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MOLTEN CARBONATE FUEL CELLS
ANSALDO FUEL CELLS: Experience &
Experimental results
Filippo Parodi /Paolo Capobianco
(Ansaldo Fuel Cells S.p.A.)
Roma , 14th & 29th March 2007
MOLTEN CARBONATE FUEL CELLS
ANSALDO FUEL CELLS EXPERIENCE
MOLTEN CARBONATE FUEL CELLS
Elements
of
Fuel
Cell
Theory
ANSALDO FUEL CELLS EXPERIENCE
Evaluation of the characteristic parameters
Flow diagram of a typical MCFC plant
ANSALDO Fuel Cells experience
Experimental results
Filippo Parodi (Ansaldo Fuel Cells S.p.A. - Italy)
Roma , 14th March 2007
FUEL CELL IS A DEVICE ...
Electrical Energy
e-
AFC
H2
H2O
PEFC
H2
H+
DMFC
CH 3OH
CO2
H+
PAFC
H2
H+
MCFC
H2
H2 O
H2
H2O
SOFC
OH -
CO =
3
O=
O2
100 °C
O2
H2O
O2
H2O
O2
H2 O
O2
CO2
O2
80 °C
80 °C
200 °C
650 °C
1000 °C
Fuel
Oxygen
H2
Air
Cathode
Anode
Electrolyte
DIRECTLY TRANSFORMS THE CHEMICAL ENERGY OF THE FUEL INTO
ELECTRICAL ENERGY BY ELECTROCHEMICAL REACTIONS
FUEL CELLS BASED vs. CONVENTIONAL
ENERGY PRODUCTION PROCESS
CO2, NOx, SOx,
particulate, ash
FUEL
Heat losses
THERMAL TO MECHANIC
CONVERSION
COMBUSTION
Mechanical losses
MECHANIC TO ELECTRICAL
CONVERSION
ELECTRIC
ENERGY
OXYGEN
Steam/Gas Turbine
CO2
FUEL
FUEL PROCESSING
Alternator
H2O
H2
FUEL CELL
ELECTRIC
ENERGY
OXYGEN
HEAT
Fuel Cells based vs. conventional power systems



Direct energy conversion (no combustion)

Less conversion steps / Lower energy losses

Higher efficiency
Environmental benefit

No moving parts in the energy converter, Low maintenance , Low noise

Low exhaust emissions,
Modularity



Size flexibility

Good performance at off-design load operation
Fuel flexibility


Modular installations to match load and increase reliability
hydrogen, Natural Gas, biogas, biomass gasification, landfill gas,
reformed heavy fuels
Possibility of remote/unattended operation
Fuel Cells Technologies
AFC
PEMFC
Potassium
hydroxide
Ion
Exchange
Membrane
100°C
80°C
205°C
650°C
800-1000°C
OH-
H+
H+
CO3=
O=
Ni, Ag,
nobel
metals
Platinum
Platinum
Not
required
Not
required
Fuel
H2
H2
H2
H2, CO
H2, CO
Oxidant
O2
O2 / Air
Air
Air, CO2
Air
Poisons
CO, CO2,
CH4, S
CO, CO2, S
CO, S
S
S
Electrolyte
Operating
Temperature
Charge
Carrier
Catalyst
PAFC
MCFC
Immobilised Immobilised
Liquid
Liquid
Phosphoric
Molten
Acid
Carbonate
SOFC
Ceramic
AFCo selects as most promising FC technology:
MCFC
Operating temperature about 650°C
No noble metal catalysts are used into the stack
Uses carbon monoxide as fuel and carbon dioxide as cathode reactant
Allows much simpler reforming section
Allows coupling to gas turbine hybrid cycles (higher efficiencies)
Plants up to 1- 2 MW size, for stationary applications, demonstrated in USA & Japan
Ansaldo Fuel Cells Labs MCFC single cells
Electrochemical Reactions:
CO2 + ½ O2 +2e-  CO3- cathode
H2 + CO3-  H2O + CO2 + 2eanode
---------------------------------------------------H2 + ½ O 2  H2 O
overall reaction
Materials:
anode: Ni / Cr
cathode: Li x Ni 1-x O
matrix: LiAlO2
electrolyte: K2CO3 e Li2CO3
MCFC STACKS
single cell voltage
=
0.6 - 1 V
current
=
up to 1000A DC
To obtain the required electrical
voltage and power, many cells
are connected in series to build
the MCFC Stack
MCFC stack
components and manufacturing

These aspects will be shown on the next lesson
29/03/07
Paolo Capobianco
Ansaldo Fuel Cells S.p.A.
Responsible for laboratories
Working principles of Fuel Cells
MCFC technology
Key materials and components
Technological development
LAB level tests
Elements of Fuel Cell theory
Characteristic parameters

Reversible cell potential




cell voltage out of reversibility




temperature effects
operating pressure effects
reversible cell potential calculation
polarisation effects: activation, ohmic, concentration
experimental data on MCFC
thermal management and operating ranges
MCFC based power plants




fuel reforming + MCFC
mass balance
performance
experimental results
reversible cell potential

The Fuel Cell is a device that directly transforms chemical energy
of the fuel into electric energy by mean of electrochemical
reactions.
From the thermodynamic point of view:
From the thermodynamic point of view:
at constant pressure:
1st Principle of Thermodynamics:
RL
H  U  P V
H
P
e-
 U  P  V
-
U  Q  L
A
for electro-chemical reactions
Q  T  S
W  P  V  Wel
C
H+
H2
for reversible transformations:
+
O2
reversibie cell potential definition
Wel is related to anode and cathode voltages:
Wel  n  F  VC ,rev  VA,rev 
with:
n
F
VC, rev
VA, rev
Number of exchanged electrons in the unit reaction
Faraday’s constant
reversible cathode potential
reversible anode potential
From thermodynamics the Gibbs potential is
G P  H P  T  S  n  F  VC ,rev  VA,rev 
defining the reversible cell potential as:
Erev  VC ,rev  V A,rev 
we have the direct relationship between available chermical energy G and the electric potential Erev
G P  n  F  Erev
Temperature effects on Erev
 Erev  S

T
nF
 Erev 
0
T
S
T
T
[K]
[°C]
298
25
54583
57973
-11.4
600
327
51147
58342
-12.0
800
527
48610
58757
-12.7
1000
727
46005
59034
-13.0
1250
977
42615
59633
-13.6
1500
1227
39202
59702
-13.7
-G
-H
[cal/gmole] [cal/gmole] [cal/gmole K]
H2  1
2
O2  H 2O
70000
1.4
60000
1.2
50000
1.0
40000
0.8
30000
-DG
-DH
E = -3E-08T2 - 0,0002T + 1,2551
20000
DG = -0,0012T2 - 10,621T + 57895
10000
0.6
0.4
E (T, pi=1ata)
0.2
DH = -0,0002T2 + 1,886T + 57371
0
0.0
0
100
200
300
400
500
600
700
800
T [K]
900 1000 1100 1200 1300 1400 1500 1600
E (T, 1ata) [V]
- DG [cal/g mole]
- DH [cal/g mole]
Temperature effects on Erev
Operating pressure effects on Erev
Erev 
 V

P T
nF
H2  1
2
Erev 
0
P T
O2  H 2O
  p products  
   products  
G  G  R  T   ln
 reactan ts  

   preact
.

 
0
 A  B  C  D
Erev 
0
Erev
0
R T 0

nF
  p products  
   products  
  ln
 react  

   preact

 
*    p products  
 
R

T
products  
*
Erev  Erev
(T * ) 
  ln

react 
nF    preact


 
Operating pressure effects on Erev
anodo
H 2  CO32  H 2O  CO2  2 e
catodo
CO2  1
H 2, A  CO2,C  1
Erev
2
O2  2 e   CO32
650C
2
O2,C  H 2OA  CO2, A
 p


p
R

T
H 2O , A
CO2 , A
*

 Erev
(T ) 
 ln 
1
2 
2F  p  p

p
 H 2 , A CO2 ,C O2 ,C 
Erev
1 

R  T  xH 2O , A  xCO2 , A  P 2 
*
 Erev (T ) 
 ln
1

2
2F  x  x

x
 H 2 , A CO2 ,C O2 ,C 
Erev : study case calculation for MCFC
T [K]
P [ata]
923
3.5
CATODO
O2
CO2
H2 O
N2
Erev
10.2
6.2
21.0
62.6
ANODO
H2
CO2
CO
H2 O
N2
CH4
51.0
6.6
8.2
33.4
0.0
0.8
1 

xH 2O , A  xCO2 , A  P 2 
R T
*

 Erev (T ) 
 ln
1


2
2F
x

x

x
 H 2 , A CO2 ,C O2 ,C 
E*rev (923K) = 1045 mV
Erev (923K) = 1039 mV
%mol
%mol
%mol
%mol
%mol
%mol
1.060
20.0
1.055
18.0
1.050
16.0
1.045
14.0
1.040
12.0
1.035
10.0
E*
1.030
8.0
Erev(P) a 650°C
1.025
6.0
dErev/dP
1.020
4.0
1.015
2.0
1.010
0.0
1
2
3
4
5
6
P [ata]
7
8
9
10
dErev/dP [mV/atm]
Erev [V]
Erev: pressure effects on MCFC
Elements of Fuel Cell theory
Characteristic parameters

Reversible cell potential




cell voltage out of reversibility




temperature effects
operating pressure effects
reversible cell potential calculation
polarisation effects: activation, ohmic, concentration
experimental data on MCFC
thermal management and operating ranges
MCFC based power plants




fuel reforming + MCFC
mass balance
performance
experimental results
cell voltage on load
RL
ne-
I
-
+
A
C
H+
combustibile
fuel
ossidante
oxidant
I
V
RL
V  Erev
out of reversibility conditions
cell voltage on load
1.5
1.4
Erev-OCV: parasitical reactions
1.3
Erev
1.2
OCV-A:
OCV
1.1
polarization for activation
A-B:
linear voltage drop - ohmic behaviour
1
B-C:
V
0.9
polarization for concentration
A
0.8
0.7
B
0.6
0.5
C
0.4
0.3
0.2
0.1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
i
V  Erev  Ri  I  att  conc
V  Erev
0.9
1
Elements of Fuel Cell theory
Characteristic parameters

Reversible cell potential




cell voltage out of reversibility




temperature effects
operating pressure effects
reversible cell potential calculation
polarisation effects: activation, ohmic, concentration
experimental data on MCFC
thermal management and operating ranges
MCFC based power plants




fuel reforming + MCFC
mass balance
performance
experimental results
Experimental results on a MCFC stack
1400
1,40
design condition
1100
1000
900
800
700
600
500
400
300
200
100
1,00
[KW/m²]
1,20
0,80
0,60
0,40
Power Density
Cell Average Voltage [mV]
1300
1200
0,20
0
0
200
400
600
800
1000
1200
Current Density [A/m²]
Voltage vs current characteristic curve is linear: V = Erev - Rpol • I
Negligible activation and parasitic voltage loss
High current density design condition is possible
1400
1600
1800
0,00
2000
By courtesy of Ansaldo Fuel Cells SpA
Concentration effects
experimental results on MCFC single cell
1.6
Experimental
Simulation
1.4
can be measured only for gas
compositions very poor in H2
Cell Voltage [V]
1.2
or
H2 Concentration
1.0
at very high current densities
0.8
good agreement with simulated
values
0.6
0.4
0.2
0.0
0
500
1000
1500
2000
2
Current density [A/m ]
2500
3000
By courtesy of Ansaldo Fuel Cells SpA
Elements of Fuel Cell theory
Characteristic parameters

Reversible cell potential




cell voltage out of reversibility




temperature effects
operating pressure effects
reversible cell potential calculation
polarisation effects: activation, ohmic, concentration
experimental data on MCFC
thermal management and operating ranges
MCFC based power plants




fuel reforming + MCFC
mass balance
performance
experimental results
Thermal management on MCFC
results from detailed simulation code (*)
exothermal
electrochemical
reaction
power generation produces heat
excess in the cell
thermal management need to avoid
high
temperature
damaging
of
components
high gas flow rate is used to cool
down the stack
(*) By courtesy of Ansaldo Fuel Cells SpA
and PERT group of Genoa University
Thermal management on real MCFC
STACK MCFC - experimental data
temperature distribution on the cell plane
700-710
690-700
680-690
670-680
660-670
650-660
640-650
630-640
620-630
610-620
600-610
By courtesy of Ansaldo Fuel Cells SpA
typical operating ranges
operating parameter
typical values
management
580 < T < 700°C
cooling system: cathode gas
high flow rates
exhaust gas recirculation
pressure and pressure drops
1  5 atm
P anode/cathode < 20 mbar
pressurised sytems
allows higher performance,
higher flow rates and lower
pressure drop
fuel utilisation
oxidant utilisation
 75%
 56%
prevent concentration effects
on V vs. I curve
temperature
necessary for cathode reaction
CO2
 5%
available by recirculation of
anode exhaust to cathode
(catalytic burner)
Oxygen concentration
 10%
necessary for cathode reaction
and catalytic burner combustion
pollutants
H2S, HCl, NH3, trace metals
proper clean up systems
Fuel Cells Plant Concept
CONTROL
SYSTEM
FUEL
FUEL processor
Steam
+
heat
H2
Steam
+
heat
COGENERATION
FUEL CELLS
O2
to accomplish with proper
AIR
AIR TREATEMENT
operating ranges the fuel cell
DC / AC
(DC / DC)
need of a Balance of Plant
tailored on the application
MOLTEN CARBONATE FUEL CELLS
ANSALDO FUEL CELLS EXPERIENCE
Elements of Fuel Cell Theory
Evaluation of the characteristic parameters
Flow diagram of a typical MCFC plant
ANSALDO Fuel Cells experience
Experimental results