Dry granulation and roller compaction
Continuous dry granulation is an established process in the pharmaceutical industry. Today, it is not only applied for moisture-
and temperature-sensitive materials but also for large-volume solid-dosage products. In comparison with classical wet-granulation
techniques, a sophisticated drying system is not required for processing. This elimination of the drying system avoids large
investments for production equipment and space and lowers manufacturing costs. An additional benefit to having an one-unit
operation is its suitability for installation in a one-floor operation. The dry granulator can be fed with a single intermediate
bulk container (IBC). To enable a continuous process, an enlarged power-feed hopper can be used with a level sensor and adequate
holding capacity to enable the change-out of additional IBCs without interrupting the process.
On the discharge side, a simple plug-flow pneumatic conveying system can be used to transfer the resulting granulation into
a receiving IBC for future blending and processing. This reduction in handling equipment can further reduce the capital costs
with a dry-granulation system.
Furthermore, for large-volume throughputs, the fast roller-compaction process is paramount to efficient processing. This efficiency
enables the production of different products and product batch sizes with one single machine (4). The market already offers
various dry granulators, which can be described by the arrangement of the two compaction rollers. They can be mounted horizontally,
vertically, or on an incline.
Depending on the supplier, the rollers differ in width, diameter, and surface properties. Furthermore, roller compactors are
distinguished between fixed-gap and moveable gap compactors, whereas the moveable roller compactors are state of the art.
Only moveable roller compactors, however, ensure homogeneous ribbon porosity at constant compaction pressure.
The granulation step, where the ribbons are transferred into final granules, is usually integrated in the roller-compaction
equipment and is performed in one or two steps (5, 6). With this in mind, manufacturers introduced a dry granulator with an
electromechanical roller drive and massive roller shafts mounted in a horizontal manner.
With this newly developed machine, minimal time is needed to achieve a steady state during process start-up, and parallel
gap is ensured during the whole production time. The proportional-integral-derivative (PID) loop control minimizes the gap
deviations during processing and enables constant granule porosities. The granulation step is achieved using a conical sieve,
which gently transforms the ribbons into final granules even at high material throughputs. Due to different sieve setups,
the desired particle-size distribution can be obtained.