Acoustic Monitoring of Plasma Arcs in Direct Current Electric Arc Furnaces
- PDF / 427,087 Bytes
- 6 Pages / 593.972 x 792 pts Page_size
- 90 Downloads / 202 Views
CTION
THE ability of the direct current electric arc furnace (DC EAF) to process fines, its increased power efficiency, and its lower electrode consumption have made it popular in industry since its introduction in the late 1970s.[1] Efficient control of the furnace’s electrical power supply is a prerequisite for efficient thermal energy control and, hence, the improved control of the smelting, or melting, operation. The voltage applied to and the current flowing through the arc determine the power that is delivered to the furnace. Although the current is controlled directly at the power source, the voltage across the arc is related to its length. A controlled power throughput, therefore, is achieved by supplying the furnace with a constant current and adjusting the arc’s length to keep the voltage to current ratio at a desired operating point. Efficient arc length control is, therefore, integral to the efficiency and, hence, profitability of the DC EAF. The motivation for this study originated from the current reliance of arc-length control on voltage measurements made externally to the furnace. It generally is accepted that such measurements suffer from the inclusion of voltage drops across the degrading electrode, voltages induced by the large current fluctuations that J.J. BURCHELL, Research Engineer, C. ALDRICH, Professor, J.J. EKSTEEN, Consulting Metallurgical Engineer, and G.T. JEMWA, Postdoctoral Research Fellow, are with the Department of Process Engineering, and T.R. NIESLER, Senior Lecturer, is with the Department of Electrical and Electronic Engineering, University of Stellenbosch, Private Bag X1, Matieland, 7602, Stellenbosch, South Africa. Contact e-mail: [email protected]. Manuscript submitted January 25, 2009. Article published online September 1, 2009. 886—VOLUME 40B, DECEMBER 2009
occur during normal furnace operation, as well as fluctuations caused by the variable impedance of the molten bath.[2] These measurement inaccuracies and unavoidable arc-length fluctuations strongly influence the efficiency of the furnace. In this article, the relationship between the nominal arc length, i.e., the distance between the electrode tip and the molten bath surface in a DC EAF, and the sound that the arc generates has been investigated. In principle, a reliable relationship of this kind could be used to develop acoustic sensors that are electrically isolated from the furnace and, therefore, are insensitive to induced measurement errors. Moreover, it may be possible to discount the unobservable electrical effects of the electrode and bath, because these variables are not responsible for the generation of the acoustic signal. The acoustic properties of plasma arcs have not received much attention in the literature. Perhaps the most relevant is a series of experiments performed by Babcock et al.,[3] in which a musical recording was reproduced by modulating the voltage applied across an acetylene oxygen plasma. According to this research, the plasma exhibits a fluid-like surface tension that acts as a membrane, which can induce pressure wa
Data Loading...
