THE INFLUENCE OF TANK SIZE AND IMPELLER GEOMETRY ON TURBULENT FLOCCULATION - I - EXPERIMENTAL

The effects of tank size and impeller geometry on the particle size di stribution after 30 min of flocculation at constant characteristic ave rage velocity gradient, G(m), were studied. Flocculation was performed in three square tanks 5-, 28-, and 560-L volume with Rushton turbines and A310 fluid foil impellers, The flee size was recorded in situ usi ng a photographic technique, and the resulting photographs were analyz ed with an image analysis system. The results show that the cumulative particle size distribution shifts to a smaller particle size range wi th increasing tank size, regardless of impeller type. A similar shift in the cumulative particle size distribution was observed when the imp eller type was switched from the A310 fluid foil to the Rushton turbin e, regardless of tank size. The volume mean flee size, flee standard d eviation, and maximum stable flee size were found to be controlled by the turbulence intensity in the impeller discharge zone and not by G(m ).