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ELECTRIC ARC FURNACE, STEELMAKING

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									                                    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 more
easy operation for meltshop units. As design, manufacturing and erection of this kind of units, CVS
Machina 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 for
cost efficient operation. Options include burners, wall mounted supersonic lances, and bottom
tuyeres for oxygen injection to name a few. The basis of all CVS design is good accessibility, low
maintenance and operational reliability.

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

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




Introduction

Today, investors worldwide are looking and waiting for new signals from steel market to understand
where 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 catch
the changing market demands.

Located near to Istanbul (Turkey) in 40.000 sqm covered manufacturing area with 700 people (200
engineers) and 75 million EURO turnover, CVS provides turn-key plants and equipment solutions for
STEEL 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 steel
producers 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 carbon
grades up to high-alloyed and stainless steel grades. Its overall furnace performance can be
additionally enhanced with the latest oxygen- and carbon-injection technologies.


                                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         cvs@cvs.com.tr
The idea of CVS for the choice of the various systems making up the plant is strictly related to the
achievement 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.




                                  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    cvs@cvs.com.tr
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 same
furnace design by changing refractory profile, by changing electrode regulation and oxygen/carbon
injection practices. By Increasing the tapping weight yields increased productivity and decreased
consumption.

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   3,000                       3,000                    3,000
(mm)
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/fuel                     5+1 EBT                     5+1 EBT                  4+1 EBT
burner+sup.Jet
SVC capacity (MVAr)          170                         175                      200




                                   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   cvs@cvs.com.tr
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
PRODUCTION
RECORD:
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 is
coming from various types and blends of scraps and scrap substitutes such as DRI and HBI. To handle
the 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-ordinate
scrap car movements by watching screens in contol pulpit.

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

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

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


                                   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      cvs@cvs.com.tr
consideration of continuous feding of DRI and/or HBI up to 30 %. The requirement for higher
productivity 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 balanced
by 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 wall
panels and the exothermic reactions, prove to be important especially with respect to the losses
indicated by the temperature increase in cooling water as well as the amount and temperature of
the off-gas. Limitations in the process are set by the heat transfer in scrap, the maximum length of
the arc, whether the arcs are submerged in foamy slag, and the decarburization rate indicated by the
specific 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. In
case the negative pressure drops to values of less than 0.1 mm WC smoke/off-gas will leave the
furnace through all openings in the furnace. In case more negative pressure is used, more cold
ingress 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 and
consists of pipes with several water circuits. The panel is sealed with a cover plate. The panel is
provided with slag pins and gunned with refractory material in order to protect it against heat. All
openings for offgases, material feeding, lime injection, furnace pressure measurement and the
taphole filling system are led through the panel. The panel is supplied with water from the roof
supporting structure (fixed piping).

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

Electric Arc Furnace (EAF) design condiders always for short tap-to-tap times thanks to several
technologies 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.

                                  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     cvs@cvs.com.tr
    -     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 a
constant ratio between electrode voltage and current to be maintained. Together with the hydraulic
system of electrode movement control, system acts on arc voltage to maximise the efficiency of
melting 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 reduces
conversion cost through improved EAF productivity. Chemical energy is supplied through special
design CVS-Combined burner system providing carbon and oxygen injection. Burners are distributed
for the aim to cancel cold spot areas and also to obtain good foamy slag. In other words, the
configuration was selected in order to have an as homogenous as possible supply of chemical energy
to the bath. The module philosophy follows the target of efficient management of electrical and
chemical energy, combining efficient dynamic control of the electric arc with a balanced injection of
oxygen and carbon in order to increase EAF productivity.




                                    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    cvs@cvs.com.tr
The oxygen jets supply the necessary oxygen amount for boosting the chemical reactions with both
elements 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 bath
stirring leading to chemical and thermal homogenisation.

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

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

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

Material Handling System is designed to reduce manual work and to avoid losing time-demanding
material 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, into
the ladle in tapping position and to the ladle refining station. All plant functions, specifically from
storage bins up to loading to the final users, are controlled automatically. The dosage is carried out
with high accuracy to obtain maximum technical results and, at the same time, to use additives and
fluxes in the best possible way to minimize expenses. Suitable interlocks are to guarantee the right
positioning of the devices.




                                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    cvs@cvs.com.tr
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: info@cvs.com.tr




                                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   cvs@cvs.com.tr

								
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