BIOMASS:

THENEEDFORBIOENERGY,THEBIOMASSCOMBUSTIONPROCESS&THEFUTUREOFBIOMASSENERGYPRODUCTION.

AndreaLuiseSchrader.

OxfordBrookesUniversity.

06098672@brookes.ac.uk

Abstract.

Theauthorshallhereinexaminebiomassandit’suseasalowcarbon,renewablesourceofbio‐energy. All ‘low tech’ and ‘high tech’ bio‐energy production methods shall be stated andBiomassCombustion‐asthemostsustainable,practicalandcommerciallymatureproductionmethod of bio‐energy ‐ shall be elaborated on. Therewill be an analysis of the combustionprocessandcurrentlyavailabletechnology.

The author shall then look at current interest in biomass and energy demands, and theeconomicandpoliticalincentivesthatdrivethemtowardagreateruseinthefuture.

Whatisbiomass?

The definition of biomass can differ through recent documentation, dependant onwhich geological or political

context it is mentioned within.1 When defining from a renewable energies standpoint; biomass is thebiodegradable fraction of products, waste and residues from agriculture (including vegetable and animal

substances)2thatcanbeusedasafuelorenergysource.Thisexcludesorganicmaterialthathasbeentransformedbygeologicalprocessessuchasoilorcoal.3

Usingbiomassasanenergysourcecaneffectivelyreducecarbondioxideemissionsbysubstitutingtheuseoffossil

fuelsinenergyproduction.Biomassprocessingreleasescarbondioxide,butonlyreleaseswhatit,itselfneededtouseduringit’sgrowth.Therefore,no“new”carbondioxideisbeingreleasedintotheatmosphere.Thisisnotthe

casewithfossilfuels,whichintroducecarbonthathasbeenremovedfromthecarboncycleformillionsofyears.4

EnergyProductionFromBiomass.

Processingbiomass forenergycanbedone innumerousways.Themostcommerciallypracticedmethod inbio‐energy production is direct combustion.5 However there are othermethods, comprising of solutions of varying

technicality. ‘LowTech’processesincludecomposting,anaerobicdigestionandfermentation.Theserequirelittleactionotherthanthenaturaldecayprocessoftheorganicmatter.6 ‘HighTech’solutions includeacidhydrolysis,

destructivedistillation,hydrogenation,pyrolysis,thermaldepolymerisationandhydrogasification.Theseallrequiremorecontrolledscientificprocessesandactivechemicalalterations to thematter, toultimatelyproduceenergy

1JuniperConsultancyServicesLimited.(2007)http://www.juniper.co.uk/services/market_sectors/biomass.htmlGloucestershire.UK.2CommissionOfTheEuropeanCommunities.(2008)“Directive On The Promotion Of The Energy Use From Renewable Sources”Brussels.3Anon.(2006)http://en.wikipedia.org/wiki/Biomass.UK.4TheCarbonTrust.(2000)http://www.carbontrust.co.uk/technology/technologyaccelerator/biomass.htm.London.UK.5Broek,R.Faaij,A.VanWilk,A.(1995)“BiomassCombustionPowerGenerationTechnologies”UtrechtUniversity.Utrecht.6Sakalauskas,J.(1996)“Introduction to Renewable Energy Technology”.NorthernMelbourneInstituteofTAFE/OpenTrainingServices.USA.

sources.7Biomasscombustion‐incomparisontothecomplicatedprocessesofthe‘HighTech’andthepotentialsofhealthissuessurroundingthedecayprocessoftheother‘LowTech’solutions‐prevailsinoverallpracticality.

Furnace.Simplestcombustiontechnology.

PileBurner.Biomassfiredboiler.Obsoletetechnology.

Stationary/TravellingGrateCombustor.Biomassfiredboiler.

FluidisedBedCombustor.Biomassfiredboiler.

In a furnace, biomass fuelburns in a combustionchamber,convertingbiomassintoheatenergy.As the biomass burns, hotgasesarereleased.

Pile burners consist of cells,each having an upper and alower combustion chamber.Biomass fuel burns on a gratein the lower chamber,releasingvolatilegases.The gases burn in the upper(secondary) combustionchamber.Operatorsmustshutdownpile burners periodicallytoremoveash.

An automatic feederdistributes the fuel onto agrate, where the fuel burns.Combustion air enters frombelowthegrate.In the stationary grate design,ashes fall into a pit forcollection.In contrast, a traveling gratesystemhasamovinggratethatdropstheashintoahopper.

Fluidized ‐ bed combustorsburnbiomassfuelinahotbedof granular material, such assand. Injection of air into thebed creates turbulenceresemblingaboilingliquid.Theturbulencedistributesandsuspendsthefuel.

The hot gases contain about85% of the fuel´s potentialenergy.Commercial / industrialfacilities use furnaces forheat either directly orindirectly through a heatexchangerintheformofhotairorwater.

Steam output contains 60 to85%ofthepotentialenergy inbiomassfuel.Pile burners are capable ofhandling high‐moisture fuelsandfuelsmixedwithdirt.

Steam output contains 60 to85%ofthepotentialenergy inbiomassfuel.Grate Combustors replacedPile Burners, for theirautomatic ash removal fromthecombustionchamber.

Steam output contains 60 to85%ofthepotentialenergy inbiomassfuel.This design increases heattransfer and allows foroperating temperaturesbelow972 °C, reducing nitrogenoxide(NOx)emissions.Fluidized‐bedcombustorscanhandle high‐ash fuels andagriculturalbiomassresidue.

 

Fig.1. Shows the different types of commercially available biomass combustors, their processes and beneficial features. Table is Author’s own. Data from Oregon Biomass (2007)8. 

Biomasscombustionisaveryenergyefficientprocesswhichhaslittletonoaffectonthecarboncycle.ControlledcombustionofbiomassinapowerplantremovesneartoallofthecarboninthebiomasstoCO2,whichresultsinlittle,tonoCH4(methane)emissionsthatcanbeproducedinotherutilisationmethodsofobtainingenergyfrombiomass,particularlyviameansofthedecayprocess.Methanegasisapotentgreenhousegas,whichisbelievedto

be21timesstrongerthanCO2,Reducingtheriseinitslevelswithintheatmosphereisthereforegreatlybeneficial.9

However,itisworthnotingthattheutilizationofmethanegasfromthedecayofmunicipalwaste/landfillbiomasstoproduceelectricalenergy, isseenasasuccessfulrenewableenergysource,asnotedbyTheLandfillMethane

OutreachProgramconductedbytheUSEPAin1994.Sincetheprogram’sinception,landfillmethaneemissionsintheUSAhavebeenreducedbymorethan28millionmetrictonsofcarbonequivalent(MMTCE).10Utilizingthisbi

productofcombustionasanotherenergysourcecouldbepossible.

7Anon.(2006)http://en.wikipedia.org/wiki/Biomass.UK.8OregonBiomass.(2007)http://www.oregon.gov/ENERGY/RENEW/Biomass/bioenergy.shtml#Industrial_Biomass_CombustionUSA.9EnvironmentalProtectionAgency.(1994)“Landfill Methane Outreach Program”. http://www.epa.gov/lmop/benefits.htm.USA.10EnvironmentalProtectionAgency.(1994)“Landfill Methane Outreach Program”. http://www.epa.gov/lmop/benefits.htm.USA.

Biomass combustion can lead to the production of NOx (Mono Nitrogen Oxides), which can contribute togreenhouse gases and acid rain, however this can avoided by incinerating at lower temperatures, within a

fluidized‐bedconverter,asdescribedinFig.1.11

Thefutureofbiomassandbioenergy.

Numerousstudiesindicatethatthereisconsiderablepotentialforbio‐energy,andinparticularbiomass,forfuture

energyproductionintheEU.12IndependentlyfromEUcountries,theUKalonehasasignificantbiomassresource,estimated at an annual 20million tonnes. Only a small amount of this is being utilized for energy production,

contributingapproximately4.1%oftheUK'sheatandelectricity.13

Fig. 2. Shows the three key contributing factors to the successful  integration of bio‐energy  into future energy systems. Graphic Author’s own. Data represented accredited to ABS Energy Research. (2004).14 

 

Twopointsofconcern for the futuresuccessofbiomassasanenergysource,wereaddressed instudiesbyABSEnergy Research; the public remain poorly informed of the importance of bio‐energy utilisation, and current

publicisedstudiesarebasedonunrealisticassumptions,whichhavepotentialtomisinformfutureproposalsandinhibitpolicydevelopment.ABSstatedthattheseissuesneedtobeaddressedbeforeeffectivestrategies,utilising

bio‐energysources,canberealisticallysustainedincurrentEUenergymarkets.15

If theUK intendstoembracebiomassasa feasibleenergysource,preparationmustbemadeto improveon it’scurrentutilisation.Currently, thereare fullymaturecommercialapplicationsofbiomasscombustiontechnology,

butmanagementofUK(biomass)feedstockneedstobeimproved;cropyieldsmustbeincreasedinasustainablemanner,alsowithlowchemicalinputstoensureminimalcarbonfootprintfortheoverallcropproduction.16

11EnvironmentalProtectionAgency.(2008)“Health And Environmental Impacts Of NOx”http://www.epa.gov/airprogm/oar/urbanair/nox/hlth.html.USA.12ABSEnergyResearch.(2004)“Bio‐Energy’s Role In The EU Energy Market”London.UK.13DepartmentforEnvironment,FoodandRuralAffairs,(2007)“UK Biomass Strategy” http://www.defra.gov.uk/Environment/climatechange/uk/energy/renewablefuel/pdf/ukbiomassstrategy‐0507.pdfLondon.UK.14EnergyResearch.(2004)“Bio‐Energy’s Role In The EU Energy Market”London.UK.15ABSEnergyResearch.(2004)“Bio‐Energy’s Role In The EU Energy Market”London.UK.16Taylor,G.(2008)“Bio‐energy for heat and electricity in the UK: A research atlas and roadmap”.UKEnergyResearchCentre.UK.

DemandFunction.

Thedemandforbio‐energy(biomassenergy

production). SupplyFunction.

Thesupplyofbiomass,feedstockforbio‐energy.

TechnologyDevelopmentFunction.

Thecharacteristicsofbiomassfuelledenergyconversion

techniques.

TheFuture

RoleOfBio‐energy

Economically, improving thisagricultural industrywithin theEuropeanUnion,wouldcombat theEU’s increasingdependenceonenergyimports,politicalandcostconcernsregardingreducingsecurityofsupply.17

“[Renewableenergysources,suchasbiomass]arethekeyelementofasustainableenergyfuture.”18

Presently, it couldbeuseful for theUK to focusondevelopingbio‐energy chains, linked to combinedheat andpower (CHP) micro‐generation for community and public sector projects, allowing small communities to be

predominantly self sustaining on bio‐energy sources.19 Progress such as this, could allow biomass to becomecentraltoourenvironmentalandeconomicalenergyneeds.Inparticular,actiontowardamoresustainablefuture

is necessary with immediate effect, as stated in the EU Directive On The Promotion Of The Energy Use FromRenewableSources(2008):

“Recentstudieshavecontributedtothegrowingawarenessandknowledgeoftheproblem[ofclimatechange

causedbyemissionsofgreenhousegases]andit’slongtermconsequencesandhavestressedtheneedfordecisiveandimmediateaction.”20

Conclusion.

ItisproposedbytheAuthorthatbio‐energy,andbiomass,canplayasignificantroleinthefutureofenergyproductionwithintheUKandtheEU,providedthedemandfactors(political,environmentalandsocialincentives),

supplyfactors(biomassproduction)andtechnologydevelopmentfunctionsaremanagedandsustained.

17CommissionOfTheEuropeanCommunities.(2008)“Directive On The Promotion Of The Energy Use From Renewable Sources”Brussels.18CommissionOfTheEuropeanCommunities.(2008)“Directive On The Promotion Of The Energy Use From Renewable Sources”Brussels.19Taylor,G.(2008)“Bio‐energy for heat and electricity in the UK: A research atlas and roadmap”.UKEnergyResearchCentre.UK.20CommissionOfTheEuropeanCommunities.(2008)“Directive On The Promotion Of The Energy Use From Renewable Sources”Brussels.