Molecular scale studies that inform trace element sulfide evaporation and atomization behavior during coal combustion

Abstract

Understanding the chemical mechanisms of trace element (TE) evolution is essential for accurate modeling of coal combustion. A novel graphite furnace atomic absorption spectrometry (GFAAS) method was used to simulate the evaporation and atomization behavior of TE sulfides (arsenic, antimony and selenium) in the two distinct microenvironments that mineral inclusions and exclusions experience during the onset of coal combustion. Additional insights were obtained using thermogravimetric analysis-differential scanning calorimetry (TGA-DSC) Potassium polysulfide was used as an additive to water to facilitate the dissolution of all three TE sulfides. TE sulfides in inclusions were studied by adding the test mixture to a graphite tube in a reducing (anaerobic) micro-environment whereas the TE evolution in excluded sulfide minerals was studied by blocking the graphite tube surface with an inert ZrO 2 or WO 3 coating. Arsenic sulfide, As 2 S 3 , exhibits a lower Arrhenius activation energy of atomization, E a , than that of the corresponding oxide in both mineral inclusions and exclusions, apparently because of the availability of a specific facile path to atomization. A higher E a was observed for antimony sulfide, Sb 2 S 3 , than that of the corresponding oxide from inclusions and is most likely due to its strong binding affinity to the carbon tube surface. The low GFAAS signal of selenium sulfide suggests the formation of molecular clusters, e.g., Se 2 , Se 8 or similar mixed clusters with sulfur atoms prior to vaporization, an effect not observed for selenium oxide evaporation. For all three

Thermal Behavior of Coal Used in Rotary Kiln and Its Combustion Intensification

“…The thermal degradation kinetics of the three coals was calculated by the Freeman-Carroll method. Combustion kinetics of coal can be revealed by Equation (1) [20,21].…”