Experimental characterization of a solid industrial by-product as material for high temperature sensible thermal energy storage (TES)

Nowadays, industrial processes use large quantities of fuel and electricity that produce heat, but much of which is wasted either to the atmosphere or to water. Many types of equipment have been developed to re-use some of this waste heat. Waste heat usefulness is determined by its temperature and its exergy; the higher the temperature the higher the quality or value. There are mainly three reversible methods to store it: sensible, latent and chemical. In this case, a solid by-product from the potash industry is tested in two different shapes to be used for industrial sensible heat recovery in high temperature, in a range of 100–200 °C. This heat recovery could be used for cogeneration, energy efficiency measures, passive heat recovery, solar cooling, etc. Within all the properties that define the suitability of a material to store sensible heat, waste materials stand out especially for their low costs and availability. This heat recovery could be used for cogeneration, energy efficiency measures, passive heat recovery, solar cooling, etc. For that, a complete analysis of thermophysical properties was done both, at laboratory and a pilot plant scale. At the laboratory, the material composition was found to be NaCl as major phase. With differential scanning calorimetry (DSC) the specific heat capacity was determined as 0.738 kJ/kg°C. The thermal stability was checked from ambient temperature to 800 °C and the density and the conductivity at room temperature were also calculated. Also, a corrosion test was performed using samples of stainless steel at three degradation times, these results were compared with those obtained with Solar salt, a commercial and extended option for thermal energy storage (TES) applications at high temperature. At pilot plant scale, using 59 kg of storage material, thermal cycles were performed with the storage material heating and cooling it from 100 to 200 °C varying parameters as the heat transfer fluid (HTF) flow rate and the duration of the cycles.