07 December 2012
U.S. Military scientists have made revisions to a prototype mobile waste gasification system which can produce power and fuel, the Tactical Garbage to Energy Refinery (TGER).
Developed by the U.S. Army Edgewood Chemical Biological Center (ECBC), the first two systems were initially deployed for 90 days at Camp Victory in Baghdad back in 2008.
The army said that the deployable machine tactically designed to convert military field waste into immediate usable energy for forward operating bases.
The biorefinery system is a trailer-mounted hybrid technology which the army said said support a 550 person unit generates around 2500 pounds (1130 kg) of waste per day, and converts paper, plastic, packaging and food waste into electricity via a standard 60 kW diesel generator.
"We picked a forward operating base in Iraq because we wanted to really stress the system," explained Dr. James Valdes, a senior technologist at the U.S. Army ECBC.
"All other energy systems had been tested in laboratories or under ideal conditions and temperature climates. What we really wanted to do was stress it with heat, sand and real world trash in a low infrastructure environment," continued Valdes.
"We learned an awful lot over there about what works, what doesn't work and what'll break," he added.
As ECBC project director for TGER, Valdes is responsible for leading a team which has implemented the necessary re-engineering of the new prototype, TGER 2.0.
Among the modifications is an automated interface which uses a touch-screen panel, to make it easier for operators to input information and monitor every part of the machine, from oxygen levels in the gasifier-to-ethanol production and power output.
According to the ECBC while the machine used to take three technicians to operate it now takes two - one to feed the waste and another to monitor the progress.
But Valdes hopes that as the prototypes advance, TGER could eventually be used by one technician or Soldier.
The ECBC said that one of the most valuable lessons it learned while the TGER was deployed in Iraq was the realisation that the downdraft gasifier had a tendency to get clogged if there was too much plastic in the fuel pellets. Additionally, a large%age of the synthetic gas was inert and could not be used as viable fuel.
To fix the problem, Valdes' team developed a horizontal gasifier with an auger device that rotates the waste, eliminating the mechanical step of pelletising the trash. The TGER 2.0 prototype also enables steam to be injected into the gasifier, which allows a larger conversion of output gas to become energetic.
According to Valdes, the old system produced 155 BTUs (British Thermal Unit)/cubic foot of gas, whereas the new TGER 2.0 prototype produces 550, more than tripling the amount of usable energy.
The ECBC also claimed that the new TGER 2.0 is environmentally friendly with its zero-carbon footprint.
"We think of garbage in terms of volume, not weight. There are things that take up a lot of space in landfills but they don't weigh much, like Styrofoam," explained Valdes.
"TGER reduces the volume of waste in 30 to one ratio. If you start off with 30 cubic yards of trash, you end up with one cubic yard of ash, and that ash has been tested by the Environmental Protection Agency. They call it a benign soil additive. You could actually throw it on your roses," he added.
The advanced prototype was shipped back to the manufacturer for modifications after undergoing a final field trial in September where the technology was tested to see how long it could run at the highest levels of garbage input before breaking down.
According to the ECBC, within two hours of powering on, TGER 2.0 can make synthetic gas which enables a generator to be run on about 75% power. Within 12 hours, alcohol is produced and blended with the synthetic gas to run on full power at a steady state if the machine is continually fed.
One of the innovations Valdes said he would like to capitalise on is recapturing the excess heat that the machine produces with a heat exchanger that can apply the energy to field sanitation and heating water.
Valdes added that the new TGER prototype could also be transitioned into the commercial sector.
"Longer term, we will be talking to project managers about transitioning it but we'll also be talking to some companies that do things like support oil and gas operations in places such as Mongolia and parts of the world that are difficult to have camps in," he said.
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