Research Of Physical Fields In Inert-Anode Aluminum Reduction Cell

Aluminum reduction cell is the core equipment for extracting aluminum, and its development and progress represent the renovation of aluminum electrolysis. Consumable carbon anodes have always been adopted in conventional aluminum electrolysis process, which has a series of problems. Owing to the problem-solving capabilities, inert anode and new reduction techniques using inert anode have become the research focus of international aluminum industry. Thus the research in designing aluminum reduction cell using inert anode has great significance.With the construction of an experimental (5kA grade) inert-anode aluminum reduction cell prepared for a national "863" program as the main target of this research and with a kind of cermet inert anode prepared by our research group as the application prototype, methods for simulating physical fields in inert-anode aluminum reduction cell have been developed. The main conclusions and achievements are as follows:(1) Based on full study of the remarkable change of cell structure and technical parameters caused by the replacement of carbon anode with inert anode, methods and procedures for the simulation of "electric-magnetic-thermal-flow-stress" fields in the inert-anode aluminum reduction cell have been developed, which have been proved to be reasonable and feasible with good convergence and high precision and can provide technical support for the development of inert-anode aluminum reduction cell.(2) Focusing on a kind of "deep-cup" cermet inert anode developed by our group, the distribution and evolution of its thermal stress have been studied thoroughly. The results show that compressive stress exists on most region of the anode and large tensile stress exists at the three-phase contact surface of the anode, bath and air, which is the major cause of anode cracking. By optimizing the anode structure parameters, anode immersion depth and technical parameters including current intensity and electrolysis temperature etc., the thermal stress of the inert anode can be relaxed. For example, increasing the anode height and central hole depth and reducing central hole radius, anode immersion depth and electrolysis temperature properly can be helpful to the reduction of the thermal stress of the inert anode.(3) As the calculation effect of the existing method for simulation of the flow-field in aluminum reduction cell, especially of the flow field around the inert anodes with complicated structure, is not good enough, a quasi simulation method has been put forward. By equating the gas effect to volume force, the complex calculation of electrolyte-aluminum-bubble three-phase flow can be converted to the multi-step calculation of two-phase flow, which can realize the coupled calculation of electrolyte and aluminum under the combined effect of gas and electromagnetic force. The flow field simulation of the inert-anode aluminum reduction cell shows that the flow field of electrolyte and aluminum can be optimized by optimizing the anode structure, anode immersion depth and technical parameters.(4) Several structure prototypes of 5kA-grade inert-anode aluminum reduction cell have been put forward and the distribution of the physical fields including thermoelectric, thermal stress, electromagnetic and flow fields has been investigated. The comparison and analysis show that distribution of the physical fields in the cell with six anodes as an anode group is better than that in the cell with eight anodes as an anode group, so the former is more suitable for 5kA-grade inert-anode aluminum reduction cell. On the basis of above investigation, the effect of superheat temperature and current intensity on the physical fields has been studied. All these conclusions provide technical support for the building and experiment of the inert-anode aluminum reduction cell.