Mercury oxidation by halogens under air-fired and oxy-fuel conditions

Mercury oxidation by halogens under air-fired and oxy-fuel conditions Ignacio Preciado, Tessora Young, Geoffrey Silcox, Jost Wendt Chemical Engineering, University of Utah Brydger Van Otten, Andrew Fry Reaction Engineering International AFRC, Salt Lake City September 7, 2012 REACTION ENGINEERING INTERNATIONAL Outline • Introduction • Objectives • Experimental - Bench scale - Experimental set up - Results * Air firing vs. Oxy-firing. Oxidation by Chlorine and bromine * Effects of SO2 and NO in air firing tests • Experimental - Pilot scale - Experimental set up - Results * Air firing vs. Oxy-firing. Oxidation by bromine • Conclusions REACTION ENGINEERING INTERNATIONAL Co c us o s Introduction • Hg transformations in coal combustion systems - Forms of mercury: Hg0, Hg2+ and HgP - Hg2+ may be captured in the wet FGD scrubbers - HgP may be captured in an ESP of FF - Extent of conversion of Hg0 to Hg2+ and HgP depends of many factors - Predicting Hg speciation and capture is difficult Hg2+ and HgP forms, important for capture REACTION ENGINEERING INTERNATIONAL http://www.epa.gov/mercury/control_emissions/tech_exist.htm Introduction • Hg oxidation by halogens - Chlorine content of coal has some impact on Hg speciation. Afonso and Senior, 2001; Kilgroe et al., 2002 - Activated carbon more effective for capturing Hg when chlorine added to AC. Gorishi et al., 2002 - Bromine mixed with AC and brominated sorbents are effective for mitigating Hg emissions. Sjostrom, 2006, Benson et al., 2006; Holmes et al., 2006; Dombrowski et al., 2007; Landreth et al., 2007 - Bromine and chlorine mechanisms still unclear. • Hg in oxy-fuel systems - Emission and corrosion problems. - Little is known about the Hg transformation mechanisms and fate of Hg in oxy-combustion processes. - Interactions between mercury and other flue gas components might be affected by a change in combustion conditions. REACTION ENGINEERING INTERNATIONAL Objectives • Compare the effects of air-firing and oxy-firin Co pa e t e e ects o a g a d o y g conditions on mercury speciation and removal in a bench-scale, methane-fired facility and in a pilot-scale, coal-fired facility. • Bench scale: determine the extents of elemental mercury oxidation in presence of various flue gas components such as chlorine, bromine, SO2, and NO for air-firing and oxy-firing of methane. • Pilot scale: evaluate mercury speciation and capture during air-firing and oxy-firing with PRB coal. • Provide unique data for validation of homogeneous mercury oxidation models. • Use data and models to evaluate the fate of mercury in full-scale t thtfi PRB l REACTION ENGINEERING INTERNATIONAL systems that fire coals Bench-scale experiments Homogeneous oxidation REACTION ENGINEERING INTERNATIONAL Experimental setup Mercury source Permeation tube • 300 W (1000 Btu/h), methane-fired, laminar, quartz reactor High Temperature Section ~ 1100°C • Quartz burner allows all species to pass through the flame • Temperature 1100 profile representative of industrial boiler Reaction Chamber • 6 SLPM exhaust gas 4.7 cm inside diameter 1.3 meters long (Total) Quench Region ~ 1000°C - 400°C S l S ti REACTION ENGINEERING INTERNATIONAL Sample Section ~350°C Two ¼ inch sample nozzles Sample conditioning system Tekran 2537A Mercury Analyzer (CVAFS) Hg source. Permeation tube H T H 0 Reactor Chiller HgT Hg0 Intermittent Hg0 and HgT SnCl2 HCl KCl Na2S2O3 4 Port Sampler Peristaltic Pump NaOH NaOH Hg2+ = HgTotal - Hg0 Fresh Reagents Hg0 NaOH SnCl2 KCl NaOH To gas analyzers Waste Reagents Vacuum Pump HgT Hg SnCl2 NaOH KCl NaOH REACTION ENGINEERING INTERNATIONAL Hg Sodium thiosulfate added to KCl impinger to prevent oxidation of Hg0 by hypochlorous acid. Example of homogeneous Hg oxidation data Hg2+ = HgTotal - Hg0 35 Mercury Oxidation. Air-firing, chlorine 30 ) Hg baseline Hg baseline 20 25 centration (g/m3) HgT 100 ppm as 200 ppm as 500 ppm as 10 15 Mercury conc HCl HCl HCl Hg0 0 5 10 48 12 00 13 12 14 24 15 36 16 48 18 00 REACTION ENGINEERING INTERNATIONAL 10:48:00 12:00:00 13:12:00 14:24:00 15:36:00 16:48:00 18:00:00 Time Quartz tubular reactor. Temperature profiles 1200 Temperature Profiles in Mercury Oxidation Reactor 800 1000 Methane flame SR = 1.06 6 slpm flue gas Air 600 emperature (°C) 27% O2 / 73% CO2 200 400 Te 0 0 20 40 60 80 100 120 140 Distance from end of quatz burner cm) Heater Heat tapes REACTION ENGINEERING INTERNATIONAL q ( ) Air firing Oxy firing Oxidation by chlorine 30 % Hg oxidation for air and oxy-firing tests 25 g/m3 Hg 20 25 ation m 2.0 % O2 (dry) in flue gas 10 15 % Hg oxid 0 5 0 100 200 300 400 500 600 Chlorine as HCl (ppm) Air-firing Oxy-firing(27% O2 - 73% CO2) H H Cl M thidb d REACTION ENGINEERING INTERNATIONAL Hg + Cl + M  HgCl + M HgCl + Cl2  HgCl2 + Cl = third body Sliger et al., 2000. Niksa et al., 2001 Air firing. Oxidation by chlorine - effect of SO2 Chlorine concentration = 200 ppm as HCl % H id ti f i fi i t t 15 20 Hg oxidation for air firing tests 25 g/m3 Hg 2.0 % O2 (dry) in flue gas 10 Hg oxidation 0 5 % H Range of % Hg oxidation for 200 ppm as HCl, without SO2 0 100 200 300 400 500 SO2 (ppm) REACTION ENGINEERING INTERNATIONAL Oxy firing. Oxidation by chlorine - effect of SO2 Chlorine concentration = 200 ppm as HCl % H id ti f fi i t t 15 20 Hg oxidation for oxy-firing tests 25 g/m3 Hg 2.0 % O2 (dry) in flue gas 10 Hg oxidation Range of % Hg oxidation for 200 ppm as HCl, without 0 5 % H pp SO2 0 100 200 300 400 500 SO2 (ppm) REACTION ENGINEERING INTERNATIONAL Air firing. Oxidation by chlorine - effect of NO % H id ti f i fi i t t Chlorine concentration = 200 ppm as HCl 15 20 Hg oxidation for air firing tests 25 g/m3 Hg 2.0 % O2 (dry) in flue gas 10 Hg oxidation 0 5 % H Range of % Hg oxidation for 200 ppm as HCl, without NO 0 100 200 300 400 500 600 NO (ppm) REACTION ENGINEERING INTERNATIONAL Oxidation by bromine 70 % Hg oxidation for air and oxy-firing tests 50 60 ion 25 g/m3 Hg 2.0 % O2 (dry) in flue gas 20 30 40 % Hg oxidat 0 10 0 0 10 20 30 40 50 60 Bromine as HBr (ppm) Air-firing Oxy-firing (27% O2 - 73% CO2) REACTION ENGINEERING INTERNATIONAL Hg + Br + M  HgBr + M HgBr + Br2  HgBr2 + Br M = third body Sliger et al., 2000. Niksa et al., 2001 Comparison - chlorine vs bromine 70 % Hg oxidation for air and oxy-firing tests 50 60 ion 25 g/m3 Hg 2.0 % O2 (dry) in flue gas 20 30 40 % Hg oxidat 0 10 0 100 200 300 400 500 600 Halogen concentration (ppm) Air-bromine Oxy-bromine Air-Chlorine Oxy-chlorine 10 50 REACTION ENGINEERING INTERNATIONAL Gas-phase. Thermodynamics of Cl and Br 1.00E-04 HCl 1.00E-06 1.00E-06 1.00E-05 ion Cl2(g) HCl(g) Cl(g) 1.00E-08 1.00E-07 ion Br2(g) HBr(g) Cl2 HBr 1.00E-08 1.00E-07 Mole Fracti 1 00E 1.00E-10 1.00E-09 Mole Fract Br(g) Cl Br Br2 1.00E-10 1.00E-09 0 200 400 600 800 1000 1200 Temperature °C 1.00E-12 1.00E-11 0 200 400 600 800 1000 1200 Temperature, °C HCl is dominant species at all T. Br2 is dominant species below 400C. REACTION ENGINEERING INTERNATIONAL Chemical equilibrium calculations, Connie Senior (2003) Pilot-scale, coal fired tests REACTION ENGINEERING INTERNATIONAL Experimental setup Rate O CO CO NO SO Oxy-combustion is performed without flue gas recycle. O2 is diluted with CO2 from a tank. Firing (kW) O2 (%, dry) CO2 (%, dry) (ppmv, dry) NOx (ppmv, dry) SO2 (ppmv, dry) Air- Fired 27 4.0 15.4 57 425 105 2 Oxy 3 0 92 6 Mixture (vol.) 27 % O2 Oxy- Fired 27 3.0 92.6 130 283 113 Br addition-solid CaBr2 added to coal (~20 or 40 ppm Br wet on coal) ACI-Darco Hg injected through third port in horizontal section (~2.1 or 4.5 lb/MMacf air-fired ~2.7 or 6.0 lb/MMacf oxy-fired) Sampling Temp ~ 150 F (65 C) Particulate Hg collected in baghouse ash REACTION ENGINEERING INTERNATIONAL Sampling Temp : 320 - 350 F (160 - 175 C) Experimental setup Sampling probe - mercury measurement system 30b carbon traps = total Hg Speciated carbon traps = oxidized Hg T = 100 C REACTION ENGINEERING INTERNATIONAL Carbon traps were analyzed by Ohio Lumex to determine gas-phase Hg concentrations Coal analysis North Antelope PRB Coal Analyses Mineral Matter Analyses C 53.72 Al 14.78 H 3.57 Ca 22.19 N 0.78 Fe 5.20 gas-phase mercury S 0.23 Mg 5.17 O 13.07 Mn 0.01 Ash 4.94 P 1.07 Produces gas concentrations of ~ 7.4 g/dscm (5 lb/TBtu) Moisture 23.69 K 0.35 Volatile Matter 33.36 Si 30.46 Fixed Carbon 38.01 Na 1.94 HHV, Btu/lb 9078 S 8.83 Cl, g/g, dry <10 Ti 1.30 Hg, g/g 0.045±0.009 REACTION ENGINEERING INTERNATIONAL Total Hg in gas phase HgTG  Hg0  Hg2 11 12 8 9 10 O2, traps) Baseline Br 20 ppm Br 40 ppm ACI low ACI high 5 6 7 dscm @ 3% O 2 3 4 HgT (ug/d Air, before BH Air, before BH Air, before BH Air, before BH Air, before BH 0 1 REACTION ENGINEERING INTERNATIONAL Air, after BH Oxy, before BH Oxy, after BH Air, after BH Oxy, before BH Oxy, after BH Air, after BH Oxy, before BH Oxy, after BH Air, after BH Oxy, before BH Oxy, after BH Air, after BH Oxy, before BH Oxy, after BH Mercury removal Mercury HgTG HgTG  Hg0  Hg2 removal : HgCoal 1 Hg 90% 100% Hg Hg Hg 70% 80% , Trap) 50% 60% emoval (Coal, 20% 30% 40% Hg Re Ai b f Ai b f Ai b f Ai b f Ai b f 0% 10% Baseline Br 20 ppm Br 40 ppm ACI low ACI high REACTION ENGINEERING INTERNATIONAL Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Gas phase Hg oxidation 90% 100% Baseline Br 20 Br 40 ACI ACI high 70% 80% ps ppm ppm low g 40% 50% 60% Oxidation, tra 20% 30% % O 0% 10% Air Air Air Air Air REACTION ENGINEERING INTERNATIONAL Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Mercury mass balance T Gas phase Ash Mercury mass balance : Coal Hg Hg HgT  Hg0  Hg2  Hg P Total measured mercury : 160% 120% 140% Traps) 80% 100% (Coal, Ash, T 40% 60% Mass Balance 0% 20% Hg M Baseline Br 20 ppm Br 40 ppm ACI low ACI high REACTION ENGINEERING INTERNATIONAL Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Air, after BH Air, before BH Oxy, before BH Oxy, after BH Conclusions Bench-scale tests • Air firing vs Oxy-firing, oxidation with chlorine The measured homogeneous mercury oxidation levels ranged from 6 to 21% for oxy-oxy firings vs 4 to 15% for air-firing at reactor chlorine levels of 100 to 500 ppmv (as HCl). • Air firing vs Oxy-firing, oxidation with bromine The measured homogeneous mercury oxidation levels ranged from 36 to 58% for oxy-firing vs 9 to 36% for air-firing at reactor bromine levels of 10 to 50 ppmv (as HBr). • Homogeneous oxidation of mercury by chlorine is unaffected by SO2 and NO under air firing conditions and by SO2 under oxy-firing conditions. • Hg oxidation by bromine was 2 - 4 times higher than by chlorine, with 10 REACTION ENGINEERING INTERNATIONAL times less content of halogen. Conclusions Pilot-scale tests • The mercury mass balance was poor for many conditions, most likely due to unrepresentative ash samples. • Mercury emissions decreased with the addition of bromine or activated carbon. Removal levels increased with increase additive dosage. • No significant difference in additive performance was seen between air-and oxy-firing. • There was little difference in gas-phase Hg speciation between air- and oxy-fired conditions. REACTION ENGINEERING INTERNATIONAL Future work • Oxidation by bromine - effect of SO2 and NO • Modifications in wet sampling conditioning system, making it better for bromine + SO2 • Modeling - homogeneous reactions REACTION ENGINEERING INTERNATIONAL