A Full-scale Study on the Partitioning of Trace Elements in Municipal Solid Waste IncinerationEffects of Firing Different Waste Types

Waste incineration on a grate is a well-established thermal treatment technology in Denmark and several other countries. The method is flexible with respect to operation, it allows for recovery of energy, it reduces the volume of solid waste significantly (by a factor of 8−10), and advanced flue gas cleaning technologies ensures very low emissions from modern incineration plants. In 2005, 24% of the total reported Danish waste production was incinerated. However, the presence of inorganic constituents such as alkali metals, Cl, S, and heavy metals in the waste constitute an essential challenge in waste incineration, both with respect to operational issues and due to environmental concerns. Formation of acidic pollutants, high mass loading of aerosols, and deposition of potentially corrosive components on heat transfer surfaces are among the encountered problems caused by volatile alkali compounds and heavy metals during combustion, and the potential leaching of heavy metals from the solid residues upon disposal is another major environmental concern. In this work the partitioning of trace elements in a waste-to-energy (WtE) boiler was studied experimentally, based on results from a full-scale measuring campaign at a Danish WtE plant while applying changes in waste composition and grate operation, respectively. The changes in waste composition were applied by adding (one-by-one): dedicated waste fractions, comprising road salt (NaCl), household batteries, automotive shredder waste, CCA (copper−chromate−arsenate)-impregnated wood, PVC, and, shoes, to a base-load waste. Special focus in the present work was on the partitioning of the elements Pb, Zn, Cl, S, Na, and K, which are all considered problematic elements with respect to deposition and corrosion problems. The partitioning of the elements was found to be influenced by various effects, and there was not necessarily a correlation between the input concentration of an element in the feedstock and the amounts recovered in the fly ash and flue gas fractions. The study indicated that Cl and S played an important role for the partitioning of Pb, and maybe also Zn. When firing Cl-rich waste fractions (PVC, salt, shoes), the partitioning of Pb seemed to shift toward increased vaporization (and subsequent recovery in fly ash and aerosol fractions). The full-scale study also implied that organically bound Cl (as in PVC, shoes) was preferably released (as HCl(g)) to the gas phase, whereas the inorganically bound C