Evaluation of rhyolite rock as thermocline storage material for medium and high temperature applications

Abstract

Nowadays, the packed bed filled with aggregates, which replaces a large part of the used fluid and prevents convective mixing in the storage liquid, has a better cost/storage time ratio. It is easily integrated with some types of renewable energy. Besides, it is cheap and more efficient without environmental impact. As a result, it was crucial to check some criteria to select the storage materials. In this regard, this paper aims to examine the properties of the rhyolite rock as a candidate for heat storage. It was collected from Oued Tensift near Marrakech, Morocco. The optimal temperature range for this rock was defined. Chemical and structural composition and thermo-physical properties of the rock are carried out by using XRF, EDX, DRX and TGA-DTA. Experimental heating and cooling tests were also performed at two different temperatures 300 °C and 600 °C to determine the effect of thermal cycling on the mineralogical structure of rhyolite rock. The found results indicate that this material can be used to store thermal energy for medium temperature (100–300 °C) as well as for high-temperature applications (below 650 °C) such as CSP plants.Rhyolite is a good candidate for heat storage as it exhibits structural stability even after undergoing thermal cycling. This stability means that the thermophysical and chemical properties required for heat storage can be maintained. When heated to 1000 °C, rhyolite undergoes minimal mass loss, which doesn’t exceed 1.5 %. This characteristic confirms its suitability for heat storage applications. Rhyolite has an almost constant bulk density (decrease around 0.18 kg/ m3) over a temperature of 600 °C, rhyolite's average capacity and thermal conductivity values are 1.92 MJ/m3. °C and 2.16 W/m.°C, respectively, when heated from ambient temperature to 400 °C. These values indicate the rock's ability to store and release heat efficiently.