EAF furnace clean production problems and technical innovations

Compared with foreign EAF steelmaking, my country's EAF has always been the main force in the production of special steel. With the increasing requirements for the quality of special steel in the domestic manufacturing industry, improving the process and equipment level of EAF steelmaking in my country has become the key to improving the quality of EAF steel products.

From the development of electric arc furnace steelmaking technology in recent years, it is not difficult to find that on the basis of the original high-efficiency and energy-saving smelting, electric arc furnace steelmaking has made great progress in clean smelting, and the quality of products has been significantly improved. The construction of a clean production platform for the furnace steelmaking process is of great significance.

Electric arc furnace steelmaking cleaning problems

1. Raw materials for electric arc furnace 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. However, there are still the following problems in scrap steel at this stage:

(1) With the development and progress of society, the number of scrapped automobiles and home appliances has increased rapidly, resulting in a relatively 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 scrap steel is more complex, containing a lot of impurity elements such as Zn, Sn, Mo, and Cu. As a result, in the process of electric arc furnace steelmaking, these harmful substances continue to accumulate and increase.

(2) In the process of electric arc furnace steelmaking, the added auxiliary materials will also lead to 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 according to the actual situation. For example, in the production of high-quality alloy bars, molten iron and scrap steel can be used as raw materials; in the production of low-sulfur steel, low-sulfur lime can be used as auxiliary materials.

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. 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. The main reason is that the raw material structure of EAF steelmaking is complex, and the molten phosphorus content fluctuates greatly. 

The carbon content of the whole scrap steel after smelting and melting is low, and the viscosity of the molten steel is high, and the flow rate of the molten pool is slow due to the limitation of the furnace structure of the electric arc furnace, the dephosphorization kinetic conditions are poor, and the dephosphorization during the smelting process is difficult. Traditional electric arc furnace smelting low phosphorus steel usually adopts multiple slag making and slag flow operations, which has long smelting cycle, large slag amount, high final slag (FeO) content, serious molten steel overoxidation, and difficult to control smelting cost.

3. Control of oxygen and inclusions in steel

   Stable control of oxygen content in molten steel at the end of EAF smelting is the key to reducing inclusions in steel. Electric arc furnace steelmaking generally adopts enhanced oxygen supply operation to speed up the smelting rhythm and improve production efficiency, but the control of the end point of electric arc furnace steelmaking is not precise, the liquid steel overoxidation is more serious, and the carbon and oxygen product is significantly higher than that of the converter.

This not only leads to excessive consumption of deoxidizers in the later refining process, but also significantly increases the amount of inclusions generated during refining. In order to reduce the oxygen content of the molten steel at the end point, the electric arc furnace steelmaking mainly controls the amount of oxygen blowing before tapping, and at the same time injects inert gas to strengthen the stirring; eccentric bottom tapping is used to control the amount of slag during tapping; iron carbon is added before tapping. Magnesium balls to reduce the oxygen content of molten steel. In the LF refining process, the deoxidation method of "aluminum + composite deoxidizer" is used to convert the Al2O3 inclusions into larger-sized easy-to-float inclusions and then remove them; the double vacuum process is used, and the pre-vacuum light treatment is performed before the LF refining. The vacuum treatment method deeply removes active oxygen and inclusions in the steel.

Innovation of clean smelting technology in EAF steelmaking process

1. Scrap crushing and sorting technology

By crushing the scrap raw materials, using dry and wet sorting systems to screen metals, non-metals, non-ferrous metals, etc. in the scrap raw materials, recycling them separately, and removing the paint and coating on the surface, it can effectively It can greatly reduce the content of harmful elements in scrap steel and greatly improve the cleanliness of EAF steelmaking products.

There are two main types of scrap shredders: shredders and shredders. The chipper is used to crush steel chips, and the crusher is used to crush large scrap; the crusher has several types: hammer type, roll type and blade type. The scrap iron and steel after crushing can be easily sorted and recycled for metal, non-metal, non-ferrous metal and ferrous metal by the thousand-type, wet or semi-wet sorting system, and 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 clean and reliable raw material guarantee for electric arc furnace steelmaking.

2. Electric arc furnace steelmaking compound blowing technology

In the traditional electric arc furnace steelmaking production process, the stirring ability of the molten pool is weak, which limits the effective transfer of materials 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. However, it fails to fundamentally solve the problems of insufficient stirring strength of molten pool and slow transfer of material energy.

Modern electric arc furnace steelmaking widely uses oxygen blowing technology to speed up the smelting rhythm and reduce production costs. Strengthened oxygen supply technologies such as furnace wall oxygen supply, furnace door oxygen supply, and cluster jet have been successively developed. In order to solve the problems of insufficient stirring strength of the molten pool and slow material energy transfer, key technologies such as bottom-blown stirring and electric arc furnace steelmaking composite blowing have been developed.

Aiming at high efficiency, low consumption, energy saving and high-quality production, research and develop a new generation of electric arc furnace smelting technology. The operation integration of steel power supply, oxygen supply and bottom blowing units meets the technical requirements of EAF steelmaking composite blowing under the condition of multiple charge materials.

The application of electric arc furnace steelmaking composite blowing technology realizes the integration of power supply, oxygen supply and low blowing operations in the production process of electric arc furnace, effectively solving the problem of weak stirring ability of the molten pool.

3. New gas-solid injection technology for electric arc furnace steelmaking

On the basis of traditional furnace wall powder spraying and buried oxygen supply injection technology, a new process of gas-solid injection cleaning and smelting in the electric arc furnace molten pool has been developed. 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, use air or CO2-O2 to spray carbon powder into the molten pool to accelerate the melting of scrap steel, achieve rapid melting and increase the carbon content of molten steel; 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, the severe carbon-oxygen reaction produces a large number of CO bubbles, which can realize deep denitrification and dehydrogenation, and significantly improve the cleanliness of molten steel at the end point.