12. Investigation of Turbulent Gas-Solid Flow Multi-scale Dynamics in a Circulating Fluidized Bed Riser

Circulating Fluidized Bed (CFB) reactors have been extensively used for industrial applications such as mixing, drying, catalytic, and non-catalytic reactions. Due to the nonlinear and non-equilibrium gas-solid flow structures, the dynamic behaviors in a gas-solid multiphase flow remain far from being completely understood. In addition, considerable differences in the flow state occur under different operation conditions, resulting in different structures. These structures cause an impact on gas-solid momentum, mass, and heat transfer, affecting productivity. Pressure fluctuations are usually used to characterize dynamic behaviors of heterogeneous structures in fluidization. The signal of measured fluctuation contains the information about the multiscale flow characteristics and may also be associated with different phenomena. Identifying which scales of the flow are the most affected can help to reveal the dynamics of these different structures in gas-solid flow. The present work investigates pressure signals obtained through physical experiments at different experimental conditions in order to identify which scales were affected by the turbulent gas-solid flow. These signals were obtained in a CFB riser using glass beads particles, which were classified as group B of Geldart. Additionally, the gas velocity and mass flow were varied with the purpose of evaluating their influence over the turbulent scales. The obtained signals were investigated on the frequency and time-frequency domains. The power spectrum density (PSD) was applied to identify the dominant frequencies, as well the Wavelet transform was used as a mechanism to obtain the scales where its fluctuations were evaluated. The combination of such analyses resulted in the identification of the most affected scales, where it was observed that the mesoscales were attenuated with the addition of particles resulting in an increase in the fluctuation of the microscales.