Feb 082011
 
plasma torch 2

Atomising trash eliminates the need to dump it, and generates useful power too

DISPOSING of household rubbish is not, at first glance, a task that looks amenable to high-tech solutions. But Hilburn Hillestad of Geoplasma, a firm based in Atlanta, Georgia, begs to differ. Burying trash—the usual way of disposing of the stuff—is old-fashioned and polluting. Instead, Geoplasma, part of a conglomerate called the Jacoby Group, proposes to tear it into its constituent atoms with electricity. It is clean. It is modern. And, what is more, it might even be profitable.

For years, some particularly toxic types of waste, such as the sludge from oil refineries, have been destroyed with artificial lightning from electric plasma torches—devices that heat matter to a temperature higher than that of the sun’s surface. Until recently this has been an expensive process, costing as much as $2,000 per tonne of waste, according to SRL Plasma, an Australian firm that has manufactured torches for 13 of the roughly two dozen plants around the world that work this way.

Now, though, costs are coming down. Moreover, it has occurred to people such as Dr Hillestad that the process could be used to generate power as well as consuming it. Appropriately tweaked, the destruction of organic materials (including paper and plastics) by plasma torches produces a mixture of carbon monoxide and hydrogen called syngas. That, in turn, can be burned to generate electricity. Add in the value of the tipping fees that do not have to be paid if rubbish is simply vaporised, plus the fact that energy prices in general are rising, and plasma torches start to look like a plausible alternative to burial.

An electric atmosphere

The technology has got better, too. The core of a plasma torch is a pair of electrodes, usually made from a nickel-based alloy. A current arcs between them and turns the surrounding air into a plasma by stripping electrons from their parent atoms. Waste (chopped up into small pieces if it is solid) is fed into this plasma. The heat and electric charges of the plasma break the chemical bonds in the waste, vaporising it. Then, if the mix of waste is correct, the carbon and oxygen atoms involved recombine to form carbon monoxide and the hydrogen atoms link up into diatomic hydrogen molecules. Both of these are fuels (they burn in air to form carbon dioxide and water, respectively). Metals and other inorganic materials that do not turn into gas fall to the bottom of the chamber as molten slag. Once it has cooled, this slag can be used to make bricks or to pave roads.

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