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The Short Service Life of Refractory Materials in Electric Furnace Walls and Its Related Factors

Electric furnace walls can be divided into three parts: the ordinary wall zone, slag line zone, and hot spot zone, based on different working environments. During the smelting process, electric furnace walls are subjected to the radiation of high-temperature electric arcs, temperature changes during feeding and tapping of molten steel. Additionally, they face the direct erosion of molten steel, chemical corrosion from high-temperature furnace slag, and mechanical impacts and vibrations during material charging, especially near the slag line zone where erosion is particularly severe.

In the schematic diagram of an electric arc steelmaking furnace

In a three-phase alternating current electric arc furnace, the temperature distribution in different parts of the furnace wall is uneven. The hottest area corresponds to the hot spot region of the three-phase electrodes. This region, in addition to being eroded by molten slag and steel, is also directly exposed to the high-temperature electric arc radiation. Consequently, it experiences the fastest wear, with the slag line area near the electrodes being the weakest link in the furnace wall and most susceptible to erosion. Furthermore, the areas around the electric furnace door and the sidewalls are prone to damage due to the erosion of molten slag and the impact of slag removal equipment, often becoming the main reasons for furnace shutdowns. Table 1 provides an analysis of the damaged parts of refractory materials in the furnace wall and the reasons for their damage.

Factors Affecting the Service Life of Refractory Materials in Electric Furnace Walls

The service life of refractory materials used in electric furnace walls is closely related to the smelting technology adopted by the electric furnace plant. To strengthen smelting operations and reduce the impact of smelting conditions on refractory materials, various companies have adopted the following smelting technologies:

  1. Electric furnace water-cooled wall technology: The water-cooled walls of electric furnaces are usually made of cast steel or steel plates, with steel plates commonly used for large electric furnace walls. The size, number, and installation positions of cooling wall blocks are determined based on actual production conditions. The goal is to achieve a relatively balanced service life for various parts of the furnace lining material. An inner layer of refractory material can be sprayed on the internal surface of the water-cooled wall blocks for convenient attachment or a layer of magnesia carbon bricks can be built on the inside of the water-cooled wall to protect the water-cooled blocks. The use of water-cooled wall technology can form a slag layer on the surface of the furnace wall, reducing the erosion of furnace slag and molten iron on refractory materials. Currently, installed water-cooled walls account for over 60% of electric furnace walls, significantly reducing refractory material consumption and saving smelting costs.
  2. Foam slag technology: While water-cooled wall technology can strengthen smelting operations, it inevitably brings about significant heat loss. By spraying carbon and blowing oxygen into the molten pool or adding a foaming agent to generate a large amount of foam, the long electric arcs generated due to increased voltage can be covered. This accelerates the temperature rise of the electric furnace, improves the heat transfer efficiency of the electric arc to the molten pool, reduces power consumption, and lowers electrode consumption.
  3. Oxygen-assisted melting technology: Using an assisted melting oxygen combustion nozzle to spray fuel and oxygen into the molten pool can eliminate cold spots in the furnace, allowing synchronous melting of the entire furnace. This method can increase the total heat input to the furnace, reduce power consumption, and lower electrode and refractory material consumption, thereby shortening the smelting cycle.
  4. Oxygen-coal injection technology: Using the high-temperature flame produced by the combustion of coal and oxygen as an auxiliary heat source during the melting period of the electric furnace can increase the heat in the furnace, reduce electrode heating and operation, improve the service life of the furnace lining.

Electric furnace walls are divided into three parts based on usage conditions: the main wall, slag line, and hot spot. Due to the different working conditions of these three parts, their service lives also vary. Therefore, most electric furnaces use a comprehensive brick-laying method to achieve a balanced wear and tear of the entire furnace lining.

Technical Measures to Improve the Service Life of Electric Furnace Walls

  1. Further improve the quality of refractory lining materials. Using large crystal magnesia to make magnesia carbon bricks helps improve their erosion resistance and oxidation resistance. Using high-purity flake large crystal graphite as the carbon source for magnesia carbon bricks can significantly enhance their erosion resistance and oxidation resistance, improving the service life of the furnace lining. Adding an appropriate amount of antioxidant can prevent the oxidation of carbon in magnesia carbon bricks. Additionally, after oxidation, some antioxidants can react with magnesia to form new substances with a high melting point, blocking pores and enhancing the erosion resistance of the material. Vacuum impregnation of magnesia carbon bricks can close the pores, reduce the pore rate after carbonization, and improve the erosion resistance of the material. The use of asphalt and resin composite binders can create an embedded bonding mode in the material, enhance the carbon-bonding fracture toughness, and improve the oxidation resistance of magnesia carbon bricks.
  2. Strengthen the wall’s spraying and repairing technology. Using appropriate spraying and repairing processes can extend the service life of furnace lining materials and reduce smelting costs. Commonly used binders for spray repair materials include silicates, phosphates, and various magnesium salts. Since phosphate-bonded repair materials have high adhesion strength, they result in a longer service life.
  3. Strictly control the smelting process. Strict control of the smelting process not only ensures the production of qualified products and reduces waste but also is extremely beneficial for the oxidation and maintenance of the lining. It can significantly save costs. Strict control of the smelting process mainly involves creating good foam slag. The shielding effect of foam slag not only improves the thermal efficiency of the electric furnace but also effectively protects the furnace wall from the radiation of arc light, reducing refractory material consumption considerably.
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