Effect of organic additives on NO<sub>2</sub> removal in the simultaneous absorption of SO<sub>2</sub> and NO<sub>2</sub> into limestone slurry

Abstract

When SO<sub>2</sub> and NO<sub>2</sub> are simultaneously absorbed into limestone slurry, the SO<sub>3</sub><sup>2-</sup> (including HSO3 -) ions formed by the hydrolysis of SO<sub>2</sub> enhance the absorption rate of NO<sub>2</sub>. However, NO<sub>2</sub> absorption decreases due to the oxidation of SO<sub>3</sub><sup>2-</sup> in the presence of O<sub>2</sub>. To address this issue, simultaneous absorption was performed by adding organic additives: formic, acetic, propionic acid, monoethanolamine (MEA), diethanolamine (DEA), and triethanolamine (TEA). These limestone slurries were denoted FS, AS, PS, MS, DS, and TS, respectively. As the acidity of the organic acid increases, SO<sub>3</sub><sup>2-</sup> oxidation inhibition also increases. Accordingly, the denitrification rate of the slurries with added organic acid was in the order of PS < AS < FS. SO<sub>3</sub><sup>2-</sup> oxidation inhibition by the ethanolamine additives increased with the number of 2-hydroxyethyl. The denitrification rate within 50 min of reaction was in the order of MS < TS < DS, which is attributed to the basicity and SO<sub>3</sub><sup>2-</sup> oxidation inhibition by ethanolamine. The denitrification rate after 50 min of the reaction was in the order of MS < DS < TS, which is presumed to be the result of SO<sub>3</sub><sup>2-</sup> oxidation inhibition and degradation due to the CO<sub>2</sub> absorption rate.