Overview of Speciated Mercury at Anthropogenic Emission Sources

Transcription

1 3 rd International Conference on Earth Science & Climate Change, San Francisco, July 28-30, 2014 Overview of Speciated Mercury at Anthropogenic Emission Sources 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5 Speciation profile of Hg emissions The data used is for outdated industrial process/air pollution control techniques not from field tests Streets et al., 2005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 Economizer Exhausted Flue Gas PC Boiler Ammonia SCR Limestone Coal Air APH ESP/FF FGD Bottom Ash Fly Ash Gypsum Stack

8 Hg speciation in coal combustion flue gas Hg 2+ proportion in flue gas (%) Chlorine concentration Correlation Coefficient = Chlorine concentration in flue gas (mg/m 3 ) 10 Chlorine in flue gas (µg/m 3 )100 1 Percentage of oxidized mercury (29) 30 24(21) 41(43) 25 Hg concentration 29(25) 28(35) (11) 15(16) 10 9(11) Calculated(Measured) Mercury in flue gas (ng/m 3 ) Percentage of oxidized mercury (%) 50 Surface area 40 R² = Bhardwaj et al. (2009) This study Specific surface area (m 2 /g) Zhang et al., in preparation Proportion Hg 2+ proportion of oxidized in flue mercury gas (%) (%) temperature S S Galbreath K C & Zygarlicke C J, 2000, 65 66: Time (s) C) Flue gas temperature (

9 Hg oxidation across SCR SCR catalysts significantly oxidize Hg 0 PC Boiler Economizer Ammonia SCR Limestone Exhausted Flue Gas 2HCl + Hg 0 + 1/2 O 2 HgCl 2 + H 2 O 2NH HgCl 2 N Hg HCl Coal Air 2NO + 2 NH 3 + 1/2 O 2 2 N H 2 O APH FF FGD Bottom Ash Fly Ash Gypsum Stack Senior, 2005

10 Hg transformation across ESP/FF PC Boiler Over 99% of Hg p can be removed by ESP/FF Economizer Ammonia FF has no influence on Hg 0 SCR Limestone Exhausted Flue Gas Complicated Hg 0 Hg 2+ transformation in ESP About 60% of Hg 2+ can be removed by FF Coal Air APH ESP/FF FGD Bottom Ash Fly Ash Gypsum Stack

11 Hg transformation across WFGD About 80% of Hg 2+ can be removed by WFGD Economizer Exhausted Flue Gas PC Boiler Ammonia SCR Limestone Coal Air HgCl (g) APH HgCl (aq) 2 2 ESP/FF FGD HgCl (aq) + SO (aq) + H O Hg(g) + SO (aq) + 2Cl (aq) + 2H (aq) Bottom Ash Fly Ash Gypsum Hg(g) + 2Cl(ads) HgCl (g) 2 Stack

12 Summary of Hg speciation after APCDs Hg 0 Hg 2+ Hg p No. of tests None 56 (8-94) 34 (5-82) 10 (1-28) 13 ESP 58 (16-95) 41 (5-84) 1.3 (0.1-10) 31 ESP+WFGD 84 (74-96) 16 (4-25) 0.6 ( ) 7 FF 31 (10-58) 58 (34-76) 11 (1-25) 3 WS 65 (39-87) 33 (10-60) 2.0 ( ) 6 SCR+ESP+WFGD 73.8 (16-96) 26 (4-84) 0.2 ( ) 6 FF+WFGD (CFB+)ESP Chen et al., 2007; Zhou et al., 2008; Wang et al., 2008; Yang et al., 2007; Duan et 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 Hg 0 to Hg 2+ by O and Cl Remove over 98% of Hg p Remove a large amount of Hg 2+ Oxidize Hg 0 to Hg + by HgCl 2 to form insoluble Hg 2 Cl 2 Remove most of Hg 0 and Hg 2+ Oxidize Hg 0 to Hg 2+ via catalyst Remove a large amount of Hg 2+ 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 Hg 2+ dominates in flue gas after acid plants DCDA DCDA DCDA DCDA SCSA DCDA DCDA double conversion double absorption SCSA single conversion single absorption Zhang et al., 2012

17 Hg speciation in flue gas of various kilns Hg 0 is the main chemical form in exhaust gases from cooling cylinder and volatilization kiln, accounting for up to 97.8% of total Hg ROA process ZnO recovery process Hg concentration in the flue gas (µg m -3 ) Hg 0 Hg 2+ 0 Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Flue gas sampling site Site 1: Exhaust cooling cylinder gas Site 4: Exhaust dehydration gas Site 2: Roasting flue gas before DCA Site 5: Volatilization kiln flue gas before FGD Site 3: Exhaust roasting gas Site 6: Exhaust volatilization kiln gas Wu et al., submitted

18 Summary of Hg speciation after APCDs Hg 0 Hg 2+ Hg p DC+FGS+ESD+DCDA DC+FGS+ESD+MRT+DCDA DC+FGS+ESD+SCSA DC+FGS DC FGS None 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 330 o C Kiln Feed Temperature from 350 to 850,,Hg vaporization/ decomposition Stack Temperature from 200 to 50,Hg adsorption on raw materials and dust 90 o C 1000 o C Fuels From Kiln & Precalciner Raw Mill BH Catch Sikkema et al., 2011 Coal Mill Long residence time (>25s)and high PM concentration (>10g/m3), Hg oxidation and adsorption when flue gas cooling

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 250 mercury concentration(ug/m 3 ) Hg0 Hg2+ Hgp 0 Raw mill on Raw mill off Plant 1 Plant 2 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 mercury concentrat tion(ug/m 3 ) Before raw mill Before raw mill Stack Before raw mill Hg0 Hg2+ Hgp 0 Stack Stack Stack Raw mil on Raw mil off Plant 1 Plant 2 Mlakar et al., 2010 Wang et al., 2014

24 Summary of Hg speciation profiles The mercury emission profile used in previous inventories: 80% Hg 0, 15% Hg 2+ and 5% Hg p Recent tests indicate that the mercury emitted from cement plant is mainly in oxidized form, accounting for % Proportions of emitted mercury species (%) Hg 0 Hg 2+ Hg p Streets et al., 2005 Cement production Mlakar et al., 2010 Raw mill off Raw mill on Plant Wang et al., 2014 Plant Plant

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 stack stack coking waste dust collector dust collector coking rotary kiln rotary kiln stack coke dust collector limestone dolomite sintering machine iron ore dust collector dust collector desulfurization stack Fukuda et al., 2011 sinter coke coal stack stack dust collector power plant blast furnace stack dust collector gas dust limestone pig iron iron cake steel scrap stack stack convertor electric furnace dust collector dust collector molten steel steel slag gas dust molten steel steel slag Solid samples Flue gas samples Wang et al., in preparation Fugitive emissions

28 Hg transformation in iron & steel plants Mercury is vaporized into the flue gas as Hg 0 (>1000 C) The predominant species before ESPs is Hg 2+, possibly caused by the Fe2O3-containing particles in the flue gas The Hg removal of ESPs and FGD are correlated with the proportion of Hg p and Hg 2+ in the flue gas before the facility ESP Desulfurization devices 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 Proportions of emitted mercury species (%) Hg 0 Hg 2+ Hg p Streets et al., 2005 Iron and steel production rotary kiln for limestone rotary kiln for dolomite Wang et al., 2014 Sintering machine Plant 1 electric furnace Power plant Sintering machine-high-sulfur Sintering machine-low-sulfur Sintering machine tail Wang et al., 2014 Blast furnace-pig iron Plant 2 Blast furnace-iron scrap Convertor-crude steel Power plant

30 Summary of Hg speciation profiles electric furnace 4% Power plant 17% Sintering machine 50% rotary kilnlimestone 16% rotary kilndolomite 13% 100% 80% 60% 40% 20% Hgp Hg2+ Hg0 0% Streets et al. Plant 1 Plant 2 Sintering machinehigh-sulfur 3.5% Sintering machine-lowsulfur 41.0% Power plant 48.8% Sintering machine tail 1.8% Fugitive- Blast furnace 4.4% Convertorcrude steel 0.5% Sintering and power plants are predominant emission sources Hg 2+ accounts for 59-73% of total Hg in flue gas emitted to air Speciation profile used in previous study is: 80% Hg 0, 15% Hg 2+ and 5% Hg p

31 Speciated Hg emissions for China

32 Updated speciation profile of Hg emissions Sub-category Updated Streets et al. (2005) Hg 0 Hg 2+ Hg p Hg 0 Hg 2+ Hg p Coal-fired power plants Industrial coal combustion Residential coal combustion Other coal combustion Stationary oil combustion Mobile oil combustion Biomass fuel combustion Waste incineration Cremation Zinc smelting Lead smelting Copper smelting Gold production Mercury production Cement production Iron and steel production Aluminum production

33 Speciated Hg emissions for China Hgp Hg2+ Hg Coal-fired power plants Industrial coal combustion Zinc smelting Lead smelting Copper smelting Cement production Iron and steel production HgT Hg0 Hg2+ Hgp 1999 emission (Streets et al., 2005) emissions (Wang et al., 2013)

34 Conclusions

35 Conclusions Homogeneous process at high temperature ( C) and heterogeneous process at low temperature ( 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

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