An electric arc furnace for steelmaking powered by a DC power source. Like the AC electric arc furnace, it uses the arc generated between the electrode and the charge (or molten pool) to generate heat, so as to achieve the purpose of smelting and can be used to smelt steel or alloys.
The main advantages of DC EAF compared to traditional AC EAF are:
(1) The arc is stable and concentrated, the molten pool is well stirred, the temperature distribution in the furnace is uniform, and the erosion 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 prolonged;
(3) The electrode loss is less, and the electrode consumption per ton of steel is 50% less than that of the AC electric arc furnace.
The performance of the DC electric arc furnace is better than that of the AC electric arc furnace, but it has been suffering from the inability to obtain a high-power DC power supply so it has not been developed for a long time.
With the application of thyristor technology, the manufacturing technology of high-power DC power supply equipment has been solved, so in the late 1970s, the metallurgical community re-launched the research on DC electric arc furnaces, and in the early 1980s, the construction and use of DC electric arc furnaces Technical issues have been resolved one by one.
The world’s first DC electric arc furnace was built and put into operation in 1982 at the Bush Steel Plant in Germany. In the next six or seven years, the United States, France, Italy, Japan and other countries have successively rebuilt or built their own DC electric arc furnaces. Ranging from 30t to 60t.
In 1989, Tokyo Steel Corporation of Japan built the largest DC electric arc furnace with a capacity of 130t at that time. In recent years, countries around the world have successively built and put into operation a number of DC electric arc furnaces with capacities ranging from 60t to 180t.
In 1989, China Taiyuan Machinery Foundry developed China’s first small DC electric arc furnace and put it into operation. In the same year, a 2000kVA submerged arc DC electric arc furnace in Xuanhua Ferroalloy Plant was put into operation to produce ferrosilicon, ferromanganese, silicon calcium and other ferroalloys.
After entering the 1990s, more and more attention has been paid to DC electric arc furnaces. Shanghai No. 3 Steel Plant, Great Wall Steel Plant, Qiqihar Steel Plant, Jiangyin Yanshan Steel Plant, and Shanghai No. 1 Iron and Steel Plant have successively introduced large DC electric arc furnaces with a capacity of 80~ 100t range.
Baoshan Iron and Steel (Group) Company introduced a set of 150t DC electric arc furnace equipment with double furnace shells (one power source) from France.
There is only one electrode above the DC arc furnace, which is the negative electrode, and the bottom electrode is the positive electrode. Its power supply system is different from the AC electric arc furnace. It is equipped with a rectifier and a reactor. The contacts are installed on the furnace bottom to form a current loop.
The maintenance and life of the contacts are the key issues in the operation of the DC arc furnace. Generally, a copper plate is placed on the bottom steel plate. , In order to facilitate electrical conduction, three layers of magnesia-carbon bricks are built on the copper plate, and then refractory materials are placed on it.