Multi-air-pollutant removal by using an integrated system: Key parameters assessment and reaction mechanism

How to cost-efficiently and cooperatively remove SO₂, NO and Hg⁰ in flue gas is a hot topic in the field of air pollution control. This work developed an integrated system that consists of a dual-absorption system and a vapor oxidation system, in which Na₂CO₃ and H₂O₂/Na₂S₂O₈ were used as the absorbent and oxidant. The results indicated that the efficiencies of SO₂ removal and NO conversion reached 99.5% and 93% respectively. Rising the vaporization temperature and decreasing the pH of H₂O₂/Na₂S₂O₈ could facilitate the NO conversion. The spent Na₂CO₃ after desulfurization was demonstrated to be a good absorbent for NO₂ removal. The best conditions of pH and temperatures for the dual-absorber were determined as 10/8 and 60/60 °C, respectively. The presence of 1000 mg/m³ SO₂ and 300 mg/m³ NO favored the Hg⁰ removal. TMT-15, an organic sulfur compound, was demonstrated to be useful in retaining Hg²⁺, with an efficiency of 92%. According to the analyses of electron spin resonance (ESR), ion chromatography (IC), atom fluorescence spectrometry (AFS) and X-ray photoelectron spectroscopy (XPS), SO₄^- and HO were proved to be the key radicals, and the existing forms of N- and Hg- species in the product were identified as NaNO₂/NaNO₃ and HgCl₂.