Kinetic study of droplet swelling in BOF steelmaking

Previous work in the authors' laboratory has shown that an understanding of droplet swelling is essential in predicting droplet residence times in basic oxygen steelmaking. Several workers have observed swelling of high carbon droplets when exposed to oxidising slags. In the present work, the authors present data on swelling rates measured by X-ray fluoroscopy and compare this with the total volume of gas evolved during the reaction. It is shown that only a small percentage of the gas generated is retained in the droplet to contribute to swelling. The gas generation rate is shown to be controlled by the rate of nucleation of CO bubbles inside the droplet. The critical supersaturation pressure for nucleation is found to be two orders of magnitude less than predicted from theory, which is in keeping with many other studies on nucleation of gases in liquids. However, the effect of surface tension, temperature and saturation pressure shows quantitative agreement with theory.