Entwicklung eines neuartigen korrosionsfesten Schutzschichtsystems für einen Prozess zur thermochemischen Aufarbeitung von Klärschlammasche zu Düngemitteln

Sewage sludge is a practically endless source of the essential plant nutrient phosphorus. However, removal of their heavy metal contents is obligatory to enable the application of sewage sludge ashes as fertilizer material. A thermochemical process accomplishes this separation in high chlorine containing environments at temperatures of up to 1000°C.

Unfor­tunately there are no furnace materials commercially available that can withstand such conditions over longer periods of time.

Previous experiments have shown - in accordance with thermodynamic calculations - that corundum is resistant to oxidizing high-temperature chlorine corrosion conditions. Although it offers outstanding corrosion resistance, its mechanical properties - in particular its brittleness and low thermal shock resistance - make it inapplicable as a material for large moving components such as rotary furnace tubes.

A new coating concept combines the chemical resistance of corundum with the mechanical properties of an alloy. It consists of a two-layer thermal spray coating system with a ceramic top coat (APS) and a corrosion resistant metallic NiAlMo bond coat (HVOF) that is specially designed for the use in reducing chlorine environments as can be expected under the ceramic top coat.

Das IGF-Vorhaben 16432 N des DECHEMA-Forschungsinstituts, Theodor-Heuss-Allee 25, 60486 Frankfurt am Main wurde über die AiF im Rahmen des Programms zur Förderung der industriellen Gemeinschaftsforschung und -entwicklung (IGF) vom Bundesministerium für Wirtschaft und Technologie aufgrund eines Beschlusses des Deutschen Bundestages gefördert.