Fireside Corrosion of Superheater Materials in Oxyfuel Combustion

Oxyfuel combustion is considered as one of the most promising technologies to facilitate CO₂ capture from flue gases. The oxyfuel combustion characteristics differ from those in conventional air-fired combustion, because oxyfuel combustion process involves burning fuels in pure or nearly pure oxygen as opposed to air. The oxyfuel process affects e.g. combustion gas chemistry, deposit formation and chemistry with potentially increasing corrosion rates and reduced mechanical properties of the boiler components that are in contact with the combustion and flue gas environment.
Corrosion resistance of three conventional superheater tube materials 10CrMo9-10, X20CrMoV12-1 and AISI 347 as well as three thermal spray coatings (Inconel 625, Ni-20Cr and Ni-50Cr) on 10CrMo9-10 were evaluated under simulated oxyfuel combustion environments (3.6% O₂ – 60% CO₂ – 30% H₂O) at temperature of 580°C. Reference tests were performed at the same temperature in atmosphere typical those in conventional air-fired coal combustion (1.8% O₂ – 74.2% N₂ – 16% CO₂ – 8% H₂O). Test durations were 168h, 500h and 1000h. Corrosion resistance was evaluated with weight loss measurements and metallographic examinations. Results are presented and future research needs are discussed.