Electric arc furnace raw material preparation and supply design
By:Yvonne Aug 31, 2020
Selection and determination of the supply method and facility design of the metal materials, bulk materials and electrodes required for electric furnace steelmaking are the main components of the design of the electric furnace steelmaking workshop.
Including scrap steel, pig iron, direct reduced iron and ferroalloys. Scrap steel is the main raw material for electric furnace steelmaking. Pig iron is generally used to increase the carbon content of the charge, and sometimes it is also used as a recarburizer. The content of pig iron usually does not exceed 30% of the charge. Direct reduced iron can be used to replace part (30% to 70%) of scrap steel. Because it is relatively pure, it can improve the quality of molten steel. Some iron alloys, such as ferromanganese, ferrosilicon, ferrochromium, nickel and rare earth alloys, are mainly used as alloy additives in electric furnace steelmaking to adjust the composition of molten steel. Some iron alloys, such as ferromanganese, ferrosilicon, aluminum and silicon-calcium alloys, are used as deoxidizers for molten steel.
1) Scrap steel. According to its source, it is divided into foreign steel scrap and return steel scrap, and according to its alloy element content, it is divided into carbon steel scrap and alloy steel scrap. Alloy scrap mainly comes from the returned scrap from the factory, and is the most economical raw material for smelting alloy steel. The surface of scrap steel used in electric furnaces should be clean and less rusty, and the silt, slag and refractory materials on the scrap steel should be removed as much as possible. Tubes and utensils closed at both ends, flammable, explosive, and drugs should be treated and removed separately. Waste weapons must be safely disposed of. It is necessary to strictly control the non-ferrous metals remaining in the scrap steel into the furnace. When smelting steel grades with limited content such as nickel, molybdenum, tungsten, chromium and copper, according to the impurities in the scrap steel, a part of direct reduced iron can be used. The volume density of scrap steel entering the furnace is required to be greater than 1.0t/m3. Please refer to the table for the size requirements of scrap steel entering the furnace of various capacities.
2) Pig iron
The chemical composition must meet the requirements of the standard. Steel-making pig iron is generally used when using pig iron with carbon. Low-phosphorus and low-sulfur pig iron is used to increase carbon during refining. Carbonized pig iron is added with scrap steel, and carbon-increased pig iron is added in front of the furnace.
3) Direct reduction of iron. Direct reduced iron for electric furnace requires TFe>90%, metallization rate>92%, C<2%, gangue<6% (where SiO2<2.5%, P<0.03%, S<0.01%, Cu+Ni +Cr+Mo+Sn<0.02%). There are two types of direct reduced iron produced from reduced iron plants: sponge iron and hot briquette. The particle size requirements are: sponge iron ≥3mm; hot briquette is generally 90×30×60mm3, and bulk density>1.75t/m3.
The factory has a dedicated ferroalloy warehouse, strictly classified storage, and accurate measurement facilities. The block size is required to be 20-60 mm. Large electric furnace workshops generally use belt conveyors or cranes for feeding, and ferroalloys pass through vibrating feeders, weighing hoppers and chutes. Add electric furnace or ladle. Small electric furnace workshops generally use bins or grids to store materials, and manually add electric furnaces or ladle.
Including slagging materials (lime, light burned dolomite, fluorite, silica and clay bricks, etc.), oxidizers (iron ore, etc.), recarburizing and deoxidizing powders (electrode powder, coke powder, ferrosilicon powder, aluminum powder and Calcium carbide, etc.).
Electrodes for electric furnaces include ordinary power electrodes and ultra-high power electrodes, and the ultra-high power electrodes should be able to allow current density greater than 25 A/cm2. The requirements for the electrode are: good electrical conductivity, high temperature resistance, high mechanical strength, good oxidation resistance, high temperature at which strong oxidation starts in the air, low ash and sulfur content, and correct geometry to make the electrode and The electrode holder is in close contact, and the physical and chemical properties must meet the standard requirements.
Electrodes for electric furnaces should be stored in a dry place to prevent the electrodes from being damaged by moisture and sliding. In order to increase the service life of electrodes and reduce electrode consumption, water-cooled composite electrodes and surface protective coatings can be used.