Effects of gas distributors on hydrodynamics of three-phase biological fluidized bed reactor with internal circulation

The gas hold-up, liquid circulation velocity and volumetric oxygen mass transfer coefficient were investigated by experiments in an internal circulation three-phase biological fluidized bed reactor with three different gas distributors. The results showed that, besides the gas flow rate Qg, the gas hole diameter and the hole number per unit area of distributor are also important factors that affect gas holdup εginside the reactor. Under a given Qg, the distributor with smaller hole helps to achieve higher εg (as did the micropore distributor in this work), but the over-densely distributed holes on distributor will cause the small bubbles to merge into large bubbles, leading to decreased εg (as did the ceramic distributor in this work). For the cases of lower gas flow-rate (Qg <260 L/h), the liquid circulation velocity Uc mainly depends on the gas holdup difference Δεg between riser and downcomer, while for the cases of higher gas flow-rate, both Δεgand flow resistance are dominating factors. When Qg keeps constant, the distributor which achieves a larger Δεg leads to a higher circulation velocity. The volumetric oxygen mass transfer coefficient KLa increases with increasing Qg, to which the increased specific surface area contributes mostly. Under a given Qg, the distributor which achieves a higher gas holdup results in a higher mass transfer coefficient KLa. ©, 2015, Editorial Department of Journal of Sichuan University. All right reserved.