Temperature-Dependence of Corrosion of Ni-Based Superalloys in Hot CO2-Rich Gases Containing SO2 Impurities

摘要

Future power plants will require Ni-based superalloys resistant to high-temperature corrosion in CO2-rich environments containing impurities. In this work, several commercially available Ni-based alloys (617, 230, 625, 263, 740H) were exposed at 600 degrees C, 650 degrees C, 750 degrees C and 1 atm to 95% CO2, 4% H2O, 1% O-2 without/with 0.1% SO2 to simulate compositions expected in a direct-fired supercritical CO2 power cycle. The results indicate no effect of SO2 at 750 degrees C, a small negative effect at 650 degrees C, and a large negative effect at 600 degrees C. Alloys exposed at the higher temperatures (650-750 degrees C) formed thin Cr-rich oxide scales, whereas the lowest temperature (600 degrees C) resulted in thicker scales consisting of non-protective oxides and sulfates. Thermodynamic analysis indicates this increased corrosion is associated with a transition in the stable compounds in contact with the gas. Understanding the factors that affect this transition will aid in the selection or design of alloys for future CO2-based power systems.