Abstract
Concentrating solar power plant designers are interested in supercritical CO2 (sCO2) for the power block to achieve > 50% electrical efficiency at > 700 °C. The goal of this project was to develop a long-term (> 100 kh) lifetime model for sCO2 compatibility using 10–15 kh laboratory exposures. Three Ni-based alloys (625, 282 and 740H) and an advanced austenitic stainless steel were evaluated in long-term exposures at 700–800 °C using 500-h cycles in laboratory air, 0.1 MPa industrial grade (IG) CO2 and 30 MPa supercritical IG CO2 and using 10-h cycles in 0.1 MPa IG CO2 and O2. Mass change data and quantification of the oxide scale thickness and depth of internal attack after 1000–10,000 h exposures at 750 °C indicate that these materials are compatible with the sCO2 environments with modeling used to predict long-term behavior. Comparison of the 0.1 and 30 MPa 500-h cycle results did not show a significant effect of pressure on the reaction, and no significant internal carburization was observed under these conditions, even for the stainless steel, suggesting that chromia scales may be better C diffusion barriers than expected. For the Ni-based alloys, thermal cycling to simulate the solar duty cycle did not result in scale spallation after 15 kh in 10-h cycles or 4 kh in 1-h cycles at 750 °C. However, the stainless steel specimens formed an Fe-rich oxide after ~ 1500-h cumulative exposure time in both 1- and 10-h cycles.
| Original language | English |
|---|---|
| Pages (from-to) | 505-526 |
| Number of pages | 22 |
| Journal | Oxidation of Metals |
| Volume | 94 |
| Issue number | 5-6 |
| DOIs | |
| State | Published - Dec 2020 |
Funding
The authors would like to thank M. Howell, M. Stephens, G. Garner, T. M. Lowe and T. Jordan for assistance with the experimental work at ORNL. M. Romedenne and K. A. Kane at ORNL provided helpful comments on the manuscript. This research was funded by the SunShot Initiative under the US Department of Energy’s Office of Energy Efficiency and Renewable Energy, Solar Energy Technology Program: SuNLaMP award number DE-EE0001556. Special thanks to the Project partners on the team, Brayton Energy, LLC and alloy providers, Haynes International (V. Deodeshmukh), Special Metals (S. Coryell, J. deBarbadillo, B. Baker) and Sandvik (K. Day) and the helpful input and guidance of the DOE SETO Project monitors (L. Irwin and M. Bauer). The authors would like to thank M. Howell, M. Stephens, G. Garner, T. M. Lowe and T. Jordan for assistance with the experimental work at ORNL. M. Romedenne and K. A. Kane at ORNL provided helpful comments on the manuscript. This research was funded by the SunShot Initiative under the US Department of Energy’s Office of Energy Efficiency and Renewable Energy, Solar Energy Technology Program: SuNLaMP award number DE-EE0001556. Special thanks to the Project partners on the team, Brayton Energy, LLC and alloy providers, Haynes International (V. Deodeshmukh), Special Metals (S. Coryell, J. deBarbadillo, B. Baker) and Sandvik (K. Day) and the helpful input and guidance of the DOE SETO Project monitors (L. Irwin and M. Bauer). Regarding the effect of IG CO used in these experiments, companion experiments were conducted in 0.1 and 30 MPa research grade (RG) CO with < 5 ppm HO and O [] (funded by the DOE Office of Fossil Energy). No significant effect on reaction rates or reaction products was observed between RG and IG CO. A 2500-h experiment at 30 MPa with controlled impurity levels of 50 ppm HO and 50 ppm O also showed no significant change in rates or reaction products []. Fossil energy research to support the direct-fired, Allam cycle [, ] has shown an increase in the reaction rates when 1%O and 0.25%HO are added to 30 MPa RG CO []. 2 2 2 2 2 2 2 2 2 2
Keywords
- Lifetime model
- Supercritical carbon dioxide
- Thermal cycling
