The evolution of steel and energy markets in recent years

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1 300 tonne EAF for thin slb minimill complex A single 300t ultr high power EAF linked to twin ldle furnce, twin degsser nd thin slb cster nd mill is under construction in Turkey. It is mjor technology dvnce for minimill opertion producing 2.4Mt/yr. The design im ws to chieve high qulity, high productivity nd low cost opertion derived from dvnced technology, low mnpower nd low specific energy consumption. Authors: Romno Selln nd Murizio Fbbro Dnieli Centro Met The evolution of steel nd energy mrkets in recent yers hs required steel producers to focus incresingly on meltshop productivity nd efficiency, s well s producing high qulity steel products. However, the productivity increse must be obtined with limited investment in order not to ffect mrgins with high fixed nd vrible costs. This tendency hs brought considerble increse in meltshop het sizes nd simultneous reduction of the cycle times (tp to tp) with, s n immedite consequence, significnt increse in power usge both electricl nd chemicl. In line with this trend MKK-Atks, joint venture between MMK Mgnitogorsk Iron & Steel Works, Russi, nd Atks, Turkey, wrded Dnieli contrct for the supply of new 2.4Mt/yr minimill nd finishing opertions complex to be instlled in Iskenderun,Turkey. The minimill includes n ultr high power (UHP) 300t FstArc AC EAF equipped with the Dnrc system for extensive use of lterntive energy sources. Due for completion in 2010, it will be the most powerful EAF in the world. The plnt lso includes secondry metllurgy equipment, fume tretment, compct strip plnt (CSP) comprising two-strnd thin slb cster, nd hot rolling mill, plus glvnising line nd colour coting line. Only the steelmking re is described in this rticle. The plnt will be locted on the cost so se port will be built on-site cpble of receiving ships of up to 80,000t with consequent dvntges in terms of logisticl mteril flow from ships to nd from the plnt. This project is of gret interest s Turkey is growing mrket with n verge nnul growth in steel consumption over the pst seven yers of 15%, while locl production hs grown only 8% nnully. The fstest growth hs been in flt products. Plnt concept The innovtive technologicl solutions im to chieve extremely efficient opertions nd high qulity steel, with r Fig 1 Plnt lyout low mnpower nd specific energy consumption, mking the plnt highly competitive. The plnt lyout is shown in Figure 1. Liquid steel will be provided from single 300t Ultr 3 High Power EAF nd single by concept meltshop lyout, which provides the best results in term of process hndling nd cost optimistion. Secondry steelmking is performed by twin sttion 250t ldle furnce (LF) nd twin tnk vcuum sttion (VD) with 5-stge stem ejector vcuum pump. The steel is then cst with twin strnd thin slb cster (TSC), which feeds the hot rolling mill nd finishing complex downstrem. The meltshop includes n integrted mteril hndling system (IMHS) nd powerful fume tretment plnt equipped with twin 77

2 r Fig 2 Reltionship between EAF tp weight nd dimeter pulse jet bg filter (FTP). All equipment will be controlled nd optimised by n innovtive nd fully integrted utomtion system. r Fig 3 EAF lyout with injector positions EAF DESIGN Until now n output of 2.4Mt/yr would hve required two or more EAFs, so the choice of single high-cpcity EAF is considerble technologicl dvnce. The lyout optimises the required spce nd contributes to n extremely compct nd efficient plnt rrngement. During design we preferred lrge furnce concept so longer rcs cn be pplied s well s llowing more oxygen injection units to be plced round the furnce. Figure 2 shows the reltionship between tp weight nd EAF shell dimeter. There re three min ims tht hd to be optimised: ` Very high meltshop productivity ` All the EAF metllurgicl rections hve to be fulfilled within short tp to tp time in terms of uniformity (distribution of oxygen input) nd homogenistion (stirring nd mixing of the bth) ` The finl product qulity demnds low residuls, low crbon nd high purity (inclusion level) r Fig 3b Oxygen jet + burner, with shrouding effect r Fig 3c Crbon jet + burner, with shrouding effect The requirements of this project re extremely high from technologicl process design point of view s the furnce must produce low crbon, medium crbon nd HSLA steel grdes with the following performnces: ` Chrging mix: 80% scrp, 20% pig iron ` Power-on time: 36 minutes, implying melting rte of 9.3t/min ` Productivity: 320t/hr ` Tpped steel weight: 250t ` Tp to tp time: 47 minutes ` Electricl consumption: kWh/t, bsed on severl chrging mixes Some design fetures re: ` Btch chrging vi two buckets 78

3 r Fig 3d Bulged pnel rer view r Fig 3e Bulged pnel inner view r Fig 3f Copper block with Oxyjet ` Split shell design with conductive rms ` EAF volume: 330m 3 ³ ` EAF cpcity: 310t ` 300MVA trnsformer (1,200kVA/t tp wt) ` Electrode dimeter: 810mm Prticulr ttention hs been pid to the selection of the trnsformer to obtin the required melting rte. The 300MVA trnsformer, together with the selected rnge for the secondry tp voltges, meets the requirement for flexibility in opertion during the process, nmely: rpid power growth during boring, melting t mximum ctive power with long rcs, nd refining t mximum current with covered rcs by foming slg. The current conductive rms nd the secondry bus hve been designed to conduct the mximum llowed current of 110kA. Prticulr ttention hs been pid to the stiff design of the electrode msts nd rms in order to prevent resonnce nd nomlous vibrtion ffecting the stbility nd robustness of electrode regultion. The electrode control pckge HiReg Plus contins the ltest improvements to gurntee power delivery in stble nd relible conditions. In prticulr, the bility to evlute rc stbility nd slg cover by rel-time hrmonic monitoring gives efficient supervision of preset operting points nd foming slg controller. The short power-on time vilble requires rpid heting to tpping temperture to gurntee tht the best melt temperture homogenistion of bth stirring system vi bottom porous plugs will be provided. Chemicl energy The high melting rte in this prticulr process nd dimension of bth require the proper injection nd distribution of lrge mount of oxygen nd col round the furnce wlls. We intend to instll eight oxygen nd five col Jet FstArc injectors in order to: r Fig 4 Typicl forecst melting profile chieve n even distribution of col nd oxygen, llow decrburistion rte up to 300kg/hr/m 2 with oxygen consumption up to 40-45Nm/t, promote good steel homogenistion, nd blnce hot nd cold spots. The injectors re instlled round the furnce t specified positions nd injection ngles in order to chieve the mximum performnce in ccordnce with ll the process prmeters. Figures 3-3f illustrte some of the key fetures. Figure 4 depicts typicl forecst melting profile for two-bucket het using scrp nd pig iron. The ppliction of FstArc injection technology provides the following benefits: Process ` Reduced electrode consumption ` More homogeneous bth temperture nd chemistry 79

4 r Fig 6 Ldle furnce with inert roof furnce performnce in terms of energy consumption nd steel output re more repetble. Consistent output is prticulrly beneficil due to its impct on the cost of ll downstrem ctivities, eg, lloying, LF refining nd superheting. r Fig 5 Twin position ldle furnce ` Lower slg FeO content ` Reduced refrctory consumption, furnce shell nd ldles ` Improved rc efficiency with high degree of repetbility, incresed verge power input nd shorter power on times, principlly relted to erlier nd greter fomy slg performnce vi utomtic oxygen nd col injection Automtion optimistion Injection is controlled by the furnce utomtion system, limiting the opertor s role to one of supervision. Furthermore, ll vritions in working set points re crried out utomticlly nd, hving fixed injector configurtion, the system does not require ny mnully executed movement to perform its functions. Reduced mintennce The simplifiction of on-bord equipment, together with the system s fixed configurtion, significntly reduce mintennce time. Furnce vilbility is incresed, llowing subsequent increse in productivity nd reduction in costs. Consistency Due to the positive spects described bove, Chrge mterils Product qulity requirements will be obtined by djusting the chrging mterils. In this respect the EAF hs been designed to hve full flexibility in terms of selection of rw mteril mix, but this does hve n impct on the process, s shown by the following two exmples: 1 80% scrp, 20% pig iron 2 65% scrp, 35% DRI In one, the decrburistion speed is the limiting fctor; in two, power consumption is the criticl point. Secondry Metllurgy Finl steel qulity is obtined by mens of powerful 250t twin position ldle furnce nd twin tnk vcuum sttion, with deslgging fcilities for removl of slg before degssing (see Figure 5). The twin position fcility is designed to increse the production cycle flexibility in ccordnce with the short tp to tp time of the EAF. The ldle furnce is equipped with: ` Swivelling electrode system nd double inert roofs ` % MVA trnsformer ` Two ldle crs ` Automtic smpling equipment for ech working position ` Wire feeding system for ech working position The inert roof system (see Figure 6) hs smll positive (or 80

5 r Fig 7 Twin-tnk vcuum sttion Gs Pick-up, ppm remrks N < 5 Slg thickness must cover rcs, mesured in 100t LF H 0.22 Averge vlue over 24 hets, mesured in 130t LF r Tble 1 Gs pick-up during norml heting neutrl) pressure inside the furnce vi pressure dmper in the hood suction line. This reduces ir infiltrtion to the furnce with the following benefits: ` Reduced side oxidtion of the electrodes nd hence lower electrode consumption ` Reduced oxidtion of the slg nd hence lower FeO content nd consequently of the oxygen content in the steel ` Less hydrogen nd nitrogen pick-up from the furnce tmosphere Tble 1 illustrtes wht cn be chieved with this type of system in terms of pick-up of gses from the tmosphere with exmples from other fcilities. The Vcuum sttion (see Figure 7) is equipped with: ` Twin tnk with switchble suction line ` Single cover ` Automtic smpling mnipultor for steel, temperture, oxygen nd hydrogen ` Wire feeding system ` 5-stge stem ejector vcuum pump with suction cpcity up to 500kg/hr Fume Tretment Plnt The extremely powerful melting process requires fume de-dusting plnt ble to process gs flow rte up to 430,000Nm 3 /hr from the primry system, nd lmost 3M Nm 3 /hr in totl (see Figure 8). The huge flow rte leds to twin design pulse jet filter with 6MVA powered fns of highly efficient design. Along the suction line extensive cooling is provided by nturl twin-type cooler coupled with two cyclone type sprk rresters. Electricl nd Automtion system The utomtion system proposed, covering both equipment control (Level 1) nd process control (Level 2), is bsed on stte of the rt hrdwre nd softwre pltforms, while the ppliction softwre is the well-proven Dnieli utomtion pckge, the result of over 40 yers experience in steelmking. The system chrcteristics re 81

6 r Fig 9 Hireg Plus illustrtion of benefits common for the entire plnt. In order to chieve the best performnce for the EAF, Dnieli utomtion fetures the Hireg Plus system, which improves rc regultion in the EAF. This system, thnks to the nlysis of the hrmonic content in the power circuit, cn evlute rc stbility nd rc coverge indices, incresing the efficiency of the electric rc. Thus the rc is kept protected by foming slg nd with mximum stbility, providing high power without incresing refrctory wer. The benefits re: minimum power on time, mximum verge power, reduced energy consumption (electricl energy nd crbon injected) nd reduced electrode consumption (see Figure 9). The on-line monitoring of process dt nd recording of process dt for subsequent nlysis will lso improve the knowledge of rc behviour, which is prticulrly importnt considering the extremely high power input. r Fig 8 Fume tretment plnt Conclusions Choice of single 300t ultr high power EAF linked to twin ldle furnce, twin degsser nd thin slb cster nd mill is mjor dvnce for minimill opertion producing 2.4Mt/yr, illustrting stte of the rt technology. The design im ws to chieve extremely efficient opertions nd high qulity steel, with low mnpower nd specific energy consumption, thereby mking the plnt highly competitive. MS Romno Selln is Director Engineering, Meltshops nd Murizio Fbbro is Senior Engineer, Process Technology, both t Dnieli Centro Met, Buttrio, Itly. Contct:.frgicomo@dnieli.it 82