Grate Kiln systems consist of three major pieces of equipment. The Grate, the Kiln and the Cooler. The object of the process is to transform the pelletized concentrate into hardened pellets that can be used as blast furnace feed or direct reduction furnace feed.
The Travelling Grate is where pellets are dried and then heated up to a temperature of about 800-900 deg C. The heat used to dry and preheat the pellets is typically hot air pulled from the Kiln and cooler. The recycling of the the hot air from the different zones increases energy efficiencies.
In the Kiln, pellets are brought up to final indurating temps. Rotation of kiln exposes entire pellet bed to heat radiating from the burner resulting in uniform pellet quality. The kiln burner utilizes cooler off gas to heat material bed to nominal of 1200-1340 °C completing the slag bonding and mineral bridging to form pellets.
In the Cooler, pellets are brought down to a suitable temperature for downstream material handling equipment. The gases from the cooler are recycled to the kiln and the grate, resulting in the Grate-Kiln being the most energy efficient system for producing indurated pellets.