Compaction and Granulation

What is Compaction?

In compaction processes, the primary goal is to increase the bulk density of powders and solids. In particular, small, fine particles are connected by compression to larger particles. It may also be the goal that high air fractions should be removed from the bulk materials, so that lower volumes can be generated at the end. Pure compaction processes are used primarily in the chemical industry.

Depending on the nature of the starting material of the compaction is still followed by a crushing or milling process. Thereby, the compacted, but partly coarse agglomerates (flakes, ribbons, needles) are to be divided into smaller particles with a certain particle size distribution (PSD).Compacting with roller presses is a highly efficient way of compacting bulk materials. The starting material is compacted in the roller compaction via two counter-rotating rollers. A special case of compacting is briquetting. Here, the roller surfaces are provided with pockets, so that the briquettes are formed during pressing.

Depending on the plastic deformability of the starting material, endless flakes, but also fine needle agglomerates, are produced by pressing. Needle agglomerates are e.g. generated during the compaction of silicates.

Figure 1: The main regions of the compaction zone in roller compaction

The slugs are comminuted in the following crushing process granules desired shape. This results in bulk materials with higher densities (lower volume), better flow and dosing properties and certain particle size distributions. Alexanderwerk roller compactors are used in compacting (and granulation) processes in the following applications:

  • Compaction & Granulation of pharmaceutical materials
  • Compaction & Granulation of battery batterie mass
  • Compaction & Granulation of catalysts
  • Compaction & Granulation of color pigments
  • Compaction & Granulation of enzymes
  • Compaction & Granulation of natural / biological bulk materials
  • Compaction & Granulation of food
  • Compaction & Granulation of coffee powder
  • Compaction & Granulation of minerals
  • Compaction & Granulation of ores
  • Compaction & Granulation of lignite
  • Compaction & Granulation of various salts
  • Compaction & Granulation of fertilizers
  • Compaction & Granulation of brown coal
  • Compaction & Granulation of metal and metal oxide powders
  • Compaction & Granulation of used nuclear fuel elements (U3O8)
  • Compaction & Granulation for the enrichment of nuclear fuel elements (UF2)
  • Compaction & Granulation of airbag powders
  • and many, many more …

What is (Dry) Granulation?

Granulation is mainly used in pharmaceutical or similar applications. During granulation, fine, poorly flowing powders, and the agglomeration of particles, produce larger particles called granulates. The main aim of granulation in pharmacy is to achieve good meterability of the bulk material, since the active ingredients (APIs) in the non-granulated state are difficult to compress into tablets in the subsequent process step (tableting). In principle, two different processes for the production of granules can be used.

  • Wet granulation
  • Dry granulation

In so-called wet granulation, binders are added in liquid form to the powders. The binder, usually based on water or alcohol, acts as an adhesive, so that individual particles are connected to each other via the liquid bridges. Wet granulation also requires a downstream drying process to reduce the moisture in the granules. Both the addition of binders and the drying process can have a negative impact on the quality of the granules and the active ingredients.

In dry granulation, granules of the desired quality (density, particle size distribution, porosity) are generated by compacting and subsequent comminution. An addition of binders with subsequent drying process is not required here. Basically, two methods are common:

  • Slugging
  • Roller compaction

In so-called slugging, large tablets are pressed from the starting material. These are then crushed using mills. The huge disadvantage of slugging is above all the non-continuous process, as well as the uneven compression of the poor, flowable starting material. This is also reflected in the final granules, as slugged granules are characterized by an unstable and difficult-to-control quality. Slugging is no longer regarded as “state-of-the-art” and therefore rarely used.

Roller compaction has become very important in recent years. It produces stable granules by continuously compressing powders between two counter-rotating rollers. The agglomerates, also called flakes or ribbons, are then comminuted via a downstream comminution unit into well-flowing and easy-to-dose granules. Among other things, Alexanderwerk roller presses of the WP series are characterized by their particularly gentle comminution. Furthermore, the compression process is unique, as the vertically arranged rollers, in conjunction with a special control logic, continuously produce slugs of consistent thickness and density, which is essential for a consistent granule quality.

Structure of a Roller Compactor

The basic structure of all  Alexanderwerk roller compactors, in particular of our WP Pharma Series can be described as follows:

  1. Hopper with stirrer for receiving the raw product
  2. Patented Combi-Vent-Feeder System for Optimizing Blend Uniformity (BU)
  3. Feeding unit with vacuum zone
  4. Vertically arranged rollers for pressing the raw material
  5. Separation possibility of uncompressed material
  6. Flake Crusher for controlled pre-shredding of flakes
  7. Integrated 2-stage granulating unit with 2 rotor fine granulators (RFGs)
Figure 2: Basic structure of an Alexanderwerk roller compactor (WP Pharma series)