sofcs for power plants current status and future...
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Professor Nigel Brandon OBE FREng
Chair, Sustainable Development in Energy
Director, Energy Futures Lab
RCUK Energy Senior Research Fellow
www.imperial.ac.uk/energyfutureslab
SOFCs for power plants – current status and future
perspectives
- Established in 2005 to promote and stimulate multi-disciplinary energy research.
- Research budget of £50M pa for energy research, one third from industry.
- ~370 projects & 600 research staff and PhD students undertaking energy research.
Integrating Themes
-Energy systems engineering
-Energy policy
-Energy business
-Energy in society
The Energy Future Lab| Integrates across Science, Engineering, Policy and Business in
the energy sector
Energy Technologies
-Fuel cells and batteries
-Bio-energy
-Hydrogen
-Solar
-Carbon capture and storage
-Oil and gas
-Smart grids
-Transport
-Nuclear fission and fusion
-Future fuels
-Electric and hybrid vehicles
-Green aviation
Introduction
• What is a Solid Oxide Fuel Cell?
• Why Solid Oxide Fuel Cells?
• SOFC technology overview.
•SOFC-GT hybrids for distributed generation.
•SOFC mCHP for highly distributed systems.
• Some key challenges and opportunities
• Summary.
Introduction to Fuel Cells
H2
H2
H2
H2
H2
O2
O2
O2
O2
O2
Fluid-Flow Plate (FFP)Flow Channel
Membrane Electrode Assembly (MEA)/Positive - Electrolyte - Negative (PEN)
AnodeCathode
O22H2
4H+
4e-
2H O250 m
200 m
10 m
Catalyst
GDL
Mem
braneC
ath
ode
An
od
e
2H O2
2H2
2O2-
15 m
50 mca. 1000 m
4e-
4e-
+
+
O2
4e-+
Anode: 2H + 2O 2
2- 2H O + 4e2
-
Cathode: O + 4e2
-2O
2-
Anode: 2H24H + 4e
+ -
Cathode:4H + O + 4e+ -
2 2H O2
PEMFCSOFC
Electrolyte
CathodeAnode
20 m
Solid Oxide Fuel Cell Proton Exchange
Membrane Fuel Cell
•Cell Voltage is given by:
Ecell = E - h - IRcell
Ecell voltage of cell
E Nernst (OCV) voltage
h sum of overpotentials
IRcell ohmic cell resistance
Cell and Stack Characteristics
Schematic Solid Oxide Fuel Cell System
Fuel Processing Options
Thermodynamic predictions of
the equilibrium composition for
methane fed at different
temperatures and steam-to-
carbon ratios. The combined
CH4 + H2O input amount is 1
kmol in each case.
UK: Share of fuels contributing to primary energy supply
Source: UK Energy Sector Indicators. 2008. DECC.
2007 UK CO2 emissions were 544Mt
Heat: 39% UK CO2
Power: 33% UK CO2
Transport: 28% UK CO2
Motivation for SOFC/GT Integration
10
• High efficiency
-Electrical efficiency up to ~70%
• Environmental Attractions
-No SOx/NOx, lower CO2 emission
-Quiet
-No vibration
• Distributed power potential
-Modularity
-Siting flexibility
• Cogeneration potential
• Fuel flexibility
-Natural gas
-Biogas
-Biomass
-Coal gasification syngas
-Higher voltage-Improved power output-GT pressure ratio and inlet temperature limited by fuel cell
-kW to several hundred kW-Natural gas, biomass, gasoline…
AtmosphericPressurized
Sub DepartmentConfigurations
SOFC-GT Hybrid Cycle
11
-GT pressure independent of fuel cell pressure
-Less complex/expensive to develop and implement
-Accommodate a wider variety of GT-MW-class and multi-MW-Natural gas, syngas from coal…
Heat Exchangers
Fuel Processor
Waste Heat Recycle
Heat Loss
SOFC GT
Electronic Controllers
Blowers
Generator
Sensors
Valves
Pumps
Electrodes
Electrolyte
Interconnect
Reformer
Blower
Afterburner
Compressors
Turbines
Recuperated/Intercooled
Key System Features
Thermal
Management
Control
System
10
Two Optimization Options
Efficiency
Power Density
0)/()(/)(2
0/
0/)(2)/()()/()(
0/
2
6
2
62566255
4423
2
4
2
42334
2
4242
RTdRTddkddRTddkdRTd
bydeterminedisii
dRTddkdRTdRTddkdRTdiRTdRTddkRTdd
bydeterminedisiiP
fc
P
Pfc
hh
20%
40%
60%
80%
100%Maximum Efficiency
Maximum Power
1000
2000
3000
4000
5000
6000
Pihi
Piii h
16
Zhao Y, Shah N, Brandon NP, The Development and Application of a Novel Optimisation Strategy for Solid
Oxide Fuel Cell-Gas Turbine Hybrid Cycles, Fuel Cells, 2010, Vol:10, Pages:181-193
Rolls-Royce
Mitsubishi
Siemens Westinghouse
14
Technology Status of SOFC-GT HybridTechnology Status of SOFC-GT Hybrid
Rolls-Royce data-private; Confidential
1
1-Megawatt Solid Oxide Fuel Cell System
SOFC-GT Hybrid by Rolls-Royce Fuel Cell Systems
Porous
support
Fuel
Air
Ni-YSZ anode YSZ
electrolyte
LSM-YSZ cathode
Rolls-Royce data-private; Confidential
1
1-Megawatt Solid Oxide Fuel Cell System
Final Energy Consumption of Thermal Energy in
the UK in 2006 Space heating and hot water in UK residential sector = 78Mt CO2 pa. In 2008
BERR, Energy Trends: September 2008 (Special feature – Estimates of Heat use in the UK). 2008, Department
for Business, Enterprise & Regulatory Reform (now Department of Energy and Climate Change): London, UK.
p. 31-42.
UK: Ownership of central heating
Source: GfK Home Audit from the Domestic Energy Fact File. Building Research Establishment.
Fuel
Fuel
CellFuel
Heat
Electrical
50%
40%
Energy
100%Power station
55% losses
Transmission
5% losses
Delivered
40%
Fuel Cell
10% lossesDelivered
90%
Energy
100%
Conventional
Micro-CHP
Fuel Cell Boilers for the Home (micro-CHP)
Micro-CHP Technologies
Baxi Stirling engineVaillant and Plug Power PEMFC
Ceres Power and British Gas SOFC
Honda ECOWILL ICE
Honda ECOWILL ICE with Storage
mCHP electrical efficiency against load factor
A.D. Hawkes, P. Aguiar, C.A. Hernandez-Aramburo, M.A. Leach , N.P. Brandon , T.C. Green, C.S. Adjiman. Techno-economic
modelling of a solid oxide fuel cell stack for micro CHP, J Power Sources, 156 (2006) pp. 321–333.
0 4 8 12 16 20 240
2
4
6
8
10
12
14
16
Time (Hours)
Dem
and (
kW
)
Space Heating and DHW Demand
Electricity Demand
Residential heat and power demand
Heat and Power Demand over 1 Day in a Typical UK Dwelling
Economic Drivers for m-CHP Systems
• Dwelling Annual Electricity Demand•The main value driver for micro-CHP is (the ability to displace) onsite electricity demand.
•If onsite electricity demand exists, the ability to access the value available (in displacing it) is dependent on the heat-to-power ratio (HPR) and presence of thermal demand.
0 2500 5000 7500 100000
200
400
600
800
1000
1200
IC Engine
0 2500 5000 7500 100000
200
400
600
800
1000
1200
PEMFC
0 2500 5000 7500 100000
200
400
600
800
1000
1200
SOFC
0 2500 5000 7500 100000
200
400
600
800
1000
1200
Annual Electricity Demand (kWh/year)
Maxim
um
Cost
Diffe
rence B
etw
een
Mic
ro-C
HP
Syste
m a
nd B
oiler
Syste
m (
£)
Stirling Engine
Low Thermal Demand
Average Thermal Demand
High Thermal Demand
HPR = 1
HPR = 3 HPR = 2
HPR = 8
Dwelling Annual Electricity Demand
Hawkes, AD, Staffell, I, Brett, DJL, Brandon, NP, Fuel Cells for Micro-Combined Heat and Power Generation, Energy &
Environmental Science, 2009, Vol: 2, Pages: 729 - 744
5000 10000 15000 20000 25000 300000
500
1000
1500ICE
5000 10000 15000 20000 25000 300000
500
1000
1500PEMFC
5000 10000 15000 20000 25000 300000
500
1000
1500SOFC
5000 10000 15000 20000 25000 300000
500
1000
1500
Annual Thermal Demand (kWh/year)
Annual C
O2 R
eduction w
.r.t. R
efe
rence S
yste
m (
kg C
O2/y
ear)
)
Stirling
Flat
Bungalow
Terrace
Semi-Detached
Detached
Environmental Drivers for m-CHP Systems
CO2 Reduction – Thermal Demand •CO2 reduction is dependent on ability to displace grid electricity.
•Ability to displace grid electricity, and thus bring about CO2
reduction, is dependent on annual thermal demand and prime mover heat-to-power ratio.
Hawkes, AD, Staffell, I, Brett, DJL, Brandon, NP, Fuel Cells for Micro-Combined Heat and Power Generation, Energy &
Environmental Science, 2009, Vol: 2, Pages: 729 - 744
Carbon Intensity of Electricity Options
marginal CO2 intensity of UK
electricity 0.69kgCO2/kWh
Ceres Power SOFC micro-CHP unit• Developed in collaboration with British Gas (with natural gas fuel) and
Calor Gas (with LPG fuel). Prototype unit now demonstrated.
• Reduces the energy bill of a customer by around 25% and saves around 1.5 tonnes of CO2 pa.
• In addition, under the new UK feed in tariff (FIT), a household installing a SOFC mCHP product will receive, for a period of ten years, a generation payment of 10p/kWh for all electricity generated plus an additional export payment of 3p/kWh for any electricity that is not consumed in the home and is fed back into the grid.
Tubular/flat tube or Planar Cell Designs
Typical planar SOFC geometries
Brett DJL, Atkinson A, Brandon NP, Skinner SJ, Intermediate temperature solid oxide fuel cells, CHEM SOC REV, 2008, Vol:37,
Pages:1568-1578
Relationship between electrolyte and temperature
Brett DJL, Atkinson A, Brandon NP, Skinner SJ, Intermediate temperature solid oxide fuel cells, CHEM SOC REV, 2008, Vol:37,
Pages:1568-1578
YSB ((Bi2O3)0.75(Y2O3)0.25); LSGMC (LaxSr1-xGayMg1-y-zCozO3; x~0.8, y~0.8, z~0.085); CGO (Ce0.9Gd0.1O1.95); SSZ
((ZrO2)0.8(Sc2O3)0.2); YDC (Ce0.8Y0.2O1.96); CDC (Ce0.9Ca0.1O1.8); YSZ ((ZrO2)0.92(Y2O3)0.08); CaSZ (Zr0.85Ca0.15O1.85).
SOFC Cathode Design
• The Three Phase Boundary
(TPB) is a zone in which the:
– open pore (reactant fluid),
– catalyst and
– electrolyte are in close contact.
• The process requires:
– flow of ions via the electrolyte,
– supply of reactant through open
pores
– reaction at the catalyst active sites
SOFC Anode Design
Illustration of the effect of extending the TPB using a MIEC electrolyte. (a)
Electrolyte / cermet anode with active TPB circled; (b) mechanism of
reaction at the TPB; (c) mechanism of reaction at the extended TPB.
Electrode Microstructure in three dimensions
TPB 2
TPB 3
TPB 1
TPB 2
TPB 3
TPB 1
Combining Modelling with Experiment
3D Reconstruction of Ni-
YSZ Anode. Ceramtec
NiO-YSZ sintered at
1350C.
100 images at 15 nm
intervals with 20 nm pixels
- 6.7 x 5 x 1.5 µm (x,y,z).
Red=YSZ; Blue=Ni.
Total TPB density = 10.4
m-2 with 63% percolated
in x-y plane and 72%
percolated in x-z plane.
Porosity = 20%.
P Shearing, Q Cai, J Golbert, V Yufit, C S Adjiman, N P Brandon, Microstructural analysis of a solid oxide fuel cell anode using
focused ion beam techniques coupled with electrochemical simulation, J Power Sources, 195 (2010) pp. 4804-4810.
Zeiss xB1540 FIB-FEG SEM, milled at 30 kV, 30 pA, imaged at 2kV in secondary
electron mode.
T
ºC
RHF
Ω cm-2
RMF
Ω cm-2
RLF
Ω cm-2
1000 0.076 0.857 0.161
900 0.387 1.365 0.138
800 0.803 1.543 0.1690.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
0.000
0.002
0.004
0.006
0.008
0.010
0.012
y=0.076x
y=0.387x
y=0.803x
800 oC
900 oC
1000 oC
Over-
pote
ntial (V
)
Current density (A/cm2)
Exchange Current per unit TPB length
800 °C: 9.4×10-11 A/μm
900 °C: 2.14×10-10 A/μm
1000 °C: 1.22×10-9 A/μm
Model and experiment – an first step
3.5 4.0 4.5 5.0 5.5 6.0 6.5
-0.5
0.0
0.5
1.0
1000 C
900 C
800 C
Zim
g [
Oh
m c
m-2]
Zreal
[Ohm cm-2]
97 % H2 , 3 % H
2O
P Shearing, Q Cai, J Golbert, V Yufit, C S Adjiman, N P Brandon, Microstructural analysis of a solid oxide fuel cell anode using
focused ion beam techniques coupled with electrochemical simulation, J Power Sources, 195 (2010) pp. 4804-4810.
Electrode Thickness Investigation – current density
The current density
reaches a maximum at a
different thickness as a
function of overpotential.
At over potential of 400
mV, active electrode
thickness = 9 µm
At over potential of 300
mV, active electrode
thickness =12 µm
At over potential of 50-
200 mV, active electrode
thickness =15-18 µm0 2 4 6 8 10 12 14 16 18 20 22 24
0
1
2
3
4
5
6
400 mV
300 mV
200 mV
100 mV
50 mV
Curr
ent
density (
A/c
m2)
Electrode thickness (µm)
T=1073 K; Ionic conductivity: 4.28×10-6 S/μm
PH2:PH20=1; Electronic conductivity: 2.4 S/μm
Exchange current : 9.4×10-11 A/μm
Binary diffusion coeff: 8.28x10-4 m2 s-1
Case 1: 21% Porosity VNi: VYSZ=1.3
Electrode Thickness Investigation
0 2 4 6 8 10 12 14 16 18
02
46
8
0
2
4
6
8
xy
z
0
1
2
3
4
5
6
7
8
9x 10
-6×10-6 A/µm3×10-2 A/cm3The 3D map of current density distribution in the electrode of Case 1. x is the electrode
thickness dimension, y and z dimensions form the cross section of the electrode. At x=0
is the interface of current collector with the electrode, and at x=18, the interface of the
electrode with the electrolyte.
A A
200
σP1
(MPa)
0YSZ Phase
Ni Phase
FEM analysis of 3D electrode structures
(ScanFE V3.1, Simpleware Ltd, UK). The FE model consisted of 285,000 four-
node tetrahedral elements (Abaqus type C3D4)
R Clague, P Shearing, PD Lee, Z Zhang, DJL Brett, AJ Marquis, NP Brandon, Stress analysis of SOFC anode microstructure reconstructed from focused
ion beam tomography, J Power Sources (2011) in press.
1. Manufacture Cell2. Electrochemical
Characterisation
3. Microstructural
Characterisation
4. Simulation5. Validate & Re-
iterate
Summary
•SOFC offer improved efficiency, and hence reduced carbon
emissions, using a wide range of fuels, and over a wide range of
power levels, with a strong fit with distributed power generation.
•Key SOFC challenges in the near term are related to demonstrating
durable fuel cell system performance under real world operating
conditions, and a number of programmes are under way around the
world to do this.
•Future challenges lie in enabling operation on renewable and/or
lower carbon fuels, continuing to reduce device cost, and further
extending device performance and lifetime.
•At the 100 MWe’s scale SOFC technology can contribute to CCS
schemes, and syngas production from CO2 and steam by electrolysis
using renewable energy.
Konda N, Shah N, Brandon NP, Optimal transition towards a large-scale hydrogen
infrastructure for the transport sector: The case for the Netherlands, INT J HYDROGEN
ENERGY, 2011, Vol:36, Pages:4619-4635
Thank you
n.brandon@imperial.ac.uk
www.imperial.ac.uk/energyfutureslab
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