Upload
others
View
0
Download
0
Embed Size (px)
Citation preview
SECA Core Program–Recent Development of Modeling
Activities at PNNL
SECA Core ProgramSECA Core Program––Recent Development of Modeling Recent Development of Modeling
Activities at PNNLActivities at PNNL
MA KhaleelEmail: [email protected] Phone: (509) 375-2438
KP Recknagle, X Sun, BJ Koeppel, EV Stephens, BN Nguyen, KI Johnson, VN Korolev, JS Vetrano* and P Singh
Pacific Northwest National LaboratoryRichland, WA 99352
Travis Shultz, Wayne Surdoval, Don Collins National Energy Technology Laboratory
SECA Core Technology Program Peer ReviewPhiladelphia, PA
September 12-14, 2006
2
R&D Objectives & ApproachR&D Objectives & ApproachR&D Objectives & Approach
Objective: Develop integrated modeling tools to: Evaluate the tightly coupled multi-physical phenomena in SOFCsAid SOFC manufacturers with materials development Allow SOFC manufacturers to numerically test changes in stack design to meet DOE technical targets
Approach: Finite element-based analysis tools:Mentat-FC: Easy-to-use pre- and post-processor to construct a complete analytical model from generic geometry or templatesSOFC-MP: A multi-physics solver that quickly computes the coupled flow-thermal-electrochemical response for multi-cell SOFC stacksTargeted evaluation tools for eminent engineering challenges:
Interface and coating durabilityReliable sealingOn-cell reformation for thermal managementScale upTime dependent material degradation
3
Technical Issues AddressedTechnical Issues AddressedTechnical Issues Addressed
Provide a flexible, multi-physics SOFC stack design tool capable of importing SOFC manufacturer designs (planar & tubular) for electrochemical/thermal/structural analyses.Provide a coarse design methodology by which SOFC manufacturers can develop a stack design.Provide analysis tools for evaluating the effects of on-cell steam-methane reformation in stacks for optimal thermal management.Address the challenging reliability issues of glass-ceramic seals, interfaces, and scales due to steady operation and thermal cycling of stacks.Experimentally gather necessary physical and mechanical property data to support model development.
4
AccomplishmentsAccomplishmentsAccomplishmentsCommercially Available SOFC Stack Design Tool: PNNL and MSC-Software combined efforts to develop and release a user-friendly electrochemical-thermal-structural stack design software package. Design tool capability includes import of planar and non-planar SOFC stack designsTools and Methods for Optimization of Internal Reforming: Methodology developed in which control of the reaction rate via custom anode and/or control of the percentage of reformation to occur on-cell is used to optimize the thermal management of a proposed stack designGlass-Ceramic Sealant Damage Model: Developed a viscoelastic continuum damage mechanics model based on experimental characterization of G18 glass-ceramic to evaluate sealants in SOFC stack models to prevent failure/delaminationInterconnect Creep and Degradation: Developed a modeling methodology to predict interconnect integrity at different stages of oxide scale growth. Examined influence of interconnect creep on the possible stack geometry change and stress redistribution Experiments Provide Critical Properties: Testing has provided fundamental material properties enabling model development
5
PublicationsPublicationsPublications
SECA PresentationsKhaleel MA, KP Recknagle, JS Vetrano, X Sun, BJ Koeppel, KI Johnson, V Korolev, BN Nguyen, AM Tartakovsky, and P Singh, "SECA Core Program-Recent Development of Modeling Activities at PNNL." SECA Core Technology Peer Review, Lakewood, CO, October 25-26, 2005.
Topical ReportsVetrano J.S., Y.-S. Chou, G.J. Grant, B.J. Koeppel, B.N. Nguyen and M.A. Khaleel, “Mechanical Testing of Glass Seals for Solid Oxide Fuel Cells.” PNNL-15463.Koeppel BJ, BN Nguyen, JS Vetrano, and MA Khaleel, “Experimental Characterization, Model Development, and Numerical Analysis of Glass-Ceramic Sealant Relaxation Under Thermal-Mechanical Loading.” PNNL-15659.Recknagle KP, ST Yokuda, DT Jarboe, MA Khaleel, “Analysis of Percent On-Cell Reformation of Methane in SOFC Stacks: Thermal, Electrical, and Stress Analysis.” PNNL-15787.Sun X, WN Liu, P Singh, and MA Khaleel, “Effects of Oxide Thickness on Scale and Interface Stresses under Isothermal Cooling and Micro-Indentation.” PNNL-15794.
Conference Papers & PresentationsVetrano JS, Y-S Chou, BJ Koeppel, BN Nguyen and MA Khaleel, “Modeling and Measurement of Material Behavior in Solid Oxide Fuel Cells,” Fuel Cell Seminar, November 15, 2005, Palm Springs, CA. PNNL-46383.Khaleel MA, X Sun and A Tartakovsky, "Multi-Component-Based Reliability Design for SOFC- A Coarse Design Methodology," Fuel Cell Seminar, November 15, 2005, Palm Springs, CA. PNNL-SA- 47472.Recknagle KP, KI Johnson, V Korolev, DT Jarboe, MA Khaleel, and P Singh, “Electrochemistry and On-Cell Reformation Modeling for Solid Oxide Fuel Cell Stacks,” 30th International Conference & Exposition Advanced Ceramics, January 24, 2006, Cocoa Beach, FL.Koeppel BJ, JS Vetrano, BN Nguyen, X Sun, and MA Khaleel, “Mechanical Property Characterizations and Performance Modeling of SOFC Seals,” 30th International Conference & Exposition Advanced Ceramics, January 24, 2006, Cocoa Beach, FL.Nguyen BN, BJ Koeppel, JS Vetrano, and MA Khaleel, “On the Nonlinear Behavior of a Glass-Ceramic Seal and Its Application in Planar SOFC Systems,” 4th International Conference on Fuel Cell Science, Engineering, andTechnology, June 19-21, 2006, Irvine, CA.
Journal ArticlesNguyen BN, BJ Koeppel, S Ahzi, MA Khaleel, and P Singh. 2006. “Crack Growth in Solid Oxide Fuel Cell Materials: From Discrete to Continuum Damage Modeling.” J Am Ceram Soc 89(4):1135-1368.
6
Teaming & CollaborationsTeaming & CollaborationsTeaming & Collaborations
IndustryModeling and Software Training
GEDelphiAcumentricsSiemensFCE
University & National LabsModeling
U of Illinois, ChicagoGeorgia Tech
MaterialsORNLCarnegie Mellon UniversityPenn State
Software TrainingU of Connecticut
ResultsResultsResults
SOFC Analysis OverviewSOFC-MP/Mentat-FC
On-Cell Reformation & Thermal ManagementSeal Property & Time Dependent Behavior
Interconnect-Coating Interface & Interconnect CreepExperimental Property Measurement
8
SOFC Analysis OverviewSOFC Analysis OverviewSOFC Analysis Overview
Developed tools to build/analyze SOFC cells and stacks
Mentat-FC: GUI to build models from templates, CAD files, or FEA meshesSOFC-MP: Coupled thermal, flow, and electrochemistry solverMSC.Marc: Structural finite element analysis using SOFC-MP temperatures
9
SOFC-MP/Mentat-FCSOFCSOFC--MP/MentatMP/Mentat--FCFCMentat-FC GUI
Guides user through entire analysisBuilds geometry from CAD files, FEA meshes, or templates (planar co-, counter-, cross-flow)SOFC operating parameters (I-V, fuel/oxidant inputs, polarizations)Exterior thermal boundary conditionsMaterial properties databaseHas tubular capability
SOFC-MP SolverFinite element basedGeneric fuel and oxidants (CEA)Efficient reduced order dimensional analyses for electrochemistry and gas flowsContact algorithms treatincompatible meshes
Post-processing of electrical output, species, thermal distribution, deformations, and stresses
10
On-Cell Reforming & Thermal Management:Optimization of Percent On-Cell ReformationOnOn--Cell Reforming & Thermal Management:Cell Reforming & Thermal Management:Optimization of Percent OnOptimization of Percent On--Cell ReformationCell Reformation
40% OCR
80% OCR
0% OCR
FuelIN
Air IN
% OCR ∆T Tmax Anode S1max Seal S1max
0 85 781 25.8 11.340 45 768 13.8 8.750 47 768 14.7 8.860 54 769 16.3 9.280 69 773 19.0 10.2
Principal Stress Max
At 0% OCR temperature reached maximum at air exit
40% OCR heat load was decreased with cooling at fuel inflow
80% OCR heat load was minimum but air temperature was high
10x10 counter-flowCell Temperature = 750°C All Cases
0
10
20
30
40
50
60
70
80
90
100
0 20 40 60 80
Percent On-Cell Reforming
500
550
600
650
700
750
800
850
900
Inflow
Tem
per
ature
, °C
Temperature Difference, °C
Inflow Air Temperature, °C
SUMMARY:To maintain 750°C, inflow temperature increased to offset decreased heat load due to reforming (all configurations and sizes)Seal stresses, anode stresses, and ∆T had minimums at 40-50% OCR for this configuration and cell size
11
Seal Property & Time Dependent Behavior:Glass-Ceramic Seals
Seal Property & Time Dependent Behavior:Seal Property & Time Dependent Behavior:GlassGlass--Ceramic SealsCeramic Seals
CharacteristicSeal Assembly
Interface
0.0
0.5
1.0
1.5
2.0
2.5
0 20 40 60 80 100 120 140 160 180 200Time (min)
Raw
Cre
ep E
xten
sion
(mm
)
G800-20 Raw Creep ExtG800-21 Raw Creep ExtG800-22 Raw Creep ExtG750-23 Raw Creep ExtG700-33 Raw Creep ExtG750-36 Raw Creep ExtG750-43 Raw Creep ExtG700-47 Raw Creep ExtG700-51 Raw Creep Ext
TorsionTension
0
10
20
30
40
50
60
0 200 400 600 800 1000Temperature (C)
Stre
ss (M
Pa)
Normal StrengthShear Strength
Glass-CeramicInterface
0
20
40
60
80
100
120
0.000 0.002 0.004 0.006 0.008Strain (mm/mm)
Stre
ss (M
Pa)
4hr-25C4hr-600C4hr-700C4hr-750C4hr-800C
2. Test the weakerinterface strength
1. Test the glass-ceramic strength and creep behavior
CreepBending
3. Obtain coefficient of thermal expansion (CTE) and elastic modulus
12
Seal Property & Time Dependent Behavior:Creep of Glass-Ceramics
Seal Property & Time Dependent Behavior:Seal Property & Time Dependent Behavior:Creep of GlassCreep of Glass--CeramicsCeramics
Evaluated short-term creep behavior of G18
Glassy matrix above its Tg at cell operating temperaturesCreep rate increased with applied stress and temperature
Estimated G18 viscosityAssume Maxwell material model
Derived viscosity is very high (5-65e6 MPa-s) but still important for assessing steady state seal stresses in the stack
)1(o DEE −=
σσ
ε
0.E+00
1.E+07
2.E+07
3.E+07
4.E+07
5.E+07
6.E+07
7.E+07
8.E+07
0 10 20 30 40 50 60Applied Stress (MPa)
Visc
osity
(MPa
-s)
800C Viscosity750C Viscosity700C Viscosity
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0 50 100 150 200Time (min)
Cre
ep S
train
800C 30MPa800C 20MPa800C 10MPa
13
Seal Property & Time Dependent Behavior:Glass-Ceramic Constitutive Model
Seal Property & Time Dependent Behavior:Seal Property & Time Dependent Behavior:GlassGlass--Ceramic Constitutive ModelCeramic Constitutive Model
Stress-strain response of G18 glass-ceramic shows strong rate dependence
Due to viscoelastic response of residual glassProcessing/microstructure variations noted
Viscoelastic damage model predictions compare reasonably well to experimental data
Failure strain prediction goodStress prediction possibly affected by heterogeneous structure
0
10
20
30
40
50
60
0.000 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008Strain (mm/mm)
Stre
ss (M
Pa)
0.025 mm/min
0.05 mm/min0.5 mm/min
14
Seal Property & Time Dependent Behavior:Stack Modeling Results
Seal Property & Time Dependent Behavior:Seal Property & Time Dependent Behavior:Stack Modeling ResultsStack Modeling Results
Temperature (C) Elastic Model: Anode Maximum Principal Stress
(MPa)
Viscoelastic Model: Anode
Maximum Principal Stress
(MPa)
Change
Cycle 1 Operation
38.4 366.3%
Cycle 1 Shut-Down
65.6 62.74.4%
Cycle 2 Operation
40.2 400.5%
Cycle 2 Shut-Down
74.4 67.49.4%
Seal Failure After 2 Thermal CyclesSeal
Damage Distribution
Anode Principal Stress Distribution
15
Interconnect Life PredictionInterconnect Life PredictionInterconnect Life Prediction
Sources of interconnect stress studied:
Thermal stressGrowth stress
Predicted interfacial stress compared with interface strength
scale delaminationPredicted scale stress compared with critical buckling stress
scale spallation Residual stresses measurements in Cr2O3 films*
-2000
-1500
-1000
-500
0
500
0 0.1 0.2 0.3 0.4 0.5Distance from Bottom Surface of IC (mm)
Nor
mal
Str
ess
-S11
(MPa
)
Case 1 - 5micorn scale
scale/substrate interface
Predicted stress profile through thethickness of the IC/oxide
-2000
-1500
-1000
-500
0
500
0 0.1 0.2 0.3 0.4 0.5Distance from Bottom Surface of IC (mm)
Nor
mal
Str
ess
-S11
(MPa
)
Case 1 - 5micorn scale
scale/substrate interface
Predicted stress profile through thethickness of the IC/oxide
Predicted scale stressPredicted scale stress
Near the sample edge
800
1200
1600
2000
0 10 20 30Thickness of Scale (microns)
Nor
mal
str
ess
S11
(MPa
)
0
200
400
600
800
Shea
r str
ess
S13
(MPa
)S11 (in compression)S13
16
Interconnect Life PredictionInterconnect Life PredictionInterconnect Life PredictionUsing indentation test to quantify strength of oxide/interconnect interface:
Effect of scale growth on interfacial shear stressEffects of thermal stress on indentation stress
Conclusions:Shear stress on the interface caused by indenter contact is high enough to lead to delaminationShear stress dominates the fracture mode of the interfaceThe thinner the thickness of oxide scale is, the bigger the interfacial shear stress is, at the small indentation depthEffect of thermal stress on the interfacial shear stress may be neglected
Effect of Scale Thickness on S12
0
2000
4000
6000
8000
0 1 2 3 4 5
Indentation Depth (micron)
Shea
r Str
ess
(MPa
)
2 microns 5 microns15 microns30 microns
Scale Thickness: 5 microns
0
1000
2000
3000
4000
5000
6000
0 1 2 3 4 5Indentation Depth (micron)
Shea
r Stre
ss (M
Pa)
-25000
-20000
-15000
-10000
-5000
0
Nor
mal
Stre
ss (M
Pa)
S12 w/o thermal stressS12 w thermal stressS11 w/o thermal stressS11 w thermal stress
17
Interconnect Scale Growth Kinetics and Growth Stress Prediction
Interconnect Scale Growth Kinetics and Interconnect Scale Growth Kinetics and Growth Stress PredictionGrowth Stress Prediction
Diffusion potential used to govern stress-diffusion interactionPredicting:
Oxidation kineticsDiffusion and concentration evolution of species Stress distribution in scale and substrate
[74]. Mikkelsen, L. and S. Linderoth,. Materials Science & Engineering A (Structural Materials: Properties, Microstructure and Processing), 2003. A361(1-2): p. 198-212
Oxidation kinetics profile (22% CrOxidation kinetics profile (22% Cr--Fe alloy) Fe alloy)
Stress distribution and evolution
0.01 0.02 0.040.03 0.05
18
Interconnect Creep and Stress Re-distribution
Interconnect Creep and Stress ReInterconnect Creep and Stress Re--distributiondistribution
Creep law used for IC
⎩⎨⎧
≤×≥
=−
−
C710for1065.1C725for72.1
o/4887008.511
o/2774005.5
TeTe
RT
RT
c σσ
ε&
⎩⎨⎧
≤×≥>
=−
−
C710for2.28C725for10
o/4887005.10
o3
TeT
RTc σε&
MPa100<σ
MPa100>σ
Time = 0.01 h Time = 70 h
IC
anode
seal
19
Experimental Support of ModelingExperimental Support of ModelingExperimental Support of Modeling
Providing input data to the material models and validating the models through experimental testing. In addition, contributing
to the materials database maintained by NETL.
Creep testing of G18 glass to measure long-term deformation behavior
Torsion testing of thin glass-seal analogs to determine failure stress
and fracture behavior
4-pt bend bar testing of G18 glass to capture constitutive and failure
behavior of the material
20
Experimental Property MeasurementExperimental Property MeasurementExperimental Property MeasurementSeal Property & Time –Dependent Behavior
Creep tests of the G-18 glass performed to support damage models in predicting the long-term stack performance
Interfacial Degradation and Failure Mechanisms
Investigating failure locations and mechanisms to incorporate into seal and coating development models
A
B
C
D
SEM cross-section of a torsion sample that failed at 800oC
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0 50 100 150 200Time (min)
Cre
ep S
train
800C 30MPa800C 20MPa800C 10MPa
Comparison of a non-tested creep sample
and a sample tested at 800oC and loaded at 129lb. Forty-three
percent strain observed.
Creep strain results of samples tested at 800oC under three different loadings
Creep specimen
21
Experimental Property MeasurementsExperimental Property MeasurementsExperimental Property Measurements
Interconnect-Scale/Coating Interface PropertiesIndentation tests performed to support interface models in establishing a stress-based criteria for interfacial strength and fracture toughness
Scale
Crofer 22 substrate
SEM image of the cross-section of a crofer plate oxidized at 800oC for 12hr
Top view of the indent test. Spallation of the oxide observed under 150kg load
22
Activities for the Next 6 MonthsActivities for the Next 6 MonthsActivities for the Next 6 Months
Mentat-FC/SOFC-MP: Deploy at the 6 industry sites and provide training and support.Scale-up: Examine planar SOFC design limitations considering electrochemistry, flow, and structural Parametric studies on the effects of creep of various SOFC components on long-term behavior of multiple cell stacksContinue interconnect degradation and life prediction workDevelopment of structure-property relationships for glass-ceramic sealants; improvement via microstructural designEffect of high pressure on electrochemistry and stack performanceMeasurement of Oxide-Crofer and Spinel-Crofer interfacial properties
23
Looking Forward- Phase IILooking ForwardLooking Forward-- Phase IIPhase II
Design Limitations for Scale-up of SOFC StacksVirtual feasibility study on:
Stack EC performance and thermal managementStack structural reliability
Degradation modeling and life predictionCreep considerations on the structural stability of stacksSeal and seal interfacesInterconnect scale and coatingsCell and cell interfacesCurrent collector interfaces
System integrationStack thermal management and cell thermal profilesSystem integration, power electronics and control
Validation