Treatment of MSWI bottom ash from grate incineration and fluidized bed combustion: a comparison

Abstract

The different firing conditions in grate incineration and fluidized bed combustion are an important factor that influence the properties of incineration bottom ashes (IBAs) from municipal solid waste incineration and therefore also their treatment behavior. To gain a deeper understanding of which amounts and qualities of valuable goods, especially metals and glass, can be recovered by means of state-of-the art IBA processing and how this depends on the incineration technology, an industrial-scale experiment was conducted. In the course of this experiment, ~200 tons of one IBA from grate and one from fluidized bed were processed in an IBA treatment plant. This plant splits the input material into more than 15 output flows and allows for optimal recovery of metals and also glass. Based on an extensive sampling and sorting campaign, a mass flow analysis for the total IBA masses, Aluminum, ferrous metals and glass was created. Results showed that for both IBAs about 60 % of the input are found as mineral or glass fraction after the treatment. Whereas no glass was separated from the grate IBA, more glass than mineral fraction was obtained from the fluidized bed IBA. An assessment of the quality of the metal fractions indicates that due to the different process conditions metals from grate incineration show a lower quality than from fluidized bed combustion. In general, advantages of fluidized bed IBA could be shown in terms of recyclability of metals and glass.