Ökonomische Grenzen der sauren Flugaschenwäsche von Müllverbrennungsflugaschen als Alternative zu herkömmlichen Entsorgungslösungen

Abstract

The proposed transformation of the economy towards higher circularity increases also the importance of waste incineration residues as source of secondary raw material. While metals, glass and mineral fractions are recoverable from bottom ash using mainly mechanical technologies, heavy metals, condensed on fly ash particles, are chemically extractable with acids. Besides the recovery of metals, especially Zinc, mass reduction as well as decontamination to fulfill criteria for non-hazardous waste landfills are the main economic drivers for acidic fly ash washing. A hypothetical scenario of different disposal options for 20.000 tons fly ash per annual was investigated. The specific costs per ton of fly ash were evaluated when acidic washing according to the FLUWA process was applied and compared to the specific costs per ton of fly ash of a conventional disposal of fly ash either stabilization with cement and subsequent landfilling on a non-hazardous waste landfill, or disposal on an underground disposal facility for hazardous waste. On the basis of literature data, a material-flow-analysis was performed to analyze material flows associated with the application of the FLUWA process. For an economic evaluation the energy demand was taken from literature. The investment costs were roughly estimated. Information about disposal and landfill fees of the output fractions were gathered from FLUWA operators and taken from literature. Two scenarios were considered: in the first one, the acidic washed fly ash is assumed to satisfy regulations for non-hazardous waste landfills. In the second one, the acidic washed fly ash exceeds threshold values of non-hazardous landfills is hence recirculated back into the incinerator. The economic evaluation showed that the specific disposal costs per ton of fly ash are much higher when FLUWA is applied (increase of about 30%). The main reasons for this are high costs for the recycling of the zinc-containing hydroxidesludge. Operational costs are mainly depending on the consumption of HCl and H2O2. Acidity of the scrubber water and alkalinity of the fly ash are the key parameters for the HCl consumption, while the content of metallic alumina and Fe2+ influence the H2O2 consumption.