eaf makale

CVS MAKINA İNŞ. SAN. ve TİC. LTD. ŞTİ.

Dilovası Organize Sanayii Bölgesi 3. Kısım Muallimköy Cad. No:21 Gebze 41400 KOCAELİ / TURKEY

Tel. +90 262 759 15 05 Fax. +90 262 759 18 80 www.cvs.com.tr [email protected]

MORE FLEXIBLE, MORE EASY

REASONS BEHIND THE SUCCESS OF CVS MAKINA’S FURNACE DESIGN

(M. OZDEMIR & D. ERTAS – Project & Contracting Department – CVS Makina Ltd.)

Steelmaking is always a growing sector and steelmakers are always asking for more flexible and moreeasy operation for meltshop units. As design, manufacturing and erection of this kind of units, CVSMachina put his experience for combining more simple design with flexible operation. Additionally,CVS fulfills any requirement when it comes to the choice of furnace type and melting technology forcost efficient operation. Options include burners, wall mounted supersonic lances, and bottomtuyeres for oxygen injection to name a few. The basis of all CVS design is good accessibility, lowmaintenance and operational reliability.

The CVS electric steelmaking technology is the solution for strong, simple and reliable design. As theproduct of continuous development improvements, our furnaces features maximized power-on-time, high-speed movements and easy access to all components for maintenance. The furnace isideal for ultra-high-power input and overall furnace performance can be additionally enhanced withthe latest oxygen and carbon injection technologies.

Following paper will explain the features of EAF units designed and manufactured by CVS MAKINAfor flexible operation. Comparison of three EAF units designed for different Steeplants and forproduction of different tapping weights will also be covered.

Introduction

Today, investors worldwide are looking and waiting for new signals from steel market to understandwhere to direct and dedicate their money, energy and resources for possible alternative business.Because of uncertainty in the market, steelmakers are looking for more flexible operation to catchthe changing market demands.

Located near to Istanbul (Turkey) in 40.000 sqm covered manufacturing area with 700 people (200engineers) and 75 million EURO turnover, CVS provides turn-key plants and equipment solutions forSTEEL SHOPS and ROLLING MILLS for long products.

On the basis of long experience in the design of electric arc furnaces (EAF), CVS offers to the steelproducers a broad range of powerful options for high-performance electric steelmaking.

EAF from CVS is the ideal melting unit for the production of all types of steel, from standard carbongrades up to high-alloyed and stainless steel grades. Its overall furnace performance can beadditionally enhanced with the latest oxygen- and carbon-injection technologies.




The idea of CVS for the choice of the various systems making up the plant is strictly related to theachievement of the following high-priority objectives, namely:

- Limited investment costs- High quality products- High productivity- Maximum simplicity of operation- Operation reliability- Maximum flexibility to meet various market demands.




To get more flexible operation, CVS has developed a new type of project, i.e.:

Ø The super-flexible EAF base Minimill concept

Idea behind this concept and general features of CVS design furnaces are explained below:

General EAF Concept

In the following table, it can be seen that, different tapping weights can be applied in the samefurnace design by changing refractory profile, by changing electrode regulation and oxygen/carboninjection practices. By Increasing the tapping weight yields increased productivity and decreasedconsumption.

Company Plant A Plant B Plant C

Plant unit: E.A.F.

Furnace Type AC-EBT/Turret gantry AC-EBT/Turret gantry AC-EBT/Buggy gantry

Upper shell (Ømm) 7,200 7,200 7,200

Lower shell (Ømm) 7,400 7,400 7,400

Upper shell height(mm)

3,000 3,000 3,000

Serios reactor(MVAr) ON-LOAD 36 ON-LOAD 46 ON-LOAD

Transformer (MVA) 120+10% 135 130+20%

Max. Sec.Volt (V) 1200 1305 1300

Inner volume (m³) ≥155 ≥155 ≥155

Scrap bucket vol (m³) 146 130 140

Electrode (Ømm) 24” (610) 26” (660) 24” (610)

Max. Sec. Current (kA) 70 70 75

PCD (Ømm) 1300 1300 1300

Electrod arm Cu-cladded Cu-cladded Cu-cladded

Oxy/fuelburner+sup.Jet

5+1 EBT 5+1 EBT 4+1 EBT

SVC capacity (MVAr) 170 175 200




EAF PERFORMANCES Plant A Plant B Plant C

Design start-up / present start-up / present start-up / present

Tapping weight (t) 130 140 100 135 130 150

TTT (min.) 50-56 40-48 38-42 48-55 42-47 44-50

Productivity (t/h) 170 185 150 167 165-185 180-204

Electric consp.( kWh/t) 380-410 340-380 380-410 370-400 360-390 350-370

Electrode consp. (kg/t) 1.5-1.6 1.20-1.30 1.5-1.6 1.35-1.50 1.25-1.35 1.10-1.25

O2 consp. (Nm³ /t) 43 42 38 40 30-35 38

Carbon consp.(kg/t) 15 15-20 20 22 18-22 18-22

Refractory (kg/t) 4.20 3.60 3.67 3.35 4,05 3,54

Shell life (# of heat) 480 500 450 750 700 850

Roof delta life (heat) 520 560 450 700 400 750

Lime comp. (kg/t) 45-50 30-35 45 42 45-50 40-45

PRODUCTIONRECORD:

heat/day 32 33 37 29 25 28

t/day 4100 4440 3597 4013 3750 4.250

Starting point of steelmaking is the scrap yard. The complexity of minimill based steelmaking iscoming from various types and blends of scraps and scrap substitutes such as DRI and HBI. To handlethe complexity automatic operation shall be applied.

The scrap yard design always condiders as fully automated systems with pre-defined scrap recipies.Scrap cars and cranes are considered as remote controlled. Crane operators can easily co-ordinatescrap car movements by watching screens in contol pulpit.

To respect the idea of minimum areas occupied for investment, special design is considered thankingto intelligent volume increase by deepness in closed scrap yard. With the same design, distribution ofscrap blends and truck unloading are very easy.

The main feature of the three EAF is its extremely high available power. Considering the nominaltapped weight of 130 ton, specific available power of the furnace is 1,2 MVA/t, which is much higherthan the Standard values used for EAF design.

Charging in 2 bucket sequence with 100 % scrap practice is considered. Furnace roof is consideredwith 5th hole for lime and/or dololime feeding by fully automated by MHS and 6th hole for future




consideration of continuous feding of DRI and/or HBI up to 30 %. The requirement for higherproductivity while charging significant amounts of scrap blends is maintained by four scrap cranes.

The energy required to meltdown and superheat the steel and slag including all losses are balancedby the energy input by means of electrical energy and exothermic reactions.

The influences by scrap and other metallic input materials, the radiation by the arcs to the side wallpanels and the exothermic reactions, prove to be important especially with respect to the lossesindicated by the temperature increase in cooling water as well as the amount and temperature ofthe off-gas. Limitations in the process are set by the heat transfer in scrap, the maximum length ofthe arc, whether the arcs are submerged in foamy slag, and the decarburization rate indicated by thespecific carbon throughput.

The regulation of the negative pressure inside the furnace is important due to its specific influences.The negative pressure is regulated in the range of -0.8 mm WC (water column) during melt-down. Incase the negative pressure drops to values of less than 0.1 mm WC smoke/off-gas will leave thefurnace through all openings in the furnace. In case more negative pressure is used, more coldingress air will in the furnace , with negative influence on the energy requirements.

The cooling element (roof/pipe panel) is designed as a water-cooled, exchangeable panel andconsists of pipes with several water circuits. The panel is sealed with a cover plate. The panel isprovided with slag pins and gunned with refractory material in order to protect it against heat. Allopenings for offgases, material feeding, lime injection, furnace pressure measurement and thetaphole filling system are led through the panel. The panel is supplied with water from the roofsupporting structure (fixed piping).

Special roof lifting mechanism is designed for easy maintenance and easy roof delta changeoperation. Roof is hanged only from side of the roof to gantry. There is only electrode arms abovethe roof which results very easy maintenance.

Electric Arc Furnace (EAF) design condiders always for short tap-to-tap times thanks to severaltechnologies such as:

- UHP (Ultra High Power) design, with high secondary voltages and longer arc

- High-current-conducting electrode arms in copper-clad box design

- State-of-the-art electrode control system

- Extensive use of alternative energy sources (chemical energy)

- Better energy and thermal balance inside the furnace thanks to the multiunit injection.

- High yield of alloy additives and high ladle refractory life thanks to EBT slag-free tapping.

- More heat input in cold EBT area thanks to special design of EBT-burner system.

- Heavy construction design to sustain hard working conditions, allowing very fast movements

and safe operations.




- High flexibility and high efficiency of furnace operation with closed slag door application.

- Easy maintenance operation for special design like roof lifting system, furnace locking

system.

- Split-shell design

- Copper or combi-panels with high-speed cooling water flow

- Continuous DRI/HBI feeding systems

- Additional chemical energy based on carbon, fuel and oxygen is used as substitute of electric

power.

- SIM-ARC electrode regulation design

- Hot heel practice

- Fast scrap charging

- Scrap yard flexibility.

Electrode movements of EAF are controlled by SIM-ARC electrode regulation system which allows aconstant ratio between electrode voltage and current to be maintained. Together with the hydraulicsystem of electrode movement control, system acts on arc voltage to maximise the efficiency ofmelting process. Using special algorithm following benefits can be obtained:

- Fast adjustment of arc length,

- Fast response and fast and stable control,

- Minimizing of power consumption,

- Minimizing of flicker effects due to regulation quality,

- Minimizing of electrode and refractory consumption.

EAF also employs supplementary chemical energy to save electrical power and thereby reducesconversion cost through improved EAF productivity. Chemical energy is supplied through specialdesign CVS-Combined burner system providing carbon and oxygen injection. Burners are distributedfor the aim to cancel cold spot areas and also to obtain good foamy slag. In other words, theconfiguration was selected in order to have an as homogenous as possible supply of chemical energyto the bath. The module philosophy follows the target of efficient management of electrical andchemical energy, combining efficient dynamic control of the electric arc with a balanced injection ofoxygen and carbon in order to increase EAF productivity.




The oxygen jets supply the necessary oxygen amount for boosting the chemical reactions with bothelements in the bath and also injected and/or charged carbon. The injectors, designed as laval nozzle,provide a highly coherent and efficient flow. Moreover, they make an important contribution to bathstirring leading to chemical and thermal homogenisation.

The evolution in electric arc furnace technology has progresively led to the utilisation of alternativeenergy contributing to the heat balance, optimising the consumption of electrical energy andincreasing productivity. A further effect of the correct adoption of this practice is the formation of ahigh level of foaming slag, with all the benefits arising from the resulting arc coverage. To obtainbetter slag foaming, additional slag door manipulator with two oxygen and one carbon lance isinstalled which yields faster operation.

The carbon injectors provide the possibility to control the bath conditions by regulating the flowrateand promoting slag foaming. This slag condition has many advantages in terms of furnace wallprotection, more efficient power utilisation and reduced maintenance.

To create quickly foamy slag, the carbon flow rate is initiated with an appropriate flow rate as soonas a certain temperature increase is indicating the exposure of the panels. As the volume of slagincrease, the furnace is slightly tilted into tapping direction in order to retain slag foam. Deslagingwill be started as soon as the slag fluidity is sufficient and the required tapping temperature is aboutto be expected.

Material Handling System is designed to reduce manual work and to avoid losing time-demandingmaterial handling and automatic operation. The main operations are the storage into bins,extraction, weighing, transport and charging of ferroalloy, additives and fluxes into scrap bucket, intothe ladle in tapping position and to the ladle refining station. All plant functions, specifically fromstorage bins up to loading to the final users, are controlled automatically. The dosage is carried outwith high accuracy to obtain maximum technical results and, at the same time, to use additives andfluxes in the best possible way to minimize expenses. Suitable interlocks are to guarantee the rightpositioning of the devices.




Conclusion

In the last few years, CVS has supplied nr. 3 same size EAF’s. One of those projects was also a

complete “turn-key” green-field project and it has been completed in 16 months. The three EAF’s are

using in the range of 90t to 150t liquid steel without modifications. Since many restrictions at their

beginning stage of start-up. 160t is expected in the near future either with high bulk density scrap or

with 3 charges. These superflexible approach to steel making practise is giving significant advantages

to investers in terms of their present and future’s plans.

For further information, please contact from: [email protected]

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