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Siemens develops new method of measuring the level of foaming slag in arc furnaces

09.03.2006 - (idw) Siemens AG

The Industrial Solutions and Services (I&S) Group and the Corporate Technology (CT) department of Siemens AG have developed a new method of measuring the changes in the level of foaming slag in arc furnaces over time and in the various parts of the furnace. The method is based on the measurement of structure-borne noise at the furnace shell. The signals picked up at several measuring points enable spatial mapping of the foaming slag around the electrode and panel. Series of tests carried out on a 70-tonne arc furnace of Lech-Stahlwerke GmbH (LSW) showed a very high match with visually determined levels of slag. With the help of the new measuring method, the plant controller will be able to meter the nutty slack and the oxygen - the foaming agents - in such a way that baring of the arcs will largely be avoided. This reduces electrode wear, improves the power intake in the arc furnaces and increases productivity. Bare arcs cause increased electrode wear and undesired temperature increases in the walls of the furnace. Other consequences include lower energy efficiency, longer process times and thus reduced productivity. In order to envelope the arc, foaming slag is produced, whose level can be controlled by the metered addition of nutty slack and oxygen. Today, these foaming agents are added either by hand or according to an operating diagram defined in advance. These two methods, however, are no longer able to cope with the frequently changing operating conditions and are standing in the way of a largely automated procedure.

The steel industry would therefore like to see the development of measuring methods with the help of which the behavior of the foaming slag can be determined precisely over time and in respect of its location. The aim is to develop a closed-loop control circuit for metering the foaming agents and to integrate slag foaming into the arc furnace's higher-level automation system. Measuring methods available today either reflect slag foaming with insufficient precision or cannot be used in the rough environment of a steelworks with the required degree of reliability.

The new measuring method developed by Siemens uses the structure-borne noise of the arc furnace as a measurement variable. The signals of acceleration sensors fitted to the walls of the arc furnace are amplified and transmitted to an evaluation unit via fiber-optic cables. Here, the current spatial slag distribution is calculated. The measuring system was tested in spring 2005 on a 70-tonne arc furnace of LSW in Meitingen, Germany. As a control, measurements were carried out with a video camera at the same time. A comparison of the two sets of results showed that they were very close together. Other measuring methods such as noise evaluation with a directional microphone or electrode current analysis were also investigated but their results were considerably worse.

Wolfgang Wichert, manager of the steelworks at LSW, made the following comments: "The new measuring system will enable the arc furnace to be operated in a much more stable manner. At the same time, it will serve as the basis for operating the furnaces in a closed-loop control circuit."
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