CurrentDevelopments inBiotechnologyand Bioengineering
BiocharTowardsSustainable
Environment
Editors
HuuHaoNgo
CentreforTechnologyinWaterandWastewater,SchoolofCivil andEnvironmentalEngineering,UniversityofTechnologySydney, Sydney,NSW,Australia
WenshanGuo
CentreforTechnologyinWaterandWastewater,SchoolofCivil andEnvironmentalEngineering,UniversityofTechnologySydney, Sydney,NSW,Australia
AshokPandey
CentreforInnovationandTranslationalResearch,CSIR-IndianInstituteof ToxicologyResearch,Lucknow,India;SustainabilityCluster,School ofEngineering,UniversityofPetroleumandEnergyStudies,Dehradun,India
SunitaVarjani
GujaratPollutionControlBoard,Gandhinagar,Gujarat,India
DanielC.W.Tsang
DepartmentofCivilandEnvironmentalEngineering,TheHongKongPolytechnic University,Kowloon,HongKong,China
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Contributors
MukeshKumarAwasthi CollegeofNaturalResourcesandEnvironment,NorthwestA&F University,Yangling,ShaanxiProvince,PRChina
SanjeevKumarAwasthi CollegeofNaturalResourcesandEnvironment,NorthwestA&F University,Yangling,ShaanxiProvince,PRChina
YazidBindar DepartmentofChemicalEngineering;DepartmentofBioenergyand Chemurgy,FacultyofIndustrialTechnology,InstitutTeknologiBandung,Bandung, Indonesia
YogiWibisonoBudhi DepartmentofChemicalEngineering,FacultyofIndustrial Technology,InstitutTeknologiBandung,Bandung,Indonesia
S.WoongChang DepartmentofEnvironmentalEnergyEngineering,KyonggiUniversity, Suwon,RepublicofKorea
ZhuoChen EnvironmentalSimulationandPollutionControlStateKeyJointLaboratory, StateEnvironmentalProtectionKeyLaboratoryofMicroorganismApplicationandRisk Control(SMARC),BeijingLaboratoryforEnvironmentalFrontierTechnologies,Schoolof Environment,TsinghuaUniversity,Beijing,PRChina
DongleCheng CentreforTechnologyinWaterandWastewater,SchoolofCiviland EnvironmentalEngineering,UniversityofTechnologySydney,Sydney,NSW,Australia
LijuanDeng CentreforTechnologyinWaterandWastewater,SchoolofCiviland EnvironmentalEngineering,UniversityofTechnologySydney,Sydney,NSW,Australia
QuocCuongDo Chemical&ProcessTechnologyDivision,KoreaResearchInstituteof ChemicalTechnology(KRICT);DepartmentofCivilandEnvironmentalEngineering, KoreaAdvancedInstituteofScienceandTechnology(KAIST),Daejeon,RepublicofKorea
VivekK.Gaur AmityInstituteofBiotechnology,AmityUniversityUttarPradesh,Lucknow, India
WenshanGuo CentreforTechnologyinWaterandWastewater,SchoolofCiviland EnvironmentalEngineering,UniversityofTechnologySydney,Sydney,NSW,Australia
ZizhangGuo ShandongKeyLaboratoryofWaterPollutionControlandResourceReuse, SchoolofEnvironmentalScienceandTechnology,ShandongUniversity,Qingdao,China
MingjingHe DepartmentofCivilandEnvironmentalEngineering,TheHongKong PolytechnicUniversity,Kowloon,HongKong,China
PanditHernowo DepartmentofChemicalEngineering,FacultyofIndustrialTechnology, InstitutTeknologiBandung,Bandung,Indonesia
ZhenHu ShandongKeyLaboratoryofWaterPollutionControlandResourceReuse, SchoolofEnvironmentalScienceandTechnology,ShandongUniversity,Qingdao,China
WeiJiang SchoolofEnvironmentalScienceandEngineering,HuazhongUniversityof ScienceandTechnology,Wuhan,PRChina
JianxiongKang SchoolofEnvironmentalScienceandEngineering,HuazhongUniversity ofScienceandTechnology,Wuhan,PRChina
YanKang CollegeofEnvironmentandSafetyEngineering,QingdaoUniversityofScience andTechnology,Qingdao,China
GajasingheArachchigeGangaKavindi FacultyofLifeandEnvironmentalSciences, UniversityofTsukuba,Ibaraki,Japan
SunilKumar CSIR-NationalEnvironmentalEngineeringResearchInstitute,Nagpur,India
D.DuongLa InstituteofChemistryandMaterials,Hanoi,Vietnam
ZhongfangLei FacultyofLifeandEnvironmentalSciences,UniversityofTsukuba,Ibaraki, Japan
HuanyuLi InstituteofConstructionMaterials,TechnischeUniversit € atDresden,Dresden, Germany;SchoolofNavalArchitecture,OceanandCivilEngineering,ShanghaiJiaoTong University,Shanghai,China
ShuangLiang ShandongKeyLaboratoryofWaterPollutionControlandResourceReuse, SchoolofEnvironmentalScienceandTechnology,ShandongUniversity,Qingdao,China
DongqiLiu SchoolofEnvironmentalScienceandEngineering,HuazhongUniversityof ScienceandTechnology,Wuhan,PRChina
MishaLiu FacultyofLifeandEnvironmentalSciences,UniversityofTsukuba,Ibaraki, Japan
TaoLiu CollegeofNaturalResourcesandEnvironment,NorthwestA&FUniversity, Yangling,ShaanxiProvince,PRChina
XiaoningLiu StateKeyLaboratoryofWaterResourcesandHydropowerEngineering Science,SchoolofWaterResourcesandHydropowerEngineering,WuhanUniversity, Wuhan,PRChina
YangLiu JointResearchCentreforProtectiveInfrastructureTechnologyand EnvironmentalGreenBioprocess,SchoolofEnvironmentalandMunicipalEngineering, TianjinChengjianUniversity,Tianjin,China
YiLiu DepartmentofEnvironmentalScienceandEngineering,FudanUniversity, Shanghai,China
ViktorMechtcherine InstituteofConstructionMaterials,TechnischeUniversitat Dresden,Dresden,Germany
AminMojiri DepartmentofCivilandEnvironmentalEngineering,GraduateSchoolof AdvancedScienceandEngineering,HiroshimaUniversity,Hiroshima,Japan
HuuHaoNgo CentreforTechnologyinWaterandWastewater,SchoolofCiviland EnvironmentalEngineering,UniversityofTechnologySydney,Sydney,NSW,Australia
DinhDucNguyen DepartmentofEnvironmentalEnergyEngineering,KyonggiUniversity, Suwon,RepublicofKorea
ManhKhaiNguyen FacultyofEnvironmentalSciences,UniversityofScience,Vietnam NationalUniversity,Hanoi,Vietnam
ThuThuyNguyen CentreforTechnologyinWaterandWastewater,SchoolofCiviland EnvironmentalEngineering,UniversityofTechnologySydney,Sydney,NSW,Australia
Bing-JieNi CentreforTechnologyinWaterandWastewater,SchoolofCiviland EnvironmentalEngineering,UniversityofTechnologySydney,Sydney,NSW,Australia
AshokPandey CentreforInnovationandTranslationalResearch,CSIR-IndianInstituteof ToxicologyResearch,Lucknow;SustainabilityCluster,SchoolofEngineering,University ofPetroleumandEnergyStudies,Dehradun,India
AshutoshKumarPandey CentreforEnergyandEnvironmentalSustainability,Lucknow; CSIR-NationalEnvironmentalEngineeringResearchInstitute,Nagpur,India
AnpingPeng JointResearchCentreforProtectiveInfrastructureTechnologyand EnvironmentalGreenBioprocess,SchoolofEnvironmentalandMunicipalEngineering, TianjinChengjianUniversity,Tianjin,China
YongzhengRen SchoolofEnvironmentalScienceandEngineering,HuazhongUniversity ofScienceandTechnology,Wuhan,PRChina
SyedSaquib DepartmentofChemicalEngineering,FacultyofIndustrialTechnology, InstitutTeknologiBandung,Bandung,Indonesia
TjandraSetiadi DepartmentofChemicalEngineering,FacultyofIndustrialTechnology, InstitutTeknologiBandung,Bandung,Indonesia
XingdongShi CentreforTechnologyinWaterandWastewater,SchoolofCiviland EnvironmentalEngineering,UniversityofTechnologySydney,Sydney,NSW,Australia
YuqingSun DepartmentofCivilandEnvironmentalEngineering,TheHongKong PolytechnicUniversity,Kowloon,HongKong,China
B.X.Thanh KeyLaboratoryofAdvancedWasteTreatmentTechnology,VietnamNational UniversityHoChiMinh(VNU-HCM),HoChiMinhCity,Vietnam
ThiHienTran InstituteofEnvironmentalScience,EngineeringandManagement, IndustrialUniversityofHoChiMinhCity,HoChiMinhCity,Vietnam
ThiNhungTran DepartmentofCivilandEnvironmentalEngineering,KoreaAdvanced InstituteofScienceandTechnology(KAIST),Daejeon,RepublicofKorea
VanSonTran FacultyofEnvironmentalSciences,UniversityofScience,VietnamNational University,Hanoi,Vietnam
DanielC.W.Tsang StateKeyLaboratoryofCleanEnergyUtilization,ZhejiangUniversity, Hangzhou;DepartmentofCivilandEnvironmentalEngineering,TheHongKong PolytechnicUniversity,Kowloon,HongKong,China
SunitaVarjani GujaratPollutionControlBoard,Gandhinagar,Gujarat,India
StevenWahyu DepartmentofChemicalEngineering,FacultyofIndustrialTechnology, InstitutTeknologiBandung,Bandung,Indonesia
DanWang IntegratedResearchofEnergy,EnvironmentandSociety(IREES),Energyand SustainabilityResearchInstitute(ESRIG),UniversityofGroningen,Groningen,The Netherlands
LeiWang StateKeyLaboratoryofCleanEnergyUtilization,ZhejiangUniversity, Hangzhou,China
WeiWei CentreforTechnologyinWaterandWastewater,SchoolofCiviland EnvironmentalEngineering,UniversityofTechnologySydney,Sydney,NSW,Australia
JonathanW.C.Wong InstituteofBioresourceandAgriculture,HongKongBaptist University,KowloonTong,HongKong
LanWu CentreforTechnologyinWaterandWastewater,SchoolofCiviland EnvironmentalEngineering,UniversityofTechnologySydney,Sydney,NSW,Australia
HuijunXie EnvironmentalResearchInstitute,ShandongUniversity,Qingdao,China
JingtaoXu SchoolofMunicipalandEnvironmentalEngineering,ShandongJianzhu University,Jinan,China
JianYang SchoolofNavalArchitecture,OceanandCivilEngineering,ShanghaiJiaoTong University,Shanghai,China
YuanyaoYe SchoolofEnvironmentalScienceandEngineering,HuazhongUniversityof ScienceandTechnology,Wuhan,PRChina
JianZhang CollegeofSafetyandEnvironmentalEngineering,ShandongUniversityof ScienceandTechnology;ShandongKeyLaboratoryofWaterPollutionControland ResourceReuse,SchoolofEnvironmentalScienceandTechnology,ShandongUniversity, Qingdao,China
XinboZhang JointResearchCentreforProtectiveInfrastructureTechnologyand EnvironmentalGreenBioprocess,SchoolofEnvironmentalandMunicipalEngineering, TianjinChengjianUniversity,Tianjin,China
YuyingZhang DepartmentofCivilandEnvironmentalEngineering,TheHongKong PolytechnicUniversity,Kowloon,HongKong,China
ZengqiangZhang CollegeofNaturalResourcesandEnvironment,NorthwestA&F University,Yangling,ShaanxiProvince,PRChina
JohnZhou SchoolofCivilandEnvironmentalEngineering,UniversityofTechnology Sydney,Sydney,NSW,Australia
YuwenZhou CollegeofNaturalResourcesandEnvironment,NorthwestA&FUniversity, Yangling,ShaanxiProvince,PRChina
Preface
Thebooktitled BiocharTowardsSustainableEnvironment isapartoftheElseviercomprehensivebookserieson CurrentDevelopmentsinBiotechnologyandBioengineering (Editor-in-Chief:AshokPandey).Biochar,asarenewablematerial,canbeproducedfrom varioussustainablebiomassfeedstocksthroughpyrolysistechnologies.Reuseofbiomass wastesforbiocharproductionisasustainablestrategyforbiowastemanagementand environmentalprotection.Theobtainedbiocharwithspecificphysicochemicalandsurfacecharacteristicscanbefurtherappliedinwaterandwastewaterpurification,constructionanddrainagesystems,soilremediation,sustainableagriculturedevelopment, resourcerecycling,energystorageandconversion,aswellasclimatechangemitigation. Thisbookhighlightsthecontributionofbiochartoenvironmentalsustainability.Thebook providesadetailedoverviewofthesustainablebiomasswastesfeedstocksanddifferent technologiesforbiocharproduction,anditssustainableapplicationsinvariousfields. Thebookcomprises16chapters. Chapter1 discussesthesustainablebiocharproductiontechnologiesincludingsustainablebiomassresourcesforbiochar,reviewsof availablebiocharproductiontechnologies, projectionsonbiochardemand,environmentallyfriendlyandintensifiedbiocharproductiontechno logies,andtradeandeconomyofbiochar. Chapter2 describesthereuseofvarious biowastesasfeedstocksfor biocharproductionsustainablyinbiowastemanagementwhilefocusingontheenvironmentalbenefitsofthisstrategy. Chapter3 dealswiththetailoredproductionof engineeredbiochar,rolesandinteractionsof biocharinconstructionproducts,significanceofchemicalcompositionsandphysicalproperties,andmechanicalperformanceandfunctionalityofbiochar-augmentedconstructionproducts. Chapter4 focusesonthesignificanceanddesignofs ustainabledrainagesystems,identified needsforbiocharamendment,physicalimprovementbybiocharamendment,chemicalimprovementbybiocharamendment,bio logicalimprovementbybiocharamendment,andfutureresearchdirections. Chapter5 introducestheadvancesinthe sustainableapplicationofbiocharforwaterpurification,applicationofdifferentbiocharinwaterenvironment,mechanismofbi ocharinwaterpurification,andsustainableapplicationexamples. Chapter6 describestheapplicationofbiocharfortreating wastewaternotonlyasthemaintreatmentmethodbutalsoasthepretreatmentand theposttreatmentmethodsinintegratedtreatmentsystems. Chapter7 summarizesthe preparationandphysicochemicalcharacteristicsofbiocharandintroducestheperformanceofnutrients(i.e.,nitrogenandphosphorus)recoveryfromwastewater.This chapteralsodiscussestheexistingchallenges,futureresearchefforts,andopportunitiesforbiocharinnutrientsrecoveryfromwastewater. Chapter8 outlines
comprehensivelytherecentprogressesandbreakthroughsintheuseofbiocharinthe fieldofsludgetreatmentincludingsludgedewatering,aerobic/anaerobicsludgedigestion,andanaerobicsludgefermentationbyapplyingitsspecificproperties.Thischapterprovidesatheoreticalbasisandtechnicalreferencefortheapplicationofbiochar forimprovingsludgetreatment. Chapter9 reviewsstormwaterreuse,harvesting issues,characterizationofstormwater,po tentialforreuse,andthequantityandcharacteristicsofbiomass.Themodifyingtechniquesforbiocharproductionandtheapplicationandfutureperspectivesofbiochar forstormwaterreusearealsodiscussed.
Chapter10 providesareviewofcurrentbiocharproperties,itsuseasanadsorbent/ amendmentforsoilremediation,anditseffectonmicroorganismcommunitiesaswell asplantgrowth.Inaddition,thecontributionofbiochartobioeconomyisdiscussed. Chapter11 dealswiththeevolutionofbiocharprod uctiontechnologiesforsustainable agriculturepurposes,modificationofbiocha rforsustainableagriculture,influenceof biocharonsoilnutrientdynamicsandenzymes,andimpactofbiocharoncropgrowth andyield. Chapter12 providesanoverviewofthecommercialbiocharsanditsapplicationsforenergystorageandconversion.T hechallengesandopportunitiestogether withfutureperspectivesarealsodiscussed. Chapter13 describestheapplicationof biocharinpolyaromatichydrocarbonsremed iation.Integrationofbiocharwithother availabletechnologieshasbeendiscussedforenvironmentmanagement.Knowledge gapsandperspectivesinpolyaromatichydrocarbonsremediationaresummarized. Chapter14 comparestheproductionconditions,phy siochemicalproperties,andexistingandpotentialapplicatio nsbetweenbiocharandhydrocharinadditiontofuture challengesandresearchdirections,partic ularlyfromanenvironmentallysustainable perspective. Chapter15 providesanoverviewofthesignificance,application,and futuredevelopmentsofbiocharandintroduc esthesustainabilityassessmentconcept intermsofenvironmental,economic,social, andintegratedaspectsfortheevaluation oftheapplicationofbiochartowardssustainability. Chapter16 focusesonidentifying thesustainabilityimpactsofbiocharprodu ction,incombinationwithitsapplication viaanintegratedlife-cycleassessmentframeworkthatutilizesthreemethodologies: life-cycleassessment(LCA),life-cyclecosting(LCC),andsociallife-cycleassessment (S-LCA).
Weexpressourdeepestappreciationtotheauthorsandreviewersfortheirvaluable contributionstothebook.WearealsoverygratefultotheElsevierteamcomprisingDr. KostasMarinakis,formerSeniorAcquisitionsEditor;Dr.KatieHammon,currentSenior AcquisitionsEditor;BernadineA.Miralles,EditorialProjectManager;andtheentireproductionteamofElsevierforsupportingusconstantlyduringtheeditorialprocess.
DanielC.W.Tsang
HuuHaoNgo WenshanGuo AshokPandey SunitaVarjani
Sustainabletechnologiesforbiochar production
YazidBindara,b,YogiWibisonoBudhia,PanditHernowoa, StevenWahyua,SyedSaquiba,andTjandraSetiadia a DEPARTMENTOFCHEMICAL ENGINEERING,FACULTYOFINDUSTRIALTECHNOLOGY, INSTITUTTEKNOLOGIBA NDUNG,BANDUNG,INDONESIA b DEPARTMENTOFBIOENERGYAND CHEMURGY,FACULTYOFINDUSTRIALTECHNOLOGY,INSTITUTTEKNOLOGIBANDUNG, BANDUNG,INDONESIA
1.Introduction
Biocharisasolidproductleftoverfromthethermalconversionofbiomass.Thisthermal conversionprocessisknownasthepyrolysis.Biomasspyrolysisgivesthreeproductsat once.Thefirstproductisanoncondensablegasnamedbio-pyrolysisgas(BPG).Thesecondoneisaliquidproductresultingfromthecondensationofvolatileproductsreleased bythebiomasspyrolysisprocess.ThisliquidproductiscommonlytermedasBio-oil. However,itpresentsinacrudeform,i.e.,bio-crudeoil(BCO)whichwillfurtherprocessed forproperutilization.Theremainingsolidmaterialresultingfromthepyrolysisisreferred toasBiochar.Biocharhasacomplexchemicalmolecularstructurewithmolecularformulawhichisstillnotknownwithcertainty.Itischemicallyquantifiedfromthemassfractionoftheleadingorganicelementsthatmakeitup.Themainorganicelementsconsistof carbon(C),hydrogen(H),andoxygen(O).Besidesthem,Biocharisalsoformedbyminor elements,ifany,suchasnitrogen(N),sulfur(S),chlorine(Cl),andothers.Italsocontains inorganiccompoundssuchasmineralelementsthatarepresentinformofash.
Biocharstabilityisdescribedusingproximateanalysis.Thismethodprovidesinformationonthemassfractionofbiocharthatthermallydecomposedatatemperatureof900°C.It alsogiveinformationregardingthemassfractionofvariousotherconstituentsincluding volatilematter,fixedcarbonandashcontent.Highmassfractionofvolatilesindicateshigher degradabilitypotentialofBiochar.Whilehighfixedcarboncontentresultedinhighstability againstthedegradationinthesoil.Biocharparticlesasawholeareformedbyorganicmaterialresultingfromthecarbonizationprocess,uncarbonizedorganicmaterial,andinorganic ashformedbyvariousminerals(Oketal.,2016).Carbonizedorganicmatterbiocharhasa highCcontent.Thismaterialisformedbycarbonbondswithastructurethatisstillamorphous,withoutconstructingcrystallinestructurelikegraphite.Specificfunctionalgroups formsthesurfaceofsuchorganicmatter,thenporesformedinsideit.Themorphological characteristicsofBiochardescribetheexistenceoftheseholesinamicroview.
Biocharproductiontechnologyschemesaregenerallybasedontheheatingmethod, heatingrateandrawmaterialfeeding.Thefirstschemeinvolvesanindirectheating methodtobiomassforbiocharproductionwiththeabsenceofanycombustionreaction withoxygenattemperatureabove250°C(Basu,2013).Thesecondschemeemploysa directheatingmethodbysupplyingthehotcombustiongasestothepyrolysischamber toundergothepyrolysisreactionsofthebiomass.Thethirdschemeistheburningthe samebiomassontopofthebiomassforpyrolysisbysupplyingverysmallamountof theairinpyrolysischamber.Inthismethod,theproducedpyrolysisgasisburnedtogether withbiomassinthetopsectionofpyrolysischamber.Forasmall-scale,thisproduction technologywasshownby Shepard(2011).
Anotherbiocharproductiontechnologyisbasedoncontinuoustechnologywherethe pyrolysischamberisintheformofacylinderwhosebiomassisdrivenbyascrew.This pyrolysiscylindergetsheatingindirectlythroughitsouterwall.Thebiocharproductthat comesoutofthepyrolysiscylinderisfedtotheseparationchamberforobtainingbiochar andtheresultingvolatilegas.Biocharisthendischargedfromthebottomofthischamber throughascrewconveyorandcooleddownusingcoldwater.Suchproductiontechnology isalreadyexistsonacommercialscaleknownasthePyregtechnology(Pyreg,2021; Fesharaki andRath,2018).Variousbiocharproductiontechnologiesweredevelopedwithdifferent technologicalschemes;however,eachonehasthereadvantagesanddisadvantages.
Sustainableandenvironmentfriendlytechnologywithlesserpollutionisanessential requirementforlargescalecommercialbiocharproductionwithhigheconomicoutput. Acontinuousbiocharproductiontechnologywithaprocessingcapacityof240kg/daybiomassproduces72kg/dayofbiocharwithdieselfuelforheatinganauger-typepyrolyzer. TheeconomicsellingpriceofabiocharwassetatUS$ 1165pertonwiththebiomassfeed stockcostatUS$ 72pertonwhilethemarketpriceitselfwasaroundUS$ 2300perton(Pawar andPanwar,2020).Ahighyieldofqualitybiocharachievedwithoutreleasingvolatilematerialsandwithoutdirectcontactoflaterwithwateristhepreferredprocessflow.Thebiochar productionprocessdevelopedforcommercialuseshouldalsomaintainsimplerprocess technology.Biocharproducedfromthefastorlightningpyrolysisprovidesloweryields, morecomplexproductiontechnology,andhighproductioncosts.
Biocharproductiontechnologydevelopedmustmeettherulesofahighrecoveryrate, aproductioncapacitythatcanmeettheneeds,andattractiveeconomicfeasibility. Besidesthis,theproductiontechnologymustrelyonlyonthebiomassenergysource withoutinvolvingexternalenergysourcestobecomesustainable.Theuseofmaterials otherthanbiomasswhichmakestheproductiontechnologyunsustainableandcauses highproductioncostsshouldbeavoided.
Thefulfillmentofenvironmentallyfriendlyproductiontechnologyisacrucialrequirementforlargescaleproduction.Thepyrolysisofbiocharreleasesvolatilematerialswhich maycausepollutionwhendischargedintotheenvironment.Volatilematerialsconsisting ofhydroxycarboncompoundsmustbeburnedinthecombustionchambertoonlyliberateCO2 andH2Owhicharenonhazardouspollutingagents.Theproblemsthatexistare indeedrelatedtothesupplyofbiomassthatcanbeprovided.Sincetheavailablebiomass
ismostlyresiduefromagriculturalproducts,theavailabilityofthisbiomassisnotcentralized.Itisprovidedatcertaintimesoftheyearinmerequantities.Thedeterminedbiochar productiontechnologymustadapttosuchbiomasssupplyconditions.
2.Biomassasrawmaterialforproductionofbiochar
Therawmaterialusedfortheproductionofbiocharisbiomass.Thisbiomassincludes intentionallygrownrawmaterial,residuefromcrops,residuefromforestryproducts, ororganicwaste.Biomassthatisintentionallygrownasrawmaterialgenerallydoes notconsiderasfoodandhasashortgrowinglife.Agriculturalresiduebiomassgenerally hasnoorveryloweconomicvalue,suchasricehusksandstraw.Biomassobtainedfrom organicwasteisdisposedoforsortedasamaterialwithnoeconomicvalueanymore.
Sourcesofagriculturalresiduebiomassincludecorn( Tippayawongetal.,2018),wheat (Sedmihradska ´ etal.,2020),rice( Tsaietal.,2021),barley( Jazinietal.,2017),sorghum (Naiketal.,2017),soybean(Kongetal.,2011),rapeseed(AnginandSens € oz,2014),olive (Abdelhadietal.,2017),oilpalm(Idrisetal.,2014),sunflower(Klimek-Kopyraetal., 2021),coconut(Castilla-Caballeroetal.,2020),cassava( Tippayawongetal.,2017),sugarcane( Jeongetal.,2016),beet( Yaoetal.,2011),coffee(KiggunduandSittamukyoto,2019), cotton(Shenetal.,2015),andothers.
Theworld’spotentialforresidualbiomassin2017istheoreticallyestimatedinbetween 4000and12,000milliontons( WBA(Producer),2019).Theestimatedresidualbiomass potentialishigherthanthe2010estimate,whichwasaround3300milliontons(Born etal.,2014).Ofthisresidualbiomasspotential,10%isusedasfeed,78%isreturnedto agriculturallandintheformofburningorbiomassalone(Bornetal.,2014).Woodproductionforfuelwasreportedas1944millionm3 for2019.Thiswoodwasconvertedinto woodpelletsasmuchas38.9milliontonsandintocharcoalasmuchas53.1milliontons for2019( WBA(Producer),2020).Estimatesforbiomassplantedforenergyusearealso basedontheavailabilityof3500millionhaoflandwithbiomassproductivityof8tons/ha peryear(Hoogwijketal.,2005).
Biomassfromplantsisdividedintowoodandnonwood.Theprimaryconstituentof woodbiomassiscelluloseandlignin(Basu,2013).Inadditiontolignocellulose,plantsalso containextractivesandash.Forexamples,switchgrassisformedby40%cellulose,25% hemicellulose,and15%lignin(Milesetal.,1995),andfruitemptybunchconsistsof 44.4%cellulose,24.3%hemicellulose,and31.3%lignin(Nasseretal.(2016).Eachoflignocellulosiccomponentshasadifferentchemicalstructure.Biomasshasbeendesignated asarenewableenergysource.Biomassconversionintothermalenergyisdonethrough burning.Forthisconversiontothermalenergy,biomassisquantifiedbythecontentof volatilematerialsasproductsofthermaldecomposition,thefixedcarboncontentas organicsolidsleftafterthebiomassisthermallydecomposed,andtheashcontentas materialsthatdonotcontainthermalenergy.Biomassanalysisforthiscompositionis knownasproximateanalysis,whichprovidesdataonthemassfractionofvolatilematter (VM),fixedcarbonmaterial(FC),ashmaterial(A),andwater(M)ownedbybiomass.Its
calorificvalueofcombustionmeasuresthepotentialenergycontentofbiomass,reported inhighcalorificvalue(HHV)orlowcalorificvalue(LHV).Thesevaluesareusedinthe energyassessmentofbiomass.Thecurrentbiomassenergyassessoriscomparedtothe energycontentofcoal.Thelevelofitsenergycontentalsoreferredtomeasurestheeconomicvalue.
3.Biocharproductionprocesstechnology
Biocharproductiontechnologyisgenerallybasedonathermochemicalprocess.Thethermochemicalprocesscommonlyusedinbiocharproductiontechnologyispyrolysis (Brown,2009; Mullenetal.,2010; Manya ` etal.,2018; Kazawadietal.,2021).Anotherthermochemicalmethodusedforbiocharalongwithsynthesisgasproductionisthegasificationprocess.Anothermethodusedforbiocharproductionalongwithsynthesisgas productionisthegasificationprocess( Yaoetal.,2018).Thehydrothermalprocessthat useswaterasaheatingmediumathighpressureandtemperaturetoconvertbiomassinto biocharproductshasalsoreceivedattentioninthebiocharproduction.Theproductof thisprocessisoftencalledhydrochar(Sharmaetal.,2019).
Pyrolysismethodsinbiocharproductionbasedontheoperatingconditionsare expressedasslowpyrolysis,intermediatepyrolysis,fastpyrolysis,andflashpyrolysis ( Table1).Theslowpyrolysisoccursatlowheatingrate.Pyrolysiswithmoderateheating rateiscategorizedasanintermediatepyrolysis.Thefastpyrolysisitselftakesplaceathigh heatingrate.Flashpyrolysisiscarriedoutbyheatingthepyrolyzedbiomassveryrapidlyin amatterofmilliseconds(Basu,2013).Therequiredtimetoheatupthepyrolyzedbiomass atpyrolysistemperature Tpf isreferredasheatingtime tht.Theheatingrate β is approachedas ΔT/tht andconsideredtobeconstantduringtheprocess.Thetotaltime betweentheheatingtimeandthepyrolysisreactiontimecanbedefinedastheresidence time tct ofthepyrolyzedbiomass.Otherparameterstocategorizethepyrolysisprocess conditionarethetemperaturelevel,residencetimeandbiomassparticlediameter.
Theslowpyrolysisisoperatedattheheatingratebelow60°C/min.Thefastpyrolysis employstheheatingrateintherangeof600–12,000°C/min,whereasflashpyrolysisuse theheatingrateabove60,000°C/min(Balatetal.,2009).Theintermediatepyrolysisiscarried outatheatingrateabout200°C/min( Jouharaetal.,2018)orintherangeof60°C/minto600°C ( Tripathietal.,2016).Theyieldofbiocharsbecomeslowerforhigherheatingrateatthesame
Pyrolysismethod
Operatingconditions
Table1 Pyrolysiscategory.
pyrolysistemperaturethatisshownby29%biocharyieldatheatingrate6000°C/minand42% atheatingrate120°C/minforthepyrolysistemperatureat527°C(Demirbas,2004).Fastor flashpyrolysisprocessismeantforbio-oilproductionbecauseitproduceshighyieldof bio-oilproductabove70%andlowyieldofbiocharofnotmorethan15%.Sloworintermediatepyrolysisresultsbiocharabove20%yield(Bridgwater,2010).
Theheatsupplytechniqueforthebiomasspyrolysisprocessiscarriedoutwiththree possiblescenarios.Theheatissuppliedtothewallsofpyrolysischambertoheatupthe biomasspresentinside.Thisheatingscenarioisknownasanindirectheatingprocess.The secondheatingscenarioisthedirectcontactheatingwithaheatingmediumasaninertto thepyrolyzedbiomassinthepyrolysischamber.Thethirdispartialoxidationheatingsupplyinwhichsomeofthepyrolyzedbiomassinthepyrolysischamberisoxidizedwitha minimalamountofoxidizingairtogeneratetheheatforpyrolysis.
Themethodofsupplyingtherawmaterialaspyrolyzedbiomassiscarriedoutin batchesorcontinuously.Thispartyingmethodsuppliesrawmaterialsintothepyrolysis chamberinacertainamountwithinthepyrolysiscontinuityperiod.Duringthepyrolysisperiod,thebiomassinthepyrolysischamberissuppliedindirectlythroughthe wallsofthepyrolysischamber.Theheatsourcefordirectheatingofbiomassistheheat resultingfromfuelcombustion,whichhas alowereconomicvaluethanthepyrolyzed biomass.Theconceptualdesignofthispartialindirectheatingpyrolyzerisgiven in Fig.1 .
Thebatchmethodofproducingbiocharisalsocarriedoutbydirectheatingwiththe heatgeneratedbypartialoxidationofthepyrolyzedbiomassinthepyrolysischamber itself.Thismethodisdonebysupplyingtheairinaminimalamount.Directheatingwith aninertheatingmediumisrarelyusedforthepartialoxidationmethodinbiocharproductiontechnologyunlessdoneonalaboratoryscale.Theconceptofpartialoxidation fortheheatingmechanisminthepyrolyzerisshownin Fig.1.Onesuchpyrolyzerwas manufacturedfromanoilbarrelvesselwith200Lvolumeandusedtoproducethebiochar fromcorncobs,longanprunings,ricestraw,andbamboo( Tiyayonetal.,2016).Study reportedthepyrolysistemperatureabove400°C,77minofthetotalresidencetimeof thepyrolyzedbiomassand20%–40%ofthebiocharyields.
Theproductionofbiocharisalsocarriedoutthroughcontinuoussupplyofrawmaterials.Heatingforthiscontinuousmethodcanbedoneindirectly,directly,orincombination.Indirectheatingalonemightnotbeenoughtofulfilltheheatingraterequirementin continuousbiocharproductiontechnology.Duetothehighheatingraterequirementfor continuousprocesses,thisheatratecannotbesuppliedwithindirectheatingatarealistic operatingtemperature.Continuousbiocharproductiontechnologyismorecomplexthan batchproduction.
3.1Simpleautothermalbiocharproductiontechnology
Themethodofconvertingbiomasstobiocharproductscanbedoneautothermally (Nsambaetal.,2015).Therequiredheatisgeneratedfromthepartialcombustionof
FIG.1 Conceptualdesignofpyrolyzerforbiocharproductionwithpartialoxidationheatingforheatgenerationand batchslowpyrolysisofbiomass(Tiyayonetal.,2016).
thebiomassinthepyrolysischamber.Airissuppliedtothechamberinaregulated amountsothatonlyasmallportionofthebiomassisburned.Theburntbiomassispresentatthetopofthepyrolysischamber,andtheheatgeneratedpropagatesthroughconductiontothepyrolyzedbiomassatthebottomlayer.Thisautothermalpyrolysismethod ispresentedintheformofadiagramin Fig.2.
FIG.2 Conceptdesignofautothermalpyrolysismethod.
Biocharproductionprocesstechnologywasdevelopedfromtraditionalmethodsto industrialmethods.Thesetraditionalmethodsaregenerallyappliedtosmall-scalebiocharproduction.Theyareconsideredasnoneconomicalandalsoleadtoenvironmental degradation. Fig.2 showstheautothermalconceptualtechnologyforthetraditional,lowcost,andsimplebiocharproductionprocess.Thebiocharproductionprocesstechnology describedaboveisconceptuallyeasytomanufactureandoperateatcommunitylevel. Stepsformanufacturingandinstallingthistechnologyinthefieldareshownin Fig.3.
Averysimplepyrolyzerusesanopenproductionunit,suchasstackinginabiomass mound.Thepileofbiomassisopenlyundergoingapartialoxidationprocessonthe topandsurface.Theheatgeneratedfromthepartiallyoxidizedbiomassistransferred byconductiontotheinnerbiomasspilewhichundergoesapyrolysisprocess.Thisbiomassstackisintheformofadomewithholesonthesidesandtopforairsupply.The airinthebiomasspileflowsfreelybynaturaldraft.Thewallsofthebiomasspilearemade ofsoilwhichactsasaninsulatortopreventheatlossandlimittheflowofairinthereactor. Theworkingprincipleofthemoundbiocharproductionunitisthatthebiomassis arrangedintheformofadomecoveredwithamoundofsoilasaninsulator.Someof thebiomassisburnedwithverylittleair.Thiscombustionprocesswillproduceheat whichwillbepartiallyretainedonthereactorwallsduetoitsinsulation.Afterthecombustionisdeemedsufficient,theholesinthemoundarecompletelyclosedsothatthe reactorisairtight.Fireisformedslowly,andheatgeneratedisusedtopyrolyzeunburned biomass.Thisprocesscantakeuptodaysuntilalltheheatisgone.Theweaknessofthe moundproductionunitisthedifficultyofcontrollingthetemperatureandheatingrate duringpyrolysis.Inaddition,theamountofbiomassburnedandpyrolyzedisalsochallengingtocontrol.Mostoftheheatduringthecombustionphasewillbewastedalong
1. Oil drum
3. Secondary air manufacture
4. Chimney opening manufacture
7. Simple Biochar production unit
6.Chimney
5. Secondary air holes
2. Holes on bottom for primary air
FIG.3 Onsitefieldlevelsimpleandinexpensivebiocharproductionunit(UrbanFoodPlus,2015).
withthecombustionsmoke.Therefore,thisunithasalowcharyieldofabout1kgforevery 8–12kgofbiomassfeedstockwhichisnotsufficient(Stassen,2002).Environmentalproblemswithsmokereleasedintotheopenairareaconcernassociatedwiththismethod.The advantagesarelowproductioncostsandeaseofimplementationatthetraditionaluser level.
Asmall,verysimpleandlow-costpyrolyzerisknownasthe“Kon-Tiki”openfire (SchmidtandTaylor,2014).Theairaroundthepyrolyzerwithheatedwallsflowsvertically bynaturalconvection.Thisairflowatthetopofthepyrolyzerwithanenlargedcrosssectionalareaformsacirculatingflowthatenteredtheinternalsectionreferredtoasvortexflow.Itservesasthecombustionairforthebiomassatthetopofthepyrolyzer.The burningbiomassatthetopgeneratesheat.Theheatgeneratedbythiscombustion,heats thebiomassinsidethepyrolyzerwhichundergoesapyrolysisprocesstoproducebiochar.
Therearemanytraditionalandstraightforwardmodelsofbiocharproductiontechnology.Thematerialsusedinthesimpletechnologyarelocallyavailableandinexpensive includesclay,bricks,anddrums.BiocharproductiontechnologiesincludeEarthKiln,PortableMetalKiln,DrumKiln,andCasamanceKiln(Oduoeetal.,2006).Generally,traditionalbiocharproductiontechnologyusestheautothermalmethod.Theproblems facedbythistraditionaltechnologyarelowproductivity,lessereconomyandtheenvironmentalconcerns.
3.2Simpleallothermalbiocharproductiontechnology
Pyrolysisofbiomassisalsocarriedoutbyheatingwithanexternalheatsource.Thistechniqueisknownasallothermalpyrolysis(Nsambaetal.,2015)(Fig.4).Theheatrequiredis generatedbythefuelcombustionwhichiscarriedoutoutsidethepyrolysischamber.Walls physicallyboundthepyrolysischamberandcombustionchamber.Theheatfromthefuel combustionoutsideistransferredtothepyrolysischamberwallsurfacethroughconvection andradiation.Theheatreachestheouterwallbyconductionthroughthepyrolysischamber wallandthentobiomassinthepyrolysischamber.Theheatreceivedbythebiomassisused
FIG.4 Conceptualdesignofallothermalmethodforbiomasspyrolysistoproducebiochar.
toraiseitstemperature.Thenitcarriesoutthepyrolysisreactionatsufficienttemperature. Anallothermalfixedbedpyrolyzerasapilotscalewiththebiomasscapacityof20kgwas testedtoproducebiocharfrompalmkernelshell(Zainaletal.,2018).Theoperationalconditionswerereportedtohavethepyrolysistemperatureintherangeof400–600°Candthe residencetimefrom30to60min.Theirbiocharyieldsare52%at400°Cfortheresidence time30minand33%at600°Cfortheresidencetime60min.
Thesimplebiocharproductiontechnologythatiswidelyusediscarriedoutusing drummethod.Thisproductiontechnologyisconceptuallysketchedin Fig.5.Biomass feedstockisfedintothedrumthroughthedoor(7).Thebiomassputintothedrumchamberreferredaspyrolysischamber(1)variesfromlargetosmallsize.Withthispattern,the efforttoadjustthesizeofthepyrolyzedbiomassisminimal.Theheatingofthepyrolyzed biomassinthedrumiscarriedoutwiththeheatgeneratedbythecombustionofthebiomassinthecombustionchamber(2),whichisseparatedbyawallfromthispyrolysis chamber.Heatingtakesplacebyindirectheating.Thevolatilegas(4)producedfrom thepyrolysischamberischanneledintothecombustionchambertobeburnedthrough aspeciallyconstructedpipeline.
Theburningofvolatileproductsiscarriedout.Thevolatilesdonotpollutetheenvironmentwhenthevolatilegasresultingfrompyrolysisisthrownawayoftendoneinvery simpleproductionunits.Furthermore,thepyrolysisprocesstakesplaceoveralong period.Thepeaktemperatureinsidesuchpyrolysischamberrangedbetween300and 700°C.Thetimetoreachthepeaktemperaturewasabout100–200minandthebiochar yieldwasreportedtobewithin24%–34%mass(Khawkomoletal.,2021).Theadvantages
FIG.5 Simplebatchbiocharproductionunitinadrumretortwithvolatilegascombustionsysteminthecombustion chamber. ModifiedfromthedrumretortdesignofKhawkomol,S.,Neamchan,R.,Thongsamer,T.,Vinitnantharat,S., Panpradit,B.,Sohsalam,P.,Werner,D.,Mrozik,W.,2021.Potentialofbiocharderivedfromagriculturalresiduesfor sustainablemanagement.Sustainability13,8147.
ofthisbiocharproductiontechnologyaresimplicity,easeofoperation,andeaseofmanufactureatalowcost.Theproblemisthatsmallproductioncapacity,longproduction time,andhighfuelconsumptionwiththermalefficiencyinheattransferarestillvery low.Theheatingrateofthisunitisrelativelylong.Itisbecausethediameterofthe Dpyr pyrolysischamberisverylarge.
Small-scalebiocharproducerswidelyusethisretortmodelproductiontechnology.The NGOs(nongovernmentalinstitutions)providemuchinformationabouttheproduction andperformanceofthebiocharproductunits.Informationlikethisisprovidedonline invideosonhowtomanufactureandoperateaproductionunitpubliclypublishedvia YouTube.Avideooftheoperationofthebiocharproductionunitmodelwaspublished by JP(Producer)(2018) viaYouTubeintermsofthesequenceofheatingoperationsby burningwoodfuelinthebiocharproductionunitisgivenwiththehighlightsofthe screenshotstakeninthisvideoasshownin Fig.6.Thevolatileproductsproducedare channeledintothecombustionchamberforburningtoformajetflamewithbrightfire shownin Fig.6 frame(c).Thejetfirefromthecombustionofvolatileproductsinthecombustionchamberisshownin Fig.6 frame(f).
Thedevelopmentofthebiocharproductiontechnologywascarriedoutwithvertical orientationasamodifiedconceptualdesignfromCharcoalRetortV.2.0(Blacksmith, 2012).Thismodifiedtechnologyisdepictedin Fig.7.Thefirefromburningbiomass asfuelintheprimarycombustionchamberheatsthelowerpartofthepyrolysischamber.Thehotgasresultingfromthecombustionofbiomassmaterialsintheprimary combustionchamberflowsthroughachannelintothepyrolysischamber.Thehot gasthatnolongercontainsoxygendirectlyheatsthebiomassinthepyrolysischamber. Thepyrolysisproductisamixtureoffluegasandvolatilegasfromthepyrolysisproduct
FIG.6 Operationhighlightsoftheretortmodelbiocharproductionunitwiththecombustionofbiomassfuelfor heatingthedrum-shapedpyrolysischamber(JP(Producer),2018).
FIG.7 Simplebatchbiocharproductionunitinaverticaldrumretortwithindirectanddirectheatingandvolatilegas combustionsysteminthesecondarycombustionchamber.ModifiedconceptualdesignfromCharcoalRetortV.2.0 (Blacksmith,2012).
thatexitstothebottomofthepyrolysischambertothesecondarycombustionchamber. Theprimaryandsecondarycombustionchambertemperaturesweremonitoredwith thermocouples TC1 and TC2.Thetemperatureofthepyrolysischamberwasmeasured witha Tp thermocouple.
Anotherbiocharbatchproductiontechnologywasdevelopedfromtheimprovement inthebiomassfuelcombustionsystem.Oneformofthedevelopedtechnologymodelis depictedin Fig.8 reportedinPatentUS20110252699A1(Shepard,2011).Thistechnology hasaretortasacylindricalpyrolysischamberthatismountedhorizontally.Thecylindrical pyrolysischamberismountedhorizontallyabovethecombustionchamber.Thisprimary airflowsintothesidechamber,whichisboundedbythesidebafflewallwhichsimultaneouslyentersthecombustionchamberthroughthebackwallasshownin Fig.8.
Biocharproductiontechnologywithacylindricalverticalretortwithindirectheatingis givenin Fig.9.Thecombustionchamberwithbiomassfuelisplacedatthebottomofthe retortwhereheatingtakesplaceindirectly.Thisverticalretortisplacedintheheating chambersothatitssideandtopwallsgetheatedbythehotgasesfromthecombustion thatflowintothisheatingchamber.Thecombustiongasesaredischargedthroughtheflue gasexhaustduct.Airissuppliedforthecombustionthroughholesthathavebeenmadeat thebottomofthecombustionchamber.
Theproductiontechnologyofbiocharandbio-crudeoil(BCO)withoptimaldiameterverticalmultitubepyrolysischamberswasdevelopedby Bindaretal.(2021).Thecompleteflow
FIG.8 Simplebatchbiocharproductionunitinahorizontalretortdrumwithindirectheatingwiththeuseofanair guideandcombustiongases(Shepard,2011).
ofthisproductionprocessisshownin Fig.10.Thisproductionunitisorientedtoproducebiocrudeoil,bio-pyrolysisgas,andbiocharproducts.Whenthisproductionunitisusedtoproducebiocharonly,thevolatilegasproducedisreturnedtothecombustionchamberwithouta condensationprocess.Volatilegaswillburninthecombustionchamber.
Thesequenceofprocessesinthebiocharproductiontechnologyin Fig.10 involvesthe stagesoftheprocessandthestagesofproductionoperations.Thesestagesaresizereductionofbiomass(1),dryingshreddedbiomass(4)indryingunit(5),feedingthedryshreddedbiomassintopyrolysistube(11),supplyingthebiomassasfuelintothecombustion chamberthroughthefuelfeedline(10)tothecombustionchamber(12),combustionof biomassfuelinthecombustionchamber(12)withcombustionair(13)suppliedbya blower(15),indirectheatingofthewallsofthepyrolysistube(11)inthecombustion chamberandheating(12)byfireandhotgasesresultingfromcombustion,distribution ofvolatilegasproducts(16)outofthepyrolysistube(11),fullopeningofvalves(32) andfullclosingofvalves(30)and(34)forbiocharproductiononlywithoutBCOproduction,distributionofvolatilegasproductsthroughthereturnline(33)tothecombustion chamber,monitoringthetemperatureofthepyrolysischamberwithathermocouple(35), monitoringthetemperatureofthecombustionchamberwithathermocouple(36),operationofthebiocharproductionunitwiththedurationoftheheatingandholdingtimeat
FIG.9 Verticalretortbiocharproductionunitinanindirectheatingchamberfromthebottomandsideswithvolatile gasexpellingfromthepyrolysischambertothelowercombustionchambertobeburned.Modifiedconceptual designfromCharcoalRetortV.2.0(Blacksmith,2012).
FIG.10 Productiontechnologyofbiocharandbio-crudeoil(BCO)withoptimaldiameterverticalmultitubepyrolysis chamber(Bindaretal.,2021).
thespecifiedpyrolysistemperature,cessationofsupplyoffuelandcombustionairwhen thetargetoperatingtemperatureandtimehavebeenreached,coolingthebiocharproduct(27)inapyrolysistube(11)bynaturalcooling,andtakingoutthecoldbiochar(27)by openingthebiocharoutlet(28).
ThebiocharandBCOproductionunitin Fig.10 consistsof10verticalpyrolysistubes(11). Theseverticalpyrolysistubesarearrangedintwoparallelrows.Thediameterofeachtubeis 4in.Thisunitisequippedwithathermocoupletomonitorthetemperatureofthepyrolysis chamber(11)andthetemperatureofthecombustionchamber(12).Theindirectcontact condenserunit(17)isusedtocondensetheproductgasresultingfromthepyrolysiscoming outofthetopofthecylindricalreactoroftheuprightpyrolysisfurnace(11).Thecoolingwater pump(21)pumpsthecoolingwater(22)whichissuppliedtothecondenserunit(17).Thegas andliquidphaseseparationunit(18)separatesthenoncondensablegaseousproduct(20) andtheliquidproduct(19).Thenoncondensablegasreturnline(20)tothecombustion chamber(12)isusedtoburnthegaseousproductsinthecombustionchamber(12).The productholdingtankunit(29)isintendedforstoringBCOliquidproducts.Thebiocharproduct(27)isremovedfromthetubebyopeningthebottomcapofthetube(28).
TheproductionofbiocharandBCOiscarriedoutatthebiocharproductionunit in Fig.10 with60kgoflightbiomassthatwaschoppedtoasizeof15mm.Atotalof 30kgoflightbiomassisfedinto10verticalpyrolysistubesinthisunit.Eachtubecontains asmuchas3kgtobepyrolyzed.Theremaininglightbiomassispreparedtobeusedasfuel inthecombustionchamber(12).Thepyrolysisprocesslastsfor2h.Thecombustion biomassisfedcontinuously.Thebiomassfedtothecylindermodulewillbeconverted intoBCO,biochar,andbiopyrolysisgas(BPG).Biocharyieldis25%,withaBCOof 50%.Thepyrolysistemperaturewasmaintainedat500°C.
3.3Continuousbiocharproductiontechnology
Therearevariouscontinuouspyrolysistechnologiesdevelopedbyvariousresearchers. Suchtechnologiesarerotatinghotdiscablative,circulatedfluidizedbed(CFB),molten saltvacuumvessel,bubblingfluidizedbed,screw(auger),rotatingconeandrotarykiln pyrolysistechnologies( VenderboschandPrins,2010; Bridgwater,2012; Kernetal., 2012; Nacheniusetal.,2013; Ronsse,2016).Mostofthesetechnologiesarefastpyrolysis technologiesthatweredevelopedmainlytoproducethebio-oilproduct.Forthepurpose ofthebiocharproduction,fastpyrolysistechnologiesaretoocomplex,considerablyhigh capitalandoperationalcostandlowbiocharyield.Therefore,thesuitabletechnologyfor thebiocharproductionissloworintermediatepyrolysistechnology.Amongthesetechnologies,screw(auger)androtarykilnarecategorizedintocontinuesandsloworintermediatepyrolysistechnologies.Thenthecontinuousbiocharproductiontechnologiesto befocusedherearescrew(auger)androtarykilnpyrolysistechnologies.
3.3.1Augerpyrolysistechnology
Continuousbiocharproductiontechnologywasdevelopedwiththeprincipleofallthermalheatingmethods.Theheatingrateiskeptatahighlevelaspossible.Thepyrolyzed
