Pelletizing & Steel Making
Pelletizing
Iron ore pellets are produced from iron concentrate or run-of-mine iron fines in an integrated plant consisting of several key process areas: mixing, balling, induration, and product handling.
Mixing:
Ground iron ore is blended with binding agents (e.g., bentonite or organic binders), fluxing agents (e.g., limestone or dolomite), and, for hematite ores, coke or anthracite coal as an internal fuel source. High-intensity vertical or horizontal mixers ensure a homogeneous mixture of ore and additives.
Balling:
The resulting mixture, or filter cake, is formed into green (unfired) pellets on balling discs or drums, typically ranging from 9 to 16 mm in diameter. Drum balling circuits operate with high recycle rates, using screening systems to separate undersized and oversized material for reprocessing, while balling discs generally do not include separate screening.
Induration:
Green pellets are screened to remove oversize, undersize, and fines, which are returned to the mixer or balling sections. Pellets of the correct size are fed into induration machine, typically straight grate or rotary kiln systems. Pellets are first dried, then preheated to 800–900 °C, and finally indurated at 1200–1350 °C. After induration, pellets are cooled before transport to the load-out facility. Both systems incorporate heat recycling to improve energy efficiency and reduce fuel consumption.
Steel Making
Iron ore typically contains iron combined with impurities such as sand and clay, collectively called gangue.
The iron is primarily present as iron oxides, which must be separated from the gangue and converted into pure iron through pyrometallurgical which involves oxidation-reduction processes.
Worldwide, steel is mainly produced via two routes: the Blast Furnace–Basic Oxygen Furnace (BF–BOF) route and the Direct Reduced Iron–Electric Arc Furnace (DRI–EAF) route.
Blast Furnace (BF–BOF) Route:
The blast furnace is a vertical shaft furnace that produces molten pig iron by injecting pressurized air at the base, which reacts with iron ore, coke, and flux introduced from the top. Pig iron is subsequently refined into steel in a Basic Oxygen Furnace (BOF). Although BF–BOF remains dominant, its use has declined due to challenges such as declining coke quality, limited scrap metal availability, and environmental concerns.
Direct Reduction (DR–EAF) Route:
Direct reduction converts iron ore—lumps, pellets, or fines—into solid state using a reducing gas. DR processes are classified as gas-based or coal-based, depending on the gas source.
Direct Reduced Iron (DRI), or sponge iron, is produced at relatively low temperatures (~1,000 °C) using reformed natural gas or carbon from natural gas or coal. The Midrex and HYL processes are the most widely used DR technologies.
Both sponge iron and pig iron are semi-finished intermediates requiring melting and purification. Excess carbon is removed in either a Basic Oxygen Furnace (BOF) or an Electric Arc Furnace (EAF) to produce steel products such as slabs, blooms, or billets. The BOF primarily refines pig iron, while the EAF mainly processes sponge iron.
• Electric Arc Furnace (EAF):
Heats materials using an electric arc and chemical reactions with oxygen and fuel to produce steel.
• Basic Oxygen Furnace (BOF):
Blows oxygen through molten pig iron at ~1,600 °C to convert it into steel efficiently.