The process is called plasma gasification and the technology for creating and harnessing plasma has been around for decades. However, plasma gasification technology is now being used for a new purpose-the conversion of municipal solid waste-to-energy.
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.
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.
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."
The ash from that first gasification chamber is transferred to a separate plasma torch compartment where it is converted into syngas and a hard glass-like material that is broken into pieces and sold for use as a construction aggregate. All the syngas that's produced is collected and piped to a bank of generators that converts it into electricity. In the end, out of 100 tons of MSW that enters the system, 4 megawatts (MW) of electricity are sold to the grid and used to power about 3,600 homes, 1 MW of electricity is used to power the plant, 15 tons of slag aggregate is produced and sold, and 500 kilograms (kg) of sulfur is sold as fertilizer. In addition, 1 kg of ash-made up of heavy metals-is landfilled. "You could fit a day's disposal requirement in the glove compartment of your car," Bryden says.
The plant in Ottawa will run for two years at which time the city will either dismantle the facility, continue to use it for MSW treatment or operate the plant as a development facility for the processing of other energetic materials that pose disposal challenges such as paper mill waste and the sludge from sewage treatment. In addition, Plasco has a memorandum of understanding with a waste management company in Spain to build a plant in Barcelona that will process 200 tons of MSW per day and two other contracts are in the works for plants in Canada. "We expect that by October we'll be moving forward with commercial plants in a number of places," Bryden says.
Growing in Popularity
Over the past several years, about 12 commercial plasma waste processing facilities have been operating in Europe and North America, and about 10 in Asia. The waste processed at these facilities varies and ranges from MSW to medical waste, catalytic converters, asbestos and ammunition.
The largest facility in the world to date is slated for start up in 2010. The plant will be built in St. Lucie County, a beach destination along Florida's south-central Atlantic coast. On April 10, Geoplasma LLC, an energy developer based in Atlanta, Ga., signed an agreement with the county. The company will finance, permit, construct, own and operate the $425 million MSW-to-energy plant for 20 years.
The new plant will be constructed in two stages. The first will likely start up in the winter of 2010 and will process at least 1,000 tons of MSW each day and produce enough electricity to power about 25,000 homes. Each gasifier unit will house up to six plasma torches and will process between 500 to 750 tons of waste. Within five years, Geoplasma intends to scale-up the plant by adding more gasifier reactors. At this time, the plant, which will stand on about eight acres, will process 3,000 tons of MSW per day, two-thirds of which will come from the existing landfill. "We'll be able to consume the landfill within our 20-year contract. This will be the first time that a landfill like this has been recovered to our knowledge," explains Hilburn Hillestad, president of Geoplasma.
The plasma torches and gasification reactors for the modules will be supplied by Westinghouse Plasma Corp., the technology developer Geoplasma has teamed with. Westinghouse has been in the plasma gasification business since the 1960s. The company's technology is being used in two waste processing facilities in Japan and in a General Motors Corp. plant in Definance, Ohio, for scrap metal melting. The torches in the latter plant have been in use for 17 years and the electrodes have been in use for more than 500,000 hours. Westinghouse was recently acquired by Alter Nrg Corp. of Canada and Geoplasma will be the exclusive marketer for the Westinghouse technology in Canada and the United States, Hillestad explains.
"The technology is proven and reliable," says Shyam Dighe, president and chief technology officer for Westinghouse Plasma Corp. Although the technology has been around for a while, "now, several factors have come together to make plasma gasification like a perfect storm," he adds.
Hillestad agrees with Dighe and adds that "over the past few years we've seen a steep increase in energy prices in this country and worldwide. Before those energy prices spiked the natural gas community generated a lot of power with natural gas and we couldn't compete with that. Now, however, our syngas can compete with natural gas to generate electricity. It's the most sustainable alternative technology for disposing of MSW that we know of at a time when we critically need alternative energy supplies."
Jessica Ebert is a Biomass Magazine staff writer. She can be reached at firstname.lastname@example.org or (701) 746-8385.