Particle Mixing in a Two-Section Two-Zone Fluidized Bed Reactor. Experimental Technique and Counter-Current Back-Mixing Model Validation

Abstract

Effective particle circulation between the two zones is a prerequisite for ensuring the simultaneous reaction and catalyst regeneration inside a two-zone fluidized bed reactor (TZFBR). An appropriate degree of particle mixing provides a steady state catalytic operation, whereas poor solid circulation between the bed zones leads to unhampered catalyst deactivation. To achieve effective control of the fluid dynamic regime within the two bed regions, a new design has been proposed with a different cross sectional area in each zone. The transition angle (α) between these zones represents the most characteristic feature of the so-called two-section TZFBR (TS-TZFBR). In the present study, the influence of operational variables (α, gas velocities, gas distributor location) on the particle circulation has been determined. Phosphorescent particles have been used as optical tracers to measure the solid axial mixing between the zones in a cold pseudo-2D TS-TZFBR facility. Additionally, a modified counter-current back-mixing model (CCBM) without adjustable parameters has been developed to explain and predict the solid mixing rate for different TS-TZFBR geometries. The experimental mixing results show a reasonably good agreement with the suggested mixing model predictions in a wide range of operational conditions: ugas–umf = [5–20] cm3/(cm2 s), α = [0°–85°].