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

Because of higher CO 2 , and possibly H 2 O and SO 2 , 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 CO 2 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 CO 2 –H 2 O environment showed the most rapid oxidation rate for Fe‐based alloys with <20% Cr and varying the CO 2 content or adding a 0.15% O 2 buffer had little effect on the mass change. However, at 650 °C, the O 2 ‐buffered CO 2 –H 2 O environment showed a similar rate of oxidation as 100% H 2 O, again requiring more than 20% Cr for a thin protective Cr‐rich oxide to form. With synthetic coal ash, increasing the CO 2 , H 2 O, and/or SO 2 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 CO 2 contents with oxy‐firing do not increase the rate of oxidation.