Abstract
The most common commercial process for SO2 removal from flue gas is the wet limestone flue gas desulfurization process, in which sulfite oxidation represents an important limiting phenomenon. A detailed knowledge of the oxidation process is important to determine the dewatering properties of the sludge produced, and a good understanding of the oxidation kinetics is also useful for the development of computer codes aimed at modeling the whole flue gas desulfurization process. Sulfite oxidation was studied both in homogeneous conditions, obtained by contacting a sulfite solution with an oxygen saturated solution, and in heterogeneous conditions, obtained by contacting a sulfurous solution with an oxygen containing gas phase. As far as the bisulfite oxidation reaction in heterogeneous conditions is concerned, a previous experimental study by the same research group in absolute catalyst free conditions found a kinetic equation for calcium bisulfite oxidation which is of zero order in oxygen and three halves in HSO3- ions. The reaction has then been carried out in the presence of other catalysts, namely manganese and ferrous ions, into a laboratory-scale well-mixed reactor. Experimental results have shown that, when catalyst concentration increases, three different reaction regimes (slow kinetic, slow diffusional and fastreaction regime) can be detected. This paper proposes a numerical model to describe the interaction between oxygen absorption and oxidation reaction, in which an in-parallel kinetic equation is used to describe the slow kinetic reaction results, according to which the overall reaction rate can be calculated as the sum of the uncatalyzed and catalyzed reaction rate, also taking into account that the oxidation kinetics are zero order in oxygen. Moreover, this paper shows how the model is capable of describing the experimental results obtained by this research group, as far as the manganese catalyzed bisulfite oxidation rate is concerned.
