Requirements for the use of quicklime in steel smelting
Lime plays an important role in the process of steel smelting. As a flux, it participates in multiple key smelting processes and has a significant impact on the quality and smelting efficiency of steel. Therefore, steel plants have specific requirements for the use of quicklime in smelting to meet the needs of complex smelting processes and high-quality steel production.
1、 Activity requirements
The quicklime used in steel plant smelting requires high activity. Activity is an important indicator for measuring the reactivity of quicklime, which reflects the ability of quicklime to undergo chemical reactions with other substances. In steel smelting, high activity quicklime can react more quickly and effectively with impurities such as silicon dioxide in iron ore, forming low melting point slag, thereby promoting the separation of iron and impurities and improving the purity of steel. Generally speaking, the activity level of quicklime used in steel smelting is required to be above 260ml/4N HCl (specific values may vary depending on different steel plants and smelting processes). In order to ensure the high activity of quicklime, it is necessary to strictly control the calcination temperature and time of limestone during the production process. Appropriate calcination conditions can give quicklime a good crystalline structure and a larger specific surface area, thereby improving its reactivity.
2、 Chemical composition requirements
Calcium oxide content
The content of calcium oxide (CaO) in quicklime is one of its main chemical composition indicators. In steel smelting, it is required that the calcium oxide content in quicklime be as high as possible, generally between 60% and 90% (the specific value depends on the actual situation). High calcium oxide content means that quicklime has stronger alkalinity and fluxing ability, which can better react with acidic impurities in iron ore, promote the formation and discharge of slag. At the same time, high calcium oxide content also helps to improve the yield and quality of steel, reducing the adverse effects of other impurities on steel properties.
Impurity content control
(1) Silicon dioxide (SiO ₂): The silicon dioxide content in quicklime should be kept as low as possible, as silicon dioxide reacts with calcium oxide to form high melting point calcium silicate, increasing the viscosity of slag and hindering its flow and discharge. Generally, it is required that the silicon dioxide content does not exceed 2.5%.
(2) Magnesium oxide (MgO): The content of magnesium oxide also needs to be controlled within a certain range. Moderate magnesium oxide can improve the fluidity and stability of slag, but excessive magnesium oxide content can lead to an increase in the melting point of slag, affecting the smelting effect. Usually, the magnesium oxide content is controlled at around 5%.
(3) Sulfur (S) and phosphorus (P): Sulfur and phosphorus are harmful elements in steel, which can seriously affect the quality and performance of steel. Therefore, the sulfur and phosphorus content in quicklime must be extremely low, generally requiring a sulfur content of no more than 0.3% and a phosphorus content of no more than 0.07%.
3、 Granularity requirements
The particle size of quicklime used in steel smelting also has certain requirements. Appropriate particle size can ensure uniform distribution of quicklime in the furnace, sufficient contact with iron ore and other raw materials, and improve reaction efficiency. Generally speaking, the particle size range of quicklime is 20-40mm and 40-80mm (the specific particle size range may be adjusted according to different smelting processes and equipment). Excessive particle size can lead to incomplete reaction of quicklime in the furnace, affecting the effectiveness of the flux; However, a particle size that is too small can easily generate dust, increase environmental pressure, and may be blown out by the airflow inside the furnace, resulting in waste of raw materials. Therefore, in the production and processing of quicklime, it is necessary to strictly control its particle size distribution through processes such as crushing and screening to meet the requirements of steel smelting.
4、 Other requirements
Quality stability
Steel production is a continuous process that requires ensuring stable quality of quicklime. This requires the manufacturer of quicklime to have a strict quality control system to ensure that the chemical composition, activity, particle size, and other indicators of each batch of quicklime meet the requirements of the steel plant, and remain relatively stable during the long-term supply process. Excessive quality fluctuations in quicklime can have many adverse effects on steel smelting, such as unstable furnace conditions and product quality fluctuations. Therefore, steel plants usually establish long-term cooperative relationships with reliable quicklime suppliers.
Supply capacity
The production scale of steel plants is usually large, and the demand for quicklime is also high. Therefore, quicklime suppliers need to have sufficient production and supply capacity to provide the required quicklime to steel plants on time and in quantity. At the same time, it is also necessary to have good logistics and distribution capabilities to ensure that quicklime can be transported to the steel plant in a timely and safe manner, in order to meet the continuity requirements of steel production.
5、 Conclusion
The requirements for quicklime in steel smelting are multifaceted, including high activity, suitable chemical composition, specific particle size, quality stability, and supply capacity. Only quicklime that meets these requirements can play a good role as a flux in the steel smelting process, promoting efficient production and high-quality output of steel. Both steel mills and quicklime manufacturers should attach great importance to these requirements, and ensure that the quality of quicklime meets the standards of steel smelting through strict production control and quality testing, providing strong support for the development of the steel industry. Meanwhile, with the continuous advancement of steel smelting technology and increasingly strict environmental requirements, the requirements for quicklime may also be constantly adjusted and improved, requiring continuous attention and research from relevant industries.
