Pyrolysisoflowgradebiogenicfeedstockwithin-situsorptionofChlorineforemissionreduction

YashaDave

ThesistoobtaintheMasterofScienceDegreein

EnergyEngineeringandManagement

Supervisors:Prof.DieterStapfProf.JorgeManuelFigueiredoCoelhodeOliveira

ExaminationCommittee

Chairperson:Prof.FranciscoManueldaSilvaLemosSupervisor:Prof.JorgeManuelFigueiredoCoelhodeOliveiraMemberoftheCommittee:Prof.JoãoCarlosMouraBordado

November2017

i

Acknowledgements

IwouldtakethisopportunitytothankalmightyGodforshoweringHisblessingsuponme,inthisjourneyofmymaster

studies.Ialsothankmyparentsandfriendsforsupportingmeinallmydecisionsandmotivatingmetoworkhard.It

wasmypleasureandhonourtostudyinthemasterschoolprogramofEITInnoEnergywhichhasprovidedmethis

opportunitytostudyintwogooduniversitiesofEurope.

IamgratefultoMr.MarcoTomasiMorgano,myadvisorwhothoughtIwouldbesuitableforworkingonthisproject.

Heisasourceofmotivationformebecauseoftheeffortanddedicationheputsinhiswork,thisconstantlykeptme

focusedonmywork.Ialsothankhimforhistime,patienceandvaluableremarks.

Ialsothankthehard-workingstaffofInstituteofTechnicalChemistry(ITC),KarlsruheInstituteofTechnology(KIT)

withaspecialmentionofMr.FrankRichterwhohelpedmeunderstandtheexperimentalsetupandgavemevaluable

advicethroughoutmythesis.IexpressspecialgratitudetowardsMrs.MonikaSchleinkoferwhoanalysedmysamples

andhelpedmesubmitmyworkontime.Mr.PatrickSchieberperformedGCanalysisformysamplesandhenceI

thankhimforhistimeandexpertise.

IwouldalsoliketothankMr.HansLeiboldandProf.DieterStapfforlettingmeusethefacilitiesofITCandforthe

warmwelcomeinthePyrolysisgroup.

Iwouldliketospeciallymentioncontributionofafriend,Mr.BhargavRavindranathforproofreadingmythesis.

Finally,Ithankmysupervisorsfrommyhomeuniversities,Prof.JorgeOliveira(IST,Lisbon),Prof.WojciechNowak

(AGH-UST,Krakow),Ms.AgataMlonkaMedrala(AGH-UST,Krakow)fortheirtimeandsuggestions.

ii

AbstratoAutilizaçãocomercialdebiomassacomorecursodeenergiarenováveltemvindoaaumentarnaúltimadécada.O

desperdíciodediferentescomposiçõesoriginabiomassadebaixaqualidadeque,apósautilização térmica,pode

ajudaraumamelhordisposição.AstecnologiastérmicasincluemCombustão,PiróliseeGasificação.Odesafiomais

crucialparaessastecnologiaségarantirqueasemissõesestejamabaixodos limitesderegulaçãorespectivos.As

emissõesdeenxofreegásácidoforamamplamentediscutidaseadessulfurizaçãodegasesdecombustão(FGD)

mostrou uma implementação bem sucedida em vários casos. Devido à composição diversa e, eventualmente, a

naturezadasemissões,amatéria-primadebiomassarequerométododedisposiçãodefonteespecífica.

Comopartedestetrabalhode investigação,aPirólisedeLododeEsgotocomsorção in-situdeCloro/Enxofre foi

avaliadausandosorventesàbasedeCálcioeSódio.Ainvestigaçãotambémexaminaaeficiênciadeutilizarsorção

in-situemcomparaçãocomousodeumequipamentoseparadodelimpezadegás,apósumestudocuidadosoda

literaturaeobtençãoderesultadosexperimentais.OCloroestápresenteemquantidadesignificativanofenode

Trigo,portanto,requerumapiróliseparacomparaçãocomasemissõesdapirólisedasLamasdeEsgoto.Estudos

sobre a utilização de sorção com Óxido de Cálcio (CaO) e Carbonato de Hidrogénio de Sódio (NaHCO3) foram

conduzidosusandoPlantaFixaePirólisedeParafusoIntegrada(STYX).

OsresultadosexperimentaisreflectemumasorçãonotáveldeCleSnaconfiguraçãoSTYX;NoReactordeCamaFixa

foramencontradasproblemasdereprodutibilidadedosresultadosdesejados.Orendimentodosprodutosdepirólise

dependedediferentescondiçõescomoanaturezadamatéria-prima,atemperaturadeoperação,otipodereactor,

otempoderesidência,etc.Acomparaçãodoequilíbriodemassaentreutilizaçãocomesemabsorventenesteestudo

demonstrouumaumentodafracçãodegásPermanente,aumentoligeironaquantidadedecarvão,diminuiçãoda

fracçãoorgânicaefracçãoaquosadosprodutoslíquidosobtidos.

Palavras-chave:Emissãodecloro,Reatordepirólisedeparafusointegrado,Lododeesgoto,Sorçãoin-situ.

iii

AbstractCommercialattentiononBiomass,asanenergyresourcehasincreasedinthepastdecade.Wasteofdifferentnature

andoriginrepresentslowgradebiomasswhichuponthermalutilisationcanaidinbetterdisposal.Thermalutilization

technologiesareCombustion,PyrolysisandGasification.Mostcrucialchallengeforthesetechnologiesistoensure

theemissionsarebelowtherespectiveregulationlimits.Sulphurandacidgasemissionshavebeendiscussedwidely

and Flue Gas Desulphurization (FGD) has shown successful implementation in many cases. Due to the diverse

compositionandeventuallynatureofemissions,biomassfeedstockrequiressourcespecificdisposalmethod.

Aspartofthisresearchwork,SewageSludgePyrolysiswithin-situsorptionofChlorine/Sulphurwasevaluatedusing

CalciumandSodiumbasedsorbents.Theworkalsoexaminesefficiencyofusingin-situsorptionascomparedtousing

aseparategascleaningequipment,aftercarefulstudyofliteratureandobtainedexperimentalresults.Chlorineis

present insignificantamount inWheatStraw,hence it isalsopyrolyzedforcomparisonwiththeemissions from

SewageSludgepyrolysis.SorptionstudieswithCalciumOxide(CaO)andSodiumHydrogenCarbonate(NaHCO3)were

conductedusingFixedBedandIntegratedScrewPyrolysis(STYX)plant.

TheresultsofexperimentalcampaignreflectednotablesorptionofClandSinSTYXconfiguration;intheFixedBed

Reactor issues of reproducibility of desired results were encountered. Yield of pyrolysis products depends on

conditionslikenatureoffeedstock,temperatureofoperation,reactortype,residencetimeetc.TheMassBalance

comparisonbetweencasesofwithandwithoutsorbentuse,inthisstudy,showedincreaseoffractionofPermanent

gas,slightincreaseinthecharamount,decreaseintheorganicandaqueousfractionofliquidproductsobtained.

Keywords:Chlorineemission,IntegratedScrewPyrolysisReactor,SewageSludge,In-SituSorption.

iv

TableofContentsAcknowledgements.........................................................................................................................................................i

Abstrato..........................................................................................................................................................................ii

Abstract.........................................................................................................................................................................iii

TableofContents..........................................................................................................................................................iv

Abbreviations................................................................................................................................................................vi

ListofFigures...............................................................................................................................................................vii

ListofTables..................................................................................................................................................................ix

1. ObjectiveoftheWork...........................................................................................................................................1

1.1 Introduction......................................................................................................................................................1

1.2 ResearchObjective............................................................................................................................................5

1.3 ThesisOutline....................................................................................................................................................5

2. UnderstandingBiomassanditsThermochemicalConversion..............................................................................7

2.1 BiomassCharacteristics.....................................................................................................................................7

2.2 BiomassComposition........................................................................................................................................8

2.2.1 WoodandNon-WoodChemistry.............................................................................................................9

2.2.2 Moisturecontent:...................................................................................................................................10

2.2.1 Mineralogy.............................................................................................................................................11

2.2.2 ElementalcompositionofOrganicmatter.............................................................................................11

2.3 ThermochemicalConversionProcesses..........................................................................................................12

2.3.1 Combustion............................................................................................................................................13

2.3.2 Gasification.............................................................................................................................................13

2.3.3 Pyrolysis..................................................................................................................................................14

3. SewageSludge:CharacteristicsandDisposal......................................................................................................16

3.1 Sewagesludge.................................................................................................................................................16

3.2 TreatmentofSewage......................................................................................................................................17

3.3 CompositionofSewageSludge.......................................................................................................................18

3.4 Disposal...........................................................................................................................................................21

3.5 EULegislationsforSewageSludgehandlinganddisposal..............................................................................25

4. ChlorineemissionsfromBiomassThermalConversion......................................................................................26

4.1 ReleaseofChlorinefromdifferentfeedstock.................................................................................................26

4.2 ChlorineemissionsfromSewageSludgePyrolysis..........................................................................................30

5. UseofSorbentsforChlorineCapture..................................................................................................................31

5.1 RemovalofHClandmetalchlorides...............................................................................................................31

v

5.2 AlkaliandAlkalineearthmetalsassorbents...................................................................................................32

6. ExperimentalSetUp............................................................................................................................................36

6.1 FixedBedReactor...........................................................................................................................................36

6.1.1 ExperimentalProcedure.........................................................................................................................37

6.2 ScrewPyrolysisReactor(STYX).......................................................................................................................38

6.2.1 FeedingSystem......................................................................................................................................40

6.2.2 SequentialExtractionandFiltrationunit................................................................................................40

6.2.3 CondensationAssembly.........................................................................................................................41

6.2.4 OnlineGasAnalysis................................................................................................................................41

6.2.5 ExperimentalProcedure.........................................................................................................................41

6.3 FeedstockProperties.......................................................................................................................................42

6.4 ChemicalAnalysisoftheProducts..................................................................................................................45

7. ResultsandDiscussion.........................................................................................................................................46

7.1 FixedBedReactor...........................................................................................................................................46

7.1.1 MassBalance..........................................................................................................................................47

7.1.2 SorbentEfficiencyComparisonforSSandWS.......................................................................................51

7.2 STYXExperimentalReactor.............................................................................................................................55

7.2.1 MassBalance..........................................................................................................................................56

7.2.2 SorbentPerformance.............................................................................................................................58

7.2.3 PermanentGasCombustion...................................................................................................................59

8. Conclusions..........................................................................................................................................................62

9. FutureWork........................................................................................................................................................63

References....................................................................................................................................................................64

vi

Abbreviations1. BIGCC:IntegratedGasificationCombinedCycle

2. CHP:CombinedHeatandPower

3. EEA:EuropeanEconomicArea

4. ESP:ElectroStaticPrecipitator

5. EU:EuropeanUnion

6. FBR:FixedBedReactor

7. FGD:FlueGasDesulphurisation

8. FID:Flameionizationdetector

9. GC:GasChromatography

10. GC-MS:GasChromatography-MassSpectroscopy

11. GHG:GreenHouseGases

12. IGCC:IntegratedGasCombinedCycle

13. MSW:MunicipalSolidWaste

14. NS:NoSorbent

15. PAH:PolycyclicAromaticHydrocarbon

16. PCB:Poly-chlorinatedBiphenyl

17. PCDD:Polychlorinateddibenzodioxins(dioxins)

18. P.Gas:PermanentGas

19. SFG:SimulatedFluegas

20. SS:SewageSludge

21. STYX:(IntegratedPyrolysisPlant)ScrewPyrolysisReactorwithintegratedhotgasfiltration

22. TCD:ThermalConductivitydetector

23. WBA:WorldBiomassAssociation

24. WS:WheatStraw

vii

ListofFiguresFigure1:TotalEnergySupplyintheWorld,2014[1]....................................................................................................1

Figure2:GrossFinalConsumptionofEnergyResourcesin2014[1].............................................................................2

Figure3:GrossFinalConsumptioncomparingtop10Countries,2014[1]...................................................................2

Figure4:Wastegenerationbyeconomicactivitiesandhouseholds,EU-28,2014(%),Eurostat..................................3

Figure5:Electricitygeneratedfromrenewableenergysources,EU-28,2005-2015,Eurostat.....................................4

Figure6:SourcesofBiomassfeedstock[1]....................................................................................................................7

Figure7:BasicClassificationofBiomassFeedstock.......................................................................................................8

Figure8:Distributionofthethreemostcommoncomponentsoflignocellulosicbiomassdrymatter[13]................8

Figure9:PolymericStructureofCellulose[15]..............................................................................................................9

Figure10:PolysaccaharideunitsofHemicellulose[9]...................................................................................................9

Figure11:Thefourmainmono-lignolscomposingLigninstructure[19]....................................................................10

Figure12:H/CvsO/CgraphofBiomassFuels[12]......................................................................................................12

Figure13:AccumulatedexperienceinbiomassgasificationintermsofnumberofprojectsandMW[27]...............14

Figure14:Detailedwastewatertreatmentprocess[36]............................................................................................17

Figure15:ClassificationofSewageSludgetreatment.................................................................................................17

Figure16:TypicalDryingCurveforSewageSludge[35]..............................................................................................18

Figure17:ThermalwastetreatmentinGermany,2012(StatistischesBundesamtWiesbaden2015)........................22

Figure18:EEASewagesludgedisposalbyprocessused(%oftotalmass),EUROSTAT2015.....................................23

Figure19:PercentagedistributionofdisposalmethodsinGermanregionalstatesfor2011(Umweltbundesamt)..24

Figure20:AlkalimetalandChloroatoms(mmol/100gfuel)inBiomass[8]...............................................................27

Figure21:PossiblereactionpathforKreleaseduringdevolatilizationandcombustionofannualcrops[47]...........29

Figure22:PossiblereactionpathforClreleaseduringdevolatilizationandcombustionofannualcrops[47]..........29

Figure23:Limeconversionfordifferenttemperaturewithrespecttotime[79].......................................................33

Figure24:Performanceofsorbentswiththepollutantpartialpressures[87]............................................................35

Figure25:Laboratoryscalefixedbedreactor..............................................................................................................36

Figure26:Reactoroutsideandinsideview.................................................................................................................37

Figure27:FlowdiagramoftheBenchscalePyrolysisReactor(STYX)..........................................................................39

Figure28:SchematicdiagramofHotgasFiltrationAssembly[9]................................................................................41

Figure29:Benchscaleexperimentalsetup(actualpicturesfromKIT).......................................................................42

Figure30:ClandSinFeed...........................................................................................................................................45

Figure31:OverallMassBalanceforSS........................................................................................................................47

Figure32:OverallMassBalanceforWSPyrolysis........................................................................................................48

Figure33:Volume%DistributionofP.Gas,SS+NaHCO3.............................................................................................49

viii

Figure34:Vol%CO2Released......................................................................................................................................49

Figure35:IncreaseinP.GasforSSandNaHCO3.........................................................................................................50

Figure36:P.GasdecreaseinthecaseofSS+CaO........................................................................................................50

Figure37:Tabulationofg-CO2releasedperKgfeed....................................................................................................51

Figure38:NaHCO3PerformanceinthecaseofSS.......................................................................................................52

Figure39:StandarddeviationforthecaseofSSandNaHCO3.....................................................................................53

Figure40:PerformanceandStandardDeviation,SS+CaO...........................................................................................54

Figure41:PerformanceofNaHCO3incaseofWS.......................................................................................................54

Figure42:ComparisonofFeedstockwithrespecttoClandSemissionsandtheirsorption......................................55

Figure43:MassBalanceandYielddistributionofexperimentsusingSTYX................................................................57

Figure44:MassBalanceWSforSTYXexperiments.....................................................................................................57

Figure45:ComparisonofChlorineYieldforSSandWSforSTYX................................................................................58

Figure46:ComparisonofSulphurYieldforSS.............................................................................................................59

Figure47:Permanentgas,vol%...................................................................................................................................59

Figure48:HydrocarbonshareofthePermanentgasinFigure47...............................................................................60

ix

ListofTablesTable1:TypicalRangeofMineralmatter,wt%[12]....................................................................................................11

Table2:ThermochemicalConversionProcesses.........................................................................................................12

Table3:Bios-Bioenergyreport,2012[24,26].............................................................................................................13

Table4:ComparisonofCalorificValuesofSewageSludgeandBiomasswithcoal[41]..............................................19

Table5:BasiccharacteristicsandelementalcompositionofSewageSludge[43].......................................................19

Table6:OrganicandInorganiccomponentsofSewageSludge[43]...........................................................................20

Table7:RangeofvaluesformajorheavymetalspresentinSludge[40,49]..............................................................21

Table8:UseandDisposalofSludgebasedonmethodused[50]...............................................................................22

Table9:DisposalmethodsforsewagesludgeinEUMemberStatesaspercentage[52]............................................24

Table10:Airemissionlimitvaluesasperthe2001WasteIncinerationDirective......................................................25

Table11:CompositionofSorbentsused[83]..............................................................................................................34

Table12:Sorbentproperties[88]...............................................................................................................................35

Table13:BreakthroughpointforChlorine[88]...........................................................................................................35

Table14:ReactorSpecifications..................................................................................................................................39

Table15:UltimateandProximateanalysis,HeatingValueofdriedsewagesludge....................................................43

Table16:AshAnalysisofsewagesludge.....................................................................................................................43

Table17:EstimatedPhosphorousRecyclingPotentialinGermany.............................................................................43

Table18:MetalconcentrationinthisstudyandcomparisonwithGermanpermissibleamount[37].......................44

Table19:UltimateandProximateanalysis,HeatingValueofWheatStraw...............................................................44

Table20:AshAnalysisofWheatStraw........................................................................................................................45

Table21:SummaryofExperimentsinFBRsystem......................................................................................................46

Table22:ListofExperimentsperformedonSTYX.......................................................................................................56

Table23:TabulatedvaluesofSO2andHClemissionsfromCombustion.....................................................................61

1

1. ObjectiveoftheWork1.1 Introduction

Growing energy demand and climate change have led to complex sustainability concerns. The green-house gas

emissions and dwindling fossil fuel reserves and their costs have led to widespread research and commercial

attentiononBiomassasanenergyresource.Currently,developingcountriesarethehighestconsumersofBioenergy,

traditionallyincookingandheatingpurposes,whilemodernusageoftheseresourcescanhelpinprovidingenergy

accessandsecuritytotheworld.TheavailabilityoffeedstockintheformofMSW,agriculturalwaste,Organicwaste

etc.isnotaconcernbutmoderntechnologiesarenotaccessibleandaffordabletomostofthedevelopingcountries.

Althoughtherehasbeenashiftintheregimeofutilizationofbioresources,butatthesametimesomearguments

havebeenraisedaboutthreebroadissues:Firstly,ifBioenergytranslatestonetGHGsavings.Secondly,iflargescale

bioenergyexploitationadverselyaffectsfoodsecurity.Lastly,environmentalill-effectsofusingBioenergy.

Figure1:TotalEnergySupplyintheWorld,2014[1]

TheTotalEnergysuppliedasdefinedbyWBA[1]intermsofenergycontentofthefuel,comparesthetotalproduction

ofenergysourcesincludingimports,exportsandstoragefacilities.Theshareoffossilfuelisthehighestasshownin

Figure1.,Asiahasthehighesttotalenergysupplyintheworldalongwiththehighestrenewableenergysupply.The

Africancontinent,duetoitslargeuseofbiomassandhydropower,providesalmosthalfofalltheenergysupplyby

renewableenergysources.Incomparison,Europehasonly10.3%shareofrenewableresourcesinitsenergysupply

statistics[1].TheGrossfinalenergyconsumptiondefinedbyWBAis,thesumofthefollowingis[1]:

𝐓𝐨𝐭𝐚𝐥𝐅𝐢𝐧𝐚𝐥𝐂𝐨𝐧𝐬𝐮𝐦𝐩𝐭𝐢𝐨𝐧 + 𝐄𝐥𝐞𝐜𝐭𝐫𝐢𝐜𝐢𝐭𝐲𝐚𝐧𝐝𝐇𝐞𝐚𝐭𝐂𝐨𝐧𝐬𝐮𝐦𝐩𝐭𝐢𝐨𝐧 + 𝐋𝐨𝐬𝐬𝐞𝐬𝐢𝐧𝐝𝐢𝐬𝐭𝐫𝐢𝐛𝐮𝐭𝐢𝐨𝐧𝐚𝐧𝐝𝐭𝐫𝐚𝐧𝐬𝐦𝐢𝐬𝐬𝐢𝐨𝐧

2

Where,

TotalFinalConsumptionistheenergythatisspentintheendusessector,calculatedusingtheenergycontentofthe

fuelandElectricityandHeatconsumptionistheheatandelectricitygeneratedinthepowerplants.Figure2below

clearlyshowsthatAfricahasamajorpartofenergysuppliedbyBiomass,whereasOceaniahasthelowestshareof

biomassintheprimarysupplyofenergy.ThemainsourceofenergyinAfricaandpoorpartsofAsia,forcookingis

woodandotheragriculturalresidues.Theselow-gradefuelsposeathreattohealthandenvironmentboth.

Figure2:GrossFinalConsumptionofEnergyResourcesin2014[1]

Figure3:GrossFinalConsumptioncomparingtop10Countries,2014[1]

3

China consumes the highest amount of energywhich accounts to 80 EJ,with global consumption of renewable

resourcesaccountingforasignificantshare.InFigure3itisimportanttonotethattherenewableresourceuseisnot

justintheelectricitysectorbutinheatingandtransportationtoo.

Figure4:Wastegenerationbyeconomicactivitiesandhouseholds,EU-28,2014(%),Eurostat

Figure4andFigure5showthestatisticsofwastegenerationandutilizationintheelectricitysectorinEU-28.Since

thereisalotofattentiongiventominimizingwasteandutilizingBiomassenergy,theshareofBiomassinelectricity

generation has increased over the years 2005-2015 (Figure 5). It is evident that a visible portion of the waste

generatediswastewaterwhichis9.1%,henceitisrequiredthatthiswateristreatedensuringthatcontaminants

are well under the legal limit, by products are re-used and nutrients are recovered. Sewage sludge disposal

technologiesarecurrentlydiscussedandimplementedintheEUbecauseoftheharmfuleffectscausedbylandfilling

sewagesludge.Thelandfillgasandtheleachatesaretoxicfortheenvironment,plantsandgroundwatertable.One

ofthemosttechnologicallymatureprocessesofsludgeutilizationisanaerobicdigestion,whichproducesbiogas.One

ofthekeyconcernswiththistechnology isthatthedigestatematterafterdigestionstillhasenergyandnutrient

contentthatcanberecoveredusingthermalutilizationtechniques.Pyrolysisisoneofthethermalprocessesused

forutilizationofenergyfromtheorganiccontentpresentinthesludge;aspyrolysisisendothermicinnatureitshould

benotedthatahighenergyyielddoesnotcorrespondtohigherefficiencybecausetheproductsgettheirenergy

fromtheexternalheatofpyrolysisthatisbeingsupplied.

4

Figure5:Electricitygeneratedfromrenewableenergysources,EU-28,2005-2015,Eurostat.

Pyrolysis ispreferredovergasificationand incinerationbecauseof itsversatilityandalso theefficientuseof the

productsobtained,forexample,thepyrolysisoilsuponfurtherprocessingcanbeusedastransportfuels[2].The

productsofsewagesludgepyrolysiscanbeutilizedinsoilqualityenhancement(stabilizedbiochar)andthefluegas

canbecombustedtobeusedinenergygenerationapplications[3].However,thereareconcernsrelatedtorelease

oftoxicpolychlorinatedcompoundsandacidicgaseslikeHClandH2Sinthefluegas.Therefore,suitablemethods

shouldbeemployedpostorpre-utilizationsothattheemissionsarewithinthesafelimitsandtheenergyutilization

efficiencyiseconomicallyviable.Theconstraintsofusingsewagesludgeforthermaltreatmentsarenotlimitedonly

topresenceofpathogensandheavymetalsbutincludealsothecorrosiveeffectsofsomecompoundsformedduring

pyrolysisandtheacidicgases influegas.Alkalimetals inthesewagesludgeformmetalchloridesresponsiblefor

corrosionandfoulingofthereactorandhenceevenifchlorineispresentinconsiderablysmallamountsinthesludge,

itcanformmultiplecompoundsdependingonprocessconditionsthatarehazardousforenvironmentandhealth

[4].Ithasalsobeenreportedthattorrefaction(lowtemperaturepyrolysis)inthetemperaturerangeof200-350°C

causestheemissionofnitrogen-containingcompoundslikeN2O,NO,NO2,NH3andHCN,amongwhichNOandHCN

arethemostcommonones[5].Gascleaningandfeedpre-treatmentmethodsareprevalentinBiomasstoenergy

applicationsbutifthefeedismixedwithasorbentthatcancapturethechlorineinbiomasstoconcentrateitinthe

ash, it can prove to be an interesting alternative. Use of suitable compounds as sorbents like kaolin, bauxite,

limestoneetc.havebeenreportedtoreleasechlorinefromalkalimetalchloridesandhenceavoiddepositformation

[6].Thermodynamiccalculationsonsyngas,carriedoutbyJosephLeeetal.[7]inthetemperaturerangeof300-

1500K,Pressure0.1-11MPaandinitialcontaminant(HClandH2S)concentrationbetween1-10000ppmresultedin

CaO,K2CO3,Na2CO3andNaHCO3tobethefourbestcandidatesamong12othersforeffectivechlorineremovalat

moderatetohightemperatures.

5

1.2 ResearchObjective

Theobjectiveofthisstudywastoevaluatetheso-calledIn-situsorptionofChlorine/Sulphurbyco-feedingBiomass

andsorbentinaPyrolysisprocess.Toattainthisobjective,laboratoryscaleandbenchscale(STYX)experimentswere

conductedusingSewageSludge(SS)andWheatStraw(WS)asfeedandfindingasuitablesorbenttoreducechlorine

andsulphuremissions.Thisisrelevantbecauseitisevidentthatwastegenerationwillincreaseandhenceitisthe

need of the hour to invest in technologies for efficient utilization of it, without compromising environmental

regulations. Sewage sludge combustion ispracticed in someEuropean countriesbut if theprocessandprinciple

modificationscanleadtoenergygenerationwithoutincreasingtoxicemissionsthentheprocesswillbeadvantageous

inanoveralllifecycleaspect.Presenceofchlorineinthesewagesludgecatalysessomecrucialprocesses:promotes

themobilityofinorganiccompoundslikePotassium,Sodiumetc.,Clcanformgasphasemetalchlorides,whichare

stableinnature,HClandothercarboncompoundsaretheprecursorsfordioxinformationandthisoccursmainlyin

thepostcombustionzone[8].

1.3 ThesisOutline

Thisresearchworkispresentedin2sections,firstistheLiteratureReviewandsecondistheExperimentalCampaign

withresultsanddiscussion.

The thesis continues inChapter 2,marking the beginning of Literature review. It consists of three sub chapters

describing the basic concepts of biomass properties, composition and structure, Thermochemical Conversion

processesrespectively.

Chapter3 is dedicated for cradle to gravedescriptionof SewageSludge,divided in to5 sub chapters. Since the

feedstockexaminedinthisthesisissewageSludge,knowingitscharacteristics,composition,treatmentetc.isvital

fortheselectionofsuitablesorbent.TheGermanandEUregulationsaresummarizedinthelastsubchapter4.5,so

thatthequantificationofresultsisrelevantandasperthelimitsmentioned.

Theevaluationoffactorsresponsibleforchlorineemission,Pyrolysisprinciplesspecifictosewagesludgeandtheir

comparisonwithcombustion,arediscussedelaboratelyinChapter4.Thisprovidesreasoningfortheresearchwork

conductedastherootcauseofemissionisbeingaddressed.

Thelastchapter intheliteraturereview,Chapter5,ofthisworkmentionsthesignificanceandroleofarangeof

sorbentsstudiedinliteratureforsorptionofClandSincombustionandpyrolysis.Thechaptergivesaninsightfor

selection of sorbent to conduct this study. The extensive literature review focusing on use of sorbent, their

characteristics and efficiency for combustion and pyrolysis, biomass feedstock composition and its effect on

thermochemicalconversiontechnologiesaredescribedindetail.

6

ThesecondsectionofthesisstartsfromChapter6,whichdescribesboththeexperimentalsetups:fixedbedreactor

and bench-scale Screw Pyrolysis (STYX1) reactor (developed by Institute of Technical Chemistry (ITC), Karlsruhe

Institute of Technology (KIT), Germany). Experimental procedure to evaluate performance of sorbents for both

SewageSludge(SS)andWheatStraw(WS)ispresentedseparately.

Lastly,theexperimentalresultsarepresentedintheChapter7forbothreactorconfigurations.Thesorbentstested

arecompared,overallmassbalanceiscalculatedanddepictedingraphs.Comparisonoftheresultsproducedinthis

study and the observations from literature is conducted, providing probable reasons for some deviations. The

experiencesandlearningfromtheconductofexperimentsandresultanalysispavedwayforfutureworkandoutlook

whicharealsolistedinthislastchapter.

1STYXstandsfortheriveroftheGreekmythology.ItistheriveroverwhichCharon,theferryman,transportsthesoulsofthedeadfromtheEarthtoanewlifeintheUnderworld.

7

2. UnderstandingBiomassanditsThermochemicalConversion

2.1 BiomassCharacteristics

Figure6:SourcesofBiomassfeedstock[1]

Biomass isaverygeneral termandcanbedescribedasallorganicmatter (excluding the fossil fuels,which took

millionsofyearstogettransformedbeneaththeearth’ssurface[9]) inwhichtheenergyderivedfromtheSunis

storedintheformofchemicalbonds,alsoincludingwastefromagriculture,Industryandmunicipality[10].Itisan

abundant raw resource, which requires processing depending on its use and composition. Biomass is a non-

homogeneoustypeofresourcebecauseitscompositionishighlyvariabledependingonthesource,location,climate,

seasonandotherfactors.ThebasicelementsbondedtogetherintheformofBiomassareC,HandO

AccordingtoWBA2017report[1],intheyear2014,10.3%ofallsupplyofenergyintheworldwasfromBiomass.As

showninFigure6,themajorsourceofBiomassisforestrythatcontributesto87%ofallthefeedstock.Thequality

andutilityoftheBiomassdependsonthecompoundsthatmakeitup.McKendry[10]classifiedBiomassas:Woody

Plants,HerbaceousPlants,AquaticplantsandManure. In therecentdecades,waste toenergyapplicationshave

gainedmomentumandthusMSW,Sewagesludge,Deadanimals,etc.canalsobeclassifiedunderBiomass.Theuse

ofBiomassisbroadlyobtainingChemicals,EnergyorFuels,wheredifferentconversionprocessesareusedtogetthe

8

desiredproduct.AsshowninFigure7below,Biomassfeedstockcanbeofavarietyoftypesanddifferentresearchers

categorizeditbasedontheiranalysis[10–12].

Figure7:BasicClassificationofBiomassFeedstock

ForestProducts:Wood,deadtreesandshrubs,SawdustandBark

WastesandResidues:Organicwastefrom-Municipality,Industry,Hospitals,Agriculture.Manureandsewagesludge

canalsobeincludedhere.

EnergyandFoodCrops:Woodycrops,Grasses,StarchandSugarCrops,Oilseedcrops,Grains.

PlantandAnimalOrigin:AquaticanimalsandPlants,Algae,deadanimalsetc.

2.2 BiomassComposition

Biomassconsistsprimarilyofthreetypesofmacromolecules:Cellulose,HemicelluloseandLignin.Thefirsttwoare

carbohydrateswhereasLigninisanimportantpartofthecellwallofvascularplants,ferns,clubmossesandhasnon-

sugary polymeric units. For ease of understanding the diverse components of Biomass, one can classify its

physicochemicalproperties,whicharementionedinthenextsubsection.

Figure8:Distributionofthethreemostcommoncomponentsoflignocellulosicbiomassdrymatter[13]

9

2.2.1 WoodandNon-WoodChemistry

LignocellulosicBiomassconsistsofCelluloseasmajorconstituent.Celluloseisawater-insolublepolymercomposed

ofglucoseunits(>10 000),whicharelinkedbyβ-(1-4)-glycosidicbonds[14].

Figure9:PolymericStructureofCellulose[15]

HemicellulosesareheterogeneouspolysaccharidesmadeupofpolymersofPentoses(Xylose,Arabinose),Hexoses

(Mannose, Glucose, Galactose) and sugar acids [16]. Hemicellulose is also composed by a number of different

pentoseandhexosemonosaccharidesandittendstobemuchshorterinlengththancellulose,withthemolecular

structureslightlybranched[17].AsshowninFigure9,alllignocellulosicBiomassesfollowthegeneralcomposition

butitisarangeofpercentagebecauseofvariabilityinthecarbohydratecontent,whichalsoleadstodifferencein

yieldsofBiofuelsandeconomics[13].WhenBiomass isusedforproductionofBiofuelsorBio-power,theoverall

energycontentofthefeedisaveryimportantparameterforeconomicsandyield.Thecarbohydratecontentpresent

inthefeed isthemainsourceofenergycontentbut it isnotexplicitlyusedasaspecification inthermochemical

conversionprocesses.

Figure10:PolysaccaharideunitsofHemicellulose[9]

10

Lignin falls in the category of most abundant compounds on Earth after Cellulose and Chitin. It is a complex

compound,hydrophobicandaromatic,withhighlycross-linkedunitsofhydroxyl-phenylpropaneunits,thesebeing

thephenollikestructuresactingasmonomericbase.TheimportantfunctionofLigninistoimpartstructuralstrength,

sealingthewaterconductingsystemthatlinksrootswithleaves,anditalsoprotectsplantsagainstdegradation[18,

19]

Figure11:Thefourmainmono-lignolscomposingLigninstructure[19]

Thenon-woodycompoundspresentinbiomassarebroadlyclassifiedasSaccharides,LipidsandProteins.Theseare

thenaturallyoccurringelementsinplantsandanimals.Saccharidesinthelivingorganismsprovideenergyandalso

act as key codemolecules in important functions of the body [19]. Lipids are a heterogeneous class of organic

compoundsthatareinsolubleinwaterbutsolubleinnon-aqueoussolventslikeChloroform,alcoholetc.Theyare

naturallypresentinplantsandanimalsusedfordirectproductionofBiodiesel[14].Proteinsarethemostimportant

compoundsconsistingofaminoacids,whichareneededbybiologicalcellsforfunctioning.Aminoacidsof20different

typesformthestructureofproteinsandbasedonthemfurtherthermochemicalprocessescanhavelimitations.The

presenceofaminegroupsinproteinsadverselyaffectsthethermochemicaltechnologieslikepyrolysis,gasification

etc.becausethenitrogenleadstoacidicgasescausingpollutionandcorrosion[20].

2.2.2 Moisturecontent:

TherearetwotypesofmoisturepresentinBiomass,namely:IntrinsicMoistureandExtrinsicMoisture[10].Asthe

namesuggests,whenmoistureispresentnaturallythenitisintrinsicwhereaswhenitoccursbecauseofclimateand

storage conditions then it is called extrinsic moisture. Moisture content has a different effect on the process

dependingonthedesiredendproductandthetechnologyused.Forexample,thermochemicalprocessesrequirelow

moisturecontentbiomass(lessthan40%)whilebiochemicaltechnologieslikefermentationanddigestionfavorhigh

moisturesaturatedbiomassfeedstock[19].Hydrothermalprocessingtechnologiesaredevelopedforaddressingthe

11

highmoisturebiomassforthermalprocessing.Oneofthemaindisadvantagesofmoisturepresenceinbiomassisthe

increaseoftransportationcoststhatadverselyaffectstheeconomics[21].

2.2.1 Mineralogy

Theagriculturebasedbiomasscanhaveseveralfactorsresponsibleforthemineralcontentlikesoilquality,useof

fertilizersetc.Ingeneral,themineralmatterpresentinbiomassisofinorganicnaturebutsometimessomeorganic

compoundsmayalsobepresentdependingontheextentofcontaminationfromindustrialprocesses.Themineral

matterrepresentsthemajorconstituentofpostprocessingresidues likeAsh.Alkalimetals,suchassodium(Na),

potassium(K),calcium(Ca),phosphorous(P)andmagnesium(Mg),arepresent indifferentformsandconvertto

differentcompoundsdependingonthetypeofthermalprocess.Theyalsoreactwithsilica(SiO2)toproduceasticky

andmobileliquidphase,whichleadstoblockageinBoilers[9].Thepostprocessingresiduescanbeutilisedinother

applicationsdependingonthecomposition,ifitisrichinN,P,Kthenitcanbeusedasfertilizer,butiftoxicmetalsare

presentthentheycanbeamajorlimitationforfurtheruse[19].TheTable1showstypicalrangesinpercentageof

differentbiomassfeedstockforMineralmatterpresentanditisclearthatthevaluesvarydrastically(2%woodytrees

tomorethan45%formanureandsewage),thisdeterminesthesuitabilityofthefeedforthetreatmentandprocesses

thatcanbeconsidered.

Table1:TypicalRangeofMineralmatter,wt%[12]

Feedstock Minimum(%) Maximum(%) Average(%)

WoodTrees 0.1 6 2

EnergyCrops(grasses) 1.1 17 6

CerealStraw 1.3 20 7

CerealHusks 1 20 9

Sewage 21 74 49

Manure 11 74 49

Ashhasanegativeeffectonthermochemicalconversionasitreplacescarbohydratesthatarevaluableandhence

theconvertiblebiomasscontentdecreases.Whenpyrolysisisusedforthermochemicalconversionofbiomass,the

ashspecificationislessthan1%,whichclearlyshowsthedisadvantageofhavinglargepercentagesofashasitcan

taketheplaceofvaluablecarbohydrates[13].

2.2.2 ElementalcompositionofOrganicmatter

Theorganicmatterelementalcompositionisdeterminedbyusingtwoimportantmethods(whichweredeveloped

forthecoal industry)UltimateandProximateanalysis.Biomassisheatedto700°Cinaninertatmosphere,which

helpsinclassificationofbiomassintovolatiles,fixedcarbon,ashandfreemoisture.Thevolatilesandmoistureare

releasedleavingbehindthefixedcarbonresidue,andthisistheproximateanalysisofBiomass[22].Itisimportant

12

toknowthecontentofvolatilesandfixedcarbonastheyareimportantparametersforignitionandthermochemical

conversionpotentialofthefuel.Ultimateanalysisisdonetofindtheelementalcompositionofvolatilematterand

fixedcarbon.ThemajorelementsdeterminedareC,H,N,SandO;NandScontentisveryimportantastheyarethe

causeofenvironmentalpollution.Generally,biomasshaslowScontent(upto1%)exceptSewagesludge,Blackliquor

andsomemarinealgaewhereScontentismorethan1%,andinsomecasessewagesludgecanalsoleadto6%or

highersulphurcontent.OneofthedisadvantagesofbiomassisthatithasahigherNcontentcomparedtocoal,10-

12%forsomealgae,sewagesludgeandsomeseedandseedcakes[12].Figure12,showstheVanKrevelenatomic

H/CtoO/Cdiagramfordifferentbiomasstypes;CarbonandHydrogencontenthelpinestimatingthecalorificvalue

offuelandOdeterminesthelossesandCO2emissionduringprocessing.Carbontocarbonbondpossessmoreenergy

thanC-OandC-Hbondsinthecaseofthermochemicalconversion[10]

2.3 ThermochemicalConversionProcesses

Pre-processing is required for economical use of Biomass in thermochemical processes. These include Density

increasebycompaction,thermaltreatmentthroughTorrefaction,Sizereductionbycrushingandgrinding(although

uniformsizecannotbeobtained,itcanassuretobeinaspecificsizerange)[23].

Figure12:H/CvsO/CgraphofBiomassFuels[12]

Table2:ThermochemicalConversionProcesses

ThermochemicalProcessingTechnology Products

Combustion Heat,Steam,Electricity

Gasification Heat,Steam,Electricity,Methane,Hydrogen

Pyrolysis Biogas,Bio-oil,Charcoal/Bio-char

HydrothermalProcessing Biogas,Bio-oil,Charcoal

13

ThermochemicalconversionofBiomasstoproducefuelandCHPunitshavebeenwidelyresearchedgivingriseto

commercialscaleplantsinmanydevelopedpartsoftheworld.Pyrolysisisoneofthemethodsofthermaltreatment

inwhichthecarbonaceousmatterdecomposesintheabsenceofoxygen.Theproductsofthisprocessconsistofoil,

gasandcharofdifferent compositionsdependingon theprocess (pyrolysis) conditions.Biomassappropriate for

pyrolysisislignocellulosic,chemicallycomposedofcelluloseandlignin,whichformsthebasehardstructureofthe

plantmatterandHemicellulosebindstheligninandcellulose.Lignocellulosicbiomassgenerallyusedforpyrolysis

are-Cropresidues,Forestresidue,OrganicMSWandsewagesludge[12].

2.3.1 Combustion

Itisthemostwidelyproventechnologyforproductionofheatandpowerininstallationsbetweenafewkilowatts

andmore than 100MW [24]. Combustion is burning biomass using an oxidant, leading to a series of complex

exothermicreactionsbetweenthebiomassfuelandoxidant.Thecommercialviabilityofthisprocessisduetothe

high level technicalmaturity and considerable heat production, achieving economic feasibility [25]. The current

researchincombustionofbiomassdealswithoptimizationoffurnacedesign,increaseincontrolofcombustionand

overall efficiency. Early research on the commercial implementation of this process concluded that biomass

combustionoccursviafourbasicstages:Drying,devolatilization,Combustionofvolatilematter,Combustionofchar

[25].

Table3:Bios-Bioenergyreport,2012[24,26]

Year/growthrate Approximate

Primaryenergy

consumption,

PJ(petajoule)per

annum

ApproximateTurnoverofBiomassCombustionplants,

MillionEurosperannum

Turnoverof

Smallscale

plants

Turnoverof

Mediumscale

plants

TotalTurnover

2008 3800 3500 2800 6300

2020 7700 9800 6700 16500

Expectedgrowthratefrom

2008to2020

100% 180% 140% 160%

2.3.2 Gasification

Biomassgasification isburningbiomass fuel to combustiblegasesusinga limited supplyofoxygenonanyother

oxidantlikeCO2orsteam.ThegasthusobtainediscomposedbyHydrogen(12-20%),Carbonmonoxide(17-22%),

Methane (2-3%), Carbondioxide ( 9-15%),water vapour,Nitrogen andother impurities dependingonoperating

conditionsandthetypeofgasifier[10].Biomassgasificationalsoinvolvescomplexchemicalreactionstakingplace

insideagasifier,whichhasfourseparatezones:Dryingzone,Pyrolysiszone,PartialCombustionzoneandReduction

14

zone[24].TheFigure13belowshowsthatintotal24biomassgasificationplantshavebeenconstructedandsupplied

bytenmajorcompaniesfromfourcountries(Sweden,Finland,GermanyandAustria).

Figure13:AccumulatedexperienceinbiomassgasificationintermsofnumberofprojectsandMW[27]

2.3.3 Pyrolysis

Biomasspyrolysishasbeenexploredthroughouttheworldforhundredsofyearsandwithtimeandtechnological

progress better control over the process and products has been attained. Biomass Pyrolysis can operate in two

differentmodesdependingontheresidencetimeandheatingrateofthefeedinthereactor:FastPyrolysisandSlow

Pyrolysis.Slowpyrolysisistheconventionalprocess,whichyieldsamajorportionofcharandlowlevelofliquids,

whereasinfastpyrolysishighliquidyieldscanbeobtained[20].TheheatingratesinSlowpyrolysiscanbeseveral

degrees perminute, temperature 500°Cor less [28] and residence time is a fewminutes [29]. Flashpyrolysis is

anothertermforfastpyrolysis,whichischaracterizedbyreactordesignscapableofprovidingshortandintensive

heatfluxtosmallsizedbiomassparticles.Thesolidandvapourresidencetimesareveryshortandthetemperature

canrangefrom450-550°C[30].Theheatingrateforfastpyrolysisisbetween1000°C/sto10,000°C/s[29]andfor

gettinghighliquidyieldsthetemperatureisbetween500-520°C[30].Fastpyrolysisyieldsamixtureofvapoursand

gases,vapourscanbefurthercondensedtoseparatetheoilsandaerosols.Theshareofliquidsdominateswith50-

80%, for fast pyrolysis of lignocellulosic biomass, the remainder being char and gaseswith approximately equal

proportions[29–31].Somepyrolyticprocessesarecarriedoutintheintermediateregimeofslowandfastpyrolysis

andtermedasIntermediatePyrolysis.Someoftheconstraintsthatlimittheuseofbothfastandslowpyrolysisare:

15

Feedpreparationandpre-treatmentaccordingtosize,dryingandgrinding,capitalcosts,productquality,scalability,

lowenergyefficiency.Atpresent,therearenoreactordesignsreportedthatcanovercometheselimitations[12].

SomeofthefactorsplayingakeyroleinthermalutilisationofBiomassaredescribedbelow:

1. Particlesize:Inthecaseofslowpyrolysisthereisnorequirementforrapidheatingandhenceitcantakeparticle

sizeupto50mmwhereasinFastpyrolysis,dependingonthetypeofreactorused,theappropriateparticlesize

changes.Forablativepyrolysis,itsdesigncanprocessbiomassofsizesupto20mmasaresultofconstantshear

ontheparticle,butforotherreactorsthefeedparticlesizeshouldbebetween0.5-6mmindiameter[12].

2. MoistureContentintheFeed:Itisoneofthefactorsthatcausesanincreaseinthecapitalinvestmentbecause

dryingisrequiredtoremovewater,leadingtodecreaseintheprocessefficiencyasthelatentheatofvaporisation

ofwatercannotberecoveredeasily.Ithasbeenreportedthattypicallythemoisturecontentinharvestedstraw

is18%[32]andinwoodchips55%[33]hencerequiringdryingsystems.Thecurrentpyrolysisreactordesignsrun

withafeedmoisturecontentoflessthan10%[2].

3. EnergyEfficiency:Theenergyrequirementdependsonfeedquality,typeandmoisturecontentastheprocesses

ofdryingandgrindingaredependentonit.Thecostandtheprocessefficiencyareaffectedmostbydrying,asit

needsmorethan10%oftheenergyvalueofrawBiomasswhenwoodyfeedstocksareused[12].Othertypesof

restrictivefactorsareheatlosses,whichcanbecausedincaseofexternalheatingsources.Ifthemixingisalso

improper thenheat transferwill bepoor andwill result innon-uniform temperatureprofile along the cross-

sectionofreactor.Theuseoffossilfuelsforthedemandoffeedpreparation,heatingratesetcdecreasesthe

overalloutputandthereforethecurrentmaximumefficiencyobtainedfromPyrolysishasseveralrestrictions.

4. ScalabilityandEconomics:Thedesignofthereactorisanimportantlimitationinscalability,especiallyforthose

thathavea criticalheating surfacearea tovolume ratio.When thesedesignsareused foran increased feed

volumetheyareunabletoprovidetherequiredareaforoptimumheattransfer.Somefacilitieshaveincreased

theircapacitybyusingmodularplantsbutthiscanbeexpensiveifthedesigniscostintensive.Capitalcostsare

highforaplantwithcomplicateddesignandrequirealotofauxiliaryequipmentfordryingandgrindingthefeed.

In most of the currently operational pyrolysis methods, the vapours have to be extracted, condensed and

separated;thisalongwiththegashandlingsystemsincreasethecostsignificantly[12].

5. ProductQuality:Inmostofthelignocellulosicbiomasspyrolysis,thequalityoftheoilisofconcernbecauseofthe

presenceofoxygen,waterandlowpH.Thesefactorsmaketheoildifficultforupgradingtouseastransportfuel

and as feedstock for refineries. Theoil can also contain some finedust and charcoal particles thatwerenot

separatedandhenceitmustbecleaned.Thewatercontentintheoilisanindicatorofthemoisturecontentof

thefeed[12].

16

3. SewageSludge:CharacteristicsandDisposal

3.1 Sewagesludge

WastewatertreatmentfacilitiesgenerateSewageSludge,whichdiffersinpropertiesdependingonthetypeofplant,

physical and chemical properties of waste water used as feed. According to the European Council Directive

86/278/EEC,Sewagesludgecanbedefinedas:

a)Residual sludge fromsewageplants that treatdomesticorurbanwastewatersand fromothersewageplants

treatingwastewatersofacompositionlikedomesticandurbanwastewaters;

b)Residualsludgefromseptictanksandothersimilarinstallationsforthetreatmentofsewage;

c)Residualsludgefromsewageplantsotherthanthosementionedina)andb).

Sewage contains a large amount ofwater but after it undergoes treatment the particulatematter and colloidal

substancesareconcentratedtoformsludge[34].Thus,sludgecontainsasubstantialfractionofwaterandstudies

haveshownthatitcanbeupto90%oftotalwetweight[35].Presenceofwaterinhighamountcanhindertreatment

processes likethermochemicalconversion,hencethesludgeobtained isdehydratedusingsuitablemethods.The

unitoperationsthususedtoreducewatercontentofsludgearedependentonthetypeofmoisture.Waterinsludge

can be of four types: Free moisture (which can be removed by mechanical processes like thickening and

compression), CapillaryMoisture (removed by thermal drying), Adhesive or surfacemoisture (also removed by

thermal drying), Interstitial or chemically bondedwater (which canonly be separatedby changing the chemical

structureofsludgeparticles[35–37]).Ingeneral,73-84%ofmoistureispresentindewateredsewagesludge.Before

sendingsludgefordryingitisrequiredthatallthesolidsareaggregatedandhenceflocculantsareused,likeLime,

saltsoftrivalentFeorAl[37].Hence,onecanfindthereasonsforinhomogeneityofSewagesludge,tremendous

differencesintheconcentrationsofitscomponentsareobservedleadingtodifficultiesindeterminingordefininga

standardcompositionforsewagesludge(mainlycomposedoforganiccompounds)[38].

Duetothephysicalandchemicaltreatmentprocessesinvolved,sludgetendstoconcentrateheavymetalsandpoorly

biodegradabletraceorganiccompoundsaswellaspotentiallypathogenicorganisms(viruses,bacteria,fungietc.)

present in waste water streams. It is also rich in nutrients, such as nitrogen and phosphorous, containing vital

compoundsandorganicmatterthatisusefulwhensoilsaredepletedoraresubjectedtoerosion.Thispropertyof

thesludgeenablesspreadingofthiskindofwasteonagriculturallandasafertilizer[38].Researchershaveexplored

differentmethodsofSewagesludgedisposalbutthereisnoagreementastowhichisthemostappropriatemethod.

17

However,recentresearchhasshownthatenergyrecoverywilldominatethetreatmentmethodsinthefuture[39].

ThemethodsofdisposalinEUarealsonothomogeneousdependingonthelevelofimplementationofdirectives

andnumberofhouseholdsconnectedtothesewers[40].

3.2 TreatmentofSewage

Figure14:Detailedwastewatertreatmentprocess[36]

AsshowninFigure14,wastewateristreatedusingdifferentmethodstargetedatdifferentconstituents(seelistof

sewage sludge composition in Table 5 and Table 6) to be removed ormodified within the safe limits. Physical

processesincludeSedimentation,floatation;ChemicalprocesseslikeCoagulation,Flocculation;Biologicalmethods.

The individual waste water treatment procedures are further distinguished as Primary, Secondary and Tertiary

methodsdependingontheextentofremovalofcontaminants(followingtheEUregulations)[36](Figure15).

Figure15:ClassificationofSewageSludgetreatment.

18

Figure16:TypicalDryingCurveforSewageSludge[35]

Thedryingcurve,sketchedinFigure16,isanimportantcharacteristicofsewagesludgetreatment.Asmentionedin

theprevioussection,waterisassociatedwithsewagesludgeinfourseparateways,sowhenitissubjectedtodrying,

sewagesludgeshowstwofallingrate intervalsafterthe initialconstantdryingrateperiod.This isbecauseofthe

difference in thewaywater is bound to sewage sludge, in the initial constant rate period the freemoisture is

evaporated.Whileinterstitialwaterisremovedinthefirstfallingrateperiods,thesurfacewaterisevaporatedinthe

secondperiod[41].

3.3 CompositionofSewageSludge

Sewagesludgeisacomplexmixtureofconstituents;organic,inorganicandwidevarietyofmicro-organisms.Hence,

asdiscussedintheprevioussection,differenttreatmentmethodsareusedtoensurethatregulationsaremet.Also,

itshouldbenotedthatsewagesludgeindryformhasahighcalorificvalue,whichiscomparabletofossilcoals[42].

Basedonextensiveresearchandreviewpapers,HassanandWangetal.reportedacomparisonofcalorificvalues,

showninTable4[41].Thepresenceofundigestedorganics,suchaspaper,plantresidues,oils,faecalmaterial,isone

ofthecausesofpollutionandtoxicityassociatedwithsewagesludge,becauseitcontainshighlycomplexmolecules

ofphenolic,aromatic,aliphaticstructuresandpolycyclicaromatichydrocarbons(microorganicpollutants)[39–43].

Theinorganiccompoundspresentintheliquidsarederivedfromsoilandsyntheticpolymershavinganthropogenic

roots[44].Therefore,thecompositionofthesewagesludgesamplesobtainedfromdifferenttreatmentplantscan

varyevenifthesamewastewatertreatmentproceduresareemployed[45].Table5showsthatdriedsewagesludge

canbearichsourceofenergywhencomparedtolignitecoalandbiomass(onaverage).However,Sewagesludge

19

hasahighNcontent,which itgets fromproteins,peptides,acidetc.whereas theScontentof sewagesludge is

significantlyhigherthantheBiomassaverage,butcomparabletoLignite[41].

Table4:ComparisonofCalorificValuesofSewageSludgeandBiomasswithcoal[41]

Fuel HHV,drybasis(MJ/Kg) (wt%,drybasis) (wt%,dryashfree

basis)

Volatile

Matter

Ash N S

WoodPellet 18.30-19.60 82 17.4 1.5 0.9

Lignite 11.80-21.90 42.62 26.23 1.49 1.93

Bituminouscoal 25.40-33.15 35.5 6.37 1.59 0.55

WheatStraw 16 77.04 9.07 1.06 0.12

SewageSludge 11.10-22.10 48.41 43.99 7.15 1.41

Therearediverseways inwhichthesewagesludge isprocessedbeforethermochemicalconversionandtheyare

DigestedanddryrawSS,AnaerobicallydigestedanddrySS,chemicalandactivatedsludge,etc.Ithasbeenreported

thatanaerobicallydigestedandthermallydriedSSismostwidelyusedforpyrolysisexperimentsbecausethistype

ofSSisproducedinhighcapacityurbanwastewatertreatmentplants[39].Oneofthebasicpurposesfordryingthe

sewage sludge is that the resultant particles have good fluid-dynamic properties and hence can be used in

applicationslikefluidizationwhereparticlesizeisacrucialparameterforoperation[46].

Table5:BasiccharacteristicsandelementalcompositionofSewageSludge[43]

Constituent A B1 B2 C D

DryMatter(DM),g/l 12 9 7 10 30

VolatileMatter,%DM 65 67 77 72 50

CalorificValue,KWh/t

DM

4200 4100 4800 4600 3000

pH,VM 6 7 7 6.5 7

C,%VM 51.5 52.5 53 51 49

H,%VM 7 6 6.7 7.4 7.7

O,%VM 35.5 33 33 33 35

S,%VM 1.5 1 1 1.5 2.1

N,%VM 4.5 7.5 6.3 7.1 6.2

20

Sewagesludgealsocontainsavarietyofheavymetals,whichoriginateinindustrialwastewater,runoffandcorrosion

ofthesewersystem.Ithasbeenreportedthatapproximately50-80%oftheheavymetalcontentinthewastewater

isconcentratedinthesewagesludgebydifferenttreatmentmethods[47].AsshowninTable6,K,Al,Ca,Mgcontent

insewagesludgeiscomparabletothatofCl;ononehandmetalslikeAlandCatendtoretainClwhereasonthe

otherhandithasbeenreportedthatthereleaseofchlorineisdependentonKcontent[48].

Table6:OrganicandInorganiccomponentsofSewageSludge[43]

Constituent A B1 B2 C D

Protein,%DM 24 36 34 30 18

Fibers,%DM 16 17 10 13 10

Fat,%DM 18 8 10 14 10

P,%DM 2 2 2 2 2

Cl,%DM 0.8 0.8 0.8 0.8 0.8

Ca,%DM 10 10 10 10 10

K,%VM 0.3 0.3 0.3 0.3 0.3

Al,%VM 0.2 0.2 0.2 0.2 0.2

Fe,%DM 2 2 2 2 2

Mg,%DM 0.6 0.6 0.6 0.6 0.6

HeavymetalslikeTin,Lead,Cobalt,Cadmium,Chromium,Nickeletc.arethemajorelementsforrejectionofSewage

sludgeinagriculturalpurposes.Iftheyarepresentinhumanbodiesbymakingwayfromfoodchain,theycancreate

detrimentaleffectstohealth.Itisdifficulttogeneralizeanytreatmentmethodbecausethecontentofheavymetals

variessignificantlydependingontheoriginsite.Itwasreported(Table7)thatCd,Ni,Tiifpresentinlowlevelsare

safeascomparedtoCr,Cu,Pbwhicharegenerallypresentinatoxicrange[49].(Table7,onnextpage)

21

Table7:RangeofvaluesformajorheavymetalspresentinSludge[40,49]

Metal DrySludge(mg/Kg)

TypicalRange MedianValue

Tin 2.6-329 14

Lead 13-26,000 500

Cadmium 20-40 30

Cobalt 11.3-2490 30

Nickel 2-5300 80

Copper 84-17,000 800

Iron 1000-154,000 17,000

Molybdenum 0.1-214 4

Mercury 0.6-5.6 6

3.4 Disposal

Studiesconductedin2001,reportedthattherewere50,000wastewatertreatmentplantsworkingintheEuropean

Uniongeneratingabout7.9milliontonnesofdrysolids.By2006,thisnumberincreasedto8.3milliontonnesdry

solidperyear,thisclearlyshowsthatimplementationoftheEUdirectivewillleadtoanincreaseintheamountof

sludge[50].Sewagesludgeisaverychallengingwastetobemanagedbecauseoftheinflatedcostsandenvironmental

problemsassociatedwithit.Thereareseveralconstraintsinutilizingitforagriculture,althoughitisfeasiblefroma

policyperspective.Thepresenceofheavymetalsandpathogensrestrictstheuseofsewagesludgeasthequalityis

highlyvariable,whichleadstohighstandardcontrolandtreatmentmeasure.Itistheneedofthehour,forthepolicy

makerstofindabalancebetweenpreferredpolicyandsustainabledevelopmentinenvironmentalperspective.There

arefourmethodstohandlesewagesludge:Landfilling,Composting,andmorethan60%ofitisutilizedinagriculture

becauseofthepresenceofnutrientslikeP,Netc.[50,51].CountrieslikeAustria,Netherlands,Germany,Slovenia

useincinerationastheirmajortoolfordisposalwhile,Malta,Italy,Romaniausecontrolledlandfillforthesame,as

shown in Figure18.Biologicalmethodsof conversionof sewage sludge touseful product canbeAnaerobic and

aerobicdigestionandcomposting;butconstraintslikeodour,qualitycontrol,monitoringandheavymetalcontent

make itdifficult tobeused.Although thesemethodshelp inphaseseparationof sewagesludge, theyalsoneed

dewatering.

22

Table8:UseandDisposalofSludgebasedonmethodused[50].

Method Examples Constraints

LandBased Agriculture,Forestry Qualityandvariability,Impact,Vulnerability

Landfill MonoandCo-Disposal Leachate,Gasemissions,Potentialresourceloss

Thermal Incineration,Gasification HighCosts,Ashdisposal,Emissions,PublicPerception

Figure17:ThermalwastetreatmentinGermany,2012(StatistischesBundesamtWiesbaden2015)

Incinerationalsohas its shareof criticismbecauseof several reasons, it is said that incineration is justaway to

minimize the sludge but it cannot completely dispose it. The ash produced by incineration is classified under

hazardouswasteandmustbecarefullyhandledanddisposedinspeciallandfills.Thecostofthetechnologyisalso

high and requires precise information of the calorific value, pre-treatment and should comply with emission

standards.ThepresenceofpollutantslikePCB,PAH,PCDD,etc.requirecarefulinvestigation,otherwisethesludge

willfallunderhazardouswastecategory[50].

23

Figure18:EEASewagesludgedisposalbyprocessused(%oftotalmass),EUROSTAT2015

Thecostincreaseoftheincinerationprocessisduetothehighwatercontentofthesewagesludgeandtheremoval

ofwatercorrespondstoanenergyrequirement.Table9belowshowsthemethodsofsewagesludgedisposalused

bysomeoftheEUcountries.Somecountriespreferincinerationoverlandusebecauseoftheharmfuleffectsbutat

thesametimetheyshouldtakecareoftheashdisposalfromincineration.AsshownintheFigure17,Germanyused

thermaltreatmentmethodtodisposemostofitswastegenerated(totalof24.2Milliontonnes)in2012.Also,sewage

sludgehasbeenincreasingdisposedinmostsustainablemethodinGermanstates,asreportedbyUmweltBundesamt

intheyear2011[38](Figure19).

24

Figure19:PercentagedistributionofdisposalmethodsinGermanregionalstatesfor2011(Umweltbundesamt)

Table9:DisposalmethodsforsewagesludgeinEUMemberStatesaspercentage[52]

Whereitshouldbenotedthat,(i)3outof16federalstatesintendtostopagriculturalsludgeuse,(ii)Whilein2004,therewasstill9%ofsludgerecycledtoagriculture,

itdecreasedto3%in2005.In2000,otheroutletsinclude27%aslandfillcoverand53%forlandscaping.

Country Yearofdata Agriculture Landfill Incineration Other

Germany 2003 30 3 38 29(i)

Austria 2005 18 1 47 34

Denmark 2002 55 2 43

France 2002 62 16 20 3

Poland 2000 14 87 7

Netherlands 2006 0 60 40

Finland 2000 12 6 80(ii)

Belgium,BrusselsRegion 2002 32 2 66

25

3.5 EULegislationsforSewageSludgehandlinganddisposal

1. Earlyin1975,thememberstateswererequiredtohaveenvironmentallyfriendlywaysofdisposalandwaste

preventionandmanagement.

2. TheSewagesludgedirective-86/278/EEC laidrules for theuseofsewagesludge inagriculturalactivitiesby

definingthevaluesofpermissiblelimitsofheavymetalslikeCd,Cu,Hg,Ni,Pb,Zninthesludge.Itdirectedthe

memberstatestousesludgeinagriculturalactivitiesbyfirsttreatingitusingbiological,chemicalorthermal

treatmentssothattheextentoffermentationandhealthhazardsareminimised[53].

3. In1991theEUalsosetuprulesforhandlinghazardouswasteandtheUrbanWastewaterDirective-91/271/EEC

wasamended to98/15/EC, tobeapplicable from2005. This amendmentensured stricter rules andquality

standardforwastewaterwitharticle14statingthatmemberstatesshouldensurethatsewagesludgeshould

no longer be disposed in water bodies and surface waters. It also directed that sludge should be re-used

wheneverappropriate[49,54].

4. In 2005 the EuropeanUnion also declared the implementation of theDirective, approved in 2000, for the

reductionofdioxinsby90%emittedduringincineration[40].

5. In2001,theEUsetupstrictemissionlimitsforthefollowingcomponentsemittedduringincinerationofwaste

[55].

Table10:Airemissionlimitvaluesasperthe2001WasteIncinerationDirective.

Component Incinerators,mg/m3 CementKilnsmg/m3

TotalOrganicCarbon 10 10

TotalDust 10 30

HCl 10 10

CO 50

HF 1 1

SO2 50 50

DioxinsandFurans 0.1ng/m3 0.1

Hg 0.05 0.05

Cd,Ti(total) 0.05 0.05

Sb,As,Pb,Cr,Co,Cu,Mn,Ni,V

(total)

0.5 0.5

NO/NO2 Plants>6t/h200

Plants<6t/h400

ExistingPlants800

Newplants500

26

4. ChlorineemissionsfromBiomassThermalConversion

4.1 ReleaseofChlorinefromdifferentfeedstock

Chlorinecanbepresentindifferentformsdependingontheoriginandnatureoffuel.Incoal,theconcentrationof

Clvariesfrom50-2000mg/Kgwhereastheoriginisfromthegroundwaterthatpercolatesthroughlayersbelowthe

surfaceduringittheformation[55].ThepresenceofClincoalwasstudiedbydifferentresearchersbuttheproblem

is very complicatedbecauseofpoordataagreementobtainedbydifferentmethods.Chlorine ispresent inboth

inorganicandorganicformincoal.ThemineralchlorinepresentincoalisintheformofNaClandoxychlorides[55].

ItwasalsoassumedbyCrossleyetal.[56]thatwatersolublechlorineexistsincoalasNaCl,KCl,CaCl2,MgCl2etc.

WhileorganicchlorinemakesupthemainpartofthetotalClincoal.TheorganicClconsistsoftwoforms:1.Water-

insolubleClorganiccompounds,whereCliscovalentlybondedwithorganicmatterofcoal,2.Partlyorfullywater-

solubleClwhichissorbedontheporesurfaceofcoalorganicmatter[55].Inthecaseofcoalpyrolysis,Clisreleased

in the formofHClmostly in thetemperaturerangeof400-600°C.This releasedHClcanreadily reactwithmetal

impurities (likeCa) to form inorganicandorganic chlorine functionalities.Upon, further increaseof temperature

thesecanreleaseHClagain[57].Coalcombustionandthehotfluegaswerestudiedextensivelyinthelate1980sto

find suitable solutions for the undesirable and toxic components present in the flue gas. The presence of alkali

vapoursinthefluegaswasagraveconcernandhenceitsformationwasstudiedforcoalcombustionatatemperature

of800°C.ForthispurposeKaolinitewasusedasasorbenttoremovealkalichloridesfromfluegas[58].Inthisstudy

the adsorption of NaCl and KCl vapours on kaolinite (under nitrogen and simulated flue gas atmospheres) was

studied.Theauthorsproposeamodelwhichsuggestssurfaceadsorptionanddiffusionthroughboththesaturated

productlayerandporesoftheactivekaolinite.TheconclusionwasthatKaoliniteisaneffectivesorbentforremoving

vapoursofbothNaClandKClfromthesyngasproducedbycoalgasificationandcombustion.

InthecaseofBiomass,chlorinecontentvariesfromlessthan200mg/Kgtoamaximumof7000mg/Kg;pyrolysisof

woodybiomassleadstocompletereleaseofchlorineat350°C,whichconfirmedtheresultsofstudiesstatingthat

the fractionof chlorine released ishigher for lowCl contentbiomass [8,59].Theextentofpresenceof chlorine

determinesitsreleasebehaviourasitwasshowedinaresearchthatwithbiomassofmoderatealkalicontent,the

increaseofCalciumcontentseemstobemoreeffectiveindecreasingtheHClemissionsthanincreasingtheKcontent

[5].ThermalutilizationstudiesusingdifferenttypeofBiomasslikestraw,wood,agriculturalresiduesetc.suggested

thatchlorineisreleasedasseveraltypesofcompoundsbecauseofthedifferenceintheoriginoffeed.Inthecaseof

combustionorgasificationofstrawandsewagesludgeseparately,increasingtheexcessaircoefficientledtoincrease

ofchlorineemissionsviaKClorNaClformationontheotherhand,additionofKaolinincreasesthereleaseofHCland

significantlyreducestheformationofKClinstrawcombustion[60].Pectinisamajorcomponentoftheprimarycell

27

wallofplants,whichactsasamethyldonorfortheformationofChloromethane(CH3Cl)byabioticconversion[61].

The emission of CH3Cl during biomass combustion has been reported to be either a free radical process during

combustionofcelluloseor thecoal-charcatalysedreactionofmethanolwithHClproducedduringpyrolysis [61].

ResearchersalsoconductedstudyofchlorinereleaseasafunctionofpectincontentvsCl/Pectinratioandfoundthat

concentrationofpectininthebiomassisnotaratelimitingstepandotherorganiccompoundscanalsoactasCH3

donors[60].TheinorganicchlorinereleasedduringbiomasscombustionismajorlyintheformofHClandparticulate

chlorine[5].Thepredictedchlorinatedcompoundsdependonthetemperatureofpyrolysisorcombustion.Bjorkman

etal.[8]reportedthatthedistributionofchlorinebetweensolidliquidandgaseousstateisdependentontheprocess

conditions, dominantly pressure and temperature. Also, they stated that composition of gaseous mixture after

pyrolysisorgasificationdependsonthetemperature,ifitisbelow600°CthenHClisthedominantproductbutabove

800°CKClandNaCldominates(meltingpointofKClis770°CandthatofNaClis801°C[5,8].Chlorineemissionduring

pyrolysis of some selectedBiomass feedstock: Sugarcane trash, switch grass, Lucerne, straw(rape) and synthetic

wastewerestudiedunderpyrolysisconditions[8]andtheyreleasedintothegasphase,between20-50%ofallthe

chlorinecontentat400°C,exceptstraw(rape).Theauthorsalsomadeaveryimportantpointclear,thattherewas

nosignificantdifferenceintheemissionofchlorine(mixtureofinorganicandorganicchlorides)fromBiomassand

syntheticwaste.Ithasbeenfoundthatformajorityofbiomassfeedstockthetorrefactionandpyrolysis(upto700°C)

chlorinereleaseisintheformofHCl[5].Chlorineoccursintheformofalkalimetalsaltsinthebiomassandhence

canreadilyconvertintovapourformduringthepyrolysisandgasificationprocesses.MostcommonisHClwhichcan

furtherformcompoundslikeNH4ClandNaClcausingfouling;hotcorrosionofgasturbinebladeswhichcanoccur

withconcentrationsofchlorineandalkalievenaslowas0.024ppm[62].Thepresenceofpotassiuminbiomassas

showninFigure20ishighenoughforthecompletebindingofchlorineasKCl[8].

Figure20:AlkalimetalandChloroatoms(mmol/100gfuel)inBiomass[8]

28

Thereleaseofchlorinefromthebiomassmatrixdependslargelyontheparticlesizeandheatingrate;ithasalsobeen

shownthatthepyrolysisofamixtureofKClwithchlorinefreebiomassleadtoreleaseofchlorine(30-50%)evenat

temperatures below 400°C, this is because of reaction between KCl and the carboxylic groups in biomass [63].

Another observation about release of chlorine from biomass with considerable silicon content is the reaction

betweenKClandsteam(formedbydryingofbiomass),sincetheequilibriumofthisreactionislargelyaffectedbythe

presenceofacidicSiO2,atatemperatureof400°CthispathofreleaseofchlorineasHClissignificant[8].

𝟐𝐊𝐂𝐥 + 𝐧𝐒𝐢𝐎𝟐 + 𝐇𝟐𝐎 𝐠 → 𝐊𝟐𝐎(𝐒𝐢𝐎𝟐)𝐧 + 𝟐𝐇𝐂𝐥(𝐠)

Thisalsoshowsthateveniftheoriginofchlorineinbiomassisofinorganicnatureitcanreleaseatatemperature

lessthanthemeltingpointofthesalt[8,63].InthecaseofhighchlorinebiomasslikecornStover,morethan50wt%

ofchlorineandSulphurwerereleasedbelow500°C.SinceSulphurisalsoassociatedwiththeorganicmatrixofthe

biomasswhichdecomposesat500°ChencethereleaseofSulphuratconsiderablylowtemperaturewasobserved(S

exists inarangeofoxidationstatesfrom-2to+4bothorganicand inorganic innature[64])while inthecaseof

chlorine it ismostlythe ionexchangereaction leadingtoHCl formation [47].RecentpyrolysisstudiesofClandS

releaseusingtwodifferentreactorconfigurations(RotaryandFixedbedreactor)showedthat20%ofClwasreleased

fromstrawatatemperatureof250°Cand64%at350°C,thelowtemperaturereleaseofClwasattributedtopresence

ofCH3donors[59].Zintletal.[65]performedreactionsofKClandwoodinthetemperaturerangeof200-700°Cand

proposedthat the initial lowtemperaturechlorinereleasewasaresultofareactionbetweenKClandcarboxylic

groups(shownbelow).

𝐊𝐂𝐥 𝐬 + 𝐑 − 𝐂𝐎𝐎𝐇 𝐬 → 𝐑 − 𝐂𝐎𝐎𝐊 𝐬 + 𝐇𝐂𝐥 𝐠 − − − 𝟏

TounderstandthereleaseofchlorinefromstrawandcornStoverpyrolysisinanitrogenatmosphere,between200-

1050°C,inasystematicmanner,Jensenetal.reportedtwo-stepprocessofchlorinerelease[47,63]:

1. 60%Clreleasebetween200-400°C,(reaction1)thisstepdependsonthefunctionalgroupspresentinthe

organicmatrix.

2. The rest between 700-900°C, (reaction 2) aluminosilicates reacts with alkali metals (at moderate

temperature this step is kinetically limited and at temperature above700°C it competeswith the alkali

chlorideevaporation).InthereactionbelowY(s)canbesilica,aluminaoracombinationofboth.

𝐇𝟐𝐎 + 𝟐𝐍𝐚𝐂𝐥 + 𝐱𝐘 𝐬 ↔ 𝐍𝐚𝟐𝐎. 𝐱𝐘 𝐬, 𝐥 + 𝟐𝐇𝐂𝐥 − − − 𝟐

29

Figure21:PossiblereactionpathforKreleaseduringdevolatilizationandcombustionofannualcrops[47]

As reportedearlier,Potassium isoneof thesourceofdeposit formation in reactors.Acloser lookat therelease

mechanismasshownintheFigure21,showsthatitisacomplexprocesswhichisrelatedtothecontentofSi,S,Clin

thebiomass.Theorganic fractionofKpresent inthebiomass isreleasedduringthedevolatilizationstageandat

elevatedtemperatureKClundergoessublimation.Thecharburnoutstagecan leadto formationofKsilicatesor

alumino silicates. The alkali release in to the gas phase is slow and limited till 600°C because of the diffusional

resistanceofferedbyintactorganicmatrix[47].Ithasalsobeenshowedthattheincreaseofalkalimetalcontentof

biomassdecreasestheamountsofthecombustiongeneratedemissionsofchlorine.Hence,theHClemissionsfrom

thecombustionofbiomassareinverselyproportionaltotheiralkalitochlorineratio[5].

Figure22:PossiblereactionpathforClreleaseduringdevolatilizationandcombustionofannualcrops[47]

30

4.2 ChlorineemissionsfromSewageSludgePyrolysis

Themotiveofusingthermo-chemicalmethodsfordisposalofsewagesludgeistoextracttheusableenergyfromit

andreducetheharmfuleffectsontheenvironment.Inthecaseofforsewagesludgedisposal,combustionhasbeen

researchedandimplementedextensivelyinEurope.Eachthermaldisposaltechniquehasitsownadvantagesand

disadvantagesbutasmentionedinchapter4,sewagesludgeishighlyvariableintermsofcomposition,henceitisa

crucialfactorforchoosingthetechnologytobeused.Combustionisoneofthemostresearchedmethodconcerning

sewagesludgeasitreducesthedisposalvolumeandcompletedestructionofpathogens.Butthemaindrawbackof

usingcombustionisthegenerationofhazardousairpollutantsinthefluegas,combustordesignsarehencemade

takingcareofthechlorinecontentofsludge[66].Co-incinerationisoneofthesuggestedwaystodealwithsewage

sludgeasitcanbeusedincombinationwithotherfuelslikecoalandMSWetc.togenerateenergy[48].Ithasalso

beenfoundthatco-incineratingMSWandsewagesludgereducesthecostoftheprocessbecausesufficientenergy

canbeproducedfordryingthesludgefromMSW[66].Approximately30wt%ofthedrysolidsremainfinallyasash

incombustionofsewagesludgeandthisitdoesnotcontributesignificantlytocompletedisposal[48].Thekinetics

ofpyrolysissuggeststhatreactionconfigurationandresidencetimearecrucialindeterminingthefinalresidueand

pollutants inthefluegas.This isbecauseprimary(rawmaterialdecomposition)andsecondaryreactionsaretwo

basicstepsoccurringduringpyrolysiswheresecondaryreactions(primaryvolatilesreactwiththechar)arearesult

ofhigh residence timeandhigh temperatures [67].Pyrolysishasemergedasanefficientway for sewagesludge

handlingbecauseitproduceslessemissionsbythevirtueofitsprocessconditions,theheavymetalemissionisnilin

thegasphaseastheyarecollectedinthecharwhichisalsoknownasbio-char[68].Sewagesludgecompositionis

veryimportantparameterfordeterminingthethermodynamicfeasibilityofthereactionsleadingtoemissionofHCl.

OnesuchobservationwasreportedbyMatsudaetal.[69]andconfirmedbyKassmannetal.[70]whentheycarried

outextensivethermodynamicstudiesconsideringallthepossiblereactionpathways.Theyreportedthatpresenceof

SO3affectstheformationofHClfrommetalchloridesaccordingtothefollowingreaction[69]:

𝐌𝐂𝐥𝐱 +𝐱𝟐𝐇𝟐𝐎 +

𝐱𝟐𝐒𝐎𝟐 →

𝐱𝟐𝐌𝟐/𝐱𝐒𝐎𝟑 + 𝐱𝐇𝐂𝐥

Chlorine and Sulphur emission reduction was studies since early 1990s as the acidic gases posed threat to

environment and the reactors. Calcium based sorbents have been extensively studied for this purpose andwet

scrubbingisreportedtobeabetterchoicewhenthebiomasshashighmetalcontent[62].

31

5. UseofSorbentsforChlorineCaptureChlorineisamicroelementpresentinthehighestquantitywhencomparedtoothermicroelements.Itisabsorbed

asCl-anionbytherootsoftheplantsandthenassimilatedintheleavesandstem.Researchershaveconcludedthat

biomasshavinghighpercentageofClreleaseslowerfractionofClthanbiomasswithlowpercentageofCl.Studies

havealsorevealedthatchlorineemissionsfrompyrolysiscanbeoriginatingfrombothorganicandinorganiccontents

ofthebiomass.Also,thereleaseisstronglydependentontheinorganicconstituentslikealkaliandalkalineearth

metals in thebiomass [71].Anothercompound released in the formofCH3Cl is thecauseofClemissions in the

pyrolysisofwoodyandleafybiomassstudiedbyHamiltonandco-workers[61].TheyshowedthatthePectinpresent

intheleavesactsasaCH3donorandplaysakeyroleinClemissions,thiskindofreleasestartsatatemperatureof

150°Candincreasesupto300°C.Also,pectinisnottheonlycomponentforClrelease,theyconcludedthatCH3Cl

emissions during combustionofwoodybiomass can also beoriginated from the reactionof Cl-with lignin [61].

Chlorineemissionsfrompyrolysisofbiomassintheformofhydrogenchlorideormetalchloridescanbecapturedby

using sorbents. These chemical substances undergo chemical reactions with chlorine or by physical adsorption

removeschlorinefromthefluegas.Basedonthedesiredpropertiesofsorbentslikefastrateofadsorption,high

loadingcapacity,irreversibleadsorption,costetc.studieshavebeenconductedtocheckthecaptureefficiencyand

processcalculations.

5.1 RemovalofHClandmetalchlorides

In the early 1980s researchers observed the presence of alkali metal compounds in the vapour phase during

gasificationorcombustion[72].Thesecompoundscausefurtherprocesscomplicationsanddamageforexample,

corrosioninthepostprocessutilization.IfcontentofchlorineinBiomassishigh,thenitcanformdepositionsofalkali

chloridesonthewallsoftheboilerwhichslowsdowntheheattransfer.ChlorineintheformofHCl,influegaswhich

is utilized for combined cycle process, can cause corrosion of the turbine parts [58]. Since a sizeable portion of

chlorineinthefluegasisassociatedwithalkalimetals,reportswerepublishedillustratingbenchscaleandlabscale

experimentsunderdifferentreactorandprocesssetup.

Aluminosilicatesbecamepopularascatalystsbecauseoftheirhighsurfaceareaandporosity,henceKaolinitewas

investigated as a sorbent for removal of alkali chlorides fromhot flue gases. Theexperimentusednitrogenand

simulatedfluegasenvironmenttocaptureNaClat800°C.Mathematicalmodelssuggestedthatthe initialrateof

adsorption isdirectlyproportional to thealkali concentration in thebulkgas, also it isnearly the same forboth

environments considered. The adsorption is irreversible and depends on the gas composition. As in a SFG

environmentonlysodiumwasretained,unlikewithN2atmosphere,itwasproposedthattheadsorbedNaClwould

havereactedwithKaoliniteinthepresenceofwatertoformnepheliteandHClvapours[58].Sorbentsthatcontain

ahighpercentageofSilicacouldadsorb irreversibly just thealkaliandnotchlorine, releasing itasHCl.Activated

bauxiteandemathliteinthediameterrangeof2.4-3.4-mmwereusedforalkaliremoval,theyalsodemonstrated

32

thattheproductgaschlorineconcentrationwasunaffectedorwasreducedtohalfinthebestcasescenario,whileK

andNaremovalefficiencywere98%and92%respectively[73].

5.2 AlkaliandAlkalineearthmetalsassorbents

Alkalimetalsorbentsareincreasinglyusedforhalideremoval,commonlyHClremovalresultingfromthermochemical

conversionofBiomass.ThesemetalsorbentsformsaltslikeNaCl,KCletc.onreactionwithhalidesandhenceprove

tobeuseful[74].Similarly,alkalineearthmetals(BaO,CaO,MgO)alsoshowedtobethermodynamicallyfeasiblefor

removalofhalides[75].

HClformedduringpyrolysisisfoundtoberemovedmostefficientlyinthetemperaturerangeof500-550°Cbecause

ofthechemicalequilibriumconditionsbetweentheconstituentgasesandsolidsinvolved[76].Thesorbentselection

also depends on cost, hence sodium based compounds like sodium bicarbonate, sodium carbonate, Ca(OH)2,

Mg(OH)2 and their calcined versionsofCaO,MgOare reported tobeuseful and inexpensive. Experimentsusing

calcium based sorbents have shown 80% removal of HCl [77]. Ketov et al. (1968) [78] showed that there is an

optimumtemperaturerange,whichleadstomaximumCaCO3toCaCl2conversion(dependingonthekindoflime

taken),thatwasfoundtobebetween540-550°C.Onpilotscaletheuseofslakedlimeparticlesasasorbentforflue

gasdemonstrated.Theresultsweremonitoredatatemperatureof260-400°C,HClretentionwasintherangeof40-

100%which increasedbasedonthetemperature increase,watercontent inthegasandwithdecreasingparticle

diameter from11-39µm.The limeconversion ratewas rapid in thebeginningasmostof theHCl in thegaswas

absorbed, after some time it decreased and then gradually became constant (depending on other reaction

parameters)asshownbyFigure23[79].Duoetal.(1994)[80]studiedthereactionbetweenCaCO3andHClanddue

to the lowvalueof chemicalpotential concluded that the reactionwas slow,aswell as the sorbent conversion.

Anotherstudybysameauthors,forIGCCFuelgascleaningsorbentalsoconfirmedtheaboveresultsoflowconversion

ofCaCO3at400°C,whiletheyalsotestedNa2CO3,NaHCO3andNa2CO3.10H20[81].TheconcentrationofCO2affects

theCabasedsorbentsshowingbetterresultsinoxygenblownthanairblownfuelgases,whileitdoesnotaffectthe

Na based sorbents in the temperature range of 300-600°C. Na2CO3.10H2Owas found to be better thanNa2CO3

becauseofhighporosityofitsdehydratedcompound[81].

AstudyofbindingofHClwiththesorbentparticleswasdonebyClausandco-workers;thesorbentsusedwereslaked

LimeandLimestone.Thebindingcapacitywasdependentonchemicalequilibriumofsolidandgasabove500°C,it

wasindependentoftheparticlesizeandslightlydependentonspecificsurfacearea.Inthetemperaturerangeof

500-600°Candbelow150°Cthebindingcapacitywashighest,almostfullconversionoflimetoCaCl2wasobserved.

Thekineticswasdependentonthediffusioninsidethesolidparticlesandfollowedunreactedgrain-coremodel[82].

33

Figure23:Limeconversionfordifferenttemperaturewithrespecttotime[79]

Somefixedbedreactorstudiesweredoneinthecontextofchlorineremovalandthereactionkinetics;onesuggested

thatthetestedalkaliandalkalineearthmetalsorbentslikeNa2CO3,CaCO3,MgOetc.couldreducetheHClvapour

concentration from10-3 to 10-6 at a temperatureof 500°C and space velocityof 3000h-1. The reaction kinetics

followedfirstorderwithrespecttoinitialHClconcentration[76].AnotherstudyofHClremovalinfixedbedusing

NaHCO3,CaCO3,Ca(OH)2,Mg(OH)2andAl2O3wasconductedatatemperatureof550°C,showingsignificantreduction

of lessthan2wt%indownstreamascomparedtofullysaturatedupstreamend[83].SorbentECl1asdepictedin

Table11,showedhigheradsorptioncapacity,probablybecauseofthecompositionandstructure,asthereactive

component was 87 wt% while in ECl2 it is 11 wt%. The combination of Dolomite and Silica as a catalyst for

decompositionofpyrolysis tar showedgoodefficiencyevenathigh temperature [84].Karlssonetal. (1981) [85]

studiedCa(OH)2asasorbentinfixedbedreactorfrom150-400°C,,confirmingthatthereactionfollowsfirstorder

kinetics,aspreviouslymentionedbyothers,alsotheavailablemaximumCa(OH)2forthesorptionwasaround55%.

Amagazinereport[86]publishedin2014,showedtheadvantagesofretrofittingacidgasremovalsystemsoftwo

wastetoenergyplantsinGermany.TheoldsystemsusedCa(OH)2assorbentwhichwasreplacedwithNaHCO3.The

resultsshowedbetterefficiencyofremovalofHClwithcomparableeconomicfeasibility.

34

Table11:CompositionofSorbentsused[83]

Sorbent

ECl1 ECl2

MainComponents NaHCO3,CaCO3,

Ca(OH)2,Mg(OH)2:87%

Ca(OH)2,11%,Al2O3,89%

Preparation Drymixing Wetimpregnation

BulkDensity(g/cm3) 0.66 0.73

SurfaceArea(m2/g) 3.24 127.89

AveragePorediameter(Å) 247.80 47.34

DryinjectionofCalciumbasedsorbentsinlaboratoryscalefurnaceexperimentsatgastemperaturesof600-1000°C

wereconductedtochecktheHClcapture.Thesorbentswerepowderedcalciumformate(CF),calciummagnesium

acetate(CMA),calciumpropionate(CP),calciumoxide(CX),andcalciumcarbonate(CC).Thesorbentsfluidizedina

streamofairwereintroducedinthefurnaceconcurrently,showingrelativeutilizationof80%.Calciumcarbonate

andcalciumoxideweretheinexpensiveandlowporositysorbents,theyperformedwellwithCaCO3utilizationof

54%atmidtemperaturerangeandCaOof80%inthelowesttemperatureofinvestigation.Calciumsaltsvolatilizein

thetemperaturerangeof300-460°Ctoformcalciumcarbonate,whichisstableupto700°CandaboveitformsCaO

andliberatesCO2.TheremainingCaCO3reactswithHClasfollows[77]:

𝐂𝐚𝐂𝐎𝟑 𝐬 + 𝟐𝐇𝐂𝐥 𝐠 → 𝐂𝐚𝐂𝐥𝟐 𝐬 + 𝐂𝐎𝟐 𝐠 + 𝐇𝟐𝐎 𝐠

Thethermodynamicstudiesweredone inthe2000stocomparesorbentsandtheirefficiencybyvaryingprocess

parameters.Nicolaetal.[87]conductedincinerationexperiment,toremovepollutantsinfluegasinanin-ductdry

removal set up to compare Ca and Na based sorbents by establishing theoretical limits achieved by them,

thermodynamically.Theycheckedthelimitingvaluesofequilibriumvapourpressuresofthepollutants(withboth

NaHCO3andCa(OH)2)byvarying the temperature from100-600°Candkept themolar ratiobetweenamountof

sorbentinjectedandtheamountofpollutantsinthegas,constant.Thesecondcasekeptthetemperatureconstant

andvariedthemolarratiofrom0-1.2.AsshowninFigure24,NaHCO3issuperiortoCa(OH)2intheentiretemperature

rangeconsideredbecausebicarbonateallowstoobtaintheoreticallimitsforHClatcomparativelylowervalue(six

ordersofmagnitude)thanwithLime.NaHCO3wasfoundtobeeffectiveevenat600°CreducingHCltoNaCl.When

themolarratioofsodiumbicarbonatewasincreasedthedecreasingvalueofHClinthegasshowedthatitisbetter

thanLime[87].

35

Figure24:Performanceofsorbentswiththepollutantpartialpressures[87]

Anotherstudywasconductedbythesameauthorsinafixedbedreactorsystemwiththereactionconditions:550°C,

spacevelocity3000h-1andinletHClconcentrationof1000mg/m3.AsshowninTable13,thebreakthroughpointfor

sorbentE1wasthebestforthetemperatureof550°Canditwasabletoreducetheoutletconcentrationto1mg/m3,

whichisneartothedesirablelimitoflessthan1mg/m3[88].

Table12:Sorbentproperties[88]

Sorbent Compositionwt% Surface

Area(m2/g)

Porevolume

(mL/g)

Pore

diameter(Å)

HClremoval

E1 MgO,30%;MMt,70% 136.20 0.20 89.80

E2 Commercialcatalyst 127.90 0.15 47.30

E3 MgO,50%;MMt,50% 12.10 0.05 300.8

E4 MgO,70%;MMt,30% 16.40 0.07 289.2

Table13:BreakthroughpointforChlorine[88]

Sorbent E1 E2 E3 E4

Breakthroughtime(h) 7.20 4.00 2.10 2.00

Breakthroughchlorine

content(%)

8.60 3.60 3.20 3.00

Saturationchlorine

content(%)

48.3 32.15 19.70 19.20

36

6. ExperimentalSetUpThischapterprovidesthedetaileddescriptionofthereactorconfigurationusedfortheexperiments,theprocess

conditions,feedcharacteristicsandIntegralMassBalanceequation.

Thepyrolysisexperimentswereconductedusingtwodifferentreactorconfigurations:FixedbedbatchReactorand

ScrewPyrolysisReactor(STYX).ThefeedusedwasSewageSludge,obtainedfromawastewatertreatmentfacilityin

Germany,havingparticlesizeintherangeof4-8mm.Wheatstrawwasalsousedtocarryoutsameexperimentsas

alternativefeedforcomparisonpurposes.Thefeedstocksampleswereanalysedbyultimateandproximateanalysis

accordingtoGermanstandards.Themetal,halogensandothercompounds inashwerealsoanalysedasperDIN

22022-1andDIN51729-1standards.Thenextsubheadingwilldiscussboththereactorconfigurationindetailalong

withtheexperimentalprocedure.

6.1 FixedBedReactor

Thefixedbedreactorsetupusedforpyrolysisexperimentsconsistedofacylindricalreactormadeupofstainless

steelcoiledwithtubesallrounditsoutersurface.Thesecoilscarriednitrogengaswhichwasinjectedfromthetop.

Themantle,asshownintheFigure25below,wasthesourceofheating,temperaturerampwasprogrammedupto

500°Candheldconstantuntiltheexperimentwascompleted.

Figure25:Laboratoryscalefixedbedreactor

37

Threepositionswerechosenformeasuringthetemperatureinsidethereactor(oneinthemidofthereactorand

twoon the sides)using thermocouples.Thepyrolysis liquid containing somevolatilematterwas condensedand

collectedbeneaththereactor,withthehelpofacondenser(maintainedat7-10°C)havingparalleltubesinsideand

amixture of ethylene glycol andwater as the cooling fluid. The next stage involved capture of aerosols, using

ElectrostaticPrecipitator(ESP),fromthevolatilegaseousmixturecomingfromthecondensationstage.Anabsorber

columnwasusedwithNaOHsolutiontoremoveHClvapoursfromthefluegasbeforeitwassenttoagasanalyser

andsubsequentlyouttotheatmosphere.ThechangeinpHofthissolutionindicatedthepresenceofHClinthegas

streamenteringthecolumn.

Figure26:Reactoroutsideandinsideview

6.1.1 ExperimentalProcedure

PyrolysisoftheSewagesludge(Klärschlamm)orofWheatStraw(Weizenstroh)wascarriedoutwithandwithout

theuseofasorbent.ThesorbentsusedinthisstudywereSodiumHydrogenCarbonate(NaHCO3)andCalciumoxide

(CaO),variedwithrespecttothemolarratioof feed/sorbent.Thetemperatureofthereactorwasmaintainedat

500°Candthetemperatureoftheovenwas670°C.Thefeedstockineachexperimentwasweighedto100gprecision,

mixedwithsuitableamountofsorbent(basedonmolarcalculations)andthenintroducedtothereactor.Awashing

solutionofNaOH0.1Mwasusedintheabsorbercolumn,measuringitsinitialpHvalue.Theemptycondensateglass

bottlewasconnectedtotheendofthecondenser.Thecoolingsystemwasswitchedonforthecondenserwiththe

38

temperaturesetas9°C.Thenitrogenconnectiontubewasscrewedtightlyandtheflowratecontrolledasdesired,

generally5 litersperminute(L/min).Thevoltagevaluefortheelectrostaticprecipitatorwasnotmorethan7kV

initially,butoncethegasstartedfillingitcouldbeincreasedtoamaximumof14kV.Afterthereactorreached500°C,

itwasallowedtorunfor15-20minandthentheovenshutoff.ThepHchangeoftheabsorbercolumnsolutionwas

monitored.Aftertheexperimentalsetupcooledovernight,thefilledcondensatebottleandthecharwereweighed

forthenecessarymassbalance.

6.2 ScrewPyrolysisReactor(STYX)

ThebenchscaleScrewPyrolysisReactorwithintegratedhotgasfiltration(STYX2)wasdevelopedbytheInstituteof

TechnicalChemistry(ITC),KarlsruheInstituteofTechnology(KarlsruherInstitutfürTechnologie),inGermany.Itwas

usedinthestudyofintermediatepyrolysisoflowgradebiogenicresiduesinanisothermalreactionenvironment.It

consistedof a feeding system, through screw reactor, char collectiondrum, condensationunits andgas analysis

systems.Thesignificanceofusingascrewreactoristhatitenablesthefeedtohaveawell-definedresidencetimeby

virtueofitsdesign.Thefeedingzonewaspurgedwithnitrogensothatoxygenwasremovedfromthebulkofbiomass

feed. The reactor contained twomain units, first the screw conveyor and second the sequential extraction and

filtrationunit.Thermocoupleswerelocatedthroughoutthelengthofthereactoratfixedpositionstomeasurethe

temperatureandcontrolitwhenrequired.Sincethereactorassemblyhasafiltrationunit,therawvapoursgenerated

wereextractedfromthereactorandthesolidparticlescollectedseparatelyaschar.Afterfiltration,thecleangas

mixturewasextractedthroughapipe,whichwaspositionedinsidetheoventomaintainthesametemperatureas

the reactor. This is necessary to avoid any possibility of condensation or cracking of the pyrolysis vapours. The

condensation assembly consisted of two parallel condensers maintained at 15°C and an ESP (Electrostatic

Precipitator), which provided capture of aerosols and thus removed the last residues of tar. The flow rate,

temperatureandabsolutepressureofthepermanentgaswasdeterminedbyusingaflowmeter,athermocouple

and a manometer, respectively. A gas analysis device by Swedish company, ABB, was used to determine the

composition of the permanent gas in volume% (methane, carbon-dioxide, carbon-monoxide, oxygen). For this

purpose,asmallpartofthegaswaswithdrawnassampleandpumpedintotheassembly.Thestreamofpermanent

gaswassenttoatorchviaasuctiontrain.

ThereactorwasconstructedofsteelalloyEN1.4571andcouldhandleupto15kg/hofsewagesludge(thermalinput

45kWTH).Isothermalconditionsinsidethereactorweremaintainedandcontrolledbythermocoupleslocatedonthe

bedofthescrewandinthefilterunits.Thereactortemperaturewasheldconstantwiththetemperaturecontrol

system that controlled theheatingelements fora totalheating capacityof40kW.The reactorwasdivided in7

segments. Themaximumnumber of filtration elements could be 14, in this study therewere 6 filter cartridges

2STYXstandsfortheriveroftheGreekmythology.ItistheriveroverwhichCharon,theferryman,transportsthedeathsoulsfromtheEarthtoanewlifeintheUnderworld.

39

presentinthe2,4and6segmentsofthereactor.Thedescriptionofindividualvitalcomponentsoftheexperimental

apparatusisdescribedinthenextsections.

ThespecificationsofthereactorassemblyaretabulatedbelowinTable14:

Table14:ReactorSpecifications

HeatedLength 2m

Diameter 0.15m

ResidenceTime(inthisstudy) 7.5min

Numberoffilterelements 14

Numberofsegmentsinthereactor 7

Temperature 500°C(maximum600°C)

Flowrate(inthisstudy) 2kg/h(maximumis10

kg/h)

Lengthoffilterelements 200mm

Diameteroffilterelements 60mm

MaximumElectricPower 40kW

RelativePressuredrop Ca.-2….-20mbarrel.

Figure27:FlowdiagramoftheBenchscalePyrolysisReactor(STYX)

40

6.2.1 FeedingSystem

Theplantwasdesignedforprocessingdifferenttypeandgradeofbiomass.Inthisstudy,SSandWSwereused,which

havedifferentcomposition,particlesizeandmoisturecontent.Hence,thefeedingunitconsistedofalock-hopper

andadosingscrewconveyor.Thefeedingsystemwasprovidedwithfourindependentinlets,whichenablesinjecting

multiplefeedstocksandadditives(inthiscase,sorbent).

Thelock-hopperisthecrucialelement,consistingoftwomixers.Thefirstonehadaverticalaxisandwasattached

totheplugsuchthatitwasdirectlyintroducedinthelock-hopper.Thesecondonewasplacedatthesamelevelof

thedosingscrewwaslocatedinthechamberbehindthelock-hopper.Thesemixersweredrivenbyelectricmotors

foratotalpowerof100W.Thescrewconveyorfunctionedasdosingdeviceanddidnotcontainashaft.Thedosing

protocol(correlationbetweenrotationspeedandflowrate)waspreviouslycalculatedandwasprovidedbysetting

therotationalspeedofthemotordrivingthescrewconveyor

6.2.2 SequentialExtractionandFiltrationunit

ThepresenceoffiltersinsidethereactorwasoneofthestrikingfeaturesoftheSTYXused.Theinclusionofsucha

filtrationhasadvantageslikeparticlefreecondensates,whichmakesthemstableandlesspronetoageing.Also,it

avoidsthecloggingandfoulingofthepipelines,whichisamajorconstraintinthermalprocessingofbiomass.

The filtrationunitwas locatedabove the screwconveyoranddirectly inside the reactor. Itwasdivided in seven

segmentsandeachsegmentaccommodated two filter candles. Thehotgas filtrationunitwasequippedwithan

automaticonlinere-cleaningsystemtomaintainsuitablepressuredropamongthefilters.Thefiltercandleswere

constructed with a coarse-grained support made of silicon carbide associated with fine alumino-silicate filter

membrane;candleshadtwoopenings:oneforthehotvapoursthatareextractedfromthereactorandtheother

sideworkedastheinletforre-cleaninggas(heatednitrogenwasusedforre-cleaning).ReferringtoFigure28,there

weretwogascollectionsections:oneforthecleangasandtheotherforthenitrogenusedtocleanthefilters.The

filter candleswere placed perpendicular to the screw axis. The raw pyrolysis gaswas sucked from the reaction

chambertothefilterswhilethecleanedvapoursweresenttothecondensationunit.

41

Figure28:SchematicdiagramofHotgasFiltrationAssembly[9]

6.2.3 CondensationAssembly

Thecondensationunitconsistedoftwocondensersplacedinseries,leadingtoanElectrostaticprecipitator(ESP)at

theend.Asthemixturecomingtothecondenserhasrecoverablecomponents,thecondensationoccuredintwo

stages.Inthefirststage,heavyoilandtheaqueouscondensatewererecovered,theywerecollectedinaglassbottle

locatedoutsidethereactorasshowninFigure29,whileinthesecondstagethevapourswerecooleddownto15°C

andmovedtotheElectrostaticprecipitator(ESP).Thefunctionoftheelectrostaticprecipitatorwastoremovethe

aerosolsfromthenon-condensablegases(alsoknownaspermanentgases).Thecondensatesgetnaturallyseparated

inorganicandaqueousphases.Insomecases,whenitisdifficulttoseparatenaturallytheoilandaqueousphases,a

decantercouldbeused.

6.2.4 OnlineGasAnalysis

AftertheESPunitthegasenteredtheanalysisunitwherethecombustioncalorimeterCDW200wasusedtomeasure

density,WobbeindexandtheLHV;BINOS100-MmeasuredthevolumetricconcentrationsofCO,CO2;OXYNOS100

wasusedtomeasuretheconcentrationofmolecularoxygen(O2).Theconcentrationofhydrocarbons,particularly

methane,wasmeasuredbythegasanalysisfacilityusingaflameionizationdetector(FID),Agilent/HP6890GC,for

theprecision.

6.2.5 ExperimentalProcedure

Thesewagesludgewasfedthroughthefeedingunitandittransportedwiththescrewsinsidethereactor.Themass

flowrateofthefeedwassetto2kg/hinalltheexperiments.Themassflowrateofthefeedstockwasdetermined

beforeconductingtheexperimentsbasedonthedosingprotocol.About4kgoffeed(sewagesludgeorwheatstraw)

wastakenwithsuitableamountofsorbenttobepyrolyzedatatemperatureof500°C.SodiumHydrogencarbonate

(NaHCO3)wasusedasasorbenttoconductexperimentsusingsewagesludgeandwheatstrawandwasfedwiththe

42

biomassaftermanualmixing.Thenitrogenflowratewassetto6litresperminuteandthescrewrotationspeedset

accordingtothedosingcurve.Thefeedmovedalongtheaxiswiththescrew(whichprovideswelldefinedresidence

timeofthesolids)byadjustingitsrotation,leadingtoaresidencetimeof7.5minutes.Theamountofcharcollected

wasweighedwhilethecondensateswereseparatedandweighed.Thecompositionanddensityofthepermanent

gasesweremeasuredonline,sampleswerealsotakentobeanalysedbyGasChromatography(GC),forgettingthe

detailedgascomposition.

Figure29:Benchscaleexperimentalsetup(actualpicturesfromKIT)

6.3 FeedstockProperties

a)Sewagesludgewasthefeedofprimaryfocuswhilewheatstrawwasusedforcomparisonpurposesasitcontains

asignificantamountofchlorine.Theultimateandproximateanalysisofbothfeedsweredoneandareshownin

Table15andTable16below.ItcanbeclearlyseenthatthesewagesludgehasahighcontentofNitrogen,Sulphur

and Phosphorous, while the ash was rich in Silicon, Calcium and Phosphorous present as SiO2, CaO and P2O5

respectively.Chlorinecontentwasalsocomparativelyhigh,andit,arisesfromthetreatmentanddisinfectionprocess

ofthewastewater.Thelowheatingvaluewasattributedtoahighashcontentandlowfixedcarbonofthesewage

sludge[89].

43

Table15:UltimateandProximateanalysis,HeatingValueofdriedsewagesludge

UltimateAnalysiswt%ondrybasis Halogensmg/kgondrybasis

C H N S Cl F

30.10 4.27 4.95 1.32 1260 299

ProximateAnalysiswt%asreceivedbasis HeatingValueKJ/Kgasreceivedbasis

Moisture Ash(550°C) VolatileMatter FixedCarbon HHV LHV

10.30 39.40 47.60 2.80 11708 10630

Table16:AshAnalysisofsewagesludge

AshComposition,wt%ofashondrybasis

SiO2 CaO Na2O K2O Al2O3 MgO SO3 P2O5

29.7 13.30 0.40 1.30 10.40 2.10 5.40 15.50

TheGermanlaw(AbfKlärV2010)specifiesthepermissiblelimitofvariousmetalsinsewagesludge.Itisclearfrom

theTable18below that theamountofChromium,Copper,ManganeseandNickelwashigher than theallowed

standards.Therestofthemetalswerebelowthedesiredrequirements.Extensiveandelaborateresearchhasbeen

done on phosphorous recovery from sewage sludge and according to German Sewage Sludge statistics a large

amountofinorganicphosphorouscanberecovered[37].

Table17:EstimatedPhosphorousRecyclingPotentialinGermany

NatureofsewageSludge EstimatedPhosphorousRecovery,tonnes/year

IndustrialSewage 15,000

MunicipalSewageSludge 50,000

Manure 444,000

EstimatedPhosphorousDemandinGermany 170

44

Table18:MetalconcentrationinthisstudyandcomparisonwithGermanpermissibleamount[37]

Metalname SewageSludgeusedfor

thisstudy(mg/Kg)

AllowedinSoil(mg/Kg) AllowedinSewage

sludge(mg/Kg)

Lead 61 40-100 150

Antimony 7 - -

Copper 390 20-60 800

Mercury 0.60 0.1-1 2

Nickel 110 15-70 100

Chromium 230 30-100 120

Thallium 0.2 - 1.5

Manganese 740 - -

Cobalt 8 - -

Arsenic 6.3 - 18

Cadmium 1.2 0.4-1.5 3

Tin 20 - -

b)WheatStraw

WheatstrawwasusedforpyrolysisexperimentswithScrewreactorandcomparisonwiththeresultsfromSewage

sludgepyrolysis.ItisevidentfromTable20thattheashfromwheatstrawhadasignificantamountofPotassium,

whichhasbeenreportedtopromotetheformationofKClandcausedepositformationinsidereactors[63,64].The

ultimateandproximateanalysisof thewheatstrawusedas feed for this study (Table19) shows thatchlorine is

presentinsubstantialamountscomparedtoSulphur,onweightbasis.

Table19:UltimateandProximateanalysis,HeatingValueofWheatStraw

UltimateAnalysiswt%ondrybasis Halogensmg/Kgondrybasis

C H N S Cl F

43.60 5.80 0.55 0.04 1420 <10

ProximateAnalysiswt%asreceivedbasis HeatingValueKJ/Kgasreceivedbasis

Moisture Ash(550°C) VolatileMatter FixedCarbon HHV LHV

8.60 11.60 65.50 14.40 15260 13880

45

Table20:AshAnalysisofWheatStraw

AshComposition,wt%ofashondrybasis

SiO2 CaO Na2O K2O Al2O3 MgO SO3 P2O5

72.70 3.70 <0.10 11.30 0.50 1.00 1.30 1.10

Figure30:ClandSinFeed

6.4 ChemicalAnalysisoftheProducts

Samplesoftheproductswerecollecteddependingontheirphysicalstateandanalysismethodtobeused.Forliquids,

thecollectionwasdonesimultaneouslyduringtheexperiment,buttheseparationandanalysiswasdoneafterthe

experimenthasfinished.Thesolidproduct,char,wascollectedinadrum,weighedandsentforanalysisafterthe

experiment.GaseoussampleswerecollectedduringtheexperimentforGCanalysislater.Sewagesludgehasnon-

homogenouscompositionandhence reproducibilityof results isachallenge.Wheatstrawcompositiondoesnot

poseaproblem,butthecharobtainedundergoeschemicalchangesandinturngetsheatedup.Also,thenatureof

bio-oilsobtained fromwheatstrawandsewagesludgediffer inphysicalandchemicalproperties.Bothsolidand

liquidproductsarecharacterizedbyelementalandproximateanalysis.Theliquidproductsconsistoforganicand

aqueousphase,analysedbyGasChromatography-MassSpectroscopy(GC-MS),(Agilent5975CVLMSDwith6890

GC) and pH determination. The solid product, char, was characterised by ash and metal content analysis. The

permanentgaseswereanalysedonlinebyusingagasvolume%detectorandbyGCanalysisbyAgilent/HP6890GC

(TCDandFIDdetectors).

46

7. ResultsandDiscussionInthisstudy,insitusorptionofClandSisexaminedusingtwotypesofexperimentalapparatusforlowgradebiogenic

feedstock (in this case, SS and WS). The basic screening of suitable sorbents was done taking into account

observationsinliterature,thefeedcharacteristicsanddesiredlimitofemissionasperGermanStandards.Theeffect

andperformanceof the sorbentson reducing emissionswas evaluatedbasedon the amountof Cl and S in the

pyrolysisvapoursandchar.

Theexperimentscarriedoutusingtworeactorconfigurations(FixedbedreactorandSTYX)aresummarizedbelow.

Theresultsarediscussedintermsthefollowingpoints:

• Efficiencyofusinginsitusorptionforreductionofacidgasfrompyrolysisvapours.

• Reactorconfigurationanditsinfluenceonthesorptionperformanceofthesorbent.

• Massbalanceshowingdistributionoftheproductsobtainedinboththereactorconfigurations.

• Comparisonofcharobtainedfromusingandnotusingsorbent.

• Compositionofpyrolysisvapoursandpotentialofusingitforgasturbineoperation.

7.1 FixedBedReactor

Experimentsweredividedintwocategories:1.NoSorbentused2.Usingsorbent.Table21showsasummaryofthe

experimentsconductedatafixedtemperatureof500°Cinthefixedbedreactorsystem.

Table21:SummaryofExperimentsinFBRsystem

Feed(Biomass+Sorbent) Amount(Biomass+Sorbent),g Temperature

SewageSludge 100+0

500°C

SewageSludge+NaHCO3 100+(0.3,6,15,30)

SewageSludge+CaO 100+(26.1,52.3)

WheatStraw 100+0

WheatStraw+NaHCO3 100+30

CaOistestedinfixedbedreactoronlywhileNaHCO3wasusedassorbentbothinFBRandSTYXconfigurations.There

aretworeasonsforthisselection,firstistheextensiveliteraturereportedonefficiencyofbothsorbentsandNaHCO3

beingsuperiorinperformance.Secondis,theresultsobtainedduringexperimentsonFBRshowedlowreproducibility

in using both sorbents, but visible efficiency of NaHCO3 for Wheat Straw, in capturing Cl from 50% to 70%

approximately.

47

7.1.1 MassBalance

Themassbalanceofeachexperimentwascarriedout.Duetothesizeofthedesignofthecondenser,therecovery

oftheliquidwaschallenging.Therefore,thecondensateiscalculatedbydifference.Nevertheless,sincethemotive

of these experiments was to test the efficiency of Cl sorption, char and gas analysis were the most crucial

measurements.

OverallmassbalanceofsorbentandnosorbentcasefromFigure31,showsthatthefractionofgasproductsincrease

whensorbent isused.This isadesirable resultas thisgasaftercleaningcanbecombustedandused forenergy

generation.Moreover,theamountofSandClretainedincharallowsforconsideringsorptionasaneffectiveprocess.

Throughouttheexperiments,thebestcasewasselectedforsorbenttofeedmolarratiowhichis(NaorCa):Clmolar

=349.60

Figure31:OverallMassBalanceforSS

48

Figure32:OverallMassBalanceforWSPyrolysis

Theresultsofgasmeasurementsystemwhichgivesonlinevolume%ofCO2producedareshowninFigure33.The

comparison between CO2 release shows that significant amount is contributed by sorbent decomposition. A

comparisonismadebetweentheamountsofCO2releasedwhenCO2wasusedassorbentandwhennosorbentwas

used,showninFigure34.TheamountofCO2releasedinvol%ofP.Gasisfarlessthannosorbentcase.Thisisbecause

oftheoccurrenceoffollowingreaction:

𝐂𝐎𝟐 𝐠 + 𝐂𝐚𝐎(𝐬) → 𝐂𝐚𝐂𝐎𝟑(𝐬)

Hence,majorfractionofCO2iscapturedbythesorbent.Becauseofwhich,whileinthecaseofNaHCO3+SStheshare

ofP.Gasincreasesfrom71.03to95.35g/Kgfeed,inthecaseofCaO+SSitdecreasesfrom71.03to2.53g/Kgfeed,

referfigureFigure37.

49

Figure33:Volume%DistributionofP.Gas,SS+NaHCO3

Figure34:Vol%CO2Released

50

Figure35:IncreaseinP.GasforSSandNaHCO3

Figure36:P.GasdecreaseinthecaseofSS+CaO

51

Figure37:Tabulationofg-CO2releasedperKgfeed

7.1.2 SorbentEfficiencyComparisonforSSandWS

Twosorbents(NaHCO3andCaO)wereselectedforinsitusorptionpyrolysisexperimentswithSewageSludgeafter

careful screening of information from literature. The Sorbent/Feed mass ratio was set based on theoretical

calculationsandtheeffectofchangingthisratiowasexamined.AsshownintheFigure38below,thequantitiesof

sorbentused(NaHCO3) isvariedfrom0.3-30gwith100g(fixed)ofSewagesludge.Yaxisshowstheyieldofthe

desiredelementwithrespecttothechangeofsorbentamountandisdefinedasfollows:

𝐘𝐢𝐞𝐥𝐝𝐨𝐟𝐂𝐥𝐨𝐫𝐒 = 𝐀𝐦𝐨𝐮𝐧𝐭𝐫𝐞𝐭𝐚𝐢𝐧𝐞𝐝𝐢𝐧𝐭𝐡𝐞𝐜𝐡𝐚𝐫, 𝐠

𝐀𝐦𝐨𝐮𝐧𝐭𝐢𝐧𝐢𝐭𝐢𝐚𝐥𝐥𝐲𝐩𝐫𝐞𝐬𝐞𝐧𝐭𝐢𝐧𝐭𝐡𝐞𝐟𝐞𝐞𝐝, 𝐠

ChangingtheamountofNaHCO3used,affectedSandClcaptureindiverseways.ForClthetrendwasnotclearand

wasabruptintheextentofincreaseordecrease.WhileforS,initialincreasefrom0.3to6gdidnotshowanyeffect

butfurtherincreaseto15and30gofsorbentshowedanincreaseinyieldofSulphur.ThisincreaseinSyieldagrees

withliterature[89,90]previouslyreportedforthedrysorbentinjectiontotargetSO2removal.Accordingtosuch

expectations,anincreaseintheratioofNa/SorCa/SshouldincreasetheSulphurcapturebecauseofavailabilityof

moresurfaceareaforadsorption,duetoincreaseinsorbentamount.Accordingtootherstudies[91],Sulphurcapture

isverysensitivetotemperatureandismaximumintherangeof120-175°C, itdecreaseswithfurther increaseof

temperature inaNaHCO3-Ssystem. In-SitusorptionofCl, inFixedBedReactor (FBR)pyrolysisofSewageSludge

showedvaryingefficiency(from80%captureofClinchartoaslowas49%)eventhough3-5repetitionsofthesame

52

experimentwerecarriedout.WhiletheScaptureincharshowedamildincreasefromNoSorbent(NS)casetousing

asorbentcase.WhenNaHCO3wasusedassorbenttheScaptureincharincreasedfrom42%to52%.

Figure38:NaHCO3PerformanceinthecaseofSS

For the clear understanding of Cl capture with increase of sorbent amount, two modes of sorbent use were

considered.One,inwhichthesorbentandSSweremixedmanually,andtheother,inwhichseparatelayersofSSand

sorbentwereplacedinthereactoroneuponanother.Inbothmethods,thetrendwasnotasexpectedandreported

in literature.Thereasonforsuchabehaviour isnotclear.Somepossibilitiescanbetheoccurrenceofsecondary

reactionsbetweenNaHCO3andcharmatrix[47]therebydecreasingtheamountavailableforCladsorption(ithas

beenreported[90,91]thatahighstoichiometricamountofNaHCO3isrequiredforeffectivesorptionefficiencyof

Cl, typically more than 90%), the contacting pattern and flow regime between solid-gas components (low HCl

concentrationinincineratorshavereportedmodificationindesignofreactorsuchthatthecontactbetweenashand

fluegasisenhanced[66].Hence,furtheranalyticalandstructuralanalysisofthecharandliquidproductsneedsto

bedonetounderstandthecause.Sorbent/SSratiowasvariedfrom0.003to0.3 inthecaseoftheFBR-NaHCO3

system,whichshowedabruptandnon-conclusiveresultsforClsorptionprobablybecauseofunevendistributionof

sorbentevenaftermanualmixingortheanalysedcharsampletobenotarepresentativeone.However,Scapture

inthecharwasinitiallyconstantforSorbent/SSratiointherangeof0.003-0.06but,itincreasedsteadilywhenthe

sorbent amount was increased. Literature reports mentioned that in the case of NaHCO3 as sorbent higher

stoichiometricratiosaredesirableastheyshowbetterefficiency.

53

Figure39:StandarddeviationforthecaseofSSandNaHCO3

ResultsobtainedagreedwithliteraturethatthesorptionreactionrateofCaOislowerforacidgasesascomparedto

NaHCO3.Chlorinecapturewasmarginal(69%to72%)whencomparedtoSulphurwhichincreasedfrom41%to76%.

WhenCaO/SSratiowasincreasedfrom0.26to0.52,theScaptureshowedsignificantincreaseasmoresorbentwas

availableforreaction.AnotherimportantresultinthiscaseisaffinityofCaOtowardsCO2capturewhencompared

tonosorbentcaseofSSpyrolysis,Figure34andFigure37

TheSulphurcaptureincreasedsignificantlywiththeamountofCaOincrease,fromapproximately42%to72.This

couldbeattributedtohighaffinityofalkaliandalkalineearthmetalstowardsSulphurcompounds,thealkalimetals

presentinthecharalsocontributetofixingofSulphurbyfavourablereactions[92].ReleaseofSulphurinpyrolysisis

thermodynamically favoured towards formation of reduced Sulphur compounds as the stable ones and not the

gaseous form of S [87]. In the range of 175-500°C most of the organically bound S is released following the

devolatilizationstageandifthesystemtemperaturereachesashighas1000°Cthencharburnoutcontributesto

furtherreleaseofS[47].Sulphurcaptureinbothfeedstockfollowthisreleasepatternmentionedinliteratureand

maximumamountofthereleasedSiscapturedatthepyrolysistemperature.Whenwheatstrawwasusedasfeed

forpyrolysisandNaHCO3usedassorbentintheFBRsystemthechlorineyieldwasvisiblyhigherandthesamewas

thecasewithS,whichisanexpectedresultandhasbeenreportedelsewhere[47,63,93].Thechlorinereleasein

wheatstrawwashigherthanSSandhencethesorbentcancapturemostofitinchar.Thiscausestheincreaseof

precisionwithwhichitcanbedetectedinthecharanalysisdonelater.Whenboththefeedstocksarecomparedin

54

termsofClandScaptureyield,forthecaseofNaHCO3assorbent,WSshowsbetteryieldforyieldofbothClandS

thanSS.

Figure40:PerformanceandStandardDeviation,SS+CaO

IntheFBR-WSsystem,onlyNaHCO3wastestedasthepreviousexperimentsshowedNaHCO3toberelativelybetter

sorbent.TheClcaptureincharincreasedfrom51%to69%,Scapturefrom25%to51%;whichisadecentefficiency

ascomparedtoFBR-SSsystem.

Figure41:PerformanceofNaHCO3incaseofWS

55

Standarddeviation isameasureoftheextentofdeviationordispersionofresultsobtainedfromperformingthe

sameexperimentmultipletimes.Inthiscase,itgivesaninsightontheabruptvaluesobtainedinthecaseofClcapture

forSSusingbothNaHCO3andCaO.Thisdeviationcanbebecauseofanalyticalerrorand inhomogeneity inchar

compositioninthesampletakenforanalysis.AnalyticalerrorcanbejustifiedbythelowcontentofClascompared

toSinthefeedstockwhichischallengingtobedeterminedwithprecisionusingtheavailableinstrumentsforanalysis

Figure42:ComparisonofFeedstockwithrespecttoClandSemissionsandtheirsorption

TheanalyticalerrorcanbejustifiedbythelowcontentofClcomparedtoSinthefeedstock,whichischallengingto

bedeterminedwithprecisionusingtheavailable instrumentsforanalysis(alsothefeedusedis100g inFBRand

approximately2kginSTYX,hencethebetterprecisionobservedinthelattercase).

7.2 STYXExperimentalReactor

Thein-situsorptionofClandSwereinvestigatedatthebench-scalescrewpyrolysisreactorSTYX,adoptingNaHCO3

assorbent.ThisselectionwasacombinationofobservationsfromthesmallscaleFBRexperimentsandtheextensive

literaturepublishedalready.Fourexperimentswerecarriedout(2repetitionofeachone).Theprocessconditions

areenlistedinTable22

56

Table22:ListofExperimentsperformedonSTYX

Feed(Biomass+Sorbent) Amount(Biomass+

Sorbent),g

Temperature Residence

Time(min)

FlowRateof

Feed

SewageSludge 4000+0

500°C 7.5 2kg/hSewageSludge+NaHCO3 4000+(1199.7)

WheatStraw 4000+0

WheatStraw+NaHCO3 4000+(1199.7)

Themassratioof feedtoSorbentwasheldconstantas itwas intheexperimentswithFBRconfiguration. Inthe

followingparagraphs,themassbalanceswillbefirstdiscussed,thenthesorbentperformanceevaluation.

7.2.1 MassBalance

TheresultsofthemassbalanceareshownintheFigure43.Thebalanceiswithrespecttothefeedwhichincludes

both the biomass feedstock and the sorbent. Two sets of experiment were conducted with both the biomass

feedstockseparately.BiomassfeedstockstudiedwereSewageSludge(SS)andWheatStraw(WS).Firstexperiment

wasdonetoknowhowmuchClisreleasedduringpyrolysisoftherespectivefeedstockwithoutsorbent.Thenboth

thefeedstocksweremixedwithNaHCO3andpyrolyzedatthesameprocessconditions.Thedepictionofthemass

balanceoftheexperimentsperformedintheIntegratedpyrolysisSTYXplantaredemarcatedasshowninFigure43

andFigure44.Theyieldsofsolid,liquidandgaseousproductsforbothcasesarecompared;duetoreleaseofCO2

fromthedecompositionofNaHCO3thegasfractionofSS+NaHCO3,ishigherthanthenosorbentexperimentand

leadtoanoverallbalanceof108wt%).Sorbentadditionincreasesthecrackingreactionsbetweenvolatilesandchar

leadingtobreakdownofhigherhydrocarbonstolighterones,eventuallyincreasingtheshareofgas[40].Also,the

increaseinP.GasforSS+NaHCO3andWS+NaHCO3iscompensatedbyadecreaseinthecontentofliquidproducts

(OrganicandAqueousfractions).Thereasonforthedecreaseintheliquidyieldforthecasewhensorbentisused

withboth the feedstocks, isattributed to thepresenceofalkalimetalsandalkalineearthmetals in the reaction

mixture.Thesespeciespromotesecondaryreactions(cracking)ofvolatileswiththechar[38,40,44].Inthecaseof

sewagesludgewithouttheutilizationofsorbent,theyieldofthecharwas52%.While,inthecaseofUtilizationof

the sorbent, yield of char decreased to 49.3%.Wheat straw showed slightly different response towards using a

sorbent.TheincreaseinP.Gasyieldwassignificant(from26.3%to32.6%)whileincreaseintheyieldofcharwas

marginal(36.5%to37).ItshouldbenotedthatsincethepyrolysisgasfromWSexperimentswerenotanalysedby

GC,theyellowcomponentinFigure44representsP.Gas+loss.

57

Figure43:MassBalanceandYielddistributionofexperimentsusingSTYX

Figure44:MassBalanceWSforSTYXexperiments

58

7.2.2 SorbentPerformance

Since release of chlorine compounds, in this study, mainly takes place between 350-550°C [94], Intermediate

pyrolysiswithhotgasfiltrationledtoanincreaseofP.Gasbecauseoflowheatratesandhighresidencetimeas

comparedtofastpyrolysis[95].UsingNaHCO3assorbentwithSewageSludge,increasedthecaptureofClinchar

from83%to93%approximatelyasshowninFigure45.

Figure45:ComparisonofChlorineYieldforSSandWSforSTYX

Asdiscussedpreviously,incaseofFBRClcaptureincharcouldnotbemeasuredwithhighprecisionbecauseofissues

relatedtomixingandsampling(lessClcontent),differentheatingprogramandtemperaturedistributioninthebulk

solid also contributed to thisproblem.Nevertheless, in caseof SSwhichhashighS content, sorbenthas shown

reliableperformanceofin-situsorption(from50%to68%)depictedinFigure46.Thepresenceofalkalimetalsinthe

reactorintheformofNaOHorNaHCO3reducestheemissionofH2Sintwoways.Firstistheoxidationofunstable

aliphaticandaromaticsulphurstomorestablesulphoxidesandsulphonicacidatatemperatureof250°C.Secondis

thefixationofsulphurintheformofin-organicsulfideandsulphateinchar,furtherreducingthereleaseofsulfur

intogasphase[92].Hence,thesereportsexplainthereductionofSinthegasphasewhensorbentisused,inthis

study.

59

Figure46:ComparisonofSulphurYieldforSS

7.2.3 PermanentGasCombustion

Inordertoevaluatethereductionoftheemissionsduetotheimplementationofthein-situsorption,calculationsof

permanentgascombustionwerecarriedout.ThepermanentgeneratedbysewagesludgepyrolysisinSTYXreactor,

wereanalysedusingGCbyAgilent/HP6890GC(FIDandTCDdetectors).ThecompositionoftheP.Gasisevaluated

intodetails.QuantitativeanalysisofN2,H2,CO,CO2andthehydrocarbonsuptoC4waspossible(seeFigure47).

Figure47:Permanentgas,vol%

60

Itwasalsoobservedthatshareofhydrocarbonscontributingtothecalorificvalue,increasedinthecaseofuseof

NaHCO3evenconsideringthatadditionalCO2 is released insuchsituation. (Note:Thepermanentgas is thenon-

condensablepartofthepyrolysisvapours.Uponcombustionofthispermanentgaswegetthefluegaswhichisbeing

analysedaspertheGermanregulations)

Figure48:HydrocarbonshareofthePermanentgasinFigure47

Combustionofpermanentgasusingexcessairaspertheguidelinesmentionedin17.BImSchV[96]limitstheHCl

andSO2emissionstobenotmorethan10and50mg/m3respectively.Italsopreciselymentionstheamountofoxygen

presentinthefluegas.Theoxygencontentpresentinthefluegasshouldbe11%andhencetherequiredamountof

air is re-calculatedbasedonthisvalue.Usingtheseguidelinesandtheequationbelow,combustionscalculations

weredone.GeneralcombustionequationsfortherangeofhydrocarbonsandH2Spresentinthepermanentgasare

shownbelowTable23.

𝐂𝐧𝐇𝐦 +𝐚𝐎𝟐 → 𝐛𝐂𝐎𝟐 + 𝐜𝐇𝟐𝐎

𝐇𝟐𝐒 + 𝟏. 𝟓𝐎𝟐 → 𝐒𝐎𝟐 +𝐇𝟐𝐎

61

Table23:TabulatedvaluesofSO2andHClemissionsfromCombustion

Experiment

Type

SO2emission(mg/m3) HClemission(mg/m3)

Calculatedin

thisStudy

17.BImSchV

regulation

(11%O2)

Calculatedin

thisStudy

17.BImSchV

regulation

(11%O2)

NoSorbent,SS 36044.49 17164.04 231.69 110.33

NaHCO3+SS 24867.20 11841.52 81.90 39.00

InTable23,theemissionsarereportedbothunderstoichiometricconditionsaswellasaftertheGerman17.BImSchV

regulation (11%O2) [96]. Emissions ofHCl are reducedby a factor 3.However, itwas not possible tomeet the

requiredemissionlimits.Nevertheless,thetargetappearsachievablebyimprovingthemixingqualityaswellasby

slightlyincreasingthesorbenttofeedratio.Ontheotherhand,theemissionsofSO2arefarawayfromtherequired

target.AlternativestrategiesfortheremovalofsulphurfromtheP.Gasneedtobeinvestigated.Inconclusion,the

co-feeding of sorbent for the reduction of Cl emission appears a suitable approach; however, optimization is

required.InthecaseofcombinedremovalofClandSfromtheP.Gas,thein-situsorptionapproachshowedlimited

results.

62

8. ConclusionsInthisthesis,PyrolysisofSewageSludge(SS)andWheatStraw(WS)wascarriedoutwithfocusonin-situsorptionof

ClandSusingSodiumHydrogencarbonate(NaHCO3)andCalciumOxide(CaO)assorbents.Thefollowinginformative

remarksandconclusionscanbedrawnfromthestudiesconducted:

a) Use of NaHCO3 and CaO as sorbents for Cl and S capture in the FBR showed varying results and issues of

reproducibility.ThestandarddeviationofClcapture incharshowedthatananalyticalerror is thepredicted

causeofthedwindlingvalues.TherelativeamountofClissmallascomparedtoSintheSSfeedstockwhichgives

risetodecreaseofprecisionwhilemeasurementinasmall-scaleexperiment(100gSSasfeed).

b) Higher stoichiometric ratio of Sorbent and Feed could lead to better capture of Cl and S, literature reports

mentionedthat,inthecaseofNaHCO3higherstoichiometricratiosaredesirableastheyshowbetterefficiency.

However,economicconsiderationsmayalsobeconsidered.

c) CalciumOxideassorbentforbothSSandWSshowedcompetitivesorptionofCO2andacidgases.Thecapture

ofSinthecharusingCaO,wasmoreefficientthanCl,forsewagesludge.Thisisbecauseofthehighamountof

SpresentinSS,whichenablesbetteranalysisofthecontentsinchar.CaOundergoesothercompetitivereactions

forexample,withCO2toformCaCO3atthereactionconditions,whichwasmentionedinliteraturebefore.When

CaO/SSratiowasincreasedfrom0.26to0.52,theScaptureshowedsignificantincreaseasmoresorbentwas

availableforreaction.

d) IntheFBR-WSsystem,onlyNaHCO3wastestedasthepreviousexperimentsshowedNaHCO3toberelatively

bettersorbent.TheClcaptureincharincreasedfrom51%to69%,Scapturefrom25%to51%;whichisadecent

efficiencyascomparedtoFBR-SSsystem.Hence,itwasconcludedthatNaHCO3duetoitssuperiorperformance,

willalsobetestedinSTYXexperimentsforcaptureofSandCl.

e) WhenSewageSludgeandwheatstrawisusedasfeedandSodiumHydrogenCarbonate(NaHCO3)assorbentin

STYX,chlorineremovaltrendisincreasingfromnosorbenttousingasorbent.InthecaseofSulphurwhichis

presentinveryhighamountinSSvisiblyhighSsorptionefficiencywasobserved.Hence,itwasconcludedthat

furtherstudiesmustbeconductedonNaHCO3+SSsystemforSTYXpyrolysisplanttogethigherefficiencyofCl

sorption.

f) CombustionCalculationsofpermanentgasfromSSobtainedfromtwostreams:WithNaHCO3assorbentand

without a sorbent, showed that the values of SO2 and HCl emissions are above the regulation limit. The

limitationsinHClemissionsappearachievablebyoptimizationoftheprocess.TheremovalofSulphurrequires

adifferent strategy. Further componentbalance from theanalysisofbio-oil andaqueousphasecan lead to

betterunderstandingoftheefficiencyofsorbentandthepathwaysofformationofClandScompounds.

63

9. FutureWorkFuture works related to the reduction Cl emissions should follow two main strategies. On the one hand, an

optimizationofthein-situsorptionisrequired:

• Improvementandoptimizationofthesorbent/feedratio

• Evaluationofmoreeconomicsorbents,suchasCaCO3ordolomite.

Moreover, the analysis of the bio-oilwill assess the chance of direct combustion of the pyrolysis vapours as an

alternativetothecombustionoftheP.Gas.InthecaseoflimitedClcontentintheliquids,theincreaseofthemass

flowwouldhelptoachievetheemissionstargets.

ThesecondstrategythatshouldbeinvestigatedconsistsofinvestigatingdifferentapproachesfortheremovalofCl

fromthepyrolysisvapoursorfromtheP.Gas.

Thedryinjectionofthesorbentinthegas-phase(entrainedflowsorption)appearstobeaninterestingalternative

fortheSTYXreactor.Thepresenceofthehightemperaturefilterswillremovethereactedsorbentfromthegas.The

sorbentwillberetainedonthesurfaceofthefiltergeneratinganadditionalopportunityforsorption.Thisapproach

appearsinterestinginboththecaseofdirectcombustionofthepyrolysisvapoursoroftheP.Gasaftercondensation

ofthebio-oil.

InthecaseofcombustionoftheP.Gas,theutilizationofanabsorbentafterthecondensationofthebio-oilmight

alsobeasuitableoption.Inthiscase,bothClandScanbereducedtoverylowlevels.However,anadditionalaqueous

wastestreamisgenerated;therefore,atechno-economiccomparisonofthedescribedoptionsismandatoryforthe

overalloptimizationoftheprocess.

64

References[1] KummamuruB.WBAGlobalBioenergyStatistics2017.Sweden.[2] BridgwaterAV.Renewablefuelsandchemicalsbythermalprocessingofbiomass.Chemical

EngineeringJournal2003;91(2):87–102.[3] CaoY,PawłowskiA.Sewagesludge-to-energyapproachesbasedonanaerobicdigestionand

pyrolysis:Briefoverviewandenergyefficiencyassessment.RenewableandSustainableEnergyReviews2012;16(3):1657–65.

[4] KnudsenJN,JensenPA,LinW,Dam-JohansenK.SecondaryCaptureofChlorineandSulfurduringThermalConversionofBiomass.EnergyFuels2005;19(2):606–17.

[5] RenX,SunR,ChiH-H,MengX,LiY,LevendisYA.Hydrogenchlorideemissionsfromcombustionofrawandtorrefiedbiomass.Fuel2017;200:37–46.

[6] CodaB,AhoM,BergerR,HeinKRG.BehaviorofChlorineandEnrichmentofRiskyElementsinBubblingFluidizedBedCombustionofBiomassandWasteAssistedbyAdditives.EnergyFuels2001;15(3):680–90.

[7] LeeJ,FengB.AthermodynamicstudyoftheremovalofHClandH2Sfromsyngas.FrontiersofChemicalScienceandEngineering2012;6(1):67–83.

[8] BjörkmanE,StrömbergB.ReleaseofChlorinefromBiomassatPyrolysisandGasificationConditions.EnergyFuels1997;11(5):1026–32.

[9] MarcoTomasiMorgano.AnExperimentalStudyoftheEfficientconversionofbiomassintoCHPwithPyrolysisandHotGasCleaning-Massenergybalancesandprimaryplantanalysis-MSc.Tomasi.

[10] McKendryP.Energyproductionfrombiomass(part1):overviewofbiomass2002;83:37–46.[11] DemirbasA.Effectsoftemperatureandparticlesizeonbio-charyieldfrompyrolysisofagricultural

residues.JournalofAnalyticalandAppliedPyrolysis2004;72(2):243–8.[12] StrezovV,EvansTJ.Biomassprocessingtechnologies:CRCPress;2014.[13] KenneyKL,SmithWA,GreshamGL,WestoverTL.Understandingbiomassfeedstockvariability.

Biofuels2014;4(1):111–27.[14] Kögel-KnabnerI.Themacromolecularorganiccompositionofplantandmicrobialresiduesas

inputstosoilorganicmatter.SoilBiologyandBiochemistry2002;34(2):139–62.[15] DemirbasA.PyrolysisMechanismsofBiomassMaterials.EnergySources,PartA:Recovery,

Utilization,andEnvironmentalEffects2009;31(13):1186–93.[16] SahaBC.Hemicellulosebioconversion.JournalofIndustrialMicrobiologyandBiotechnology

2003;30(5):279–91.[17] DemirbasA.Biofuelssecuringtheplanet’sfutureenergyneeds.EnergyConversionand

Management2009;50(9):2239–49.[18] GlasserWG,Sarkanen.Lignin.Washington,DC:AmericanChemicalSociety;1989.[19] DemirbasA.Biofuels:Securingtheplanet'sfutureenergyneeds.1sted.London:Springer;2009.[20] MeierD,FaixO.Stateoftheartofappliedfastpyrolysisoflignocellulosicmaterials-areview.

BioresourceTechnology1999;68:71–7.[21] LewandowskiI,KichererA.Combustionqualityofbiomass:Practicalrelevanceandexperimentsto

modifythebiomassqualityofMiscanthusxgiganteus.EuropeanJournalofAgronomy1997;6(3):163–77.

65

[22] StahlR,HenrichE,GehrmannHJ,VodegelV.Definitionofastandardbiomass,DeliverableWP2.1/D2.1.1:RENEW,Renewablefuelsforadvancedpowertrains.IntegratedProject,Sustainableenergysystems.Karlsruhe,Germany;2004.

[23] EvansA,StrezovV,EvansTJ.Sustainabilityconsiderationsforelectricitygenerationfrombiomass.RenewableandSustainableEnergyReviews2010;14(5):1419–27.

[24] NussbaumerT.CombustionandCo-combustionofBiomass: Fundamentals,Technologies,andPrimaryMeasuresforEmissionReduction.EnergyFuels2003;17(6):1510–21.

[25] ObernbergerI(ed.).ReachedDevelopmentsofBiomasscombustiontechnologiesandfutureoutlook.Florence,Italy:ETARenewableEnergy;2009.

[26] Hensmark.H.UnfoldingtheformativephaseofgasifiedbiomassintheEuropeanUnion:Theroleofsystembuildersinrealisingthepotentialofsecond-generationtransportationfuelsfrombiomass.DoctorofPhilosophy.Göteborg,Sweden;2010.

[27] WilliamsPT,BeslerS.Theinfluenceoftemperatureandheatingrateontheslowpyrolysisofbiomass.RenewableEnergy1996;7(3):233–50.

[28] MaggiR,DelmonB.Characterizationandupgradingofbio-oilsproducedbyrapidthermalprocessing.BiomassandBioenergy1994;7(1-6):245–9.

[29] ScottDS,MajerskiP,PiskorzJ,RadleinD.Asecondlookatfastpyrolysisofbiomass—theRTIprocess.JournalofAnalyticalandAppliedPyrolysis1999;51(1-2):23–37.

[30] BridgwaterAV.Principlesandpracticeofbiomassfastpyrolysisprocessesforliquids.JournalofAnalyticalandAppliedPyrolysis1999;51(1-2):3–22.

[31] KadamKL,ForrestLH,JacobsonWA.Ricestrawasalignocellulosicresource:Collection,processing,transportation,andenvironmentalaspects.BiomassandBioenergy2000;18(5):369–89.

[32] BainRL,OverendRP,CraigKR.Biomass-firedpowergeneration.FuelProcessingTechnology1998;54(1):1–16.

[33] WilliamsPT.SewageSludgeinWasteTreatmentandDisposal,SecondEdition.Chichester,UK.:JohnWiley&Sons,Ltd;2005.

[34] XuG.AnalysisofSewageSludgeRecoverySysteminEU-inPerspectivesofNutrientsandEnergyRecoveryEfficiency,andEnvironmentalImpacts.Master'sDissertation.Trondheim;2014.

[35] ManaraP,ZabaniotouA.Towardssewagesludgebasedbiofuelsviathermochemicalconversion–Areview.RenewableandSustainableEnergyReviews2012;16(5):2566–82.

[36] ChenG,LockY.Po.,MujumdarAS.Sludgedewateringanddrying.DryingTechnology2002;20(4-5):883–916.

[37] WiechmannB,DeinmannC,KabbeC,VogelI,RoskoschA.SewagesludgemanagementinGermany.Bonn,Germany;2013.

[38] FontsI,GeaG,AzuaraM,ÁbregoJ,ArauzoJ.Sewagesludgepyrolysisforliquidproduction:Areview.RenewableandSustainableEnergyReviews2012;16(5):2781–805.

[39] EuropeanCommission.SewageSludge:RevisionoftheSewageSludgeDirective:http://ec.europa.eu/environment/waste/sludge/index.htm.Brussels.

[40] HassanSSA,WangY,HuS,SuS,XiangJ.ThermochemicalprocessingofsewagesludgetoenergyandfuelFundamentals,challengesandconsiderations.RenewableandSustainableEnergyReviews2017;80:888–913.

[41] HoranNJ.Biologicalwastewatertreatmentsystems:Theoryandoperation:JohnWiley&SonsLtd;1989.

66

[42] EuropeanCommission.Disposalandrecyclingroutesforsewagesludge:Part3-Scientificandtechnicalsub-componentreport.Scientificandtechnicalsub-componentreport.Luxembourg;2001.

[43] GrønC.Organiccontaminantsfromsewagesludgeappliedtoagriculturalsoils.Falsealarmregardingpossibleproblemsforfoodsafety?(8pp).EnvironmentalScienceandPollutionResearch2007;14:53–60.

[44] FontsI,AzuaraM,GeaG,MurilloMB.Studyofthepyrolysisliquidsobtainedfromdifferentsewagesludge.JournalofAnalyticalandAppliedPyrolysis2009;85(1):184–91.

[45] PiskorzJ,ScottDS,WesterbergIB.Flashpyrolysisofsewagesludge.Industrial&EngineeringChemistryProcessDesignandDevelopment1986;25(1):265–70.

[46] LesterJN,SterrittRM,KirkPWW.SignificanceandbehaviourofheavymetalsinwastewatertreatmentprocessesII.:Sludgetreatmentanddisposal.Scienceofthetotalenvironment1983;30:45–83.

[47] JohansenJM,JakobsenJG,FrandsenFJ,GlarborgP.ReleaseofK,Cl,andSduringPyrolysisandCombustionofHigh-ChlorineBiomass.EnergyFuels2011;25(11):4961–71.

[48] FytiliD,ZabaniotouA.UtilizationofsewagesludgeinEUapplicationofoldandnewmethods—Areview.RenewableandSustainableEnergyReviews2008;12(1):116–40.

[49] EuropeanCommission.Technologyandinnovativeoptionsrelatedtosludgemanagement.[50] EuropeanCommission,Eurostat.Waterstatistics.Brussels;2017.[51] GendebienA.Environmental,economicandsocialimpactsoftheuseofsewagesludgeonland:

FinalReportPartIII:ProjectInterimReports.Belgium;2010.[52] DirectiveC.Councildirectiveontheprotectionoftheenvironment,andinparticularofthesoil,

whensewagesludgeisusedinagriculture:86/278/EEC;1986.[53] MininniG,BlanchAR,LucenaF,BerselliS.EUpolicyonsewagesludgeutilizationandperspectives

onnewapproachesofsludgemanagement.EnvironmentalScienceandPollutionResearch2015;22(10):7361–74.

[54] TheEuropeanParliamentandtheCouncilofEuropeanUnion.Directive2000/76/ECoftheEuropeanParliamentandofthecouncilontheincinerationofwaste:2000/76/EC;2000.

[55] YudovichYE,KetrisMP.Chlorineincoal:Areview.InternationalJournalofCoalGeology2006;67(1-2):127–44.

[56] CrossleyHE,EdwardsAH.TheanalysisofexternaldepositsfromboilerspartI.Generalremarksonthenatureofboilerdepositsandtheirexamination.JournaloftheSocietyofChemicalIndustry1946;65(9):251–4.

[57] TakedaM,UedaA,HashimotoH,YamadaT,SuzukiN,SatoMetal.Fateofthechlorineandfluorineinasub-bituminouscoalduringpyrolysisandgasification.Fuel2006;85(2):235–42.

[58] PunjakWA,ShadmanF.Aluminosilicatesorbentsforcontrolofalkalivaporsduringcoalcombustionandgasification.EnergyFuels1988;2(5):702–8.

[59] SalehSB,FlensborgJP,ShoulaifarTK,SárossyZ,HansenBB,EgsgaardHetal.ReleaseofChlorineandSulfurduringBiomassTorrefactionandPyrolysis.EnergyFuels2014;28(6):3738–46.

[60] WeiX,SchnellU,HeinK.Behaviourofgaseouschlorineandalkalimetalsduringbiomassthermalutilisation.Fuel2005;84(7-8):841–8.

[61] HamiltonJTG,McRobertsWC,KepplerF,KalinRM,HarperDB.ChlorideMethylationbyPlantPectin:AnEfficientEnvironmentallySignificantProcess.Science2003;301(5630):206–9.

67

[62] WoolcockPJ,BrownRC.Areviewofcleaningtechnologiesforbiomass-derivedsyngas.BiomassandBioenergy2013;52:54–84.

[63] JensenPA,FrandsenFJ,Dam-JohansenK,SanderB.ExperimentalInvestigationoftheTransformationandReleasetoGasPhaseofPotassiumandChlorineduringStrawPyrolysis.EnergyFuels2000;14(6):1280–5.

[64] KnudsenJN,JensenPA,LinW,FrandsenFJ,Dam-JohansenK.SulfurTransformationsduringThermalConversionofHerbaceousBiomass.EnergyFuels2004;18(3):810–9.

[65] KopetzK,WeberT,PalzW,ChartierP,FerreroGL(eds.).BiomassforEnergyandIndustry:C.A.R.M.E.N;1998.

[66] FullanaA,ConesaJA,FontR,SidhuS.FormationandDestructionofChlorinatedPollutantsduringSewageSludgeIncineration.Environ.Sci.Technol.2004;38(10):2953–8.

[67] ConesaJ.KineticsStudyofthePyrolysisofSewageSludge.WasteManagement&Research1997;15(3):293–305.

[68] SamoladaMC,ZabaniotouAA.Comparativeassessmentofmunicipalsewagesludgeincineration,gasificationandpyrolysisforasustainablesludge-to-energymanagementinGreece.Wastemanagement(NewYork,N.Y.)2014;34(2):411–20.

[69] MatsudaH,OzawaS,NaruseK,ItoK,KojimaY,YanaseT.KineticsofHClemissionfrominorganicchloridesinsimulatedmunicipalwastesincinerationconditions.ChemicalEngineeringScience2005;60(2):545–52.

[70] KassmanH.StrategiestoreducegaseousKClandchlorineindepositsduringcombustionofbiomassinfluidisedbedboilers.Zugl.:Göteborg,Univ.,Diss.,2012.Göteborg:ChalmersUniv.ofTechnology;2012.

[71] LiuWJ,LiWW,JiangH,YuHQ.FatesofChemicalElementsinBiomassduringItsPyrolysis.Chemicalreviews2017;117(9):6367–98.

[72] VorresKS(ed.).MineralMatterandAshinCoal.Washington,DC:AmericanChemicalSociety;1986.[73] TurnSQ,KinoshitaCM,IshimuraDM,HirakiTT,ZhouJ,MasutaniSM.AnExperimental

InvestigationofAlkaliRemovalfromBiomassProducerGasUsingaFixedBedofSolidSorbent.Ind.Eng.Chem.Res.2001;40(8):1960–7.

[74] LiuQ,ChmelySC,AbdoulmoumineN.BiomassTreatmentStrategiesforThermochemicalConversion.EnergyFuels2017;31(4):3525–36.

[75] AbdoulmoumineN,AdhikariS,KulkarniA,ChattanathanS.Areviewonbiomassgasificationsyngascleanup.AppliedEnergy2015;155:294–307.

[76] DouB-l,GaoJ-s,ShaX-z.AstudyonthereactionkineticsofHClremovalfromhigh-temperaturecoalgas.FuelProcessingTechnology2001;72(1):23–33.

[77] ShemwellB,LevendisYA,SimonsGA.Laboratorystudyonthehigh-temperaturecaptureofHClgasbydry-injectionofcalcium-basedsorbents.Chemosphere2001;42(5-7):785–96.

[78] KetovAN,LarikovVV,ShligerskiiAS.Influenceofthenatureandpreliminarytreatmentofthereagentonthedegreeofpurificationofgases.[Comparisonofchalk,limestone,calciumcarbonateandcalciumoxide,andcalciumoxide].J.Appl.Chem.USSR(Engl.Transl.);(UnitedStates)1968.

[79] WeinellCE,JensenPI,Dam-JohansenK,LivbjergH.HydrogenChlorideReactionwithLimeandLimestoneKineticsandsorptioncapacity.Ind.Eng.Chem.Res.1992;31:164–71.

[80] DuoW,SevillJPK,KirkbyNF,CliftR.Formationofproductlayersinsolid-gasreactionsforremovalofacidgases.ChemicalEngineeringScience1994;49(24):4429–42.

68

[81] DuoW,KirkbyN,SevilleJPK,KielJHA,BosA,DenUilH.KineticsofHClreactionswithCalciumandSodiumbasedsorbentsforIGCCfuelgascleaning.ChemicalEngineeringScience1996;51:2541-2546,

[82] WeinellCE,JensenPI,Dam-JohansenK,LivbjergH.Hydrogenchloridereactionwithlimeandlimestone:Kineticsandsorptioncapacity.Ind.Eng.Chem.Res.1992;31(1):164–71.

[83] DouB,GaoJ,BaekSW,ShaX.High-TemperatureHClRemovalwithSorbentsinaFixed-BedReactor.EnergyFuels2003;17(4):874–8.

[84] MyrenC,HörnellC,BjörnbomE,SjöströmK.Catalytictardecompositionofbiomasspyrolysisgaswithacombinationofdolomiteandsilica.BiomassandBioenergy2002;23(3):217–27.

[85] KarlssonHT,KlingsporJ,BjerleI.AdsorptionofHydrochloricAcidonSolidSlakedLimeforFlueGasCleanUp.JournaloftheAirPollutionControlAssociation1981;31(11):1177–80.

[86] QuickerP,RotheutM,NoelY,SchultenM,AthmannU.TreatingWTEPlantFlueGaseswithSodiumBicarbonate.Aachen,Germany:Power,Business&TechnologyfortheGlobalGenerationIndustrySince1882;2014.

[87] VerdoneN,FilippisPde.Thermodynamicbehaviourofsodiumandcalciumbasedsorbentsintheemissioncontrolofwasteincinerators.Chemosphere2004;54(7):975–85.

[88] VerdoneN,FilippisPde.Reactionkineticsofhydrogenchloridewithsodiumcarbonate.ChemicalEngineeringScience2006;61(22):7487–96.

[89] YassinL,LettieriP,SimonsSJR,GermanàA.StudyoftheProcessDesignandFlueGasTreatmentofanIndustrial-ScaleEnergy-from-WasteCombustionPlant.Ind.Eng.Chem.Res.2007;46(8):2648–56.

[90] KongY,WoodM.DryInjectIonofsoDIumsorbentsforDryInjectIonofSodiumSorbentsforAirpollutIoncontrol.NewYork.

[91] FellowsKT,PilatMJ.HCISorptionbyDryNaHCO3forIncineratorEmissionsControl.JournaloftheAir&WasteManagementAssociation2012;40(6):887–93.

[92] ChengS,QiaoY,HuangJ,CaoL,YangH,LiuHetal.Effectofalkaliadditiononsulfurtransformationduringlowtemperaturepyrolysisofsewagesludge.ProceedingsoftheCombustionInstitute2017;36(2):2253–61.

[93] WangX,SiJ,TanH,MaL,PourkashanianM,XuT.Nitrogen,Sulfur,andChlorineTransformationsduringthePyrolysisofStraw.EnergyFuels2010;24(9):5215–21.

[94] MorganoMT,LeiboldH,RichterF,StapfD,SeifertH.Screwpyrolysistechnologyforsewagesludgetreatment.WasteManagement2017.

[95] BridgwaterAV.Reviewoffastpyrolysisofbiomassandproductupgrading.BiomassandBioenergy2012;38:68–94.

[96] BundesministeriumsderJustiz,jurisGmbH.SiebzehnteVerordnungzurDurchführungdesBundesImmissionsschutzgesetzes(VerordnungüberdieVerbrennungunddieMitverbrennungvonAbfällen-17.BImSchV).Germany;2013.