Energy efficiency in microwave-assisted drying for iron ore pellets: a comparative study of microwave and convective systems

• Novel HOME and DOME metrics introduced to quantitatively evaluate drying efficiency. • Microwave achieves significantly faster drying rates than conventional systems. • Multi-mode microwave systems provide better heating uniformity. • Microwave drying lowers energy consumption enhancing sustainable pellet production. The growing demand for high-quality iron has intensified interest in using iron ore pellets for iron production. Among the most energy-intensive stages of this process is pellet drying. Conventional convective-based drying methods are not only time-consuming and inefficient but also heavily dependent on fossil fuels, contributing to a high carbon footprint. This study investigates microwave-assisted drying as an energy-efficient alternative. A comparative analysis is conducted using both single-mode and multi-mode microwave systems, benchmarked against conventional convective oven drying. To better evaluate performance, two novel indicators, Heat Over Microwave Efficiency (HOME) and Drying Over Microwave Energy (DOME), are introduced to quantify the effectiveness and energy efficiency of the drying process. Results show that targeted microwave heating significantly improves both energy efficiency and drying rate. Microwave drying achieved 90 % moisture removal in under 2 min, compared to over 16 min with convective drying under similar conditions. Moreover, while convective drying efficiency plateaued at approximately 30 %, microwave drying reached up to 56 %. Similar trends were observed in HOME and DOME values, which were over 2 and 1.5 times higher, respectively, for microwave systems. Between the microwave setups, the single-mode system produced more localized heating, while the multi-mode system offered a more uniform temperature distribution and superior energy-normalized drying performance. These findings underscore the potential of microwave-assisted drying technologies to enhance energy efficiency, reduce processing time, and improve control in iron ore pelletization, contributing to a more sustainable and low-carbon iron production process.