Estudo da eficiência do arrefecimento dos anodos de carbono no forno de cozimento para um ciclo de 24 e 25 horas na Mozal

Abstract

Moçambique Alumínio is a company dedicated to the production of aluminum, with an installed capacity of 580 thousand tons per year, making it the second largest on the African continent. Aluminum is obtained through the Hall-Heroult process, in which the igneous electrolysis of fused alumina in cryolite is performed. In the aluminum production process, among several components, the highlight is the carbon anodes, which play a preponderant role in the production of aluminum. In the carbon anode baking process, the relationship between the cycles and their final cooling temperature has been taken into account. Therefore, in this study, the analysis of the cooling efficiency of the carbon anode for the 24 and 25-hour cycles constituted the general objective, with the following specific objectives: (i) analysis of the cooling efficiency of carbon anodes in 26- and 30-hour cycles, (ii) estimation of temperatures for a 24- and 25-hour cycle, (iii) description of the carbon anode cooking process, and (iv) identification of the factors that affect cooling. In order to meet the specific objectives, the following methodological procedures were observed: a thermocouple cable, a data logger, and a combustion thermocouple were used as instruments for collecting cooling temperature samples, which were processed and analyzed using Excel. This software helped to generate graphs for each sample, followed by the respective models, namely: linear, exponential, logarithmic, and polynomial. Then, the equations were chosen to determine the final temperature for the 24- and 25-hour cycles, with the Polynomial model being the appropriate model for estimation, as it presented the highest coefficient of determination. For this work, twelve samples were taken, four in each test. Two tests were performed in baking oven 1 for a 26-hour cycle and one test in baking oven 2 for a 30-hour cycle. This means that the cooling temperatures for 24 and 25 hours were estimated from the polynomial models for 26 and 30 hours. As results and conclusions, the study found that the final cooling temperature of the carbon anodes increased with the reduction of the baking cycles. The factors that impact the cooling process are the air flow, the position of the cooling ramp, the dimensions of the peephole, the settings of the peephole (open/closed), the thickness of the smoke walls and the power of the cooling ramp. Due to the increase in temperature with the reduction of the cooking cycle, the study recommends increasing the air flow to ensure that the cooling reaches the defined parameters and increasing another cooling ramp. With this measure, the company must ensure that all peepholes are 100% open in the sections where the cooling ramp is located and ensure zero point control, so that the increased air does not affect the heating zone.