Abstract
Identifying optimum anode baking level and mixing temperature are important when producing high quality anodes. The effect of varying mixing temperature and baking level were investigated in terms of the resulting apparent anode density, specific electrical resistivity (SER), air permeability, coefficient of thermal expansion (CTE), air reactivity, and CO2 reactivity. Six pilot-scale anodes were prepared at Hydro Aluminium using a single source petroleum coke and <2 mm coke fractions. A coal tar pitch was used with Mettler softening point of 119.1 °C. The aggregate was mixed at 150 °C or 210 °C and baked to a low, medium, or high baking level. A 22 full-factorial design analysis was performed to determine the response of the analyzed properties to the applied mixing and baking temperature. Apparent density, SER, and air permeability were found to be highly dependent on mixing temperature. Apparent density and SER were also slightly affected by baking level. CTE was found to be independent of both baking level and mixing temperature. Air reactivity was found to be mainly dependent on baking level, while CO2 reactivity was dependent on both mixing temperature and baking level.
Highlights
Aluminum is produced according to the reaction described in Equation (1) [1]: (1)Carbon anodes serve as the carbon source on the left-hand side of the equation
It has been shown that density and air permeability were highly affected by the mixing temperature—a higher mixing temperature increased the density and decreased the air permeability
Air permeability was not affected by baking level to a large extent, and the interaction effect between baking level and mixing temperature was low
Summary
Aluminum is produced according to the reaction described in Equation (1) [1]: (1)Carbon anodes serve as the carbon source on the left-hand side of the equation. Anode change is part of the routine work in a potroom, and causes temporary instability in each individual cell. This instability includes freezing of electrolyte onto the surface of the cold new anode, and during the time it takes for the electrolyte to melt, no current is drawn by this anode. This in turn causes increased current to be drawn by the remaining anodes. The optimization of carbon anodes relies on many different production parameters, such as mixing temperature, baking level, coke and pitch quality, aggregate composition, etc. The optimum baking level and mixing temperature are dependent on the coke and pitch qualities used [2]
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