Abstract
Thermal storage of the energy is essential for district heating systems to mitigate intermittency related issues. The extensive cavities created after extraction of ores/coal in mines could provide a unique opportunity for storage and extraction of thermal energy. This paper shows that underground backfilled stopes present a viable potential for being retrofitted to thermal energy storage batteries. The present study evaluates the energy performance of thermal energy storage in underground backfilled stopes by installing heat exchange tubes prior to backfill placement. A numerical fluid mechanics and heat transfer model for backfill stopes was developed in Fluent to investigate the heat exchange inside the tubes as well as the heat transfer happening within the backfill during the heat storage and extraction process. The proposed model is compared against an analytical heat transfer model to determine its reliability and accuracy. The results obtained from the validated numerical model showed that energy storage system in a typical underground backfilled stope of coal mines can provide about 23 GWh of thermal energy storage capacity with an average recovery rate of 60% during extraction cycles. Accordingly, several sensitivity analyses were conducted to define the optimum center-to-center distance for the pipe installation to attain the best system performance. Through a series of parametric studies, it was found that thermal conductivity of backfill and rock, circulating fluid mass flow rate, initial rock temperature and thermal saturation time constitute the most significant influencing parameters on energy storage performance of such applications. It can be concluded that thermal energy storage systems in backfilled stopes are relatively more techno-economically feasible, compared to conventional borehole energy storage systems, in terms of their significantly lower drilling/installation costs and higher hosting temperature.
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