【作者】 武成利；

【导师】 董众兵； 曹晏；

【作者基本信息】 安徽理工大学 ， 环境工程， 2010， 博士

【摘要】 本文采用安大略法(OHM)对4套不同装机容量(90 MW、205 MW、190 MW和450 MW)的美国燃煤机组烟气中汞进行现场采样和分析,评价各污染物控制工艺(选择性催化还原SCR脱硝、静电除尘ESP和湿法烟道气脱硫WFGD)对汞的形态转化和汞脱除效率的影响。SCR具有明显的氧化零价汞的作用,SCR的零价汞的氧化效率在55.2%～70.4%范围内变化；当烟气不经过SCR和经过SCR时,ESP脱除汞效率分别为0.9%～2.9%和5.3%～9.6%,WFGD脱汞效率分别为30.9%～77.4%和37.8%～89.5%。同时发现烟气经过湿法脱硫工艺发生了零价汞再析出现象,即经过WFGD吸收的离子汞又被还原成零价汞,导致在WFGD出口处零价汞的浓度高于其入口值。通过建立一套连续测试零价汞再析出的实验室评价装置,对现场循环脱硫浆液、脱硫废水和不同自制脱硫浆液(CaO、CaSO3、CaSO4和Na2SO3)的零价汞再析出的影响进行实验研究,实验结果表明亚硫酸根离子是导致零价汞再析出的主要原因。同时对不同操作条件下(温度、浆液pH值、氧气浓度和不同载气)及低价态金属离子溶液对零价汞再析出的影响进行了研究。低价态金属离子Sn2+、Pb2+、Fe2+、Ni2+、AsO2-和Cu+能还原离子汞,而高价态金属离子Fe3+和Cu2+不能使离子汞还原,定量分析表明金属离子还原离子汞能力的强弱顺序为Sn2+>Pb2+>Cu+>Fe2+>AsO2->Ni2+。并对外加添加剂(H2S、Na2S4、TMT15、NaHS和HI)抑制零价汞再析出进行了实验评价,结果表明外加添加剂与离子汞生成的汞沉淀HgS或HgI2降低了离子汞的还原势,阻止了离子汞继续被还原性离子还原；价格便宜及容易得到PY系列添加剂也对抑制零价汞再析出有较好效果。实验研究还发现浆液的氧化还原电位(ORP)与零价汞再析出存在明显的相关性,浆液的ORP为负值,能发生零价汞的再析出现象；浆液的ORP为正值,出现零价汞再析出的可能性大大降低。更多还原

【Abstract】 Ontario hydro method (OHM), a mercury speciation method certificated by American Society for Testing and Materials (ASTM), was applied to collect speciated mercury in the flue gas at the four full-scale coal-fired utilities with different electricity capacities (90MW,205MW,190MW and 450MW). Mercury transformation and removal efficiencies through SCR, ESP and WFGD in these four utilities were evaluated. It was found that Hg0 oxidation efficiencies across SCR ranged from 55.2% to 70.4%. When the flue gas passing SCR and no passing SCR, The mercury capture efficiencies by ESP were the 0.9%～2.9% and 5.3%～9.6%, The total mercury removal efficiencies across WFGD were respectively 30.9%-77.4% and 37.8%～89.5%. The Hg0 re-emission phenomena (Hg2+being reduced to Hg0) were observed in two WFGD of utilities, i.e the HgO concentrations at WFGD out were higher than they were at WFGD inlet.A lab-scale simulated WFGD system was set up to investigate the Hg0 re-emission, and effects of the recirculating slurries, waste water collected from a full-scale WFGD and home-made slurries (CaO, CaSO3, CaSO4 and Na2SO3) were performed. There is a significant correlation between Hg0 re-emission and sulfite ion in home-made or natural WFGD slurries. Further, effects of major operational parameters (temperatures, pH values of slurries, oxygen gas concentrations and different carrier gases) and some metal ions on Hg0 re-emission were intensively investigated. The effects of some ions respectively including Sn2+, Pb2+, Fe2+, Ni2+, AsO2-, Cu+, Fe3+and Cu+on Hg0 re-emission were studied. Low chemical valence ions being oxidized by Hg2+led to Hg0 re-emission, and the order of Hg2+reduction capacity was Sn2+>Pb2+>Cu+>Fe2+>As02>Ni2+. In the followed-up Hg0 re-emission suppression tests, the performances of five additives, including H2S, Na2S4, TMT15, NaHS and HI were evaluated. It was found that the produced precipitates HgS and HgI2 can prevent Hg2+from being reduced to Hg0. The cheaper home-made additives also had better effects on suppressing Hg0 re-emission. There also existed the significant correlation between oxidation-reduction potential (ORP) of slurries and Hg0 re-emission. Only the slurries with minus ORP values can result in occurrence of Hg0 re-emission.Figure [67] table [21] reference [151]更多还原