燃煤烟气中Hg/Cl均相与非均相氧化机理

摘要

建立了燃煤烟气中Hg/Cl均相与非均相氧化动力学模型,其中非均相模型涉及到飞灰中未燃尽炭表面上的8个不可逆基元反应.将均相模型与非均相模型有效地结合起来形成多相反应模型,预测实际燃煤烟气中汞的形态分布.考虑了烟气成分、降温速率以及飞灰负荷对汞氧化的影响.结果表明,模拟预测结果与实验数据吻合较好,H2O通过反应StCl(s)+H2O→HCl+OH+StSA(s)抑制了汞的氧化.反应路径分析显示燃煤烟气中Hg/Cl氧化的主要反应路径是Hg0→StHgCl(s)→HgCl2.Hg0的氧化过程是:Hg0首先在未燃尽炭表面上被氯化活性位氧化成StHgCl(s),然后被进一步氧化成HgCl2并释放到烟气中.%A kinetic model consisting of a homogeneous mechanism and a new heterogeneous mechanism with eight irreversible elementary reactions on unburned carbon surface was developed.The homogeneous mechanism was com-bined with the heterogeneous mechanism to predict mercury speciation in actual coal-fired flue gas.The effects of flue gas composition,quench rate and fly ash loading on mercury oxidation were considered.The results show that model predic-tions are in good agreement with the experimental data.H2O exhibits an inhibitory effect on mercury oxidation via the reaction StCl(s) +H2O→HCl+OH+StSA(s).Reaction path analysis indicates that the dominant reaction pathway of mercury oxidation by chlorine in coal-fired flue gas is a two-step process(Hg0→StHgCl(s)→ HgCl2),in which Hg0 is first oxidized by chlorinated carbon sites into StHgCl(s),which is further oxidized into HgCl2 and released into flue gas.