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ORANGE COUNTY SANITATION DISTRICT BIOSOLIDS MASTER PLAN TECHNICAL MEMORANDUM 9: AQUA CRITOX REVIEW OCSD PROJECT NO. PS15‐01
Orange County Sanitation District 9 MAY 2017
©Black & Veatch Holding Company 2015. A
ll rights reserved.
In association with
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Table of Contents AcronymandAbbreviationsList....................................................................................................................iv
ExecutiveSummary........................................................................................................................................ES‐1
1.0 Introduction............................................................................................................................................1‐1
2.0 Aims...........................................................................................................................................................2‐1
3.0 MethodologyandApproach..............................................................................................................3‐1
4.0 LiteratureReview.................................................................................................................................4‐1
4.1 GeneralBackgroundonSCWO.......................................................................................................................4‐1
4.2 LiteratureReview................................................................................................................................................4‐4
4.2.1 Lab‐ScaleandPilot‐ScaleExperiments.......................................................................................4‐44.2.2 SCWOSystemandComponentDesign,OperabilityConsiderations,and
Challenges...............................................................................................................................................4‐64.2.3 EnvironmentalAssessmentofSCWO..........................................................................................4‐94.2.4 EconomicConsiderations...............................................................................................................4‐10
4.3 StatusoftheSCWOTechnology...................................................................................................................4‐11
5.0 SCFIProposal..........................................................................................................................................5‐1
5.1 ReviewofSCFIProposals.................................................................................................................................5‐2
5.1.1 General.....................................................................................................................................................5‐25.1.2 Feedstock................................................................................................................................................5‐25.1.3 GritRemoval..........................................................................................................................................5‐35.1.4 ScreeningRequirements...................................................................................................................5‐35.1.5 SCWOTechnicalComments.............................................................................................................5‐35.1.6 OperationsandStaffing.....................................................................................................................5‐45.1.7 Safety.........................................................................................................................................................5‐45.1.8 CriticalParts...........................................................................................................................................5‐45.1.9 Procurement..........................................................................................................................................5‐55.1.10 Mass&EnergyBalance......................................................................................................................5‐5
5.2 ReviewofCapitalandoperatingCosts.......................................................................................................5‐6
6.0 SCFIPilotPlantinValencia,Spain...................................................................................................6‐1
7.0 SCFIProposals–CapitalandOperatingCostEvaluation........................................................7‐1
7.1 SCFIBusinessCaseEvaluation.......................................................................................................................7‐1
7.1.1 ConstructionCostConsiderations.................................................................................................7‐17.1.2 Operating,MaintenanceandBenefitCostConsiderations.................................................7‐37.1.3 Repair&Replacement(R&R)CostConsiderations...............................................................7‐37.1.4 NetPresentValueAnalysisResults..............................................................................................7‐3
7.2 BV/BCBusinessCaseEvaluation..................................................................................................................7‐4
7.2.1 ConstructionCostConsiderations.................................................................................................7‐47.2.2 Operating,MaintenanceandBenefitCostConsiderations.................................................7‐67.2.3 Repair&ReplacementCostsandBenefitsConsiderations................................................7‐6
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7.2.4 NetPresentValueAnalysisResults..............................................................................................7‐67.3 ComparisonofSCFIandBV/BCCosts.........................................................................................................7‐7
8.0 Conclusions&Recommendations...................................................................................................8‐1
9.0 References...............................................................................................................................................9‐1
SeeEnclosedFlashDriveforAppendices
AppendixA–TabularSummaryofLiteratureonSuperCriticalWaterOxidation....................A‐1
AppendixB–QCReviewAffidavits.............................................................................................................B‐1
LIST OF FIGURES Figure4‐1.PhaseDiagramforWaterShowingCriticalPoint(Source:SCFI).............................................4‐1
Figure4‐2.GeneralizedSuperCriticalWaterOxidationFlowDiagram.......................................................4‐3
LIST OF TABLES Table4‐1.AdvantagesandDisadvantagesofSCWOTechnology....................................................................4‐4
Table4‐2.WastewaterIdealRequirementstobeTreatedbySCWOinTubularReactor(reproducedfromVadilloetal,2015)................................................................................................4‐8
Table5‐1.SummaryofEnergyInputsforAquaCritoxA30................................................................................5‐5
Table7‐1.InitialBusinessCaseEvaluationConstructionCosts1...................................................................7‐2
Table7‐2.InitialNetPresentValueAnalysisforBothAlternatives...............................................................7‐4
Table7‐3.RevisedBusinessCaseEvaluationConstructionCosts..................................................................7‐5
Table7‐4.RevisedNetPresentValueComparativeAssessment(w/osteambenefit)..........................7‐7
Table7‐5.RevisedNetPresentValueComparativeAssessment(w/steambenefit)............................7‐7
Table7‐6.ComparisonofSCFIandBV/BCCostEstimates................................................................................7‐8
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Acronym and Abbreviations List Thefollowingacronymsandabbreviationsareusedinthisdocument.
% percentAP acidificationpotentialASCE AmericanSocietyofCivilEngineersBtu/lb BritishthermalunitperpoundC CelsiusCaCl2 CalciumchlorideCIP CapitalImprovementProgramCO2 carbondioxideCOD ChemicalOxygenDemandDE destructionefficiencyDGSWR DynamicGasSealWallReactorDMT Drymetrictonsdtpa Drytonsperpoundactiveea eachEP eutrophicationpotentialEPS EnvironmentalprioritystrategyET EnvironmentalthemeEWT EcoWasteTechnologiesFL Floridag/l Gallonsperlitergal/hr Gallonperhourgph GallonsperhourGWP globalwarmingpotentialH2O waterHHV HighheatvalveHPHT highpressureandhightemperatureHPSCW hydrolysisofpolymersinsupercriticalwaterHTO hydrothermaloxidationsystemIC intercrystallinecorrosionkg/hr KilogramperhourKW KilowattskWh Kilowattsperhourlb poundlb/hr PoundsperhourLCAs life‐cycleassessmentsLOX Liquidoxygenm3/h CubicmetersperhourMG Milliongallonsmils/h TensofmicrometersperhourMIT MassachusettsInstituteofTechnologyMPa MillionPascalsMW megawatt
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N2 nitrogengasN2O nitrousoxideNa2SO4 sodiumsulfateNaCl sodiumchlorideNCH Near‐CriticalHydrolysisNH3‐N AmmoniaasNitrogenNOx oxidesofnitrogenNPV NetPresentValueO&M Operation&MaintenanceOCSD OrangeCountySanitationDistrictPFD ProcessflowdiagrampH PotentialofhydrogenPOCP photo‐oxidantcreationpotentialppm PoundsperminutePSI Poundspersquareinchpsig PoundspersquareinchgaugeR&R Repair&ReplacementSCAQMD SouthCoastAirQualityManagementDistrictSCBG supercriticalwaterbiomassgasificationSCC stresscorrosioncrackingSCFI SuperCriticalFluidsInternationalGroupSCW SupercriticalWaterSCWG supercriticalwatergasificationSCWO SupercriticalWaterOxidationSOx oxidesofsulfurSWPO supercriticalpartialoxidationTDI treatingtoluenediisocyanateTM‐3 TechnicalMemorandum 3TOC TotalOrganicCarbonTPAD TemperaturePhasedAnaerobicDigestionTS TotalsolidsTWR TranspiringWallReactorTX Texasµm/h MicrometersperhourVS VolatilesolidsWAS wasteactivatedsludgeWERF WaterEnvironmentalResearchFoundationWWTP WastewaterTreatmentPlantyr year
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Executive Summary OrangeCountySanitationDistrict(OCSD)isconsideringimplementationofademonstrationscalesupercriticalwateroxidation(SCWO)plantfortreatmentofwastewaterbiosolidsatoneoftheirwastewatertreatmentfacilities.AreviewhasbeenconductedofavailableliteratureontheSCWOprocessandadetailedreviewofproposalsfromtheSCWOvendor,SCFIfortheirproposedAquaCritoxsystemwasundertaken.
TheliteraturereviewconfirmedthatSCWOisanembryonictechnologyinrelationtoitsapplicationfortreatmentofwastewaterbiosolids.Whilepilotscaleworkonwastewaterbiosolidshasbeencarriedout,therearecurrentlynosuccessfulcontinuousoperatingSCWOfacilitiestreatingwastewaterbiosolids.TheliteraturereviewalsoconfirmedthatscalingandcorrosionaresignificantchallengesassociatedwithSCWOoperation.
AreviewofSCFIproposalsfortheOCSDfacilityidentifiedanumberofpotentialchallengesassociatedwithsuccessfulimplementationofthedemonstrationproject,aswellasseveralareaswhereitwasfeltthattheconstructionandoperatingcostestimateforthefacilityneededmodification.ArevisedcostanalysiswasundertakenwhichidentifiedthecostoftreatmentusingtheproposedAquaCritoxsystem.CostswerecomparedonaunitsolidsbasistotreatmentusingTemperaturePhasedAnaerobicDigestion(TPAD)whichOCSDisproposingtoutilizeforreplacementofdigestersatPlant2.TheunitcostforSCWOwasfoundtobeapproximatelydoublethatoftreatmentusingTPAD.Thisresultwasnotthoughttobesurprisinggiventhatitcomparesasmallerscaledemonstrationfacilityusingembryonictechnologywithafullscaletreatmentsolutionusingestablishedtechnology.
AsitevisitwasplannedtoanSCFIAquaCritoxpilottreatmentsystemlocatedinValencia,Spainaspartofthisevaluation.However,thisfacilityisnotincontinuousoperationtreatingwastewatersludgeinautothermalconditions.Therefore,thesitevisitwasindefinitelypostponed.
Longtermoperatingdatafromapilotfacilitytreatingwastewatersludgeisrecommendedinordertoevaluatethetechnicalconcerns,cost,andnoneconomicissuesidentifiedinthisTM.SincethepilotfacilityinValencia,Spainhasnotachievedthedesiredoperationaltrackrecordtodate,itisrecommendedthatOCSDpostponeanydecisionregardingademonstrationfacilityasproposedbySCFI.
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1.0 Introduction OrangeCountySanitationDistrict(OCSD)currentlyoperatestwoWaterResourceRecoveryFacilitiestermedPlant1andPlant2.Bothplantscurrentlystabilizebiosolidsusingconventionalmesophilicanaerobicdigestion.OCSDisplanningupgradestothesefacilitiesaspartoftheBiosolidsMasterPlan,projectPS15‐01.Aswellasconsideringestablishedtechnologiesforreliabletreatmentofbiosolidsoverthecomingyears,OCSDisinterestedinemergingtechnologieswhichhavethepotentialtoreducebiosolidstreatmentcostsinthefutureandprovideadditionalenergyrecovery.
OnesuchtechnologyisSuperCriticalWaterOxidation(SCWO)whichinvolvesheatingbiosolidsatveryhightemperaturesandpressures,leadingtochangesinthebehaviorofwaterandadramaticincreaseinsolubilityoftheconstituentsofbiosolids,allowingforalmostcompleteoxidationoforganiccomponents.OCSDhasbeenworkingwithSuperCriticalFluidsInternationalGroup(SCFI)whooffertheirAquaCritox®processforsupercriticalwateroxidationofmunicipalsludges.Becausethetechnologyhasonlybeenusedpreviouslyatverysmallscale,OCSDisconsideringademonstrationscalefacilitytofurtherevaluatethepotentialoftheprocessforfullscaleinstallationattheirfacilities.
SCFIhasbeenworkingwithOCSDtoplantheproposeddemonstrationfacilityandtogenerateanestimateofbothassociatedcapitalandoperatingcosts.OCSDhascommissionedBlack&VeatchwithsubconsultantsBrownandCaldwellandTimHaugtoconductareviewoftheSCFIproposals.
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2.0 Aims Theaimsofthisreviewareasfollows:
ToprovideanobjectivetechnicalandcommercialreviewofSCFI’sproposalsforademonstrationplantatOCSD.
ToprovideOCSDwithguidanceregardingthelikelytechnicalchallengesandrequirementsassociatedwithoperationofthefacility.
ToprovideOCSDwithanobjectiveevaluationofthelikelycapitalandoperatingcostsassociatedwiththefacilitysothattheycanreachadecisionastowhetheritistheirbestintereststoproceedwithconstructionofademonstrationplant.
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3.0 Methodology and Approach Thegeneralapproachtakenwiththisstudyisoutlinedasfollows:
1. AreviewoftheavailableliteratureonSCWOwasconductedtoensurethatOCSDisprovidedwithafullpictureregardingthestatusofthetechnologyandhistoryassociatedwithitsimplementation.
2. AtechnicalreviewoftheSCFIproposalswascarriedoutinordertoprovideOSCDwithrecommendationsregardingtheapproachtothedemonstrationplant,likelychallengesassociatedwithitsimplementationandmitigationmeasures.
3. AcommercialreviewoftheSCFIproposalswasconducted.ThebaseproposalfromSCFIwasreviewedandareaswereidentifiedwhereitwasthoughthatcapitalandoperatingcostsmaydifferfromthoseproposed.Acostcomparisonwasthenpreparedtocomparethefollowingscenariosonaunitdrysolidsthroughputbasis:
a. BaseproposalfromSCFIassumingallcostsstatedintheproposalareaccurate.
b. BaseproposalfromSCFIbutwithcostsadjustedinareaswhereitwasfeltthatcapitaloroperatingcostsmaydifferfromthoseputforwardbySCFI.
c. Acapitalandoperatingcostbaseline.Thiswasbasedontheexpectedcapitalandoperatingcostsforthenewtemperaturephasedanaerobicdigestion(TPAD)systemproposedforPlant2.
4. Baseontheabovework,recommendationsweremadetoadviseOCSDregardingtheirapproachtothedemonstrationproject.
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4.0 Literature Review Theliteraturereviewispresentedinthreesections.ThefirstsectionprovidesageneralbackgroundonSCWOforreaderswhomaynotbefamiliarwiththetechnology.ThesecondsectionprovidesasummaryoftheavailableliteratureonSCWOandthemainconclusionsreachedbyvariousresearchers.Thethirdsectionprovidesanoverviewofthecurrentstatusofthetechnologybasedontheliterature.ThesecondandthirdsectionsaresupportedbyadetailedtabularsummaryoftheliteraturewhichispresentedinAppendixA.
4.1 GENERAL BACKGROUND ON SCWO ThissectionprovidesageneralbackgroundonSCWOforreaderswhomaynotbefamiliarwiththetechnology.
Undernormalconditions,waterexistsinoneofthreestates;gas(steam),liquid(water),orsolid(ice).Anotherstateofwateremergesunderhightemperatureandpressureknownassupercriticalwater(SCW).Supercriticalwaterisatatemperatureandpressurewhichisabovethecriticalpointatwhichwatercanexistinallthreestates.AsimplifiedphasediagramofwaterisshowninFigureFigure4‐1.
Figure 4‐1. Phase Diagram for Water Showing Critical Point (Source: SCFI)
Undersupercriticalcondition,thebehaviourofwaterchangesanddependingonitsdensity,SCWbehavesasbothagasandaliquid.Diffusionratesarehigh(astheywouldbeinagas),collisionratesbetweenmoleculesarehigh(astheywouldbeinaliquid)andwatermoleculesbecomemuchlesspolar.Thisleadstoorganicmoleculesinthefluidbecomingfarmoresolubleandleadstoveryrapiddiffusionrates,thusallowingthepotentialforrapidandcompletechemicalreactions.
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Supercriticalwateroxidation(SCWO)makesuseofthesepropertiestooxidizeorganicsthroughtheinjectionofoxygenunderthesupercriticalconditionofwater.TheuniquepropertiesofSCWprovideareactormediuminwhichdiffusionisfast,organicmaterialsreactquicklywithoxygen,andthesaltsprecipitate.SCWOreadilyachieveshighdestructionefficiencyoforganics(morethan99.99percent)inshortreactiontime(lessthan1minute)buttemperaturesaresufficientlylowtoprecludeorminimisetheformationofSOxandNOxgases.
IntheSCWOprocess,organicsarecompletelyoxidized,carbonisconvertedtocarbondioxide,hydrogentowater,andnitrogentonitrogengasornitrousoxide.SaltmayremaindissolvedintheSCWmediumorcondensedasaconcentratedbrinesolutionorasasolidparticulate.Heavymetalscanformoxidesorcarbonates,whichmayormaynotprecipitate,dependingontheirvolatility.Inertsolidswilllargelybeunaffectedbytheprocessandwillremainassolids.
Thesolidsfromtheeffluentsettleveryeasilyandhaveverylowsolubility.Recoveryofusefulnutrients(suchasrecoveryofphosphorusbychemicalprecipitation)andby‐products(CO2andN2)canbeaccomplished.
AtypicalflowsheetforSCWOisprovidedinFigure4‐2.
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Figure 4‐2. Generalized Super Critical Water Oxidation Flow Diagram
Thewaste,aseitheranaqueoussolutionorslurry,ispressurisedanddeliveredtothereactorinlet.Oxygenissuppliedintheformofeithercompressedairorpureoxygen.Normally,theuseofoxygenisconsiderablylessexpensivethanairforlargescaleapplications.
TheorganicsareoxidizedintheSCWOreactor.Theeffluentfromthereactorisfedtoacyclonethatseparatessolids(saltsfromtheoriginalfeedaswellasthoseformedintheSCWOreaction)fromliquideffluent.Theliquideffluentofthesolidseparatorisamixtureofwater(H2O),nitrogengas(N2)andcarbondioxide(CO2).
Aportionoftheeffluentisrecycledtoprovidesupercriticalconditionsattheoxidiserinlet.Theremainderoftheeffluent,whichisahightemperaturehigh‐pressurefluid,iscooledtoasubcriticaltemperatureinaheatexchanger.Heatrecoveredfromtheheatexchangerisusedtogenerateloworhigh‐pressuresteamorhotwater,dependingontheneed.Theoutletstreamfromtheheatexchangerisfedtoaliquid–vapourseparator,wheretheN2andmostoftheCO2isremovedascleangaseffluent.Alternately,thegasstreamcanbeexpandedthroughaturbinetogeneratepower.Theefficiencyofthereaction(forthecompletedecompositionofthetargetchemical)isafunctionofreactiontemperatureandresidencetime.
ThepropertiesthatmakeSCWOagoodreactionmediumcanalsobeadisadvantagetotheprocess.ThematerialsandothercompoundspresentinthefeedstreamareheatedintheSCWOreactorandcanbecomeveryreactiveandthereforecausecorrosiontothereactor.Designofsystemstominimisecorrosionhasbeenamajorchallengeintheapplicationofthistechnology.Anotherchallengeisheatexchangerfoulingandscalebuild‐upfromtheinertsandsalts.TheadvantagesanddisadvantagesofSCWOprocessaresummarizedinTable4‐1.
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Table 4‐1. Advantages and Disadvantages of SCWO Technology
ADVANTAGES DISADVANTAGES
Complete oxidation of organics, COD removal > 99.9
percent
Severe corrosion in post‐reactor heat exchanger
High quality effluent Scaling formation caused by salt deposition
Low air emissions Problems with let‐down valves from high pressures
Provides significant reduction in greenhouse gas if CO2
is recovered
Feed waste must be homogenous and free from grit
(< 100 µm)
Immobilization of heavy metals in form of hydroxides,
carbonates and insoluble phosphates
Scale up of SCWO is challenging, due to the increased
size and number of heat exchangers and pumps and
increased complexity of maintenance and operations
4.2 LITERATURE REVIEW OverthepastalmostfourdecadesanumberofSCWOlab‐scaleanddemonstrationfacilitieshavebeenbuiltbyvariouscompanies,nationallaboratories,andfederalagencies.Althoughextensiveresearchhasbeenconducted,thecommercializationofSCWOprocesseshasbeenhinderedbyconcernsaboutcorrosion,scalebuildup/foulingandplantscalability.
Theconsultantteamreviewed25scientificpublicationssupplementedbyadditionalinternet‐basedinformationgathering.Thissectionprovidesahigh‐levelsummaryofthekeyfindings,groupedintothefollowingfivemaincategories:
1. Lab‐scaleandpilot‐scaleexperimentsandfindingsundersubcriticalandsupercriticalconditions.
2. SCWOsystemandcomponentdesign,operabilityconsiderations,andchallengesundersubcriticalandsupercriticalconditions.
3. EnvironmentalassessmentofSCWO.
4. Economicconsiderations.
5. HistoricdevelopmentandstatusofSCWOtechnology.
4.2.1 Lab‐Scale and Pilot‐Scale Experiments
Subcriticalwateroxidation(SubCWO)conditions:
ThedestructionofCODrepresentingtheorganiccompoundsinthefeedisdominatedbythegenerationofacidssuchasaceticacidwhichismostresistanttohydrothermaloxidationandretardsthereactiontime(ShanablehandShimizu,2000;ImteazandShanableh,2004).
SCWOconditions:
Thereactiontemperature,pressureandresidencetimearethemaininterdependentfactorswhichcanbeadjusted,withthefollowingorderofsignificance:pressure>reactiontemperature>reactionretentiontime(Gaoetal,2014).
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Whenthepressureisabovethecriticalpressureofwater(22.1MPa),conversionisnotimprovedbyelevatingthepressure.Atlowerpressures,theconversionsdecrease,butifthereactiontemperatureishighenoughthedetrimentaleffectofpressurecanbecompensated.(BermejoandCocero,2006).
AmmoniaandaceticacidarefoundtoberefractoryintermediatesinSCWOoforganicwastesandarereactionratelimiting.Ammoniadestructionwasfoundtobeslowerthanforaceticacid.(Gotoetal,1999).
CODdestruction:
o Whenmorethanthestoichiometricdemandofoxidantisused,organiccarbonintheliquidphaseisalmostcompletelydestroyed(Gotoetal,1997).
o Thedestructionrateisfasteratahighertemperature,andthetotalorganiccarbon(TOC)reducedtoalmostzeroin60sat773K[500°C](Gotoetal1999).
o RemovalrateofCODwasobviouslyincreasedastemperature,residencetimeandoxidationcoefficientareincreased.ThereisanoptimalvaluefortimetoinfluenceremovalofCOD.ThereisanoptimalvalueforoxidationcoefficientandtheinfluenceonCODremovalbecomesverysmall.(Zhangetal,2016).
o TheoxidantdosehadasmalleffectonremovalofCODinmunicipalwastewatersludgewhenappliedabovestoichiometricrequirements.Temperature,pressureandresidencetimeinthetreatmentofsludgeweremoreimportant.OrganicmaterialinmunicipalsewagesludgecouldbeefficientlyremovedusingSCWO(Lietal,2013).
DestructionofN‐components:
o Concentrationofammonia‐nitrogenincreasedwithoxidationcoefficient.Concentrationofammonia‐nitrogenincreasedwithreactiontimebeforedecreasing.TotalnitrogenistransformedtoNH3‐Nbeforedegradingovertime.(Zhangetal,2016).
o Completedestructionofammoniaproducedinthereactionrequiredhighertemperaturesthanfordestructionofaceticacid(Gotoetal,1998).
o Thedecompositionofnitrogencomponentsinthesludgetoammoniawasfoundtobemuchfasterthanthecompletedecompositionofammoniatomolecularnitrogen,carbondioxideandwater(Gotoetal,1999).
o Previousworkreportedcatalyticoxidationofammoniaassociatedwiththealloyused(Inconel635)inthereactorwallmaterial(Gotoetal,1999).
HeavymetalscontainedinthesludgewhentreatedviaSCWOareincorporatedinthenon‐leachableash.Anincreaseinheavymetalsintheashcanbedetectedifstainlesssteel316isusedasreactormaterialduetocorrosion(ShanablehandShimizu2000).
TheSCWOprocesscanproduceamultitudeofintermediatesandpotentialby‐products.Experimentshaveshownthatthedegradationorformationofthesecompoundscanbeenhancedbyacatalyst;e.g.transitionmetaloxideshaveshowndesirablecatalyticeffects(GloynaandLi,1995).
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Reactor,heatexchangerandrecoveryunitsaresusceptibletoscalingofsaltsandcorrosion.Thelowdensityofthefluidlimitstheabilitytodissolvetheinorganicswhichcausesthemtodropoutofsolutionandresultsinscaling.(ShanablehandShimizu,2000).
4.2.2 SCWO System and Component Design, Operability Considerations, and Challenges
Pilot‐andfull‐scalecommercialSCWOinstallationshavebeenencounteringsubstantialoperationalchallengesduetocorrosion,solidsprecipitation,andpluggingoccurringmainlyinthehighpressureandhightemperaturesectionsoftheprocessincludingthepreheater,reactor,coolerandheatexchanger(Zhong,etal,2015).
AssaltsinthefeedhavelowsolubilityinSCW,whentheyprecipitatetheyoftenformagglomeratesandcoatinternalsurfaces,therebyinhibitingheattransferfrom/toexteriorsurfaces.Whenscalebuild‐upisleftuncontrolled,pluggingoftransportlinesand/orthereactorcanoccur.TherequiredcleaningcanresultinsubstantialandcostlydowntimeintheSCWOprocess(Hodesaetal,2004).
Morroneexplainsthatcorrosionismostsevereinthehot,subcriticalregionsbefore(preheater)andafter(cooldownheatexchanger)thereactor,butcanalsooccurinthemicroenvironmentformedundersaltlayersinthereactor(Marrone,2013).Dependingontheparticularfeedsandmaterialsofconstructioninvolved,corrosionratesinSCWprocessessuchasSCWOarereportedtobeashighasseveralmils/h[tensofµm/h](Marroneaetal,2009).
ManyofthecompaniesthathaveattemptedtocommercializetheSCWOtechnologyoverthepasttwodecadeshavedevelopedinnovativeapproachestodealingwiththecorrosionandsaltprecipitation/solidsbuildupproblems.Theseareoftenthedistinguishingfeaturesofeachcompany'sSCWOprocess.Furthermore,researcheffortsonalaboratoryandpilot‐scalehasbeenongoingfocusingontheoverallsystemandprocessdesign(suchasimprovementsinthereactordesignandnewmaterialofconstruction)tominimizetheseadverseeffects.
Thefollowingprovidesahigh‐leveloverviewofthevarioussystemdesignconsiderationsandmeasuresimplementedandunderinvestigationtoavoidcorrosionandpluggingtosupportsuccessfulcontinuousfeedprocessingforanacceptableperiodoftime:
Constructionmaterials‐mostwidelyusedmaterialsintheSCWOprocess(BermejoandCocero,(2006;Marroneaetal,2009):
ThemostcommonmaterialsofconstructionforSCWOsystemstoobtainhighresistancetocorrosionathightemperaturesarenickel‐basedalloys(Nialloys625andC‐276)andausteniticstainlesssteels.Stainlesssteelalloysareacceptableonlyforrelativelybenignfeeds(i.e.,containingnoheteroatoms1)orincoolersectionsoftheprocess.Forhighertemperaturesectionsoftheprocess,nickel‐basedalloysaremostoftenusedduetotheircombinationofreasonablygoodcorrosionresistanceandhightemperaturestrengthunderthewidestrangeofconditions.
However,Zhongnotesthatno‘supermaterial’hasbeenreportedthatcanwithstandallcorrosionconditionsinSCWO(Zhong,C.etal,2015).
1 Atoms other than carbon or hydrogen which are bonded to carbon in organic compounds.
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Fourreactorconceptshavebeendevelopedandstudiedtosolvecorrosionandsaltdeposition/accumulationproblems(Loppinet‐Serani2010):
a) abasictubularreactorwithspecifichydrodynamicsandconstructionmaterial;
b) atankreactorwiththereactionzoneintheupperpartandacoolzoneinthelowerparttodissolvethesalts;
c) a‘transpiringwall’reactorwithaninnerporouspipe,whichisrinsedwithwatertopreventsaltdepositsandcorrosiononthewall;and
d) a‘film‐cooled’reactorwithcoolingofthewallbycoaxialintroductionoflargeamountsofwater.
Tubularreactorsoperatedathighvelocitiesarebeingusedbyseveralcompaniesfortreatingsewagesludges,whichhavearelativelyhighproportionofnon‐saltsolids.Vadillonotedthatforsafeoperatingconditionsandoptimalenergyrecovery,aSCWOplantwithtubularreactorrequiresstringentthermalcontrole.g.viacoolingwaterinjectionsandmulti‐oxidantinjectionsindifferentpointsalongthereactor.ThisdesignapproachhasbeenrealizedintheSCFIAqua‐Critox®Reactorwhereexcesstemperaturealongthereactoriscontrolledthroughtheuseofamulti‐injectionofcoolwaterstreamsindifferentpartsofthereactor.However,multi‐coolwaterinjectionsproducethermalfatigueofthereactormaterial(Vadilloetal,2015).
Modellingtoolshaveincreasinglybeenappliedtodevelopnewreactorconcepts.Anovelreactorconceptnamedas‘DynamicGasSealWallReactor’wasrecentlydeveloped,whichwasoptimizedfrom‘TranspiringWallReactor’designandwasdesignedtohandlethereactorcorrosionandpluggingproblems(Zhongetal2015).
Saltseparation:solid–fluidseparation(e.g.hydrocyclonsorfiltrationsystems)aremethodsofrecoveringsolidsattheoutletofthereactorareeffectiveonlywhenthesolidsdonottendtosticktothewallofthereactor.Thiscanhappenifthesolidisnotstickyorifasystemforremovingthesolidsfromthewallsisimplementedinthereactor(suchastranspiringwallreactor).
StrategiestocontrolscalebuildupduringSCWOwillcontinuetorelyheavilyonexperiments.Researchonphasebehavior,heattransfer,andmasstransferwillcontinuetobeinvaluablefordevelopingmethodstocontroloreliminatescalebuildupduringSCWO.
Alsosomemodelshavebeendevelopedtocalculatethesolubilityofinorganicsaltsinthehightemperature,highpressureenvironmentofsupercriticalwater.Differentsolutionshavebeenproposedtosolvethepluggingproblem.Asaconclusion,onestudyindicatedthatthebestsolutiontoavoidsaltprecipitationinsidethereactoristoreducethequantityofsaltpresentinthefeed(Bermejo,andCocero,2006).
SpecifictechniquestocontrolsaltprecipitationandscalingareprovidedbyMarronea(Marronea,2004).Suggestedcontrolmeasuresincludehighvelocityflow,mechanicalbrushing,rotatingscraper,reactorflushing,additives,lowturbulence,homogeneousprecipitation,crossflowfiltration,densityseparation,extremepressureoperation.
VadillonotedthatinordertoadvanceinthecommercialdevelopmentofSCWOitiscrucialtonotonlychoosethemostsuitablereactorconceptbutalsotocharacterizeandselectanappropriate
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wastewatersludgefeedintubularSCWOreactorsystems(Vadilloetal,2015;seeTable4‐2fordetails).
Table 4‐2. Wastewater Ideal Requirements to be Treated by SCWO in Tubular Reactor (reproduced from Vadillo et al, 2015)
PARAMETER VALUE COMMENTS
Type of wastewater Toxic
Non biodegradable
Incineration not recommended
Not suitable for biological treatment
Flow rate >100 kg/h
<4000 kg/h
To be considered as a semi‐industrial scale
Due to equipment availability
Wastewater COD concentration >50 g/l
<150 g/l
To release the heat necessary for autothermal operation
To keep reactor temperature under safe values
Salt content NaCl <200 ppmNa2SO4 <1 ppm CaCl2 <3 ppm Mg(OH)2 <0.003 ppm
To avoid salt plugging in the reactor
pH 2 < pH <11 To avoid corrosion
Chlorides <1.77ppm To avoid corrosion
Notethatwithrespecttosaltcontentandchlorideconcentration,thelimitspresentedbyVadillointheabovetablearebelowlevelstypicallyexperiencedwithwastewaterbiosolidsandtheselimitsdonottieinwithreportedoperatingexperienceofSCFI.
Vadillopointedoutthatsuspendedsolidparticlesinthefeedcanproduceproblemsduringtheeffluentdepressurizationresultinginerosionofinternalpartsofthe“backpressureregulator”valves.Providedsolutionstomitigatesystemcorrosionincludeavoidanceofcorrosivefeedsorthepretreatmentofthefeedtoremovecorrosivespecies.ThechlorideconcentrationlimitstatedbyVadilloinTable4‐2iswellbelowtypicalconcentrationsfoundindomesticwastewatersludgeandalsobelowchloridelimitstypicallystatedbySCWOproviders.
ShanablehandShimizunotedthatSCWOisbestsuitedforwastestreamswithadequateorganiccontenttogenerateenoughheattosustainthereactiontemperature.BesteconomicalsystemoperationcanbeachievedwithafeedstockTSrangingbetween5and10percent.However,atoohighVScontentposestheriskofoverheating(ShanablehandShimizu2000).
InregardtoachievepermittingandregulatorycomplianceGriffithandRaymondprovidethefollowingcommentsbasedontheirexperienceduringtheimplementationthefirstcommercial‐scaleSCWOplantforsewagesludgeinHarlingen,Texas(GriffithandRaymond(2002):
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Regulatoryagencieswereinitiallyuncertainoftheapplicableregulationsforthisprocessbecausetheprocessdoesnotclearlyfitinacategory.TheHarlingenplantwillprovidetheopportunityforregulatorstoviewafull‐scaleoperatingunitprocessingsludge.
Boththefederalandvariousstateregulationsmayneedtoberewrittentospecificallyrecognizethedisposalofresidualsolidsfromahydrothermaloxidationprocess.
4.2.3 Environmental Assessment of SCWO
Svanström(Svanström,2004and2005)publishedtwopapersonlife‐cycleassessments(LCAs)processingsludgewithSCWO:
a) LCAonthefirstcommercial‐scaleSCWOplantforsewagesludgeintheworld,treatingsludge(7%TS)fromthemunicipalwastewatertreatmentfacilityinHarlingen,TX.TheplantisbasedonTheHydroProcessing’s‘HydroSolids’processwithaprocessingcapacityofupto9.8drytonsperdayofsludge.
b) LCAapplyingtheAquaCritoxprocessfordigestedsludge(15%TS)andcomparingitwithLCAsoffourother(somerelativelynewanduntried)sludgemanagementoptionsspecificallyrelatedtoCityofGöteborg’sWWTP(Sweden)anditlocalcharacteristics.Optionsevaluatedincludedagriculturaluse,co‐incinerationwithmunicipalsolidwaste,incinerationwithsubsequentphosphorusextraction(Bio‐Con)andsludgefractionationwithphosphorusrecovery.InventorydatafortheAquaCritoxprocessfromChematurEngineering’sKarlskoga(Sweden)pilotplantwasusedandscaledup.
Findings–A)‘HydroSolids’processforsludgefromHarlingen,TXfacility:
Gas‐firedpreheatingofthesludgeisthemajorcontributortoenvironmentalimpacts;emissionsfromgeneratingelectricityforpumpingandforoxygenproductionarealsoimportant.
Energy‐conservingmeasuresandrecoveryofexcessoxygenfromtheSCWOprocessshouldbeconsideredforimprovingthesustainabilitypotential.
ResultsfromanLCAstudyofSCWOprocessingofsewagesludgearetoalargeextentdeterminedbythesystemsurroundingtheactualSCWOunit.Thisresultunderscoresthenecessitytolooknotonlyatdirectemissionsfromaspecificprocess,buttoinvestigatethewholelifecycle.
Findings–B)Aqua‐CritoxprocessforsludgefromCityofGöteborg’sWWTP:
Allsystemsevaluated,exceptagriculturaluse,resultinsavingsoftheresourcesfossilfuels,mainlyduetothereplacementofdistrictheatproductionbythesludgeoxidationheat.
Allmethodsperformwellintheglobalwarmingpotentialcharacterization,showingnetsavingsingreenhousegasemissions.
Theenergyrecoverymethodsperformbetterthanagriculturaluse.Energysavingsbyavoidedproductionofchemicalsgiveadvantagestoagriculturaluse.
N2OEmissions:IntermsofglobalwarmingtheemissionofN2OformedintheSCWOprocessprovedtobeimportant:ThetotalN2OemissionsfromtheSCWOprocessthatwasusedinthisstudy,measuredbyChematurEngineeringAB,ishigherthangenerallyexpectedforSCWO
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processingofsewagesludge.AdecreaseinN2OemissionswouldprovideconsiderableimprovementstotheAquaCritoxsystem.
Phosphorous:FortheLCAoftheAquaCritoxsystemextractionofphosphorousfromtheproducedsolidswasnotconsidered.Aphosphorusextractionstepcouldbeadded.LessmaterialwouldthenneedtobelandfilledandacreditwouldbegivenforreplacedphosphorusandotherproductsthusimprovingtheLCAresults.
4.2.4 Economic Considerations
GriffithandRaymond(GriffithandRaymond2002),Svanström(Svanström,2004)andVadillo(Vadilloetal,2015)providedsomeinformationoneconomicdataforprocessingsludgewithSCWO:
SCWOduringstart‐uprequiresahighamountofenergy.Theonlywaytoachieveeconomicfeasibilityattheindustrialscaleisrunningtheprocessforlongperiodsoftime.Specifically,itisnecessarytoachieve95%ofavailability.Forinstance,inthecaseofplantsof250t/dayofcapacitythethermalenergynecessaryisaround5MW.
SCWOprocessinvolveshighinvestmentcostsassociatedwithsuitableequipmenttoworkathighpressureandtemperature,useofhighcorrosionresistancealloystobuildreactorsandheat.Duetohighpressureoperationalconditionsmaterialcostsareveryhighinadditiontomaintenanceandrepaircostsofequipment.
Reactorcostisoneofthemaincostsinthedesign.Theobjectiveistodesignitwithasmallvolume.Inthiswayoneestimatestatesthatthetubularreactorcostsrepresent10%oftheoverallequipmentcostsinaSCWOplantabletotreat100kg/hofwastewater.
Atpresent,economicalstudiesonSCWOattheindustrialscalearescarceintheliterature.Datapointsfromseveralstudiesareasfollows:
o ‘GidnerandStenmark’estimatedoperationalcostsofasewagesludgeSCWOplantbasedonaflowrateof7m3/hofsewagesludgebeing137€/tofdriedsludge.
o ‘Svanstroetal.’estimatedtotalcostfora1t/dayplantbeing243$/tdriedsludge.
o ‘O’Reganetal.’claimedthattreatmentcostofsewagesludgeSCWOisintherange36.6−73.15€/t.
o ‘Abelnetal.’first,estimatedtreatmentcostofanidealwastewatermadeofamixtureofethanol10%weightandwaterusingairasoxidantinaplantof100kg/hwithtwodifferentreactors:tubularandtranspiringwallreactor,beingthetreatmentcosts406€/tand660€/t,respectively.Later,theyestimatedthetreatmentcostfora1t/hplantbeing330−430€/tforthetranspiringwallreactorplantand203−264€/tforthetubularreactorplant.
o ‘Vadilloetal.’estimatedthetreatmentcostforarealwastewaterSCWOina1t/hplantthatamountsto230€/t.EconomicresultsshowedthatalthoughSCWOtechnologywasinitiallyshownasatechnologysuitableforallkindsofwastes,researchconductedoverthelastthreedecadesshowedthatthistechnologycanonlybeappliedattheindustrialscaleusingatubularreactorandtotreatwastewatersthatmeetcertainfeedcharacteristics.
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o A2001analysisfoundthatthetotalcostforSCWOprocessingofsewagesludgeisaboutUS$120–200perDMTat10%solids.
Operationalcost:thechoiceoftheoxidantisakeypointintheoperationalbudget:
o ‘BermejoandCocero’claimedthatitismoreeconomicaltousepureoxygeninsteadofairbecauseatindustrialscalethecompressioncostisveryhigh.
o ‘Savageetal.’suggestedthatacatalyticSCWOprocessisamorecompetitivealternativebecausewiththeuseofacatalystthetemperaturenecessarytoreachremovalefficiencieshigherthan99%isreducedsignificantlydecreasingtheenergydemand.
FortheHydroSolidsprocessinstalledatHarlingen,Texasthefollowingcostestimatewasprovided:thenetoperationandmaintenancecostwillbeabout$100/dryton.Thecapitalcomponentofthecompletesolidstreatmentsystemrepresentsacostofabout$80/drytontreated.Thetotalcostforsolidsprocessingforthesystemisexpectedtobeabout$180/drytonofsolidsprocessed.
4.3 STATUS OF THE SCWO TECHNOLOGY CommercializationofSCWOtechnologyhasbeeninprogressforoverthreedecadessinceitspotentialfordestructionofaqueousorganicwasteswasfirstrealized.AnumberofSCWOdemonstrationfacilitiesexistinvariouscompanies,nationallaboratories,andfederalagencies.TheearlyapplicationsofSCWOweremainlyformilitaryhazardouswastedestruction.
ThefirstcommercialSCWOcompany,MODAR,wasestablishedin1980(whichwasboughtbyGeneralAtomicsin1996)[Marronea,2004].ThefirstSCWOcommercialfacility(1100Liter/hour)focusedonhazardousorganicwastetreatmentandwasdevelopedbyEcoWasteTechnologies(EWT)atHuntsman’sChemicalCompanyinAustin,TX.TheplantwascommissionedinAugust1994[ShanablehandShimizu,2000].
Forprocessingindustrialwastewatersmostoftheinstallationswere/areatthelaboratoryscaleorpilotplantwithindustrialscaleinstallationsbeingscarce.Incontrasttothesituationwithsubcriticaloxidation,wheretechnologyhasreachedmaturity,therearefarfewerfacilitiesassociatedwithSCWO.Thisislikelytobeduetothechallengesassociatedwiththeimplementationofthetechnology.
InAprilof2001,thefirstSCWOplantforthedestructionofsludgesbeganitsoperationofthefirstoftwounitsintheU.S.attheHarlingenWastewatertreatmentplant,Texas,withaprocessingcapacityof9.8drytonsperdayofWASwith7%TS.ThisplantisbasedontheHydrosolidsProcesswithatubularreactordesign,developedbyHydroprocessingLLC.[GriffithandRaymond,2002;BermejoandCocero,2006].Thefacilitystoppeditoperationin2002duetocorrosionissuesintheheatexchanger[Vadillo,etal,2015].
InEurope,ChematurEngineeringABacquiredalicensingagreementfortheEWTprocessin1995followedbyobtainingitsexclusiveworld‐widerightsin1999andhascommercializeditsSCWOprocessunderthebrandnameAquaCritox®[BermejoandCocero,2006].Chematurbuilta550lb/h(250kg/h)pilot‐scaleSCWOsystemin1998inKarlskoga,Swedenthathassincebeentestedwithseveralmostlynitrogen‐containingwastes(amineproductionwastes,n‐halogenatedspentcuttingfluid,de‐inkingsludge,andsewagesludge)[Marronea,2004].
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Chematurhasalsodevelopedtwootherprocesses[BermejoandCocero,2006]:
TheAquaReci®processisajointdevelopmentofChematurandFeralcoAB.Theprocesscanbeappliedtomunicipalanddrinkingwatersludges.TheAquaCritox®processiscombinedwithrecoveryofcoagulantsand/orphosphorousfromthepure,solidinorganicresidueresultingfromthesupercriticaloxidationstep.
TheAquaCat®technologywasjointlydevelopedbyChematurandJohnsonMattheyfortherecoveryofpreciousmetalsfromspentcatalysts.Inthiswaytransportationofhazardouswastecanbeeliminated.Thefirstcommercial‐sizeunitwasbuiltatJohnsonMatthey’sBrimsdownsite,andstartedupin2004.TheunitisthefirstcommercialunitinEuropebasedonsupercriticalwateroxidation,andthelargestSCWOunitintheworld.
ChematurlicensedtheEWTSCWOprocesstotheShinkoPantecCo.ofJapan.Underthislicenseagreement,ShinkoPantec(EcoWaste),Japanconstructeda1100kg/h(2425lb/h)SCWOplantfortreatingmunicipalsludge,whichwascommissionedin2000[Marronea,2004].Theplantstoppedoperationin2004duetoproblemswithequipmentmaterialdurability[Marrone,2013].
In2007,ChematursoldtheirsupercriticalfluidsdivisionandequipmenttoCork,Ireland‐basedfirmSuperCriticalFluidsInternational(SCFI).SCFIhascontinuedtoimproveontheChematurSCWOtubularreactordesign,thoughtheyhaveconsolidatedChematur’smanyversionsofSCWOunderthesingleAquacritox®brandnameforeaseofmarketing.SCFIutilizesatubularreactordesignandhaschosentofocusprimarilyonsewagesludgeanddigestatefeedapplications.SCFIbuiltisfirstdemonstrationplantinRingaskiddy,Co.Cork,Irelandin2008.In2013/2014SCFIreceivedagrantofjustunder€1millionfromtheEuropeanUnion’sLIFEEco‐innovationInitiative.Theso‐calledLO2Xproject2involvestheconstructionandoperationofademonstrationscaleprototypeforthetreatmentofasignificantfractionofmunicipalrawsludgeattheCityofPaterna’surbanwastewatertreatmentplantclosetoValencia,Spain.
SuperWaterSolutionsLLCisanotherfirmthathasbeenworkingonthecommercializationofSCWOforwastewatersludge.Itwasco‐foundedbyDr.MichaelModell,whoseexperimentsatMITinthe1970sformedthebasisofSCWOtechnologyandwhosubsequentlyfoundedMODAR.Super‐WaterSolutionswasstartedin2006andisbasedinWellington,FL.TheSuperWaterSolutionsSCWOdesignissimilartothatofModell’spreviouscompany,MODECandfeaturesatubularreactorsystem.Since2007,SuperWaterSolutionshasworkedcloselywiththecityofOrlando,FL,withthecityfundingdevelopmentoftheirsystem.Inreturnforthisinvestment,Orlandohasauniquearrangementinwhichitwillreceivearoyaltyof$2.50foreverytonofsludgetreatedatanyfutureSCWOfacilitybuiltbySuperWaterSolutionsforothercustomers.From2009to2011,theyinstalledandsuccessfullytesteda4536kg/day(5tons/day)SCWOsystemattheCityofOrlando’sIronBridgewastewatertreatment.Sincethattime,thecityhascontinuedtoleasespacetoSuperWaterSolutionsforfurtherdevelopmentworkoftheirsystemdesign.Afull‐scale9072kg/day(10tons/day)SCWOsystemwasplannedtobebuiltforthecityin2013[Marrone,2013].OnMarch2014theOrlandoSentinelnewspaper[Sentinel,2014]reportedthatinJuly2013anexpansiontankofthepilotplanthadsufferedablowoutcausingsignificantdamagetotheplantanditsbuildingenclosure.AccordingtothenewspaperarticletheCityofOrlandohadinvested$8.5
2 http://www.lo2x.com/eng/descripcion.html
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millionandyearsofitsworkers'labor;thereactorhassatidleeversince,asthecity'sprivate‐sectorpartnertriestoraisethecapitaltobuildanewone.
Vadillo[Vadillo,V.etal,2015]reportedanotherSCWOpilotplantforwastewatersludgelocatedattheSchoolofEnergyandPowerEngineeringinChina.Hereatranspiringwallreactorcombinedwithreverseflowtankisusedwithpurgeoxygenastheoxidanttoprocess125kg/h(2011data).
AccordingtoMarrone[Marrone,2013]asofJanuary2012,thereweresixcompaniesthatarestillactive3incommercializingSCWOtechnology:GeneralAtomics(theoldestamongactivecompanies),SRIInternational,HanwhaChemical,SuperWaterSolutions,SCFI,andInnoveox.
EachSCWOcompanyhasoneormoreuniquefeaturestotheirsystemdesign(foroperationandcontrolofcorrosionandsaltbuildup)and/orbusinessplan,andeachonehastargetedaspecificfeedniche.
SeveralcommercialSCWOplantswerebuiltinthelastthreedecades;however,nowadaysonlytwoofthemareinoperation.Thefollowingprovidesabriefsummaryoftheseactivefull‐scaleplantsincludingoneundernear‐criticalconditions:
SRI/MitsubishiinTokyo,Japan:oldestplant,inoperationsince2005:Theplanthasacapacityof2000kg/dayofPCBsand100,000kg/dayofwater.
Innoveox,Arthez‐de‐Béarn,France:inoperationsince2011;processeshazardousindustrialwasteatarelativelylowcapacityof100kg/hr.Feedcompositionislimitedto<1g/Lchlorideand<10g/Lsalt.
HanwhaChemicalCorp.forKorea,inoperationsince2008:Near‐CriticalHydrolysis(NCH)facilityfortreatingtoluenediisocyanate(TDI)residuetoproducetoluenediamineintermediateforrecyclingbackintotheTDImanufactureprocess.Theplanthasacapacityof20,000kg/day.
Asbestascanbedetermined,alloftheplantsthatshutdownduetoequipmentcorrosiondidnothaveamechanismforhandlingcorrosionotherthanlimitingoperationtonon‐corrosivefeedssuchashydrocarbonsandsewagesludge.
TheuseofthistechnologyforbiosolidsmanagementisstillinitsearlydevelopmentalstagesandiscategorizedasemergingtechnologybytheWaterEnvironmentalResearchFoundation(WERF,2012).
3 ActiveisreferredtoasthefirmiscurrentlymarketingSCWOtechnologyandhasatleastonefull‐scale
SCWOfacilityinoperation,inconstruction,orindesign.
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5.0 SCFI Proposal Since2015,SCFIhasbeenworkingwithOCSDtodevelopproposalsfortheSCWOdemonstrationfacility.SCFIhassubmittedthreetechnicalmemorandaandoneevaluationreportwhichhavebeenreviewedaspartofthisstudy.Abriefsummaryofthecontentofthesereportsisprovidedbelow.
TechnicalMemorandumNo.1–ProjectDefinition(Undated)
ThisTechnicalMemodetailsworkcarriedoutunderTask1–ProjectDefinition.ThedocumentprimarilyprovidesdiscussionoffouroptionswhichwereconsideredforlocationofaSCWOplantateitherPlant1orPlant2.ItincludesdetailsofdatarequisitionbySCFIinordertoidentifyapreferredlocationandasummaryofmeetingsheldwithOCSD.
ThereportdetailstheoutcomeofanInterimProjectdefinitionworkshopheldon4thNovember2015.
Rough,“orderofmagnitude”costsarepresentedtoAACEClass5(‐50to+100%)forseveraltreatmentoptionsincluding:
AnA‐30unitsizedfor800gal/hrwithandwithoutposttreatmentprocessing.
AnA‐100unitsizedfor2,600gal/hrwithandwithoutposttreatmentprocessing.
AnA‐30unitsizedfor800gal/hrwithpreandpostprocessingsizedtoaccommodatefutureinstallationofanA‐100unit,withandwithoutposttreatmentprocessing.
Thefollowingrecommendationsaremadeinthestudy:
InstallationofthedemonstrationAquaCritoxfacilityatthesiteofredundantdigestersatPlant2.
TheinstallationofanAquaCritoxA‐30systemwithappropriateupstreamequipmentandtankagesizedtomatchtherequirementofanAquaCritoxA‐100.Transferoftreatedeffluenttotheexistingonsitedewateringequipment.
TechnicalMemorandumNo.2–ProjectDevelopment(Undated)
ThisdocumentcoversworkcarriedoutunderTask2–ProjectDevelopmentandcoversthefollowingscopefocusedonestablishingthescopeoftheproposedproject.
EstablishessludgecharacteristicsandperformancecharacteristicsoftheAquaCritoxsystem.
Coversproposedsitecivilarrangementofthenewsystem.
Detailsrequirementsforupstream/ancillarysystemsincludingsludgesupply,sludgedegritting,feedsludgestorage,oxygensupplyandnaturalgassupply.
ProvidesanoverviewoftheAquaCritoxequipment.
ProvidesmechanicallayoutsoftheA‐30andA‐100AquaCritoxsystems.
Discussesfoundationdesignandanchorage.
Coversrequirementsfordownstreamequipmentincludingoffgashandling,residualshandlingandconveyanceandsteamfacilities.
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Identifiesrelatedancillaryfacilitiesincludingprocessdrainage,odorcontrol,flocculantsupplyandstorageandelectrical,instrumentationandcontrolsystems.
TechnicalMemorandumNo.3–ImplementationPlan(May2016)
ThisTechnicalMemocoversworkcarriedoutunderTask3whichdevelopsanimplementationplanfortheproposedproject.
Thememocovers:
Operationandstaffing
Operationalcosts
ConstructioncostestimatesquotedtoAACEClass4(‐30to+50%)fortheproposedA‐30solutionProjectdelivery
Schedule
Regulatoryandcoderequirements
FinalEvaluationStudyReport
ThefinalevaluationstudyreportprovidesasummaryoftheworkcarriedoutunderTasks1,2and3includingsiteselection,sludgefeed,AquaCritoxoptionsconsidered,majorequipmentassociatedwiththeAquaCritoxpackage,procurementandprojectdeliveryapproachandasummaryofcapitalandoperatingcostsassociatedwiththedifferenttreatmentoptionsavailable.
5.1 REVIEW OF SCFI PROPOSALS AreviewwasconductedoftheSCFIproposalsoutlinedabove.Technicalandothercommentsareprovidedinthefollowingsections.
5.1.1 General
ItisnotrecommendedthatthesizeofthedigestionfacilityatPlant2shouldbereducedbasedontheinstallationofthedemonstrationSCWOplant.Aswithanydemonstrationplant,itisexpectedthattheremaybesignificantdowntimeinitsoperation.
5.1.2 Feedstock
ThecurrentproposalfromSCFIinvolvestreatmentofbothprimaryandwasteactivatedsludge(WAS).Itisrecommendedthatthefacilityshouldinitiallyfocusontreatmentofwasteactivatedsludgeforthefollowingreasons.
WAStendstobemoredifficulttoanaerobicallydigestthanprimarysludge.TreatmentofalargerproportionofWASintheSCWOplantwouldremovealargerportionofthisdifficulttodigestfeedstockfromthedigester.
PrimarysludgetendstohaveasignificantlyhighergritcontentthanWAS.GiventhatgritisaconcernforSCWOplantoperation,itseemssensibletominimizethegritcontentofthefeedasfaraspossiblebyutilizingfeedstockswithlowgritcontent.
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IftreatmentofWASonlyissuccessful,thenthiscouldbefollowedupbytreatmentofablendofprimaryandWASatalaterdate.
5.1.3 Grit Removal
SCFIproposalsincludearequirementfor95%removalofgritparticlesgreaterthan75µminsize.Inourexperienceandbasedondiscussionswiththesupplychain,itisnotpossibletoguaranteethiscriterioncanbemetwithcurrenttechnologyavailable.Also,the75%removalrequirementdoesnotprovidealimitongritcontenttotheSCWOsystembecausethegritcontentofthefeedcouldbevariable.Amassbasedgritcontentbasedonsizewouldbemoreappropriate.
Whilesystemscanbedesignedtoachieveremovalofparticlesofagivensizeanddensity,inpracticesomegritparticlestendtocombinewithsludgeflocwhichreducestheirdensityandtheresultingremovalefficiency.
Giventhecriticalityofgritcontentforthisprocess,itisrecommendedthatOCSDshouldconsiderpilotingtheproposedgritremovaltechnologypriortoinstallationofthefulldemonstrationfacility.ThiswouldenableOCSDtoconfirmwhetherornotSCFI’srequirementsforupstreamgritremovalcanbemetwithoutcommittingtowiderprojectexpenditure.
5.1.4 Screening Requirements
WhiletheProcessFlowDiagrams(1&2)intheEvaluationStudyReportshowasludgescreen,andcostsforsludgescreeningareincludedinAppendixAofTM‐3,nodetailsareprovidedregardingthemethodofsludgescreening,proposedequipmentorassociatedtechnicalspecifications.
WiththesmallaperturesinvolvedintheSCWOprocessitisexpectedthatveryfinescreeningwillberequired.ItisrecommendedthatspecificationsforthesludgescreeningandproposedmanufacturersshouldbeconfirmedwithSCFIinordertoensurethatafeasiblesolutionisavailablewhichmeetsSCFIrequirementswithoutundueimpactonprojectcosts.
5.1.5 SCWO Technical Comments
ThefollowingtechnicalcommentswereraisedduringreviewoftheSCFIproposals.Itisreadilyacknowledgethatsomeofthesearequerieswhichmayberesolvedthroughfurtherinvestigationand/orasitevisittothepilotunitatValencia,Spain.
Bakingofsludgeontheeconomizingheatexchangerisapotentialriskat16%feedsolids.ThismaybemitigatedbytheCIPregime.WhentheValenciaplantbeginsoperationat16%feedsolidsitisrecommendedthatcloseattentionbepaidtothedifferentialpressureandrecoveryduringCIPtoconfirmifortowhatextentthisisaconcern.
Itisrecommendedthat25%contingencybeaddedtothescrewpressvendor’ssizingforthescrewpresstoensurethatthiscanfullysupporttheSCWOplantoperation.
Oxygenmustbesuppliedtothereactorvesselatapressureofabout3,500psig.ThereportsdonotprovidemuchdiscussionabouthowthiswillbeachievedotherthanthatthesupplyandcompressionofoxygenwillbetheresponsibilityofAirProducts.Itshouldbenotedthatsupplyingoxygenatthesepressuresisamajorconsideration.Determiningthesafetyandpracticalityofthisoperationwouldneedtobeoneofthegoalsofthedemonstrationproject.Itshouldalsobenotedthatnoorganicmaterialcanbeexposedtotheoxygenduetotheriskoffire.
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Thisincludeslubricatingoilsofanykind.Eventhemetalsusedtoconstructthepumpscanbesubjecttorapidoxidationifthereisanignitionsource.Thepossibilityofthistypeofflashoxidationshouldbeconsideredinthesafetyreviewrecommendedbelow.Inordertoverifythepracticalityofprovidingoxygenatthesehighpressures,AirProductswascontactedbytheconsultantteamforcommentsontheirproposals.AirProductsconfirmedthatindeedthisisaspecialapplicationbutthattheoxygensupplycouldbemetwithoneoftheir‘advanced’systemswhichusehighpressurepumpstoelevatetheliquidoxygentotherequiredpressurefordelivery.AirProductsalsoconfirmedthatinbroadterms,theliquidoxygenequipmentrentalcostsandliquidoxygenpurchasecostsincludedinSCFI’sproposalsarerealistic.
Pressuredropattheendofthereactorfrom3500PSIisamajorundertaking.ItisencouragingthatSCFIhastakenanalternativeapproachtothisusingsmalldiameterpressurereductioncoilswithchokingwater.However,giventhatthetreatedmaterialwillcontainashandanygritwhichisnotremovedpriortotreatment,potentialforerosionandpluggingofthesmalldiametertubingexistsandshouldbeinvestigated.
5.1.6 Operations and Staffing
TheproposedoperationofthefacilityisbyOCSDbutwithoperationalsupportprovidedbySCFIwithasinglepersonavailablefrom8amto5pm.Thereislittlementionofplantmaintenance.GiventhatthistechnologyisstillindevelopmentandSCFIdoesnotcurrentlyhaveaplantofthesizebeingproposedinoperation,theoperatingandmaintenanceeffortrequiredtokeeptheplantinoperationwillbesignificantandshouldnotbeunderestimated.
ItisrecommendedthatOCSDshouldconsiderafulloperatingandmaintenanceagreementwithSCFI.
5.1.7 Safety
Onreviewingtheproposalandcosts,itappearsthatthereisnobuildingfortheSCFIsystemincludedintheplansorcosts.AttheIronBridgefacilityinFlorida,10foothighblastswallssurroundedtheinstallationandnopersonnelwereadmittedduringoperation,duetothehighpressuresinvolved.Plantwasoperatedremotely.AlthoughitisfullyacceptedthattherearesignificantdifferencesbetweentheSCFIsystembeingproposedandtheSuperWaterSolutionssysteminstalledatIronBridge,theexperienceatIronBridge(withthesystemexperiencingasignificantfailurewithdamagetotheenclosure)doesseemtojustifyacautiousapproachindesignofthesafetysystemsassociatedwiththesesystems.ItisstronglyrecommendedthatasimilarapproachistakeniftheinstallationproceedsatOCSD.Theplantshouldberemotelyoperatedandshouldbesurroundedbyprotectiveinfrastructuretoensurethatnopersonnelareexposedtopotentialrisksduringoperationofthesystem.
Theproposalsdidnotdiscussseismictesting,bracingorrestraints.Giventhelocation,carefulattentionshouldbegiventotheseismicdesign.
5.1.8 Critical Parts
Thereisnodiscussionintheproposalofcriticalpartsandspares.Giventhatthisisaspecialistsystem,itislikelythatitemsofequipmentmaybesubjecttolongleadtimes,particularlyiftheyarebeingsuppliedfromoverseas.Theproposaldoesnotprovidedetailsofmanufacturersformajor
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equipmentitems.Althoughthisisademonstrationfacility,giventhesignificantinvestmentbeingconsideredbyOCSDitisrecommendedthatthedesignshouldbebasedaroundcontinuousornearcontinuousoperationandsuitablesparesshouldbeheldtoavoidlonginterruptionsintheoperationofthefacility.
ItisrecommendedthatOCSDconfirmwithSCFIthemanufacturersforallkeyequipmentitems,identifywhichofthesesystemsareconsideredcriticaltooperationanddevelopalistandcostsforshelfspares.
5.1.9 Procurement
TheproposedprocurementapproachisforatraditionaldesignbidbuildwithSCFIasthedesigner.Itshouldbenotedthatthisprocurementapproachplacesmostoftheperformance/operationsriskforanundemonstratedprocesswithOCSD.OtheroptionscouldbeconsideredwhichwouldreduceOCSD’srisksuchasdesignbuildoperate,designbuildownoperateetc.ItishoweverrecognizedthatSCFIisasmallentityandmaynothavethefinancialbackingtosupportsuchanapproach.NotealsothatthedesignerwillrequireastatePElicense.
5.1.10 Mass & Energy Balance
Areviewoftheenergyinputsandoutputsindicatedthatthesearebalanced,butactualperformanceandenergybalancewouldrequiremoredetailedevaluationbasedonpilotplantresults.Thefollowingpointshowevershouldbenoted.
Energybalanceinformationinthereportisinconsistentwiththatintheenergybalanceintheappendix.
Itisanticipatedthatsteamturbineefficiencywillbelessthantheassumed25%.
ItisexpectedthatemissionswillrequireSCAQMDpermitting.Atleast6‐12monthsshouldbeplannedforthepermittingprocesses.
Basedontypicalindustryvaluesforprimaryandsecondarysludgeheatingvalues,theenergybalancefortheA30presentedintheevaluationreportlistedreasonableassumptionsforenergyinput.
Table 5‐1. Summary of Energy Inputs for AquaCritox A30
SLUDGEHHV
(BTU/LB VS)% VS
VS LOADING (LB/HR)
SLUDGE CHEMICAL ENERGY (KW)
AQUACRITOX SLUDGE
CHEMICAL ENERGY (KW)
Primary 10,800 73.7 781 2,472 2,169
Secondary 9,700 81.1 862 2,450 1,542
ElectricalenergyinputsfortheA30werealsoreasonableconsideringpumpingof800gphto3,600psig.Theevaluationreportisassumingenergyrecoveryat75‐80%;itisrecommendedthatthesevaluesbeconfirmedbasedonpilotresults.
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5.2 REVIEW OF CAPITAL AND OPERATING COSTS OnreviewofthecapitalcostsassociatedwiththeSCFIproposal,thefollowingcommentsaremade:
Inlinewithcommentsabove,itisrecommendedthatblastwallsandremoteoperationshouldbeincludedintheproposal.Costsarenotcurrentlyincluded.
Itisnormalatthislevelofcostestimatingtomarkupequipmentcosttogiveaconstructioncost.Themarkupcurrentlyincludedappearstobeontheorderof150%(withsomevariationdependingonthetreatmentoption).Inourexperiencethisistoolowanditisrecommendedthatequipmentcostmarkupshouldmatchtheapproachtakenwiththewiderbiosolidsstudy.
OCSDshouldnotethecostsarepresentedasASCEClass4andassuch,thetruecost(followingadjustmentsasnotedelsewhereinthissection)couldbeupto50%higherthanthebaseestimate.Thismaybeimportantforbudgetaryplanning.
Anumberofitemswereidentifiedforwhichitwasuncertainastowhethercostshavebeenincluded.Whileitislikelythatformanyoftheseitems,costsarealreadyincorporatedunderotherlineitems,thisshouldbeconfirmedwithSCFI.Theseitemsinclude:
o CIPsystem
o Instrumentaircompressors
o Sludgetankmixingsystems
o Odorcontrolsystems/piping
o AllpumpsshownonPFD
o Polymermakeupsystem
o Steamline&condensatereturntoturbine
o Criticalshelfspares
OnreviewoftheoperatingandmaintenancecostsassociatedwiththeSCFIproposal,thefollowingcommentsaremade:
TakingtheexampleoftheA‐30primarysystem,upstreampolymercostsarestatedas$105,954/yr.Evenusingalowendpolymerdoserateof12lb/dryton,thepolymercostwouldbecalculatedat3,968dtpa*12lb/dt*$2.65/lbpolywhichgivesacostof$126,182peryear.(Actualpolymerconsumptioninthevolutescrewpressreportwasaround12lb/dtforprimarysludgeandaround16‐18lb/dtforWAS.)Thereisasimilarerroronthecostsfortheothersystems.
MaintenancecostsforupstreamanddownstreamequipmentareexcludedonthebasisthattheseareoffsetbysavingsinmaintenanceonOCSD’sothersolidsprocessingfacilities.Thesecostsshouldnotbeexcluded.Inourexperience,maintenanceismoredependentontheamountofequipmentinstalledthanonthroughput.
Ingeneral,themaintenanceallowanceisverylow.Atypicalmaintenanceallowanceforconventionalmechanicalplantequipmentwouldbe2%ofequipmentcostperyearwithhighervaluesuptoapproximately4%peryearformoremaintenanceintensiveitemsusingestablishedtechnology.GiventhatSCWOisanemergingtechnologyandtheoperatingconditionsarevery
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onerous,itispossiblethatsignificantlyhighermaintenancecostscouldbeexperiencedonademonstrationfacility.
TakingtheA‐30primarysystemasanexample,sludgedisposalcostoffsetisstatedas$1,240,100peryear.Withtypicalvolatilesolidsdestructionindigestionof50%andbasedon$62.50perwetton,thedisposalcostoffsetiscalculatedatapproximately$744,000peryear.ItappearsthatVSreductionthroughdigestionwasnottakenintoaccountinSCFI’scalculationasitshouldbe.
Asnotedabove,25%efficiencyforthesteamturbineisunrealisticallyhigh.Anefficiencyofjustunder20%wouldbemoretypical.
Theoxygendemandassumptionwasinconsistentbetweenthedesigncriteriaandtheannualoperationcostprojections.
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6.0 SCFI Pilot Plant in Valencia, Spain AsitevisitwasplannedtoanSCFIAquaCritoxpilottreatmentsystemlocatedinValencia,Spainaspartofthisevaluation.However,thisfacilityisnotincontinuousoperationtreatingwastewatersludgeinautothermalconditions.Therefore,thesitevisitwasindefinitelypostponed.
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7.0 SCFI Proposals – Capital and Operating Cost Evaluation TwoanalysesweredevelopedtoassesstheeconomicfeasibilityofanAquaCritoxdemonstrationfacility.AninitialreviewoftheSCFIproposals(OCSDAquaCritoxDemonstrationprojectEvaluationStudyTM)fortheA‐30unitwasperformedinordertodevelopa20‐yearNetPresentValue(NPV)comparisonbetweentheAquaCritoxA‐30ModelandTPADClassAandBalternatives(developedfromPlant2BiosolidsMasterPlan,ProjectPS15‐01,Task4).ThisinitialevaluationusedcostsidentifiedintheSCFIproposalwithoutanymodification.TheseinitialresultswerediscussedinaprojectmeetingonNovember9,2017,andrefinementstotheconstructionandoperatingcostswereidentifiedtoimprovetheaccuracyoftheoverallanalysis.Followingthismeeting,arevisedanalysiswasdevelopedtoassesstheeconomicfeasibilityoftheAquaCritoxA30unitusingupdatedinformationonthepilotsystemcapitalandoperatingcosts.
Resultsoftheinitialbusinesscaseevaluation(whichisbasedonSCFIproposedcostswithnomodification)arepresentedinSection7.1.ResultsoftherevisedanalysiswhichisbasedoncostassumptionsagreedwithOCSDarepresentedinSection7.2.
7.1 SCFI BUSINESS CASE EVALUATION AninitialreviewoftheSCFIproposalsfortheA‐30unitwasperformedtoreplicatethecostsforCapital,Operating&MaintenanceandanybenefitsderivedfromsteamorpowergenerationdevelopedintheOCSDAquaCritoxDemonstrationProjectEvaluationStudyTM.A20‐yearNetPresentValue(NPV)analysiswasperformedbetweentheAquaCritoxA‐30ModelandTPADClassB,developedfromPS15‐01Task4.
7.1.1 Construction Cost Considerations
ThefollowingaretheconstructioncostconsiderationsthatwereincludedfortheNPVanalysis.
DirectcostsforconstructionwerecopiedfromtheOCSDAquaCritoxDemonstrationProjectEvaluationStudyTM.Theconstructioncostsincludedallcostsrelatedtoconstructionofabasicpilotfacility.Thefollowingwereassumedaspartoftheconstructioncost:
o Itwasassumedthattheconstructioncostsalsoincludedtwocoolingtowersforprocesscooling,inadditiontoassociatedwatertreatmentandconditioningsystemsforthecoolingtowermakeupwater.Plantwatermaybeusedforcooling;however,duetopoorwaterqualityatPlantNo.2forcoolingapplications,thisapproachwouldlikelyrequireasecondarycoolingloopandwatersoftening.
o Allmodificationstotheexistinginfrastructureandprocesseswereincludedintheconstructioncost.
ConstructioncostsforTPADClassBweredevelopedinprojectPS15‐01,Task4.
AllconstructioncostsarebasedonDecember2016estimates.
Thefollowingconstructionmarkupswereapplied:
o Contingency–25%
o GeneralConditions–10%
o GeneralContractorOverhead,Profit,andRisk–15%
o EscalationtoConstructionStart–0%
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o SalesTax(Basedon50%ofdirectcostsandcontingency)–8%
o BidMarketAllowance–0%
Table7‐1summarizesthecapitalcostsrelatedtotheinitialbusinesscaseevaluation.
Table 7‐1. Initial Business Case Evaluation Construction Costs 1
DESCRIPTION TOTAL DIRECT COST2
Pre‐processing Facilities, Site Work, and Power Distribution $ 8,100,000
Sitework, Yard Piping, and Structural/Foundation $ 2,500,000
Sludge Screen $ 200,000
Influent Sludge Storage $ 400,000
Degrit System $ 500,000
Degritted Sludge Storage $ 300,000
Volute Press $ 1,200,000
Dewatered Sludge Storage $ 600,000
Electrical Bldg & Power Distribution $ 2,500,000
Aquacritox Facilities $ 7,700,000
Aquacritox Package $ 7,200,000
LOX Facilities $ 600,000
Post‐Processing Facilities $ 1,800,000
Effluent Storage $ 200,000
Effluent Flocc_CLF $ 500,100
Thickened Ash Storage $ 500,000
Thickened Ash Dewatering $ 600,000
TOTAL DIRECT COST $ 17,700,000
Contingency $ 2,600,000
Subtotal $ 20,300,000
General Conditions $ 2,000,000
Subtotal $ 22,300,000
General Contractor Overhead, Profit & Risk $ 3,4050,000
Subtotal $ 25,700,000
Escalation to Construction Start $ 0
Subtotal $ 25,700,000
Sales Tax (Based on 50% of Direct Costs + Contingency) $ 800,000
Subtotal $ 26,500,000
Bid Market Allowance $ 0
TOTAL ESTIMATED CONSTRUCTION COST $ 26,500,000
Notes: 1. Cost information copied from OCSD AquaCritox Demonstration Project Evaluation Study TM, Appendix A
– Preliminary Construction Cost Estimate. 2. Costs for each facility were obtained from the SCFI Proposal and rounded to the nearest $100,000 for
presentation purposes.
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7.1.2 Operating, Maintenance and Benefit Cost Considerations
ThefollowingaretheO&MandBenefitCostconsiderationsthatwereassumedfortheNPVanalysis.ThesecostconsiderationsweredevelopedfromtheOCSDAquaCritoxDemonstrationProjectEvaluationStudyTM.
Thefacilitywasassumedtooperatecontinuously,24hoursperdayand7daysperweek.
TheelectricaldemandwasderivedfromtheAquaCritoxTM‐2SingleLineDiagramandSCFIproposalreportingrunningkW.Assuming$0.087/kWh,annualpowercostswereassumedtobe$297,314.
Theoxygensystemmaintenancewasassumedtoinclude$129,962/yearofmaintenancecostsand$9,000/yearforoxygensystemrentalcosts.
Theoxygensystemconsumptionassumed$65/tonofoxygenand5,098tons/yearofoxygenconsumption,withatotalannualcostof$331,334.
Polymerwasassumedadosingrateof12lb/drytonand$2.65/drylbforatotalannualcostof$126,182.
TPADClassBoperatingcostsweredevelopedinprojectPS15‐01,Task4.
7.1.3 Repair & Replacement (R&R) Cost Considerations
ThefollowingaretheR&RweredevelopedfortheNPVanalysis.
R&RcostswerenotassumedfortheAquaCritoxsystem,matchingtheapproachappliedintheOCSDAquaCritoxDemonstrationProjectEvaluationStudyTM.
R&RcostsforTPADClassBweredevelopedinProjectPS15‐01,Task4.
7.1.4 Net Present Value Analysis Results
Alifecyclecostanalysiswasperformedusinganescalationrateof3.5%anddiscountrateof4%.TheresultsforAquaCritoxA‐30andTPADClassBarepresentedbelow.ThecapitalcostandpresentworthoftheO&MandR&Rcostsareincluded.
ThepreliminaryfindingsshowninTable7‐2suggestasimilarcostin$/drytonforbothalternativeswhencostitemsintheSCFIproposalaretakenatfacevalue.However,therewereseveralareaswhereitwasfeltthatcostsintheAquaCritoxproposalrequiredmodificationtoprovideatruepictureofactualcostforthedemonstrationfacility.ThemodifiedresultsarepresentedinSection7.2below.
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Table 7‐2. Initial Net Present Value Analysis for Both Alternatives
ALTERNATIVE CONSTRUCTION COST3
O&M (20‐YR PRESENT
WORTH)
R&R (20‐YR PRESENT
WORTH)
NPV $/DRY TON
1 AquaCritox Model A‐30
$26,500,000 $19,700,000 ‐$ $46,200,000 $5821
2 TPAD Class B $464,900,000 $246,200,000 $61,700,000 $772,800,000 $5332
Notes: 1. Capacity of the A30 with continuous operation is 10.9 dry tons/day. 2. The TPAD Class B process was sized to meet an average annual loading rate of 198.5 dry tons/day. Given the dramatic difference is the sizes of the two systems, the net present values are dramatically different; therefore, the present worth is also presented in $/dry ton of process capacity over a 20 year operating period to consider these alternatives in a more comparable manner. Based on this approach, the Aqua Critox A30 pilot demonstrates a comparable cost per dry ton relative to the TPAD Class B alternative.
3. Construction costs are based on December 2016 estimates.
7.2 BV/BC BUSINESS CASE EVALUATION Decisionsfromtheinitialworkshopidentifiedtheneedforfurtherrefinementoftheconstructionandoperatingcosts.Thiswouldinvolveupdatingunitcostsforoperatinglabor,water,polymerandelectricity,usingvaluesdevelopedfromTask4ofprojectPS‐15.Itwouldalsoincluderepairandreplacementcostsofmechanicalequipmentoverthesuggestedservicelifeandadditionalprovisionsforsafetysuchasbuildings/structures(whereverdeemednecessary),remoteoperationandcontrolsandseismicassessments.
7.2.1 Construction Cost Considerations
ThefollowingaretheconstructioncostconsiderationsthatwereincludedfortheNPVanalysis.
Inadditiontothedirectcostsforconstructionidentifiedintheinitialanalysis,thecostforgroundimprovementsandabuildingwereaddedtotheconstructioncosts.PreviousworkatPlantNo2hasidentifiedtheriskofliquefactionatthesite,andgroundimprovementsarerequiredtomitigatetheserisks.Also,itwasassumedthatabuildingwouldberequiredovertheprocessequipment,whichwouldassistwithodorcontainment.TheAquaCritoxreactororotherhighpressureandtemperaturevendorsystemswouldnotbeincludedwithinthisbuilding.Toaddresspotentialsafetyconcerns,awallwouldbebuiltaroundthesesystemstoprotectworkersduringnormalsystemoperation.
ConstructioncostsforTPADClassAandBoptionsweredevelopedinprojectPS15‐01,Task4.
AllconstructioncostsarebasedonDecember2016estimates.
Thefollowingconstructionmarkupswereapplied:
o Contingency–25%
o GeneralConditions–10%
o GeneralContractorOverhead,Profit,andRisk–15%
o EscalationtoConstructionStart–0%
o SalesTax(Basedon50%ofdirectcostsandcontingency)–8%
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o BidMarketAllowance–0%
Table7‐3summarizestheconstructioncostsrelatedtotheinitialbusinesscaseevaluation.
Table 7‐3. Revised Business Case Evaluation Construction Costs
DESCRIPTION TOTAL DIRECT COST
Pre‐Processing Facilities, Site Work, and Power Distribution $ 8,100,000
Sitework, Yard Piping, and Structural/Foundation $ 2,500,000
Sludge Screen $ 200,000
Influent Sludge Storage $ 400,000
Degrit System $ 500,000
Degritted Sludge Storage $ 300,000
Volute Press $ 1,200,000
Dewatered Sludge Storage $ 600,000
Electrical Bldg & Power Distribution $ 2,500,000
Aqua Critox Facilities $ 7,700,000
Aqua Critox Package $ 7,200,000
LOX Facilities $ 400,000
Post‐Processing Facilities $ 1,800,000
Effluent Storage $ 200,000
Effluent Flocc_CLF $ 500,000
Thickened Ash Storage $ 500,000
Thickened Ash Dewatering $ 600,000
Building Cost $ 800,000
Ground Improvements $ 3,000,000
TOTAL DIRECT COST $ 21,500,0007‐
General Conditions (15%) $ 24,700,000
Subtotal
Startup, Training, and O&M (4%) $ 25,700,000
Subtotal
Project level allowance (30%) $ 33,400,000
Subtotal
Builders risk, Liability, Auto Insurance (2%) $ 34,000,000
Subtotal
Contractor Bonds and Insurance (1.5%) $ 34,500,000
TOTAL ESTIMATED CONSTRUCTION COST $ 34,500,000
Note: 1. Information from OCSD Aqua Critox Demonstration Project Evaluation Study TM, Appendix A –
Preliminary Construction Cost Estimate.
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7.2.2 Operating, Maintenance and Benefit Cost Considerations
ThefollowingaretheO&MandBenefitCostconsiderationsthatwereevaluatedfortheNPVanalysis.
Thefacilitywasassumedtooperatecontinuously,24hoursperdayand7daysperweek.
UnitcostswereidentifiedinPS15‐01,Task4.
TheelectricaldemandwasderivedfromtheAquaCritoxTM‐2SingleLineDiagramandSCFIproposalreportingrunningkW.Assuming$0.099/kWh,annualpowercostswereassumedtobe$336,798.
Theoxygensystemmaintenancewasassumedtoinclude$129,962/yearofmaintenancecostsand$9,000/yearforoxygensystemrentalcosts.
Theoxygensystemconsumptionassumed$65/tonofoxygenand5,098tons/yearofoxygenconsumption,withatotalannualcostof$331,334.
Polymerwasassumedadosingrateof12lb/drytonand$2.65/drylbforatotalannualcostof$126,182.
Plantwaterdemandwasestimatedat37.8Mgal/yearandincludedwaterdemandforthesludgedegrittingsystem,dewateringpolymerfeedsystem,andpumpsealwater.Assumingaplantwatercostof$61.22/MG,annualplantwatercostsare$2,317.
Labortoprovideadedicatedoperatorforthepilotsystem24/7,wasestimatedbySCFIat$1,314,000/year.
TPADClassAandBalternativeoperatingcostsweredevelopedinprojectPS15‐01,Task4.
7.2.3 Repair & Replacement Costs and Benefits Considerations
ThefollowingaretheR&RandbenefitscostconsiderationsthatwereevaluatedfortheNPVanalysis.
ThebenefitsderivedfromsteamwerequantifiedusingestimatesfromtheOCSDAquaCritoxDemonstrationProjectEvaluationStudyTM.Atanapproximatelysteamgenerationrateof3,491lb/hrandassumingavalueforsteamat$11.50/1,000lb,annualbenefitsfromsteamproductionwereestimatedat$301,050.
TheAquaCritoxsystemincludespreandpostprocessingequipmentandequipmentassociatedprovidedfortheSCWOprocess.Repairandreplacementcostsforthepilotsystemequipmentibasedona15‐yearservicelifewereincluded.TotalR&Rcostswereestimatedat$12.7M.
NoR&Rcostsrelatedtoreactor,heatexchangersoreconomizers(commonlycitedinliteratureasneeded)wereincluded.
R&RcostsforTPADClassAandBalternativesweredevelopedinProjectPS15‐01,Task4.
7.2.4 Net Present Value Analysis Results
Alifecyclecostanalysiswasperformedusinganescalationrateof3.5%anddiscountrateof4%andtheresultsforAquaCritoxA‐30,TPADClassAandTPADClassBarepresentedbelow.TheconstructioncostandpresentworthoftheO&MandR&Rcostsareincluded.Table7‐4presentsthecomparativeanalysisassumingsteamisnotrecoveredfromtheA30unit,andTable7‐5presentstheanalysisassumingsteamrecovery.
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Table 7‐4. Revised Net Present Value Comparative Assessment (w/o steam benefit)
ALTERNATIVE CONSTRUCTION
COST
O&M (20‐YR PRESENT
WORTH)
R&R (20‐YR PRESENT
WORTH) NPV $/DRY TON
1 Aqua Critox
Model A‐30
$34,500,000 $46,600,000 $11,700,000 $92,800,000 $1,1691
2 TPAD Class A $486,300,000 $232,700,000 $62,700,000 $781,700,000 $5402
3 TPAD Class B $464,900,000 $246,200,000 $61,700,000 $772,800,000 $5332
Notes:
1. Capacity of the A30 with continuous operation is 10.9 dry tons/day.
2. The TPAD Class B process was sized to meet an average annual loading rate of 198.5 dry tons/day.
InevaluatingtheA30systemwithoutsteamrecovery,the20‐yearpresentworthcostofprocessingsolidsisapproximatelytwicethecostoftheTPADClassAandBalternatives.Withsteamrecovery,thecosttoprocesssolidsintheA30pilotisslightlyreduced.
Table 7‐5. Revised Net Present Value Comparative Assessment (w/ steam benefit)
ALTERNATIVE CONSTRUCTION
COST
O&M (20‐YR
PRESENT
WORTH)
R&R (20‐YR PRESENT
WORTH)
TOTAL
BENEFIT (20‐YR
PRESENT
WORTH)
NPV $/DRY
TON
1 Aqua Critox
Model A‐30
$34,500,000 $46,600,000 $11,700,000 $6,000,000 $86,900,000 $1,0861
2 TPAD Class A $486,300,000 $232,700,000 $62,700,000 $0 $781,700,000 $5402
3 TPAD Class B $464,900,000 $246,200,000 $61,700,000 $0 $772,800,000 $5332
Notes:
1. Capacity of the A30 with continuous operation is 10.9 dry tons/day.
2. The TPAD Class B process was sized to meet an average annual loading rate of 198.5 dry tons/day.
Theaboveanalysisassumedcontinuousoperation.Ifthethroughputofthesystemortimeofoperationisreduced,thecosttoprocesssolids($/drylb)willincreaserelativetothenumberspresentedinthisanalysis.
7.3 COMPARISON OF SCFI AND BV/BC COSTS BasedonthecostevaluationspresentedinSection7.1andSection7.2,Table7‐6summarizesacostcomparisonbetweenSCFIcostsandBV/BCcosts.
TheresultsoftherevisedcostevaluationsuggestthatthecostfortreatingbiosolidsusingtheAquaCritoxdemonstrationfacilityarelikelytobeapproximatelydoublethatoftreatmentusingTPADonaperunitsolidsthroughputbasis.Thisresultisnotsurprisinggiventheeconomiesofscalebetweenademonstrationplantandafullscalefacility.
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Table 7‐6. Comparison of SCFI and BV/BC Cost Estimates
SCFI BV/BC Notes
Ground Improvements $0 $3,000,000 Ground improvements for AquaCritox structures
Building Costs $0 $780,000
Enclosures additions for process equipment and control room. Wall
around AquaCritox facility
Total Direct Cost $17,700,000 $17,700,000
Cost includes Pre‐Processing Facilities, site work and power
AquaCritox Facilities and Post‐Processing Facilities
Construction Cost Subtotal $17,700,000 $21,500,000
Total Direct Construction Cost $26,600,000 $34,500,000
Mark up used by SCFI = 1.5
Mark up used by BV/BC = 1.6 (From Task 6, Plant 2 CIP Cost Estimate)
Electrical $0.087/kWh $0.099/kWh BV/BC assumed the electrical power rate used in TM4
Electrical390 kWh 390 kWh
BV/BC assumed an electrical energy demand based on one‐line
demand provided in the report
Polymer $2.65/lb $2.65/lb BV/BC assumed the polymer unit costs used in TM4
Polymer 12 lbs/dry ton 12 lbs/dry ton BV/BC and SCFI used the same polymer dose
Water $0/MG $62.22/MG BV/BC assumed the plant water cost used in TM4
Water 0 Mgal/y 37.8 Mgal/y
BV/BC assumed a water demand for process equipment and seal
water.
Labor$0/y $1,314,000/y
BV/BC assumed an annual labor cost by SFCI staff (provided by
AquaCritox)
Oxygen $65/ton $65/ton BV/BC and SCFI used the same cost for oxygen
Oxygen 5,098 tons/y 5,098 tons/y BV/BC and SCFI used the same demand for oxygen
Oxygen$129,962/y $129,962/y
BV/BC and SCFI used the same cost for oxygen equipment
maintenance
Oxygen $108,000/y $108,000/y BV/BC and SCFI used the same cost for oxygen equipment rental
O&M Present Worth $19,700,000 $46,600,000
REPAIR & REPLACEMENT R&R Present Worth $0 $11,700,000
BV/BC: Assumed R&R cost equivalent to mechanical equipment base
cost after 15 years of operation.
Steam 3,491lbs steam/h 3,491lbs steam/h BV/BC and SCFI used the same amount of stream produced each hour
Steam $11.50/1000lb $11.50/1000lb BV/BC and SCFI used the same value for steam
Benefits Present Worth ‐$6,000,000 ‐$6,000,000
Total Dry Tons 79,570 79,570 for 20 year life cycle
Unit NPV Cost $507 $1,091 /dry ton
Reference Cost for TPAD Class A $540 /dry ton
Net Present Value $40,300,000 $86,800,000
CAPITAL
OPERATION & MAINTENANCE
BENEFITS
SUMMARY
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8.0 Conclusions & Recommendations Thefollowingconclusionsandrecommendationswerereachedinthecourseofthisevaluation.
TheSCWOprocesshaslimitedsuccessfuloperationalexperienceintheindustry,particularlyforwastewatersludgeapplications.
BasedonarevisedanalysisoftheAquaCritoxA30pilotsystem,thecosttoprocesssolidshasbeenestimatedasapproximatelytwicethatofthefutureTPADalternative.Furtherinvestigationintotheoperationofapilotsystem,wouldhelpidentifyifthetruecostofoperationisgreaterorlessthanthenumbersestimatedinthisTM.
LongtermoperatingdatawithapilotfacilitytreatingwastewatersludgeisnecessaryinordertofurtherevaluatetheconcernsidentifiedinthisTMabouttheSCWOprocess,includingcorrosionandscalingissues,reliabilityoftheequipment,demonstrationofperformanceandplantsafety.
ProceedingwithademonstrationscaleprojectisthereforenotrecommendeduntilOCSDareabletowitnessreal,longtermoperatingdataofapilotfacilityonwastewatersludge.
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Xu,D.etal(2013);Influenceofoxidationcoefficientonproductpropertiesinsewagesludgetreatmentbysupercriticalwater;InternationalJournalofHydrogenEnergy,v38,n4,p1850‐1858,Feb12,2013
Yang.Setal.(2013);Newdesignofsupercriticalwateroxidationreactorforsewagesludgetreatment;AdvancedMaterialsResearch,v774‐776,p212‐215,2013
Zhang,T.etal(2016);Treatmentofsludgeandwastewatermixturebysupercriticalwateroxidation;Resources,EnvironmentandEngineering‐2ndTechnicalCongressonResources,EnvironmentandEngineering,CREE2015,p499‐504,2016
Zhong,C.etal(2015);Anewsystemdesignforsupercriticalwateroxidation;ChemicalEngineeringJournal,Volume269,p343–351,1June2015
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Appendix A – Tabular Summary of Literature on Super Critical Water Oxidation
Final – May 9, 2017 A‐2 Biosolids Master Plan
RESEARCH GROUP OR BODY
SOURCE PAPER TITLE MAIN FINDINGS
Bermejo,M.D.,Cocero,M.J.(2006)
AIChEJournal,v52,n11,p3933‐3951,November2006
Supercriticalwateroxidation:Atechnicalreview
Anoverviewofthetechnicalaspectsofthesupercriticalwateroxidationprocessisprovided;reactorsdesign,constructionmaterials,corrosion,saltsprecipitationproblems,andindustrialapplicationsarediscussed.
Generalfindings:
SCWpropertiesmakeforafavorablehomogeneousreactionmediabutthelowsolubilityofpolarcompoundscausessolidsprecipitationandplugging.Thesewell‐knownproblemsoftheSCWOprocessdefinetheneedsofresearch:newreactorsthatavoidcorrosionandplugging.
CorrosionandpluggingproblemscontinuetocausesomeexistingSCWOindustrialplantstostopafterafewmonthsofoperation.Theextremeoperationalconditionsalongwiththecorrosiveenvironmentmakeitnecessarytoextensivelystudythematerialsbehavioronduty.AchallengeinSCWOistheapplicationofnewconstructionmaterialsabletostandtheharshoperationalconditionsinthemainequipment,valves,andfittings.
Modelling:o Itisanecessarytooltodevelopnewreactors.Reactormodelingisabletoprovideinsightintocharacteristicsofthereactorthataredifficulttoobtain
experimentally,andalsotofurnishabetterunderstandingofthemixingprocess.o Itwasfoundthatafirst‐orderrepresentationofapparentkineticsisadequatewheninductiontimesarenegligibleanduptoacertainconversion.Thisis
averyfrequentsituationinSCWOsofirst‐ordermodelsareconvenientformodelling.Althoughthereareagreatnumberofstudiesaboutoxidationkineticsinsupercriticalwater,theinfluenceonpressureintheoxidationrateisstillnotclear.
o Muchworkremainstoobtainaccuratevaluesofthethermodynamicandtransportpropertiesoftheaqueousmixtures:evenwhentransportpropertiesofwatercanbepredicted,thermodynamicpropertiesandphaseequilibriumoftheaqueoussystemarestillahandicap,especiallywheninorganicsaltsarepresentinthemixture.
Fromtheperspectiveofenergetics,SCWOcanbeperformedinanenergeticallyprofitableway.Corrosionresistantdevicesforseparationofsaltsmustbedeveloped,toproduceelectricitybydirectexpansionofthereactionproducts.Currently,researchconductingthedevelopmentofturbinesabletoworkattemperatures>700°Cisprogressing,whichwillfacilitateaprofitableenergyrecoveryfromtheSCWOeffluent.
SomespecificSCWOprocessrelatedaspects(extracts):
TheSCWOprocessconsistsoffourmainsteps:(1)pressurizationofthereagents,(2)reaction,(3)saltseparation,and(4)depressurizationandheatrecovery.
Pressurization:Oxygencompressioncostsareconsiderablylowerthanthosefromair(onequivalentoxygenbasis),buttheyrepresentanadditionalrawmaterialcost.Usinghydrogenperoxidemaybeadvantageousinbench‐scalefacilities,butthecommercialapplicabilityofthisoxidantislimitedbecauseofitshighcost.
ReactionTemperature:Whenthereactiontemperatureisincreased,theefficiencyoftheprocessishigherandtheresidencetimenecessaryforthetotaloxidationofthereagentsislower.Atreactiontemperaturesaround650°C,residencetimesnecessaryforcompleteconversionare<50s,withindependenceofthepollutantstreatedOperationPressure:Whenthepressureisabovethecriticalpressureofwater(22.1MPa),conversionisnotimprovedbyelevatingthepressure.Atlowerpressures,theconversionsdecrease,butifthereactiontemperatureishighenoughthedetrimentaleffectofpressurecanbecompensated.
Saltseparation:solid–fluidseparation(e.g.hydrocyclonsorfiltrationsystems)aremethodsofrecoveringsolidsattheoutletofthereactorareeffectiveonlywhenthesolidsdonottendtosticktothewallofthereactor.Thiscanhappenifthesolidisnotstickyorifasystemforremovingthesolidsfromthewallsisimplementedinthereactor(suchastranspiringwallreactor).
Corrosionforms:ThemainformsofwhatcorrosionmayappearintheSCWOprocessarethefollowing:pittingcorrosion,generalcorrosion,intergranularcorrosion[intercrystallinecorrosion(IC)],andstresscorrosioncracking(SCC).Attemperatures>600–700°C,anothercorrosionmechanism,calledhightemperaturecorrosion(creeping)canoccur.Atthesetemperatures,mostcommonlyusedmetals,suchasiron,nickel,andchromiumbegintoformvolatilecorrosionproducts,whichareeasilyretiredfromthesurfaceofthemetal,orinsomecasesmeltthematerial,leadingtofastgeneralcorrosion.CorrosionintheSCWOenvironmentiscontrolledbythedissolutionoftheprotectingoxidelayertotheprimarycorrosionproducts.Thatis,thehigherthesaltsolubility(whichdependsonthedensityofthesolution),thefasterthecorrosionrate.Thisdissolutionofthesaltscanbecarriedoutbyelectrochemicalprocess,whichisafunctionoftheelectrochemicalpotential,orbyachemicalprocessthatdependsmainlyonthepHofthesolution.
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Constructionmaterials‐mostwidelyusedmaterialsintheSCWOprocess:o Stainlesssteel(AISI316)isadequateforworkingattemperaturesbetween300and500°C,lowconcentrationsofCl‐,andvaluesofpHbetween2and11.o Titaniumalloys(Ti‐Gr2,Ti‐Gr9,andTi‐Gr12)presenthighresistancetostronglyoxidativeenvironments.Nevertheless,athightemperaturestheir
mechanicalresistanceislow(creeping).Itcouldbeagoodsolutiontouseitascoatingofanothermaterial.o Al‐orSi‐basedceramics,suchasalumina,siliciumcarbide,ornitride,aregoodoptionsforworkingbelowpH=12.AthigherpHvaluesthesematerials
aredissolved.o ThemostpromisingandcommonlyusedsolutionstoobtainhighresistancetocorrosionathightemperaturesareNialloys625andC‐276.o Newalloys,withbetterproperties,arecurrentlybeingdeveloped,buttheyhavenotbeentestedinSCW.Atthemoment,itisacceptedthatthereisnota
uniquematerialabletowithstandallthepossibleconditions.TheSCWOprocessisaveryversatiletechnologyanditsdevelopmentshouldnotbedependentontheavailableconstructionmaterials.
Saltprecipitation:AvoidingsaltprecipitationproblemsinSCWOprocessthesolubilityofinorganicsaltsinwaterdecreasesdrasticallynearthecriticalpointofwater(1–100ppm).ThepluggingofreactorsproducedbythesaltprecipitationisthemainreasonfordelayofthecommercializationoftheSCWOprocessforsomeapplications.Alsosomemodelshavebeendevelopedtocalculatethesolubility’sofinorganicsaltsinhigh‐temperature–high‐pressuresteamofsupercriticalwater.Differentsolutionshavebeenproposedtosolvethepluggingproblem.Asaconclusion,onestudyindicatedthatthebestsolutiontoavoidsaltprecipitationinsidethereactoristoreducethequantityofsaltpresentinthefeed.Thiscanbeachievedusingsolid–fluidseparationdevices.Thesedevicescanbeusedbeforeorafterthereactionstep.
TypesofreactorsfortheSCWOprocess:ThetwomaindisadvantagesposedbytheuseofSCWOarecorrosionandsaltdepositionintheequipment.Toovercomethesetwoproblems,anumberofreactordesignshavebeendeveloped.Thefourmostcommonreactorconceptsareasfollows:o Tubularreactor(becauseofitssimplicity,thetubularreactoristhemostwidelyusedSCWOreactor).
Toavoidsaltdepositionintubularreactors,theyaredesignedwithsmalldiameters,toobtainhighfluidcirculationvelocity.However,evenwhenthisdesignavoidsthedepositionofsolidsalreadypresentinthefeed,precipitatedsaltsformedinsidethereactorhaveatendencytoadherethemselvestoreactorwalls.Thusthisreactorismoreappropriateforfeedswithlowsolidscontent.Whentheorganicmatterconcentrationinthefeedisveryhigh,multi‐injectiontubularreactorsareusedtoavoidhotspotsinthereactor.AschemeofthistypeofreactorisshowninFigure5.Nowadays,tubularreactorsareusedinindustrialapplicationssuchastheAquaCatRandAquaCritoxRprocessesofChematur.Thepluggingproblemissolvedbytheusedoftwoalternatingheatexchangers,sowhenoneofthemisintheoperationsteptheothercanbeinacleaningstep
o Tankreactor,withthereactionzoneintheupperpartandacoolzoneinthelowerpartofthetanktodissolvethesalts.o Transpiringwallreactor,withaninnerporouspipe,whichisrinsedwithwatertopreventsaltdepositsatthewall.Thetranspiringwallreactorpresents
apossiblesolutionforcorrosionandpluggingproblems.Thetranspiringwallreactorpresentsthedisadvantageofthedilutionofthehotreactionproductsbymixingthemwiththetranspiringwater.Thus,thereactoreffluenttemperatureisreduced,makingtheheatrecoverylessefficient.Moreresearchisneededtoimprovematerialsconstructionandtheheatrecoveryofthisreactordesign,andindevelopingotherreactordesignsabletoachievegoodprotectionofthematerialsofthereactor,avoidingcorrosionandsaltdepositionandatthesametimemaximizingtheenergyrecovery.Thesameproblemsaffectotherequipmentasheatexchanges.Somedesignsavoidusingexternalheatexchangesbythemixtureoffeed,oxygen,andfuel.Thisalternativeislessfavorablefortheenergeticbalanceoftheprocess
o Film‐cooledreactorwhichcoolsthewallbycoaxialintroductionoflargeamountsofwater. IndustrialapplicationsoftheSCWO(extract):
InAprilof2001,thefirstSCWOplantforthedestructionofsludgesbeganitsoperationinHarlingen,TX,withaprocessingcapacityof9.8tons/dayofdrysludge.ThisplantisworkingaccordingtotheHydrosolidsProcess,developedbyHydroprocessingLLC.Atthemomenttheplantisinactivebecauseofcorrosionissues.InEurope,ChematurhascommercializeditsSCWOprocessunderthebrandnameAqua‐Critox.Chematurhasalsodevelopedtwoprocesses.o TheAquaReciRprocessisajointdevelopmentofChematurandFeralcoAB.Theprocesscanbeappliedtomunicipalanddrinkingwatersludges.The
AquaCritoxRprocessiscombinedwithrecoveryofcoagulantsand/orphosphorousfromthepure,solidinorganicresidueresultingfromthesupercriticaloxidationstep.
o TheAquaCatRtechnologywasjointlydevelopedbyChematurandJohnsonMattheyfortherecoveryofpreciousmetalsfromspentcatalysts.Inthiswaytransportationofhazardouswastecanbeeliminated.Thefirstcommercial‐sizeunitwasbuiltatJohnsonMatthey’sBrimsdownsite,andstartedupin2004.TheunitisthefirstcommercialunitinEuropebasedonsupercriticalwateroxidation,andthelargestSCWOunitintheworld.
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SOURCE PAPER TITLE MAIN FINDINGS
Gao,M.etal(2014)
AdvancedMaterialsResearch,v1010‐1012,p693‐698,2014
Parameteroptimizationofmunicipalsludgetreatedbysupercriticalwateroxidationprocess
Lab‐scalebatchtestformunicipalsludge(17.35%TS,55.18%VS)withH2O2todetermineoptimalprocessparametersfortotalnitrogendegradationviaSCWO.
Responsesurfaceanalysismethodologyusedtooptimizetheparameters.Results:
Thereactiontemperature,pressureandresidencetimearethemaininterdependentfactorswiththefollowingorderofsignificance:pressure>reactiontemperature>reactionretentiontime;
Theoptimumreactionconditionsare:reactiontemperatureat539°C,pressureat27MPa,residencetimeof434s,andoxidationcoefficientof2.16,undertheseconditions=>totalnitrogendestructionefficiencycanreach74.12%.
Gloyna,E.F.,Li,L.(1995)
EnvironmentalProgress,v14,n3,p182‐192,Aug1995
Supercriticalwateroxidationresearchanddevelopmentupdate
DuringtheearlySCWOresearchanddevelopment(R&D)period(early1980s),ithasbeendemonstratedthatSCWOcanbeaneffectivealternativetothedestructionofhazardousorganicwastewatersandsludges.ThefirstSCWOcommercialfacility(1100Liter/hour)developedbyEcoWasteTechnologieswascommissionedinAugust1994.AnumberofSCWOdemonstrationfacilitiesexistinvariouscompanies,nationallaboratories,andfederalagencies.
TheSCWOprocessishighlyadaptableanddesignrequirementscanbeadjustedtoaccommodateparametervariations.OperationalrequirementsandrelativecostsofspecificSCWOfacilitiesmaybeenhancedbyconductingtreatabilitystudies.
Threespecificdesignconsiderationsareprovided:
ThepresenceofinorganicsubstancesinfluencesSCWOdesigns.Forexample,materialsofconstructionandsolidshandlingmustbeaddressed.Withappropriatewastecharacterizationandtreatabilitydataproblemslikecorrosion,erosion,encrustation,andpluggingcanbeminimized.Newdataonsolubilityandsolidsseparationhaveevolved.Additionaldataonthefateofheavymetalshasbeenmadeavailable.
SeveralunitsofoperationforaSCWOsystemarerequired.Sincemostwastescontainmultiplecomponentsthereactordesignistobebasedondetailedkineticstudies.Kineticlumpingcanbeusedtoevaluatemulticomponentmixtures.
TheSCWOprocesscanproduceamultitudeofintermediatesandpotentialby‐products.Experimentshaveshownthatthedegradationorformationofthesecompoundscanbeenhancedbyacatalyst.E.g.transitionmetaloxideshaveshowndesirablecatalyticeffects.
Goto,M.etal(1997)
JournalofChemicalEngineeringofJapan,v30,n5,p813‐818,Oct1997
Decompositionofmunicipalsludgebysupercriticalwateroxidation
BatchSCWOtestonmunicipalexcesssludge(3.49%TS)withhydrogenperoxideasanoxidantinthetemperaturerangeof473K–873K(200– 600°C).Thereactionproductswereanalyzedintermsoftotalorganiccarbon(TOC),organicacidsandammoniumion.
Results:
Colorofresidualsolidphaseisdependentontemperatureandconcentrationofoxidant:palebrownatsupercriticaltemperatureand>100%stoichiometricoxidantdemand.
Colorofresidualliquidphaseatsupercriticaltemperaturewastransparentandcolorlesswith40%ofstoichiometricoxidantdemand. Acompleteodorlessproductwasobtainedat>100%stoichiometricoxidantdemand.Theproductcouldnotbedeodorizedbelowsupercriticaltemperature
evenatsufficientoxidantlevels. TOCdecreaseswithtemperatureandoxidantamount. Aceticacidandammoniaaredetectedasmajorrefractoryintermediatesintheproduct. Whenmorethanthestoichiometricdemandofoxidantisused,organiccarboninliquidphaseisalmostcompletelydestroyed. Completedestructionofammoniaproducedduringthereactionrequireshighertemperaturesthanthatofaceticacid.
Goto,M.etal(1998)
JournalofSupercriticalFluids,v13,n1‐3,p277‐282,June15,1998
Supercriticalwateroxidationforthedestructionofmunicipalexcesssludgeandalcoholdistillerywastewaterofmolasses
Batchandflow‐throughstainlesssteeltubeSCWOtestswithhydrogenperoxideasanoxidantonmunicipalexcesssludgeandalcoholdistillerywastewaterofmolasses.
Batchtestresultsonexcesssludge:o TOCdestructionfasterathighertemperatures.o TOCintheliquidphaseproductdramaticallydecreasedwithincreasingamountofoxidant.o Atsub‐stoichiometricoxidantlevelsorganicacidswerefoundintheliquidproduct;Organicacidscouldnotbedetectedwhentheamountofhydrogen
peroxidewasmorethan100%.
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o Atthehighesttemperature(873K=600°C),theammoniumionconcentrationintheliquidphasedramaticallydecreasedastheamountofoxidantincreased.Completedestructionwasobservedat150%ofstoichiometricoxidantamount.Atatemperatureof773K(=500°C)ammoniaioncouldnotbedestroyed.
o Atlowertemperaturesammoniumionintheliquidphasedidnotdecreasemonotonouslywithanincreasingamountofoxidant.Providedexplanation:ammoniumionisanintermediateproductintheoxidationofnitrogenproductstonitrogen;reactionfromammoniumiontonitrogenisarate‐controllingstep.
o Completedestructionofammoniaproducedinthereactionrequiredhighertemperaturesthanforaceticacid. Batchtestresultsonalcoholdistillerywastewaterofmolasses:
o SimilarobservationforTOCandorganicaciddestruction.o Theeffectofoxidantamountonresidualammoniumionwasdifferentfromthatforsludge.Evenatlowertemperature(673K=400°C),ammoniumion
wasalmostcompletelydestroyedwithoxidantamountof150%. Flow‐throughreactorresultsonmunicipalexcesssludge:
o Sludgewassufficientlydestroyed;analysisonproductsstillunderinvestigation.Goto,M.etal(1999)
IndustrialandEngineeringChemistryResearch,v38,n11,p4500‐4503,Nov1999
Kineticanalysisforammoniadecompositioninsupercriticalwateroxidationofsewagesludge
SCWOexperimentsonmunicipalsludgeinbatchstainlesssteelreactorusinghydrogenperoxideasanoxidant(200%ofstoichiometricdemand)atatemperaturerangeof723to823K(450–550°C)todetermineammonia(asammonium)destructionrate.
AmmoniaandaceticacidarefoundtoberefractoryintermediatesinSCWOoforganicwastesandarereaction(=destruction)ratecontrolling.Ammoniadestructionwasfoundtobeslowerthanforaceticacid.
PreviousworkreportedcatalyticoxidationofammoniathroughInconel635reactorwallmaterial. ThedecompositionofN‐componentsinthesludgetoammoniawasfoundtobemuchfasterthanthecompletedecompositionofammoniatomolecular
nitrogen,carbondioxideandwater. Ammoniaconcentrationproducedduringthereactionwasmeasuredasafunctionofreactiontime.Datawereanalyzedbyafirst‐orderkinetics.Thereaction
rateconstantforammoniadestructioncoincideswiththosereportedintheliterature(evaluatedactivationenergywas139kJ/molvs.157kJ/molreportedatinliteratureforaflowreactorandathighertemperatures[803to973K]).
Goto,M.etal(1999)
IndustrialandEngineeringChemistryResearch,v38,n5,p1863‐1865,1999
Kineticanalysisfordestructionofmunicipalsewagesludgeandalcoholdistillerywastewaterbysupercriticalwateroxidation
BatchSCWOtestswithhydrogenperoxideasanoxidantonmunicipalexcesssludgeandalcoholdistillerywastewaterofmolasses atatemperaturerangeof673to773K(400–500°C).Totalorganiccarbonwasmeasuredasafunctionofreactiontime.Thedynamicdatawereanalyzedbyafirst‐orderreactionmodel.
DecompositionofMunicipalExcessSewageSludge:o Thedestructionrateisfasteratahighertemperature,andtheTOCreducedtoalmostzeroin60sat773K(=500°C).
DecompositionoftheDistilleryWastewaterofMolasses:o TheTOCdecompositionbehaviorissimilartothesewagesludge.o Theinitialconcentrationofdistillerywastewaterwasmuchlargerthansewagesludge,andthetimerequiredtocompletedecompositionwasabouttwice
thatofsewagesludge. Thereactionrateconstantsdeterminedforbothtestscoincidewiththosereportedintheliterature.Theactivationenergieswere76.3and64.7kJ/molfor
sewagesludgeanddistillerywastewater,respectively.Griffith,J.W.,Raymond,D.H.(2002)
WasteManagement22(2002)453–459;Elsevier.
Thefirstcommercialsupercriticalwateroxidationsludgeprocessingplant
Ahydrothermaloxidationsystem(HTO)usingHydroProcessing,L.L.C.’sHydroSolidsprocesshasbeeninstalledatHarlingen,Texastoprocessupto9.8drytonsperdayofsludge(WAS).Basedonaliteraturereview,thissystemisthelargesthydrothermaloxidationsystemintheworld,andtheonlyonebuiltspecificallytoprocesssludge.Start‐upofUnit1oftwounitsoftheHTOsystembeganinApril2001.
HTOunitintegrationintheWaterworkstreatmentprocess
HarlingenWaterworksdevelopedaconstructionpackagethatincludedthefollowingcomponents:
Modificationstoexistinganaerobicdigesters. ConstructionofasolidshandlingbuildingtohousebothagravitybeltthickenerandtheHydroSolidsunits. Installationofagravitybeltthickenerandappurtenances. InstallationoftwoHydroSolidstrains,eachcapableofprocessing12.5gpmofsludgefeed. Ancillaryequipmentincludingoxygentankanddeliverysystem,greasetrapwastetank,andelectricalandcontrolsystems.
Final – May 9, 2017 A‐6 Biosolids Master Plan
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ExistingsludgedigestertankshavebeenconvertedtoprovideforsludgemixingandstoragetoreceivethesludgefromWastewaterPlant1andSectionsAandBofWastewaterPlantNo.2,aswellasseptagefromthecommunityandsludgefromotherentities’wastewaterplants.A3.3mgravitybeltthickenerreceivessludgedecantedinthesecondoftwostoragetanks,andthickensitto6–9wt%solids.ThethickenedsludgeistransferredtoasludgedayholdingtankandisfedfromthereintotheHydroSolidsunit.
ThefollowingresultsfromearlyoperationswithUnit1(runswithsludgewithruntimesrangingfrom4to10h)andconclusionswereachievedfromthisproject:
TheHydroSolidssystemwassuccessfullyscaledupfroma0.4gpmpilotplanttotwo12.5gpmcommercialunits. MostofthefindingsbasedonearlydevelopmentofthesystemusingsludgefromanotherwastewaterfacilityappearedtobeapplicabletoHarlingen’ssludge. RepresentativesamplesfromHarlingenincludingsludgeafterdecantfromthedigestersandalsosludgedewateredonthebeltfilterpressdidprovideafeed
forrunsthatprovidedanabilitytoreasonablyprojectresultsonafull‐scalesystem. Duringoperations,thenitrogenisquicklyhydrolyzedtoammonia,andsubsequentlymostoftheammoniaisconvertedtomolecularnitrogen.Thefeed
ammoniavaluesareestimatedbasedonatypicalmolecularformulaforsludge.Thedestructionefficiency(DE)forCODinthesludgerangedfrom99.93to99.96%whilethatforammoniawasfrom49.6to84.1%intheoverflow.TheDEvalueswere99.92–99.93%and46.0–86.4%,respectively,fortheCODandammoniaintheunderflow.Approximately75.4%ofthesolidsinthefeedwerevolatile.
Presentlythegravitybeltfilterthickeningsystemisonlyabletoprovideabout4.5wt%solids.ThustheTSandCODofthefeedintheearlyrunshasbeenlowerthandesired.Ideally,thefeedwillbe6–9wt%inTSandwillhaveaCODof100,000to125,000mg/l.
HarlingenWaterworksSystemestimatesthattheHydroSolidssystemwillcostlessthanotheralternativessuchasauto‐thermalthermophilicaerobicdigestionandmoretraditionalformsofdigestionthatstillrequiredewateringandfinaldisposal.o Thenetoperationandmaintenancecostwillbeabout$100/dryton.Thecapitalcomponentofthecompletesolidstreatmentsystemrepresentsacostof
about$80/drytontreated.Thetotalcostforsolidsprocessingforthesystemisexpectedtobeabout$180/drytonofsolidsprocessed. TheWaterworksintendstogenerateincomefromthesaleofenergyintheformofhotwaterandtheuseofcarbondioxidefromtheHydro‐Solidsprocessfor
neutralizationofhighpHindustrialeffluent.o Excellentenergymanagementprovidesforrecoveryofaportionoftheexcessheatthatisusedtoproducehotwaterforanadjacentindustry.
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Final – May 9, 2017 A‐7 Master Plan Biosolids
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o Carbondioxide,anotherbyproduct,isusedforneutralizationoftheindustrialplant’swastewaterdischarge. TheWaterworksalsoexpectstogenerateincomefromthetreatmentofseptageandgreasetrapwastes. Hydrothermaloxidationprovidesastableoperatingsystemcapableofprovidingcompleteconversionoforganicmatterandmeetingallpathogenandvector
requirementsof40CFR503regulations. Regulatoryagencieswereinitiallyuncertainoftheapplicableregulationsforthisprocessbecausetheprocessdoesnotclearlyfitinacategory.Theprocess
goesfarbeyondthetreatmentpossiblebiologically,anditisnotincineration.TheHarlingenplantwillprovidetheopportunityforregulatorstoviewafull‐scaleoperatingunitprocessingsludge.
HydroProcessing,L.L.C.believesthatboththefederalandvariousstateregulationsmayneedtoberewrittentospecificallyrecognizethedisposalofresidualsolidsfromahydrothermaloxidationprocess.
BasedontheabilityoftheHydroSolidsunittoprocessthesludgeatHarlingen,itappearsthatthisprocesscantreatmosttypesoforganicwastestreamsincludingthosewithlargeconcentrationsofsolids.
Hodesa,M.etal(2004)
TheJournalofSupercriticalFluids;Volume29,Issue3,May2004,Pages265–288
Saltprecipitationandscalecontrolinsupercriticalwateroxidation—PartA:fundamentalsandresearch
CommercializationofSCWOprocesseshasbeenhinderedbyconcernsaboutcorrosionandscalebuildup/foulingwhich,whenpresent,mustbeaccommodatedbysystemdesignand/oroperationalprocedures.SaltsareformedduringSCWOwhenacidicsolutionsareneutralizedtoreducecorrosionandmayalsobepresentinthewastestreamitself.BecausesaltshavelowsolubilityinSCW,theyprecipitate.Precipitatedsaltsoftenformagglomeratesandcoatinternalsurfaces,therebyinhibitingheattransferfrom/toexteriorsurfaces.Whenscalebuild‐upisleftuncontrolled,pluggingoftransportlinesand/orthereactorcanoccur.TherequiredcleaningcanresultinsubstantialandcostlydowntimeintheSCWOprocess.
Subjectsdiscussed:
ReviewoffundamentalprinciplesandresearchpertinenttotheprecipitationofsaltsandscalecontrolattheelevatedtemperaturesandpressuresfoundinanSCWOreactor.
SCWOisintroducedandthephysicsleadingtoscalebuildupduringSCWOisdiscussed. Thephasediagramsofmodelsalt–watersystemsatrelevantconditionsarepresented.Phasebehavior,heattransferandmasstransferprinciples,and
researchrelevanttosalt–H2OsystemsattemperaturesandpressuresfoundinSCWOreactorsarediscussed. ThemanyphenomenawhichcomplicatemodelingofheattransferinSCW(buoyancy,rapidlyvaryingthermophysicalproperties,etc.)arereviewedandaset
ofcorrelationstocalculateheattransfercoefficientsisprovided. AlimitednumberofcontrolledexperimentalstudiesonscalebuildupduringSCWOarereviewed.
Findings:
ModelingofsaltdepositionkineticsinaSCWOreactorispossibleforverysimplefeeds[discussedinSection4].However,foranarbitraryfeedandtypeofreactor,itisextremelydifficultbecausefluidmechanics,heattransfer,masstransfer,kinetics,andphasebehaviorarestronglycoupledandbecauseofthemanyothercomplicatingeffects.Moreover,manyofthethermophysicalpropertiesandphaseboundariesneededformodelingarepresentlyunavailable.
StrategiestocontrolscalebuildupduringSCWOwillcontinuetorelyheavilyonexperiments.However,thepresentcompilationofavailablephasebehavior,heattransfer,andmasstransferresearchattemperaturesandpressurestypicalofSCWOreactorsmayserveasafoundationforfuturework.
Researchonphasebehavior,heattransfer,andmasstransferwillcontinuetobeinvaluablefordevelopingmethodstocontroloreliminatescalebuildupduringSCWO.Forexample,knowledgeofsalt–waterphasebehaviorisbeingexploitedtocontrolscaleduringSCWObyintentionallyaddingsaltstoincreasethetemperatureatwhichprecipitationoccursand/ortocausetheprecipitatetobeaflowablemoltensaltmixtureasdiscussedinthecompanionpaperbyMarroneetal.[paperno.24;PartB].
Imteaz,M.A;Shanableh,A.(2004)
DevelopmentsinChemicalEngineeringandMineralProcessing,v12,n5‐6,p515‐530,2004
KineticmodelforthewateroxidationmethodfortreatingWastewatersludges
Developmentofafirst‐orderkineticmodelbasedon48experimentalresultswithatubularreactorforthehydrothermaloxidationofwastewatersludge:
ModelbasedonoxidationmechanismofsludgewithCODrepresentingtheorganiccomponentofsludge. Experimentsconductedbelowandabovesupercriticalconditions(<and>374°C). AtT>263°Cactivationenergywas:
o independentoftemperature;ando dominatedbyaceticacidwhichismostresistanttohydrothermaloxidationandretardsthereactiontime.
AgreementbetweenactualandpredictedeffluentCODnotverygoodbutacceptable.
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Li,D.etal(2013) AdvancedMaterialsResearch,v726‐731,p1732‐1738,2013
Removalefficiencyoforganicsubstanceinmunicipalsludgebysupercriticalwateroxidation
BatchSCWOtestin303SSreactorwithmunicipalwastewatersludgetostudydestructionrateoforganicmatter(asCODcr)dependingonmainreactionparameters:temperature(380~500°C),pressure(23‐30MPa),residencetime(1‐10min),andoxidant(hydrogenperoxide)dose(100%‐200%).
EffectoftemperatureontheeliminationofCODcr:o CODcrremovalrateincreaseswiththeincreaseoftemperature.After3minutes’reactioninsupercriticalwater,percentagesofCODcrremovalateach
levelallreach80%.Whenthereactiontemperatureishigherandthereactiontimegoeslonger,thepercentageofCODcreliminationishigher.CODcrremovalrateattainsto96.43%whenthereactiontemperaturereached500°C.Thepercentagedidnottotalto100%becausesomeoftheorganiccompoundsformedmayhavepresentedinliquidproducts(suchasaceticacid).
EffectofpressureontheeliminationofCODcr(at440°C):o Whenthereactiontimeandtemperatureremainconstant,CODcrremovalrateincreaseswithincreaseofpressure.E.g.att=3minandT=440°Cremoval
efficiencyincreasedfrom86%at23MPato94%at30MPa. EffectofreactiontimeontheeliminationofCODcr(at440°C):
o CODcrremovalrateincreasedrapidlyduringthefirst3minofreactionandsloweddownafterwards.after1min’sreaction,CODcrremovalraterisesto80%inapressureconditionof23MPa.Whenthepressuregoesupto30Mpa,removalrateisabout97.89%after10minreactiontime,whichisalmostahighestconversionrate.
EffectofH2O2excessontheeliminationofCODcr(t=1min,T=440°C,p=25MPa):o CODcrremovalrateis86.79%astheH2O2excessis200%,whileCODcrremovalrateis81.22%astheH2O2excessis100%.Resultindicatesthatthere
isonly7%moreCODcrconversionrateariseastheamountofoxidantdoubled.Thisimpliesthattheglobalreactionorderforoxidantissmall. Temperature,pressure,andresidenttimearemainfactorstoaffectthereaction.TheCODcrremovalefficiencyofmunicipalwastewatersludgeishigherwhen
thetemperatureandpressureishigher,theresidenttimeislongerandtheoxidantdoseincreases. TheoxidantdosehasasmalleffectonremovalofCODcrinmunicipalwastewatersludge,forremovalefficiencyisnotasremarkableastemperature,pressure
andreactiontimeinthetreatmentofsludgesamplebySCWO.Loppinet‐Serani,A.etal(2010)
JOURNALOFCHEMICALTECHNOLOGYANDBIOTECHNOLOGYVolume85,Issue5May2010Pages583–589
Supercriticalwaterforenvironmentaltechnologies
Threemainapplicationsforsupercriticalwatertechnologyareunderdevelopment:(i)supercriticalwateroxidation(SCWO);(ii)supercriticalwaterbiomassgasification(SCBG);and(iii)hydrolysisofpolymersinsupercriticalwater(HPSCW)forcomposites/plasticsrecycling.Inthispapersomefundamentalsofsupercriticalwaterarefirstpresentedtointroducetheabovethreemajordevelopments.Thenthesetechnologiesarereviewedintermsoftheirpresentandfutureindustrialdevelopmentandtheirimpactontheenvironmentandonenergyproduction.
SCW–specificpropertiesandchemicalreactivity:
Atthecriticalpoint,thetwodensities–waterandgas‐areequalandthemediumbecomeshomogeneous.AfterthispointthedensityofSCWcanbechangedcontinuouslyfromhigh(liquid‐like)tolow(gas‐like)valueswithoutaphasetransitionbyvaryingpressureandtemperature.
Pressureand/oratemperaturechangecanleadtotheadjustmentofdensity.Thefluiddensitycanbetunedbyoneorderofmagnitudeforapressurevariationof20MPa,andbecomesfourtimesasweakforanincreaseintemperatureof200◦C.Thereforethechemistryinhotcompressedwatercanbenefitionicorfreeradicalreactionmechanismsbyadjustingpressureandtemperature.
InsummarythereasonsforusingSCWforenvironmentaltechnologiesare:o Tunablepropertiesbetweenliquidandgas.o Homogeneousmediumwithorganicsandgases.o Fastkinetics.o Sustainablereactionmedium.o Hydrolysisreactionsoforganiccompounds.o Precipitationofinorganiccompounds.
SCWO:
Ittypicallyimpliespressuresandtemperaturesvaryingbetween22.1and35MPa,and400and650◦C,respectively. Organicsareoxidizedtolowermolecularweightcompounds,and,ultimately,tocarbondioxideandwater. Heteroatoms,suchaschlorine,sulfur,andphosphorous,areconvertedintotheircorrespondingacids(e.g.HCl,H2SO4,etc.). Thepresenceofcationsinthewastestreamresultsintheformationofinorganiccompounds(e.g.salts,oxides,etc.).
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Essentiallyfourreactorconceptshavebeendevelopedandstudiedtosolvecorrosionandsaltdeposition/accumulationproblems:o (i)abasictubularreactorwithspecifichydrodynamicsandconstructionmaterial;o (ii)atankreactorwiththereactionzoneintheupperpartandacoolzoneinthelowerparttodissolvethesalts;o (iii)a‘transpiringwall’reactorwithaninnerporouspipe,whichisrinsedwithwatertopreventsaltdepositsandcorrosiononthewall;ando (iv)a‘film‐cooled’reactorwithcoolingofthewallbycoaxialintroductionoflargeamountsofwater
ThefirstcommercialSCWOplantforsludgeprocessingisrepresentativeoftechnicaltroublesthatcanbemet.Hydroprocessing’sHydroSolidsprocesshasbeeninstalledatHarlingeninUSA(Texas)toprocessupto9.8drytonsperdayofsludge.ThesystembeganoperationinApril2001.Theplanthasbeenshutdownbecauseofpumpingproblemsduetogritandtrashinthesludge.
SCBGandHPSCWnotsummarizedhereaslessrelevantforSCWOreview. SCWOisthemostmatureofthethreemaintechnologies.
Marrone,P.A.(2013)
JournalofSupercriticalFluids,v79,p283‐288,2013
Supercriticalwateroxidation‐Currentstatusoffull‐scalecommercialactivityforwastedestruction
CommercializationofSCWOtechnologyhasbeeninprogressforoverthreedecadessinceitspotentialfordestructionofaqueousorganicwasteswasfirstrealized.ThefirstcommercialSCWOcompany,MODAR,wasestablishedin1980(boughtbyGeneralAtomicsin1996).
AsofJanuary2012,therearesixcompaniesthatarestillactiveincommercializingSCWOtechnology:GeneralAtomics(theoldestamongactivecompanies),SRIInternational,HanwhaChemical,SuperWaterSolutions,SuperCriticalFluidsInternational(SCFI),andInnoveox.(Byactive,itismeantthatacompanyiscurrentlymarketingSCWOtechnologyandhasatleastonefull‐scaleSCWOfacilityinoperation,inconstruction,orindesign.)
Threeofthesixcompaniesthatarestillactivetoday(Super‐WaterSolutions,SCFI,andInnoveox)wereestablishedwithinthepastfiveyears.Thus,whilenoneoftheinitialcompaniesstartedinthe1980sarestillinbusinessandmanysubsequentcompanieshavecomeandgone,newSCWOcompaniesarestillbeingestablishedeventoday.
TherearenineSCWOplantscurrentlyintheplanningstageswithsevenoftheseslatedtostartoperationwithinthenext1–2years. EachSCWOcompanyhasoneormoreuniquefeaturestotheirsystemdesign(foroperationandcontrolofcorrosionandsaltbuildup)and/orbusinessplan,
andeachonehastargetedaspecificfeedniche.Whilenotwithoutitschallenges,SCWOtechnologycommercializationremainsanareaofgreatinterestandactivity.
ThetargetednicheformostcommercialSCWOapplicationsareaqueousorganicwastesintherangeof1–20wt%organics.Heteroatom‐containingwastesaremoredifficulttoprocess,sincetheassociatedacidsand/orsaltsthatformleadtothetwobiggestchallengesforSCWOprocesses:corrosionandsaltprecipitation/accumulation.
CorrosioninSCWOsystemsismostsevereinthehot,subcriticalregionsbefore(preheater)andafterthereactor(cooldownheatexchanger),butcanalsooccurinthemicroenvironmentformedundersaltlayersinthereactor.Dependingontheparticularfeedcompositionandmaterialsofconstructioninvolved,corrosionratesinSCWOcanbeashighasseveralmils/hr(tensofmicrometer/hr).Ifnotcontrolled,corrosionandsaltprecipitationcanleadtorapidshutdownand/orfailureofexpensiveprocessequipment.Thephilosophybehindthesemethodsforcorrosionandsaltprecipitationcontrolrangefromactivelypreventingtheiroccurrence,tomanagingtheiroccurrence,tolimitingoperationtofeedswherethesephenomenacannotoccur.
Ingeneral,theparticularmethodorcombinationofmethodsutilizedbyacommercialSCWOcompanyisoftenwhatdistinguishesonecompany’sSCWOprocessdesignandoperationfromanother’s.
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Activefull‐scaleplants:o SRI/MitsubishiinTokyo,Japan:oldestplant,inoperationsince2005:Theplanthasacapacityof2000kg/dayofPCBsand100,000kg/dayofwater.o Innoveox,Arthez‐de‐Béarn,France:inoperationsince2011;processeshazardousindustrialwasteatarelativelylowcapacityof100kg/hr.Feed
compositionislimitedto<1g/Lchlorideand<10g/Lsalt.o HanwhaChemicalCorp.forKorea,inoperationsince2008:Near‐CriticalHydrolysis(NCH)facilityfortreatingtoluenediisocyanate(TDI)residueto
producetoluenediamineintermediateforrecyclingbackintotheTDImanufactureprocess.Theplanthasacapacityof20,000kg/day. Inactivefull‐scaleSCWOplantsdesignedtotreatwastewatersludge:
o HydroProcessing,Harlingen,TX,2001–2002;heatexchangercorrosiono ShinkoPantec(EcoWaste);Japan;2000–2004;lackofequipmentmaterialdurability.
Asbestascanbedetermined,alloftheplantsthatshutdownduetoequipmentcorrosiondidnothaveamechanismforhandlingcorrosionotherthanlimitingoperationtonon‐corrosivefeedssuchashydrocarbonsandsewagesludge.Whilethisisavalidandcostreducingwaytooperate,itrequiresanaccurateknowledgeoffeedcompositionandcontinuousmonitoringofthefeedtodetectanysuddenvariationsincorrosiveorsalt‐formingspecies.Theresultofnotunderstandingfeedcompositionanditsvariationsornotincorporatingcorrosionandsaltcontrolmethodsinthedesigncanleadtoplantshutdownand/orextensivelitigation,ashasunfortunatelyoccurredonmorethanoneoccasion.
HistoryandcurrentdevelopmentoftwoSCWOfirmsforwastewatersludgetreatment.o SCFI:BasedinCork,Ireland,SCFIisarelativelynewcompanywithalonghistory.TheirSCWOtechnologybeganwithEcoWasteTechnologies(EWT)of
Austin,TX,oneoftheoriginalSCWOcommercialcompanies.TheSwedishfirmChematurABfirstboughtalicensefortheEWTSCWOprocessinEuropein1995andthenboughttheworldwiderightstoEWTSCWOin1999.Withfurtherdevelopmentwork,ChematurmarketedtheirversionofSCWOunderthenameAquacritox®.TheyalsodevelopedandnameddifferentcustomizedversionsoftheAquacritox®processincollaborationwithvariousclients.In2007,ChematursoldtheirsupercriticalfluidsdivisionandequipmenttoSCFI.SCFIhascontinuedtoimproveontheChematurSCWOdesign,thoughtheyhaveconsolidatedChematur’smanyversionsofSCWOunderthesingleAquacritox®brandnameforeaseofmarketing.SCFIutilizesatubularreactordesignandhaschosentofocusprimarilyonsewagesludgeanddigestatefeedapplications.Whiletheyhaveasacrificialmixingpipeconfigurationthatcanbeusedattheentranceandexittothereactorfordealingwithcorrosivefeeds,SCFIpreferstolimitapplicationstofeedsthatarerelativelylowincorrosionandsaltformationpotential.Assuch,theytypicallyrestrictsaltlevelsinthefeedtoafewpercentanddonotprocessfeedswithchlorinatedmaterials.SCFIhaspartneredwithParsonstoprovideinternalengineeringsupportandmarketinginNorthAmerica,andwithRockwellAutomationtoprovidecontrolsystemsandconstructionsupport.SCFIhasdesignedfourdifferentmodelsoftheAquacritox®processbasedonnominalfeedrate:600,2500,10,000,and20,000kg/hr.Theyarecurrentlybuildingtheirfirstcommercialsystem(2500kg/hr)forthewastetreatmentandrecyclingfirmErasEcoinYoughal,Ireland.Thissystemwillincludetheoptionofpowergenerationfromtheprocesseffluentheatviaawasteheatboilerandturbine.
o SuperWaterSolutionsLLC:Thisisthelatestcompanythatwasco‐foundedbyDr.MichaelModell,whoseexperimentsatMITinthe1970sformedthebasisofSCWOtechnologyandwhosubsequentlyfoundedMODAR.Super‐WaterSolutionswasstartedin2006andisbasedinWellington,FL.Itsmainfocushasbeenonprocessingnon‐corrosivewastewatersludge.TheSuperWaterSolutionsSCWOdesignissimilartothatofModell’spreviouscompany,MODEC.Itfeaturesatubularreactorsystem,andutilizesahighvelocityflowandmechanicalbrushesforcontrol/removalofsalts/solidsaccumulation.Since2007,SuperWaterSolutionshasworkedcloselywiththecityofOrlando,FL,withthecityfundingdevelopmentoftheirsystem.Inreturnforthisinvestment,Orlandohasauniquedealinwhichitwillreceivearoyaltyof$2.50foreverytonofsludgetreatedatanyfutureSCWOfacilitybuiltbySuperWaterSolutionsforothercustomers.From2009to2011,theyinstalledandsuccessfullytesteda4536kg/day(5tons/day)SCWOsystematoneofthecity’swastewatertreatmentfacilities.Sincethattime,thecityhascontinuedtoleasespacetoSuperWaterSolutionsforfurtherdevelopmentworkoftheirsystemdesign.Afull‐scale9072kg/day(10tons/day)SCWOsystemwasplannedtobebuiltforthecityin2013.
Pilotplants:SCWOresearchsystemsof20kg/hrcapacityorhigherarecurrentlyinoperationattheUniversityofValladolidandUniversityofCádizinSpain,theUniversityofBritishColumbiainCanada(usedprimarilyforheattransferandfoulingresearch),andtheBoreskovInstituteofCatalysisinRussia.
Marroneaetal(2009)
TheJournalofSupercriticalFluids
Volume51,Issue2,December2009,Pages83–103
Corrosioncontrolmethodsinsupercriticalwateroxidationandgasificationprocesses
TheSCWprocessforagivenapplicationmaybeoxidizing,reducing,acidic,basic,nonionic,orhighlyionic.Itisdifficulttofindanyonematerialordesignthatcanwithstandtheeffectsofallfeedtypesunderallconditions.Nevertheless,severalapproacheshavebeendevelopedtoallowsuccessfulcontinuousprocessingwithsufficientcorrosionresistanceforanacceptableperiodoftime.ThepresentpaperreviewstheexperiencetodateformethodsofcorrosioncontrolinthetwomostprevalentSCWprocessingapplications:supercriticalwateroxidation(SCWO)andsupercriticalwatergasification(SCWG).[Note:nosummaryisprovidedforSCWGhere].
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Dependingontheparticularfeedsandmaterials ofconstructioninvolved,corrosionratesinSCWprocessessuchasSCWOcanbeashighasseveralmils/h(tensofµm/h).Thereisoftenamaximumpointofcorrosionexhibitedintheregionjustbelowthecriticalpoint—wheretemperatureishighenoughtopromotefastkineticsandconcentrationsofcorrosion‐causingspecies.Fromapracticalperspective,thismeansthatcomponentsand/orpipingusedtopreheatorcooldownfluidsinaSCWsystemaremoresusceptibletocorrosionthanthereactor.Itisimportanttonotethatwhilepotentialforcorrosionisgreatlyreducedundersupercriticalconditions,therecanstillbesignificantcorrosionthatoccursinSCWdependingontheparticularchemicalenvironment.Regardlessofthespecifictemperatureandpressure,densityvaluesthatareclosertothatofliquidwater(i.e.>0.2g/ml)aremorelikelytopromoteanenvironmentwherechargedspeciescanexistandthuscorrosioncanoccur.Conversely,densityvaluesthatarelowandclosertothatofsteam(i.e.,<0.2g/ml)aremuchlessconducivetocorrosion.
Insummary,whiletherearealwaysexceptions,theworstcorrosioninaSCWsystemcanbeexpectedtooccurinhighdensity,hightemperature,andhighaggressiveionconcentration(e.g.,acidic)environments.Althoughtherehasbeenmuchresearchovertheyearsinsearchofamaterialthatcanwithstandallthreeconditions,thecollectiveresultsindicatethatsuchamaterialisnotlikelytobefound.Itisthereforenecessaryforonetounderstandthephysicaloperatingconditionsandchemicalenvironment(includingfeedstreamcomposition)towhichmaterialswillbeexposedinanapplicationinordertochoosethemostappropriatematerialforeachsetofconditions.Thisoftenmeansusingdifferentmaterialsindifferentsectionsofthesystem(e.g.,preheatingsection,reactor,andheatexchanger)dependingonthespecificcombinationofconditionsandcompositioninanyonezone.
Acompletecorrosioncontrolstrategymayneedtoincludechoosingagoodmaterialofconstruction,activecontroloradjustmentofoperatingconditionstofavorlowcorrosion,minimizationofexposurethroughinnovativeengineeringdesign,periodiccomponentreplacement,orcombinationsofsomeorallofthese.ThemostvulnerablesectionsoftheSCWOsystemarethehotbutsubcriticalregions,suchasfoundintheheat‐upandcool‐downsections.ManySCWOdesignsavoidpreheatingofthefeedinfavorofcoldfeedtoeliminatethisconcern.Typicallycorrosionwouldthenoccurneartheendofafeednozzleorfeedentranceportstothetopofthereactor,dependingonthespecificdesign.Crevicesorrestrictedspacesformedfromoverlapofcomponentsnearthetoporbottomofthereactorcanalsobesubjecttoexcessivecorrosionheatexchangerisanothercomponent(andunlikethepreheater,unavoidable)highlysusceptibletocorrosionasthehoteffluentisbroughtdowntoambienttemperature.Severecorrosioncanoftenoccurwithinthefirstfewfeetofheatexchangertubing,althoughtherealcorrelatingfactoriswherevertheeffluenttemperatureismostoftenwithinthe150–350°Crange.Componentsthattypicallyarekeptatambienttemperatureandpressurearenotusuallyofconcernwithrespecttocorrosionandnospecialmaterialsofconstructionarerequired.
Commonmaterialsofconstruction:
ThemostcommonmaterialsofconstructionforSCWOsystemsarenickel‐basedalloysandausteniticstainlesssteels.Stainlesssteelalloysareacceptableonlyforrelativelybenignfeeds(i.e.,containingnoheteroatoms)orincoolersectionsoftheprocess.Forhighertemperaturesectionsoftheprocess,nickel‐basedalloysaremostoftenusedduetotheircombinationofreasonablygoodcorrosionresistanceandhightemperaturestrengthunderthewidestrangeofconditions.Metalssuchasnickel‐basedalloysthathavegoodcorrosionresistanceunderSCWOconditionsaresuchusuallybecausetheyformastrongimpermeableoxidesurfacecoatingwhentheycorrode(i.e.,passivate),protectingtheunderlyingmaterialfromanyfurtherdegradation.However,thehighoxygenconcentrationtypicalforSCWOsystemscreatesaveryhighelectrochemical(oxidative)potential,favoringcorrosionviametaloxidation.
Commontypescorrosion:
Generalcorrosion–uniform,predictablerateofsurfacematerialdegradation. De‐alloying–selectiveoxidationanddissolvingofalloycomponent. Pitting–localizedandaggressivefromorcorrosionobservedinanumberofstainlesssteelandnickel‐basedalloysinthepresenceofchlorideandsulfate. Stresscorrosioncracking(SCC)–combinedpresenceofmechanicalstressandaggressivechemicalspecies.Nickel‐basedalloysaremoreresistanttoSCCthan
stainlesssteel.SCCisofparticularconcernasithasthepotentialtocausecatastrophicfailureinarelativelyshorttimeperiod. Intergranularcorrosion–occursalongmetalgrainboundariesinthepresenceofchloride,sulfate,and/ornitrate. Hydriding–combinationofcorrosionandhydrogenembrittlementassociatedmainlywithtitaniumdioxidesurfacelayerinthepresenceofphosphatesalts. Crevicecorrosion–smallcrevicescanexperienceconcentrationdifferencesfromthebulksolutionresultingincorrosion;hasbeenreportedto316SS,AlloyC‐
276andMonel400. Under‐depositcorrosion–similartocrevicecorrosion.Thepresenceofprecipitatedsaltsonametalsurfacecancreateamicroenvironmentbetweenthesalt
andmetalwhereconditionsaredistinctfromthatofthebulkfluidphaseandmoreconducivetocorrosion.Undersomeconditions,depositsmayprotectagainstratherthancausecorrosion.
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Galvaniccorrosion–occurswhendissimilarmetalsareelectricallycoupledwhileexposedtoanelectricallyconductivemedium. Non‐coupledcorrosion‐undissociatedspeciesmayreactdirectlywithmetalsubstratesinlowdensitySCWOenvironments,i.e.,withoutanelectrochemical
couplingofdifferentsurfacesites.
Corrosioncontrolapproaches
Approachescanbearbitrarilydividedintofourcategoriesaccordingtotheirprimaryobjective[Table1andsubsequentsectionsofthepaperprovideamoredetailedoverviewoftheseapproaches].
Preventcorrosivespeciesfromreachingasolidsurface:o Transpiringwall/film‐cooledwallreactoro Adsorption/reactiononfluidizedsolidphase(assistedo hydrothermaloxidation)o Vortex/circulatingflowreactor(conceptual)
Formacorrosion‐resistantbarrier(allowscorrosivespeciestoreachsurfacebutnocorrosion):o Useofhighcorrosionresistancematerials(long‐termapplications)
o Liners(corrosion‐resistantmaterial)o Coatings
Manage/minimizecorrosion(allowscorrosivespeciestoreachsurfaceandcorrosiontooccur,butinacontrolled,acceptablemanner):o Liners(sacrificialmaterial)o Useofadequatecorrosionresistancematerials(short‐termapplications)
Adjustprocessconditionstoavoidorminimizecorrosion:o Pre‐neutralizationo Cold(ambienttemperature)feedinjectiono Feeddilutionwithnon‐corrosivewasteso Effluentdilution/cooling(quenchwateraddition)
Itshouldbenotedthatbasedonexperience,thereisno“right”approachthatworksbetterthanalltheothersorworksinallcases.Theparticularapproachthatisbestforagivenapplicationdependsmainlyuponthenatureofthefeedtype.ItisalsopossibletousemorethanoneoftheseapproachesinagivenSCWOprocess.Sincesaltprecipitationandcorrosionissuesareoftenpresenttogether,acompleteapproachtoSCWOoperationcanincludeoneormoreoftheapproachesforcorrosioncontrolusedinconjunctionwithmethodsforsalthandling.
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PhilipAMarronea,P.A.(2004)
TheJournalofSupercriticalFluids,Volume29,Issue3,May2004,Pages289–312
Saltprecipitationandscalecontrolinsupercriticalwateroxidation—partB:commercial/full‐scaleapplications
ManyofthecompaniesthathaveattemptedtocommercializetheSCWOtechnologyoverthepasttwodecadeshavedevelopedinnovativeapproachestodealingwiththecorrosionandsaltprecipitation/solidsbuildupproblems.Theseareoftenthedistinguishingfeaturesofeachcompany'sSCWOprocess.Thispaperobjectivelyreviewsseveralcommercialapproachesthathavebeendevelopedand/orusedtocontrolsaltprecipitationandsolidsbuildupinSCWOsystems.Theapproachesreviewedconsistofspecificreactordesignsandoperatingtechniques,andincludethefollowing:reverseflowtankreactorwithbrinepool,transpiringwallreactor,adsorption/reactiononafluidizedsolidphase,reverseflowtubularreactor,centrifugereactor,highvelocityflow,mechanicalbrushing,rotatingscraper,reactorflushing,additives,lowturbulence/homogeneousprecipitation,crossflowfiltration,densityseparation,andextremepressureoperation.RecentcommercialSCWOapplicationsutilizingtheseapproachesarealsodiscussed.
CommerciallydevelopedapproachestoSCWOsaltprecipitationandsolidsdepositioncontrol:
Reactordesigns:Reverseflow,tankreactorwithbrinepool,Transpiringwallreactor,Adsorption/reactiononfluidizedsolidphase,Reversibleflow,tubularreactor,Centrifugereactor
Specifictechniques:Highvelocityflow,Mechanicalbrushing,Rotatingscraper,Reactorflushing,Additives,Lowturbulence,homogeneousprecipitation,Crossflowfiltration,Densityseparation,Extremepressureoperation
Recentcommercial/full‐scaleapplications[Chematuronly]:
ChematurEngineeringABacquiredalicensingagreementfortheEWTSCWOprocessinEuropein1995,andacquiredtheexclusiveworld‐widerightsforEWTSCWOin1999(Gidneretal.[82]).SCWOismarketedbyChematurunderthetradenameAquaCritox®.Chematurbuilta550lb/h(250kg/h)pilot‐scaleSCWOsystemin1998thathassincebeentestedwithseveralmostlynitrogen‐containingwastes(amineproductionwastes,nn‐halogenatedspentcuttingfluid,de‐inkingsludge,andsewagesludge).
Thesewasteswouldnotbeexpectedtogeneratehighsaltquantities.Inpasttesting,however,Chematurhasutilizedbothperiodicreactorflushingwithnitricacidand/orhighvelocitiesforremoval/avoidanceofscale.
Recently,Chematurannouncedplanstoconstructitsfirstfull‐scaleSCWOfacilityforJohnsonMattheyintheUK.Theplant,whichwillhaveacapacityof3m3/h(13.2gpm),willbeusedtorecoverplatinumgroupmetalsfromspentcatalysts.CarbonaceousandorganiccontaminantsonthecatalystwillbedestroyedintheSCWOprocess,whilethemetalwillberecoveredinitsoxideform.Nodetailshavebeenprovidedastohowtheoxidesolidswillbecollected.ThisapplicationappearstobeoneofthefirstinwhichtheprecipitationandrecoveryofasolidinaSCWOprocessisthemainfocusoftheprocessinsteadofbeinganundesirablesideeffect.Atthetimeofannouncement,Chematurexpectedtocommissionthenewplantinmid‐2002.
ChematuralsohasplanstobuildalargerSCWOplantforprocessingelectronicscrap,andispursuingopportunitiesforconstructionofadditionalcommercialSCWOplantsinEurope.ChematurhaslicensedtheEWTSCWOprocesstotheShinkoPantecCo.ofJapan.Underthislicenseagreement,ShinkoPantechasconstructedan1100kg/h(2425lb/h)SCWOplantfortreatingmunicipalsludge,whichwascommissionedin2000.
Summary:
Presently,noonedesignormethodhasprovenitselftobeclearlysuperiortotheothers,althoughsomearebettersuitedforcertaintypesofwastesthanothers.Forexample,thereactorflushingandquenchingtechniqueworksbetteronfeedswithhighconcentrationsofsaltsthathaveahighsolubilityinsubcriticalwater.Tubularreactorsoperatedathighvelocitiesarebeingusedbyseveralcompaniesfortreatingsewagesludges,whichhavearelativelyhighproportionofnon‐saltsolids.Also,someapproaches(e.g.,additives,extremepressureoperation)requiremoredetailedinformationregardingthecompositionofthefeedand/orsaltsthatwillformthanotherapproachesinordertobeeffective.Continuedfundamentalresearchonsaltprecipitationanddepositiondynamicsandonphasebehaviorofmulti‐componentsystemsisimportantforfurtheradvancementofeffectiveapproachesforsaltmanagementinsomepotentialapplications.Selectionofchemicaladditivesanddeterminationofoptimalconcentrationstomaintainadequatesalttransportinareactor,forexample,requirefurtherresearchtoestablishcomprehensivephasediagramsformanydifferentsaltspeciesandmixturescommonlyencountered.Resultsofrecenton‐goingpilot‐scaletestingwithaggressivefeeds,andthecurrentoranticipatedoperationofseveralnewfull‐scaleSCWOfacilitiesbyanumberofcompanies,willalsoprovidenecessarydataforfurtherdevelopmentandrefinementofsaltprecipitationcontrolmethods.
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Qian,L.(2015) BioresourceTechnology,v176,p218‐224,January01,2015
Treatmentofsewagesludgeinsupercriticalwaterandevaluationofthecombinedprocessofsupercriticalwatergasificationandoxidation
Influencesoftemperatureandoxidationcoefficient“n”onsewagesludgetreatmentinsupercriticalwateranditscorrespondingreactionmechanismwerestudied.Moreover,thecombinedprocessofSCWGandSCWOwasalsoinvestigated.
Results:
Ammonianitrogen,phenolsandpyridinesaremainrefractoryintermediates.Theweightofsolidproductsat873K(=600°C) andn=4isonly3.5wt.%oftheinitialweight,whichislowerthanthataftercombustion.Volatileorganicsinthesolidphasehavealmostbeenreleasedthroughdissolutionandhydrolysisat723K(500°C)andn=0,butnon‐volatileorganicsstillremain,becauseobviousweightlossescanbeobservedinitsthermogravimetricprofile.
Highestyieldofcombustiblegaseswasobtainedatn=0,andH2yieldcanreach11.81mol/kgat873K(600°C).Furthermore,thecombinationofSCWGat723K(500°C)andSCWOat873K(600°C)withatotaln=1isfeasibleforitsgoodeffluentqualityandlowoperationcosts.
Sentinel(2014) SentinelNewsPaper,FL
Article OnMarch2014theOrlandoSentinelnewspaperreportedthatinJuly2013anexpansiontankoftheSuperWaterSolutionspilotplantattheCityofOrlandohadsufferedablowoutcausingsignificantdamagetotheplantanditsbuildingenclosure.
Shanableh,A.,Gloyna,E.F.(1991)
WaterScienceandTechnology,v23,n1‐3,p389‐398,1991
Supercriticalwateroxidation.Wastewatersandsludges
DevelopmentofacomprehensiveSCWOresearchlaboratoryincl.benchandpilot‐scalefacilities.HightemperatureandpressuresystemsslightlylessthanandgreaterthanSCWconditionscanbeusedfortheefficientdestructionofwastebiologicaltreatmentplantsludges,aceticacid,2‐nitrophenol,2,4‐dimethylphenol,phenol,and2,4‐dinitrotoluene.
UnderSWOconditionsdensity,dielectricconstant,viscosity,diffusivity,electricconductance,andsolvationabilityarealldifferentcomparedtothepropertiesofcommonlyencounteredwastewater.o Inthetemperaturerangeof375to450°CthedensityofSCWdecidesrapidlywithsmallchangesintemperatureatconstantpressure.o Atambientconditionswaterhasahighdielectricconstantof80mainlyduetoH‐bonding.Atthecriticaldensityof0.3g/mlthereislittle,ifany,residual
H‐bonding.o Alowdensitywaterexhibitsathighdiffusivityandarapidmasstransfer.Thedecreaseofwaterdensityanddielectricconstantresultinchangingthe
solvationcharacteristicsofwater.o WhileSCWisastrongsolventoforganiccompoundsitisapoorsolventofinorganicsalts.o Undersupercriticalconditionsmanygasesarecompletelymisciblewhilesparinglysolubleinnormalliquidwater.o Atsupercriticalconditionsthereactionsoccurinonehomogeneousphase,canproceedautogenouslyinthepresenceofoxygen,andbecomesself‐
sustainingwhenthebiologicalsludges’totalsolidconcentrationisabout5%. Above400°C,nearcompletedestructionofsludgeandtransformationcompoundssuchasaceticacidcanbeachievedwithrelativelyshortresidencetimes. AmmoniaandaceticacidaretransformationproductsintheSCWOofbiologicaltreatmentplantsludges. Aceticacidproducedfromtheoxidationofsludgeisoxidizedrapidlyatsupercriticaltemperatures,400°Cto450°C:thedestructionefficiencieswere
enhancedbydecreasingtheflowrate(akaincreasingtheresidencetime),increasingthereactiontemperature,andincreasingtheH2O2/aceticacidratio.Aceticaciddestructionefficiencyincreasedfrom40%to>90%withinareactiontimeof4minandatemperaturerangeof400to510°C.
SCWOofWASandammonia:at300to343°Cammoniaconcentrationsincreasedinitiallythendecreasedastheresidencetimeincreased.Whentheresidencetimewas<10minammoniaproductionincreasedwithincreasedreactiontemperature(300to425°C).At425°Ctheinitialincreasewasfollowedbyasignificantreductionastheresidencetimeincreased>10min.Otherresearchshowedthatammoniadidnotoxidizebelow525°Cbutsuggestthatammoniaoxidationincreasedinthepresenceofotherorganiccompounds.
Contaminantdestructionlevelswere>99%forindustrialwastewatersludges,phenol,2‐nitrophenol,2,4‐dimethylphenol,2,4‐dinitrotolueneandaceticacid.Shanableh,A.,Shimizu,Y.(2000)
WaterScienceandTechnology,v41,n8,p85‐92,2000
Treatmentofsewagesludgeusinghydrothermaloxidation‐Technologyapplicationchallenges
Overviewofhydrothermaloxidationofsludge,majorissues,andprocessanddesignconsiderations:
Supercriticalwater(SCW)hasuniquecharacteristics:rapidoxidation,notlimitedbyoxygenavailabilityormasstransfer;expansionofwaterdecreasesthefluid’sdensity,fluidvelocityresultinginadecreaseinresidencetime.
SCWO:initialfocusonhazardousorganicwastetreatmentwithfirstinstallationintheUSatHuntsman’sChemicalCompanyinAustin,TXin1994;systemdesignedbyEcoWasteTechnologies(EWT).
SCWOorganicsshownremovalefficiencies>99.99%;thisalsoincludesorganiccontaminatessuchasPCBs. Sub‐criticalwateroxidation(SubCWO)wherewaterremainsintheliquidstagegeneratesthermallyresistantproductssuchasaceticacid(30‐80%ofsoluble
COD):destructionefficienciesbetween90and95%.
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ProducedSubCWOliquorwithhighVFA(andhighoxygendemand)mayberecycledasbeneficialcarbonsourcetosupportdenitrificationandenhanceBioPremoval;alsoproduceslessdesiredammoniawhichincreasesoxygendemand.
HeavymetalscontainedinthesludgewhentreatedviaSCWOareincorporatedinthenon‐leachableash;anincreaseinheavymetalsintheashcanbedetectedife.g.316SSisusedasreactormaterialduetocorrosion.
Rapidmetallurgicaldegradationduetoaggressiveoxidizingenvironmentandpresenceofhalogens. Reactor,heatexchangerandrecoveryunitssusceptibletoscalingofsaltsandcorrosion(thelowdensityofthefluidlimitstheabilitytodissolvetheinorganic
=>dropoutofsolutionandresultsinscaling). Systemdesignconsiderations:
o mostsuitablematerialsaretypicallyexpensiveandlackstructuralintegrity=>usedasreactorinnerliner.o sludgepre‐treatment;energy,materials,solidsseparation;treatmentconditions;effluenthandling;ashdisposal.o bestsuitedforwastestreamswithadequateorganiccontenttogenerateenoughheattosustainthereactiontemperature;ifVStoohighriskof
overheating.o besteconomicalifTSoffeedstockisbetween5and10%.
SCWOvs.incineration: Treatmentofrelativelydilutewastestreams. Lowemissionprofile=>noextensiveairpollutioncontrolrequired. Suggestedloweroperationalcost(confirmedattheHuntsmaninstallation).
Svanström,M.etal(2004)
Resources,ConservationandRecycling,v41,n4,p321‐338,July2004
Environmentalassessmentofsupercriticalwateroxidationofsewagesludge
Alifecycleassessmentmethodologywasappliedtostudytheenvironmentalaspectsofthefirstcommercial‐scaleSCWOplantforsewagesludgeintheworld,treatingsludgewith7%TSfromthemunicipalwastewatertreatmentfacilityinHarlingen,TX.TheplantisbasedonTheHydroProcessing’s‘HydroSolids’processwithaprocessingcapacityofupto9.8drytonsperdayofsludge.Theenvironmentalimpactswereevaluatedusingthreespecificenvironmentalattributes:globalwarmingpotential(GWP),photo‐oxidantcreationpotential(POCP)andresourcedepletion;aswellastwodifferentweightingmethods(singlepointindicators):EPS2000andEcoIndicator99.
LCAresults:
Gas‐firedpreheatingofthesludgeisthemajorcontributortoenvironmentalimpacts. Emissionsfromgeneratingelectricityforpumpingandforoxygenproductionarealsoimportant.
o SCWOprocessingofundigestedsewagesludgeisanenvironmentallyattractivetechnology,particularlywhenheatisrecoveredfromtheprocessforreducingGWPandresourcedepletion.Bothsinglepointindicatorsalsoshowedlargeenvironmentalgainsfromrecoveryofheat.
o Excessoxygenisatpresentnotrecoveredfromthereactoreffluent.RecirculationofoxygenintothefeedcouldreducethenetamountneededintheSCWOprocessandconsequentlydecreasetheenvironmentalloadfromproductionandtransportationofoxygen.
Energy‐conservingmeasuresandrecoveryofexcessoxygenfromtheSCWOprocessshouldbeconsideredforimprovingthesustainabilitypotential. ResultsfromanLCAstudyofSCWOprocessingofsewagesludgearetoalargeextentdeterminedbythesystemsurroundingtheactualSCWOunit.Thisresult
underscoresthenecessitytolooknotonlyatdirectemissionsfromaspecificprocess,buttoinvestigatethewholelifecycle. A2001analysisfoundthatthetotalcostforSCWOprocessingofsewagesludgeisaboutUS$120–200perDMTat10%solids.
Svanström,M.etal(2005)
WasteManagementandResearch,v23,n4,p356‐366,August2005
Environmentalassessmentofsupercriticalwateroxidationandothersewagesludgehandlingoptions
Life‐cycleassessment(LCA)ofSCWOapplyingtheAqua‐CritoxprocessandcomparingitwithLCAsoffourothersludgemanagementoptionsspecificallyrelatedtoCityofGöteborg’sWWTP(digestedsludgewith15%TS)anditlocalcharacteristics:
A)agriculturaluse,B)co‐incinerationwithmunicipalsolidwaste,C)incinerationwithsubsequentphosphorusextraction(Bio‐Con),andD)sludgefractionationwithphosphorusrecovery(Cambi‐KREPRO).
Severaloftheprocessesevaluatedinthisstudyarerelativelynewanduntried. Environmentalimpactsfromconstructionofbuildings,machineryandvehicles,aswellasmaintenance,reconstructionanddecommissioning,werenot
includedintheLCA. InventorydatafortheAqua‐Critoxprocess,scaledupfromChematurEngineering’sKarlskoga(Sweden)pilotplantdata,wasused. Characterizationsaccordingtoglobalwarmingpotential(GWP),acidificationpotential(AP),eutrophicationpotential(EP),andfiniteresourcedepletionwere
performed.
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Twoweightingmethodswereused:o Environmentalprioritystrategyinproductdevelopment(EPS):humanhealth,biologicaldiversity,ecosystemproduction,resources,andaesthetic
values,anduseseconomicvalues.o Environmentaltheme(ET):globalwarming,ozonedepletion,acidification,eutrophication,smogformation,spreadingoftoxicsubstances,waste,
hazardouswaste,andresourcedepletion. TheenergysystemisofgreatimportanceforLCAs.ForSCWO,beneficialutilizationoftheheatofreactionisofcrucialimportancefortheLCAoutcome.The
electricityconsumedbypumpingandthenitrousoxide(N2O)producedareotherimportantparameters.
Findings:
Allsystems,exceptagriculturaluse,resultinsavingsoftheresourcesfossilfuels,mainlyduetothereplacementofdistrictheatproductionbythesludgeoxidationheat.
AllmethodsperformwellintheGWPcharacterization,showingnetsavingsingreenhousegasemissions. Theenergyrecoverymethodsperformbetterthanagriculturaluse.Energysavingsbyavoidedproductionofchemicalsgiveadvantagestoagriculturaluse,
Bio‐conandCambi‐KREPRO. N2OEmissions:Whenglobalwarmingisconsidered,theemissionofN2OformedintheSCWOprocessprovedtobeimportant:ThetotalN2Oemissionsfrom
theSCWOprocessthatwasusedinthisstudy,measuredbyChematurEngineeringAB,ishigherthangenerallyexpectedforSCWOprocessingofsewagesludge.=>AdecreaseinN2OemissionswouldprovideconsiderableimprovementstotheAqua‐Critoxsystem.(intheothermethods,somenitrousoxideemissionswouldbeexpected,butfordifferentreasons,theseemissionswerenotincludedintheinventoryforthesesystems.IfN2OiseliminatedordisregardedalsofromtheAqua‐Critoxsystem,Aqua‐Critoxcompareswellwiththeotherenergyrecoverymethods.=>Nitrousoxideemissionsandabatementshouldbestudiedinmoredetailforallthemethods).
Phosphorous:Recyclingofphosphorusbacktoproductivesoilisaccomplishedinagriculturaluse,theBio‐ConmethodandtheCambi‐KREPROmethod.FortheLCAoftheAqua‐Critoxsystemextractionofphosphorousfromtheproducedsolidswasnotconsidered.Aphosphorusextractionstepcouldbeadded.LessmaterialwouldthenhavetobelandfilledandacreditwouldbegivenforreplacedphosphorusandotherproductsthusimprovingtheLCAresults.
Vadillo,V.etal(2015)
INDUSTRIAL&ENGINEERINGCHEMISTRYRESEARCHInd.Eng.Chem.Res.,2013,52(23),pp7617–7629.
ProblemsinSupercriticalWaterOxidationProcessandProposedSolutions
Thisworkreviewsthemaintechnicalsolutionsstudiedbynumerousauthorstoavoidthedrawbacksandchallenges(saltdeposits,corrosion,systemscaling‐up).Sincetheeconomicfeasibilityoftheprocesswilldependontheenergyrecoveryofthereactoreffluent,thisaspectisalsopresentedinthisreview.
Thereareseveralwaystomanagecorrosionincludingacoolingstrategytoavoidtheconditionsofhightemperatureanddensity,whicharetheconditionsofhighcorrosionrates,andnewreactorconceptssuchasTranspiringWallorFilm‐CooledReactors.
ToadvanceinthecommercialdevelopmentofSCWOitiscrucialtoselectanappropriatewastewaterandtochoosethemostsuitablereactorconcept.
Corrosionandproposedmitigationapproaches:
Useofhighcorrosionresistancematerials(Inconel625andHastelloy600),useofliners,useofcoating,designSCWOsystemsincludingtranspiringwall/film‐cooledwallreactors,assistedhydrothermaloxidation,useofabasetopre‐neutralizethefeedstream,cold(ambienttemperature)feedinjection,additionofquenchwater,optimizationofprocessoperatingconditions(suchastemperature,pH,electrochemicalpotential,etc.)asisthecaseshownby‘KritzerandDinjus’,whousedacooldownstrategytominimizecorrosion.
AnothereasysolutionistoavoidcorrosivefeedsorthepretreatmentofthefeedtoremovecorrosivespeciesasinthecaseofHongetal.
SaltPrecipitationandscalecontrolmitigationapproaches:
‘Marroneetal.’summarizedthecommerciallydesignedapproachesdevelopedinthelasttwodecades.Thosemethodsarespecificreactordesigns(suchasreverseflow,tankreactorwithbrinepool,transpiringwallreactor,adsorption/reactiononfluidizedsolidphase,reversibleflowintubularreactor,andcentrifugereactor)andspecifictechniques(suchashighvelocityflow,mechanicalbrushing,rotatingscraper,reactorflushing,additives,lowturbulence,homogeneousprecipitation,crossflowfiltration,densityseparation,andextremepressureoperation).
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Wastewatersludgerequirements:
DesignAspects(extract):
Thestart‐upoftheprocessrequiresahighamountofenergy,whichattheindustrialscaleisanimportantlimitation.Theonlywaytoachieveeconomicfeasibilityattheindustrialscaleisrunningtheprocessforlongperiodsoftime;specifically,itisnecessarytoachieve95%ofavailability.Itisnecessarytodesignaheatersystemtoprovidetothehighpressurestreamenoughenergytoachievesupercriticaltemperature.Forinstance,inthecaseofplantsof250t/dayofcapacitythethermalenergynecessaryisaround5MW.o SCWOreactionisexothermic=highamountofenergyisreleased.Start‐upoftheSCWOprocessrequiresinitiallyanexternalpowersupplyincreasingthe
temperatureofthewastewaterstreamupto400°Cinthereactorinlettoinitiatetheoxidationreactions.Thispreheatingusedtobecarriedoutbyelectricalheaterswoundonthepipesorusinganauxiliaryfluidheatedinaboiler.Asaconsequenceoftheexothermalcharacteroftheoxidationreactionsandbecausethereactoristhermallyisolated,anincreaseinthetemperaturealongthereactorisproduced.Oncetheprocessisstartedup,thereactoreffluentisusedtopreheatthefeedbymeansofheatexchangers,and,ifthewastewaterissufficientlyconcentrated,theheatreleasedbythereactionisenoughtopreheatthefeed.Thismakestheprocessauto‐sufficientfromanenergeticpointofview,andtheexternalpowersupplycanbeswitchedoff.Besides,ifthereisanexcessofenergyanenergyrecoverycanbeconducted.Intermsofconcentration,anorganiccompoundconcentrationbetween2and20%weightisadequateforSCWOtreatment.
o ‘Jimenez‐Espadaforetal’proposedthatitispossibletodecreaseSCWOtreatmentcostsbyrecoveringenergyatlowtemperatureandhighfluidpressure,suchaswaterheatingandsteamgeneration.Forexample,forasupercriticalflowof1000kgh−1(waterandair),therecoveredenergyrangesfrom118kW(1700m3h−1ofhotwaterat65°C)to75kW(100kgh−1ofsteamflowat1.1barand170°C).
o Inthecaseofwastewaterswithalowreactionheat,theuseofauxiliaryfuels,toincreasethetemperatureprofilealongthereactorandtoachievetheauto‐thermaloperation,isjustified.Inthisway,itispossibletogeneratehydrothermalflamesinSCWOreactorsincludingdevicesspeciallydesignedforit.
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Pros:(i)Reactiontakesplaceinreactiontimesoforderofmilliseconds,whichimpliesthedesignofreactorswithasmallvolume.(ii)Reactantscanbedirectlyinjectedintheflamesopluggingandcorrosionproblemsrelatedtothepreheatingstepareavoided.(iii)Sincehightemperaturesareachievedenergyrecoveryoftheeffluentisimproved.Cons:(i)Inthecaseofusingairasoxidantorifthewastewaterhasnitrogen,NOxcanbeproduced.(ii)Reactorsneedaspecificdesigntoworkwithhydrothermalflames.(iii)Asaconsequenceofhightemperaturesachievedinthepresenceofhydrothermalflamestheuseofresistantmaterialsareneeded.Suchmaterialsusedtobealloyswithahighcostsotheprocesscostisincreased.(iv)Besides,generationofhydrothermalflamesimpliesanadditionalcostrelatedtotheco‐fuelcost.Experimentally,flameisproducedpreheatingthefuelandtheoxidantuntilahightemperatureisreached.Ifthetemperatureishighenoughforthewasteconcentrationtheauto‐ignitionofthemixtureisproduced.Thetemperatureatwhichtheignitionoccursiscalledthehydrothermalflameignitiontemperature.Similarly,thetemperatureoftheflameextinctionisdescribedasalowtemperaturefuelinjectionintothereactorinwhichthecombustionoftheflameismaintained.Nowadays,severalstudiesfoundintheliteraturestudydeeperhydrothermalflamesformation.
Forsafeoperatingconditionsandoptimalenergyrecovery,aSCWOplantwithtubularreactormusthavestringentthermalcontrole.g.viacoolingwaterinjectionsandmulti‐oxidantinjectionsindifferentpointsalongthereactor.o Theuseoftwooxidantinjectionsisrecommendedinthecaseofhighorganicloadandhighreactionheatwastewatersbecauseundertheseconditionsit
isnecessarytocontrolthetemperaturealongthereactormaintainingitunderthesafetymateriallimitsandtoavoidtheformationofhotspotsasaconsequenceofthereactionofahighamountofoxidantinapointofthereactor.
o Theuseofamulti‐injectionofcoolwaterstreamsindifferentpartsofthereactorisanotherwaytocontroltheexcessoftemperaturealongthereactor.o “Chematur”TypeReactor(Aqua‐Critox):Thiskindofreactorallowsconductionofathermalcontrolofthereactorassociatedtotheexothermalcharacter
oftheoxidationreactions.AscanbeseeninFigure2,multi‐oxidantandcoolwaterinjectionscanbecarriedouttodistributetheoxidantproperlyandtoavoidhotspotsalongthereactor.Theoperatingprocedureofthiskindofreactorconsistsofinjectingaquantityofoxidantbelowthestoichiometricratioatatemperaturearound400°Cinthereactorinlet.Onceoxidantiscompletelyrunoutandthetemperaturehasincreasedtoaround600°C,acoolwaterstreamisinjectedtodecreasethereactionmediumtemperaturedowntoapproximately400°C.Then,anewoxidantinjectionisconducted,increasingthetemperatureupto600°C.Thus,anewcoolwaterinjectioniscarriedouttodecreasethereactionmediumtemperatureto400°C.Thistemperatureregulationisrepeateduntilthecompletedestructionoftheorganicmatterthatiscontainedinthewastewater.Thisreactorconceptwasdevelopedandcommercializedby“ChematurEngineering”,asocietythathasdevelopedindustrialprocessessuchasAquacatandAquaCritox.ThecompanySCFIGroupLtd.(SuperCriticalFluidInternational),locatedinCork(Ireland),purchasedAquaCritoxtechnology.Advantagesofthisreactorconceptareagoodthermalcontroloftheprocessandpreventionofhotspotformationduetothecombinationofoxidantandcoolwaterinjectionsalongthereactor.However,multi‐coolwaterinjectionsproducethermalfatigueofthereactormaterial.Besides,consumptionofcoolingwaterandthepowerrequiredtopumpitareimportant,inadditiontoproducingadilutionoftheeffluent.
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Suspendedsolidparticlesinthefeedcanproduceproblemsduringtheeffluentdepressurizationresultinginerosionofinternalpartsofthe“backpressureregulator”valves.Thedepressurizationstepcanproduceproblemsattheindustrialscale,becauseathighflowratetheuseofonevalveisnotrecommendedtogettheoverallpressuredrop(250bar)inasinglestep.o ThedesignofSCWOplantstheselectionofthebestpressurecontrolsystemisveryimportant.‘Soria’suggestedthatdepressurizationinSCWOplants
shouldbeconductedinseveralstepstodiminisherosioninvalves.o Adequatedimensionsofacapillarysystemwerestudiedtodepressurizetheprocesseffluentfrom250bartoatmosphericpressureusingthepressure
dropthatafluidsufferswhenitcirculatesthroughasmalldiameterandhighlengthpipe.Resultsobtainedinthisstudyshowedthatadepressurizationsystemforaflowrateof20kg/hshouldconsistof1/16inchand21.5mlongpipe.Later,‘O’Reganetal.’proposedacapillarysystemwherepressuredropisachieveddistributingthetotalflowinseveralcapillarydeviceswithahighlength.Theyclaimedthattheuseofonlyonevalveproducedextremevelocitiesandsevereerosionproblems.Therefore,inthecaseofindustrialplants,theuseofcapillarydevicesandacombinationofvalvesisdesirable.Thisdepressurizationsystem,patentedbyOrganoCorporation,wasinstalledintheSCWOsemi‐industrialAqua‐Critoxplanttotreatsewagesludge,locatedinKarlskoga(Sweden).
Somefeedcansufferpyrolysisandhydrolysisduetothepreheatingstep(intheabsenceofoxygen)thatisnecessarytoreach400°Catthetubularreactorentrance.Asaconsequenceoftheseundesirablereactions,plugginginthepreheatingsystemcanoccurinadditiontothepresenceofgascompoundssuchasCH4andCOintheeffluent.
Economicconsiderations(extract):
SCWOprocessimplieshighinvestmentcosts:suitableequipmentabtoworkathighpressureandtemperatures;useofhighcorrosionresistancealloystobuildreactorsandheatexchangers(preferablyalloyswithhighnickelcontent).Duetohighpressureoperationalconditionsmaterialcostsareveryhighinadditiontomaintenanceandrepaircostsofequipmentthatworksunderextremeconditions.
TheonlywaytomaketheSCWOprocessfeasibleisreachingtheauto‐thermalregimeinthereactor.Reactorcostisoneofthemaincostsinthedesignobjectiveistodesignitwithasmallvolume.Inthisway,‘Abelnetal.’estimatedthatthetubularreactorcostsrepresent10%oftheoverallequipmentcostsinaSCWOplantabletotreat100kg/hofwastewater.
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Operationalcost:thechoiceoftheoxidantisakeypoint,‘BermejoandCocero’claimedthatitismoreeconomicaltousepureoxygeninsteadofairbecauseatindustrialscalethecompressioncostisveryhigh.Ontheotherhand,‘Savageetal.’suggestedthatacatalyticSCWOprocessisamorecompetitivealternativebecausewiththeuseofacatalystthetemperaturenecessarytoreachremovalefficiencieshigherthan99%isreducedsignificantlydecreasingtheenergydemand.
Atpresent,economicalstudiesonSCWOattheindustrialscalearescarceinliterature.‘GidnerandStenmark’estimatedoperationalcostsofasewagesludgeSCWOplantbasedonaflowrateof7m3/hofsewagesludgebeing137€/tofdriedsludge.‘Svanstrometal.’estimatedtotalcostfora1t/dayplantbeing243$/tdriedsludge.‘O’Reganetal.’claimedthattreatmentcostofsewagesludgeSCWOisintherange36.6−73.15€/t.‘Abelnetal.’first,estimatedtreatmentcostofanidealwastewatermadeofamixtureofethanol10%weightandwaterusingairasoxidantinaplantof100kg/hwithtwodifferentreactors:tubularandtranspiringwallreactor,beingthetreatmentcosts406€/tand660€/t,respectively.Later,theyestimatedthetreatmentcostfora1t/hplantbeing330−430€/tforthetranspiringwallreactorplantand203−264€/tforthetubularreactorplant.Finally,’Vadilloetal.’estimatedthetreatmentcostforarealwastewaterSCWOina1t/hplantthatamountsto230€/t.EconomicresultsshowedthatalthoughSCWOtechnologywasinitiallyshownasatechnologysuitableforallkindsofwastes,researchconductedoverthelastthreedecadesshowedthatthistechnologycanonlybeappliedattheindustrialscaleusingatubularreactorandtotreatwastewatersthatsatisfytherequirementshowninTable1.
SCWOplantinstallations:
TheSCWOprocesswassatisfactorilyappliedtoahighamountoforganicwastewatersatthelaboratoryandpilotplantscaleachievingremovalefficienciesupto99.9%withresidencetimesoftheorderofseconds.Forprocessingindustrialwastewatersmostoftheinstallationswere/areatthelaboratoryscalesopilotplant,industrialscaleinstallationsarescarce.Contrarytothefacilitiesofsubcriticaloxidation,wheretechnologyhasreachedmaturity,therearefarfewerfacilitiesinsupercriticalwateroxidation.
SCWOPilotPlants,(P≈25MPa,T≈550°C):Table4(extract,wastewateronly):o Aqua‐Critox(SuperCriticalFluidsInternational);tubularreactortype;oxygenasoxidant;treatmentofindustrialwastewaters;status:250kg/h1999,
Karlskoga(Sweden),2008,Cork(Ireland)o SchoolofEnergyandPowerEngineering,China;reactor:transpiringwallcombinedwithreverseflowtank;oxidant:oxygen;feed:sewagesludge;status:
125kg/h2011,(China).o SuperWaterSolutions,CityofOrlando;tubularreactortype;oxygenasoxidant;treatmentofindustrialwastewaters;status:5driedmattert/day.
CommerciallyDesignedFullScaleSCWOPlantsTable5(extract;sludgeonly):o Hydroprocessing;HarlingenWastewatertreatmentplant,Texas;feed:sewagesludge,tubular;150t/day;status:builtin2001,stoppedin2002dueto
corrosioninheatexchanger.o Severalcommercialplantswerebuiltinthelastthreedecades;however,nowadaysonlytwoofthemareinoperation.Inrelationtothefutureofthe
technology,itisnecessarytocontinueresearchingintechnicalsolutionstodecreasecapitalandoperatingcoststoachievethefullcommercialdevelopmentofthistechnology.
Xu,D.etal(2013) InternationalJournalofHydrogenEnergy,v38,n4,p1850‐1858,February12,2013
Influenceofoxidationcoefficientonproductpropertiesinsewagesludgetreatmentbysupercriticalwater
Thisworksystematicallystudiestheinfluencesofoxidationcoefficient(n=0‐2.5)onthegaseous,liquidandsolidproductsaswellasthecorrosionpropertiesofstainlesssteel316insewagesludgesupercriticalwatergasification(SCWG),supercriticalpartialoxidation(SWPO)andsupercriticalwateroxidation(SCWO).
[n=practicallyaddedoxidantamount/theoreticallyrequiredoxidantamount].
ThemajorobjectivesweretoimprovetheH2productionyield,increasetheremovalratiooforganicmattersandminimizeoxidantconsumptionsothatthetreatmentcostofsewagesludgecanbereducedasmuchaspossible.
Asequencedapproachtoprocesssludgewasappliedaswell,i.e.,sewagesludgesupercriticalpartialoxidation(SWPO)wasfirstperformedandthentheobtainedliquideffluentwasfurthertreatedbySCWO.
Results:
Asmallamountofoxidant,i.e.,alown(0<n≤0.6),helpsgenerateH2,CH4,COandC2lightgasfromhydrocarbonconversion,butexcessiveoxidant(n>0.6)enablestheabovegaseousproductsaswellasorganicmattersinliquideffluenttobeconvertedintoH2OandCO2.[Xstandsforconversionefficiency].AsdepictedinTable2theliquideffluentofsewagesludgeSCWGhascomparablyhighXCOD,XTOCandXNH3eN,soitisunnecessarytoprovideamuchhigher“n”tomaketheliquidmeetthecorrespondingdischargestandards.XCOD,XTOC,XNH3eNandXSolidriseandreachupto99.0%,96.9%,80.5%and82.6%respectivelywhennchangesfrom0to1.5at450°Cand25MPa.Whentheyfurtherincreaseupto99.95%,99.8%,99.7%and82.8%at540°C,25MPaandn=
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2.0,liquideffluentmeetsreferenceddischargelimits.Whenreactiontemperatureand“n”rise,corrosionproductsincreasebutsolidorganicmattersdecrease,whichprobablyresultsintheunremarkablechangeinXSolidfromNo.7toNo.8inTable2.ThemaximumvalueforH2formationisobtainedatn¼0.6,whichis
IfSWPOandSCWOarecoupled,acertainamountofH2andCH4canbeobtainedandmeanwhileliquideffluentcanmeettheabovestandardsevenat450°Candalowertotaln(0.74).
Furthermore,stainlesssteel316undergoeschangesfrompittingcorrosiontogeneralcorrosionwith“n”increase.Pittingcorrosioniscomparablysevereinthepresenceofhydrogenproductatalow“n”.Mainlygeneralcorrosiontakesplaceonstainlesssteel316whenoxygenissuppliedexcessively(n≥1.0),whichhelpsprolongthemateriallife.However,itisstillnecessarytomakeadeepevaluationaswellasalong‐termtestinacontinuoustypereactorplantinsubsequentwork.
Yang.Setal.(2013)
AdvancedMaterialsResearch,v774‐776,p212‐215,2013
Newdesignofsupercriticalwateroxidationreactorforsewagesludgetreatment
Doublewallreactordesign(microporousaluminumceramicinnertube,outertubefilledwithhigh‐pressureair);bench‐scaletestw/dilutedsewagesludge.Compressedairpenetratesthroughtubeandformsair/gasfilmattubesurface:
Nocorrosionandsaltprecipitationwerefoundininnertubeafteronemonthoftesting. HighCODdestructionefficiency>99%.
Zhang,T.etal(2016)
Resources,EnvironmentandEngineering‐2ndTechnicalCongressonResources,EnvironmentandEngineering,CREE2015,p499‐504,2016
Treatmentofsludgeandwastewatermixturebysupercriticalwateroxidation
MixtureofsludgeandwastewatertreatedbySCWOtechniquewasstudiedinintermittentequipmentat440‐460°C,25MPa,andreactionresidencetimebetween1and20mins.H2O2wasusedastheoxidant.
Results:
ExperimentalresultsshowedthatSCWOisahighefficiencyorganicwastetreatmentanddisposaltechnique.Removalrate‘X’ofCODwasobviouslyincreasedastemperature,residencelimeandoxidationcoefficient‘n’extend.o AtT=440°CXCODwas97.2%;atT=600°CXCODwas99.6%(10minresidencetime,p=25MPa,and‘n’=1.1).
Concentrationofammonia‐nitrogenincreasedwithtemperaturebeforedecreasing(10minresidencetime,p=25MPa,and‘n’=1.1) Increasein‘n’(n=1–3)atT=600°C,t=10minandp=25MPa:
o CODremovalratereached99.56%at‘n’=1;onlyaverymodestincreaseinXCODwasnotedwhen‘n’increased(at‘n’=3XCODwasat99.58%=>thereisanoptimalvaluefor‘n’andinfluenceof‘n’onXCODbecomesverysmall
o Concentrationofammonia‐nitrogenincreasedwith‘n’. Increaseint=1to20minatT=600°C,‘n’=1.1andp=25MPa:
o CODremovalratereached99.87%att=20min;onlyaverymodestincreaseinXCODwasnotedwhen‘t’increased>10min=>thereisanoptimalvaluefor‘t’toinfluenceXCOD.
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o Concentrationofammonia‐nitrogenincreasedwith‘t’beforedecreasing=>totalnitrogenistransformedtoNH3‐Nbeforedegradingovertime. Influenceofpressureontheoxidationrateisstillnotclear.
Zhong,C.etal(2015)
ChemicalEngineeringJournal,Volume269,1June2015,Pages343–351
Anewsystemdesignforsupercriticalwateroxidation
TheSCWO,atechnologywithgreatpotential,islaggingbehindtheexpectationincommercialdevelopment.Mostofthefull‐scalecommercialplantshavebeenshutdownandonlytwoofthemareinoperationasofJanuary2012.Corrosionandpluggingarethemainobstaclesoccurringmainlyinthehighpressureandhightemperature(HPHT)sections:Preheater,Reactor,Coolerandheatexchanger.
Sofar,asupermaterialthatcanwithstandallcorrosionconditionsinSCWOhasnotyetbeenreported.ThereforeanappropriatesystemdesignforSCWOisnecessary.
AnovelreactorconceptsnamedasDynamicGasSealWallReactor(DGSWR)wasadopted,whichwasoptimizedfromTranspiringWallReactor(TWR)designandwasdesignedtohandlethereactorcorrosionandpluggingproblems.(PurewaterwasusedasthetranspiringfluidinTWRandwasreplacedbyairinDGSWR,whichistheessentialdifferencebetweenthesetwotypesofreactors).Atechnologyofmulti‐feedinjectionwasdesignedtohandlethewastepreheatingproblems.Alab‐scaleSCWOdevicebasedonthisnoveldesignwasmanufacturedandtestedunder28–29MPaaround400°C.
SewagesludgefromXiaojiaRiverwastewatertreatmentplantwithaninitialsolidcontentof19.73%DSwasdilutedto2.62–11.78%DStoincreasethefluidity.
Alab‐scaleSCWOsystembasedondynamicgassealwallreactor(DGSWR)isdescribed,testedanddiscussedindetail.
Preliminaryexperimentalresults:
ThepreheatingproblemsofwastewithhighsolidcontenthasbeensolvedandthegassealofDGSWRhasbeensuccessfullyverifiedunder28–29MPaandaround400°C.
Throughthemulti‐feedinjectiontechnologiessewagesludgewith2.62–11.78%drysolidhasbeensafelypumpedandpreheated,andmixedwithhightemperaturewatertoformsupercriticalmedium.
TheCODremovalefficiencycanreachupto99.15%. ShortcomingsofthenewSCWOsystem:
o Solidprecipitationduetothecounter‐currentofupwardreactionmediumanddownwardsolidparticles.ThestructureoftheSCWOsystemshouldbeadjustedtoinsurethatthereactionmediumandsolidparticleswillformasaco‐currentflowratherthanacounter‐currentflow.
o Insufficientstabilityandflowrateofairstream,whichleadstoloseefficacyofgassealandlowoxygenexcess,respectively.Theairmassflowrateshouldbeincreasedandairstreamshouldbepumpedsmoothlyandisotropic‐dispersed.
o Enhancingheatpreservationisalsonecessary.o Alltheaforementionedimprovementswillbeinvestigatedinfuture.
TM‐9: Aqua Critox Review | Orange County Sanitation District
Final – May 9, 2017 B‐1 Master Plan Biosolids
Appendix B – QC Review Affidavits ThefollowingisacopyoftheQCaffidavits,whicharesignedbythefollowingpeoplewhoreviewedTM‐9:
TimHaug(TimHaugConsulting)
TomChapman(B&C)
Orange County Sanitation District I TM-9: Aqua Critox Review
QUALITY CONTROL AFFIDAVITBiosolids Master Plan, Proiect No. PSl5-01TM-9 : Aqua Critox Review
This submittal has been reviewed for technical and editorial content
Reviewer Signature
Reviewer Name
Reviewer Firm
Final - May 9,20!7 Biosolids Master Plan