Selection of Mixers

For Final design details and selection of mixer elements, refer directly to the manufacturers, as each design is different and may not perform like a competitor s. 

TABLE 18-2 Four Different Selections of Mixers with Different Mixing Characteristics on 14,000 ft of Leach Tanks... 

The mixing device is an important element in designing stirred tank reactors. Perry s handbook or the monograph of Tatterson (1991) can be consulted for the selection of mixers. A good presentation can be found in McCabe et al. (1992). 

Selection of Fractionator 11 gives pure hexane, which can be recycled to Mixer 1. The distillate Dll, however, is a problem. It cannot be distilled because of its location next to a distillation boundary. It is outside of the two-phase region, so it cannot be decanted. In essence, no further separations are possible. However, using the Recycle heuristics, it can be mixed into the MSA recycle stream without changing the operation of Mixer 1 appreciably. However, as both outlet streams are mixed together. Fractionator 11 is not really needed. The mixture of hexane and isopropanol, 07, could have been used as the MSA composition in the first place. 

The final loose end in the process is the aqueous decanter product, A7. The hexane must be removed before the mixture can be sent to wastewater treatment, ie, accepted as a water by-product. Two opportunistic separations. Fractionators 12 and 13, are possible. Selection of Fractionator 13 gives pure water underflow, and a distillate similar to D5. Distillate D13 can be recycled back and mixed with D5 without affecting the operation of Mixer 1. AH streams are processed and the flow sheet produces both desired products (Fig. 5b). 

TPEs from blends of rubber and plastics constitute an important category of TPEs. These can be prepared either by the melt mixing of plastics and rubbers in an internal mixer or by solvent casting from a suitable solvent. The commonly used plastics and rubbers include polypropylene (PP), polyethylene (PE), polystyrene (PS), nylon, ethylene propylene diene monomer rubber (EPDM), natural rubber (NR), butyl rubber, nitrile rubber, etc. TPEs from blends of rubbers and plastics have certain typical advantages over the other TPEs. In this case, the required properties can easily be achieved by the proper selection of rubbers and plastics and by the proper change in their ratios. The overall performance of the resultant TPEs can be improved by changing the phase structure and crystallinity of plastics and also by the proper incorporation of suitable fillers, crosslinkers, and interfacial agents. 

The problems relating to mass transfer may be elucidated out by two clear-cut yet different methods one using the concept of equilibrium stages, and the other built on diffusional rate processes. The selection of a method depends on the type of device in which the operation is performed. Distillation (and sometimes also liquid extraction) are carried out in equipment such as mixer settler trains, diffusion batteries, or plate towers which contain a series of discrete processing units, and problems in these spheres are usually solved by equilibrium-stage calculation. Gas absorption and other operations which are performed in packed towers and similar devices are usually dealt with utilizing the concept of a diffusional process. All mass transfer calculations, however, involve a knowledge of the equilibrium relationships between phases. 

The performance of a solids mixer was assessed by calculating the variance occurring in the mass fraction of a component amongst a selection of samples withdrawn from the mixture. The quality was tested at intervals of 30 s and the data obtained are ... 

Case-based reasoning has earlier been used for instance for equipment design. Koiranen and Hurme (1997) have used case-based reasoning for fluid mixer design and for the selection of shell-and-tube heat exchangers. They have included an estimation of design quality for the case retrieval beside technical factors. 

The types of equipment used, which range from stirred tanks and mixer-settlers to centrifugal contactors and various types of columns, affect both capital and operating costs [9]. In the decision to build a plant, the choice of the most suitable contactor for the specific situation is most important. In some systems, because of the chemistry and mass transfer rates involved, several alternative designs of contacting equipment are available. In the selection of a contactor, one must consider the capacity and stage requirements solvent type and residence time phase flow ratio physical properties direction of mass transfer phase dispersion and coalescence holdup kinetics equilibrium presence of solids overall performance and maintenance as a function of contactor complexity. This may appear very complicated, but with some experience, the choice is relatively simple. 

M 39] [P 37] Using an azo-type competitive reaction, the selectivities were compared for the P- and V-type micro mixers having straight and oblique fluid injection, respectively [41]. In this way, laminar- and turbulent-flow mixing achieved by vertical interdigital microstructured mixers can be compared. The selectivities of the turbulent V-type mixer are better to some extent as compared with the P-type device however, neither approaches the characteristics of the ideal tubular reactor. The micro devices, however, are better than a conventional jet mixer. 

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