Potential of Corundum and Metallurgical slags as filler materials for a molten-salt based thermocline storage concept

Kurzfassung

Solar thermal power plants with integrated thermal storage are promising for renewable energy production concepts. A recent idea of cost reductions in the thermocline storage by replacing a significant amount of Solar Salt by a low-cost filler material [e.g.1-2] is further investigated. The filler materials have to be resistant in molten salt at temperatures up to 560 °C. In this study degradation studies on corundum and metallurgical slag (copper recycling) in molten NaNO3/KNO3 salt are carried out. The work addresses changes of mechanical/ chemical properties and microstructure of the filler depending on the exposure time in molten salt at 560 °C. After exposure the remaining Vickers hardness is determined and the change of chemical composition and morphology is investigated using XRD, SEM and EDS. The analysis shows that corundum forms a passivation layer as sodium aluminate after prolonged ageing in solar salt. Changes in the chemical composition of the metallurgical slag stored in solar salt are mainly determined by silicate rich phases it contains. However, the structure and stability of the slag remains. Additionally, the specific heat capacity of metallurgical slag depending on the temperature is determined by calorimetry. The results are essential to verify the suitability of corundum and slag as potential filler materials in modern thermocline storage concepts or other heat storage systems.