(This article is reproduced from the World Metal Herald)
"Thirteenth Five-Year Plan" The “Plan for Comprehensive Upgrade and Upgrade (2016-2020)” points out: accelerate the development of circular economy, and follow the concept of green and recyclable, and pay attention to the development of short-process electric furnace steelmaking with scrap steel as raw material. It is foreseeable that with the conversion of China's “long-flow” steelmaking to “short-flow” steelmaking and the need for energy conservation and environmental protection, electric arc furnace steelmaking will usher in new development opportunities, coupled with China ’s waste steel resources and power energy. Gradually, the electro-metallurgical process, especially the short-flow arc furnace process, will receive more and more attention.
In recent years, EAF steelmaking has made great progress in terms of efficient smelting, energy conservation and environmental protection, and intelligent control, and the technological level of EAF steelmaking has significantly improved. At the same time, various new arc furnaces have been developed and applied, which has greatly promoted steelmaking. Advances in industrial technology.
1 Progress of EAF steelmaking technology
In the past 30 years, EAF steelmaking technology has developed rapidly. In terms of technology, technologies such as scrap steel preheating, enhanced oxygen blowing fluxing, foamed slag, secondary combustion, bottom blowing stirring, and ladle refining are adopted; in terms of equipment, increasing the input power level of the transformer and transforming the short network to achieve reasonable electrical operation and electrodes New technologies such as Consteel EAF, Quantum EAF, ECOARC EAF, CISDI-Green EAF, and SHARC EAF have also appeared in the development of new electric arc furnaces. Throughout the development process of electric arc furnace steelmaking technology, its technological progress is mainly carried out in four aspects: high efficiency, cleanliness, greenness and intelligence of electric arc furnace steelmaking.
1.1.1 Rationalization of power supply technology A reasonable electrical operation system is the most basic guarantee for electric arc furnace steelmaking. The establishment of a reasonable electrical operation system is based on the selection of the best operating point. The operating point mainly refers to the electric operation of the electric arc furnace. Working current and voltage, other electrical parameters such as apparent power, active power, reactive power, arc power and power factor can be derived from this. In order to adapt to a variety of complex charge structures and reasonably utilize transformer power supply capabilities under the smelting process conditions to achieve steelmaking efficiency and power saving purposes, the University of Science and Technology Beijing has developed an exponential nonlinear working reactance model for ultra-high power arc furnace transformers. Establish the electric operation characteristics database of electric arc furnace transformers under different capacities and multi-stage working voltages, and truly reflect the actual operating conditions of electric arc furnace transformers; by constructing mathematical models and characteristic curves of power supply operations that match the operation of electric arc furnace transformers, ensure the efficient output of electric energy from electric arc furnace transformers And stable operation with low power consumption.
1.1.2 Enhanced oxygen supply technology
How to efficiently input chemical energy (oxygen, fuel, etc.) into the electric arc furnace according to the production process directly affects the quality, energy consumption and production operation rate of the steel, which is the key to electric arc furnace steelmaking. As a result, various forms and functions of arc furnace chemical energy enhanced input technology have been developed.
1) Furnace door oxygen supply technology.
Electric arc furnace door oxygen blowing equipment is divided into two categories according to water cooling method, one is water-cooled furnace door carbon oxygen gun, and the other is consumable furnace door carbon oxygen gun. Water-cooled furnace door oxycarbon gun has the advantages of high oxygen utilization rate, good foam slag effect, stable decarburization and dephosphorization effect, and high degree of automation. However, it cannot be in contact with molten steel during operation, which has certain limitations. Consumption type furnace door carbon oxygen gun can start cutting scrap steel and contact with molten steel earlier in the furnace. There is a large space in the furnace, but it is troublesome to connect the oxygen blowing tube at intervals during the operation.
2) Furnace wall oxygen supply technology.
The oxygen supply to the furnace wall of the electric arc furnace is to eliminate the cold zone in the furnace and ensure the melting of the furnace material. The furnace wall is used to modularize the injection of pure oxygen to increase the specific power input of the electric arc furnace and improve production efficiency. The furnace wall oxygen lance mainly has the functions of decarburization, fluxing, secondary combustion and foaming slag. Compared with the traditional installation method, the furnace wall oxygen lance installation method is closer to the molten pool, and the distance between the jet and the molten pool is shortened by 40% -50% compared with the traditional installation method, which can greatly improve the decarbonization of the molten pool. Speed and oxygen utilization efficiency; Combustion in the molten pool can be combined with combustion above the molten pool to improve the thermal efficiency of the smelting process; Multi-point injection can be realized in the furnace to accurately control the amount of oxygen and carbon powder, foam Slag effect is good.
3) EBT oxygen supply technology.
Modern electric arc furnaces use eccentric furnace bottom tapping (EBT) technology, making the EBT zone one of the cold zones in the electric arc furnace, which causes problems such as slower melting of scrap steel in the zone, and large differences between the composition of the molten pool and the composition of the central zone. An EBT oxygen lance is installed on the side of the eccentric furnace for oxygen blowing and melting, which can promote the melting of scrap in the EBT area, completely solving the problems that the scrap in the EBT area has not melted during tapping and the tap opening cannot be opened. After the molten pool, increase the temperature of the molten pool in the EBT zone to uniform the composition of the molten pool. When the steel is tapped, the temperature and composition of the EBT area differ from the temperature and composition of the furnace door area by only 0.5% -1.0%.
4) Cluster oxygen supply technology.
Aiming at the problems of rapid attenuation of supersonic gas jets and low oxygen utilization rate, cluster jet technology has been developed and applied. A ring-shaped protective airflow (produced by combustion of gas and oxygen) is set around the main oxygen jet, making the main oxygen jet supersonic core. The segment length is extended to form a jet like a laser beam. The kinetic energy loss of the oxygen stream is reduced, and it has extremely strong penetrating power and stirring power. It realizes high-speed oxygen and decarburization to the molten pool, improves the heat and composition uniformity in the furnace, and promotes the slag reaction and uniform molten steel composition. And temperature, increase the utilization rate of oxygen, improve the metal yield, etc. have very obvious effects. The USTB cluster oxygen supply technology developed by the University of Science and Technology Beijing is more suitable for the characteristics of domestic EAF steelmaking furnace materials and has reached the international leading level. It has been applied to more than 100 electric arc furnaces at home and abroad.
1.1.3 Foam Slag Technology
In the arc furnace smelting process, while blowing oxygen, carbon powder or silicon carbide powder is sprayed into the molten pool to form a strong carbon-oxygen reaction, and a large amount of CO gas foam is formed in the slag layer. Generally, the foam makes the thickness of the slag reach 2.5-3.0 times the length of the arc, which can completely shield the arc, reduce the radiation of the arc to the furnace roof and the furnace wall, extend the life of the furnace body, and make the arc pass to the molten pool. The thermal efficiency is improved from 30% to 60%, the smelting cycle is shortened by 10% -14%, the smelting power consumption is reduced by about 22%, the electrode consumption is reduced by about 2kg / t, and the arc furnace age can be increased, and the lining material consumption can be reduced. As a result, the production cost is reduced, at the same time productivity is increased, noise is reduced, and noise pollution is controlled.
1.1.4 Oxygen Burner Technology
Oxygen burner technology has been commonly used in electric arc furnace steelmaking to ensure the simultaneous melting of the charge and to more effectively play the role of the electrode. At the same time, the oxygen burner can also strengthen the secondary combustion of carbon monoxide, effectively shorten the smelting time, and improve the production efficiency of the electric arc furnace. At present, depending on the fuel used, oxygen burners are mainly in the form of oil-oxygen burners, coal-oxygen burners, and gas burners. The fuels used are diesel, heavy oil, pulverized coal, and natural gas.
1.1.5 Secondary combustion technology
EAF secondary combustion technology
There are two types: foam slag operation secondary combustion technology and free space secondary combustion technology. Since the free space secondary combustion (furnace gas combustion) technology makes oxygen react with the CO gas above the molten pool, the heat generated by the secondary combustion is transferred to the slag layer through radiation and convection, and then transferred from the slag layer to the molten steel. The heat transfer efficiency is about 30% -50%; and with the foamed slag secondary combustion technology, the heat generated by the secondary combustion is directly transferred from the slag to the molten steel, and its heat transfer efficiency is about the same as that of the furnace gas secondary combustion technology. 2-3 times.
1.2.1 Scrap crushing and sorting technology The recycling of scrap steel plays an important role in energy saving, emission reduction, transformation and upgrading of the steel industry. With the increasing number of scrapped cars, machinery, electrical appliances, and other appliances, the components of waste metal recycled by society are more mixed, including ferrous metals, non-ferrous metals, and non-metals. Efficient crushing and sorting of scrap steel is the premise and key to ensure the quality of EAF steelmaking raw materials, and it is essential to achieve clean smelting of EAF steelmaking. The crushed and sorted scrap steel can greatly improve the cleanliness of raw materials and provide a clean and reliable raw material guarantee for electric arc furnace steelmaking.
1.2.2 Safe long-life bottom-blowing stirring technology for EAF steelmaking
The metallurgical reaction kinetics conditions of the EAF steelmaking molten pool are poor, the molten steel composition and temperature are not uniform, the end point oxygen content and the iron oxide content in the slag are high, which ultimately affects the smelting index and the molten steel quality. The technology of safe and long-life bottom-blowing of electric arc furnace steelmaking developed by the University of Science and Technology of Beijing has strengthened the stirring of the electric arc furnace molten pool, the oxygen consumption per ton of steel, the consumption of steel materials, the carbon and oxygen products at the smelting end point, and the iron oxide content in the final slag were significantly reduced, and the dephosphorization efficiency was further Improved, the quality of molten steel at the end of smelting improved significantly. At present, the technology has been applied to more than 20 electric arc furnaces at home and abroad, and the life of the bottom-blowing element exceeds 800 furnace times, and the life of the bottom-blowing of the arc furnace is synchronized with the furnace age.
1.2.3 EAF steelmaking composite blowing technology
Aiming at high-efficiency, low-consumption, energy-saving, and high-quality production, Beijing University of Science and Technology proposed and developed a new generation of electric arc furnace smelting technology-"Arc Furnace Steelmaking Composite Blowing Technology", with cluster oxygen supply and simultaneous long-life bottom-blowing stirring. Technology as the core, the operation integration of electric arc furnace steelmaking power supply, oxygen supply and bottom blowing and other units are realized, which meets the technical requirements of electric arc furnace steelmaking composite blowing under multiple charge conditions. At present, the project's overall and unit technology has been applied in more than 100 domestic appliance furnace factories and exported to Italy, Russia, South Korea, Iran and other countries. After the application of 50-150t electric arc furnaces in Tianjin Steel Pipe, Laiwu Steel, Hengyang Steel Pipe and other enterprises, the smelting power consumption was reduced by 13 kWh / t, the steel material consumption was reduced by 15.5 kg / t, and various technical and economic indicators were significantly improved.
1.2.4 Low-cost dephosphorization technology
Traditional electric arc furnace smelting low-phosphorus steel
Slag making and flowing slag operations are often used. The smelting cycle is long, the slag amount is large, the final slag (FeO) content is high, the molten steel is severely oxidized, and the smelting cost is difficult to control.
The University of Science and Technology Beijing has developed an arc furnace steelmaking buried oxygen supply injection technology, which moves the oxygen supply method from above the molten pool to below the molten steel level, and directly inputs oxygen into the molten pool, which accelerates the metallurgical reaction speed. This technology significantly improves the molten steel flow and chemical reaction speed, effectively controls the molten steel peroxidation, and improves the dephosphorization efficiency of the molten pool. On this basis, the oxygen-lime powder mixed injection dephosphorization process in the arc furnace steelmaking molten pool was developed, and the lime powder was directly sprayed into the steelmaking molten pool using oxygen, thereby realizing low-cost and rapid deep dephosphorization of the arc furnace steelmaking. The consumption of lime per ton of steel is improved significantly, and the dephosphorization effect is remarkable.
1.2.5 High-efficiency denitrification technology
The University of Science and Technology Beijing has developed an arc furnace CO2-Ar dynamic bottom-blowing denitrification technology based on the CO2 physical and chemical characteristics and the CO2 reaction mechanism in the high temperature metallurgical bath based on the Ar-blow bottom Ar stirring technology. The furnace molten pool is denitrified, and the liquid steel nitrogen content at the end of smelting of all scrap steel is stably controlled below 45 × 10-6, and the liquid steel quality is significantly improved.
1.3 Go Green
1.3.1 Scrap preheating technology
Regarding the preheating of EAF steelmaking scrap, pre-heated EAFs with double shells, vertical and Consteel have been developed and applied. Due to the low residual heat efficiency, large equipment maintenance and the discharge of pollutants such as dioxins, the double-shell electric arc furnace has already withdrawn from the market; due to the impact of blanking, the vertical preheating arc furnace refers to the life of the water-cooled structure, large maintenance, Disadvantages such as low equipment reliability are gradually withdrawing from the market. Consteel electric arc furnace is widely used due to its good production environment, small power grid impact, reliable and controllable feeding, and high efficiency of flue gas waste heat utilization. At present, the newly developed mainstream electric arc furnaces at home and abroad are mainly developed based on the original scrap steel preheating electric arc furnaces.
1.3.2 Waste heat recovery technology
At present, EAF waste heat recovery technologies mainly include Tenova iRecovery, MCC Sadie's total waste heat recovery and other technologies. Tenova iRecovery flows pressurized water (150 ° C / 5bar to 270 ° C / 55bar) through the exhaust pipe. The water near the boiling point absorbs the residual heat in the exhaust gas by evaporation, which can recover 35% -70% of the EAF steelmaking flue gas. Heat; Full waste heat recovery technology developed by companies such as China Metallurgical, adopting high temperature resistant long-life vaporized cooling flues, high-efficiency flue gas combustion sedimentation chambers, and tube-type waste heat boilers, etc., to realize the process from the fourth hole of the arc furnace to the waste heat boiler. The stable recovery of total waste heat and efficient dust removal have solved the problem of low utilization of traditional waste heat, and the recovery and utilization of waste heat from flue gas in electric arc furnaces has been increased by more than 10%.
1.3.3 Dioxin Management Technology
The ways to reduce dioxins in electric arc furnace steelmaking are mainly reflected in the three sources of dioxin formation, the formation process and the purification of exhaust gas. Related research focuses on source inhibition and synthetic inhibition. In terms of source suppression: through online inspection and manual selection, strict sorting of scrap steel is used to minimize or even prevent chlorine-containing source material scrap from entering the furnace. In terms of synthesis inhibition: the use of furnace temperature control, rapid cooling, and catalyst / inhibitor addition to inhibit the generation of dioxins in electric arc furnace flue gas. How to realize the dioxin treatment in the EAF steelmaking process with high efficiency and low cost will be the focus of the next research.
1.4.1 Intelligent electrode adjustment technology At present, there are many intelligent electrode adjustment technologies for electric arc furnaces. Among them, the new generation of intelligent electrode adjustment system developed by MCC Sadi, DMI-AC, includes high-speed digital signal distribution that resists strong electromagnetic interference. Acquisition-centralized processing-network digital transmission system and multi-strategy, multi-constraint optimization and flexible intelligent control system. The two core technologies are adopted by Japan's Steel Plantech and Vietnam VKS company's 90t electric arc furnace project. After adopting this technology, the electrode adjustment electrical response time is reduced. By 60ms, the current fluctuation rates during the well penetration and smelting periods were <33% and <14%, respectively, which is better than the international advanced level.
1.4.2 Smelting online detection technology In recent years, with the development of science and technology, researchers at home and abroad have developed a series of detection technologies for electric arc furnace smelting process. The USTB non-contact molten steel temperature measurement system independently developed by China uses a non-contact temperature measurement device installed on the furnace wall to obtain a characteristic signal of molten steel temperature by using a plurality of temperature measurement gas injections, and establishes a molten steel temperature signal processing model. It can realize the temperature measurement and forecast of the molten pool.
The self-developed USTB furnace gas analysis system can accurately measure the temperature, flow rate and various components of the furnace gas, and use the collected information and its own control model to analyze, judge and control the smelting process.
1.4.3 Multi-function furnace door robot
Faced with the harsh, dangerous, heavy manual operations and precise smelting process control requirements in the EAF steelmaking area, a series of new automated temperature measurement and sampling technologies have been gradually developed and applied. Relevant domestic units are conducting research and development and promotion of electric arc furnace multi-function door robots. At present, most domestic electric arc furnace steelmaking enterprises still adopt the traditional manual sampling temperature measurement method. With the localization of advanced automatic temperature measurement sampling devices, domestic electric arc furnace steelmaking has gradually adopted this technology.
1.4.4 Quality analysis monitoring and cost control system
With the development of electric arc furnace smelting technology, relying solely on the operator's experience to control electric arc furnace production, it 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, and the cost can be reduced and the efficiency can be improved. However, related systems introduced from abroad, due to the complex domestic raw material structure and special smelting process, make it difficult to exert their effectiveness. The quality analysis and monitoring and cost control system for electric arc furnace steelmaking developed by the University of Science and Technology Beijing predicts and calculates real-time costs of electric arc furnace single furnaces, and provides power supply and oxygen optimization guidance curves and optimizations for different furnace structures. Costs are predicted and calculated in real time, and optimized alloy and slag combinations are provided. At present, the system has been promoted and applied in many electric furnaces at home and abroad.
2 Analysis of the technical characteristics of major electric arc furnaces at home and abroad
In recent years, foreign electric arc furnace steelmaking technology has developed rapidly, and has successively developed a variety of new electric arc furnace types such as FastARC, Quantum, ECOARC. Comparatively speaking, China's steelmaking process has long been dominated by the “long process” with blast furnace-converter as the main body, and the research and development of electric arc furnace steelmaking is relatively weak. Developed new electric arc furnace technology such as CISDI-Green EAF.
2.1Quantum EAF Quantum EAF is the latest high-efficiency, energy-saving and environmentally friendly electric furnace developed by Primetals of Germany. Its scrap continuous preheating system utilizes the exhaust gas from the furnace during the thermal cycle to uniformly preheat all scrap steel to be melted. It is unique in that it has a high-efficiency continuous charging preheating system, a new continuous charging system, a separate tilting system for the lower and upper furnace shells at the time of tapping, and a continuous power feeding and feeding system.
Quantum EAF is highly automated and can be operated almost fully automatically. From scrap loading to tapping, all steps are performed at least semi-automatically. This is a big step towards the development of Industry 4.0. At present, a 100t quantum electric arc furnace has been put into operation at the Tyasa plant in Mexico, and Guilin Pinggang plans to invest in a 120t quantum electric arc furnace. Because the scrap steel is preheated by the flue gas generated by the electric furnace, the quantum electric arc furnace has certain advantages in reducing power consumption and shortening the smelting cycle, but the stability of its finger system needs further confirmation.
2.2 ECOARC EAF ECOARC EAF is a new type of high-efficiency electric arc furnace developed in Japan with advanced energy recovery and environmental protection technology. ECOARC EAF uses high-temperature exhaust gas to preheat the scrap steel, and loads the scrap steel into a "vertical" preheating chamber connected to the furnace shell. The preheating chamber is tightly connected with the furnace body, preventing air from penetrating into the furnace, realizing a closed operation, and significantly reducing the nitrogen content in the steel. In the ECOARC EAF production process, the scrap steel is divided into 10-13 semi-continuous continuous inputs per furnace, and the entire process is in a "flat molten pool" state.
In addition, by using the CO gas contained in the exhaust gas and burning a small amount of fuel, the exhaust gas is rapidly cooled by spraying water in the cooling chamber after the combustion, so that the generation of harmful chemicals (dioxins) can be avoided. ECOARC EAF has achieved dioxin emissions below 0.1ng-TEQ / Nm3 in Japan.
ECOARC EAF has been applied in a total of 6 steel companies including Japan, South Korea, and Thailand, and has not yet been applied in China. Compared with conventional electric arc furnaces, the reported data has obvious advantages in terms of smelting cycle, electrode consumption and other indicators, but its equipment maintenance is more difficult (larger furnace body, vertical shaft cannot be separated, refractory online replacement), investment costs Higher.
2.3 Consteel EAF
Consteel EAF is the world's first scrap steel preheating electric arc furnace that has been proven to be flexible in the use of metal raw materials. It is also the most mature continuous feed electric arc furnace in China. Consteel electric arc furnace has the characteristics of good production environment, small power grid impact, reliable and controllable feeding, and high efficiency of waste gas heat utilization. However, due to dioxin emissions, it has been restricted in the European market. At the same time, there are dynamic leaks and long production lines. And other unfavorable factors, its operating costs are also higher.
2.4 SHARC EAF
SHARC EAF hearth shape symmetrical design and DC current integration technology, this technology makes the high temperature exhaust gas stay longer in the preheated shaft furnace, heat transfer efficiency is higher, can ensure the use of low-density scrap steel (stack weight ratio of 0.25 -0.3t / m3) and without additional preheating, production can also be carried out efficiently and economically, and the scrap steel melts evenly, but the system has a large amount of equipment maintenance and the reliability of the equipment needs to be further improved.
2.5 CISDI-Green EAF
China Green Intelligent Electric Furnace Industry Alliance, which is hosted by China Metallurgical Sadi, in conjunction with Beijing University of Technology, Changchun Sanding Transformer, Wuxi Hongqi Dedusting, and other units, successfully developed a new type of energy-saving and environmentally friendly electric arc furnace CISDI-Green EAF. Requirements and difficult maintenance of scrap steel preheating equipment, the unique arc furnace differential closed-step disturbance continuous feeding and side top chute feeding technology are used to feed scrap steel close to the central area of the electric arc furnace to improve the scrap steel preheating type electric furnace. The cold zone, combined with flue gas preheating technology, can significantly reduce the operating power consumption of the arc furnace smelting process.
The technology adopts a fully enclosed feeding method, which is matched with the opening control of the dust removal port to ensure minimum dust and flue gas overflow during feeding. It solves the problem of large heat loss caused by opening the cover and reduces the dust emission during the production process.
CISDI-Green EAF controls the temperature of the flue gas during the preheating of the scrap steel through the change of its structure. By adjusting the flow ratio of the shunt dedusting pipe and the main dedusting pipe, the flue gas temperature after the preheating of the scrap steel is accurately controlled, thereby suppressing The production of dioxin. The flue gas is rapidly cooled through the quenching chamber, and suppression of dioxin resynthesis in the flue gas cooling process is achieved.
2.6 Comparison of Technical Indexes of Main Arc Furnace at 鸿运彩票是正规网站吗 and Abroad
The comparison of the above-mentioned domestic and international main electric furnace application technical indicators and environmental protection technical indicators are shown in Tables 1 and 2, respectively.
Table 1 Technical Specifications of Electric Arc Furnace Steelmaking at 鸿运彩票是正规网站吗 and Abroad (Full Scrap)
Electric arc furnace
Nominal capacity, t
Smelting cycle, min
3 /t Oxygen consumption, Nm 3 / t
Electrode consumption, kg / t
Power consumption, kWh / t
3 /t Gas consumption, Nm 3 / t
Toner consumption, kg / t
Table 2 Environmental protection indicators of EAF steelmaking applications
Electric arc furnace
Nominal capacity, t
Dust emission, kg / t
3 Dioxin emissions, ng-TEQ / Nm 3
3 Conclusions and prospects
In China, electric arc furnace steelmaking is not only the production of ordinary rods and wires, but also the main process for smelting high-quality special steels. On the basis of EAF high-efficiency energy-saving smelting, the importance of cleanliness of products, greening of production processes and intelligence in the field of EAF steelmaking will become increasingly prominent. It is foreseeable that more advanced electric arc furnace clean smelting process, greener production technology, and more reliable and comprehensive process intelligent detection and control will become the main development trend of electric arc furnace steelmaking technology in the future. Accelerating the technological innovation of EAF steelmaking, improving the product quality and product competitiveness of EAF steelmaking processes, and improving the level of green manufacturing and intelligent manufacturing of EAF steelmaking will play an important role in promoting structural adjustment and transformation and upgrading of China's steel industry.