Compatibility of Steels in Supercritical CO_2 at 450°-650°C

摘要

Supercritical CO_2 (sCO_2) power cycles, particularly direct-fired cycles, have the possibility of revolutionizing clean fossil energy. However, in the lower temperature sections of the cycle, lower cost steels are needed in order to lower the cost of the sCO_2 technology. Representative 9 and 12%Cr steels and conventional and advanced austenitic steels are being evaluated at 450-650°Cusing mass change, bulk carbon (C) content and room temperature tensile properties to determine the maximum use temperatures for both direct- and indirect-fired sCO_2 cycles. After 1000 h exposures in research grade (RG) sCO_2 at 300 bar and RG sCO_2 with 1% O_2 and 0.1% H_2O additions, the results suggest that increasing the Cr content from 9 to 12% yielded no signficant benefit under these conditions but the higher Cr and Ni contents in S31025 provided better compatibility in RG sCO_2 at 650°Cbut limited benefit at 550°Cwith impurities. For S31609, the formation of Fe-rich oxide after exposure to RG sCO_2 at 650°Cresulted in both an increase in the bulk C content and a large drop in room temperature ductility. The evidence suggests thin, protective oxides prevented C ingress in these conditions.