Evaluation of the effect of hydraulic shear intensity on coal-slime water flocculation in a gradient fluidized bed

Fluid shear plays a paramount role in flocculation. In present work, a fluidized bed flocculator with a decreasing fluid shear intensity in steps, called gradient fluidized bed (GFB) flocculator, was developed according to the self-preserving nature of floc size distribution and the flocculation kinetics. Then flocculation experiments were conducted to evaluate the performance of the GFB flocculator on flocculating coal-slime water in different flow rates. Results show that the flocculation of the GFB flocculator reducing the supernatant turbidity by 32% when compared with a pipe one, exhibiting obvious advantages. When the superficial velocity was 0.44m/s, the velocity gradient along the height of the GFB decreased from 240 to 145s−1, contributing the best result that the flocs size up to 1mm and the turbidity of the supernatant lower to 17 NTU. It can be concluded that GFB should be an efficient flocculator for flocculating coal-slime water when a reasonable apparent velocity is well conducted.