On-line version ISSN 2411-9717
J. S. Afr. Inst. Min. Metall. vol.109 n.10 Johannesburg Oct. 2009
The effectiveness of current control of submerged arc furnace electrode penetration in selected scenarios
A.C. Mulholland; P.J. Brereton-Stiles; C.J. Hockaday
Mintek, Randburg, South Africa
The electrical control of three-electrode submerged-arc furnaces suffers from a number of complexities, mostly due to the nature of the furnace electrical circuit providing power to the furnace where the three electrodes are interconnected within the furnace through the molten metal bath. This gives rise to what is known as the interaction effect2, where variations in one electrode's current can cause comparable changes to the currents in the other electrodes, particularly in larger furnaces with low power factor.
Resistance-based control of the electrode penetration has largely alleviated these problems, since the resistance encountered by each electrode is predominantly dictated by the length and conductivity of the current path from the electrode's tip to the molten metal bath, which acts as the three-phase circuit's floating neutral point. Hence resistance changes due to tip position or conductivity changes beneath one electrode do not affect the resistances beneath the others, effectively decoupling the control of the individual electrodes1.
Although resistance-based control is therefore generally accepted as superior to current-based control for the regulation of submerged-arc furnace electrode penetration, a few furnace operators still prefer to use current control under specific furnace conditions. This paper presents the results of analysing the performance of both current and resistance-based control in typical scenarios encountered on industrial furnaces, taking into account a number of factors including electrode penetration, power distribution, efficiency and asymmetry of the electrode currents. In order to accomplish this, three typically encountered scenarios were simulated.
The results obtained show that resistance control provides more benefit in all cases, however, the uneven electrode current distribution generated by resistance control when electrodes are on top stops may cause some concern if baking of the electrodes is required in this scenario.
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