Plasma Gasification Raises Hopes of Clean Energy From Garbage

David Robau tours the country promoting a system that sounds too good to be true: It devours municipal garbage, recycles metals, blasts toxic contaminants and produces electricity and usable byproducts — all with drastic reductions in emissions.

Mr. Robau, an environmental scientist for the Air Force, has been promoting a method that was developed with the Air Force to dispose of garbage with neither the harmful byproducts of conventional incineration nor the environmental impact of transporting and burying waste. It is one of several innovative techniques that the United States military has been researching to provide alternatives to the open-pit burns that some veterans of the Iraq and Afghanistan wars say have made them ill.

Already some waste companies and cities like New York have shown an interest in technology similar to what Mr. Robau has been promoting, known as plasma arc gasification. Proponents say the process can break chemical bonds and destroy medical waste, PCBs (polychlorinated biphenyls), asbestos and hydrocarbons, some of which can be hazardous if disposed of in landfills or traditional mass-burn incinerators.

Still, some environmentalists are leery. They say the ability to fully dispose of waste will discourage recycling and the development of renewable products, and the gasification will still result in toxic substances like dioxins.

Mr. Robau maintains that the process is earth-friendly. “This is not incineration,” he said. “This is gasification, so it’s a lot cleaner, a lot better for the environment.”

Mr. Robau, who also heads a nonprofit organization based in Gulf Breeze, Fla., has overseen testing of the small-scale plasma arc gasification system, which cracks complex molecules into simple elements using energy as intense as the sun’s surface, making fuel for about 350 kilowatts of electricity from about 10 tons of garbage each day, enough to run the system.

The system has been hard at work in a 6,400-square-foot building at Hurlburt Field Air Force base in Florida’s panhandle. A mechanical shredder cuts household garbage into pieces no bigger than two inches. An airtight auger feeds the waste into an oxygen-poor gasification chamber, where temperatures reach more than 9,000 degrees.

In an instant, wood disintegrates, plastics turn to gas. Bits of metal and glass fall into a molten pool.

From two graphite electrodes, an arc of electricity leaps about a foot to the molten slag, producing a cloud of ionized particles known as plasma, which heats the chamber. Most heavier metals settle to the bottom of the pool, below a layer of liquid silica and other oxides. The metals are removed, cooled and used for steel or other products.

 

 

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