Particle size analysis elutriation

Andrews Elutriator. A device for particle-size analysis. It consists of a feed vessel or tube a large hydraulic classifier an intermediate classifier a graduated measuring vessel. (L. 

Kopecky Elutriator. An elutriator consisting of three cylinders of different diameters, it has been used for the particle-size analysis of clays. (Tonind. Ztg., 42, 629,1918.)... 

Nobel Elutriator. An early type of multiple-vessel elutriator for particle-size analysis it is described in Z. Anal. 

If, for instance, the separation effect is influenced only by the mobility of particles in fluids, the terminal setding velocity or Stokes diameter could be used for the size x and the method of particle size analysis would be chosen accordingly (sedimentation or elutriation). 

The catalyst sample is confined to a small cup, into which gas is tangentially added at a high velocity (about 150 m/s). After a test run over a period of an hour, the so-called Davison Index (DI) is determined by measuring the increase in the weight fraction of particles below 20 microns. The increase is determined from both the fraction of elutriated fine material and a particle size analysis of the remaining fraction in the cup. 

The elutriation method is really a reverse sedimentation process in which the particles are dispersed in an upward flowing stream of fluid. All particles with terminal falling velocities less than the upward velocity of the fluid will be carried away. A complete size analysis can be obtained by using successively higher fluid velocities. Figure 1.4 shows the standard elutriator (BS 893)(6i for particles with settling velocities between 7 and 70 mm/s. 

Entrainment may be defined as the carryover of ejected particles, while selective entrainment of finer or less dense particles is often referred to as elutriation. In most industrial processes, neither entrainment nor elutriation are desirable, which is in sharp contrast to this particular application. Consequently, there is very little research aimed specifically at enhancing the selective removal of less dense material from fluidised beds. Most research on entrainment is based on dimensional analysis applied to experimental data either with no or very limited consideration of the underlying physics Predictions made from these correlations are limited to very simple geometries. They may vary widely even for reactor airangements close to the experimental conditions they are based on, and are often completely unreliable when conditions are markedly different. In several intemal studies they have been found inadequate for entrainment and elutriation predictions in the fluidised bed system under investigation. The problem is too complex to be adequately represented by a small number of ordinary equations that would simply require substitution of a few parameters to obtain the rales of entrainment of the different particle size ftactions. 

The shape of the average specimen is such that only rarely can it be directly placed into the diffractometer for analysis, so that special care has to be taken to achieve the random distribution of the crystallites to have meaningful peak intensities. The problems arising in sample preparation are (1) Particle size. The powdered sample must consist of particles smaller than 5 pm. Collection and separation of particles of these dimensions can be effected by sieving, sedimentation, or elutriation. (2) Surface flatness. Special precautions are needed to make the surface smooth and flat, with its plane including the diffractometer axis. If required, common binders, for instance, collodion, paraffin wax, or silicone grease, are applicable. (3) Preferred orientation. When it is necessary to ensure that the particles do not show preferred orientation, mix crushed glass or other amorphous medium with the powder or coat the plane surface of the sample carrier with a film of adhesive that dries at a moderate rate and then dust a layer of powder on the adhesive, polyfvinyl chloride), after it has become tacky. 

The above calculation is quite tedious and gets complicated by the fact that the properties which ultimately control the magnitude of these fourteen unknown quantities further depend on the physical and chemical parameters of the system such as reaction rate constants, initial size distribution of the feed, bed temperature, elutriation constants, heat and mass transfer coefficients, particle growth factors for char and limestone particles, flow rates of solid and gaseous reactants. In a complete analysis of a fluidized bed combustor with sulfur absorption by limestone, the influence of all the above parameters must be evaluated to enable us to optimize the system. In the present report we have limited the scope of our calculations by considering only the initial size of the limestone particles and the reaction rate constant for the sulfation reaction. 

BANCO CENTRIFUGAL CLASSIFIER. This is a proprietary instrument that is essentially a centrifugal air elutriator. Air and dispersed powder samples are drawn thru the cavity of a rotating hollow disc in a radially inward direction against centrifugal forces. The powder particles are thus divided into under- and oversize fractions, collected, and weighed. Separation into different size-fractions is made by altering the air velocity. About 20g of sample are required for analysis, and 8 size determinations can be made in 2 hours (Ref. 10)... 

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