Comparative Study of AC and DC Solvers Based on Current and Power Distributions in a Submerged Arc Furnace
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SUBMERGED arc furnaces (SAFs) for silicon or ferrosilicon production are subject to two principal control mechanisms. On the one hand, it is the metallurgical control, which encompasses raw material selection, feeding, stocking, and tapping, and on the other, it is the electrical control, where the power dissipation is controlled by selecting the transformer set-point voltage as well as the phase currents or resistances. The electrical control strategy depends on the raw materials in the furnace, and the goal is to control the power dissipation through the current distribution. The electrical behavior in the furnace also affects the raw materials selected for given product specifications. There are no instruments/ sensors that can measure the actual current distributions in the furnace directly. The practice in the industry is to operate the furnace based on the analysis of limited data at hand as well as by controlling the phase current or
Y.A. TESFAHUNEGN and G. SAEVARSDOTTIR are with the Department of Engineering, Reykjavik University, Menntavegur 1, 101 Reykjavı´ k, Iceland. Contact e-mail: [email protected]. T. MAGNUSSON is with the Stakksberg ehf, Stakksbraut 9, 230 Reykjanesbae, Iceland. M. TANGSTAD is with the Department of Materials Science and Engineering, Norwegian University of Science and Technology, 7491 Trondheim, Norway. Manuscript submitted February 5, 2019. Article published online February 18, 2020. 510—VOLUME 51B, APRIL 2020
resistance. Hence, developing a methodology that predicts current distribution is today’s research question. Due to recent furnace dig-outs, which provide topography information and distribution of different material and intermediate compounds and the availability of computer resources, we are at the stage where we can develop reliable numerical models to predict the furnace behavior. This, in turn, will enhance our understanding of critical process parameters and allow us to control the furnace accurately. The furnace is partitioned in various geometrical zones by taking into account the silicon furnace operation history. As reported by Tranell et al.,[1] different zones of the FeSi furnace have been described from industrial excavated furnaces. The results of the excavation published by Tranell et al.[2] find that the internal part of the furnace is divided into zones based on the materials and their degree of reduction. Myrhaug[3] reported similar features from an excavation on a pilot-scale furnace, operating around 150 kW. Mapping the material distribution gives a basis for quantifying the location-dependent physical properties of the charge materials such as electrical conductivity. Developing a comprehensive numerical model of the SAF (submerged arc furnace) includes electrical, chemical, thermal, and fluid flow considerations. However, operational experience and results from the furnace dig-outs show that the material distribution in the furnace, and thus the location-dependent electrical characteristics, is extremely variable and dependent on METALLURGICAL AND MATERIALS TRA
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