Metso is supplier of both Straight Grate and Grate Kiln pellet plants
Metso is the only supplier in the world that has both the Straight Grate and the Grate Kiln process for pelletizing. We can help our customers to determine which process is the best for their ore, fuel and pellet requirements. Our systems combine the best features of both technologies to provide the most modern plant and to produce pellets at the lowest cost and highest quality.
- Pellet plants sized from 1.2MTPA to 9MTPA
- Engineering and design of complete plants from ore receiving to pellet discharge
- Supply of the main pelletizing and indurating equipment
- Optimum processing of all types of ore including Magnetite and Hematite
Metso pelletizing plants have a faster start up and better reliability than other plants in the industry.
Iron ore can be upgraded to a higher iron ore content through beneficiation. This process generates iron ore filter cake which needs to be pelletized to be used in the steel making process. Also during the processing of high grade iron ores which don’t need beneficiated, fines which are generated can be pelletized and used instead of being disposed of.
Iron Ore Pellets are formed from beneficiated or run of mine iron fines. The iron is usually ground to a very fine level and mixed with limestone or dolomite as a fluxing agent and bentonite or organic binders as a binding agent. If the ore is a Hematite ore, coke or anthracite coal can be added to the mix to work as an internal fuel to help fire the pellets. This mixture is blended together in a mixer and fed to balling discs or drums to produce green pellets of size typically about 9-16mm. The green pellets are then fed to the induration machine. Both straight grates and grate kilns dry the pellets out in a drying section, then bring the pellets up to a temperature of about 800-900 °C in a preheat zone, then finish the induration process at roughly 1200-1350 °C. The pellets are then cooled to a suitable temperature for transporting to a load out facility. Both processes recycle the heat from the pellet back through the process to aid in energy efficiency and decrease fuel usage.
Both processes can be used to generate almost any type of desired pellet chemistry, from direct reduction pellets (DR pellets) to blast furnace pellets. By adjusting the amount of fluxing agent or limestone added, pellets can be made that are anywhere from acid (or non-fluxed) pellets to heavily fluxed pellets.
How it works
For both processes the plants consist of many pieces of equipment. The major areas or processes in the plant are mixing, balling, indurating and product handling.
Mixing is where the properly ground ore is combined with binding agents like Bentonite or organic binders, fluxing agents like limestone or dolomite, and if the ore is a Hematite with coke or anthracite coal as an internal fuel. The mixing is done usually in vertical or horizontal high intensity mixers to achieve a homogenous blend of ore and additives.
From mixing the filter cake is sent to the balling area where the ore is agglomerated on balling discs or balling drums into green(or unfired) pellets. Both drums and discs ball the ore to about 9-16mm size. Drums typically have very high recycle rates so have a screening circuit to screen out undersize and oversize pieces to be put back through the drum. Discs usually do not have a separate screening circuit at the disc.
Green pellets are then transported to the induration process. Pellets that are oversized or undersized and any fines generated during the balling or transporting process are screened right before entering the induration machine and sent back to the mixer or the balling area. The on-size pellets are then fed to the induration machine. Both straight grates and grate kilns dry the pellets out in a drying section, then bring the pellets up to a temperature of about 800-900 °C in a preheat zone, then finish the induration process at roughly 1200-1350 °C. The pellets are then cooled to a suitable temperature for transporting to a load out facility. Both processes recycle the heat from the pellet back through the process to aid in energy efficiency and decrease fuel usage.
For more detail on each process see individual pages