Granulator, solids drum

Since densification of the granules in the drums and disks is brought on by gravitational force, there is a definite upper limit on both the rate and the extent of compaction that is attainable. This is specially true in the case of fine solids. In general, compaction of the granules occurs concurrently with their growth, and it is seldom possible to exercise independent control over these two actions of the pelletizer. 

T. Gluba, Drum granulation conditions for raw material with different particle size distributions. Handbook of Conveying and Handling of Particulate Solids, Elsevier Science, B.V., 2001, pp. 717-723. 

Feed material, consisting of fresh and recycled particles, may be introduced by a belt conveyor, a chute, pipe or similar devices. Liquid phase may be introduced either before or immediately after the solids enter the cylinder. In iron ore balling, premoistened wet filter cake usually constitutes the feed but water sprays may also be located inside the drum for moisture addition to aid balling control. Although water is the usual wetting agent, various solutions and slurries may be used in mixed fertilizer granulation. These may... 

Drum and belt drying and solidification systems are discussed below. This equipment is capable of forming granular products directly from fluid pastes and melts, without intermediate preforms, by drying or solidification on solid surfaces. Drum and belt systems offer an alternative to the dispersion methods (such as the prilling of sulphur, fertilizers and resins and the spray granulation of clays) described in Chapter 7. 

The preneutralizer slurry is pumped at a controlled rate to a rotary-drum, ammoniator-granulator there it is distributed onto a rolling bed of recycled solids. The most commonly used metering system for the preneutralized slurry is a variable-speed centrifugal pump with automatic control from a magnetic flowmeter. Some plants have had success with a magnetic flowmeter and automatic control valve of a special ball type. 

The acid and the ammonia or ammoniating solution were sparged under the rolling bed of solids in the drum with a spacer arrangement, as shown in Fig. 24.16. With the proper balance of liquid and solid feeds, granulation occurs as a result of the rolling action in the action in the drum, and it is completed, with hardening, in a rotary-drum dryer. 

In the early 1950s another pressure agglomeration technique emerged as an alternative to the already conventional tumble agglomeration methods in mixers, drums, pans, and suspended solids granulators. This technology uses roller presses which can be easily adapted to a wide range of capacities and materials. 

Although there is philosophical agreement that the sample weight analyzed should equal the weight of the solid dosage unit, there has been no recent discussion of a minimum number of samples to be taken out of the blender or drums of powder/granulation. 

One of the earliest drum mixers that was applied in the fertilizer industry for agglomeration (granulation) produced a curtain of solid materials as sketched in Fig. 7.24. If acid and ammonia are sprayed onto the curtain and/or added by sparger tubes granulation occurs during ammoniation. The co-processing (ammoniation and granulation) makes this technique a most beneficial one. 

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