With the random movement of silica gel beads in a conical fluidized bed, micro-vortices resulting from the fluidization promoted the collision and aggregation of suspended fine kaolin powders. The abatement efficiencies of the suspended fine solids under several hydrodynamic conditions were studied, and a suitable control strategy for operating the conical fluidized bed flocculators was identified. The suspended solids abatement efficiency was found to increase with increasing Camp Number and flocculation time （T）, but decreased with the increase of velocity gradient （G） within the range studied in this research （165.1-189.6s-1）. The abatement efficiencies were all more than 60% at the range of G = 165-180 s 1 and T = 15-33 s at an initial kaolin solid concentration of 150mg·L-1, polymer aluminum chloride dosage of 60 mg· L -1 and sedimentation time of 20 min. However, the formation of flocs was influenced by the liquid back- mixing. Excessive backmixing caused the breakup of ftocs and resulted in difficulty for the fine powders to aggregate and sediment to the reactor bottom. The results of the calculated fractal dimension and measured free sedimenta- tion velocity of flocs obtained at different runs showed similar flocs properties, and indicated an easy control strategy for sedimentation of the flocs.
Flocculation time is conventionally believed to be proportional to the flocculation efficiency of a cylindrical fluidized bed flocculator.However,in a single-stage velocity gradient situation,the flocculation efficiency decreases when the optimal flocculation time is exceeded.A multi-stage velocity gradient was established in a cylindrical fluidized bed flocculator,based on the hydraulic classification theory.This multi-stage velocity gradient fluidized bed flocculator(MGF) created a more suitable environment for floc growth and protection,which was confirmed by the size distribution of flocs along the bed height.Correspondingly,the abatement efficiencies for Kaolin slurry and dyed wastewater treatment in the MGF were enhanced by5-10%,and by 7-20%,respectively,compared with those in the single-stage velocity gradient fluidized bed flocculators(SGFs).The initial bed height distribution ratio along the velocity gradients was an important factor for MGF optimization.
The efficiency of a fluidized-bed flocculator with 800- m particles of 1360 kg/m3 in density was studied, and the anti-shock capability of the unit was estimated for three kinds of industrial wastewater: heavy turbidity wastewater, dispersed dyeing wastewater and starch wastewater. Steady removal efficiency was contributed by the following characteristics of the flocculator: (1) the dynamic conditions, flocculation time and velocity gradient, which were stabilized at a steady level as the loading rate changed; (2) hydrodynamic characteristics, especially the considerable rise of expanded bed height with increasing superficial velocity when small and light particles were employed as the solid phase; (3) flocs growth characteristics in the fluidized bed, which caused the density and size of the flocs being maintained at a compensational relationship, resulted the stabilized settling velocity of the flocs.
