Further Understanding of Furnace Wall Corrosion in Coal-Fired Boilers

Abstract

A comprehensive low-NOx corrosion study consisting of pilot-scale combustion testing and laboratory retort exposure was performed. From the pilot-scale testing, the gas and deposit compositions in the lower furnace of utility boilers burning eight U.S. coals with a wide range of sulfur and chlorine contents were determined. These combustion conditions were then closely reproduced in a series of 1,000 h laboratory corrosion tests to evaluate the materials performance of different furnace-wall alloys and weld overlays at 399, 454, and 510°C (750, 850, and 950°F). Results of the laboratory study indicate that a typical dual-layered scale was formed on the metal surface from simultaneous oxidation/sulfidation due to the presence of sulfur in coal. A new corrosion mechanism is proposed here as “active sulfidation” to account for the accelerated corrosion attack on furnace walls resulting from the presence of chlorine in coal. The mechanism involves the conversion of iron sulfide (FeS) in the corrosion scale to...