Direct Measurement of Floc Breakage in Flowing Suspensions

Direct measurement of floc brakage behavior of silica and latex dispersions in a stirred tank and process pipeline have been performed using in situ scanning laser microscopy. The results show the effect of agitation intensity, flocculant dosage, and solids concentration on the floc formation and breakup in a stirred tank. The effect of the rms velocity gradients on the floc breakage behavior in a process pipeline is also demonstrated and modeled using a quantitative relationship between the breakage constant (K) and the rms velocity gradient (G). These data provide a means of assessing, quantitatively, the strength of a floc population. Expressions for the mean dimesionless floc size R (scaled to the maean diameter of the primary particles) have been obtained for polymer-flocculated suspensions flowing in tubes. Typically R is given by (1 + aGb), where a and b depend on the volume concentration of solids. For 0.5% solids, a = 34.7, b = -0.67; for 1.0% solids, a = 4.85, b = -0.29.