Development of Fireside Corrosion Models for Advanced Combustion Systems

A comprehensive fireside corrosion project was undertaken to better understand the corrosion mechanisms operating on the lower furnace walls and superheaters in modern coal-fired utility boilers. Eight U.S. coals commonly burned in boilers have been selected to represent a wide range of coal chemistry. These coals will be burned in a pilot-scale combustion facility to closely simulate the actual conditions of staged combustion in utility boilers. During the combustion testing, gas and deposit samples will be collected and analyzed via in-furnace probing during each of the eight coal burns in the combustion facility at selected waterwall and superheater/reheater locations. Such efforts will allow better characterization of the realistic combustion conditions present in the boilers. Once the conditions are defined, a series of long-term laboratory corrosion tests, each for 1000 hours, will follow. These fireside corrosion tests will involve exposure of different alloys and weld overlays in a wide range of compositions to the laboratory conditions that simulate the environments measured in the combustion facility. As a result of the laboratory testing, a fireside corrosion database will be generated and used for the subsequent corrosion modeling. It is anticipated that results from the modeling work will produce two predictive equations, one for the corrosion rate of waterwalls in the lower furnace and the other for the superheaters/reheaters in the upper furnace. These equations may be used to estimate the service lives of boiler tubes as a function of several key variables, such as the sulfur, chlorine, alkali, alkaline, ash, and pyrite contents in coal, as well as the metal temperatures. Applications of these predictive equations are expected to be applicable to both the conventional and advanced combustion systems and not coal specific.