Transformation of selenium during coal thermal conversion: Effects of atmosphere and inorganic content.

Study on selenium (Se) transformation during coal combustion will facilitate the development of emission–control technologies. A fixed–bed reactor was used to conduct pyrolysis and combustion experiments involving three types of coal at 600–1000 °C. In an inert atmosphere, the release ratios of Se increased slowly as temperature increased, varying between 56% and 74% for different coals at 1000 °C. All forms of Se in coal were thermally unstable and the conversion of Se in other forms into residual and organic–bound Se occurred. In an oxidizing atmosphere, the release ratios of Se differed significantly for different coals at low temperatures, but approached 100% at 1000 °C. Each form of Se in coal was released in different ratios. The water–soluble and ion–exchangeable Se, and carbonate– and oxide–bound Se were produced in the solid products. The oxidizing atmosphere was more conducive to the release of Se because the sulfide– and organic–bound Se was fully oxidized. Se could be converted into water–soluble and ion–exchangeable form and released less in Ca–rich coal. Sulfur (S) prohibited Ca from adsorbing Se by forming CaSO 4 , promoting the release of Se in S–rich coal. Unlabelled Image • Se transformations during pyrolysis and combustion of coals were investigated. • An oxidizing atmosphere facilitated the release of Se from the coal. • Se forms differ in stability and may convert to other form during thermal process. • The effect of inorganic contents in the coal on Se transformation was discussed. [ABSTRACT FROM AUTHOR]