Direct-fired or open supercritical CO2 (sCO2) cycles are expected to have impurities that may greatly alter the compatibility of structural alloys in these environments. However, there are no available laboratory facilities to simulate these environments at operating conditions of 750°C and >100 bar. As an initial assessment of the effects of H2O and SO2 on oxidation in a CO2 environment, 500 h experiments were conducted at 1 and 25 bar at 700° and 800°C in CO2, CO2+10%H2O and
CO2+10%H2O+0.1%SO2. Representative structural alloys S30409, N07230, N07208 and superalloy
N07247 were exposed and the reaction products characterized after each exposure. The Ni-based alloys generally formed thin protective oxides at both pressures and only minor changes were observed with the addition of SO2 and/or H2O. As expected, the Fe-based S30409 showed more attack, especially at 800°C. However, at 25 bar the attack was reduced at 800°C compared to the breakaway oxidation at 1 bar. For the addition of SO2 at 800°C, a more protective oxide formed at 1 bar but a thick, duplex Fe-rich oxide formed at 25 bar.
Keywords: carbon dioxide, water vapor, SO2, impurities