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Overview of Speciated Mercury at Anthropogenic Emission Sources

Overview of Speciated Mercury at Anthropogenic Emission Sources. 3 rd I nternational Conference on Earth Science & Climate Change , San Francisco, July 28-30, 2014. Shuxiao Wang Tsinghua University. Contents. Introduction of Hg emission and speciation

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Overview of Speciated Mercury at Anthropogenic Emission Sources

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  1. Overview of Speciated Mercury at Anthropogenic Emission Sources 3rdInternational Conference on Earth Science & Climate Change, San Francisco, July 28-30, 2014 Shuxiao Wang Tsinghua University

  2. Contents • Introduction of Hg emission and speciation • Hg speciation and transformation in flue gas • Coal combustion • Cement production • Non-ferrous metal smelting • Iron and steel production • Speciated Hg emissions for China • Conclusions

  3. Introduction of mercury emission and speciation

  4. Global anthropogenic Hg emissions to air UNEP. Global Mercury Assessment, 2013

  5. Speciation profile of Hg emissions • The data used is • for outdated industrial process/air pollution control techniques • not from field tests Streets et al., 2005

  6. Hg speciation and transformation in coal combustion

  7. Configuration of coal-fired power plants ESP/FF

  8. Hg speciation in coal combustion flue gas Chlorine concentration Hg concentration Surface area temperature Galbreath K C & Zygarlicke C J, 2000, 65–66: 289–310 Zhang et al., in preparation

  9. Hg oxidation across SCR SCR catalysts significantly oxidize Hg0 2HCl + Hg0 + 1/2 O2 ↔ HgCl2 + H2O 2NH3+ 3 HgCl2 ↔ N2 + 3 Hg0 + 6 HCl 2NO + 2 NH3 + 1/2 O2 ↔ 2 N2 + 3 H2O Senior, 2005

  10. Hg transformation across ESP/FF • Over 99% of Hgp can be removed by ESP/FF • Complicated Hg0 Hg2+ transformation in ESP • About 60% of Hg2+ can be removed by FF • FF has no influence on Hg0 ESP/FF

  11. Hg transformation across WFGD • About 80% of Hg2+ can be removed by WFGD ESP/FF

  12. Summary of Hg speciation after APCDs Chen et al., 2007; Zhou et al., 2008; Wang et al., 2008; Yang et al., 2007; Duanet al., 2005; Kellie et al., 2004; Shah et al., 2010; Guo et al., 2004; Tang, 2004; Goodarzi, 2004; Lee et al., 2006; Kim et al., 2009; Wang et al., 2010; Zhang et al., 2012

  13. Hg speciation and transformation in non-ferrous metal smelters

  14. Configuration of non-ferrous metal smelter

  15. Hg transformation across ROA process Oxidize Hg0 to Hg2+ by O and Cl Remove over 98% of Hgp Remove a large amount of Hg2+ Oxidize Hg0 to Hg+by HgCl2 to form insoluble Hg2Cl2 Remove most of Hg0and Hg2+ Oxidize Hg0 to Hg2+via catalyst Remove a large amount of Hg2+ Wang et al., 2010

  16. Hg speciation before and after acid plants • Conversion and absorption process has significant impact • DCDA is more effective than SCSA • Hg2+ dominates in flue gas after acid plants DCDA DCDA DCDA SCSA DCDA DCDA DCDA – double conversion double absorption SCSA – single conversion single absorption Zhang et al., 2012

  17. Hg speciation in flue gas of various kilns • Hg0 is the main chemical form in exhaust gases from cooling cylinder and volatilization kiln, accounting for up to 97.8% of total Hg Wu et al., submitted

  18. Summary of Hg speciation after APCDs Wang et al., 2010; Li et al., 2010; Zhang et al., 2012; Wu et al., 2012

  19. Hg speciation and transformation in cement plants

  20. Hg flow during cement production • Precalciner process is the predominant cement production process worldwide • The recycling of collected dust from FFs/ESPs and the preheat of raw materials/coal cause mercury cycling in cement production Wang et al., 2014

  21. Hg transformation within cement plants Kiln Feed Temperature from 350 to 850℃,Hg vaporization/ decomposition 330 oC Stack Temperature from 200 to 50℃,Hg adsorption on raw materials and dust 1000 oC Fuels From Kiln & Precalciner 90 oC Raw Mill Coal Mill Long residence time (>25s)and high PM concentration (>10g/m3), Hg oxidation and adsorption when flue gas cooling BH Catch Sikkema et al., 2011

  22. Hg species at the outlet of kiln system • The mercury species measured at the outlet of the kiln system is predominantly oxidized mercury and particle-bound mercury • The kinetically-limited mercury oxidation in the flue gas is promoted compared with power plants Mlakar et al., 2010 Wang et al., 2014

  23. Hg transformation in raw mill and FF • The removal efficiencies of raw mill+FF are more than 90% Before raw mill Before raw mill Before raw mill Before raw mill Stack Stack Stack Stack Raw mil on Plant 2 Raw mil off Plant 1 Mlakar et al., 2010 Wang et al., 2014

  24. Summary of Hg speciation profiles • The mercury emission profile used in previous inventories: 80% Hg0, 15% Hg2+ and 5% Hgp • Recent tests indicate that the mercury emitted from cement plant is mainly in oxidized form, accounting for 61.3-90.8%

  25. Summary of Hg speciation profiles Schreiber & Kellett, 2009

  26. Hg speciation and transformation in iron and steel production

  27. Iron and steel production process Fukuda et al., 2011 Wang et al., in preparation

  28. Hg transformation in iron &steel plants • Mercury is vaporized into the flue gas as Hg0 (>1000°C) • The predominant species before ESPs is Hg2+, possibly caused by the Fe2O3-containing particles in the flue gas • The Hg removal of ESPs and FGD are correlated with the proportion of Hgp and Hg2+ in the flue gas before the facility Desulfurization devices ESP Wang et al., in preparation

  29. Summary of Hg speciation profiles • The mercury species emitted into atmosphere depend on mercury speciation of each stack, and mercury emissions from each stack

  30. Summary of Hg speciation profiles • Sintering and power plants are predominant emission sources • Hg2+ accounts for 59-73% of total Hg in flue gas emitted to air • Speciation profile used in previous study is: 80% Hg0, 15% Hg2+ and 5% Hgp

  31. Speciated Hg emissions for China

  32. Updated speciation profile of Hg emissions

  33. Speciated Hg emissions for China

  34. Conclusions

  35. Conclusions • Homogeneous process at high temperature (400-750°C) and heterogeneous process at low temperature (200-400°C) have equivalent influence on Hg speciation • Composition of fuels or raw materials affects composition of flue gas (e.g. halogen) and properties of fly ash (e.g. SSA), resulting in different Hg speciation • Conventional air pollution control devices have co-benefit removal efficiencies on different Hg species and contribute to Hg transformation • Recent field tests have provided new knowledge and more reliable Hg speciation profile for emission inventories • The speciated Hg emissions have changed significantly and will have substantial impacts on atmospheric Hg transports

  36. Thanks for your attention!Contact information:Tel: 86-10-62771466 Email: shxwang@tsinghua.edu.cn

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