Simultaneous Removal of SO₂ and Hg⁰ by Composite Oxidant NaClO/NaClO₂ in a Packed Tower

Abstract

Based on the implementation of the global Minamata Convention, developing an efficient and economical technology for mercury reduction in coal-fired flue gas becomes a hotspot in the field of air pollution control. The composite oxidant NaClO/NaClO 2 combined with limestone was used in the simultaneous removal of SO 2 and Hg 0 in this study, and the three-factor and four-level orthogonal experiments were performed in a packed tower. The influential sequence of various factors on SO 2 and Hg 0 removals was investigated through range analysis of the orthogonal experiments. Results showed that factors affecting desulfurization was C > A > B (liquid–gas ratio > oxidant concentration ratio > initial pH of absorption liquid), while factors affecting Hg 0 removal was A > C > B (oxidant concentration ratio > liquid–gas ratio > initial pH of absorption liquid). Optimum conditions of simultaneous desulfurization and demercuration by NaClO/NaClO 2 were A4B1C4; that is, the oxidant concentration ratio was 10/4 (mmol/L:mmol/L), the initial pH was 5, and the liquid–gas ratio was 18 (L/m 3 ). The simultaneous removal efficiencies of SO 2 and Hg 0 reached 99.5 and 85.4% under these optimum conditions, respectively. Analysis of the characteristics of the solid products showed that the main products of the wet oxidation were CaSO 4 and CaSO 3 . Analysis of the existing form of oxidized mercury showed that 23% of mercury was in the gypsum, while 77% was in the supernatant. Results of this research would provide a practical reference for promoting the simultaneous removal of SO 2 and Hg 0 by NaClO/NaClO 2 with limestone in industrial application.

Metal-Based Ionic Liquids in Oxidative Desulfurization: A Critical Review

“…Wet flue-gas desulfurization catalyzed by metal ions with strong oxidation ability to convert S­(IV) to S­(VI) is one of the most important approaches for SO 2 removal and H 2 SO 4 /CaSO 4 ·2H 2 O recovery. ,, However, this process is usually carried out in an aqueous homogeneous phase, and it is difficult to separate the desulfurization product and reuse the catalysts.…”