Chemical Aspects of Deposition/Corrosion From Coal-Water Fuels Under Gas Turbine Conditions

A staged, subscale turbine combustor based on a promising rich-quench-lean combustion approach to reduce NO_x emissions was used to evaluate deposition, erosion, and corrosion (DEC) from coal-water fuels (CWF). This combustor was operated with three CWF at conditions of a recuperated turbine. Specimens were exposed in two test sections at temperature conditions of the first stator vanes and first rotor blades of the recuperated turbine. The resulting deposits were chemically analyzed. Deposit-covered segments of specimens were placed in a furnace to extend their exposure to the potentially corrosive deposits. The deposits produced at higher temperature first stator conditions differed significantly from those produced at lower temperature first rotor conditions. The rates of formation of the higher temperature deposits were high and the deposit chemistries were similar to the coal ash chemistry. The rates of formation of the lower temperature deposits were one to two orders of magnitude less and deposit chemistries were not the same as the coal ash chemistry. Some corrosion of a CoCrAlY coating was detected after a few hours of exposure in the DEC tests. Corrosion penetration up to one-half of the coating thickness was observed after an additional 460 h furnace exposure. Much more testing is needed to explore whether the deposition and corrosion produced by the fuels evaluated are typical of this fuel form and to assess benefits of alternate turbine protection measures.