Model of oxygen absorption into calcium sulfite solutions

Abstract

Wet limestone scrubbing is the most common flue gas desulfurization process, and in this process sulfite oxidation plays a major role determining the dewatering properties of the sludge produced and leading to the production of gypsum of high quality. A literature analysis showed that the results obtained for sulfite oxidation under homogeneous conditions are relatively easily interpreted, while the results relative to heterogeneous reaction conditions (i.e. conditions in which gaseous oxygen and a sulfurous solution are brought in contact) are much more difficult to interpret, owing to the interaction between mass transfer and chemical reaction. In this work a model is proposed to describe the interaction between oxygen absorption and the oxidation reaction under heterogeneous conditions, which takes into account the peculiar characteristics of absorption with zero order reaction. A kinetic equation of order zero in dissolved O2, 3/2 in HSO3− and 3/2 in the catalyst concentration was used to match experimental results presented in the literature and model results. Integration of the model equations led to evaluation of the oxygen absorption rate as a function of the catalyst concentration together with the concentration profiles in the liquid film for the different species.