EUROPEAN STEEL TECHNOLOGY AND APPLICATION DAYS 2017 - ESTAD 2017

The scrap used as charge material in the Electric Arc Furnace (EAF) is characterised by a high variability in yield, chemical composition, bulk density and melting behaviour. This is essential to be considered in context with online monitoring and control of the EAF process. The objective of the Pilot & Demonstration project AdaptEAF, funded within the European Research Fund for Coal and Steel (RFCS), is to develop and test an innovative EAF process control, which adapts to the varying scrap properties, striving for reduced total energy consumption and improved melting yield, and thus also for an increased productivity of the EAF process. Novel sensors and measurement systems in combination with evaluation algorithms are used to monitor the properties of the actually charged materials. An imaging system is used to estimate the filling level of the scrap baskets just before charging into the EAF. From the effective density of different scrap mixes the mean bulk density of the individual scrap types is derived. Vibration sensors at the furnace vessel are applied to monitor the scrap melting progress. For determination of steel, hot heel and slag amounts a dip sensor to measure steel and slag levels is used, and an imaging system to monitor the bath level in the furnace has been installed. This additional process information is used to enhance the functionality and prediction accuracy of previously developed dynamic energy and mass balance models for online monitoring of the EAF process status, including the continuous follow up of the hot heel amount. Furthermore the model was extended by a detailed slag balance calculation, considering besides slag former additions all oxidisable elements including iron for a metallic yield calculation. Slag weight and analysis are calculated throughout the meltdown phase and the refining phase of the EAF process. The online information on bath level, steel and slag amount, scrap melting progress, and energetic behaviour is used for model-based online control of scrap charging as well as chemical energy input via burners and oxygen injectors. The electrical and chemical energy inputs are balanced for optimised energetic performance and maximised metallic yield of the charged materials avoiding yield losses by excessive oxidation. The furnace practise is optimised regarding the timing of scrap charging as well as steel bath level and slag amount. In addition, with the help of the slag balance calculations an existing statistical model for determination of the EAF charge material properties has been improved significantly. Thus the content of oxidisable elements like Mn, Cr, etc. in the different scrap types in use can be estimated with higher accuracy. This also improves the reliability of an existing charge mix calculation, to achieve the target EAF tapping analysis with minimum charge material costs. The innovative, adaptive EAF process control is applied, tested and evaluated under industrial conditions at the well-equipped and instrumented 140 t DC Electric Arc Furnace of Georgsmarienhütte (GMH).