Predictive Kinetic Modeling and Experimental Analysis of Sulfite and Thiosulfate Consumption in NO 2 Absorption for Flue Gas Cleaning

Additive consumption during NO x removal via NO 2 absorption into aqueous solutions remains a critical challenge for sustainable flue gas cleaning and minimizing process waste. While sulfite additives are widely used to enhance NO 2 absorption rates, their effectiveness is severely compromised under aerobic conditions due to rapid oxidation of sulfite to sulfate via a NO 2 ‐induced radical chain mechanism. This not only reduces the process efficiency but also leads to excessive additive consumption and waste formation. Thiosulfate, acting as a radical scavenger, offers strategies to mitigate these undesired side reactions by interrupting the radical chain mechanism. In the present study, sulfite and thiosulfate consumption were systematically investigated under aerobic and anaerobic conditions in a laboratory‐scale NO 2 scrubber for NO 2 concentrations ranging from 50 to 200 ppm and additive concentrations between 0 and 10 mM sulfite and 0–3 mM thiosulfate. The novelty of this work lies in the development of a comprehensive kinetic model that predicts absorption efficiency as well as additive consumption across varying operating conditions. Unlike previous empirical approaches, this model provides mechanistic insights into the interplay between absorption reactions and side reactions, enabling good estimations of additive requirements and their effective contribution to the NO 2 removal process. The strong agreement between modeled and experimental data highlights its robustness and applicability. This modeling framework represents a step toward optimizing additive usage in flue gas cleaning, reducing chemical waste, and improving the sustainability of industrial flue gas cleaning processes.