Investigation Of Transfer Characteristic Of Heavy Metal During Municipal Solid Waste Incineration In O₂/CO₂ Atmosphere

Incineration of municipal solid waste is one of the most important technology for the innocent treatment of waste.The heavy metal emission during combustion arouse wide public concern.Oxy-fuel combustion technology,as a promising technology to reduce carbon emission,has the advantages of more complete combustion and less pollutant generation compared to conventional air combustion.Nowadays,the research of combustion in O₂/CO₂ atmosphere mainly focus on the field of coal combustion.Compared to the coal,the compositions of waste are much more complicated and the secondary pollution especially for heavy metal is more serious during the incineration.Therefore,it is meaningful to investigate the emission of heavy metal during typical waste combustion in O₂/CO₂ atmosphere.In this paper,the influence of temperature,atmosphere and fuel type on transfer characteristics of heavy metal（Pb,Cd,Zn,Cr,Ni and Cu）of typical waste（PVC,wood and paper）are studied during combustion in O₂/CO₂ atmosphere,using tube furnace.The result shows that temperature is the decisive factor of transfer characteristics of heavy metal and the enrichment factor of heavy metal become smaller as the temperature rise.Semi-volatile heavy metal Pb and Cd are sensitive to temperature,which have low content in bottom ash during high temperature.While Cr and Ni are less affected by temperature.Compared to 20O₂/80N2 atmosphere,the enrichment factor of heavy metal is larger during combustion in O₂/CO₂ atmosphere.The oxy-fuel combustion promote the enrichment of heavy metals in bottom ash.The transfer of heavy metals（Pb,Cd,Zn,Cr,Ni and Cu）of PVC,wood and paper are investigated during combustion in O₂/CO₂ atmosphere using thermodynamic equilibrium calculation.The result shows that Cl can increase the volatilization of Pb,Cd,Zn and Ni,while Zn and Pb begin to volatilize as ZnCl2（g）,KZnCl3（g）and PbCl2（g）at medium temperature.With the increase of temperature,the volatilization of CuCl（g）,CuCl3（g）and NiCl2（g）is promoted.There is no difference between the transfer characteristic of heavy metal during combustion in 20O₂/20CO₂ atmosphere and 20O₂/80N2 atmosphere.Moreover,oxy-fuel combustion promote the distribution of heavy metal salts and fixing of heavy metals chloride by oxides of Al,Si,Fe and Mg.Using tube furnace to investigate the capture efficiency of absorbent for heavy metal（Zn,Cu and Ni）in rubber and PE during combustion in O₂/CO₂ atmosphere.The capture efficiency of limestone for PE follow the sequence of Cu>Ni>Zn at 900℃.While,capture efficiency of limestone for rubber follow the sequence of Ni>Cu>Zn at 900℃.With the increase of limestone addition,it is beneficial to the capture efficiency of Ni and Zn.In the same combustion atmosphere,the increase of temperature promote the capture efficiency of limestone for Zn and inhibit the capture efficiency of limestone for Ni.In contrast to 20O₂/80N2 atmosphere,the capture efficiency of limestone for PE decrease in 20O₂/80CO₂ atmosphere.Meanwhile,the the capture efficiency of limestone for rubber combustion vary from different heavy metal in two atmosphere.In comparison of limes,it is found that CaO has better capture efficiency than limestone.