The idea behind waste gasification is an attractive one: Take trash and subject it to extreme heat under anoxic conditions to produce syngas, a blend of carbon monoxide and hydrogen, which can be used as a fuel source. Despite its promise, its high operating costs and relative inefficiency had heretofore limited its applicability in most countries.
Yet, as reported by Technology Review's Peter Fairley, that is all set to change with the approval of North America's first gasification plant in Ottawa, Ontario. The inaugural plant, which will use electric-plasma torches to zap waste into syngas, will be built by Ottawa-based PlascoEnergy.
The plant is expected to be able to convert up to 400 metric tons of garbage a day into 21 megawatts of net electricity, which would be enough to power roughly 19,000 homes. Fairley describes how the process will work:
"First, bulk metals are removed, and the rest of the shredded waste is conveyed to a 700 ºC gasification chamber. Most of it volatilizes to a complex blend of gases and rises toward a plasma torch operating at 1200 ºC--well below the 3000 to 5000 ºC used with hazardous wastes. The plasma reduces the complex blend to a few simple gases, such as steam, carbon monoxide, and hydrogen, plus assorted contaminants such as mercury and sulfur; subsequent cleanup systems remove the steam and mercury and scrub out the soot before the syngas is sent to an internal combustion engine generator.
The waste that doesn't volatilize forms a solid slag and drops to the bottom of the gasification chamber. The slag is then pushed to another plasma torch, which drives off remaining carbon in the slag before the slag is cooled and vitrifies. The resulting glass can be blended into asphalt road surfacing or cement."
The hefty upfront costs, about $125 million, in addition to the standard operating expenses (the process will cost the city $60 per ton) will likely keep this technology from becoming widely implemented in the near future. Once the plant is completed 3 years from now, the hope is that continuous improvements and economies of scale will quickly drive down the costs and make it a more appealing option for other communities.
Via ::Technology Review: Garbage In, Megawatts Out (magazine)
Other waste gasification projects
::Zapping Trash With Plasma Produces Clean Energy and Fuel
::Turning Radioactive Waste Into Clean Fuel