Balling drums

Larger amounts of clay are being produced in diy powdered form [Anon., Ceramics Forum International, 67(7-8), 330-4 (1990)]. After grinding, the clay is agglomerated to a flowable powder with water mist in a balling drum. 

The published data on design, scale-up, and performance characteristics of the balling drum are substantially fewer than those available for the disk. This presumably reflects the fact that the latter is a more versatile agglomer-ator it is, however, more difficult to control for a stable operation. 

The experimental results of Capes and Danckwerts (C6) and Kanetkar (K1), using a balling drum and a disk granulator, respectively, have shown that the thickness of the snowballed layer is approximately independent of the initial size of the seed pellet. It then follows that the rate of pick up of the loose particulate material is proportional to the surface area of the granule hence,... 

Fig. 3.6. Semi-logarithmic plot of agglomerate growth rate in laboratory balling drum as a function of moisture content. (Data of Capes [2] sand particles of average sizes 70/im (o), 97 jum (A) and 49 jUm ( ).)...

Fig. 3.7. Effect of particle size and size distribution on the growth rate of iron ore pellets in a laboratory balling drum [13]. (By permission The Institution of Mining and Metallurgy.) [Hematite ore, minus 300 mesh (o) and minus 120 plus 200 mesh ( ). ]...

Some typical iron ore balling drums are described in Table 3.6. The L/D ratio of these drums is generally in the range 2.5 to 3.5, somewhat higher than that for fertilizer granulation drums. 

Rotational rates, often below 20% of the critical speed in the past, are averaging 30% or more today and are trending toward 50% for fertilizer granulation [29]. The data in Table 3.6 indicate that iron ore balling drums are operating at around 50% of the critical speed. 

In a recent quantitative comparison [32] of iron ore balling drum and disc circuits, using the two systems operating in parallel in the same plant with... 

M. Cross, Mathematical model of balling-drum circuit of a pelletizing plant, Ironmaking Steelmaking, No. 3 (1977) 159—169. 

C.E. Capes, R.D. Coleman and W.L. Thayer, The production of uniformly-sized spherical agglomerates in balling drums and discs, Int. Conf. Compact, and Consolid. of Part. Matter, Proc., 1st, London, 1972. 

ASTM tumbler test, 36 balling circuit control, 75 balling drums, 78... 

Figure 79. Average pellet diameter d as a function of agglomeration time (measured in numbers of drum revolutions). Conditions 42.5 vol. % moisture, limestoiJe powder balling drum, batch operation ...

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... 

Figure 97. Diagram depicting the operating principle of the balling drum...

Agglomeration (or balling, granulating) disc (or pan) Although similar to the balling drum, the pan features distinct differences in growth phenomena and... 

Balling drums represent the most simple type of equipment for growth agglomeration by tumbling. They are typically used in industries processing large amounts of bulk solids where in the relatively crude and rough environment unsophisticated machinery performs best. 

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. 

Meloy has investigated and analyzed the basic function of a balling drum for the purpose of estimating the feasibility of scale-up. The study determined that the following variables are involved ... 

Figure 105. Sketches depicting different patterns of charge motion in balling drums ...

Figure 107. Typical balling drum circuit for iron ore pelletizing ...

Sufficient nuclei must be produced in the drum at all times to replace the pellets that are removed from the circuit, and the growth rate per pass must be such that the required production capacity of green balls is consistently maintained. Therefore, the rate of pellet production must be stabilized and the balance between material in the drum and recycle rate must be kept constant. Nevertheless, balling drum circuits tend to surging the reasons for this are only recently beginning to be understood. 

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