Industrial & Engineering Chemistry Research, Vol.36, No.11, 5015-5022, 1997
Continuous Sampling of Floating Solids Suspension from a Mixing Tank
The problem of continuous wall sampling of monomodal suspension of floating solids from a stirred vessel at complete suspension state has been studied. Dispersion and sampling of floating particles was carried out in a vessel with impeller/baffle configuration usually recommended for suspension of solid settling particles. The dependence of the sampling efficiency on the characteristics of suspension (bulk solids concentration and particle size), sample tube design, and sampling technique (withdrawal velocity, mixer speed, and location of sampling) were investigated in detail. The results are, to a considerable extent, related to solid particles low inertia, pronounced effect of the upward buoyant force, and the complex hydrodynamics in the mixing vessel. At complete suspension state it is practically impossible to obtain a representative sample of floating suspended solids in a slurry tank with axial flow by sample withdrawal. Sampling errors can be minimized changing the suspension conditions and sampling technique, pointing to a great caution when this method is applied in practice.