EvaluationofHydrogen EvaluationofHydrogen ProductionCyclesBased - - PowerPoint PPT Presentation
EvaluationofHydrogen EvaluationofHydrogen ProductionCyclesBased ProductionCyclesBased onEfficiency onEfficiency ChE4273 ChE4273 SeniorDesign SeniorDesign Spring2007
ChE4273 ChE4273 SeniorDesign SeniorDesign Spring2007 Spring2007
ImportanceofHydrogen
Thermochemical/HybridCycles
CurrentMethodsofEvaluation
OurMethodologybasedonEfficiency
Results
Advantages
Disadvantages
Methodsforproducinghydrogen
Othersuggestedeconomytypes
ThecurrentU.S.demand†
– – 11MMtons/yrtotal 11MMtons/yrtotal
Crudelightening
Producecleaner# #burningfuels burningfuels
Methanol/Ammoniaproduction
– – Steamreformationofmethane Steamreformationofmethane
DemandinHydrogenEconomy†
– – 200MMtons/yrfortransportation 200MMtons/yrfortransportation – – 450MMtons/yrforallotherenergyneeds 450MMtons/yrforallotherenergyneeds
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ThermochemicalCycles
– – Thermochemicalreactionsonly Thermochemicalreactionsonly
HybridCycles
– – Thermochemicalreactions Thermochemicalreactions – – Electrochemicalreactions Electrochemicalreactions
Somecouldbenefitfromnuclearplantheat sources sources
Over200knowncycles
ThermochemicalReactions
– – Establishedequipmentinindustry Establishedequipmentinindustry – – Oftenrequirehightemperatures Oftenrequirehightemperatures
ElectrochemicalReactions
– – Morerareinindustry Morerareinindustry – – Difficulttoimplement Difficulttoimplement – – Occuratlowertemperatures Occuratlowertemperatures
HallettAirProducts(hybrid)
USChlorine(thermochemical)
→ +
→
→ +
→
→ +
Coupledreactions
– – CyclicProcess CyclicProcess# # Degreesoffreedom Degreesoffreedom
Specialreactionmethods(high G>0) G>0)
– – Electrolysis Electrolysis – – Continuousproductremoval Continuousproductremoval
ReactionEquilibrium
– – Reversibility Reversibility – – Equilibriumconversion Equilibriumconversion
SeparationEnergy(heatandwork)may complicatethe complicatetheflowsheet flowsheet
L.C.Brown(2000,DOE)scoredcycles basedonknowncharacteristics basedonknowncharacteristics
– – Qualitativeapproach Qualitativeapproach – – Questionableevaluationtechnique Questionableevaluationtechnique
Pointsystemforprocesscomplexities
Equalweightingassignedtoallcriteria
“Judgmentcall”basis
Heavilyfavorswell# #researchedcycles researchedcycles
Lewis(2005,DOE)evaluatedcyclesbased
– – Quantitativeapproach Quantitativeapproach – – Considersequilibrium Considersequilibrium – – Assumes50%efficiencyforallworkprocesses Assumes50%efficiencyforallworkprocesses
Actualefficiencymaybebetterorworse
Differentprocesseshavedifferentefficiencies
EfficiencyBasedRankingSystem: EfficiencyBasedRankingSystem:
Findmaximumpossibleefficiency
– – Pinchtechnologytodeterminehotutility Pinchtechnologytodeterminehotutility
Streamanalysis
Heatofreaction
– – Estimateworkrequired Estimateworkrequired
Considerreactionequilibrium
DOF:optimizeflowratesand temperatures temperatures
Enthalpyofformationofwaterisminimum energyrequiredforwater energyrequiredforwater# #splitting splitting
Onlyheatandworktransferredacross systemboundaryincluded systemboundaryincluded
Heatterm
– – Hotutility Hotutility – – Heatforseparations Heatforseparations
Workterm
– – Pump/compressorwork Pump/compressorwork – – Electricalworkinelectrolysis Electricalworkinelectrolysis
°
=
=
SettingGRXN equaltozerogivesthefollowing,
SulfurIodine– – Reaction1(1123K) Reaction1(1123K)
Relatenumberofmolestoconversion n ni
i =
=n ni,o
i,o +
+ν νi
iX
Xi
i
Twoprimaryoptionsofhandling Twoprimaryoptionsofhandling
Recycle
– – Increasesseparation Increasesseparation requirement requirement – – Strategicproduct Strategicproduct placement placement
NoRecycle
– – Increasesheat Increasesheat requirement requirement – – 2configurationsforcycles 2configurationsforcycles with3ormorereactions with3ormorereactions
+ → =
StrategicSeparation MinimumSeparation
SulfurIodineCycle:
→ + +
=
→ =
StrategicSeparation
MinimumSeparation
HallettAir HallettAir Products Products
→ +
→
Causedbylinearlydependentequations
Assumedesignparameterstodefinesystem
− =
− =
=
=
+ + =
Reaction#1:
=
=
=
=
=
MixPoint#1: MixPoint#2:
Example:HallettAirProductsCycle
– – 10variables 10variables – – 9linearlyindependentequations 9linearlyindependentequations – – DOF=10 DOF=10– – 9=1 9=1
Aftersubstitutions:
– – Define Define
=
=
+ + =
HallettAir ProductsCycle ProductsCycle
– – DOF=1 DOF=1 – – Define Define
*) +) +) ++) +() , ,+ ,*
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Popularmethodoffindinghotutility
HeatcascadedfromhighT lowT lowT
Pinchoccursattemperaturewherecumulative systemheatiszero systemheatiszero
Noheatistransferredacrossthepinch
Intervalanalysis
Singlehotutility&coldutility
Isothermalreaction
Heatofreaction
min on
hot
.-
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† † Millikan,ChristopherE.,DOE2002
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† † MicheleA.Lewis,“FY2005ProgressReport” MicheleA.Lewis,“FY2005ProgressReport”
Separatespeciesintostreams
– – Dependsonexcesshandlingconfiguration Dependsonexcesshandlingconfiguration – – Phaseseparationrequiresnoenergy Phaseseparationrequiresnoenergy
Example:SulfurIodineRXN#1Separation
⋅ − ⋅ ⋅ =
)*
⋅ ⋅ =
,
Constantforallconfigurationsinvestigated
– – Doesnotincludereactiontemperatures Doesnotincludereactiontemperatures
CyclerankingsbasedonQ Qhot
hot (
( T Tmin
min=10K)
=10K)
– – Optimizedfeeds,equilibriumconsidered,reactantsrecycled Optimizedfeeds,equilibriumconsidered,reactantsrecycled
CyclerankingsbasedonQ Qhot
hot (
( T Tmin
min=10K)and
=10K)and W Welec
elec only
– – Optimizedfeeds,equilibriumconsidered Optimizedfeeds,equilibriumconsidered
CyclerankingsbasedonQ Qhot
hot (
( T Tmin
min=10K),
=10K),W Welec
elec,
, and andW Wsep
sep
– – Optimizedfeeds,equilibriumconsidered Optimizedfeeds,equilibriumconsidered
Limitedbyphasechanges
– – Optimizedfeeds,equilibriumconsidered Optimizedfeeds,equilibriumconsidered
Wisideal/0.5
Allenergytermshavebeenincluded
Differentoptionisbestdependingoncycle
Numerousrecycleconfigurations
Numerousseparationtechniques
Difficulttoachieve100%separation
Usedmembraneseparatorstoestimate separationworkforgasphaseseparations separationworkforgasphaseseparations
Membraneseparatorscannotoperateathigh temperatures temperatures
RealSeparationworkestimatedfortop4cycles
Estimatedascompressorworkformembrane separator separator
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Actualworkforagivensystemcanonly bedeterminedwithadetailedflowsheet bedeterminedwithadetailedflowsheet
Takenfrom resource
ComparisonofefficiencyforLewisseparation andrealseparationfortop4cycles andrealseparationfortop4cycles
Over200documentedcycles
Findaquickmethodoffindingefficiency
Excludeprocesswithhighexothermic reaction(s reaction(s)atlowtemperature )atlowtemperature
Efficiencybasedmethodcanquicklyrank hydrogenproducingcycles hydrogenproducingcycles
Bestconfigurationofexcesshandling dependsoncyclebeingconsidered dependsoncyclebeingconsidered
Phaseseparationandgoodcascade propertiesbenefitefficiency propertiesbenefitefficiency
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