Simultaneous removal of NOx, SO2, and Hg from flue gas in FGD absorber with oxidant injection (NaClO2)– full-scale investigation

Abstract

This article presents the results of an industrial-scale study (on 400 MWe lignite fired unit) of simultaneous NOx, SO2, and HgT removal in FGD absorber with oxidant injection (NaClO2) into flue gas. It was confirmed that the injection of sodium chlorite upstream the FGD (Flue Gas Desulfurization) absorber oxidize NO to NO2, Hg0 to Hg2+, and enhancing NOx and HgT removal efficiency from exhaust gas in FGD absorber. Mercury removal efficiency grows with the rise of degree of oxidation NO to NO2 and was limited by the phenomenon of re-emission. For NOx removal the most critical parameters is slurry pH and temperature. There was no negative effect on sulfur dioxide removal efficiency caused by oxidant injection in tested FGD absorber. Based on the data provided, NOx and HgT emissions can be reduced by adjusting the FGD absorber operating parameters combined with oxidant injection. Implications: The emissions of nitrogen oxides and mercury from coal combustion have great influence of environment and human health. The injection of sodium chlorite upstream the FGD absorber oxidize NO to NO2, Hg0 to Hg2+ and enhancing NOx and HgT removal efficiency from flue gas.