The first Grate-Kiln system pellet plant was installed in 1960. The plant took iron ore concentrate and produced superior iron ore pellets (which are spheres of high iron content and uniform quality) for blast furnace and direct reduced iron feed. In the Grate-Kiln system, independent speed control of the grate, kiln, and cooler are available to the operator. This provides process flexibility to adjust to changes in concentrate feed.
Pelletization is comprised of two main stages: (1) agglomeration and (2) induration. micronDuring agglomeration, finely ground particulates (usually 80% passi 44 microns) of ore concentrate (with a moisture content of approximately 9%) are mixed with additives and binders and sent to the balling drums or discs where the forces act between the particle grains to create a bonded pellet referred to in the industry as a “green ball.” The green balls formed during the agglomeration process are then strong enough for transport to the Grate-Kiln induration machine. There the green pellets are subjected to certain varying process zones of drying, preheating, ring and cooling. Each zone varies by temperature and residence time in order to ensure that all bonds and mineral bridging are formed, strengthening and heat hardening each green ball into an indurated pellet product which is then suitable for feed in the steel making process.
Figure Flow of Grate-Kiln System