High-Temperature Corrosion Properties of Boiler Steels under a Simulated High-Chlorine Coal-Firing Atmosphere

High-temperature corrosion of the superheater and reheater tubes in utility boilers frequently occurs upon firing high-chlorine coal, which severely impacts the safety of the boiler operation. In this work, the corrosion mechanism of several commonly used boiler steels, including T91, 12Cr1MoVG, and TP347H, was investigated. First, the types and amounts of the main corrosive elements in the flue gas and the heating surface deposits from high- and low-chlorine coals were predicted with the aid of thermodynamic equilibrium modeling. The main corrosive elements that vaporized and subsequently condensed from the flue gas were determined to be Na, Cl, and S. Varying the wall temperature of the heating surface did not dramatically change the forms of these elements but slightly influenced their amounts. Second, lab-scale experiments were conducted in a tube furnace to estimate the degree of corrosion of various boiler steels under simulated conditions upon firing high- and low-chlorine coals. A sophisticated wall temperature control method was employed to account for the influence of different heating tube surface temperatures (560 and 610 °C) on corrosion at the same simulated flue gas temperature (950 °C) around the tube. The results show that more severe material degradation is caused by firing high-chlorine coal together with a higher tube wall temperature and the resistance to corrosion was highest for the austenitic steel TP347H, which had the highest chromium and nickel contents.