COMPONENTS’ AND MATERIALS’ PERFORMANCE FOR ADVANCED SOLAR SUPERCITICAL CO2 POWERPLANTS

Project Information

COMPASsCO2

Grant agreement ID: 958418

DOI

10.3030/958418

Project closed

EC signature date 2 October 2020

Start date 1 November 2020

End date 30 April 2025

Funded under

• INDUSTRIAL LEADERSHIP - Leadership in enabling and industrial technologies - Advanced manufacturing and processing

Total cost

€ 5 996 892,50

EU contribution

€ 5 996 892,50

Coordinated by

DEUTSCHES ZENTRUM FUR LUFT - UND RAUMFAHRT EV
Germany

Periodic Reporting for period 3 - COMPASsCO2 (COMPONENTS’ AND MATERIALS’ PERFORMANCE FOR ADVANCED SOLAR SUPERCITICAL CO2 POWERPLANTS)

Reporting period: 2023-11-01 to 2025-04-30

Summary of the context and overall objectives of the project

COMPASsCO2 addresses the combined challenges of developing high performance materials and components for extreme and varying conditions that are expected in future processes, improving their target performance for a long time, as the main scope of H2020’s topic LC-SPIRE-08-2020. Current concentrated solar power (CSP) plants have temperature limitations below 600 °C. A path to increase the efficiency is supercritical CO2 Brayton cycles with a CSP plant using solid particles above 900 °C. The conditions at the plants' interface, the particle/sCO2 heat exchanger (HX), are extreme in terms of temperature, pressure, abrasion, corrosion, erosion, oxidation and carburization. The objectives were to develop, test and demonstrate new materials for the solid particles and structural materials for the HX tubes, demonstrating its lifetime by measurement and modelling methods. The project developed and tested particles and coatings. Novel Cr-alloys were developed, as well as the successful application of an innovative low-cost and scalable Cr-Si coating approach on state-of-the-art Ni-Alloys. A particle/sCO2 HX was designed, manufactured and tested, validating the performance models. Lifetime of the materials and components was modelled and the business plan for the application was updated.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

sCO2 Brayton cycles selected for the highest efficiency. Solar plant and particle-sCO2 HEX designed, selection of particles and structural materials to withstand high temperature and pressure. Business plan updated with results of performance and costs of developed materials and components.
Characterization and durability testing of 10 different particles types conducted to evaluate optical and mechanical properties. Guideline and article published about measurement of optical properties (Innovation 1). Optical properties of proppants were degrading; consequently, a new particle was developed, achieving optimal composition for CST technologies (Innovation 2). Selection determined by solar absorptance stability, mechanical stress distribution and price. 4th generation of granulated particles selected for commercialization and named FerOx. Simulations reported in D2.4. 3 coating types deposited on 3rd and 4th gen particles (Innovation 6, 7, 16). 3 articles published. Testing for temperature and abrasion resistance included worst-case receiver condition (Innovation 17). All coatings improve solar absorptance; highest under thermal conditions by DFI, under abrasion by CIEMAT. 4 poster and 8 oral presentations delivered.
State-of-the-art Fe- and Ni-based materials underwent simulated environment testing up to 900 °C, providing a benchmark. Preliminary performance of bulk novel Cr-NiAl alloys, Cr-Cr3Si alloys and coatings investigated (D3.1&D3.2). Bulk Cr-NiAl alloys and Cr-Cr3Si coating selected for WP4; sample coupons delivered (D3.3&MS11). Modelling conducted to understand structure-property relations and improve ductility (D3.4). Innovative Cr-Cr3Si slurry coating technology developed, patent protected, onward exploitation planned.
Heat exchanger tubes tested and modelled in WP4; exposures in air and CO2, erosion and creep tests enabled lifetime predictions and ranking of structural materials. Surface fracture most likely to initiate due to particle impacts at oxide asperities. Cr-oxide scale growth on Ni-base alloys influenced by alloying additions such as Ti. Haynes 282 did not necessarily impart higher erosion resistance. Ceramic granulate properties and velocity affected erosion wear. Creep data < 10-6 s-1 satisfied requirement; atmosphere had very low impact. IN740 showed highest oxidation resistance. Cr-Si slurry coating protected base materials and improved oxidation resistance.
Long-term abrasion tests (836 h, 760 °C) indicated erosion less significant than oxide layer formation; nickel-based alloys suitable for heat exchanger applications, due to their creep resistance and the formation of uniform oxide layers.
Impact test (10 m/s, 675 °C) revealed extremely high abrasion for steel-like materials; SiC and Al2O3 demonstrated excellent resistance, suitable as protective layers.
Particle/sCO2 heat exchanger mockup tested with sCO2 at 15 MPa, outlet 634 °C, overall heat transfer coefficient measured 146 W/m2K; particle stagnation zones led to failure of electric particle heater, findings have direct implication for the further development of particle-based systems and electric heaters. Results will be presented at SolarPACES 2025.
Communication strategy implemented: visual identity, leaflet, website regularly updated; LinkedIn and X for real-time updates; 9 newsletter issues. Synergies with sister projects included three webinars and joint session at MSE2024. 2 Stakeholders Workshop and Final Workshop organized. 69 conference presentations, 14 scientific articles, 3 informative papers. 17 Key Exploitable Results identified. Data Management Plan developed Feb 2021, updated with 75 datasets, 10 publicly available.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

A conceptual design of a solar plant including a solar tower, sCO2 Brayton cycles and a particle-sCO2 HX was developed. The HX design provides an industrial-scale viable solution and knowledge of materials lifetime under extreme conditions.
FerOx particles exceed state-of-the-art proppants: similar cost, mechanical properties and energy density, but superior softening temperature and thermal stability. They are made with recycled refractory bricks and iron. Three coatings on FerOx reach solar absorptance up to 97 % (state-of-the-art about 85 %) and degradation up to 5 % (state-of-the-art 9-16 %).
2 peer-reviewed papers on Cr-NiAl ‘Cr-superalloys’ and 6 conference talks including TMS, keynote talks at MSE 2024 and Plansee Seminar 2025 were delivered. The Cr-Cr3Si coating was patented and published as 2 papers. UoB Experiment + VTT modelling was presented in EUROMAT2023 and will be published. A further paper on Cr-Cr3Si alloys was published. Environmental testing on bulk/coated materials will advance materials development for CSP.
SOTA materials were tested and their application range for the CSP plant with particles and sCO2 is being determined. Beyond the SOTA alloys, novel coatings and new alloys with enhanced properties are being tested and compared with the SOTA materials. These novel materials have potential to be commercialized for other high temperature applications, e.g. turbines, molten salts, and will be taken forward in onward R&D programmes.
Most SOTA alloys met erosion and creep resistance targets for the particle-sCO2 HX. Air creep data and exposure data in CO2 can evaluate materials for high temperature CO2 environments. Novel coatings and new alloys showed similar or improved behavior and potential to be commercialized for turbines, molten salts and onward research programmes.
A particle–sCO2 heat exchanger at 634 °C and 15 MPa was demonstrated, advancing the concept to TRL-5 and laying the foundation for compact, high-efficiency solar systems with enhanced heat transfer.
Given the limited long-duration data on particle erosion and oxidation at high temperatures, data of testing for 836 h up to 760 °C was delivered, offering insights for predictive models and reducing overengineering and costs.
Tests revealed particle stagnation zones that led to heater failure, providing essential design feedback for future systems and improving reliability and safety of high temperature thermal plants.

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