Other plasma technology business Steven Vorndran of Westinghouse notes that with plasma systems, the destruction of hazardous wastes can be carried out on site “without incurring the costs and liabilities associated with [waste] transportation and disposal.” He sees plasmas as a means for the safe destruction of PCBs, dioxins, hydrocarbons, and military chemical and biclogical materials. Engineers at SKF Steel Engineering in Hofors, Sweden, are planning a facility that will handle 6 t/h (45,000 tlyr) of refuse, refuse-derived fuel, and wood waste. They estimate that the plant would use 6 M W of electric power to produce 20MW of thermal energy and that it could satisfy the needs of a region with a population of about 130,000.
This plasma arc is designed I O’ desrroy hazardous w ~ ~ s ~ e s f rhoemr Coml
By Julian Josephson One application of plasma technology for the destruction of hazardous wastes was developed by Pyrolysis Systems (Welland, Ont.) and supported by the New York State Department of Environmental Conservation (DEC) and EPA. Plasma-generating equipment for testing and demonstration is being s u p plied by Westinghouse Waste Technology Services Division (Madison, Pa.). Pyrolysis Systems president Edward Fox, Jr., explains that toxic wastes are fed into the gas discharged from the plasma arc (air is used as the process gas). The wastes are atomized and 1104 Environ. Sci. Technol.. MI. 20. NO.11. 1986
passed into the main reaction chamber where they are broken down into nonhazardous materials such as water vapor and carbon dioxide. Vice-president Thomas Barton says the plasma system has been used to destroy refractory organic substances such as carbon tetrachloride and solvents such as methyl ethyl ketone. Testing and demonstration of the plasma system were completed earlier this year at the Royal Military College in Kingston, Ont., under the auspices of DEC, EPA, and the Ontario Ministry of the Environment. In May, the system was moved to Niagara Falls, N.Y., where it will be tested on toxic sludges from Love Canal.
Metallurgy and metal refovery Plasma Energy Corporation (Raleigh, N.C.) is testing and demonstrating a plasma ladle-reheating system for maintaining or increasing the temperature of molten steel drawn from basic oxygen or electric arc furnaces. The plasma maintains the necessary temperature for vertical and horizontal continuous casting or for teeming in molds. Plasma Energy vice-president Salvador Camacho says his company is testing prototype plasma systems for recovering precious metals from automobile catalysts and electronic scrap, for making fused quartz and superalloys, and for destroying PCBs. It also is conducting refuse conversion tests for the Canadian government. In Sweden, plasma technology is being used to recover zinc, iron, and lead from electric arc steel-making wastes that otherwise would be disposed of on land and leach to contaminate soil and groundwater. In the PLASMADUST system, the dust is mixed with water to form a slurry consisting of 50% solids. The slurry is sent to a tank where it is mixed with coal and slag-forming material and then homogenized. The slurry is filtered, and the filter cake is dried and crushed. The crushed material is introduced into the coke-filled, refractory-lined
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0 1986 American Chemical Society
shaft of the plasma furnace, which has three 6-MW plasma generators for the thermal energy supply. The horizontal plasma generators are installed around the lower part of the furnace. The electrodes in the plasma generators are made of copper. A long electric arc is maintained between the electrodes at 3300 V and 1600-2000 A, converting the cold gas to a plasma that is injected continuously into the furnace together with the pulverized feedstock. The generators have an efficiency of approximately 85 % , says Sven SantBn of SKF Steel. The 300-Btu plasma gas is recirculated process gas that consists mainly of carbon monoxide and hydrogen. The carbon dioxide content of the gas is not allowed to exceed 2 % ; otherwise, its reducing potential is impaired. Zinc and lead leave the furnace as vapor and are cooled to about 500 OC and condensed. The zinc is separated and extracted in a separation furnace. The zinc and lead are then cast into ingots or slabs. The remaining exhaust gas consists mostly of carbon monoxide and hydrogen. Heavy metals and acidic gases are removed during cleaning of the gas in a hot cyclone and venturi scrubber. The wastewater is cleaned in a water treatment plant. A portion of the cleaned gas is recompressed and recycled to the furnace where it is used as a carrier gas for the raw material or for slurry drying. The rest is burned to produce hot water for the district heating system in Landskrona, Sweden. The plant is designed to convert about 70,000tlyr of electric arc furnace dust to 10,000-15,000 t/yr of metallic zinc of 98% purity, 900014,000tlyr of iron (4% carbon), 4000- 11,000 t/yr of alloyed iron, and 2000-3000 t/yr of metallic lead of 97 % purity. In addition, the plant generates 30,000 t/yr of slag, used as filling material for road construction projects (Swedish authorities are satisfied that no toxic materials will leach). Moreover, at full capacity, the ScanDust facility recovers about 65 GWh/yr (220 billion Btu) of thermal energy, equivalent to 1.7 million gal of oil. In March, Staffan Jemdahl of ScanDust said that the Landskrona facility’s capital cost was 160 million Swedish crowns (about $23 million U.S.). Later modifications have added another 50 million crowns (about $7.14 million) to the capital cost. SKF officials estimate that a similar plant in the United States would carry a capital cost of about $30 million.
Juliun Josephson is associate editor of ES&T.
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