Corrosion Mechanisms in Oxidizing, Reducing, and Alternating Combustion Gases in Refuse-Fired Boiler Environments

Abstract Corrosion has been observed in the lower furnace and superheaters of some refuse-fired boilers. This corrosion is associated with the presence of molten chloride salts on the boiler tube surface. During combustion of refuse large amounts of alkali chloride vapors can be released in the lower furnace of the boiler. These alkali chloride vapors can subsequently be condensed on the relatively cooler boiler tube surfaces. The most corrosive conditions in the refuse boiler correspond to the alkali chloride deposits, which can form molten salt mixtures on the tube surfaces in the lower furnace region. Information on the production and behavior of corrosive species, such as alkali chlorides, in refuse-fired boilers is essential if rapid corrosion is to be avoided. Rapid corrosion in molten chlorides is favored by oxidizing conditions and retarded by reducing conditions, with alternating flue gas conditions causing intermediate corrosion attack. The corrosion mechanism is believed to involve anodic dissolution of metal and its oxides into the molten salt. The composition of the molten chloride salt deposit will determine what alloys can be used for boiler tube material. Some chloride mixtures are aggressive toward only carbon steel, while others can corrode both carbon steel and stainless steel at nearly the same rates.