Heinrich J.G., Aldinger F. (Eds.) Ceramic Materials and Components for Engines
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NEW
TECHNOLOGIES IN THE LIGHT
OF
MATERIALS
Prof.
Dr.-Ing. Heinrich A. Flegel
DaimlerChrysler AG
D-70546 Stuttgart, Germany
ABSTRACT
The industrialized nations' prosperity and living
standards depend to a major extent on the rapid transfer
of technical innovations into marketable products.
Alongside classical materials
-
metals, plastics, ceram-
ics, and glass
-
tailor made combinations like composite
materials play an increasingly important role.
In the transportation sector materials are expected to
render a major contribution towards solving the target
conflicts which arise from contradictory customer re-
quirements: high performance and reliability, and mini-
mum weight and low costs. The rapid transfer into new
products can only be achieved, if the development of
materials and the pertinent production processes and
system development are closely coordinated and syn-
chronized by a simultaneous engineering approach.
INTRODUCTION
It is evident, mobility is a basic need of mankind.
Efficient, effective and flexible transport systems are
essential
for
economic activity and quality of life.
Sustainable mobility is a megatrend of the future and
therefore a major driving force for the development of
new technologies.
The awareness that resources are limited is growing.
Therefore, also political pressure towards resource con-
servation and waste reduction has significantly
in-
creased.
Fig.
1
shows the prevailing trends in the EU and
USA,
two very important segments of the world mar-
kets.
Awareness
that
resources
are
Limited
is
growing
-
in
aUape
smnger
than
in
the
US.
-"berefon,
also
political
pressure
towards
resource
CMlserVation
and
waste
reduction
bas
signiEdy
inmwd
Ewopean
end-of-live legislation
for
vehicles
almost
finalized
conrtatoneE
are
fixed:
myding
quota 95%
in
2015,
free
of
rn
al@zzzg
the
amouot
of
new
materials
in
the
uroducts
will
come
into
the
wlitid
focus
r)
eahance
use
brncycling
and
renewable
kterials
Curreatly
new
move
towards
more
product
related
envinnunental
legislation
(Integrated
Roduct
Policy,
IPPt
.r)End-of-Liivc
legislation
not
in
ptace
yet,
but
Likely
in
the
htture
=
rl)
No
strong
legislation
for
free
of
charge
iake
back
d
goods,
cmt
infrashucm
supports
dismaattiag
indusby
Fig.
1:
Resources and Environment
Sustainability of transport and other sectors is now a
major goal for the EU and progress
is
required.
Since fossil fuels will not
be
available forever in
limitless quantities, alternatives will have to be found to
meet the future energy demand. PEM (proton exchange
membrane) fuel cells are expected to be a suitable alter-
native for future mobile applications.
As
shown in
fig.
2,
the electrical energy can be generated from hy-
drogen, methanol
or
hydrocarbons. Hydrogen and
methanol can
be
generated from fossil as well as from
renewable primary energies. Therefore, both items in-
crease the security of supply and help to reduce carbon
dioxide production. Key success factor is an affordable
polymer membrane, which is coated
on
both sides with
a catalyst containing platinum
[
11.
Fig.
2:
Fuel Cells in Mobile Applications
Very often in mobile applications, progress in the
development of new, affordable materials is crucial to
the economical success in volume production.
AUTOMOTIVE LIGHTWEIGHT
ENGINEERING
Fuel efficiency regulations and the voluntary com-
mitment of the European Automobile Manufacturers
Association (ACEA) to reduce fuel consumption by
25%
over the period
1995
to
2008
are
the
main drivers
for automotive lightweight engineering. Fig.
3
shows
the amount of fuel saved per
100
km
by
100
kg weight
reduction, specified for cars powered by internal com-
bustion and Diesel engines.
3
1990:
5
1200
kg
I
2010:
c
lo00
krr
Fig.
3:
Automotive Lightweight Design
As
a secondary effect, a lighter car needs a less power-
ful engine to achieve the same performance and the
brakes as well as the load-bearing components do not
need to
be
as strong. When these effects are
also
taken
into account, the bonus offered by lightweight engi-
neering is seen to increase
to
about
0.6
liters of fuel
saved over the same distance for the same weight re-
duction.
The average car weight will presumably be reduced
by about 20% within the next
10
years. With regard to
the distribution of materials, the percentage of steel will
be steadily decreasing in favor of lighter materials like
aluminum, magnesium and plastics. However, there has
also been considerable transformation and improvement
with regard to the individual steel quality used. There is
a strong trend towards higher and high-tensile strength
steel qualities.
It is obvious that lightweight engineering is the ma-
jor
driving force for the development of new materials
in the transportation sector. However, it can only
be
completely successful, if new materials, new design
principles and suitable economic high volume manu-
facturing technologies are combined.
has excellent die casting properties, it can
be
used for
highly integrated die castings. Plastics are widely used
for bumpers and interior parts like dashboard, heading
and rear-window shelf.
It is very important to keep the complete process
chain in mind: from the raw material to the finished
part. Since lightweight design doesn't mean lightweight
at any cost.
Carbon fiber-reinforced plastics (CFRP) are well
known as structural materials from formula
1
racecars.
CFRPs have the potential to significantly reduce weight.
These laminates do not corrode and are almost immune
to material fatigue. They show excellent crash behavior
because of their high energy absorption ability.
Advaotage
*
Weight
saving
*
High
strength
and
stiffness
*
Excellent
crash
behavior
because
of
high
energy
absorption
Disadvantages
*
No
experience
in
volume
production
costs
Fig.
5:
Carbon Fiber Reinforced Plastics
However, their use is still limited to small scale feasi-
bility studies and high performance applications (fig
5).
Fig.
6:
Textile Technologies
For
automotive applications cost effective manu-
facturing technologies for volume production have to be
developed [2]. The necessary development steps are
shown in fig.
6.
Fig.
4:
Trend
for
Body
Concepts in Car Design
As
shown in fig.
4,
multi material design is the trend
of the future for body concepts in car design. Because of
high tensile strength
-
which is good for deformation
energy absorption
-
steel is used in crash relevant sec-
tors of the car body. Extruded aluminum profiles are
used for frame structures; with aluminum die castings,
high functional integration can
be
achieved. Magnesium
High temperature applications: titanium aluminides
have the potential to substitute the heavy and expensive
nickel based alloys in aircraft engines. The turbine
blades should
be
capable of withstanding temperatures
of more than
1200"
C.
Success factors are their low density and high creep
limit. Compared to ceramics ductility increases with
increasing temperature[3].
4
aeroengine automotive powertrain
I
I
PW4086Engine
Turb0charge.r
VdEnginc
clhnrst
Range:
300-450
kN)
commnents
-
Low
Pressure
Turbiie
-
High
Pressure Compress
-
HPC-Castings
Blades
or Blades
Engine
pans
-
Fig.
7:
Titanium and Titanium Aluminides in Engines
Potential applications in automotive engineering are
exhaust valves, piston rods and turbine wheels (fig.
7).
A
weight saving potential for these rapidly moving
inertial masses of up to
50%
was proven.
CERAMICS IN AUTOMOTIVE AND
AEROSPACE APPLICATIONS
Ceramics are stable at high temperatures, resistant to
chemical attack, lighter than steel but more brittle than
metals
or
polymers. Fiber reinforcement is a well
known method for reducing brittleness. The benefits of
ceramics are concisely listed in fig.8.
The favored automotive applications are carbon
pistons, brake discs and tribo-coatings. The all-ceramic
engine that was enthusiastically promoted almost
15
years ago has faded from the scene.
Potential
Components
Bnke
discs
Piston
(carbon)
Tribo-coatings
Benefits
Weight
reduction
High
temperature
resistat
Low
wear
Adjustable
friction
behav
Long
lifetime
Fig.
8:
Ceramics in Automotive Applications
C/C-Sic composite materials offer great advantages
for new lightweight and wear resistant brakes
[4].
These
CMC materials have demonstrated their high potential
for the application in disc brakes
for
high speed trains
and cars.
Fig.
9:
Ceramic High Performance Brake (CBrake)
The ceramic high performance brake
or
C-brake is a
brake disc made of fiber reinforced ceramics. The bene-
fits compared to a typical grey cast iron brake disc are:
60%
weight reduction, no corrosion, high performance
and comfort, and lifetime corresponding to the useful
life of the car (fig
9).
The C-brake will
be
introduced
in
the market in autumn
2000
in a special edition of the
Mercedes
S
class coup6 by
AMG.
Fiber reinforced ceramics for hot spacecraft struc-
tures (fig.
10):
C/SiC is an excellent material
for
light-
weight and heat resistant structures
[5].
Fig.
10:
Aerospace Components from Fiber Reinforced Ceramics
It enlarges the application range
of
fiber composites
by opening up the high temperature field of up to
1600" C.
By using this material, the spacecraft industry
can manufacture heat shields and engine components
with longer lifetime, lower operating cost and reduced
weight; e.g. replacing the metal by C/SiC in the expan-
sion nozzle of the
ARIANE
upper stage engine would
allow
60%
weight savings. First ground combustion
tests have been successfully performed just recently.
Smart materials, either piezoceramics
or
shape
memory alloys, are able to act as sensors
or
actuators
(fig.
1 1).
5
Advanced
funclionalites
by
-
PiezoCeramics
-
Shape
Memory
Alloys
(SMA)
Electrically
kqeramics)
or
thfmyUy
SMA)
mQ$led
shape
changes
areL
basts
for
the
appllcatlon
ok
smart
materials
as
Sensor
materials
(sensing
conditions)
Actuator
materials
(performing
actions)
Fig.
11:
Smart Materials
-
Function Concepts
Piezo-active structures are based on structurally in-
tegrated piezoelectric actuators to enable active shape
control, vibration damping and precision positioning.
Aerospace structures usually have to realize high
strength and stiffness at minimum weight, and are there-
fore made of CFRPs. Piezoceramics are seen as most
promising materials for low fiequency vibration damp-
ing and shape control of lightweight aerospace struc-
tures
[6]. Due to piezo-driven control flaps in the rotor
blades, the rotor induced vibrations inside the cabin as
well as the rotor noise during approach could
be
r
duced significantly (fig. 12).
BdtS
Piezo-driven
50
%
noise
reduction
control
flap
of
duringappmch
90
%
reduction
of
rotor-induced
viions
rotor
blades
inside
the
cabin
helicopter
Fig.
12:
Smart Materials
-
Helicopter Rotor Blades
The specifications for a piezo-controlled high pres-
sure injection valve for a common rail diesel injection
system are shown in fig
13.
can a
be
injected more precisely, which leads to a more
quiet engine running without the diesel
knock.
The high
precision injection leads to cleaner combustion and
lower emissions.
CONCLUSIONS
made:
0
To sum up briefly, four major statements can be
There is an increasing demand for lightweight ma-
terials and the suitable manufacturing technologies
in transportation.
There is a fierce competition among different mate-
rials.
Ceramics are preferably
used
in high performance
applications.
Application in volume production only at reduced
costs.
The key issues of structural ceramics are
0
0
0
0
-
reliability
-
interface
to
surrounding, non-ceramic compo-
nents
-
costs
ACKNOWLEDGEMENTS
Partial funding of these research activities by the Ger-
man Ministry of Education, Science, Research and
Technology (BMBF) is gratefully acknowledged.
REFERENCES
(1) K. Kordesch,
G.
Simader, Fuel Cells and their Ap-
plications; VCH, Weinheim
(1996)
(2)
J. Brandt, K. Drechsler,
F.
Strachauer, Kostengun-
stige und groherienfahige Herstellung von Ver-
bundwerkstoffen mit textilen Faserstrukturen, in
Kunststoffe im Automobilbau, VDI Verlag,
Dusseldorf
(1998) 227
(3)
N.
Eberhardt, A. Lorich, R. Jtirg, H. Kestler,
W. Knabl, W. Kiick, H. Baur, R. Joos, H. Clemens,
Pulvermetallurgische Herstellung und Charakter-
isierung einer intermetallischen Ti-463
Al-
4(Cr,Nb,Ta,B)-Legierung,
Z.
Metallkunde
89
(1998) 772
(4)
W. Krenkel, R. Renz, B. Heidenreich, Lightweight
and Wear Resistant CMC Brakes, Proceedings
of
7" International Symposium Ceramic Materials and
Components for Engines
(2000)
(5)
W.
Schafer,
H.
Knabe,
W.
D.
Vogel, Fiber Rein-
forced Ceramics for Hot Spacecraft Structures,
ICCE
7,
Denver (2000)
(6)
U.
Herold-Schmidt, E. Floeth, B. Last, W. Schafer,
H.W. Zaglauer, Qualifications of Smart Composites
for the
Use
in Aerospace Applications,
SPIE
Con-
ference on Smart Structures and Materials, San Di-
ego
(1997)
Fig.
13:
Smart Materials
-
Function Concepts
Because of the higher switching
speed
of the piezo-
controlled valves compared to solenoid valves the fuel
6
THE PROMISE
OF
SOFC POWER GENERATION TECHNOLOGY
D.S. Schmidt* and R.A. George
SOFC Power Generation Siemens Westinghouse Power Corporation
1310 Beulah Road Pittsburgh, PA 15235 USA
ABSTRACT
The tubular solid oxide fuel cell (SOFC) technology
developed by Siemens Westinghouse is rapidly
approaching commercial readiness. Cell technology
has progressed from 36cm active length cells
producing 30W/cell in the mid-1980s to our
commercial size (150cm active length) cell producing
160W/cell in the late 1990s. Further cell technology
advances currently under development related to
power output enhancement and cell cost reduction will
also be discussed. Our SOFC stack and power systems
technology has also advanced quite substantially from
a 3kW
unit
operated on H2/C0 in the late 1980s
to
a
lOOkW combined heat power unit operated
on
pipeline
natural gas in the late 1990s. In addition, the first
pressurized SOFC/gas turbine power system rated at
220kW will be in operation in the spring of 2000.
An
overview of the power system demonstrations will also
be presented.
INTRODUCTION
The Siemens-Westinghouse Power Corporation
(SWPC) tubular SOFC design is currently being
evaluated in prototype generators, but
commercialization will require a large reduction in cell
and generator costs. This focus
has
been applied
throughout the entire system, but one of the greatest
potentials for cost reduction lies in the development in
low cost cell manufacture, a function of both the
processing and raw materials.
Current State
of
Technology
Currently, SWPC has two operating field units: one
lOOkW unit in operation and one 22OkW-unit
undergoing site acceptance testing. The lOOkW unit
has been operating for 13,000
hrs
as
of
mid-June, 2000
on natural gas. Located in the Netherlands, it has been
delivering 1lOkW AC (130kW DC)
as
well
as
hot
water to the district heating system. The efficiency
of
this atmospheric pressure unit is 46%.
A
second unit has been constructed for southern
California Edison (SCE). The SCE
unit
will
produce 220kW continuously by utilizing a
combined cycle with 3 atm operating pressure.
When combined with a microturbine generator
(MTG),
the SOFC is utilized
as
a high-efficiency
burner, delivering clean exhaust gas (no
NO,/SO,)
to the gas turbine. SOFCs will deliver higher
powers at higher pressures, and in combination with
a turbine, overall efficiencies are expected to be at or
above 60% with essentially
no
emissions of CO,
NO,,
SO,,
and very low levels of CO1 emissions due
to the high efficiency.
Both units utilize the SWPC seal-less tubular design
operating near 1000°C.
This
design allows for small
footprints (the prototype SCE unit has a foot print
of
approximately 25m2)
as
well
as
eliminates the
problems associated with seals between
air
and fuel at
1000°C found
in
planar technologies.
As
with any new technology, the fxst successful
prototype SOFC involved large amounts of
developmental and first-time engineering and
processing costs. One of the main aspects of achieving
commercial success is the technical development of the
materials and processes necessary to achieve lower
SOFC cell costs. Cell costs comprised
55%
of
the
overall unit costs for the first prototype, and need to
compromise no more that 25% of the overall mature
product costs. Costs
in
this
high-temperature system
such
as
piping, insulation, recuperators, gas turbines,
valves, power electronics, and controls also need to
decrease. The cell costs represent the biggest potential
for generator cost reduction
as
production increases
due to the ability to directly affect the processes by
which
this
high-tech device is manufactured.
Therefore,
this
paper will focus
on
the reduction of cell
costs through manufacturing improvements.
TECHNOLOGY
Basic Materials
As
commercialization efforts progress, the basic
concept remains the SWPC tubular cell. The cell
consists of four basic parts: the cathode, the
electrolyte, the anode, and a cathode interconnection.
The backbone
of
the tube
is
the cathode, which
operates
in
an air environment and supports the layers
of interconnection, electrolyte, and anode, which are
placed on it. The interconnection provides an external
connection to the cathode for generator assembly,
described below. The basic requirements
of
the SOFC
parts are shown
in
Table 1.
7
conductive
in
both
air
and
fuel
An
important part of the material requirements is the
matching of the thermal expansion coefficient to YSZ
(10.0~10-~
dmm
“C)“). Without such a match, the
internal stress buildup at the material interfaces will
result in cell damage
as
it is brought from room
temperature to its operating point of 1000°C.
Cell Construction
Currently, to form a single cell, doped
LaMnO3
is
mixed with cellulose binder and water to form an
extrudable paste.
This
paste is first extruded
from
a
piston extruder to form a rounded closed end with a
radius of 1 1.6mm and wall thickness of
2.2mm.
When
the end is formed, the extrusion
is
continued to form
the cylindrical portion of the support tube with
dimensions of 181cm in length and 2.2cm in outer
diameter.
This
results in a hollow single body with
one end closed. (See Figure 1.) The binder
is
burned
out from the tube and the powder is fired at 1500°C to
form the porous gas-diffusion electrode with the
mechanical strength to support the subsequently
applied layers.
Onto one side of
this
is plasma-sprayed doped-LaCr03
in a stripe that is l00p.m thick,
1
lmm
wide, and 150cm
in length.
This
plasma-sprayed stripe is the
interconnection which will allow
an
external
conductive path to the cathode. Because it
will
reside
in both the reducing fuel atmosphere and oxidizing
air
atmosphere, it must be a fully dense body
to
prevent
gas leakage.
The next step
is
the application
of
the electrolyte to the
cell. This is performed by electrolyte vapor deposition
(EVD)
of YSZ to the surface of the tube.
This
process
involves the use
of
YC13 and
ZIC4
at
two
torr and
1300°C on the outside
of
the tube while fluxing
H20
and
02
through the tube wall.
This
process is covered
in detail el~ewhere‘~,~’, but involves
first
the closing of
pores at the surface of the cathode by
CVD
of the
chlorides in contact with the oxygen. Once the pores
have been closed, the mixed conductivity of the CVD
YSZ allows the passage of oxygen ions to the outer
surface where they can continue to react with the
chlorides, resulting in a perfectly dense and uniform
40pm layer over the entire exposed surface of the tube.
Because the entire exposed surface
will
be covered,
and a direct connection to the cathode is desired
through
the LaCr03 stripe previously deposited, a
sacrificial material is used to mask the interconnection,
which is removed after the deposition. The key to the
tubular design is the gas-tight nature of the tube,
imparted by the electrolyte and the interconnection.
These
two
surfaces, to
maintain
this integrity, must
overlap
as
shown in Figure 1. The mask on the
interconnection
is
made to be
7.5mm
in width, and
leaving
lmm
at each end.
This
allows the
growth
of
the
EVD
electrolyte layer over the edge of the
densified interconnection, ensuring a gas-tight seal.
Figure
1:
Two-part figure
of
SOFC cell showing
construction
and
orientation.
Closed
end not
shown
in
this feure.
The last
step
is the application of the anode. The ideal
material for this
is
porous nickel (Ni), but Ni
has
a
thermal expansion coefficient of 13.46~ 10amm/mm
0C(4) which would result in separation when in contact
with YSZ. However, ‘fixing’ Ni particles in a YSZ
mounting material or cermet
has
been successful for
SWC and At
SWC,
this ‘fixing’ of the
anode
is
performed by first dipping the tube into a Ni
slurry, placing a porous layer
of
Ni
on the electrolyte
surface. The interconnection is again masked, and
EVD
is
again performed on the tube. Growth of the
YSZ
occurs around the
Ni
particles, enveloping and
‘fing’ them in a l00p.m thick porous matrix to the
electrolyte surface, providing intimate electrical
contact and mitigating thermal expansion mismatch.
Estimated conductivities of the anode and
subsequently applied layers are shown in Table
2.
The last step in producing a working SOFC is ensuring
good electrical contact with the interconnection
surface. Ni plating
has
proven effective, providing a
8
very thin Ni layer with intimate contact, to which
additional nickel bonds may be made.
Cell
part
Cathode
Electrolyte
Anode
Interconnection
Electrical
Role Resistivity
Thickness
Porous gas-difision
0.0
12
Qcm
2.2mm
electrode
for
oxygen
reduction
Fully dense
gas
10~cm 40p
barrier, passing
0'-
ions
only
Porous
gas-diffision
-48
x
10-
1oOMm
electrode
for
fuel *Q-m(Ni)
oxidation
Fully dense
gas
1 Qcm
lOOp
barrier, electrical
conduction only
at
1OOO"C
Bundle Construction
Cells, once made, must be arranged for efficient space
usage and convenient electrical contact. Multiple cells
are formed into three-by-eight (twenty-four cell)
bundles. Electrical connections are made by the
application of Ni felts to the NiNSZ anode and Ni-
plated IC. Electrically, three parallel path are
provided, and the voltage across any bundle is
increased by
8x
the cell voltage. (See Figure 2) Forty-
eight bundles are joined to form a complete power unit
such
as
the 1 lOkW atmospheric or 220kW pressurized
units, which both uses
1
152 cells.
Figure
2:
Actual
8x3
bundle of SOFC cells.
Another strong indicator of cell performance is voltage
versus time for a constant current density and fuel
utilization (expressed
as
a percentage).
This
is shown
in Figure 3. This graph indicates a very low
degradation rate of O.lo/dlOOOhr. At
this
rate, after
40,OOOhr
operation, the cell would be expected to have
lost only
4.0%
of its power, or about 6.3W.
These graphs represent the highly reliable prototype
developed.
MANUFACTURING/TECHNICAL
ADVANCEMENT
For commercialization of the technology, the cost of
the product must be lowered to a level of below
$2000/kW, of which cell costs must be less than
$300/kW.
In
the past,
SOFC
development and cell
construction
has
largely been performed by highly
labor-intensive processes. With the small number of
cells produced per year, material throughput was low,
resulting in high material costs for SOFC production
as
well. The combination of these two factors led to an
actual cell cost that was well beyond a marketable
value. This must change for commercialization.
Figure 3: Cell potential at 300mA/cm2, 83% FU
over 34,000 hrs. with
11
%
H20/89%H2
atmosphere.
Manufacturing Advancement
Figure
4
shows the past, current, and projected future
cost per cell. Table 3 describes the processing path to
achieve these goals. Three actions are primarily
required volume increase, automation, and vertical
integration of the manufacturing process.
The specialized ceramics required for
SOFC
operation
can be costly due to the purities required. However, by
negotiation of long-term contracts with large volume
requirements, significant price reduction (lO-SOo/o) can
immediately be achieved.
7-
.--A-L----
Figure 4: Actual and projected costs for a cell and
power system.
9
Labor intensive processes must be highly defined and
automated for quality control
as
well
as
cost reduction
purposes. By increasing volume while labor remains
constant or reduces, the labor costs per cell can be
dramatically reduced by
as
much
95%
if high volume
levels are reached.
Process
I
Past
Cells/var
I
1000
Cathode
Received tube
Interconnection
Received
powder
Plasma
sprayed
However, the largest cost savings will be obtained by
performing previously subcontracted processing in-
house. The first step in this movement up the value
chain can be seen in the progression of
air
electrode
processing. In the past, an outside vendor
was
contracted to deliver to SWPC a complete and
processable cathode support tube.
This
type of tube
cost approximately $1600/tube. Recently,
SWPC
has
brought in-house the ability to extrude and form the
cathode support tube starting with LaMn03 powder.
This ability has been primarily responsible for drop in
cost shown in Figure
5.
The next step, due to weight,
is the in-house production of the cathode powder,
as
is
shown in future processing (Table
3).
The cathode
represents 92wt% of the completed SOFC cell.
A
second major advantage to in-house production is
the ability to optimize the overall process due to
our
control over all the processing steps. Changes and
process improvements can be quickly implemented,
with careful control and monitoring of results,
allowing quality feedback not only within the
individual step but between steps at the facility. While
feedback with
an
outside vendor is possible, it
is
difficult to reach a communication level comparable to
that developed internally. The relative role of all these
cost-cutting methods are shown in Figure
5.
Current Future
10,Ooo
lO0,OOO
Receive powder Receive raw
Produce tube Produce powder
materials
Produce tube
Receive powder Make powder
Automated Automated
plasma
spray
plasma
spray
Mask
EVD
Remove mask
I
Efectrofyte
I
Received
I
Receivepowder
I
Makepowders
I
Mask
EVD Automated
Remove mask application
I
I
powder
I
I
I
Ni-plating
Plated single Plate small
cells batches
of
cells
Fully automated
plating system
volume
I
automation
25%
Figure
5:
Relative contributions
of
increased volume,
automation, and in-house process control.
om,po3msm,sn,an,wgn,sm,momosm,mowo
-
Figure
6:
Operating History
of
EDBELSAM
The role of manufacturing improvements
is
to achieve
a reliable product at acceptable cost through the use of
the tools of volume increases, automation, and in-
house processing.
SYSTEM
STATUS
Currently, SWPC
has
two generators in operation: the
220kW SCE pressurized SOFC/gas turbine
(PSFOFC/GT) unit and the lOOkW EDBELSAM
combined heat and power (CHP) atmospheric unit.
Figure
6
shows an operating graph for the
EDBELSAM unit over its lifetime.
10
EDB/ELSAM
100
kW
Delivered in 1997 to EDBELSAM (a Dutch/Danish
utility consortium) this unit has provided electricity
and district heating to a substation in Westervoort,
Netherlands. Through 2000, it was the largest
operating SOFC system, producing between 105-
1lOkW AC to the utility grid and 65kW to the hot
water district heating system with an average electrical
efficiency of 46%. There are
two
stages of operating
shown the in the graph, which
are
termed "Build 1"
and "Build 2."
Gas turbine AC power
System net AC power
Efficiencv (net AC/LHV)
Build
1
was the originally delivered unit, started in
November 1997. The unit operated unattended for
3700 hours at 42% efficiency. This
was
significantly
below the analytical predicted efficiency of 47%.
Temperature and localized voltage anomalies were
observed, and
air
leakage to the fuel side of the cell
was suspected due to measured fuel compositions at
the cell exit.
Due to these observations, the unit was
shut down for inspection and repair on June 26, 1998,
despite the fact that no degradation
of
the terminal
voltages was observed, except for a sulfur-poisoning
incident that was corrected by replacement of the
desulfurizing reagent.
47 kW
220 kW
57Y0
The unit was returned to Siemens Westinghouse Power
Corporation for evaluation.
It was determined that
there existed a failure of the baffle boards at the open
end of the cells. Since this allowed
air
leakage into the
fuel feed, the fuel side of the cell was partially
oxidized, especially
as
the cell was cooled.
Also, it
was noted that there was a partial loss of nickel contact
between some
of
the cell within bundles.
The unit was rebuilt with improved baffle boards and
cell bundles, and sent back for restart in March 1999.
Almost immediately, significant improvement was
observed, with efficiency increasing
from
42% for
Build 1 to 46% for Build 2, very close to theoretically
calculated efficiency predictions. DC efficiency is
actually about 53%, with the disparity between the two
due parasitic loss of system loads (7-8kW) and inverter
efficiency (92.5%).
On June 1, 2000, Build 2 reached one year operation
with
>99%
availability. Overall, the unit will reach
two complete years operation in November 2000.
SCE
220kW
A 220kW unit recently completed construction for
Southern California Edison (SCE).
This
unit utilized a
high
pressure SOFC (PSOFC) at the
bottoming
cycle
in combination with a microturbine generator (MTG)
from Northern Research and Engineering Corporation.
After completing lOOhrs successful operation at SWPC
in April 2000, it was shipped and installed at Irvine,
California.
The PSOFC operates at 3-atm pressure, with the
pressure provided by the compressor portion of the
MTG. With approximately 20% of the electrical
power provided by the MTG, the overall unit
efficiency will be approximately 57%.
shows operating parameters.
Table 4
Table
4:
0
eratin arameters
267am
s
0.610 V
187 kW
176 kW
Cell Current
CellVolta e
Pressure Ratio
SOFCDC ower
SOFC ossAC ower
CONCLUSION
Siemens Westinghouse Power Corporation has shown
technical viability of the SOFC in both a lOOkW
atmospheric and 220kW pressurized system in
combination with a microturbine generator. The
biggest hurdle currently facing commercialization of
this
technology is the development of an economically
acceptable system. Key to the lowering of capital
costs is the development of a low-cost cell production
process. The three major categories available for
lowering cell costs are increased volume, automation
of production system, and process control from raw
materials through finished product. Siemens expects
to reduce overall costs significantly through these three
areas, making possible the complete commercialization
of the SOFC power systems.
REFERENCES
Shackleford, J.F., Introduction to Materials
Science for Engineers. 2"d Ed.. Macmillian, New
York, 1988, p. 372.
Pal,
U.B.,
Solid
State
Zonics,
52
(1992) 227.
Isenberg, A.
O.,
Solid
State
Zonics,
3/4
(198 1) 43 1.
Hodgeman, C.D., Weast, R. C., Selby,
S.
M.,
Handbook of Chemistw and Physics: 42"d Ed.,
Chemical Rubber Company, Cleveland, 1960,
p.2242.
Primdahl,
S.,
and Mogensen, M.,
J.
Appl.
Electrochem.,
30
(2000) 247.
Steel, B. C. H.,
Solid
State
Zonics,
86-88
(1996)
1223.
I1