Experimental Study on the Gas–Solid Flow Mechanism with Variable Particle Property in a Multistage Fluidized Bed Riser

Variable-diameter CFBs have been receiving increasing attention due to its synergistic regulation of solid holdup, contact efficiency, and residence time. Nevertheless, the influence of particle property on the complex gas–solid hydrodynamics remains poorly understood. This work experimentally investigates the effect of particle size on gas–solid flow in a three-dimensional multistage riser using instantaneous solid concentration measurements and multiscale signal analysis. Results show that the large particle intensifies flow fluctuations in the enlarged segment and increases axial nonuniformity of particle distribution. The periodic motion of the large particle is more vigorous. Mesoscale agglomerates dominate the gas–solid flow in the enlarged segment regardless of particle size, but the energy distribution across scales varies distinctly between the straight and enlarged sections. The particle concentration positively correlates with the impact of particle size on flow behavior. Overall, the effects of particle size on gas–solid flow tend to attenuate toward the center region and the upper part in the riser segment.