Waterwall corrosion mechanisms in coal combustion environments

• Published in: Materials at high temperatures 2002-08, Vol.19 (3), p.127-137
• Main Authors: Nava-Paz, J C, Plumley, A L, Chow, O K, Chen, W
• Format: Article
• Language: English
• Subjects: Boilers; Carbon; Coal; Combustion; Deposition; Failure; Firing; Thermal conductivity
• ISSN: 0960-3409; 1878-6413
• DOI: 10.3184/096034002783640431

When coal-fired boilers are operating with substoichiometric firing to limit NOx formation in order to comply with emission regulations, the reducing environments formed locally in the firing zone or under deposits can result in sulfidation attack and premature failure of components. Carbon and low-alloy steels are the preferred materials for waterwall applications due to their good thermal conductivity, creep strength (up to 550°C) and relatively low cost. However, these materials, with at best low contents of Cr, are also the most susceptible to sulfidation attack. This paper presents the results of an extensive investigation to evaluate the effect of coal combustion characteristics, gas flow in the boiler, sulfidation potential of the environment, and the formation of deposits, on the kinetics of sulfidation in typical boiler materials. An interdisciplinary approach was adopted involving combustion analysis, corrosion studies and computational fluid dynamics along with information on operational boilers. The objective was to provide support for the low NOx retrofit program and to generate authoritative information for utility customers and also to develop a capability to predict potential combinations of coal and combustion conditions which could cause enhanced rates of attack.