Here’s how it works. 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.
Under its deal with Ottawa, PlascoEnergy will cover the estimated $125 million that it takes to build the plant, which could be operating within three years, while the city will pay only standard tipping fees–on the order of $60 per metric ton.
Ze-gen plans to avoid the challenge of handling complex municipal wastes by focusing first on an easier-to-handle feedstock: construction and demolition wood wastes. The company has filed seven patents on its molten metal gasification technology and waste-to-syngas process, but the equipment itself is standard for the steel industry, which uses molten iron to catalytically drive off impurities from ore. Ze-gen’s pilot plant processes wood waste using a standard electrically heated steel-industry crucible full of molten iron.
Ze-gen CEO Bill Davis estimates that a full-size plant just slightly bigger than PlascoEnergy’s commercial plant will produce enough syngas to create 30 megawatts of electricity, but he says that the syngas is also of sufficient quality to be used in other applications. As examples, he cites synthetic gasoline, diesel production, and refinery applications.