Simulation of particle attrition by supersonic gas jets in fluidized beds

Abstract

Particle breakage by gas jet is encountered in many processes. Quite often it is necessary to evaluate the attrition performance of different equipment configurations at various flow conditions. Therefore, a simulation tool that can be applied for industrial scale devices can be very beneficial for process design and optimization. A mathematical model for particle attrition by high velocity gas jets is developed. The model utilizes an Eulerian–Eulerian approach for the gaseous and particulate phases coupled with the kinetic theory of granular flow and a novel attrition model connecting the solid phase properties and the granular temperature with the breakage rate. Modelling results allow the calculation of the grinding efficiency – a quantitative measure of the attrition performance. For validation purposes, the model is applied to a large number of cases that have been investigated experimentally. Simulation results demonstrate that the increase of the nozzle inlet pressure or the exit diameter for a forward step nozzle produces an increase of the grinding efficiency. In addition, the convergent–divergent nozzle is more efficient in breaking the particles than the nozzle that contains only the convergent section.