January 7, 2009 By Chad Vander Veen
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"Why don't they just fill a rocket full of garbage and shoot it at the sun?" Many who want to reduce pollution but have a flimsy grasp on rocket science and economics have asked this question. But what if such a feat could be accomplished without a rocket? That's essentially what plasma gasification is designed to do.
Plasma gasification is the process of breaking down matter at the atomic level by exposing it to high temperatures. Gasification isn't combustion or incineration. Those processes result in unpleasant, toxic byproducts. Gasification uses extreme heat, in the form of plasma arcs, to reduce matter to its basic elements.
Superheated plasma is nothing new. For decades, plasma arcs, which reach temperatures of up to 8,000 degrees Fahrenheit, have been used in foundries to melt metals. However, a few years ago several waste disposal startups in the United States and Japan took notice of a plasma arc technology developed by NASA that produced an arc at temperatures exceeding those on the sun's surface. Any solid matter that came into contact with such an arc would be reduced to nothing more than synthesis gas - or syngas, which is generally carbon monoxide and hydrogen - and an inert slag.
Video: City Manager Ray Kerridge describes Sacramento, Calif.'s plan to vaporize solid waste.
It turns out the syngas can be used to produce useful products like diesel and methanol or separated and sold to industries that use hydrogen and carbon monoxide in manufacturing. The slag also has several applications, such as asphalt and tile production. In addition, syngas must be cooled before it's stored. The cooling process results in considerable amounts of steam, which can run the turbine that powers the plasma arc to begin with.
Sacramento, Calif., is considering constructing a plasma gasification plant in which to dump garbage. In addition to its own landfills, Sacramento currently sends tens of thousands of tons of waste to landfills in Nevada, a costly process that's neither sustainable nor environmentally friendly. In February 2008, the city began negotiations with Sacramento-based U.S. Science and Technology (USST) to possibly make Sacramento the first American city to build a plasma gasification plant to treat waste.
"Sacramento has long been on record as being a sustainable and green city," said Jim Rinehart, Sacramento's economic development manager. "So one of the notions to support that premise of making Sacramento, the most sustainable city in the nation was to look at our municipal solid waste activities and see if we can improve upon them."
Rinehart said in late 2007 the city issued an RFP for alternatives to the city's existing waste-management policy. There were 11 respondents. One of them was USST, which proposed a plasma arc gasification procedure that would convert municipal solid waste to energy and products the U.S. Environmental Protection Agency has deemed to be safe roadbed material - all with no or few emissions.
Several gasification plants are already operating in Japan, gasifying up to 280 tons of solid waste every day. Of course, all this sounds too good to be true. Why aren't we already doing it?
David Prinzing, vice president and chief engineer of USST, said the holdup is due to the usual suspects: politics and economics.
"There are a lot of vested interests or special interest groups around municipal solid waste, and so introducing change can be difficult," Prinzing said. "It takes time. Then, on the economics side, I
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