Study On The Characteristics Of Gas-liquid Mass Transfer In The New Type Internal-loop Three-phase Biological Fluidized Bed

Internal-loop three-phase biological fluidized bed is a new type biological treatment technology. It integrates conventional activated sludge wastewater treatment process and biofilm process and utilized chemical engineering fluidized technique. Characterized as high loading and high efficiency, it is regarded as one of the most prospective biological treatment technique in the field of water pollution control.In this paper, a modified internal-loop three-phase fluidized bed (MITFB) whose draft tube was equipped with static mixers was developed. The effective volume of the experimented reactor is 94 liter. The reactor was performed for air-water system. The characteristics of hydrodynamics and oxygen mass transfer were investigated in MITFB. The effects of physical, structural and operating parameters on gas holdup, liquid circulation velocity and volumetric mass transfer of oxygen were also studied.It was bound from experiments that liquid circulation velocity, gas holdup and mass transfer coefficient increase with increase in the airflow rate. Compared with performance in conventional internal-loop three-phase fluidized bed (CITFB), the gas holdup in the riser (Er) obviously increased and average volumetric mass transfer coefficient (KLa), mass transfer efficiency (EA), mass transfer power efficiency (Ep) in MITFB increased by 21.8% to 41.5% respectively, whereas liquid circulation flow rate in MITFB decreased.The experiments performed on the optimum diameter and surface treatment of the carrier (fly ash) indicated that the optimum diameter is 0.13 to 0.45mm and the surface treatment can effectively improve the characteristics of the carrier.The optimum structure parameters and function conditions in this study are as follow: inside diameter of draft tube d = 5.5cm, number of static mixers n=10-13, superficial gas velocity Ug = 16-22cms-1. Under these circumstances, some characteristic parameters of the reactor are as follow: Er= 16.2120.68%, liquid circulation velocity in riser ULr=14.81-17.37cms-1, frictional loss coefficient of static mixers Kr= 163.7-257.9, KLa = 0.465-0.778min-1,EA =39.16-48.81%,The results can offer theoretical and practical foundation for the engineering scale-up and performances of the reactor.