Reducing the Energy Consumption during Microwave Drying of Coal Slime Dough by Optimizing Parameters: Experiment and Modeling

Reducing the energy consumption in microwave drying processes is essential for the sustainable management of coal slime. Utilizing a self-constructed microwave thermogravimetric apparatus, the research investigates critical parameters, including microwave power, spherical diameter, and granule size, affecting drying kinetics and energy efficiency. The results show that it was observed that the drying process progresses through three distinct stages, marked by variations in temperature and moisture content: the initial warming phase, a steady drying stage, and a final phase where the drying rate decreases; optimal pellet sizes for efficient moisture evaporation and diffusion were identified, with smaller particles enhancing heat transfer and drying efficiency; and the Nadhari model was determined to best represent the drying kinetics of coal slime under microwave radiation. The findings indicate a positive correlation between drying efficiency and particle size while being inversely related to increased microwave power for smaller granules. A direct positive relationship between moisture migration and increased power levels was established, while an inverse relationship with the enlargement of particle sizes was observed, negatively affecting the efficiency. For granule sizes of 30, 40, and 50 mm, a decrease in activation power was recorded, with values of 8.215 ± 2.301, 7.936 ± 1.547, and 3.393 ± 0.248 W·g–1, respectively; and through the comparative analysis of energy consumption, it was demonstrated that for coal slurry particles sized 0.15–0.18 mm subjected to a drying duration of 600 s, an increase in power leads to a reduction in drying efficiency, whereas larger diameter contributes to improved efficiency.