Combustioncharacteristicsofdifferentbiomassfuels
AyhanDemirbas
*
DepartmentofChemicalEngineering,SelcukUniversity,Konya,Turkey
Received15March2003;accepted31October2003
Abstract
Biomasnergyisoneofhumanity’arliestsourcesofenergyparticularlyinruralareaswhereitisoftentheonlyaccessible
idebiomassranksfourthasanenergyresource,providingapproximately14%ofthe
world’nergyneedsallhumanandindustrialprocessproducewastes,thatis,normallyunudandundesirableproductsofa
specifitionandrecoveryofsolidwastesvariesdramaticallyfromcountrytocountryanddervesspecial
ningveloofbiomassfuels
providessubstantialbenefisabsorbscarbondioxideduringgrowth,andemits
ationofbiomassasfuelforpowerproductionofferstheadvantageofarenewableandCO
2
-neutral
ghthestructural,proximateandultimateanalysresultsofbiomassandwastesdifferconsiderably,some
propertiesofthebiomasssamplessuchasthehydrogencontent,thesulfurcontentandtheignitiontemperatureschangedina
narrowinterval.
htsrerved.
Keywords:Biomass;Combustion;Fuelproperties;Cofiring
Contents
uction...................................................................220
ssources............................................................220
tbiomassconversiontechnologies.........................................220
astes...................................................................220
ficationofbiomass...........................................................221
eformingofbiomass...................................................221
ficationsystems.........................................................222
sisofbiomass.............................................................222
opertiesofbiomass........................................................222
tionpropertiesofbiomass...................................................224
mistryofbiomasscombustion............................................225
mbustionpropertiesoflectedbiomasssamples.............................225
ationofhigherheatingvalue..............................................226
firingofbiomassandcoalblends.................................................227
-pyrolysis..............................................................227
ismofbiomasscofiringwithcoal.........................................228
sion....................................................................228
References.......................................................................229
0360-1285/$-htsrerved.
doi:10.1016/.2003.10.004
ProgressinEnergyandCombustionScience30(2004)219–230
/locate/pecs
*
.:þ90-462-230-7831;fax:þ90-462-
248-8508.
E-mailaddress:ayhandemirbas@(as).
uction
Biomasscanbeconvertedintoliquid,solidandgaous
fuelswiththehelpofsomephysical,chemicaland
biologicalconversionprocess[1,2].Theconversionof
biomassmaterialshasapreciobjectivetotransforma
carbonaceoussolidmaterialwhichisoriginallydifficultto
handle,bulkyandoflowenergyconcentration,intothefuels
havingphysico–chemicalcharacteristicswhichpermit
economicstorageandtransferabilitythroughpumping
systems.
Worldwidebiomassranksfourthasanenergyresource,
providingapproximately14%oftheworld’nergyneeds;
biomassisthemostimportantsourceofenergyin
developingnations,providing;235%oftheirenergy[3,4].
Theuofbiomassfuelsprovidessubstantialbenefitsas
sabsorbs
carbondioxideduringgrowth,andemitsitduringcombus-
ore,biomasshelpstheatmosphericcarbon
dioxiderecyclinganddoesnotcontributetothegreenhou
sconsumesthesameamountofCO
2
fromthe
atmosphereduringgrowthasisreleadduringcombustion.
ssources
Biomassfuelspotentialincludeswood,short-rotation
woodycrops,agriculturalwastes,short-rotationherbaceous
species,woodwastes,bagas,industrialresidues,waste
paper,municipalsolidwaste,sawdust,bio-solids,grass,
wastefromfoodprocessing,aquaticplantsandalgaeanimal
wastes,wastesare
anothersignificantpotentialbiomassresourceforelectricity
generation,andlikecropresidues,havemanyapplications,
sisonlyorganic
petroleumsubstitutewhichisrenewable.
Biomassoffersimportantadvantagesasacombustion
feedstockduetothehighvolatilityofthefuelandthehigh
r,it
shouldbenoticedthatincomparisonwithsolidfossilfuels,
biomasscontainsmuchlesscarbonandmoreoxygenand
hasalowheatingvalue.
Theburningvelocityofpulverizedbiomassfuelsis
verized
biomassfuelscanbeburnedinaflameinthesamewayas
oilorgasfuelsandatthesamehighpoweroutput[5].
tbiomassconversiontechnologies
Directcombustionistheoldwayofusingbiomass.
Biomassthermo-chemicalconversiontechnologiessuchas
pyrolysisandgasificationarecertainlynotthemost
importantoptionsatprent;combustionisresponsiblefor
over97%oftheworld’sbio-energyproduction.
Someprocesssuchaspyrolysis,gasification,
anaerobicdigestionandalcoholproductionhavewidely
beenappliedtobiomassinordertoobtainitnergy
scanbedirectlyfiredindedicated
r,cofiringbiomassandcoalhastechni-
cal,economical,andenvironmentaladvantagesoverthe
firingbiomasswithcoal,incomparison
withsinglecoalfiring,helpsreducethetotalemissions
estofallfuels,wood
(orbiomass),andtheoldoriginalfueloftheindustrial
revolution,coal,arekeytothismovetoanewmission.
Technicalissuesthatcanleadtodoubtaboutofbiomass
cofiringwithcoalarebeingresolvedthroughtestingand
experience[6].
Maincurrentbiomasstechnologiesare[7]:
ctivecarbonizationofwoodybiomassto
charcoal
ficationofbiomasstogaousproducts
sisofbiomassandsolidwastestoliquid,solid
andgaousproducts
riticalfluidextractionsofbiomasstoliquid
products
actionofbiomasstoliquidproducts
ysisofbiomasstosugarsandethanol
bicdigestionofbiomasstogaousproducts
spowerforgeneratingelectricitybydirect
combustionorgasificationand
sis
firingofbiomasswithcoal
icalconversionofbiomassandwaste(biogas
production,wastewatertreatment)
sdensification(briquetting,pelleting)
iccookstovesandheatingappliancesof
fuelwood
nergyconrvationinhouholdsand
industry
hotovoltaicandbiomassbadrural
electrification
sionofbiomasstoapyrolyticoil(biofuel)for
vehiclefuel
sionofbiomasstomethanolandethanolfor
internalcombustionengines
Inearlierwork[8],groundbiomasssampleshavebeen
convertedcompletelyintowaterinsolubleandsoluble
chemicalsintheprenceofanhydrousglycerinwithalkali
suchasNa
2
CO
3
tonesolublesfrom
acidificationoftheliquefactionproductswascalledbiofuel
ubilityofthebiofuelingasolinewas
testedas1.96%herwork[9],theacetone
solublesofthepyrolysisproductsfromthebiomasssamples
wereaddedtogasoline.
astes
Thewasteproductsofahomeincludepaper,containers,
tincans,aluminiumcans,andfoodscraps,aswellaswage.
as/ProgressinEnergyandCombustionScience30(2004)219–230220
Thewasteproductsofindustryandcommerceinclude
paper,wood,andmetalscraps,aswellasagriculturalwaste
products[10,11].Biodegradablewastes,suchaspaperfines
andindustrialbiosludge,intomixedalcoholfuels(e.g.
isopropanol,isobutanol,isopentanol).Thewastesarefirst
treatedwithlimetoenhancereactivity;thentheyare
convertedtovolatilefattyacids(VFAs)suchasaceticacid,
propionicacid,andbutyricacid—usingamixedcultureof
microorganismsderivedfromcattlerumenoranaerobic
dpaperwastesmayalso
tentsofdomestic
solidwastearegiveninTable1.
Therearefourmajormethodsforconversionoforganic
wastestosyntheticfuels:(1)hydrogenation;(2)pyrolysis;
(3)gasification:and(4)bioconversion[12].Thefirstthree
havebeenadvancedtothepilot-plantstage,whilethefourth
hasbeenthesubjectofonlyminorrearcheffort,butisa
lsolidwastesincludewood
material,pulpandpaperindustryresidues,agricultural
residues,organicmunicipalmaterial,wage,manure,and
sisconsideredoneof
themainrenewableenergyresourcesofthefutureduetoits
largepotential,economicviabilityandvarioussocialand
environmentalbenefistimatedthatby2050
biomasscouldprovidenearly38%oftheworld’sdirectfuel
uand17%oftheworld’lectricity[13].Ifbiomassis
producedmoreefficientlyandudwithmodernconversion
technologies,itcansupplyaconsiderablerangeand
pal
solidwaste(MSW)isdefinedaswastedurablegoods,
nondurablegoods,containersandpackaging,foodscraps,
yardtrimmings,andmiscellaneousinorganicwastesfrom
residential,commercial,andindustrialsources.
Generationreferstotheamountofmaterialthatenters
thewastestreambeforerecovery,composting,orcombus-
ryreferstomaterialsremovedfromthewaste
streamforthepurpoofrecyclingand/orcomposting.
Table2showsthegenerationandrecoveryofMSWinthe
rgycontentofMSWintheUSis
typicallyfrom10.5to11.5MJ/erationand
recoveryofMSWvariesdramaticallyfromcountryto
mple,recent
estimatesindicateMSWgenerationintheUKofabout30
milliontonsofwhich90%islandfiarison,
Swedenlandfilledonly34%oftheirMSWgeneration[14].
ficationofbiomass
Gasificationisaformofpyrolysis,carriedoutathigh
resultinggas,knownasproducergas,isamixtureofcarbon
monoxide,hydrogenandmethane,togetherwithcarbon
dioxideandnitrogen.
Biomassgasificationtechnologieshavehistoricallybeen
baduponpartialoxidationorpartialcombustionprin-
ciples,resultingintheproductionofahot,dirty,low
calorificvaluegasthatmustbedirectlyductedintoboilers
tiontolimitingapplicationsandoften
compoundingenvironmentalproblems,thetechnologies
areaninefficientsourceofusableenergy.
Biomassgasificationisthelatestgenerationofbiomass
energyconversionprocess,andisbeingudtoimprove
theefficiency,andtoreducetheinvestmentcostsofbiomass
electricitygenerationthroughtheugasturbinetechnol-
ficiencies(uptoabout50%)areachievable
usingcombined-cyclegasturbinesystems,wherewaste
gasfromthegasturbinearerecoveredtoproducesteam
icstudiesshowthat
biomasssuffocationplantscanbeaconomicalas
conventionalcoal-firedplants.
eformingofbiomass
Mostbiomassgasificationsystemsutilizeairoroxygen
inpartialoxidationorcombustionprocessThepro-
cesssufferfromlowthermalefficienciesandlowcalorific
Table1
Contentsofdomesticsolidwaste(Percentageoftotal)
ComponentLowerlimitUpperlimit
Paperwaste33.250.7
Foodwaste18.321.2
Plasticmatter7.811.2
Metal7.310.5
Glass8.610.2
Textile2.02.8
Wood1.82.9
Leatherandrubber0.61.0
Miscellaneous1.21.8
Source:Ref.[48].
Table2
GenerationandrecoveryofMSWintheUS,1993(milliontons)
MaterialGenerationRecoveredDiscardedProjected
generated
2000
Paper70.524.046.681.0
Glass12.42.79.712.7
Metals15.54.710.817.2
Plastics17.50.616.920.4
Rubber/leather5.60.45.46.9
Textiles5.50.64.95.6
Wood12.41.211.214.5
Food12.5012.512.7
Yardtrimmings29.85.923.920.1
c2.802.83.0
Others3.00.62.43.2
Total187.540.7147.1197.3
Source:Ref.[49].
as/ProgressinEnergyandCombustionScience30(2004)219–230221
gasbecauoftheenergyrequiredtoevaporatethemoisture
typicallyinherentinthebiomassandtheoxidationofa
portionofthefeedstocktoproducethinergy.
Theprossofsynfuelsfrombiomasswilllowerthe
energycost,improvethewastemanagementandreduce
ipleassaultonplantoperating
challengesisaproprietarytechnologythatgasifiesbiomass
byreactingitwithsteamathightemperaturestoforma
cleanburningsynthesisgas(calledasthesyngas,hydrogen
andcarbonmonoxideina2to1ratio).Themoleculesinthe
biomass(primarilycarbon,hydrogenandoxygen)andthe
moleculesinthesteam(hydrogenandoxygen)reorganizeto
formthissyngas[7].
ficationsystems
Gasificationforpowerproductioninvolvesthe
devolatilizationandconversionofbiomassinan
atmosphereofsteamand/orairtoproduceamedium
orlowcalorifisprent,theratioof
numberofvariablesaffectgasificationbadprocess
fi
blownordirectlyheatedgasifiers,utheexothermic
reactionbetweenoxygenandorganicstoprovidetheheat
necessarytodevolatilizebiomassandtoconvertresidual
carbon-richchars.
Commercialgasifiersareavailableinarangeofsizeand
types,andrunonavarietyoffuels,includingwood,
charcoal,utputis
determinedbytheeconomicsupplyofbiomass,whichis
limitedto80MWinmostregions.
Thebiomassgasificationprocessissimilartoprocess
udformanyyearsbychemicalandpetrochemical
manufacturers,includingmethanol,ammoniaandethylene
echemicalprocess,naturalgasor
anotherhydrocarbonis‘reformed’intoamoredesirable
gaouschemicalfeedstockbyreactingitwithsteamat
rogenandoxygenmolecules
inthesteamareliberatedandariesofreactionsresultina
reorganizationofthecompoundstoformsynthesisgas
(primarilyH
2
,COandCO
2
).Thissynthesisgasisthen
catalyticallyconvertedintomethanol,ammoniaoranother
product.
sisofbiomass
Pyrolysisisdefinedasthethermaldestructionoforganic
sisisthebasic
thermochemicalprocessforconvertingbiomasstoamore
ufulfuel[15].Biomassisheatedintheabnceofoxygen,
orpartiallycombustedinalimitedoxygensupply,to
produceahydrocarbonrichgasmixture,anoil-likeliquid
andacarbonrichsolidresidue.
Inpyrolysisprocess,biomassconvertsintoliquid(bio-
oilorbio-crude),charcoalandnon-condensablegass,
aceticacid,acetone,andmethanolbyheatingthebiomassto
cesscanbe
adjustedtofavorcharcoal,pyrolyticoil,gas,ormethanol
productionwitha95.5%fuel-to-feedeffisis
canbeudfortheproductionofbio-oilifflashpyrolysis
processareudandarecurrentlyatpilotstage[16].
Someproblemsintheconversionprocessanduoftheoil
needtobeovercome;theincludepoorthermalstability
ingbyloweringtheoxygen
contentandremovingalkalisbymeansofhydrogenation
andcatalyticcrackingoftheoilmayberequiredforcertain
applications[12].
Pyrolysisofwoodhasbeenstudiedasazonalprocess
[17].Thermaldegradationpropertiesofhemicellulos,
cellulosandlignincanbesummarizedasfollows[18]:
ulo.
oflignin
Pyrolysisofbiomassisthermaldecompositionofthe
coal,pyrolysisisarelativelyslowchemical
ction
mechanismsofbiomasspyrolysisarecomplexbutcanbe
definedinfivestagesforwood[19]:
reandsomevolatileloss.
ownofhemicellulo;emissionofCOandCO
2
.
rmicreactioncausingthewoodybiomass
temperaturetorifrom525to625K;emissionof
methane,hydrogenandethane.
alenergyisnowrequiredtocontinuethe
process.
tedecompositionoccurs.
opertiesofbiomass
Thelimitationswereprimarilyduetorelyingonbiomass
asthesolesourceoffuel,despitethehighlyvariable
hmoistureandashcontentsin
biomassfuelscancauignitionandcombustionproblems.
Themeltingpointofthedissolvedashcanalsobelowwhich
eofthelower
heatingvaluesofbiomassaccompaniedbyflamestability
ticipatedthatblendingbiomasswithhigher
qualitycoalwillreduceflamestabilityproblems,aswellas
minimizecorrosioneffects.
Themethodsofbiomassfuelanalysaregivenin
soffersimportantadvantagesasa
combustionfeedstockduetothehighvolatilityofthefuel
andthehighreactivityofboththefuelandtheresulting
r,itshouldbenoticedthatincomparisonwith
solidfossilfuels,biomasscontainsmuchlesscarbonand
,chlorine
contentsofcertainbiofuels,likestrawcanexceedthelevel
as/ProgressinEnergyandCombustionScience30(2004)219–230222
ombustionapplications,biomasshasbeen
fireddirectlyeitheraloneoralongwithaprimaryfuel.
Chlorine,whichisfoundincertainbiomasstypes,suchas
straw,hchlorine
andalkalicontentofsomebiomassfuelsraiconcerns
atestconcernfocusonhigh-
temperaturecorrosionofsuper-heatertubesinducedby
chlorineonthesurface.
Biomassdiffersfromcoalinmanyimportantways,
includingtheorganic,inorganic,energycontent,and
vetocoal,biomassgenerally
haslesscarbon,moreoxygen,moresilicaandpotassium,
lessaluminumandiron,lowerheatingvalue,higher
moisturecontent,andlowerdensityandfriability(Table4).
Thepointontheburningprofileatwhichtherateof
weightlossduetocombustionisamaximumcalledas‘peak
temperature’.Theburningprofilepeaktemperatureis
usuallytakenasameasureofthereactivityofthesample.
Thepeaktemperaturesforbiomasssamplesgenerallyvary
from560to575K.
Thestructuralanalysoflectedbiomasssamplesare
imateanalysoftypicalfuel
samplesgivenintheliteratureanddeterminedareshownin
Tables6and7,fficulttoestablisha
reprentativebiomassduetolargepropertyvariations,but
compositionvariationsamongbiomassfuelsarelarger
thanamongcoals,butasaclassbiomasshassubstantially
viously,
nitrogen,chlorine,andashvarysignificantlyamong
omponentsaredirectlyrelatedto
NO
x
emissions,corrosion,s
generallyhasrelativelylowsulfurcomparedtocoal.
Theproximateanalysoflectedbiomasssamples
givenintheliteratureanddeterminedasdefinedbyASTM
areshowninTables8and9,rganic
propertiesoflectedfuelsamplesaregiveninTable10.
Inorganiccomponentsincoalvarybyrankandgeographic
Table3
Methodsofbiomassfuelanalys
PropertyAnalyticalmethod
HeatingvalueASTMD2015,E711
ParticlesizedistributionASTME828
Proximatecomposition
MoistureASTME871
AshASTMD1102(873K),
ASTME830(848K)
VolatilematterASTME872,ASTME897
Fixedcarbonbydifference
Ultimateelemental
Carbon,hydrogenASTME777
NitrogenASTME778
SulfurASTME775
ChlorineASTME776
OxygenBydifference
AshelementalASTMD3682,ASTMD2795,
ASTMD4278,AOAC14.7
Table4
Physical,chemicalandfuelpropertiesofbiomassandcoalfuels
PropertyBiomassCoal
Fueldensity(kg/m3),500,1300
Particlesize,3mm,100mm
Ccontent(wt%ofdryfuel)42–5465–85
Ocontent(wt%ofdryfuel)35–452–15
Scontent(wt%ofdryfuel)Max0.50.5–7.5
SiO
2
content(wt%ofdryash)23–4940–60
K
2
Ocontent(wt%ofdryash)4–482–6
Al
2
O
3
content(wt%ofdryash)2.4–9.515–25
Fe
2
O
3
content(wt%ofdryash)1.5–8.58–18
Ignationtemperature(K)418–426490–595
Peaktemperature(K)560–575–
FriabilityLowHigh
Dryheatingvalue(MJ/kg)14–2123–28
Table5
Structuralanalysoflectedbiomasssamples(wt.%daf)
FuelsampleHemicellulosCelluloLigninExtractive
mattera
Hazelnutshell30.426.842.93.3
Wheatstraw39.428.818.6–
Olivehusk23.624.048.49.4
Beechwood31.245.321.91.6
Sprucewood20.749.827.02.5
Corncob31.050.515.03.5
Teawaste19.930.240.09.9
Walnutshell22.725.652.32.8
Almondshell28.950.720.42.5
Sunflowershell34.648.417.02.7
Source:Ref.[32].
aAlcohol/benzene(1/1,v/v)extractives.
Table6
Ultimateanalysoftypicalfuelsamplesgivenintheliterature(wt
%ofdryfuelwithash)
FuelsampleCHNSO(diff.)Reference
Hazelnutshell52.85.61.40.0442.6[32,57]
Sawdust46.95.20.10.0437.8[50]
Cornstover42.55.00.80.242.6[51]
Poplar48.45.90.40.0139.6[52]
Ricehusk47.85.10.1–38.9[53]
Cottongin42.85.41.40.535.0[54]
Sugarcanebagas44.85.40.40.0139.6[52]
Peachpit53.05.90.30.0539.1[52]
Alfafastalk45.45.82.10.0936.5[55]
Switchgrass46.75.90.80.1937.4[55]
as/ProgressinEnergyandCombustionScience30(2004)219–230223
ss,coalhasmorealuminum,iron,and
shasmoresilica,potassium,
dandwoody
materialstendtobelowinnitrogenandashcontentwhile
theagriculturalmaterialscanhavehighnitrogen(Tables6
and7)andashcontents(Tables8and9).
Strawmayhaveahighcontentofchlorineand
potassium,elementswhichareveryundesirablein
ofK
2
OandClwerefoundas
20.0and3.6%inash,respectively,inwheatstraws
(Table10).Apretreatmentprocesstoremovepotassium
fromstrawfuelmaybebadonpyrolysisfollowedby
awispyrolyzedatmoderatetempera-
turesatwhichthepotassiumisretainedinthechar.
Potassiumandresidualchlorineareextractedfromthe
residualcharbywater[20].Charandpyrolysisgasmay
thenbeudinaconventionalboilerwithoutproblems
uatethis
pretreatmentprocessknowledgeaboutthecharwash
s,whenreactedwithsulfatesand
chlorine,mayharmthermochemicalconversionsystems,
foulingheatexchangesurfaces,gas-turbineblades,and
otherpowersystemcomponents[21].
tionpropertiesofbiomass
Ingeneralcombustionmodelsofbiomasscanbe
classifiro-
scopicpropertiesofbiomassaregivenwithfor
macroscopicanalysis,suchasultimateanalysis,heating
value,moisturecontent,particlesize,bulkdensity,and
tiesformicroscopic
analysisincludethermal,chemicalkinetic,andmineral
data[22].Fuelcharacteristicssuchasultimateanalysis,
heatingvalue,moisturecontent,particlesize,bulk
density,andashfusiontemperatureofbiomasshave
beenreviewed[23].Fuelpropertiesforthecombustion
analysisofbiomasscanbeconvenientlygroupedinto
physical,chemical,thermal,andmineralproperties.
Physicalpropertyvaluesvarygreatlyandproperties
suchasdensity,porosity,andinternalsurfaceareaare
relatedtobiomassspecieswhereasbulkdensity,particle
size,andshapedistributionarerelatedtofuelpreparation
methods.
Importantchemicalpropertiesforcombustionarethe
ultimateanalysis,proximateanalysis,analysisofpyrolysis
products,higherheatingvalue,heatofpyrolysis,heating
valueofthevolatiles,andheatingvalueofthechar.
Thermalpropertyvaluessuchasspecificheat,thermal
conductivity,andemissivityvarywithmoisturecontent,
temperature,anddegreeofthermaldegradationbyoneorder
ldegradationproductsofbiomass
consistofmoisture,volatiles,lesare
furthersubdividedintogassuchaslighthydrocarbons,
carbonmonoxide,carbondioxide,hydrogenandmoisture,
ldsdependonthetemperatureandheating
opertiesvarywithspecies,
locationwithinthebiomass,
Table7
Ultimateanalysoftypicalfuelsamples(wt%ofdryfuelwithash)
FulsampleCHNSClO(diff.)
Coaltype181.54.01.23.0–3.3
Redoakwood50.06.00.3––42.4
Wheatstraw41.85.50.7–1.535.5
Olivehusk49.96.21.60.050.242.0
Beechwood49.56.20.4––41.2
Sprucewood51.96.10.3––40.9
Corncob49.05.40.50.2–44.5
Teawaste48.05.50.50.060.144.0
Walnutshell53.56.61.50.10.145.4
Almondshell47.86.01.10.060.141.5
Sunflowershell47.45.81.40.050.141.3
Source:Refs.[32,34].
Table8
Proximateanalysoflectedbiomassgivenintheliterature(wt%
ofdryfuel)
FuelsampleAshVolatile
matter
FixedcarbonReference
Hazelnutshell1.576.321.2[32]
Sawdust2.882.215.0[50]
Cornstover5.184.010.9[51]
Poplar1.3–16.4[52]
Sugarcanebagas11.3–15.0[52]
Peachpit1.0–19.9[52]
Ricehusk22.661.016.7[53]
Alfafastalk6.576.117.4[55]
Switchgrass8.976.714.4[55]
Table9
Proximateanalysoflectedbiomasssamples(wt%ofdryfuel)
FuelsampleAshVolatilematterFixedcarbon
Beechwoodbark5.765.029.3
Oakwood0.577.621.9
Wheatstraw13.766.321.4
Olivehusk4.177.518.4
Beechwood0.582.517.0
Sprucewood1.780.218.1
Corncob1.187.411.5
Teawaste1.585.513.0
Walnutshell2.859.337.9
Almondshell3.374.022.7
Sunflowershell4.076.219.8
Colzaed6.578.115.4
Pineone1.07.321.7
Cottonrefu6.681.012.4
Oliverefu9.266.124.7
Source:Refs.[30,32,34].
as/ProgressinEnergyandCombustionScience30(2004)219–230224
thepropertiesarehighlyvariable,thelikelyrangeofthe
propertyisgiven[22].
mistryofbiomasscombustion
Combustionisariesofchemicalreactionsbywhich
carbonisoxidizedtocarbondioxide,andhydrogenis
oxidizedtowater.
Inordertounderstandwoodcombustion,itisimportant
tounderstandthepropertiesofwoodwhichdetermineits
fluencingproperties
includeanatomicalstructureandpathwaysformovementof
moisture,moisturecontent,specificgravity,andholocellu-
loandlignin.
Maincombustionreactionsare:
Non-reactingsolid!Heat;drying!PyrolysisðVolatiles;
SteamÞ!Precombustionreactions!Primarygaspha
combustion!Secondarycombustion!Effluentstackgas
mbustionpropertiesoflectedbiomass
samples
Non-isothermalandisothermalthermogravimetrictech-
niqueshavecommonlybeenudtoinvestigatethe
reactivitiesofcarbonaceousmaterials[24–28].Aplotof
therateofweightlossagainsttemperaturewhileburninga
sampleunderoxidizingatmosphereisreferredtoasburning
profile[29].Theburningprofilesofsunflowershellandpine
firstpeak,
obrvedontheburningprofilesofthebiomasssamples
eleasingthe
moisture,somesmalllossinthemassofthesampleoccurred
nlossin
themassofthesamplesstartedatthetemperaturesbetween
450–500K,reprentingthereleaofsomevolatilesand
apidburningregion,therateofmassloss
proceededsorapidlythatitreachedtoitsmaximumvalue.
Rapidlossofmassimmediatelysloweddownatthe
hen,burning
rateapparentlydecreadandconquentlysomesmallloss
inthemassofthesamplecontinuouslywentonaslongas
temperaturewasincreadupto1273K,indicatingtheslow
ndofhold
timeat1273K,samplesreachedtotheconstantweightafter
givenperiods[30].
Themostimportantcharacteristictemperaturesofa
burningprofileareignitiontemperatureandpeaktempera-
ture[31].Theignitiontemperaturecorrespondstothepoint
atwhichtheburningprofi
ignitiontemperaturesofsamplesweredeterminedfrom
theirburningprofiTable11,thetemperatures
weredeterminedas475Kforsunflowershell,463Kfor
colzaed,475Kforpinecone,467Kforcottonrefuand
473Kforoliverefu[30].Thepointontheburningprofile
atwhichistherateofweightlossduetocombustionis
ningprofile
peaktemperatureisusuallytakenasameasureofthe
emperatureswerefoundas
573Kforsunflowershell,as535Kforcolzaed,as565K
Table10
Inorganicpropertiesoftypicalfuelsamples(wt%ofash)
FuelsampleSi
2
OAl
2
O
2
TiO
2
Fe
2
O
3
CaOMgONa
2
OK
2
OSO
3
P
2
O
5
Cl
Coaltype142.020.01.217.05.52.11.45.85.0––
Coaltype259.719.82.18.32.11.80.82.12.00.2–
Coaltype351.522.62.014.93.30.91.02.03.50.2–
Redoakwood49.09.5–8.517.51.10.59.52.61.80.8
Wheatstraw48.03.5–0.53.71.814.520.01.93.53.6
Walnutshell23.12.40.11.516.613.41.032.82.26.20.1
Almondshell23.52.70.12.810.55.21.648.50.84.50.2
Sunflowershell29.32.90.12.115.86.11.535.61.34.80.2
Olivehusk32.78.40.36.314.54.226.24.30.62.50.2
Hazelnutshell33.73.10.13.815.47.91.330.41.13.20.1
Source:Ref.[56].
as/ProgressinEnergyandCombustionScience30(2004)219–230225
forpinecone,as598Kforcottonrefusandas537Kfor
oliverefu(Table11).Therateofweightlossatthe
burningprofilepeaktemperatureiscalledthemaximum
imumcombustionratesofthe
sunflowershell,colzaed,pinecone,cottonrefuand
oliverefuwascalculatedas5.5,2.8,5.2,3.7and3.4mg/
min,respectively[30].
Theweightlosspercentagesoffivedifferentbiomass
theFig.3,theweightlossofthesamplesincreadsharply
ghtlossdifferencesbetweenolive
refuandothersamplesstartedtoincreaabove
efuhasthelowestvolatilemattercontent
andthehighestashcontent;inotherwords,oliverefuhas
ghtlosspercentagesof
thesunflowershell,colzaed,pinecone,cottonrefuand
oliverefuat1273Kwere%95.07,91.05,84.80,86.74
and78.69,respectively[30].
ationofhigherheatingvalue
Thehigherheatingvalues(HHVs)orgrossheatof
combustionincludethelatentheatofthewatervapor
productsofcombustionbecauthewatervaporwas
(inMJ/kg)
ofthebiomassfuelsasafunctionoffixedcarbon(FC,wt%)
wascalculatedfromEq.(1)[32]:
HHV¼0:196ðFCÞþ14:119ð1Þ
Inearlierworks[33,34],formulaewerealsodevel-
opedforestimatingtheHHVsoffuelsfromdifferent
lignocellulosicmaterials,vegetableoilsanddielfuels
mass
fuelssuchascoal,theHHVwascalculatedusingthe
modifiedDulong’sformula[33,35]asafunctionofthe
carbon,hydrogen,oxygen,andnitrogencontentsfrom
Eq.(2):
HHV¼{33:5½CC
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