Experimental assessment of quartz-rich rocks as storage materials for medium and high temperatures air packed bed system

Abstract

Natural rocks have drawn a lot of interest as sensible storage materials for packed bed system based on their competitiveness in terms of properties, cost and availability compared to other storage materials. Nevertheless, their lifetime depends on the operating temperature range and the used heat transfer fluid. The purpose of this study is to experimentally determine the effects of two temperature ranges: medium range (100 °C–300 °C) and high range (300–600 °C) on the stability of the thermo-physical properties of three quartz-rich rocks namely pegmatite, quartz vein and trondhjemite. For that, firstly, a petrographic description was conducted. Additionally, preliminary stability tests were performed using thermogravimetric and dilatometry analyses to determine the safe operating temperature. Secondly, the durability with air was tested by applying 380 cycles in a laboratory furnace, with a heating/cooling rate of 5 °C/min and 1–2 °C/min respectively, for both temperature ranges. At the end of the durability test, experimental characterizations were conducted on the samples to determine the evolution of their main thermophysical properties such as: density, porosity, water absorption, thermal conductivity and diffusivity and thermal capacity. The obtained results demonstrate the influence of the structural properties on the thermo-mechanical stability of the quartz-rich rocks. We concluded that, large-grained rocks pegmatite and quartz vein are only suitable for medium temperature packed bed systems, while fine-grained trondhjemite rock is well-suited for both ranges.