biomass burn characteristics

4/4/2015 BiomassBurnCharacteristics

http://www.omafra.gov.on.ca/english/engineer/facts/11033.htm 1/7

BiomassBurnCharacteristics

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TableofContents

1. Introduction

2. WhatisBiomass?

3. EnergyContentofBiomass

4. Moisture

5. BiomassComposition

6. PropertiesofBiomass

7. ProcessestoReduceAsh,ChlorideandOtherElements

8. Summary

9. AdditionalResources

10. References

11. Acknowledgements

Introduction

Solidbiomasscanbegrownforuseasfuelonfarmsandforsale.ThisFactsheetoutlinesthephysicalandchemicalcharacteristicsofsolidbiomassfuels,explainstheirsignificanceandincludesatablecontainingdetailedinformationonthepropertiesof22commonbiomassfuelsinOntario.

WhatisBiomass?

Biomassreferstoanyorganicmaterialderivedfromplantsthatusesunlighttogrow.Whenburned,theenergystoredinbiomassisreleasedtoproduceheatorelectricity.Commonformsofsolidbiomassincludeagriculturalcrops,cropresiduesandforestryproducts.Switchgrass(Figure1)isanexample.

Usingbiomassforenergyofferspotentialadvantages:

Biomassisanabundantandrenewablesourceofenergy.

Usingbiomassforenergywoulddiversifytheenergysupplyandreducedependencyonfossilfuels.

BiomassproductionmaycreatenewjobsforthelocaleconomyinOntario.

EnergyContentofBiomass



TheheatingvalueofafuelindicatestheenergyavailableinthefuelperunitmassMJ/kg(BTU/lb).Thenetheatingvalueistheactualenergyavailableforheattransfer.Thedifferenceinavailableenergyisexplainedbythefuel'schemicalcomposition,moistureandashcontent.Forcomparison,theenergycontentoffuelsisreportedonadrybasis.Forexample,mostagriculturalresidueshaveheatingvaluesthatfallintherangeof1419MJ/kg(6,0408,200BTU/lb)coalrangesfrom1730MJ/kg(7,3001,3000BTU/lb).

Moisture

Moisturecontentisthekeyfactordeterminingthenetenergycontentofbiomassmaterial.Drybiomasshasagreaterheatingvalue(ornetenergypotential),asituseslittleofitsenergytoevaporateanymoisture.Figure2showsthisrelationshipandillustratesthecorrelationbetweenenergyandmoisturecontents.Increasedmoisturemeanslessenergyavailablefortheboiler.

TextequivalentTable1.UltimateanalysisforavarietyofbiomassfuelsinOntario

(allvaluesreportedonadrymatterbasis)BiomassType MJ/kg BTU/lb TypicalValues

Ash%

Carbon%

Hydrogen%

Nitrogen%

Sulphur%

Oxygen%

TotalChlorine(g/g)

Offspec(nonfood)grainsBeans 19 7,996 4.7 45.7 6.3 4.3 0.7 38.8 193Corn 17 7,350 1.5 42.1 6.5 1.2 0.1 48.9 472Canola 28 12,220 4.5 60.8 8.3 4.5 0.5 21.4 163Drieddistillersgrain 22 9,450 4.9 50.4 6.7 4.7 0.7 32.6 1,367Grass/foragesBigbluestem 19 8,020 6.1 44.4 6.1 0.8 0.1 42.6 1,880Miscanthus 19 8,250 2.7 47.9 5.8 0.5 0.1 43.0 1,048Sorghum 17 7,240 6.6 45.8 5.3 1.0 0.1 42.3 760Switchgrass 18 7,929 5.7 45.5 6.1 0.9 0.1 41.7 1,980Straw/residueAlfalfa 17 7,435 9.1 45.9 5.2 2.5 0.2 39.5 3,129Barleystraw 17 7,480 5.9 46.9 5.3 0.7 0.1 41.0 1,040Corncobs 18 7,927 1.5 48.1 6.0 0.4 0.1 44.0 2,907Cornstover 19 7,960 5.1 43.7 6.1 0.5 0.1 44.6 1,380Flaxstraw 18 7,810 3.7 48.2 5.6 0.9 0.1 41.6 2,594Wheatstraw 18 7,710 7.7 43.4 6.0 0.8 0.1 44.5 525

ProcessingbyproductOathulls 19 7,960 5.1 46.7 6.1 0.9 0.1 41.1 1,065

Soybeanhulls 18 7,720 4.3 43.2 6.2 1.8 0.2 44.3 266Sunflowerhulls 20 8,530 4.0 47.5 6.2 1.0 0.2 41.2 3,034WoodBark 19 8,432 1.5 47.8 5.9 0.4 0.1 45.4 257

1

23



Willow 19 8,550 2.1 50.1 5.8 0.5 0.1 41.4 134Hardwood 19 8,300 0.4 48.3 6.0 0.2 0.0 45.1 472CoalLowsulphursubbitcoalPRB

25 10,520 6.0 55.0 3.7 0.9 0.4 11.5 35

Lignite 22 9,350 22.0 58.8 4.2 0.9 0.5 13.6 25

Thecontentlevelofash,chlorineandotherelementscanbeloweredthroughcropselectivity,growingconditions,plantfractionation,harvesttimeandharvestmethod.

Calculatedbydifference.Percentbydifferencereferstothedifferencebetweentwonumbersasapercentofoneofthem.Forexample,thepercentagedifferencefrom5to3is:2/5=0.4=40%.

Amicrogram(g)isaunitofmassequalto1/1,000,000ofagram(1x106),or1/1,000ofamilligram.Itisoneofthesmallestunitsofmasscommonlyused.

PRBPowerRiverBasin

DatacompiledfromAURI,2005BIOBIBPreto,2010.

Generally,themoisturecontentofasolidisexpressedasthequantityofwaterperunitmass.Moisturecontentisusuallyreportedonan"asis"orwetbasis(w.b.)inwhichthewatercontentisgivenasafractionofthetotalweight.Allbiomassmaterialscontainsomemoisture,fromaslowas8%fordriedstrawtoover50%forfreshcutwood.

Ahighmoisturecontentadverselyaffectsthecollection,storage,preprocessing,handlingandtransportationofbiomass.Inaddition,transportingwetmaterialcostsmore.

Themoisturecontentofrawbiomasscanbereducedby:

leavingbiomassinthefieldtodryforseveralweeks

storingbiomass,shelteredfromprecipitation

commercialdrying

BiomassComposition

Thecompositionofbiomassvariessignificantlyamongbiomasstypes.Fuelperformanceisrelatedtothecompositionofthebiomaterial.Importantfactorsincludeash,carbon,hydrogen,nitrogen,sulphur,oxygenandchloridecontent.TheelementalcompositionofvariousfuelsinOntarioisindicatedinTable1.Allvaluesarereportedonadrybasis.

AshThenoncombustiblecontentofbiomassisreferredtoasash.Highashcontentleadstofoulingproblems,especiallyiftheashishighinmetalhalides(e.g.,potassium).Unfortunately,biomassfuels,especiallyagriculturalcrops/residuestendtohaveahighashwithhighpotassiumcontent.Asaresult,theashmeltsatlowertemperatures,resultingin"clinkers"thatcanjamfurnaceelements(Figure3).Alternately,slaggingandfoulingoccurwhenashisvapourizedandcondensedintheboiler,resultingintheproductionofhardformationsontheheattransfersurfaces(Figure4).

Wood(core,nobark)haslessthan1%ash.Barkcanhaveupto3%ash.Agriculturalcropshavehigherashcontent,from3%andhigher(Figure5).Someboilers/stovescannothandlefuelswithhighashcontent.Moreashmeansmoremaintenance.

Carbon

4

1

2

3

4



Thecarboncontentofbiomassisaround45%,whilecoalcontains60%orgreater(Demirbas,2007).Ahighercarboncontentleadstoahigherheatingvalue.

HydrogenThehydrogencontentofbiomassisaround6%(Jenkins,1998).Ahigherhydrogencontentleadstoahigherheatingvalue.

NitrogenThenitrogencontentofbiomassvariesfrom0.2%tomorethan1%(Jenkins,1998).Fuelboundnitrogenisresponsibleformostnitrogenoxide(NOx)emissionsproducedfrombiomasscombustion.LowernitrogencontentinthefuelshouldleadtolowerNOxemissions.

SulphurMostbiomassfuelshaveasulphurcontentbelow0.2%,withafewexceptionsashighas0.5%0.7%.Coalsrangefrom0.5%7.5%(Demirbas2007).Sulphuroxides(SOx)areformedduringcombustionandcontributesignificantlytoparticulatematter(PM)pollutionandacidrain.Sincebiomasshasnegligiblesulphurcontent,itscombustiondoesnotcontributesignificantlytosulphuremissions.

ChlorideCombustionofbiomasswithhighchlorideconcentrations(over1,000g/g)canleadtoincreasedashfouling.Highchloridecontentleadstotheformationofhydrochloricacidintheboilertubes,resultingincorrosionthatcanleadtotubefailureandwaterleaksintheboiler.Fuelswherethishasbeenobservedincludecornstoverandcorncobs.

Figure5.Typicalashcontentforselectedbiomassonadrybasis.Source:AURI,2005Preto,2010.

Textequivalent

PropertiesofBiomass

TheultimateanalysesforavarietyofbiomassmaterialsarepresentedinTable1.Allresultsaredisplayedonadrymatterbasisforcomparison.Usethecompileddataonlyasageneralcomparativeguide.

Itisimportanttonotethatbiomassmaterialsnaturallycontainvariability,whichdependson:

geographicallocation

variety

climateconditions

harvestmethods



ProcessestoReduceAsh,ChlorideandOtherElements

Variousmanagementstrategiesexisttoreducetheashandprimaryelementsthatinterferewiththecombustionprocess,includingcropselection,growingconditions,plantfractions,harvestingtimeandminimizingsoilcontamination.

CropSelectionAshisfoundinlowerlevelsinwarmseasongrasses,suchasbigbluestem,switchgrassandannualssuchascorn,comparedtocoolseasongrasses,suchasorchardgrass,fescuesandperennialryegrass(Mehdi&Samson1998).

GrowingConditionsSoiltypehighlyinfluencestheashlevelsofbiomass.Higherashlevelsarefoundincropsproducedonclaysoilsthanincropsproducedonsandysoils.

PlantFractionsThemajorcomponentsofasharesilicaandpotassium.Thedistributionandcompositionofashvariesamongdifferentplantfractions.Ashlevelsarelowestingrassstemsandhighestinleaves(Samsonetal.1999b).Harvestingbiomasswithhigherstemcontentwillreducetheplant'sashconcentration,thusimprovingthebiomassqualityfor combustion.SeeTable2.

HarvestTimingtoAllowforLeachingAsh,chlorideandpotassiumcontentareminimizedbyleavingthecutbiomassinthefieldtooverwinter.Overwinteringswitchgrassinthefieldreducesashlevelstoaslowas3.5%,duetoleachingandlossofplantcomponentsthatarehigherinash(i.e.,leaves).However,harvestinginthespringcomesatacost,withbiomasslossesofbetween20%and50%.

Component SwitchgrassAshContents(%)Leaves 7.0Leafsheaths 3.0Stems 1.0

Seedheads 2.4

MinimizingSoilContaminationItisimportanttominimizesoilcontaminationofthecropresidue,sincesoilparticlesgreatlyincreasetheashconcentrationofthebiomass.Selectmechanicalharvestingtechniquesthatavoiddiggingupthesoil(e.g.,cutthebiomasswithahigherstubbleheight).

Summary

Biomassmaterialsareverydiverse,rangingfromwood,bark,strawandotheragriculturalresidues,grassesandforages,andoffspecgrains,etc.Despitethisdiversity,thecompositionofmostbiomassmaterialsisrelativelyuniform,especiallyaftermoistureisremoved.Theenergycontent(onamassbasis)ofmostdrybiomassfuelsisinthe1719MJ/kg(7,3008,000BTU/lb)range.Differencesinenergycontentareduetodifferencesindensityandmoisturecontent.

Formostbiomassfuels,nitrogenandsulphurlevelsarequitelow,resultinginrelativelylowSOxandNOxemissions.Biomassoutsidethenormalrangeofthesecategoriesismostlyintheoffspec,nonfoodgraincategory.

Themajordifferenceinthecompositionofbiomassfuelsisashcontent.Wood,thetraditionalbiomassfuel,generallycontainslessthan0.5%ash.Withbark,thisincreasesto2%3%andjumpstoabove5%formostgrassesandagriculturalresidues.Theincreasedashcontentcancausesignificantfouling,clinkeringandhandlingissues.

Takecarewhenusingthesefuels.Designconversionsystemsspecificallyforthetargetfuels.Systemsdesignedforwood(orcoal)maynotbesuitableforotherbiomassfuels.

Conversion:

From to MultiplybyMJ/kg BTU/lb 430BTU/lb GJ/ton 0.00233

AdditionalResources



AmosNationalRenewableEnergyLaboratory.Propertiesofbiomassrelevanttogasification.

BIOBIB,TechnicalUniversityofVienna,Austria.Databaseofbiomassproperties.

CanmetENERGY.Biomasssystems.

InternationalEnergyAgency(IEA).Biomasscombustionandcofiringproperties.

OntarioMinistryofAgriculture,FoodandRuralAffairs.

Phyllis.Databaseonthepropertiesofbiomassandwaste.

TheCommonwealthScientificandIndustrialResearchOrganisation,Australia.Biomassfueldatabase.

USDOE.Feedstockcompositionandpropertydatabase.

References

AURI.(2005).Agriculturalrenewablesolidfuelsdata.RetrievedfromAgriculturalUtilizationResearchInstituteFuelsInitiativewebsite.

Amos,W.A.,&Bain,R.L.(2003).Highlightsofbiopowertechnicalassessment:Stateoftheindustryandtechnology.Golden,CO:NationalRenewableEnergyLaboratory.NREL/TP51033502.

Baxter,L.L.,etal.(1998).Combustionpropertiesofbiomass.FuelProcessingTechnology,54(1):1746.

Cherney,J.H.personalcommunication&(2008).Productionofgrassinthenortheast.GrassEnergySymposium,Shelburne,VT.

Ciolkosz,D.(2010).Renewableandalternativeenergyfactsheet.PennsylvaniaStateUniversity,PA,USA.

Demirbas,A.(2004).Combustioncharacteristicsofbiomassfuels.ProgressEnergyCombustionScience,30:219230.

Mehdi,B.,&Samson,R.(1998).Strategiestoreducetheashcontentinperennialgrasses.ResourceefficientAgriculturalProductionCanada.Ste.AnnedeBellevue,Quebec.

Pahkala,K.,Mela,T.,Hakkola,H.,Jarvi,A.,&Virkajari,P.(1996).ProductionanduseofagrofibreinFindland.Part1:Productionofagrofibrecrops:Agronomyvarieties.AgriculturalRes.CentreofFinland,Jokioinen,Finland.

Preto,F.(2010).Propertiesofthe13commonbiomassfuelsinOntario.NaturalResourceCanada(NRCan),Ottawa,ON.

Samson,R.,Girouard,P.,&Mehdi,B.(1999b).Establishementofcommercialswitchgrassplantations.ResourceefficientAgriculturalProductionCanada.Ste.AnnedeBellevue,Quebec.

Scurlock,J.(2008).Bioenergyfeedstockdevelopmentprograms.OakRidgeNationalLaboratory.OakRidge,TN,USA.

Acknowledgements

SpecialthankstoChantalQuesnelandBenjaminBronsonfortheircontributionsandconscientiousreviewandtoShalinKhosla,GreenhouseSpecialist,OMAFRA,Harrow,forhisconsiderableassistanceinevaluatingalternatefuels.

Formoreinformation:TollFree:18774241300Email:[email protected]

biomass burn characteristics

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