AdvancesinSynthesisGas: Methods,Technologies andApplications
Volume1:SyngasProductionandPreparation
Editedby
MohammadRezaRahimpour DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
MohammadAminMakarem MethanolInstitute,ShirazUniversity,Shiraz,Iran
MaryamMeshksar DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
Contributors
AmrAbdalla DepartmentofChemicalandPetroleumEngineering,UniversityofCalgary,Calgary, AB,Canada
WaqarAhmad DepartmentofChemicalandBiologicalEngineering,MonashUniversity,Clayton, VIC,Australia
PrakashAryal DepartmentofChemicalandBiologicalEngineering,MonashUniversity,Clayton, VIC,Australia
NooshinAsadi DepartmentofChemicalandBiologicalEngineering,MonashUniversity,Clayton, VIC,Australia
ManuelBailera GraduateSchoolofCreativeScienceandEngineering,WasedaUniversity,Tokyo, Japan;DepartmentofMechanicalEngineering,UniversidaddeZaragoza,CampusRı´oEbro,Bldg. Betancourt,Zaragoza,Spain
IdrisBakare InterdisciplinaryResearchCenterforHydrogenandEnergyStorage,KingFahd UniversityofPetroleum&Minerals,Dhahran,SaudiArabia
AliBakhtyari ChemicalEngineeringDepartment,ShirazUniversity,Shiraz,Iran
MohammadBonyadi DepartmentofChemicalEngineering,FacultyofEngineering,Yasouj University,Yasouj,Iran
FelipeGomesCamacho DepartmentofChemicalandPetroleumEngineering,SchulichSchoolof Engineering,UniversityofCalgary,Calgary,AB,Canada
GuoxingChen FraunhoferResearchInstitutionforMaterialsRecyclingandResourceStrategies IWKS,Alzenau,Germany
CamillaFernandesdeOliveira DepartmentofChemicalandPetroleumEngineering,Schulich SchoolofEngineering,UniversityofCalgary,Calgary,AB,Canada
SilviodeOliveiraJunior PolytechnicSchool,UniversityofSaoPaulo,DepartmentofMechanical Engineering,SaoPaulo,Brazil
MaryamDelshah DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
MeireEllenGoreteRibeiroDomingos PolytechnicSchool,UniversityofSaoPaulo,Departmentof ChemicalEngineering,SaoPaulo,Brazil
MoisesTelesdosSantos PolytechnicSchool,UniversityofSaoPaulo,DepartmentofChemical Engineering,SaoPaulo,Brazil
SwaritDwivedi DepartmentofChemicalandBiologicalEngineering,MonashUniversity,Clayton, VIC,Australia
RaziehEtezadi MorkFamilyDepartmentofChemicalEngineeringandMaterialsScience,University ofSouthernCalifornia,LosAngeles,CA,UnitedStates
AzharuddinFarooqui DepartmentofChemicalandPetroleumEngineering,UniversityofCalgary; VorsanaEnvironmentalInc,Calgary,AB,Canada
DanielFlo ´ rez-Orrego PolytechnicSchool,UniversityofSaoPaulo,DepartmentofMechanical Engineering,SaoPaulo,Brazil;FacultyofMinas,NationalUniversityofColombia,SchoolofProcesses andEnergy,Medellin,Colombia
AndreaGaleazzi PolitecnicodiMilano,DepartmentofChemistry,MaterialsandChemical Engineering“GiulioNatta”,PiazzaLeonardodaVinci,Milan,Italy
XingyuanGao DepartmentofChemistryandMaterialScience,GuangdongUniversityofEducation, EngineeringTechnologyDevelopmentCenterofAdvancedMaterials&EnergySavingandEmission ReductioninGuangdongCollegesandUniversities,Guangzhou,People’sRepublicofChina; DepartmentofChemicalandBiomolecularEngineering,NationalUniversityofSingapore,Singapore, Singapore
JonathanHarding DepartmentofElectricalEngineeringandElectronics,UniversityofLiverpool, Liverpool,UnitedKingdom
BaishaliKanjilal Bioengineering,UniversityofCalifornia,Riverside,CA,UnitedStates
MilanpreetKaur DepartmentofChemistry,FacultyofScience,UniversityofCalgary,Calgary,AB, Canada
SibudjingKawi DepartmentofChemicalandBiomolecularEngineering,NationalUniversityof Singapore,Singapore,Singapore
MohammadHasanKhademi DepartmentofChemicalEngineering,CollegeofEngineering, UniversityofIsfahan,Isfahan,Iran
ParvinKiani DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
SoheilaZandiLak DepartmentofChemicalEngineering,FacultyofEngineering,YasoujUniversity, Yasouj,Iran
PilarLisbona DepartmentofMechanicalEngineering,UniversidaddeZaragoza,CampusRı´oEbro, Bldg.Betancourt,Zaragoza,Spain
MohammadLotfi-Varnoosfaderani DepartmentofChemicalandPetroleumEngineering,Sharif UniversityofTechnology,Tehran,Iran
NaderMahinpey DepartmentofChemicalandPetroleumEngineering,SchulichSchoolof Engineering,UniversityofCalgary,Calgary,AB,Canada
MohammadAminMakarem MethanolInstitute,ShirazUniversity,Shiraz,Iran
ZuhairOmarMalaibari ChemicalEngineeringDepartment;InterdisciplinaryResearchCenterfor RefiningandAdvancedChemicals,KingFahdUniversityofPetroleum&Minerals,Dhahran,Saudi Arabia
FlavioManenti PolitecnicodiMilano,DepartmentofChemistry,MaterialsandChemical Engineering“GiulioNatta”,PiazzaLeonardodaVinci,Milan,Italy
AramehMasoumi Bioengineering,UniversityofCalifornia,Riverside,CA,UnitedStates
MaryamMeshksar DepartmentofChemicalEngineering;MethanolInstitute,ShirazUniversity, Shiraz,Iran
MasoumehMohandesi DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
GalalNasser InterdisciplinaryResearchCenterforHydrogenandEnergyStorage,KingFahd UniversityofPetroleum&Minerals,Dhahran,SaudiArabia
FrancescoNegri PolitecnicodiMilano,DepartmentofChemistry,MaterialsandChemical Engineering“GiulioNatta”,PiazzaLeonardodaVinci,Milan,Italy
RafaelNogueiraNakashima PolytechnicSchool,UniversityofSaoPaulo,Departmentof MechanicalEngineering,SaoPaulo,Brazil
ImanNoshadi Bioengineering,UniversityofCalifornia,Riverside,CA,UnitedStates
AlirezaPalizvan DepartmentofChemicalEngineering,CollegeofEngineering,Universityof Isfahan,Isfahan,Iran
SongWonPark PolytechnicSchool,UniversityofSaoPaulo,DepartmentofChemicalEngineering, SaoPaulo,Brazil
VirginiaPerez CentrefortheDevelopmentofRenewableEnergy-CentreforEnergy,Environment andTechnologyResearch(CEDER-CIEMAT),Soria,Spain
KristianoPrifti PolitecnicodiMilano,DepartmentofChemistry,MaterialsandChemical Engineering“GiulioNatta”,PiazzaLeonardodaVinci,Milan,Italy
ShuxianQiu DepartmentofChemistryandMaterialScience,GuangdongUniversityofEducation, EngineeringTechnologyDevelopmentCenterofAdvancedMaterials&EnergySavingandEmission ReductioninGuangdongCollegesandUniversities,Guangzhou,People’sRepublicofChina
HamidRezaRahimpour DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
MohammadRezaRahimpour DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
FatemehSalahi DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
MohammedSanhoob InterdisciplinaryResearchCenterforHydrogenandEnergyStorage,King FahdUniversityofPetroleum&Minerals,Dhahran,SaudiArabia
AkshatTanksale DepartmentofChemicalandBiologicalEngineering,MonashUniversity,Clayton, VIC,Australia
TheodoreTsotsis MorkFamilyDepartmentofChemicalEngineeringandMaterialsScience, UniversityofSouthernCalifornia,LosAngeles,CA,UnitedStates
XinTu DepartmentofElectricalEngineeringandElectronics,UniversityofLiverpool,Liverpool, UnitedKingdom
LuisD.Virla DepartmentofChemicalandPetroleumEngineering,SchulichSchoolofEngineering, UniversityofCalgary,Calgary,AB,Canada
NiWang DepartmentofElectricalEngineeringandElectronics,UniversityofLiverpool,Liverpool, UnitedKingdom
YaolinWang DepartmentofElectricalEngineeringandElectronics,UniversityofLiverpool, Liverpool,UnitedKingdom
ShabnamYousefi DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
SamiraZafarnak DepartmentofChemicalEngineering;MethanolInstitute,ShirazUniversity, Shiraz,Iran
ZahraZarei ChemicalEngineeringDepartment,UniversityofSistanandBaluchestan,Zahedan,Iran
FatemehZarei-Jelyani DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
LinghaoZhao MorkFamilyDepartmentofChemicalEngineeringandMaterialsScience,University ofSouthernCalifornia,LosAngeles,CA,UnitedStates
SaraZolghadri DepartmentofChemicalEngineering,MarvdashtBranch,IslamicAzadUniversity, Marvdasht,Iran
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Syngascharacteristics:Physical andchemicalproperties
MasoumehMohandesi,HamidRezaRahimpour,andMohammad RezaRahimpour
DepartmentofChemicalEngineering,ShirazUniversity,Shiraz,Iran
1.Introduction
Theusageoffuelshasevolvedsincethediscoveryoffire,withmantransitioningfromtimberto coal,thentooil,andeventuallytonaturalgas,whilesimultaneouslyincreasingtheworldwide useoffuelsbyanorderofmagnitude [1].TheensuingCO2 emissionsincreased,greaterthan 400ppmconcentrationintheatmosphere(ppm),whichmaybetheprimarydriverofclimate changeasaresultofglobalwarming [2].Asaresult,thedemandforalternativeandclean energyisamajorsubjectofinterestforacademicsaroundtheworldworkingtodevelop sustainableenergysources.Whenitcomestoproducingsustainableenergy,syntheticgashas enormouspromise.Itcanmeettherisingdemandforliquidandgaseousfuelsandpowerwhile alsoreducinggreenhousegasemissions.Synthesisgasisapromisingtechnologyforimproving energyefficiency,fuelproduction,electricitygeneration,andpollutantelimination,while servingasatransitionalstepfromcarbon-basedtohydrogen-basedfuels.Carbonmonoxide, hydrogen,andothergasesinsmallquantitiesaremixedtogethertoformsynthesisgas,whichis alsoknownassyngas.
Gasderivedfromnaturalgasandotherhydrocarbonsisusedtocreatethisgas.Theproductionof syngasisaccomplishedthroughthereformingprocessthatinvolveseitheranendothermicoran exothermicreaction,dependingonthechemicaltechniquethatisusedtoimplementthemethane catalyticreformingprocess.Biomasscanalsobeusedtogeneratesyntheticgas [3].Thiscanbe accomplishedthroughavarietyofprocessesincludingbiomassgasification [4,5] andbio-oil reformingusingsteam [6–9].Everyyear,approximately6EJofsyngasisproducedaroundthe world,about2%oftheglobaltotalprimaryenergyconsumptionatpresent.Manyapplications requirethegenerationofsynthesisgas,suchastheproductionofhydrogenfromnaturalgasfor useinfuelcelloperations.Fischer–Tropschisusedtogeneratelightsyntheticcrudeoilorheavy
waxyhydrocarbons,aswellasthesynthesisofmethanolandammonia [3,10,11].Onthe worldwidesyngasmarket(mostlyderivedfromfossilfuelssuchasnaturalgas,coal,andoil/ residues),theammoniaindustryholdsadominantposition [12].Otherimportantapplications includethecreationofhydrogenintendedforuseinrefineries,aswellashydrogensynthesisand theproductionofmethanol. Fig.1 depictssyngaspresentmarketusageatthetimeofwriting [13]. Amoreecologicallyfriendly,adaptable,andcost-effectivealternativewouldbetosynthesize higheralcoholsdirectlyfromsyngas(CO+H2),ratherthanrelyingonfermentationofsugars (ethanolandisobutanol)orhydrationofalkenesproducedfrompetroleum(heavieralcohols). Sinceitsinceptioninthe1930s,thisreaction’sresearchefforthasfluctuatedwiththepriceofoil, ithasincreasedsignificantlyinthelastdecadeduetoanincreasedfocusonshalegasandother renewableresourcesassuppliesofgaseousfeedstocks [14].Tofurtherboosttheperformanceof theinternalcombustionengine,syngashaslatelybeguntobeusedinthetransportationsector.
2.Productionofsyngas
Asyngasprocesscanbebrokendownintothefollowingfundamentalcomponents(Fig.2):
Fig.2
Processphaseinsyngaspowerplants [15].
Fig.1
Currentglobalmarketforsyngas [3].
Where:
• Feedpreparationincludesunitoperationssuchasheating,purifyingthefeedstock,and addingadditivessuchassteam,CO2,etc.
• Reactionsincludesteamreforming,gasification,pyrolysis,etc.
• Purificationsareunitoperationsthatchangethecompositionoftheproducttomeet downstreamneedsandremovethingsthataren’tgoodfortheproduct,suchaswaterifthe productneedstobedry,H2S,CO2,etc.
Syngasprocessesareoftendefinedbythefollowing:
• Hugemanufacturingvolumes
• Catalyticreactionsinthegaseousphase
• Highpressure(upto100bar)
• Temperaturesrangingfrom0°Cto2500°Cduringcondensationandcombustion
• Generationofsteam,superheatingofsteam,andcondensationofsteamaswater
• Extremelyenergy-efficientprocesseswithfeedconsumptionsofseveralhundredMW [15].
2.1Thereactionofmethanereforming
Whenitcomestoproducingsyngas,reformingisthemostcommonmethodusedinboth industryandlaboratoryresearch.Thisincludesasteamreformingofmethane(SRM),dry reformingofmethane(DRM),andpartialoxidationofmethane(POM),aswellas,bireforming ofmethane(BRM)andautothermalreformingofmethane(ARM) [16–18].Theadvantageof SRMisthatitgeneratessyngaswithalargeconcentrationofhydrogen,whichisadvantageous becausemethaneisdistinguishedtohavethehighestH/Cratioofallofthehydrocarbonsinuse. Additionally,themethodisbasedoninexpensivenickel-basedcatalysts.Heatisessentialfor thecreationofbothsteamandtheprogressionoftheendothermicreaction.Theheatfrom coolingsyngascanbeusedtomakeheatwithoutneedingtoburnmethane,whichisoftenused asaheatsource.Ataround900°C,afullconversionofmethanecanbeachieved.Theuseof hydrogenseparationduringtheprocess,suchasmembraneutilization,allowstoachieve100% methaneconversionatalowertemperature,andfocusedsolarheatmightbeusedtosubstitute methaneburning,therebyloweringtheprocess’scarbonoutput.Highpressureisdetrimentalto theprogressionofthereactionduetotheincreasedmolenumber.Butwhencompressed hydrogenisrequired,pressuresupto30bararebeingusedtoreducethecapacityofthereactor, aswellastheamountofelectricityrequiredforthecompression [18].
IntheDRM,theinteractionbetweenCH4 andCO2 isthemostimportantoneamonganumber ofotherreactions.Apartfromthefeedratioandpressure,thermodynamicpropertieshavean effectontheoptimaltemperatureforthereactionandthenumberofoccurredsidereactions. Additionally,withregardtotemperatureandCO/H2Oratio,thereactionsystemadjusts [19].In mostcases,gasification(coal,heavyhydrocarbons)andreformingaretheprimarysourcesof
thisH2/COcombination(lighthydrocarbons) [20].Carbonsourcesarereactedathigh temperaturesbysteam,oxygen,orcarbondioxidemixes.Thereactionconditionsandthe contentofthegeneratedsyngasmightsubstantiallyvarydependingontheagentusedin differenttechnologies.Adifferentmixtureisneededforeachapplication.Formethanoland Fischer–Tropschsynthesis,themostfrequentH2/COratiois2,buthigherratiosareneededfor thehydrogenproduction [18].LowerH2/COratiosofroughly1areusedintheproductionof ethanolandotheralcohols,aswellasdimethyletherandoxo-alcohols.Furtherloweringofthe ratioresultsinpurecarbonmonoxide,whichisatoxicgaswhenbreathedin.Formicacidand aceticacidaretwoexamplesoftinyorganicmoleculesthatcanbesynthesizedusingthisgas alone,withouttheassistanceofhydrogen [21]. Table1 depictsvarioustypesofreforming procedures,aswellassomeinformationabouteachmethod.
Toillustratehowdifferentfuelsreactindifferentprocessingsteps, Table2 includesequations forfourrepresentativefuels:naturalgas(CH4)andliquefiedpropanegas(LPG)forstationary use,liquidhydrocarbonfuels(CmHn),methanol(MeOH)formobileuse,andcoalgasification forlarge-scaleindustrialusetoproducesyngasandhydrogen [23].
2.2Gasificationofbiomass/coalfortheproductionoffuelsandchemicals
Whenusingasolidmaterialsuchasbiomassorcoalasastartingpoint,thefeedstockmustbe gasifiedbeforeitcanbeused.Theparticlesizedistributionisdeterminedbythekindof gasification [24].Aftergasification,theendresultisagasreferredtoasproducergas,which containsimpuritiesandmustbecleanedupbeforeitcanbeutilized.Priortosynthesis,thegas producertypicallyrequiresaratioofH2 toCO [13].
2.2.1Gasification
Aspreviouslymentioned,synthesisgascanbeproducedfromanyhydrocarbonfeedstock,such ascoal,heavyoil,orcombustiblebiomass,viagasification.Lowpressure(1–20bar)andhigh temperature(800–1000°C)arerequiredforasuccessfulreaction,andaccordingtothe technologies,theH2/COratiorangesbetween0.5and1.8.O2,H2O,air,oracombinationof theseagentsisusedtopartlyoxidizethesolidcarbon.CxHyOz isprimarilycomposedof methanewithtraceamountsofhydrocarbonssuchasethaneandethylene(Table3).Inthe majorityofgasifiers,gasmayalsocontainheavierhydrocarbonssuchastoluene,naphthalene, andbenzeneaccordingtothefeedstockandoperationalconditions.Hydrocarbonsthatare greaterinweightthanbenzenearefrequentlyreferredtoas“tars” [3]
Inmostcases,thegasificationefficiencyiscalculatedonthebasisofthelowerheatingvalue.In ordertocomputetheefficiency,thetotalamountofenergycontainedintheproducergas (practicalaswellaschemical)isexpressedasapercentageofthetotalenergycontainedinthe
Table1Compareandcontrasttheconventionalmainstreammethanereformingprocedures[22].
Reforming type Reaction conditionsH2/COratio
SRM P ¼ 3–25atm
T ¼ 250–1000°C CH4/H2O ¼ 1.5 3228
1.Agreaterconcentration oftheactiveingredient intheproduct
2.Highoperational efficiency
3.Maturityofindustry
POM P ¼ 100atm
¼ 950–1100°C
¼ 2 2 22.6
ARMCH4/H2O/ O2 ¼ 1/1/0.5 1or2based Onfeed Composition Negative value Depended onfeed Composition
1.Enhancedsusceptibility tosulfides
2.Shortdurationof contact
3.Moreenergyefficient
4.Highconversion/ selectionefficiency
1.Moreenergyefficient
2.Reducedcontact duration
3.Decreasedcoke deposition
4.Adjustableand adaptablecomposition ofthefeed
1.Relativelyinefficient energyuse
2.Relativelyhighreactionunit requirement
3.Inappropriateproductsfor F-Tsynthesis
1.ExpensivepureO2 feedstock
2.Possibilityofuncontrolled combustion
BRMCH4/H2O/ CO2 ¼3/2/1 T ¼ 650–900°C
2220 1.Lowerlevelsofcoke deposition
2.Flexibleand customizable compositionofthefeed
1.DecreasedH2 yield
2.AmaximumH2O/O2 ratio
3.Possibilityofuncontrolled combustion
1.Relativelyhighreactionunit requirement
2.ExpensiveseparatingofCO2 fromtargetgoods Continued
Table1Compareandcontrasttheconventionalmainstreammethanereformingprocedures—cont’d
Reforming type Reaction conditionsH2/COratio ΔH(KJ/mol)AdvantagesDisadvantages
DRM P ¼ 1atm
T ¼ 650–900°C
CH4/CO2 ¼ 1
Plasmaassisted T ¼ 400 ° C
Photoassisted T ¼ 400 ° C
Microwaveassisted T ¼ 800 ° C
1.Theprocessof convertingtwo greenhousegases simultaneously
2.Generationofclean powerandfuel
3.OptimumH2/COfor thesynthesisofF-T
1.Highionization activationenergy efficiency
2.Mildthermodynamic circumstancesrelative toothers
1.Breakingbeyondthe thermodynamicslimit anddecreasingenergy usage
1.Instantaneousheat generation
2.Relatively straightforward experimentaldesign
1.Difficultiesassociatedwith catalystdeactivationasa resultofcokeandmetal sintering
2.Extremelystringent requirementsforCO2 activation
1.Overpricedglowdischarge systems
2.Ambiguousmechanismof reaction
1.Availablecatalystsin photocatalyticmaterials
2.Fewcomparativeresearch
1.Inadequatemanagementofa scaldinghotzone
2.Difficultyinmonitoringthe temperatureofthecatalyst
Table2Equationsfortheprobablereactionsthatoccurduringthevariousprocessingsteps [23].
Nameofreactions Possiblereactions
SRM
POM
ARM
Gasificationofcarbon(coal,coke)
CH4 +H2O $ CO+3H2
CmHn +mH2O $ mCO+(m+n/2)H2
CH3OH+H2O $ CO2 +3H2
CH4 +O2 $ CO+2H2
CmHn +m/2O2 $ mCO+n/2H2
CH3OH $ CO+2H2
CH4 +1/2H2 +1/2O2 $ CO+5/2H2
CmHn +m/2H2O+m/4O2 $ mCO+(m/2+n/2)H2
CH3OH+1/2H2O+1/4O2 $ CO2 +2.5H2
C+H2O $ CO+H2
C+O2 $ CO2
C+0.5O2 $ CO
C+CO2 $ 2CO
CarbonformationCO+H2O $ CO2 +H2
CO2 +H2 $ CO+H2O(reversewatergasshift)
Selectiveco-oxidationCO+O2 $ CO2
H2 +O2 $ H2O
Table3Syngasfuelcompositionbycoalandgasifiertype [25]. Typeofcoal
feedstock(theheatingvalue).Mechanicalgasifierefficiencycanrangefrom60%to75%, dependentonthegasifier’skindandconstructionandalsothefuelquality.Thegasification efficiency(percent)utilizedinengineapplicationscanbedefinedasfollows:
where ηm_mdenotestheefficacyofgasification(percentage)(mechanical), Hg indicatesthe gas’sheatingvalueofthegas(kJ/m3), Qg representsthegas’svolumeflow(m3/s), Hs isthe gasifierfuel’slowerheatingvalue(kJkg 1),and Ms definesthesolidfuelconsumptionofthe gasifier(kg/s) [13,26].
3.Thepropertiesofasynthesisgas
3.1Abriefdescriptionofsynthesisgasphysicalandchemicalproperties
SyngasisablendofCOandH2.SyngasmayalsohaveCO2 plusotherconstituentssuchas H2O.Duetothefactthatsyngasistypicallyutilizedatgreaterpressurestosynthesizechemicals andfuels,theN2 levelofsyngasmusttypicallybekepttoaminimum [27].
Hydrogenisachemicalelementthatcanbeusedinavarietyofapplications.However,despite thefactthatitisnearlyexclusivelyfoundinamixedformonearth,itmightbecreatedfromany mainresourcebyseparatingitfromH2Oorothercompounds,whichincludestheelementand convertedintoelectricityandotherlow-pollutionenergyforms [24,28].Therehavebeena varietyoftechnologiesusedtocreatehydrogen(Table4),includingSRM,POM,water electrolysis,andbiomassgasification,amongothers.Whenitcomestoproducinghydrogen fromwater,electrolysisandphotocatalyticwatersplittingaretwoofthemostprevalent methods.However,inordertoproducebothhydrogenandoxygenatthesametime,further separationandpurificationofhydrogenfromoxygenarerequired.Additionally,electrolysisof wateris [30] expensive,andphotocatalyticwatersplittingislimitedbyphotoconversion efficiency.SRMandPOMofhydrocarbonsandcarbon-basedfeedstockssuchasnaturalgas, petroleum,andcoalarethemainwaystomakehydrogenforcommercialuse [31–33].
Table4Themostcommonmethodsofhydrogensynthesis [29].
Process
Coalgasification Coal Water/coal
HydrocarbonspartialoxidationHydrocarbonsWater/hydrocarbons
Hydrocarbonsreforming
Kvaernerprocess Fossil/nuclear/renewableMethane
Electrolysis Water
Thermolysis Nuclear/renewable
Photoelectrolysis Sun
Photosynthesis Water/biomass
Biomassgasification
Biomassanaerobicdigestion
Reactionwater/hydride Chemicalhydride Water/hydride
Syngascharacteristics:Physicalandchemicalproperties11
Hydrogeniscolorless,odorless,andtasteless;itisalmostinsolubleinwater;itisextremely combustible;anditisharmless(simpleasphyxiate).Hydrogenisadiatomicmolecule containingcovalentbonds,withprotonshavingeitherparallel(ortho-hydrogen)orantiparallel (para-hydrogen)spins.Themolecularweightofthiscompoundis2.016amu.Atoraboveroom temperature,H2 seemstobemix(75%ortho-hydrogen,25%para-hydrogen),whichisreferred toasnormal-hydrogen [29].Severalotherpropertiesofhydrogenarelistedin Table5.
Carbonmonoxideisacolorless,odorless,combustiblegasthatislighterthanair.While increasingamountsofCOareenteringtheatmosphereascivilizationadvances,ithasalways beenpresent,mostlyasaresultofvolcanicactivity.Unfortunately,becausetherearesomany naturalsourcesofCOintheatmosphere,itisimpossibletoaccuratelyfigureouthowmuchCO isreleasedintotheair.Inmetropolitanlocations,highlevelsofbreathedCOcanhavea detrimentaleffectonindividualshealth.Itisfrequentlygeneratedbyincompletecombustionof carbon-containingsubstances,mostnotablyininternalcombustionengines.Additionally,it canbekeptandtransportedcompacted,andcloseassociationwithfireorhightemperaturescan resultincontainerexplosions [35].COisaverypoisonousmolecule,andinhalationof significantamountsfrequentlyresultsincentralandperipheralnervoussystemand cardiovascularsystemdiseases.Theseverityofsymptomsisdose-dependentandrangesfrom mildheadachestoquickdeath:COconcentrationsgreaterthan1000ppmaredeemed life-threatening. Table5 containsasummaryofsomefeaturesofcarbonmonoxide [34]. Table5 alsodescribesthepropertiesofothergasesinsynthesisgas,suchascarbondioxideand nitrogen.
Table5Hydrogen,carbonmonoxide,carbondioxide,andnitrogencharacteristics [29,34].
1)141.86010.11232.912Noncombustible CASnumber1333-74-0630-08-0124-38-97727-37-9
3.2Syngasbasiccombustionproperties
Itiscriticaltounderstandthebasiccombustionefficiencyofsyngasfuelinordertouseit effectivelyincombustionequipment.Themosteffectivecombustiondevicesgenerate significantturbulence,whichresultsinimprovedblendofgaseousairandfuelpriortoignition, sothecombustionprocessiscategorizedaspremixedinmanyapplications.Differentsyngas propertiescanhaveaneffectonthecombustionprocedureinengineswithinternalcombustion (IC).ThelimitofflammabilityofsyngasisacriticalpropertyforICenginesafetyandfuel efficiency [36].Additionally,burningvelocityisavitalfactorthatgovernstheblended combustionprocess.Dependingonthenatureoftheburningvelocityoftheflowfield,which mightbelaminarorturbulent,itmaybeusedtomanagethepremixedcombustionprocess.The followingsectionsdiscussthesyngas’sflammabilitylimit,proceduresformeasuringits burningvelocity,thesyngas’scomposition,anditscalorificvalue [3].
3.2.1Limitsontheflammabilityofsyngas
Theflammabilityrestrictionisfrequentlyusedasaproxyfortheflammabilityofthegas.When appliedtoagiventemperatureandpressure,thisphrasereferstoavarietyoffuelcontentsinthe fuelandairmixturethatallowtheflametospreadandmaintaintheflammabilitylimitations. Thesearecommonlyreferredtoasthefuel–airareasthatallowflamepropagationandthose thatdonotallowfirepropagation.Thefuel,thedirectioninwhichitspreads,thesizeandshape ofcombustionchamber,aswellasthetemperaturesandpressuresthereinareallsignificantly affected.Besides,therearetwouniqueflammabilityboundariesforthefuel–airmixture;the smallestpossiblefuellimitacrosswhichflamescanspreadisreferredtoasthelowerlimitof flammability,whileitisregardedastheupperflammabilitylimitfortherichest.Duetothefact thathydrogenandcarbonmonoxidearetheprimarycomponentsofsyngasthatare heat-resistant,thesegases’propertiesareinherited.Inertgasessuchasnitrogenandcarbon dioxidecanbeaddedtogasmixturestomakethemlessflammable [37].
3.2.2Thevelocitiesofsyngaslaminarflames
Thefrequencyoflaminarflashesistherateatwhichaflamespreadsinthedirectionitispointed oftheexpansionwavesurfacesunderalaminarflowscenariousingunbrandedsilentfuel–oxidantmixtures [38].Becauselaminarflamevelocityisextremelysensitivetotheoperationof thecombustionchamberandtheperformanceoftheemissionsystem,itiscriticaltoconduct combustionchamberoperationinvestigations.Itisaffectedbythefuelconcentration,the equivalencyratioofmixtures,thepressure,andthetemperature.
3.2.3Syngasignitiondelaytimes
Syngasignitiondelaytimesareimportantcombustionvariablesthataffectboththe performanceandoperationofburnersandgasturbines.Usingpreignitionwhilethesupplyis lowcouldcausedamagetotheequipment,makingitcriticaltoaccuratelycharacterizeignition
Syngascharacteristics:Physicalandchemicalproperties13
delaydurations.Additionally,ignitiondelaytimesarefrequentlyusedtovalidatereaction mechanisms.Generally,machinesforfastcompressionandfacilityforshocktubeareusedto determineignitiondelaytimesunderavarietyofthermodynamiccircumstances [3,39].
3.3Compositionofsyngasanditscalorificvalue
Themanufacturer’sgascompositionisdeterminedbythegasflowrate,feedstock,flowof feedstock,particlediameter,designsofreactors,catalyst,operatingcircumstancesor gasificationprocess,gasificator,anddurationofgasresidence.However,itismostly influencedbythereactor’stemperature,whichisaffectedbytheenergyratingvalue. Additionally,thequantitiesofhydrogen,carbonmonoxide,andmethaneinproducergasare regulatedbychemicalprocessesoccurringthroughoutthegasificationprocess [37].Asaresult, thetypeofchemicalagentthatoxidizesusedingasificationhasabigimpactonthegas’s calorificvaluethatcomesoutofit.
4.Conclusionandfutureoutlook
Inordertoproducesustainableenergy,expertsfromaroundtheworldareincreasinglyfocused onfurtherinnovativeandcleanenergysources.Synthesisgashassignificantpotentialforusein theproductionofsustainableenergy,whichcanhelptomeetthegrowingneedforliquidand gaseousfuels,aswellasforelectricity.Thesynthesisgasisdescribedasagascontaining primarilyhydrogenandcarbonmonoxideasfuelcomponents,withthelimitationof flammabilityandthevelocityoflaminarflameservingastheprimarysyngasparameters. Syngascanbecreatedinavarietyofways,includingbiomassorcoalgasification,aswellas naturalgasreforming.Thefutureuseofsyngasandhydrogenwillnecessitatethedevelopment ofmoreefficienthydrogenplants,lower-costlarge-scalesyngasplantsforgas-to-liquidsplants, andsmall-scaleapplicationsofsyngastechnologiesforfuelcells,whetherforstationaryor automotiveapplicationsinthefuture [18].
Abbreviationsandsymbols
ARM autothermalreformingofmethane
BRM bireformingofmethane
CO2 carbondioxide
CO carbonmonoxide
CH4 methane
DRM dryreformingofmethane
H2 hydrogen
IC internalcombustion
POM partialoxidationofmethane
SRM steamreformingofmethane
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