An integrative process for Hg0 removal using vaporized H2O2/Na2S2O8

In this paper, a novel integrative process of preoxidation of Hg-0 to Hg2+ by a vaporized liquid-phase multi-component oxidant (LMO) made up of H2O2 and Na2S2O8 and then Ca(OH)(2) absorption for removing Hg-0 from coal-fired flue gas is proposed. For the establishment of optimal reaction conditions, the effects of various key factors such as concentration ratio of Na2S2O8 to H2O2, pH of LMO, addition rate of LMO, reaction temperature and concentrations of CO2, O-2, SO2 and NO on Hg-0 removal were investigated systematically. The results indicated that the Hg-0 removal efficiency was significantly affected by the pH of LMO, the reaction temperature and the addition rate of LMO. The influences of other gases, such as O-2, CO2 and SO2, could be neglected; however, the effect of NO was either promotion or inhibitory, depending on its concentration. Under the optimal reaction conditions, the simultaneous removal efficiencies of 100% for SO2, 83.2% for NO and 91.5% for Hg-0 were obtained. Based on the references and the characterizations of removal products by X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and cold vapor atom fluorescence spectrometry (CVAFS), the reaction mechanism of removing SO2, NO and Hg-0 and the kinetics of Hg-0 removal were put forward. (C) 2014 Elsevier Ltd. All rights reserved.