Pelletisation

Pelletisation converts iron ore concentrates — very fine particles of 50–80% Fe content, typically below 150 µm — into spherical pellets of 8–16 mm diameter suitable for blast furnace or direct reduction furnace use. Where sintering agglomerates ore fines on-site at the steel plant, pelletisation is predominantly carried out at or near the mine — pellet plants are often located at ports or mine-head facilities and supply pellets to multiple steel customers worldwide.

The pelletisation process has two distinct stages: balling (forming wet green pellets) and induration (hardening the pellets by heat treatment). In balling, the moist ore concentrate (typically 8–10% moisture) is fed to a rotating disc or drum, where capillary forces cause fine particles to accrete around nucleus particles, building up spherical green pellets over 5–15 minutes. These green pellets are fragile and must be carefully handled before induration.

Induration heats the green pellets to 1,200–1,350 °C to sinter-bond the iron oxide grains together, driving off moisture and any organic binders and creating a strong, dense pellet. The three main induration technologies — shaft furnace, straight-grate (travelling grate), and grate-kiln — each achieve this but differ in equipment layout, throughput capacity, and fuel efficiency.

Global pellet production is approximately 550 million tonnes per year. Pellets are an essential feedstock for direct reduction plants (DRI) and are increasingly substituted for sinter in blast furnaces at plants that have closed their sinter plants due to environmental restrictions.