Thermal Analysis of the Baking and Start-Up Stages for Hall –Heroult Cells at Egyptalum Smelter

Abstract

Thermal behaviour of three cells at Egyptalum smelter was investigated during baking and start-up stages by inserting twenty thermocouples in the sidewall carbon blocks and ten thermocouples in the bottom carbon blocks. The baking time, final average cathode surface temperature and the relative standard deviation for the anodic current distribution for these cells were about 71 h, 852 °C and 10 %, respectively. The heat-up rate during baking stage and the cell stability during the early operation period were improved. Temperatures in the sidewall carbon blocks at the end the baking stage in the range between 71 and 113°C and gradually increased after start-up stage to the temperatures in the range between 558 and 737 °C. The start-up time for these cells was 52 h. Valuable thermal relations were obtained between the sidewall carbon blocks and the steel shell during the baking and start-up stages. The results showed the sidewall carbon temperatures were unaffected by small voltage changes during the baking stage, but it affected by small voltage changes during the start-up stage. Voltage of cell 617 Voltage of cell 619 Voltage of cell 634 Current of cell 617 Current of cell 619 Current of cell 634 Cell current, kA

Thermal Behavior of the early Life of an Aluminum Electrolysis Cell

“…The anode effect time was about one hour, whereas the cell voltages after-treatment of the anode effect of these cells were 8.6, 9.2, and 8.5 V, respectively. Detailed results from the baking and start-up stages of these cells have been reported elsewhere [16,17].…”

“…The behavior of ledge formation of these cells is nearly similar on the same measuring days. The ledge didn't form in the first two measurements (on days 15 and 30) of cell operation [17]. This result means that the molten electrolyte and aluminium are in direct contact with the sidewall carbon blocks, and erosion of the sidewall may occur during the first month of cell operation until a decrease in the operating temperature and heat losses to the sidewalls allow the formation of a permanent protective ledge.…”

“…1 (c) shows eight locations for ledge measurement on the longitudinal sides of the cell as follows (four locations in the wide side between anode block numbers (1-2), (4-5), (8)(9) and (11)(12)). Also four locations are located in the narrow side between anode block numbers (13)(14), (16)(17), (20)(21), and (23)(24). The procedures of these measurements were as follows: removal of the anode crust at these locations, the steel rod is vertically immersed at these locations of the cell, the ruler is horizontally inserted perpendicular to the steel rod, and the steel rod is moved to the direction of the anode to measure the vertical and the horizontal distances from the cathode edge, the ledge thickness or the deterioration of the cathode sidewall carbon is measured by L and F-shaped rods, the extension of the frozen ledge under the anode is measured using the flat rod, then the measured data are plotted to form the ledge shape and the heights of electrolyte and metal are plotted on the drawing sheet [16] .…”

“…9 (a, b, and c). During the first two weeks from metal addition, the decrease in cell voltage from 4.9 to 4.4 volts was based on Egyptalum voltage schedule [17]. At the same time, the average temperature of the twenty thermocouples decreased from 690 to 610 o C. During the following period up to the end of the measurement program (which lasted for 127 days), the cell voltage stabilized, but the average twenty thermocouples temperature decreased from 610 to 582 o C. The thermal relationship between the temperatures of the twenty thermocouples and the corresponding cell voltage of cell 634 during this period is shown in Fig.…”