Effect of H2O2 on the treatment of NO and NO2 using a Mg-Al oxide slurry

Sodium ascorbate as additive in red mud slurry for simultaneous desulfurization and denitrification: Insights into the multiple influence factors and reaction mechanism

Based on the ultra-low emission demand of SO₂ and NO_x in flue gas, a new absorption method was proposed to improve the desulfurization and denitrification efficiency and reduce the amount of ozone by using sodium ascorbate as an additive in red mud slurry. Compared with pure red mud slurry, the red mud (RM) + sodium ascorbate (SA) slurry significantly improved the denitrification efficiency from 24% to 84% and the desulfurization efficiency to 98%. Meanwhile, the effects of RM, SA concentration, reaction time and O₃/NO molar ratio on desulfurization and denitrification efficiencies were studied. The results showed that the RM + SA composite slurry maintained high efficiencies of desulfurization and denitrification for 240 min under the optimized conditions. As an antioxidant, the introduction of SA inhibited the excessive oxidation of sulfite, and itself could easily react with NO₂ through the redox reaction, greatly promoting the absorption of NO₂. In addition, the reaction mechanism of the simultaneous removal of SO₂ and NO₂ by red mud and sodium ascorbic mixed slurry combined was proposed.

Nitric oxide removal by combined urea and FeIIEDTA reaction systems

(NH₂)₂CO as well as Fe^IIEDTA is an absorbent for simultaneous desulfurization and denitrification. However, they have their own drawbacks, like the oxidation of Fe^IIEDTA and the low solubility of NO in urea solution. To overcome these defects, A mixed absorbent containing both (NH₂)₂CO and Fe^IIEDTA was employed. The effects of various operating parameters (urea and Fe^IIEDTA concentration, temperature, inlet oxygen concentration, pH value) on NO removal were examined in the packed tower. The results indicated that the NO removal efficiency increased with the decrease of oxygen concentration as well as the increase of Fe^IIEDTA concentration. The NO removal efficiency had little change with a range of 25-45 °C, and sharply decreased at the temperature of above 55 °C. The NO removal efficiency initially increases up to the maximum value and then decreases with the increase of pH value as well as the raise of urea concentration. In addition, the synergistic mechanism of (NH₂)₂CO and Fe^IIEDTA on NO removal was investigated. Results showed that urea could react with Fe^IIEDTA-NO to produce Fe^IIEDTA, N₂, and CO₂, and hinder oxidation of Fe^IIEDTA. Finally, to evaluate the effect of SO₃^2- on NO removal, a mixed absorbent containing Fe^IIEDTA, urea, and Na₂SO₃ was employed to absorb NO. The mixed absorbent could maintain more than 78% for 80 min at 25 °C, pH = 7.0, (NH₂)₂CO concentration of 5 wt%, Fe^IIEDTA concentration of 0.02 M, O₂ concentration of 7% (v/v), and Na₂SO₃ concentration of 0.2 M.

Establishment of a novel advanced oxidation process for economical and effective removal of SO2 and NO

SO2 and NO have caused serious haze in China. For coping with the terrible problem, this paper proposed a novel advanced oxidation process of ultraviolet (UV) catalyzing vaporized H2O2 for simultaneous removal of SO2 and NO. Effects of various factors on simultaneous removal of SO2 and NO were investigated, such as the mass concentration of H2O2, the UV energy density, the UV wavelength, the H2O2 pH, the temperatures of H2O2 vaporization and UV-catalysis, the flue gas residence time, the concentrations of SO2, NO and O2, and radical scavenger. The removal efficiencies of 100% for SO2 and 87.8% for NO were obtained under the optimal conditions. The proposed approach has some superiorities, i.e. less dosage and high utilization of oxidant, short flue gas residence time and inhibiting the competition between SO2 and NO for oxidants. The results indicated that the desulfurization process was dominated by the absorption by HA-Na, whereas the denitrification was primarily affected by the H2O2 dosage, UV energy density and H2O2 pH. Interestingly, an appropriate amount of SO2 was beneficial for NO removal. The reaction mechanism was speculated based on the characterizations of removal products by XRD, FT-IR and IC.