Hindered batch settling

Renko, E. K. (1998). Modelling hindered batch settling part II A model for compnting solids profile of calcium carbonate slurry. Water S.A. 24, 4, 331-336. 

In this equation, V0 is the relative velocity between the unhindered particle and the fluid. However, in a hindered suspension this velocity is increased by the velocity of the displaced fluid, which flows back up through the suspension in the void space between the particles. Thus, if Fs is the (superficial) settling velocity of the suspension (e.g., swarm ) and VL is the velocity of the fluid, the total flux of solids and liquid is relative velocity between the fluid and solids in the swarm is Vr = Vs — VL. If the total net flux is zero (e.g., batch settling in a closed-bottom container with no outflow), elimination of VL gives... 

Batch Settling Hindered Systems. In these more concentrated suspensions the proximity of the particles to each other is such that the settling rate is independent of the size and density of individual particles. Laboratory examination of the set g bdbLaviour will show the development of a clear inter ce between the settling solids and an uppermost layer of clear liquid. 

Combining Equation (3.19) with Equation (3.18) gives the following expression for Up, the hindered settling velocity of particles relative to the vessel wall in batch settling ... 

The thickener is the industrial unit in which the concentration of a suspension is increased by sedimentation, with the formation of a clear liquid. In most cases, the concentration of the suspension is high and hindered settling takes place. Thickeners may operate as batch or continuous units, and consist of tanks from which the clear liquid is taken off at the top and the thickened liquor at the bottom. 

Figure 5.4.4 Interface positions as a function of time in batch sedimentation with hindered settling of the suspension.

Figure 5.4.5 Flux curve for batch sedimentation with hindered settling.

Figure 5.4.6 Simple concave downward flux curve with a maximum and no inflection point for batch sedimentation with hindered settling.

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