Materials problems in fluidized-bed combustion systems: review of the information on gas turbine materials in coal combustion environments

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Abstract
This report condenses into a single document the available information related to the performance of gas turbine materials operated in the effluent from the combustion of coal. The information summarized originated from three sources: work performed in the period 1940-1970 to establish the potential for a direct coal-fired gas turbine, actual operating experience of gas turbines in particulate-laden environments, and recent efforts to evaluate gas turbines for firing with a pressurized fluidized-bed combustor. Results of these studies show clearly that the potential for erosion, corrosion, and deposition exists in gas turbines operated on coal to the extent that the performance and endurance may be substantially reduced. The choice of gas turbine materials strongly influenced the lifetimes of components exposed to coal-derived environments. Bare alloys, such as IN-738, U-700, and X-40, exposed to the hot gas path degraded more rapidly than MCrAlY coatings or claddings which produce protective layers of alumina or chromia. Extremely hard coatings containing high concentration of carbides in a ductile matrix were particularly resistant to erosion. The interaction between corrosion and erosion appears to be synergistic; however, the exact relationships between these processes are still unknown.

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