August 2008
Emissions from Carpet Combustion in a Pilot-Scale Rotary Kiln: Comparison with Coal and Particle-Board Combustion
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Stephanie Lucero Konopa and James A. Mulholland,
School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA
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Matthew J. Realff,
School of Chemical and Biomedical Engineering, Georgia Institute of Technology, Atlanta, GA
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Paul M. Lemieux,
U.S. Environmental Protection Agency, Office of Research and Development, Research Triangle Park, NC
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AbstractThe use of post-consumer carpet as a potential fuel substitute in cement kilns and other high-temperature processes is being considered to address the problem of huge volumes of carpet waste and the opportunity of waste-to-energy recovery. Carpet represents a high volume waste stream, provides high energy value, and contains other recoverable materials for the production of cement. This research studied the emission characteristics of burning 0.46-kg charges of chopped nylon carpet squares, pulverized coal, and particle-board pellets in a pilot-scale natural gas-fired rotary kiln. Carpet was tested with different amounts of water added. Emissions of oxygen, carbon dioxide, nitric oxide (NO), sulfur dioxide (SO2), carbon monoxide (CO), and total hydrocarbons and temperatures were continuously monitored. It was found that carpet burned faster and more completely than coal and particle board, with a rapid volatile release that resulted in large and variable transient emission peaks. NO emissions from carpet combustion ranged from 0.06 to 0.15 g/MJ and were inversely related to CO emissions. Carpet combustion yielded higher NO emissions than coal and particleboard combustion, consistent with its higher nitrogen content. SO2 emissions were highest for coal combustion, consistent with its higher sulfur content than carpet or particle board. Adding water to carpet slowed its burn time and reduced variability in the emission transients, reducing the CO peak but increasing NO emissions. Results of this study indicate that carpet waste can be used as an effective alternative fuel, with the caveats that it might be necessary to wet carpet or chop it finely to avoid excessive transient puff emissions due to its high volatility compared with other solid fuels, and that controlled mixing of combustion air might be used to control NO emissions from nylon carpet.
ImplicationsAn understanding of carpet combustion emissions is needed to inform carpet industry and public policy decisionmakers on the potential environmental benefits and costs of using carpet waste as an alternative fuel. Results from this research successfully demonstrate this use of carpet waste, providing information on the burn rate and transient emissions associated with feeding chopped carpet and two other solid fuels, pulverized coal and particle-board pellets, into a pilot-scale rotary kiln. Findings suggest the need to control both the rate of volatile release and the conversion of nitrogen in nylon carpet to NO.
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