Numerical Study of a Structured Thermocline Storage Tank Using Vitrified Waste as Filler Material

Thermocline storage may be, today, the cheapest way to store solar thermal energy at high temperatures. Several estimations lead to a potential cost reduction of 35% compared to a two tank configuration while retaining a good efficiency. Thermocline tanks, in packed bed configurations, are mostly designed using filler materials to reduce the required amount of the expensive molten salt. The main problem of this technology is the thermal ratcheting which can lead to dramatic structural failure of the tank. One solution could be to use a structured bed configuration. With this goal, and as a part of the OPTS Project (OPtimization of a Thermal energy Storage system with integrated Steam Generator), after preliminary investigations driven by the necessity to have a low manufacturing cost, a brick design, made of industrial wastes, is proposed allowing both good thermal and mechanical properties. The implementation of the tank with the filler material of this geometry does not require a specific know- how other than building a classic wall. In order to study the behavior of the thermocline in this structured configuration, a numerical model is developed. A parametrical study was performed and the results are presented and discussed in this paper. The influences of the geometrical ratio of our ‘pattern’, of the physicals properties of the storage material and of the flow rate of the solar salt inside the tank are characterized. The aim is to study the theoretical feasibility of a direct high temperature structured thermocline tank for concentrated solar power, using cheap filler materials.