterization variability appeared in Solar Energy Materials and Solar Cells in July 2023, alongside research published in January 2024 on spinel absorber coatings enhancing CSP receiver efficiency. Durability testing of novel particles was also reported in Solar Energy Materials & Solar Cells in November 2024. In the area of alloy development, publications in Physical Chemistry Chemical Physics (May 2023) and Acta Materialia (July 2023) explored advanced techniques for precipitate measurement using deep learning and the strengthening of chromium-based bccsuperalloys through iron supplements. Protective coating technologies were further advanced through research on Cr/Si-slurry diffusion coatings published in Materials (December 2023), as well as studies on nanocrystalline Y₂O₃-modified coatings and chromium-silicon slurry coatings, which appeared in Surface and Coatings Technology (June 2024) and High Temperature Corrosion of Materials (July 2024), respectively. A collaborative Round Robin Test on absorptance and emittance measurements was also presented at the SolarPACES 2022 Conference in March 2024. Finally, a study focusing on material challenges and alloy selection for particle/supercritical CO₂ heat exchangers was accepted for publication in Solar Energy in 2024. Altogether, these publications across high-impact journals such as Solar Energy Materials and Solar Cells, Coatings Journal, Materials, and Acta Materialia reflect the project's strong scientific output and its significant contribution to advancing CSP technology and high-temperature material performance. Beyond the project’s duration, the COMPASsCO2 project will produce more than 15 papers focused on materials for hightemperature applications, especially in concentrated solar power (CSP) systems. Topics include the oxide scale formation and hot corrosion resistance of chromized Ni-based alloys, novel Cr-Si alloys for high temperatures, and the stability of coatings in particle heat exchangers under thermal cycling. Additional studies will address high-temperature erosion, abrasion testing of coated particles, and screening of chromium-based high entropy superalloys. Research will also explore oxidation behavior of materials for CSP plants with CO2 heat-transfer systems and the design of BCC superalloys. Finally, papers will cover the development of chromium-silicon slurry coatings and the creep behavior of Feand Nibased alloys in CO2 environments. These studies will continue to contribute to material advancements beyond the project's completion. In addition to scientific papers, he COMPASsCO2 team produced informative papers to share key project results with a general audience to raise awareness of research developments and their industrial applications for a Net Zero Carbon future. Three papers were released: 1. First Paper (March 2022) – Focused on the development and testing of new particles for high-temperature concentrating solar receivers, highlighting innovations from COMPASsCO2. 10.5281/zenodo.11386468 2. Second Paper (November 2023) – Covered new metal alloys for sCO2 heat exchangers in next-gen solar plants, including properties of bulk materials, coatings, and interactions with heat exchanger steel. 10.5281/zenodo.11385843 3. Third Paper (April 2025) – Discussed the development of chromium-based alloys for future concentrating solar technologies. 10.5281/zenodo.15310616 COMPASsCO2 Participation at Conferences The COMPASsCO2 project has been widely presented at various international conferences, workshops, and events. Presentations (69 in total) include detailed discussions on new material solutions for thermal energy storage at SolarPACES2021, and contributions on BCCsuperalloys and Cr-Si alloys at TMS 2022. The project also featured several oral presentations and posters at conferences such as ICMCTF, Plansee Seminar, and SolarPACES, highlighting topics like the development of advanced coatings for CSP systems, oxidation behaviors of superalloys, and thermal and environmental durability of novel particles. Other notable sessions included corrosion behavior in molten salts, mechanical testing of materials for solar heat exchangers, and innovations in high temperature corrosion and erosion resistance. Other presentations covered topics like alloy development, material testing, and performance evaluation at major conferences such as TMS 2025 and SolarPACES 2024. Marta Navas (CIEMAT) at EUROCORR 2024 conference, Paris, France, 2-5 September 2024 Florian Lebendig (FZJ) Wins Best Poster Award at HTCPM 2024 Symposium, Île des Embiez, France, 9 -14 June 2024 Tom Blackburn (UoB) at the High Corrosion and Oxidation Workshop 2023, Marktheidenfeld, Germany, 2529 September 2023 COMPASsCO2 partners at the EUROMAT2023, 03-07 September 2023, Frankfurt, Germany CIEMAT colleagues at the 2023 MRS Conference, San Francisco, USA, 14 April 2023 Florian Lebendig (FZJ) at the trade fair for industry that was organized from 22 to 26 April 2024 at Hannover, Germany. with Ms. Victoria Petrova, Head of Unit (HaDEA, Industry Unit). COMPASsCO2 Workshops COMPASsCO2 Stakeholders Workshops In order to interact with stakeholders to exchange knowledge, validate results and identify areas for collaboration, the first COMPASsCO2 stakeholders workshop was organized on 10 June 2021 via videoconferencing. The workshop had the purpose to introduce the project, discuss the main research activities conducted, and identify areas in which to cooperate with other projects, institutions or companies. The main focus areas for this workshop were: the use of concentrating solar technology and its integration in the Brayton cycle; evaluation of state-of-the-art materials that could withstand the extreme operating conditions; and research, development and testing of innovative materials that guarantee reliability and sustainability under harsh conditions. The Second Stakeholders Workshop of the COMPASsCO2 Project was held on 25 September 2023 in a hybrid format (Marktheidenfeld, Germany and online), at the occasion of the international conference on high temperature corrosion and oxidation. The workshop was organized around two main sessions, the first dealing with advanced materials for abrasive environments and the second one focusing on material behaviour in sCO2 environments. Representatives from the COMPASsCO2 consortium presented the preliminary results of their analysis and had the opportunity to interact with experts industry and academia to further advance on the work and validate the findings. The meeting saw the participation of about 60 participants. First Stakeholders Workshop Second Stakeholders Workshop COMPASsCO2 Final Workshop The COMPASsCO₂ Final Workshop took place in a hybrid format on 24 April 2025 – at CVR premises, in Husinec u Řeže, Czech Republic and online—bringing together leading experts to reflect on four years and a half of innovation in supercritical CO₂ (sCO₂) power systems. Under the theme "Back to the Future: A ForwardThinking Approach to Concentrating Solar Technologies", the workshop agenda (shown below) was structured in such a way to highlight the main innovations brought by the project: advancements in CST receiver technologies using new particle materials; design and testing of high-temperature alloys and coatings; realworld validation of materials and systems under extreme conditions; and final industrial design and business case for sCO₂ implementation. The afternoon technical tour offered participants a hands-on look at: sCO₂ autoclave & erosion test lab, sCO₂ loop & heat exchanger test setup, and material testing & hot cell labs. 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