Extension of lance life used in the smelting furnace in Mitsubishi process for Cu refining

Abstract

Smelting is the first step in the Mitsubishi continuous process for Cu production, resulting in the production of 68% copper matte and Fe-silicate slag. One of the main issues pertaining to the smelting furnace is the frequent interruption of operations required to allow the inspection and replacement of lances since lances are frequently fractured. First, the present study was aimed at modifying the operating conditions of the smelting furnace to suppress lance fractures. A numerical model was developed to simulate the transport phenomena including multi-phase behaviors in the furnace. The simulation results showed that the lances were exposed to a severely erosive atmosphere with high temperatures. Further calculation indicated that raising the positions of the lances could lower the temperature of the lances, and reduce the occurrence of splashed melt, which contains erosive sulfides. This condition was applied and observed in the field operation. It was confirmed that by implementing such a change of the lance heights, the occurrence of lance failures had been considerably reduced without notably affecting the reaction ability of the smelting furnace. Additionally, modifying the feeding system was suggested that feeding continuously as a method of stabilizing the interior of smelting furnace during the process because the effective reactivity could be increased. Second, investigation of lances used in field operations, thermodynamic analysis and laboratory experiments were conducted for studying the reaction mechanism. By analyzing the lances, the surface of the lances was damaged and penetration of matte components into the lance was observed and the damage occurred to a certain height. Since the lance temperature varies depending on the height, we could estimate that damage on the lance is directly related to the temperature. Therefore, thermodynamics calculations were conducted and Cu-Fe alloy existed as a liquid phase at approximately 1100℃. Based on the experimental results, laboratory experiments were conducted and liquid copper was also produced at above 1100℃. From these results, it can be considered that temperature above 1100℃ can cause the lance fracture and part of the lance located at higher temperature than 1100℃ can be deteriorated and finally fractured. Thus, during the Mitsubishi process, when the lance is kept at a temperature below 1100 in the furnace, surface damage can be reduced and the lance life-time can be increased. Through the present study, a numerical model within the S-furnace was developed and we suggested conditions to reduce the fracture of lance using this model. From microstructure analysis of lance, we found out the mechanism by which lance fracture occurs, and confirmed that maintaining the lance tip below 1100℃ can result in stable conditions for increasing lance life-time.