Distribution behavior of heavy metals investigated in a laboratory-scale incinerator
Introduction
Literature coverage of the investigation of the emission of heavy metals during combustion processes has been extensive (Wichmann et al., 2000). The spectrum of experiments reaches from detailed investigation in laboratory-scale incinerators to sampling at operating municipal solid waste incinerators (MSW). The partitioning of heavy metals during combustion processes in MSW incinerators was examined repeatedly. Only a few experiments were done to determine the distribution behavior of heavy metals during fire accidents or in full size test fires (Meharg and French, 1995, Wichmann et al., 1999).
Within the scope of the simulation of fire accidents, experiments in our laboratory were carried out in a remodeled incinerator (see Section 2). It was determined that after fire accidents the heavy metals such as Pb, Cd, Fe, Mo and Zn were generally released in relevant amounts. Investigations determined the distribution behavior of these heavy metals. In this context, Fe has been barely considered and the distribution behavior of Mo was examined for the first time. In the literature, the input material was spiked with organic and inorganic Cl (Jakob et al., 1995, Jakob et al., 1996, Wang et al., 1997, Wang et al., 1999, Chiang et al., 1997a, Chiang et al., 1997b). In contrast, the combustion air of our apparatus was spiked with gaseous HCl to create more realistic combustion conditions for a better simulation of a real fire atmosphere. This strategy traced back to the experiments of Wirts et al. (1998), who pointed out that combustion of PVC, for example, did not lead to a quite stable HCl concentration in the combustion atmosphere, which often occurs during real fire accidents. Several parameters contribute to the distribution of heavy metals during combustion processes. This paper focuses on the investigation of temperature, chemical composition of the atmosphere and its HCl content.
Section snippets
Materials and methods
The experiments were carried out in a horizontal tube furnace reactor with a quartz tube and gas supply. A quartz boat carried the input material. After the reactor gas stream had passed the tube, it was conducted through a plug of glass wool, a cooler, a glass fiber filter and finally through an absorption bottle filled with 10% HNO3. The laboratory-scale incinerator assembly is shown in Fig. 1. Samples were taken at five different points: quartz boat (6), plug of glass wool (9), cooler (10),
Results and discussion
Most of the experiments described in the literature were carried out in horizontal tube furnace reactors to simulate incineration processes in MSW incinerators. After the gas stream had passed through those reactors, it was conducted through cooler and/or absorption bottles to determine the heavy metals. Ground filter ash, synthetic fly ash, and synthetic waste with different compositions were used there. These input materials were spiked with organic (PVC, C2Cl4) or inorganic (NaCl, CaCl2) Cl.
Conclusion and outlook
The experiments described in this paper allow to evaluate the effects of temperature, combustion atmosphere, and matrix on the evaporation of the heavy metals Cd, Cu, Fe, Mo, Pb and Zn. In air and N2 atmosphere only the evaporation rate of Cd was effected by the matrix and the temperature increase. Addition of gaseous HCl led to an increase of the release of some heavy metals. It is expected that in case of real fire accidents HCl in different amounts is produced and influences the release of
Acknowledgments
We would like to gratefully acknowledge the language check by Dr. Anton Dikmans.
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