Numerical simulation study of the hydrodynamic regimes in large to micro fluidized beds based on a Two-Fluid Model

Abstract

Although the hydrodynamic properties of fluidized bed reactors have been investigated experimentally in the macro- to micro-scale range, the measurements and diagnostic tools needed for this analysis are complex. This in turn increases the difficulties experienced when trying to account for various specific phenomena, which occur within very small, i.e. Micro-Fluidized Beds (MFBs). In the present study, a numerical approach has been used to better understand the hydrodynamic behaviour of microreactors. The influence of a reduced value of bed diameter (Dt), the value of the static bed height (Hs), and the role of changing boundary conditions on various hydrodynamic parameters, bubble behaviours and particle circulation patterns were simulated using a Two-Fluid Model (TFM), and compared with our previous experimental results. It was found that a reasonable setting of the solid volume fraction in a fixed bed (εs,0) was key to successful simulation of the onset of minimum fluidization (and minimum bubbling), which is delayed for decreasing values of Dt. Setting the specularity coefficient (ϕ) to 1 resulted in bubble and particle movements being more consistent with those observed in the MFB experiment. In the simulation, a round-nosed slug rose along the center of the bed for small values of Hs, whereas it transformed into a wall slug in the upper region at greater values of Hs, which is in good agreement with our experimental observations. In addition, the experimental phenomenon in which slug is prevented from rising upwards within the MFB was successfully reproduced in the simulation.