Dry process for SO₂ and NOx removal via gas-to-particle conversion with ozone and ammonia injection

Because of the stability of its production and cost-effectiveness, coal is expected to be a primary energy source in near future. However, SO₂ and NOx emissions from the coal combustion have been considered a serious environmental issue in the last few decades; they react with water vapor and ammonia (NH₃) in the atmosphere to form secondary aerosols. In this study, ozone (O₃) was injected to oxidize NO into NO₂. Thereafter, NH₃ was injected to convert SO₂ into (NH₄)₂SO₃ particles, which further reacted with NO₂ to produce N₂ and (NH₄)₂SO₄ particles. These reaction mechanisms were discussed employing different chemical analyses of the products. Moreover, the size of the product particles was analyzed by online particle size analysis and the scanning electron microscopy images. Further, the quantitative analysis of the product was performed by ion chromatography, and the atomic balance of sulfur was verified by gas analysis. A higher SO₂ concentration increased the NOx removal efficiency because the product ((NH₄)₂SO₃), which was obtained from SO₂ removal, acted as a reactant for the removal of NOx. Therefore, a higher concentration of O₃ favored the improvement of the NOx removal efficiency since O₃ oxidizes NO into NO₂, which reacts with (NH₄)₂SO₃. Thus, the SO₂ and NOx removal efficiencies were 93.6% and 69.6%, respectively, at SO₂, NO, and O₃ concentrations of 900, 30, and 30 ppm, respectively.