(68e) Particulate Flow Dynamics in Structured Gas-Solid Fluidized Beds

The performance of bubbling fluidized reactors relies highly on the macroscopic flow of bubbles, which is usually unstable, due to the complex dissipative interparticle collisions and interphase friction occurring at multiple scales. To control the system hydrodynamics, a lot of effort has been spent on investigating how to impose extra flexibilities, including internals, force fields, etc. The improvement associated with these designs is often dependent on the particle type, operation conditions and reactor type, which makes it difficult to obtain a universally valid standard across all scales [1,2]. Nature provides many examples of ordered granular patterns, such as the sandy ripples on dunes, as a consequence of complex interplays between the solid and surrounding airflows. Drawing inspiration from it, we have demonstrated, at specific conditions, that an oscillatory perturbation can suppress instabilities and induce a periodic flow structure at which bubbles self-organize into a regular array of triangular tessellations.

Such a regular array of bubbles is fully scalable and predictable, providing the potential to bypass operational challenges and intensify many solid processes. We have demonstrated the capability to replicate similarly structured bubbles in a cylindrical geometry, extending its appearance from a flat-2D to an annular-3D configuration, while maintaining its degree-of-order and controllability over gas bubbles. Over the last few years, results from our experiments and simulations have demonstrated that operation under such a flow structure would allow us to control bubble properties, such as size, residence time, and separation with unusual precision [3-5]. On the other hand, particles move and bridge bubbles in different arrays, but also impede coalescence of adjacent bubbles, Overall, an ordered macroscopic network of particulate flow paths emerges, which is coupled to the movement of the bubbles.

In this contribution, experimental results are shown to investigate the spatiotemporal coupling between solids and rising bubbles, as seen in Fig.1. Comparisons of particle image velocimetry (PIV) measurements across oscillations at different conditions and bed heights, as well as CFD-DEM simulations, provide insights into the processes of formation, propagation, and collapse of dense solid regions. We also discuss the evolution of short-range and long-range solid motion over different arrays, and their impacts on the stability of macroscopic patterns. These results form a theoretical basis for future developments in process intensification of fluidized beds.

[1] M.-O. Coppens, J.R. van Ommen, Structuring chaotic fluidized beds, Chem. Eng. J., 96 (2003) 117-124

[2] J.R. van Ommen, J. Nijenhuis, & M.-O. Coppens, Reshaping the structure of fluidized beds, CEP, (2009), 49-57.

[3] K. Wu, L. de Martín, M.-O. Coppens, Pattern formation in pulsed gas-solid fluidized beds - the role of granular solid mechanics. Chem. Eng. J., 329 (2017) 4-14.

[4] K. Wu, L. de Martín, L. Mazzei, M.-O. Coppens, Pattern formation in fluidized beds as a tool for model validation: a two-fluid model based study, Powder Technol., 295 (2016) 35-42.

[5] K. Wu, V. Francia, & M.-O. Coppens. Dynamic viscoplastic granular flows: A persistent challenge in gas-solid fluidization, Powder Technol., 365 (2020) 172-185.