Introduction Agglomeration Processes

In contrast to chemical processes, where the feed materials and process aids (catalysts) are in most cases well defined, clean, and consistent, the particulate solids in mechanical process technologies, especially if they are or were derived from naturally occurring raw materials (minerals, concentrates), may vary widely in composition and/ or physical characteristics. As mentioned before (Chapter 3), when agglomeration processes are involved, the surface properties of the particles (macroscopic and microscopic shape, roughness, contamination by adsorption and absorption) are of particular importance and modifications that are sometimes difficult to detect, may require a new set of operating parameters or the introduction of for example, binders, surfactants, or other additives. 

Figure 5.2 Tensile strength of agglomerates. From Smith, P.G., Introduction to food process engineering, Kluwer, 2003, figure 13.22. With kind permission of Springer Science and Business Media.

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. 

In the following, after a short introduction into the sintering mechanisms, sintering as a size enlargement process by agglomeration will be covered. Different parts of the book should be consulted for information on the other meanings of the word. 

To improve the development, design, and selection process, some guidelines will be developed below and in the two subsections that follow this introduction. As wiU be seen and is easily imderstandable, selection of the proper agglomeration equipment, that which is best suited for a specific task, as well as procurement of the optimal peripheral equipment and system layout depend greatly on the application and the industry for which the process and plant are destined. 

These examples clearly demonstrate that the oligomerization process can be easily shifted by organometallic species anchoring on alkoxo oxygens or by the introduction of weak donors such as THF to the reaction (Scheme 32.2). These two synthetic pathways effectively prevent agglomeration and allow the production of well-defined calcium-aluminum species that possess metal-to-metal ratios equivalent to those for spinels. 

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