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. Using the data extracted from volume images, the primary particles contained in the agglomerate can be labeled and counted, providing the number of primary particles per agglomerate. Center coordinates, radius and volume of each primary particle are identified and stored in matrices, which contain all the data needed for further evaluation. [Display omitted] ► First in-depth study of the structure of spray fluid bed agglomerates ► Successful application of X-ray micro-computer-tomography ► Access to concealed 3D information ► Evaluation and discussions of several morphological descriptors