Scale operational aspects

Markov theory can be applied advantageously to a variety of technological problems of day-to-day operation in an industrial environment. Such problems transcend the realm of purely physico-chemical and fundamental electrochemical considerations, and are closely linked to (large-scale) technological aspects. This Section demonstrates the utility of the Markovian approach to selected examples. 

Then, a survey of micro reactors for heterogeneous catalyst screening introduces the technological methods used for screening. The description of microstructured reactors will be supplemented by other, conventional small-scale equipment such as mini-batch and fixed-bed reactors and small monoliths. For each of these reactors, exemplary applications will be given in order to demonstrate the properties of small-scale operation. Among a number of examples, methane oxidation as a sample reaction will be considered in detail. In a detailed case study, some intrinsic theoretical aspects of micro devices are discussed with respect to reactor design and experimental evaluation under the transient mode of reactor operation. It will be shown that, as soon as fluid dynamic information is added to the pure experimental data, more complex aspects of catalysis are derivable from overall conversion data, such as the intrinsic reaction kinetics. 

It is pertinent to provide an overview of the environmental concerns associated with the major aspects of chemical processing in large-scale operations, particularly... 

The safety aspects of ozonization—i.e., ozone, pyridine, and solvent toxicity, explosive nature of oxygen—hydrocarbon mixtures, etc., need to be considered in the design and running of any ozonization process, especially large scale operations. However, with the proper design and operating conditions the problems involved are surmountable. 

In radioactive waste treatment, significant operational aspects include the following. Since the operation requires the use of high pressures, there is a need to ensure control of the activity release from possible leaks. As with evaporation, pretreatment of the feed may be necessary to prevent scaling, and where dirty waters are to be fed directly it would be advisable to consider the use of equipment with larger membrane flow channels, which would permit periodic foam ball cleaning of the membrane surface. 

Pyrochemical and dry reprocessing methods are relatively easily adapted to modest scale operation and hence are amenable to close-coupling with reactors. This aspect has been demonstrated at EBR-II (6) and is probably most suitable to fast breeder reactors. 

Three-phase fluidized beds and slurry reactors (see Figs. 30g-l) in which the solid catalyst is suspended in the liquid usually operate under conditions of homogeneous bubbly flow or chum turbulent flow (see regime map in Fig. 33). The presence of solids alters the bubble hydrodynamics to a significant extent. In recent years there has been considerable research effort on the study of the hydrodynamics of such systems (see, e.g., Fan, 1989). However, the scale-up aspects of such reactors are still a mater of some uncertainty, especially for systems with high solids concentration and operations at increased pressures it is for this reason that the Shell Middle Distillate Synthesis process adopts the multi-tubular trickle bed reactor concept (cf. Fig. 30e). The even distribution of liquid to thousands of tubes packed with catalyst, however poses problems of a different engineering nature. 

The validation of a new BPC entails practices that parallel those utilized for the introduction of a new pharmaceutical formulation. Thus, a large part of the initial validation effort must be linked to the developmental activities that precede commercial-scale operation. The similarity is such that aspects of reaction, and purification methodologies should be as similar as possible given of course the difference in the scale of the equipment utilized in the commercial facilities. Any differences between the BPC process utilized for the formulation batches used to establish clinical efficacy and the commercial material must be closely evaluated and their impact on the BPC products chemistry, purity profile, stability, crystal morphology, and other key attributes. 

All mass spectrometers require some degree of day-to-day tuning of operational parameters to provide optimal peak shapes, resolution, and sensitivity, as well as calibration of the mass scale. These aspects are important for the characterization of molecules and their fragments, the resolution of one compound from another, and... 

In evaluating data from small-scale tests, therefore, the sensitivity of the tests needs to be considered in relation to the large-scale operation. In addition, the physicochemical aspects of the reaction — for example, is it heterogeneous does agitation play a major role — need to be taken into account. Reactions with low activation energies which are indicated by broad exotherm peaks also need further evaluation. 

Laboratory and bench-scale operations may not provide a trne picture of the generation of pollutants. But it is essential that the methods for treating efflnent streams to remove pollutants and the types of equipment used for environmental control be a very necessary part of the design and operation of any potential coal liqnefaction procedures. Therefore, it is essential that some consideration be given to this aspect of coal liquefaction (Nowacki, 1979,1980 Kimball and Munro, 1981 Speight, 2011). 

Reversed micellar enzymology has been studied by many researchers [1, 2]. The conversion of apolar compounds by enzymes entrapped in aqueous cores of reversed micelles has drawn the most attention. Reversed micellar enzymology requires not only a large-scale operation, but also enzyme and product recoveries for its practical application. There is still a lack of understanding of many aspects of enzyme behavior in reversed micelles. 

Physical manipulation of such films may be possible through variation in mixing intensity, primarily by local shear. Such interactions would be very scale dependent and could readily be masked in smaller scale operations. The extent to which reactions can be affected by coating of particles is illustrated in an excellent example by Wiederkehr (1988). This study also includes other aspects of reaction system design, such as the choice of continuous smaller volume reactors over batch reactors to reduce the size (and potential energy) of the reacting mass as well as the criticality of residence time distribution in complex reactions. 

The partitioning of a solute i between two immiscible liquid phases 7 = 1 and 2 and the selectivity between two solutes in the two-phase system have so far been considered primarily in the conteid of liquid extraction/solvent extraction in large-scale operations. Many such aspects and some other considerations are also important far the basic equilibria in liquid-liquid chromatography (LLC) (see Section 7.1.5). In LLC, a mobile liquid phase (7 = 2) flows over a porous, finely divided solid phase whose surflice has been coated with a liquid, the stationary phase (J = 1). Any solute introduced via the mobile phase is partitioned between the two liquid phases. For cases where the regular solution-theory based expression (4.1.34f) for Ki may be written as... 

Representativeness can be examined from two aspects statistical and deterministic. Any statistical test of representativeness is lacking becau.se many histories are needed for statistical significance. In the absence of this, PSAs use statistical methods to synthesize data to represent the equipment, operation, and maintenance. How well this represents the plant being modeled is not known. Deterministic representativeness can be answered by full-scale tests on like equipment. Such is the responsibility of the NSSS vendor, but for economic reasons, recourse to simplillcd and scaled models is often necessary. System success criteria for a PSA may be taken from the FSAR which may have a conservative bias for licensing. Realism is more expensive than conservatism. 

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