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BiomassgasificationforvillageelectrificationCasestudypreparedbyBartFrederiks(FACTFoundation)ReviewedbySeyhaRin(SMERenewableEnergyLtd.)1.IntroductionBiomassgasificationisathermochemicalprocessinwhichsolidbiomassisconvertedintoacombustiblegas.Thisgascanbeusedinageneratorsetfortheproductionofelectricity.Gasificationisoneoftherenewableenergytechnologiessuitableforruralelectrification,asitcanbeappliedonasmallscale(fromseveralkWeupwards),withareasonableefficiency(typicallymorethan15%).Ontheotherhand,gasifiersaresensitivetofuelqualityfluctuations,andoperatingagasifierrequiresmoreskillsthanoperatingadieselengineset.AlthoughbiomassgasificationisnotanewprocessduringtheSecondWorldWar,millionsofcarswerefueledwithwoodgasithassofarnotbeencommercializedonalargescale.Particularlysmallscalegasificationforelectricityproductionhassufferedfrompersistenttechnicalproblemsrelatedtofuelandgasquality,andveryfewsystemshaveproventhemselvesreliableenoughtobesuppliedundercommercialconditions.However,theIndiansupplierofbiomassgasificationsystemsAnkurScientificseemstobeverysuccessfulwiththeirdowndraftfixedbedgasifier.Thissystem,whichcomesindifferentvariationsforbiomasslikewood,ricehuskorcorncobs,producesacleangasthatcanbeusedinadieselorgasengine.Thesystemsareofferedinarangeof5to850kWe,atmodestinvestmentcosts(some15002000US$/kWeinthesmallerscalerange).InrecentyearshundredsofunitshavebeeninstalledinSouthandSoutheastAsia.ThiscasestudyongasificationforruralelectrificationisbasedoninformationgatheredduringafactfindingmissioninCambodia,November2009.Duringthismission,anumberofAnkurgasificationsystemshavebeenvisitedbyFACTandSMERenewableEnergyLtd.,thelocalsupplieroftheunits.2.TechnicaldescriptionThebasisofthiscasestudyisabiomassgasificationsystemthatsupplieselectricitytoasmallisolatedgridinaruralarea.Theselectedsystemcapacityis50kWe,whichshouldbesufficienttoserveseveralhundredsofhouseholds1.Itoperatesfor12hoursperday,350daysperyear,so4200hoursperyear.Theaverageloadingrateis25%,sothe(gross)electricityproductionis52,500kWh/a.Technicallossesandownconsumptionaccountfor20%,so42,000kWhiseventuallysuppliedtotheconsumers.Thegasificationsystemconsistsofseveralparts.Firstofallthereisthegasifieritself(seefigure1),whichisafixedbeddowndraftsystemthatisfueledwithwoodorcorncobs.Thebiomassandairareintroducedintoahopperontopofthereactor.Thebiomasschunksareuptoseveralcminsizeand 1Themaximumnumberofconnectionsdependsonanumberoffactors,suchasthemaximumloadperhouseholdandthepresenceofproductive(generallylarger)loads.InCambodiaforexample,averageperhouseholdloadsinsmallvillagesarearound100W,sothata50kWesystemcouldinprincipleserve500households(notaccountingfordistributionlossesandthepowerplantsownconsumption).

Figure1:A22kWgasifierusedforvillageelectrificationinCambodia

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haveamaximummoisturecontentof20%.Theyareconvertedtogasinthereactor,andtheremainingcharandashareremovedfromthebottomofthegasifierandcarriedawaywithawatersystem.

Figure2:Gascleaningsystem Figure3:30kVAgeneratorset(gas)Thegasthatexitsthegasifierneedstobecooleddownandcleanedbeforeitcanbeusedinthegasengine.Thefirststepisawaterscrubber,whichcoolsthegasandremovespartofthetarsandash.Afterthat,thegasisledthroughanumberoffiltersthatarepackedwithabiologicalfiltermaterial(e.g.sawdustorricehusk),andfinallyabagfiltertoremoveanyremainingparticles.Thecleangasisthenusedinagasenginewhichdrivesanalternator,producingelectricityfortheminigrid.Thebiomassconsumptionofthesystemdependsonthetypeoffuelanditscharacteristics.Forwoodandcorncobs,withamoisturecontentof20%,fuelconsumptionisabout1.5kgperkWhofelectricity,providedthatthegasisusedinagasengine.Whenthegasifierisrunningatalowload,thiswillbesomewhathigher.Annualbiomassconsumptionisthusnearly80tonnes.Woodcanbecollectedorgrowninthevicinityofthegasifierplant,aslongasitiscutdowntotherightsizeanddrieddowntotherequiredmoisturecontentbeforeuse.Corncobscanbecollectedfromvillagesinthearea.

Figure4:Fuelwoodchunk Figure5:CorncobsInAnlungTameyvillageinCambodia,farmershaveplantedsome10hectaresofLeucaena,afastgrowingspeciesthatcanbecutseveraltimesperyear.Thewoodisharvestedwhenthestemsareabout35cmindiameter,andissoldtothecommunityenergycooperative.Leuceanaisanattractivecropforfarmers:thetreeimprovessoilfertilitybynitrogenfixation,andapartfromtheadditionalincomefromthewood,theleavescanbeusedasanimalfodder.

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Figure6:Leucaenatree Figure7:CowsfeastingonLeucaenaleavesOperationandmaintenanceofthegasifierplantdoesrequirecontinuousattentionandsometechnicalskills.Itisveryimportantthatthefuelissuppliedtothegasifierregularly,andattherightspecifications.Thegasfiltersystemsneedtobecheckedregularlyforsaturation,andthefilterbedmaterialneedstobereplacedwhennecessary.Charandashneedtoberemovedfromthewatersystem,andscrubberwaterneedstoberefreshedevery34weeks.Thegasenginerequiresregularmaintenance;thegasifierneedstobeoverhauledbythesupplieronceeveryfewyears.Personnelrequirementsdependontheextenttowhichdifferentactivitiesareexecutedbyasingleperson,orbydifferentpersonsworkingparttime.Presumably,theplantcanberunbytwofulltimestaff,butinpractice,severalpeoplemaybeinvolvedparttime(e.g.atechnician,aplantoperator,afueloperator,andsomepeopleintheorganizationandadministrationofacooperative).3.FinancialassessmentWhenassessingelectricityproductioncosts,onecanbroadlydistinguishoperationalcosts(fuel,personnel,andmaintenance)andcapitalcosts(depreciationandfinancialcosts).Inthetablebelow,theresultsofafirstorderassessmentofthedifferentcostitemsarelisted.Table1:Electricityproductioncostsusinga50kWgasifiersystemItem Units Unitcost(US$) Costs(US$/a) Costs(US$/kWh*)Woodfuel(tonnes) 78.8 25 1,969 0.05Personnel(fte) 2 1200 2,400 0.06Maintenance(%ofinvestmentcost) 2%

1,450 0.03

Operationalcosts 5,819 0.14Depreciation(%ofinvestmentcost) 10%

72,500 7,250 0.17

Financialcosts(interestover10yearloan) 10%

4,549 0.11

Capitalcosts 11,799 0.28Totalproductioncosts 17,618 0.42*perkWhsoldRemarks: Woodfuelispurchasedatapriceof25US$/tonne(at20%moisture).Thispricelevelisbasedon

whatispaidinAnlungTameyvillageinCambodia.Ifotherbiomassresiduesareavailable,suchascorncobs,thecostsmaybesomewhatlower.

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Inthisanalysis,personnelcostsarebasedontwofulltimestaffwithasalaryof100US$permonth.Althoughinrealitymorepeoplecanbeemployed,themonthlypersonnelcostscorrespondtothosefoundinCambodia.

Averageannualmaintenancecostsareestimatedusingapercentageoftheinvestmentcosts. Allhardware(gasifierandgeneratorset)isdepreciatedoveraperiodof10years. Financialcostsconcerninterestspaidovera10yearloancoveringallinvestmentcosts. Distributioncostshavenotbeenincludedinthecalculations;theseamountto14US/kWh

(includingmaintenance,depreciationandfinancialcosts).Theanalysisshowsproductioncostsofabout42US/kWh2,ofwhichtwothirdsconcernscapitalcosts(particularlydepreciation).Thismeansthatproductioncostsaremostsensitivetovariationsininvestmentcostsandinterestrate(e.g.toscaleincreasesandsoftloans,investmentsupportmeasures)andmuchlesstooperationalcostitemslikefuelpricesandpersonnel.Moreover,amoreextensiveuseofthesystem(higherloadingrateormoreoperatinghours)resultsinlargecostreductions.Forexample,increasingtheloadingratefrom25%to30%resultsinacostdecreasefrom42to36US/kWh.Higherloadingratescanbeachievedbyadding(continuous)productiveloadssuchaswaterpumps,cerealmillsorbatterychargers.

Figure8showsacomparisonofcostcomponentsofsystemsofdifferentscales,andofa50kWedieselpoweredelectrificationsystem.Itshowsthatatthesamescale,dieselgenerationappearssubstantiallymoreexpensive(52US/kWhatafuelpriceof0.85US$/l),butthatinthiscasesome80%ofthecostsconcernsoperationalcosts(mainlyfuelcosts).Anydieselpricechangeswillthushavealargeeffectontheproductioncosts.Italsoshowsthatproductionscalehasaconsiderableeffectonproductioncosts.Thisisduetodecreasingperunitinvestmentcosts,andtosomeextenttodecreasingoperationalcosts(e.g.personnel). 2Forcomparison:theelectricitytariffinAnlungTameyvillageinCambodiaisabout58US/kWh,ataproductioncapacityof35kWe.TherateatBatDoengvillage,wherea200kWgasifierisoperatedincombinationwithadieselgenerator,is54US/kWh.Theseratesincludedistributioncosts.

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Figure8:Electricityproductioncostsforgasificationondifferentscales(25,50and100kWe)anddiesel(50kWe).

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4.ConclusionsItcanbeconcludedthatgasificationisaviablerenewableenergytechnologythatcanbeappliedforruralelectrification.ExamplesfromCambodiaandelsewhereshowthatdespitetheorganizationalchallenges,gasifiersystemscanindeedbeoperatedinaruralvillageenvironment.Incontrasttootherbiofuelproduction(e.g.certainoilcrops),gasifierfuelproductioncanofferrealincomeopportunitiesforlocalfarmers.Withrespecttoproductioncosts,gasificationcanresultinlowerproductioncostsincomparisontodieselgeneratedelectricity,andislesssensitivetovariationsinoperationalcosts(e.g.fuelcosts).Nevertheless,perunitcostsremainsubstantialsooptimizationisrecommended,forexampleby: Lookingforcombinationswithproductiveapplicationssuchaswaterpumping,milling,battery

chargingorotheractivitieswithacontinuousload.Thiswillresultinbetterloadingratesandallowproductiononalargerscale.

Lookingforpossibleinvestmentcostreductions,forexamplebyproducingpartsofthesystemlocally.

Inaddition,possiblebenefitsfromthevalorizationofcharresiduesshouldbeassessed.Sofar,theoptionsthatarebeingconsideredareproductionofcookingfuelbriquettes,orforagriculturalsoilimprovement.Bothrequirefurtherinvestigation.Oneimportantaspectthatrequiresadditionalattentionisthatoftheliquideffluents(i.e.spentscrubberwater).Theeffectsofdisposingtheseeffluentsshouldbeinvestigated;ifneeded,measuresshouldbetakentoavoidthereleaseofanypotentiallyharmfulsubstancestothelocalenvironment.