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otizie The new VAI FUCHS ultimate EAF:

Dawn of a New Era in Electric SteelmakingT. Narholz, B. Villemin

TThrough the combination of advanced electric steelmaking technologies and design features VAI FUCHS isnow in a position to offer an electric arc furnace capable of producing approximately 1,800,000 tons of

liquid steel per annum. Referred to as the ULTIMATE EAF, this furnace features a tapping weight of 120 tonsand an average tap-to- tap time of only 30 minutes. How such a furnace could look, the respective design

figures and which technologies are employed is the topic of this paper.

INTRODUCTION

During the past twenty years electricsteelmaking has been the primary drivingforce behind the growth in the steel indu-stry. Modern EAF-based steelmakingplants feature following main advantages:• Relatively low investment costs com-

pared to the integrated blast-furna-ce/oxygen steelmaking route

• Utilization of a wide range of raw ma-terials such as scrap, DRI, HBI and hotmetal

• Ability to fulfill a wide range of pro-duction targets and steel qualities tomeet the specific market requirements

• Low operational and thus conversioncosts, promoting a relatively short re-turn-on-investment.

For more than 35 years VAI FUCHS hasbeen a frontrunner in the developmentof new technologies for electric steel-making. Highlights include the introduc-tion of water-cooled equipment, current-conducting electrode arms, single-pointroof lifting, shaft furnaces, twin-shellEAFs and refining combined burner sy-stems for enhancing productivity. Inno-vation has always been a trademark ofthe company philosophy. To date, VAIFUCHS has supplied more that 100 elec-tric arc furnaces of AC and DC design, in-cluding shaft furnaces for scrap pre-hea-ting and twin-shell EAF installations. As a result of their continued emphasison research and development and throu-gh the combination of all of their advan-ced technologies and EAF design featu-res VAI FUCHS is now in a position to of-fer a new generation of electric arc fur-naces. Referred to as the ULTIMATE se-ries, a single EAF vessel with a tappingweight of 120 ton and an average tap-to- tap time of about 30 minutes is nowcapable of producing approximately1,800,000 tons of steel per annum. Thepossibility of previously unattained pro-ductivity levels at record-low conversioncosts now opens the door to a new era in

electric steelmaking. A general view ofan ULTIMATE EAF can be seen in Figure 1.

PLANT DESIGN

General The new ULTIMATE EAF has been desi-gned by VAI FUCHS on the basis of ex-tensive know-how and plant-building ex-perience in electric steelmaking. In addi-tion to changes in the basic design ofthe EAF, a number of additional improve-ments were carried out in connectionwith the mechanical equipment, powersupply, water-cooled parts, robotic sy-

stems, measurement units, oxygen- andcarbon-injection systems, process con-trol, automation as well as on dedustingand environmental equipment. Overallplant logistics were also reviewed toavoid operational bottlenecks, to perfec-tly match the capacities of all EAF-rela-ted facilities and systems with eachother, and to ensure an optimized pro-duction route for achieving the designedproduction targets.On the basis of detailed calculations incombination with the results from va-rious operating plants the main designfeatures of this new furnace type can besummarized in Table 1.

T. Narholz, B. VilleminVAI FUCHS GmbH, Germany

Figure 1: GeneralView of a VAI

FUCHS ULTIMATEElectric Arc

Furnace.

Tapping weight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120 tHot heel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40 tTapping temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1,620 °C1 Scrap bucket . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .130 tYield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90%Scrap density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0.8 t/m3

EOEBT* design . . . . . . . . . . . . . . . . . . . . . . . . . . . . .for Ø of 7.2 mTotal panel length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.4 mRoof height . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.5 m4 RCBs (O2 and C injection) . . . . . . . . . . . . . . . . . . . .2,500 Nm3/h

3.6 MW2 Burners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.6 MW3 PC** injectors (O2) . . . . . . . . . . . . . . . . . . . . . . . . . . .400 Nm3/h3 Carbon injectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70 kg/min

*EOEBT = Energy-Optimized Eccentric Bottom Tapping** PC = Postcombustion

Table 1: Key Dataof a 120-t

ULTIMATE EAF.

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Equipment and Systems An ULTIMATE EAF includes the installa-tion of the following equipment and sy-stems, each of which is reliably opera-ting in various furnaces worldwide: • Automatic scrap bucket pre-positio-

ning • Door-cleaning robot• Contact-free temperature measure-

ment of the steel bath• Ultra-high-power oxygen- and carbon-

injection technology with RCB (Refi-ning Combined Burner)

• Automatic tap control from the mainEAF pulpit via video camera

• Automatic slag detection during tap-ping with the IRIS system (InfraRedIdentification System)

• Tap-hole cleaning robot• Crane equipped with two auxiliary

hooks for quick electrode exchange• Electrode stand with spray-water cool-

ing.As proven in more than 35 installationsworldwide (status: September 2004),the RCB oxygen- and carbon-injectionsystem (Figures 2 and 3) boosts theexothermic energy input and activelypromotes postcombustion. Deep bathpenetration with highly effective oxy-gen/carbon reactions are ensured on thebasis of the unique design of the sy-stem’s nose panel (Figure 4).The doorcleaning robot keeps the door area freeof scrap during charging. Therefore, adoor burner or door lance is no longernecessary. The IRIS slag detection sy-stem exactly defines the ideal tappingtime for minimized slag carry-over (Figu-re 5). With the tap-hole-cleaning robotnot only are tap-hole cleaning timesconsiderably shortened and plant availa-bility increased, but risks to maintenan-ce operators are also greatly reduced (Fi-gure 6).

Figure 2:Arrangement of

Oxygen and CarbonInjection Tools

(Top View).

Figure 3: RCBOperation in the"Low-Fire" Mode(longer flame).

Figure 4: Nose-Panel DesignAllowing 50°

Impact Angle.

Figure 5: Example of an IRIS Monitor Screen (InfraRed Identification System).

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Mechanical DesignThe mechanical components of an ULTI-MATE EAF have been specially designedon the basis of the latest operationalfeedback and process requirements.

Their advantages and reliability are al-ready well proven in existing VAI FUCHSinstallations. Design features of key me-chanical components include:• Strong, simple and reliable construc-

tion (heavy mill-type)• High vessel shell designed to allow for

one-bucket charging• Gantry design with single-point roof-

lifting system• Prismatic roller-guide system for elec-

trode columns to reduce vibration• Split-shell EAF design with the upper

vessel section divided into the fol-lowing panel sections (Figure 7):(a) Steel-panel section in the upper

part (b) Copper-panel section in the lower

part and in the slag zone, inclu-ding specially fixed high-velocitypanels for O2 and carbon injection(RCB)

• Tightest possible sealing between thepanels and panel fixation on the shellcage to avoid panel movement (Figure8)

• Improved, sturdy construction of thetilt platform,

Also, it would be possible to reduce thenumber of operators of an ULTIMATE EAFto three persons per shift: 1 EAF pulpit operator1 Floor operator1 Crane operator.

Consumption FiguresThe use of modern calculation programshave shown that the operation of an UL-TIMATE EAF would result in reducedpower-off times, a more constant pro-duction level, improved consumption fi-gures and lower overall costs. The expec-ted performance figures of this furnacetype are summarized in Table 2. To achieve a 30 minute tap-to-tap timethe power-on time is maximized throughan optimization of physical and chemicalprocess-related factors. The power-offtime is reduced through the clever utili-zation of existing equipment and tools.

Figure 6: Tap-Hole-Cleaning Robot .

Figure 7: PanelArrangement for

High-Shell EAFDesign.

Figure 8: Panel Sealing and Fixation.

Electricity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .340 KWh/tLS*Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.2 kg/tLS

Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35 Nm3/tLSGas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Nm3/tLS

Charge coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 kg/tLSCoal powder (foamy slag) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7 kg/tLS

Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40 kg/tLS

*LS = Liquid Steel

Table 2: Specific Consumption Figures (Calculated).

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