Large Capacity 420t Ultra-high Power Double Graphite Electrode DC Electric Arc Furnace

For a long time, the steelmaking electric arc furnace has been using AC E-phase electric arc furnace. However, the AC electric arc furnace itself has a series of insurmountable shortcomings. From the 1970s to the 1980s, some industrially developed countries developed DC Steelmaking Electric Arc Furnaces (DCEAF) and made significant progress. Japan started late in the development of DC electric arc furnaces, but developed the fastest, and is the country with the largest number of DC electric arc furnaces currently in use. A single large-capacity electric arc furnace is the development trend of the steelmaking industry in recent years, which can meet the steel mills' demand for higher productivity.

Features of DC electric furnace

The mechanical equipment of this DC electric arc furnace is composed of furnace body, furnace cover and its lifting and rotating mechanism, electrode, and its lifting mechanism, high current circuit, hydraulic system, cooling water and compressed air system, etc. Its power supply system is different from the AC electric arc furnace. It is equipped with a rectifier and a reactor. The electric connection point at the bottom of the furnace forms a current loop. The maintenance and life of the electric connection point are key issues in the operation of the DC electric arc furnace. Generally, the furnace bottom steel plate Puts a copper plate on it to facilitate electrical conduction. Three layers of magnesia carbon bricks are built on the copper plate, and then refractory materials are knotted on the copper plate.

Tokyo Steel's Tahara Plant produces medium carbon steel, low carbon steel, and ultra-low carbon steel. The furnace is designed as a full platform, split furnace shell, using continuous scrap feeding Conestee and dual graphite electrode DC technology. The main technical parameters of the DC electric arc furnace are shown in Table 1.

Main technical parameters of 420t ultra-high power double graphite electrode DC electric arc furnace：

Total Capacity/t	420	Steel Output/t	300
Steel Reserve/t	120	Shell Diameter/m	9.7
Power-on Time/min	42	Steel tapping-steel tapping time/min	50
Productivity/t·h-1	360	Charge Ratio	100% Steel Scrap
Loading Amount/t·min-1	＞9	Power Consumption/kw·h·t-1	387
Oxygen Consumption/m³·t-1	33	Electrode Consumption/kg·t-1	1.2
Primary Side Voltage/kV	33	Transformer Capacity/MVA	4x(2x32)
AC/DC Converter Current/kA	8x35	DC Reactor Resistance Value/ μ H	8x350
Operating Current/kA	4-70	Operating Voltage/V	600V
Cathode Diameter/mm	762

The power supply of this DC electric arc furnace is composed of a transformer, thyristor, DC reactor, and other auxiliary equipment. The core of the DC electric arc furnace power supply is a thyristor. With the application and development of thyristor technology, the manufacturing technical problems of high-power DC power supply equipment have been solved. This DC EAF is designed with 2 cathodes (double graphite top electrode direct current technology) and 4 water-cooled bottom anodes. The current of each anode is 70kA, and the total current is 280KA. Compared with a single cathode design, the dual graphite electrode technology can provide very high power and a smaller electrode diameter, with less interference to the power grid (Welcome to pay attention to "Xian Hani Tech Co., Ltd.")

Because the DC arc furnace eliminates the influence of electromagnetic induction, there is only DC resistance loss on the secondary conductor, the mechanical structure around the conductor does not need to use non-magnetic materials, and the vibration phenomenon of the electrode is also eliminated. In order to prevent sudden currents and stabilize arcs, a DC reactor must be installed in the DC loop. In the AC electric arc furnace, the arc is always inclined to the furnace wall at an angle of 30°~45°, thus forming a hot spot. In the DC electric arc furnace, the arc points to the molten pool at an angle of 15*~30° and rotates randomly around the center several times per second under the action of electromagnetic force. The arc length refers to the linear distance from the end of the electrode to the molten pool. In the case of AC, the arc length is 1mm/V arc. Because the DC arc is particularly stable, it is expected to be longer than the AC arc. The maximum flexibility of power adjustment can be achieved by individually controlling the current conduction and distribution of the 4 anodes. At the same time, the water-cooled bottom anode with special design features can use ordinary refractory materials. The design of the tilting platform is based on 3 rocker arms, which can provide better running stability in the bearing area. The 3 rocker arms are matched with the furnace body to ensure that the furnace body is tilted back safely.

The above is an introduction to the 420t large-capacity DC electric arc furnace. If you have other questions or supplements, please feel free to contact us. If there are other production volume product and process requirements, please also let us know. We are committed to providing the right products to every customer.

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Daisy Zhai