orange county sanitation district biosolids master …

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.

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TM‐9: Aqua Critox Review | Orange County Sanitation District

Final – May 9, 2017 ii Biosolids Master Plan

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

Orange County Sanitation District | TM‐9: Aqua Critox Review

Final – May 9, 2017 iii Biosolids Master Plan

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


Final – May 9, 2017 iv Biosolids Master Plan

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


Final – May 9, 2017 v Biosolids Master Plan

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


Final – May 9, 2017 ES‐1 Biosolids Master Plan

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.


Final – May 9, 2017 1‐1 Master Plan Biosolids

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.



2.0 Aims Theaimsofthisreviewareasfollows:

ToprovideanobjectivetechnicalandcommercialreviewofSCFI’sproposalsforademonstrationplantatOCSD.

ToprovideOCSDwithguidanceregardingthelikelytechnicalchallengesandrequirementsassociatedwithoperationofthefacility.

ToprovideOCSDwithanobjectiveevaluationofthelikelycapitalandoperatingcostsassociatedwiththefacilitysothattheycanreachadecisionastowhetheritistheirbestintereststoproceedwithconstructionofademonstrationplant.



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.



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.


Final – May 9, 2017 4‐2 Biosolids Master Plan

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.



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.



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).



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).



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.



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



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):



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



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.



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].



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



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.



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.



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.



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.



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



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.



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



onerous,itispossiblethatsignificantlyhighermaintenancecostscouldbeexperiencedonademonstrationfacility.

TakingtheA‐30primarysystemasanexample,sludgedisposalcostoffsetisstatedas$1,240,100peryear.Withtypicalvolatilesolidsdestructionindigestionof50%andbasedon$62.50perwetton,thedisposalcostoffsetiscalculatedatapproximately$744,000peryear.ItappearsthatVSreductionthroughdigestionwasnottakenintoaccountinSCFI’scalculationasitshouldbe.

Asnotedabove,25%efficiencyforthesteamturbineisunrealisticallyhigh.Anefficiencyofjustunder20%wouldbemoretypical.

Theoxygendemandassumptionwasinconsistentbetweenthedesigncriteriaandtheannualoperationcostprojections.



6.0 SCFI Pilot Plant in Valencia, Spain AsitevisitwasplannedtoanSCFIAquaCritoxpilottreatmentsystemlocatedinValencia,Spainaspartofthisevaluation.However,thisfacilityisnotincontinuousoperationtreatingwastewatersludgeinautothermalconditions.Therefore,thesitevisitwasindefinitelypostponed.



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%



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.



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.



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%



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.



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.



Table 7‐4. Revised Net Present Value Comparative Assessment (w/o steam benefit)

ALTERNATIVE CONSTRUCTION

COST

O&M (20‐YR PRESENT

WORTH)


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)


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.



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



8.0 Conclusions & Recommendations Thefollowingconclusionsandrecommendationswerereachedinthecourseofthisevaluation.

TheSCWOprocesshaslimitedsuccessfuloperationalexperienceintheindustry,particularlyforwastewatersludgeapplications.

BasedonarevisedanalysisoftheAquaCritoxA30pilotsystem,thecosttoprocesssolidshasbeenestimatedasapproximatelytwicethatofthefutureTPADalternative.Furtherinvestigationintotheoperationofapilotsystem,wouldhelpidentifyifthetruecostofoperationisgreaterorlessthanthenumbersestimatedinthisTM.

LongtermoperatingdatawithapilotfacilitytreatingwastewatersludgeisnecessaryinordertofurtherevaluatetheconcernsidentifiedinthisTMabouttheSCWOprocess,includingcorrosionandscalingissues,reliabilityoftheequipment,demonstrationofperformanceandplantsafety.

ProceedingwithademonstrationscaleprojectisthereforenotrecommendeduntilOCSDareabletowitnessreal,longtermoperatingdataofapilotfacilityonwastewatersludge.



9.0 References Bermejo,M.D.,Cocero,M.J.(2006);Supercriticalwateroxidation:Atechnicalreview;AIChEJournal,v52,n11,p3933‐3951,Nov2006

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Final – May 9, 2017 A‐1 Master Plan Biosolids

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.





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.




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%.





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.




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.





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.




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.).





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.




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].





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.




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.





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.




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%.





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.




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).





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.




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.





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.




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=





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.




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.


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

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