Characterization of flow properties of pharmaceutical pellets in draft tube conical spout-fluid beds

[Display omitted] •Hydrodynamic of a draft tube conical spout fluid bed was studied using pharmaceutical pellets.•Three different hydrodynamic structures were identified in draft tube conical spout fluid bed.•Frequency signature for the stable spouting is: (i) 6–9Hz and (ii) 12–15Hz.•The effects of bed height, entrainment zone and distributor hole pitch were discussed.•ΔPd increases with the height of draft tube and distance of the entrainment zone. Experimental studies of the hydrodynamic performance of the draft tube conical spout-fluid bed (DCSF) were conducted using pharmaceutical pellets. The experiments were carried out in a DCSF consisted of two sections: (a) a conical section with the cross section of 120 mm×250mm and the height of 270mm, (b) a cylindrical section with the diameter of 250mm and the height of 600mm. The flow characteristics of solids were investigated with a high speed camera and a pezoresistive absolute pressure transducer simultaneously. These characteristics revealed different flow regimes in the DCSF: packed bed at low gas velocities, fluidized bed in draft tube at higher gas velocities until minimum spouting, and spouted bed. The stable spouting was identified by the presence of two dominant frequencies of the power spectrum density of pressure fluctuation signature: (i) the frequency band 6–9Hz and (ii) the frequency band 12–15Hz. The pressure drops across the draft tube as well as the annulus measured in order to better recognize the flow structure in the DCSF. It was observed that the pressure drop across the draft tube, the pressure drop across the annulus, and the minimum spouting velocity increase with the increase in the height of draft tube and distance of the entrainment zone, but with the decrease in the distributor hole pitch. Finally, this study provided novel insight into the hydrodynamic of DCSF, particularly minimum spouting and stable spouting in the DCSF which contains valuable information for process design and scale-up of spouted bed equipment.