Reactor design, optimal multiple

Dynamic Modeling of Molecular Weight and Particle Size Development and Application to Optimal Multiple Reactor System Design... 

Pollock, M. J., MacGregor, J. F., and Hamielec, A. E. (1981) Continuous poly (vinyl acetate) emulsion polymerization reactors dynamic modeling of molecular weight and particle size development and application to optimal multiple reactor system design. Computer Applications in Applied Polymer Science, (ed. T. Provder), ACS, Washington, pp. 209-20. 

Design of sonochemical reactors is a very important parameter in deciding the net cavitational effects. Use of multiple transducers and multiple frequencies with possibility of variable power dissipation is recommended. Theoretical analysis for predicting the cavitational activity distribution is recommended for optimization of the geometry of the reactor including the transducer locations in the case of multiple transducer reactors. Use of process intensifying parameters at zones with minimum cavitational intensity should help in enhancing the net cavitational effects. 

The above analysis is, of course, based on the assumption of simple order reactions under Tafel operation and on the availability of sufficiently accurate data ( 5-10%). With complex reaction kinetics, for example, those involving surface adsorption terms (Eq. 16), a nonlinear regression analysis would yield the best estimate of a, Uj, and for a possible kinetic model. In all cases, use of these parameters for predicting the performance of an electrochemical reactor or the selectivity of a reaction scheme should be restricted within the potential, concentration, and temperature range that they were determined. We should stress here that kinetic information is presently scanty for complex, multiple electrochemical reactions, yet it is essential for the design, optimization, and control of electrochemical processes. 

Reactor effluents are almost never products that meet purity specifications. Besides the products, effluents may contain reactants, inerts, products of undesired side reactions, and feed impurities. Thus, almost every chemical process that involves a chemical reaction section also involves one or more separation sections in addition to one or more recycle streams. A major challenge of process design is to devise an optimal scheme for uniting the reaction and separation functions of a process. This chapter presents many of the considerations involved in that optimization. Although Figure 7.1 shows only one reactor section, multiple reactor sections are sometimes required, with separation sections located between each pair of reactor sections... 

The simplification made possible by the use of the reactor point effectiveness allows a close examination of the design of a reactor affected by catalyst deactivation, the characteristic of which is time-dependence. This leads to the optimal design for a reactor whose performance is time-dependent. Finally, reactor design involving multiple reactions is considered, using essentially the approach of reactor point effectiveness. 

There are innumerable industrially significant reactions that involve the formation of a stable intermediate product that is capable of subsequent reaction to form yet another stable product. These include condensation polymerization reactions, partial oxidation reactions, and reactions in which it is possible to effect multiple substitutions of a particular functional group on the parent species. If an intermediate is the desired product, commercial reactors should be designed to optimize the production of this species. This section is devoted to a discussion of this and related topics for reaction systems in which the reactions may be considered as sequential or consecutive in character. 

Separations are an important phase in almost all chemical engineering processes. Separations are needed because the chemical species from a single source stream must be sent to multiple destinations with specified concentrations. The sources usually are raw material inputs and reactor effluents the destinations are reactor inputs and product and waste streams. To achieve a desired species allocation you must determine the best types and sequence of separators to be used, evaluate the physical or chemical property differences to be exploited at each separator, fix the phases at each separator, and prescribe operating conditions for the entire process. Optimization is involved both in the design of the equipment and in the determination of the optimal operating conditions for the equipment. 

These numbers show that the optimal economic steady-state design is the multiple-stage reactor system. The higher the conversion, the larger the economic incentive to have multiple stages. At 95 percent conversion, the capital cost of a three-CSTR process is 67 percent that of a one-CSTR process. At 99 percent conversion, the cost is only 38 percent. Thus, if only steady-state economics is considered, the design of choice in these numerical cases is a process with two or three CSTRs in series. 

While the potential for highly effective RVACS heat removal exists for the AHTR, detailed design will be required to optimize and maximize its heat removal capability. There are multiple RVACS cooling options, including operating the reactor vessel at lower temperatures than the molten salt coolant. Scaling of both the thermal inertia and RVACS heat removal capability of the AHTR suggest that reactor thermal... 

The alternative to traditional scale-up, proposed in the context of microreaction technology and coined scale-out or numbering-up , has attracted considerable academic interest. With this approach, the system of interest is studied only on a small scale in so-called microreactors and the final reactor design is simply a multiplication of interconnected small-scale devices. No attempt is made at large-scale optimization. Instead, the optimal functioning point is found for a small-scale device by empirical laboratory studies and then is simply reproduced by replication into the large interconnected structure. 

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