Grate-Kiln iron ore pelletizing system provides process flexibility

Features

There are two main processes for producing iron ore pellets: The Grate-Kiln system and the straight grate system. In the straight grate system, a continuous parade of grate cars moves at the same speed though the drying, induration and cooling zones. Any change in one section effects the residence time in another.
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.

Benefits

The use of control systems employing expert system designs increases the opportunity to
optimize plant performance on a continual basis. By being able to correlate changes
continually, the plant can anticipate operational changes and make corrections. Metso’s
implementation of this type of control technology for Grate-KilnTM pellet plant will
make it possible for operators to increase capacity, reduce fuel and power consumption,
and reduce maintenance costs.

Pelletization process

Because the induration of the pellets occur in the rotary kiln, the pellets produced in a Grate-KilnTM system are consistently of higher quality than those produced in a straight grate.
The rotary kiln provides constant mixing of the pellets, bringing all the pellets to the same temperature. In a straight grate, the pellets at the top of the bed are “over cooked” and those at the bottom are “under cooked”. Higher quality means fewer fines, better reducibility and less variation in compression strength.

Ported kiln operation

By injecting air under the bed of pellets in the rotary kiln, complete oxidation can occur in magnetite pellets prior to the annualar cooler. This patented development by Metso, in addition to lowering fuel consumption, significantly improves pellet quality. Full oxidation at induration temperatures produces stronger pellets, while maintaining reducibility. This capability is unique to the Grate-Kiln system.

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