Quantification of local structure of disordered packing of spherical particles

Abstract

Industrial packed beds reactors, working as three-phase trickle bed reactors, are generally packed by directing or conveying the catalyst particles through chutes or through specially designed and patented packing devices. Nevertheless, it is known that these methods are rather primitive and lead to malformations on the bed surface. In turn, these propagate deep into the bed. The limited liquid flow in trickle beds, coupled with these bed-scale inhomogeneities, leads to non-uniform irrigation of the catalyst, non-uniform wetting, and axial dispersion, all leading to underperformance of the reactor. In extreme cases, these non-uniformities are the points where local hot spots are formed, and serve as the starting point for deactivation fronts. Thus, packing non-uniformities not only affect reactor performance but also catalyst life.In this work, we have attempted to simulate these packing abnormalities in the laboratory. The beds are created with packing defects created artificially, and then the local voidage distribution is measured in three-dimensions in the bed through resin-freezing followed by bed dissection. Details of this are discussed in the paper. As a result of this exercise, detailed arrangement of particles in three-dimensions could be ascertained. Rigorous analysis of the bed structure has been done using Dirichlet tessellation and studying the properties of the tessellation tiles. The impact of different packing methods are presented.