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Hg 2014_v0_slideshare

Date post:02-Jul-2015
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Sampling methods using sorbent traps have been used extensively over the past 20 years for speciating mercury in flue gas. The Flue Gas Adsorbent Mercury Speciation (FAMS) method is an example. This method has gained widespread acceptance as the preferred alternative for mercury speciation due to its simplicity, sensitivity, and repeatability. However, FAMS and other sorbent trap methods were developed primarily for measurements made in the relatively clean, dry, and cool flue gas present downstream of the particulate control devices. Application of sorbent traps to measure mercury in the high temperatures and high particulate loadings that exist upstream of the APC system or the saturated drop-laden gas downstream of FGD requires modifications to the approach. This presentation addresses the use of sorbent traps to speciate mercury throughout the air pollution control system of a coal-fired utility. Specific sampling approaches to accommodate testing at high temperatures, high dust loadings, and saturated gas streams are discussed. Data are presented for measurements made from points ranging from near the exit of the boiler to the outlet of a wet scrubber. We discuss the interpretation of the results and examine metrics used to assess data quality.
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  • 1. Mercury SpeciationMeasurements fromBoiler to StackPresented byClean Air Engineering

2. There is a growing need to measure speciatedmercury throughout air pollution controlsystems at coal-fired power plants. 3. There are two major drivers for this 4. Emissions Standards forBoilers and Process Heatersand Commercial/IndustrialSolid Waste Incinerators 5. Emissions Standards forBoilers and Process Heatersand Commercial/IndustrialSolid Waste Incineratorsaka, the Boiler MACT 6. National Emission Standardsfor Hazardous Air Pollutants:Coal- and Oil-Fired ElectricUtility Steam GeneratingUnitsAnd 7. National Emission Standardsfor Hazardous Air Pollutants:Coal- and Oil-Fired ElectricUtility Steam GeneratingUnitsAndaka, the EGU MATS 8. Both of these rules require reductions inmercury emissions 9. So-called co-benefit control from existing airpollution control devices is one approach toreduce mercury emitted to the atmosphere 10. Another would be add-on controls, such assorbent injection 11. Consequently, there is much interest in the fateof mercury across the various air pollutioncontrol systems of power plants700F + Flue Gas Temperature 130F +Sorbent Sorbent Sorbent SorbentAPHFGDSCR ESP/FFBoilerHg0Hg0Hg+2HgPHg0Hg+2HgPHg0Hg+2HgP Hg+2Hg0Hg+2Hg0Hg+2Sorbent 12. Co-benefit and add-on controls generallyrely on operational measures to Promote oxidation of Hg0 to Hg+2 Promote adsorption of Hg onto particles 13. To understand these relationships requiresknowledge of the different species ofmercury throughout the APC system 14. i.e., from boiler to stack 15. This is difficult thing to model 16. It relies on a variety of factors 17. Such as coal ash flue gastemperature flue gas chemistry retention time inAPCDs scrubber chemistry boiler operation 18. And previous efforts to measure it havebeen handicapped by a lack ofstandardization in the test methods 19. Not to mention the characteristics of theflue gas being measuredhot, dirty,interferences such as NH3, HBr, etc. 20. The traditional testmethod to measurespeciated mercury isthe Ontario HydroMethod(ASTM D6784) 21. It looks like this schematically 22. This method has a reputation of beingcumbersome and difficult to reproduce... 23. And there is a known issue with mercurypartitioning in the particulate fraction 24. And it takes several hours to perform. Thecost of data is relatively high. 25. All of which has led to theprevalence of using SorbentTrap Methods to measure Hg 26. EPA Method 30B is the sorbent trapreference method 27. Method 30BSection 1 Section 2Spiked 28. Method 30B does not speciate Hg. For that,we turn to the FAMS approach (aka,Modified Method 30B) 29. FAMS MethodParticulate Mercury Oxidized Mercury Section (S1-S3)Elemental Mercury Section (S4-S5)(semi-quantitative)PotassiumChloridePotassiumChlorideActivatedCarbonActivatedCarbonPMFilter Gas FlowSection 1GlassWoolPlugGlassWoolPlugGlassWoolPlugGlassWoolPlugGlassWoolPlugSection 2 Section 3 Section 4 Section 5AGSGlassWoolPlugHg+2 Hg0HgP 30. FAMS has its limitations though 31. You can measure particulate-bound mercurywith FAMS 32. by adding a filter ahead of the traps.Filter KCl Trap Carbon Trap 33. But there is a problem with this when usedupstream of particulate control.Unless the duct is traversed and sampling isperformed isokinetically, particle sizevariation will bias the particulate collected. 34. Does the particulate captured from this locationusing only one test port mean anything? 35. Does the particulate captured from this locationusing only one test port mean anything?Probably not! 36. Does the particulate captured from this locationusing only one test port mean anything?Probably not!But often,that is theapproachtaken. 37. There are other limitations to FAMS, such astemperature 38. The carbon should not exceed about 450FSection 1 Section 2 Section 3 Section 4Section 5PM Filter AGS KCl Carbon 39. The KCl should stay below 250FSection 1 Section 2 Section 3 Section 4Section 5PM Filter AGS KCl Carbon 40. There are also known flue gas matrixinterferences 41. Speciation TrapsLimitationsSection 1 Section 2 Section 3 Section 4Section 5Such asNO/SO2oxidationeffectsPM Filter AGS KCl CarbonNO + SO2 NO2Hg0 + NO2 Hg2+ 42. This is mitigated by the addition of an acidgas scrubber (AGS) ahead of the sorbents 43. But do we know how the AGS affectsspeciation? The assumption is that only oxidizedmercury collects on it. Is that true? Does theAGS promote any conversion?Section 1 Section 2 Section 3 Section 4Section 5PM Filter AGS KCl Carbon 44. And then there are the interactions betweenmercury, flue gas, and particulate thatcollects on the pre-filter 45. For exampleSpecies Flyash Effects:HgP Increase from adsorption of Hg2+ and Hg0Hg2+ Increase from catalytic oxidation of Hg0Hg0 Loss through adsorptionSection 1 Section 2 Section 3 Section 4Section 5PM Filter AGS KCl CarbonSO3HClNOxLOIIron{ 46. And the location of the filter also has an effectnsSpecies Flyash Effects:HgP Increase from adsorption of Hg2+ and Hg0Hg2+ Increase from catalytic oxidation of Hg0Hg0 Loss through adsorptionSection 1 Section 2 Section 3 Section 4Section 5PM Filter AGS KCl Carbon 47. And the location of the filter also has an effectSpecies Flyash Effects:HgP Increase from adsorption of Hg2+ and Hg0Hg2+ Increase from catalytic oxidation of Hg0Hg0 Loss through adsorptionSection 1 Section 2 Section 3 Section 4Section 5PM Filter AGS KCl CarbonIn hot gases, being at the front can reduce these impacts. 48. To combat the temperature limitations,some tests have been done with the trapslocated outside of the hot flue gas 49. Like this...300-700F 250FTemperaturecontrolledbox 50. APHSometimesthis data doesnot makesense.FGDSCR ESP 51. Paired Trap Agreement (%RD)Relative DeviationLocation HgP Hg+2 Hg0 HgT HgvapRun 1 SCR Inlet 1% 11% 7% 9% 9%AH Inlet 25% 21% 88% 19% 19%ESP Inlet 79% 44% 30% 13% 23%WFGD Inlet 35% 6% 17% 6% 7%Stack 15% 12% 20% 17% 18%And paired trapagreement is poorRun 2 SCR Inlet 66% 2% 42% 4% 5%AH Inlet 32% 8% 2% 5% 8%ESP Inlet 86% 8% 42% 6% 11%WFGD Inlet 4% 1% 76% 3% 3%Stack 5% 13% 12% 5% 5%Run 3 SCR Inlet 44% 1% 54% 3% 4%AH Inlet 22% 12% 2% 12% 12%ESP Inlet 90% 43% 9% 24% 35%WFGD Inlet 59% 4% 1% 3% 4%Stack 1% 65% 2% 6% 6% 52. Hg0Hg+2HgPThe problem is that mercury will re-partitionand convert as it traversesthe temperature gradient of the probe. 53. Hg0Hg+2HgPHg0Hg+2HgPAnd what you collect in the cool traps isdifferent than what was in the gas stream. 54. Problem StatementSo we need to design a sorbent trap probeto allow Hg speciation measurements influe gas with: high dust high temperature reactive interferences 55. A solution is to filter hot, shorten the gaspath prior to adsorption, and cool the trapsin-situ. 56. Here is onewaya Forced-AirCooled Probe300-700F 57. And take some additional measures 58. Minimize test durationTemperatureTest DurationParticulate 59. Minimize sample flow rateTemperatureSample RateParticulate 60. Move pre-filter up frontParticulate Mercury Oxidized Mercury Section (S1-S3)Elemental Mercury Section (S4-S5)(semi-quantitative)PotassiumChloridePotassiumChlorideActivatedCarbonActivatedCarbonPMFilter Gas FlowSection 1GlassWoolPlugGlassWoolPlugGlassWoolPlugGlassWoolPlugGlassWoolPlugSection 2 Section 3 Section 4 Section 5AGSGlassWoolPlug 61. Add a dust shield 62. AlsoPlacement of trap thermocouplesis criticalParticulate Mercury Oxidized Mercury Section (S1-S3)Elemental Mercury Section (S4-S5)(semi-quantitative)PotassiumChloridePotassiumChlorideActivatedCarbonActivatedCarbonPMFilter Gas FlowSection 1GlassWoolPlugGlassWoolPlugGlassWoolPlugGlassWoolPlugGlassWoolPlugSection 2 Section 3 Section 4 Section 5AGSGlassWoolPlug 63. AndStrict QA/QC is criticalParticulate Mercury Oxidized Mercury Section (S1-S3)Elemental Mercury Section (S4-S5)(semi-quantitative)PotassiumChloridePotassiumChlorideActivatedCarbonActivatedCarbonPMFilter Gas FlowSection 1GlassWoolPlugGlassWoolPlugGlassWoolPlugGlassWoolPlugGlassWoolPlugSection 2 Section 3 Section 4 Section 5AGSGlassWoolPlug 64. You cannot waive your hands at QA/QC forFAMS. Just as in 30B 65. If the goal is to measure speciated mercury,PAIRED FAMS traps should be collected 66. Common industry practice of pairing a totaltrap with a FAMS trap does not giveadequate QC metrics. 67. These are important QC metrics for eachspecies measured. Relative Deviation Breakthrough Spike Recovery 68. Our recommendations 69. Paired Trap Agreement (%RD)QA/QCSpecificationApplicableSampleFraction Acceptance Criteria FrequencyConsequences ifNot MetPaired sorbenttrap agreementHgP None N/A N/AHg+2 15% RD if Hg+2>1 g/dscm, 25% RD or0.25 g/dscm absolute difference ifHg+21 g/dscmEvery run Invalidate run forHg+2Hg0 10% RD if Hg0>1 g/dscm, 20% RD or0.2 g/dscm absolute difference if Hg01g/dscmEvery run Invalidate run forHg0HgvapHgT10% RD if Hgi>1 g/dscm, 20% RD or0.2 g/dscm absolute difference if Hgi1g/dscmEvery run Invalidate run forHgT or Hgvap 70. Breakthrough & Spike RecoveryQA/QC SpecificationApplicableSampleFraction Acceptance Criteria FrequencyConsequences if NotMetOxidizedBreakthrough(KCl sections)Hg+2 Section 3 KCl contains 10% ofthe Section 1 and 2 masses ifHg+2>1 g/dscm, Section 3contains 20% of the Section 1and 2 masses if Hg+21 g/dscmEvery trap Invalidate trap data forHg+2 and Hg0ElementalBreakthrough(carbon sections)Hg0 Section 2 carbon contains 10%of the Section 1 mass if Hg0>1g/dscm, Section 2 contains 20%of the Section 1 mass if Hg01g/dscm,Every trap Invalidate trap for Hg0,HgT, and HgvapField Recovery Test Hg0 Average recovery between 85%and 115% for Hg0Minimum threespikes perprogramFlag data 71. Following these measures, good data thatmakes sense can be obtained 72. APHFGDSCR ESP 73. Paired Trap Agreement (%RD)Relative DeviationLocation HgP Hg+2 Hg0 HgT HgvapRun 1 SCR Inlet 2% 20% 7% 1% 1%AH Inlet 1% 1% 3% 0% 0%ESP Inlet 5% 0% 1% 0% 0%WFGD Inlet 1% 1% 7% 1% 1%Stack 13% 8% 6% 3% 5%Run 2 SCR Inlet 1%

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