Application of a dual-grid multiscale CFD-DEM coupling method to model the raceway dynamics in packed bed reactors

Abstract

A CFD-DEM coupling model with dual-grid multiscale approach is used to model high-speed injection into a packed bed reactor. The present CFD-DEM coupling uses a separate coarse grid for the discrete phase (DEM model) and a fine grid for the continuum phase (CFD model). This CFD-DEM approach allows high grid resolution for solving the gas phase and preserving the accuracy of the CFD solution at higher Reynolds numbers. The dual-grid multiscale approach is used to model high-speed lateral gas injection in a two-dimensional blast furnace reactor. Blast velocities up to u=230ms-1, as in real blast furnace operation, are used to investigate the formation and dynamics of the raceway inside the reactor. The effect of the blast velocity on the size and shape of the raceway was investigated using different jet velocities. It is shown how the use of an adequate grid resolution for the continuum phase is needed in order to achieve a grid independent solution and how it influenced on the discrete solution. It was observed that the variation of the blast velocity directly influenced on the size and shape of the cavity. However, the particles and the flow showed the same pattern and behavior at the different investigated blast velocities, with a proportional scaling according to the gas velocity. At the investigated blast velocities the raceway formed very rapidly showing a transition period with lateral periodic oscillations before stabilization was observed.