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Development of SOFC-GTCombined Cycle System
with Tubular Type Cell Stack
1
Fuel Cell Seminar 2010 at San Antonio
October 19, 2010
Kazuo Tomida, M. Nishiura, S. Koga, K. Miyamoto, Y. Teramoto,S. Yoshida, N. Matake, S. Suemori, T. Kabata, Y. Ando, Y. Kobayashi
Mitsubishi Heavy Industries, LTD
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Contents1. About Mitsubishi Heavy Industries (MHI)
2. Strategy of SOFC-GTCC Development at MHI
3. 200kW-Class SOFC-MGTCC System
2
. ct v ty an rogress o eve opment5. Conclusion
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Net sales : 3,200 billion yen (2007-2009 average)Manufacturing about 700 items in a very broadrange of fields:
Power systemsAerospaceMachinery & steel structuresShipbuilding & ocean development
About MHI
3
Air conditioning & refrigeration systemsMachine tools, others
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Operating bases
Total number of employees (consolidated basis): 67,669 (as of March 31, 2010)
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Contributing to achieve a low-carbon society withMHIs integrationResponding to community needs for rebuilding infrastructure of energy and environment byapplying a wide range of MHI product technologies to realize smart community.
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Contents1. About Mitsubishi Heavy Industries (MHI)
2. Strategy of SOFC-GTCC Development at MHI
3. 200kW-Class SOFC-MGTCC System
6
. ct v ty an rogress o eve opment5. Conclusion
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SOFC-GT Combined Cycle System
Fuel
Inverter
Air
RecirculationBlower
SOFC
Combustor
Steam Turbine
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Gas Turbine
Heat Recovery Steam Generator
Efficiency LNG : 70%-LHV (800MW-class)
Coal : 60%-LHV (700MW-class)
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Efficiency Improvement by combining SOFC with GT
50
55
60
65
70
75
ncy%n
etA
C/LHV
1400C class GTCC
1500C class GTCC
1700C class GTCC
SOFC-GT combined cycle
8
35
40
45
1100 1200 1300 1400 1500 1600 1700 1800
Turbine inlet temperature (T1T) (C)
Effic
ie
1200C class GTCC
Obtaining higher effect of efficiencyimprovements by combining SOFC
The efficiency of SOFC-GTCC is expected to improve 10% or more
compared with that of GTCC, since exhaust fuel and heat of SOFC are
able to use for operation of GT.
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(-netAC/L
HV)
Efficiency of SOFC-GTCC in various power range
70
6560
55
50
45
Central power station applyingSOFC-GT-ST combined cycle system
Residential, CommercialCHP using SOFC
SOFC-MGT combined cyclesystem (SOFC-MGTCC)
Central powerstation
9
Power (kW)
Efficienc
Industrial GE (special high voltage)Commercial, Industrial GE (high voltage)
4035
30
25
5,000 500,000
Cogeneration
10 25 200 400 600 800 1,000 3,000
Residential, CommercialCHP using PEFC
Residential, commercial GE (low voltage)
MGT: Micro Gas TurbineGE: Gas Engine
SOFC-GTCC is a key technology to realize sustainable society of reducingCO2 emissions, since high efficiency is obtained even in the system ofsmall capacity.
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Strategy of SOFC-GTCC development at MHI
Several hundreds MW classusing NG as fuel
Coal gasificationgas as fuel (IGFC)
Efficiency: 60%-LHV
Partial topping system for GTCC(SOFC : several tens MW class)
Efficiency: maximum +15%
Efficiency: 70%-LHV
10
20052010 2020
30
2015
200kW class CommercializationEfficiency: 5560%-LHVEfficiency: 52%-LHV
SOFC-MGTCC(200kW - several MW class)
Test result
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Contents
1. About Mitsubishi Heavy Industries (MHI)
2. Strategy of SOFC-GTCC Development at MHI
3. 200kW-Class SOFC-MGTCC System
11
. ct v ty an rogress o eve opment5. Conclusion
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Development of 200kW-class SOFC-MGTCC
Improvement ofElemental Technology
Cell stack
Verification test of system integration
200kW-class SOFC-MGTCC System
Fuel
Air
MGT
SOFC
SOFC Module
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Cartridge MGT Customization Preparatory Operation Tests
Module40kW classSub-Module
MGT Test StandLow-calorificFuel Combustor
PressureVessel
Micro Gas Turbine
Sub-Module
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Natural GasRecirculation
Blower
SOFC
TE
DPXDifferential pressure controlbetween fuel and air of SOFC
PX
Independent control of MGTfuel pressure at outlet ofrecirculation blower
Additional volumeof SOFC for MGT
Flow diagram of 200kW-class SOFC-MGTCC
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Exhaust Gas
Air
Micro GasTurbine (MGT)
Combustor
Temperaturecontrol of SOFC
Recuperator
Air feed to SOFC atconstant pressure
Dual fuel combustor(1) Start up for natural gas(2) Depleted fuel of SOFC
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Appearance of the 200kW-class SOFC-MGTCC
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Initial performance of the 200kW-classSOFC-MGTCC
200
300
400
500
owerOutput
[kW-DC]
owerOutput[
kW-AC]
400
600
800
1000
ge[V],SOFC
Current[A]
emperature[
]
SOFC Current
SOFC Temperature
SOFC Power Output
Max. Power229kW Efficiency52%
15
0
100
0 10 20 30 40 50 60 70 80 90
SOFC
MGT
0
200
SOFCVo
lt
To age
MGT Power Output
Power Generation Hours [Hr]
Firstly starting MGT, SOFC temperature was raised, and then load current of SOFC wasincreased simultaneously after warming up to approximately 600C of the temperature.
The state of combined cycle power generation of SOFC and MGT was established, and229kW of maximum power and 52% of the maximum efficiency were achieved.
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40
60
80
100
120
Power()
400
600
800
1000
1200
Ctemperature()
SOFC Temperature SOFC Power
MGT Power
Stop Stop StopStop
Stop
Long-term operation result of the SOFC-MGTCC
16
0
20
0 500 1000 1500 2000 2500 3000 3500
Operation hours (h)
0
200 SO
F
Operation hours : 3,224hThermal Cycle : 4 Times
No degradation of SOFC performance.
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Results of the 200kW-class SOFC-MGTCC
200200200200
229229229229
204204204204
188188188188
41414141
17
50%50%50%50% 52.1%52.1%52.1%52.1% / / / /
0.25%/10000.25%/10000.25%/10000.25%/1000 0%/10000%/10000%/10000%/1000
3,2243,2243,2243,224
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Contents
1. About Mitsubishi Heavy Industries (MHI)
2. Strategy of SOFC-GTCC Development at MHI
3. 200kW-Class SOFC-MGTCC System
18
. ct v ty an rogress o eve opment5. Conclusion
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Activity and progress of SOFC development
MHI joined to following NEDO projects.
(1) Durability and reliability improvementCollaborating with research institutions and universities to
understand degradation phenomena and to investigate ofdegradation mechanism.Improvement of Redox robustness.
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-
in elevated pressureDevelopment of compact SOFC module and the preparatory test
in elevated pressure.Development of simplified system with improved reliability.
(3) Research of lower cost materials for cell stackCollaborating with stack developers and materials suppliers torealize the common specifications of cathode and anode materials.
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AirCathode
Electrolyte
Length : 1500 mm, diameter : 28mm
Segmented-in-series tubular cell stack
Air
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n erconnec
Substrate tube
AnodeFuel
(, )(, )(, )(, )
(, )(, )(, )(, )
10101010 (, )(, )(, )(, )
Fuel
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O2Cathode
ElectrolyteInterconnect
Substrate tube
Anode
Weak point of the tubular cell stack
H2Fuel
Air
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Issue : Relative density of interconnect region overlapping withelectrolyte is lower than that of the effective region.
Cross leak of hydrogen and oxygen through the interconnect.
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Damage process via anode re-oxidation
(1) Oxygen leak to anode side through interconnect.
(2) Volume expansion via re-oxidation of partial anode.
Steady: oxygen is consumed by hydrogen.Transient: oxygen reacts with Ni when hydrogen of anode
side is shortage for amount of leaked oxygen.
O2
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(3) Inducing compression stressto reduced anode layer.
(4) Inducing tensile stresses to electrolyte/interconnect layerand inner side of substrate tube.
Fuel
(5) Cracks will be induced when the tensile stressexceeds the material strengths.
Increasing the relative density of interconnect by modifyingthe sintering characteristics.
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Characteristics of improved interconnect
90
100
110
120
edensity(%)
0.6
0.8
1.0
1.2
1.4
rength(-)
Relative density (%)
Sterngth (-)
0.6
0.8
1
1.2
nvoltage(V)
60
80
100
120
140
ower(W)
Fuel : H2/N2 = 70/30(H2 = 1.77Nl/m, N2 = 0.76 Nl/m)Oxidant : Air (11.6 Nl/m)Temperature : 900CPressure : 0.1MPa
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Improvements of relativedensity and strength. Cell stack performance applying
improved interconnect is almost
equivalent to that of conventional type.
60
70
80
Conventional Improved
Relati
0.0
0.2
0.4
S
0
0.2
0.4
0 100 200 300 400
Current density (mA/cm2)
M
e
0
20
40
Voltage of conventionalVoltage of improvementPower of conventionalPower of improvement
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Comparison of N2 purge tolerance in anode
Fuel : H2/N2 = 5/95, N2 =100Oxidant : Air
Temperature : 900
CPressure : 0.1MPa
Cell voltages have not0.6
0.8
1
1.2
ltage(V)
Coventional cell stack Improved cell stack
Switching anode gasfrom H2/N2 to N2
Switching anode gasfrom N2 to H2/N2
Anode: (1)H2/N2(5/95) (2)N2 (3)H2/N2(5/95)
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Redox robustness of the improved cell stack increased to about2 times than that of conventional cell stack.
Restriction relief of system managementSimplification of protection system.
Crack was inducedin the electrolyte orinterconnect.
0
0.2
0.4
-0.5 0.5 1.5 2.5 3.5 4.5 5.5 6.5 7.5 8.5 9.5
Time (h)
Cellv
3.2h
Improved 6.2h
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Activity and progress of SOFC development
MHI joined to following NEDO projects.
(1) Durability and reliability improvementCollaborating with research institutions and universities to
understand degradation phenomena and to investigate ofdegradation mechanism.Improvement of Redox robustness.
25
-
in elevated pressureDevelopment of compact SOFC module and the preparatory test
in elevated pressure.Development of simplified system with improved reliability.
(3) Research of lower cost materials for cell stackCollaborating with stack developers and materials suppliers torealize the common specifications of cathode and anode materials.
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Durability test of LSM-YSZ interlayer
20
30
ltage[V]
0.92%/1,000h (9,000-10,000h)No.4 Cell-Stack
1.21%/1,000h (4,000-5,000h)No.3 Cell-Stack
0%/1,000h (1,500-2,500h)
No.2 Cell-Stack
0.22%/1,000h (1,500-2,500h)No.1 Cell-Stack
[V]
at CRIEPI (Central Research Institute of Electric Power Industry)
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0 2000 4000 6000 8000 100000
10
Power generation hours [h]
0 1000 2000 3000
23
24
25
Cell-StackVo
No.4 Cell-StackNo.3 Cell-Stack
No.2 Cell-StackNo.1 Cell-Stack
Power generation hours [h]Ce
ll-StackVoltag
e
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Nernst loss (ne)
Anode Polarization
(RAJ)
Pressure : 0.101MPa
Temperature : 900C
Current Density : 150mA/cm2
Overvoltage analysis of the durability test
77 7787
35 30 45 56 64
1922
18 20 17
35 35 35 35 35
800
850
900
950
geofCell-St
acks[mV]
at CRIEPI
27
(RCJ)Ohmic Loss
(RIRJ)
Operating Voltage
750 751729
710 702
97
650
700
750
255 2487 5439 7960 9999
Power generation hours [h]
Averagevo
lta
Degradation is due to the increase of cathode polarizationand IR loss after 2500h.
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SEM Images of cathode/electrolyte interface
Initial
LSM/YSZ
YSZ
LSCM
3000h
YSZ
LSCMLSM/YSZ
28
5000h 10,000h
YSZ
LSCMLSM/YSZ LSM/YSZ
YSZ
LSCM
Interface Voids increased as durability test became long.
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Investigation on increase of cathode polarization
Cell Stack
Electric Furnace
Fuel Inlet
Fuel Injection tube
Air su l /0.00E+00
5.00E-08
1.00E-07
1.50E-07
2.00E-07
2.50E-07
integratedw
eightofCr(g)
Fuel Outlet
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Amount of Cr diffusion increases in the three phaseboundary with operation time.
Cr poisoning is also a cause ofthe increase of cathode polarization.
Air OutletAir Inlet
exhaust tubeOperation time (h)Integrated weight of chromium deposition in theboundary layer of cathode/electrolyte of 4m as afunction of operation time.
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Durability test of SDC interlayerCathode interlayer : LSM-YSZ SDC
Air supply and discharge tube : metal and ceramic
0.7
0.8
0.9
voltage(V)
Ceramics tube wihout containing Cr
Metal tube containin Cr
Pressure : 0.101MPa
Temperature : 900C
30
0.5
0.6
0 2000 4000 6000
Operation time (h)
Mea
urrent ens ty : m cm
Fuel: H2/N2 = 70/30, Oxidant: airFuel utilization rate: 60%
Air Utilization rate: 20%
Degradation rate: LSM-YSZ using metal tube = 0.83 %/1000hSDC using metal tube = 0.38 %/1000h
SDC using ceramics tube = 0.23%/1000h
The increase of cathode polarization was also observed in SDC interlayer.
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MHIDurabilitytest
AISTSIMS, FE-SEM
Kyushu Univ.: STEM
K oto Univ.: FIB-SEM
CRIEPI: Performance anddurability evaluations
technology Understanding degradationphenomena and investigationof degradation mechanism
Cooperation framework in NEDO PJ
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Tohoku Univ.:Mechanical analysis
MHISEM/EPMA
MHI: improvement of cell stack
Focus: investigation on the change of micro structureand element migration at the cathode side.
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Activity and progress of SOFC development
MHI joined to following NEDO projects.
(1) Durability and reliability improvementCollaborating with research institutions and universities to
understand degradation phenomena and to investigate ofdegradation mechanism.Improvement of Redox robustness.
32
-
in elevated pressureDevelopment of compact SOFC module and the preparatory test
in elevated pressure.Development of simplified system with improved reliability.
(3) Research of lower cost materials for cell stackCollaborating with stack developers and materials suppliers torealize the common specifications of cathode and anode materials.
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Comparison of module structures
Upper heatexchange part
Powergenerationpart
Lower heat
Fuel
Flow
Part
Upper
HEX
Part
Tubular
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Conventionalcartridge
Compactcartridge
Compactness: 400 700 Cell-Stack/m2
Optimizing air flow and temperaturedistribution by simulating heat transfer.
AirFlow
Generatio
Lower
HEX
Part
Cell- stack
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Appearance of the compact cartridge
Pressure vessel
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Compact cartridge Test stand
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I-V characteristics of compact cartridge
Pressure : 0.3MPaFuel: Natural gas
Oxidant: air
0.4
0.6
0.8
1.0
1.2
anvoltage(V)
35
The performance of compact cartridge is almostequivalent to that of conventional type.
0.0
0.2
0 200 400 600
Current density (mA/cm2)
M
Compact cartridge
Coventional module
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600
800
1000
1200
1400
gthdirection
(mm)
Test result (0.63V, UA=15%)
Test result (0.73V, UA=26%)
Simulation (0.7V, UA=17%)
Fuel inlet
Air outlet
Temperature distribution in the generation room
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0
200
400
400 600 800 1000
Surface temperature ofcell stack (C)
Positionof
len
The compact cartridge also exchanged heat quantity as the designdemand, and the temperature distribution in generation room wasgood agreement with the simulation value.
Fuel outlet
Air inlet
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SOFC
MGT (MHI)Conventional
Conventional
Configuration and layout planning
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SOFC
MGT (TOYOTA) CompactCompact
The footprint of improved system will become smaller to about 1/2than that of conventional system.
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300kW Class SOFC-MGT Combined Cycle System
MGT
Pressure Vessel
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Total Net AC Output 300 kW Class
Electrical Net Efficiency >55 % (LHV)
Target performance.
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Conclusion1. 200kW-class SOFC-MGTCC test was successful, since
efficiency of 52.1% and the durability test of 3000h wasattained.
2. Durability and reliability improvement(1) Improvement of Redox robustness of the cell stack
by increasing the density of interconnect.
39
by applying SDC interlayer.(3) Obtaining the equivalent performance of the compact
cartridge as well as the conventional module.
We are accelerating the technological developments inbroad range to improve reliability, durability, compactnessand simplicity for the practical use of SOFC-MGTCC.
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Acknowledgments
This work was supported by
New Energy and Industrial TechnologyDevelopment Organization (NEDO).
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We would appreciate NEDO.
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