S. А. Khramenko, Candidate of Technical Sciences

LLC RUSAL ITTs (Krasnoyarsk, Russia)
S. А. Zykov, Manager, Semen.Zykov@rusal.com

LLC RUSAL Anode Plant, (Staryy Akulshet, Russia)
Е. А. Startsev, General Director

Prebaked carbon anodes are produced from approximately 85% calcined petroleum coke and 15% coal tar pitch binder. The structure and properties of baked anodes are formed during coke crushing and the preparation of the coke aggregate particle-size distribution. The shape, size, and porosity of petroleum coke particles determine the high bulk density of the coke aggregate. Mixing such an aggregate with molten coal tar pitch makes it possible to obtain an optimal anode paste for pressing “green” anodes. The quality indicators of baked anodes exhibit a nonlinear dependence on the binder pitch content. The quantity and quality of pitch largely determine the technological parameters of mixing required for effective impregnation of coke porosity. “Green” anodes are baked in chamber furnaces for 24–28 days with a gradual temperature increase to 1100–1150 °C. This study investigated the influence of technological factors on the impregnation of coke with coal tar pitch during mixing in order to optimize the composition of prebaked anodes. Based on the results of a full factorial experiment, a dataset of coke aggregate impregnation degrees was obtained as a function of pitch content, mixing temperature and time. When interpreting the results of physical and chemical testing of baked anodes, the degree of impregnation was used as an independent variable. The consumption of prebaked anodes represents a significant cost component in aluminum production. The main non-electrolytic carbon consumption occurs as a result of the selective oxidation of the highly reactive binder coke through the Boudouard reaction. The amount of pitch and the technological parameters of mixing should be optimized with respect to both pitch content in the anode paste and the degree of coke pore impregnation. Under laboratory conditions, the effects of technological factors, including mixing temperature, mixing time, and pitch content, on the degree of coke porosity impregnation were investigated. The vibro compacted bulk density method was used to evaluate the degree of coke impregnation. Considering the multifactorial nature of the wetting process, design of experiments (DOE) methods were applied to assess the influence of pitch content and mixing conditions on the degree of impregnation.

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