Introduction of electric arc furnace steelmaking process

Characteristics of electric arc furnace in steelmaking process

The function of electric furnace steelmaking in the process is to process raw materials into molten steel with qualified composition and temperature at a certain rate. As far as the current general engineering technology level is concerned, the main characteristics of the electric furnace steelmaking process in the process are two points:

1. The electric furnace steelmaking process is an intermittent operation, and the smelting cycle is about 60 minutes. In order to ensure the continuous casting process to achieve multi-furnace continuous casting, the input of electrical energy, chemical energy, and physical energy should be matched with it. To further increase the production rate, the smelting cycle tends to be lower than 50 min or even 45 min. However, the shortening of the smelting cycle shortens the power-on time and increases the proportion of the non-power-on time, which is unreasonable for the utilization of power supply capacity. According to the current development trend, we can see the signs of making full use of waste heat and realizing continuous steelmaking. At present, the number of tappings per electric furnace should be 7000 to 10000 times per year, that is, the utilization factor or annual production rate of unit furnace capacity is (0.7 to 1.0) million t/(t a).

2. The qualified molten steel provided by EAF steelmaking is the material basis to ensure the efficient and smooth operation of downstream processes. The productivity of EAF steelmaking should match that of hot rolling. In the 1960s and 1970s, the productivity of the hot tandem rolling mill for long sections was about 300,000 t/a. If the annual production rate of EAF steelmaking was 5,000 t/(t a), the corresponding electric furnace capacity was 60t. The productivity of the current long-section hot tandem mill has been increased to (70-800,000 t/a), and the corresponding electric furnace capacity should be 70-100 t. The productivity of the single-strand thin slab continuous casting and rolling process is (100-1.2 million) t/a, and the capacity of the steelmaking electric furnace can be 120-150 t.

The productivity of hot continuous rolling will reach more than 2 million t/a, and the capacity of the steelmaking electric furnace will exceed 200 t. Due to the limited technical conditions of electric furnace transformers and graphite electrodes, it is unreasonable. Therefore, hot rolling broadband enterprises should not be equipped with electric furnace steelmaking (in addition to The adverse effect of metal residual elements in the scrap raw material on the quality of the strip should also be considered).

Matching of arc furnace steelmaking and upstream processes

1. The traditional electric furnace steelmaking uses scrap steel as the main raw material, and 10% to 15% pig iron is added to ensure a certain amount of carbon. Generally speaking, scrap raw materials at room temperature (25 °C) have very little physical heat. Under the condition of oxygen blowing, the chemical heat generated by the cold charge is not much, and the smelting process requires a large amount of external heat energy.

According to various statistical data in my country in recent years, the energy consumption of electric furnace steelmaking process (including refining, continuous casting and workshop auxiliary projects) is 250-300kg, which is slightly higher than the results of IISI of the International Iron and Steel Institute.

2. Using different proportions of hot iron as raw material, the electric furnace steelmaking process has achieved obvious benefits, the main reason is that hot iron is an energy carrier with high physical heat and chemical heat, and the cost is low. Putting electric furnace steelmaking into the process, it is not difficult to see that the physical heat and chemical heat carried by hot molten iron come from the previous blast furnace ironmaking process. According to the actual data of 300-380 m3 blast furnaces in some enterprises, to produce 1 t of hot molten iron, the energy consumption of the blast furnace ironmaking process is 377 kg, equivalent to 3080 kW h / t.

Considering processes such as sintering, pelletizing and coking, the energy consumption per ton of hot iron is 500-550 kg/t, or 4084-4493kW h/t. The total chemical energy is only 600 to 650 kW h/t.

3. At present, the proportion of domestic electric furnaces equipped with heated molten iron is 25% to 30%. According to the annual output of 1 million t of steel, 300,000 to 350,000 t/a of molten iron are required. The blast furnace utilization factor is taken as 3 t/(m3:d), and the blast furnace volume is 300-350 m3.

4. Use of direct reduced iron. The use of direct reduced iron to provide pure iron source for electric furnace steelmaking is an important development direction in the world in recent years. The worldwide output of various direct reduced iron has more than doubled since 1990, and in recent years, the output has exceeded 40 million t/a, accounting for about 15% of the output of EAF steel, which has become an important part of EAF steelmaking. source of iron.

The production technology of direct reduced iron has progressed rapidly, especially hot briquettes (HBI) with w(C) close to 2%, which provide a pure iron source with high density and high chemical energy for electric furnace steelmaking. In the world, the production technology of DRI is dominated by the gas-based method, and the gas-based method accounts for 90% of the DRI production. However, my country lacks natural gas and has few high-quality iron ore, and the resources limit the development of DRI production technology. At present, the largest direct-reduced iron production plant in China is Tianjin Steel Pipe Co., Ltd., and the energy consumption per ton of direct-reduced iron is about 900-1 000kg.