Portable refinery efficiently generates electricity from trash
19 February 2007
A portable refinery developed by researchers at Purdue University
efficiently converts food, paper and plastic trash into electricity,
producing 90% more energy than it consumes.
The machine, originally designed for the US military to allow soldiers in
the field to convert waste into power, could have widespread civilian
applications said Michael Ladisch, professor of agricultural and biological
engineering at Purdue University who leads the project. This, of course,
could include hospitals, which are large producers of waste.
The "tactical biorefinery" processes several kinds of waste at once,
which it converts into fuel via two parallel processes. The system then
burns the different fuels in a diesel engine to power a generator. Ladisch
said the machine's ability to burn multiple fuels at once, along with its
mobility, make it unique.
Roughly the size a small moving van, the biorefinery could alleviate the
expense and potential danger associated with transporting waste and fuel.
Also, by eliminating garbage remnants — known in the military as a unit's
"signature" — it could protect the unit's security by destroying clues that
such refuse could provide to enemies.
Purdue professor Nathan Mosier works with the tactical
(Purdue Agricultural Communication photo/Tom Campbell)
Researchers tested the first tactical biorefinery prototype in November
and found that it produced approximately 90% more energy than it consumed,
said Jerry Warner, founder of Defense Life Sciences LLC, a private company
working with Purdue researchers on the project. He said the results were
better than expected.
The US Army subsequently commissioned the biorefinery upon completion of
a functional prototype, and the machine is being considered for future Army
The tactical biorefinery first separates organic food material from
residual trash, such as paper, plastic, Styrofoam and cardboard. The food
waste goes to a bioreactor where industrial yeast ferments it into ethanol,
a "green" fuel. Residual materials go to a gasifier where they are heated
under low-oxygen conditions and eventually become low-grade propane gas and
methane. The gas and ethanol are then combusted in a modified diesel engine
that powers a generator to produce electricity.
Ladisch and Warner said the machine eventually could be deployed in
disaster situations, similar to Hurricane Katrina, or at any crisis location
where people are stranded without power. Emergency crews could then use the
machine to turn debris such as woodchips into much-needed electricity,
The refinery also could provide supplementary power for factories,
restaurants or stores, Ladisch said.
"At any place with a fair amount of food and scrap waste the biorefinery
could help reduce electricity costs, and you might even be able to produce
some surplus energy to put back on the electrical grid," he said.
Much of the fuel the system combusts is carbon-neutral, said Nathan
Mosier, a Purdue professor of agricultural and biological engineering
involved in the project. Carbon-neutral fuels like ethanol do not cause an
appreciable net increase in atmospheric levels of the greenhouse gas carbon
dioxide. This is because the fuel releases carbon that has only recently
been taken up by plants during photosynthesis, the process by which plants
convert carbon dioxide to oxygen and sugars. The same is not true for
petroleum, in which the carbon contents were removed from the atmosphere
millions of years ago.
The biorefinery generator initially runs on diesel oil for several hours
until the gasifier and the bioreactor begin to produce fuel, Warner said. In
the initial commissioning test, researchers measured the amount of diesel
oil burned and electricity produced to calculate its efficiency.
The machine produces a very small amount of its own waste, Warner said,
mostly in the form of ash that the Environmental Protection Agency has
designated as "benign," or non-hazardous. Any leftover materials from the
bioreactor are put into the gasifier, which has to be emptied every two to
three days. "It's about enough to fill a regular sized trash bag, and it
represents about a 30-to-1 volume reduction," Warner said.
Other companies collaborated in this project, including Bowen Engineering
of Indianapolis, Huston Electric of Lafayette, Ind., and Community Power
Corp. of Littleton, Colo.