Modeling Sulfite Oxidation Reactions in Co-Absorption of Nitrogen Oxides and Sulfur Oxides

Novel mechanisms for sulfite oxidation in a system with nitrogen dioxide (NO2(g)) and thiosulfate are proposed. The oxidation reaction is of particular interest as it drives the depletion of sulfite, which leads to economic challenges in a system designed for the coremoval of nitrogen oxides (NOx) and sulfur oxides (SOx). New reaction sets that capture sulfite radical chain oxidation by NO2 are formulated by integrating previously reported mechanisms and experimental observations. Two new mechanisms are presented with regard to sulfite oxidation by NO2. The sulfur radical reaction set describes the sequence of radicals that result in the rapid consumption of sulfite. This mechanism is simplified into a single global reaction, to allow integration into the process modeling software. For the system involving thiosulfate, two reaction sets are proposed, where the presence of polythionate intermediates is evaluated. Kinetic expressions are estimated by fitting the calculated and measured sulfite concentrations, where an error in the range of 1.07–2.41 mol/m3 is achieved. The sensitivity analysis indicates that NO2 absorption predictions are strongly affected by mass transfer parameters, whereas their impact on the liquid-phase is of low significance.