Access the mechanical and thermal fatigue in packed bed thermal energy storage concept

The thermocline Thermal Energy Storage (TES) systems are key elements to boost renewable energies and to improve the efficiency in energy intensive industries. Among TES technologies, air based packed bed represent a promising option since they allow using low-cost materials. Some of the most interesting filler materials recently studied are steel slag, a byproduct from the steel production, since they fulfil the criteria established in the International Energy Agency (IEA) for TES material, that consist on being inexpensive, available in large quantity without conflict of use, stable up to 1000 °C, compatible with heat transfer fluids and non-toxic. Preceding works have also revealed suitable thermo-physical and mechanical properties to be used as storage material for sensible heat transfer in packed beds. 

However, one of the critical aspects often not addressed is the durability of the filler material (slag particles) subjected simultaneously to mechanical and thermal stresses over a large quantity of charging and discharging operations. During cyclic thermal charging and discharging, the slag inside the tank is subjected to heavy loads at high temperatures and undergo thermal expansion and shrinkage, which can lead to individual particle degradation and also damage of the tank. For this purpose, different model approaches and tools are addressed in this paper. Specifically designed test rig is introduced in order to test long-term mechanical stability of the steel slag under thermal and mechanical fatigue.