Field Testing ofActivated Carbon InjectionOptions for Mercury Control atTXU’s Big Brown StationJohn PavlishEnergy & Environmental Research CenterDOE NETL Mercury Control Technology ConferenceDecember 13, 2006Pittsburgh, PennsylvaniaAcid Gas SolutionsALhoist Group CompanyProject ParticipantsProject ParticipantsDecember 20063Big Brown Power StationBig Brown Power Station,Fairfield, Texas



# Test Location Location Unit 2, Unit 2, Side BDecember 20064Big Brown Unit InformationBig Brown Unit InformationBig Brown Station, Freestone County, near Fairfield, Texas• Plant capacity: Approximately 1200 MW totalcapacity with two 600-MW units• Test unit: Tested one-quarter of BB Unit 2,baghouse Module 2-4 (FF 2-4)• Boiler type: Tangentially fired with eight coalfeeders per unit• Typical fuel: 70% Texas lignite–30% PRB blend• SO2control: None• NOxcontrol: Low-NOxburners• Particulatecontrol: COHPACTM configurationDecember 20065Field Testing ObjectivesField Testing Objectives• Establish baseline Hg concentrations and speciation acrossFF 2-4.• Screen control technologies with short-duration parametrictests, including ACI-only, enhanced ACI, and ACI plus SEA4.• Perform a monthlong test with the most promising technology,and evaluate long-term Hg capture and balance-of-plant(BOP) issues.70% Lignite–30% Powder River Basin (PRB)• Establish baseline Hg concentrations and speciation acrossFF 2-4.• Parametric tests, including ACI-only and enhanced ACI.100% PRB (under separate project)Mercury Control Options for TXUMercury Control Options for TXUBig Brown ConfigurationBig Brown ConfigurationStackTXU’s Big Brown Unit–Sampling Locations1) Coal: Hg, Cl, Prox./Ult., Heating Value2a) Ash: Hg, Cl, LOI, C2b) Ash: Hg, Cl, LOI, C3) ESP Inlet Flue Gas: OH4) Baghouse Inlet FlueGas: OH, Hg CEM5) Baghouse Outlet Flue Gas: OH, Hg CEM6)ACIand AdditiveInjectionCoalBunkerFeeders(8)Pulverizers(8)AirHeatersESPsID FansFabric FiltersBoosterFans1342a56AdditiveStandard AC&Treated/Enhanced AC2bUnit 2Boiler 

# Side B ~ 300 M w 4 ~ 150 M w

F FDecember 20067Baseline Coal ComparisonBaseline Coal Comparison70–30 Blend and 100% PRB Averages30 Blend and 100% PRB AveragesNominal70–30 Blend *100% PRB *Hg, ppm (dry)0.2870.102Cl, ppm (dry)17**8**Moisture, %31.1731.17Ash, %9.914.94Sulfur, %0.680.39Heating Value, Btu/lb75318101Fd, dscf/106Btu97299294Hg,μg/dNm3, 3% O237.0112.80All values on an as-received basis unless otherwise noted.* Assumed ratio based on plant information.** Single value.December 20068Baseline* Hg Speciation for 70Baseline* Hg Speciation for 70–30 Blend30 BlendAverage of 1/18/06, 1/19/06, and 1/20/06Average of 1/18/06, 1/19/06, and 1/20/06Coal Inlet OH Inlet CMM Outlet OH Outlet CMM0102030405060

Mercury Concentration, μ g/dNm

3 (3% O 2 )Coal BasedOH Particulate-bound HgOH Oxidized HgOH Elemental HgCMM Total Gas Phase* Measurement taken at inlet and outlet of FF2-4.December 20069Baseline* Hg Speciation for 100% PRBBaseline* Hg Speciation for 100% PRBAverage of 3/30/06, 3/31/06, and 4/1/06Average of 3/30/06, 3/31/06, and 4/1/06Coal Inlet OH Inlet CMM Outlet OH Outlet CMM0102030

Mercury Concentration, μ g/dNm

3 (3% O 2 )Coal BasedOH Particulate-bound HgOH Oxidized HgOH Elemental HgCMM Total Gas Phase* Measurement taken at inlet and outlet of FF2-4.December 200610Parametric Results SummaryParametric Results Summary70–30 Blend30 Blend0123456780102030405060708090100

% Hg Removal across FF 2-4Sorbent Feed, lb/MacfAC Component of AC+SEA4Enhanced ACAC OnlyTotal AC and SEA4December 200611Comparison of Parametric TestingComparison of Parametric Testing70–30 Blend and 100% PRB30 Blend and 100% PRB012345670102030405060708090100

% Hg Removal across FF 2-4Sorbent Feed, lb/Macf100% PRB, Enhanced AC70/30 Blend, Enhanced AC70/30 Blend, AC Only100% PRB, AC OnlyDecember 200612Comparison of Blend and PRB Hg EmissionsComparison of Blend and PRB Hg Emissions(based on CMM data)(based on CMM data)FF 2-4Inletμg/dNm3,3% O2FF 2-4Outletμg/dNm3,3% O2FF 2-4Removal,%FF 2-4OutletEmissions,lb/TBtuBlend Baseline23.326.0018.4PRB Baseline7.28.405.7Blend withEnhanced AC*18.15.1753.2PRB withEnhanced AC*8.51.6810.9* Enhanced AC rate was 1.5 lb/MacfDecember 200613Comparison of Blend Parametric DataComparison of Blend Parametric Datato Gaston Resultsto Gaston Results0123456780102030405060708090100Gaston AC Only (Norit FGD)TXU-BB Enhanced ACTXU-BB AC OnlyTXU-BB AC+SEA4

% Hg Removal across FF 2-4Sorbent Feed, lb/MacfDecember 200614MonthlongMonthlongTest RationaleTest RationaleEnhanced ACI at a target rate of 1.5 lb/Macf (loadfollowing) was selected for the monthlong testingbecause it had a favorable balance among thefollowing factors:• Hg removal goals, parametric testing indicated>55% capture was possible.• Preliminary economics based on sorbentconsumption and equipment needs.• Reducing plant impacts by minimizing thequantity of injected sorbent. Could inject onlywhen dP was below 10 in. W.G.December 200615Hg Sampling ThroughoutHg Sampling ThroughoutMonthlongMonthlongTestCoal, OH, and CMM, 70Coal, OH, and CMM, 70–30 Blend30 Blend0102030405060AverageMar 20-22Mar 16-17

CMM Out

OH Out

Coal CMM In

OH In

Mercury Concentration, μ g/dNm

3 (3% O 2 )Coal BasedOH Particulate-bound HgOH Oxidized HgOH Elemental HgCMM Total Gas Phase

Coal OH In CMM In OH Out CMM Out Coal OH In CMM In OH Out CMM Out Coal OH In CMM In OH Out CMM OutFeb 27-Mar 1Hg Control:1.5 lb/MacfEnhanced ACDecember 200616Big Brown Field TestingBig Brown Field TestingBalanceBalance-of-Plant (BOP) IssuesPlant (BOP) Issues•Bag Blinding—Following Hg field testing, the residualdrag across FF 2-4 had reached a point where TXU wasnot confident in its performance for the upcomingsummer season; therefore, the plant initiated a full bagreplacement of FF 2-4 in May 2006. Because of manyconfounding factors, the exact cause is still underinvestigation.•Plugged Hoppers/Deposits—During the bag change, itwas discovered that two of the eight hoppers (Hoppers Cand H) on FF 2-4 were plugged and filled with ash. Inthese two hoppers, unusual deposits were found mixedwith the loose ash, which was reported to be very hotand smoldering.December 200617ThermocoupleAccess DoorDecember 200618Hoppers C and HHoppers C and H–Ash LevelAsh Level• When opened for the bagchange, both Hoppers C and Hwere completely full of ash to aheight above the access door.• The operators did note thatash had collected in the inletduct and was probably at leastto that level and, therefore,completely filling the bottomcone.• They did not think ashcontacted the bags since thatwould require the entire inletduct to become blocked.Bag BundleInlet PoppetValve (2)Access DoorPossible Ash LevelsDecember 200619ConclusionsConclusionsBig Brown Hg Field TestingBig Brown Hg Field Testing• Under baseline test conditions, mercury capture across thebaghouse is effectively zero for both the 70–30 blend and 100%PRB.• Both the AC+SEA4 and enhanced ACoptions performed better thanAC alone. Testing showed that>70% capture could be achievedwith rates lower than 2 lb/Macf.• Hg removal efficiencies were similar for the 70–30 blend and 100%PRB, but emissions were much lower with the PRB because of thelower Hg-in-coal content.• Month-long testing with the enhanced AC showed an averageremoval greater than 70%, however, there were fluctuations due tointerruptions in the ACI feed andthe ACI equipment settings. Atsteady state conditionswith the target ACI rate of 1.5 lb/Macf,average removals were greater than 80%.• The narrow and limited operating margin of the COHPAC differentialpressure proved to be the limiting factor for applying sorbentinjection at Big Brown. Short termtests were successful, but forlong-term sustainable ACI operation,substantial modifications to theplant are required to provide a greater operating margin.December 200620ConclusionsConclusionsBig Brown Balance of Plant EffectsBig Brown Balance of Plant Effects• The residual drag across FF 2-4 appears to have increased by anamount that was unexpected based on past experience. Theinvestigation into the root cause is still underway and includes plantoperating conditions as well as the effects of sorbent injection.• The plugged hoppers and the associated deposits appear to be aresult of the hopper heaters being off for compartments C and H.The heaters being off likely ledto formation of deposits thateventually grew to a size large enough and strong enough to plughopper C and H discharge. Subsequently, this led to accumulationof ash and AC of adequate quantityto promote self heating andeventual ignition. The deposits are a mix of hydration products,heated to varying degrees, and ash sintered with heat from thesmoldering ash-AC mixture. More work is needed to determineexact mechanism of self ignitionand conditions under which it canoccur.