The effects of tank size and impeller type on turbulent flocculation

A basic conceptual and experimental study of the flocculation process is described. The turbulence in three square flocculation reactors of size (6.7in);The steady state floc size distribution was measured in situ using a photographic technique. The results of the photographic measurements show a shift in the cumulative particle size distribution from larger particles to smaller particles with increasing tank size regardless of impeller type. These photographic results also indicate a shift in the distribution from larger particles to smaller particles moving from the A310 foil impeller to the Rushton turbine. As a measure of the steady state floc size distribution, the volume mean particle size, standard deviation, and maximum particle size were evaluated for each tank size and impeller type setup. These three particle distribution statistics were found to be a function of ;A population balance model was developed that included the turbulence intensity in the impeller discharge zone in the breakup part of the population balance rate equation. Reinforcing the photographic results of the floc size distribution, the population balance model predicts the shift in the particle size distribution from larger particles to smaller particles with increasing tank size. The model is also effective at predicting the shift in the particle size distribution from larger particles to smaller particles moving from the A310 foil impeller to the Rushton turbine. The results from the flocculation experiments and model simulations suggest that the steady state floc size distribution is limited by the turbulence intensity in the impeller discharge zone. These results clearly show that steady state floc size distribution is not a function of the average intensity of the turbulent motion throughout the reactor volume as suggested in the models based on G...