Numerical Study Of Vortex Flow Of Melts And Transport Process Of Alumina In Aluminum Reduction Cells

As a typical multiphase fluid system rolled by multiphysics, modem aluminum reduction cell obviously possesses the characteristic of vortex flow, whose energy consumption largely depends on the flowing form and interphase substance transport. The object of this thesis is to build up a reliable mathematical model to study the multicomponent and multiphase flow in the cells comprehensively and meticulously, thus the discipline of fluid motion and transport of alumina would be uncovered, which can provide an important theoretical basis and technical method for the structural design and process optimization of large aluminum cells.There are some limitations in the flow modeling for aluminum electrolysis home and abroad, such as the lack of quantitative methods of analyzing the vortical structures of melt, and the insufficient of the simulation during the transfer process of alumina. In view of the above research status, a vortex analytic method has been developed in this paper, and the mathematical model suitable for the simulation of the transport process of alumina has been built, which is supported by the National Natural Science Foundation of China. The main conclusions and achievements are as follows:(1) Taking account of the rotation flow of melt in aluminum reduction cells, the methods of vorticity and swirling strength were introduced to analyze vortical structures of three phases (bath-metal-anode bubble) flow quantatively and concisely. Results show that the vortex motion of bath are affected both by bubbles and electromagnetic forces (EMFs), but the function characteristics are different:small vortexes occur as reverse symmetrical pairs around anode because of the stirring of anode gas, while large asymmetric vortexes are caused under some anodes by the EMFs, and the nonuniform distribution of electromagnetic field causes the asymmetry of vertical structures.(2) The transient multicomponent and multiphase flow model for simulating the transport process of alumina in aluminum reduction cells has been developed, which realized the accurate transient analysis of the alumina concentration distribution within the whole cell. Calculation results show that the alumina concentration distribution reflects the spiral shape characteristics, and it has remarkable timeliness and spatiality differences. Single factor research shows that anode gas is the main driving force for the transport of alumina, but the EMFs has a wider range of influence and may promote the transporting of alumina in the whole cell, although its strength is weaker.(3) Contrast simulation study of the optimization allocation of alumina feeders in large pre-baked aluminum reduction cells has been made, based on which the configuration rule of alumina feeders was proposed. Results show that the alumina feeding points should be set at the intersection position of center channel and anode slots to achieve the best mixing effect of alumina, where the stirring of bubbles may help to break the alumina pile. And the feeders should also be located on the board of large vortexes, where the streamlines should be very dense, thus it is good for the transport of alumina in great range of the whole cell.