COMBINED EFFECTS OF OXYGEN, CHWRINE AND WATER VAPOR ON THE VAPORIZATION OF HEAVY METALS DURING FLY ASHES VITRIFICATION BY PLASMA

The vaporization of fly ash from municipal waste incinerators during vitrification by plasma is the result of the complex interaction of 0₂, Cl₂, H₂0 with a multicompounds molten bath at different temperatures. It is shown theoretically that vaporization rate decreases with 0₂ partial pressure and that H₂0 affects mainly the equilibrium pressure of alkali (Na,K). The influence of Cl₂, is proved to be temperature dependent. At low temperature (1500K) the Cl₂ pressure increase causes the enhancement of the heavy metals vaporization (Pb and Zn), whereas the effect is negligible at high temperature. The main part of chlorine is associated with Na and K in the fumes.
Concerning the interest of chlorine elimination by ash washing, the theoretical analysis shows the possible decrease of heavy metal evaporation, but it is not observed experimentally due to the modification of electric arc characteristics and bath temperature with and without chlorine.