| Conventionally, the control of sulfur dioxide, nitric oxides and mercury emitted from coal-fired power plants could be realized by the limestone-gypsum desulfurization, the selective catalytic reduction denitrificationand the active carbon injection demercuration systems. The stage treatment arrangement exists the shortages of larger occupying area, higher costs of capital construction and operation, and poor stability of systems. Hence, the development of simultaneous removal of SO2, NO and Hg0 with lower costs that equipment and operation needed and environmental friendly, has the important theory meaning and application value, and become a hot topic in the air pollution control field.Based on large investigations, some complex oxidants for simultaneous desulfurization and denitrification or simultaneous removal of SO2, NO and Hg0 were prepared, including H2O2/S, Fenton/P, Fenton/P/C, NaC102/B and NaC102/H. And the effects of preparation conditions of complex oxidant and reaction condi-tions on the removal of SO2, NO and Hg0 were investigated through a self-design pre-oxidation combing post-absorption bench scale platform, and then the optimal experiment conditions for various complex oxidants were established. (1) the opti-mal reaction conditions for H2O2/S are that molar ratio of S and H2O2 is 0.2/8 mol/mol, complex oxidant pH is 5.5, reaction temperature is 120℃, simulated flue gas flow is 2.0L/min, adding rate of complex oxidant is 40μl/min, and the obtained simultaneous removal efficiencies are 100% for SO2,83.2% for NO and 91.5%for Hg0 (2) the optimal reaction conditions for Fenton/P/C are that molar ratio of H2O2,FeSO4, P and C is 8mol/L,4mol/L,4mol/L and 40mmol/L, complex oxidant pH is 1.1, reaction temperature is 130℃, simulated flue gas flow is 1.0L/min, adding rate of complex oxidant is 150 μl/min, and the obtained simultaneous re-moval efficiencies are 100% for SO2,78.9% for NO and 83.9% for Hg0. (3) the op-timal reaction conditions for NaClO2/B are that molar ratio of NaClO2 and B is 1.5:0.05 mol/mol, complex oxidant pH is 7.0, reaction temperature is 140℃, add-ing rate of complex oxidant is 250 pi/min and simulated flue gas flow is 3.0L/min and the obtained simultaneous removal efficiencies are 100% for SO2,91% for NO and 93% for Hg0. (4) the optimal reaction conditions for NaC102/H are that molar ratio of H and NaClO2 is 4:0.1 mol/mol, complex oxidant pH is 4.5, reaction tem-perature is 150℃, adding rate of complex oxidant is 200 μl/min and simulated flue gas flow is 3.0L/min and the obtained simultaneous removal efficiencies are 100% for SO2,87% for NO and 92% for Hg0. In addition, the abosption of SO2 and NOX by HA-Na solution was carried out, the optimal reaction conditions were as fol-lowed:the molar concentration of HA-Na is 0.04 mol/L, the complex oxidant pH is 12, the reaction temperature is 50℃ and the simulated flue gas flow is 3.0L/min and the obtained removal efficiencies are 100% for S02,99.6% for NO2 and 65% for NO. According to the above studies, a novel gas-phase likeness pre-oxidation combing post-absorption process for simultaneous removal of SO2, NO and Hg0 was proposed.According to the characterizations of pre-oxidation removal products by EDS, XRD, SEM, CVAFS and XPS, the components in removal products were identified as that:for SO2, its main products were calcium sulfate and calcium sulfite, and those of NO were calcium nitrate and calcium nitrite, and those of Hg0 were Hg0, HgCl2 and HgSO4. Based on the characterizations of absorption products by FT-IR, XRD and EDS, the main products were sodium sulfate and HA sediment. And then the reaction mechanisms of H2O2-based and NaClO2-based complex oxidants re-moving SO2, NO and Hg0 as well as HA-Na absorbing SO2, NO and NO2 were speculated according to the characterization results and related references.According to the macrokinetics experiments, the reaction orders of removal of SO2, NO and Hg by H2O2-based complex oxidants were conformed to pseu-do-first-order reaction, and the apparent activation energies were 22.33,23.75 and 4.11 kJ/mol respectively for H2O2/S complex oxidant, and the apparent activation energy for NO removal by Fenton/P was 14.1 kJ/mol, and the apparent activation energy for Hg0 removal by Fenton/P/C was 14.3 kJ/mol. The experiment of denitri-fication kinetics indicated that the existences of P and ferrous accelerated the oxi-dation rate. The experiment of demercuration kinetics demonstrated that B can sig-nificantly promote Hg0 removal.For the future industrial application, two pre-oxidation devices were designed, namely whirlwind type and inverse U-type. And then the flow field, concentration field, pressure field and temperature field of the two kind pre-oxidation devices were simulated by FLUENT software. |
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