Evaluation of the Life Cycle Greenhouse Gas Emissions from Different Biomass Feedstock ...

12 Pages·2016·0.64 MB·English

sustainability
Article
Evaluation of the Life Cycle Greenhouse Gas
Emissions from Different Biomass Feedstock
Electricity Generation Systems
AkhilKadiyala1,RaghavaKommalapati1,2,*andZiaulHuque1,3
1 CenterforEnergy&EnvironmentalSustainability,PrairieViewA&MUniversity,
PrairieView,TX77446,USA;[email protected](A.K.);[email protected](Z.H.)
2 DepartmentofCivil&EnvironmentalEngineering,PrairieViewA&MUniversity,
PrairieView,TX77446,USA
3 DepartmentofMechanicalEngineering,PrairieViewA&MUniversity,PrairieView,TX77446,USA
* Correspondence:[email protected];Tel.:[phone]
AcademicEditors:ArnulfJäger-WaldauandMarcA.Rosen
Received:19August2016;Accepted:11November2016;Published:16November2016
Abstract: Thispaperevaluateslifecyclegreenhousegas(GHG)emissionsfromtheuseofdifferent
biomass feedstock categories (agriculture residues, dedicated energy crops, forestry, industry,
parks and gardens, wastes) independently on biomass-only (biomass as a standalone fuel) and
cofiring (biomass used in combination with coal) electricity generation systems. The statistical
evaluation of the life cycle GHG emissions (expressed in grams of carbon dioxide equivalent
per kilowatt hour, gCO e/kWh) for biomass electricity generation systems was based on the
2
review of 19 life cycle assessment studies (representing 66 biomass cases). The mean life cycle
GHG emissions resulting from the use of agriculture residues (N = 4), dedicated energy crops
(N = 19), forestry (N = 6), industry (N = 4), and wastes (N = 2) in biomass-only electricity
generationsystemsare291.25gCO e/kWh,208.41gCO e/kWh,43gCO e/kWh,45.93gCO e/kWh,
2 2 2 2
and1731.36gCO e/kWh,respectively. ThemeanlifecycleGHGemissionsforcofiringelectricity
2
generation systems using agriculture residues (N = 10), dedicated energy crops (N = 9), forestry
(N=9),industry(N=2),andparksandgardens(N=1)are1039.92gCO e/kWh,1001.38gCO e/kWh,
2 2
961.45gCO e/kWh,926.1gCO e/kWh,and1065.92gCO e/kWh,respectively.Forestryandindustry
2 2 2
(avoidingtheimpactsofbiomassproductionandemissionsfromwastemanagement)contributethe
leastamountofGHGs,irrespectiveofthebiomasselectricitygenerationsystem.
Keywords:lifecycleassessment;greenhousegasemissions;biomass;biomass-only;cofiring;biomass
feedstock;agricultureresidue;dedicatedenergycrop;forestry;industry;parksandgardens;waste
1. Introduction
Biomass energy, also referred to as bioenergy, may be defined as the energy harnessed from
plantsandtheirderivatives(e.g.,wood,foodcrops,residuesfromagricultureorforestry,oil-richalgae,
andtheorganiccomponentofmunicipal/industrialwastes). Biomassisaproductofphotosynthesis,
inwhichthesun’senergyconvertswaterandcarbondioxide(CO )inplantsintoorganicmaterial[1].
2
The organic material stores sunlight in the form of chemical energy. The components of biomass
includecellulose,hemicellulose,lignin,extractives,lipids,proteins,simplesugars,starches,water,
hydrocarbons, ash, and other compounds. The composition of biomass varies among species.
In general, lignin (~25%) and carbohydrates or sugars (~75%) are identified to be the dominant
components [2–5]. The carbohydrate fraction contains many sugar molecules linked together in
long chains or polymers. There are two distinguished categories of carbohydrates: cellulose and
Sustainability2016,8,1181;doi:10.3390/su8111181 www.mdpi.com/journal/sustainability
Sustainability2016,8,1181 2of12
hemicellulose. Theenergyvalueofbiomassisdependentonthemoisturecontent. Asthemoisture
contentincreases,theenergycalorificvaluesofbiomassdecreases. Thedecreaseinenergycalorific
valuesisaresultofthereductionincombustiontemperatures[6]. Biomasswithhighmoisturecontent
mayleadtoincompletecombustion,therebyincreasingtheairemissions.
Thetotalelectricitygenerationin2012acrosstheworldwasreportedtobe21.53trillionkilowatt
hours(kWh)[7]. Theprojectedworldelectricitygenerationfor2040is39trillionkWh(anincreaseby
81%from2012)[8]. Therenewableenergysourceshavebeenprojectedtoaccountfor9.6trillionkWh
(25%)oftheworld’stotalelectricitygenerationin2040. Withthecontinuingdepletionoftraditional
nonrenewableenergysources,thenecessityforgeneratingelectricitythroughtheuseofrenewable
energysources(hydro, wind,biomass,geothermal,solar)increasedmanifold. Biomassaccounted
foronly0.384trillionkWh(2%)oftheworld’stotalelectricitygeneratedin2012despiteitsabundant
availability across the world. Based on the 2012 statistics, biomass was identified to be the third
largestrenewableenergysourceforelectricitygenerationafterhydro(3.646trillionkWh)andwind
(0.52trillionkWh)[7]. Themajorityoftheglobalenergy-useprojectionstudiesanticipatebiomassto
contributeabout10%–45%ofthetotalprimaryenergydemandinthecomingdecades[9].
One may adopt the use of the life cycle assessment (LCA) method to evaluate the net CO
2
equivalent (CO e) greenhouse gas (GHG) emissions from the use of biomass as a fuel. LCA is an
2
analyticalmethodthatprovidesanassessmentoftheenvironmentalimpactsoftheconsideredproducts
andtechnologiesfroma“cradletograve”systemsperspective,utilizingthedetailedinputandoutput
parametersthatoperatewithinthedesignatedsystemboundaries. DependingonthenetCO eGHGs
2
emittedacrosstheentirelifecycleprocessesconsidered,thebioenergyresourcesmaybeconsideredto
becarbonneutral(noneteffectonGHGs),carbonnegative(netreductioninGHGs),orcarbonpositive
(netincreaseinGHGs)[10].
Electricitygenerationfrombiomassonalargescaleisachievedthroughtheuseof(a)biomass-only
fired power plants and (b) cofiring in existing coal power plants by replacing coal with biomass.
Several studies have analyzed the LCA of biomass-only combustion [11–21] and biomass cofiring
with coal [12,13,20,22–29]. The two distinct advantages of cofiring in existing coal power plants
are the achievement of a higher net efficiency of biofuels conversion to electricity (the generally
higherefficiencyofverylarge-scalepowerplantsoffsetsthelowerefficiencyofthecoalboiler)and
a significant reduction in the investment costs. However, the option of cofiring requires higher
pretreatment consumption to achieve complete biofuel conversion in the coal utility boiler and
longertransportationcostsoftheresourcesassociatedwiththecoalpowerplantsnotbeingplacedin
potentiallyimportantbiomassproductionareas[20].AmoredetaileddescriptionoftheLCAboundary
conditions,GHGemissions,andsite-specificcharacteristicsassociatedwitheachoftheaforementioned
biomasselectricitygenerationsystemstudiesareprovidedinthesectionstitled“ReviewofBiomass-Only
LCAStudies”and“ReviewofBiomassCofiringwithCoalLCAStudies”.
AllthepriorbiomassLCAstudiesfocusedonthedeterminationoflifecycleGHGemissionsfrom
theuseofindividualbiomassfeedstockforelectricitygeneration. Noneoftheearlierstudiescompared
thelifecycleGHGemissionsforbiomasselectricitygenerationsystemsacrosstheindividualdistinct
feedstockcategories. Thisstudyaimstofillthisknowledgegapbyfollowingatwo-stepapproach;
thestudyincludedareviewoftheliteratureonbiomassLCAstudiesfollowedbyastatisticalevaluation
ofthelifecycleGHGemissionsfromfeedstock-basedbiomass-onlyandcofiringelectricitygeneration
systemsseparately. AmajorityofthebiomassLCAstudiesnotedintheliteraturehavenotincluded
specificdetailsonthetypeoffeedstockusedforelectricitygeneration. Resultantly,onlythebiomass
LCAstudiesthatclearlydefinedthebiomassfeedstocktypeutilizedforelectricitygenerationwere
consideredforthereview,classification,andstatisticalevaluationinthisstudy. Theperformanceofa
comprehensivestatisticalevaluationofthelifecycleGHGemissionswillhelpunderstandthedegree
ofconfidenceandvariabilityinGHGemissionsfromdifferentfeedstockcategoriesfortheconsidered
biomasselectricitygenerationsystem. Thisstudywillassistenergypolicymakersandenvironmental
professionalsinidentifyingandencouragingtheuseofenvironmental-friendlybiomassfeedstock
optionstogenerateelectricitywithminimalGHGemissions.
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2. Methodology
Areviewofthebiomassliteratureshowedthattherearewide-rangingtypesofbiomassthatmay
beutilizedingeneratingelectricity. Thenumeroustypesofbiomassmaybeclassifiedintodistinct
categoriesdependingonthetypeoffeedstock. TheIdahoNationalLaboratoryReport[30]providedan
extensiveclassificationoffeedstock-basedbiomassthatincludedsevendistinctcategoriesasfollows:
• Agricultureresidues(AR):includesdrylignocellulosicagricultureresidues(straw,sugarbeet
leaves)andlivestockwaste(solidmanure,liquidmanure)
• Dedicatedenergycrops(DEC):includesdrylignocellulosicwoodenergycrops(smallroundwood
(SRW)—willow,shortrotationcoppice(SRC)—poplar,eucalyptus),drylignocellulosicherbaceous
energycrops(miscanthus,switchgrass,commonreed,reedcanarygrass,giantreed,cynaracardu,
Indianshrub),oilenergycrops(sugarbeet,canebeet,sweetsorghum,Jerusalemartichoke,sugar
millet),starchenergycrops(wheat,potatoes,maize,barley,triticae,corn,amaranth),andother
energycrops(flax(Linum),hemp(Cannabis),tobaccostems,aquaticplants(lipidsfromalgae),
cottonstalks,kenaf)
• Forestry(F):includesforestrybyproducts(bark,woodblocks,woodchipsfromtopsandbranches,
woodchipsfromthinning,logsfromthinning)
• Industry (I): includes wood industry residues (industrial waste wood from sawmills/timber
mills(bark,sawdust,woodchips,slabs,off-cuts)),foodindustryresidues(wetcellulosicmaterial
(beetroottails),fats(usedcookingoils),tallow,yellowgrease,proteins(slaughterhousewaste)),
and industrial products (pellets from sawdust and shavings, briquettes from sawdust and
shavings,bio-oil(pyrolysisoil),ethanol,biodiesel)
• Parksandgardens(P-G):includesherbaceous(grass)andwoody(pruning)
• Wastes(W):includescontaminatedwastes(demolitionwood,biodegradable,municipalwaste,
sewagesludge,landfillgas,sewagegas)
• Others (O): includes roadside hay (grass/hay) and husks/shells (almond, olive, walnut,
palmpit,cacao)
Thisstudyadoptedthesameclassification(agricultureresidues,dedicatedenergycrops,forestry,
industry,parksandgardens,wastes,others)asproposedbytheIdahoNationalLaboratoryReport[30]
toevaluatethelifecycleGHGemissionsofbiomass-onlyandbiomasscofiringwithcoalelectricity
generation systems utilizing different feedstock options. Each of the reviewed biomass-only and
biomasscofiringLCAstudies(withspecificdetailsonthebiomassfeedstocktype)werefirstassigned
a biomass category. Next, the feedstock-based GHG emissions from biomass-only and biomass
cofiringelectricitygenerationsystemswereevaluatedusingstatisticalmetrics(samplesize,mean,
standarddeviation,minimum,maximum,standarderrorofthemean,quartile1,quartile2ormedian,
quartile 3) and graphical representations (error bars representing the mean with 95% confidence
intervals, box plots representing the quartiles with outliers). The sample size is a measure that
indicatesthetotalnumberofobservations. Themeanisameasurethatrepresentsthecentraltendency
oftheobserveddata. Thestandarddeviationisameasureusedtoquantifythedegreeofvariation
withinasetofobservationsfromasinglesample. Theminimumandmaximummeasuresdefinethe
lowestobservationandthehighestobservationwithaconsideredsample,respectively. Thestandard
errorofthemeanisameasurethatestimatesthevariabilitybetweensamplemeansobtainedbytaking
multiplesamplesfromthesamepopulation. Thestandarderrorofthemeandeterminestheprecision
betweenthemeanofthesampleestimatesandthepopulationmean. Thequartilestatisticsareaset
ofthreemeasuresthatdividearankedsetofobserveddatavaluesintofourequalgroups,witheach
groupcomprisingaquarterofthedata. Whiletheerrorbarsdemonstratethedegreeofconfidencein
themeanGHGemissions,theboxplotsprovideinformationonthedegreeofvariationamongthe
LCAstudiescharacterizedbydifferentbiomassfeedstockcategories.
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3. ResultsandDiscussion
3.1. ReviewofBiomass-OnlyLCAStudies
Several studies [11–21] evaluated the life cycle environmental impacts of using biomass as
a standalone fuel for electricity generation. When performing an LCA, one needs to define
the system boundary conditions (which includes details on the activities or processes to be
considered in the analysis) and a functional unit of measure (which enables quantification of the
netenvironmentalimpactsfromcarryingoutanactivityoraprocessasdefinedwithintheLCAsystem
boundaryconditions).
Themajorityoftheaforementionedstudies[13,17,18,21]thatperformedtheLCAofbiomass-only
electricity generation systems defined the system boundary conditions to include activities such
asbiomasscultivation,harvesting,processing,transportationtowarehousesandpowerplant,and
combustion. Other studies [12,14,16] set up their LCA system boundary conditions by including
the ash disposal activity in addition to the list of all activities associated with the majority of the
studies. Sebastiánetal.[20]consideredtheLCAsystemboundariesthatincludedbiomasscultivation,
harvesting,processing,transportationtowarehousesandpowerplant,constructionanddismantlingof
powerstation,combustion,andashdisposal. Onemaynotethatalltheabove-mentionedactivitiesare
associatedwiththeuseofdedicatedenergycropsandagricultureresiduesasfeedstockinbiomass-only
electricitygenerationsystems.
The Environment Agency Report [14] defined the LCA system boundaries to include wood
cutting,transportation,storage,andcombustionforthecasescenarioofusingforestryasfeedstockfor
biomass-onlyelectricitygeneration. Theactivityofashdisposalwasadditionallyconsideredtobe
withintheLCAsystemboundariesbyanotherstudy[18]thatexaminedtheenvironmentallifecycle
impactsofusingforestryasafeedstockforbiomass-onlyelectricitygeneration. Intinietal.[19]used
industryresidueasfeedstockforbiomass-onlyelectricitygeneration,wherethesystemboundaries
includedtheactivitiesofextractingvirginpomacefromanoliveoilmill,extractingdrypomaceby
dryingvirginpomace,extractingdeoiledpomacefrompomaceoil,combustion,andelectricitytransfer
tothegrid. Theremainingstudies[11,15]consideredtheLCAsystemboundariestoincludecollection,
segregationandsorting,transportation,andincinerationusingwasteasfeedstockforbiomass-only
electricitygeneration.
Thecommonfunctionalunitofmeasureadoptedbyamajorityofthebiomass-onlyLCAstudies
isgramsofCO eperkilowatthour(gCO e/kWh)ofelectricityproduced. Accordingly,thisstudyalso
2 2
adoptsthefunctionalunitofmeasureforGHGemissionstobegCO e/kWhofelectricityproduced.
2
Table1providesasummaryofthebiomassfeedstockcategorization(basedonthetypeofbiomass)
andthecorrespondingGHGemissions(ingCO e/kWh)foreachbiomass-onlyelectricitygeneration
2
LCAstudy. Additionalsite-specificdetailsonthepowergenerationcapacity(PGC,inMW),thepower
plantefficiency(η,in%),thepowergenerationmethod(PGM—directcombustion(DC),pyrolysis
combustion(PC)),andthegeographicallocation(GL)forthebiomass-onlyelectricitygenerationsystem
studiescanalsobeobtainedfromTable1.Basedonthereviewof11biomass-onlyelectricitygeneration
LCAstudies(refertoTable1),onemaynotethatdedicatedenergycrops(N =19)feedstock-based
biomass-only electricity generation systems were more in number compared to forestry (N = 6),
agriculture residues (N = 4), industry (N = 4), and waste (N = 2) feedstock-based biomass-only
electricity generation systems. There were no studies on the use of parks and gardens and other
feedstock-basedbiomass-onlyelectricitygenerationapplications.
In addition to computing the GHG emissions, one study [21] computed the acidification
potential (expressed in grams of sulfur dioxide equivalent per kilowatt hour (gSO e/kWh)) and
2
the eutrophication potential (expressed in grams of phosphates per kilowatt hour (gPO e/kWh))
4
fortheAR(ricestraw)biomassfeedstocktobe6.78gSO e/kWhand1.46gPO e/kWh,respectively.
2 4
AnotherstudynotedthattheuseoftheDEC(switchgrass)havinglowsulfurcontentproducedless
SO emissionswhengeneratingelectricitythroughdirectcombustion[12].
2
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Table1.Greenhousegas(GHG)emissionsforbiomass-onlyelectricitygenerationsystems.
BiomassFeedstock GHGEmissions AdditionalFeatures
Source
Category(BiomassType) (gCO2e/kWh) PGC(MW),η(%),PGM,GL
PGM=DC;GL=Germany
Intergovernmental W(municipalsolidwaste (GHGemissionsarecomputedusing415kgCO2per
PanelonClimate 922.22 tonofmunicipalsolidwasteandaveragedelectricity
incineration)
Change[11] generationpotentialof450kWhpertonofmunicipal
solidwaste)
Qinetal.[12] DEC(switchgrass) 68.5 η=17–25;PGM=DC;GL=USA
Stylesand DEC(miscanthus) 131 PGC=100–150MW;PGM=DC;GL=Ireland
Jones[13] DEC(willow) 132 PGC=100–150MW;PGM=DC;GL=Ireland
F(UKforest
10 PGM=DC;GL=UK
residues—chips)
F(Balticforest
22 PGM=DC;GL=UK
residues—chips)
I(wastewood—chips) 7 PGM=DC;GL=UK
DEC(SRC—chips) 17 PGM=DC;GL=UK
DEC(miscanthus—chips) 18 PGM=DC;GL=UK
Environment F(UKforest
38 PGM=DC;GL=UK
Agency[14] residues—pellets)
F(Balticforest
50 PGM=DC;GL=UK
residues—pellets)
I(wastewood—pellets) 51 PGM=DC;GL=UK
I(Balticwaste
66 PGM=DC;GL=UK
wood—pellets)
DEC(SRC—pellets) 100 PGM=DC;GL=UK
DEC
65 PGM=DC;GL=UK
(miscanthus—pellets)
AR(straw) 73 PGM=DC;GL=UK
W(municipalsolidwaste
Zaman[15] 2540.5 PGM=DC;GL=Sweden
incineration)
90 PGC=10MW;η=25;PGM=DC;GL=Spain
DEC(poplar)
95 PGC=25MW;η=28;PGM=DC;GL=Spain
100 PGC=50MW;η=30;PGM=DC;GL=Spain
Butnaretal.[16]
250 PGC=10MW;η=25;PGM=DC;GL=Spain
DEC(Ethiopianmustard)
260 PGC=25MW;η=28;PGM=DC;GL=Spain
260 PGC=50MW;η=30;PGM=DC;GL=Spain
AR(ricehusk) 67 PGC=190MW;η=20;PGM=DC;GL=Thailand
Siemers[17]
AR(ricestraw) 180 PGC=1-60MW;η=18;PGM=DC;GL=Thailand
76 PGC=10MW;η=18;PGM=PC;GL=USA
DEC(poplar)
50 PGC=10MW;η=25;PGM=PC;GL=USA
50 PGC=10MW;η=18;PGM=PC;GL=USA
Fanetal.[18] DEC(willow)
35 PGC=10MW;η=25;PGM=PC;GL=USA
82 PGC=10MW;η=18;PGM=PC;GL=USA
F(loggingresidues)
56 PGC=10MW;η=25;PGM=PC;GL=USA
I(deoiledoliveoil
Intinietal.[19] 59.7 PGC=12MW;PGM=DC;GL=Italy
pomace,wastewood)
Sebastián DEC(wheatstraw) 1076.39 PGC=100MW;η=25.8;PGM=DC;GL=Spain
etal.[20] DEC(Brassicacarinata) 1085.94 PGC=100MW;η=25.8;PGM=DC;GL=Spain
Shafieetal.[21] AR(ricestraw) 845 PGM=DC;GL=Malaysia
3.2. ReviewofBiomassCofiringwithCoalLCAStudies
Therearenumerousstudies[12,13,20,22–29]thatevaluatedthelifecycleenvironmentalimpacts
ofusingbiomassincombinationwithcoalfuelforelectricitygeneration.
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Themajorityofthebiomasscofiringstudies[12,13,22,28,29]definedtheLCAboundaryconditions
toincludeactivitiessuchasextractionoftherawmaterials(miningofcoal,cultivationandharvesting
ofbiomass),processingoffuel(coalandbiomasstorrefaction/pelletization),transportanddistribution
ofcoalandbiomass,combustioninpowerplant,andfinalwaste(ash)disposal. Inadditiontothese
activities, some studies [20,25] also included the construction and dismantling of a power station
withintheirsystemboundaries. Otherstudies[23,24,26,27]didnotconsiderashdisposalwithintheir
systemboundaries.
Paengjuntueketal.[29]evaluatedthelifecycleGHGemissionsforcofiringutilizinganintegrated
biomassgasificationfuelcell(BGFC)thatcombinedtheuseofsolidoxidefuelcellwiththeintegrated
gasificationcombinedcycle(IGCC)technologytoenhancetheenergyefficiency. TheIGCCtechnology
enablestheconversionofcoalandbiomassfuelintoapressurizedgas(referredtoassynthesisgas
(syngas))usingahigh-pressuregasifier. Theremaining10cofiringstudiesreviewedforthispaper
wereperformedthoughdirectcombustionincoalpowerplants.
Table 2 provides a summary of the biomass feedstock categorization (based on the type of
biomass)andthecorrespondingGHGemissions(ingCO e/kWh)foreachbiomasscofiringelectricity
2
generationLCAstudy. Additionalsite-specificdetailsonthePGC(inMW),η(in%),PGM(DC,PC,
gasification(G)),GL,andthebiomasscontributionlevelincofiringwithcoal(BCL)forthebiomass
cofiringelectricitygenerationsystemstudiescanbeobtainedfromTable2. Basedonthereviewof
11biomass-cofiringelectricitygenerationLCAstudies(refertoTable2),onemaynotethatagriculture
residue(N=10)feedstock-basedbiomass-cofiringelectricitygenerationsystemsweremoreinnumber
comparedtodedicatedenergycrops(N=9),forestry(N=9),industry(N=2),andparksandgardens
(N=1)feedstock-basedbiomasscofiringelectricitygenerationsystems. Therewerenostudiesonthe
useofwasteandotherfeedstock-basedbiomass-cofiringelectricitygenerationapplications.
Table2.GHGemissionsforbiomasscofiringelectricitygenerationsystems.
BiomassFeedstockCategory GHGEmissions AdditionalFeatures
Source
(BiomassType) (gCO2e/kWh) PGC(MW),η(%),PGM,GL,BCL
935.1 PGC=100MW;η=34.13;PGM=DC;GL=USA;BCL=10%
DEC(switchgrass)
Qinetal.[12] 966 PGC=100MW;η=34.13;PGM=DC;GL=USA;BCL=5%
875.6 PGC=100MW;η=34.13;PGM=DC;GL=USA;BCL=20%
Stylesand DEC(miscanthus) 1150 PGC=100-150MW;η=38.4;PGM=DC;GL=Ireland;BCL=30%
Jones[13] DEC(willow) 990 PGC=915MW;η=37.5;PGM=DC;GL=Ireland;BCL=10%
Sebastián DEC(wheatstraw) 1065.92 PGC=350MW;η=36.55;PGM=DC;GL=Spain;BCL=10%
etal.[20] DEC(Brassicacarinata) 1072.79 PGC=350MW;η=36.55;PGM=DC;GL=Spain;BCL=10%
I(woodresidue:cleanurban
wastewood,millresidue, 849.3 PGC=350MW;η=31.1;PGM=DC;GL=USA;BCL=15%
Mannand biomassgeneratedduring
Spath[22] timberstandimprovements,
someconstructionand
1002.9 PGC=354MW;η=31.5;PGM=DC;GL=USA;BCL=5%
demolitionresidues,and
industrialwoodresidues)
Heller
DEC(willow) 883 PGC=96MW;η=33.17;PGM=DC;GL=USA;BCL=10%
etal.[23]
F(forestresidue—torrefied
957 PGC=450MW;η=34;PGM=DC;GL=Canada;BCL=20.45%
pellets)
F(forestresidue—pellets) 1004 PGC=450MW;η=34;PGM=DC;GL=Canada;BCL=17.04%
F(forestresidue—chips) 1003 PGC=450MW;η=33;PGM=DC;GL=Canada;BCL=16.54%
Kabirand F(wholetree—torrefiedpellets) 967 PGC=450MW;η=34;PGM=DC;GL=Canada;BCL=20.45%
Kumar[24]
F(wholetree—pellets) 1014 PGC=450MW;η=34;PGM=DC;GL=Canada;BCL=17.04%
F(wholetree—chips) 1013 PGC=450MW;η=33;PGM=DC;GL=Canada;BCL=16.54%
AR(straw—torrefiedpellets) 1065 PGC=450MW;η=34;PGM=DC;GL=Canada;BCL=7.76%
AR(straw—pellets) 1082.8 PGC=450MW;η=34;PGM=DC;GL=Canada;BCL=9.3%
AR(straw—bale) 1083.4 PGC=450MW;η=33;PGM=DC;GL=Canada;BCL=7.53%
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Table2.Cont.
BiomassFeedstockCategory GHGEmissions AdditionalFeatures
Source
(BiomassType) (gCO2e/kWh) PGC(MW),η(%),PGM,GL,BCL
AR(wheatstraw) 1059.95 PGC=350MW;η=36.55;PGM=DC;GL=Spain;BCL=10%
P-G(fruittreepruning) 1065.92 PGC=350MW;η=36.55;PGM=DC;GL=Spain;BCL=10%
Royoetal.
[25] F(Spainforest) 1066.03 PGC=350MW;η=36.55;PGM=DC;GL=Spain;BCL=10%
DEC(brassicacarinata) 1073.99 PGC=350MW;η=36.55;PGM=DC;GL=Spain;BCL=10%
Huangetal. 1040 PGM=DC;GL=Taiwan;BCL=10%
AR(ricestrawtorrefaction)
[26]
990 PGM=DC;GL=Taiwan;BCL=20%
1181.7 PGM=DC;GL=USA;BCL=10%
Kaliyanetal. AR(cornstover)
1071.2 PGM=DC;GL=USA;BCL=20%
[27]
960.8 PGM=DC;GL=USA;BCL=30%
Tsalidisetal. F(Dutchforestrymaterials) 811 PGC=500MW;η=40;PGM=DC;GL=TheNetherlands
[28]
F(Canadianforestrymaterials) 818 PGC=500MW;η=40;PGM=DC;GL=TheNetherlands
Paengjuntuek
AR(ricestraw) 864.3 PGC=0.65MW;PGM=G;GL=Thailand
etal.[29]
Some of the LCA studies [24,26,28,29] summarized in Table 2 computed the acidification
and the eutrophication potentials for the corresponding biomass feedstocks considered in their
respectivestudies. Onestudy[24]notedtheacidificationpotentialsforF(forestresidue—torrefied
pellets,20.45%cofiring),F(forestresidue—pellets,17.04%cofiring),F(forestresidue—chips,16.54%
cofiring),F(wholetree—torrefiedpellets,20.45%cofiring),F(wholetree—pellets,17.04%cofiring),
F(wholetree—chips,16.54%cofiring),AR(ricestraw,7.76%cofiring),AR(ricestraw,9.3%cofiring),
and AR (rice straw, 7.53% cofiring) biomass feedstocks to be 5.16 gSO e/kWh, 5.38 gSO e/kWh,
2 2
5.39 gSO e/kWh, 5.18 gSO e/kWh, 5.41 gSO e/kWh, 5.41 gSO e/kWh, 5.86 gSO e/kWh,
2 2 2 2 2
5.77gSO e/kWh,and5.93gSO e/kWh,respectively. Another[26]notedtheacidificationpotentialfor
2 2
theAR(ricestraw)biomassfeedstocktobe21.07gSO e/kWhunder10%cofiringoperatingconditions
2
and 22.04 gSO e/kWh with 20% cofiring operating conditions, while that of the eutrophication
2
potential was computed to be 0.02 gPO e/kWh under 10% cofiring operating conditions and
4
0.06gPO e/kWhwith20%cofiringoperatingconditions. TheacidificationpotentialsforF(Dutch
4
forestrymaterialswithpelletization)andF(Canadianforestrymaterialswithtorrefiedpellets)were
determinedtobe88.1gSO e/kWhand105gSO e/kWh,respectively[28]. Theacidificationandthe
2 2
eutrophicationpotentialsfortheAR(ricestraw)biomassfeedstockwerenotedtobe2.6gSO e/kWh
2
and 0.15 gPO e/kWh, respectively [29]. The variations in the acidification and eutrophication
4
potentialsmaybeattributedtothevariationsinthelifecycleprocessstagesandthecofiringconditions.
3.3. StatisticalEvaluationofBiomass-OnlyLCAStudies
Figure1providesagraphicalpresentationofthe(a)errorbars(mean±95%confidenceinterval
(CI)statistics)and(b)boxplots(quartiles+outlierstatistics)forGHGemissionsfromthedifferent
feedstock-basedbiomass-onlyelectricitygenerationsystemsreviewedinthisstudy. Table3provides
astatisticalsummaryofthelifecycleGHGemissionsthatprovidesdetailsonthesamplesize(N),
mean(X)±standarddeviation(SD),minimum(Min.),maximum(Max.),standarderrorofthemean
(SE),quartile1(Q1),quartile2ormedian(Q2),andquartile3(Q3)forthedifferentfeedstock-based
biomass-onlyelectricitygenerationsystemsreviewedinthisstudy.
FromFigure1aandTable3,onemaynotethemeanlifecycleGHGemissionsobtainedfromthe
useofagricultureresidues,dedicatedenergycrops,forestry,industry,andwastesinbiomass-only
electricity generation systems are 291.25 gCO e/kWh, 208.41 gCO e/kWh, 43 gCO e/kWh,
2 2 2
45.92gCO e/kWh,and1731.36gCO e/kWh,respectively. Theforestryandindustryfeedstock-based
2 2
biomassproducedconsiderablylowerGHGemissionsthantheremainingthreebiomassfeedstock
categories. ThelowerGHGemissionsresultingfromtheuseofforestryandindustryfeedstock-based
biomass may be attributed to the fact that bioenergy chains having resources/residues as raw
Sustainability2016,8,1181 8of12
materials avoid the high impacts of dedicated energy crop production and emissions from waste
management[19,31,32].
Oftheremainingthreebiomassfeedstockcategories,dedicatedenergycropsproducedlower
meanlifecycleGHGemissions,followedbyagricultureresidues,andwastes. Theuseofdedicated
energycropsinexistingpowerstationshassignificantpotentialtoreduceGHGemissions[13].Mineral
fertilizersaccountedforthemajority(62%–82%)oftheGHGemissionsresultingfromcultivationof
dedicatedenergycrops[16]. Oneneedstoadopttheuseofnaturalfertilizerstofurtherreducethe
GHGsemittedfromtheuseofdedicatedenergycrops. Appropriatemitigatingstrategies, suchas
bestfarmingpracticestomaximizetheyield, areessentialtocontroltheGHGemissionsresulting
from an increased land footprint for natural fertilizers. Transportation accounted for the majority
oftheGHGemissionsfromricestrawpreparationunderthecategoryofagricultureresidues[21].
Thecompositionandsegregationofwastewereidentifiedtobethecriticalfactorsinfluencinglifecycle
GHGemissionsfromthewastefeedstock-basedbiomass-onlyelectricitygenerationsystems[33].
From Figure 1b, one may note the degree of variation in GHG emissions was less between
LCAstudiesbasedonforestry,followedbyindustry,dedicatedenergycrops,agricultureresidues,
andwastes.Themedianquartilestatistic(Q2)showedaconsistentpatterntothatobservedinthemean
lifecycleGHGemissionspattern,withforestrybeingtheminimum,followedbyindustry,dedicated
Seusntaeirngabyilictryo 2p01s6,, a8g, 1r1ic8u1 ltureresidues,andwastes(refertotheboxplotsfromFigure1bandTable83 )o.f 12
(a) (b)
Figure 1. GHG emissions from biomass-only electricity generation systems: (a) mean ± 95%
Figure1.GHGemissionsfrombiomass-onlyelectricitygenerationsystems:(a)mean±95%confidence
confidence interval (CI) error bars and (b) quartile box plots.
interval(CI)errorbarsand(b)quartileboxplots.
TTaabbllee 33.. GGHHGG eemmiissssiioonn ((ggCCOO2ee/k/WkWh)h s)tsattaistitsictisc sfrformom biboimomasass-so-nolnyl yeleelcetcrtirciictiyt ygegnenereartaitoinon sysystsetmems.s .
2
Biomass Type N X ± SD Min. Max. SE Q1 Q2 Q3
agBriiocumltausres rTeysipdeue N4 291X.25± ± 3S7D2.8 6M7 in. 8M45a x. 18S6.E4 67Q 1 126.Q5 2 180Q 3
dedicated energy crops 19 208.41 ± 316.54 17 1085.94 72.62 50 95 250
agricultureresidue 4 291.25±372.8 67 845 186.4 67 126.5 180
forestry 6 43 ± 25.67 10 82 10.48 22 44 56
dedicatedenergycrops 19 208.41±316.54 17 1085.94 72.62 50 95 250
industry 4 45.92 ± 26.67 7 66 13.33 7 55.35 59.7
forestry 6 43±25.67 10 82 10.48 22 44 56
waste 2 1731.36 ± 1144.3 922.22 2540.5 809.14 922.22 1731.36 922.22
industry 4 45.92±26.67 7 66 13.33 7 55.35 59.7
waste 2 1731.36±1144.3 922.22 2540.5 809.14 922.22 1731.36 922.22
3.4. Statistical Evaluation of Biomass Cofiring with Coal LCA Studies
Figure 2 provides a graphical presentation of the (a) error bars (mean ± 95% CI statistics) and (b)
The use of biomass has a potential to reduce the life cycle GHG emissions by 77%–99% in
box plots (quartiles + outlier statistics) for GHG emissions from the different feedstock-based biomass
comparisontofossilfuelcombustion,dependingonthefeedstockcategoryandcombustiontechnology
cofiring electricity generation systems reviewed in this study. Table 4 provides a statistical summary
used [18]. The biomass-only electricity generation system net electric efficiency was identified to
of the life cycle GHG emissions for the different feedstock-based biomass cofiring electricity
be the most important factor that influences the final GHG emission savings [20]. The mode of
generation systems reviewed in this study.
From Figure 2a and Table 4, the mean life cycle GHG emissions from the use of agriculture
residues (N = 10), dedicated energy crops (N = 9), forestry (N = 9), industry (N = 2), and parks and
gardens (N = 1) in biomass cofiring electricity generation systems are 1039.92 gCO2e/kWh, 1001.38
gCO2e/kWh, 961.45 gCO2e/kWh, 926.1 gCO2e/kWh, and 1065.92 gCO2e/kWh, respectively. These
results indicate that there is not much difference in the mean life cycle GHG emissions from cofiring
electricity generation systems utilizing different biomass feedstock categories. This may be attributed
to the fact that considerably higher GHGs are emitted from the combustion of coal than the
combustion of biomass. More LCA studies utilizing parks and gardens feedstock-based biomass for
biomass cofiring electricity generation systems are to be considered before one generalizes the
influence of parks and gardens feedstock on life cycle GHG emissions (considering the need to have
a minimum sample size of two to determine the degree of confidence in the mean life cycle GHG
emission statistic of parks and gardens feedstock-based biomass). Amongst the different feedstock
categories considered for biomass cofiring electricity generation systems, the mean life cycle GHG
emissions were noted to be the minimum for industry, followed by forestry, dedicated energy crops,
agriculture residues, and parks and gardens. One may note that the industry and the forestry
feedstock-based biomass cofiring electricity generation systems produced the lowest GHG emissions
(as also noted in the case for biomass-only electricity generation systems) owing to the elimination of
GHG emissions resulting from biomass production and waste management during the
implementation of bioenergy projects. The GHG mitigation per ton of dedicated energy crop during
cofiring was noted to be better than that for dedicated energy crop biomass-only combustion [12].
Sustainability2016,8,1181 9of12
transportation and distance would largely influence the GHG emissions from biomass electricity
generationsystems[14].
3.4. StatisticalEvaluationofBiomassCofiringwithCoalLCAStudies
Figure2providesagraphicalpresentationofthe(a)errorbars(mean±95%CIstatistics)and
(b) box plots (quartiles + outlier statistics) for GHG emissions from the different feedstock-based
biomasscofiringelectricitygenerationsystemsreviewedinthisstudy. Table4providesastatistical
summaryofthelifecycleGHGemissionsforthedifferentfeedstock-basedbiomasscofiringelectricity
generationsystemsreviewedinthisstudy.
From Figure 2a and Table 4, the mean life cycle GHG emissions from the use of agriculture
residues (N = 10), dedicated energy crops (N = 9), forestry (N = 9), industry (N = 2), and parks
and gardens (N=1) in biomass cofiring electricity generation systems are 1039.92 gCO e/kWh,
2
1001.38gCO e/kWh,961.45gCO e/kWh,926.1gCO e/kWh,and1065.92gCO e/kWh,respectively.
2 2 2 2
TheseresultsindicatethatthereisnotmuchdifferenceinthemeanlifecycleGHGemissionsfrom
cofiringelectricitygenerationsystemsutilizingdifferentbiomassfeedstockcategories. Thismaybe
attributedtothefactthatconsiderablyhigherGHGsareemittedfromthecombustionofcoalthanthe
Sustainability 2016, 8, 1181 9 of 12
combustionofbiomass. MoreLCAstudiesutilizingparksandgardensfeedstock-basedbiomassfor
Tbhieo mobasssercvoafitriionngs eolefc ltirfiec itcyycgleen GerHatGio nemsyisstseimonssa rbeetiongb escimonilsaidr ebreetdwbeeefno rdeeodniecagteende reanliezregsyt hceroinpflsu aenndce
foorfepsatrryk sinan tdheg acrodfeirnisnfge epdrsotcoecsks ownelirfee acylscole nGoHteGd einm iasnsiootnhser( csotnusdidye r[2in3g]. tThehen euesde toofh cahveemaimcailnsi manudm
fesratmilipzleerssi zweaosf itdweonttiofieddet etorm bien ethteh emdaejogrr eceoonftrciobnufitodre ntoce liifne tchyecmle eGanHlGife ecmycislesioGnHs Gweitmhi srseifoenresntcaeti sttoic
boiofmpaarskss parnoddugacrtidoenn [s3f4e]e.d stock-basedbiomass). Amongstthedifferentfeedstockcategoriesconsidered
forbFiroomma Fssigcuorfier 2inbg, oenleec tmriacyit ynogteen tehrea tdioengrseyes otef mvas,ritahteiomn eina nGlHifeGc eymcliessGioHnGs beemtwiseseionn LsCwAe rsetundoiteesd
fotor bfoertehsetrym winaims umminifmorailn, dfoulslotrwy,efdo lbloyw aegdricbuyltfuorree srterysi,ddueedsi,c dateeddiceanteedrg eyncerrogpys ,carogprisc,u alntudr einrdesuisdturye.s ,
Tahned mpeadrkiasna nqduagratirlde esntas.tiOstince (mQ2a)y snhootweethda at tdhieffienrdenuts tpryatatenrdn tthoe tfhoarte sotbrysefreveedds tionc kth-bea mseedanb ioGmHaGss
ecmoifisrsiinogn eplaecttterricni,t ywgitehn einradtuiosntrysy bsteeinmgs tphreo dmuicneimduthme,l ofowlleoswtGedH bGye dmeidsisciaotnesd( aesnearlsgoy ncorotepds,i nfotrheestcrays,e
afnodr bagiormicuasltsu-oren lryeseildecutersic (irtyefgere ntoe rtahteio bnosxy pstleomts sf)roomwi Fniggtuoreth 2ebe alinmdi nTaatbiolen 4o).f GHGemissionsresulting
fromAblli othmea rsesvpireowdeudc tsitoundaiensd owna csotefimrinagn angoetmede nctodnusirdinergatbhlee irmedpulecmtioennst aitnio GnHofGb ieomenisesrigoynsp rwohjeecnts .
cTomhepGarHeGd wmiitthig faotsiosinl fpueerl tcoonmobfudsetdioicna. tIetd meanye rbgey ncortoepdd furormin gthceo firerviniegww oafs sneoletecdt sttoubdeiebse [t1te2r,2t2h,a2n6,2th7a] t
thfoart daesd tihcaet epderecneenrgtaygcer oopf bbiioommaassss- oinnl ycocfoimrinbgu sitniocnre[a1s2e]d.,T htheeo lbisfee rcvyactiloen GsHofGli feemcyiscsleioGnHs Gdeecmreiasssieodn. s
Cboeminbgussitmioinla ranbedt wtreaennspdoerdtiactaiotend weneerreg yidcernotpifsieadn dtof obrees ttrhye inmtahjeorc ocfiornintrgibpurtoocress stow leirfee aclyscolen oGteHdGin
eamniostshioenrss tiund cyof[i2r3in].gT [h2e8]u. sSeomofec hsteumdiiceas l[s2a4n,2d6]f enrotitleizde arsn winacsreidaseen tiinfi ethdet oenbeergthye dmenasjoitryc aonndtr icboufitroinrgto
elfiffieciceyncclye wGHillG heelmp irsesdiouncse wthieth lirfeef ecryecnlec eGtHoGbi oemmaissssiopnros.d uction[34].
(a) (b)
FFigiguurere 22. .GGHHGG eemmisisssioionns sfrfroomm bbioiommaassss ccooffiirriningg eelleeccttrricicitityy ggeenneerraattioionn ssyysstteemmss: :(a(a) )mmeeaann ±± 9955%% CCI I
eerrroror rbbaarsr saanndd (b(b) )qquuaartritliele bbooxx pplolotsts. .
Table 4. GHG emission (gCO2e/kWh) statistics from biomass cofiring electricity generation systems.
Biomass Type N Mean ± SD Min. Max. SE Q1 Q2 Q3
agriculture residue 10 1039.92 ± 85.27 864.3 1181.7 26.96 990 1062.48 1082.8
dedicated energy crops 9 1001.38 ± 95.02 875.6 1150 31.67 935.1 990 1072.79
forestry 9 961.45 ± 88.85 811 1066.03 29.62 957 1003 1013
industry 2 926.1 ± 108.61 849.3 1002.9 76.8 849.3 926.1 1002.9
parks and gardens 1 1065.92 ± 0 1065.92 1065.92 0 1065.92 1065.92 1065.92
4. Conclusions
This paper evaluated the life cycle GHG emissions from different feedstock category-based
biomass-only and cofiring electricity generation systems using a two-step approach. The first step
involved a comprehensive search for biomass-only and cofiring LCA studies, followed by a
comprehensive review that included categorization of each of the identified biomass-only and
cofiring LCA based on the type of feedstock. The second step involved the computation of statistical
parameters that enables quantification of the life cycle GHG emissions with a degree of confidence
and examination of the variability in life cycle GHG emissions.
A total of 11 biomass-only and 11 cofiring electricity generation LCA case studies were identified
from the literature. The identified biomass-only and cofiring electricity generation LCA studies were
Sustainability2016,8,1181 10of12
Table4.GHGemission(gCO e/kWh)statisticsfrombiomasscofiringelectricitygenerationsystems.
2
BiomassType N Mean±SD Min. Max. SE Q1 Q2 Q3
agricultureresidue 10 1039.92±85.27 864.3 1181.7 26.96 990 1062.48 1082.8
dedicatedenergycrops 9 1001.38±95.02 875.6 1150 31.67 935.1 990 1072.79
forestry 9 961.45±88.85 811 1066.03 29.62 957 1003 1013
industry 2 926.1±108.61 849.3 1002.9 76.8 849.3 926.1 1002.9
parksandgardens 1 1065.92±0 1065.92 1065.92 0 1065.92 1065.92 1065.92
FromFigure2b,onemaynotethedegreeofvariationinGHGemissionsbetweenLCAstudies
for forestry was minimal, followed by agriculture residues, dedicated energy crops, and industry.
The median quartile statistic (Q2) showed a different pattern to that observed in the mean GHG
emissionpattern,withindustrybeingtheminimum,followedbydedicatedenergycrops,forestry,
andagricultureresidues(refertotheboxplotsfromFigure2bandTable4).
All the reviewed studies on cofiring noted considerable reductions in GHG emissions when
comparedwithfossilfuelcombustion. Itmaybenotedfromthereviewofselectstudies[12,22,26,27]
that as the percentage of biomass in cofiring increased, the life cycle GHG emissions decreased.
CombustionandtransportationwereidentifiedtobethemajorcontributorstolifecycleGHGemissions
incofiring[28]. Somestudies[24,26]notedanincreaseintheenergydensityandcofiringefficiency
willhelpreducethelifecycleGHGemissions.
4. Conclusions
This paper evaluated the life cycle GHG emissions from different feedstock category-based
biomass-onlyandcofiringelectricitygenerationsystemsusingatwo-stepapproach. Thefirststep
involved a comprehensive search for biomass-only and cofiring LCA studies, followed by
a comprehensive review that included categorization of each of the identified biomass-only and
cofiringLCAbasedonthetypeoffeedstock. Thesecondstepinvolvedthecomputationofstatistical
parametersthatenablesquantificationofthelifecycleGHGemissionswithadegreeofconfidenceand
examinationofthevariabilityinlifecycleGHGemissions.
Atotalof11biomass-onlyand11cofiringelectricitygenerationLCAcasestudieswereidentified
fromtheliterature. Theidentifiedbiomass-onlyandcofiringelectricitygenerationLCAstudieswere
categorizedonthebasisofthetypeoffeedstock(agricultureresidues,dedicatedenergycrops,forestry,
industry,parksandgardens,wastes). Whiletheuseofmineralfertilizerswasidentifiedtobethemajor
contributortoGHGemissionsfromdedicatedenergycropproduction,transportationwasidentified
tobethemajorcontributortoGHGemissionsfromagricultureresiduepreparation. Theuseofforestry
andindustryfeedstockcategoriesavoidedthehigheremissionsthatwouldhavebeenassociatedwith
the crop production and the waste management activities. For the biomass feedstock category of
wastes,thecompositionandsegregationofwastewereidentifiedtobetheprimaryfactorsaffectinglife
cycleGHGemissions. Asthepercentageofbiomassincreasedincofiring,theGHGemissionsreduced.
Based on the statistical evaluation of the biomass-only LCA studies, the mean life cycle
GHG emissions for agriculture residues (N = 4), dedicated energy crops (N = 19), forestry
(N = 6), industry (N=4), and wastes (N = 2) were computed to be 291.25 gCO e/kWh,
2
208.41gCO e/kWh,43gCO e/kWh,45.93gCO e/kWh,and1731.36gCO e/kWh,respectively. Inthe
2 2 2 2
case of cofiring, the mean life cycle GHG emissions for agriculture residues (N = 10), dedicated
energy crops (N=9), forestry (N = 9), industry (N = 2), and parks and gardens (N = 1) were
computedtobe1039.92gCO e/kWh,1001.38gCO e/kWh,961.45gCO e/kWh,926.1gCO e/kWh,
2 2 2 2
and 1065.92 gCO e/kWh, respectively. The use of forestry and industry feedstock categories is
2
recommended for extensive use in both biomass-only and cofiring electricity generation systems
(considering that the mean life cycle GHG emissions were the lowest and there was not much
difference). ThevariationinmeanlifecycleGHGemissionsincofiringelectricitygenerationsystems
with respect to biomass feedstock categories was minimal (a consequence of considerably higher