Characterization of transient puff emissions from the burning of carpet waste charges in a rotary kiln combustor

Transient puff emissions were characterized from burning carpet charges that were fed to a pilot-scale rotary kiln combustor to assess the potential impact on emissions of using post-consumer carpet as an alternative fuel in cement kilns. Carpet with polypropylene, nylon 6, and nylon 6,6 face fiber was cut in one to three inch square pieces and fed as 0.4 kg charges to a 73 kW natural gas fired rotary kiln simulator. Gas emissions monitored included O₂, CO₂, CO, NO, NO_X, N₂O, NH₃, total hydrocarbons, and total polycyclic aromatic hydrocarbons. The charges required about two minutes to burn, and the emission transient exhibited three phases. In the first phase lasting about 30 seconds, fuel-lean combustion of volatiles occurred. In the middle phase lasting about one minute, fuel-rich burning occurred and a CO spike was observed. In the final phase lasting about 30 seconds, fuel-lean burning occurred. For nylon carpets, the fuel-lean combustion periods were characterized by elevated NO emissions. Integrated over the duration of the transient, the NO emission corresponded to a one to two percent conversion of fuel-nitrogen (i.e. nitrogen in the nylon fiber) to NO. These tests demonstrate the feasibility of burning waste carpet as an alternative fuel, that rapid volatilization of batch fed carpet can lead to emission transients, and that NO emissions may result from the burning of nylon carpets.