Garbage In, Energy Out

Now, he says, the combination of overflowing landfills,skyrocketing energy costs and growing concern over global warming has made solutions like plasma gasification an attractive proposition whose time has come.

“It is well recognized that methane is one of themajor sources of CO2, and that the decay of municipal solid waste is one of the key sources of methane,” he says. “There is an urgency here thatresults in governments looking for ways to have new technologies becomeeffective very soon.”

How It Works

While plasma gasification is relatively new, the basic conceptbehind it has been in use for more than 100 years. As early as 1850, it was used toproduce “town gas” for light and heat. In fact,until the advent of natural gas supplies and transmission lines in the1940s and ’50s, virtually all gas for fuel and light wasmanufactured from the gasification of coal.

Until recently, however, the materials used in the processwere limited to combustible minerals, such as coal and biomass (organic waste). In the ’80s, however, that limitation was lifted with the widespreaduse of plasma torches, industrial cutters typically used inmanufacturing.

Plasma torches work by sending a pressurizedgas, such as nitrogen, argon or oxygen, through a small channel. Anegatively charged electrode sends a spark through the channel, heatingthe gas until it becomes plasma, the fourth phase of matter. Thisdirected plasma, at approximately 30,000˚F(16,649˚C), releases free electrons that break down themolecular structure of any matter it comes in contact with. Thetorch’s intense heat makes it possible for any material to begasified to its elemental components.

Over the last 20 years, a handful of companies, includingStartech, Geoplasma, PyroGenesis and EnviroArc, have been pursuing the Holy Grail of plasma gasification, with greater or lesser success, but they employ a similarprocess.

When municipal waste is delivered, high-valueferrous and non-ferrous metals are removed for recycling before thewaste is chopped into small chunks. That processed material is then fedinto a conversion chamber where it’s typically passed throughthe intense heat of the plasma torches.

Free electrons in the low-oxygen atmosphere of the chamberattack the chemical bonds of the solid waste and push the resultant mixture of gases into a plasma state where only the elemental components, largely carbon and hydrogenatoms, are left. As they cool, those elements reform into a mixture ofhydrogen gas and carbon monoxide, a synthetic fuel called syngas, whichis then burned to create the steam that powers turbine generators.