Performance of theBoswell Energy Center Unit 3Environmental Improvement ProjectKaren E. Burchardt, P.E., Burns & McDonnellTom Coughlin, P.E., Minnesota PowerPaper #57MEGA SymposiumBaltimore, MDSeptember 1, 2010Outline• Introduction• Description of unit• Description of project• Project challenges• Performance testing results• ConclusionsIntroductionRegulatory DriversClean AirMercury RuleClean AirInterstate RuleMinnesotaMercury RuleRegional HazeRuleRegulatoryDriversObjectives• Install APC equipment to comply withfuture regulations by 2010• Significantly reduce SO2, NOx, mercuryemissionsDescription of UnitBoswell Unit 3• 335 MW (net)355 MW (gross)• Cohasset, MN• COD 1973• C-E (Alstom)tangentially-fired unit• Fuel: PRB coalBoswell Unit 3• NOxcontrol:– BOOS to simulate OFA• SO2/PM control:– Single-stage wet particulate scrubber (Krebs)• Shares chimney with Boswell Units 1 & 2Boswell Unit 3Unit 3 BoilerUnit 3 ScrubberUnit 1, 2, & 3 StackUnit 4Unit 1 & 2Description of ProjectEquipment Added• Low NOxburners and overfire airsystem• SCR system• Wet FGD system• Fabric filter baghouse• Activated carbon injection system• ID fans{{Equipment Added• Ammonia storage system• Limestone handling and prep. system– Conversion of existing Unit 4 lime system– Powdered limestone delivered to site• Fly ash handling and storage systemSchedule• Engineering kickoff – February 2006• Main equipment contracts in place:– SCR, FGD, ductwork: Dec. 2006– Baghouse, SI system: Dec. 2006– ID fans: March 2007Schedule• Construction:– SCR: Oct. 2007 – Oct. 2008– FGD: March 2008 – July 2009– Baghouse: April 2008 – April 2009• Unit outage: Aug. – Nov. 2009• Start-up: Nov. – Dec. 2009• Performance testing: Jan. – Feb. 2010Project ChallengesChallenges• Limited site space• Installation of SCR reactor and supporttruss• Tight scheduleLimited Site SpaceLakeExistingscrubberBoilerLimited Site SpaceExistingscrubberExistingstackLakeLimited Site SpaceLakeExistingscrubberLimited Site Space• Needed to reclaim some of the lake– Sheet pile wall needed– Limited to 3 acres total area reclaimed– Limited to 1 acre wetland impactSheet Pile WallSheet Pile WallLimited Site SpaceCrane placed on baghouse foundation for SCR erectionLimited Site SpaceBaghouse pre-assembled in laydown areaLimited Site SpaceAbsorber building space minimizedNew FGDBuilding OutlineSCR Reactor/Truss• SCR elevated above existing scrubber• Supported by truss (160 ft. long)SCR SupportTrussSCR Reactor/Truss• Large foundations needed– Highly compressive soil– Existing underground utilities to re-route• Settling near existing structures– Pressure grouted augercast piles used– Pile installation limited to 7 months of year dueto cold climateSCR Reactor/Truss• Single large crane used– Maintain access to existing scrubber– Space for crane available on N side only• Placed on baghouse foundation• Deep foundation needed for craneSCR Reactor/TrussSCR Reactor/TrussSCR SupportTrussSCR ReactorScheduling• Alliance contractors worked on T&M basisto construct “work packages”• Work packages issued ASAP to expediteconstruction• Winter construction in Northern MN• Foundation design earlyPerformance Testing ResultsPerformance Targets• SO2: 98% removal• HF: 90% removal• HCl: 95% removal• H2SO4: 25% removalPerformance Targets• NOx:– 0.18 lb/mmBtu at economizer outlet– 0.05 lb/mmBtu at SCR outlet• Ammonia slip: 2 ppmvd at 3% O2• SO2–to-SO3oxidation: 3.1% across SCRcatalystPerformance Targets• PM10: 0.012 lb/mmBtu (filterable),0.08 lb/mmBtu (filt. + cond.)• Opacity: 5% at FF outlet• Mercury (total): 90% removal• Mercury (oxidized): 70% removalFGD SystemPerformance Testing• Measured at inlet and outlet of FGDabsorber:– SO2, PM10(filt. and cond.), Hg2+, HCl, HF, andH2SO4• Inlet and outlet measurements used todetermine % removal in absorberFGD SystemPerformance Testing• SO2:– EPA Method 6C– Average: 99+% removal• PM10:– EPA Methods 5B and 202– Average filterable: 0.0010 lb/mmBtu– Average condensible: 0.0033 lb/mmBtu– Average total: 0.0044 lb/mmBtuFGD SystemPerformance Testing• Hg2+:– Ontario-Hydro Method– Hg2+below detection limit at inlet and outlet– Cannot determine % removal• H2SO4:– Controlled Condensate Method– H2SO4below detection limit at inlet and outlet– Cannot determine % removalFGD SystemPerformance Testing• HCl and HF– EPA Method 26A– Average HCl removal: 82.6%– Average HF removal: 71.2%– Test results being further evaluated to see ifdesign performance was met.SCR SystemPerformance Testing• NOx:– EPA Method 7E– Econ. outlet/SCR inlet: 0.15 lb/mmBtu (average)– SCR outlet: 0.029 lb/mmBtu (average)• NH3:– CTM-027– Average: 0.04 ppm at 3% O2SCR SystemPerformance Testing• SO2–to-SO3oxidation:– SO3: Controlled Condensate Method– SO2: EPA Method 6C– Oxidation = (SO3,outlet– SO3,inlet)/SO2,inlet– Average: 1.33%SCR SystemPerformance Testing• SCR performance exceeded design– Common with new catalyst• Catalyst deactivatesÆperformancedegrades• Change catalyst as approach design pointFabric FilterPerformance Testing• PM10(filterable):– EPA Method 5B– Average: 0.0038 lb/mmBtu• Mercury (total):– Measured based on coal data, stack CEMS– Average: 92% removalConclusionsConclusions• Challenges– Tight space– Tight schedule• Construction completed on schedule• Performance testing completed– Most design performance criteria metNear CompletionSCRBaghouseID Fan andFGD Bldg.Sheet PileWallPAC SiloConclusions“It’s an amazing engineering feat. And notjust an engineering feat, but execution ofthe engineering. It’s beautiful and veryexciting.” – Senator Al FrankenQuestions?Karen Burchardt, Burns & McDonnellkburchardt@burnsmcd.com816-822-3430Tom Coughlin, Minnesota Powertcoughlin@mnpower.com218-722-5642, ext. 3549