Deposition and aggregation of Brownian particles in trickle-bed reactors

When dilute liquid suspensions contaminated with Brownian fine solids are treated in catalytic trickle-bed reactors, bed plugging develops and increases the resistance to two-phase flow until ultimate unit shutdown for bed substitution with pristine catalyst is imposed. One of the important aspects during plugging with Brownian particles is the aggregation of fines and the release of the fine particles and aggregates from pore bodies within the porous bed as a result of the hydrodynamic or colloidal forces. Current physical models linking gas-liquid flow to the filtration process in high-pressure/temperature trickle beds neglect the possible colloidal particle aggregation and the release of aggregates. This work attempts to fill this gap by developing a Euler-Euler fluid dynamic model based on the volume average mass, momentum, and species balance equations, filtration equations for the Brownian particles and the aggregates, and the discrete population balance equations for the agglomeration of particles. Both monolayer and multilayer depositions were considered for Brownian particles and only the monolayer deposition in the case of the detaching aggregates. The release of fine particles and aggregates from the collector surface was assumed to be induced by the colloidal forces in the case of Brownian particles/aggregates or by the hydrodynamic forces in the case of non-Brownian aggregates. Brownian particle aggregation was described by the rate at which a certain size aggregate is being formed by smaller aggregates less the rate at which the aggregate combines to form a larger aggregate. (c) 2006 American Institute of Chemical Engineers.