Agglomeration disc

The well-defined motion and growth patterns in agglomerating discs allows some generalized statements in regard to agglomerate quality. Characteristics that are of particular importance are ... 

Dust (-0.5 mm) Tumble agglomeration (disc, drum, fluid bed), briquetting, compacting, pelletizing (extrusion) Build-up, caking... 

Crowth/Tumble Agglomeration Disc (Pan)/Drum/Mixer... 

Other advantages claimed for the disc graniilator include low equipment cost, sensitivity to operating controls, and easy observation of the granulation/classification action, all of which lend versatility in agglomerating many different materials. Dusty materials and Chernies reactions such as the ammoniation of fertilizer are handled less readily in the disc granulator than in the drum. 

These incorporate membranes fabricated from insoluble crystalline materials. They can be in the form of a single crystal, a compressed disc of micro-crystalline material or an agglomerate of micro-crystals embedded in a silicone rubber or paraffin matrix which is moulded in the form of a thin disc. The materials used are highly insoluble salts such as lanthanum fluoride, barium sulphate, silver halides and metal sulphides. These types of membrane show a selective and Nemstian response to solutions containing either the cation or the anion of the salt used. Factors to be considered in the fabrication of a suitable membrane include solubility, mechanical strength, conductivity and resistance to abrasion or corrosion. 

With many materials, agglomeration may be achieved by heating as a result of which softening occurs in the surface layers. For the formation of porous metal sheets and discs, high temperatures are required. 

We have been Agglomeration material. Size of disc Operating conditions... 

The addition of fines to a powder system allows a larger top size of particle to be agglomerated due to the attendant increase in cohesive forces caused by a decrease in surface mean particle diameter and increase in agglomerate density. Thus, although eqn. (1) indicates a top size of about 150 pm for monosized particles with aqueous binders, the top size of feed for industrial disc pelletizers is usually higher at 30 to 50 mesh (300 to 600 /zm) with the provision that at least 25% should be finer than 200 mesh (75 /zm) [7]. Other liquids with surface tensions lower than that of water, or liquid/ solid systems in which the particle surface is imperfectly wetted, require finer particle sizes to make successful balling possible. 

Fig. 3.9. Schematic diagram of an inclined disc agglomerator. (In many applications, subsequent screening is not required because of size classification on the disc see Fig. 3.10.)...

Agglomerate size is controlled primarily by retention time on the disc and the amount of added binder liquid. The relationship between these variables is shown qualitatively in Fig. 3.11. Residence time and hence pellet size can... 

Available models range from laboratory units 1 ft (0.3 m) diameter to production models greater than 20 ft (6.1 m) diameter. Pietsch [24] has surveyed scale-up for inclined disc agglomerators and offers the following relationships for the approximate design of a unit of diameter, D, in metres ... 

The rotational speed of inclined discs is normally considered in relation to the critical speed, Nc (min-1), of the agglomerator ... 

Most manufacturers quote dimensional, capacity and installed power data for their range of disc agglomerators. One such set of data is given in Table... 

The above relationships may be used for preliminary design of inclined disc agglomerators. Each application should be analyzed individually, however, with small scale test work in which the behaviour of the material in question can be compared with that of materials whose plant-scale agglomeration characteristics are known. 

A well-known addition to the basic machine is a separate reroll ring beyond the rim of the main disc (see Fig. 3.14). Formed product-size agglomerates are ejected over the rim into this peripheral ring where they are further smoothed and formed into more spherical shapes. A surface layer of fines, such as coke breeze in iron ore green balls or an anti-caking dust to improve storage properties, may be added in the reroll ring. 

Finally, an agglomerator design combining features of both the inclined disc and the horizontal drum should be noted. This machine, known as a cone pelletizer, is described in Fig. 3.17 and Table 3.4. As the name implies, the vessel is in the form of a truncated cone and the scraped inner surface has a bowl-like shape as build-up takes place during operation. The cone... 

O. Lofgren, C.-G. Nilsson and R. Odman, Operational experiences on balling circuits with drums, discs, and roller seed screens, in K.V.S. Sastry (Ed.), Agglomeration 77, AIME, New York, 1977, pp. 425-435. 

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