1 ©2017ConvergentScience.AllRightsReserved

Zhaoyu Luo*,Parvez Sukheswalla,ScottDrennan,Mingjie Wang,PeterKellySenecal

ConvergentScienceInc.

3DNUMERICALSIMULATIONSOFSELECTIVECATALYTICREDUCTIONOFNOXWITHDETAILEDSURFACECHEMISTRY

Preparedfor2017CLEERWorkshopPresentationOct4th 2017

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GeneralPurposeCFDPackage:CONVERGE

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Outline• Introduction• Methodologies

- CONVERGE’ssteadystatesolver- Adaptivemeshrefinement- Ureadecomposition:Moltensolidmodel- Surfacechemistrysolver

• ResultsandDiscussion- 3DSingleSCRblockvalidations- 3DUrea/SCRSystemvalidations

• Conclusion

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Introduction

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ModernUrea/SCRSystemDesignChallenges• Meetingemissionsregulationsincost-effectivemanner

- FastproductdesigntimelineswithcomplexATsystems

• Movetocompact,lowtemperatureUrea/SCRdesigns- Relyondynamicsplashing/filmingandpulsedinjectors(i.e.,transient)

• Needtoaddressdifferentflowandcatalysttime-scales- Spray,film,mixingversusSCRsurfacechemistry

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ConventionalSCRSystemSimulationApproaches• Focuson1Dsurfacechemistrysimulations

- AccurateCFDcouplingtakestoolong• ReducedfidelityCFDandCatalystwithcoupled3D/1Dsimulations- Steady-stateCFDwithpulsedsprays,filmsandmixing- TransientCFDwithverylargetime-steps

• ManualCFDmeshgeneration- Time-consuming,limitingproductivityanddevelopmentofBestPractices

Fullycoupled3DsimulationsofUrea/SCRsystemwastimeconsumingandimpractical

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CONVERGESpeedsUREA/SCRCFDSimulations• Automaticmeshing

- Nouser-meshing- Automaticgrid-scaling- AdaptiveMeshRefinement(AMR)- Meshdependentà Grid-converged

• Superfasttransientsolver- Time-accurate- Pseudosteadystatesolver

• Comprehensivesetofaccuratemodels- Spray/Film- Ureadecomposition- Surfacechemistrysolver

Fullycoupled3DsimulationsofUrea/SCRsystemisnowapplicableandcanprovidemorephysicaldetails

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Methodologies

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SteadyStateSolverinCONVERGE(1/2)

• Densitybased• Fast,andaccuracyalmostasgoodastransientsetup

• Automatedcontrolofsolversettings

• HigherCFLnumbersattainable(20-30fornon-Reactingflows;10-15forReactingflows)

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SteadyStateSolverinCONVERGE(2/2)

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AdaptiveMeshRefinement(AMR)

• BaseGridsize:(Δ𝑥,Δ𝑦,Δ𝑧)- BasegridisatLEVEL0- LEVELn=(𝒃𝒂𝒔𝒆_𝒈𝒓𝒊𝒅)/𝟐^𝒏 [1]- GridsizeatanyLEVELisrelativetobasegridsize- Example:(1mmbasemesh,3levelsofrefinement)- Levels0,1,2,3=1.0,0.5,0.25,0.125mm

• AdaptiveMeshRefinement(AMR)- Refinemeshbasedonvelocity,temperature,species,Y+,etc.gradients

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UreaMolten-SolidModel• Birkhold,F.etal,2007

• ValidatedinKimetalICEF2004-889

WaterEvaporating

WaterEvaporatedOnlyUrealeft

Ureadecomposing(Solidtogas)Nozzle Hydrolysisof

HNCOAmmonia(NH3)

Ammonia(NH3)Iso-cyanicacid(HNCO)

Molten-SolidApproach

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SurfaceChemistrySolver

• CONVERGEusesimplicitsolverforsurfacechemistry

• Coupledwithgasphase• Fastandaccurate DetailedsurfacemodelfromOlssonetal2008

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ResultsandDiscussion

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Validation1:3DSingleSCRblock

• Experiment:SAE2013-01-1575

• Inlet:Exhaustgaswith~422ppmNOx

• P=~0.9atm,T=666K

• Surfacemechanism:Olssonetal;2008

• NOxconversionoverCu-Zeolites

NOxconversion

CONVERGE 38.87%

exp 37.8%

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Validation2:3DUreaSCRSystem:Geometry• SurfacechemistryisactivatedintheSCRblockregion(red)ofthegeometry

• Totalmeshsizeatsteadystate:~2000000

• SimulationwasterminatedwhentheNOxmassreachedsteady-stateThecasewasrunwithbothasteady-statesolverandatransientsolver

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Validation2:3DUreaSCRSystem:BoundaryandInitialConditions

No. Speed[rpm] BMEP[bar] Temp[K] UWS flowrate[g/s]

1 1200 11.6 666 0.12172 1200 11.6 678 0.1916

TwoSCRsystemsaresimulatedinthecurrentstudy:

ExamplespecificationforSCR-1

Speciescomposition CO2,N2,O2,H2O,NO,NO2Pressure(bar) 0.96

Steadytime(s) 20.0

Mechanism Olssonetal2008

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Validation2:3DUreaSCRSystem:PressureDropinSCR

PorousmediamodelisusedintheSCRsystem;largeuncertaintyexistsandparameteroptimizationisperformed

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Validation2:3DUreaSCRSystem:NOxConversions

0

0.1

0.2

0.3

0.4

0.5

1 2

SCR-1NOxCo

nversion

Rate

Experiment Simulation

(a)

(b)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1 2

SCR-2NOxConversionRate

Experiment Simulation

(a)

(b)

SCR-1 SCR-2

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Validation2:3DUreaSCRSystem:TransientvsSteadyStateSolver(1/2)

0.0 0.5 1.0 1.5 2.0

0.0

2.0x10-7

4.0x10-7

6.0x10-7

8.0x10-7

1.0x10-60 2000 4000 6000

Transcient Approach

NH3

Flow

Rat

e, kg

/s

Time, s

Steady State Approach

Pseudo Time Step

0.0 0.5 1.0 1.5 2.0

0.0

1.0x10-5

2.0x10-5

3.0x10-5

4.0x10-5

5.0x10-5

6.0x10-50 2000 4000 6000 8000

Flow

Rat

e, kg

/s

Time, s

NO

NO2

(a)

(b)

0.0 0.5 1.0 1.5 2.0

0.0

2.0x10-7

4.0x10-7

6.0x10-7

8.0x10-7

1.0x10-60 2000 4000 6000

Transcient Approach

NH3

Flow

Rat

e, kg

/s

Time, s

Steady State Approach

Pseudo Time Step

0.0 0.5 1.0 1.5 2.0

0.0

1.0x10-5

2.0x10-5

3.0x10-5

4.0x10-5

5.0x10-5

6.0x10-50 2000 4000 6000 8000

Flow

Rat

e, kg

/s

Time, s

NO

NO2

(a)

(b)

SteadystatesolverwellcapturethesteadyresultsofNOxconversion

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Validation2:3DUreaSCRSystem:TransientvsSteadyStateSolver(2/2)

0

5

10

15

20

1 2Speedup

Factor,Transient/SteadyS

tate

SCR-1 SCR-2

NH3contourvalidations Steadystatesolverspeedupfactor

*steadystatesolverresultsin~15-20timesspeedupcomparedtothetransientsolver,whichrenditpossibleforover-night 3DfullycoupledUREA/SCRsystemsimulations

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Summary

• Afull-scale3DmodelofUREA/SCRsystemwassetupusingCONVERGEandvalidatedagainsttheexperiments.

• SteadystatesolvercoupledwithsurfacechemistryinCONVERGEcouldhelpacceleratingthesimulationsbyfactorsof15-20 whileretaininggoodaccuracy.

• Futurework- Issuenotaddressed:uncertaintyofthecouplingofdifferentphysicalmodel->sensitivityanalysis

- Baselinetovalidatemorehighfidelitymodels

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SurfaceChemistry(Olssonetal;2008)

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