Clean and intelligent production technology of electric arc furnace steelmaking

Electric arc furnace steelmaking is one of the main steelmaking methods at present, which has the characteristics of short process, low energy consumption and low carbon emissions. Compared with the “blast furnace-converter” long process steelmaking, the electric arc furnace short process steelmaking uses scrap steel as the main raw material, which has outstanding advantages such as short process, low investment, fast construction, energy saving and environmental protection. Starting from the clean and intelligent smelting technology of the electric arc furnace, it introduces and analyzes the key smelting technologies such as scrap crushing and sorting, electric arc furnace steelmaking composite blowing, gas-solid injection, quality analysis and monitoring, cost control, and foam slag detection and control. Innovation and development status. It is pointed out that accelerating the technological innovation of electric arc furnace steelmaking process, especially the improvement and breakthrough of clean smelting technology, building a clean production platform for electric arc furnace steelmaking process, and improving the quality and competitiveness of electric arc furnace steelmaking process products will be the future of electric arc furnace steelmaking. The development direction of steel

  • Key issues of clean production of electric arc furnace steelmaking process

1.1 Raw materials for smelting

In the process of electric arc furnace steelmaking, the main raw material is scrap steel, and auxiliary materials such as alloy and lime are applied [6]. However, at this stage scrap steel still has the following problems:

1)With the development and progress of society, the number of scraps such as automobiles and home appliances has increased rapidly, resulting in a more complex composition of scrap steel, including various non-ferrous metals, ferrous metals and non-metallic substances. In addition, coupled with the application of composite materials, the composition of the scrap steel is more complex, containing a lot of impurity elements such as Zn, Sn, Mo, and Cu. As a result, these hazardous substances continue to accumulate and increase in the process of electric arc furnace steelmaking.

2)In the process of electric arc furnace steelmaking, the added auxiliary materials will also cause the increase of harmful elements, which will affect the cleanliness of molten steel to a certain extent. Therefore, in the smelting process, different raw material standards must be selected based on actual conditions. For example, in the production of high-quality alloy bars, molten iron and scrap steel can be selected as raw materials; in the production of low-sulfur steel, low-sulfur lime can be used as auxiliary materials.

1.2 Dephosphorization operation

Phosphorus is a harmful element in most steel grades, and dephosphorization is one of the important tasks of electric arc furnace smelting [7]. In recent years, with the development of the national economy, the demand for low-phosphorus and ultra-low-phosphorus high-quality special steel has increased, and it is difficult for the existing electric arc furnace steelmaking process to achieve the smelting requirements of rapid and low-cost dephosphorization. The main reason is that the structure of the raw materials for electric arc furnace steelmaking is complex, and the phosphorus content of the molten steel fluctuates greatly; after the smelting of all scrap steel, the carbon content is low, the viscosity of the molten steel is high, and limited by the structure of the electric arc furnace, the molten pool flow rate is slow , Dephosphorization kinetic conditions are poor, and dephosphorization is difficult in the smelting process. Traditional electric arc furnace smelting low-phosphorus steel usually uses multiple slagging and slagging operations. The smelting cycle is long, the slag volume is large, the final slag (FeO) content is high, the molten steel is over-oxidized, and the smelting cost is difficult to control.

  • Control of oxygen and inclusions in steel

The stable control of the liquid steel oxygen content at the end of electric arc furnace smelting is the key to reducing the inclusions in the steel. Electric arc furnace steelmaking generally adopts enhanced oxygen supply operation to speed up the smelting rhythm and improve production efficiency, but the end point control of the electric arc furnace steelmaking is not precise, the molten steel is more severely peroxidized, and the carbon oxygen content is significantly higher than that of the converter [8]. This not only leads to excessive consumption of deoxidizer in the later refining process, but also significantly increases the amount of inclusions during the refining period. In order to reduce the liquid oxygen content of the final steel, the electric arc furnace steelmaking mainly controls the oxygen blowing amount before tapping, and at the same time injects inert gas to strengthen the stirring; when tapping, the eccentric bottom tapping is used to control the slag amount; iron carbon is added before tapping Magnesium balls reduce the oxygen content of liquid steel. In the LF refining process, the “aluminum+composite deoxidizer” deoxidation method is adopted to convert Al2O3 inclusions into larger-size and easy-to-float inclusions and then remove; double vacuum process operation, pre-vacuum light treatment before, and LF refining The vacuum treatment method deeply removes active oxygen and inclusions in the steel.

2.1 Control of N and H in steel

When the electric arc furnace uses high-power power supply to strengthen the melting of scrap steel, the high-temperature arc generated by the electrode discharge will ionize the N2 in the nearby air, resulting in a significant increase in the nitrogen absorption capacity of the molten steel; in the electric arc furnace smelting process, N2 is sometimes used as bottom blowing gas or powder The injected carrier gas is immersed into the molten pool, and the molten steel further absorbs nitrogen. At the same time, the raw materials for electric arc furnace smelting contain moisture and are exposed to air, which will cause high hydrogen content in molten steel. However, the carbon content of the molten pool after the electric arc furnace steelmaking is low, the oxygen supply strength is insufficient, and the number of CO bubbles generated in the molten pool during the later stage of smelting decarburization is small, so [N] and [H] cannot be effectively removed. The method to solve such problems is mainly to remove the water by preheating the scrap steel to reduce the hydrogen element into the furnace; adjust the charge structure, increase the carbon content of the molten pool by adding DRI, increasing the ratio of molten iron, etc. [11], in the later stage of the electric arc furnace Carry out high-strength decarburization and boiling operation to remove [N] and [H] in the molten steel, and then protect it during subsequent refining and pouring to control the content of [N] and [H] in the steel.

  • Clean smelting technology innovation for electric arc furnace steelmaking process

3.1 Scrap crushing and sorting technology

By crushing the scrap steel raw materials, the dry and wet sorting systems are used to screen the metals, non-metals, and non-ferrous metals in the scrap steel raw materials, and they are recycled separately, and the paint and plating on the surface are removed, which can be effective It reduces the content of harmful elements in the scrap steel and greatly improves the cleanliness of electric arc furnace steelmaking products. Scrap crushing and sorting began in the 1960s, and the most representative ones are Newell in the United States and Lindemann, Henschel and Baker in Germany. They took the lead in introducing shred into the furnace. It has significant effects in improving the quality of recycled steel and increasing economic benefits. The Shredder introduced by Germany in the late 1980s has surpassed the United States in some respects. There are two main types of scrap steel crushers: chip crushers and crushers [12]. The chip crusher is used for crushing steel chips, and the crusher is used for crushing large scrap steel; the crusher has hammer type, roll type and knife edge type. After crushing, the scrap steel can be easily sorted and recycled for metals, non-metals, non-ferrous metals, and ferrous metals by a thousand-type, wet or semi-wet sorting system. The paint and coating on the surface of the scrap steel can be removed or partially removed . The scrap steel after crushing and sorting can greatly improve the cleanliness of raw materials, and provide a clean and reliable raw material guarantee for electric arc furnace steelmaking.

3.2 Electric arc furnace steelmaking compound blowing technology

In the traditional electric arc furnace steelmaking production process, the stirring capacity of the molten pool is weak, which limits the effective transfer of material and energy to a certain extent. In order to improve this problem, most of them use ultra-high power power supply or high-intensity chemical energy input. Method, but failed to fundamentally solve the problems of insufficient stirring strength of the molten pool and slow material energy transfer speed. Modern electric arc furnace steelmaking widely uses oxygen blowing technology to speed up the smelting rhythm and reduce production costs. Intensified oxygen supply technologies such as furnace wall oxygen supply, furnace door oxygen supply, and cluster jet are successively developed. In order to solve the problems of insufficient stirring strength in the molten pool and slow material energy transfer speed, key technologies such as bottom blowing stirring, electric arc furnace steelmaking and composite blowing have been developed. With the goal of high efficiency, low consumption, energy saving, and high-quality production, the research and development of a new generation of electric arc furnace smelting technology, electric arc furnace steelmaking and composite blowing technology. The core of new technologies such as cluster oxygen supply [12] and synchronous long-life bottom blowing and stirring has achieved The operation integration of electric arc furnace steelmaking power supply, oxygen supply and bottom blowing unit meets the technical requirements of electric arc furnace steelmaking composite blowing under the condition of multiple charge.

The application of electric arc furnace steelmaking composite blowing technology realizes that the electric arc furnace can integrate power supply, oxygen supply, and low blowing operations during the production process, effectively solving the problem of weak stirring capacity of the molten pool. The principle is shown in Figure 1.

1) Electric arc furnace cluster modular energy supply technology, including the method of cluster oxygen supply on furnace wall and furnace roof. Furnace wall bundling oxygen supply mode. The oxygen blowing and powder injection unit are coaxially installed on the integrated water-cooling module on the furnace wall. It is equipped with fluxing and decarburization modes to realize gas-solid mixed injection and gas powder (carbon powder, dephosphorization) The dynamic switching of spraying to meet the requirements of foaming slag, dephosphorization and controlling the peroxidation of molten steel, enhancing the kinetic energy of the particles, enabling oxygen and powder to be efficiently transported to the slag-steel reaction interface, stabilizing the foaming slag, and reducing smelting power consumption. Improve the metal recovery rate. Aiming at the smelting of multiple charge structures with high iron-to-water ratio, the research team has developed a clustered oxygen injection technology on the top of the electric arc furnace to increase the intensity of oxygen supply in the electric arc furnace and strengthen the stirring of the molten pool. This technology can switch between power supply and oxygen supply, complete smelting tasks such as decarbonization and dephosphorization, improve oxygen supply efficiency, and achieve the effects of shortening smelting time and reducing smelting power consumption. To complete clean smelting tasks such as dephosphorization.

2)Embedded oxygen injection technology: Inject oxygen and fuel into the furnace through a multifunctional cluster oxygen lance on the furnace wall to strengthen the chemical energy input during the smelting process. It is currently the most common electric arc furnace steelmaking method. In recent years, based on the development of multifunctional cluster modular energy supply technology, in order to further improve the oxygen utilization efficiency and improve the metallurgical reaction kinetic conditions of the electric arc furnace bath, the electric arc furnace steelmaking buried oxygen injection technology has been developed. This technology moves the oxygen supply mode from above the molten pool to below the steel surface, and uses a dual-channel spray gun to directly input oxygen into the molten pool, which speeds up the metallurgical reaction rate and increases the oxygen utilization rate to 98%. Aiming at the problem that the buried spray gun is easy to burn and the oxygen stream erodes the refractory material of the furnace wall, the annular cyclone protection technology is adopted, and the central main jet “protection smelting-tapping” control mode is used to control the erosion rate and realize the spray gun life Synchronize with furnace age. This technology significantly improves the flow of molten steel and the speed of chemical reaction, effectively controls the over-oxidation of molten steel, and improves the efficiency of molten pool dephosphorization.

3.3 New technology of electric arc furnace steelmaking gas-solid injection

In the 1980s, the electric arc furnace steelmaking gas-solid injection system was also restricted to the furnace door and roof, and could not be injected through the furnace wall. The furnace door powder injection system was first applied in Eschweiler in 1980, and then developed rapidly, and has been applied in more than 40 steel companies around the world. The furnace top powder injection system was started by Krupp Steel in Germany and became popular in the late 1990s; until 1990 The furnace wall powder spraying system was only applied in Triest, Italy, and the number of applications surged after 2000, becoming the most mainstream powder spraying method. Based on the traditional furnace wall powder injection and buried oxygen injection technology, a new clean smelting process of gas-solid injection in the arc furnace bath has been developed [13]. The traditional powder spraying method above the molten pool is moved to the bottom of the molten pool, and the efficient and clean smelting of the electric arc furnace is realized by spraying carbon powder and lime powder inside the molten pool, showing obvious technical advantages in terms of production efficiency, technical indicators, and molten steel quality. In the early stage of smelting, air or CO2-O2 is used to spray carbon powder into the molten pool to accelerate the melting of scrap steel, and achieve rapid melting while increasing the carbon content of the molten pool; in the later stage of smelting, use O2 or O2-CO2 to spray lime powder into the molten pool to strengthen At the same time of dephosphorization, a large number of CO bubbles generated by the violent carbon-oxygen reaction can achieve deep denitrification and dehydrogenation, which significantly improves the cleanliness of the final molten steel.

3.4 Electric arc furnace steelmaking quality analysis monitoring and cost control system

With the development of electric arc furnace smelting technology, only relying on the operator’s traditional experience mode to control electric arc furnace production has been unable to adapt to the production rhythm of modern electric arc furnace steelmaking. Through the exchange of data information and process optimization control, the cost control and reasonable energy supply of the electric arc furnace steelmaking process can be optimized to reduce costs and improve efficiency. Analyze the composition data of the EAF→LF steelmaking process through the EAF-→LF steelmaking process end-point composition control model [14], dynamically adjust the composition control relational parameters, predict the real-time oxygen content and alloy element recovery rate, and guide the deoxidation process With the alloy feeding process, it can realize the precise control of the composition of the EAF-→LF steelmaking process. By recording the historical data of the electric arc furnace smelting process, establish a database; according to the principle of cost, minimum energy consumption or shortest smelting time, select the best historical data similar to the current smelting furnace charge structure and smelting environment, and then according to the optimal furnace The second smelting process is smelted to achieve the best smelting effect. Through the establishment of a cost monitoring system for electric arc furnaces and refining processes, the cost of a single electric arc furnace is predicted and calculated in real time, and the power supply and oxygen supply optimization guide curve and optimization of different furnace charge structures are provided. Prediction and real-time calculation of single furnace cost of refining furnace, and provide optimized alloy and slag combination. At present, the system has been popularized and applied in many electric arc furnaces at home and abroad.

  • Development of Intelligent Technology of Electric Arc Furnace Steelmaking

In recent years, electric arc furnace steelmaking has made great progress in the field of intelligent smelting, and a series of advanced detection technologies and control models have been developed, which greatly improved the automation level of the electric arc furnace steelmaking process and promoted the development of the steelmaking industry.

4.1 Foam slag detection and control technology

The foaming slag operation of the electric arc furnace steelmaking process can isolate the molten steel from the air, cover the electric arc, reduce the heat loss radiated to the furnace wall and furnace cover, and efficiently convert electric energy into heat energy to be transported to the molten pool, improve heating efficiency, and shorten smelting cycle. Foaming and maintaining foamed slag during the smelting process is the key to low-consumption and high-productivity electric arc furnace steelmaking. In recent years, related monitoring and control technologies for foam slag operations have been researched and applied, with good results. figure 2

The Simelt SonArc FSM foam slag monitoring system developed by Siemens is shown in Figure 19. The system can ensure the fully automatic process of foaming slag. The sound sensor installed on the furnace lays the foundation for accurately detecting and analyzing the height of foam slag. The zone detection of the foam slag height related to the electrode can provide guidance for the automatic carbon injection operation, thereby minimizing consumption indicators. In addition to reducing power consumption and carbon consumption, and reducing production costs, it can also shorten power-on time and increase productivity. The electric arc furnace door cleaning and foam slag control system PTI SwingDoor TM developed by the American PTI Company is shown in Figure 3. The system reduces the entry of outside air and improves the tightness of the steelmaking process. An integrated oxygen lance system is installed on the furnace door, which can replace the furnace door cleaning manipulator or the furnace door oxygen lance to automatically clean the furnace door area. The system controls the flow of slag by controlling the closing of the furnace door instead of the furnace body tilting device, and can also control the level and existence of foamed slag in the furnace, thereby ensuring the thickness of the slag layer in the furnace during the smelting process, reducing energy consumption and improving the efficiency of arc heat transfer . Figure three

At present, most domestic steel plants still use manual methods for foamed slag operations, and some steel plants have adopted electric arc furnace door systems for optimization, which has significantly improved energy efficiency. However, based on the complexity of the furnace conditions in the electric arc furnace, the reliability of the operation based on the sounding foam slag in the furnace remains to be investigated.

4.2 Multifunctional furnace door robot

Facing the harsh, dangerous, heavy manual work and precise process control requirements of the electric arc furnace steelmaking area [14], a series of new automatic temperature measurement and sampling technologies are gradually developed and promoted. The Simetal Liquid-Rob automatic temperature measurement and sampling robot designed by Siemens VAI in Germany is shown in Figure 4. The system has 6 degrees of freedom of movement, automatic replacement of samplers and temperature probes, detection of invalid temperature probes, and can be fully automated through the man-machine interface.

  • Conclusion and Outlook

In summary, the level of cleanliness of molten steel is related to the quality of steel products. The importance of intelligent technology in the field of electric arc furnace steelmaking will become increasingly prominent. Based on the improvement of the existing key technology of electric arc furnace steelmaking and clean smelting , To further build a clean production platform for the electric arc furnace steelmaking process, and to realize the continuous improvement of production efficiency, product quality, energy saving and environmental protection level and intelligence, will be one of the key development directions of electric arc furnace steelmaking in the future. Speed up the technological innovation of electric arc furnace steelmaking process, especially the improvement and breakthrough of clean and intelligent smelting technology, build a clean production platform for electric arc furnace steelmaking process, and improve the product quality and product competitiveness of electric arc furnace steelmaking process. Industrial restructuring and transformation and upgrading have played an important role in promoting.

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