Quality assessment of needle coke used in the production of graphite electrodes for metallurgical furnaces

Abstract

Needle coke is a special kind of carbon material that has a developed anisotropic fibrous structure, high current conductivity in the fiber direction and low coefficient of linear thermal expansion. This material has found a wide application in steel industry where it is used for the production of graphite electrodes of the SHP (50–75 kA) and UHP (up to 100 kA) grades designed for high-power electric arc furnaces. This paper describes the results of assessing the quality of the needle coke that is commercially used at El 6 for the production of carbon and graphite products. The quality of the material was analyzed based on two groups of techniques: spectral analysis (SEM and optical microscopy, XRD, Raman spectroscopy) and analysis of physical and chemical properties (CTE, real density, sulfur, ash, moisture, electrical resistivity). A study and a comparative analysis were carried out using seven samples of calcined petroleum and pitch needle cokes. Six of them are used commercially (imported) and one was produced in laboratory conditions from Russian raw materials. The study confirmed that a better needle coke structure tends to form from petroleum coke versus pitch coke. Using the results of spectral analysis, the studied samples of needle cokes were classified into three groups based on their morphology and structure, which correlates with the results of the analysis that looked at their physical and chemical properties. The combination of research and data processing techniques presented in the paper ensures a comprehensive analysis of the studied needle coke and suggests that the material in view can be used in the production of graphite electrodes.The authors would like to thank Evgeny S. Gorlanov, deputy director of the Research Center for the Problems of Processing Mineral and Man-Made Resources at Saint Petersburg Mining University, and Andrey L. Kvanin, who oversees research and engineering projects at El 6, for their valuable advice and assistance in preparing this paper.This research was carried out as part of the State Assignment 0792-2020-0010 by the Ministry of Education and Science of the Russian Federation: Elaborating the innovative technologies of processing heavy hydrocarbons into environmentally friendly motor fuels and new carbon materials with controllable macro- and microstructures of the mesophase”.