Influencing particle sizes in bulk solids

In mechanical process engineering, agglomeration refers to the enlargement of particles in a bulk material. As the Latin word "agglomerare" (= to come together) describes, smaller particles or even primary particles are brought together to form larger ones in order to achieve a different particle size distribution. Agglomeration is related to granulation, subject areas that overlap and, depending on the source, are not defined with absolute selectivity. In the context of this analysis, we use the term agglomeration as described above.

Agglomeration can offer more favorable properties for the subsequent process or the end product, for example to produce the desired flowability or the required particle size for a subsequent process. Particles can be agglomerated in various ways, either specifically or as a by-product in a process, using thermal or mechanical methods. Both options are relevant for IBU-tec.

Reasons for Agglomeration Processes

Targeted agglomeration is intended to improve material properties, either for properties in an end product or to simplify or enable downstream processes as an upstream process step. Here are some examples:

  • Improving the handling of powders
  • Increasing the flowability of materials
  • Changing the solubility
  • Facilitation of dosing
  • Increasing the stability of intermediate and end products
  • Adjustment of the particle size to improve the behavior in a subsequent shaping process (e.g. tableting or extrusion)
  • Agglomerates can also have specifications that qualify them as end products or intermediate products

Mechanical Agglomeration

In mechanical agglomeration, raw materials are agglomerated by pressing, rolling or stirring to produce pellets, tablets or similar - which can take place both upstream and downstream of the thermal process. Binders support agglomeration in some cases. For example, agglomerated pellets may be required as feed material for the thermal process in the rotary kiln in order to ultimately achieve the desired product properties or to minimize dust discharge and optimize the yield.

Agglomeration in Thermal Processes

Agglomeration in thermal processes, for example in rotary kilns, can also take place through sintering, even if the melting temperature is not reached during thermal treatment. Such agglomeration can be deliberately induced and be part of the process design. However, it can also occur as a side effect. The latter in particular must often be prevented by careful process control and trials during scale-up. However, if the critical melting or sintering temperatures cannot be prevented because they are necessary for the thermal treatment of the material, agglomeration must be interrupted or reduced by physically designing the process control.

Chemical Agglomeration

Although not directly relevant to processes in our thermal process engineering, chemical agglomeration, in which substances are agglomerated by chemical reaction, must also be mentioned. One possibility is the addition of catalysts or binding agents with an effect on the particle surfaces.

Agglomeration at IBU-tec

At IBU-tec, we often prepare the reactants for the thermal process mechanically, e.g. as agglomeration in Eirich intensive mixers of various sizes. We also carry out agglomeration in the thermal process itself: in rotary kilns of different designs, for example, in order to set certain particle size distributions. Another example is the achievement of defined bulk densities or tapped densities for insulating materials or cathode materials for batteries. Here, a certain amount of material per unit volume is often required, which can be achieved through appropriate particle size distributions. Material systems in which we at IBU-tec have agglomeration experience include: Silica, aluminum oxides for various applications, battery materials or building materials.

Economic Importance of Agglomeration

Agglomerates are particles of cohesive primary particles that together make up the grain sizes and their distribution throughout the bulk material. Larger agglomerates are often more stable when it comes to thermal or physical environmental influences. Agglomeration is of particular economic importance in industries that process bulk materials, such as the chemical and pharmaceutical industries, food processing and ore processing.