Structural Components
Shell and Roof
The furnace shell is usually welded from steel plates and has certain strength and stiffness. Construction is usually heavy duty steel. The roof is removable and is used to charge raw materials into the furnace. Additionally, electrode ports, through which the electrodes penetrate into the furnace are found in the roof.
Furnace lining
Refractory Material Furnace lining contains refractory materials which are high heat resistant. It protects the shell of the furnace, preventing it from being priced by molten metal. In addition to this, refractory lining assists in insulating the furnace. Eventually the lining will need to be replaced in order for it to perform at its best.
Charging System
The charging system feeds raw materials like scrap steel straight into the furnace. In this system, cranes and buckets called as “charging baskets” are generally used to load the scrap into furnace quickly and safely. More recent charging systems may be conveyor belts, or other automated system that enable continuous charging.
Electrical Arc Furnace Transformer
The electrical arc furnace transformer converts and transports the required power to the electrodes. It also transforms the high voltage electricity from the power grid into lower voltage suitable for electric arc. Current regulation provided by the transformer is important for allowing stable arc conditions and controlling melting.
Cooling System
Because the temperatures produced from an electric arc furnace are exceptionally high, a cooling system is required to prevent melting. Generally, the cooling takes place through water cooled panels. These absorb excessive heat and maintain the temperatures of the furnace at safer levels.
Electric Arc Furnace Dust System
While operating a side product of electric arc furnace dust is produced. This dust includes harmful materials such as metal oxides and other materials. Some of this dust is captured by a dust collection system, where the harmful components are separated and destroyed or recycled valuable metals.
Operating Principle
Charging:
The furnace’s roof is opened, and large buckets of scrap steel are loaded into the furnace chamber.
Arc formation:
The roof and electrodes are closed, and the electrodes are lowered to make contact with the scrap.
Melting:
A high-power electric arc is generated, producing temperatures of up to 20,000°C to melt the metal.
Refining:
Oxygen and other materials like lime are added to the molten metal to remove impurities and form a slag, which separates from the molten iron.
Tapping:
The molten metal is then poured out of a tapping spout for further processing into steel of various qualities.
Features and Benefits
Recycling: Electrical arc furnaces are crucial for recycling scrap steel and other metals, making the steelmaking process more resource-efficient.
Sustainability: Electrical arc furnaces have a lower carbon footprint than blast furnaces, especially when using renewable electricity, and can operate with almost zero direct emissions.
Flexibility: Electrical arc furnaces offer flexibility in steelmaking, allowing for the production of high-quality steel from various recycled feedstocks.
Efficiency: The process allows for increased production time by reducing dead times associated with charging and other stages.
Applications of Electric Arc Furnace
Steelmaking
Electrical arc furnace is mainly used for steel making. The furnace has a broad carbon to specialty alloy steel capability. This fine control over the composition is why Electrical arc furnaces can produce both bulk steel and specialty steel products. In addition, electric arc furnaces can smelt iron ore, and the iron ore is gradually melted in the furnace, and then the metal is separated.
Alloy Production
Electric arc furnaces also work to create alloys through different metals mixed together. An Electrical arc furnace can be use for producing alloys like stainless steel (chromium and nickel). This is why materials for different industries like construction, automotive and aerospace can easily be manufactured.
Capacity and Types of Electric Arc Furnaces
Direct Electric Arc Furnace (DC EAF)
The electric arc is produced using direct current (DC) in a DC Electric Arc Furnace (DC EAF). A DC EAF requires fewer electrodes than an AC EAF, in turn saving costs. Typically, there is just one graphite electrode in a DC furnace which tends to stay in place longer and provides arc stability. In addition, DC furnaces also tend to be quieter and have the potential for greater energy efficiency. But while they are generally more complicated structurally, the upfront cost to install may also be greater.
Indirect Electric Arc Furnace
An AC Electric Arc Furnace (AC EAF) utilizes Alternating Current (AC) flowing through the graphite electrodes to produce the electric arc used for melting. AC EAFs are the most popular furnace type used for steel melting and offering flexibility, they can serve multiple applications. These furnaces are rather simple designs and can melt nearly any type of scrap metal. AC furnaces are a very versatile type of electric furnace which can be turned on and off quickly, ideal for small- to medium-scale steel making.
Submerged Electric Arc Furnace
Submerged arc furnace (SAF) is a specific kind of furnace that is primarily used for producing ferroalloys or other metals. Electrodes are partially immersed in the charge materials to create a reducing atmosphere appropriate for some metallurgical reactions in e.g. SAF. SAFs are not used for melting steel, as is the case with standard EAFs, but rather to process ores such as manganese or chromium in order produce alloy components. Specialized submerged electric arc furnaces can be designed to attain high melting temperatures which facilitates finding suitable profiles for alloys with desired properties.
Refractory bricks of Electric Arc Furnace
Furnace roof
High-alumina bricks with an alumina content of 75%-85% are commonly used. Basic bricks such as fired or unfired magnesia bricks and magnesia-chrome bricks may also be used, or cast refractory precast components may be used.
Furnace walls
Magnesia bricks, unfired magnesia basic bricks, and asphalt-bonded magnesia and dolomite ramming materials are commonly used for furnace walls. Magnesia-chrome bricks and high-quality magnesia bricks are used for ultra-high power electric arc furnaces or those used for smelting special steels. Magnesia-carbon bricks are widely used in the slag line and hotspots.
Furnace bottom
The furnace bottom and bank form the melt pool. The working layer is constructed with tar-asphalt-bonded magnesia bricks, and the permanent lining is mostly constructed with magnesia bricks. At the slag line above the bank, fused-cast magnesia-chrome bricks or re-bonded magnesia-chrome bricks are commonly used, with magnesia-carbon bricks also being an option.
Taphole
The taphole bricks are asphalt impregnated fired magnesia bricks, the tube bricks are magnesia carbon bricks with a resin-bound carbon content of 15%, and the end bricks are magnesia carbon bricks with a resin-bound carbon content of 10%-15%.
