(76d) Influence of Liquid Binder Dispersion on Agglomeration in an Intensive Mixer

In industrial scale mixer granulation, liquid binder is usually sprayed onto the agitated powder bed by means of a nozzle in order to start the agglomeration process. The early stage of this process, where granule nuclei are formed and grow, is not well understood. As it is desirable to model the agglomeration process right from the beginning for the purposes of control and modeling, this nucleation step is therefore an important field of interest.

To investigate the influence of binder droplet size on the nucleation stage of the agglomeration process, experiments were carried out with lactose and water in an intensive mixer. Water was sprayed in to the mixer with different nozzles to vary the size of the produced droplets. As a comparison, water was also directly poured into the turning mixer. Samples of the produced nuclei were taken at specific time intervals and analysed for size and water content. As the experiments were focused on examining short granulation times, the first samples were taken after only half of the water was added.

Particle size distribution and liquid distribution in the wet granule samples were analyzed. It was found, that the droplet size of the binder liquid has great influence on agglomerate size and binder distribution at short mixing times, with increasing time, the mechanical stresses acting in the mixer becomes more and more dominating in the process. Preliminary comparisons with single drop penetration tests are carried out in an attempt to correlate drop size to penetration time and also to produced nuclei size.

In conclusion this paper studies the effect of different drop size conditions and subsequent spray flux on the kinetics of the nucleation and early stage of the agglomeration process. The context of these findings for agglomeration in an intensive mixer is examined.