Investigation on the removal of NO from marine exhaust gas using the Na₂S₂O₈-urea redox system in seawater carrier

Abstract

The sodium persulfate (Na₂S₂O₈)-urea system has been proven to be an excellent scrubbing solution for the wet removal of NO. Commonly, seawater is used as a wet carrier in marine applications. To further explore the feasibility of marine denitrification using Na₂S₂O₈-urea system, this study proposed the Na₂S₂O₈-urea-seawater composite redox system for NO removal from the marine exhaust gas. The effects of seawater carrier, reaction temperature, Na₂S₂O₈ concentration, urea concentration, pH value, and NO concentration on NO removal were investigated. Additionally, the NO₃⁻ concentration in the solution was measured. Results showed that the lowest normalized NO concentration was 0.099, with the corresponding mass of NO absorbed per unit volume of solution reaching 0.108 g·L⁻¹. The addition of seawater carrier and incremental reaction temperature, Na₂S₂O₈, and urea concentration promoted the NO removal performance. When the pH value increased within the range of 4–7, the NO removal performance decreased. The NO removal performance increased as the pH value further increased to 8, but decreased again when the pH value increased to 11. An increase in NO concentration was detrimental to NO removal. The Cl⁻, HCO₃⁻, and CO₃²⁻ in seawater could augment the total concentration of active free radicals to improve denitrification performance.

Graphical abstract

Keywords

marine diesel exhaust gas / denitrification / wet scrubbing / redox / seawater carrier

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