Bubble Bursting Phenomena on the Free Surface of Iron Melt and at the Slag/Iron Interface

摘要

The aim of this study was to understand the mechanisms of interaction of the ascending gas bubbles with iron and slag/iron systems when bubbles burst on the free surface of iron melt and pass through the slag/iron interface.The bubble bursting experiments on a free surface were investigated both by water modelling and hot modelling with liquid iron. The results clearly showed that the mechanisms for the ejection of droplets are quite similar in both low and high temperature systems.The effect of the equivalent bubble diameter on the mass of ejections was investigated in both water and liquid iron systems. It was found that there exists a critical diameter of a bubble with regard to the maximum quantity of the droplet production. This critical diameter is about 4 mm in water, and about 9 and 12.5 mm in molten iron when the surface tension is about 1.4 and 1.8 N/m, respectively. Above this critical bubble size, formation of jet droplets tends to decrease. The similarity of these two systems was discussed on the basis of the theory of dimensionless numbers, and a new dimensionless group was proposed to link the two systems. The new dimensionless group takes into account also viscosity which was not considered by Eotvos number, previously used in this context. Based on the mechanism studies and the detailed knowledge of the relation between the bubble size, physical properties of the liquid and the amount and size distribution of the ejected droplets obtained in this work, it is possible to minimize dust generation and formation of accretions or skulls in metallurgical reactors utilising gas bubbling.Entrainment of iron droplets into slag by gas bubbles passing through the slag/iron interface was investigated experimentally by using in-situ x-ray transmission techniques and optical microscopy of the cooled specimens afterwards. The mechanisms of metal droplet formation and their entrainment into the slag were detected and discussed as well.The effects of bubble size, interfacial tension and viscosity of the slag were investigated. The results showed that the mass of the entrainment increased with the increasing bubble size, but decreased with increasing interfacial tension and slag viscosity. A dimensionless equation was derived to describe the relation between the entrainment of metal into slag and the above-mentioned parameters. This information can be used to optimise heat and mass transfer in the ladle furnace and to reduce the financial loss due to metal discard within the slag.