Sedimentation Behavior of Liquid Iron Droplets during Smelting Reduction of Converter Slag by Considering the Coalescence of Droplets

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To improve the sedimentation efficiency during the smelting reduction process of converter slag for iron extraction, the interaction and sedimentation behavior of liquid iron droplets have been studied under the condition of experimental crucible scale by numerical simulation. The effects of slag viscosity and density difference between slag and iron droplet have also been investigated. The results show that sedimentation process in molten converter slag can be divided into early and latter settling stages, and increasing the coalescence of small droplets in the middle and lower region of slag pool and accelerating the droplet sedimentation at later settling stage are crucial for shortening the settling time of whole iron droplet cluster. During the sedimentation process, the coalescence phenomenon is accompanied, whereas rebound may not happen probably due to the relatively large metal-slag interfacial tension, small slag viscosity and small relative velocities of colliding droplets (≤8×10−3 m·s−1) caused by the creeping flow. The sedimentation velocities for a droplet is increased by about 13%–17% after coalescence. The sedimentation efficiency with interaction is significantly higher than that without interaction when iron droplets coalesce frequently. As the slag viscosity increases from 0.065 Pa·s to 0.195 Pa·s, the sedimentation efficiency decreases from 90% to 59%, while it increases from 89% to 92% with the density difference increasing from 3700 kg·m−3 to 4300 kg·m−3 at the settling time of 24 s. Therefore, molten slags with better fluidity and lower density are favored in the practical iron extraction process.