- EAF is direct arc furnace.
- Steelmaking temp is maintained by an electric arc struck between the graphite electrodes &the metallic charge.
- The arc temperature is above 4000°C and is used to heat the bath by radiative heat transfer.
- Only process wherein either oxidizing or reducing condition can be maintained as desired.
- Different slag types can be carried out.
- High cost of electrical energy makes this process costly.
Parts Of EAF
- Furnace body consisting of the shell,
- the hearth, the walls, the spout, doors, etc.
- Gears for furnace body movement
- Arrangements for moving the roof
- Electrodes with their holders and supports
- Electrode lifting and lowering mechanism
- Electrical equipment
- Steel scrap is the principle raw material. It may constitute 60 to 80% of the charge.
- In some practices sponge iron and or pig iron is also used for chemical balance.
- In basic furnaces slag formers like limestone, fluorspar, sand, and quartzite are used to form a slag to refine the metal.
- Oxygen lancing is used for decarburization
- For the purpose of deoxidation Ferro-manganese, ferrosilicon or aluminum is used.
- Alloying elements are added for the production of alloy steels.
Basically EAF operations consists of three steps
- Melt down period
- Heavy and light scrap are preheated through the exit gas. Burnt lime and spar are added to help early slag formation.
- Iron ore may also be added if refining is required during melt- down period.
- The furnace is charged from the top (Hot metal is also charged as per the requirement).
- Some furnaces are equipped with continuous charging.
2. MELT DOWN PERIOD
- Electrodes are lowered and bored into the scrap.
- To protect the roof and walls from excessive heat and damage from the arcs, Lower voltages are selected.
- When the arc is shielded by scrap, voltage is increased to form molten metal pool to reduce the meltdown period.
- During meltdown period, silicon, manganese and carbon oxidizes.
- Oxidizing and limy slag is produces which promotes dephosphorization as well.
Melt down period depends on Arc conditions and Deep/shallow bath.
- Larger arc requires lower current and lower heat losses.
- Deep bath shortens the meltdown period.
- Refining continues even during melting.
- Removal of phosphorus must be complete before the rise in temperature and carbon boil.
- When removal of sulphur is not required single oxidizing slag practice is used.
- When both Phosphorous and Sulphur is not required double slag practice is used.
- In double slag practice, oxidizing slag is removed and reducing slag is formed after deoxidation.
- Reducing slag helps to avoid loss of alloying elements.
Once the bath chemistry and its temperature are attained, heat is deoxidized and finished for tapping.
Advantages of EAF Steelmaking
- The use of EAFs allows steel to be made from a 100% scrap metal feedstock.
- The large reduction in specific energy (energy per unit weight) required to produce the steel.
- EAFs can be rapidly started and stopped, allowing the steel mill to vary production according to demand.
- Hot metal from Blast furnace can be directly used.
- Flexibility to produce a variety of grades.
Limitations of EAF Steelmaking
- Running cost is high because of electrical energy consumptions and other attached equipments.
- When EAF repairs are necessary they are often quite expensive.
- Scrap availability as Scrap is principle charge material in EAF.
Modern Developments in EAF Steelmaking
- Ultra high power supply (UHP)
- Oxygen lancing
- Foamy slag practice
- Use of DRI/Hot briquetted iron
- Pre-heating of scrap and DRI
- Bath stirring by argon
- Eccentric bottom tapping
- Emission and noise control
- Process automation and control
———On demand topic by Rupesh Yadav———-
Credit- Rohit Jha