One of the biggest logistical problems the U.S. Army has to contend with is garbage, according to James Valdes, scientific adviser for biotechnology for the U.S. Army Research, Development and Engineering Command (RDECOM). Typically, local contractors are hired to come on base and haul trash away, which causes a security risk and requires military personnel to follow them around to ensure base safety. In some cases, the trash is burned in large incinerators, which use a considerable amount of fuel. Fortunately, a mobile biorefinery unit has been developed that can transform the waste into fuel for stoves and generators and help the U.S. Army get rid of the garbage safely and efficiently.

The tactical garbage-to-energy refinery (TGER, pronounced tiger) was developed jointly by RDECOM, Defense Life Sciences LLC of McLean, Va., and a team of Purdue University researchers.

Purdue scientists were intimately involved in the inception, design and fabrication of TGER, says Jerry Warner, founder of Defense Life Sciences. “In particular, Purdue supported the biological aspects of the system addressing the biocatalysts, bioreactor and systems integration with other elements.” The university conducted the majority of the basic and applied science with the development of the materials and energy balance modeling, which supported the design and fabrication, he says.

Nathan Mosier, Purdue professor of agricultural and biological engineering, says the original prototype was built in late 2006. “We tested it and made a number of design improvements—some upgrades to the initial prototype—and then did some more testing in fall of 2007,” he says. Based on additional improvements and lessons learned, the second prototype was built in March during a two-week period, and has been undergoing testing since the TGER was transported to Camp Victory in Baghdad, Iraq, in May.

Invention Anatomy
Though much of the engineering and research was performed at Purdue, a number of other companies were involved in the development process of TGER. Bowen Engineering Co. of Indianapolis supplied engineering and much of the equipment assembly for TGER, and Community Power Corp. of Littleton, Colo., provided the gasifier.

The mobile TGER, often described as the size of a small moving van, can handle nearly a ton of garbage daily and effectively run a 60 kilowatt (kW) generator. Valdes hopes as improvements continue, the output can be doubled.

The TGER system is a hybrid design that uses thermal gasification to produce synthetic gas, or syngas, from paper, ammunition wrappers, Styrofoam and plastic garbage, and a fermentation process to produce ethanol from a mixed waste stream of food slop and juice waste. Valdes says the troops consume a lot of high sugar and carbohydrate drinks and foods.

TGER takes six hours to reach full power, Valdes says. During that time, it runs on diesel. As it is brought to full power it uses less diesel fuel, until it is down to 5 percent—from 5 gallons hourly to 1 gallon. The other 95 percent of the energy it produces comes from the waste.

At a bloggers round table in June, Valdes described the wet waste as being “washed off,” and then taken into a tank where yeast and enzymes are added. “The other waste gets ground up, then pelletized into little fuel pellets that are about an inch long and quarter-of-an-inch thick. Those pellets then go into the down-draft gasifier and are heated up and broken down.”

“The syngas produced is similar to low-grade propane and is blended with the ethanol, then aspirated into a 60 kilowatt generator, which produces the electrical power,” Valdes says. “The power is then used directly or is put into a power micro-grid.” TGER’s design has two main advantages over unitary designs that use only gasification. “The system can convert a broader range of wastes into energy—gasification doesn’t do well with liquid wastes, whereas fermentation loves them—and the ethanol, which is 15 percent water, adds power and reduces engine knock, allowing the generator to run at full power,” Valdes says. With only syngas, the TGER runs at approximately 75 percent power, and will top out at 40 kW and overheat. “The ethanol adds a lot of power,” he says. “It’s also got water. It cools it down. So as it worked out, this blend of the syngas with the hydrous ethanol is a really nice fuel for generators.”

To test the TGER in extreme weather conditions it was sent to Iraq, where temperatures can swell to well-over 100 degrees Fahrenheit. The gasifier, distillation column and tanks have sensors that collect data and show how effectively TGER is operating. This data will be used to make further improvements to the system.

Surprisingly, the top three consumers of fuel in the U.S. Army are stoves, generators and the trucks that carry the fuel, not tanks and helicopters. “If you look at fuel, about 50 percent is used to transport more fuel,” Valdes says. “That’s a big waste right there.” Unlike tanks and helicopters, which require high-quality fuel, stoves and generators will be the primary consumers of the fuel produced by TGER.

	1   2	Next Page -->
View Entire Article