The role of NO2-induced sulfite oxidation in process modeling of nitrogen oxides and sulfur oxides absorption

Simultaneous removal of NO x and SO x in a wet scrubber is simulated in a process modeling software with the addition of a proposed reaction, aiming to capture the rapid consumption of S(IV) ions (SO 3 2- and HSO 3 - ). Previous work has shown that the presence of NO 2 drives the oxidation of S(IV) ions due to the formation of radical species, with reported oxidation rates that vary between authors. The complexity of simulating the highly reactive and complex radicals is addressed through a newly proposed mechanism which omits radical species, allowing integration into process simulation. The kinetic coefficients estimation is performed by fitting modeling results to a range of experimental data at varied operational conditions and two process configurations. A good agreement in both NO 2 absorption and S(IV) oxidation is obtained in the open-loop configuration, with slight deviations in S(IV) oxidation observed at lower S(IV) concentration. Sensitivity analysis shows that S(IV) oxidation is mainly governed by nitrogen-sulfur reactions, while NO 2 absorption is also influenced by mass-transfer parameters such as residence time and interfacial area. Applying the reaction to the closed-loop system requires an increase in the kinetic coefficient in order to obtain a good fit in the NO 2 absorption level, showing that the proposed reaction is specific to each evaluated set-up. S(IV) oxidation in the absorber sump is investigated, where the significant effect of NO 2 concentration is identified.