Impact of random packing on residence time distribution of particles in bubbling fluidized beds: Part 2 - Counter-current flow reactors

Journal article, 2025

The influence of employing random packings on the residence time distribution of bed solids in a counter-current bubbling fluidized bed is investigated. Magnetic solids tracing experiments have been performed in a bubbling fluidized bed setup (0.12 m in diameter) that allows for a continuous solids throughflow downwards. Two types of packings, aluminum silicate balls (ASB) and expanded clay aggregate (ECA) are employed in the experiments. Besides the effect of the packing type, the impact of fluidization number (15.6 and 21.9), and bed height (30 cm and 50 cm) are also studied. Two models are used to analyze the solids vertical flow patterns in the packed-fluidized beds, these are the axial dispersion and tank-in-series models. Findings indicate that the presence of packings provides the vertical throughflow of solids with a mixing pattern much closer to that of a plug-flow reactor, resulting in an increase in the Péclet number (Pe = uL/D) from 1.44 up to 18 and increasing the number of tanks by up to ninefold. The axial dispersion coefficient for the solids decreases almost tenfold (from approximately 0.06 m2/s in the unpacked bed to 0.006 m2/s in the packed-fluidized bed). The possibility of using packings to achieve plug-flow behavior of solids in a countercurrent fluidized bed could have positive implications for many current and future fluidized-bed conversion processes.