Table Of ContentSUSTAINABLE HYDROGEN
PRODUCTION
SUSTAINABLE
HYDROGEN
PRODUCTION
I D
BRAHIM INCER
C Z
ALIN AMFIRESCU
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Preface
Increases in population and living standards in growing economies have put an unprecedented pressure on the
production infrastructure of worldwide economies.Thereis arapidly increasing need for syntheticmaterials, fuels,
power,andthermalenergy.Thehydrogeneconomyisakeysolutioninthiscontextbecausehydrogenisatthesame
timeaconstituentofalargepaletteofessentialmaterials,chemicals,andfuels,anditisasourceofpowerandheat.
Therefore,thisbookonsustainablemethodsofhydrogenproductionwillbenefitscientistsandengineersworking
onmethodsofefficientandcleanhydrogengenerationfromrenewable(sustainable)energies.Itstressesthescientific
understanding,analysis,andassessmentofsustainablehydrogenproduction,andtheevaluationandimprovementof
theseprocessesandmethods.Thisapproachisdesignedtopresentanintellectuallyrichandinterestingtextthatisalso
practical.Thisisaccomplishedbyintroducingthefundamentalmethodsofhydrogenproductioncategorizedbythe
typeofenergysourceused:electrical,thermal,photonic,andbiochemical.Whereappropriate,thehistoricalcontextof
these methods is introduced. Thermodynamic concepts, through energy and exergy analysis methods, are used as
examples and case studies to solve concrete power engineering problems. The book also serves as a unique source
ofinformationonadvancedhydrogengenerationsystemsandapplication,includingintegrated,hybrid,andmulti-
generation. It links advanced and clean technologies to environmental impact issues and sustainable development,
and provides methodologies, models, and analysis techniques, to help achieve a more efficient and cost-effective
useofresourcesandtoimproveenergysecurityandsustainability.Finally,itscontentmayalsomakeitadistinguished
book forsenior undergraduate and graduate students and practicing engineers.
Chapter 1 introduces the fundamental aspects of thermodynamics, as well as process and system assessment
methods.Thelawsofthermodynamicsandrelatedanalysismethodswithenergyandexergyarepresentedindetail,
particularlythroughbalanceequations.Bothenergyandexergyefficienciesforvarioushydrogenproductionsystems
andapplicationsaredefinedforuse.Theuseofexergymethodsforeconomic,environmental,andsustainabilityanal-
ysisarepresented.Twocasestudiesaregiventoillustratetheapplicationoffundamentalconceptsofsystemassess-
ment for renewableenergy and hydrogen.
In Chapter 2, hydrogen and its production methods are classified, and the sustainable development and use of
hydrogenasanenergystoragemediumandcarriertoharvestrenewableenergysourcesisdiscussed.Acomparative
evaluation of hydrogen and other fuel options is also presented, as well as an introduction to the main material
resourcesfromwhich hydrogen canbeextracted,andto the main methodsandpathways of hydrogen production.
Chapter3primarilyfocusesonhydrogenproductionmethodsdrivenbyelectricalenergybycoveringthefundamentals
ofelectrochemicalhydrogenproduction,andmostimportantlythermodynamicparametersandelectrochemicalreactions.
Further,themaintypesofwaterelectrolyzers,includingalkaline,protonexchangemembrane,andsolidoxide,areana-
lyzed.Theefficiencyofhydrogenproductionthroughelectrochemicalmethodsisformulatedintermsofenergy,exergy,
andFaradayefficiency.Beyondwaterorsteamelectrolysis,someotherelectrochemicalmethodsofhydrogenproduction
areincluded,suchasthechloralkaliprocess,andbothhydrogensulphide,andammoniatedwater,electrolysismethods.
In Chapter 4, hydrogen production methods driven by thermal energy are introduced, analyzed, and discussed
through fundamentals of thermochemical hydrogen production, thermodynamic parameters, thermochemical reac-
tions,andthemaintypesofthermochemicalprocesses,suchaswaterthermolysis,thermochemicalcyclesandthegas-
ificationandreformingoffuels.Thechapterendswithapresentationofsomeoftheintegratedsystemsthatproduce
green hydrogen from thermal energy. These systems are based on nuclear energy, solar thermal energy, biomass
energy, and clean coaltechnology.
Chapter 5 dwells on hydrogen production methods driven by photonic energy. It focuses on the photochemical
reactionspotentiallyavailableforhydrogenproduction.Italsopresentssomeoftheintegratedsystemsthatproduce
green hydrogen from photonic energy. Such systems do not emit harmful chemicals or greenhouse gases (GHG)
during operation.
Chapter 6 is about how to produce hydrogen through biochemical energy and bio-photochemical energy.
Itdiscussesthebasicpathwaysofbiochemicalhydrogenproduction,andsomeoftheintegratedsystemsthatproduce
sustainablehydrogen from biochemical energy: either lightassisted, or darkfermentation.
ix
x
PREFACE
Chapter 7 focuses on some hybrid water splitting cycles, such as photothermochemical, photoelectro-
thermochemical and radiothermochemical. It presents nuclear-based hydrogasification of coal and nuclear-based
natural gas reforming as two potential methods for very large-scale hydrogen production. Solar fuel reforming for
hydrogen production is also covered, and hasapotentialapplicationinsmallandintermediatescalesofproduction.
Somefuelsenvisagedforthisprocessarenaturalgas,orsyntheticnaturalgas,andmethanol.Anotherlesscommonfuel
isurea,whichisalsoafertilizer.Ureaisasourceofhydrogenaswell,asitcanbeconvertedthermochemically.Water
electrolysisinmoltenalkalihydroxidesisstudiedasamethodinconductingelectrolysisathightemperatures.Thischap-
terendswithafocusonthehydrogen-ammoniaparadigm,discussingammoniasynthesis,storage,anditsconversionto
hydrogen.
Chapter8discussestherecentprogressmadeonsomenovelandnewlydevelopedhydrogenproductionprocesses,
methods,techniques,technologies,etc.inordertoreflectpotentialoptionsandfuturedirectionsonhydrogenproduction
technologies.Thetopicscoveredinthischapterinvolvenumeroushydrogenproductionmethods,rangingfrombiolog-
icaltophotoelectrochemicaloptions.Variouspathways,throughwhichthefourkindsofenergies(electrical,thermal,
photonic and biochemical) drive hydrogen production, are discussed. Note that electrical and thermal energy can be
derivedfromrenewableenergies,suchassolar,wind,geothermal,tidal,wave,oceanthermal,hydro,andbiomass;from
nuclearenergy;orfromrecoveredenergy.
Referencesareincludedtodirectthereadertosourceswheremoredetailscanbefound,andtoassistthereaderwho
issimplycurioustolearnmore.Thesereferencescanalsohelpidentifyinformationontopicsnotcoveredcomprehen-
sivelyin this book.
Inthisbook,greenmethodsforhydrogenproductionarepresentedcomprehensively.Conventional,butenviron-
mentallybenign,methodsaswellaspotentialmethodsareintroduced,discussed,assessedandcomparedforvarious
applications, along with many illustrative examples and case studies using various sources of renewables. This
approach is aimed to make thisbook auniquesource on hydrogen production technologies andto satisfyreaders.
The selection ofthetopicforthisbookwasdesignedtoprovidethereader with anintroductiontothelanguage,
concepts and technologies used in all major hydrogen production methods that are expected to contribute to the
21stcentury.
We hopethisbookwillopen anew windowto carbonfreesolutionsthrough sustainablehydrogen production.
Ibrahim Dincer and Calin Zamfirescu
January2016
Acknowledgments
The illustrations provided by several past and current graduate students of Prof. Dincer are gratefully
acknowledged, including Canan Acar, Seyedali Aghahosseini, Ehsan Baniasadi, Camilo Cassallas, Sayantan Gosh,
Hasan Ozcan, Musharaf Rabbani, TahirRatlamwala, Ron Roberts,and RafayShamim.
Inaddition, Yusuf Bicer’shelp in materializing the literature review forChapter8 is acknowledged.
Last but not least, we warmly thank our wives, Gulsen Dincer and Iuliana Maria Zamfirescu, and our children
Meliha, Miray,IbrahimEren, Zeynep,andIbrahimEmir Dincer, and Ioana, Cosmin,and Paulina Zamfirescu. They
have been a great source of support and motivation.
Ibrahim Dincer and Calin Zamfirescu
January 2016
xi
C H A P T E R
1
Fundamental Aspects
O U T L I N E
1.1 Introduction 1 1.11.1 Assumptions 48
1.11.2 Thermodynamic Analysis 49
1.2 Physical Quantities and Unit Systems 2
1.11.3 Environmental Impact Analysis 51
1.3 Ideal-Gas Theory 9 1.11.4 EconomicAnalysis 52
1.11.5 Exergosustainability Analysis 53
1.4 Equations ofState 12
1.11.6 Results 54
1.5 The Laws ofThermodynamics 16 1.11.7 Closing Remark 55
1.6 Exergy 20 1.12 CaseStudy 2: Exergosustainability
Assessment of aHigh-Temperature Steam
1.7 Thermodynamic Analysis Through
Photo-Electrolysis Plant 55
Energy and Exergy 24
1.12.1 Assumptions 55
1.7.1 Mass Balance Equation 24
1.12.2 Thermodynamic Analysis 56
1.7.2 EnergyBalanceEquation 24
1.12.3 Environmental Impact Analysis 57
1.7.3 Entropy Balance Equation 25
1.12.4 EconomicAnalysis 57
1.7.4 ExergyBalanceEquation 26
1.12.5 Exergosustainability Analysis 58
1.7.5 Formulations for System Efficiency 27
1.12.6 Results 59
1.7.6 Cost Accounting of Exergy 28
1.12.7 Closing Remarks 60
1.8 Exergoeconomic Analysis 33
1.13 Concluding Remarks 60
1.8.1 EXCEM Method 33
1.8.2 SPECO Method 36 Nomenclature 61
1.9 Exergoenvironmental Analysis 37 References 62
1.10 Exergosustainability Assessment 39 Study Problems 63
1.11 Case Study1: Exergosustainability Assessment
ofa Concentrated Photovoltaic-Thermal
System forResidential Cogeneration 47
1.1 INTRODUCTION
Hydrogenbecomesincreasinglyimportanttosociety,asitisconsideredoneofthekeysolutionstosustainability.
Since the global population and its demand for services, materials, transportation, commodities, etc., are rapidly
increasing,manyconcernsariserelatedtothesupplyofenergy andtheenvironmentalimpact relatedtoitsconver-
sion/transformation,distributionanduse.Thence,thereisaclearmotivationworldwidetodevelopcleanerprocesses
andmoreefficientproductionmethodsinallsectors,whichwillbecomeabletosupplementandreplacetheconven-
tional power generation and production methods by incorporating hydrogen and sustainable energies, including
renewables and nuclear.
SustainableHydrogenProduction 1 ©2016ElsevierInc.Allrightsreserved.
http://dx.doi.org/10.1016/B978-0-12-801563-6.00001-7
2
1. FUNDAMENTALASPECTS
Hydrogencanbeproducedfromawealthofmaterialsexistentinabundanceonearthandeasilyaccessible.Wateris
themostabundantsourceofhydrogen.Biomass,anthropogenicwastesandevenfossilfuels,whenprocessedthrough
cleanmethods,representsourcesforsustainablehydrogenproduction.AsreviewedinDincerandZamfirescu(2012),
fivegeneralmethodscanbeidentifiedforhydrogenproduction,namely:electrochemical,photochemical,biochemical,
thermochemical and radiochemical. In addition, hybrid methods may be possible such as photo-electrochemical,
photo-biochemical,etc.
Developing,designing,optimizing,andassessingthemethodsforhydrogenproduction,includinghydrogenstor-
age and distribution, requires an interdisciplinary effort. Thermodynamics as a tool and its applications to electro-
chemical, thermochemical, photochemical, biochemical processes, and catalysis are treated as the masterpiece for
systemdesign,analysis,assessment,andoptimizationinviewofmakinghydrogenproductionmoreefficient,more
cost-effective, more environmentallybenign and more sustainable.
Inthischapter,fundamentalaspectsrelatedtohydrogenproductionarereviewedwithafocusonthermodynamics.
Ofparticularattentionisthermodynamicsapplicationinthestudyofchemicalreactions,especiallythoserelevantto
hydrogenproduction.Somegeneral aspects chemicalthermodynamics areintroducedandcomplementedwithkey
methodsonchemicalkinetics.Ofparticularinterestistheuseoftheconceptofexergyandchemicalexergyforprocess
assessment in accordance with the second law of thermodynamics (SLT) and by accounting for the influence of the
surroundingsenvironment.Thechapterisexpandedwiththeenhanceduseofexergoeconomic,exergoenvironmental
and exergosustainability assessments.
1.2 PHYSICAL QUANTITIES AND UNIT SYSTEMS
Thescientificmethodinnaturalsciencesappealstoempiricalevidencesinordertoconstructandvalidatemodels
topredictandunderstandnature’sphenomena.Therefore,oneneedstorelatetoquantitiesthataremeasurableby
instruments, which are known as “physical quantities.” Physical quantities are of two types, namely:
(cid:129) Extensive quantity: which by definition isthe sum of quantities in all system constituents (e.g., mass,volume,
electric charge,energy)
(cid:129) Intensivequantity:whichisindependentoftheextentofthesystem(e.g.,temperature,pressure,specificvolume)
Sevenphysicalquantities—denotedasfundamentalquantities—havebeenchosentorepresenttheInternationalSys-
temofUnits(ISU)accordingtoISU(2006).Thesearelength,mass,time,electriccurrent,thermodynamictemperature,
amountofsubstance(molar)andluminousintensity(measuredincandela).Thestandarddefinitionofthesequantitiesis
giveninTable1.1.Notethatallotherphysicalquantitiescanbederivedfromthefundamentalonesbasedonconstit-
uencyrelationships.
Eachofthephysicalquantitytypeshasanassociatedunit,formingthustheISU.Table1.2givesthedefinitionsofthe
fundamentalunitsofmeasureaccordingtoISUformulations.Adoptionofasystemofunitsisanimportantstepinthe
analyses.Therearetwomainsystemsofunits:theISU,whichisusuallyreferredtoasSIunits,andtheEnglishSystemof
Units(sometimesreferredasImperial).TheSIunitsareusedmostwidelythroughouttheworld,althoughtheEnglish
SystemistraditionalintheUnitedStates.SIunitsareprimarilyemployedthroughoutthisbook;however,relevantunit
TABLE1.1 DefinitionsandStandardSymbolsfortheFundamentalPhysicalQuantities
Quantity Symbol Quantitydefinition
Length l Geometricdistancebetweentwopointsinspace
Mass m Quantitativemeasurementofinertiathatistheresistancetoacceleration
Time t Ameasurableperiodoftheprogressofobservableornonobservableevents
Electriccurrent I Rateofflowofelectriccharge
Thermodynamic T Ameasureofkineticenergystoredinasubstancethathasaminimumofzero(nokinetic
temperature “internal”)energy
Amountofsubstance n Thenumberofunambiguouslyspecifiedentitiesofasubstancesuchaselectrons,atoms,molecules,etc.
Luminousintensity I Luminousfluxofalightsourceperdirectionandsolidangle,forastandardmodelofhuman-eye
v
sensitivity
From:ISU,2006.TheInternationalSystemofUnits(SI),eighthed.
3
1.2 PHYSICALQUANTITIESANDUNITSYSTEMS
TABLE1.2 DefinitionoftheFundamentalUnitsAccordingtoInternationalSystemofUnits
Dimensional
Quantity symbol Unit Symbol Measurementunitdefinition
Length L Meter m Thelengthofthepathtraveledbylightinavacuumduringatimeinterval
of1/299,792,458ofasecond
Mass M Kilogram kg TheweightoftheInternationalPrototypeofthekilogrammadeinplatinum-iridiumalloy
Time T Second s Thedurationof9,192,631,770periodsoftheradiationcorrespondingtothetransition
betweenthetwohyperfinelevelsofthegroundstateofthecesium133atom
Electriccurrent I Ampere A Theconstantcurrentwhich,ifmaintainedintwostraightparallelconductorsofinfinite
length,ofnegligiblecircularcross-section,andplaced1mapartinavacuum,would
producebetweentheseconductorsaforceequalto2(cid:3)10(cid:2)7N/moflength
Thermodynamic Θ Kelvin K Thefraction1/273.16ofthethermodynamictemperatureofthetriplepointofwater
temperature (havingtheisotopiccompositiondefinedexactlybythefollowingamountofsubstance
ratios:0.00015576moleof2Hpermoleof1H,0.0003799moleof17Opermoleof16O,and
0.0020052moleof18Opermoleof16O)
Amountof N Mole mol Theamountofsubstanceofasystemthatcontainsasmanyelementaryentitiesasthereare
substance atomsin0.012kgofcarbon12
Luminous J Candela cd Theluminousintensity,inagivendirection,ofasourcethatemitsmonochromatic
intensity radiationoffrequency540THzandthathasaradiantintensityinthatdirectionof1/683W
persteradian
From:ISU,2006.TheInternationalSystemofUnits(SI),eighthed.
conversionsandrelationshipsbetweentheSIandEnglishunitsystemsforfundamentalpropertiesandquantitiesare
listedinAppendixA.
AnyotherphysicalquantitybesidesthosegiveninTable1.1canbederivedfromthefundamentalquantitiesusing
constitutiverelationships.Theunitsofmeasureofanyderivedphysicalquantitycanbedeterminedbasedontheunits
of fundamental quantities and the constitutive relationships according to the dimensional analysis method. In this
respect,thedimensionalsymbolsforthefundamentalquantitymustbeusedtoexpressthedimensionforthederived
quantities. The list of dimension symbols forthe fundamental physical quantities is given in Table 1.2.
Now,wewillreviewthemainderivedphysicalquantitieswhicharethemostrelevantwithinthisbook.First,the
thermodynamicpropertiespressure,specificvolumeandtemperatureareintroduced,andtheirinterconnectionsand
interpretationsareprovided.Asknown,thethermodynamicstateofasystemisgenerallyspecifiedwhenitspressure,
temperature and specificvolume are known.
Tobegin,letusintroducethespecificvolume,definedastheratiobetweenthevolumeandthemassofasystem.
Here,massisafundamentalquantitybutvolumeisnot.Thence,thenotionofvolumemustbefirstdefined.Volumeis
a physical quantity, representing a three-dimensional extent of a system. This is an extensive property, having the
dimension equalto length to the power 3, noted L3.Thecommonsymbolfor volume is V,therefore onewrites
(cid:1) (cid:3)
V¼L3 m3
Here,thenotationbetweenbracketsistheunitofvolume,namelycubicmeter.Thespecificvolumeisthusdefined
as follows
(cid:1) (cid:3)
V
v¼ m3=kg
m
Indimensionalanalysisnotation,onewritesthatthedimensionofthespecificvolumeisgivenbyL3M(cid:2)1,whereLis
thedimensionforlengthandMisthedimensionformass.Specificvolumeisinfactthereciprocalofdensity,ρ¼v(cid:2)1.
Furthermore, one notes that specific volume can be expressed with respect to the amount of substance in moles
(molar-specific volume)by the following equation
(cid:2) =V m3
(cid:3) mol
Here,thedimensionofthemolar-specificvolumeis,therefore,L3N(cid:2)1.Pressureisdefinedastheforce(action)per
unitofsurfacearea.Sinceboththeforceandsurfacearenotfundamentalphysicalquantities,definitionrelationships
4
1. FUNDAMENTALASPECTS
mustfirstbeintroducedforthose.Area,denotedwithsymbolA,representsthetwo-dimensionalextentofasystem,
havingthusthe dimension L2 and the unit m2.
Forcerepresentsameasureofactionorinteractionbetweensystems.Forcesdoexistinanyregionastheymanifest
theirpresenceintheformofforcefields(e.g.,electromagneticorgravitationalfields).Theforceactingbetweentwo
systems canproduce acceleration,meaningachange ofvelocity.Ifanobjectchangesitsvelocity,then itnecessarily
behavessobecauseitisundertheactionofanetforce.Herewedefinevelocityasavector(havingthusdirectionand
magnitude)andrepresentingthespeedofasystemtowardadefinedtarget.Sincespeedisdefinedasthedisplacement
per unit of time, one notes that the dimension for velocity is LT(cid:2)1 with the unit of SI (ISU) m/s, and the definition
relationship follows
dl
υ¼ ½m=s(cid:4)
dt
Theaccelerationmagnitudeisthederivativeofspeedwithrespecttotimeandwhencewillhavethedimensionof
LT(cid:2)2 and the SI unit of m/s2; the definition acceleration is written as
dυ d2l(cid:1) (cid:3)
a¼ ¼ m=s2
dt dt2
Forceisavectorquantityhavingthesamedirectionastheaccelerationthatitproduces.Forceisdefinedastheprod-
uctofmassandacceleration.Thatis,ifasystemofmassmisacceleratedwiththeaccelerationa,thenanetforceacts
uponit as follows
!F¼m!a
ThedimensionforforceisMLT(cid:2)2,meaningthatforceismeasuredinSIinkgm/s2,aunitthatisshorthandedas
Newton(symbolN);thence1N¼1kgm/s2.InBritishSystemofUnits,forceismeasuredinpound-forcedenotedas
lb.Pressureisdefinednowastheratiobetweenaforceandthenormalareaofthesurfaceoverwhichforceisexerted
f
uniformly (here the term “normal” stands for a direction perpendicular on force vector direction). Therefore, one
writes
F
P¼ ½Pa(cid:4)
A
Notethatalthoughforceisavector,pressureisdefinedasascalar.Furthermore,pressureisanintensivequantity.The
dimensionofpressureisequaltothedimensionofforcedividedbythedimensionofarea,thatis,ML(cid:2)1T(cid:2)2,having
theSIunitofkg/s2m,whichisthesameasN/m2andshorthandedasPa(Pascal).Onesaysthat1Pascalrepresents
the force of 1N (Newton) exerted on 1m2 surface. Pressure is a very important parameter for the thermodynamics
ofgasesandliquids.
The atmosphere that surrounds the earth acts as a reservoir of low-pressure air. Its weight exerts a pressure that
varieswithtemperature,humidity,andaltitude.Atmosphericpressurealsovariestemporarilyatagivengeographic
location,duetothemovementofweatherpatterns.Thestandardvalueoftheatmosphericpressure(orthepressureof
standard atmosphere) is 101,325Paor 760mmHg.
Theatmosphericpressureistypicallymeasuredwithaninstrumentcalledbarometer;fromhereitcomesthename
ofbarometric pressure.Whilethechangesinbarometricpressureare usually asminoras<12.5mmof mercury,they
need to betaken into account only when precisemeasurements are required.
Gaugepressureisanypressureforwhichthebaseformeasurementistheatmosphericpressure.Thegaugepressure
isexpressedaskPagauge.Atmosphericpressureservesasareferencelevelforothertypesofpressuremeasurements,
forexample,gaugepressure.AsshowninFig.1.1,thegaugepressureiseitherpositiveornegative,dependingonits
level aboveor below atmospheric level. At the level of atmosphericpressure, the gauge pressurebecomeszero.
Adifferentreferencelevelisutilizedtoobtainavalueforabsolutepressure.Theabsolutepressurecanbeanypres-
sureforwhichthebaseformeasurementisacompletevacuum,expressedinkPa(absolute).Absolutepressureiscom-
posed of the sum of thegauge pressure(positive or negative) andthe atmospheric pressure as follows
(cid:4) (cid:5)
Pressure gauge + Atmosphericpressure ¼ PressureðabsoluteÞ (1.1)
Forexample,toobtaintheabsolutepressure,wesimplyaddthevalueofatmosphericpressure.Absolutepressureis
themostcommontypeusedinthermodynamiccalculations,despitehavingthepressuredifferencebetweentheabso-
lute pressure and the atmospheric pressure existing in the gauge being what is read by most pressure gauges and
indicators.
