High Current Arc Modeling for Silicon Submerged Arc furnaces

Abstract

Electric arcs are a necessary heat source in many industrial processes that take place in Submerged Arc Furnaces (SAFs). Arcs exhibit non-linear electrical characteristics and behave in a complex manner. Therefore, an improved understanding of their behavior enables better control of furnace operation. Modeling of industrial arcs is a multiphysics process that involves simultaneously solving several coupled physical phenomena, such as electromagnetics, uid dynamics and heat transfer, including a radiative heat transfer from the plasma arc. Coupling uid dynamics and electromagnetics is known as Magnetohydrodynamics (MHD). However, there are also simpler approaches to arc modeling, either based on simplifed physical principles or empirical behaviour. Direct measurement of the arc characteristics is impossible due to hostile conditions inside the SAF, so controlling the heat dissipation is both a science and an art. The arcs exhibit non-linear electrical characteristics and behave in a complex manner. We start by discussing a DAQ system gathering data from a FeSi SAF, the data is processed and used to determine various furnace conditions including arc and charge current as well as harmonics. In this work, several computational models for arc are implemented. First a combined Cassie-Mayr model (CMM) and a channel arc model (CAM), are implemented and coupled with a submerged arc furnace electrical circuit model. The complete circuit model parameters such as resistances and inductances are estimated using measurements conducted on an operational furnace which are also used to validate the models. Both models are then used to estimate harmonic distortion in a SAF for different arc power ratios. Secondly a MHD model implemented by the author is used to simulate alternating current arcs with different plasma gas compositions, and compared to second MHD model. The thermophysical properties of each composition are calculated using specialized code as well as gathered from literature. We investigate the dependence of the results on both the MHD models used and the input plasma data for three argon data sets and compare the results to data obtained from laboratory experiments. Finally, we investigate furnace conditions using different ratios of SiO to CO gases. Finally a new implementation of a special sub model for cathode and anode surface conditions is presented. The models is first used with the channel arc model and then integrated into the MHD model as a module. This model is used to investigate the electrode erosion as well as the sheat voltage present close the the plasma wall.