Simultaneous removal of sulfur dioxide and nitrogen oxide from flue gas by phosphorus sludge: The performance and absorption mechanism

Abstract

Developing low-cost and green simultaneous desulfurization and denitrification technologies is of great significance for sulfur dioxide (SO2) and nitrogen oxide (NOx) emission control at low temperatures, especially for small and medium-sized coal-fired boilers and furnaces. Herein, phosphorus sludge, an industrial waste from the production process of yellow phosphorus, has been developed to simultaneously eliminate SO2 and NOx from coal-fired flue gas. The key factors affecting the experimental results indicate that desulfurization and denitrification efficiency of over 95% can be achieved at a low temperature of 55 °C. Further, the absorption mechanism was investigated by characterizing the solid and liquid phases of the phosphorus sludge during the absorption process. The efficient removal of SO2 is attributed to the abundance of iron (Fe3+) and manganese (Mn2+) in the absorbent. SO2 can be rapidly catalyzed and converted to SO42− by them. The key to NOx removal is the oxidation of NO toward water-soluble high-valent nitrogen oxides by oxidizing reactive substances induced via yellow phosphorus, which are then absorbed by water and converted to NO3−. Meanwhile, yellow phosphorus is oxidized to phosphoric acid (H3PO4). The spent absorption slurry can be reused through wet process phosphoric acid production, as it contains sulfuric acid (H2SO4), nitric acid (HNO3), and H3PO4. Accordingly, this is a technology with broad application prospects.