Pellet (steel industry)
This enrichment process improves the iron concentration and imparts specific chemical and mechanical properties that enhance the efficiency of steel production.
The pelletizing of powdered iron ores was first introduced at the end of the nineteenth century, utilizing tar as a binding agent, comprising 1% by weight.
[1] This method involved firing the mixture in a rotating drum to create pellets suitable for blast furnaces, while also facilitating the removal of undesirable elements such as sulfur and arsenic through the emitted fumes.
Pellets produced through this method demonstrated faster reduction rates compared to calibrated ores and agglomerates made from the same feedstock.
In 1926, an industrial pilot plant was constructed by Krupp in Rheinhausen to explore the potential of this pelletizing technology.
However, the plant was later dismantled to make way for the installation of a large-scale grate sintering line, which emerged as a competing process in the industry.
In the United States, this technique was employed to process fine concentrates from the Mesabi Range during World War II.
The development of pelletizing fine magnetite ores, which typically have less than 44 mm in size and are around 85% iron, began around 1943 with support from the University of Minnesota.
The following data illustrates pellet production over several years:[5] Pellets are produced directly at the extraction site by mining companies and are marketed as a distinct product, unlike agglomerates which are typically manufactured at blast furnace sites through the mixing of iron ores from various sources.
The production process for pellets can vary significantly depending on the local characteristics of the iron ore, and some facilities may include additional stages, such as arsenic removal.
These processes ensure that the pellets are produced to meet specific quality standards and can withstand the demands of handling and transportation.
Due to their inherent fragility, which persists despite the binder used, pellets are generally more suitable for processing in a cooking oven rather than a consumption plant.
With a vaporization temperature of 907°C, zinc is effectively removed during the roasting process, making pelletizing a suitable method for this application.
[3] This unusual behavior is attributed to sulfur's strong affinity for the metallic iron that forms on the pellet surface, which inhibits the penetration of carbon.
[16] Due to iron's superior absorption characteristics, a substantial portion of gas transport happens at the iron/iron oxide phase boundary.
This ratio helps in assessing the relative basicity of the pellets, which is important for optimizing their use in blast furnaces and other metallurgical processes.
This is due to the fact that a high hematite content can cause the pellets to disintegrate, compromising their integrity and usability in the reduction process.
Additionally, they are prone to swelling when exposed to lime, especially when the basicity index (i = CaO / SiO2) exceeds 0.25, which may potentially cause issues in a blast furnace.
Self-melting pellets are appreciated for their enhanced performance in blast furnaces but require consideration of the trade-offs in production efficiency.
[6] To cater to specific customer needs, manufacturers have developed alternative pellet types that offer distinct properties and performance characteristics:[6] These alternative pellet types are designed to address different operational requirements and enhance the flexibility of iron-making processes.
