Tumble growth agglomeration

Characteristic Agglomeration by tumbling (growth) Agglomeration by pressure Agglomeration by other methods ... 

Fig. 5.42 Conceptual model depicting how a small particle Is Incorporated Into the surface of a (wet) agglomerate in a high density tumbling bed of particles during tumble/growth agglomeration.

The basic mechanism of tumble/growth agglomeration is shown in Fig. 6.1. Adhesion of individual particles to each other or to solid surfaces is controlled by the competition between volume and surface related forces (see also Section 5.4). To cause permanent adhesion, certain criteria must be fulfilled. The most important of all is that any system force (e.g. caused by gravity, inertia, drag, etc.) must be smaller than the attraction forces between the adhering partners. According to Fig. 6.2 and Equation 6.1, the ratio between the binding forces Bj(x) and the sum of the active components of all ambient forces F y(x) is a measure for the adhesion tendency T ... 

Fig. 6.3 Schematic representation of typical equipment for size enlargement by tumble/ growth agglomeration (left) and the post-treatment steps required to obtain a final product (right). Left, from the top Inclined disc (pan), drum, continuous mixer, batch mixer, fluidized bed.

The limitation to small dimensions of the particles forming the agglomerate and the fact that, in most cases, only temporary bonds are formed constitute major drawbacks of all tumble/growth agglomeration methods. If particles are larger than required, crushing to achieve the necessary fineness is normally uneconomical. 

With the exception of very few applications where particles are so small that they naturally agglomerate in the dry state, tumble/growth agglomeration methods utilize binders. Even if materials contain binder components inherently, this constituent is so obvious in the bulk mass that the process can not be classified as binderless. 

In tumble/growth agglomeration distinct process steps can be defined in which (see also Chapter 6, Fig. 6.3) ... 

In a broad sense, process equipment for tumble/growth agglomeration itself may be divided into ... 

Fig. 7.1 Sketches explaining the different processes taking place during tumble/growth agglomeration [B.42],...

The problems encountered in mathematical modeling of tumble/growth agglomeration do not relate to the theories, formulas, and possibilities to solve the ever more complicated equations. With modem computing possibilities, a whole series of assumptions can be introduced into the model equations and responses to certain imaginary process conditions can be predicted. However, the real system often produces unexpected results intermittently or even consistently without offering a clear indication of why such deviations occur. Introduction of new mathematical methods, such as, for example, fuzzy logic or chaos theory, produce more complicated model equations and closer to life results but still are not able to serve as unequivocal bases for control schemes. 

Measurement and analysis of the power consumption during tumble/growth agglomeration in a drum have been carried out by many researchers [e.g. 7.4, 7.5]. 

As compared with the structure of tumble/growth agglomerates (see Chapter 6, Fig. 

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