Books on Demand Temperature control on hot pots in the aluminium production: Analysis and Improvement

Diplomarbeit, die am 15.07.2003 erfolgreich an einer Technische Universität in Deutschland im Fachbereich Bergbau, Hüttenwesen und Geowissenschaften eingereicht wurde. Introduction: The process of aluminium production is, even nearly 150 years after its discovery, not totally understood. Such a large quantity of factors influences the production process that no standard can be applied on it. In an aluminium reduction plant there are no two identical electrolysis cells. Differences in the start-up and operational disturbances alter the thermal and electrical behaviour of each cell individually. So every cell has to be monitored individually through the continuous changing bath composition and temperature variation. Every cell needs an individual dynamic optimisation of the chemical and thermal input, e.g. the AlF3- and CaF2-addition and the regulation of the anode-cathode distance. Self-regulating mechanism are the melting and freezing of the sidewall ledge, external mechanisms the lifting and lowering of the anodes. In this work a cell control system at Alumar (Brazil) was analysed and improved. The focus laid on controlling the cell temperature through a variation of the anode-cathode distance. The main objective was to analyse the effect and influence of a so-called temperature resistance modifier on hot pots (electrolysis cells). When the temperature of an electrolysis cell exceeds a certain limit, the pot operates outside its optimal working conditions, thus it has to be cooled down. This can happen by reducing the anode-cathode distance and therefore the resistance of the pot. The reduction is controlled by the so-called temperature resistance modifier. The concept of the temperature modifier was introduced less than one year ago at Alumar and is also within the Alcoa group a quite unexplored field. This work is structured in two parts, first an introduction to theory, then the practical part. Chapter 2 gives