Effect of oxy‐firing on corrosion rates at 600–650 °C

Abstract

Because of higher CO2, and possibly H2O and SO2, levels in the boiler, there are concerns about increased corrosion rates after retrofitting current coal fired boilers from air‐firing to oxy‐firing to assist in CO2 capture. The oxidation behavior of a combination of commercial and model alloys were investigated both with and without the presence of synthetic coal ash at 600 and 650 °C. At 600 °C, a CO2–H2O environment showed the most rapid oxidation rate for Fe‐based alloys with <20% Cr and varying the CO2 content or adding a 0.15% O2 buffer had little effect on the mass change. However, at 650 °C, the O2‐buffered CO2–H2O environment showed a similar rate of oxidation as 100% H2O, again requiring more than 20% Cr for a thin protective Cr‐rich oxide to form. With synthetic coal ash, increasing the CO2, H2O, and/or SO2 levels in the gas phase tended to show a lower oxide thickness after a 500 h exposure at 600 °C, compared to the base line air‐firing condition. At 650 °C, no systematic increase in the reaction rate was observed when switching from the air firing to the oxy‐firing gas. These simulations suggest that higher CO2 contents with oxy‐firing do not increase the rate of oxidation.