Roller Screens for Pellet Plants

Metso's Roller Screens are designed to optimize the pelletizing process, ensuring high plant efficiency and superior pellet quality. With decades of expertise in iron ore pelletizing, Metso offers advanced and reliable equipment that enhances capacity and maintains a low environmental footprint.

Ensures pellets with excellent and consistent metallurgical and physical properties

Optimal plant performance with regard to productivity, energy efficiency, process stability and product quality

Designed by the technology leader, focusing on the entire pelletizing process

Lowest TCO due to longevity and maintainability of the equipment and service support

Importance of green pellet quality and size distribution

The quality and size distribution of green pellets are crucial for the gas permeability of the pellet bed in the induration machine. Properly sized green pellets ensure uniform gas flow through the pellet bed, which is essential for consistent heat distribution and efficient induration. This results in high-quality pellets with excellent physical and metallurgical properties, reduced energy consumption and improved process stability.

Green pellet screening concepts

In general, the green pellets can be screened at two locations: directly under the green pelletizing discs or drums and directly before feeding them onto the pallet cars of the travelling grate or onto the preheat grate. The general set-up of the green pellet screening is mainly determined by the plant capacities:

For plants < 4 Mtpy normally no screening is foreseen directly after balling, therefore a Double Deck Roller Feeder (DDRF) is installed at the feed station of the furnace to separate over- and undersize pellets.

Modern pellet plants with capacities > 4 Mtpy are equipped with Single Deck Roller Screens (SDRS) under the balling equipment to size the green pellets and relieve the downstream green pellet handling by the burden of off-spec pellets. These plants can have different screening configurations at the feed station.

Single Deck Roller Screens in the green pelletizing area

Metso's Single Deck Roller Screens (SDRS) provide a reliable and efficient solution for screening undersize pellets directly after the discharge of pelletizing discs or drums. The screens provide excellent screening efficiency and can be delivered with single roll drive and chain drive, each with its own benefits. Important for the performance of the plant is the arrangement of these screens to:

reduce overall drop-height through direct charge to the collecting belt
optimize pellet distribution on the collecting belt with movable screens

Roller screen options in the feed area of the induration furnace

Single Deck Roller Screens (SDRS)

Economic solution in plants with roller screens in the green pelletizing area. Removes once again under-size pellets and ensures uniform pellet distribution to the furnace.

Double Deck Roller Feeder (DDRF)

Standard set-up in smaller pellet plants without screening in the green pelletizing section to screen out over- and undersize pellets and feed the pellets evenly to the furnace.

In the recent years plants with bigger capacities and roller screens in the pelletizing section were equipped with DDRF to further improve the pellet size distribution.

Bi-layer feeders

A relatively new solution is the bi-layer feeders, a advancement of the DDRF with the target to homogenize and improve the pellet quality. It utilizes the bi-layer principle to segregate pellets into two distinct layers in the pellet bed. Larger pellets are charged in the upper section.

Advantages of the bi-layer concept

The bi-layer feeder significantly enhances pellet bed properties in the induration furnace, resulting in better average Cold Crushing Strength (CCS) and Abrasion Index figures. It performs two key functions:

Size Segregation. Removes fines on the lower deck, ensuring uniformity in the production line.
Layering. Larger pellets are placed in the upper section, exposed to the firing temperature for a longer time. Smaller pellets, requiring less heat, are placed underneath.

Enhancing performance with VisioPellet

With Metso's VisioPellet system the green pellet size distribution can be further improved. Based on online green pellet size measurement directly under the pelletizing discs or drums the process control system optimizes relevant process parameters like the rotation speed and inclination of pelletizing discs, feed rate, and the addition of additives or water.

The pellet size distribution data can be used to determine a medium pellet diameter and optimize the gapping of the Bi-Layer Feeder, which is even more significant with varying raw material properties such as grain size, moisture, and different ore sources.