METAL VOLATILITY DURING PLASTIC COMBUSTION

The hazardous pollutants, such as heavy metals, nitrogen oxides, sulfu r oxides, hydrogen chloride, and Dioxins, are emitted during incinerat ion process. This study is intended to evaluate different factors affe cting Pb or Cd emission during combustion of plastic powder and plasti c membrane, of which plastics constitute 20% of solid wastes in Taipei . A laboratory scale incineration system was employed with a controlle r to adjust temperature, fuel velocity and other parameters. The major operation factors for heavy metal volatilization included combustion temperature and time. The results indicate that the combustion tempera ture exerts a significant effect on metal volatilization. For example, at the combustion time of 5 minutes at 600 degrees C, Pb emission is approximately 20% of the value initially present in the plastic powder , but it increases to 90% at 1000 degrees C. Also, metal emission incr eases with combustion time, until it reaches a plateau. Cd volatility after 5 minutes combustion is much higher than Pb at lower temperature s. The other factors evaluated include fuel gas flow (350-3600 mL/min) , fuel N-2:O-2 ratio (4:1 and 1.4), fuel humidity (40 and 60 %), and t he addition of Ca(OH),. Generally, these factors exhibit some degree o f retardation/enhancement of metal emission. The X-ray diffraction tes t indicates that the bottom ash consists of quartz (SiO2), laurionite (PbClOH), and calcite (CaCO3). The EDAX(energy dispersive analysis of X-ray) analysis further demonstrates a much higher ratio of Cl:Ca:Pb p resent in the bottom ash.