Effects of Operating Conditions on the Performance of Cross-Flow Filtration of Viscoelastic Slurry.

Abstract

The effects of operating conditions, such as rheology of fluid, cross-flow velocity, and filtration pressure, on the cake formation and the performance of cross-flow filtration of viscoelastic slurry are studied. The viscoelastic fluid is prepared by adding a polymer, sodium polyacrylate, into de-ionized water. The results show that the viscoelastic behavior of polymeric fluid plays an important role on the performance of filtration, which results in a more compact cake but a higher filtration rate as the polymer concentration in slurry increases. Although the elastic effect of fluid increases the difficulty of filtration, and cause the filtration rate to decay quickly at the beginning of filtration, the cake mass decreases with increasing the polymer concentration due to the increase of drag force exerted on particles in the cross-flow direction. An increase in filtration pressure or a decrease in cross-flow velocity causes the filtration rate to increase. The parameter of elastic effect, E, decreases continuously during a filtration and becomes a negligible value when the filtration rate is lower than a certain value. The value of E increases with decreasing filtration pressure for a given filtration rate. The average cake porosity decreases with filtration time from the start of filtration due to the elastic effect and then increases and approaches gradually to a constant when this effect diminished. The cake porosity at pseudo-steady state decreases with increasing polymer concentration, increasing filtration pressure, and decreasing cross-flow velocity. Furthermore, the probability of particle deposition and the size distribution of particles in filter cake under various conditions are measured. The phenomenon of “selective deposition of particles” can be observed, and the size distribution of particles in the cake decreases with decreasing filtration rate or increasing polymer concentration.