Dilute batch settling

Batch Settling Dilute Systems. The residence time required for tire batch settling of a suspension that is con osed of a size distribution of particles of the same material can be calculated easily using the size of the smallest particle to estimate the time it will take to settle the full hei t of the vessel firom surface to base. 

This is a batch size analyzer [33] (Figure 10.1). An extremely dilute sample of milled ore is introduced, at a constant flow rate, to a coarse separator in the form of a tangentially fed cylindrical screen. The coarse fraction is allowed to settle and the fine fraction is further separated with an efficient hydrocyclone into a fine and a very fine fraction. The very fine fraction is discarded and the fine fraction is allowed to settle. The ratio of the times taken to fill the coarse and fine fraction collection vessels to indicated levels can be related directly to the particle size distribution. The cyclosensor has a sensitivity whereby a change of 1.8% passing 100... 

Batch-operated gravity separations avoid the complications of turbulence in continuous separators. They can be designed besed on Stokes Law for dilute dispersions, where die separation time is that for a dispersed-phase drop to go from the farthest point to the interface 6 = Hill, where 6 is separation dme, H is the height from the farthest point to die interface, and V, is the Stokes Law settling velocity. For systems where coalescence is the limiting mechanism, the ratio of die volume to cross-sectional area should be proportioanl to separation time and is the key parameter. Smell-scale batch tests can be used to confirm sizing or separation time. 

The nature of these two trajectories changes if batch sedimentation involves a more concentrated suspension (for an introduction, see the general treatment in Probstein (1989) of the subject). First, the settling velocity of an individual particle is reduced due to the close proximity of many other particles. This is due to an increased viscosity of the Uquid, as well as an increased drag force experienced by the particle due to the other particles. The effective settling velocity is less than f/p, for a dilute suspension of the same particle size ... 

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