Plasma Gasification Raises Hopes of Clean Energy From Garbage
- September 11, 2012
- / RANDY LEONARD NY Times
- / Post Tags
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.
“Effectively, 100 percent of all the metals on the base are being recycled,” Mr. Robau said.
The liquid oxides are removed and form a glassy solid when cooled. The slag traps contaminants like errant lead molecules and other heavy metals in a vitreous matrix that takes up 1 percent of the volume of the original waste, Mr. Robau said, a tenth of the volume left over after traditional incineration.
The vitrified component meets standards for disposal and may even be suitable for use as a construction aggregate, according to Mr. Robau and other industry professionals.
In the chamber, organic gases break down into hydrogen and carbon monoxide — the components of a fuel called synthesis gas, or syngas — which exits the furnace.
The gas passes through a plasma torch polisher, which breaks down remaining complex molecules and soot.
Injected water cools the syngas to less than 200 degrees. The extreme temperature of the plasma followed by quick cooling inhibits the formation of dioxins and furans (another organic compound), according to Mr. Robau and other industry experts.
The lack of dioxin creation would be a benefit over traditional incinerators and other types of gasifiers, in which lower temperatures and incomplete burning result in toxic compounds.
Emissions rules forced a 99 percent cut in dioxin and furan emissions and a 96 percent reduction in mercury from traditional incinerators between 1990 and 2005, according to the Environmental Protection Agency. However, companies have to dispose of the toxic ash filtered from mass-burn facilities.
After water quenches the gas in the Hurlburt system, stripping processes produce sodium bisulfate and hydrochloric acid, which can be sold, Mr. Robau said.
The gas passes through three types of filters to catch remaining impurities. The resulting syngas is as clean or cleaner than natural gas, and the system produces less than half the nitrogen oxides and 5 percent of the sulfur oxides and mercury of a traditional incinerator, Mr. Robau said. The Air Force uses the syngas to produce enough electricity to power the system.
Companies have used plasma arc technology in steel refining for more than a century. Some small-scale plasma gasifiers are specialized to process materials like asbestos or medical waste.
In Japan, a plasma facility originally designed to zap residue from automobile shredding now handles up to 150 tons of municipal solid waste each day in the city of Utashinai. And construction on a plant of similar size, designed to process industrial waste and wood chips, wrapped up this summer in Morcenx, in southern France.
Companies have been eying plasma gasification of municipal waste with eager hopes, but until recently financing has lagged. Plasma facilities are expensive, and the energy-hungry arcs and torches can consume half of the generated electricity. On the other hand, the systems can also handle medical and hazardous waste, which can command two to four times the fees associated with municipal waste.
“The problem has been over the years trying to find that economic sweet spot,” said Joe Vaillancourt, who evaluates newer technologies for Waste Management, a $15.4 billion company with headquarters in Texas.
In the past five years, with increased interest in energy independence and sustainability, venture capitalists and companies have financed testing of small-scale systems, including a 25-ton system built and run by InEnTec in Arlington, Ore., Mr. Vaillancourt said. Waste Management now holds an equity stake in InEnTec.
Last month the Agriculture Department announced a conditional $105 million loan guarantee for Fulcrum BioEnergy to build a much larger system outside Reno, Nev. It will use three InEnTec plasma melters to process 400 tons of garbage a day, an unprecedented scale for a plasma municipal waste facility, said Mr. Vaillancourt and others in the industry. Fulcrum plans to create ethanol from the syngas, and expects the Reno plant to be running in 2014.
New York City, too, is looking for innovative technology to deal with some of the city’s waste. In March, the Bloomberg administration requested proposals to build a facility that would use newer techniques like plasma gasification or anaerobic digestion to process as much as 900 tons of garbage a day.
“New Yorkers want their trash to be handled in an environmentally friendly way,” said Caswell F. Holloway, deputy mayor for operations. “Anything would be better than putting it in the ground.” The city is reviewing the proposals.
Still, some environmental groups, like the Sierra Club and the Global Alliance for Incinerator Alternatives, lump these techniques in with traditional incinerators, claiming that they still produce dioxin. They also oppose renewable energy credits for these facilities.
Allen Hershkowitz, a scientist with the Natural Resources Defense Council, said he believed there was a place for waste-to-energy operations, but only after recycling and composting programs had been maximized.
He said he still believed that communities could reach recycling rates of 60 to 70 percent. In his view it is premature for a city like New York, with a recycling rate of about 15 percent, to be considering setting up a new waste facility. “They’re not even at the point where they should be thinking about waste-to-energy,” Mr. Hershkowitz said.
An article on Tuesday about the plasma arc gasification method of waste disposal misstated part of the name of the organization with which Allen Hershkowitz, a scientist who said he believed that New York City’s low recycling rate makes its interest in waste-to-energy technology premature, is affiliated. Mr. Hershkowitz is with the Natural Resources Defense Council, not the National Resources Defense Council.