How to Reduce Electrode Consumption in Electric Arc Furnaces? ​

How to Reduce Electrode Consumption in Electric Arc Furnaces?

In recent years, with the vigorous development of China's electric furnace steel industry and the demand for energy conservation, consumption reduction, and cost reduction in production, especially in the cost reduction of electrode consumption in electric arc furnace steelmaking, experts, scholars, and frontline workers in related fields at home and abroad have conducted extensive research, exploration, and practice, and several relatively effective processes have been formed, which are summarized as follows:

2.1 Surface Modification Research on Graphite Electrode Melting System

Through the development of surface alloying processes for molten system materials, systematic research has been conducted on the surface alloying process of graphite electrodes and the kinetics of graphite electrode oxidation. A kinetic model for graphite electrode oxidation has been established. Comparative experiments have demonstrated that surface alloying treatment using the melting method can reduce the oxidation loss of graphite electrodes.

2.2 Optimizing Power Supply System Parameters

Power supply parameters are a crucial factor affecting electrode consumption. Choosing a secondary side voltage of 410V and a current of 23kA can minimize the consumption at the front end of the electrode.  Stabilizing and smoothing the electric arc furnace equipment and improving the operation process can effectively reduce the mechanical wear of the electrode.  Practical results have shown that through the optimization of the power supply parameter system and continuous exploration to reduce electrode mechanical wear, the electrode consumption at Lianyuan Iron and Steel's No.1 Steelmaking Plant has decreased from 5.0kg/t to 3.81kg/t. Selecting optimal power supply parameters, stabilizing and smoothing the electric furnace equipment, and improving the process can effectively reduce the unit consumption of electrodes.

2.3 Water-cooled Composite Electrode

The water-cooled composite electrode is a new type of electrode developed abroad in recent years. Using water-cooled composite electrodes in steelmaking can generally reduce electrode consumption by 20% to 40%.  The water-cooled composite electrode consists of an upper water-cooled steel pipe section and a lower graphite working section, with the water-cooled section accounting for about 1/3 of the entire electrode length.  Since the water-cooled steel pipe section does not undergo high-temperature oxidation (graphite oxidation), it reduces electrode oxidation, while maintaining good contact between the water-cooled steel pipe section and the holder.  Due to the water-cooled thread design between the water-cooled section and the graphite section, the shape is stable and free from damage.  It can withstand high torque, improving the strength of the electrode interface, thus significantly reducing electrode consumption.

2.4 Anti-oxidation Mechanism of Water Spraying on Graphite Electrodes

Regarding the consumption of electrodes during the smelting process, the focus of reducing electrode consumption should be placed on reducing tip consumption, thereby significantly reducing the unit consumption of electrodes per ton of steel.  In the consumption of graphite electrodes, side oxidation accounts for approximately 50%, with a maximum of 70%.  Over the years, extensive research has been conducted both domestically and internationally to prevent side oxidation of graphite electrodes, and various technical measures have been implemented with success, gradually reducing the consumption of graphite electrodes in electric furnaces.  Drawing on existing achievements, the technical measure of spraying anti-oxidation solution on graphite electrodes has been adopted. Experimental research has shown that this technique significantly prevents side oxidation of graphite electrodes, increasing the oxidation resistance index of graphite electrodes by 6-7 times, and the technical measures are feasible.  The water spray electrode protection method is a new electrode protection technology pioneered by Japan.  This technology involves using an annular water spray device below the electrode holder to spray water onto the electrode surface, allowing the water to flow down along the electrode surface. Above the electrode hole on the furnace cover, an annular tube is used to blow compressed air onto the current surface, atomizing the water.  After adopting this method, the consumption of electrodes per ton of steel has been reduced to 1.9-2.2kg. At the same time, due to the effect of atomized steam, the lifespan of refractory furnace covers has doubled.

This new technology was first applied to ultra-high power electric furnaces.  The direct water-spraying electrode method is simple in device, easy to operate, and safe.  It can achieve a significant cooling effect with a small amount of water.  However, the main problems encountered in actual industrial production are:

1) There are many broken electrodes.  Some of them are caused by improper operation, while others may be due to localized chilling of the dry electrode by water, resulting in uneven temperature and internal stress, which makes it prone to breaking during improper operation.

2) The small holes on the spray ring are often blocked by cold slag and molten steel.  Its cooling effect is mainly in the range from the upper part of the furnace cover to the spray ring where the electrode is located.  It does not increase power consumption or hydrogen content in steel.  High-temperature oxidation of the electrode surface is an important factor causing electrode wear.  Water-cooled electrodes are an effective way to reduce electrode consumption.  Different water cooling methods have different effects on the heating conditions and surface temperature distribution of the electrode, each with its own characteristics and shortcomings.  Currently, Canada, Germany, the United States, and other countries have conducted research on composite water-cooled electrodes, and Japan has conducted water-spraying electrode tests. These are methods that use indirect or direct water cooling of electrodes to reduce electrode surface oxidation, thereby reducing electrode consumption.

2.5 Hollow Electrode

Electrodes are also one of the main raw material consumptions in ferroalloy smelting.  In recent years, Western Europe and Sweden have begun to use hollow electrodes in the production of ferroalloy submerged arc furnaces.  Hollow electrodes are generally self-sealing electrodes, which are cylindrical in shape with an inner shell that is properly pressurized with inert gas.  The hollow design of the electrodes improves the baking conditions of the electrodes, increasing their strength.  Generally, using hollow electrodes can save 30% to 40% of the electrodes, with the best case being up to 50%.  The use of hollow electrodes not only improves the usage conditions of the electrodes but also brings a series of benefits to ferroalloy smelting, such as directly using powder ore for smelting and blowing reducing powder agents through the hollow electrodes.

2.6 DC Electric Arc Furnace

DC electric arc furnace is a new type of smelting electric arc furnace that has been newly developed in the world in recent years.  According to published information from abroad, DC electric arc furnace is the most effective technology to reduce electrode consumption, which can generally reduce electrode consumption by about 40% to 60%. In a DC electric arc furnace, the negative pole of the rectifier is connected to the graphite, while the positive pole is connected to the bottom electrode of the furnace (usually composed of water-cooled metal plates and refractory materials). The graphite electrode, metal molten pool, bottom electrode of the furnace, and rectifier form a current loop, and an arc is struck between the graphite electrode and the metal molten pool.

2.7 Permanent Electrode

In recent years, developed countries have been leveraging their comprehensive technological advantages to develop permanent electrodes.  A permanent electrode refers to a water-cooled ceramic electrode made of conductive cermet materials through special processing.  It exhibits extremely low oxidation, sublimation, and fracture losses. The permanent electrode developed in Sweden has been tested on a 1.5-ton electric arc furnace, and a ceramic electrode (with a segment length of 500mm) has a service life of over one year.

2.8 Improve Electrode Quality to Reduce Natural Wear and Tear

The electrode must conduct high current, operate at high temperatures, and endure mechanical vibration, all under harsh working conditions. Therefore, strict requirements are placed on the quality of the electrode, which must:

① Good conductivity, meaning a low resistivity;

② Capable of withstanding high temperatures and possessing high mechanical strength;

③ Good oxidation resistance, with a high temperature threshold for initiating strong oxidation in the air;

④ Requirements such as regular geometric shapes.

2.9 Electrode Surface Coating Technology

Electrode coating technology is a simple and effective method to reduce electrode consumption, typically reducing it by around 20%.  Commonly used electrode coating materials include aluminum and various ceramic materials, which exhibit strong oxidation resistance at high temperatures and can effectively reduce the oxidation consumption of the electrode's side surface.  The Ceracon coating developed in Japan has been tested by some manufacturers and has been shown to not only reduce electrode consumption but also reduce steelmaking power consumption by 20-30 kW·h/t of steel.  The main method of electrode coating is spray coating and grinding, which is a simple and easy-to-implement process and is the most commonly used method for protecting electrodes.

2.10 Impregnated Electrode

Impregnating electrodes typically involves immersing the electrodes in chemical agents to allow chemical reactions between the electrode surface and the agents, thereby enhancing the electrodes' resistance to high-temperature oxidation. The use of impregnated electrodes can reduce electrode consumption by approximately 10% to 15% compared to regular electrodes.