Electrode consumption forms a large part of the costs of EAF steelmaking and electrode prices have been very volatile during recent years. Therefore, it is important to understand what causes the consumption of electrodes and how it can be reduced with more precise EAF control practices.
The consumption of graphite electrode in electric steelmaking is related to different parameters of the steel production technology and electrical parameters of the supply system. These parameters are, for example, the quality of the electrodes and amount of electric current. The four most important components of electrode consumption mechanisms are tip consumption, sidewall oxidation, stub loss and top joint breakage. (Migas & Karbowniczek 2013)
Tip consumption of graphite electrodes occurs when the temperature is 3000°C or above. The high temperature of the electric arc causes the graphite material to sublimate. In this phenomenon, graphite is converted directly from a solid to carbon monoxide gas. Various factors affect the sublimation rate of graphite. These factors include the magnitude of used current when the arc is present, the diameter of the electrode tip, the duration of time that current is passing through the electrode, the resistivity of the electrode and arc stability. (LMM Group 2007)
Electrode sidewall oxidation is caused by the reaction between oxygen and graphite in the furnace atmosphere, which forms carbon monoxide. Electrode surface area and smelting time are the two major factors affecting the amount of electrode sidewall oxidation. (Rongxing Carbon 2007)
Oxidation and the penetration of cracks can also cause a small section of the electrode or the joint to break. Top joint breakage is influenced by different factors of furnace operation, such as poor scrap loading. (Migas & Karbowniczek 2013)
How to reduce electrode wear
The graphite electrode consumption is an essential component of the cost of steel production in the EAF process route, but this cost can be lowered with optimized EAF process practices. With real-time melting information, voltage and current can be dynamically controlled. Higher voltage reduces the consumption of electrodes as the arc current decreases, but the increased arc length requires careful control. Real-time melting information from the furnace ensures that the voltage levels are lowered when the sidewall protecting scrap has melted. This has been proven to lead to even 10% reduction in electrode consumption. In addition, this optimal control of voltage levels and electric current also reduces the wear of the protecting refractory mass. These benefits combined decrease the operating costs of EAF significantly.
Real-time information from the EAF can be measured reliably with our ArcSpec system. ArcSpec monitors and analyses the emitted light from the EAF with Optical Emission Spectrometry (OES). The system makes it possible to operate the EAF with higher voltage and longer arc without significantly increasing the refractory wear. The system has also a built-in feature to optimize the voltage and electric current levels to reduce electrode consumption, among other benefits.
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LMM Group 2007. Study on the technology of reducing the consumption of graphite electrode [online]. Dalian: LMM Group.
Migas, P. and Karbowniczek, M., 2013. Selected Aspects of Graphite Applications in Ferrous Metallurgy [online]. Krakow: AGH University of Science and Technology.
Rongxing Carbon 2007. The consumption mechanism of graphite electrode in electric steelmaking [online]. Zhengzhou: Rongxing Carbon. Available from: https://www.graphite-product.com/news/PI/2020-03-24/187.html# [Accessed 6 November 2020]