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Finding Clean Energy in Trash
A revolutionary new process could make landfills a thing of the past.
By Ben Jervey
December 31, 2007

The Power of Waste—An Intro

What if we could get rid of all our waste, not by shipping it off to some unseen landfill in somebody else’s backyard, but by heating it to temperatures more typical of the sun than the earth, in a process that generated more energy than it used, and didn’t produce a bit of air pollution?  It may sound like the stuff of science fiction (or of Doc Brown’s Delorean in Back to the Future), but it’s actually an innovative and potentially revolutionary technology that could well change the way we humans view waste.  

The process—called plasma gasification—does indeed sound almost too good to be true.  A plasma converter—the very device that might make the landfill obsolete—can turn just about any waste, from household trash to the most toxic of contaminants, into clean energy and some benign glassy solid byproduct fit for reuse in a bundle of forms.  

How the Heck Does It Work?

To understand how a plasma converter turns our filthiest waste into energy and a safe, reusable solid material, we’ll need a little bit of a science lesson.  And first, we’ve got to understand plasma—that mysterious “fourth state of matter” that’s actually an ionized gas occuring only at extremely high temperatures.  While we’ve only recently come to really understand plasma, it’s as old as the universe, as is plasma gasification.  The best example of a plasma field here on Earth is in the form of lightning, where the gas creates a current and has a magnetic field, because of its unattached, free-roaming electrons.  

Thus the key element of a plasma converter is the plasma torch, a device that sends high voltage current through the air-tight chamber to temperatures higher than those found on the surface of the sun, maybe 30,000 degrees Fahrenheit.  Essentially, it creates lightning in the sealed container, stripping electrons from the air and creating an energy field so intense that solids don’t stand a chance.  At these extreme temperatures, waste (or anything else unfortunate enough to be stuck inside) is totally disintegrated, as molecular bonds are broken and solids are reduced to their fundamental elements.  A noxious chemical like cyanide, for instance, is broken down to basic carbon and nitrogen.  Even something as dangerous as Agent Orange will come out of this plasma bath as a harmless glass and synthetic gas, commonly called “syngas,” which can pretty easily be converted into valuable alternative fuels like ethanol, natural gas, and hydrogen. 

Good in Theory…Is It Practical?

If the science is still a bit confusing, it might help to take a look at the process in practice.  Imagine for a moment a typical load of municipal solid waste (that’s the formal term for everything we think of as trash):  some household garbage - food scraps, spent batteries, an old stereo, take-out containers; some concrete, wood or other building materials;chemicals; paper; tires - anything really.  All this refuse is dumped into an industrial-strength grinder, which churns this brew into pea-sized pellets.  These are then fed into the converter, where the lightning-hot plasma field makes short work of the waste. 

At this point, you might be wondering how much energy it takes to pump such heat, to power this whole operation.  It does, after all, demand a continuous 650-volt current charging through the sealed chamber.  Indeed, to get the process started, electricity must be pulled from the grid.  But after that initial jolt, the gasification is underway, and this is where it gets really interesting.  The syngas produced is a smoldering 2,200 degrees Fahrenheit, and is immediately pumped into a cooling chamber, at which point a heavy stream of steam is released.  Any sensibly designed converter will use this steam to spin turbines, thus producing electricity.  More than enough juice, in fact, to power the whole operation—grinder, plasma torch, and every other moving part.  The entire process becomes, after the initial spark, self-sustaining.  Your typical plasma converter could keep burning straight through a blackout.  In all, about one-third of the power generated by the cooling syngas’s steam can be put back into the grid.

Besides this excess electricity, the syngas itself is valuable as it can be sold on the fuel market, and the glassy solid byproduct—called “slag” in the industry—can be repurposed in any number of materials, like asphalt or even home insulation. 

I’ve heard of Waste-to-Power plants.  Is this the same thing?

While plasma conversion is a method of turning waste to energy, it’s not to be confused with the much more widespread process of waste incineration, which also happens to be much less efficient and much more polluting.  Around the world, municipalities, waste management companies and power utilities have long been burning trash.  ....read more

SOURCES :

Behar, Michael (March 2007). “The Prophet of Garbage”. Popular Science.  Available from: http://www.popsci.com/popsci/science/873 aae7bf86c0110vgnvcm1000004eecbccdrcrd.html   [accessed 9 December 2007]

Chan, C.C., (1997).  Behaviour of metals in MSW fly ash during roasting with chlorinating agents.  PhD Thesis, Chemical Engineering Department at University of Toronto.
Available from: http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ27620.pdf [accessed 9 December 2007] 

Childress, Jim, GTC, (August 2007).  The Gasification Industry: 2007 Status & Forecast. 
Presentation from August 3, 2007 COALGEN Gasification Session.  Available from: http://www.gasification.org/Docs/News/2007/COALGEN/GTC%20COALGEN%2007.pdf   [accessed 9 December 2007]

Environmental Technology Evaluation Center (EvTEC), (May 2002).  Environmental Technology Verification Report for the Plasma Enhanced Melter.  CERF/IIEC Report: #40633.  Available from: http://www.clu-in.org/download/contaminantfocus/pops/evtec_finalreport.pdf [acccessed 9 December 2007]

Philips, Jeffrey, Electric Power Research Institute (March 2006).  Fundamentals of Gasification. Paper from the March 2-3, 2006, Gasification Technologies Workshop in Tampa, FL.  Available from: http://www.gasification.org/Docs/Workshops/2006/Tampa%2006/Phillips.pdf [accessed 9 December 2007]

Strickland, Jonathan (undated).  How Plasma Converters Work.  Available from: http://science.howstuffworks.com/plasma-converter.htm [accessed 9 December 2007]

 
 
 
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