Melting Mechanism of Water-Cooled Billet-Type Bottom Electrode of Direct Current Arc Furnace: A Numerical Approach

Abstract

The direct current (DC) furnace, the earliest type of the electric arc furnace (EAF), was popularized at the end of the 1980s. Even in its heyday, there were always doubts about its superiority due to some imperfections of the DC furnace (e.g., the problems of the bottom electrode system). The water-cooled billet electrode, which is classified as one of the four types of the bottom electrodes, has been in use for more than two decades. However, so far its melting mechanism has not been well understood. A sophisticated numerical model was thus constructed by coupling the heat transfer and the fluid flow, and taking into account the electromagnetic effect as well as the influence of the gap between the billet and the copper jacket. The observed phenomena could readily be explained using the model. The computed results show that the axial component of the electromagnetic force plays an essential role in driving the strong flow within the electrode hole, and that the Joule effect does not contribute the majority of the heat taken away by cooling water. An important conclusion is reached that there is a double-edged effect by changing the billet diameter. Accordingly, a modification of the billet shape is suggested, i.e., a diameter-variable structure, which should greatly assist in improving the thermal state of the billet.