IN DEGREE PROJECT ENVIRONMENTAL ENGINEERING,SECOND CYCLE, 30 CREDITS

, STOCKHOLM SWEDEN 2016

OPTIMIZED WTE CONVERSION OF MUNICIPAL SOLID WASTE IN SHANGHAI APPLYING THERMOCHEMICAL TECHNOLOGIES

SIYANG DAI

KTH ROYAL INSTITUTE OF TECHNOLOGYSCHOOL OF ARCHITECTURE AND THE BUILT ENVIRONMENT

OPTIMIZED WTE CONVERSION OF

MUNICIPAL SOLID WASTE IN SHANGHAI

APPLYING THERMOCHEMICAL

TECHNOLOGIES

Siyang Dai

Master Thesis Report KTH School of Architecture and the Built Environment

Sustainable Technology SE-100 44 STOCKHOLM

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AbstractThermochemical technologieshavebeenproveneffective in treatingmunicipal solidwaste (MSW)for many years. China, with a rapid increase of MSW, plans to implement more environmentalfriendlywaystotreatMSWthanlandfill,whichtreatsabout79%oftotalMSWcurrently.TheaimofthismasterthesiswastofindoutasuitablethermochemicaltechnologytotreatMSWinShanghai,China. Several different thermochemical technologies are compared in this thesis and plasmagasificationwasselectedforacasestudyinShanghai.Amodeloftheplasmagasificationplantwascreatedandanalysed.OtherprocessesintheplantincludingMSWpre-treatingandgascleaningarealsoproposed.Bycalculatingtheenergybalance,itisdemonstratedthatplasmatreatmentof1000ton/dayMSWwith70%moisturereachesanefficiencyof33.5%whenproducingelectricity,whichis higher than an incineration WtE plant (27 % maximum) and a gasification WtE plant (30 %maximum). Besides of the efficiency comparison, costs and environmental impacts of differenttechnologiesarealsocomparedinthispaper.TheresultindicatedthatgiventhecharacteristicsandmanagementsituationofMSW inShanghai,plasmagasification isabetterchoice to treatMSW inShanghai.

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TableofContentAbstract...................................................................................................................................................1

1. Introduction....................................................................................................................................3

AimandObjective...............................................................................................................................3

2. LiteratureReview............................................................................................................................4

Background.............................................................................................................................42.1.

2.1.1. MSWGenerationandComposition................................................................................4

2.1.2. MSWCollectioninShanghai...........................................................................................5

2.1.3. MSWTreatmentsinShanghai.........................................................................................5

2.1.4. EffortsofShanghaiGovernmentduringtheYear2013..................................................8

2.1.5. ConclusionsfortheBackgroundPart..............................................................................8

DifferentThermalTechnologiesforMSWTreatment.............................................................92.2.

2.2.1. Incineration.....................................................................................................................9

2.2.2. Gasification....................................................................................................................11

2.2.3. PlasmaGasification.......................................................................................................14

ConclusionsfromLiteratureReview.....................................................................................172.3.

3. Methodology.................................................................................................................................18

CaseStudy.............................................................................................................................183.1.

AnalysisandCalculation........................................................................................................183.2.

4. ResultsandDiscussion..................................................................................................................19

SelectingCaseSite.................................................................................................................194.1.

AModelCaseStudyofaGasificationPlant..........................................................................214.2.

4.2.1. ModelofMSWTreatmentPlantUsingPlasmaGasification.........................................21

4.2.2. WasteCharacteristics....................................................................................................22

4.2.3. EffluentGasesCleaningSystems...................................................................................23

4.2.4. SlagandTreatment.......................................................................................................24

4.2.5. MassBalanceCalculation..............................................................................................24

4.2.6. EnergyBalanceCalculation...........................................................................................26

EnergyBalance......................................................................................................................324.3.

FeasibilityStudy....................................................................................................................324.4.

5. Conclusions...................................................................................................................................36

6. Reference......................................................................................................................................37

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1. IntroductionChina,withitsrapideconomicgrowthandurbanexpansion,hasbeennoticeablyimprovingthelifestyle of its 1.3 billion citizens. However, it is also facing tremendous issues and unprecedentedchallenges in terms of producing colossal amounts ofwaste, as exemplified by the approximately178.6milliontonsofwasteproducedintheyear2014(NationalBureauofStatisticsofChina,2015).A major part of this waste, 79 % is landfilled, 20 % is incinerated while 1 % is composted. Alsoimportanttocommentisthattheamountofwasteincreaseswitharound4%everyyear(Huang,etal.,2013).Therefore,asustainablewastemanagementwillmostlikelyincludebothenergyrecovery(“WtEorwaste-to-energy”)andmaterialrecovery/recycling.Generally,thereisnoconflictbetweenmaterial recycling and energy recovery, because energy recovery process can convert the energyfrom the waste material into electricity or thermal energy. Countries with the most successfullyreduceddependencyonlandfill(1%andbelow)havethehighestrecyclingratesinEurope,achievingthisincombinationwithWtE(SwedishInstitute,2016).

AimandObjective

TheaimofthismasterprojectwastofromatechnicalperspectivedesignaWtEsysteminShanghaibased on a thermochemical conversion technology, e.g. gasification or incineration. The goal is toconvert theenergygained frommunicipal solidwaste intoelectricity.Choiceof technologywillbebasedonthefeedstockprovidedandutilizationofproductsgenerated,suchaspower,heat,coolingaswellaspossiblyotherenergycarriers.

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2. LiteratureReviewIn this part, a detailed description of the current situations of Municipal Solid Waste (MSW)management in Shanghai is described. Existing thermal technologies to treat MSW are alsopresentedinthispart.Finally,whyplasmagasificationischosenforthecasestudyisdiscussed.

Background2.1.

As a fast developing andmost industrialized city in China, Shanghai produced 7.42million tons ofmunicipalsolidwaste(MSW)in2014,whichismorethananyothercityinChina(Chinadaily,2015).With an average increase of 3.9% per year,MSW is becoming amajor environmental concern inShanghai(Huang,etal.,2013).Shanghai’sMunicipalGovernmenthasputaloteffortintreatingMSWduringtherecentyears.Theamountofwastethatrequiresanyfinaltreatmenthasbeenreducedby20%from0.82kgperpersonperdayin2011to0.66kgperpersonperday(People'sDaily,2015).

2.1.1. MSWGenerationandCompositionInShanghai,thecompositionofMSWisdominatedbyahighorganicandmoisturecontent,sincetheorganic garbage (especially the kitchen waste) in MSW occupied the highest proportion atapproximately60%.TheamountofMSWgeneratedinShanghaiinrecentyearsisshowninFigure1below.

Figure1:GenerationofMSWinShanghaifrom2005to2014(ShanghaiMunicipalStatisticsBureau,2014)

WasteComposition

InTable1below,allthecomponentsandtheirpercentageofMSWinShanghaiarelisted.

5,605,806,006,206,406,606,807,007,207,407,60

2005 2006 2007 2008 2009 2010 2011 2012 2013

Genera5onofMSWinShanghaifrom2005to2013

MSW(Mil.tons)

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Table1:MSWCompositioninShanghai,2013(Luo,2014)

Material PercentagePaper 9.57Plastic 15.71Wood 2.69Cloth 2.30KitchenWaste 58.37Fruit 6.60Metal 0.33Glass 2.53Stone 0.53CoalAsh 0.00HazardWaste 0.05Others 1.31

2.1.2. MSWCollectioninShanghaiInShanghai,thecollectionofMSWisdividedintofourgroups(Eastday.com,2012):

RecyclableWaste:includingpaper,plastic,glass,metalandcloth.

KitchenWaste:includingleftoverfood,bone,vegetableandfruitetc.

Hazardous Waste: including used battery, used bulb, used mercury thermometer and expiredmedicineetc.

OtherWaste:wastesthatnotmentionedabove.Forexample:toiletpaper,brick,potteryetc.

However,theseparationofwasteisarelativelynewapproachinShanghaiandthepublicawarenessofwasteclassificationisnotyetwidelyspread.TheparticipationrateoftheMSWclassifiedcollectionneeds to be improved. Sometimes garbage bins in residential areas have to rely on sanitationworkerstodosecond-timeclassification,whichleadstohighercostofwastetreatment.

Thecollection,transportationanddisposalfacilitiesinShanghaialsoneedtobestandardized.Therearealotofproblemsintheresidentialareas,whichareimplementingwasteseparation.Manyoftherecycling stations do not meet the regulatory requirements. Such as classified waste collectioncontainerismissing,theclassificationtagisnotobviousor ismissing.Besidesthat,residentialarearenovationwaste,bulkywastecollectionmanagementarenotstandardized,someoftheresidentialareas do not have special dump sites, the environment of some of the dump sites is poor andwithoutobvioustag.(Jing,2012)

2.1.3. MSWTreatmentsinShanghaiDuringtheyear2014,7.42milliontonsofMSWweregeneratedinShanghaiand7.06milliontonsofthemweretreated. Inwhich,3.29milliontonswent to landfill,2.39milliontonswere incinerated,0.37milliontonsweretreatedbycomposting,0.09milliontonswererecycled,0.88milliontonsof

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kitchen waste were treated, 0.037 million tons were treated by other methods. (ShanghaiEnvironmentalProtectionBureau,2015)

ThemostcommonwaystotreatMSWinChina(whichcanalsobeappliedtoShanghai)iscomposting,incinerationandlandfilling.

• Composting

The process of composting is relatively simple and suitable for wastes that contain higherorganic content. In European and American countries, the study of composting began earlierandithasreachedthelevelofindustrialapplications.

However,compostingisnotwidelyusedinChina.SomeresearchinstitutionsandenterprisesinChina have already started working in this area, and have made certain achievements infundamental study and application study of composting (Wei, et al., 2000). In the wastesituationinChina,thecontentofperishableorganicmatterisrelativelyhigh.Sotechnically,theapplication of composting technology can achieve a better treatment effect. But thedisadvantage of composting is that it can not handle non-decaying organic and inorganicmatters.Therefore,thevolumereductionanddetoxificationlevel is low.Alsotheresultoftheapplication of composting in China being not satisfying is due to low efficiency of sourceseparation, poor quality of composting fertilizer and small market demand (Baidu, 2014).Accordingtoastudyby(Chen,etal.,2010),duetothedecliningofthedemandofcomposting,thetreatmentcapacityin2006inChinadecreasedtoabout9000tonsperdayor37%ofthatin2001.Andbecauseoftheproblemsofthesourceseparating,theexistinghazardousmaterialsinthe MSW in China can also contaminate the finished compost. It is likely that much of thecontaminationhasalreadyaffectedtheorganicfractionbeforetheMSWistreated(Hoornweg,etal.,1999).

• Incineration

Incineration technology was firstly introduced to China in 1980’s, and developed rapidly in1990’s.AccordingtoChina’s12th5-yearplan,bytheendof2015,thereshouldbeat least300incinerationplantsinChina,whichcandealwith310,000tonsofwasteperdayintotal,whichconsistsof25.6%ofthetotalamountofwastegeneratedinChinaperday(around1.21milliontonsperday).Besidesthat,bytheendof2015,incinerationshouldtreat35%(48%intheeastcoastpartofChina)ofalltheMSWinChinesecities.(TheCentralPeople'sGovernmentofChina,2012)

However,duringthepastseveralyears,someexistingandplannedincinerationplantsreceivedstrongprotests fromthe residentsnearby,due to the lowemissionstandardsof thoseplants,poormanagement system, poor government supervision and no public information. Also theexceedingemissionofdioxinhascaughtmanyattentionsinthesociety.Thisresultedinaseriesof not-in-my-back-yard protests against the construction of new incineration plants in somecities over the past few years. For example, inMay 2014, thousands of people in Hangzhouprotestedagainstthebuildingofalargeincinerationplant,whichwastobelocatedinavillage25 kilometers away from the city. The capacity of the incineration plant was designed to be5,600 tons per day, which could be used to treat about half of MSW generated daily in

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Hangzhou.Buttheresidentsfearedthatsuchlargecapacitymightcauseseveredamagetotheenvironmentandthusputtheirhealthatrisk.Asaresult,thegovernmentofHangzhouhadtopostponetheconstructionoftheincinerationplant(Cao&Wang,2014).Anotherproblemwithincineration plants in China is the handling of wastes generated during the incinerationprocesses. For example slags and fly ashes.Most of the incineration slags are used tomakebricks for construction, but effective ways to deal with fly ashes have not yet been found.(People.cn,2015)

On theother side, somenewlybuilt incinerationplantsaredoingbetterbynotonlypersuing“environmentalfriendly”but“socialfriendly”aswell.Theyhavehigheremissionstandardsandthe real time data of incineration process can be found online. For example, Gaoantunincineration plant in Beijing opens to public visitors two days per week. But to meet higheremission standards means more investments. Without subsidy from the government, theelectricitygeneratedfromincinerationplantsismuchmoreexpensivecomparetotheelectricitygenerated fromcoal-firedpowerplant inChina (Li, 2013).Although thecostof incineration ishighercomparing to landfilling, it ismoreenvironmental friendly.Thecostandenvironmentalimpactcomparisonofdifferenttechnologieswillbediscussedinsection4.4.

• Landfilling

LandfillingisthesimplestwaytotreatMSWbyoperation.Intheyearof2012,72%ofthetotalamountsofMSWinChinaweretreatedbylandfilling.(Dai,2014)LandfillingisusedtohandleallkindsofwasteinChina.However,itoccupiesalargearea.Inthemeantime,thereisachanceofsecondarypollution.Suchastheleachateofwastecancontaminategroundwaterandsoil;themethanegasproducedbywastefermentationcancausefireandexplosion;andtheemissionsofthemethanegasintotheatmospherecancausethegreenhouseeffect.SomecitiesinChinahavealreadybeenawareof thisproblem.Theyestablishedsomehigh-levelsanitary landfillingsites,whichsolvedtheproblemofsecondarypollution.However, theconstruction investmentand operating costs are rather high. And themost critical part is the limited capacity of thelandfillingsite.Onceaparticularsiteisfull,newinvestmentshallbemadeandnewlandwillbeoccupied.(Baidu,2014)

TheadvantagesanddisadvantagesofthecurrentMSWtreatingmethodsinShanghaiisconcludedinTable2.

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Table2:ProsandconsofthecurrentMSWtreatingmethodsinShanghai

Advantages DisadvantagesLandfilling 1. Lowinvestment;

2. Highcapacity;3. FastspeedofdisposingMSW.

1. Occupiesalargearea;2. Leachate of waste can contaminate

groundwater and soil, causingsecondarypollution;

3. Theemissionsofthemethanegasintothe atmosphere can cause thegreenhouseeffect.

Composting 1. Onlyoccupiesasmallarea;2. Low investment and good

economic benefit andenvironmentalbenefit.

1. Buildingcompostingplantnearcitycanaffectresidencesnearby(smell,dust);

2. The market demand is not high sincefertilizerischeaperandeasiertouse;

3. TheheavymetalorhazardouswasteinMSWmaycontaminatethecompost.

Incineration 1. Onlyoccupiesasmallarea;2. Highwastevolumereduction;3. Less emissions to soil and

water;4. It won’t be affected by

weather.

1. High investment comparing to theothertwomethods;

2. TheheatingvalueoftheMSWcannotbetoolow;

3. Maycausepollution(e.g.dioxin)totheenvironment.

2.1.4. EffortsofShanghaiGovernmentduringtheYear2013AccordingtoShanghaiEnvironmentalBulletingof2014(ShanghaiEnvironmentalProtectionBureau,2014),thegovernmenthasmadealotofeffortsconcerningtreatmentofMSWintheyear2013:

• Phase-one construction of Laogang Centre for Utilization of Renewable Source of Energy wasfinished;

• TheprojectofpipelinesforemergencydischargeofpercolatingwaterinLaogangandtheprojectof inlandwaterway in Laogangwere completed;Constructionof TianmaandFengxianCentersforUtilizationofRenewableSourceofEnergyhavebeeninitiated;

• The expansion project of the platform for regional collection of waste in Jinqiao ExportProcessingZonewasaccomplishedso thataprofessional transport systemofhazardouswastewasestablished.

2.1.5. ConclusionsfortheBackgroundPartWiththefastdevelopmentofChinainrecentyears,theamountofMSWalsoincreasesrapidlyoverthe years. Shanghai, the financial centreofChina, is facinga seriouswastemanagementproblem.How to solve this problem and reduce the damage dealt to the environment at the same time isbecomingapriority issue.With thevacant land inShanghaibecomingmoreandmore limited, thegovernment is encouraging applying thermal technologies instead of landfilling, which is thedominant method nowadays. Different thermal technologies and their pros and cons will bediscussedinthefollowingsection.

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DifferentThermalTechnologiesforMSWTreatment2.2.

Themostcommonthreethermaltechnologiesforwastetreatmentare: incineration,pyrolysis,andgasification.ThedifferencesofthethreemethodscanbeseeninFigure2:

Figure2:DifferencesbetweenPyrolysis,GasificationandIncineration(EMIS,2010)

Incineration,gasificationandanewtechnology:plasmagasificationwillbeintroducedanddiscussedinthissection.Pyrolysiswillnotbediscussedbecauseit ismoresuitablefortreatingwasteplasticsandtiresratherthantreatingofMSW.

2.2.1. IncinerationIncineration, the combustionof organicmaterial, such aswastewith energy recovery, is themostcommon WtE implementation. Incineration transforms heterogeneous wastes into morehomogeneous residues (flue gas, fly ash, and bottom ash)with the primary benefit of substantialreductionofthewaste’sweight(upto75%)andvolume(upto90%)(Cheng&Hu,2010).

Duringincineration,MSWiscombustedinaspeciallydesignedchamberathightemperature(>850°C).Thesolidresiduescanbesenttolandfillsorcleanedupandusedoff-siteforcertainconstructionpurposes(Cheng&Hu,2010). Mostmodernincinerationplantscombineheatrecoverytogetherwithpowergenerationtorecovertheheatenergyinthewaste(EnvironmentalProtectionDepartmentofHongKong,2015).

A typical incineration flow chart can be seen in Figure 3 below (Environmental ProtectionDepartmentofHongKong,2015):

Combustion-Wasteiscontinuouslyfedintothefurnacebyacrane.Thewasteiscombustedinthefurnaceatahightemperatureformorethan2seconds,whereairiscontinuouslysuppliedtoensurecomplete combustion, preventing formation of carbon monoxide. The temperature window andresidencetimeisalsocontrolledtominimizedioxinformation.

Boiler/steamturbine–Afterthecombustionprocess,theheatproducedisusedtogeneratesteamintheboiler.Thenthesteamisusedtodriveaturbinewhichisdesignedtogenerateelectricity.Theheatcanalsobeusedtoprovideheattootherfacilities,e.g.heatingnearbybuildingsinthewinter.

Exhaustgascleaning-Theexhaustgasfromtheboilerneedstobecleanedsoastopreventpollutionto theenvironment.Theexhaustgasmaycontainacidicgases (sulphuroxides,hydrogenchloride),heavy metal, dioxins, dust and fine particulates, and nitrogen oxides. The gas cleaning systemthereforeincludesseveralstepstoremoveallpossiblepollutions.

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Ashresidues-Theashresiduesfromincinerationgenerallyincludebottomashfromthefurnaceandflyashfromtheexhaustgascleaningsystem.Thebottomashcanbedisposedatlandfillsites.Itmayalsobeusedasconstructionmaterials.Flyash is typicallydisposedat landfill sites. (EnvironmentalProtectionDepartmentofHongKong,2015)

Figure3:TypicalIncinerationFlowChart(EnvironmentalProtectionDepartmentofHongKong,2015)

Theheatproducedinincinerationcanbeutilizedinthefollowingways(DepartmentforEnvironment,Food&RuralAffairsofUK,2013):

• GenerationofPower(electricity),• GenerationofHeat,• GenerationofHeatandPower(CombinedHeatandPower)

ThedifferentefficiencyanduseofthethreemethodsmentionedabovecanbeshowninTable3.

Table3:ExamplesofEnergyEfficiencyforIncineration(DepartmentforEnvironment,Food&RuralAffairsofUK,2013)

Outputs Efficiency Use

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Heat Only Up to 80-90 % thermal efficiency Local district heating for buildings (residential, commercial) and or for industrial processes.

Electricity 14 %-27 % Can be supplied to national grid for sale and distribution.

Heat and Power Dependent on specific demand for heat and power. Combination of above.

FromthetableaboveitcanbeseenthatitismoreefficientforanincinerationplanttorecoverheatfromMSWcomparedtoelectricity.However,currentlocalheatdistributionforbuildingsinShanghaiisnotviable,becausemostofthebuildingsinShanghaidonotusedistrictheatingasindoorheatingmethod.Neither is thegovernmentplanningtodistributeheat forbuildings. (People.cn,2013)Theresidences in Shanghai typically use air conditioneror electrical heater as indoorheatingmethodswhenitiscold.Bothmethodsaredrivenbyelectricity.SotreatingMSWwithincinerationtechnologyinShanghaiisnotanoptimizedoption.

2.2.2. GasificationTheory

Ingasification,oxygen isaddedbut theamountsarenot sufficient toallow the full combustion tooccur.Thetemperaturesoftheprocessaretypicallyabove650°C.Themainproductofgasificationisraw gas, which contains carbon monoxide, hydrogen and methane, carbon dioxide, H2O, ashes,hydrocarbonsandinorganicgasimpuritiessuchasHCN,H2S,COSandNH3.Thegasnetcalorificvalue(NCV) is typically between 4 -10 MJ/Nm3, depending on the technology and gasifying agent (air,oxygen, CO2, H2O or combinations of these) applied. The raw gas can be combusted to produceelectricityor furtherprocessedtomanufacturechemicals, fertilizers, liquidfuels,substitutenaturalgas (SNG), or hydrogen (Department for Environment Food and Rural Affairs of UK, 2013). Thecomposition of waste is important to gasification, because gasification can only convert organicwastes.Waste gasification will therefore bemost successful in communities where there is goodrecycling practice recycling non-combustible and combustible wastes (Zafar, 2009). A typicalgasificationprocessisshowninFigure4below:

• Thefeedstocksaresenttothereactorafterpre-treatments(shredding,dryingetc.)ifneeded.• Gasification is conducted using equipment known as "gasifiers". At a high temperature

(usually above650 °C) andwith a controlled amountof oxygen supply, the feedstocks areconvertedtotherawgas.

• Theslagsgeneratedduringthegasificationprocessarecollectedatthebottomofthegasifierandthentreatedproperly(e.g.landfill).

• Therawgasafterthegasifierneedstobecleanedbecauseitcontainsimpurities.Dependingonthefeedstock,itmaycontainacidgas(e.g.sulfur,nitrogen),particulatematter,tarandsoon.

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• After that, the raw gas can be used to generate electricity, produce combined heat andpower(CHP),orproducesynthesisgas(syngas).

Figure4:TheGasificationProcess(GasificationTechnologiesCouncil,2015)

Technology

Currently, there are several types of gasifiers that are available for commercial use: fixed bed,fluidizedbed,entrainedflowandplasma.

FixedBedGasifier�

Therearemainly twotypesof fixedbedgasifiers:counter-currentgasifier (updraft)andco-currentgasifier(downdraft).TheirreactorsareshowninFigure5.

The counter-current gasifier (updraft) is the simplest and oldest kind of gasifier. In this type ofgasifier,aircomesinatthebottomandproductgasgoesoutatthetopofthegasifier.Thefuelisfedatthetopofthegasifier.DifferentreactionzonesinthegasifierareshownintheleftsideofFigure5.The feedstock and the reactive material flow in opposite directions in counter-current gasifier.(Enggcyclopedia,2015)

Themajoradvantagesof this typeofgasifierare its simplicity,highcharcoalburnoutand internalheatexchangethatleadtolowtemperatureoftheproductgasandhighefficiencyoftheequipment.Major drawbacks result from the possibility of "channelling" in the equipment,which can lead tooxygen break-through and dangerous, explosive situations and the necessity to install automaticmovinggrate.(Enggcyclopedia,2015)

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Figure5:FixedBedGasifiers(Warnecke,2000)

In the co-current gasifier (downdraft), the feedstock and the reactive material flow in the samedirection.Thefuelisalsofedatthetopofthegasifierbuttheairflowisinthedownwarddirection.DifferentreactionzonesinthegasifierareshownintherightsideofFigure5.

Themainadvantageofdowndraftgasifieristhattheamountoftarintheproductgasismuchlowerthan updraft. Disadvantages are: it is rather inflexible in utilizing different feedstocks; low densityfeedstock gives rise to flowproblems andexcessivepressuredrop; it gives lower efficiency, sincethereisnoprovisioninternalexchangecomparetoupdraftgasifier;theproductstreamalsohaslowcalorificvalue.(Enggcyclopedia,2015)

FluidizedBedGasifier:

There are mainly two types of fluidized bed gasifiers as well: bubbling fluidized bed (BFB), andcirculatingfluidizedbed(CFB).TheirreactorsareshowninFigure6.

Figure6:FluidizedBedGasifiers(Warnecke,2000)

InaBubblingFluidizedBed (BFB),thebedmaterial ismadeof solidparticlesoftena sandmaterialsuchassilicasand.Thegasvelocityshouldbehighenoughinordertoliftthesolidparticles.Sothe

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bedisexpendedandcausedtobubblelikealiquid.Typically,thechamberofthereactoroftheBFBisdesignedinacylindricalorrectangularshape.Inthiswaythecontactbetweenthegasandsolidscanhelp drying and size reduction. Typical desiredoperating temperatures of BFB range from900° to1000°C.(Angelova,etal.,2014)

Acirculatingfluidizedbed(CFB)isdifferentiatedfromabubblingfluidbedinthatthereisnodistinctseparationbetweenthedensesolidszoneandthedilutesolidszone.Someoftheparticlesareblownoutofthebed.Acollectorcanbeimplementedinordertorecycletheparticlesandreturnthemintothe bed. The capacity to process different feedstock with varying compositions and moisturecontentsisamajoradvantageofCFB.(Angelova,etal.,2014)

ThermalCapacitiesandChallenge

For treating MSW, the thermal capacity of different gasifiers also needs to be taken in toconsideration. Table 4 shows the thermal capacity ranges for the four types of gasifiers discussedabove.

Table4:ThermalCapacityofDifferentGasifiers(Zafar,2009)

Gasifier FuelCapacityDowndraft 1kW–1MWUpdraft 1.1MW–12MWBubblingfluidizedbed 1MW–50MWCirculatingfluidizedbed 10MW–200MW

Akeyissuewithgasificationistheproblemrelatedtotheformationoftar.Thedepositionoftarscancausemanyissuesforoperatingforexampleblockage.Manyplantfailuresandinefficienciesatsomepilotandcommercialscalefacilitieswerealsocausedbytheformationoftar. Inordertosolvethisproblem,someprocesseswhicharesometimesreferredtoas‘rawgascleanup’or‘polishing’maybeappliedto‘crack’thetarsandcleanuptherawgasafterthegasifierandpriortotheenergyrecoverysystems. These processes could increase the energy recovery efficiency of gasification. The othermain product from the gasification process is a solid residue of non-combustible materials (ash)whichcontainsarelativelylowlevelofcarbon.(DepartmentforEnvironmentFoodandRuralAffairsofUK,2013)Recently,anewtypeofgasificationtechnologycalledplasmagasificationisshowingthepotentialthatitcanproduceanotaroraverylowtarcontainingrawgas(Talebi&Goethem,2014).It can alsohandle awide rangeofwasteswhich is suitable for Shanghai due to its relatively poorwasteclassification.Introductiontoplasmagasificationisinthefollowingsubchapter.

2.2.3. PlasmaGasificationPlasmagasification is a relativelynew technologywhich canbeused to convert carbon-containingmaterials intofuels (rawgas)whichcanbeusedtogeneratepowerorsomeotherusefulproducts(e.g.synthesisgas).Unlikeconventionalgasification,inplasmagasificationthewasteisheatedwithaplasmaarc(upto10,000°C)tocreaterawgasandvitrifiedslag.(Dodge,2009)

Plasma is an ionized gas that is formedwhen an electrical discharge passes through a gas.Whenappliedinagasificationplant,insidethegasifier,plasmatorchesandarcsgenerateintenseheat.This

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extreme heat maintains the gasification reactions, which break apart the chemical bonds of thefeedstockandconvertsthemtoarawgas.Thehightemperaturecanevenincreasetherateofthereaction,makinggasificationmoreefficient.(GasificationTechnologiesCouncil,2015)

Figure7:SketchofaPlasmaGasifier(Westinghouse,2015)

GasTreatmentaftertheGasifier

Rawgasiscooleddownafterthegasifier.Beforeenteringthegasturbine,severalstepsneedtobeappliedtocleantherawgas.Gascleaningstepsshouldbebasedonthesourceandcompositionofthewaste.Therawgasmainlycontains:H2,CO,CO2,H2O,andN2andbasedonthefeedstockitmaycontain:HCL,H2S,NOx, SOx, heavymetal etc. TheAlterNRG companyprovides anexampleof gascleaningprocessforatypicalMSWtreatmentplant(AlterNRG,2015):Rawgasiscooledthroughacaustic venturi quench scrubber and scrubber system and then it goes to a wet electrostaticprecipitator (WESP).TheventuriquenchandWESPcanserveapurpose toremovetheparticulatematterintherawgasandalsoconvertchlorinewithintherawgasintosaltaswell.Afterthat,theraw gas goes through different gas cleaning processes in order to remove chlorine, sulphur, lead,cadmium,zincandmercury.

WasteTreatmentaftertheGasifier

Inorganicmaterialsinthefeedstockaremeltedinthegasifier.Duetodifferencesindensity,theyareeasilyseparatedintotwolayers:ametalandaglassysilicatelayer.Themetallayercanberecycledasmetal alloys, while the glassy product can be used in different commercial applications, includingconcreteaggregate,roadbedconstructionetc.(PEATInternational,2008)

ExamplesofFacilitiesUsingPlasmaGasificationTechnology

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An example of WtE facility, using plasma gasification, is the EcoValley plasma gasification facilitylocatedinUtashinai,JapanontheislandofHokkaido.Thefacilityprocessedupto220tons-perdayofMSWorupto165tonsperdayofa50/50mixtureofMSWandautoshredderresidue.Until2010,ithadbeensuccessfullyprocessingMSWwithplasmaforoversevenyears.Aprocessflowpictureofthe facility is shown in thepicturebelow. (Willis, et al., 2010)Theplantwas closeddue to lackoffeedstock(lossoflongtermfeedcontracts).(WestinghousePlasmaCorp.,2015)

In addition, two large renewable energy plants (approximately 50 MW per plant), using plasmagasificationtechnology,areunderconstructioninTeesValley,UK.(AirProductsandChemicals,Inc.,2015)

Figure8:ProcessFlowFigureforEcoVallyMSWandASRGasificationFacility

AdvantagesofPlasmaGasification

The main advantages of plasma technologies for waste treatment are (Gasification TechnologiesCouncil,2015):

• Itunlocksthegreatestamountofenergyfromwaste.

• Feedstocks can be mixed, such as municipal solid waste, biomass, tires, hazardous waste,

andautoshredderwaste.

• Itdoesnotgeneratemethane,apotentgreenhousegas.

• Itisnotincinerationandthereforedoesnotproduceleachablebottomashorflyash.

• Itreducestheneedforlandfillingofwaste.

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• It produces raw gas, which can be combusted in a gas turbine or reciprocating to produce

electricity or further processed into chemicals, fertilizers, or transportation fuels—thereby

reducingtheneedforvirginmaterialstoproducetheseproducts.

• Ithaslowenvironmentalemissions.

• Comparingtotraditionalgasification,itdoesn’tgeneratetarduringthegasificationprocess.

DisadvantagesofPlasmaGasification:

• Ithasnotbeenprovedinlargescaleplant,sotheremightbesomedrawbacksthatarenotyet

known.

• Theinitialinvestmentisveryhigh.

• Plasmatorchesconsumealotofpower.

ConclusionsfromLiteratureReview2.3.

Fromthediscussionabove,itcanbeseenthatamongthecurrentexistingMSWtreatmentmethodsinShanghai,incinerationismoresuitablethanlandfillingandcomposting.Compostinghastoosmallmarket in Shanghai and the MSW in Shanghai contains hazardous waste and many inorganicmaterials.Landfillingcausesa lotofenvironmentalproblemssuchasreleaseofmethaneandtoxicgas,toxinsleakingintosoilandgroundwatercausingcontamination,anditoccupiesalargeamountoflandandwilleventuallyreachtheircapacityinthenearbyfuture,implyingnewsitestobeused.

However, comparing toother thermal technologies likedifferent typesof gasification, incinerationhasmanydrawbackssuchastheformationofdioxinandtoxicashesthatstillcanendupinlandfills.SincethecitizensinShanghaiprotestedincinerationplantsmanytimes, italsohassocialproblems.Moredetailedcomparisonsofdifferentthermaltechnologiesaredoneinsection4.4ofthispaper.

Plasma gasification hasmany advantages over traditional gasification: it does not have tar-relatedproblemsandthefuelcanbemoreflexible.SincethesortingofMSWinShanghaiisnotmanagedsowell,itmaycontainhazardouswasteandmanyinorganicmaterials.ItwouldthereforebebettertochooseplasmagasificationtotreatMSWinShanghai,sincetheashesisenvironmentallyfriendlyandcanbeutilized.

SobasedonthecharacteristicsandthesituationofmanagementofMSWinShanghai,aWtEfacilityusing plasma gasification technology is a better option to treat MSW. A detailed case study andanalysisarediscussedinChapter4ofthispaper.

18

3. MethodologyInthissection,themethodsusedinthethesisarepresented.

CaseStudy3.1.

In this paper, a case studyof Shanghai is carriedout. Theproperpositionof thewaste treatmentplantisselected.Amodeloftheplantisalsocreated,aswellasabackgroundoftheMSWstatusinShanghai isdescribed.Suchacasestudy isaneasymethodforthereadertounderstand.ThedatausedincasestudyaregainedfromliteraturereviewthroughScopusdatabasefromKTHB,aChinesepaperdatabasesearchengine,interviewsduringastudytriptoShanghai,andInternetsearchengine.

DuringthestudytriptoShanghai,interviewswerecarriedoutwithProf.YonghaoLuofromInstituteof Thermal Energy Engineering of Shanghai Jiaotong University, Prof. Shanping Chen: CTO ofShanghai Institute for Design and Research in Environmental Engineering, and Prof. Jingcheng Xu:vicedeanofCollegeofEnvironmentalScience&EngineeringofTongjiUniversity,respectively.Theyprovided someup-to-datedataof theMSWofShanghaiaswell as insightsof thedevelopmentofwastetreatmentinShanghai.

AnalysisandCalculation3.2.

BasedontheultimateanalysisoftheMSWinShanghai,thegascompositionaftertheplasmagasifieris predicted and analysed using mass balance. The heat exchange process is calculated by theequationofspecificheatandthetableofsuperheatedvapourpropertiesforsteam.

The energy cost and gain from different processes of the gasification plant is calculated. Energybalance gives the reader a clear idea of the energy flow and the energy input and output of thesystemaswell.Basedontheenergybalance,energyefficiencyoftheplantisalsocalculated.

Besides that, comparison among incineration, traditional gasification, plasma gasification, andlandfillingintermsofcost,efficiency,andenvironmentalimpactsarealsoanalysed.

19

4. ResultsandDiscussionInthispart,acasestudyiscarriedouttofindoutwhetheritissuitableforaplasmagasificationplanttobebuiltinShanghai.

SelectingCaseSite4.1.

Casesitewasselectedaccordingtothepopulationdensityandexistingwastetreatmentplants.

PopulationdensityinShanghai

Table5:PopulationDensityinShanghai(ShanghaiMunicipalStatisticsBureau,2011)

District Population(tenthousandpeople)

Percentageoftotal

population%

Totalarea(square

kilometer)

Populationdensity(people/square

kilometer)Thewholecity 2301.92 100 6340.50 3631Urbandistricts 698.63 30.4 289.44 24137

HunagpuDistrict

42.99 1.9 12.41 34641

LuwanDistrict 24.88 1.1 8.05 30907XuhuiDistrict 108.51 4.7 54.76 19816ChangningDistrict

69.06 3.0 38.30 18031

Jing’anDistrict 24.68 1.1 7.62 32388PutuoDistrict 128.89 5.6 54.83 23507ZhabeiDistrict 83.05 3.6 29.26 28383

HongkouDistrict

85.25 3.7 23.48 36307

YangpuDistrict 131.32 5.7 60.73 21624Suburbandistricts

1084.99 47.1 2316.35 4684

MinhangDistrict

242.94 10.5 370.75 6553

BaoshanDistrict

190.49 8.3 270.99 7029

JiadingDistrict 147.12 6.4 464.20 3169PudongNew

Area 504.44 21.9 1210.41 4168

Outersuburbandistricts

518.30 22.5 3734.71 1388

JinshanDistrict 73.24 3.2 586.05 1250SongjiangDistrict

158.24 6.9 605.64 2613

QingpuDistrict 108.10 4.7 670.14 1613FengxianDistrict

108.35 4.7 687.39 1576

ChongmingDistrict

70.37 3.0 1185.49 594

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LocationofPlant

According to Table 5, the population density is far less in suburban districts. The distribution ofdifferentdistricts inShanghai isshowninFigure9.Therearetwowaste incinerationplantsalreadyexisting inPudongNewDistrict(intheeastoftheurbanarea)andJiadingDistrict(inthesuburbanareanorthwesttotheurbanareaandveryclosetotheurbandistrictPutuo),respectively.There isalso a huge landfill site called Laogang located in the southeast of Pudong New District near thePudongInternationalAirport.

ThenewplantshouldbelocatedinMinhangDistrict(markedinbluecolourinTable5).Becausetheurban districts are too crowded in Shanghai, and since the existing twoMSW incineration plants(Jiangqiao in JiadingDistrictandYuqiao inPudongNewDistrict)havereceivedmanyprotests fromthe nearby neighborhoods because of bad smell, etc. Since most of the wastes in Shanghai aregeneratedintheurbanarea,aplantlocalizedinthesuburbareabutnottoofarfromthecitycenter(urbanarea)couldbeagoodchoiceof thenewplant.Consideringthe locationof theexistingtwoMSWincinerationplants,thenewplantshouldlocateintheareatothesouthwestofurbandistricts.Comcluively,MinhangDistrictisproposedasasuitablesiteforaplant.

Figure9:MapofShanghaiDistricts(ChinaTouristMaps,2013)

21

ThelocationsoftheexistingthreeMSWtreatingplantsinShanghai(Jiangqiao,Yuqiao,andLaogang)aremarkedinredinFigure9.TheproposedlocationofthenewplantismarkedinblueinFigure9.

AModelCaseStudyofaGasificationPlant4.2.

Inthispart,amodelofagasificationplantisbuilt.Basedonthecharacteristicsandultimateanalysisofthewaste inShanghai,massbalance isusedtopredicttherawgascomposition.Furthermore,agascleaningsystemisproposedtoremoveflyash,particlesandacidgasintherawgas.Lastbutnotleast, power consumed or gained in different processes is calculated in order to do the energybalanceinSection4.3.

4.2.1. ModelofMSWTreatmentPlantUsingPlasmaGasification

Gasifier

GasCleaningUnit

Combustionchamberofgasturbine

HeatexchangerHeatrecoveryDryingShreddingMSW

Slag

Gasturbine

Steamturbine

ElectricityHeatrecovery

Baghouse filter

Waterquencher

scrubberScrubber

including

Figure10:AFlowChartModelofaPlasmaGasificationPlantinShanghai

Theflowchartmodelofaplasmagasificationplant isshowninFigure10.MSWaretransportedtotheplantandshreddedtosmallersizesothatit ismoresuitableforgasificationreaction.Thenthedrying process will reduce the moisture content from 70 % to 30 %. After that, the gasificationprocessoccurswherethefeedstockisconvertedtorawgas.Theinorganicportionofthefeedstockexits through a tap hole at the bottom of the gasifier as slag. The raw gas goes through a heatexchangerand is cooleddown from1000oC to150oC.The rawgas is thensent to thegascleaningunitwhichconsistsofabaghousefilter,waterquencher,andascrubber.Aftertherawgasiscleaned,it iscombusted inagas turbine.Acombinedcycle isusedtoconvert theenergyof therawgas toelectricity.

TheinputofMSWis1000tpd,whichisabout42tonsperhour.Detailsofdifferentprocessesandwhytheyarechosenaredescribedinthefollowingsubsections.

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4.2.2. WasteCharacteristicsIn this part, the characteristics of theMSW in Shanghai are described and discussed such as themoisturecontent,particlesize,ultimateanalysis,andthelowerheatingvalue.

PercentageofmoistureinMSW

According toa studyby (Sun,etal.,2008) thepercentageofmoisture inMSW inShanghai is veryhighasshowninTable6below.Soadryingprocessshouldbeaddedasapre-processbeforetreatingoftheMSWinordertoreducethemoistureto30%.

Table6:ThepercentageofmoistureinMSWinShanghai(Sun,etal.,2008)

Moisture percentage of organic MSW

Moisture percentage of MSW except organics

MSW with particle size from 40 to 120mm

84 60.1

MSW with particle size from 8 to 40mm

76.7 NA

ParticlesizesofMSW

Thestudyby(Sun,etal.,2008)alsoestimatedtheparticlesizeofMSWinShanghaibyexperiments.TheresultisshowninTable7.

Table7:SizeofMSWinShanghai(Sun,etal.,2008)

MSW’s Particle Size Percentage of MSW Larger than 120mm 15.7 40 to 120mm 43.5 8 to 40mm 35 Smaller than 8mm 5.8

According to a report by (Willis, et al., 2010), the EcoValleyplasmagasificationplant inUtashinai,Japanusedashreddertoreducethesizeofthefeedstockto2.5incheswhichequalsto63.5mm.SotheMSWinShanghaineedtobeshreddedaswellbeforetheyaretreated.

UltimateanalysisofMSW

Accordingtoastudyby(Zhou,etal.,2014),theultimateanalysisofMSWinShanghaiintheyearof2005canbeseeninTable8,andthelowerheatingvalueofthewasteis6650kJ/kg.

Table8:UltimateAnalysisofMSWinShanghai,2005

C (%) 55.75 H (%) 7.54 O (%) 34.57 N (%) 1.87 S (%) 0.27

23

In1kgofMSW,theamountofelementsandtheirmolescanthenbecalculatedinTable9.

Table9:TheNumberofMolesofDifferentElementsin1kgMSWinShanghai

1 kg MSW in Shanghai C 557.5g 46.46 mole H 75.4g 75.4 mole O 345.7g 21.6 mole N 18.7g 1.34 mole S 2.7g 0.084 mole

Sincesulphuraccountsforonlyaverysmallproportionandwillberemovedduringthegascleaningprocess,itwillbeignoredinthecalculationsofmassbalancelater.

4.2.3. EffluentGasesCleaningSystems

Gasifier GasCleaningUnit CombustionChamber

BaghouseFilter

WaterQuencher scrubberScrubber

CleanedRawGasHeatExchangerRawGas

HeatRecovery

T=1000oC T=150oC

T=150oC T=30oCT=150oC T=30oC

T=30oC

Figure11FlowChartoftheGasCleaningSystem

From Table 8, it can be seen that theMSW in Shanghai contain sulphur and nitrogen. After thegasifier, sulphur may form SOx in the raw gas; the nitrogen from waste and air added in thegasificationprocessmayformNOxintherawgas.Theseacidgasescancausecorrosionanderosioninthesystem.Moreover,ifNOxandSOxarenotremovedinthegascleaningandareemittedtotheatmosphere,theycanbecapturedbymoisturetoformacidrain.Acidraincanseverelyaffectcertainecosystems, some part of our economy as well as public health (U.S. EPA, 1999). There are alsoparticulatesintherawgas,whichalsoneedtoberemoved.Particulatesthatare10micrometersindiameterorsmallercancausehealthproblems,becausethoseparticlescanpassthroughthethroatandnoseandenterthelungs.Onceinhaled,theseparticlescanaffecttheheartandlungsandcauseserioushealtheffects(U.S.EPA,2015).

Thegascleaningsystemseliminateacidicgasesandsuspendedparticulatespriortothegasenteringthecombustionchamberofthegasturbine.Forthispurpose,abaghousefilter,waterquencher,andscrubberareinstalledinseries.

Aftersteamgenerator,thetemperatureoftherawgasdropsfrom1000oCtoaround150oC.Thenitenters the baghouse filter. The filter captures and removes small particles from the gas. Ca(OH)2powder is injected intothe frontof thebag filter inorder toremoveacidicgasesand increasetheefficiencyofparticulatecapture.(Byun,etal.,2010)

24

The water quencher and scrubber are located at the outlet of the baghouse filter. The waterquencher can cool the gas to around 30 oC quickly. NaOH solution (40 %) is used in the waterquencher,whichcancleantheacidgas.Thescrubberisdesignedtoremovetherestoftheacidgasintherawgas.ThescrubbingsolutioniscontrolledatpH9.0,andisalsorecirculated.(Byun,etal.,2010)

4.2.4. SlagandTreatmentThe inorganicportionofthefeedstockmaterial (metalsandash)aremeltedduringthegasificationprocess due to high temperature exits as amolten slag through a tap hole at the bottom of thereactor.Becauseofdensitydifferences, themetalswill concentrateat thebottomof the collectorwhiletheslagwillfloatonit.(Willis,etal.,2010)Themetallayercanthenberecycledasmetalalloys,while theglassyproductof slag isnon-hazardousandnon-leachingwhich canbeused indifferentcommercial applications including concrete aggregate, roadbed construction etc. (WestinghousePlasmaCorporation,2013)

4.2.5. MassBalanceCalculationAccordingtoastudyby(Mountouris,etal.,2006),intherawgasafterthegasifier,thepercentageofCOandCO2 in the rawgas is around18%and6% respectively (30%moisture in theMSWafterdrying).TheultimateanalysisofthefeedstockinthatpaperbyMountourisetal.is(C:54.8,H:8,O:33.4, N: 3.8), themoisture content consists of 30%w/w after drying, and the amount of oxygenaddedequalsto0.3mol/moldrywaste.

TheultimateanalysisofthewasteinShanghaicanbefoundinTable8:(C:55.75,H:7.54,O:34.57,N:1.87,S:0.27),which isveryclosetothedataofthestudybyMountourisetal. (Mountouris,etal.,2006). Same condition (themoisture content consists of 30%w/wafterdrying) is used todo themassbalance.Sincethefeedstockandmoisturecontentissimilar,assumethepercentageofCOandCO2intherawgasisaround18%and6%respectively.

ThemassbalancecalculationisbasedonCarbonbalancebeforeandafterthegasifier.

Considering 1 kg waste, the reaction before and after the gasifier can be shown in the equationbelowandalltheunitsintheequationismole:

CXHYOZ+aH2O+bO2+3.71bN2=n1H2O+n2H2+n3N2+n4CO+n5CO2(Eq4.1)

Intheequationabove,XYandZaremolesofelementsfromMSWbasedonultimateanalysisandtheirvalues(C=46.46,H=75.4,andO=21.6)canbefoundintable8.

aequalstothemolesofwaterin1kgMSW.Sincethemoisturecontentis30%,a=1000g*30%/18g/mol=16.67moles.

bequalstothemolesofO2fromairaddedintheprocess.Aircanbeconsideredwith78%nitrogenand21%oxygen.Sointhemeantime,3.71bmolesofN2fromairareaddedintheprocessaswell.

n1,n2,n3,n4,andn5equalstothemolesofdifferentgascompositionafterthereaction.

25

Carbonbalance:

Beforereaction:X=46.46

Afterreaction:n4+n5=46.46.SincethepercentageofCOandCO2intherawgas is18%and6%respectively,n4:n5=3:1. Itcanbecalculatedthatn4=34.845,n5=11.615.ThentheamountofoxygenfromCOandCO2afterthereactionis46.46*3/4+46.46*1/4*2=58.075moles.

Nitrogenbalance:

Beforereaction:3.71b*2=7.42b

Afterreaction:SinceCOandCO2consistof24%ofrawgas,therestofgasesconsistof76%ofrawgaswhichmeansmolesfromtherestofthegasesequalsto(molesofCO+molesofCO2)/24%*76%=46.46/24%*76%=147.12moles.

Sothenitrogenamountafterreactioncanthenbeshownas:2*(147.12–n1–n2).

Accordingtonitrogenbalance,weget:

b=(147.12-n1-n2)/3.71

Oxygenbalance:

Beforereaction:21.6+a+2*(147.12-n1-n2)/3.71

Afterreaction:n1+58.075

Accordingtooxygenbalance,weget:

220.77=5.71n1+2n2

Hydrogenbalance:

Beforereaction:75.4+2a=108.74

Afterreaction:2n1+2n2

Accordingtohydrogenbalance,weget:

108.74=2n1+2n2

By solving the two linear equations in twounknowns fromoxygen andhydrogenbalance, the gascompositionoftherawgasisshowninTable10:

26

Table10:GasCompositionsandVolumesaftergasifier

Gas Vol%CO2 6N2 47.91CO 18H2 12.49H2O 15.90

4.2.6. EnergyBalanceCalculationInthispart,theenergycostandgainedfromdifferentprocessesiscalculated:Systemenergyinputisdetermined by MSW’s HHV and the plant capacity. Calculation of shredding machine’s powerconsumptionisbasedonplantcapacityandthemodelofmachine.Powerconsumptionofthedryingprocessisassumedaccordingtoanotherpaper.Heatfromgascooling,heatingvalueoftherawgas,andpowerconsumptionofplasmatorchesarealsocalculatedanddiscussed.

MSWEnergyInput

Thecapacityoftheplantis1000tpd,whichis41.67tonsperhour.

BasedontheultimateanalysisoftheMSWinTable8,thehighheatingvalue(HHV)oftheMSWcanbecalculatedbyDulongFormula(Enggcyclopedia,2015):

HHVinMJ/kg=33.86×C+144.4×(H-O/8)+9.428×S (Eq4.2)

WhereC,H,OandSarethemassfractionobtainedfromultimateanalysis.

AccordingtoEq.4.2andtheultimateanalysisinTable8,theHHVoftheMSWinShanghaiequalsto23.55MJ/kg

Therefore,theenergyinputfromtheMSWcanbecalculated:

Energyinput=23550*103J/kg*41.67*103kg/3600S=272.59MW

ShreddingMachinePowerConsumption

AGermancompanyWEIMAhasdifferentmodelsofshredderstoshredMSW.Oneoftheirproducttypes called PowerLine is suitable for this plant. The details are shown in Figure 10. The outputparticle sizes of the PowerLine shredder are between 30 to 100 mm. Based on the outputrequirementwhichshouldbeatleast41.67tonsperhour,threeWPL3000/800shreddersshouldbeused intheplant. Ifeachshredderappliestheoutputof14tonsperhourandassumestheoutputabilityhasalinerrelationshipwiththedrivingpowerandcompactdriveisused,thedrivingpowerbycalculation is 339 kW. The operation needs three shredders, so the total energy consumption byshreddersis339*3≈1MW.(WEIMA,2013)

27

Figure12:DetailsofShreddingMachine(WEIMA,2013)

PowerConsumptionoftheMSWDryingProcess

In the study byMountouris et al. (Mountouris, et al., 2008), amodel of sewage treatment plantusingplasmagasificationtechnologytreats250tonsperday.Thethermalenergyusedinthedryingprocess is4.56MW.Themoisturepercentagesof initialandafterdryingare68%w/wand26.7%w/w respectively. Since the moisture percentage is close to the moisture percentage of MSW inShanghaishownintable5andthecapacityoftheMSWtreatmentplant inthispaper is1000tonsper day, an assumption can bemade that the drying process of theMSW takes 4 times asmuchenergyasthesewagetreatmentplantwhichis18.24MW.

HeatCalculationofGasCoolingafterGasifier

Afterthegasifier,therawgashasatemperatureof1000oC,thenitgoesthroughaheatexchangerandthetemperaturedropsto150oC.Theamountofthermalenergytransferredinthisprocesscanbecalculatedusingthisequation(withoutconsideringwater):

Q=cmΔT

Where:

Q=thethermalenergytransferred(J)

m=themassofthegasbeingtreated(g)

c=theheatcapacityofthegas(J/goC)

28

ΔT=thechangeintemperatureofthegas(oC)

TheheatcapacityofthedifferentgasesintherawgasislistedinTable11:

Table11:HeatCapacityoftheDifferentGasesintheRawGas

Gas HeatCapacityJ/kgoCCO2 840N2 1040CO 1040H2 14000

For a given temperature and pressure, the molar volume is the same for all ideal gases. Hence,according to thecompositionof the rawgas inTable10, theamountofmolesandweightofeachcompositionoftherawgasgeneratedform1kgMSWcanbeapproximatelyconsideredasinTable12:

Table12:MolesandWeightofDifferentCompositionintheRawGas

Gas Moles Weight(g)CO2 11.61 510.84N2 92,7 2595.6CO 34.85 975.8H2 24.8 49.6

Forcoolingtherawgasfrom1000oCto150oC,thethermalenergyistransferredfromtwoparts:therawgasandthewatersteaminthegas.

Part1:Heatfromtherawgas:

Qtotal=QCO2+QN2+QCO+QH2 (Eq4.3)

=cCO2mco2ΔT+cN2mN2ΔT+cCOmCOΔT+cH2mH2ΔT

=(840*0.51+1040*2.60+1040*0.9758+14000*0.05)*(1000-150)

=4120147.2J

Theplanttreats1000tonsMSWperday,whichequalsto11.574kg/s.

Thethermalenergyinputoftheheatexchangeraftergasifierfromthispartis47.69MW.

Part2:Heatfromwatersteamingas:

AccordingtothetableofSuperheatedVaporPropertiesforSteam(OhioUniversity,2008):

AtP=0.1Mpa,enthalpyof1kgwatersteamat1000oCis4642.6kJ/kg,at150oCis2776.6kJ/kg.

Thedifferenceis1.866MJ/kg.

Thereis30.78moleH2O=0.554kgintherawgasfrom1kgwaste,

29

Thethermalenergyinputoftheheatexchangerfromwatersteam:0.554*1.866*11.574=11.96MW.

So,thetotalthermalenergyinputtoheatexchangeris:47.69+11.96=59.65MW.

It ishardtodeterminetheefficiencyoftheheatexchangergenerally.Accordingto(Fakheri,2007),theefficiencyofaheatexchangercanrangefrom40%to90%.Assumeatleasttheefficiencyof50%isachievedinthismodel.Thenaround30MWthermalenergyisusedfortheMSWdryingprocess.

HeatingValueofRawGas

According to a report by (Waldheim&Nilsson, 2001), TheHHVof COandH2 are 12.6MJ/m3 and12.74MJ/m3respectively.

HHVoftherawgas:12.49%*12.74+18%*12.6=3.86MJ/m3.

Themolarvolumeofanidealgasat1atmosphereofpressureis22.4L/mol.

Inrawgascomposition,CO+CO2=24%.1kgwastecontains46.46moleC.

Sototalrawgasmoles=46.46/24%=193.58moles.Sinceapartofwatervaporiscondensedoutduringthegascleaningprocess,theactualmolesofthegasafterthecleaningprocessneedstoberecalculated.

Accordingtothepressuredewpointtable, instandardpressure,themaximumamountofwater inairin30g/Nm3.Thewatervaporconsistsof15.9%ofrawgasaccordingtoTable10,sotherawgasmoleswithoutwateris193.58*(1–0.159)=162.8moles.AssumethereareXmolesofwatervaporleftintherawgas,Xcanbecalculatedby:

![(!"#.! ! !) ∗ !!.!]=

!"!"

!"""

X=6.31 moles

Sothetotalamountofrawgasmoles=162.8+6.31=169.11moles

Gasyield=169.11*23.63/1000=4m3/kg.

ThefeedingrateofMSWis11.574kg/s.

So theenergy input fromtherawgas to thecombustionchamberof thegas turbine is:3.86*4*11.574=178.7MW.

PowerInputofPlasmaTorch

Accordingtoareportby(Circeo,2009),aplannedproject inSt.LucieCounty,FL isgoingtousesixplasmatorches(powerlevelsof1.2to2.4MWpertorch)totreat500tpdofMSW.Assumedoubleamountoftheenergyofthetorchesisusedina1000tpdplantandtheaveragepowerlevelsofthetorchesis1.8MW,theenergyinputofplasmatorchshouldbe2*6*1.8=21.6MW.

30

GasTurbineandSteamTurbine

Afterthesecondburningchamber,acombinedcycleisusedtocovertheenergyfromtherawgastoelectricity.Acombinedcycleusesasteamturbineandagasturbine.WorkingprincipleofacombinedcyclepowerplantisshowninFigure13.(Wikipedia,2015)

Figure13:CombinedCyclePowerPlant(Wikipedia,2015)

According to Spakovszky (Spakovszky, 2002), if the efficiency of a steam turbine (Rankine cycle)equals toηSand theefficiencyofagas turbine (Braytoncycle)equals toηG, then theefficiencyofcombinedcycleηCCcanbewrittenas

ηCC=ηS+ηG-ηSηG(Eq4.3)

Eq4.3showsthatcombinedcyclehashigherefficiencythaneitherofthesinglecyclealone.Whencombined, the Brayton cycle of the gas turbine and the Rankine cycle of the steam turbinecomplementeachothertoformanefficientcombinedcycle.TheBraytoncycleofthegasturbinehasahighsourcetemperatureandtheheatgeneratedcanbeconvenientlyusedastheenergysourcefortheRankinecycle(Mohanty&Venkatesh,2014).

A single cycle gas turbine can achieve energy conversion efficiencies ranging between 20 and 35percent (U.S. Department of Energy, 2015). The efficiency is assumed to be 27.5 in the presentcalculation.

Asinglecyclesteamturbinehastheefficienciesofaround35-42%(Mohanty&Venkatesh,2014).Anefficiencyof38.5isassumedinthepresentmodel.

AccordingtoEq4.3,theefficiencyofthecombinedcycleistherefore55.4%inthepresentmodel.

SiemensclaimedthatthecombinedcyclepowerplantsequippedwiththelatestSiemenstechnologyachievedefficiencylevelsofmorethan60percent(Siemens,2016).Asimilarresultoftheefficiencyofcombinedcycle (canbereachedover60percent,upto65percent) ispresented inthestudyofMohantyandVenkatesh(Mohanty&Venkatesh,2014).

Siemenshasdifferentmodelsofgas turbinesandsteamturbineswhicharedesignedforwaste-to-energyplants.AsshowninFigure14and15.(Siemens,2013)

31

Figure14:SiemensIndustrialSteamTurbines(Siemens,2013)

Figure15:SiemensIndustrialGasTurbines(Siemens,2013)

32

Sincenodataofdetailedefficienciesoftheturbinesarefound,weassumethatthegasturbinehasandsteamturbinehas27.5%and38.5%efficiency,respectively,inthemodelasdiscussedabove.

After the combustion chamber, it’s hard to tell howmuchenergy is generatedby gas turbineandhowmuchbysteamturbine.Basedontheassumptionoftheefficiencyofthecombinedcyclewhichis 55.4% as discussed in Section 4.2.6, the amount of electricity generated in this process can beassumedas178.7MW*58%=99MW.

EnergyBalance4.3.

Aftertheenergycalculationinthesection4.2above,theenergybalanceoftheplasmagasificationplantmodelisshowninFigure16below.

Gasifier

GasCleaningUnit

Combustionchamber

Baghouse filter

Waterquencher

scrubberScrubber

HeatExchangerHeatrecoveryDryingShreddingMSW

Slag

Gasturbine

Steamturbine

ElectricityHeatrecovery

272.59MW 1MW 18.24MW 21.6MW 30MW

178.70MWfromcleaned

rawgas

99MW

Goestothedryingprocess

HeatlossQincluding

Figure16:EnergyBalanceofthePlasmaGasificationPlantModel

Theoverallelectricityefficiencyoftheplantcanbecalculated:99/(272.59+1+21.6)=33.5%.

FeasibilityStudy4.4.

Efficiencycomparison:

Asdescribedabove,ShanghaidoesnothavelocalheatdistributionforbuildingsbecausemostofthebuildingsinShanghaidonotusedistrictheatingasindoorheatingmethod.Soonlytheefficiencyinpowergenerationiscomparedinthispart.

Incineration: In the case of generating electricity, incineration plant can only use steam turbine.AccordingtoTable3,theefficiencyofatypicalincinerationplantwhengeneratingelectricityis14%-27%.

Gasification:AccordingtoareviewbyArena(Arena,2012),theefficiencyofagasificationplantusingsteamturbineis15%-24%,usinggasturbineis20%–30%.

33

Plasmagasification:inthiscaseiscalculatedinsection4.3:33.5%.

Landfill: according to the studybyWilson et al. (Wilson, et al., 2013), the efficiencyof landfill gasrecoveryisonlyintherangeof5%-10%asefficientasWtEconversionofthermalprocesses.

Costcomparison:

Based on a study byWilson et al. (Wilson, et al., 2013), the running cost of a 250tpd air fed RDFgasification plant is around 112US$ / Ton. Running cost of a 3000tpdMSW incineration plant inSingaporeis52US$/TonasproposedbyKhooetal.(Khoo,etal.,2006).Anotherpaper(Ducharme,2010),studiedandanalyzedthecostofplasmagasificationfromdifferentcompaniesandtheresultsare: 123US$ / Ton (AlterNRG plant), 130US$ / Ton (InEnTec plant), 149US$ / Ton (Europlasmaplant), 149US$ / Ton (Plascoplant).Although the cost is still higher comparing to theair fedRDFgasificationinTable13,thedifferenceisnotsomuch.InthestudybyByunetal.(Byun,etal.,2014),a100tpdplasmagasificationplanttreatingMSWisevaluated.Theoperationcostisestimatedtobe111US$/Ton.Theaveragerunningcostofplasmagasificationplantsabove is132US$/Ton.ThecostsofdifferenttechnologiesaresummarizedinTable13.

Table13:CostComparisonofDifferentThermochemicalWasteTreatment

Technology PlantCapacity(tpd) OperatingCost(US$/ton)

Incineration 3000 52

AirFedRDFGasification

250 112

PlasmaGasification 100 132inaverage

Assumealargerplanthasrelativelylowerunitcost;theairfedRDFgasificationplantwillhavehighercost if it has the capacity of 100 tpd. Not mentioning if it use MSW instead of RDF fuel. Theincinerationplantwillalsohavehigherrunningcostifithaslowercapacity.

Asforlandfill,theprocessingcostsforasanitarylandfillinChinaisaround8.41US$/ton(Qiu,2012).It seems tobemuchcheaper comparing to those thermalprocesses.However, this solution is theleast sustainableonebecause asmentioned in section2.1.3, it has a chanceof causing secondarypollution to the soil and groundwater. And Shanghai, together withmany large cities in China, isrunningoutoflandfillspace(TheEconomist,2015).

Environmentalimpactscomparison:

Residuescomparison:

ResiduesfromdifferenttechnologiescanbeconcludedinTable1.

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Table14:ResiduesfromDifferentTechnologies

Technology Residues

Incineration around20%ash

Gasification upto5%ash

PlasmaGasification

non-hazardousandnon-leachingslag

Landfill NA

Theashesfromincinerationandgasificationcanbetoxicandtheymaystillendupinlandfillwiththechanceofcausingsecondarypollution.Theslagfromplasmagasificationisnon-hazardousandnon-leaching and it has commercial use as discussed earlier. Landfill is the least environmentalwayofdisposingMSWunderthiscriterion.

CO2emission:

ThestudybyWilsonetal.(Wilson,etal.,2013)summarizedthatgasificationproducesabout1kgofCO2equivalentperkWhofgeneratedpower,whilelandfillproducesapproximately2.75kg/kWhandincineration releases approximately 1.6 kg/kWh of power generated. The report of Ducharme(Ducharme, 2010) mentioned that Europlasma claimed that the emission of CO2 by the plasmagasificationisdownto0.2kg/kWhproduced.

Figure 17: Comparison of NOx, SOx and Particulate Emission by Landfill Gas Capture, Gasification andIncineration(Wilson,etal.,2013)

31,1

9 6,3

192,1

94,6

17,1

68,053,0

5,30

20406080100120140160180200

NOx SO2 Pari|culateMa}er

Emission

s,g/ton

ofW

asteProcessed

ComparisononWtECriteriaPollutants

Gasifica|on

Incinera|on

Landfill

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Otheremissions:

The study ofWilson et al. (Wilson,Williams, Liss, &Wilson, 2013) showed that gasification emitsmuchlessNOx,SOxthanincinerationandlandfill.Inthecaseofparticulatematter,italsoemitslessthanincinerationwhilealittlebitmorethanlandfill.TheresultsofthecomparisonareillustratedinFigure17.

Another study by (Arena, 2012) compared the emission of different gasification technologies(includingplasmagasification).TheresultscanbeseeninTable15below.

Table15:EmissionsfromDifferentGasificationTechnology(Arena,2012)

Company NipponSteel

JFE/Thermoselect

EbaraTwinRec

MitsuiR21

Energos PlascoEn.

ECStandard/Japanese

standard

Plantlocation

Kazusa,Japan

Nagasaki,Japan

Kawaguchi,Japan

Toyohashi,Japan

Averoy,Norway

Ottawa,Canada

Gasifiertype

Down-draft(Oxygenenriched-airgasifiers)

Down-draft(Oxygengasifiers)

Internallycirculatingfluidizedbed (Airgasifiers)

Rotarykilngasifiers(Airgasifiers)

Movinggrategasifiers(Airgasifiers)

Plasmagasifiers

Wastecapacity

200tons/dayMSW

300tons/dayMSW

420tons/dayMSW

400tons/dayMSW

100tons/dayMSW

110tons/dayMSW

Emissions,mg/Nm3(at11%O2)Particulate 10.1 <3.4 <1 <0.71 0.24 9.1 10/11HCl <8.9 8.3 <2 39.9 3.61 2.2 10/90NOx 22.3 – 29 59.1 42 107 200/229SOx <15.6 – <2.9 18.5 19.8 19 50/161Hg – – <0.005 – 0.0026 0.0001 0.03/–Dioxins/furans, n-TEQ/m3N

0.032 0.018 0.000051 0.0032 0.0008 0.006 0.1/0.1

From Table 15, it can be seen that plasma gasification has similar environmental impacts astraditionalgasificationandallthetechnologiesinTable15meetstheEuropeanCommitteeStandardexcept for HCl emission from rotary kiln gasification. Shanghai has higher emission standardscomparing to other cities in China. According to a report by Shanghai Environmental ProtectionBureau,theemissionstandardfornewincinerationplantbuiltafterJanuary1,2014isthesameastheEuropeanCommitteestandard listed inTable14.Thisdecision iseffectiveuntil June30,2016.(ShanghaiEnvironmentalProtectionBureau,2013)

Fromthecomparisonsabove,theconclusioncanbemadethatplasmagasificationhastheadvantagetreatingMSWinefficiencyasanelectricitygeneratingWtEplantcomparingto landfill, incinerationandtraditionalgasification.Ithassimilaremissionsastraditionalgasificationbuthasloweremissionsthanincinerationandlandfill.

36

5. ConclusionsAccordingtothecasestudyinsection4,plasmagasificationoffersanattractiveandenvironmentallyfriendlyoptionfortheenergyutilizationandtreatmentofMSWinShanghai.Apartfromthat,sincethesortingandrecyclingsystemsofMSWinShanghaistillneedstobeimprovedalot,itisnotidealto treat MSW using other methods like incineration, traditional gasification and landfill for theexistenceofnonorganicwasteandhazardouswasteintheMSWinShanghai.

Althoughtheplasmagasificationtechnologyisrelativelynewandmostoftheexistingplantarenon-commercial demonstrationplant,UK isbuilding two1000 tpd facilities (TeesValley1and2)usingplasmagasificationtechnologytotreatMSWinTeesValleylocatedinthenortheastofEngland.(AirProductsandChemicals,Inc.,2015)Thisshowsthatplasmagasificationisreadytobeusedinlarge-scalecommercialplants.The futureworkcanbecollectingandanalyzing relevantdata fromthosetwofacilitiesinordertogetmoreaccuratedatatoseeifplasmagasificationisstillabetterchoicetotreatMSWinShanghai.AlsoanAspenmodelcanbebuiltinthefutureoncemoredataarecollected,sothatthepredictionofgascompositionaftertheplasmagasifierandthetotalenergybalancecanbemoreaccurate.

One limitationofthisthesis isaboutthecostcomparisonandanalysisofdifferentMSWtreatmenttechnologies.Due to lackofdata,only the runningcostofa3000 tpd incinerationplant,a250tpdgasificationplantandseveral100tpdplasmagasificationplantsarecomparedinthisthesisreport.Itwouldbemuchmoreconvincingifnotonlytherunningcostoftheplantsofdifferenttechnologiesarecomparedinthesamesize,butalsoincludingtheinvestmentcostofthosefacilities.Besidesthat,if different environmental impact indexes and social opinions (opinion value) of differenttechnologiescanbemeasuredinmonetaryvalue,thenaspecificcost-benefitanalysis(CBA)canbecarriedoutfordecisionmakingofdifferentstakeholders(e.g.governmentofShanghai).

Anotherpointworthmentioningisthatsuchaprojectlikethescaleofa1000tpdWtEplantwilltakedecisionmakersatleastseveralmonthsorevenyearstodiscuss,notmentioningthetimeneededtobuildsuchplant.However, theanalysisof this thesis report isbasedonpresentdataand it isveryhardtopredicttheMSWcharacteristicsandmanagementstatusinShanghaiinthefuture.

Nevertheless,plasmagasification isan interestingtechnologythathasthepotential for futureWtEapplication.ItwouldbeexcitingtofindoutitsperformanceinthenewplantinUK.

37

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