Experimental Study on the Potential Use of South African Ferroalloy Slags as Filler Materials in Sensible Thermal Energy Storage Systems for High-Temperature Applications

The global energy transition to sustainable renewable energy sources has caused a growing demand for advanced energy storage systems, particularly sensible thermal energy storage systems because of their low cost and high performance. This work experimentally investigates the potential use of South African ferroalloy slags as filler materials in packed bed configurations. Ferrochrome and silicomanganese slags are characterised and used as filler materials, and air is used as the heat transfer fluid. The experiments are designed for high-temperature systems, with working temperatures of up to 600 °C and usable energy limited to 400 °C. The slags’ thermophysical properties are evaluated and used to assess their performance during thermal cycling. Material phase composition, grain size, and porosity distributions are analysed with automatic scanning electron microscopy. Thermogravimetric analysis is done to study the chemical stability of the slags at temperatures reaching up to 1000 °C. The slags’ thermophysical properties and thermal energy storage capacities are comparable to other candidate filler materials for high thermal energy storage systems. High thermal energy storage efficiencies of 70–90% are achieved in the experiments. However, a high pressure drop of up to 2 bar is recorded. The slags are found to be chemically stable for use in systems with working temperatures of up to 1000 °C. Volumetric energy densities of 165–187 kWh/m3 are recorded during thermal energy recoveries at temperatures above 400 °C. The slags were found to be suitable for use as filler materials in sensible energy storage systems with working temperatures of up to 1000 °C.