Electric arc furnace

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Electric arc furnace

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Electric arc furnace

  1. 1. PRESENTATION ON:ELECTRIC ARC FURNACEGulfam Hussain
  2. 2. ELECTRIC ARC FURNACEELECTRIC ARC FURNACE:An Electric Arc Furnace (EAF) is a furnacethat heats charged material by means of anelectric arc.Arc furnaces range in size from small unitsof approximately one ton capacity (used infoundries for producing cast iron products)up to about 400 ton units used for secondarysteelmaking
  3. 3. TEMPERATURE RANGE Industrial electric arc furnace temperaturescan be up to 1,800 °C, (3272 °F) whilelaboratory units can exceed 3,000 °C. (5432°F) Arc furnaces differ from induction furnaces inthat the charge material is directly exposedto an electric arc, and the current in thefurnace terminals passes through thecharged material.
  4. 4. HISTORY The first electric arc furnaces weredeveloped by Paul Héroult, of France, with acommercial plant established in the UnitedStates in 1907. The Sanderson brothers formed TheSanderson Brothers steel Co. in Syracuse,New York, installing the first electric arcfurnace in the U.S. This furnace is now on display at StationSquare, Pittsburgh, Pennsylvania.
  5. 5. TYPES OF EAF Two kinds of electric current may be used inElectric Arc Furnaces: direct (DC) EAF alternating (AC) EAF Three-phase AC Electric Arc Furnaces withgraphite electrodes are commonly used insteel making.
  6. 6. CONSTRUCTION The furnace consists of a spherical hearth(bottom), cylindrical shell and a swingingwater-cooled dome-shaped roof. The roof has three holes for consumablegraphite electrodes held by a clampingmechanism. The mechanism provides independent liftingand lowering of each electrode.
  7. 7.  The water-cooled electrode holders servealso as contacts for transmitting electriccurrent supplied by water-cooled cables(tubes). The electrode and the scrap form the starconnection of three-phase current, in whichthe scrap is common junction. The furnace is mounted on a tiltingmechanism for tapping the molten steelthrough a tap hole with a pour spout locatedon the back side of the shell.
  8. 8.  The charge door, through which the slagcomponents and alloying additives arecharged, is located on the front side of thefurnace shell. The charge door is also used for removingthe slag (de-slagging).
  9. 9. REFRACTORY LINING OF AN EAF Refractory linings of Electric Arc Furnaces aremade generally of resin-bonded magnesia-carbon bricks. When the bricks are heated the bondingmaterial is coked and turns into a carbonnetwork binding the refractory grains,preventingwetting by the slag and protecting the lining thefrom erosion and chemical attack of the moltenmetal and slag.
  10. 10. OPERATION/WORKING The scrap is charged commonly from thefurnace top. The roof with the electrodes is swung asidebefore the scrap charging. The scrap arranged in the charge basket istransferred to the furnace by a crane andthen dropped into the shell.
  11. 11.  Lower voltages are selected for this first partof the operation to protect the roof and wallsfrom excessive heat and damage from thearcs. Once the electrodes have reached the heavymelt at the base of the furnace and the arcsare shielded by the scrap, the voltage can be increased and theelectrodes raised slightly, lengthening thearcs and increasing power to the melt.
  12. 12. CHEMICAL AND PHYSICAL PROCESSES IN ANEAFMelting Melting process starts at low voltage (short arc)between the electrodes and the scrap. The arc during this period is unstable. In order to improve the arc stability small piecesof the scrap are placed in the upper layer of thecharge. The electrodes descend melting the charge andpenetrating into the scrap forming bores.
  13. 13.  The molten metal flows down to thefurnace bottom. When the electrodes reach the liquid baththe arc becomes stable and the voltagemay be increased (long arc). The electrodes are lifting together with themelt level. Most of scrap (85%) melt duringthis period.Temperature of the arc reaches 6300ºF(3500ºC).
  14. 14. OXIDIZING STAGE At this stage excessive carbon,phosphorous, silicon and manganeseoxidize.The process is similar to that in BasicOxygen Furnace. Basic oxidizing slag composed of lime (CaO)and ion ore (FeO) is used during theoxidizing period.Gaseous oxygen may be blown into the meltfor additional oxidizing.
  15. 15. REDUCING STAGE New slag composed mainly of lime (CaO),CaF2 (as slag fluidizer) is added at this stagefor formation of basic reducing conditions. The function of this slag is refining of the steel from sulfur andabsorption of oxides, formed as a result of deoxidation (”killing”). The excessive oxygen dissolved in the melt during oxidizing period isremoved by metallic deoxidizersMn, Si, Al:[Mn] + [O] = (MnO)[Si] + 2[O] = (SiO2)2[Al] + 3[O] = (Al2O3)Basic reducing slag is favorable for desulfurization in accordance to thereaction:[S] + (CaO) = (CaS) + [O]
  16. 16.  Iron oxide causes increase of Oxygen content in themolten steel according to the reaction:(square brackets [ ] - signify solution in steel, roundbrackets ( ) - in slag, curly brackets {} - in gas)(FeO) = [Fe] + [O]Oxygen dissolved in the melt oxidizes carbon,phosphorous, silicon and manganese:[C] + [O] = {CO}[Si] + {O2} = (SiO2)[Mn] + 1/2{O2} = (MnO)2[P] + 5/2{O2} = (P2O5)Carbon monoxide partially burns in the atmosphere:{CO} + {O2} = {CO2}
  17. 17. ADVANTAGES OF ELECTRIC ARC FURNACE The use of EAFs allows steel to be madefrom a 100% scrap metal feedstock. This greatly reduces the energy required tomake steel when compared with primarysteelmaking from ores . Another benefit is flexibility: while blastfurnaces cannot vary their production bymuch and can remain in operation for yearsat a time,
  18. 18.  EAFs can be rapidly started and stopped,allowing the steel mill to vary productionaccording to demand. During the peak of global financial meltdownin 2009, an estimated quantity of only 1million tonne was produced in USAemploying EAF technique. Although steelmaking arc furnaces generallyuse scrap steel as their primary feedstock,
  19. 19.  if hot metal from a blast furnace or direct-reduced iron is available economically, thesecan also be used as furnace feed. A typical steelmaking arc furnace is the sourceof steel for a mini-mill, which may make bars orstrip product. Mini-mills can be sited relativelynear to the markets for steel products, and thetransport requirements are less than for anintegrated mill, which would commonly be sitednear a harbour for access to shipping.
  20. 20. ENVIRONMENTAL ISSUES Although the modern electric arc furnace is a highly efficient recycler ofsteel scrap, operation of an arc furnace shop can have adverseenvironmental effects. Much of the capital cost of a new installation willbe devoted to systems intended to reduce these effects, which include: Enclosures to reduce high sound levels Dust collector for furnace off-gas Slag production Cooling water demand Heavy truck traffic for scrap, materials handling, and product Environmental effects of electricity generation Because of the very dynamic quality of the arc furnace load, powersystems may require technical measures to maintain the quality ofpower for other customers; flicker and harmonic distortion are commonside-effects of arc furnace operation on a power system.

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