3. Balling technologies

The balling equipment that can be either a disc or a drum produces green pellets in a variable size distribution.

The height and width of the trajectory increase as the ball size increases until the balls hit the scraper blades. After that, they move down and pass under the water sprayers so that they can

The balling disc works in close circuit with the screening step, where pellets smaller than 8 mm or larger than 16 mm are desegregated and the material is recirculated to the balling process.

The balling drum equipment fundamentally consists of an inclined rotating cylindrical shell with water sprays in its inlet end, where the feed material is introduced to make balls. All formed pellets are discharged, regardless of particle size, which is different from the disc where only balls larger than a certain size are discharged. Because of this, the product has to be screened by a roller screen, which has increasingly replaced vibrating screen to extract

The small pellets in the undersize will serve as seeds forming rightly sized pellets [4], the oversize is shredded, and both return to the feed addition point, forming a closed circuit. The water sprays promote nucleation and seed growth in the feed addition zone, while the assimilation process, responsible for the ball growth, occurs along the length of the drum [1].

The drums usually have a length-to-diameter ratio of 2.5–3.5 and very low slope with angles of inclination of the drum axis to the horizontal between 6 and 10�. The optimum rotating speed is generally between 25 and 35% of the critical speed that is the speed in which balls will centrifuge causing their degradation [1]. Speed control is necessary to develop a correct rolling

The rotation speed, the depth of the material in the drum (controlled by scrappers), and the time required for balling are constraints that need to be satisfied. The residence time in a drum

<sup>T</sup> <sup>¼</sup> <sup>0</sup>:0037ð Þ <sup>α</sup> <sup>þ</sup> <sup>24</sup> <sup>L</sup>

nDS (1)

Iron Ore Pelletizing Process: An Overview http://dx.doi.org/10.5772/intechopen.73164 47

find fresh feed.

3.2. Balling drum

undersize and oversize [4].

and tumbling action to produce balls.

where: T is the residence time (minutes).

n is the speed of revolution (revolutions per minute).

S is the slope of the drum (inches/foot length).

α is the angle of repose of the feed material. Figure 4 shows a balling drum arrangement.

is given by Eq. (1):

L is the drum length (feet).

D is the drum diameter (feet).

### 3.1. Balling disc or disc pelletizer

Figure 3 schematically shows a laboratory disc pelletizer. The balling disc basically consists of a pan with a peripheral wall, which rotates with a certain inclination to the horizontal [1]. In general, in a balling disc, the pan angle can be adjusted between 40 and 60 [11].

When the disc rotates, the feed material with less moisture than that required for the pellets formation, is charged to the bottom of the disc, where it get in contact with the water from the sprayers, initiating the nucleation stage. At this stage, the nuclei begin to take the form of small pellets, which by rolling action, occur in the lower section, to the left of the disc, toward the top. As the added ore aggregates unto the surface of the pellets, they increase in size and the coefficient of friction is reduced causing the pellets to acquire a centrifugal force that carries them out of the nucleation zone. This movement takes the pellets to the top of the disc following a semicircular trajectory before returning to the base of the disc [1, 12].

Figure 3. Schematic diagram of laboratory balling disc. Source: Modified by the authors with data from Ball [1].

The height and width of the trajectory increase as the ball size increases until the balls hit the scraper blades. After that, they move down and pass under the water sprayers so that they can find fresh feed.

The balling disc works in close circuit with the screening step, where pellets smaller than 8 mm or larger than 16 mm are desegregated and the material is recirculated to the balling process.
