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.
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.
S.A. Sherif, a University of Florida mechanical engineering professor and an expert in refrigeration, then tied the system to absorption units, which further cooled the gases. Users can either tap all the cooling power to obtain peak efficiency for the turbine or divert some energy for refrigeration or air conditioning.
Lear says his experiments and computer models suggest that with all the cooling directed to the turbine, it will be 5% to 8% more efficient than traditional turbines. With some cooling siphoned for other purposes, the system can still be 3% to 5% more efficient than conventional turbines. Additionally, compared with traditional gas turbines, the system maintains its efficiency whether operated at peak or partial power.
A few percentage points might not seem like very much. But it makes a spectacular difference when fuel is scarce or expensive, particularly if refrigeration and water are added bonuses. "Power companies would kill for a 1% gain," Lear says.
The system, which makes water by condensing the turbine's combustion gases, can produce about one gallon of water for every gallon of fuel burned. The water would need to be treated to be potable. Untreated, however, it could still be used for cleaning or other purposes. Because the system reuses gases so efficiently, it also has a very low pollution output.
Lear says further research is needed to make the plant more compact and to enhance its performance. He notes that larger, more powerful versions could be used in fixed locations as part of the standard power grid. Power utilities, for instance, could build the plant close to a grocery store warehouse that requires both electricity and cooling.Electric Navy
Like most of the world, the U.S. Navy is very interested in developing electric vehicles. Currently dependent on diesel fuel and nuclear energy to power its fleet, the Navy is looking forward to the day when it will be able to run at least some of its vessels off of batteries. To test the concept, the Navy has awarded Altairnano, a ceramic nanomaterial developer and manufacturer, a contract to develop a ship-mountable 1-MW power station.
"The ship would still be powered by diesel fuel and generators, but the Altairnano battery would act as the backup," says Alan Gotcher, Altairnano's president and CEO.
Altairnano's battery approach represents a new and safer take on lithium-ion technology. Since their development, lithium batteries have been considered too unstable and volatile for use in vehicles. The problem is that lithium batteries can explode: the bigger the battery, the bigger the potential explosion.
Gotcher says his company's NanoSafe battery eliminates lithium ion's explosive nature by forming the anode, the part that discharges electrons, out of lithium-titanate spinels (Fig. 2). These particles comprise two lithium atoms, three oxygen atoms, and a titanium atom. Conventional anodes are based on graphite. Graphite flakes can come loose and react with the electrolyte, the liquid carrying the lithium particles, and start a thermal runaway reaction. Altairnano's anode, however, is inert.
"It won't interact with the electrolyte," Gotcher says. "We haven't had a single failure of a cell in any safety tests, and that includes putting a nail through the cell and overcharging it."
Beyond Navy ships, Altairnano's technology promises to help pave the way for clean-running, better-performing electric cars, trucks, and buses. Gotcher says it's possible to power a full-sized five-passenger SUV with a NanoSafe battery (Fig. 3).
"It's very fast, meaning \[the vehicle\] can go from a standing start to 60 miles per hour in eight seconds," Gotcher says. "It has a range of 135 miles, and you can connect it to a rapid-charge station and completely recharge the battery pack in less than 10 minutes." The battery can also operate over a wide temperature range, Gotcher notes.
"To our knowledge, we're the only company anywhere in the world who has titanate spinels being used in batteries," Gotcher says (Fig. 4). "People are stunned at how quickly these batteries can be charged."
Gotcher believes it's inevitable that the military will increase its sponsorship of green research simply because so many eco-friendly technologies have definable tactical and operational benefits.
"The military has its energy needs, and businesses and consumers have theirs," Gotcher says. "It's great when these interests can meet in the area of green technology."