Recovery of Metals from Combustion Residues

Thermal waste treatment using grate-based systems has gained world-wide acceptance as the preferred method for the sustainable treatment of waste. Key factors are not only the reduction of waste volume and mass and the destruction or separation of pollutants but also the efficient production and use of energy (electricity, district heating, process steam), compliant disposal and optimization of the quality of the combustion residues.

From a quality and quantity perspective, waste avoidance and waste recovery measures play a significant role in reducing the throughput of recyclables in thermal waste treatment. Nevertheless, in Germany, for example, it can be assumed that residual waste has an average metal content of 4 % by weight. Consequently, the combustion residues bottom ash and fly ash contain substantial amounts of metals which are finite resources and whose primary production is associated with high power consumption. The most important metals include aluminium, copper, zinc, non-ferrous alloys, chromium-nickel steels and iron.
In conventional grate-based waste-to-energy plants bottom ash is removed from the furnace via a wet-type discharger filled with water. In combination with the recovery of raw materials from combustion residues, the dry discharge of bottom ash is becoming more and more important. Particularly in Switzerland, but also in several other countries, this process has generated a great deal of interest in the past few years. On the one hand, the discharge of classified dry bottom ash is economically viable due to effective metal separation, maximization of revenues from metal recovery (non-ferrous metals, above all), reduction of disposal costs as a result of weight reduction, and associated lower transport costs. On the other hand, there are additional benefits due to the enhanced quality of the discharged dry bottom ash and simpler bottom ash handling in subsequent treatment, preparation and recovery processes.



Copyright: © Thomé-Kozmiensky Verlag GmbH
Quelle: Waste Management, Volume 2 (September 2011)
Seiten: 13
Preis: € 0,00
Autor: Dr.-Ing. Ralf Koralewska
 
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