Elutriation constant for

Here x, is the mass fraction of particle-size fraction i in the bed material and x( is the elutriation rate constant for this fraction... 

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. 

First calculate the elutriation rate constants for the three size ranges under these conditions from the Zenz and Weil correlation [Equation (7.46)]. The value of particle size X used in the correlation is the arithmetic mean of each size range ... 

Correlations compiled by Leva (1960) for the elutriation rate coefficient are shown in Figure 11.5. The elutriation constant is obtained from the definition of and data from steady state runs (see Problem 11.2) ... 

FIG. 7.32. Correlation for the elutriation constant (S. Yagi and T. Aoichi, quoted by Kunii and Levenspiel [47]) O, continuous operation, batch operation. 

The real coating process in the studied Wurster coater apparatus with the bed mass of 3 kg contains about 21.8x10 particles with the size of 550 im. Unfortunately, the numerical effort for the calculation of the DPM model increases with increasing the number of simulated particles. The DPM model is unable to represent this number of particles, at least with the actually available computing power. However, the number of particles can be reduced by conservation of the particle and fluid dynamics in the simulated apparatus and its real geometry. In this work a scaling approach proposed by Link et al. (2009) and extended by Sutkar et al. (2013) has been used, in which the scahng of the particle size was carried out. Due to the size increase, the adequate properties of sohd and gas phase have been adapted to keep the dimensionless numbers Archimedes At) and Reynolds Re) and the velocities of minimal fluidization and elutriation constant. 

Beckman Elutriation Method. The Beckman elutriation method uses a chamber designed so that the centrifugal effect of the radial inward fluid flow is constant (Fig. 3). The separation chambers are made of transparent epoxy resin which faciUtates observation of the movements of the cell boundary in strobe light illumination. This enables detection of the radius at which the cells are separating. When a mixture of cells, eg, mononuclear white cells, enters the chamber, separation can be achieved by fine tuning centrifuge speed and inward fluid flow to the specific cell group. This is a laboratory method suitable for relatively small numbers of cells. Chambers are available in sizes to handle 2-3 x 10 , 1 2 x 10 , and 1 x 10 ° cells. The Beckman chambers can be appHed to collect mononuclear cells from bone marrow aspirates. 

Stojkovski, V, and Kostic , Z. Empirical Correlation for Prediction of the Elutriation Rate Constant. Thermal Sci., 1 (2003) 43-58. 

The fraction mc e/mF lost by elutriation is determined by the elutriation rate constant K(R), the particle size distribution p(R) of carbon in the bed, and the carbon loading WQ (Eq. 10). A first approximation for this loss may be obtained by assuming that that particles of feed diameter d shrink to an elutriable size d, approximately 300 ym from Figure 4, and are then blown out of the bed. For this simple model... 

Elutriation—the selective removal of fines by entrainment—has been studied by several workers (K25, L6, M23, 08, T7, W2). Most of this work has been reviewed by Kunii and Levenspiel (K24) and Leva and Wen (in D5). However, Merrick and Highley (M13) point out that early correlations for elutriation rate constant are inaccurate for very fine particles, since they assume m, proportional. od% (rather than toc/p) and hence predict that the elutriation rate constant reduces to zero as the particle size reduces to zero. Thus, care must be taken when such empirical equations are applied to a fluid bed containing fine particles. 

For specific situations, such as constant-size feed, linear kinetics, or no elutriation, these equations can be simplified to obtain analytical solutions. 

Drying air temperature and flow rate are normally fixed at a constant value. However, by adjusting the airflow rate and its temperature, it is possible to save energy and reduce attrition. Mechanical assistance such as agitation or vibration is normally applied for processing materials that are difficult to fluidize. Figure 8.6 shows a typical batch FBD with expanded freeboard and built-in internal bag fillers. Expanded freeboard is used to reduce elutriation of fine particles. 

The quartz made fluidized-bed reactor used for catalyst preparation was electrically heated a cyclone was incorporated into the freeboard of the reactor to prevent elutriation of fines. The support, which was fluidized by N2 was first thermally pretreated to remove physisorbed water. Then the vaporized metal acetyl acetonate was adsorbed on the support at 400 K at constant partial pressure in a flow of N2 for a ven period of time. The subsequent decomposition of the adsorbate was carried out by increasing the fluidized-bed temperature with a rate of 4 K/min. Pt was deposited in either N2 or air at 573 K Cr203 and V2O5 were deposited in air at 673 K. Pt catalysts which were decomposed in N2 were additionally treated in air at 573 K (Pt/Si02 catalysts) respectively at 773 K (Pt/Al203 catalysts) [4, 5]. 

Various sedimentation and elutriation methods are available but these are of value only after standardization for a given type of powder or gel with constant aggregate density. The same applies to measurement of permeability to a stream of air or liquid. The external surface area of porous aggregates, which is an indirect measure of aggregate, size, can be measured by ambient pressure permeametric measurements. Gas is forced through a bed of powder and the flow rate and pressure drop are measured. The apparatus that is used for the flow method of measuring surface area by nitrogen adsorption (Quantasorb from Quantochrome Corporation) can be adapted to this measurement. 

Schnitzler s Gold Purple. A tin-gold colour, produced by a wet method it has been used for the decoration of porcelain. Schone s Apparatus. An elutriator consisting of a tall glass vessel tapering towards the bottom, where water enters at a constant rate. Schone s formula is V = 104.7(5 - l)i-57 )i.57 where V is the velocity of water (mm/s) required to carry away particles of diameter D and sp. gr. S. (E. 5chone, Uber Schlammanalyse und einen neuen Schlammapparat, Berlin, 1867.)... 

For fine particles with a terminal velocity below the gas velocity in the freeboard, the elutriation rate constant K increases with decreasing particles size. While there is a general consensus about this when... 

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