Coalescence And Sedimentation Behavior Of Metal Droplets During Smelting Reduction Process Of Converter Slag

Converter slag is one of the most discharged metallurgical slag by iron and steel enterprises,and its output is about 15-20%of crude steel output.Because of its complex composition,unstable performance,high hardness and poor grindability,the treatment has been a difficult problem in metallurgical industry.A large amount of discharged converter steel not only occupies a large amount of land,affects the ecological environment,but also causes serious waste of resources.Converter slag contains about 20-30%iron,and thus the economy of effective extraction of iron element is considerable.During the iron extraction process from molten converter slag by reduction,the metal droplets are generated and suspended in the slag,and the coalescence and sedimentation of metal droplets are very important to improve the separation efficiency of metal iron.Therefore,it is of great theoretical and practical significance to study the collision,coalescence and sedimentation behavior of metal droplets in molten slag for improving the sedimentation and separation efficiency and reducing energy consumption.In this work,the coalescence and sedimentation of metal droplets during the process of smelting reduction of converter slag with aluminium ash are studied by means of high temperature experiment and numerical simulation.The effects of mechanical stirring,slag viscosity,metal-slag density difference,smelting reduction temperature and holding time are revealed,and the interaction mechanism between droplets are obtained.The main conclusions are as follows:(1)The sedimentation process of metal droplets in molten converter slag can be divided into the early stage and the later stage.During the early settling stage,the sedimentation efficiency of metal droplets increases rapidly,while in the later stage,the sedimentation efficiency of metal droplets increases slowly.Enhancing the collision and coalescence of droplets in the middle and lower region of slag pool can accelerate the sedimentation of droplets in the later settling stage,which is vital to shorten the settling time of metal droplets in molten slag.(2)In this study,the coalescence phenomenon is accompanied during the sedimentation process of metal droplets in molten slag.Due to the larger metal-slag interfacial tension,the smaller slag viscosity and the smaller relative velocity of colliding droplets,there is no rebound after droplets colliding during the whole sedimentation process.In addition,mechanical stirring increases the difficulty of coalescence between droplets in molten slag compared with non-stirred slag pool.(3)During the iron extraction process,with the slag viscosity increasing from 0.065 Pa·s to 0.195 Pa·s,the sedimentation efficiency of metal droplets in slag decreases from 90%to 59%;With the metal-slag density difference increasing from 3700 kg/m3 to 4300 kg/m3,the sedimentation efficiency of droplets increases from 89%to 92%.The molten slag with better fluidity and lower density is more conducive to improving the sedimentation efficiency of metal droplets,and the influence of slag viscosity on the sedimentation efficiency is more significant than the metal-slag density difference.(4)When mechanical stirring is applied to the slag pool,the radial shear and the axial"double circulation" of molten slag make the movement of metal droplets with stirring no longer a simple vertical uniform sedimentation,but a spiral sedimentation movement that accelerates first,then decelerates,and finally uniform.The mechanical stirring increases the sedimentation efficiency of metal droplets by 3.4%and reduces the total settling time by 6.8%compared with non-stirring.Therefore,the mechanical stiring is more conducive to the sedimentation and extraction of metal iron during the smelting reduction process.(5)In this work,the coalescence and sedimentation effect of metal droplets with different reduction temperatures and holding time are investigated by high-temperature experiments,and the interaction model of metal droplets proposed in this work is well verified.(6)When the reduction temperature increases from 1530℃ to 1600℃,the viscosity of molten slag decreases,and the coalescence and sedimentation of metal droplets are better;With the holding time prolonging from 1 minute to 3 minutes,the coalescence and sedimentation of metal droplets at the bottom of the slag pool increase significantly,With the mechanical stirring in slag pool,the coalescence and sedimentation behavior is more significant.