Analysis of Horizontal Solids Convection and Dispersion in Fluidized Beds

The horizontal transport of solids in a fluidized bed is typically described by means of a dispersive process. A solids crossflow, however, also involves a macroscopic convective component, which needs to be considered. The latter applies to systems consisting of interconnected fluidized beds, which are expected to form the basis for various applications in the future energy system. Understanding the interplay between dispersive and convective solids mixing in the lateral direction is key to determining the solids residence time distributions and, thereby, the closure of the mass balance in interconnected fluidized bed reactors with a horizontal solids crossflow. This work aims at investigating the lateral transport mechanisms for solids in a bubbling fluidized bed with such horizontal solids cross flow.

Lateral solid dispersion induced by the bubble flow is quantified and compared with a net horizontal solids convection forced onto the bed, along with the interaction between dispersion and convective processes. The experiments are conducted in a set-up designed to force a horizontal flow of bubbling fluidized solids around a closed horizontal loop. The loop contains a horizontal straight channel through which the concentration of a ferromagnetic solids tracer injected upstream is measured non-intrusively (at 100 Hz) by means of an impedance coil at four different positions along the channel. The set-up is designed in accordance with Glicksman's complete set of fluid-dynamic scaling laws, allowing measurement scale-up to large-scale hot conditions. The measured values are used to fit a mathematical model of a one-dimensional transient convection-dispersion process, thereby obtaining the lateral solids dispersion coefficient. Three operational parameters were examined: bed height, fluidization velocity, and lateral solids convection.