Shrinkage behavior of FCC catalyst droplets in a spray drying process

FCC catalyst is spray dried at several nozzle pressures and air inlet temperatures. The following physical properties of the obtained powder are measured: water content, mean particle size and particle size distribution, tapped bulk density and pore volume. All the investigated properties are directly related to the initial droplet size (distribution) and the shrinkage behaviour and crust formation of the droplet during drying. Next to the
final particle size distribution, shrinkage also determines directly the porosity of the particle and hence the particle density. The bulk density depends on the particle density and is often influenced by the particle size distribution. In a part of this research the nozzle system and the physical properties of the feed have been kept constant. Results show that higher drying temperatures lead to an increase of the porosity. The bulk density decreases with higher drying temperatures. So it is likely that the mean particle size increases with increasing drying temperatures, although this was not measured. A theoretical model predicts a very rapid crust formation, during which shrinkage only occurs for a few percent. The experimental data show a volume shrinkage of about 90%, and so it is plausible that the crust remains deformable. This phenomenon can have large consequences for calculations of drying rates in spray drying of FCC catalyst.