A CFD analysis of slag properties, electrode shape and immersion depth effects on electric submerged arc furnace heating in ferronickel processing

Abstract

a b s t r a c tA 2D, steady-state computational fluid dynamics (CFD) analysis of an industrial electric arc furnace (EAF) is presented. The analysis accounts for the electrode shape and immersion depth, as well as for the dependence of Joule heating on the properties of the slag. The equations for the electric potential, momentum and heat transfer were solved across four distinct regions (i.e. air, slag, ferronickel and firebricks) and the final profile of the slag/metal interface was calculated as a function of the operating parameters of the furnace. The results indicate that the amount of Joule heat produced by the Söderberg electrodes increased with increasing applied voltage and electrical conductivity of the slag; the Joule heat peaked for a value of slag electrical conductivity equal to 3 S/m. A highly conductive slag along with a greater electrode immersion depth was found to facilitate the melting process. The maximum slag velocity values computed were of the order of 0.8 m/s in the vicinity of the electrode tips.

Pragmatic analysis of the electric submerged arc furnace continuum

“…Owing to the poor electric conductivity of the calcine, the electric energy leads to the formation of a molten slag layer due to the effect of Joule heating and, to a lesser extent, because of the development of multiple small-scale electric arcs formed in the vicinity of the electrodes [ 6 ]. The shape of the electrode tip (most frequently rectangular or ellipsoidal) and the immersion depth of the electrodes affect slag transport properties—principally viscosity, thermal and electrical conductivity [ 7 – 9 ]. In turn, transport properties affect the maximum temperatures achieved, the temporal distribution of liquid fraction and the formation of stirring velocity gradients in the slag melt.…”

Three-dimensional Computational Fluid Dynamics Analysis of an Electric Submerged Arc Furnace

“…where B0 and b represent the contributions from the external and induced magnetic field, respectively; in the current model, B0 is by definition zero and we have previously shown b to be infinitesimal 7,8 and may, thus, be ignored. We note that Eq.4 is valid under the additional provision that charge mobility is sufficiently low.…”

“…Materials properties. The air, slag and ferronickel phases were considered as homogeneous fluid continua 7 . The density, viscosity and electrical conductivity of the slag layer as well as the electrical conductivity of the ferronickel layer were modeled as functions of temperature (see Table 1).…”

“…The principal ferronickel production route involves reductive roasting of lateritic ores in rotary kilns towards formation of calcine 1 , which further undergoes excess-carbon smelting 2 in megawatt electric arc furnaces (EAF) [3][4][5] . EAFs typically operate at temperatures as high as 2000 K 6 under the effect of Joule heating maintained by a number of self-backing Söderberg electrodes 7 which are continuously consumed via submersion into a slag melt 1,7 . FeNi recovery is, then, achieved by continuous chemical reduction promoted by high-temperature (fast) metal/slag reaction kinetics, enhanced mass and heat transfer, electromagnetic stirring of the slag bath owing to buoyancy effects 7,8 and low slag viscosity 9 .…”

“…EAFs typically operate at temperatures as high as 2000 K 6 under the effect of Joule heating maintained by a number of self-backing Söderberg electrodes 7 which are continuously consumed via submersion into a slag melt 1,7 . FeNi recovery is, then, achieved by continuous chemical reduction promoted by high-temperature (fast) metal/slag reaction kinetics, enhanced mass and heat transfer, electromagnetic stirring of the slag bath owing to buoyancy effects 7,8 and low slag viscosity 9 . Intrinsically, however, metal recovery is dependent on the slag's electrical conductivity (EC) and its effect on transport properties of the mesoscale [10][11][12] ; slag EC itself is very sensitive to even fractional changes in the chemical concentration of the ore, which reflect on final nickel quality.…”