Ligament-type granulation of molten slag in different rotary disk configurations

Rotary disk granulation is an energy saving and more stable method for waste heat recovery from high temperature molten slag, and the quality and values of the generated cement product are primary determined by the granulating characteristic. The present work performed the analogue experiments in four types of rotary disks with Rosin/Paraffin mixture as the working fluid. The influence of rotary disk configurations on characteristics of ligament-type granulation, which include ligament number K_L, ligament diameter d_L, capillary wavelength λ and droplets mean diameter d_m were investigated through visualized method. Also the mechanism of droplets pitch-off process was revealed. The results indicated that the surface tension forces that determine the most of ligament and droplet breakup processes. The K_L is predominately affected by We number, while the influence of RP mixture volume flow rate Q, St number and disk configurations is negligible. The d_L decreases with the increase in angular speed ω. The d_L of arc-edge disk is lower than that of the flat/slotted/bulged-block disks due to the effect of gravity force. The short-wave mode is the dominant mode for droplets pinch-off process. Most of the predicted d_m for different disk configurations are within the band of ±15% of the measured values, and the arc-edge disk configuration is recommended because it can produce the smallest droplets compared with the other types of disks. Accordingly, the correlations for K_L, d_L, λ and d_m are proposed in a wide range of operational conditions. Further investigations will focus on the droplets characteristics, as well as the optimal design or selection of different disk configurations.