DescriptionThe objective of biomass incinerators is to generate heat by burning organic material, such as wood chips, pellets or bark. The advantage of biomass-incineration is its CO2-neutrality by not taking into account emissions due to the production (wood cutting, transport, …). During the incineration process the organic input material is decomposed and mostly transformed into gaseous components, while inorganic material remains as solid ash. The coarse residue (bottom ash) is collected at the bottom of the incinerator, smaller ash particles can leave the incinerator and are collected as fly ash in gas cleaning filters. The inorganic part of biomass material consists of high amounts of Ca, K, Mg which are important nutrients for soils. Therefore it is advantageous to use the ashes as fertilisers for greenlands. Unfortunately, not only nutritive components are in the ashes but also harmful heavy metals can be found (depending strongly on the input material and the incineration process). In order to be able to use the ashes as fertilisers, the heavy metals concentrations have to be under certain limit values given by legislation. Limit concentrations for the most important elements in terms of harmfulness are prescribed in the recommendation of the Austrian Ministry for Agriculture “The use of plant-ashes on fields and grassland” of 1998. In this study in the first half year of 2008 35 incinerators of Upper Austria (150 kWth – 32 MWth) were investigated with regard to heavy metal concentrations in fly ash and in bottom ash. Also the feed material (mainly wood chips) of the incinerators was analysed Each sample was microwave-digested and then measured by ICP-OES. It was found that most bottom ash can be used as agricultural fertilizer. In contrary fly ash has to be disposed in most cases because the concentrations of As, Cd and Zn often exceed the limit values.
|Period||25 Aug 2009|
|Event title||13. Österreichische Chemietage|