Characterization of natural rocks as filler materials for medium-temperature packed bed thermal energy storage system

Abstract

Abstract Packed bed thermal energy storage system is a promising alternative to reduce the overall investment cost of a concentrating solar power plant. However, the choice of suitable filler materials depends on different steps and criteria in order to satisfy the requirements of the target application (e.g. operating temperatures, charging/discharging thermal power, thermal and mechanical stabilities, etc.). Most of the previous experimental investigations have focused on the lifetime stability of rocks at high-temperature up to 500°C. However, they have not discussed the suitability of the unsuccessful ones and their application for medium temperatures (up to 300°C). In this scope, the main aim of the present experimental work is to correlate the petrographic properties of the investigated rocks with their effect on their thermophysical properties, and their thermal stability for a medium-range temperature between 100°C and 300°C. To achieve this objective, four natural rocks (two varieties of pegmatite, cipolin and garnetite) are subjected to several experimental characterizations: At first, a petrographic analysis is done in order to identify the mineralogical composition and the texture of the samples. Secondly, chemical and structural analyses are conducted on the rocks using scanning electron microscopy, energy-dispersive x-ray and x-ray power diffraction techniques. Their thermophysical properties (density, specific heat capacity, thermal conductivity and diffusivity) are also measured. Finally, a thermo-gravimetric analysis is performed in order to test the thermal stability of the investigated rocks. The obtained results suggest that all the studied rocks are potential candidates to be used as filler materials in a packed bed configuration for a medium-range temperature.