Modeling Kinetics of Cd, Pb, and Zn Vaporization during Municipal Solid Waste Bed Incineration

Abstract

The fate of heavy metals contained in municipal solid waste is of major concern in the incineration process. This study is the first attempt to analyze the kinetic behavior of Cd, Pb, and Zn in a waste bed burning on the grate of an incinerator. The vaporization rates of the three heavy metals were derived from laboratory experiments. The kinetic law was then introduced into Garbed-ss, a mathematical model of the on-grate incineration of a refuse bed. Results show that the calculated vaporization of the three metals is fast, proceeds to nearly full completion, occurs at the pyrolysis front, and is indeed controlled by the thermal degradation of the waste. Alhough in agreement with thermodynamic calculations, the vaporization of lead and zinc seems to be overestimated. The model would be improved by accounting for the initial physical and chemical speciation of the heavy metals in the waste feed.

Trace element partitioning in ashes from boilers firing pure wood or mixtures of solid waste with respect to fuel composition, chlorine content and temperature

“…In the post combustion section PbO is gradually substituted by PbCl 2 (g) and then by PbSO 4 (s) so thermodynamic calculations also support the formation of lead chlorides. Kinetic studies by Asthana et al (2010) also confirmed the rapid vaporization of lead. Comparatively low distribution of lead in the Umeå fly ash could also be attributed to the melting and dripping of metal through grates prior to reaching the vaporization temperature (Chandler et al, 1997).…”

“…It has been reported that during waste incineration Hg is most likely to vaporize, followed by Cd, Pb, and Zn, while Cr and Ni are least likely to evaporate (Jianxin et al, 2007). Impact of temperature on trace element partitioning has been subject to some studies (Abanades et al, 2002;Zhang and Kasai, 2004;Asthana et al, 2010).…”

Distribution and leaching characteristics of trace elements in ashes as a function of different waste fuels and incineration technologies

“…Sources of organic and inorganic chlorine (PVC, NaCl) in waste caused high transfer of Pb to fly ash through the formation of lead chloride (Astrup et al, 2011). A kinetic study by Asthana et al (2010) also supported rapid and complete vaporization of Pb during MSW incineration. Ménard et al (2006) have reported that the Pb and Zn chloride species are stable in the entire incineration temperature range, and that evaporation and entrainment processes govern distribution, thus explaining excessive presence of Pb in some fly ashes in this study (Fig.…”

Coupling scales for modelling heavy metal vaporization from municipal solid waste incineration in a fluid bed by CFD

“…Homogeneous reactionŝ r j Reaction description Reaction rate (kmol m À3 s À1 ) During the consumption of the solid by combustion, HM is released and several transformations may occur to the HM (Asthana et al, 2010a).…”