Sulfite removal from flue-gas desulfurization residues of coal-fired power plants: Oxidation experiments and kinetic parameters estimation

Abstract

Semi-dry flue-gas desulfurization (FGD) processes abate 99% of atmospheric emissions of sulfur dioxide from coal-fired power plants at the expense of producing daily tones of solid FGD residues containing sulfites, sulfates, carbonates and hydroxides of calcium and magnesium, besides fly-ashes. In this work, a fluidized-bed reactor pilot plant was used for experiments of dry-oxidation of FGD residues aiming at converting sulfites into sulfates in order to upgrade such residues for utilization as raw material to the cement industry. A two-dimensional design of experiments on the plane of feed air temperature and reactor time-on-stream was conducted in the pilot plant generating sulfite conversion data and transient reactor temperature profiles. These data were used for estimating the first-order kinetic parameters of sulfite conversion via non-linear regression following the Maximum Likelihood Principle. The optimized Arrhenius factor and Arrhenius activation energy obtained via the Nelder–Mead Flexible Simplex method were, respectively, 0.001 mol/kg.s.bar and 14146.5 J/mol. This kinetic model allows designing large-scale plants for treatment of semi-dry FGD residues in order to beneficiate it for utilization in the cement industry, avoiding the disposal and environmental costs of landfilling such residues.

Keywords

• Coal-fired power plants
• Flue-gas desulfurization
• FGD
• Flue-gas desulfurization residue
• Dry-oxidation
• Kinetic model