Saving on fuel isn't a question of conservation for the military. It's about saving lives.
The U.S. Army is testing two prototype generators in Iraq that run on garbage, rather than diesel fuel.
The Tactical Garbage to Energy Refinery (TGER, pronounced "tiger"), was co-developed with Purdue University and deployed in May at Victory Base camp in Baghdad, where it will be tested until August.
The purpose of the unit is to cut down on the amount of diesel fuel used and to cut down on the amount of garbage that camps generate, which are both security risks.
"Those convoys that carry fuel are also known as targets," said James Valdes, scientific adviser for biotechnology at the U.S. Army Research, Development & Engineering Command. "Officers say 'We don't calculate the cost of fuel in dollars, we calculate it in blood.'"
Handling garbage is a logistical challenge, too, because the Army hires contractors who need to be followed.
Right now, the Army's trash goes up in smoke by burning it. The problem with incinerators, though, is that they require a lot of energy to run and many people to operate it.
TGER uses a variety of technologies to fuel a standard 60-kilowatt electrical generator.
People put trash into a chute and then the wet waste--like food slop--is separated from the rest. The cardboard, plastic, and other dry trash are crushed and pelletized.
Those pellets are then put into a gasifier, which heats them until they turn into synthetic gas--fuel for the generator.
Developers found that the relatively low-grade fuel from the trash over-heated the generators and maxed output at about 40 kilowatts.
So it created a system to convert the sugar-rich wet wastes (apparently, U.S. soldiers drink a good amount of Kool-Aid) into a form of ethanol. The wet waste is treated with enzymes and then fermented into hydrous ethanol--a mix of 85 percent pure ethanol and water, Valdes explained.
That ethanol is blended in with the synthetic gas, which boosts the generator's output to 55 kilowatts.
Starting up the contraption takes 6 hours and still requires 5 percent of the diesel the generator usually uses, or about 1 gallon per hour.
Compared to an incinerator, TGER is far more efficient at converting garbage to usable energy, said Valdes, who also said it runs at 90 percent efficiency. And it significantly cuts down on the amount of garbage that needs to be trucked around.
"Ultimately, what we would like to do is have a clean-sheet design so that you could automate it more. So you literally put trash in one end and electricity comes out the other," Valdes said.
If the TGER units work well in the harsh Baghdad conditions, he envisions the generator will be deployed in smaller camps, where the higher percentage of food waste can improve efficiency.
Valdes said the portable generator could also be used in disaster-relief situations where there is a lot of trash and the need for generators. The U.S. Navy has shown interest in the unit as well.
Trash, as it turns out, is an attractive feedstock. There are several commercial companies developing technologies that use wastes as fuel.
Cellulosic ethanol companies convert agricultural or forestry residues into ethanol, while portable generators use similar feedstock, such as wood chips, to make electricity.
A number of companies are also trying to convert municipal solid waste into ethanol using a range of processes.