Combustion behaviors of wasted plastics coated around electric cables in electrically heated drop tube furnaces

For thermal recycle by wasted plastics coated around electric cables, ignition and combustion experiments of the pulverized samples were carried out, using two types of electrically heated drop tube furnace, in which the particles are pulsatively fed and continuously fed, respectively. The ignition phenomenon was defined as occurrence of luminous emission from a cloud of the particles fed in the former furnace. The wasted plastics coated around the electric cables mainly make of polyethylene with a little amount of carbon particles. The ignition characteristics of the pulverized plastic samples as well as graphite particles as a reference sample were studied, changing the particle diameters and the furnace wall temperatures. In the electrically heated drop tube furnace with the continuous feeding system, the wall temperature and stoichiometric combustion air ratio were varied to elucidate the fundamental combustion characteristics. As a result, the ignition temperature depended on the particle diameter. The plastics with the particle diameter ranged from 150 to 300 µm could ignite at the lowest furnace temperature. From the continuous combustion tests, CO and lower molecule hydrocarbons like CH₄, C₂H₂ and C₂H₄ were produced in the upper region of furnace. Finally, all of them gradually burned out.