Mass transfer and kinetics study on the sulfite forced oxidation with manganese ion catalyst

Abstract

Wet limestone scrubbing is the most common flue gas desulfurization process (FGD) for control of sulfur dioxide emissions from the combustion of fossil fuels. Forced oxidation, which controls the overall reaction of the sulfur dioxide absorption, is the key path of the process. Manganese which comes from the coal is one of the catalysts during the forced oxidation process. In the present work, the two-film theory was used to analyze the sulfite forced oxidation reaction with an image boundary recognition technique, and the oxidation rate was experimentally studied by contacting pure oxygen with a sodium sulfite solution. There was a critical sulfite concentration 0.328 mol/L without catalyst or at a constant catalyst concentration value. The kinetics study focused on the active energy of the reaction and the reaction constant k; furthermore, we obtained the order with respect to the sulfite and Mn²⁺ concentrations. When the Mn²⁺ catalyst concentration was kept unchanged, the sulfite oxidation reaction rate was controlled by dual film and the reaction kinetics was first order with respect to sulfite while SO ²⁻₃ concentration was below 0.328 mol/L; the sulfite oxidation reaction rate was controlled by gas film only and the reaction kinetics was zero order with respect to sulfite while SO ²⁻₃ concentration over 0.328 mol/L. When SO ²⁻₃ concentration was kept unchanged, the sulfite oxidation reaction rate depended on gas-liquid mass transfer and the reaction kinetics was different in various stages with respect to Mn²⁺ concentrations.