Vitrified asbestos waste used as filler material in a thermocline storage tank

Abstract : Thermocline systems could be an economically viable solution for thermal energy storage (TES) in concentrated solar power (CSP) plants. In this work, the use of Cofalit® as solid filler material inside a thermocline TES in a CSP is studied experimentally with the MicroSol-R pilot-scale facility. Cofalit® is an inert and low cost post-industrial process rocks (recycled material from asbestos wastes), supplied by the French company Inertam [1]. The thermal performance of the thermocline filled with Cofalit® is compared to previous research [2] performed with alumina spheres as filler materials for typical charge and discharge process. Experimentally, it was first observed that the overall porosity of the solid bed increased with Cofalit® with respect to Alumina, due to random shapes and distributed size of the particles. This results in a decrease in volumetric heat capacity from 3.3 MJ/m3K with alumina spheres to 2.7 MJ/m3K for Cofalit® between 200 and 300 °C. The temperature distribution in the tank during both charging and discharging phases is also investigated and compared to the reference case. The development of the temperature gradient and its progression exhibit better performance than the reference Alumina case, thus showing a very good thermocline behavior. Thermocline thickness during charge was found 26% of the tank height in Cofalit® case, 7% lower than with Alumina. While charge efficiency was similar for both materials around 79%, Cofalit® has better discharge efficiency (8% better than alumina). The good thermal performance of Cofalit® as filler material is attributed mainly to a greater heat exchange area afforded by its irregular shape. Considering the cost saving of due to the use of Cofalit® and resulted thermal performance of the thermocline, Cofalit® appear as a very good candidate as filler material.