Balling discs

During the past twenty years the balling disc has found many additional uses for the agglomeration of fine powders. These applications utilize the special characteristics of the pan to economically produce narrowly sized pellets. 

Smaller balling discs with diameters of less than 3 m are usually driven directly with variable speed drives larger discs feature motor, gear reducer, and pinion/ring gear arrangements. 

The more recent development of the balling disc and its unique pattern of movement, as well as the possibility to control agglomerate size, has triggered the interest of many researchers and scientists to investigate the balling disc theoretically and experimentally. 

In this formula n is in revolutions per minute if the pan diameter D is introduced in meters. 

As for balling drums (see Section 4.2.1.3.4), a general formula was developed for the balling disc. Bhrany determined that the following variables are involved  

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Pig 3 15. Flying Saucer Balling Disc showing multi-stepped sidewall design. (Courtesy McDowell Wellman Company.)... 

The balling disc circuit requires about 10% less building space. 

In the overall cost comparison (items 1—4 above), the balling disc circuit was only about 2% lower in cost than the drum circuit. This difference was considered not to be significant and it was concluded that the choice between the two types of circuits must be made on other factors, including personal choice. 

Figure 83 shows schematically the most commonly used apparatus for large scale tumble agglomeration the balling disc (a), balling cone (b), and balling drum All three employ the same size enlargement mechanisms. While... 

While many of these and newer plants are still using balling drums, quite a few of the later installations employ the balling disc to eliminate the need for large closed-circuit recycle loops. 

In contrast to the angle of, for example, balling discs (see Section 4,2.1.4), the inclination of drums is rather small and has almost no influence on power requirement (cos a = 1) and agglomeration behavior. It only serves to provide the required axial transport. As a result of the rather undefined movement of the charge a size classification does not take place and the discharging agglomerated mass features a rather wide particle size distribution. 

Normally, the balling disc is a simple, inclined, and shallow dish which, due to the pattern of material motion, features a distinctive classification effect whereby only the largest pellets discharge over the rim (Figures 99 and 109). To achieve special effects, modified pan designs are available (see Section 4.2.1.4.6). 

Figure 110. Photographs of a typical shallow pan balling disc. (Courtesy of Teledyne Readco, York, Pa., USA)...

Figure 113 depicts patterns of charge movement at different rotational speeds. Normally, balling discs are operated at approximately n = 0.15 Aicru-... 

Ng/ii ) from which the power requirement for the operation of balling discs can be derived. 

In addition to the angle of inclination of the pan bottom / , the angle of repose of the material 7 plays an important role in the development of the pattern of charge motion in the balling disc. Bhrany correlated the tilt angle of pans... 

Froude number DrP-/g should remain constant. Bhrany showed (Table 9) that this is approximately true for a considerable range of actual balling disc operations. 

This means that with increasing pan diameter the loading, i.e. the relative mass in a balling disc, decreases. 

Test results " showed that, as in the case of drum granulators, the specific energy N/C must be kept constant during scale-up of balling discs ... 

Specifically, for the balling disc and cement raw material, Klatt " determined that optimum operating conditions are only found for a narrow band of parameters and concluded that the capacity C (in tons per hour) may be calculated from the pan diameter D (in meters) by... 

Figure 121, The driving power required for balling discs N2ls2l function of pan diameter D. Data points according to Klatt and Ball ...

Y must be experimentally determined during tests in a laboratory balling disc. 

Because the specific energy required for granulation in a balling disc is constant (equation 67) it follows from equation (80) that power input to the disc is also proportionate to the pan diameter squared ... 

Furthermore, from equations (76) and (80) it can be deduced that the average residence time, m/C, in a balling disc remains constant during scale-up ... 

Figure 122. Photographs of typical spherical pellets produced in balling discs...

During early phases of balling disc development several authors reported on the relationships between these parameters. It was found that... 

Table 10. Change of the average pellet diameter in the discharge of balling discs after an increase by 10° (45° 55°) of pan inclination ...

Figure 129. Qualitative relationship between moisture, residence time, or throughput and average pellet size for balling discs " ...

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