Experimental Investigation on Bubble and Agglomerate Behaviors of Geldart B Particles in a 3D Gas–Solid Fluidized Bed Reactor

For Geldart B particles, published works have mostly focused on macroscopic fluid mechanics. The analysis of mesoscopic structure in 2D fluidized beds used nonintrusive techniques, such as digital image analysis. For 3D fluidized beds, pressure fluctuation was employed to estimate the size of bubbles, which measured the entire flow field without focusing on the local flow structures. In this work, the local behaviors of bubbles and agglomerates were experimentally investigated in a pilot-scale bubbling fluidized bed by an optical fiber probe. The experimental investigation explored the radial distributions of bubbles and agglomerates at various heights and superficial gas velocities. The volume fraction of the bubble phase was below 0.5, and the emulsion dominated the flow. The bubble frequency was less than 1.7 Hz, and it within the central region was greater than near the wall. The bottom of the bed had a higher bubble frequency than the upper. The bubble chord length, remaining almost 45 mm, was approximately 3 times greater than that observed in the Geldart A particles. The result showed that Geldart B particles are characterized by larger size and lower frequency of bubbles compared to Geldart A particles. Moreover, the agglomeration frequency remained below 0.6 Hz. The force balance analysis further presented that aggregation was less likely for Geldart B particles.