EAF Electric Arc Furnace (Electric Arc Furnace) Steelmaking

Basic structure:

EAF furnace mainly consists of furnace body, electrode system, electrical system, water cooling system, slag treatment system and other parts. The furnace body is the space for holding the charge and melting, including the furnace shell, furnace lining, etc.; the electrode system delivers electric current to the furnace through graphite electrodes to generate an electric arc; the electrical system provides electric energy for the arc and controls the operating parameters of the furnace; the water-cooling system is used to cool down the furnace body, the electrodes and other components to prevent the equipment from overheating; and the slag treatment system is responsible for treating slag generated during the melting process.

Working Principle:

The EAF furnace utilizes the phenomenon of electric arc discharge generated between the electrode and the charge to convert electrical energy into thermal energy, thus enabling the charge to rapidly heat up to the melting temperature. Specifically, when the electrode and the charge are close to a certain distance, under the action of high voltage, the gas between the electrode and the charge is ionized, forming a conductive channel and generating an electric arc. The temperature of the arc is extremely high, generally up to 3000 ℃ or more, can quickly melt the charge to achieve the melting of the metal.

Main Features:

High flexibility: the melting temperature, time and other parameters can be flexibly adjusted according to the production demand, which is suitable for melting different kinds and specifications of metals. At the same time, it can be quickly started and stopped, so that it is easy to adjust the production plan according to the market demand in a timely manner.

Environmental protection and energy saving: Compared with traditional melting equipment such as cupola, EAF furnace adopts electric energy as heat source, and does not produce a large amount of exhaust gas and slag during the combustion process, so it is less polluting to the environment. In addition, through rational design and operation, EAF furnace can realize efficient utilization of energy and reduce energy consumption.

Good product quality: Due to the uniform and controllable temperature inside the EAF, the melting process of the metal can be precisely controlled to reduce the mixing of impurities, thus improving the purity and quality of the metal. At the same time, the composition of the metal can also be precisely adjusted by adding alloying elements, etc. to meet the needs of different users.

Application areas:

EAF furnaces are mainly used in the metal melting process in the iron and steel, non-ferrous metal and other industries. In the steel industry, commonly used in the production of a variety of high-quality steel and special steel, such as stainless steel, alloy steel, etc.; in the non-ferrous metal industry, can be used for melting copper, aluminum, nickel and other metals and their alloys. With the continuous development of technology, the application fields of EAF furnace are still expanding, such as in the field of scrap metal recycling, EAF furnace can efficiently melt the scrap metal and realize the recycling of resources.

An Electric Arc Furnace (EAF) is a cylindrical refractory lined vessel equipped with graphite electrodes that utilizes the high temperatures generated by an electric arc to melt scrap, direct reduced iron or pig iron. The process is widely and increasingly used in modern steelmaking due to its efficiency, flexibility and relatively low environmental impact.

Charging Stage

The process starts with charging the furnace with scrap, alloys and fluxes. The composition and layering of the scrap is carefully planned to ensure efficient melting and the required chemical properties of the final steel product.

Melting Stage

After charging, the high current generates extremely high heat (up to 3,000°C in the arc zone). During the initial drilling, 15% of the scrap is melted. After a few minutes, the electrode penetrates the scrap deep enough to allow higher voltages without damaging the furnace structure.

Refining Stage

The refining stage is essential for adjusting the chemical composition of the steel and removing impurities.

1. Oxidation period: Oxygen is injected to form oxides which escape as gases or form part of the slag, thus oxidizing the impurities.

Fe + 1/2O₂ → FeO(slags)

Si + O₂ → SiO₂(slags)

Mn + 1/2O₂ → MnO(slags)

2 Cr + 3/2 O₂ → Cr₂O₃(slags)

4P + 5O₂ → P₂O₅(slags)

S + O₂ → SO₂(gase)

2Al + 3/2 O₂ → Al₂O₃(slags)

2.Decarburization: Reduction of the total carbon content of the steel.

C + O₂ → CO₂

C + 1/2O₂ → CO

3.Reduction phase:

After oxidation, a reduction environment is established in specific quantities (through the addition of reducing agents such as carbon and silicon) in order to recover metallic elements to improve the quality of the steel.

Slag Formation

Slag plays a vital role in trapping impurities and protecting the steel from atmospheric gases. It consists of a combination of oxidized impurities and added fluxes

2 Cr₂O₃ + 3 Si → 4 Cr + 3 SiO₂

SiO₂ + CaO → CaSiO₃

P₂O₅ + 3CaO → Ca₃(PO₄)₂

EAFs are not as effective as blast furnaces at removing impurities because they rely heavily on scrap, which can contain difficult-to-remove residual elements such as copper, nickel and tin. While the BF operates under optimized reducing conditions to remove impurities such as sulfur and phosphorus through slag chemistry, the oxidizing atmosphere and limited slag capacity of the EAF make it less efficient at removing impurities. In addition, the BF-BOF process offers integrated refining, whereas EAF is more focused on recycling and sustainability.

Out of steel

Once the desired chemical composition and temperature are reached, the steel is withdrawn from the furnace into a ladle for further processing or casting.

Furnace Bottom

(1) magnesium carbon bricks: high refractoriness, good thermal shock resistance and slag erosion resistance, can withstand high-temperature steel and slag scouring and erosion, but also has a certain degree of electrical conductivity, suitable for DC electric arc furnace furnace bottom, can improve the service life of the bottom.

(2) magnesium brick: the main component is magnesium oxide, has a high melting point and good resistance to alkaline slag erosion performance, can effectively resist the penetration and erosion of slag, to maintain the stability of the bottom of the furnace, but its resistance to thermal shock is relatively weak, generally used in the bottom of the furnace for thermal shock requirements are not high.

(3) graphite refractory: good electrical conductivity, thermal conductivity and thermal shock resistance, can withstand the high temperature of the bottom of the arc furnace and the current impact, commonly used in DC arc furnace bottom of the conductive layer, to ensure stable transmission of current.

Furnace Wall

(1) magnesium carbon brick: one of the refractory materials commonly used in the furnace wall, especially in the slag line area, magnesium carbon brick's high refractoriness, slag erosion resistance and thermal shock resistance make it able to withstand the strong erosion of the slag and the drastic changes in temperature, prolonging the service life of the furnace wall.

(2) magnesium-chromium bricks: with good high-temperature strength, slag erosion resistance and thermal shock resistance, alkaline slag and oxidizing atmosphere has a better resistance, suitable for high-temperature parts of the furnace wall and the slag line area, but due to the presence of chromium, in the use and disposal of waste need to pay attention to environmental protection issues.

(3) high alumina brick: alumina as the main component, with high refractoriness, mechanical strength and thermal shock resistance, can withstand a certain degree of slag erosion and mechanical shock, commonly used in the non-slag line parts of the furnace wall, can reduce costs.

Furnace Cover

(1) Chrome corundum prefabricated parts: with high refractoriness, good thermal shock resistance and erosion resistance, it can withstand the high temperature radiation of the electrode arc and the scouring of the furnace airflow, effectively protect the structure of the cover and improve the service life of the cover, which is commonly used in the cover of large electric arc furnace.

(2) High-aluminum prefabricated parts: based on high-aluminum materials, with high strength and refractoriness, can better resist the high temperature and dust erosion in the furnace, applicable to small and medium-sized electric arc furnace cover, the cost is relatively low.

(3) Aluminum-carbon bricks: with a certain degree of refractoriness and resistance to thermal shock, and at the same time, the price is relatively low, was widely used in the electric furnace cover, but with the improvement of the requirements for the life of the furnace cover, it is gradually replaced by other materials with better performance.

Steel Outlet

(1) Magnesia-carbon steel outlet bricks: with high refractoriness, slag erosion resistance and good thermal shock resistance, they can withstand the scouring of steel and slag in the process of steel discharge to ensure the stability of the shape and size of the steel outlet and prolong the service life of the steel outlet.

(2) Corundum outlet brick: corundum as the main raw material, with high hardness and wear resistance, good resistance to the erosion of liquid steel and slag, can make the steel flow more smoothly, reduce the blockage of the outlet and the phenomenon of tuberculosis.

Electrode Holes

(1) Mullite refractory material: with good thermal stability, thermal shock resistance and low coefficient of thermal expansion, it can maintain stability under high-temperature heat radiation and frequent lifting and lowering movements of the electrode, and effectively prevent the leakage of hot gas and dust in the furnace.

(2) Graphite electrode hole material: with good electrical conductivity, thermal conductivity and self-lubrication, it can be closely matched with the electrode to reduce the friction between the electrode and the hole wall, and at the same time, it can also withstand the ablation of high-temperature arc to extend the service life of the electrode hole.

To select the refractory material suitable for EAF furnace (electric arc furnace), it is necessary to comprehensively consider the use of parts, working conditions, material performance and other factors, the following are the specific points:

1. Using parts: The working conditions of different parts of EAF furnace are very different, which need to be matched with corresponding refractory materials. Like the bottom of the furnace to withstand high temperature liquid steel static pressure, slag erosion and thermal stress, you can choose magnesium carbon bricks, magnesium bricks, etc.; furnace wall slag line part of the slag erosion and thermal shock is serious, magnesium carbon bricks, magnesium chromium bricks is a better choice; furnace cover facing the high temperature of the electrode arc radiation, suitable for chrome corundum pre-fabricated parts, etc.; out of the mouth of the steel need to be able to resist the liquid steel and slag scouring of magnesium carbon or corundum out of the mouth of the steel bricks.

2. Working conditions: the refractories should be selected according to the specific working environment of EAF furnace. If the smelting temperature is high, you need high refractoriness materials, such as refractories containing alumina, magnesium oxide and other high melting point components; if the furnace is an oxidizing atmosphere, magnesium-chromium bricks and other antioxidant materials are more suitable; for the frequent opening and stopping of the electric furnace, you need to choose the refractories with good thermal shock resistance, such as magnesium-carbon bricks, aluminum-carbon bricks and so on.

3. Refractory performance: the key performance indicators of the material determines its applicability. High refractoriness is the basis to ensure that at high temperatures do not soften, do not melt; good thermal shock resistance can prevent the material in the rapid changes in temperature cracking, spalling; strong resistance to slag erosion can resist slag chemical erosion and penetration, prolonging the service life; sufficient high-temperature strength allows the material to withstand the load at high temperatures without deformation.

4. Material compatibility: refractory materials should be compatible with the slag, steel and other furnace lining materials in the EAF furnace. For example, alkaline refractory material is suitable for alkaline slag environment, acid refractory material is suitable for acid slag environment, otherwise chemical reaction will occur, accelerate the refractory material erosion. At the same time, different parts of the refractory material should also have good compatibility, to avoid the thermal expansion coefficient and other differences are too large, resulting in the combination of cracks and other problems.

5. Cost factor: under the premise of meeting the use requirements, cost is an important consideration. To consider the procurement cost of refractory materials, transportation costs, construction costs and service life. Some high-performance materials, although high price, but long service life, the comprehensive cost may be more cost-effective. For example, the use of high-quality magnesium carbon bricks in the key parts of the large EAF furnace, although the procurement cost is high, but can reduce the number of maintenance stoppages, improve production efficiency, and in the long run the economic benefits are better.

(1) Furnace lining damage: If the furnace lining appears to be partially dislodged, pierced holes and other serious damage, it is necessary to stop the furnace in time for repair.

Repair method: first of all, the damaged part of the furnace lining completely removed, and then in accordance with the requirements of the furnace lining masonry process, re-lining the new furnace. In the process of masonry, we should strictly control the quality of refractory materials and construction quality to ensure that the quality of masonry lining meets the requirements.

(2) Electrode failure: If the electrode breaks, cracks and other failures, immediately stop using the electrode and replace it with a new one. At the same time, analyze the causes of electrode failure, such as electrode quality problems, improper operation, etc., and take appropriate measures to solve the problem to prevent similar failures from occurring again.

(3) Electrical failure: When the electrical system fails, such as short circuit, overload, leakage, etc., the power supply should be cut off immediately and overhauled by professional electrical maintenance personnel. Maintenance personnel need to use professional testing tools, such as multimeter, insulation resistance tester, etc., to find the failure point, determine the cause of the failure, and repair or replace the damaged electrical equipment.

(4) cooling system failure: if the cooling system leakage, high water temperature or poor water flow and other faults, the furnace should be stopped in time to check. For water leakage fault, to find the leakage point, repair or replace the damaged water pipes, valves and other components. For the problem of high water temperature or poor water flow, clean up the scale and impurities in the cooling water pipeline, check the operation of the water pump to ensure the normal operation of the cooling system.

Zinfon Refractory Technology Co.,Ltd

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We are offering various magnesia and alumina refractories including both shaped and unshaped products, raw materials and related chemical products.

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