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Electric Arc Furnace SM

AMMASI A CSIR –National Metallurgical Laboratory

Jamshedpur ,Indiamasi@nmlindia.org & masi.mett@gmail.com

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Steel making flow diagram

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What is IRON making ??? Steel ???

Composition of pig iron,DRI ,Steel scrap??

Final required composition ??? Why steel required ??

Why pig iron is not suitable for application ???

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Introduction Sir Humphry Davy conducted an experimental demonstration in 1810; welding was investigated by Pepys in 1815; Pinchon attempted to create an electrothermic furnace in 1853; and, in 1878–79, Sir William Siemens took out patents for electric furnaces of the arc type.

The first electric arc furnaces were developed by Paul Héroult, of France, with a commercial plant established in the United States in 1907.

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Type of electric arc furnace

(1) Direct electric arc furnace (2) Indirect electric arc furnace

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Construction featureDC EAF

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FURNACE OPERATIONS Furnace charging

Melting

Refining

De-slagging

Tapping

Furnace turn-around

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Furnace charging To select the grade of steel Steel scrap(60 to 80%) Sponge iron(DRI) and Pig iron molten metal. Limestone, fluorspar, sand, and quartzite Oxygen ,Coke & Iron ore The charge can include lime and carbon or these can be injected into the furnace during the heat

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Melting The melting period is the heart of EAF operations Melting is accomplished by supplying energy to the furnace interior. This energy can be electrical or chemical. Electrical energy is supplied via the graphite electrodes and is usually the largest contributor in melting operations Chemical heat generation due to oxidation of Si,Mn,P & C At the end of melting basic slag of FeO, CaO ,SiO2,MnO , Al2O3 etc formed.

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Refining Favorable condition for removing P,Si,Mn

&C ???

Condition for sulfur removal ??

What is the basicity ??

Why is basicity necessary ???

Thermodynamics of steel making ??

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Refining cond… Refining operations in the electric arc furnace have traditionally involved the removal of phosphorus, sulfur, aluminum, silicon, manganese and carbon from the steel. In recent times, dissolved gases, especially hydrogen and nitrogen, been recognized as a concern. Traditionally, refining operations were carried out following meltdown These refining reactions are all dependent on the availability of oxygen- Basic Oxidizing slag and Temperature as well.

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(1)Evolution of CO gas stirs the bath

and the phenomenon is known as carbon boil.(3) In modern EAF operations,

especially those operating with a "hot heel" of molten steel and slag retained from the prior heat. Unfortunately the conditions favorable for removing phosphorus are the opposite of those promoting the removal of sulfur Phosphorus removal is usually carried out as early as possible in the heat. Hot heel practice is very beneficial for phosphorus removal because oxygen can be lanced into the bath while its temperature is quite low

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In order maintain the basicity of the slag by periodic addition of lime-Flush slag practice Periodic addition of iron ore assists in continuing the oxidization reaction. At end of the oxidizing period the slag is drained out. the bath is killed by addition of Fe-Si,Fe-Mn and finally by addition of aluminum. Desulphurization favoured by a High temp,high basicity

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De-Slagging De-Slagging operations are carried out to remove impurities from the furnace as oxide phase. During melting and refining operations, some of the undesirable materials within the bath are oxidized and enter the slag phase. Double slag practice ???

Why is it necessary ???

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Tapping Once the desired steel composition and temperature are achieved in the furnace, the tap-hole is opened, the furnace is tilted, and the steel pours into a ladle for transfer to the next batch operation During the tapping process bulk alloy additions are made based on the bath analysis and the desired steel grade De-oxidizers may be added to the steel to lower the oxygen content prior to further processing Most carbon steel operations aim for minimal slag carry-over

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Furnace Turn-around Furnace turn-around is the period

following completion of tapping until the furnace is recharged for the next heat. During this period, the electrodes and roof are raised and the furnace lining is inspected for refractory damage. If necessary, repairs are made to the hearth, slag-line, tap-hole and spout. In the case of a bottom-tapping furnace, the tap hole is filled with sand. Repairs to the furnace are made using gunned refractories or mud slingers In most modern furnaces, the increased use of water-cooled panels has reduced the amount of patching or "fettling" required between heats

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Modern development in EAF Technology

New design of electrode

DC electric arc furnace

Ultrahigh power furnace

EBT

Use of HOT METAL as charge

Iron carbide as charge

Use of DRI as charge

Foamy slag practice

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Use ultra high power UHP enables faster melting of solid charge

there by decreasing the tap to tap time Increase in production of steel

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Foamy slag practice C+ O2 = CO

Thermal efficiency is improved because the foamy slag provides an improved medium for

energy transfer.

Advantage 1.Reduce power input 2.Melting time 3.Incresed yield4.Reduce electrode consumption5.Resue energy loss6.Reduce ref erosion

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New design of electrode

(1) Water cooled electrode – electrode run cooler and graphite losses reduced.

(2) Ar injection through hollow electrode

- quicker and more stable furnace arc with high level of heat release

-Production rate ↑ and electrode consumption↓

-Hydrogen & Nitrogen pick up by steel is reduced with the argon hallow electrode practice.

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DC electric arc furnace

(1) Improved operating economy due to significantly lower electrode consumption. (2) Only one electrode exposed (3) Electrode surface wear greatly reduced (4)Noise emission reduced

(5)Arc is more sable with DC

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USE OF HOT METAL AS CHARGE MATERIALS

Modification EAF done to use hot metal upto 80% of charge

Oxygen may introduced into furnace from submerged tuyeres ,atmospheric injector and door lances. As result of oxidation of impurities , required electrical energy are reduced

Sensible heat available in hot metal charge , less time on power ,shortening of heat time leads to reduction in electrode consumption .

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Use of iron carbide as charge materials

Iron carbide is introduced into molten steel by injecting it below the slag layer using lance

When Carbon introduced into bath via iron carbide addition is burnt with oxygen, large amount het released

1.Foamy slag is easier 2.It also contribute to an increase in

metallic yield 3.Exothermic reaction.

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Use of DRI as charge materials

(1) USA , Brazil & India do not have much obsolete scrap nor do they generate large amount scrap and the stock of which coming down

(2) Availability of tramp element in scrap

1. Steel maker prefer metallization between 92 % to 96 %

2. High carbon containing DRI gives CO evolution ,which contribute towards the formation of a foamy slag

3. In some EAF shop even up to 100 % DRI is used by adopting what is known as hot heel practice

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Eccentric bottom tapping In case BOF , most of the slag is retained in vessel and not allowed to flow into ladle during tapping by use of slag arresting device

In modern EAFs ,the bottom made eccentric to achieve the same result EBT is suitably covered and insulated

During tapping , when the furnace is tilted ,liquid steel primarily flows out with very little slag.

Some liquid steel is retained in furnace (hot heel )

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Conclusion 1.Initially EAF were developed only for solid

charge.2.Then EAF extended to liquid charge as

well.3.35 % of world steel production comes

from EAF4.Initially tool steel, alloy steel and

stainless steel were produced 5.Nowaday all type or grade of steel can

produce by EAF 6.100 % Solid charge material are possible

for charge 7.Different variety of

charge mix are possible

Need Electrical energy

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Thank you