A Model for the Size Distribution of Product from a Granulating Drum

Abstract

Carefully controlled granulation experiments were carried out on a haematite ore with a wide size distribution (0-8mm) over a range of moisture contents. At any one moisture content, the finest size fractions could be classified solely as layering particles whilst the largest size fractions acted only as nuclei particles. Between these two extremes, a proportion of particles in any one size fraction behaved as nuclei particles, the remainder being layering particles. Hence each particle size fraction could he characterised by a partition coefficient. The partitioning of an individual size range between nuclei and adhering particles was shown to be dependent on the moisture content. For each moisture content, the partition curve could be modelled using a log-normal function. The variation of adhering layer mass with granule size was investigated and it was found that adhering layer thickness was approximately proportional to nuclei diameter at lower moisture contents. At higher moisture contents there was an optimum nuclei particle size for which the ratio of granule mass to total nuclei mass was a maximum.
A population balance model to predict granule size distribution was developed and tested against experimental data. The important model parameters were those describing the particle partition curve. Excellent agreement was found between experimental and model predicted granule size distributions for the full range of moisture contents covered.