Characterization of the internal morphology of agglomerates produced in a spray fluidized bed by X-ray tomography

The internal structure of granules produced by spray fluidized bed agglomeration was investigated by means of X-ray micro-computer-tomography. The X-ray tomography delivers three-dimensional volume images, which are first used to count primary particles and derive center coordinate position, radius and volume for each of them. Further analysis by add-on algorithms results in a variety of morphological descriptors: radius of gyration, porosity, fractal dimension and pre-factor, coordination number distribution, and coordination angle distribution. Values and the behavior of these descriptors are presented and discussed for agglomerates consisting of a different number of primary particles, from 4 up to 310. The primary particles were made of porous γ-Al2O3, and they were nearly mono-dispersed and spherical. The distribution of solidified binder (hydroxyl-propyl-methylcellulose, originally as dilute solution in water) was not investigated. The agglomerates were produced in a top-spray fluidized bed at constant operating parameters.