DC arc furnace

DC arc furnace

DC electric arc furnace refers to the electric arc furnace using DC electricity as energy. Like the AC electric arc furnace, it uses the electric arc generated between the electrode and the furnace charge (or molten bath) to heat, so as to achieve the purpose of smelting. It can be used for smelting steel or alloy and non-ferrous metals.

Chinese name

DC arc furnace

Foreign name

DC Arc Furnace

Discipline

metallurgy

Purpose

Melted steel or alloy and non-ferrous metals

Energy

Direct current

Principle

Electric arc heating generated by electrode and charge

catalogue

1 Product introduction

2. Form of furnace bottom electrode

3 Product Advantages

4 Product development

Product introduction

In the development process of electric furnace steelmaking, the ultra-high power three-phase AC electric furnace has made great progress in electric furnace steelmaking, and the output of electric furnace steel has reached 40% of the total steel in the world. However, with the substantial increase of the capacity and power level of AC electric furnace, some problems have also been brought, namely, the stability of high-power AC arc is poor, the impact on the power grid is large, and there is a large noise pollution. DC electric arc furnace has many advantages, such as stable arc, low noise, low electrode consumption, etc. It has been rapidly developed in industrial developed countries, especially in large capacity (70-150t) ultra-high power DC electric furnace. DC arc furnace is mainly developed by Sweden's General Electric Company (ASEA), France's CIECLM and Germany's MAH/GHH. At present, the strongest DC arc furnace manufacturers are ABB, CLECIM/DAVY, MAH/GHH and NKK.

The DC electric arc furnaces introduced in China are all large ultra high power DC electric furnaces, which are used to cooperate with the efficient continuous casting and rolling production line. However, the application of the DC electric arc furnace technology in traditional die casting production is basically blank. Most of the special steel varieties used for die casting by domestic special steel enterprises are small electric furnaces (below 30t), and most of them are backward AC arc furnaces. The application of advanced DC electric arc furnace technology in the production of special steel die casting will promote the improvement of special steel smelting technology [1].

Type of furnace bottom electrode

DC electric arc furnace is to convert three-phase alternating current into single-phase direct current through thyristor rectification, and produce electric arc on the metal furnace charge between furnace bottom electrode (anode) and graphite electrode (cathode) for smelting. The main differences between DC arc furnace and AC arc furnace equipment are as follows: the rectifier device is added, the top graphite electrode is changed from three to one, and the bottom electrode is added. The setting of bottom electrode is the biggest feature of DC arc furnace. The bottom electrode is the key of DC electric arc furnace technology. At present, the basic forms of several representative DC electric arc furnaces operating in the world are mainly different in the structure of the bottom electrode. According to the structural characteristics of furnace bottom electrode, it can be roughly divided into the following categories: steel rod water-cooled bottom electrode developed by French companies such as CLECIM, stylus air-cooled bottom electrode developed by German companies such as GHH, contact plate type bottom electrode developed by Austrian company DVAI, and conductive furnace bottom air-cooled bottom electrode developed by Swiss company ABB [2].

Product benefits

Direct current arc furnace

Compared with the traditional AC electric arc furnace, the main advantages of DC electric arc furnace are:

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

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

(3) The electrode loss is less, and the electrode consumption per ton of steel is 50% less than that of AC electric arc furnace. The performance of DC arc furnace is better than that of AC arc furnace, but it has not been able to obtain high-power DC power supply for a long time.

product development

With the application of silicon controlled rectifier technology, the manufacturing technology of high-power DC power supply equipment has been solved. Therefore, in the late 1970s, the metallurgical industry carried out research on DC arc furnace again. By the early 1980s, the technical problems of construction and use of DC arc furnace had been solved one by one. The first DC electric arc furnace in the world was built and put into operation at Bush Steel Plant in Germany in 1982. In the following six or seven years, the United States, France, Italy, Japan and other countries have successively rebuilt or newly built their own DC electric arc furnaces, with capacities ranging from 30t to 60t. In 1989, Tokyo Iron and Steel Corporation of Japan built the largest DC electric arc furnace with a capacity of 130t at that time. In recent years, many DC electric arc furnaces have been built and put into operation all over the world, with capacities ranging from 60t to 180t. In 1989, China Taiyuan Machinery Foundry developed the first small DC electric arc furnace in China and put it into operation. In the same year, a 2000kVA submerged arc DC electric arc furnace was put into operation in Xuanhua Ferroalloy Plant to produce ferrosilicon, ferromanganese, calcium silicate and other ferroalloys. Since the 1990s, DC electric arc furnaces have been paid more and more attention. Shanghai No.3 Iron and Steel Works, Great Wall Steel Works, Qiqihar Steel Works, Jiangyin Yanshan Steel Works and Shanghai No.1 Iron and Steel Works have successively introduced large DC electric arc furnaces with capacities ranging from 80 t to 100 t. Baoshan Iron and Steel (Group) Co., Ltd. introduced a set of 150t DC electric arc furnace with double furnace shells (one power supply) from France.

There is only one electrode above 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 the AC arc furnace. It is equipped with a rectifier and reactor. The furnace bottom is equipped with contacts to form a current loop. The maintenance and life of the contacts are key issues in the operation of the DC arc furnace. Generally, copper plates are placed on the furnace bottom steel plates to facilitate conductivity. Three layers of magnesia carbon bricks are laid on the copper plates, and then refractory materials are tied on them.

Recent product progress

1. The capacity of DC electric arc furnace is rapidly expanded and the number of sets is sharply increased. Since the first DC electric arc furnace for steelmaking was put into industrial production in the former West Germany, due to its series of advantages, DC electric arc has mushroomed in many countries such as Germany, France, Sweden, Italy, the United States, the former Soviet Union, Türkiye, Japan, South Korea, Malaysia and China (including Taiwan Province). Since the 1990s, DC electric arc furnace has been popularized and applied more rapidly.

2. DC electric arc furnace has remarkable technical and economic benefits. The consumption of graphite electrode is reduced by more than 50% - 60%, the electric energy consumption is saved by 5% - 10%, the refractory material is saved by 30% - 35%, the right graphite electrode selection mechanism and the automatic regulating system are saved, the cable material of the short network is 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 benefit is remarkable.

3. The bottom electrode structure of DC arc furnace is constantly updated. The new conductive refractory bottom electrode has developed rapidly, and the water-cooled steel column bottom electrode has been popularized and applied again