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.

A Tracer Study on sCO2 Corrosion with Multiple Oxygen-Bearing Impurities

“…The effects of impurities on high-temperature oxidation in sCO 2 and specifically the reaction mechanisms are still not well defined. The effect of O 2 (0.15 vol.%) or H 2 O (10 vol.%) additions to CO 2 (0.1 MPa) at 700 °C resulted in very similar mass changes than what was observed in pure CO 2 [27]. The thicknesses of the scales formed at 700 °C in air, CO 2 , or in CO 2 + H 2 O were also very close to one another.…”

Effect of pressure and impurities on oxidation in supercritical CO2

“…Considerable testing has been conducted at ambient pressure in CO 2 with and without H 2 O, O 2 and SO 2 additions to support a variety of technologies including fuel cells, oxy-combustion of coal and the direct-fired sCO 2 cycle. [28][29][30][31][32][33][34][35][36][37][38][39][40] In these experiments, the addition of H 2 O resulted in much faster oxidation rates, especially for Febase alloys. [29][30][31][32][33][38][39][40] The addition of O 2 showed both positive and negative effects as has the addition of SO 2 .…”

“…[28][29][30][31][32][33][34][35][36][37][38][39][40] In these experiments, the addition of H 2 O resulted in much faster oxidation rates, especially for Febase alloys. [29][30][31][32][33][38][39][40] The addition of O 2 showed both positive and negative effects as has the addition of SO 2 . [35][36][37]40] At high pressure, O 2 additions have shown slightly negative effects [19,23] or little effect.…”

Development of Creep-Resistant, Alumina-Forming Ferrous Alloys for High-Temperature Structural Use

“…The authors recently proposed a new alloy design with a base alloy composition of Fe-30Cr-3Al (wt.%) combined with minor alloy additions of Nb, Zr, Ti, Mo, W, Mn, Si, and C, which yields a "creep-resistant, high Cr containing FeCrAl alloys". The Cr content with ~30 wt.% was selected to improve ash-corrosion resistance in fire-side corrosive environments encountered in fossil-fired power plants [23]. The combined additions of Al and Nb were also found to promote both steam/water vapor oxidation resistance and ash-corrosion resistance [14,15].…”