The Effect of Impurities on Supercritical CO₂ Compatibility of Structural Alloys Free

In both direct- and indirect-fired supercritical CO₂ (sCO₂) cycles, there is considerable interest in increasing the size and efficiency of such systems, perhaps by increasing the peak temperature to >700°C. However, relatively little experimental data are available under these conditions with pressures of 200-300 bar. Furthermore, impurities such as O₂ and H₂O in the CO₂ may greatly alter the compatibility of structural alloys in these environments. While an experimental rig is being constructed that can measure and control the impurity levels in sCO₂ at 200-300 bar, initial 1 bar experiments at 700°-800°C for 500 h have been conducted in high-purity and industrial grade CO₂, CO₂+0.15O₂ and CO₂+10%H₂O and compared to exposures in dry air and 200 bar sCO₂. These results, focusing on Fe- and Ni-base structural alloys and commercial chromia- and alumina-forming alloys, indicate that modifications in the environment did not strongly affect the reaction products at 700°-800°C.