Fate of selenium in coal combustion: Volatilization and speciation in the flue gas

In light of Title I of the Clean Air Act Amendments of 1990, selenium will most probably be considered for regulation in the electric power industry. This has generated interest for removing this element from fossil-fired flu e gas. This study deals with coal combustion: selenium volatilization and i ts speciation in the cooled flue gas were investigated to better understand its chemical behavior to validate the thermodynamic approach to such compl ex systems and to begin developing emission control strategies. Se volatili ty is influenced by several factors such as temperature, residence time, fu el type, particle size, and Se speciation of the fuels, as well as the form s of the Se in the spiked coal/coke. Spiked coke and coal samples were burn ed in a thermobalance, and atomic Se and its dioxide were identified in the cooled combustion flue gas by X-ray photoelectron spectroscopy (XPS). A th ermodynamic calculation was applied to a complex system including 54 elemen ts and 3200 species that describes the coal combustion. Several theoretical predictions concerning Se behavior, such as its speciation in flue gas, ag reed well with experiments, which supports using thermodynamics for predict ing trace element chemistry in combustion systems.