Electric furnace steelmaking
The broad types of steelmaking electric furnaces include electric arc furnace, induction furnace, electric slag furnace, electron beam furnace, etc.
Usually electric furnace steel refers to steel produced in a basic electric arc furnace, so this article focuses on the electric arc furnace (EAF).
There are two types of electric arc furnaces: direct current electric arc furnaces (DC-EAF) and alternating current electric arc furnaces (AC-EAF). Since DC arc furnaces can reduce the use of refractory materials, are more energy-efficient, have lower noise levels, and halve flicker, their applications are increasing and developing rapidly.
DC Arc Furnace
For DC electric arc furnaces, new technologies such as eccentric bottom tapping, water-cooled furnace wall, water-cooled furnace cover, oxygen-burner, and scrap preheating are more suitable and have better effects.
The 1990s was a period of rapid development of DC-EAF. In industrialized countries with high scrap steel recycling rates (such as the United States, Japan, and South Korea) and developing countries with insufficient power supply (such as China and Southeast Asian countries), more than 100 electric arc furnaces with a capacity of more than 50 tons were built in a few years. Among them, the more representative ones are Japan’s 240t DC-EAF and the United States’ 280t DC-EAF.
The DC arc furnace has a graphite electrode on the top of the furnace. The arc is stable and concentrated, with the characteristics of good molten pool stirring and uniform temperature distribution in the furnace, and the melting efficiency is improved.
The typical feature of a DC electric arc furnace is that the graphite electrode on the top of the furnace is the cathode, and the anode is connected to the furnace bottom. This requires that the furnace bottom must be conductive. The conductive materials that can be used for the furnace bottom are mainly: (1) conductive refractory materials (ABB); (2) metal components: including steel rod electrodes (Irsid-Clecim), steel sheet electrodes (VAI), multiple steel needle electrodes (GHH) and copper-steel composite water-cooled bottom electrodes.
Except for the refractory materials used in the bottom of the DC arc furnace, which have special requirements, the refractory materials used in other parts are very similar.
AC Electric Arc Furnace (AC-EAF)
The most widely used type of AC electric arc furnace (AC-EAF) is the ultra-high power electric furnace (UHP-EAF). This type of electric arc furnace has the advantages of high production efficiency, slow furnace wall loss, shortened melting time, improved thermal efficiency, reduced power consumption, and stable arc.
Therefore, ultra-high power electric furnaces were widely used in the late 1970s. In recent years, UHP technology has developed towards large capacity and high power. The power of some UHP-EAFs abroad has reached 1000kVA/t or even higher, which is called ultra-high power electric arc furnace. In order to better play the advantages of UHP, technologies matching ultra-high power have been developed successively, mainly including water-cooled furnace wall, water-cooled furnace cover and long arc foam slag smelting technology.
All arc furnaces above 30t in Europe are equipped with water-cooled slag furnace walls and water-cooled furnace covers. More than 70% of arc furnaces in Japan are equipped with water-cooled furnace walls. Western Europe and the United States have also adopted water-cooled slag furnace walls. The use of water-cooled furnace wall technology can extend the service life of the furnace wall to more than 2,000 furnaces, reduce refractory consumption by more than 60%, increase productivity by 8% to 10%, reduce electrode consumption by 0.5kg/t, and reduce production costs by 5% to 10%. The use of water-cooled furnace covers can extend the service life of the furnace covers to 4,000 times.
Electric furnaces can be divided into trough-type tapping electric arc furnaces and eccentric bottom tapping electric arc furnaces (EBT) according to the type of steel tapping, and their structures are shown in Figure 1. Since the eccentric bottom (EBT) tapping port can expand the water cooling area, reduce the cost of refractory materials and reduce the amount of slag discharged from the ladle, its application is gradually increasing.
Electric furnace steelmaking uses scrap steel, metallized pellets, etc. as raw materials, and mainly uses arc heat to make scrap steel into new steel through a series of metallurgical chemical reactions under the condition that the temperature in the arc action zone is as high as 4000℃. The smelting process is generally divided into melting period, oxidation period and reduction period. Not only can an oxidizing atmosphere be created in the furnace, but also a reducing atmosphere can be created, so the efficiency of dephosphorization and desulfurization is very high.
In recent years, with the continuous changes in electric furnace steelmaking technology, including higher operating temperatures, larger and larger steelmaking electric furnace capacity, stronger temperature shocks, and increasingly improved alloy steel quality, higher requirements have been placed on refractory materials.
