Sehr geehrte Leserinnen und Leser!

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2 Vorwort BHM (2013) Vol. 158 (1): 1 2 DOI /s Springer-Verlag Wien 2012 Berg- und Hüttenmännische Monatshefte Sehr geehrte Leserinnen und Leser! Online publiziert am 5. Februar 2013 Im September letzten Jahres fand im Grazer Congress die im Bereich der Elektrostahlerzeugung bekannteste Veranstaltung EEC European Electric Steelmaking Conference statt. Die von der ASMET organisierte viertägige Elektrostahlkonferenz knüpfte an eine bis 1983 zurückreichende Tradition erfolgreich an. Die 10th EEC konnte über 430 Interessierte aus den verschiedensten Ländern, auch über Europa hinaus, für eine Teilnahme begeistern (Abb. 1). Das Ziel der 10th EEC als weltweit bedeutendste Konferenz der Elektrostahl-Branche war es, ein Forum zum Erfahrungs- und Know-How Austausch zwischen Stahlproduzenten, Anlagenhersteller, Forschungsinstituten, Lieferanten und allen weiteren Interessierten zu bieten. 68 Referenten aus den verschiedensten Fachbereichen trugen dabei zum Gelingen der Veranstaltung bei. Die Schwerpunkte lagen in den Bereichen Rohstoffe Prozesssteuerung und Betriebsergebnisse Anlagentechnik Innovationen und zukünftige Trends Nachhaltigkeit, Umweltaspekte und Effizienz. Im Jahr 2011 wurden in Europa 177 Mio. t Rohstahl erzeugt. Der Anteil der Elektrostahlerzeugung betrug dabei 43,7 %. Das Wachstum der auf dem Elektrolichtbogenofenverfahren basierten Stahlerzeugung in den letzten 20 Jahren war enorm. Der EAF (Electric Arc Furnace, Elektrolichtbogenofen) wurde in vielen Teilen der Welt das Verfahren erster Wahl, was vor allem auf die flexible Rohstoffauswahl und flexible Produktionskapazität zurückzuführen ist. Die treibenden Kräfte in der Elektrostahlerzeugung sind Produktionskosten, Verfügbarkeit der Rohstoffe, Effizienz der eingesetzten Prozesse, Nachhaltigkeitsaspekte und nicht zuletzt ein adäquater Produktmix. Einige dieser Faktoren sind natürlich beeinflusst von regionalen Bedingungen. So sind es auch die verschiedenen regionalen Anforderungen, welche auf die Entwicklung von Elektrolichtbogenofentechnologien maßgeblichen Einfluss ausüben. Die Stahlerzeuger sind Abb. 1: Die 10th European Electric Steelmaking Conference konfrontiert mit eingeschränkter Schrottverfügbarkeit bei gleichzeitigem Anstieg unerwünschter Begleitelemente, steigenden Energiekosten, schwachen Netzen und strengen Umweltauflagen. Ein oftmals unterschätzter Faktor ist der Ausbildungsgrad der Mitarbeiter, welcher mit den Prozessnebenzeiten extrem korreliert und somit die Produktionskosten bei der Stahlerzeugung maßgeblich beeinflusst. Der sogenannte Fight for talents, vor allem in Europa, stellt die Industrie vor die neuen Herausforderungen, junge Menschen für die Technik zu begeistern. Die Anlagenbauer sind gefordert, Lösungen anzubieten, die diesen Anforderungen gerecht werden. Energieeffizienz, Flexibilität im Rohstoffeinsatz und hoher Automatisierungsgrad spielen dabei eine zentrale Rolle. Die Technologieanbieter treten dabei nicht mehr als einfache Lieferanten, sondern als Lifecycle-Partner des Anlagenbetreibers in Erscheinung. Nur eine enge Partnerschaft ermöglicht die Entstehung von Innovation und somit Wettbewerbsfähigkeit. Die Vortragenden und Aussteller der 10th EEC konnten dem Anspruch als Impulsgeber für Innovation bestens gerecht werden (Abb. 2). BHM, 158. Jg. (2013), Heft 1 Springer-Verlag Wien Vorwort 1

3 Vorwort Abb. 2: Organisation & Scientific Committee Abb. 3: Grazer Congress Die sehr gute Organisation und der reibungslose Ablauf der Konferenz war dem professionellem Eventmanagement zu verdanken. Das kulturelle Rahmenprogramm, insbesondere das Konzert des Wiener Kammermusikorchesters, setzte neue Maßstäbe. Österreich und Graz konnten sich im besten Licht präsentieren (Abb. 3). Die in diesem Heft ausgewählten Beiträge der EEC zeigen, dass der zukünftige Fokus der Technologieentwicklung in der weiteren Optimierung der Produktionsprozesse, im effizienteren Einsatz von Rohstoffen und Energie und in der Minimierung schädlicher Emissionen liegt. Extrem kosteneffiziente Stahlwerke mit minimalem ökologischem Fußabdruck werden die nächste Generation der modernen Mini Mills prägen. Glück Auf! Hans-Jörg Krassnig Peter Fauland Bruno Hribernik Johannes Schenk Scientific Chairman Conference Chairman GF ASMET Editor-in-Chief Hans-Jörg Krassnig Linz, Austria Vorwort 2 Vorwort Springer-Verlag Wien BHM, 158. Jg. (2013), Heft 1

4 BHM (2013) Vol. 158 (1): 3 12 DOI /s y Springer-Verlag Wien 2012 Berg- und Hüttenmännische Monatshefte Cost and Energy Effective Management of EAF with Flexible Charge Material Mix Enrico Malfa 1, Pierre Nyssen 2, Eric Filippini 3, Bernd Dettmer 4, Inigo Unamuno 5, Anders Gustafsson 6, Erik Sandberg 7, Bernd Kleimt 8 1 Centro Sviluppo Materiali S.P.A, Italy 2 CRM, Belgium 3 Feralpi Siderurgica S.P.A, Italy 4 Georgsmarienhütte, Germany 5 Gerdau I+D Europa, Basauri, Spain 6 Ovako, Sweden 7 Swerea MEFOS AB, Sweden 8 VDEh Betriebsforschungsinstitut GmbH, Germany Received November 16, 2012; accepted November 21, 2012; published online January 26, 2013 Abstract: Within the framework of the project FLEX- CHARGE, performed within the RFCS steel research program, a team including research institutes and steel producers developed and tested in an industrial environment a methodology to effectively manage the EAF charged with variable materials. Statistical and deterministic methods were used together to determine yield and composition of different scrap types as well as the influence of the scrap mix on the off-gas emission and the slag composition. The paper summarizes the most relevant results obtained at four different EAF plants by applying the improved process control and by performing industrial trials for different steel grades. It also shows how the use of low quality scrap types in the charge mix has been maximized, considering the tramp element restrictions and scrap availability, yield as well as specific energy consumption. Keywords: Electric Arc Furnace, Process control, Scrap mix, Optimisation Kosten- und energieeffizientes Management von Lichtbogenöfen mit variierenden Einsatzstoffen Zusammenfassung: Im Rahmen des Projekts FLEXCHAR- GE, das im RFCS-Stahlforschungsprogramm von einem Team aus Forschungsinstituten und Stahlherstellern durchgeführt wurde, wurden Verfahren zur Prozessfüh- P. Nyssen ( ) CRM GROUP, Avenue du Bois Saint Jean, 21, 4000 Liège, Belgium pierre.nyssen@crmgroup.be rung des Lichtbogenofens mit variierenden Einsatzstoffen entwickelt und in industriellem Maßstab getestet. Statistische und deterministische Methoden wurden genutzt, um Ausbringen und Zusammensetzung verschiedener Schrottsorten und den Einfluss des Schrottmixes auf die Abgasanalyse und die Schlackenzusammensetzung zu ermitteln. Der Beitrag fasst die wichtigsten Ergebnisse zusammen, die durch Anwendung einer verbesserten Prozessführung in Betriebsversuchen an vier verschiedenen Öfen für unterschiedliche Stahlgüten erzielt wurden. Er zeigt weiterhin, wie der Einsatz von preiswerten Schrottsorten niedrigerer Qualität unter Berücksichtigung der Einschränkungen hinsichtlich unerwünschter Begleitelemente, des Ausbringens und des spezifischen Energieverbrauchs maximiert werden kann. Schlüsselwörter: Lichtbogenofen, Prozessführung, Schrottmix, Optimierung 1. Introduction The goal of the modern Electric Arc Furnace process is to produce liquid steel with a target quality at minimum costs and with low environmental impact. One of the main factors to be considered to reach these objectives is the mix of different charged scrap grades, which contributes between 60 and 80 % to the liquid steel production cost (Fig. 1) and, at the same time, has a direct influence on furnace operation, on liquid steel quality, on the off-gas emission, and on the composition of the slag. Today the pressures arising from increasing scrap prices [1] and from legislation [2 4] BHM, 158. Jg. (2013), Heft 1 Springer-Verlag Wien Malfa et al. 3

5 Waste Management 2% Consumables 3% Alloys & Additives 4% Capital Costs 3% Personnel 3% Electrodes 5% Energy 7% Typical costs for EAF steel Source: IISI, steelonthenet.com Steel Scrap 73% laboratory, pilot plant investigations, and plant tests in combination with multivariate statistical methods for characterisation of different charge mixes in terms of element composition, ferrous and element yield, and specific energy consumption; fundamentals of metallurgy and thermodynamics to extend existing analytical energy and mass balance models for the EAF regarding the effect of varying charge materials and operation practices with low quality scrap types; multivariate and dynamic statistical techniques to develop self-adaptive statistical models for continuous tracking of dynamic changes of the charge material properties. Fig. 1: Typical costs for EAF steel force the steel industry to address the issue of how to deal with the use of more recycled lower quality scraps. This requires industry to overcome the currently highly selective scrap policies adopted by most steelmakers for ensuring the use of only good quality clean scrap. One of the main problems is that the ferrous scrap is contaminated with impurities such as copper, tin and antimony that cause various adverse effects on steel properties. Further, the increased use of the scrap in mini-mills results in a decrease in scrap quality due to the accumulation of these impurities. None of the numerous processes attempted to remove the impurities (especially copper) from either solid or molten scrap have proven practical. Presently the scrap grades [5] and amounts to be charged for production of a specific steel grade under minimum costs are normally determined with the help of a charge mix calculation [6 8]. In parallel to scrap issues, several approaches for EAF process control [9 12] have been discussed in literature. However, in these works the effect of a variable charge mix on EAF process control and especially the issue of maximising the use of low quality scrap in the charge mix have not been addressed. With this in mind the project named FLEXCHARGE has been launched within the framework of the RFCS research program by a team including research institutes and steel producers with the goal of setting-up a methodology to effectively manage the EAF charge to: maximize the quantities of low quality scraps; use scrap substitutes like pig iron, DRI, and HBI in conjunction with low quality scrap, mainly to optimise the cost of charge mix in relation to the quality of crude steel; minimize the energy input and the CO 2 emissions required to melt the charged materials. 2. Methods and Techniques To achieve the scientific objectives of the project, the following methods and techniques have been applied: 2.1 Data Collection As the first step of the project, historical process data of more than 18,000 heats from the steel producers GMH, Gerdau, Feralpi, and Ovako (Table 1) have been collected and stored in a dedicated data base (DB) for a detailed statistical evaluation of the EAF process regarding scrap melt down and achieved liquid steel analysis as well as for EAF energetic performance evaluation by mass and energy balance calculations. The DB also includes data from: lab tests for the characterisation of different scrap grades (E1, E5H, E40, E46 [5]) performed in a 35 kg induction furnace of CRM. Examples of the results of these trials regarding scrap composition and melting yield are reported in Tables 2 and 3; two melting campaigns of reference scrap mixes as defined by partners (including addition of HBI) at the 1 ton CSM EAF pilot plant; dedicated industrial trials performed with different charge mixes using increased quantities of low quality scraps and scrap mix corrections by DRI and pig iron. 2.2 Tool Development As a further step, tools (models and virtual sensors) necessary for the extension of EAF control have been developed: tools for statistical evaluation of available data with respect to the properties of the charge material mix in terms of the metallic yield (furnace yield, i.e. the effect of the process is taken into account), steel chemistry and specific energy consumption. Examples are reported for Ovako Smedjebacken in Figs. 2, 3, and 4. mass and energy balance calculations to calculate steel and slag composition as well as melt temperature in a dynamic way. Results of a pseudo-dynamic BFI model applied at GMH DC EAF are reported in [10] while the application of icsmelt at Feralpi Calvisano is explained in [13]. When available, the off-gas data at 4th hole have 4 Malfa et al. Springer-Verlag Wien BHM, 158. Jg. (2013), Heft 1

6 Table 1: Characteristics of industrial partners EAF FERALPI GMH OVAKO GERBAU Feralpi Calvisano Georgsmarienhütte Smedjebacken Basauri Type EAF AC with EBT EAF AC with EBT EAF DC with EBT EAF AC with EBT EAF AC with EBT Manufacturer Tagliaferri Tagliaferri GHH / SMS Demag Fuchs Sidernaval-Demag Tapping weight (t) Transformer Power /150 in 2007 (MVA) Power supply AC AC DC AC AC Construction steel X X X Special steel X X X Carbon content at tapping Mean oxygen input (Nm 3 /t) % % % about 0.10 % % (EAF) % (LF) 35 Nm 3 /ton 38 Nm 3 /ton 34 Nm 3 /ton 22 Nm 3 /ton 20 Nm 3 /ton Gas burner NO NO 3 by Air Liquid 1 (0.5 MW) 1 5 MW MuLtifunction injectors 4 by Concast 4 by BSE 3 by Air Liquid NO 3 (2 wall + 1 EBT) by LABEA C, lime AI,...injectors 2 by Concast 3 by STEIN 3(C) + 1 (dust) NO 2 wall Door lance 2 O 2 (only refining) 1 O 2 by Elti (only 2 lines O line C 2 O C 1 O 2 (door cleaning) refining) Off-gas measurement NO YES Real time CO CO 2 with Diode Laser by Air liquide Mass spectrometer NO NO Scrap grade presently used* *Based on European List of Scrap Grades E1, E1C, E202, E3, E3C, E5H, E5M, E8 (minor), E40, steel skulls E1, E2, E3, E5M, E6, E8 pig iron skulls, steel skulls E3, E1, E8, E40, E6, E5M, pig iron and special low grade scraps like shredded cans, metal residue from burning of municipal waste (E46) E2, E3, E5M, E6, E8, home scrap (C, CrNiMo) pig iron skulls, steel skulls (E1: scarce use) been integrated in the BFI and CSM mass and energy balance to optimise the multiple energy input: to give an indication regarding the optimal distribution between electrical and chemical energy input depending on charge material mix and treatment phase [10], and to provide the basis for set-up of heat-individual operating patterns [13]; to obtain an optimised operative practice to reduce FeO in the slag (metallic yield control). virtual (or soft) sensors for off-gas properties (flow rate, temperature, composition) at the 4th hole of EAF based on statistical approaches and analytical models in combination with indirect measurements. Fig. 5 shows respectively the measured and predicted temperature and mass flow rate of off-gas at 4th hole at Feralpi Calvisano EAF. The soft sensor is based on relationships between: continuous measurement of off-gas composition at the 4th hole, elbow cooling water temperature, flow rate and quencher temperature spot measurement of flow rate and temperature in the fume duct before quenching, and of off-gas temperature at 4th hole by thermocamera. adaptive charge mix recipes derived from a cost optimisation calculation based on statistical tools to determine the scrap grade properties as above. Different approaches have been investigated (Table 4). The BFI tool in principle can be applied at any charge mix if the single scrap grade parameters are known, while the MEFOS tool requires a training in which the charge mix is included (needs variation of charge in historical data). Both use large data sets. The Gerdau approach, by contrast, is related to a small group of heats (between 50 and 60 heats) in order to study the temporary evolution of the scrap yield. 2.3 Tool Integration Process simulation, optimisation and statistical tools have been linked in order to provide a basis for process control and for heat management and were applied at different steel plants as summarized in Table 5. BHM, 158. Jg. (2013), Heft 1 Springer-Verlag Wien Malfa et al. 5

7 Table 2: Chemical composition of selected scrap grades from melting trials Mn P S Cr Ni Cu Sn E40 average Stdev E46 average Stdev E1 average Stdev E5H average Stdev Table 3: Scrap melting yield of selected scrap grades E40 Melting yield (%) E1 Melting yield (%) E46 Melting yield (%) E5H Melting yield (%) Trial Trial Trial Trial Trial Trial Average Stdev Fig. 2: Estimations of individual yield coefficients for scrap grades at Ovako Metallic yield (w%) E3 Imp E5 Iron E3 Iron E1 Iron Steel sculls E3 Intemal E3 E1 E5M E8 Si E40 E8 E6 Sn E8 Sheared Scrap grade ID E8 Coated E6 E2 Slag sculls E46 Pig Iron sculls Slag sculls Imp E5 Iron Briq 3. Field Test and Best Practice Industrial trials with the goal to maximize the amounts of low quality scraps in the charge mix, having as constrains the tramp element requirements, availability, yield, specific consumption of energy and costs, have been performed at the different industrial plant sites with different steel grades: GMH for engineering steel grades with max Cu content of 0.25 %; Gerdau for SBQ (alloyed, spring, carbon, free cutting, bearing) steel grades initially with max Cu allowed of %; OVAKO for low alloy special bar steel (0.05 < Cu < 0.4 %); Feralpi Calvisano for construction and low alloyed steel grades, with maximum Cu allowed of 0.6 %. 6 Malfa et al. Springer-Verlag Wien BHM, 158. Jg. (2013), Heft 1

8 Fig. 3: Estimated concentrations of elements in scrap grades at Ovako Fig. 4: Estimations of specific energy consumption for individual scrap grades at Ovako 3.1 OVAKO A scrap mix optimisation tool in which four statistical prediction models (Partial Least Squares PLS) have been connected in a mathematical network has been installed at OVAKO-Smedjebacken plant to calculate the: 1. chemical composition of the steel; 2. consumption of materials added during EAF operation (slag formers and foam carbon); 3. energy consumption (electricity, natural gas, oxygen, power-on time); 4. metallic yield, with the goal to optimise the charge mix vs. energy consumption and production costs. Optimisation with regard to multiple objective functions have been performed showing: savings of 2 3 % of the production costs by simple adjustments of the scrap mix; an additional decrease (in total 4 6 %) by minor changes in purchase strategy (exchanging E3 to E1/E3 mix and E6 to E2) and allowing three basket practice when the plant is not operating at maximum capacity; savings of 9 15 % with major changes to the scrap loading and purchasing strategy, increasing low quality materials like steel and slag skulls, E46 and E1 and high quality materials like E8 and E2 on the expense of common materials like E3 and E40. In general a conflict between the two objectives, namely minimising production costs and minimising energy consumption (Fig. 6), has been underlined and the best compromise has been defined. BHM, 158. Jg. (2013), Heft 1 Springer-Verlag Wien Malfa et al. 7

9 Fig. 5: Comparison between measured and calculated off-gas temperature and MFR at EAF 4th hole of Feralpi Calvisano Table 4: Statistical modules for charge mix optimization Module BFI MEFOS Gerdau Tramp elements Linear regression coupled with minimisation tool For each scrap grade Linear regression For charge mix Linear regression For each scrap grade Yield Specific energy consumption Minimisation tool (hot heel) For each scrap grade Linear regression (electrical energy only) For each scrap grade Linear regression For charge mix (20 heat average) Linear regression (20 heat average) Electrical and chemical energy For charge mix Linear regression For each scrap grade Linear regression (electrical energy only) For each scrap grade 3.2 Gerdau In the case of Gerdau, trials with scrap mix recipes determined by scrap optimized including regression analysis of tramp elements, metallic yield, and energetic requirements were performed with the goal to verify the maximum amounts of low quality scraps in the blend mix as a function of maximum allowable percentages of undesired elements in the steel, such as Cu, Cr, or Sn. An example of the optimized mix and real mix is shown in Fig. 7 for all 8 Malfa et al. Springer-Verlag Wien BHM, 158. Jg. (2013), Heft 1

10 Table 5: Application of developed tools at the different steel plants heats done in January 2010 at Gerdau-Basauri. The optimizer suggested the use of 4A and 4C bundles instead of consuming sheared scrap type (E8C). Using this framework, the information was made available to meltshop, scrap yard operators and engineers, R&D, and purchasing Fig. 6: Pareto front for minimizing production costs and energy consumption department within the company intranet. Due to the quick variation of scrap characteristics in terms of scrap chemistry and metallic yield, the software developed allowed to generate reports and scrap master files for any period of time, selected by the user. This master file was used by the mix optimizer to work with updated information. 3.3 GMH The BFI scrap mix optimisation tool has been installed at the scrap yard. The application is divided into three sections. The first section consists of the subroutines to determine the properties of the different scrap types by analysing historical data from a large number of heats. The second section includes the management of the quality properties of the different produced steel grades, and, in the third section, the calculation of the optimal scrap mix for a single heat or a sequence of heats is started. The approach has been extensively discussed in [14]. Table 6 shows typical results for a sequence of heats that con- Fig. 7: Optimised mix and real consumption scrap mix in January 2010 for 361 heats at Gerdau BHM, 158. Jg. (2013), Heft 1 Springer-Verlag Wien Malfa et al. 9

11 Table 6: Savings of the production costs by adjustments of the scrap mix at GMH October 2010 heats sequence Scrap type group Consumed scrap amounts/t Optimised scrap amounts/t Scrap type group Consumed scrap amounts/t Optimised scrap amounts/t Pig iron skulls E5M Pig iron E5H Cast iron Briquetted turnings E Steel skulls E Casting residuals E Return Cr E Return CrMo E1/E Return CrNiMo Cans E E Remaining scrap types Optimised scrap mix leads to a cost benefits of 8.9 % Menu No. of usage Cost benefit (%) Fig. 8: Scheme for integrated control system Panel temperature Electrical variables Harmonics Off-gas: - Composition - Mass flow - Temperature Metallurgical model (refining) Charge material mix recipes Charge mix composition Energy demand Electrode Burners Carbon injectors Dynamic evaluation of: - Bath T - Bath & slag comp. Static energy & mass balance Process data (L1) Optimisation tool operating patterns for each individual heat Oxygen injection Post-Combustion injectors Fluxes additions (L2) firm the achievement of similar levels of cost savings as obtained at OVAKO. As a further step at GMH, the actual scrap mix input/ optimisation has been coupled with the dynamic process model, together with the off-gas analysis at the 4th hole implemented into a new L2 system allowing to reduce the electrical energy consumption by 5 % [15], thus helping to reach the main goal of GMH, namely to obtain the EAF steel target composition at minimum cost. 3.4 Feralpi Calvisano At Feralpi Calvisano an approach to integrate the different tools as represented in the scheme of Fig. 8 has been pursued to reach the goal of reducing the production cost by increasing metallic yield while controlling the level of Cu in the liquid steel. The BFI scrap charge mix optimizer was applied at Feralpi Calvisano, where the main issue was the copper content of the steel to be produced (between 0.2 and 0.8 %). The scrap mix optimization was performed for intermediate steel quality four (Cu 0.5 %) and lower quality 10 Malfa et al. Springer-Verlag Wien BHM, 158. Jg. (2013), Heft 1

12 Table 7: Summary of standard and optimized scrap mix recipes (%) at Feralpi Calvisano Scrap Quality 4 Quality 6 STD Optimised Delta STD Optimised Delta E E E5H E5M E Internal mix (Cu 0.8 % quality 6), that is also the main production share (Table 7). Using the optimised charge, the icsmelt has been applied on-site to define a new operating practice with the goal to reduce %FeO in the slag at tapping and to increase the metallic yield. The management of coal injection has been imposed as optimization strategy, while fixed values of oxygen and methane with respect to SOP have been requested. Global process results with the optimized practice require an increase of 400 kg of injected coal with a consequent reduction of 6.5 % of FeO in the tapped slag compared to reference heats. Details of the optimisation strategy are reported in [13]. As further step virtual sensors for the off-gas MFR and T at the 4th hole have been implemented in the L2 system and coupled with CSM dynamic mass and energy balance for modeling metal bath and slag metallurgical evolution (dycosmelt ) [5] adapted to the Feralpi Calvisano AC EAF (Iron Oxide Ratio tool). The IOR runs on-line as supervisor of the FeO evolution during the refining step (Fig. 9). The optimised charge, the new operative practice, and the IOR allow the increase of yield of about 3.5 % points corresponding to a 15 /ton saving (300 /ton scrap price). 4. Conclusions The main conclusions derived from the project activities are: the developed statistical tools are appropriate for determining the most relevant properties of the different scrap types typically used in EAF steelmaking plants: the metallic yield (furnace yield) of each scrap type can be calculated with reasonable accuracy. The effect of the variation of the amount of the hot heel, which in most EAF plants is difficult to estimate, and the uncertainties in determination of the actual tap weight are the main reasons for inaccuracies in calculating the metallic yield of an individual scrap type and individual heat; the element-wise yield of an individual scrap type regarding the most relevant tramp elements Cu and Sn as well as of the alloy elements Cr, Ni, and Mo can be calculated with good accuracy. Typical errors lie in the range of % of the absolute value; the scrap-type specific energy consumption depends on the applied energy (electrical/chemical) mix. the optimization of the scrap mix according to the given quality requirements and the determined scrap properties regarding metallic and element-wise yield as well as specific meltdown energy consumption can be performed at industrial level by user-friendly applications. The industrial trials have shown that savings in the order of 2 3 % of the production costs can be achieved by simple adjustments of the scrap mix; the accuracy of dynamic mass and energy balance models to calculate the evolution of steel and slag composition as well as melt temperature throughout the complete EAF treatment can be improved including continuous information on the furnace off-gas at the 4th hole. The gas composition measurement requires dedicated systems while virtual or SW sensors can be used to estimate off-gas flow rate and temperature; the recommended control of O/C injection during the refining phase is based on a semi-empirical approach derived by steel and slag sampling campaign or based on a deterministic approach based on a kinetic metallurgical model coupled with the virtual sensors. 5. Acknowledgements The research leading to these results has received funding from the European Union s Research Fund for Coal and Steel (RFCS) research programme under contracts N [RFSR-CT ]. The authors wish to thank colleagues involved in FLEXCHARGE projects:, A. Di Donato, P. Frittella, A. Lucarelli, M. Scotto, V. Volponi of CSM, M. Dormann of CRM, A. Tolettini of Feralpi Siderurgica S.p.A. Fig. 9: IOR visualization at Feralpi Calvisano on-line installation Iron Oxide Ratio % IOR = kg FeO/kg FeO target * Time, sec 800 IOR & SW sensors on line implementation at Feralpi Calvisano BHM, 158. Jg. (2013), Heft 1 Springer-Verlag Wien Malfa et al. 11

13 References 1. Moffat, G.: EUROFER, the European Steel Association Website, DIRECTIVE 2009/31/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 23 April Anonymous: Scrap car challenge for recycling regulators, Ends Report, May 2001, (316), pp DIRECTIVE 2000/53/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 18 September 2000 on end-of life vehicles (OJ L 269, , p. 34) 5. Moffat, G.: EUROFER, the European Steel Association European Steel Scrap Specification, Bliss, N.G.: Scrap management and processing, cradle to ladle. Iron & Steelmaker, February 2000, pp Whipp, R.; Martin, R.: Effective use of scrap optimization in melt shop operations Electric Furnace Conference Proceedings, pp Sandberg, E.; Lennox, B.; Marjanovic, O.; Smith, K.: Multivariate process monitoring of electric arc furnaces, 8th EESC, Birmingham, United Kingdom, 7 9 May 2005, pp Pfeifer H.; Kirschen M.: Thermodynamic Analysis of EAF Energy Efficiency and Comparison with a Statistical Model of Electric Energy Demand.7th EESC, Venice, Italy, May 26 29, Pierre, R.; Kleimt, B.; Dettmer, B.; Schliephakr, H.: Model-based automation and optimisation of EAF steelmaking from charging to tapping. EAF Perspective on Automation, Material, Energy & Environment, Milan, Italy, March Maiolo, J.; Scipolo, V.: ieaf Technology: Dynamic Process Control for the Electric Arc Furnace, AISTech 2009, St. Louis, USA, May 4 7, 2009, pp Baumert J.C.: Artificial Neural Networks Model the Electrical Arc Furnace Process. 7th EESC, Venice, Italy, May 26 29, Fritella, P.; Lucarelli, A.; Angelini, L.; Filippini, E.; Poizot, B.; Legrand, M.: icsmelt Applications to EAF Operating Practice Optimization., AISTech 2011, Indianapolis, USA, May 2 5, 2011, Proc. Vol. 1, pp Pierre, R.; Kleimt, B.; Dettmer, B.; Schliephake, H.: Quality and cost optimal charge material selection for the EAF. 10th EEC 2012, Graz, Austria, September 25 28, Kleimt, B.; Pierre, R.; Dettmer, B.; Deng, J.; Schlinge, L.; Schliephake, H.: Continuous dynamic EAF process control for increased energy and resource efficiency. 10th EEC 2012, Graz, Austria, September 25 28, Malfa et al. Springer-Verlag Wien BHM, 158. Jg. (2013), Heft 1

14 BHM (2013) Vol. 158 (1): DOI /s x Springer-Verlag Wien 2012 Berg- und Hüttenmännische Monatshefte State of the Art Tapping Solutions for Bottom Tapping EAFs Karl Zettl, Peter Zottler, Josse Bachmayer, Marcus Kirschen RHI AG, Product Management EAF, Vienna, Austria Received November 15, 2012; accepted November 26, 2012; published online January 26, 2013 Abstract: One of the latest generation developments regarding EAF taphole technology is the CFD-optimised EBT taphole, which is currently replacing common cylindrical tapholes all over the world. This paper compares the standard taphole (cylindrical geometry) with the new, flow-optimised solution. Influence on tapping time, taphole lifetime, and metallurgical benefits are explained. Additionally well proved systems to ensure a quick and safe taphole removal and exchange are discussed. Keywords: EAF, EBT, Eccentric bottom tapping, Taphole, Tapping time, Slag carry over Stand der Technik bezüglich Abstichlösungen für Elektrolichtbogenöfen mit Bodenabstich Zusammenfassung: Eine Entwicklung der letzten Generation der Abstichtechnolgie bei Elektrolichtbogenöfen stellt der CFD-optimierte EBT-Abstich dar. Aktuell werden weltweit die herkömmlichen Abstiche mit zylindrischem Abstichkanal durch diese Neuentwicklung ersetzt. Der vorliegende Artikel vergleicht die herkömmliche Lösung mit dem CFD-optimierten Abstich und erläutert die Einflüsse auf Abstichzeit, Abstichstandzeit und metallurgische Faktoren. Abschließend werden praxiserprobte Systemlösungen für schnellen und sicheren Abstichausbruch und Abstichwechsel vorgestellt. Schlüsselwörter: EAF, EBT, Exzentrischer Bodenabstich, Abstich, Abstichzeit, Mitlaufschlacke Dipl.-Ing. K. M. Zettl ( ) RHI AG, Product Management EAF, Wienerbergstraße 9, 1100 Vienna, Austria karl-michael.zettl@rhi-ag.com 1. Introduction The productivity of any individual steelmaking unit has a considerable influence on the overall economic results of the steel plant. For example, electrical arc furnaces must be stopped for various maintenance tasks resulting in non-productive intervals. Steel plants attempt to increase furnace availability by extending the time frame between shutdowns and reducing their duration. The taphole is one of the areas with the shortest maintenance interval [1]. Improving taphole lifetime and decreasing maintenance times (necessary to change the tapholes) leads to clear advantages and higher productivity for steelmakers. 2. The CFD-optimised EBT Taphole The design of the exchangeable EBT taphole channel is differentiated in two alternatives as shown in Fig. 1. The taphole with the CFD-optimised inner taphole channel is a further development of the common taphole with cylindrical inner surface. For numerous specific EAF, a CFD-simulation is done, considering factors such as bath height, target tapping time, service life, and tapping weight. The result is a flow-optimised inner surface adjusted to the specific conditions on-site. There are several advantages of the CFD-optimised taphole channels, compared to common cylindrical channels, due to the flow-optimised design: fluid dynamics optimisation ensures less turbulent flow; less turbulent flow reduces tapping time; less turbulent flow increases service life of taphole channel due to less wear by erosion; BHM, 158. Jg. (2013), Heft 1 Springer-Verlag Wien Zettl et al. 13

15 Cylindrical Ø = 170mm Turbulences CFD-optimised Ø = 170mm end Turbulence Intensity non turbulent flow less wear Higher Lifetime Fig. 3: Increased Lifetime with CFD-optimised Taphole Fig. 1: Cylindrical vs. CFD-optimised EBT Taphole 1.0 Velocity (m/s) Cylindrical Ø = 170mm Flow Rate: 740 kg/s CFD-optimised Ø = 170mm end Flow Rate: 930 kg/s Turbulence [%] Cylindrical Ø = 170mm high trubulences CFD-optimised Ø end= 170mm lower turbulences higher flow rate increased throuput Less Tapping Time non turbulent flow at outlet bundeled tapping stream Less reoxidation and N 2 -pick-up Fig. 4: Reduced Reoxidation and N 2 -Pick-up with CFD-optimised Taphole Fig. 2: Reduced Tapping Time with CFD-optimised Taphole less turbulent tapping results in a bundled tapping stream. This impedes reoxidation and N2-pickup and cuts consumption of alloy and desoxidation agents; reduced slag carry over. As a result of reduced turbulences in the tapping channel of a CFD-optimised taphole, the pressure drop of the steel flow and tapping time is decreased. The example shown in Fig. 2 compares one and the same EAF with cylindrical and CFD-optimised taphole design. Both tapholes are defined by the inner channel diameter of the endbrick with 170 mm. In this case, the mass flow rate is increased from 740 kg/s to 930 kg/s by using the flow optimised channel. This reflects the potential to decrease tapping time at same outlet diameter. Non turbulent, laminar steel results not only in an increased flow rate. An additional benefit out of the flow optimised design is the reduced erosion. Erosion is the most important wear mechanism for tapholes. By reducing this parameter, a significant improvement of the taphole service life can be achieved as shown in Fig. 3. An additional advantage of the CFD-optimised taphole is the potential reduction of oxygen and nitrogen pickup during steel transfer to the ladle. Figure 4 shows the reason for that: lower turbulences in the steel stream of the CFD-optimised taphole after leaving the taphole channel, compared to the steel stream of the cylindrical taphole during tapping procedure. This leads to reduced interaction with the atmosphere and finally a decreased N 2 and O 2 pickup from atmosphere [2]. The flow profiles of steel as it streamed from either a cylindrical or CFD-optimised taphole during one of the trials held in a North American steelplant are shown in Fig. 5. This picture verifies the theoretical simulations results shown above in Fig. 4. Compared to the cylindrical taphole, first slag entrainment to the taphole occurs at a lower steel bath level for the CFD-optimised taphole. This means the critical height of liquid heel in the case of a cylindrical taphole is more than that of a CFD-optimised taphole [3, 4]. In other words, by using a CFD-optimised taphole, the amount of carry over slag can be reduced as shown in Fig Zettl et al. Springer-Verlag Wien BHM, 158. Jg. (2013), Heft 1

16 Fig. 5: Reduced Reoxidation and N 2 -Pick-up with CFD-optimised Taphole [2] Fig. 7: Hot Taphole Jacker (HTJ) Cylindrical Ø = 170mm carry-over slag CFD-optimised Ø = 170mm end expanded move-in area carry-over starts at lower steel bath level Less carry-over slag Fig. 8: Prompt Taphole Xchange (PTX) Fig. 6: Reduced Carry-over Slag with CFD-optimised Taphole 3. The HTJ (Hot Taphole Jacker): Taphole Breaking out Device The HTJ hammer (shown in Fig. 7), held by a chain on the crane, demolishes and completely removes the worn taphole bricks from top to bottom. The principal parts are a pneumatically driven extractor hammer and a chisel specially adapted to the taphole dimensions on-site. The parts are designed specifically for extreme conditions and require virtually no service and maintenance. The following advantages have been achieved by using the HTJ-system [1]: rapid demolition of taphole bricks; short taphole changing times; reduced physical strain for the operator; reduced accident risk; clean inner surface of the surrounding blocks. 4. The PTX-System (Prompt Tap Xchange) The PTX (Prompt Tap Xchange) system enables the annular gap between the channel bricks and the surrounding blocks to be filled from the bottom (Fig. 8). A mortar pump mixes an injection mix with water and pumps it through a rubber hose which is connected to the end brick flange of the taphole. The flange and the end brick contain a pumping duct leading to the annular gap (Fig. 8). Once the mix is pumped into the gap, it is dried by the residual heat from the surrounding blocks. Therefore, this system may only be employed when the furnace is hot [1]. 5. Conclusion One of the latest generation developments regarding EAF taphole technology is the CFD-optimized EBT taphole, which is currently replacing common cylindrical tapholes all over the world. Benefits including reduced tapping time and a longer taphole lifetime have been demonstrated in various plant trials. Furthermore, the decreased taphole requirement and reduced annual exchange time provide cost savings as well as additional production time. Since BHM, 158. Jg. (2013), Heft 1 Springer-Verlag Wien Zettl et al. 15

17 the taphole geometry is tailored to the individual EAF capacity and tapping requirement, the tapping process can be specifically optimized. Furthermore, the CFD-optimised tapholes result in reduced turbulence in the steel stream during tapping, which has a positive impact on the required downstream secondary metallurgy. By achieving a bundled steel stream, it is possible to reduce N2 and O2 pick-up from the atmosphere during tapping. Finally, it is possible to reduce the phosphor pick-up from slag during the ladle treatment by achieving a reduced slag carry over. Additionally, high losses of production time can occur especially during the taphole exchange process. However, one is using a CFD-optimised tapholes together with appropriate machinery, for example the HTJ (Hot Taphole Jacker) or PTX-System (Prompt Taphole Xchange), was able to fully optimize the tapping process and minimize production time loss. The HTJ was developed to demolish and remove worn taphole bricks safely in the shortest possible time frame and without physical stress on the operators. After applying the HTJ and inserting the new taphole set, the PTX-System enables the annular gap between the channel bricks and the surrounding bricks to be efficiently filled from the bottom, by pumping a mix rapidly and accurately into this gap. These systems and their combinatorial advantages have already convinced many steelworkers to adopt this technology References 1. Bachmayer, J.; Sorger, R: Electric Arc Furnace Taphole Changing Systems, RHI Bulletin 2 (2006), p Badr, K; Kirschen, M; Rahm C; Cappel, J: Improvements in EAF by using a smart refractory system conical tapholes; Innovation in EAF and in Steelmaking Processes, In: Associatione Italiana di Metallurgia (ed.), AIM Conference Proceedings (2009), Italy, Milano 3. Badr, K; Tomas, M.; Kirschen, M; McIlveney, G: Refractory Solutions to Improve Steel Cleanliness, RHI Bulletin 1 (2011), p Kirschen, M.; Rahm, C.; Jeitler, J; Hackl, G.: Steel flow characteristics in CFD optimized EAF bottom tapping systems, In: SITPH Polish Association of Metallurgical Engineers and Technicians (ed.) 9th European Electric Steelmaking Conference, Conference Proceedings (2008), Poland, Krakow, pp Zettl et al. Springer-Verlag Wien BHM, 158. Jg. (2013), Heft 1

18 BHM (2013) Vol. 158 (1): DOI /s Springer-Verlag Wien 2012 Berg- und Hüttenmännische Monatshefte Sustainable Electric Arc Furnace Steel Production: GREENEAF Loris Bianco 1, Giulia Baracchini 1, Filippo Cirilli 2, Loredana Di Sante 2, Andrea Moriconi 3, Erica Moriconi 3, Millan Marcos Agorio 4, Herbert Pfeifer 5, Thomas Echterhof 5, Thorsten Demus 5, Hans Peter Jung 6, C. Beiler 6, Hans-Jörg Krassnig 7 1 Ferriere Nord S.p.A., Osoppo, Italy 2 Centro Sviluppo Materiali, Rome, Italy 3 Tecnocentro eng. srl, Terni, Italy 4 Imperial College of Science, Technology and Medicine, London, UK 5 RWTH Aachen University, Department for Industrial Furnaces and Heat Engineering, Aachen, Germany 6 Deutsche Edelstahlwerke, Witten, Germany 7 Stahl und Walzwerk MARIENHÜTTE GesmbH, Graz, Austria Received November 5, 2012; accepted November 8, 2012; published online January 24, 2013 Abstract: In the modern electric arc furnace (EAF), more than 40 % of energy comes from chemical sources by fossil fuels: natural gas is used in dedicated burners during the melting of the scrap, while lump coal (mainly anthracite) is added to the basket and pulverized coal is injected as a foaming agent. Within the frame of the European Research Fund for Coal and Steel (RFCS), the ongoing project GREENEAF (RFSR-CT ) is studying the possibility to replace coal and natural gas in EAF with char and syngas produced by biomass pyrolysis. The best pyrolysis conditions to obtain the proper syngas and char quality have been defined by laboratory tests using biomass available in the surrounding of the partners steel shops. Industrial trials have been performed in three different EAF plants. The results demonstrated the technical feasibility of the approaches, while the economical evaluation has showed the sustainability of replacing the coal with char from biomass in addition to environmental benefits due to CO 2 reduction. Keywords: Biomass, CO 2, Greenhouse gas, EAF, Steelmaking, Pyrolysis, Char L. Bianco ( ) Ferriere Nord S.p.A., Zona Ind. Rivoli, Osoppo, Italy LBianco@pittini.it Nachhaltigkeit der Stahlproduktion mit dem Elektro- Lichtbogenofen: GREENEAF Zusammenfassung: Im modernen Elektro-Lichtbogenofen (EAF) werden mehr als 40 % der Energie in Form von fossilen Brennstoffe eingebracht: Erdgas wird mit speziellen Brennern während des Schmelzens des Schrotts verwendet, während Kohle (hauptsächlich Anthrazit), in stückiger Form mit dem Schrottkorb chargiert wird und als Feinkohle über Einblaselanzen zur Schaumschlackenbildung eingebracht wird. Im Rahmen des Europäischen Forschungsfonds für Kohle und Stahl (RFCS), untersucht das laufende Projekt GREENEAF (RFSR-CT ) die Möglichkeit, Kohle und Erdgas im EAF durch Char (dem festen Pyrolyserückstand) und Synthesegas aus der Pyrolyse von Biomasse zu ersetzen. Die besten Pyrolysebedingungen, um die erforderliche Qualität des Synthesegases und Chars zu erreichen, wurden durch Labortests definiert, in denen Biomasse verwendet wurde, die in der näheren Umgebung der Stahlwerke der beteiligten Projektpartner verfügbar sind. Industrielle Untersuchungen wurden in drei verschiedenen EAF Anlagen durchgeführt. Die Ergebnisse zeigten die technische Machbarkeit der Ansätze, während die wirtschaftliche Bewertung die Nachhaltigkeit für den Ersatz der Kohle mit Char aus Biomasse, zusätzlich zu ökologischen Nutzen aufgrund der CO 2 -Reduktion, gezeigt hat. Schlüsselwörter: Biomasse, CO 2, Treibhausgase, Elektrolichtbogenofen, Stahlerzeugung, Pyrolyse, Char BHM, 158. Jg. (2013), Heft 1 Springer-Verlag Wien Bianco et al. 17

19 1. Introduction In the modern electric arc furnace (EAF), more than 40 % of energy comes from chemical sources by fossil fuels: natural gas is used in dedicated burners during the melting of the scrap. while coal (mainly anthracite), lumped in the basket and pulverized by wall injectors, is used as a foaming agent [1]. The partial introduction of biomass in steel production is considered a good option to reduce the environmental impact and greenhouse gas emission [2, 3]. Moreover it can be considered an economical option considering increasing prices of oil, coal, and market of CO 2 quotes. In the year 2009, the ECSC project Sustainable EAF Steel Production GREENEAF started to study the EAF cycle in order to investigate the partial or total substitution of coal and natural gas with charcoal and syngas produced by pyrolysis of biomass. Generally speaking, in the electric furnace, coal (and consequently char) can be used as injected powder or charged into the basket. The syngas can be used for EAF burners. The characteristics of char and syngas and the related pyrolysis process must be tailored in order to match the requirements for their utilization in EAF. Biomass has been selected and characterized with regard to origin. Laboratory tests to define the pyrolysis kinetics of the selected biomass have been conducted, and, on the basis of these results, the design of industrial pyrolysis has been done; then the char produced by biomass pyrolysis has been chemically and physically characterized to define pyrolysis plant process parameters. About 15 tons of char have been produced for pilot and industrial trials. Due to the difficulties to have syngas available close to the steel plant, the use in EAF burners has been simulated by CFD calculation. The results of CFD simulation are not presented in this paper. 2. Biomass Selection for EAF Char Production The first activity was aimed to analyse the availability and the quality of biomass in the area around the steel plants participating to the project: Ferriere Nord (Italy), DEW (Germany), and MH (Austria). The following biomass species have been selected: ligneous biomass and forest residues (including ligneous species like saw dust for pellets or pulp); grapevine and corn stalk as agricultural residues; miscantus and sorghum as biomass from cultivations. Table 1: Characterization activities performed on selected biomass Ligneous Corn straw Grapewine Mischanthus biomass LHV a [kj/kg] 20,000 18,000 18,900 19,100 Volatiles (%) Ash (%) C (%) H (%) N (%) O (%) S (%) Cl (%) a Lower heating value Samples of the different types of biomass described have been collected and characterized in terms of physicochemical characteristics Table (1) and pyrolysis behavior. The performed analysis showed that the selected biomasses have very similar elemental characteristics in terms of C/H/O and similar volatile matter content. Biomass s heating value is also very similar. the main differences can be found in minor elements (as N, S and Cl) and ash amount. Pyrolysis products from biomass are charcoal, condensable vapors, and syngas. The percentages and characteristics of formed products depend on pyrolysis heating rate, residence time, and reaction temperature. For this reason, a laboratory activity has been carried out to study thermal behavior of selected biomass with the purpose to define the best conditions for the pyrolysis in order to obtain char suitable as a charge material in the basket of injected to promote slag foaming. 3. Definition of the Pyrolysis Conditions Laboratory tests have been purposely conducted to define the pyrolysis conditions. Tests are done with thermobalance (TGA tests) to observe the weight variations of the material as a function of temperature, under controlled atmosphere. TGA tests have been carried out on biomass to obtain information about pyrolysis kinetic as well as on char to compare the reactivity of char with reactivity of standard used coals. 3.1 Characteristics of Pyrolysis Temperatures Three biomass samples were used: agricultural residues, biomass from cultivations, and wood biomass. Figure 1 shows an example of TGA curve (expressed as derivative of weight loss with temperature) obtained with agricultural residues. TGA tests showed that the pyrolysis process starts at about 200 C for all the biomass samples, with two peaks centered at about 300 C and 400 C; the temperature of 400 C can be considered the minimum temperature for the biomass pyrolysis process. 18 Bianco et al. Springer-Verlag Wien BHM, 158. Jg. (2013), Heft 1