Lab- and pilot-scale wet scrubber study on the redox-mediated simultaneous removal of NOx and SO2 using a CaCO3-based slurry with KI as a redox catalyst

Abstract

This study presents a novel approach that integrates ozone-driven chemical oxidation to convert NO into soluble NO₂, followed by the simultaneous absorption of NO₂ and SO₂ into a CaCO₃-based slurry using the redox catalyst potassium iodide (KI). Using cyclic voltammetry, we demonstrate the redox properties of the I₂/2I^- couple, which facilitates NO₂ reduction into soluble NO₂^- and catalyst regeneration through sulfite (SO₃^2-)-driven reduction, thus establishing a closed catalytic cycle within the components of flue gas. In lab-scale wet-scrubbing tests, we explore the effect of various operational parameters (i.e., KI concentration, pH, and SO₂ concentration), with a 15 h stability test demonstrating >60% NO_x and >99% SO₂ removal efficiency when the pH is controlled between 7.5 and 8.5. A successful pilot-scale implementation conducted at an inlet flow rate of 1000 m³ h^-1 further confirmed the reproducibility of the proposed redox-catalytic cycle. Our study offers a cost-effective, sustainable, and scalable solution for effectively mitigating NO_x and SO₂ emissions at low temperatures.

Keywords: Nitrogen oxides; Ozone; Redox catalyst; Sulfur dioxide; Wet scrubbing.