Sintering

Sintering converts iron ore fines — the majority fraction of iron ore that is too small to be charged directly to the blast furnace — into a porous, lumpy material called sinter. Most iron ore is mined and processed as fines (<6 mm); direct charging of fines to the blast furnace would block the gas flow and reduce permeability. The sinter plant is therefore the primary burden preparation step for integrated steelmakers worldwide, processing approximately 70% of all iron ore used in blast furnaces globally.

The sinter plant mixes iron ore fines with coke breeze (fuel), limestone and dolomite (fluxes), return fines, and plant waste materials (dusts, scales, sludges) into a raw mix. This mix is laid onto a moving steel pallet (the sinter strand) and ignited from above by burners. Suction fans below the strand draw air down through the mix, sustaining a narrow combustion front — the "burn-through point" — that travels vertically downward through the bed at ~15–25 mm/min. The strand speed is set so that the burn-through point reaches the bottom of the bed just as the pallet reaches the end of the strand (the "discharge end").

After discharge, the hot sinter cake is crushed, screened, and cooled before dispatch to the blast furnace stockhouse. Return fines (<10 mm) are recycled to the raw mix.