In this kind of gasification, plasma arcs are created by passing a high-voltage current through a chamber filled with an unreactive gas such as nitrogen (see diagram). As the current flows through the enclosed space, it tears electrons from the gas to form a superheated plasma that rips apart the molecules in whatever is fed into the chamber. "It's like a continuous bolt of lightning that disintegrates almost anything that crosses its path," says Daniel Cohn of the Massachusetts Institute of Technology, who has been working on plasma gasification since the 1980s and now sits on the board of InEnTec, another waste-to-energy company.
A further advantage of this technique is that the very high temperatures cause the waste to end up not as fine ash but as a glassy solid, which could in principle be used as filler in the construction industry. And while the power required to run InEnTec's pilot plant in Richland, Washington, amounts to one-third to half of the power it produces, Cohn insists that the process is financially viable. He says syngas can be converted to ethanol and synthetic diesel at costs that can compete with petroleum-based equivalents. "We think we can produce fuel at a cost of about $2 a gallon of gas equivalent," he says. If he's right, trash could become the new oil.
Pilot gasification plants are being set up at various sites in the US, Canada, France, the UK and Portugal, most of them using the plasma technique. Japan already has two commercial plasma plants, but these are focused primarily on simply disposing of household waste rather than generating energy from it.
While these new plants will all be large installations, IST Energy believes that small is the way to go. Its container-sized non-plasma GEM system (short for Green Energy Machine) can convert almost 3 tonnes of municipal waste a day into enough syngas to heat and power an office building holding 500 people.
Keeping the system small and avoiding the expense of creating plasma makes it affordable for businesses to deploy: excluding the gas burner, the system costs $850,000 and, according to Haber, will pay for itself in four years through savings on electricity, heating and waste disposal charges.
Haber says the entire system can save the equivalent of about 500 tonnes of carbon dioxide emissions a year through reductions in landfill gases, fossil-fuel use and the transport of waste. Haber also claims that, compared with traditional incineration, the quantity of toxic gases produced by the GEM system is negligible. "It's really a night-and-day difference," he says.
Gasification is not without its detractors, partly because early attempts to gasify garbage were environmentally and financially disastrous. A series of economic and environmental problems at an early commercial gasification plant in Karlsruhe, Germany, including a leak of toxic gases that temporarily closed the plant in 2000, caused the facility to shut down for good in 2004. These troubles have tainted the reputation of gasification - and, by association, plasma gasification - ever since.
One objection that sceptics raise is that gasification still produces CO2 emissions. Neil Tangri of the Global Alliance for Incinerator Alternatives (GAIA) dismisses gasification plants as glorified incinerators. "There is an intermediate step with gasification, but the end result is always combustion," he says.