Electric furnace steelmaking is a method in which scrap steel is used as the main raw material, lime, silicon carbide and recarburizer are used as auxiliary materials, and a strong electric current is passed into the electric furnace for melting and refining. In addition to iron, scrap steel also contains 1 to 2% impurities, mainly carbon, as well as sulfur and phosphorus. The steelmaking process is to remove impurities in iron and refine it into the required composition and content in a molten state. The smelting points of the 100-ton electric furnace are as follows:
- Raw material preparation
（1）Scrap Preparation (Scrap Preheating)
The scrap steel adopts the continuous feeding method. The continuous preheating feeding equipment consists of two parts: the feeding section and the preheating section. The continuous preheating and feeding system composed of fully enclosed scrap preheating transportation, flue gas purification, waste heat recovery and other continuous feeding and continuous preheating. The hot section is sealed with the furnace body of the electric furnace, and the flue gas (primary flue gas) from the fourth hole in the furnace is led to the preheating section through the sealed pipe, where it is in direct contact with the scrap steel in the reverse direction, and the scrap steel is preheated. The heating time is about 20~40min, so that the scrap steel temperature reaches 400~500℃ and then enters the electric furnace, and the flue gas temperature can be reduced to 600~700℃. The project is opened at the contact position between the end of the feeding section and the preheating section, and the exhaust gas from the fourth hole in the furnace (the primary flue gas of the electric furnace) is drawn out by the exhaust fan, and then processed by the bag filter after settling and quenching, and merged into the electric furnace tertiary flue gas Exhaust pipe discharge.
（2）Preparation of powder materials
The particle size of the purchased dolomite is 10~40mm. It is a block material and does not involve the crushing and screening process. It is bagged and transported to the factory area by a truck. Storage; the particle size of the lime purchased from the project is 5~10mm, which does not involve the crushing and screening process. It is transported to the factory area in a bag by a truck, and then manually unpacked and poured into a semi-closed lifting pump, and then lifted to a closed hopper for temporary storage; carbon The particle size of the powder is 2~3mm, which does not involve the crushing and screening process. It is bagged and transported to the factory area by a truck. After being manually unpacked, it is poured into a semi-closed lifting pump and lifted to a closed hopper for temporary storage; the particle size of the carburizer is 0-5mm, does not involve the crushing and screening process, and is transported to the factory in bags by trucks. After manually unpacking, it is poured into a semi-closed lifting pump and lifted to a closed hopper for temporary storage. In the process of unpacking and lifting of chemicals, etc., a gas collecting hood is provided to collect dust, and a set of bag filter is equipped at the end for treatment.
In the production process, lime, carbon powder, dolomite, recarburizer and other bulk materials are pumped into the weighing meter through a closed pipeline for weighing, and then sent to the electric furnace from the furnace top of the electric furnace through the closed pipeline.
- Electric furnace smelting
The smelting of electric furnace steelmaking is an intermittent production process. A smelting cycle consists of smelting furnace → charging → melting period → oxidation period → reduction period → tapping. Electric furnace smelting is generally divided into three smelting periods: melting, oxidation and reduction. Each smelting period and the main chemical reactions are as follows: Melting period:
2FeO+Si→SiO2+2Fe
FeO+Mn→MnO+Fe
CaO+ SiO2→CaO·SiO2
Oxidation period:
C+FeO→Fe+CO (decarburization reaction)
2P+45FeO+4CaO→4CaO·P2O5+5Fe (de-P reaction)
Restoration period:
x[FeO]+y[Me]→MeyOx+xFe (deoxygenation reaction, Me is deoxygenation element)
FeS+CaO→CaS+FeO (desulfurization reaction)
Electric furnace energy is electric energy, and one smelting cycle is about 45min. The scrap steel is preheated by the electric furnace flue gas and then melted in the electric furnace. The melting time is about 10~20min. When the temperature in the electric furnace reaches 600~800℃, the melting of the electric furnace scrap steel is completed, and it is about to enter the oxidation period.
During the oxidation period, after the temperature in the electric furnace continues to rise to 1400~1500℃, oxygen is continuously fed into the furnace through a water-cooled oxygen lance. In the furnace, enough oxygen is transferred to the metal liquid surface, so that slag with sufficient fluidity and basicity can be generated after adding a slag-forming agent later. When oxygen is introduced, lime and dolomite weighed in a certain proportion by a hopper are added from a closed pipe, so that carbon, silicon, manganese, sulfur, phosphorus and other impurities in the molten steel are oxidized and combined with lime and dolomite to form slag.
During the reduction period, carbon powder and lime are added, among which carbon powder is mainly used for desulfurization, and lime is mainly used as a slag-forming agent. In this process, part of the iron oxide is reduced to metallic iron, and the sulfur in the molten iron is removed to form slag (ie, steel slag). The molten steel after removing the slag is sent to the refining furnace for out-of-furnace refining according to the smelting requirements.
Every time a furnace of molten steel is smelted in the electric furnace, the steel slag in the furnace must be removed. There is a furnace door at the lower part of the electric furnace. When the slag is scraped, the furnace door is automatically opened, and the steel slag carries part of the molten steel and is led out from the furnace door in liquid form, and the material is discharged in the semi-closed steel slag cooling area. The temperature of the unloading steel slag is about 1300~1400℃, and the steel slag is sprayed with water through the water spray pipe arranged at the top of the steel slag cooling area to cool down and change the strength of the steel slag, so that the temperature is reduced to 400~500℃, and the steel slag is changed. break easily. The cooled steel slag is transported by truck to the steel slag storage yard of the plant for pretreatment.