Some design considerations of a draft tube gas-liquid-solid spouted bed

Abstract

The optimal design of a draft tube gas-liquid-solid spouted bed was experimentally evaluated by considering four design variables including the draft tube diameter, gas-liquid injector, top (above-draft-tube) spacing and bottom (below-draft-tube) spacing. The effects of these design variables on the overall gas holdup were comprehensively examined for various gas and liquid velocities and solid particle properties. The diameter of the outer column of the draft tube three-phase spouted bed was fixed at 15.24 cm. The overall gas holdup increases with an increase in gas or liquid velocity. It was found that, of the three diameters of draft tubes considered (7.62, 10.16 and 12.7 cm), the draft tube of 7.62 cm inside diameter has the highest overall gas holdup. Of the two liquid velocities considered (2.28 and 3.41 cm s −1), a higher overall gas holdup is obtained at a higher liquid velocity for each of the four bottom spacings considered (0.44, 1.27, 2.54 and 5.08 cm). Of these four bottom spacings, the 1.27 cm spacing has the highest overall gas holdup. The overall gas holdup increases with decreasing top spacing. 2.5 mm nylon balls have the highest overall gas holdup, followed by 4 mm glass beads. 3 mm glass beads have the lowest overall gas holdup. The concentric tube gas-liquid injector with the gas distributor plate of smallest pore size placed on the top of the outer tube gives rise to the highest overall gas holdup.