Mechanism of carbon anode sticking during baking: Effect of the interaction of process parameters

• A design of experiments (DOE) approach was employed to evaluate the impacts of process parameters on sticking mass and area. • Pitch ratio and heating rate were identified as the two most influential factors affecting anode sticking. • Pitch marker characterization revealed no evidence of pitch squeezing along the radial direction. • Pitch exhibited longitudinal migration during anode baking. • Porosity evolution was pronounced in the bottom sections of the anodes, particularly under severe-sticking condition. Anode sticking is an undesirable phenomenon that occasionally occurs in industrial carbon anode plants during the baking process for primary aluminum production, leading to the adhesion of multiple anodes or the sticking of packing coke to the anode surface. This issue increases material losses, energy consumption, and overall production costs. This study investigated the influence of three key process parameters—pitch ratio, compressive stress during baking, and heating rate during pitch devolatilization—on anode sticking. A design of experiment (DOE) approach combined with analysis of variance (ANOVA) identified pitch ratio and heating rate as the most significant contributors, while compressive stress had a negligible effect. Lab-scale anodes containing a tungsten (W) pitch marker were fabricated under three defined sticking conditions (no-sticking, medium-sticking, and severe-sticking), based on variations in the two dominant parameters. X-ray fluorescence (XRF) mapping and composition analysis revealed no significant radial pitch distribution but confirmed notable downward pitch migration, which correlated with reduced pycnometer density due to the high concentration of closed pores in the bottom sections. Significant decrease in apparent density and increase in porosity from top to bottom indicated anode expansion and porosity formation driven by internal pressure generated from excessive volatile release, especially under severe-sticking condition. This phenomenon was identified as a primary factor contributing to anode sticking in this region. The results established a direct correlation between anode sticking, longitudinal pitch migration, and porosity development, providing valuable insight for modifying the process parameters to reduce anode sticking to some extent.