Scale solids mixing

Chlorine oxidation of sodium chlorite has also been used on both an industrial scale (by mixing concentrated aqueous solutions) or on a laboratory scale (by passing CVair through a column packed with the solid chlorite) ... 

Scale-up techniques for using the results of pilot plant or bench scale test w ork to establish the equivalent process results for a commercial or large scale plant mixing system design require careful specialized considerations and usually are best handled by the mixer manufacturer s specialist. The methods to accomplish scale-up will vary considerably, depending on whether the actual operation is one of blending, chemical reaction tvith product concentrations, gas dispersions, heat transfer, solids suspensions, or others. 

One discouraging problem is the decrease in reactor or combustor performance when a pilot plant is scaled up to a larger commercial plant. These problems can be related to poor gas flow patterns, undesirable solid mixing patterns and physical operating problems (Matsen, 1985). In the synthol CFB reactors constructed in South Africa, first scale-up from the pilot plant increased the gas throughput by a factor of 500. Shingles and McDonald (1988) describe the severe problems initially encountered and their resolution. 

As fluidized beds are scaled up from bench scale to commercial plant size the hydrodynamic behavior of the bed changes, resulting, in many cases, in a loss of performance. Although there have been some studies of the influence of bed diameter on overall performance as well as detailed behavior such as solids mixing and bubble characteristics, generalized rules to guide scale-up are not available. The influence of bed diameter on performance will differ for different flow regimes of fluidization. 

Farrell, P. A., Hydrodynamic Scaling and Solids Mixing in Pressurized Fluidized Bed Combustors, Ph.D. Thesis, Massachusetts Institute of Technology (1996)... 

Experimentally, the use of mixed acid for the nitration of aromatic substrates is very convenient. Reactions are often quenched by the addition of water, where the product usually precipitates. Solids are simply filtered from the acid liquors and oils are either separated or extracted into organic solvents. However, on an industrial scale, these mixed acid nitrations create environmental problems from air and water pollution (Sections 4.3.5 and 4.8.2). 

Gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are widely used in the chemical and petrochemical industries for processes such as methanol synthesis, coal liquefaction, Fischer-Tropsch synthesis and separation methods such as solvent extraction and particle/gas flotation. The hydrodynamic behavior of gas-liquid bubble columns and gas-liquid-solid slurry bubble columns are of great importance for the design and scale-up of reactors. Although the hydrodynamics of the bubble and slurry bubble columns has been a subject of intensive research through experiments and computations, the flow structure quantification of complex multi-phase flows are still not well understood, especially in the three-dimensional region. In bubble and slurry bubble columns, the presence of gas bubbles plays an important role to induce appreciable liquid/solids mixing as well as mass transfer. The flows within these systems are divided into two... 

Figure 7 Illustration of the mixing between two resonances — for the double-well potential shown in (a) — as a function of the potential parameter a (the width of the inner potential well) and its influence on the resonance energies (middle two panels) and widths r (lower two panels, plotted on logarithmic scales). Solid lines represent the narrow resonance n located in the inner well, while the dashed lines indicate the broad resonance b localized in the outer well. The weak-coupling limit is shown in (b) and (c), while the strong-coupling limit is illustrated in (d) and (e). In the example discussed in the text, Vi = 8 and V2 = 17 for (b) and (c) and V2 = 11 for (d) and (e).

A familiar experimental technique used in solids mixing is method 4, which involves analysis of a number of samples of size v. Danckwerts Computes the volume scale of segregation F, from this analysis as follows ... 

When substances in liquids or solids mix completely on an atomic scale, that is, when they mix homogeneously and randomly, the mixing usually decreases the es-... 

In Fig. 9.21, each experimental curve showed an overshoot before settling into its asymptotic value. This overshoot was a consequence of the large-scale solids recirculation in contrast to smaller scale diffusion. The overshoot was characteristic at lower velocities and it disappeared at greater velocities. The mixing behavior is similar for particles of differing size. 

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