What is Electric Arc Furnace?

What is Electric Arc Furnace?

What is Electric Arc Furnace? The Electric arc furnace steelmaking process uses electricity as its energy source.  Electric arc furnace (EAF) steelmaking primarily utilizes electric arc heat, reaching temperatures as high as 4000℃ in the arc zone. The smelting process generally consists of a melting phase, an oxidation phase, and a reduction phase. Within the furnace, both oxidizing and reducing atmospheres can be created, resulting in highly efficient dephosphorization and desulfurization.

Types of Electric Arc  Furnaces

Electric arc furnaces can be categorized based on the form of the electric arc into three-phase electric arc furnaces, consumable electric arc furnaces, single-phase electric arc furnaces, and resistance electric arc furnaces (submerged arc furnace). 

The body of an electric arc steelmaking furnace consists of a furnace cover, a furnace door, a taphole, and a furnace stack, with the furnace bottom and walls constructed using basic refractory materials or acidic refractory materials.

Electric arc steelmaking furnaces are classified into ordinary power electric arc furnaces, high-power electric arc furnaces, and ultra-high-power electric arc furnaces based on the transformer capacity allocated per ton of furnace capacity. 

Electric arc steelmaking involves inputting electrical energy into the electric arc steelmaking furnace through graphite electrodes, using the electric arc generated between the electrode tip and the furnace charge as the heat source for steelmaking. 

Electric arc furnaces utilize electrical energy as a heat source, allowing for the adjustment of the furnace atmosphere, which is particularly advantageous for melting steel grades containing a high proportion of easily oxidizable elements. Shortly after the invention of electric arc steelmaking, it was applied to the smelting of alloy steel and has since undergone significant development.

Typically, EAF steelmaking is produced using basic oxygen arc furnaces.  Steelmaking EAF is commonly used to produce carbon structural steel, tool steel, and alloy steel. These steels are of high quality and uniform performance. 

At the same carbon content, EAF steelmaking exhibits superior strength and plasticity compared to open hearth furnace steel.

EAF steelmaking primarily uses scrap from similar steel grades as raw material, though sponge iron can replace some of the scrap. Chemical composition and alloy element content are adjusted by adding ferroalloys.
Steelmaking with scrap as the raw material in EAFs requires less capital investment than the blast furnace-converter method. 

Additionally, advancements in direct reduction have provided metallized pellets to replace most scrap in EAFs, significantly promoting EAF steelmaking. 

Currently, there are about 1,400 large EAFs worldwide, with ongoing development towards larger capacities, higher power, and automation through electronic computer control. The largest EAFs have capacities of up to 400 tons. 

In foreign countries, EAFs larger than 150 tons are almost exclusively used for producing plain steel, with many nations' EAF steel output comprising 60–80% low-carbon steel. Due to limitations in electricity and scrap availability, China mainly uses EAFs for producing steel and alloy steel.

Short Process Steelmaking Technology

Short process technology refers to processes that deviate from the traditional long process (also known as conventional processes), which includes the blast furnace—converter—continuous casting (or mold casting) route. The short process in EAFs is represented by the early 1990s American EAF—thin slab continuous casting process. 
Since its introduction, this process has garnered significant attention within the steel industry. Compact EAF short processes are a typical example. 

Compared to traditional processes, EAF short processes offer several advantages:

1. Investment is more than halved compared to the blast furnace—converter route. For instance, the actual costs of the EAF thin slab short process in countries like the United States and Japan are about a quarter of those for traditional processes.Production costs are lower, and labor productivity is higher. Steel conglomerates typically consume around 23 kJ/t of energy per ton of steel from ironmaking through hot rolling coil production, whereas EAF steel plants using scrap as raw material in short processes consume nearly 10 kJ/t, reducing energy consumption by approximately 60%.

2. With annual scrap production exceeding 300 million tons, the development of EAF short processes plays a crucial role in promoting environmental protection, recycling scrap, and purifying the environment in metallurgical plants. 

3. As a result, developed countries prioritize the development of compact EAF short processes. In recent years, although China's EAF process development has received attention, the expansion of EAF short processes should be cautious and appropriately managed to avoid recklessness, given the current lack of advantages in electricity and scrap resources, meaning no cost advantage. 

Larger capacity furnaces offer higher thermal efficiency, reducing electricity consumption per ton of steel while also significantly lowering average equipment investment per ton of steel, thus reducing steel costs and improving labor productivity.

For example, a furnace with a capacity of 320 tons has a productivity more than 100 times higher than a small furnace of 1.5 tons. In certain special cases requiring large volumes of molten steel, only large-capacity arc furnaces can meet the demands. 

Many countries adopt large-capacity arc furnaces; currently, there are over 30 EAFs with capacities exceeding 180 tons, the largest being 400 tons. Baosteel's arc furnace in China has the largest capacity at 150 tons.

Development of Electric Arc Furnace

P.L.T. Héroult of France developed an alternative energy source to coal by utilizing the high temperature of electric arcs from electrodes between 1888 and 1892, inventing the electric arc furnace for industrial direct smelting. Initially, electric arc furnaces were only used for the production of calcium carbide and ferroalloys. It was not until 1906 that they were developed for steelmaking, enabling the economical and large-scale recycling of scrap steel. Electric arc furnaces convert electrical energy into thermal energy through the electric arc occurring between the end of the graphite electrode and the furnace charge, melting the furnace charge and completing subsequent high-temperature metallurgical reactions. Due to its use of electrical energy, it is convenient to adjust the atmosphere inside the furnace, making it possible to smelt various types of alloy steels, including those containing easily oxidizable elements. With the development of the electric power industry, continuous improvements in process equipment, and advancements in smelting technology, electric arc furnaces have become increasingly widely used, with production capacity and scale growing larger. In the 1930s, the maximum capacity of electric arc furnaces was 100t, in the 1950s it was 200t, and by the early 1970s, electric arc furnaces with a capacity of 400t had been put into production.

Especially over the past 50 years, the technical performance of electric arc steelmaking furnaces has gradually improved, and production costs have significantly decreased. In developed countries in Europe and America, the proportion of electric furnace steel has exceeded 50%.

The development of modern electric arc furnace (EAF) smelting technology has progressed with the times. In the 1960s and 1970s, the focus was mainly on the development of ultra-high power (UHP) power supply and related technologies. High-power electric arc furnaces (HP) and ultra-high-power electric arc furnaces (UHP) are relative to the general regular-power electric arc furnaces (RP). They are mainly distinguished by the transformer capacity allocated per ton of furnace capacity, which has been increasing in recent years. This means that the thermal energy input into the electric arc furnace per unit time has increased significantly, significantly reducing melting time, thereby improving production capacity, reducing electrode consumption, reducing heat loss, and reducing electric energy consumption. As a result, while production capacity is further increased, costs are also significantly reduced.

High-pressure long arc operation, water-cooled furnace walls, water-cooled furnace covers, foam slag technology, and the use of external heat sources for melting assistance have been widely adopted in conjunction with ultra-high power electric arc furnaces. Ladle refining and oxygen intensification have also been adopted. In the 1980s, the development of LF and EBT technologies made the modern electric arc furnace steelmaking process, which includes electric arc furnace smelting and external refining, essentially mature. It is worth noting that since then, the focus has shifted from whether to use direct current or alternating current power supply to the utilization of secondary combustion and sensible heat of flue gas, namely the issue of scrap preheating. Different scrap preheating methods have led to different types of modern electric arc furnaces, including ordinary electric arc furnaces with scrap preheating using material baskets, flue shaft furnaces with holding claws, double-shell electric arc furnaces, and Consteel electric arc furnaces.

Currently, the equipment and production technology of electric arc furnaces are still under continuous development.

Key Characteristics of Electric Arc Furnaces

Electric arc steelmaking furnaces primarily utilize electrical energy as their source of power. Through the discharge of electric current between graphite electrodes and the furnace charge, an electric arc is ignited, generating temperatures ranging from 2000 to 6000°C or higher. This process melts the scrap steel raw materials via arc radiation, temperature convection, and thermal conduction. During the majority of the melting process, the high-temperature heat source is surrounded by the furnace charge, resulting in relatively minimal heat loss due to high-temperature exhaust gases. Consequently, the thermal efficiency of electric arc steelmaking furnaces surpasses that of other steelmaking equipment, such as converters. Furthermore, electric heating facilitates precise control over furnace temperature, allowing heating operations to be conducted under any desired conditions, including oxidizing or reducing atmospheres, atmospheric pressure, or vacuum, according to specific process requirements.

The electric arc furnace steelmaking process is characterized by a short workflow, simple equipment, convenient operation, relatively easy pollution control, low construction investment, small footprint, and does not require the complex ironmaking system necessary for converter steelmaking.

Electric arc furnace steelmaking exhibits strong adaptability to furnace materials. It primarily utilizes scrap steel as the raw material, but can also accommodate molten iron (from blast furnaces or cupola iron), sponge iron (DRI), or hot briquettes (HBI), as well as solid and liquid iron-containing materials such as pig iron blocks.

Owing to the controllable atmosphere within electric arc furnaces for steelmaking, the operations for slag adjustment or replacement are relatively feasible. Moreover, within the same operational system, complex process operations such as melting, decarburization, dephosphorization, degassing, inclusion removal, temperature control, and composition adjustment (alloying) can be accomplished. Electric arc steelmaking allows for intermittent production, offering flexibility in switching product varieties within a certain range. Furthermore, modern electric arc furnaces can extensively utilize auxiliary energy sources, such as heavy (light) oil injection, pulverized coal, natural gas, etc. Consequently, the electric arc steelmaking process exhibits strong adaptability, operational flexibility, and widespread application.

Electric arc furnaces are not only capable of smelting high-quality steel with low phosphorus, sulfur, and oxygen content, but also allow for alloying with various elements (including lead, boron, vanadium, titanium, and rare earths, which are prone to oxidation), thereby producing a range of premium and alloy steels such as ball bearing steel, stainless acid-resistant steel, tool steel, electrical steel, heat-resistant steel, magnetic materials, and special alloys.

Although electric arc furnace steelmaking possesses numerous advantages, due to the current issues related to scrap steel and electricity costs in China, it cannot compete with converter steelmaking in the production of general steel and long-term products. Electric arc furnace steelmaking predominantly holds a dominant position only in the specialized steel production sector, characterized by small batches, a wide variety, and a high proportion of alloys.

Currently, some international short-process electric furnace manufacturers generally employ high-output power electric arc furnaces. Furthermore, the traditional three-phase operation process with a reduction period has gradually been replaced by combined process technologies such as external furnace refining, electric arc furnaces, and the public auxiliary facilities and equipment are also more comprehensive and rational. The proportion of electric furnace steel production worldwide is increasing year by year.

China is a developing country, with its fundamental infrastructure just commencing development. The era of large-scale scrap steel recycling has not yet arrived, and furthermore, the development of electric power in China is uneven. Currently, electricity prices remain at a relatively high level. Consequently, the development speed of electric arc furnace steelmaking in China is constrained, and it has not progressed as rapidly as converter steelmaking. Although the total volume of electric furnace steel is increasing, the proportion of electric furnace steel production to total steel production has been declining annually, contradicting the global trend of electric arc furnace development.

With the development of China's electric power facilities and the accumulation of scrap steel resources, coupled with the intensified national efforts in environmental protection and mineral resource management, the development trend of electric arc furnace steelmaking in China is expected to enhance. By then, the electric arc furnace steelmaking technology in China will undergo more comprehensive development.