Gas Lateral Mixing in a Fluidized Bed – the Effect of the Solid Particles

The mixing of different components in the gas phase is to a great extent responsible for the extent to which homogeneous reactions occur in a fluidized bed reactor. With regards to the lateral directions, gas mixing is often described as a dispersive process governed by a coefficient, which has been object of previous studies. This work, which is an initial step in a more exhaustive study of the gas mixing in fluidized beds, presents an investigation of the impact of the presence of a solids phase on the lateral mixing of the gas phase. The present work uses gas (CO₂) tracing measurements in a fluidized bed (3.1 m in height and 0.45 m² in cross section) operated at ambient conditions, using 106 µm glass beads as bed material and a range of fluidization velocities yielding both bubbling and circulating flow conditions. The concentration of the tracer gas was sensed at up to 35 positions over the cross section of the unit at different vertical distances from the tracer injection. The tracer gas concentration maps obtained experimentally were used to fit a convection-dispersion model and to calculate in that way the gas lateral dispersion coefficient. Measurements performed under solids-free conditions are compared to those in presence of solid particles, where the solids inventory and the fluidization velocity were varied, yielding different levels of solids concentration and fluxes.