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Progress in Plasma Processing of Materials, 2001

ISBN Print: 1-56700-165-3

High-Power AC Arcs in Metallurgical Furnaces

Abstract

A typical three-phase submerged-arc furnace for production of silicon metal and ferrosilicon has electrode currents ∼100 kA, phase voltages ∼100 V and total furnace power ∼10 - 60 MW. The arcs bum in gas filled cavities or "craters", where the main atomic components of the plasma mixture are silicon, oxygen and carbon. Two quite different simulation models for high-current AC arcs have been developed: the simple PC based Channel Arc Model (CAM) [1], and the more sophisticated Magneto-Fluid-Dynamic (MFD) model, which is here described in some detail. The coupling between the arcs and the AC power source is described by a complete three-phase Electric Circuit Model.
Modelling results for ∼1 kA laboratory AC arcs agree satisfactorily with electrical measurements. In the industrial ∼100 kA case the simulations clearly show that the maximum possible arc length is 5 - 10 cm, which is much less than previously assumed.
Preliminary results with a Cathode Sub-Model for high-current AC arcs indicate that the cathode current density varies considerably during an AC period, while the spot radius remains almost constant.
Model simulations further show that the influence of the easily ionised contaminants Ca and Al on arc behaviour is much less than expected. Preliminary studies of the effect of Fe vapour on the plasma properties suggest that modelling results obtained for silicon metal are also applicable to ferrosilicon furnaces.
Arc splitting - i.e. several parallel arcs appearing simultaneously - may also playa role in the furnace craters.
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