What are the Advantages of DC Electric Arc Furnaces?

What are the Advantages of DC Electric Arc Furnaces?

What are the Advantages of DC Electric Arc Furnaces Compared to Traditional AC Electric Arc Furnaces?

Electric arc furnaces (electric arc furnaces) use the high temperature generated by the electrode arc to melt ores and metals. When the gas discharge forms an arc, the energy is very concentrated, and the temperature of the arc zone is above 3000℃. For smelting metals, electric arc furnaces have greater process flexibility than other steelmaking furnaces, can effectively remove impurities such as sulfur and phosphorus, the furnace temperature is easy to control, and the equipment occupies a small area, which is suitable for the smelting of high-quality alloy steel. DC electric arc furnaces are steelmaking electric arc furnaces that use DC power to supply electricity. Like AC electric arc furnaces, it uses the arc generated between the electrode and the charge (or molten pool) to generate heat to achieve the purpose of smelting, and can be used to melt steel or alloys. There is only one electrode on the top of the DC electric arc furnace, which is the negative electrode, and the bottom electrode is the positive electrode. Its power supply system is different from that of AC arc furnace. It is equipped with rectifier and reactor. Contacts are installed on the bottom of the furnace to form a current loop. The maintenance and life of the contacts are key issues in the operation of DC arc furnace. Generally, copper plates are placed on the steel plates at the bottom of the furnace to facilitate conductivity. Three layers of magnesia carbon bricks are laid on the copper plates, and refractory materials are tied on them.

Compared with AC Arc Furnace, DC Arc Furnace has the Following Advantages:

(1) The arc of DC arc furnace is stable and concentrated, the molten pool is well stirred, the temperature distribution in the furnace is uniform, and the lining erosion is small;

(2) The current and voltage fluctuations of DC arc furnace are small, the impact on the power grid is reduced, and the cable life is extended accordingly;

(3) The electrode loss of DC arc furnace is small, and the electrode consumption is 50% less than that of AC arc furnace. The performance of DC arc furnace is better than that of AC arc furnace, but it has been suffering from the lack of high-power DC power supply, which has prevented it from being developed for a long time.

(4) The electrode consumption of DC arc furnace is reduced by more than half, and the consumption is only The electrode consumption is reduced because the anode spot with higher temperature is always located on the molten pool, while the temperature of the graphite electrode as the cathode is lower, so the consumption of the graphite electrode end, such as the rise, cracking and shedding, is greatly reduced. The reduction in the number of electrodes reduces the consumption of side surface oxidation.

(5) The temperature distribution of the DC arc furnace is more uniform, and the consumption of refractory materials is reduced. In a three-phase DC furnace, the external suction effect caused by the electromotive force of the three arcs makes the heat on the furnace wall near the arc more developed, becoming the weak link of the furnace wall. In a DC single-electrode furnace, when the magnetic field of the bottom electrode conductor does not affect the arc, the arc will overlap vertically with the center line of the electrode, and the furnace wall will be heated evenly.

In a DC furnace, because the current passes through the molten pool and then to the dispersed bottom electrode, the electromotive force in the molten pool causes the part of the metal under the arc to move downward and around, and then turn to the surface. This agitation makes the temperature and composition of the molten pool uniform. In a small ladle refining furnace, it is quite difficult to place three electrodes because the distance between the arc and the furnace wall is too small. If DC arc heating is used, the heat load on the ladle wall is reduced by more than half at the same heating power.

This opens up the possibility of heating small ladle furnaces.

(6) DC arc furnaces have low noise. The amplitude of the sound waves emitted by the arc is proportional to the change in the instantaneous power of the arc over time. Because the DC arc has good stability and small instantaneous power fluctuations, the noise is reduced. The peak value of the DC furnace noise level is similar to that of the AC furnace, but its duration is much shorter. The reason is that the scrap steel melts faster under the arc with a power three times greater, and the liquid molten pool is also formed faster. Therefore, the average noise level during the entire melting period can be reduced.

(7) Smaller voltage fluctuations. Under the same scrap steel operation method, the voltage fluctuation accumulated by the DC furnace is about 1/10 of that of the AC arc furnace, which is similar to that of the AC arc furnace after the molten pool is formed or when operating with direct reduced iron.

(8) The technical and economic benefits of DC arc furnaces are significant. The consumption of graphite electrodes is reduced by more than 50%-60%, the electricity consumption is saved by 5%-10%, the refractory materials are saved by 30%-35%, the right graphite electrode support mechanism and automatic adjustment system are saved, the cable materials of the short network are saved, the molten steel is well stirred, the power factor is improved, the voltage flicker rate is reduced, the noise is reduced, and the economic benefits are significant.

(9) The bottom electrode structure of the DC arc furnace is constantly updated. The new conductive refractory bottom electrode is rapidly developing, and the water-cooled steel column bottom electrode is being promoted and applied again.