co-combustion of solid recovered fuel (srf) and coal and ... · nowadays, the addition of...

gospodarka surowcami mineralnymi – mineral resources management

2018 Volume 34 Issue 2 Pages 117–136

DOI: 10.24425/118651

1InstituteofAdvancedEnergyTechnologies,CzęstochowaUniversityofTechnology,Częstochowa,Poland; e-mail: [email protected],FacultyofEnergyandFuels,Kraków,Poland; e-mail:[email protected];ORCID:0000-0001-7700-9909.

AlEKSAnDRAŚCIUbIDłO1,WOjCIECHnOWAK2

Co-combustion of solid recovered fuel (SRF) and coal and its impact on fly ash quality

Introduction

Increasingtheenergyconsumptionandtheclimatechangearetwoofworld’smostcrit-icalproblems,andnowreceivethehighestpriorityforresearch,economyandinnovation.TheEUbudgetisassigneddirectlyaddressingtheneedforrenewableandsustainableenergysolutions, and indicates to mitigate climate change, including the reduction of emissions, the introductionofrenewableandalternativeenergysources,lowcarbontechnologies,energyconservationinbuildingsandadditionally,thewastesrecyclinganditseffectiveapplication.

AccordingtotheRegulationofthePolishMinisterofEconomy(1/1/2016)thelandfilldepositionofmunicipalwastewiththehigherheatingvalue(HHV)than6Mj/kgispro-hibited. Implementation of the requirements of this regulation is currently one of the big-gestchallengesformunicipalwastemanagementinPoland.basedonthestatisticaldata,10,863 thousandMg of municipal waste was collected in Poland in 2015, out of which8326.1thousandMgwascollectedasresidual/mixedwaste,243,2thousandMgpaperandcardboard,424.1thousandMgglass,303.2thousandMgplastics,19.2thousandMgmet-als,1.7 thousandMgtextiles,1.2 thousandMghazardous,262.4 thousandMgbulkyand657thousandMgbiodegradable.Only13.24%ofwasteswerethermallyconverted(CouncilofMinisters2016).

118 Ściubidło and Nowak 2018 / Gospodarka Surowcami Mineralnymi – Mineral Resources Management 34(2), 117–136

Theapplicationofwastederivedfuelsforenergyproductionseemstobegoodoptiontakingintoaccounttheenvironmentalprotectionandthereductionofdisposal.Morewastefractionsarecharacterizedbyhighcalorificvalue,thatiswhycanbeusedasanalternativefuel.Theuseofwasteasanenergysource isan integralpartofwastemanagementandnationalSmartSpecializations.Thewastederivedfuelsfromvarioustypesofwastessuchasmunicipalsolidwastes(MSW),industrialwastesorcommercialwastesarecommonlycalledrefuse-derivedfuel(RDF)andsolidrecoveredfuel(SRF),dependingonthefuel’scharacteristics (RadaandAndreottola2012;bessietal.2016;Medic-Pejicetal.2016;Iacov-idouetal.2018).

RDF is generated from domestic wastes, which includes biodegradable materials aswellasplastics.non-combustiblematerialssuchasglassandmetalsareremovedandtheresidualmaterial is thenremoved.Whereas,solidrecoveredfuel(SRF)isproducedfromnon-hazardouswastesincludingpaper,wood,textilesandplasticwithacalorificvalueupto30Mj/kg(dependingoncomposition),andcarbonandhydrogencontentsc.a.50and7%,respectively.Thenetcalorificvalue,chlorineandmercurycontentsofSRFarethemainre-quirementswhichareclassifyingtheSRFandtheyaredescribedinSRFstandardEn15359.(Pn-En15359:2012;Schwarzböcketal.2016;nam-Choletal.2017).

Refusederivedfuelisusedincombinedheatandpowerfacilities,manyoftheminEu-rope.Withamoisturecontentoflessthan15%solidrecoveredfuelhasahighcalorificvalueandisusedinfacilitiessuchascementkilns.

The additional parameters are organic element contents, sulphur, bromine andmajor(Al,Ca,Fe,K,Mg,na,P,Si,Ti)andtrace(As,ba,be,Cd,Co,Cr,Cu,Hg,Mo)elements.

TheSRFcontainsmineralmatter,generallyinproportionssubstantiallydifferentfromthosefoundincoal.Moreover,thenatureandmineralogicaloriginofSRFashismoredi-verseandmoredifficulttoclassify.Mineralcompoundsincoaldepositsaremainlyintheformofsilicates(upto50%wt.),carbonates(upto20%wt.),sulphides(upto20%wt.)andsulphates.Themainchemical compositionofcoalflyashareSiO2 (30−50%wt.),Al2O3 (15−30%wt.),Fe2O3(2−22%wt.),CaO(1.5−15%wt.),MgO(1−8%wt.),SO3(1−5%wt.),P2O5(0.2−1.5%wt.)andK2O+na2O(1−5%wt.)(Adrianetal.1986;VassilevandVassi-leva2005;blissettandRowson2012).WhereasthechemicalcompositionofSRFisvaried,strongly depends on the origin (Dunnuetal.2010).

nowadays,theadditionofalternativefuels(likeSRFandRDF)inco-combustionhasincreased.Severalauthorshavebeenstudiedtheco-combustionofcoalandSRFe.g.(Wuetal.2011;Iacovidouet.al.2018;Wasielewskietal.2018). The most important factor that influencesthisprocessisthecompositionofalternativefuels.Itisworthtomentioned,thattheusingSRFinsteadofcoalinco-combustionprocesshelpstopreservenaturalresourcesandlimitingtheuseoffossilfuelsandreducingtheimpactontheenvironmentthroughlow-erCO2 emissions (Waglandetal.2011;PsomopoulosandThemelis2015;Vainioetal.2016).

InEurope, therearesomepowerplantswhere theSRFisusedasanalternativefuel. Theco-combustionofcoalandSRFinCFbtechnologyseemstobesuccessfullycarriedout(Fuetal.2008;Czakiertetal.2012;Zhangetal.2012).

119Ściubidło and Nowak 2018 / Gospodarka Surowcami Mineralnymi – Mineral Resources Management 34(2), 117–136

InPoland,thereisanewcombined-heat-and-power(CHP)plantinZabrze,wherevariedsolidfuelscanbecombusted.ThefuelmixturesconsistofRDFandcoal,andbiomassandcoalarecombusted.Theamountofalternativefuel(RDF)canbeupto50%ofthetotalfuelmixture.Thepowerplantwillhaveaproductioncapacityof220MW,including145MWofheatand75MWofelectricity,anditsannualproductionisestimatedtobeapproximately730and550GWhofheatandelectricityrespectively.

Thus,themainaimofthispaperistostudytheco-combustionprocessofcoalandSRF(withdifferentamount)inafluidisedbedcombustor.Theashesobtainedfromcoal+SRFfuelmixtureswerestudiedtocomparetheinfluenceofpercentageamountofSRFonashproperties.Themorphologicalstudiesandthethermalbehaviourofasheswereperformed.

Studiesoftheseashespresentedabovewerealsocarriedouttoascertaintheirapplica-bilitytozeolitesynthesis.Synthesiszeolitesfromflyashisoneoftheeffective,economicalandsimplemethodsofflyashutilization.Duetothechemicalcomposition-highcontentofSiO2 and Al2O3–flyashissuitablestartingmaterialforthesynthesisofzeolites(WhiteandCase1990;Hansenetal.1997;Henmi1997).CFAandzeoliteconsistmainlyofAlandSi(Queroletal.2002)andthemajordifferencebetweenthemisthecrystallinestructure.CFAiscomposedmostlyofamorphousstructure,whereaszeolitehasawell-definedcrystallinestructure.Due to these similarities in thecompositionbetweenCFAandzeolite,CFA ispotential candidate for conversion to zeolite (Zhaoetal.1997).Themainelementofflyash-aluminosilicates,isconvertedtozeoliticcrystalsbyalkalihydrothermalreaction.

naturalzeoliteshaverestrictedporesizesandchannels,whereasflyashbased-zeolitespossess a variety of pore structures and are economically viable sorbent minerals for remov-ingcontaminantsfromwaterandgases.Thesesynthesizedzeolitescanbeusedassorbentsandionexchangersforremovingionsanddangerousmoleculesfromwastewaterandradio-activewasteaswellasadsorbentsforgasescontainingatmosphericpollution(breck1974;Singerandberkgaut1995;Huietal.2005).

1. Experimental

1.1. Materials

ThecoalusedforthecombustionexperimentswasalignitecoalfromTurow,Poland.Forexperimentalpurposes,thecoalwassievedtoprovideaparticlesizebetween5and13mm.FuelSRFwas alsogrindedandhomogenised.TheSRFcomes fromanalternative fuelsplantinGermany.ThechemicalcompositionofcoalandSRFispresentedintheTable1.

ThecarbonandhydrogencontentsofcoalandSFRaresimilar.necessary,theSRFchar-acterizesveryhighcontentofsulphur,whatcanbenegativeaspectofSRFcombustion,tak-ing into account the sulphur compounds emissions. The coal contains higher the moisture andashcontentsthatSRFbutlowercontentofvolatilematter.Thecalorificvalueofcoal


andSFRaresimilar.Thefourfuelblendswereprepared:coal+1%SRF,coal+5%SRF, coal+10%SRFcoal+20%SRF.

1.2. Co-combustion process in CFB

Theco-combustionofstudiedfuelblendswerecarriedoutat0.1MWthfluidizedbedcombustor (Fig. 1) at the Institute ofAdvancedPowerTechnologies of theCzęstochowaUniversityofTechnology.

Theunitconsistsofa0.1m innerdiameterandapproximately5.0m tallcombustionchamber,connectedtoa0.25minnerdiameterhotcyclone.Solidsseparatedinthecyclonereturntothecombustionchamberviaa0.075minnerdiameterdowncomerandanon-me-chanicalloopseal.Theunitisprovidedwiththreeheatersaroundthecombustionchamber.Theseheatersareusedtoheat theunit to(orbeyond)theignitionpointofthefuelbeingused.Primarygas(PG)issuppliedthroughaceramicgridatthebottomofthecombustionchamber.Thisgascanbepreheatedwiththehelpoftwoheaters(HEandPGH)installedinseries.Secondarygas(SG)canbesuppliedoptionallythroughacommon-railfittedwiththreenozzlesatthelevelof0.55mabovethegrid.Fuelisfedcontinuouslybyascrewfeederlocatedona return leg,between thecombustionchamberand the loopseal.bedmaterialcanbefedbyanadditionalscrewfeederatthebottomofthecombustionchamber.Asinglefabric baghousefilter, installed downstreamof the cyclone, is used for ultimateflue gas

Table1. ChemicalanalysisofcoalandSRF

Tabela1. AnalizachemicznawęglaiSRF

Element Coal SRF

Elementaryanalysis(%drybasis)

C(%) 45.28 43.81

H(%) 4.50 5.60

n(%) 0.42 1.51

S(%) 1.60 6.49

Proximateanalysis

Moisture(%) 6.23 4.6

Ash(%)(db) 22.44 12.15

VM/Volatilematter(%)(daf) 39.87 68.39

CV/calorificvalue(Mj/kg) 17.52 16.22

Daf–dry-ash-free-basis;db–drbasis.


particulatecleanup.Thebaghousecanbebypassedifnecessary.Thefluegasleavingthebaghouse(orbypassingthebaghouse)isventedwiththehelpofaninduceddraft(ID)fantotheatmosphere,throughastack.Thetestrigisequippedwithadevelopeddataacquisitionsystemfortemperature(T)andpressure(P)measurements,aswellasanumberofportsforfluegas(FG),bottomash(bA),flyash(FA),andcirculatingmaterial(CM)sampling.

Fig.1.Schematicdiagramoffluidizedbedcombustor(0.1MWth)

Rys.1.Schematstanowiskadoświadczalnegozcyrkulacyjnąwarstwąfluidalną(0,1MWt)


Inthisstudy,coal+1%SRF,coal+5%SRF,coal+10%SRFandcoal+20%SRFfu-elsweretested.Duringcombustionexperiments,thefluidizedbedtemperaturewasabout850°C.TheflyashsampleswerecollectedfromaCFb.Variousexperimentalmethodsforthe physical and chemical characterization of ashes are required. The most important param-eter determining the character of ash is the chemical composition and thermal behaviour. ThedetailchemicalcompositionoftheobtainedashesispresentedinTable2and3.

1.3. Instrumental methods

The samples of fly ashes were collected and prepared according to the standards bn-81-0623-01 (for slag, ash, and slag-ashmixtures). The investigation of the chemicalcompositionincludedadeterminationofabasicchemicalcomposition(SiO2, Al2O3,Fe2O3, CaO,MgO,na2O,K2O,SO3,MnO2,TiO2,P2O5)of ashwasperformedbyusingX-rayfluorescence(XRF).AMinipal4wavelengthdispersiveXRFspectrometerwasusedforthispurpose.TheXRFwascalibratedoverarangeofglasscompositionsusingstandardrefer-encematerials.Themajorelementsoftheashesweregivenaswt%.oxides.

Anidentificationofcrystallinephasespresentintheflyashes,alongwithdefiningtheirrelativeamountsinthesampleswascarriedoutbymeansoftheX-raymethodontheD8Advance(bruker)powderdiffractometer,equippedwithamonochromaticdeviceGe(thelengthofradiation:CuKα1=1.5406Å).Diffractionpatternswereidentifiedinaroomtem-perature,intherangeof6–60°of2thetaangle,witha0.05°step.Relativeamountsofcrys-tallinecomponents in theashessamplesweredeterminedbymeansofaninternalmodelmethod.Modeldiffractionpatternswerereceivedinthesamemeasurementconditionsasinthe case of the selected samples.

Morphology investigation and sample textureswere conductedusingof the scanningmicroscopetypeTeslabS-301-Satellite,equippedwithspectrometerofenergydispersion(EDX),whichallowed todetermine thechemicalcompositionof the selectedsamplesofmaterials. Preparations for SEMmicroscopewere obtained bymeans of a deposition ofsurfacesof the investigatedmaterialswith a thinfilmofAu−Pd in avacuumdepositionapparatus,followedbytakingdigitalphotosfromtheSEMmicroscope’sdetectorofdiffer-entfragmentsofthosesurfacesandwithdifferentmagnificationlevels(5000,15000and 50000times).

nitrogenadsorption/desorptionwasconductedusingtheMicrometricsASAP2010(Mi-crometricsInstrumentCorporation,norcross,GA,USA)apparatus.beforethenitrogenad-sorption,thesamples(200mg)weresubjecttodegasificationinthetemperatureof573Kfor3hours.Theapparatuswasusedtomeasurethelow-temperature(–196°C)nitrogenad-sorption/desorptionisotherm,onthebasisofwhichsuchparametersweremeasuredas:thespecificsurfacearea,thetotalvolumeofthepores,theaverageporesdiameter,distributionofporesvolumesinthefunctionoftheirdiameteraswellasthedistributionofthespecificsurfaceareainthefunctionoftheporesdiameters.Severalconclusionsonthestructureof


Table2.

Themainelem

entsoftheashesintheformofoxides,%(X

RFmethod)

Tabela2.Składpierwiastkowypopiołów

wpostacitlenkowej(m

etodaXRF)

Ash

SiO

2A

l 2O3

CaO

Fe2O

3MgO

P 2O5

K2O

na 2O

TiO

2MnO

SO3

Coa

l46.30

30.95

1.96

4.99

1.54

0.12

1.21

0.40

2.40

0.03

1.60

SRF

23.90

7.90

31.55

3.14

2.99

1.72

1.07

0.35

2.45

0.18

6.50

Coa

l*41.02

29.03

1.89

4.83

1.37

0.10

1.13

0.35

2.00

0.03

1.39

Coal+1%SRF*

40.98

29.07

3.29

10.23

1.97

0.07

1.57

0.39

1.67

0.03

3.04

Coal+5%SRF*

40.73

29.05

3.58

9.28

2.01

0.08

1.57

0.39

1.67

0.03

3.75

Coal+10%

SRF*

39.97

27.89

3.59

9.99

2.16

0.10

1.56

0.35

1.67

0.04

3.93

Coal+20%

SRF*

37.02

25.10

3.85

9.99

2.45

0.17

1.46

0.35

1.56

0.05

4.34

*CFb

boilercom

bustion.

Table3.

Contentofm

inorelementsinstudiedashes,ppm

Tabela3.Zawartośćśladow

ychpierwiastkówwpopiołach,ppm

Ash

Cd

Co

Cr

Cu

Hg

ni

PbSb

VZn

Coa

l0.62

18.59

141.27

60.20

–115.45

34.07

7.61

250.23

112.87

SRF

0.49

12.26

556.81

650.97

0.09

52.00

196.35

3.58

77.74

1955.78

Coa

l*0.64

18.01

142.02

61.00

–112.00

33.25

7.01

248.04

113.00

Coal+1%SRF*

0.69

28.00

167.20

106.40

0.09

134.85

51.77

5.56

249.07

242.56

Coal+5%SRF*

0.58

24.39

169.69

107.48

0.11

124.46

54.20

5.30

196.54

288.81

Coal+10%

SRF*

0.55

24.22

174.54

199.43

0.14

118.81

57.12

5.22

164.08

299.81

Coal+20%

SRF*

0.55

23.33

195.91

127.82

0.19

116.98

58.61

5.18

154.09

302.91

*CFb

boilercom

bustion.


theinvestigatedcompoundweremadeonthebasisofthequalitativeanalysisofthereceivedadsorption-and-desorption isotherms.

AMastersizer2000ParticleSizeAnalyzerwasusedtomeasuretheparticlesizedis-tributionoftheflyashsamples.Waterwasusedasacarrieragentsinceitwasfoundtobecapableofdispersingandwettingtheparticles.Anultrasoundsonicatorbathwasusedtodisperse the particles.

Thermal analysis can provide important information about the thermal behaviour of the sample(phasetransition,decomposition,etc.).TGA/DSC1thermalanalyzer(producedbyMettlerToledowasusedin thisstudy.Theflyashwasheatedinaplatinumcrucibleun-der theatmosphericpressureand inaneutralatmosphere(n2),withaflowratioofa re-actiongasequalto50cm3/min,andinarangeoftemperaturesbetween20–1000°C,withtheheatingrateequalto20°C/min.Inordertoensureanaccuracyofmassmeasurements,receivedTGcurveswerecorrected(i.e. reduced)byaso-calledblanktest (i.e.TGcurveof an appropriate inerrant sample, registered in particularmeasurement conditions). Foratemperaturecalibrationmodelsubstances,withknowntemperaturesofphaseconversion, wereused.

2. Results and discussion

Theash,mineralpartofthefuel,playssignificantroleinthermalprocesses.Theforma-tionofashdepositsinfluencingontheheatingsurfacelimitingtheheattransferandaccel-eratingthecorrosionprocess.Consequently,thecombustionefficiencyisdecreasedbytheslagging, fouling and bed agglomeration phenomena(Magdziarzetal.2016).

Thus, the chemical composition of studied ashes obtained after co-combustion of coal andSRFispresentedTable2and3.

To comparison the chemical composition of coal and SRF are presented, too. Theconcertationof themainoxides is different, becauseofdifferentoriginof studied fuels.ThechemicalpositionreportedinTable2showsthatcoalashinmainlycomposedofsil-icon(SiO2),aluminium(Al2O3)andiron(Fe2O3).WhereastheSRFashisrichincalcium(CaO),whatcouldbeusefulness forSO2 capture. The concertation of potassium and so-dium are not high and comparable, this can suggest that slagging of these ashes should not to appear. It iswell observed, that the chemical composition of ashes fromco-com-bustion of blends reflects the amount of SRF addition. The amount of themajor oxidesinstudiedashes is listedfromthehighest to the lowervalues:SiO2, Al2O3,Fe2O3,CaO,SO3, MgO, TiO2, K2O. The concentration of trace elements in the ashes is presented inTable3.

AnalysingcoalandSRFashesthecontentoftraceelementsisdifferent.ThecoalashcharacterisesthehighconcentrationofV,Cr,Zn,Pb,theHgwasnotdetected.ForSRFashtheconcertationofZn,Cu,Cr,Pb,niaswellasHgwasdetected.Additionally,thesumoftraceelementsinSRFashismuchhigherthanincoalash.


Considering the chemical composition of studied ashes, they can be utilize as a zeolites andporousmaterials,duetothehighcontentofSiO2 and Al2O3 in these ashes (Wangetal.2009;Vainikkaetal.2011;Zhouaetal.2016).

The parameter which determines ash usefulness as a zeolite is the Si/Al ratio. The SiO2/Al2O3contentofashes,beingoptimalforzeolitesAisc.a.2,whatreflectstoallstudiedallashes.TheSiO2/Al2O3contentofash,beingoptimalforzeolitesXintherangeof2.2–3.3andforzeolitesYintherangeof3.1–6.0.Unfortunately,thisratiowastoolowtosynthesiszeolitesXandY.Traceelements suchasTiO2,MnO,K2O,na2O,andMgOalongwithanions – sulfate, carbonate appear to promote nucleation and crystallization of zeolite. Iron oxidesmaydecreasethequalityoftheproductbyincorporatingthemselvesintothezeolitematrixgivingtheproductabrownishshade(Rayaluetal.2001). In addition, these cations mayfavoriteonetypeofzeoliteoveranother,thereforeitisimportanttochoosethespecificzeolitethatcanbeconvertedfromaspecificCFA(bukharietal.2015).

2.1. Thermogravimetric experiments

Figure2presentstheTGandDTGcurvesduringheatingthestudiedashesunderthenitrogen atmosphere. TG (thermogravimetry) curve presents the weight loss of studied

Fig.2.TGandDTGcurvesforstudiedashes

Rys.2.KrzyweTGiDTGpopiołów


samplesincontrasttotheinitialmassunderincreasingtemperature,andDTG(differentialthermogravimetry)isbasedontherateofweightlosswiththeincreasingtemperature.

TGresultsshowthatthermalconversionupto1000°Cofstudiedasheshavedifferentcourse.Forcoal+1%SRFashthemasslossgoesintotwostagesfromc.a.350°Cto883°C.Thefirststepfrom25°Cto352°Ccorrespondstoremovalofmoistureandlightvolatileswithatotallossofabout3.36%.Thesignificantweightlossisobservedbetweenc.a.352°Cto670°Cwiththetotallossof6.66%withmaximumweightlossrateat585°C,whichwasindicatedtotheoxidationofcoal.Thesecondweightlossbetween670°Cto883°Cwastheresultoftheoxidationofcarbonbytheironoxideswiththetotallossof4.69%.Theresidueatc.a.1000°Cwasabout83,57%oftheoriginalsampleweight.

TheadditionofSRFisobservedforthecoal+5%SRFwherethethermalbehaviouroftheashisquitedifferent,themasslossrateismuchsmallerthanforpreviousone.Thetwostagescanbedefine,too.Thefirstweightlossisobservedbetweenc.a.350°Cto780°Cwithtotallossofabout3.10%andthesecondweightlossbetween780°Cto990°Cwithtotaldeg-radationof2.04%.Thefirstweightlosswasfollowedbytheactivepyrolysisandoxidationandthesecondwastheresultoftheoxidationofcarbonbytheironoxides.Theresidueatc.a.1000°Cwasabout92.36%oftheoriginalsampleweight.

Forcoal+10%SRFash themass lossabove200°Cgoesdifferent thanforotherashsamples.Up to 750°C the thermal decomposition takes placewith nearly the same rate.Above750°Cthemasslossissignificantandmaximumweightlossisobservedat883°C.Thisweightlosswastheresultoftheoxidationofcarbonbytheironoxides.Theresidueatc.a.1000°Cisabout90.9%oftheoriginalsampleweight.

ThemajoradditionofSRF(20%)tocoalinfluencesonitsashthermalbehaviour.Thesignificantmasslossisobservedinthetemperaturerange400°Cand600°C.Above600°Cthemasslossinnearlyconstant.Theweightlossisobservedbetweenc.a.352to670°Cwiththetotallossof2.74%withmaximumweightlossrateat544°C,whichwasindicatedtotheoxidationofcoal.Thesecondweightlossbetween670°Cto777°Cwastheresultoftheox-idationofcarbonbytheironoxideswiththetotallossof0.83%.Theresidueatc.a.1000°Cwasabout83.57%oftheoriginalsampleweight.

Duetoseveraloverlappingpeaks,themineralsaredifficulttoidentify.ThemostoftheeffectsdetectedontheTGAdiagramsarerelatedtothelossofhumiditybetweenroomtem-peratureandapproximately300°C.Thermalreactionsbetween275–450°Cwasoxidationofthesurface(Fe3O4)andbetween480–1000°Cwasoxidationofthebulk2Fe3O4→3Fe2O3. between100°Cand200°C:escapeofadsorbedandinterlayerwater.About550°Cwasde-hydroxylationofilliteandatca.900°Cwasdestructionofthelatticeandformationofspinel(illite).CaSO4isdecomposedonlyattemperatureshigherthan1000°C.Inacaseofhematitein temperature400–500°Cshowssomeweight lossandoxideundergoingdecompositionand dehydration of hematite(Földvári2011).

Concluding, theweight losses of studied asheswith the increaseof temperature takeplace due to moisture loss and the decomposition of some minerals.


2.2. BET specific surface area

low-temperaturenitrogenadsorptionwasusedforthecharacterizationofporousmate-rials.Table3showsthespecificsurfacearea(bET)ofstudiedashes.

The specific surface area (SbET) of studied ashes is in the range from14.87m2/g to 29.80m2/g.TheadditionofSRFtothecombustionprocesscausedtheashgenerationwiththelowerspecificsurfacearea.

Theashadsorptioncapacityisamajorpropertyforthebeneficialutilizationofash.Theadsorptioncapacityofflyashmainlyindicatesfromamountofcarboncontentbutalsofromother properties such as the particle size, surface chemistry, and positioning of carbon in the flyashparticle.ThevaluesofsorptioncapacityofstudiedashesdecreasewiththeshareofSRFinfuelmixture.Figure3showsthen2adsorptionisothermat77Kforstudiedashes.

Fig.3.n2 adsorption isotherm for studied ashes

Rys.3.Izotermyadsorpcjin2popiołów

Table4. ThebETspecificsurfaceareasoftheflyashsamples

Tabela4. PowierzchniawłaściwabETpopiołówlotnych

Ash bETSurfaceareaSbET m2/g

Coal+1%SRF 29.8028

Coal+5%SRF 22.7251

Coal+10%SRF 17.9218

Coal+20%SRF 14.8691


Then2adsorptionisothermisthegraphbetweentheamountsofadsorbateadsorbedonthesurface of adsorbent and pressure at constant temperature.

n2adsorption isothermsforallasheswereclassifiedaccording to IUPACregulationsas isotherms of type II. This type of isotherms is typical for macro-pores materials, and is connectedtosituationsinwhichlowrelativepartialpressuresofanadsorptiveonasurfaceof an adsorbent result in occurrence of some monomolecular mini-layer of the adsorbed substance(n2),whereasinthecaseofhighrelativepartialpressuressomemulti-molecularlayerofadsorbentonthesurfaceofadsorbentiscreated.Intheisothermsoftheflyasheswereobservedthattheloopofhysteresis(typeH3),beginswithrelativelowpressuresthatprovealowcontentofmicroporesinthatstructure.TheloopofH3hysteresisistypicalforadsorbentswithporesformedintheshapeofgaps.

2.3. Particle size distribution

TheparticlesizeanalysisbylaserScatteringAnalyzer forallstudiedasheswascar-riedout.Athree-pointspecificationincludingD10,D50,andD90particlesizevaluesofferappropriateinformationforpresentingtheparticlesizespanwidthofflyashes.D50isthediameterthatsplitsthedistributionwithhalfaboveandhalfbelowthisdiameter.TheD90andD10representthecoarsestandfinestpartsofthedistribution,respectively.

Thedistributionofgrainsoftheflyashesisasymmetricdistribution.Thevolumeweight-edpercentilesD10,D50,D90offlyasheswerereportedinTable5andthecumulativecurveofallflyasheswasshowninFig.4b.

Table5. Particlesizedistributionofflyashes

Tabela5. Rozkładuziarnieniapopiołówlotnych

Ash D10,μm D50,μm D90,μm

Coal+1%SRF 3.00 15.30 47.93

Coal+5%SRF 3.67 18.87 43.62

Coal+10%SRF 3.47 18.57 45.70

Coal+20%SRF 3.30 17.71 44.26

90%oftheparticlesforstudiedasheshaddiameterssmallerthan47.93μm,43.62μm,45.70μm,and44.26μm,respectively.ThedatafortheD50valuesfortheflyasheswerelessthan15.30µm,18.78µm,18.57µmand17.71µm.Tenpercentforflyasheshaddiameterssmallerthan3.00μm,3.67μm,3.47µmand3.30µm,respectively.


Thedifferentialparticle sizedistributionsofflyashes (Fig.4a)were in a range from 0.51to85,31micronsforashno.2and4,from0.514to224,41micronsforashno.3andfrom0.514to295.00micronsorashno.1.Theasheshadsimilardistributionofthegrainsvolumes.ThedistributionofgrainsoftheflyashesisasymmetricGaussdistribution.

2.4. Texture analysis

Inordertodeterminethemorphologyandtheporousstructure,thesamplesofflyashesweresubjectedtoananalysisofSEM-EDXscanningmicroscopy.Theresultswerepresent-edinFigure5.

Themorphologyoftheco-combustionasheswerequitesimilartoeachother.Thedom-inantparticlesof all asheswere containedmainly coarse andangular,flaky,drossy, andirregularparticleswithabroadparticlesizerange.

Themorphology of a fly ash particlewas controlled by combustion temperature andcooling rate. Themulti-mineral, subangular particles of fly ash often were consisted ofacoreofquartzoraluminosilicatethatwerereactedwithcalciumtoproduceacalcium-richaluminosilicate followedbycalciumand ironoxides. In allflyasheswerealsoobservedirregularly shaped unburned carbon particles.

ThegrainsofCFbasheshadirregularshapesbecauseinthetemperatureoftheCFbboiler,mineralsubstancesaccompanyingthecoalwerenotsubjecttopartialmelting.DuetolowtemperatureinCFbboiler,intheCFbashesmullitewasnotpresent.

Fig.4.a)Differentialparticlesizedistributionofflyashes; b)Cumulativeparticlesizedistributionofflyashes

Rys.4.a)Krzywaróżniczkowarozkładuwielkościcząstek; b)Krzywakumulacyjnarozkładuwielkościcząstek


2.5. Mineralogical composition

ThemineralogicalcharacteristicsoftheflyasheswereanalysedbyXRD(Fig.6).Quartz,anhydriteandillitewereidentifiedinallstudiedashes.Thesemineralsareusuallypresentincoalflyashes.

Inaddition,magnetiteandironoxidewerealsopresent.IntheflyashseveralpeakswerepresentthatcouldnotberelatedtospecificXRD-patternsofminerals.Thepresenceofthe

Fig.5.SEMphotographsofthestudiedashes a)coal+1%SRF;b)coal+5%SRF;c)coal+10%SRF;d)coal+20%SRF

Rys.5.ZdjęciaSEMpopiołów a)węgiel+1%SRF;b)węgiel+5%SRF;c)węgiel+10%SRF;d)węgiel+20%SRF


backgroundinthediffractionpatternpointstoamorphousphases,whichwasrepresentedawidepeakfrom15°to35°2Θ.Thepositionofthebackgroundisinfluencedbythecompo-sition of the amorphous phase.

Conclusions

In theworkwerepresentedadetail analysisof ashesobtainedduringco-combustionofcoalandSRFusinganumberofinstrumentaltechniquesincludingXRF,XRD,SEM-EDS.ThevaluesofsorptioncapacityofstudiedashesdecreasedwiththeshareofSRFinfuelmixture.Themorphologyoftheco-combustionasheswerequitesimilartoeachother.

Fig.6.X-raydiffractionanalysis q−quartz(SiO2),f−Fe2O3,a−anhydrite(CaSO4),g−magnetite(Fe3O4),r−forsterite(Mg2SiO4),

i−illite(K0.6–0.85Al2(Si,Al)4O10(OH)2)

Rys.6.DyfraktogramyXRD q−kwarc(SiO2),f−Fe2O3,a−anhydryt(CaSO4),g−magnetyt(Fe3O4),r−forsteryt(Mg2SiO4),

i−illit(K0,6–0,85Al2(Si,Al)4O10(OH)2)


Thedominantparticlesofallasheswerecontainedmainlycoarseandangular,flakyandirregularparticleswithabroadparticlesizerange.Inallflyasheswerealsoobservedirreg-ularly shaped unburned carbon particles.

DuetolowtemperatureinCFbboiler,intheCFbashesmullitewasnotpresent.Quartz,anhydriteandillitewereidentifiedinallstudiedashes.Inaddition,magnetiteandironox-idewerealsopresent.Thepresenceofthebackgroundinthediffractionpatternpointstoamorphousphases.Theresearchshowsthatcoalashinmainlycomposedofsilicon(SiO2),aluminium(Al2O3)andiron(Fe2O3).WhereastheSRFashisrichincalcium(CaO).Theconcertation of potassium and sodium are not high and comparable, this can suggest that slaggingoftheseashesshouldnottoappear.Itwaswellobserved,thatthechemicalcompo-sitionofashesfromco-combustionofblendsreflectstheamountofSRFaddition.

Theamountofthemajoroxidesinstudiedashesislistedfromthehighesttothelowervalues:SiO2, Al2O3,Fe2O3,CaO,SO3,MgO,TiO2,K2O.ThecoalashcharacterisesthehighconcentrationofV,Cr,Zn,Pb,theHgwasnotdetected.ForSRFashtheconcertationofZn,Cu,Cr,Pb,niaswellasHgwasdetected.Additionally,thesumoftraceelementsinSRFash is much higher than in coal ash.

Thehighsilicacontentofflyashmakesitapotentialusefulsourceforthesynthesisofnanoporousmaterials,suchaszeolites.Synthesisofthesematerialsfromflyashisoneofthemethodsofflyashutilizationanditiseconomical,effective,safeandsimple.Thepa-rameterwhichdeterminesashusefulnessasazeoliteistheSi/Alratio.ThusallSRF-flyashsampleswiththeSiO2/Al2O3ratioca.2.0canbeconvertedtozeoliteA.Theefficiencyofflyashconversionisalsodependentonthecontentsofnon-reactivephases(mainlyhematite,magnetite,lime)andresistantaluminum–silicatephases,suchasmulliteandquartz,andthegrainsizedistribution.TheAl-andSi-bearingphasesaredissolvedduringdifferentstagesof thezeolitization in theorderglass>quartz>mullite.Due to theSiO2/Al2O3 content andhighcontentofSiO2andnomulliteinSRF–flyash,flyashescanbeusedtosynthesis zeolite A.

TheresultsofstudywereconfirmedthatSRFcanbesuccessfullycombustedwithcoalinCFbtechnologyandcanplayroleasanalternativefuelandtheflyashesobtainedfromcoal+SRFfuelmixturescanbeusedtosynthesiszeolites.

The research was supported by The National Science Centre in Poland, based on the decision DEC-2011/03/B/ST8/05916.

The part of research was financed by statutory funds no. BSPB-406-301/11.


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Co-CoMBuStIon oF SolId RECovEREd FuEl (SRF) and Coal and ItS IMPaCt on Fly aSh qualIty

A b s t r a c t

Duetothefactthatthelandfilldepositionofmunicipalwastewiththehigherheatingvalue(HHV)than6Mj/kg inPoland isprohibited, theapplicationofwastederivedfuelsforenergyproductionseems tobegoodoption.There is anewcombined-heat-and-power (CHP)plant inZabrze,wherevaried solid fuels can be combusted. The formation of ashes originating from the combustion of al-ternativefuelscausesaneedtofindwaysfortheirpracticalapplicationanddemandstheknowledgeabouttheirproperties.Therefore,thepresentworkisdevotedtostudyingtheco-combustionofsolidrecoveredfuel(SRF)andcoal,itsimpactonflyashqualityandthepotentialapplicationofashestosynthesis zeolites.

Themajorobjectivesofthispaperistopresentthedetailcharacteristicsofashgeneratedduringthisprocessbyusingtheadvancedinstrumentaltechniques(XRF,XRD,SEM,bET,TGA).

Theco-combustionwerecarriedoutat0.1MWthfluidizedbedcombustor.TheamountofSRFinfuelmixturewas1,5,10and20%,respectively.Thefocusisonthecomparisontheashesdepending


onthefuelmixturecomposition.Generally,theashescharacterisehighamountsofSiO2, Al2O3 and Fe2O3.Itiswellobserved,thatthechemicalcompositionofashesfromco-combustionofblendsre-flectstheamountofSRFaddition.Consideringthechemicalcompositionofstudiedashes,theycanbeutilizeasazeolitesA.ThemainconclusionsisthatSRFcanbesuccessfullycombustedwithcoalinCFbtechnologyandtheflyashesobtainedfromcoal+SRFfuelmixturescanbeusedtosynthesiszeolites.

Keywo r d s :SRF,co-combustion,flyash,CFb

WspółspalanIE sTałEgo palIWa WTórnEgo (srF) WęglEM I jEgo WpłyW na jakość popIołu loTnEgo

S t r e s z c z e n i e

Mającnauwadze,iżskładowanieodpadówkomunalnychowyższejwartościopałowej(HHV)niż6Mj/kgwPolscejestzabronione,dobrymrozwiązaniemjestzastosowaniepaliwodpadowychdoprodukcjienergii.WZabrzubudowanajestnowaelektrociepłownia(CHP),wktórejmożnabędziespalać różnepaliwastałe.Powstawaniepopiołówpochodzącychze spalaniapaliwalternatywnychpowodujepotrzebęznalezieniasposobówichpraktycznegozastosowania,atowymagapoznaniaichwłaściwości.Dlategoniniejszapracaskupiasięnabadaniuwspółspalaniastałegopaliwawtórnego(SRF)zwęglem,jegowpływienajakośćotrzymanychpopiołówlotnychorazmożliwościwykorzy-staniapopiołówdosyntezyzeolitów.

Głównymcelemtegoartykułujestokreśleniewłaściwościpopiołulotnegopowstającegopodczastegoprocesuzapomocązaawansowanychtechnikinstrumentalnych(XRF,XRD,SEM,bET,TGA).Współspalanie przeprowadzono na stanowisku doświadczalnymz cyrkulacyjnąwarstwąfluidalnąomocy0,1MWt.IlośćSRFwmieszaniniepaliwwynosiła1,5,10i20%.Wpracyzwróconouwa-gęnaporównaniewłaściwościpopiołówwzależnościodskładumieszankipaliwowej.ZasadniczootrzymanepopiołycharakteryzująsiędużąilościąSiO2, Al2O3iFe2O3,azawartośćpotasuisodunie jestwysoka i jestporównywalna.Zauważono,że składchemicznypopiołówzewspółspalaniaodzwierciedlailośćdodanegoSRF.biorącpoduwagęskładchemicznybadanychpopiołówmożnajewykorzystaćdosyntezyzeolituA.Podsumowując,SRFmożebyćzpowodzeniemwspółspalanyzwęglemwCFb,aotrzymanepopiołylotnemogąbyćużytedosyntezyzeolitów.

S ł owa k l u c z owe :SRF,współspalanie,popiółlotny,CFb

co-combustion of solid recovered fuel (srf) and coal and ... · nowadays, the addition of...

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