Executive Summary
This is the first annual report for the IFPRI project 37 Powder-Binder Agglomeration. The aims of this project are to:
- Define the controlling groups for each of the following classes of granulation process (1) binder dispersion, wetting and nucleation (2) consolidation and growth (3) attrition and breakage;
- Use appropriate models to link these groups to key product attributes eg. size, size distribution, density (porosity);
- In each case, qualify the models for the effects of complicating powder-binder interactions eg. dissolution, reaction, drying.
The report summarises progress in both wetting and nucleation, and consolidation and growth. Drop penetration time and dimensionless spray flux are proposed as two controlling groups for wetting and nucleation. The drop penetration time, which depends mainly depends on formulation properties, is a promising tool for studying nucleation processes. Preliminary studies show that penetration time varies widely, particularly with binder viscosity. Combining the existing models for drop penetration (Denesuk, 1993) and nuclei growth (Schaafsma, 1998b) will create a more complete picture of nuclei formation and morphology, and the effect of material properties. Ex-granulator experiments demonstrated different nucleation regimes from drop-controlled nucleation to caking. In the drop controlled regime, each drop forms a single nucleus and the nuclei distribution can be controlled by controlling the drop size distribution form the spray. A single dimensionless group, the dimensionless spray flux, characterises the main process parameters with respect to spraying. An experimental plan and methodology for studying wetting and nucleation is presented.
For granule growth and consolidation, a regime map of granule growth behavior is proposed based on granule deformation during collision and the granule liquid content measured as the maximum pore saturation. The granule deformability on collision is represented by a deformation number, which is a ratio of granule impact energy to the plastic energy absorbed per unit strain. Granule growth regimes such as steady growth, induction, nucleation, crumb, and slurry are defined. This regime map qualitatively explains the variations in granulation behavior. Laboratory drum granulation experiments were used to test the regime map. Increasing granule yield stress by decreasing particle size and increasing binder viscosity caused the system to move from steady growth to induction behavior as predicted by the regime map. Preliminary validation with literature data was also encouraging. More work, however, is required to better quantify the boundaries between different growth regimes and to investigate the effect of process agitation intensity. This regime map has great potential to help design and control granulation systems, because it is based on properties of the powder/binder system that can be measured or estimated without performing any granulation tests.