fuel cells systems analysis - hydrogen.energy.gov
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Fuel Cells Systems Analysis
R. K. Ahluwalia, X. Wang and R. Kumar
2011 DOE Hydrogen Program Review
Washington, DC
May 9-13, 2011
This presentation does not contain any proprietary, confidential, or otherwise restricted information.
Project ID: FC017
2
Overview
Timeline Start date: Oct 2003 End date: Open Percent complete: NA
BarriersB. CostC. PerformanceE. System Thermal and Water
ManagementF. Air ManagementJ. Startup and Shut-down Time,
Energy/Transient Operation
Budget FY11 funding: $650K
DOE share: 100% FY10 funding: $650K
Partners/Interactions Honeywell CEM+TWM projects DTI, TIAX 3M, Gore, NJIT ISO-TC192 WG12, HNEI,
JARI, LANL IEA Annexes 22 and 25 FreedomCAR fuel cell tech team
This project addresses system, stack and air management targets for efficiency, power density, specific power, transient response time, cold start-up time, start up and shut down energy
3
Objectives and Relevance
Develop a validated system model and use it to assess design-point, part-load and dynamic performance of automotive and stationary fuel cell systems. Support DOE in setting technical targets and directing
component development Establish metrics for gauging progress of R&D projects Provide data and specifications to DOE projects on
high-volume manufacturing cost estimation
4
Approach
Develop, document & make available versatile system design and analysis tools. GCtool: Stand-alone code on PC platform GCtool-Autonomie: Drive-cycle analysis of hybrid fuel
cell systems
Validate the models against data obtained in laboratory and at Argonne’s Fuel Cell Test Facility. Collaborate with external organizations
Apply models to issues of current interest. Work with FreedomCAR Technical Teams Work with DOE contractors as requested by DOE
5
Collaborations
– Argonne develops the fuel cell system configuration, determines performance, identifies and sizes components, and provides this information to TIAX for high-volume manufacturing cost estimation
– Establishing closer ties with DTI, conducting joint life-cycle cost studies
Air Management Honeywell Turbo TechnologiesStack 3M, NuveraWater Management Honeywell Aerospace, Gore, NJITThermal Management Honeywell Thermal SystemsFuel Economy ANL (Autonomie)H2 Impurities JARI, LANL, ISO-TC-192 WGSystem Cost DTI, TIAXDissemination IEA Annex 22 and 25
6
Summary: Technical Accomplishments
System analysis to update the status of technology Stack: Determined the performance of NSTF stacks at low
temperatures and on drive cycles Air Management: Evaluated the dynamic performance of
Honeywell’s compressor-expander-motor (CEM) and compressor-expander-motor/generator (CEMG) modules
Fuel Management: Evaluated the dynamic performance of parallel ejector-pump hybrids
Water Management: Analyzed the dynamic performance of planar and supported liquid membrane (SLM) humidifiers
Thermal Management: Analyzed the dynamic performance of microchannel automotive radiators and PEFC stack during cold start on drive cycles
Drive Cycle Simulations: GCtool-Autonomie simulations for fuel economy, ownership cost, and optimum FCS operating parameters
Cost: Collaborated with DTI in projecting system cost for different sizes and efficiencies and estimating the life cycle costs
7
Argonne 2011 FCS Configuration
2011 FCSMEA- 3M NSTFC MEA- 20-µm 3M membrane- 0.05(a)/0.1(c) mg/cm2 Pt- Metal bipolar plates
Air Management System- Honeywell CEMM- Air-cooled motor/AFB
Water Management System- Cathode MH with precooler
Thermal Management System- Advanced 40-fpi
microchannel fins
Fuel Management System- Parallel ejector-pump hybrid
S1 – Pressurized FCS, 2.5 atm stack inlet pressure at rated power S2 – Low-pressure FCS, 1.5 atm stack inlet pressure at rated power Dynamic performance of the components and the system
8
Cost vs. Performance Trade-off Study Saving in Pt by accepting rated-power efficiency <50% (system S2):
45% at η=45%, 59% at η=40%, 62% at η=35% Cost estimates from DTI correlations with Argonne data for
components and subsystems Projected saving in stack cost by accepting rated-power efficiency
<50%: 34% at η=45%, 46% at η=40%, 50% at η=35% Projected saving in system cost by accepting rated-power efficiency
<50%: 19% at η=45%, 25% at η=40%, 26% at η=35%
10
20
30
40
50
60
35 40 45 50System Efficiency (%)
Cos
t ($/
kWe)
FCS
BOP
Stack
Cost Breakdown (45% Efficiency S2)
2.46
2.59
5.70
4.81
7.84 23.02
PEFC Stack
Air Management
Fuel Management
Water Management
Thermal Management
Balance of System
9
Cell Voltage to Reach 60% Peak Efficiency Parasitic losses: 7.1% of net power at peak efficiency point 37% CEM M/C efficiency near idle H2 losses to crossover & purge Target not met with improved M/C
efficiency aloneCurrent Cell Stack CEM M/C Peak FCS
Pressure Temperature Density Voltage Efficiency Efficiency Efficiency(atm) (oC) (A/cm2) (mV) (%) (%) (%)1.2 75 0.1 784 60.2 37 561.2 75 0.1 784 60.2 60 57.4
Cell V to reach 60% peak efficiency 32 mV ∆V at 0.1 A/cm2, 1.1 atm,
SR = 2 Needed cell V lower at 0.2 A/cm2
Required cell V higher at higher P Required cell V even higher at
SR = 5750
775
800
825
850
1.10 1.15 1.20 1.25 1.30 1.35Stack Inlet Pressure, atm
Cel
l Vol
tage
, mV
0.2 A/cm2
H2 Cross-over: 3 mA/cm2
Cathode SR: 2CEM M/C Efficiency: 60%
0.1 A/cm2
20
30
40
50
60
0 10 20 30 40 50 60 70 80FCS Net Power, kW
FCS
Effic
ienc
y, %
50%
45%40%
35%
Rated Power Efficiency
S2 Configuration1.5-atm peak pressure0.15 mg-Pt/cm2
20-mm membrane
10
Catalyst Activity to Reach Target Cell Voltages Reference activity is for ternary Pt68(CoMn)32 catalyst with
0.1 mg/cm2 Pt loading– Reaching 60% peak efficiency is very difficult if the cell has to
operate at >2 SR or >1.25 atm at low current densities – Easier to reach the peak efficiency target at 0.1 A/cm2 than at
0.2 A/cm2 for P < 1.3 atm, SR = 2– Inset for 4X absolute activity which can be reached with higher
Pt loading, or higher mass activity, or combination of the two
0
10
20
30
40
50
60
70
80
90
100
1.10 1.15 1.20 1.25 1.30 1.35Stack Inlet Pressure, atm
Act
ivity
Mul
tiplie
r
0.1 A/cm2
0.2 A/cm2
H2 Cross-over: 3 mA/cm2
Cathode SR: 5CEM M/C Efficiency: 60%
0
2
4
6
8
10
1.10 1.15 1.20 1.25 1.30 1.35Stack Inlet Pressure, atm
Act
ivity
Mul
tiplie
r
0.2 A/cm2
0.1 A/cm2
H2 Cross-over: 3 mA/cm2
Cathode SR: 2CEM M/C Efficiency: 60%
4X Activity Map
11
Air Management System Determined the performance of Honeywell’s CEMM in S1 and S2
systems for two modes of cooling the motor– GCtool model, performance maps from component data
Expander reduces CEM parasitic power by 4 kW in S1, 1.5 kW in S2– Recovering cooling air reduces CEM power by 0.4-1.6 kW
Turndown is a function of the minimum rpm and may be limited by the surge line– Turndown >10 and minimum rpm <35k desirable else parasitic
power at Idle >500 W
5
7
9
11
13
15
1.5 2.0 2.5Stack Inlet Pressure, atm
CEM
Par
asiti
c Po
wer
, kW
Tamb=40°C
with Expander
w/o Expander
b
a
b
a
(a) (b)
0
100
200
300
400
500
600
700
10 20 30 40 50
Turndown
CEM
Par
asiti
c Po
wer
, W
30 krpm
35 krpm
40 krpm
Surge Line
12
Dynamic Performance of Integrated CEM Module Dynamic simulations on hybrid UDDSand HWFET cyclesOperation as motor/generator (CEMG) Faster response during deceleration SR >2 in deceleration, >>5 at low
power Parasitic power >> steady-state
values during acceleration, lower or even negative during deceleration
-6
-4
-2
0
2
4
6
8
10
0 20 40 60 80FCS Power, kW
CEM
Par
asiti
c Po
wer
, kW
Generator Mode
Motor Mode
0
10
20
30
40
50
60
0 20 40 60 80FCS Power, kW
O2 U
tiliz
atio
n, %
CEMG Mode
0
10
20
30
40
50
60
0 20 40 60 80FCS Power, kW
O2 U
tiliz
atio
n, %
CEM Mode
Solid lines indicate results from steady-state simulations
13
Fuel Management System Parallel ejector-pump hybrid
– Ejector for >45% power (zone I), blower for <30% power (zone II), hybrid for intermediate power (zone III)
– Motive gas pressure regulated to <8 atm Dynamic simulations with single-speed blower (always on)
– Ejector pumping power up to 400 W (parasitic reduced by 1 kWe)– H2 utilization maintained around 50% in zone I, << 50% in zone II
0
20
40
60
80
100
0 20 40 60 80
FCS Power, kW
H2 U
tiliz
atio
n (%
)
0
100
200
300
400
500
Ejec
tor P
umpi
ng P
ower
, W
H2 Utilization
EjectorPower
H2 feed rate proportional to pressure differential between cathode and anode– >60% H2 utilization during
depressurization– H2 utilization affected by
impurity buildup that reduces ejector entrainment
14
Purge Losses Dynamic simulations on UDDS and HWFET cycles, hybrid mode ISO-TC 192 specs for N2 (100 ppm) and He (200 ppm) impurities
– Purge schedule determined by N2 buildup due to crossover from air– Cyclic buildup of reactive hydrocarbon impurities– NH3 does not accumulate due to significant crossover to cathode– Cumulative degradation due to H2S– Anode purged (15 sl) when inerts (N2 + He) build up to 10 mol%– H2 loss and purge schedule depend on duty cycles and allowable
inert concentration (maximum)
0
2
4
6
8
10
0 500 1000 1500 2000Time, s
Mol
e Fr
actio
n, %
UDDS HWFET
N2
He
0
10
20
30
40
0 10 20 30 40 50 60FCS Power, kW
Purg
e Lo
ss, %
100
150
200
250
300
Sche
dule
, s
UDDSHWFET
Schedule
Purge Loss
UDDS
HWFET
15
Water Management System (Humidifier) Completed analysis of Honeywell data for full-scale, half-scale, and
1/10th sub-scale membrane humidifiers – Data received for planar humidifier with a composite membrane
Summary of model results– Optimum dry-air inlet temperature for maximum flux (last year) – Thinner membrane: higher water flux, but lower optimum T and
mechanical support may be needed– Lower P: Higher flux, but required water transfer rate also greater – Cathode RH reported at stack inlet T (air concurrent with coolant)– Anode RH reported at stack outlet T (air countercurrent with fuel)
40
60
80
100
120
0 20 40 60 80FCS Power, kW
Cat
hode
Inle
t RH
, %
0
20
40
60
80
100
0 20 40 60 80FCS Power, kW
Ano
de In
let R
H, %
Anode humidification is due to recycle (no anode humidifier in the system)
16
Supported Liquid Membrane (SLM) Moisture diffusion coefficient higher in liquid membranes than in solid
membranes Composite SLM by Zhang, J. Membrane Science 276 (2006) 91-100
– LiCl solution immobilized in hydrophilic cellulose acetate (CA) membrane, 50-70 µm thick, 0.22 µm pores
– Hydrophobic PVDF membranes as protective layers, 45 µm thick, 0.15 µm pores
– Composite SLM considered experimental, not optimal
0
1
2
3
4
5
6
45 55 65 75 85 95Dry Air Inlet Temperature, oC
Wat
er F
lux,
g m
-2s-1
P = 1.5 atmWet Air T = 75oCWet Air RH = 100%20 µm Membrane
Nafion
SLM
15˚C Approach TDP
10˚C Approach TDP
Modeled Performance For same membrane thickness
higher flux at high T Flux limited by resistance in the
protective layers Many SLM configurations
reported in literature– Higher flux – Eliminate pre-cooler
17
Thermal Management System – Heat Loads Heat loads at rated power and on 6.5%-grade at 55 mph
– Stack heat load proportional to Stacked HT radiator, LT radiator and AC condenser, 40-fpi MC fins
– On grade, stack T allowed to rise to 95oC, P to 2.3-2.4 atm– Expander needed even in S2 – Depending on vehicle platform and FCS rated power, 35-40%
efficiency at rated power may be acceptable
PEFCPEFCPEFCP ηη /)1( −
500
600
700
mV
80 kW
61.5 kW
30
40
50
60
% 80 kW
61.5 kW
507090
110130
35 40 45 50System Efficiency, %
kW 80 kW
61.5 kW
Cell Voltage
Stack Efficiency
Heat Load 200
400
600
800
35 40 45 50System Efficiency, %
W
Radiator Fan
Coolant Pump
12
14
16
18
m2
Pumping Power
Fin Area
18
Dynamics of Cold Start Improving water transport model using 3M’s polarization and water
balance data at 30-80oC and data without anode MPL Cold-start simulation on 1 UDDS and 1 HWFET starting at 27oC
– Flooding limits stack power to 32 kW at 30oC, 50 kW at 45oC– Stack heat-up time and temperature depend on the drive cycle– FCS efficiency is a function of stack temperature and drive cycle
0.5
0.6
0.7
0.8
0.9
0.0 0.2 0.4 0.6 0.8 1.0 1.2Current Density, A cm-2
Cel
l Vol
tage
, V
27°C
75°C
35°C
0
20
40
60
80
100
0 500 1000 1500 2000Time, s
FCS
Pow
er, k
WC
oola
nt O
utle
t T,
o CCoolant T
FCS Power
UDDS HWFET
0
20
40
60
80
100
0 20 40 60 80FCS Power, kW
FCS
Effic
ienc
y, % CEMG Mode
0
20
40
60
80
100
0 20 40 60 80FCS Power, kW
FCS
Effic
ienc
y, % CEM Mode
19
Optimum FCS Control Parameters Drive cycle simulations for 35-50% rated-power efficiency and 65-120
kW FCS rated power– Mid-size hybrid vehicle, Kansas City drive cycles– FCS provides the hotel loads, 250-W idle power
Determined optimum control parameters: power threshold for turning FCS on, threshold for idling FCS, minimum FCS power, battery power
Minimum FCS power and traction power (at motor) for turning on the FCS is a function of the rated power and the rated-power efficiency– Depending on battery SOC, FCS operates at low traction power
Preliminary results, control strategy will depend on stack/battery durability considerations
0
5
10
15
20
60 70 80 90 100 110 120FCS Power, kW
Thre
shol
d Po
wer
, kW
FCS Minimum
FCS Off
FCS On35% FCS Efficiency at Rated Power
0
5
10
15
20
60 70 80 90 100 110 120
FCS Power, kW
Thre
shol
d Po
wer
, kW
FCS Minimum
FCS Off
FCS On45% FCS Efficiency at Rated Power
20
Summary: System Performance on Drive Cycles Relationship between rated-power efficiency, FCS rated power, FCS
cost (DTI input), fuel economy, ownership cost– Optimum FCS control parameters
Net present value (NPV) shows that 85-kW FCS with 40% rated-power efficiency offers the best solution (3.70/5 $/gge gasoline/H2)– NPV: present value of investments and future savings, compared to
reference ICEV Fuel economy higher with the largest FCS, small dependence on rated
power efficiency
0
500
1000
1500
2000
2500
3000
3500
4000
60 70 80 90 100 110 120FCS Rated Power, kW
Net
Pre
sent
Val
ue, $
FCS Efficiency at Rated Power: 50%
45%
40%
35%
40
45
50
55
60
65
70
75
80
65 70 75 80 85 90 95 100 105 110 115 120
FCS Rated Power, kW
Fuel
Eco
nom
y, m
pgge
50% 45% 40% 35%FCS Efficiency at Rated Power
21
Future Work Support DOE/FreedomCAR development effort at system,
component, and phenomenological levels Continue collaboration with 3M to validate, calibrate and document
the stack model– Alternate membranes, catalyst structures, and system
configurations Continue cooperation with partners to validate air, fuel, thermal, and
water management models– Establish closer collaborations with the OEMs
Support DTI and TIAX in high-volume manufacturing cost projections, collaborate in life-cycle cost studies
Collaborate with 3M to develop durability models for NSTFC electrode structures– System optimization for cost, performance, and durability– Drive cycle simulations for durability enhancement
GCtool model of PEFC systems for fork-lift applications Performance of PEFC systems for stationary applications
27
Effect of Stoichiometry and Operating Pressure At low current densities, cells are sometimes operated at higher
SR because of limited CEM turndown or catalyst flooding issues– Cell voltage for 60% peak efficiency is ~50 mV higher if the
cathode SR is 5 instead of 2 at 0.2 A/cm2, 1.2 atm – Needed cell voltage is ~17 mV higher if the pressure is
increased from 1.2 to 1.3 atm at 0.2 A/cm2, SR = 2
775
800
825
850
875
900
925
950
1.1 1.2 1.3 1.4 1.5Stack Inlet Pressure, atm
Cel
l Vol
tage
, mV
0.2 A/cm2
0.1 A/cm2
0.1 A/cm2
Cathode SR = 5 0.2 A/cm2
Cathode SR = 2
H2 Cross-over: 3 mA/cm2
CEM M/C Efficiency: 60%
28
Advanced Binary vs. Ternary Catalyst
0.10
0.15
0.20
0.25
0.30
0.00 0.05 0.10 0.15 0.20
Pt Loading, mg/cm2
Mas
s A
ctiv
ity, A
/mg-
Pt
Pt68(CoMn)32
PtM
50
75
100
125
150
175
0.00 0.05 0.10 0.15 0.20Pt Loading, mg/cm2
ECSA
, cm
2 -Pt/m
g-Pt
Pt68(CoMn)32
PtM
0.5
1.0
1.5
2.0
2.5
0.00 0.05 0.10 0.15 0.20Pt Loading, mg/cm2
Spec
ific
Act
ivity
, mA
/cm
2 -Pt
Pt68(CoMn)32
PtM
0
10
20
30
40
0.00 0.05 0.10 0.15 0.20
Pt Loading, mg/cm2
Abs
olut
e A
ctiv
ity, m
A/c
m2
Pt68(CoMn)32
PtM
For same Pt loading, PtM has 1.5-1.7 times the absolute activity of PtCoMn
29
Approach to Reach 60% Peak FCS Efficiency
Redesign the CEMM controller
– Improve M/C efficiency at low power from 35% to >60%
AND operate at low SR (<2) and low pressures (<1.2 atm)
AND increase Pt loading in PtCoMn
– 40% improvement in absolute activity by increasing Pt loading from 0.1 mg/cm2 to 0.2 mg/cm2
OR use more active binary PtM catalyst (still under development, mass transfer issues at high current densities, durability yet to be demonstrated)
– Compared to 0.1-mg-Pt/cm2 ternary catalyst, the activity of binary catalyst is 70% higher for same Pt loading and 120% higher at 0.15 mg-Pt/cm2 loading
30
Water Management System Completed analysis of Honeywell data for full-scale, half-scale, and
1/10th sub-scale membrane humidifiers – Data received for planar humidifier with a composite membrane
Summary of model results– Optimum dry-air inlet temperature for maximum flux (last year) – Thinner membrane: higher water flux, but lower optimum T and
mechanical support may be needed– Lower P: Higher flux, but required water transfer rate also greater
0
1
2
3
4
5
6
7
45 55 65 75 85 95
Dry Air Inlet Temperature, oC
Wat
er F
lux,
g/m
2 .s
Approach TDP, Membrane Thickness
30oC, 20 mm
10oC, 40 mm
10oC, 20 mm
P = 1.5 atmWet Air T = 75oCWet Air RH = 100%
30oC, 40 mm
0
1
2
3
4
5
6
7
45 55 65 75 85 95Dry Air Inlet Temperature, oC
Wat
er F
lux,
g/m
2 .s
Membrane Thickness = 20 mmWet Air T = 75oCWet Air RH = 100%
30oC, 2.5 atm
Approach TDP, P
10oC, 2.5 atm
10oC, 1.5 atm30oC, 1.5 atm