Gravity settlers settling chambers

The length of chamber required to settle a given particle size can be estimated from the settling velocity (calculated using Stokes law) and the gas velocity. A design procedure is given by Jacob and Dhodapkar (1997). 

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A gravity settler is to be used to separate particles less than 75 qm from a flowrate of gas of 1.6 m3s 1. The density of the particles is 2100 kg-rn 3. The density of the gas is 1.18 kg-m-3 and its viscosity is 1.85x 10 5 kg-rn 1 -s 1 Estimate the dimensions of the settling chamber assuming a rectangular cross section with length to be twice that of the breadth. 

For a given type of gravity settler, the pick-up velocity and the minimum diameter of particles which can be collected must be defined. The pick-up velocity is the onset velocity for particle reentrainment and depends on the particle diameter. The gas flow rate is to be controlled in such a way that the average gas velocity in the settling chamber is much smaller than the pick-up velocity. The minimum diameter of collected particles can be evaluated by the following analysis. 

Figure 14.3-5. Gravity settling lanfcs (a) settler for liquid-liquid dispersion, (b) dustsettling chamber.

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