Avaliação do impacto do pré-aquecimento do cátodo no desempenho e tempo de vida útil da célula electrolítica – caso de estudo Mozal S.A

Abstract

The present work aimed to evaluate the impact of cathode preheating on the operational performance and lifespan of electrolytic cells, using the Mozal S.A. aluminum smelting plant as a case study. The adopted methodology combined a bibliographic and empirical approach, where three electrolytic cells (B053, B106, and B122) were selected. Thermal and electrical monitoring procedures were applied during their preheating phase, and their behavior was evaluated over the first 45 days of operation (early life). The data collected were processed and analyzed using statistical and comparative methods. The results demonstrated that efficient preheating is crucial for achieving thermal uniformity and optimized cathodic current distribution. It was observed that cells with final preheating temperatures above 850 °C exhibited lower thermal standard deviations, whereas cells with temperatures below 850 °C showed higher deviations. Cell B053 displayed a more acceptable preheating rate and consistently maintained its standard deviation within the acceptable limit throughout the process, indicating uniform temperature distribution across the cathode surface. Moreover, during early life, electrical current efficiency was higher in the cells that showed better performance during the preheating phase, with cell B053 standing out. It was also noted that in cells with more homogeneous preheating, the instability index (WRMI) remained below 100 μΩ (the maximum acceptable limit for a stable cell) for most of the early life period. The occurrence of stresses generated by thermal shock during cell startup, stresses caused by excessive deformation in the cathode, and metal infiltration into the joints of cathode blocks were identified as the main failure mechanisms due to inadequate preheating.