Drawdown of floating solids in liquid by means of mechanical agitation: effect of system geometry

This research focuses on drawdown of floating solids with up-pumping agitators in a batch vessel equipped with baffles for solid-liquid system. Up-pumping agitators incorporate floating solids via a combination of different mechanisms turbulence engulfment, mean drag and vortices formed behind baffle. After screening five different baffle arrangements, standard full length baffle was found to work well with up-pumping agitators. The use of standard baffling for solids drawdown lead to better understanding of power and torque. The optimum design of the up-pumping agitator for drawdown of floating solids requires understanding effects of various design parameters, such as impeller type, diameter, and submergence and their effect on drawdown speed, torque and power. This study considers comparing two types of impeller Pitched Blade Turbine (P-4) and Chemineer HE-3. Totally nine different impeller to tank diameter ratios ranging from twenty to fifty percentage of tank diameter with submergences varying from ten to seventy percent of the liquid height which is equal to tank diameter were tested to find optimum design.The drawdown speed for P-4 and HE-3 increased with increase in submergence and decreased with increase in the impeller diameter. The drawdown speed of P-4 and HE-3 are related to impeller to tank diameter ratio by a power-law relation. The drawdown speed of P-4 and HE-3 are also related to impeller submergence by a power-law relation. The power correlations are given below. P-4 HE-3 Njd (D/T) -1.39 Njd (D/T) -1.60 0.2 \u3c D/T \u3c 0.5 and 0.1 \u3c S/T \u3c0.7 Njd (S/T) 0.32 Njd (S/T) 0.15 0.2 \u3c D/T \u3c 0.5 and 0.1 \u3c S/T \u3c0.4Njd (S/T) 1.45 Njd (S/T) 0.47 0.2 \u3c D/T \u3c 0.5 and 0.4 \u3c S/T \u3c0.7The drawdown power for P-4 impeller has a minimum value at D/T=0.33 and for D/T=0.4 and above the power is very high. HE-3 drawdown power has a broad minimum between D/T of 0.23 to 0.44. The torque of both impellers increases with increase in impeller diameter and submergenc