Research Of SO₂ Oxidation Over SCR Catalyst And Regulatory Mechanism

Pollutant emission from coal-fired power plants attracts more and more attention from the government. In power plants, high-efficiency De-NOx technology must be adopted to meet the pollutant emission limit. Selective catalytic reduction (SCR) of NOx using NH3 as reductant has become the most mature and efficient technologies for NOx abatement. Catalyst is the core part SCR system. The exiting of SCR catalyst would cause the oxidation of SO2 to SO3, resulting in the erosion and blocking of the equipments and more serious haze.The main research point of this paper is studying the mechanism of SO2 oxidation over V2O5/TiO2 catalyst first. Based on the mechanism, the effect of different component addition on V2O5/TiO2 catalyst to the NOx removal efficiency and SO2 oxidation was studied. The distribution of SCR reaction and SO2 oxidation reaction in the wall of the honeycomb catalyst was studied by numerical modeling. The main results are shown as follow:1. The surface structure of V2O5/TiO2 catalyst and the mechanism of SO2 oxidation over V2O5/TiO2 catalyst were investigated. Isolated vanadia species were dispersed on the TiO2 surface as Ti-O-V bonds at VOx coverage far below the monolayer. Polymeric vanadia species were then formed through V-O-V bonds as the VOx coverage increased. SO2 temperature-programmed desorption and in situ diffuse reflectance infrared Fourier transform spectroscopy were conducted to study the interaction between SO2 and V2O5/TiO2. It was found that V=O was demonstrated to play a critical role in the SO2 adsorption and oxidation. A possible reaction mechanism of SO2 oxidation over V2O5/TiO2 catalyst was established in this study.2. The effect of different component addition on V2O5/TiO2 catalyst to the NOx removal efficiency and SO2 oxidation was studied. The addition of WO3 or MoO3 would increase the NOx removal efficiency and SO2 oxidation efficiency. The effect of SO2 oxidation by MoO3 was more effective than WO3. Effect of different precursor of MoO3 to NOx removal efficiency and SO2 oxidation of V2O5/TiO2 catalyst was studied. High-efficiency NOx removal efficiency and low SO2 Oxidation rate were achieved by the addition of MoO3 when the precursor was phosphomolybdic acid. The comparison of different phosphomolybdic acid content showed that 7% addition of MoO3 (with the precursor of phosphomolybdic acid) on V2O5/TiO2 catalyst would ensure high-efficiency NOx removal efficiency, while keeping lower SO2 oxidation than normal V2O5/TiO2 catalyst.3. Based on the Eley-Rideal SCR reaction mechanism, the NOx removal reaction kinetics equation was obtained by experiments study. The dynamics of SO2 oxidation was studied and relevant dynamics equation was obtained. Based on the above reaction kinetics, a numerical model of SCR reaction and SO2 oxidation reaction over honeycomb catalyst was established and the results of the model conformed with relevant experiment results. Through the model results, it is found that the SCR reaction only occurred in a thin layer on the catalyst surface. The thickness of the thin layer was only about a third of the thickness of the catalyst wall. The SO2 oxidation reactions occurred within the entire catalyst wall.