As farfetched as it may sound, the technology for producing plasmas dates back nearly a century. Plasmas are gases that have been heated to the point of ionization—meaning they are composed of charged particles such as electrons that can conduct electricity and generate tremendous amounts of heat. Lightning is an example of naturally occurring plasma. Since the early 1900s, plasmas have been used to melt metals and to make acetylene fuel from natural gas. In the 1960s, NASA developed plasma technology to simulate the intense heat of re-entry for testing the durability of certain pieces of shuttle equipment. The technology continues to be used in the metal and chemical industries and has now begun to filter into waste management.
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In the latter case, the scenario goes something like this: MSW is shredded into one- to two-inch waste strips, which are dumped into a steel cylinder. This cupola is typically equipped with two torches near the bottom or top, which protrude like perches in a canary cage. These torches house electrodes, and when a continuous flow of electricity is applied, an arc forms between them. The air in the torch pushes this extremely hot artificial bolt of lightning into a furnace, where the MSW enters. The torrid temperatures generated by this process, which can be hotter than the surface of the sun, rip apart compounds and convert inorganic solids into a glassy obsidian-like rock that can be used in road construction. The process also transforms organic materials into syngas that can be used to make electricity and liquid fuels. Since the entire process is closed to the atmosphere, no emissions are released during the conversion of MSW to syngas and slag. “Plasma processing of MSW has unique treatment capabilities unequaled by existing technologies,” says Lou Circeo, director of plasma applications research at Georgia Tech Research Institute. “Plasma gasification could revolutionize the whole field of waste management.”
That’s certainly the hope of city planners, county commissioners and their comrades worldwide who feel the crunch of ever diminishing landfill space. The city of Ottawa for instance, has partnered with Plasco Energy Group Inc., a private high-technology company based in Canada, to process 85 tons of MSW per day over the next two years. The company holds 19 patents for its process technologies including one for the overall plasma gasification system, explains Rod Bryden, president and CEO of the company. Bryden, who owned Ottawa’s National Hockey League team from the time it was an expansion franchise until about two years ago, has been building businesses since 1974. “Plasma-based technologies have been around for some time but I saw the opportunity to create a conversion business that would deliver environmental quality while creating net energy for sale,” he says.
Plasco broke ground for the new demonstration facility in September 2006. Construction was completed in June and the plant, which covers three acres of grassland across the road from the Trail Road Landfill southwest of Ottawa, started in July. The plant began receiving waste from city trucks in late September.
Process Variation
The Plasco plasma gasification process differs from the general scheme previously described. Instead of directly dumping the shredded MSW into a plasma torch chamber, Plasco’s process uses a separate gasification chamber to heat the strips of waste to about 700 degrees Celsius (1,292 degrees Fahrenheit). In this step, some components of the MSW such as water are converted into gas while everything else is transformed to ash. The gas rises to a vertical chamber that holds two plasma torches, which blast the gas into its basic elements. Some of these elements reform into syngas, a mixture of carbon monoxide and hydrogen. Before the syngas can be scrubbed of heavy metals such as mercury, cadmium and lead as well as other undesirable chemicals like chlorine and sulfur, the syngas is cooled. Some of the heat released during this cooling is shuttled back to the initial chamber. This is the only process that recycles heat to convert waste into syngas, Bryden explains. “We don’t use these plasma torches to generate gas,” Bryden explains. “We use these plasma torches to refine the gases that have already been released from the waste.” Refining gases rather than whole MSW requires less heat from the torches, which saves energy. “This is one of the reasons our system produces so much more power than it consumes.”
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