Cows, as many people know, have four
stomachs. Cows also generate lots of methane.
So, if your goal is to describe a machine that turns food waste and
cardboard into methane gas, the bovine digestive system is an analogy that
makes some sense.
“Our reactor is some ways a two-stomach
cow,” says Jorge Gonzalez-Estrella, a post-doctoral research associate in the
Chemical and Biological Engineering Department at Mines.
Gonzalez-Estrella is one of the researchers
working on the Gas Cube project. The
semi-trailer-sized reactor is much larger than a cow, but it’s still portable. It’s
one of the projects in development at Mines aimed at turning a range of remote
base waste into energy. This is all thanks to a $4.8 million grant from the
United States Air Force, $1.2 million of which funds the Gas Cube. A remote Air Force Base can produce lots of
waste. The Air Force seeks to save waste handling and fuel costs at
mission-based remote bases. This is a challenge that the Gas Cube is designed
to overcome.
How does it work? Back to the cow analogy. At the Gas Cube’s input,
or mouth, a shredder grinds up the solid cardboard or food waste and deposits it
in chamber number one. This is sort of like a cow chewing and swallowing its
food. Then in that first chamber, or stomach number one, hydrolytic microorganisms break down the mix of
food waste and cardboard into sugars, and fermenting microbes then break up
those sugars into smaller parts called volatile fatty acids. Next, in a
vertical chamber or second stomach, methanogenic microbes turn the volatile fatty
acids into methane gas. Then in a separate
chamber any leftover solids are given more time to react and give off any
remaining methane. The gas generated in this reactor can be piped out to run
generators or other equipment needed to power a remote base. “This process is
well established, it very solid and robust,” says Gonzalez-Estrella.
One challenge in this research is
making this reactor portable. Jim Schultze (ChE 81) is helping construct the
gas cube, “Usually these things take up acres if they’re industrial, we put it
in a twenty-by-eight-foot space,” he says. The Gas Cube can be carried on a
truck bed, and multiple units can be added together as a remote operation
grows.
Another challenge in this project it is
making it user-friendly. “It’s going to
be transported to remote places, and it needs to be easy to run for the operator,”
says Gonzalez-Estrella.
Besides being portable and user
friendly, researchers must also provide proof of concept. Caitlin Asato, a research scientist and
engineer in the Department of Chemical and Biological Engineering at Mines, is
helping bring the Gas Cube from the bench scale up to the working prototype.
This is no small task. “The nature of
scaling up these kind of chemical and biological systems is an imperfect
science or engineering exercise,” says Patrick Gilcrease, Ph.D., a professor in
the Department of Chemical and Biological Engineering and the principal investigator for the
project.
Gilcrease adds that another unique
aspect of this project is the interdisciplinary nature, it includes researchers
with expertise in agricultural engineering, chemical engineering and
civil/environmental engineering.
Gilcrease says this diversity brings strength to this team, “A nice
learning aspect of this project for me has been being able to see how different
disciplines approach the same problem, and the unique advantages of the
different approaches we’re bringing to the project,” says Gilcrease.
Like many technologies initially developed
for the military, the Gas Cube may have wider applications. The reactor could
be deployed to disaster areas or refugee camps, and put into use when waste-handling
infrastructure is down. The reactor could also be used for waste generated by
agricultural operations. “Microbreweries are often located inside
municipalities, and they often can’t dump their wastewater into sewer systems,
so they’re looking for ways to treat their wastewater,” says Dave Litzen (ChE
81) president of Litzen Process Consulting, Inc. who is helping build and test
the working prototype. “But, I can’t
think of a better first customer to have than the Air Force,” he adds.
The Gas Cube
team is currently undertaking the first testing phase on the prototype. If
these tests are successful, the team plans to build a second lighter and more
nimble prototype.