Model of raw iron smelting in blast furnace
Cast iron is produced by blast furnace (BF) technology shown in the figure above (also known as “traditional metallurgical technology”) with iron ore raw materials (clump ore, sinter ore, pellets), coke and flux materials (limestone, dolomite, quocsite). The blast furnace casting process removes impurities and deoxidizes iron ore to obtain liquid iron. The liquid iron is removed from the furnace through the iron outlet holes and then cast into a mold to produce pig iron or the liquid iron will be transported to the steel furnace to produce steel billets.
Along with pig iron, cast iron slag (BFSlag) is made up mainly of oxides and calcareous soils in iron ore and flux materials and coke ash. The slag is periodically removed from the furnace through the slag outlet holes. The volume of cast iron slag generated with the level of 0.300 - 390 kg of cast iron slag/ton of liquid iron. For cast iron plants with large capacity blast furnaces (V furnace >1,000 - 5,000 M3) in the world, the level of production of cast iron slag is only from 230 - 290 kg of slag/ton of liquid iron.
Cast iron slag contains various minerals, about 70% silicate and aluminum silicate, 14% spinel, 4% free oxide and 9% other minerals. Cast iron slag is divided into 2 types: i) Acidic slag is mainly SiO2 (accounting for 50 - 60%); ii) Basic slag containing alkali oxides such as CaO, Al2O3, MgO...
2. Steel slag production process in steel production Transfer furnace and Electric furnace
- The process of creating steel slag in the Transfer Furnace (BOF): Liquid iron of the Blast Furnace, oxygen and reducing agents (soda, lime, calcium carbide, dolomite...) are loaded into the BOF Furnace to produce steel. The steelmaking process has created a slag amount of about 150kg of steel slag/ton of liquid steel. Mineral composition of BOF steel slag includes olivine (CaO.RO, SiO2), Rhodonite (3CaO.RO, 2SiO2) dicalcium silicate (2CaO, SiO2) and tricalcium silicate (3CaO, SiO2).
- The process of creating steel slag in the Electric Arc Furnace (EAF): The raw materials for steelmaking by the EAF furnace are scrap steel (imported or purchased domestically) and reducing agent (mainly lime). Currently, in the world as well as in Vietnam, up to 50% of liquid iron is used from Blast furnace instead of scrap steel, resulting in this application has reduced electricity and electrode consumption for steelmaking by EAF furnace. EAF furnace steelmaking process has created a slag amount of about 100-150kg of steel slag/1 ton of liquid steel.
3. Solutions for managing, processing and using cast iron and steel slag in the world:
Due to the large amount of iron and steel slag generated annually during the production of iron and steel, many countries have managed, researched, processed, and used cast iron and steel slag to bring economic benefits to the producers. steel enterprises and effectively contribute to environmental protection.
- Processing and using cast iron slag: From the results of research on chemical and mineral composition of cast iron slag, countries have processed blast furnace cast iron slag in two ways: i) Water cooling produces granulated slag; ii) Slow cooling by air produces clumps of large particle size. Blast furnace slag in European countries is mainly processed for cement production (60%), sugar making (24%), internal use (14%) and other purposes (2%).
- Processing and using steel slag: Countries have processed steel slag by crushing, then separating from scrap steel (iron filings) and iron oxide to reuse for sintering ore production and steelmaking. the rest is used for different fields, mainly road construction (43%) and internal use (19%).
For blast furnace slag, more than 80% is used for cement production (more than half has been exported), 15% for road construction, 1% for civil works and 3% for other purposes; For steel slag used for road construction 32%), civil works 29%), reuse for steel production 22%, internal road construction 5%, cement production 3%, land reclamation 3 % and the rest for other purposes. Here are some practical solutions applied by advanced manufacturers in the world:
a/ Japan
b/ European countries:
4, Advice for steel manufacturers in Vietnam about iron slag, steel slag
- Handling raw materials for iron smelting: Input materials for iron smelting (iron ore, coke, anthracite bran for blast furnace blasting and other raw materials) need to be treated to ensure quality before loading. into the blast furnace. Increasing the Fe content of iron ore by 1% reduces coking coal consumption by 2% and increases pig iron production by 3%. This solution also reduces the production cost of cast iron and reduces dust and GHG emissions (CO2).
- Treatment of scrap steel (pressing and mincing scrap steel) before loading into an electric furnace (EAF) will increase equipment efficiency, reduce fuel and energy consumption (oil and electricity consumption) per unit of production. Products. As a result, the solution directly reduced costs and indirectly reduced dust and GHG emissions.
- Solutions on processing and using cast iron slag and steel slag of Vietnam Steel industry
In addition to implementing the "Technical and technological solutions" to limit the emission of iron slag and steel slag mentioned above, it is necessary to synchronously implement "Solutions for processing and using iron slag and steel slag" with some contents. stand behind:
- Implement research - development (R&D) projects related to the management, processing and use of cast iron and steel slag;
- Promote and propagate the use of products made from cast iron and steel slag;
- Steel enterprises must support establishments that have demand for products processed from iron slag and steel slag. In which, focus on road works in rural areas;
- Continue to invest in building iron slag and steel slag processing plants with a capacity of over 1 million tons of slag products of all kinds/year from social capital sources, mainly investment capital from Steel enterprises.