Transcript Fuel Cells From Corn Fields

Fuel Tanks From Corn Fields
Activated carbons used for natural gas storage
Lacy Hardcastle, Peter Pfeifer, Ph.D
Department of Physics, University of Missouri-Columbia
Introduction
(above) This is
the test truck
used by the
Midwest
Research Institute
and is filled with
carbon produced
by the University
of Missouri.
(right) Here is a
closer look at a
fuel tank, which
contains carbon
briquettes. This
tank is identical to
ours except in
shape.
Alternative energy sources are a high priority for our oil dependent economy and fuels
such as bio diesel and hydrogen are still a long way from developing
into a viable technology. However, there are already commercial
vehicles running on natural gas, which is composed mainly of
methane and burns much more cleanly than fossil fuels. Also, by
itself, methane is a greenhouse gas, but is broken down by burning
into less harmful chemicals like carbon dioxide and water. One
drawback of natural gas is that unlike gasoline and diesel fuels, it is
indeed a vapor, and and must currently be stored at very high
pressures (usually around 3600 psi) in order to maintain a useful fuel
supply. These bulky high pressure tanks take up a lot of storage
space which makes them undesirable for private use. However, the
technology under development by the University of Missouri and its
partner institutions would allow the natural gas to be stored at a much
lower pressure of 500 psi (pounds per square inch), enabling natural
gas tanks to be shaped much like our current gas tanks. Another
advantage of the lower pressure is that this is the pressure at which
methane is transferred through pipe lines, so the cost of further
compressing the gas (for higher pressure tanks) is eliminated.
Another exciting aspect of this technology is that we are also doing
research to enable it to store hydrogen as well, making it a versatile
solution to energy storage issues.
(left) This is the test fixture which is used for taking preliminary uptake measurements on the carbon briquettes we
produce. If a briquette performs well, it is sent to the physics department for further analysis. (right) Here are the
initial and final products in the carbon making process. The ground corncobs are carbonized, ground into a fine
powder, and then combined with a binding agent before they are pressed into hockey puck shaped briquettes.
Carbon Production
The first step in producing our activated carbons is to take
ground corn cobs and soak them in phosphoric acid which has
been diluted by 50% with water. Then this mixture is placed in an
oven where it is baked at a low temperature for several hours in
order to begin the carbonization process. Then the carbon is
allowed to cool and is baked a second time at a much higher
temperature. During this second step, nitrogen gas is pumped
into the mixture in order to keep the carbon from catching on fire.
Once the carbon cools again, the phosphoric acid is rinsed out
and the carbon is placed in another low temp oven, this time to
dry. After drying, the carbon is ground into a very fine powder
and then a binder is added so that the carbon can be
compressed into a briquette, much like charcoal. The amount of
binder used is very important because it affects the density of the
carbon, which is a measure of how much empty space there is in
the interior of the carbon. These briquettes are now ready for
either testing or to be installed in the test vehicle which is in
Kansas City.
After the production process the carbon is first tested the
chemical engineering lab (where the carbon is initially produced).
Carbons which show high storage levels are then brought to the
physics department for further testing.
The picture in the background is a microscopic image of the carbon
which we produce. Note how the carbon is full of
pores. This is for the natural gas storage. The
outermost pores must be slightly larger than the
inner ones in order to aid the penetration of natural
gas to the interior of the carbon. Our goal is to
produce the most ideal pore structure for the
storage of natural gas and eventually hydrogen.
When storing hydrogen a little bit of boron is added
to the carbon in order to enhance the attractive force
between the carbon and the hydrogen atoms.
Facts About Natural Gas Technology
Natural Gas storage Capacity
250
208
200
NG capacity in V/V
(top) The natural gas molecules (blue) while in
a carbon nanopore. Note how they are close
together and lie in an orderly fashion. This is
because they have less energy with which to
move because of the attractive force of the
nearby carbon atoms. This is due to the strong
molecular force.
(bottom) The natural gas molecules in an
empty tank. They fly about in a random
disorderly fashion, thus taking up lots of space.
85% of the natural gas in the us is domestic-the methane hydrate fields off of
the Oregon coast alone could supply US energy needs for over 100 years.
Replacing gasoline and diesel as fuels would save the United States over
$300 billion dollars per year, which averages to $4,000 dollars per year for
each family.
On an energy equivalent basis, natural gas is cheaper than gasoline and
diesel fuel. In June 2006, the cost of compressed natural gas was 94 cents
cheaper than the average cost of gasoline.
In light-duty, or private, applications air emissions from natural gas vehicles
are lower than emissions from gasoline-powered vehicles. Carbon monoxide
and nitrogen oxides, smog-producing gases, are reduced by more than 90
percent and 60 percent, respectively. Carbon dioxide, a greenhouse gas, is
reduced by 30 to 40 percent.
180
180
142
150
100
50
0
ALL-CRAFT
AGLARG
DOE standard
CNG @3000psi
Here is a graph demonstrating
how well our carbons perform
compared to the Department of
Energy’s standard. Compressed
natural gas cylinders can store
208 volumes of methane gas per
volume of carbon (in other words,
you can fit 208 tanks worth of
methane at 1 psi (pressure per
square inch) into one tank at
3,000 psi) As you can see, our
current best carbon has already
met the DOE’s standard of
performance; we are continuing to
produce carbons in the hope of
obtaining more and more efficient
fuel tanks.