Overview of arc furnace steelmaking technology development

My country's "Thirteenth Five-Year Plan" "Steel Industry Adjustment and Upgrading Plan (2016-2020)" pointed out: to accelerate the development of circular economy, in accordance with the concept of green and recyclable, pay attention to the development of short-process electric furnace steelmaking using scrap steel as raw material. It is foreseeable that with the transformation of my country's "long-process" steelmaking to "short-process" steelmaking and the need for energy conservation and environmental protection, electric arc furnace steelmaking will usher in new development opportunities. Gradually abundant, the electro-metallurgical process, especially the electric arc furnace short-flow process, will receive more and more attention.

In recent years, electric arc furnace steelmaking has made great progress in efficient smelting, energy saving, environmental protection and intelligent control, and the technological level of electric arc furnace steelmaking has been significantly improved; at the same time, various new electric arc furnaces have been developed and applied, which has greatly promoted steel Advances in industrial technology.

Development of eaf technology for steelmaking 

In the past 30 years, electric arc furnace steelmaking technology has developed rapidly. In terms of technology, technologies such as scrap steel preheating, enhanced oxygen blowing, foaming slag, secondary combustion, bottom blowing stirring and ladle refining are adopted; Automatic adjustment, automatic furnace door robot, scrap crushing and sorting and other technologies; in the development of new electric arc furnaces, there are also many new technologies such as Consteel EAF, Quantum EAF, ECOARC EAF, CISDI-Green EAF and SHARC EAF. Throughout the development history of electric arc furnace steelmaking technology, its technological progress mainly revolves around the four aspects of EAF steelmaking efficiency, cleanliness, greenness and intelligence.

1. Efficiency

(1) Rationalized power supply technology A reasonable electrical operation system is the most basic guarantee for electric arc furnace steelmaking. The formulation of a reasonable electrical operation system is based on the selection of the best working point. The working point mainly refers to the electrical 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, under the conditions of the smelting process, to give full play to the power supply capacity of the transformer, and to achieve the purpose of high efficiency and power saving in steelmaking, Beijing University of Science and Technology has developed an exponential nonlinear working reactance model for ultra-high power electric arc furnace transformers. Establish a database of electrical operation characteristics of electric arc furnace transformers with different capacities and multi-level working voltages to truly reflect the actual operating conditions of electric arc furnace transformers; by constructing mathematical models and characteristic curves of power supply operation that match the operation of electric arc furnace transformers, ensure the efficient output of electric arc furnace transformers. and stable operation with low consumption.

(2) Strengthening 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 steel quality, energy consumption and production operation rate, and is the key to the electric arc furnace steelmaking. As a result, various forms and functions of electric arc furnace chemical energy enhancement input technology have been developed.

a. Furnace door oxygen supply technology: Electric arc furnace door oxygen blowing equipment is divided into two categories according to the water cooling method, one is water-cooled furnace door carbon oxygen lance, and the other is consumable furnace door carbon oxygen lance. The water-cooled furnace door carbon oxygen lance has the advantages of high oxygen utilization rate, good foaming slag effect, stable decarburization and dephosphorization effect and high degree of automation, but it cannot be in contact with molten steel during operation, which has certain limitations. Consumable furnace door carbon-oxygen guns can start cutting scrap steel earlier in the furnace and contact with molten steel. The furnace has a large space for movement, but it needs to be connected to the oxygen blowing pipe at intervals during the operation process, which is more troublesome.

b. Furnace wall oxygen supply technology: The purpose of oxygen supply to the furnace wall of the electric arc furnace is to eliminate the cooling zone in the furnace and ensure the balanced melting of the charge. The modular control of the furnace wall is used to inject pure oxygen to improve 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 installation method of the furnace wall oxygen lance is closer to the molten pool, and the distance from the jet to the molten pool is shortened by 40%-50% compared with the traditional installation method, which can greatly improve the decarburization of the molten pool. speed and oxygen utilization efficiency; the combustion in the molten pool can be organically combined with the combustion above the molten pool, which improves the thermal efficiency of the smelting process; multi-point injection can be realized in the furnace, and the amount of oxygen blowing and carbon powder injection can be accurately controlled. Slag works well.

c. EBT oxygen supply technology: Modern electric arc furnaces all use eccentric bottom tapping (EBT) technology, which makes the EBT area one of the inner cooling areas of the electric arc furnace, resulting in a slower melting rate of scrap steel in this area, and the composition of the molten pool and the central area. Differences in ingredients, etc. The EBT oxygen lance is installed above the eccentric furnace side for oxygen blowing and fluxing, which can promote the melting of the scrap in the EBT area, and completely solve the problems that the scrap in the EBT area has not been melted during tapping and the tapping port cannot be opened. After the molten pool, increase the temperature of the molten pool in the EBT zone to uniformize the composition of the molten pool. The difference between the temperature and composition of the EBT area and the temperature and composition of the furnace door area during tapping is only 0.5%-1.0%.

d. Cluster oxygen supply technology: In view of the problems of fast decay of supersonic gas jet speed and low oxygen utilization rate, cluster jet technology has been developed and applied, and an annular protective airflow (generated by combustion of fuel gas and oxygen) is set around the main oxygen jet. The length of the supersonic core section of the main oxygen jet is extended to form a jet similar to a laser beam. The kinetic energy loss of the oxygen stream is reduced, and it has strong penetrating power and stirring force, realizing high-speed oxygen supply and decarburization to the molten pool, improving the uniformity of heat and composition in the furnace, and promoting the slag reaction and uniform molten steel composition. It has obvious effects on temperature, oxygen utilization rate, metal yield and so on. The USTB cluster oxygen supply technology developed by the University of Science and Technology Beijing is more suitable for the structural characteristics of domestic electric arc furnace steelmaking charge, reaching the international leading level, and has been applied in more than 100 electric arc furnaces at home and abroad.

(3) Foamed slag technology

In the process of electric arc furnace smelting, 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. Usually the foam makes the thickness of the slag reach 2.5-3.0 times the arc length, which can completely shield the arc, reduce the radiation of the arc to the furnace top and furnace wall, prolong the life of the arc furnace body, and make the arc transfer to the molten pool. The thermal efficiency is increased from 30% to 60%, the smelting cycle is shortened by 10%-14%, the smelting power consumption is reduced by about 22%, and the electrode consumption is reduced by about 2kg/t. As a result, the production cost is reduced, the productivity is improved, the noise is reduced, and the noise pollution is controlled.

(4) Oxygen burner technology

Oxygen burner technology has been widely used in electric arc furnace steelmaking to ensure synchronous melting of the charge and to play the role of electrodes more effectively. 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, according to the different fuels used, oxygen burners mainly include oil-oxygen burners, coal-oxygen burners, gas burners, etc. The fuels used include diesel, heavy oil, pulverized coal and natural gas.

(5) Secondary combustion technology

There are two main types of secondary combustion technologies in electric arc furnaces: foamed slag operation secondary combustion technology and free space secondary combustion technology. Since the free space secondary combustion (furnace gas combustion) technology is to make oxygen react with the CO gas above the molten pool, the heat generated by the secondary combustion is transferred to the slag layer by radiation and convection, and then transferred from the slag layer to the molten steel. The heat transfer efficiency is about 30%-50%; while the foamed slag secondary combustion technology is used, the heat generated by the secondary combustion is directly transferred from the slag to the molten steel, and the heat transfer efficiency is about the same as that of the furnace gas secondary combustion technology.

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