Investigation of thermal energy storage system based on mining by-products for the recovery of Moroccan mining industrial waste heat

Implementing thermal energy storage system for energy intensive industrial processes such as mining industry is regarded as viable alternative to increase the energy efficiency by capturing waste heat, storing it, and then using it to produce power during night or for daily demand-supply matching. The present work aims at examining the integration of thermocline packed-bed system to recover waste heat for a Moroccan mining industry from numerical, technical and economic viewpoints. The storage single tank uses thermal oil as the heat transfer fluid, and the mining by-product (Porcellanite) issued from the same industry as storage material. An earlier developed and validated model is deployed to simulate the thermocline behavior of the storage tank and assess the performances of the investigated storage material. The mining by-product undergone extensive experimental characterization including chemical and structural composition, thermophysical properties, mechanical behavior, and durability testing, before and after thermal cycling. Porcellanite is predominantly composed of quartz with a porosity of around 0.31 and a bulk and skeletal densities of 1650 and 2420 kg/m3, respectively. Thermal cycling impacts positively its heat capacity by raising it from 0.4 J/g.K to 0.98 J/g.K resulting in a considerable increase of energy density. The thermal stability of the storage material was also demonstrated. Less than 2% of mass loss are reported after heating tests. These results revealed the suitability of the by-product for medium-temperature range. Furthermore, numerical outcomes demonstrate the great potential of the storage material to store and/or release energy with a charge efficiency of 87% and discharge efficiency of 88%. Finally, the proposed solution to recover waste heat (heat exchanger and thermal energy storage system) was economically evaluated for the Moroccan mining industrial process. Findings demonstrate an economic profitability of the proposed solution opening an important prospect for circular economy.