Prediction of particle size and layer-thickness distributions in a continuous horizontal fluidized-bed coating process
P. Bachmanna,*, K. Chena, A. Bückb, E. Tsotsasa
To predict the particle size and layer-thickness distributions (LTDs) in a continuously operated horizontal fluidized-bed granulation process, two alternative models were considered. A one-dimensional two-zone model was proposed, which describes with population-balance equations the particle growth in a spraying zone that is separated from the drying zone. The residence-time distribution (RTD) was calculated from a literature correlation and was coupled with a population-balance model via a tank-in-series model with reflux. A two-dimensional, one-zone population-balance model, which was based directly on the RTD and the feed particle-size distribution (PSD) was also used. Granulation experiments were conducted and analyzed microscopically and with a camera optical device to determine the sample PSDs. LTDs over the particle population were derived from the PSDs and were analyzed directly by micro-computer-tomography. To compare the simulated data with the experimentally determined distributions, the PSDs were converted to LTDs. The good agreement shows that both methods are suitable to determine the PSD from an RTD of an arbitrary granulation process in a horizontal fluidized bed. Improvement appears necessary with regards to the LTD spread.
Fluidized bed; Continuous process; Coating; Residence-time distribution; Particle-size distribution; Layer-thickness distribution