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Abstract
Increasing amperage in aluminium reduction cells enhances production but introduces the risk of causing significant disturbance to the thermal balance of the electrolytic cells which will cause early failure. This can cause production losses and generate considerable waste material that is toxic and expensive to dispose. There are many approaches adopted in Aluminium industry for amperage increase varying from constant power to constant anode cathode distance. However operating the cells with higher heat input (or out of the cell’s thermal operating window) at one stage is encountered in many smelters. Hence, various cell design modifications are required to cope with such extra heat input to maintain cell thermal balance
The objective of this thesis is to determine design criteria that will enable optimum manipulation of heat dissipation from the sides of the electrolytic cells in order to have better side ledge freeze and to build a model to represent the experimental results. Both selective controlled air faced cooling and different cooling fins designs to the electrolytic cells shells were tested.
Design features of a controlled air forced cooling network in term of nozzle diameters, distance from end of nozzles to the shell plate, nozzle angles and air velocity at the nozzle outlet (nozzle Reynolds number) were determined through extensive experiments on an industrial electrolytic cell. The optimum combinations of these manipulated parameters reduced the shell temperature by around 120 °C and improved the side ledge of the tested cell. This contributed to an increased life of the tested cell by 300 days. A two dimensional (2D) model was developed to represent the results of the experiments using the theoretical equations from the literature. The results of the model were found to be in agreement with actual results. The specific energy consumption of the cell increased by 132 kWhr due to the power required to operate the air supply (blower) to the network. Nevertheless, the selective air forced cooling can be considered as an option to enable electrolytic cells to operate beyond its thermal balance window.
Extensive experiments were carried out as well to manipulate the impact of cooling fins design i.e. Fins thickness, height, spacing and thermal conductivity on the heat dissipation from the sides of electrolytic cells and the reduction in shell temperature. This reduction in shell temperature in turn enables better side ledge protection. It was found that the temperature of the steel plate could be reduced by up to 50 °C.