Fireside Corrosion and Carburization of Superheater Materials in Simulated Oxyfuel Combustion Conditions

Oxyfuel combustion is considered as one of the most promising technologies to facilitate CO₂ capture from flue gases. In oxyfuel combustion, the fuel is burned in a mixture of oxygen and recirculated flue gas. Flue gas recirculation increases the levels of fireside CO₂, SO₂, Cl and moisture, and thus promotes fouling and corrosion. In this paper the corrosion performance of two superheater austenitic stainless steels (UNS S34710 and S31035) and one Ni base alloy (UNS N06617) has been determined in laboratory tests under simulated oxyfuel conditions with and without a synthetic carbonate based deposits (CaCO₃ - 15 wt% CaSO₄, CaCO₃ - 14wt% CaSO₄ - 1 KCl) at 650 and 720°C up to 1000 hours. No carburization of the metal substrate was observed after exposure to simulated oxyfuel gas atmospheres without deposit, although some carbon enrichment was detected near the oxide metal interface. At 720°C a very thin oxide formed on all alloy surfaces while the weight changes were negative. This negative weight change observed is due to chromium evaporation in the moist testing condition. At the presence of deposits, corrosion accelerated and considerable metal loss of austenitic alloys was observed at 720°C. In addition, clear carburization of austenitic steel UNS S34710 occurred.