[Technology Report]
In Today's Military, More Than Just Fatigues Are Green
The world's mightiest fighting force also is a leading sponsor of environmentally friendly power systems.
Garbage is power. At least that's true for Jerry B. Warner, president of Defense Life Sciences, which is developing a trash-to-electricity generator. The fact that the company is working on a "green" energy technology isn't unusual. What's out of the ordinary is that Warner happens to be a retired U.S. Army colonel, and his prime customer is his former employer.
The U.S. military is investigating green technologies—particularly environmentally friendly power-generation systems. This interest in clean power isn't entirely altruistic, of course. Cutting-edge alternate energy technologies will help the military move troops and equipment faster and safer without relying solely on conventional power sources.
"In this instance, it's a case of where the military's needs dovetail very nicely with the development of alternate energy sources," says Warner.
Waste Not Warner describes his company's trash-to-electricity generator as a "tactical biorefinery." The system is designed to allow soldiers in the field to convert leftover food, paper, and plastic into usable power. Approximately the size of a moving van, the generator rumbles along with a unit as it moves from place to place.
At startup, the system runs on conventional diesel fuel. As it's fed leftover boxes and plastics, a gasifier heats the materials in a low-oxygen environment. Within an hour, the system begins generating energy in the form of low-grade propane gas and methane. Later, as food waste is poured in, a bioreactor uses industrial yeast to ferment the waste into ethanol, a "green" fuel. Both the gas and ethanol are combusted in a modified diesel engine that powers a generator to produce electricity.
"In about 24 hours, we drive the diesel fuel consumption down to the single digits," Warner says. In fact, Defense Life Sciences developed the system in association with Purdue University at the military's behest. "It was an Army-funded program where we were asked to solve two problems simultaneously," he says.
The first goal was to create energy from available resources during expeditionary operations, which are typically during a conflict's first six months. A secondary aim was finding an efficient way to destroy garbage, known in the military as a unit's "signature." This would effectively remove any potential clues leftover refuse might provide an enemy.
"We were shooting for a two-fer," Warner says.
A working prototype was delivered to the Army last December. Warner says the system can also be used for civilian applications. For example, it could be deployed in the aftermath of a hurricane or tornado or at any location where people are stranded without power. Emergency crews could then use the machine to turn debris like woodchips into much-needed electricity, Warner says. It could also provide supplementary power for factories, restaurants, or stores.
Triple Threat Another type of generator, being developed at the University of Florida in Gainesville, aims to provide an all-in-one power, water, and refrigeration source for moving troops (Fig. 1). The Army-funded supergenerator links a gas turbine power plant to a heat-operated refrigeration system. The refrigeration capability makes the gas turbine more efficient while also producing cool air and potable water. The turbine can run on conventional fossil fuels as well as biomass-produced fuels or hydrogen.
"It's actually a fairly common kind of refrigeration system, but when you put it together with a gas turbine engine you wind up with a system that you could think of simply as a more efficient gas turbine plant," says William E. Lear, director of the University of Florida's Energy and Gasdynamic Systems Laboratory. Unlike Defense Life Sciences' trash-to-electricity generator, which is the size of a moving van, the school's three-way system can be small enough to fit into a pickup truck's bed.
The system is designed to serve the needs of soldiers serving in desert environments, like Iraq, where power, cold air, and drinkable water are almost always in short supply. "[The military] would certainly like to be able to reduce how much water they have to transport to the front lines," Lear says. "It costs them just as much to transport water as it does fuel."
Lear points out that gas turbines are a common power generator used in everything from jet engines to power plants. The problem with traditional systems is that they lose efficiency both when not operated at full power and in warm temperatures. Seeking to ease this loss, Lear rerouted the path of gases passing through the turbine, cooling them via heat exchangers.
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