Controlled Tapping—The Research Project

Controlled Tapping is a research project funded by the Norwegian Research Council and the Norwegian silicon and ferroalloy industry. The overall goal of the industry is to minimize the amount of uneven tappings and thus to reduce the energy consumption and the risk of hazardous events. In addition, the gassing, in the silicon industry, and the slag/metal separation in the ferroalloy industry, is a concern. The project Controlled Tapping will give fundamental and industrial knowledge to the industry, so these concerns can be addressed. The project focus is how the furnace interior, that is the furnace operation, is affecting the tapping. Tapping is an experience based sub-process that is developed over time at the various plants. To expand the knowledge into the scientific world, numerical modelling is a valuable tool and is the basis in the project. This has been done in SINTEF, NTNU in cooperation with Mintek. A variety of models have been developed calculating the tapping rate. Models describing the whole furnace with accumulated materials, e.g. TiC banks in the SiMn furnace, models that describes the slag metal separation in cascade tapping with various ladle positions, and models describing the tapping where the slag and metal properties are changed, has been developed. For a models to give the true picture, realistic input data is needed, and one of the Ph.D. projects has been to measure the interfacial tension between slag and metal in Mn-ferroalloy production. We also need to know the mechanisms affecting the tapping of industrial furnaces and on the consequences if furnaces accumulate metal and slag. Both industrial campaigns and investigations on mechanisms and material at the lab has been conducted. The industrial campaigns have been to excavate both Mn-ferroalloy and Si furnaces, to find that the tapped silicon is above 1800 °C when all literature says 1600 °C, to see the variances of the metal and slag during a tapping-cycle and over a year and investigating the energy in the gassing. In lab scale, the formation of TiC banks in the SiMn furnaces, the formation of slag, and the formation of SiO gas in Si furnaces and the pressure build up in charges by fines, have been investigated.