Reactor, networks types

You have been asked to carry out a residence time distribution study on a reactor network that has evolved over the years by adding whatever size and type of reactor was available at the moment. The feed stream presently contains 1... 

Here, the last two equations define the flow rate and the mean residence time, respectively. This formulation is an optimal control problem, where the control profiles are q a), f(a), and r(a). The solution to this problem will give us a lower bound on the objective function for the nonisothermal reactor network along with the optimal temperature and mixing profiles. Similar to the isothermal formulation (P3), we discretize (P6) based on orthogonal collocation (Cuthrell and Biegler, 1987) on finite elements, as the differential equations can no longer be solved offline. This type of discretization leads to a reactor network more... 

What general principle concerning the order in which different reactor types should be employed in an isothermal reactor network does this problem exemplify Hint Consider rate expressions of the general nth-order form and ask yourself how the various types of reactors should be employed for optimum productivity.)... 

In the present section we indicate how tracer residence time data may be used to predict the conversion levels that will be obtained in reactors with nonideal flow patterns. As indicated earlier, there are two types of limiting processes that can lead to a distribution of residence times within a reactor network. 

By a reactor structure, we have in mind a well-defined arrangement of reactors (a reactor network) that produces a particular output. The network might typically be composed of various reactor types. The kinds of problems that we will investigate in this book all fall into this category. We will be interested in looking at how combinations of reactors (as opposed to a single reactor) can often provide meaningful improvements to a problem. 

In Chapter 4, we shall expand our knowledge of the geometric viewpoint to include reaction, and describe the function of three fundamental reactor types that are used in AR theory. With this knowledge, we will be in a position to generate candidate ARs efficiently, and use this information to form optimal reactor networks, which may be applied to optimize complex reactive systems. 

I Shunt reactors These are provided as shown in Figure 24.23 to compensate for the distributed lumped capacitances, C , on EHV networks and also to limit temporary overvoltages caused during a load rejection, followed by a ground fault or a phase fault within the prescribed steady-state voltage limits, as noted in Table 24.3. They ab.sorb reactive power to offset the charging power demand of EHV lines (Table 24.2, column 9). The selection of a reactor can be made on the basis of the duty it has to perform and the compensation required. Some of the different types of reactors and their characteristics are described in Chapter 27. 

The selection of reactor type in the traditionally continuous bulk chemicals industry has always been dominated by considering the number and type of phases present, the relative importance of transport processes (both heat and mass transfer) and reaction kinetics plus the reaction network relating to required and undesired reactions and any aspects of catalyst deactivation. The opportunity for economic... 

In previous chapters, we deal with simple systems in which the stoichiometry and kinetics can each be represented by a single equation. In this chapter we deal with complex systems, which require more than one equation, and this introduces the additional features of product distribution and reaction network. Product distribution is not uniquely determined by a single stoichiometric equation, but depends on the reactor type, as well as on the relative rates of two or more simultaneous processes, which form a reaction network. From the point of view of kinetics, we must follow the course of reaction with respect to more than one species in order to determine values of more than one rate constant. We continue to consider only systems in which reaction occurs in a single phase. This includes some catalytic reactions, which, for our purpose in this chapter, may be treated as pseudohomogeneous. Some development is done with those famous fictitious species A, B, C, etc. to illustrate some features as simply as possible, but real systems are introduced to explore details of product distribution and reaction networks involving more than one reaction step. 

In this chapter, we develop some guidelines regarding choice of reactor and operating conditions for reaction networks of the types introduced in Chapter 5. These involve features of reversible, parallel, and series reactions. We first consider these features separately in turn, and then in some combinations. The necessary aspects of reaction kinetics for these systems are developed in Chapter 5, together with stoichiometric analysis and variables, such as yield and fractional yield or selectivity, describing product distribution. We continue to consider only ideal reactor models and homogeneous or pseudohomogeneous systems. 

An RTD curve, for instance, can be represented in algebraic form in more than one way and for different purposes. The characteristic bell shape of many RTDs is evident in the real examples of Figure 5.4. Such shapes invite comparison with some well-known statistical distributions and representation of the RTD by their equations. Or a realistic mechanism may be postulated, such as a network of reactor elements and a type of flow pattern, and the parameters of that mechanism evaluated from a measured RTD. 

A distinction is to be drawn between situations in which (a) the flow pattern is known in detail (b) only the residence time distribution is known or can be calculated from tracer response data. Different networks of reactor elements can have similar RTDs, but fixing the network also fixes the RTD. Accordingly reaction conversions in a known network will be unique for any type of rate equation, whereas conversions figured when only the RTD is known proceed uniquely only for linear kinetics, although they can be bracketed in the general case. 

The networks considered in this study are of three main types (identified as A, B, and C), differing from one another by the mode of connection between the participating biochemical neurons (see Table 5.1). For each network considered, an analytical model was written describing the performance of the network in kinetic terms. As the first stage in this program, analytical models were developed for the case when the reactions of the biochemical networks take place in fed-batch reactors. It is envisaged that these models will be extended to packed bed reactors in the future. 

The optimal distribution of silver catalyst in a-Al203 pellets is investigated experimentally for the ethylene epoxidation reaction network, using a novel single-pellet reactor. Previous theoretical work suggests that a Dirac-delta type distribution of the catalyst is optimal. This distribution is approximated in practice by a step-distribution of narrow width. The effect of the location and width of the active layer on the conversion of ethylene and the selectivity to ethylene oxide, for various ethylene feed concentrations and reaction temperatures, is discussed. The results clearly demonstrate that for optimum selectivity, the silver catalyst should be placed in a thin layer at the external surface of the pellet. 

Although this reaction network has been studied extensively, its mechanism is still under debate (10). In this study, a single-pellet reactor was used, and the pellet was prepared mechanically by pressing the active catalyst layer between two alumina layers. In this way a step-type catalyst pellet was produced, which approximated a Dirac-type catalyst distribution. 

The wide spectrum of external conditions which can influence the conformational state of charged gels (the variation of these conditions can induce collapse or decollapse transition), makes these gels possible materials for data control devices of different types, absorbers, reactors and catalysts with regulated diffusion characteristics, carriers of immobilized enzymes, etc. The networks synthesized at high dilution are also new mechano-chemical systems which show very high sensitivity to external actions. 

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