Electric Arc Furnace STEEL MAKING

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EAF - History , process and thermodynamics of EAF steel making .

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AMMASI A CSIR –National Metallurgical Laboratory Jamshedpur ,India [email protected] & [email protected]
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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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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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(1) Direct electric arc furnace

(2) Indirect electric arc furnace

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DC EAF

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Furnace charging

Melting
Refining De-slagging Tapping Furnace turnaround
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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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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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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 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,FeMn and finally by addition of aluminum. Desulphurization favoured by a High temp,high basicity

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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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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 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 watercooled panels has reduced the amount of patching or "fettling" required between heats
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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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UHP enables faster melting of solid charge there by decreasing the tap to tap time Increase in production of steel

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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 yield 4.Reduce electrode consumption 5.Resue energy loss 6.Reduce ref erosion
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(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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(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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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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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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(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 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
1.

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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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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 EAF 4.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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