Computational modelling and parameter estimation in fixed beds of non-spherical pellets

Abstract

Fixed bed arrangements find wide applications, particularly in reaction engineering, where they are employed as multi-tubular catalytic reactors for the transformation of reactants into desired products. The importance of such complicated reactors can be realized by their extensive applications as the process workhorse in various industries, e.g. chemical, pharmaceutical and petrochemical. The design of such systems is predominantly rooted in macroscopic models, e.g. pseudo-continuum approaches, with effective parameters extracted from averaged semi-empirical correlations. However, such simplistic design procedures are inadequate for design of tubular fixed beds with low tube-to-particle diameter ratios, say dt/dp<10, where lateral heterogeneities of the tortuous structure lead to dominance of localised phenomena. These local or “pellet-scale“ effects cannot be captured nor explained by pseudocontinuum models, and call for 3D spatially-resolved simulations of flow and transport scalars. However, majority of the prevailing efforts within the context of “particle-revolved CFD simulation”, have dealt with fixed beds of spheres, because generating random packing of nonspherical pellets necessitates a cumbersome and complicated strategy to account for the orientation freedom of such pellets, specifically when collisions occur...