Runlong Hao

Simultaneous removal of SO₂, NO and Hg⁰ through an integrative process utilizing a cost-effective complex oxidant.

A novel process of pre-oxidation combining with post-absorption to simultaneously remove SO2, NO and Hg(0) from flue gas was proposed. A vaporized complex oxidant (CO) consisted of cost-effective H2O2 and NaClO2 was prepared to oxidize Hg(0) and NO, then the oxidation products were absorbed by the Ca(OH)2 solution that was followed. For the establishment of the optimal reaction conditions, the influences of various reaction factors on the simultaneous removal of SO2, NO and Hg(0) were investigated, i.e., the molar ratio of H2O2 to NaClO2 in CO, the adding rate of CO, the pH of CO, the reaction temperature, the flue gas residence time and the coexistence gases. The experimental results indicated that the desulfurization was constant in all tests, whereas the removal of NO and Hg(0) was primarily affected by the NaClO2 addition, the adding rate of CO, the pH of CO, and the reaction temperature. Meanwhile, NO and SO2 were characterized as the promoters for the Hg(0) removal. Under the optimal reaction conditions, the best simultaneous removal efficiencies were 100% for SO2, 87% for NO and 92% for Hg(0). According to the characterizations of removal products by UV-vis, EDX, XRD, AFS and XPS, the reaction mechanism was speculated.

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.

A novel pre-oxidation method for elemental mercury removal utilizing a complex vaporized absorbent

A novel semi-dry integrative method for elemental mercury (Hg(0)) removal has been proposed in this paper, in which Hg(0) was initially pre-oxidized by a vaporized liquid-phase complex absorbent (LCA) composed of a Fenton reagent, peracetic acid (CH3COOOH) and sodium chloride (NaCl), after which Hg(2+) was absorbed by the resultant Ca(OH)2. The experimental results indicated that CH3COOOH and NaCl were the best additives for Hg(0) oxidation. Among the influencing factors, the pH of the LCA and the adding rate of the LCA significantly affected the Hg(0) removal. The coexisting gases, SO2 and NO, were characterized as either increasing or inhibiting in the removal process, depending on their concentrations. Under optimal reaction conditions, the efficiency for the single removal of Hg(0) was 91%. Under identical conditions, the efficiencies of the simultaneous removal of SO2, NO and Hg(0) were 100%, 79.5% and 80.4%, respectively. Finally, the reaction mechanism for the simultaneous removal of SO2, NO and Hg(0) was proposed based on the characteristics of the removal products as determined by X-ray diffraction (XRD), atomic fluorescence spectrometry (AFS), the analysis of the electrode potentials, and through data from related research references.

Simultaneous removal of multi-pollutants from flue gas by a vaporized composite absorbent.

An economical process that was used to remove SO2, NO and Hg0 simultaneously was developed, based on the pre-oxidations of Hg0 and NO by a vaporized Fenton-based complex oxidant (FO) consisted of Fenton and NaClO. The effects of concentrations of FeSO4 and NaClO in the oxidant, the molar ratio of vaporized oxidant to multi-pollutant, the oxidant solution pH, the reaction temperature, the gas flow ratio of vaporized FO to multi-pollutants, the flue gas flow and the concentrations of coexistence gases in flue gas on the simultaneous removals were investigated experimentally. The results showed that the removals of NO and Hg0 were significantly depended on FeSO4 and NaClO concentrations, the molar ratio of vaporized oxidant to multi-pollutants, the FO solution pH, the reaction temperature, the gas flow ratio of vaporized FO to multi-pollutants and flue gas flow. And higher concentration of SO2 and an appropriate concentration of NO had the promotion for Hg0 removal. The average simultaneous removal efficiencies of 100% for SO2, 81% for NO and 91% for Hg0 were obtained under the optimal reaction conditions. According to the characterization of the reaction removal products by SEM, EDS, XRD and AFS, the reaction mechanism was speculated.

Combustion behavior, emission characteristics of SO2, SO3 and NO, and in situ control of SO2 and NO during the co-combustion of anthracite and dried sawdust sludge

The combustion behaviors of anthracite and dried sawmill sludge (DSS) were studied using thermogravimetric analysis (TGA) and derivative thermogravimetric analysis (DTG). DSS was found to be a promoter for anthracite combustion, the addition of DSS in anthracite decreased the burnout temperature and time. But DSS caused the rapid releases of SO2 and NO in the initial combustion stage. In overall, the increasing of DSS significantly decreased the emission factor of SO2 from 13.42 ± 1.80 to 0.31 ± 0.08 g/kg; while the emission factor of NO was not obviously changed and stable at 0.7-0.8 g/kg in all cases. The oxygen-rich atmosphere was helpful for the rapid and sufficient combustion of blend; the oxygen-lean atmosphere delayed the combustion process and slowed down the releases of SO2 and NO. The increasing combustion temperature improved the anthracite combustion, and the emission factors of SO2 and NO were all increased with the temperature increasing. 900 °C was found to be the best combustion temperature for NO generation. SO3 was detected in the combustion of anthracite under 21% and 30% of O2. Two promising ways for control of SO2 and NO were provided: 1) urea-fuel mixture combustion combined with the post-combustion wet absorption by Na2CO3; 2) post-combustion wet absorption by NaClO/Na2CO3. The removal efficiencies of SO2 and NO could reach 100% and over 95% respectively. The removal products were determined as sulfate, sulfite and nitrate by IC, with no toxic byproducts being produced.

Removal of multi-pollutant from flue gas utilizing ammonium persulfate solution catalyzed by Fe/ZSM-5

A nano-sized iron loaded ZSM-5 zeolite (Fe/ZSM-5) catalyst was firstly used to activate (NH4)2S2O8 solution for the simultaneous removal of multi-pollutant from flue gas. The simultaneous removal efficiencies 100% of SO2, 72.6% of NO and 93.4% of Hg° were achieved under the condition that the catalyst dose was 0.8 g/L, concentration, pH and temperature of (NH4)2S2O8 solution were 0.03 mol/L, 5 and 65 °C, respectively. The stability of catalyst was checked by a continuous test, proving that the catalytic activity was maintained for 4 h and the leached iron reached low levels. Based on the catalyst characterizations, product analysis and literatures, the removal mechanism was speculated preliminarily, during which, OH and SO4- played key roles for oxidizing NO and Hg° into NO3- and Hg2+.

Simultaneous removal of NO and SO2 from flue gas using vaporized H2O2 catalyzed by nanoscale zero-valent iron

To remove NO and SO2 from flue gas simultaneously, a heterogeneous catalytic oxidation system was developed with the nanoscale zero-valent iron (nZVI), vaporized H2O2, and sodium humate (HA-Na) acting as the catalyst, oxidant, and absorbent, respectively. The experimental results indicated that the desulfurization was mainly influenced by the absorption, and the denitrification was significantly affected by the catalytic oxidation parameters. Under the optimal conditions, the simultaneous removal efficiencies of SO2 and NO were 100 and 88.4%, respectively. The presence of ·OH during the removal process was proved by the scavenger tests, and the production of ·OH with and without nZVI was indirectly evaluated by the electron paramagnetic resonance (EPR) and methylene blue experiments. Moreover, the fresh and aged nZVI were characterized by a series of techniques and the results suggested that the redox pair Fe2+/Fe3+ released by nZVI could react with H2O2 to provide the sustainable ·OH, which was important for the oxidation from NO and SO2 to NO3− and SO42−. The removal mechanism was proposed preliminarily based on the correlative experiments, characterizations, and references.