Substantiation of thermophysical action over electrode paste to achieve an even structure of electrodes of needle coke for thermal furnaces

Abstract

The aim was to develop a procedure for obtaining an electrode paste of needle coke in case of thermophysical action in the extruder circuit to produce graphitized carbon electrodes with the required structure and properties for thermal furnaces. To study the properties and composition of electrode pastes and electrodes, X-ray powder diffraction, electron microscopy, infrared spectroscopy, and calorimetry analysis were used. To evaluate the electrode behavior upon its heating in a melt, mathematical and statistical analysis was used. The data were processed using standard MS Office programs. Experiments with graphitized carbon materials were conducted in a calorimetric laboratory at the Scientific Center for Problems of Processing Mineral and Man-Made Resources, Department of Metallurgy, Saint Petersburg Mining University (Russia), using a developed proprietary prototype of the extruder. The conditions and technological parameters for processing electrode pastes were defined and substantiated (rate of extrusion and electrode paste flow, pressure, and heating rate within the defined temperature range to achieve stable structural indicators of electrodes). According to XRD data, the proposed method of thermophysical processing of an electrode paste via a special extruder within 550–620°C and a die pressure of 60–80 MPa provides an evenly directed structure of needle coke with an average needle thickness of 12–20 nm and a length of needle phases of 5–10 mm. The behavior of electrode samples was examined in the furnace melt within 1500–1700°C. The obtained stable levels of the thermal-expansion coefficient (0.3·10-6 °C-1) and specific electrical resistance (4.5–6.0 μmOhm·m) were manifested in reduced electrode sublimation, low losses of overall weight at the electrode end, decreased oxidation, and reduced damage on its side. The proposed electrode structure ensures stable heat and electrical conductivity, as well as high heat capacity, which levels are equivalent to those of imported electrodes and electrode pastes.