Enhanced moisture removal and loosening of coal slime via steam flash drying

Coal slime, a by-product of coal preparation, exhibits high moisture content and viscosity, which hinder its efficient utilization. This study proposes a steam flash drying method comprising four stages: steam heating, pressure holding, transient drying, and mild evaporation. The effects of steam pressure, particle size, and holding time on the loosening behavior and transient drying performance of coal slime were examined, and the evolution of residual moisture during the mild evaporation stage was analyzed. Results show that increasing steam pressure enhances moisture removal during the transient stage and promotes the loosening and fragmentation of the material structure. Larger particle sizes facilitate rupture and expansion of internal pores, while extending the holding time to 5 min promotes internal cracking and accelerates drying. During the transient stage, macropore and mesopore water are primarily removed, and the crushing ratio exhibits a coupled relationship with the moisture removal ratio. In the mild evaporation stage, an additional 2.5–5.0% of residual moisture is eliminated. With waste heat recovery, the effective moisture diffusion coefficient exceeds that of conventional hot-air drying. The specific energy consumption of steam flash drying (2.67 kJ/g H2O) is lower than hot-air drying, offering a new pathway for efficient drying of high-moisture, viscous materials.