Alpha: Many people don't spend much time
thinking about global energy problems, at
least until they have to fill up their car's gas
tank or pay their monthly heating bill. That's
when the issue becomes personal. From an
industry perspective, what are the challenges?
Khaleel: The most visible industry that's
impacted is the automotive industry, which
faces two major challenges. The first is
environmental, regarding CO2 emissions
from vehicles. For every 1,000 pounds of vehicle weight, about 100 pounds of
CO2 are emitted over the vehicle's lifetime. The second is the issue of fuel consumption
and sufficient energy supplies. The industry
attempted to address energy efficiency
through a joint partnership between
industry and the U.S. government called
the Partnership for New Generation
Vehicles. Hybrid vehicles, in which an
internal combustion engine is supplemented
with batteries and other electrical supplies, are
actually an offshoot of that initiative.
That program made some, but not sufficient,
progress, so a new initiative called
FreedomCAR has been created. Its primary goal is freeing people from
dependence on foreign oil and pollutant
emissions. That initiative is targeted at
building next-generation vehicles powered
by hydrogen, with fuel cells as the main
drivetrain in these vehicles.
In all of these initiatives, the major driver is
fuel consumption. There is a big gap between
the amount of oil we in the U.S. produce
daily -- less than eight million barrels -- and
what we consume daily, which is on the order
of 16-20 million barrels a day. Sixty percent
of what we consume, we import, and it's only
increasing. By 2020 that gap will be growing,
and it'll be on the order of tens of millions of
barrels daily.
These issues -- fuel consumption and
environmental impact -- affect all industries. In the trucking industry, for example, the
majority of fuel consumption happens during
idling at truck stops. That takes about
100,000 miles off the life of the engine, and
a Canadian study showed that idling costs
about $60 CDN per day. Fuel cell technology
could be used for these 'auxiliary power needs'
when they're not being used to propel the
truck. There are initiatives by the major
trucking companies and some engine
manufacturers to develop what they call the
'More Electric Truck.' It still has an internal
combustion engine, but replaces belt-driven
systems with electrical components. By using
a fuel cell to provide the auxiliary electrical
needs, fuel consumption could be cut by
10%. That's huge. In addition, the trucks
would be driven at their maximum efficiency
because the engine would be operating at its
maximum efficiency, since all other needs are
driven by the fuel cells. Likewise, if you go
the route of the hydrogen-powered car with
fuel cells, there would be literally no
emissions. What comes out of the tailpipe
would be water.
In the aerospace industry, when you board
an airplane, they normally run a turbine to
provide air conditioning while on the ground. This is fairly fuel-intensive. Using fuel
cells for this auxiliary power supply would
consume only about 60% of the fuel that
a turbine consumes. NASA and Boeing are
pursuing fuel cells for auxiliary power needs
when the airplane is parked and also
during flight.
There are other industries outside automotive
and aerospace that suffer from energy
problems. Take, for instance, the crisis in the Northeast in the summer of 2003, when a
fuel fault in the system, along with a number
of mistakes, cascaded and resulted in a
widespread outage. One way to provide for a
more reliable system, and frankly, a more
secure system, would be to generate electricity
in a distributive manner using fuel cells.
Fuel cells also have benefits on an individual
level. Instead of using a heat pump in your
house, you could use a fuel cell to provide all
of the electrical needs for your house so you
don't have to draw anything off of the grid. When you're not home, the fuel cell is still
working, and you could sell electricity to the
grid. Banks and stores and so forth could do
the same thing. That's something I think is
fairly important.
The point is, we need to look for alternative
routes to meet our energy needs in each industry.
Alpha: What is it about the solid oxide fuel
cell that is so promising?
MK: There are several types of fuel cells --
proton exchange membrane, or PEM fuel
cells, molten carbonate, alkaline, solid oxide
fuel cells. Each one of them has certain
operating conditions, such as temperature
ranges and the type of fuel they will accept. The PEM fuel cell, which is the most likely candidate for propulsion of automobiles,
operates on hydrogen fuel. However, if other
species in the fuel stream mix with the
hydrogen, the fuel cell could be poisoned. You either have to have pure hydrogen
onboard the vehicle, or you have gasoline
and go through a reforming process. There
are issues with onboard reforming and many
of the automotive companies are not in favor
of it today.
Solid oxide fuel cells are high-temperature
fuel cells. They run at 700 degrees Celsius
while PEM fuel cells run at 120 degrees C. On the outside, the systems look the same
but the beauty of the solid oxide fuel cell is
that it's fuel-flexible. When you reform
gasoline you get hydrogen and carbon
monoxide and so on. CO2 can be used in the
solid oxide fuel cell. It will be converted to
hydrogen and utilized. Also, with solid oxide
fuel cells, you could do 'on-cell reforming'
where you have methane or hydrocarbon
fuel that a PEM fuel cell couldn't take,
but it comes into the solid oxide fuel cell
and gets reformed right on the cell itself. So it's very forgiving.
Alpha: It doesn't poison the fuel cell if there's
something else in the flow?
MK: That's correct. Another problem with
PEM fuel cells is water management. This
issue is nonexistent in solid oxide fuel cells. Both produce water, but with the PEM fuel
cell, a lot of the conductive properties of the
cell depend on the level of water. You have to
add water in the vapor in the PEM fuel cell
with hydrogen to make sure that the
membranes and so on continue to function,
while in the solid oxide fuel cells you don't
have to do that at all.
Alpha: In an industrial application, are
SOFCs used in stacks?
MK: A five-kilowatt fuel cell actually consists
of multiple cells that are stacked vertically.
The current state-of-the-art is what's called a
'flat plate design.'
Solid oxide fuel cells are not new.
Westinghouse has demonstrated them for
many years. The main issue is cost. To bring
the cost down, you need to have mass
customization. You need to look at modular
designs and high power-density fuel cells. The
high power-density fuel cells are flat plate
designs, so you take one and stack the next
one, the next one, the next one, and that's
how you get to five kilowatts.
Alpha: What are the challenges in designing
and testing a fuel cell?
MK: There are many. The first challenge is
in the materials. The whole idea is to come
up with a ceramic cell material that provides
the highest power density and is very stable. Then the cells have to be sealed. There is a
rigid seal made from glass, so we consider its
stability and other characteristics to be sure it
is durable, won't crack, and so on. There are
also flexible seals made of mica. The leak rate
out of these has to be acceptable and they
need to accommodate air between the bulk
of the cell, which is metal, and the cell, which
is ceramic. The thermal mismatch between
the cell and the metal causes the materials
to impart stresses on one another, so the right
accommodation of air is needed. In addition,
these materials operate at very high
temperatures, so material will migrate and
move from one spot to the other. We want
to make sure that they don't move from a
favorable spot to an unfavorable spot. We
also want to reduce the use of noble metal
in these fuel cells.
Thermal management is a critical issue. Because there are electrochemical reactions
happening within the cell, heat is generated
and must be dissipated in order to avoid hot
spots and so on. We don't want some cells
with very low electrochemical activities and
others with very high electrochemical activities.
Finally, manufacturing cost is a significant
concern. We need lowest-cost manufacturing
techniques while maintaining quality to make
sure that the fuel cell operates as it is designed
to do. Getting fuel cells to the right cost level
is actually in favor of solid oxide fuel cells. We're able to use more commodity materials,
much cheaper materials, that I believe will get
us there. Much of this progress is due to the
SECA program.
Alpha: What is SECA?
MK: SECA is the Solid State Energy
Convergence Alliance, a program initiated
in 1999 by the U.S. Department of Energy
(DOE) Office of Fossil Energy. The goal is
to develop an environmentally friendly,
commercially cost-effective, and reliable
solid oxide fuel cell for a wide range of
applications. The DOE's National Energy
Technology Laboratory (NETL) and PNNL
are responsible for program development.
SECA has two major components -- industrial
teams and a core technology program. There
are six industrial teams, each led by one
company and drawing its membership from
other companies, universities, national labs,
and such. Teams are led by Siemens
Westinghouse, Cummins Power, Delphi
Automotive, Acumentrics, Fuel Cell Energy,
and GE Power Systems.
PNNL runs the core technology program,
which has six teams dealing with materials,
manufacturing, fuel reforming and
processing, power electronics, controls and
diagnostics, and modeling and simulation. I'm the national coordinator for the modeling
and simulation team, along with Travis
Schultz from NETL. In the core technology
program, we look for the next technological
challenges and what we need to do to
overcome them. We engage universities,
national labs, industries, small business,
whoever can help with these activities.
SECA is a goal-driven alliance, which is
extremely important for its success. I honestly
believe this approach -- working toward
established goals in an integrated fashion
-- will make a big difference.
Alpha: So what are the drivers behind
modeling and simulation in fuel cell development?
MK: First of all, we're trying to get rid of
trial-and-error procedures. We want to guide
development activities, manufacturing, the
material development itself. When we
consider modeling and simulation, we group
its use into three activities. The first is
material design -- looking at the qualities of
nickel, ceramic, how porous a material is,
what will provide the best behavior.
The second is stack design. There are many
issues associated with trying to optimize flow
design, finding the best flow possible to
remove unneeded heat so there are no hot
spots. But at the same time, we want to
maximize electrochemical activities so we get
the highest power density possible in these
fuel cells. Above all, we want to make sure
stresses don't build up and lead to the cell
breaking down. We also need to understand
how potential degradation mechanisms --
thermal fatigue, degradation of the interfaces,
material creep -- can be avoided.
The third activity is using modeling and
simulation broadly to set requirements for the
different components. There is the exterior
system, the stack, the heat exchanges, the
reformers and so on, and we need to
understand the interactions between these
subcomponents. What is the stack required
to do? What is the flow rate, what will be the
concentration of the different species in the
fuel, what should the temperature of the
incoming air be, things like this. Those are
system-level modeling activities, and require
understanding not just the fuel cell, but the
reformer, and so on. We want to optimize not
just the performance in terms of output, but
also the life of these systems. We don't want
a cell with extremely high performance but
a very short life.
The finite element [FE] framework really
fits the physics we need to study at the stack
level. What we're trying to do is model the
flow, which in these systems is laminar flow. There is no turbulence, and FE works
beautifully there. Another area is the heat
associated with electrochemical activities. Again, that fits in the FE framework, and
the electrochemistry itself can be handled
with user-defined functions or routines. After that we can calculate the stresses using
just the normal things that we do in the finite
element framework.
So for design purposes, a finite element
framework is a very flexible framework where
you can make design changes and see the
impact of these design changes on
performance and safety.
Alpha: How has the use of simulation
impacted fuel cell design?
MK: Well, for example, we ran simulations
on three different designs: cross-flow, in
which the fuel is going in one direction on
top of the cell, and the air is crossing under it.
In a co-flow design, the fuel is going one way
and the air under the cell is going the same
way. In counter-flow, the fuel is going one
way and the air is going the other. The
industry has been using cross-flow, but
based on the simulation results, we found
that the co-flow design provides the lowest
temperature gradient and the lowest
distressors. The co-flow design also gives
the highest power density possible. We
wouldn't have been able to discover this
experimentally. It's very difficult to see
what's inside the stack. Through
simulation we were able to do that.
Alpha: The primary Virtual Product
Development tool you use is MSC.Marc. How did you first use it?
MK: We first started using MSC.Marc in
1992 to look at a new class of metal forming,
a superplastic forming of aluminum. It
suffered from what we call low forming times,
and by combining MSC.Marc and certain
internal tools that PNNL built for understanding
material behavior, we were able to
come up with ways to make sure that the
forming time was reduced by more than an
order of magnitude, which made that process
suitable for low-volume automotive
production. We enhanced our materials,
came up with new sets of materials, and
ultimately GM adopted the technology,
calling it quick forming.
Alpha: What led you to use MSC.Marc
in fuel cell development?
MK: MSC.Marc is a multi-physics tool with
capabilities for flow, heat, mechanical stress,
and electrical modeling. By adding
electrochemistry capabilities and certain
enhancements to the existing flow
simulations, MSC.Marc becomes a very
powerful tool for us. In addition, the open
structure of MSC.Marc allows customization -- databases, user routines, and so on.
We've been working with MSC.Software to
design a graphical user interface [GUI] with
all the 'smart' in it, so we know the range of
parameters for different materials in terms of
thicknesses and dimensions and so on. We
also put in the right constrictive equations,
material relations based on extremely
thorough experimental studies done at
PNNL. One can easily extrude complex
designs that normally take engineers days to
build. The customized GUI allows you to
build the design or import it from any of the
major CAD systems, and the GUI is smart
enough to recognize the different material
sets. It allows all types of analysis, from flow,
thermal, and electrochemical to mechanical.
The next step is to look at the life of
the stack. Certain degradation will happen,
and MSC.Marc has capabilities to deal
with material creep. We are also about to
add capabilities to look at degradational
interfaces in terms of resistances so we can
enable long life.
Our goal is to use this customized MSC.Marc
tool to minimize degradation -- not just
predict it, but minimize it, remedy it. But
to come up with remedies you need to
understand the root cause of why things
happen, where they happen, when they
happen. This enhanced MSC.Marc package
does that. It gives us viable designs very
quickly. We know that a design works and
how to make a fuel cell last for a long time.
Alpha: How was this done before
simulation tools?
MK: Only in an ad hoc fashion. There wasn't
an integrated set of tools to look at it. You
addressed one part of the problem with this
tool, one part of the problem with that tool,
and so on. To make the discoveries we seek,
you really need all of these tools together.
Alpha: So will the work that PNNL and
MSC.Software are doing with MSC.Marc,
building the electrochemistry routines into
the customized GUI, be provided to SECA's
industrial teams?
MK: Yes. We work with many software
vendors, and our assessment was that
MSC.Marc is the best tool for these
multi-physics activities. We embarked on
our relationship with MSC.Software in order
to build this tool, and to make it available to
all of the industrial teams to accelerate development.
Alpha: Obviously modeling and simulation
within scientific research and development
offers many advantages. In your experience,
how quickly is it being adopted? What
cultural issues does this new technology raise?
MK: I believe scientific discovery is enabled
by three main pillars -- experimentation,
theory, and computing. Many discoveries in
the scientific arena are enabled by this
integrated approach, and I believe there will
be even more recognition of modeling and
simulation as we go forward.
I honestly believe there is still a culture where
the experimentalists work by themselves, and
the computing people work by themselves,
but certain institutions are trying to change
that culture. At PNNL, we talk about 'system'
science, which means integrating multiple
scientific fields -- chemistry, biology -- within
that integrated approach of theory,
experiments, and computing. And computing
is really the underpinning of a lot of this. Today we're bringing the experimentalists and
the modeling people together. There's a need
for a cultural change.
Simulating three different flow designs led to the unexpected discovery that a co-flow design (center) provided the
lowest temperature gradient and the highest power density.
On the Web:
www.pnl.gov
www.seca.doe.gov
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