Worldwide Pollution Control Association

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1 Worldwide Pollution Control Association WPCA- Southern Company Mercury Seminar October 30-31, 2012 All presentations posted on this website are copyrighted by the Worldwide Pollution Control Association (WPCA). Any unauthorized downloading, attempts to modify or to incorporate into other presentations, link to other websites, or to obtain copies for any other purposes than the training of attendees to WPCA Conferences is expressly prohibited, unless approved in writing by the WPCA or the original presenter. The WPCA does not assume any liability for the accuracy or contents of any materials contained in this library which were presented and/or created by persons who were not employees of the WPCA. Visit our website at

2 Mercury Control and Combustion Connie Senior WPCA Mercury Seminar Birmingham, Alabama October 30, 2012 ADA: Innovate, Develop, Commercialize

3 Motivation for This Presentation There s more than activated carbon, when it comes to mercury control in coal-fired boilers Chemistry of mercury in the boiler and the interaction of mercury with other control processes, like SCR, affect the performance of downstream mercury control from activated carbon injection or scrubbers Topics to be discussed: mercury chemistry in boilers, halogen injection, impact of SCRs and SO 3 on mercury control

4 Hg Removal in the Boiler Hg isn t removed in the boiler But, some things that happen in the boiler affect how much mercury can be removed downstream How is Hg removed? Adsorption on particles (fly ash, sorbents) and removal in the particulate control device Absorption of oxidized mercury in scrubbers

5 Adsorption How do we get more mercury onto particles? More halogens generally mean more particulate Hg Other factors: Type of PCD %Hg p at PCD Inlet 100% 80% 60% 40% 20% Cold-side ESP & FF Hot-side ESP SO 3 Unburned carbon in ash 0% ,000 10,000 Coal Chlorine, ppm dry Source: 1999 ICR Data

6 Unburned Carbon & ESPs Data from bituminous coals in pcfired boilers Hg Removal across PCD 100% 80% 60% 40% 20% 0% 0% 10% 20% 30% Loss on ignition (LOI) in fly ash, wt%

7 Unburned Carbon & Fabric Filter T-fired boiler with low-nox combustion system, low-sulfur fuel Unburned carbon changed by changing combustion parameters Hg Removal across FF 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Total Hg Gaseous Hg Unburned carbon in ash, wt%

8 Absorption How do we get more Hg into the scrubber? Higher fraction of 100% oxidized Hg at 90% Dry FGD, FF scrubber inlet => 80% Wet FGD higher Hg 70% 60% removal 50% Factors: 40% 30% Halogen in fuel 20% Re-emission of 10% Hg 0 in wet FGD 0% Removal of Hg across FGD 0% 20% 40% 60% 80% 100% Fraction Hg 2+ at Inlet Source: NETL, EPRI demos

9 What Happens in the Boiler? 1. Hg is released from fuel, while UBC and SO 3 develop in the flame zone 2. After the convective pass, halogens can begin to oxidize Hg in the flue gas 3. If SCR present, oxidation of Hg 0 and production of SO 3 4. Oxidation of Hg 0 across APH and removal of some SO 3 Temperature, o C Radiant Heat Transfer Time, seconds Convective Heat Transfer Air Preheater (Gas-Gas Heat Transfer) Flue Gas to Particulate Control Temperature, o F 8

10 Mercury Chemistry in Flue Gas 9

11 Mercury Chemistry in Flue Gas HgCl 2 Gas-phase reactions Hg 0 Oxidation Hg Adsorption Hg p Heterogeneous reactions 10

12 Oxidation Across Full-Scale SCRs Full-scale data Large variation in observed oxidation 100% 100% Oxidation of Hg 0 Across SCR 80% 60% 40% 20% 0% NH3 On NH3 Off Oxidation of Hg 0 Across SCR 80% 60% 40% 20% 0% NH3 On NH3 Off Coal chlorine, ug/g Temperature, o F Effect of Cl: Low oxidation with PRB (low chlorine coal) Effect of T: Lower oxidation at higher temperatures 11

13 Oxidation of Hg Across APHs %Hg 0 oxidation across APH 100% 80% 60% 40% 20% Subbit (incl.blends) Bitum. Full-scale Hg speciation measurements Significant oxidation across Air Preheater: APH exit temperature 0% Chlorine Coal chlorine, ug/g dry SO 2 /SO 3 LOI 12

14 Why Add Halogens? Adding halogens to fuel or flue gas: Halogen content of US coals varies widely

15 ADA-ES. All Rights Reserved

16 Why Add Halogens? Adding halogens to fuel or flue gas: Halogen content of US coals varies widely Br, ug/g Source: USGS COALQUAL database Bromine content typically 1% to 4% of chlorine content Eastern Interior (Illinois Basin) y = x R² = Cl, ug/g

17 Why Add Halogens? Adding halogens to fuel or flue gas: HX in gas, ppmv, 3% O 2 dry 500 ug/g Cl in coal = ~40 ppmv HCl in flue gas 500 ug/g Br in coal = ~17 ppmv HBr in flue gas HCl HBr ,000 Halogen in Coal, µg/g dry

18 Why Add Halogens? Adding halogens to fuel or flue gas: Halogen content of US coals varies widely Oxidation of Hg and capture of Hg on fly ash enhanced with additions of halogens, like Cl and Br %Oxidized Hg at Air Preheater Outlet Halogen addition at various full-scale PRB boilers Halogen in Coal, ppmw dry NaCl MgCl2 CaCl2 HCl CaBr2 Source: Dombrowski et al., 2006

19 Why Add Halogens? Adding halogens to fuel or flue gas: Halogen content of US coals varies widely Oxidation of Hg and capture of Hg on fly ash enhanced with additions of halogens, like Cl and Br Many plants APCDs can take advantage of native capture Hg Removal across FGD 100% 80% 60% 40% 20% 0% ,000 10,000 Coal Chlorine, ppm dry Source: 1999 ICR

20 Effect of SCRs on Added Halogens Catalysts drive reactions toward equilibrium Results will be catalyst-specific Adding Br to the fuel makes the shift to Hg 2+ take place at higher temperatures (than Cl) Hg 0, ug/dnm SCR Inlet SCR Outlet Equilibrium Added Br, ug/g coal equivalent Comparison of Plant Miller data of Berry et al. with calculated equilibrium

21 Effect of SCRs on Added Halogens Bromine is more efficient (equal mass basis) than chlorine at oxidizing Hg across SCRs Hg 0, ug/dnm Equilibrium at 720 o F Subbituminous Coals Bromine Results will be catalyst-specific Subbituminous (low-chlorine) coals only Chlorine Halogen, ug/g coal equivalent

22 Summary: Why Add Halogens? Adding halogens to fuel or flue gas: Halogen content of US coals varies widely Oxidation of Hg (especially in SCRs) and capture of Hg on fly ash enhanced with additions of halogens, like Cl and Br Many plants APCDs can take advantage of native capture Adding halogens to activated carbon increases the ability to capture elemental Hg in lowhalogen flue gas

23 How Effective Are Halogens? Halogens increase oxidized mercury: Br more effective than Cl (on an equal mass basis) Increased Hg removal across scrubbers Total Hg Removal (coal-to-stack) 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Monticello: PRB/lignite, ESP, wet FGD Chlorine addition Bromine injection Halogen in coal, ug/g

24 How Effective Are Halogens? Halogens increase oxidized mercury: Br more effective than Cl (on an equal mass basis) Increased Hg removal across scrubbers Halogens increase effectiveness of PAC Hg Removal Plant Hardin: SCR/SDA/FF KNX lb/mmacf PAC KNX 0% 20% 40% 60% Percent recommended KNX rate Source: DOE/EPRI sampling campaigns

25 SO 3 Affects Hg Control SO 3 affects Hg control with activated carbon Any SO 3 in gas phase appears to affect Hg capture with PAC SO 3 is used to condition fly ash for better capture in ESPs SO 3 higher in bituminous flue gas, especially after SCR Hg removal across ESP 100% 80% 60% 40% 20% 0% MRC Results: 10 lb/mmacf, injection upstream of APH APHInlet: 627 F; APH outlet: 300 F (assume 1 ppm baseline SO 3 ) Norit Hg LH Calgon MC ppm SO 3 24

26 The SO 3 Story 1. SO 3 is produced in the flame zone by oxidation of SO 2 2. In the convective pass, high-iron fly ash can act as a catalyst and produce more SO 3 3. OR high-calcium fly ash can reduce SO 3 by adsorption Temperature, o C Radiant Heat Transfer Time, seconds Convective Heat Transfer 2 3 Air Preheater (Gas-Gas Heat Transfer) Flue Gas to Particulate Control Temperature, o F 25

27 SO 3 Production in SCRs Selective Catalytic Reduction (SCR) process uses a catalyst to destroy NOx But SCR creates SO 3 by oxidation of SO 2 1.4% Example: SO 3 production in SCR with 3 layers 1.2% 1.0% SO 2 conversion 0.8% 0.6% 0.4% 0.2% 0.0% Temperature, F Source: D. Ritzenthaler,

28 Removal of SO 3 in Air Preheaters Two mechanisms for removal of SO 3 across APHs: Condensation on surfaces below dew point temperature Formation of ammonium bisulfate (ABS) solid (reaction between ammonia and SO ) 3 Source: Biggs et al.,

29 Formation of Ammonium Bisulfate Temperature (Degrees F) NH3 Concentration (ppm) SO3 (ppm) Source: Marshall et al.,

30 Dew Point of SO 3 in Flue Gas Dewpoint, o F % H 2 0 5% H 2 0 SO 3 dew point depends on flue gas temperature and water content T SO 3, ppmv T Dewpoint in Kelvin Partial pressures in mm Hg 5 ( P ) 8.58x10 ln( P ) x10 ln( P ) ( P ) = 2.276x x10 ln H 6 Dewpoint 2O H ln 2SO4 H 2O H 2 SO 4 29

31 Condensation of SO 3 in APH: Example SO 3 measured across duct downstream of regenerative APH Correlation between APH exit temperature and SO 3 concentration Temperature, F Port location SO 3, ppmv 30 Source: DeVito, 1999

32 Summary: SO 3 Sources/Sinks Catalytic oxidation of SO 2 in furnace and/or adsorption by CaO Condensation in APH Adsorption on alkaline fly ash Stack Oxidation of SO 2 in furnace Boiler SCR Air Heater Fuel Burners Catalytic oxidation of SO 2 by SCR catalyst Particulate Collector SO 2 Scrubber Induced Draft Fan Removal of sulfuric acid aerosol in scrubbers 31 Coal Pulverization Coal Supply

33 Fate and Impacts of Halogens What are the potential impacts of halogen addition on the boiler, APCDs, and emissions? Corrosion Fly ash Stack emissions Scrubber interactions Boiler SCR Air Heater Stack Fuel Burners Particulate Collector SO 2 Scrubber Induced Draft Fan Coal Pulverization Coal Supply

34 Corrosion in Flue Gas Chlorine corrosion in furnaces can occur for very high levels of chlorine in coal (> 2000 µg/g) Bromine addition at much lower concentrations Indirect evidence that HBr might be more corrosive than HCl at flue gas temperature No direct comparison, but HBr corrosion higher than baseline (no HBr) in simulated flue gas (6-month study) Corrosion loss, mm Baseline 51 ppmv HBr Temperature, o F Zhuang et al., 2009

35 Bromine Addition: Fly Ash Impacts Bromine additive or brominated PAC results in increase in Br in fly ash Example: Br injection at Monticello (C-ESP) Br, µg/g Br in fly ash Br injected /1/05 11/15/05 11/29/05 12/13/05 Bromine injection at Monticello (EERC, URS data) Br addedm µg/g coal

36 Bromine Addition: Fly Ash Impacts Fly Ash, µg/g Bromine additive or brominated PAC results in increase in Br in fly ash Example: Br injection at Plant Miller (PRB, C-ESP) According to the authors: Br in Fly Ash Br in Leachate Added Br, µg/g coal equivalent Leachate, mg/l Hg concentration in fly ash didn't increase with Br injection 1% of Br captured by fly ash 50% of Br on fly ash leached in SPLP test Dombrowski et al., 2008

37 Chlorine Emission from APCDs Source: 2010 ICR

38 Bromine Emission from APCDs PIPP Meramec FF C-ESP Brominated PAC injection Boiler 1 Boiler 2 C-ESP C-ESP Fuel addition Boiler 3 C-ESP 0% 50% 100% Percent of added halogen emitted in stack All boilers are pulverized coal, burning subbituminous coal

39 Chlorine Emission from APCDs Source: 2010 ICR

40 Halogens in Wet Scrubbers Adding halogens (Cl or Br) increases oxidized Hg, which increases capture of Hg in scrubber Wet FGD scrubbers remove halogens efficiently Average Cl removals for wet FGDs (2010 ICR): 81% for subbituminous, 97% for bituminous Removal of Br at Plant Miller wet FGD: 94-96% (Dombrowski et al., 2008) Halogens build up in wet scrubber liquor

41 Halogens in Wet Scrubbers Halogens and Hg build up in wet scrubber liquor slowly, depending on scrubber design Br, mg/l, Hg, µg/l Br in FGD liquor Hg in FGD liquor Br injected /1/05 11/15/05 11/29/05 12/13/ Br addedm µg/g coal Bromine injection at Monticello (EERC, URS data)

42 Halogens and Wet Scrubbers Increased Cl, Br concentration in scrubber liquor can decrease Hg re-emission

43 Halogens and Wet Scrubbers Recent observations (Air Quality VIII) that Br addition to the fuel increases Se in scrubber liquor Data from bituminous site with C ESP, wet FGD Se in fly ash, µg/g % Se capture by fly ash Se in FGD liquor, µg/l Baseline 24 70% 300 Br addition 10 20% 4900 (Dombrowski et al., 2011) Less uptake of Se by fly ash means more Se enters FGD

44 Halogens Summary Halogen fuel/flue gas additives OR halogenated PAC Where do halogens go? Some removal in particulate control devices Efficient removal in FGDs Br is new kid on the block information needed: Corrosion Multi-media fate Trace metal interactions Fuel Halogen Injection Boiler Burners Coal Pulverization SCR Air Heater Halogenated Carbon Injection Particulate Collector Fly Ash Coal Supply Stack SO 2 Induced Scrubber Draft Fan Scrubber Blowdown Stack Emission

45 Hg Removal in the Boiler How is Hg removed? Adsorption on particles (fly ash, sorbents) and removal in the particulate control device Absorption of oxidized mercury in scrubbers How can we improve removal by what happens in the boiler? Increase unburned carbon if you can Consider adding more halogens if There s enough LOI, but halogens are low There s a scrubber Keep SO 3 low post-aph

46 Questions? 45