Fireside Corrosion and Carburization of Superheater Materials in Oxyfuel Combustion

摘要

Oxyfuel combustion is considered as one of the most promising technologies to facilitate CO_2 capture from flue gases. In oxy-fuel combustion, the fuel is burned in a mixture of oxygen and recirculated flue gas. Flue gas recirculation increases the levels of fireside CO_2, SO_2, Cl and moisture, and thus promotes fouling and corrosion. It has been suggested that oxide scales developing in O_2/CO_2/H_2O atmospheres are not well protective and internal carburization may occur. In this study three boiler tube steels X20CrMoV11-1, UNS S34710 and UNS S31042 were subjected to oxidation/corrosion testing at 600 and 650°C under simulated oxyfuel fired atmospheres (60% CO_2-30% H_2O-4% O_2-Ar) with and without CaCO_3-CaSO_4 deposit up to 1000 h. Reference tests were performed at the same temperatures in an atmosphere simulating conventional air-fired coal combustion. The results at 600 °C and 650 °C showed that the corrosion resistance increased when the chromium content increased but that without added impurities like sulfur and chlorides, the simulated oxyfuel conditions did not result in more severe corrosion than under air firing environment. 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-surface interface. With extended exposure time, the oxide scale properties may change to enable metal carburization. The exposure with CaCO_3-CaSO_4 deposit at 650°C resulted in corrosion of all tested alloys and clear carburization of steels X20CrMoV11-1 and UNS S34710.