How to Choose Electric Arc Furnace?

Electric furnace is the abbreviation of an electric arc furnace. It is a kind of process equipment with scrap as the main raw material, some molten iron or pig iron as the additional part, electricity as the main energy and chemical energy as the auxiliary energy for smelting. Because there is no coking, sintering and iron making process in the process flow, it is also called a short process, which is different from the long process of converter smelting.

Due to the characteristics of low greenhouse gas emission and low energy consumption, the short process has been widely concerned by metallurgical workers and has experienced rapid development in the historical development process. At present, the annual output of converter steel accounts for about 2 / 3 of the world's steel output, and that of electric furnace steel accounts for about 1 / 3 of the world's steel output.

Classification of electric furnaces
According to the power supply mode, the electric furnace can be divided into DC electric furnace and AC electric furnace.

Direct current furnace

DC electric furnace uses DC power as the main energy to provide heat source for the furnace. Generally, there is only one anode on the top of the furnace, forming a circuit with the cathode at the bottom of the furnace. It is characterized by very low electrode consumption, generally less than 1kg / ton steel, and stable molten pool. Because only one electrode and molten pool form arc column, the radiation damage to furnace lining is low, the consumption of refractory materials is relatively low, and the damage of water-cooled plate on the furnace wall is relatively small. The disadvantage is that the bottom electrode is relatively complex, there are several forms of water-cooled, conductive bottom type and needle-like distribution in the bottom refractory, but the service life is relatively short, the maintenance cost is high, resulting in high smelting cost. In addition, the rectifier equipment investment is relatively high, resulting in higher one-time investment.

The direct current electric furnace is not the main equipment in the electric furnace plant. In recent years, new progress has been made in the research of the bottom electrode, which basically solves the problem of short bottom life of the bottom electrode furnace. IThe low consumption of the graphite electrode shows a great advantage in smelting cost. It is expected that the DC electric furnace will be put into production in the new round of electric furnace construction.

Alternating current electric arc furnace

The three-phase alternating current furnace has been used in industrial production for more than 100 years. Its equipment is characterized by the use of three-phase alternating current power supply. When the three-phase graphite electrode contacts with scrap steel, an arc is generated under the action of huge current. The high temperature of the arc is used to melt scrap steel and molten steel. Compared with the direct current furnace, because there are three-phase electrodes, the electrode consumption is higher than that of the direct current furnace. The three-phase electrode has a polar circle, which is relatively close to the furnace wall, and the refractory consumption is relatively high, but the furnace bottom is relatively safer and has a long service life. 

At the beginning of this century, the EAF steelmaking technology has made great progress. On the basis of electric energy as the main energy, auxiliary energy and chemical energy have been introduced. With the development of automatic control technology, power input has increased from ordinary power to high power and ultra-high power, consumption has decreased and productivity has increased. In the case of all scrap steel as raw material, the smelting cycle of this furnace is less than 60 minutes, the power consumption is less than 280kwh / ton steel, the electrode consumption is less than 1.2kg/ton steel, and the annual steel output per nominal capacity has exceeded 10000 tons (i.e. the furnace with a nominal capacity of 100 tons, with an annual steel output of more than 1 million tons), the productivity is greatly improved, and at the same time, the process changes have also derived a variety of furnace types. 

  

 
Common type 3 AC electric furnace

Traditional electric furnace
The traditional electric furnace is the early mainstream electric arc furnace. Scrap steel is added from the top of the furnace, that is, the crown block basket is used to open the furnace cover and scrap steel is added. Each furnace needs to be charged twice to three times or more. The power consumption is relatively high, the electrode consumption is high, the noise is large when melting, the amount of flue gas at the moment of charging is large, the overflow is very obvious, the heat loss is large, the capacity of transformer is large, and the impact on the power grid is relatively large. Generally, mining In addition to the three-electrode holes, the fourth hole of the furnace cover is used for dust removal. The dust removal effect is relatively poor. In areas with strict dust and noise requirements, the way of increasing smoke hood for dust removal or building isolation hood, commonly known as doghouse, is used for secondary dust collection and noise collection. The early electric furnaces in China belong to the traditional type. However, the furnace technology is relatively mature, low failure rate, wide application, strong adaptability of raw materials, but the main technical and economic indicators are general.

Continuous charge furnace

In recent years, the continuous charging type electric furnace is one of the more furnace types newly put into operation. The biggest feature is that the scrap steel is continuously added in the smelting process, the furnace cover can be kept open, the energy input can be kept uninterrupted, the huge energy loss can be avoided, and the smoke and dust can not overflow. The high-temperature flue gas extracted from the furnace passes through the continuous charging tunnel, which also plays the role of preheating the scrap steel The consumption can be reduced by 30kwh-100kwh, and the molten pool is relatively stable, which reduces the huge noise and impact on the power grid produced by the traditional electric furnace during the electrode well penetration period, and the electrode consumption per ton of steel can be reduced by 0.1kg-0.3kg. In addition, in the smelting process, the molten pool is stable, the preheating temperature of scrap is generally not more than 400 ℃, the smelting cycle is shortened, the productivity is improved, the main technical and economic indicators are superior to the traditional electric furnace, but the one-time investment is higher than the traditional electric furnace.

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