Controlled tapping

The metal producing industry in Norway contribute to large export values, increase in value of the Norwegian energy as well as advanced technological knowledge. A major part of the metal produced in Norway is ferroalloys and silicon. These metals are produced in industrial furnaces at high temperatures, and molten metal is tapped. After the furnace, the metal is cast into moulds before it is crushed and shipped to the customers. The tapping process is an important subprocess. Deviations in the tapping process leads to a higher energy consumption, less metal yield and consequential security risks. A huge part of the knowledge surrounding the subprocess is based on experience, and the goal of this project is therefore to improve the tapping process through a close cooperation between NTNU, SINTEF and the industrial companies involved. The project has developed various models of industrial sub-processes. This varies from overall metal and slag flow with inactive zones and semi-permeable materials. As the CFD models are quite time consuming and costly, simplified Reduced-Order-Models have been developed. The modelling has been shown to agree well with experimental work and industrial experience. Sensitivity analyses have shown which variables are most important in the tapping process. Quite a number of industrial measurement campaign have been performed both as input to the CFD models as well as verification. This ranges from measurement of variables like metal temperature and energy content of tap-gas to excavations of industrial furnaces. Fundamental experimental studies have also given knowledge to SiO formation in the furnaces, the effect of interfacial tension on slag/metal separation, carbide formation, slag formation in quartz, quartz dissolution in slag and dissolution of lime in slags. Recruitment is included by the involvement of MSc students, PhD candidates and PostDoc researchers.

The overall results of this project is a better knowledge base when operating the industrial furnaces. The knowledge base is three folded: 1. The industrial campaign has given information about the industrial operation that was not known or not accepted, and it can especially be mentioned the tapping temperatures and the amount of slag in silicon furnaces, that has lead to new projects. 2. The modelling of flow mechanisms inside of the furnaces, on the outside, and in the interface have shown both which mechanisms that govern the tapping, and also the sensitivity of the various parameters. These models has also lead to new activities. 3. Experimental fundamental information regarding sub-reactions that is needed both for understanding the furnace operation and for modelling. Here, both the development of experimental techniques and the reactions in it self is focused. Together this knowledge will affect the way the operational furnaces is operated, especially in the high temperature area. The potential impact from this is a lower energy consumption and CO2 emissions, but equally important an increased safety for peoples and equipment. Some examples of outcomes : - CFD model of industrial furnace flows including inactive zones - CFD model of metal slag separation during tapping in Mn-ferroalloy production - CFD model of gassing through the tap hole in Si furnaces - Reduced Order models of the tapping variations - Knowledge of industrial tapping temperatures. This knowledge has changed the way we look at the tapping process and behavior of metal and slag in the furnaces. - Knowledge of slag amount, slag composition and slag position in the industrial furnaces. This knowledge has changed the way we look at the tapping process and behavior of metal and slag in the furnaces. - New experimental technique to measure the interfacial tension between liquid slag and liquid metal. With this new method, new information on the interfacial tension between Mn-slag and metal is determined. - Industrial knowledge of inactive zones in Mn-furnaces is determined, and mechanisms on the development of TiC in inactive zones is found experimentally. - SiO production from SiO2 and Si has fundamentally been investigated and a mathematical model is developed to be used in larger furnace models. It also showed that the quartz type was not affecting the SiO production. - The development of permeability apparatus lead to permeability data for the Si-process and the Mn-process. This may broaden the possible raw materials added to the furnaces and hence lead to less waste materials.

In the metal producing processes, hot liquid metal will be tapped from the industrial furnaces. In this project NTNU and SINTEF, with the Norwegian industry, determine the fundamentals affecting the tapping operation. Existing knowledge is mainly regarding taphole maintance, the operation of the furnace and the production process. Hence, the new knowledge produced in this project will be the simultaneous effect of the furnace operation, the taphole geometry and the physical parameters of the phases in the furnace, and how they all affect the tapping operation when it comes to metal, slag and gas flow through the tap-hole. The first part of the project will be an intelligence gathering, collecting industrial experience, previous published knowledge combined with scientific input with the purpose of summarizing theories and knowledge needed. This will give the basis for knowledge needed regarding physical knowledge of condensed and liquid materials, regarding flow mechanisms and regarding geometrical knowledge as a function of furnace operation. Since tapping performance is governed by physics affecting the flow in a multi phase system, a numerical tapping model accounting for the governing physics will be applied. However, enhanced input to the tapping model is required. Data from more recent and (potentially upcoming) furnace excavation needs to be analyzed and prepared for the tapping model. This input is collected in a physical model describing furnace design, furnace-materials and their physical state. The physical model will also be strengthened by lab.scale experiments. Industrial measurements will be carried out giving fundamental competence of the real world phenomena. This competence will be used to give input to the model, as well as verifying the results from the model. In this project the recruitment base for this industry will be strengthen by the education of 2 PhD's, 1 Postdoc and more than 8 MSc.