Screening Tests in Lead of Filler Material for a Packed-Bed Thermocline Energy Storage Facility

Packed-bed thermal energy storage (PBTES) systems are a promising alternative for cost intensive two-tank molten salt systems that are used in most commercial concentrating solar power (CSP) plants. For high temperature (>500°C) thermal energy storage systems, liquid metals like lead have great potential as heat transfer media due to their chemical stability and their wide fluid temperature range. A drawback of liquid metals is its corrosiveness, which increases with temperature. Liquid metals can dissolve elements out of the structure material allowing liquid metal penetration or they can form intermetallic compounds.
Little research has been carried out to date on the behaviour of possible filler materials in contact with liquid metal especially at temperatures above 600°C. In this study seven different ceramics were tested at 650 and 750°C in lead (Pb) up to 5000h in reducing conditions. It appears to be neither a temperature dependency nor a time dependency in the attack on the ceramic beads. The glass content is more important. How deeply Pb penetrates often depends on the defects on the surface. If there are already cracks into which lead can penetrate, the attack will be correspondingly deeper. ... mehrFurthermore, thermal shock resistance plays an more important role at these higher temperatures. The best behaviour with neglectable reaction with Pb showed Yttrium-stabilized ZrO2 (YTZ) and the zirconium-toughened Al2O3 (Minerax) ceramics. A slightly inferior behaviour had the two alumina ceramics (90% and 92%) and the zirconium silicate RIMAX. In contrast, the zirconium silicate ER120 and the Cerium-stabilized ZrO2 cannot be used due to its high glass phase content with the associated Pb attack and the poor thermal shock resistance, respectively. The next step will be to test the materials that have performed well in isothermal condition also under frequent thermal fluctuations. A test facility which is currently being set up for this purpose will be presented.