Klaus W. Lange

A Mathematical Approach for the Mass Transfer Between Liquid Steel and an Ascending Bubble

A mathematical model which is adaptable to practical conditions has been put forward to deseribe adequately the purging of liquid steel with an inert gas. The mass transfer between liquid steel with varying C, O, H, N, and S contents and an ascending argon bubble has been investigated. The simultaneous mass transfer of all possible gaseous compounds is considered as a function of the initial bubble mass, height of the steel bath, the bulk concentrations in the melt, and the external pressure. The model takes into account the change in size and form of the bubble resulting from its rise and the mass transfer between the bubble and the melt, and also the influence of surface active agents such as sulfur and oxygen. The following general conclusions can be drawn: 1) the gases flushed (out of the melt) by the bubble can be related to the amount of argon injected into the bath. 2) Increase in the initial bubble size and the content of the gas in the bath to be purged, and decrease in the external pressure result in more pronounced deviations from equilibrium saturation within the bubble. 3) Lower external pressure, increasing supersaturation of CO, and greater amounts of purging gas at higher dispersion are the chief factors responsible for increasing, purging efficiency for H, N2, CO in steel melts. 4) Surface-active agents decrease the purging ratio for nitrogen in a carbon-free melt, but, in carbon-containing melts, increasing amounts of oxygen alone lead to a considerable increase in the purging ratios for nitrogen due to the high mass transfer of CO to the bubble. In the latter case, the effect of increasing sulfur content on the purging ratios is of no significance.