Effects of Mixing on Reactor Performance

In a previous work (5), it was shown that the effect of mixing on reactor performances is very important. In particular, it was discussed that a) the mixing inside the reactor can be characterized by a recirculating flow rate caused by the impeller in the reaction zone, and that b) an imperfectly mixed reactor requires a higher initiator consumption per polymer produced than a perfectly mixed one operating at the same conditions. 

Effects of Mixing on Reactor Performance 7.2.2.1 Uniformly Mixed Batch Reactor... 

Ritchie, B.W. Simulating the effects of mixing on the performance of unpremixed flow chemical reactors. The Canad. J. of Chem. Eng. 8 (1980), 626-633... 

Effects of Back-mixing on the Performance of Immobilized-biocatalyst Reactors... 

The tank-in-series (TIS) and the dispersion plug flow (DPF) models can be adopted as reactor models once their parameters (e.g., N, Del and NPe) are known. However, these are macromixing models, which are unable to account for non-ideal mixing behavior at the microscopic level. This chapter reviews two micromixing models for evaluating the performance of a reactor— the segregrated flow model and the maximum mixedness model—and considers the effect of micromixing on conversion. 

The statistical description of multiphase flow is developed based on the Boltzmann theory of gases [37, 121, 93, 11, 94, 58, 61]. The fundamental variable is the particle distribution function with an appropriate choice of internal coordinates relevant for the particular problem in question. Most of the multiphase flow modeling work performed so far has focused on isothermal, non-reactive mono-disperse mixtures. However, in chemical reactor engineering the industrial interest lies in multiphase systems that include multiple particle t3q)es and reactive flow mixtures, with their associated effects of mixing, segregation and heat transfer. 

Modeling of Nonideal Flow or Mixing Effects on Reactor Performance... 

In this section we will develop the techniques for modeling mixing effects on reactor performance. As pointed out above, three approaches have received the most attention (1) direct use of RTD information, (2) mixing-cell approximations, and (3) dispersion-plug-flow models. 

The reader may very well wonder what happened to the chemical reaction, since we have mostly discussed mixing models in this chapter without reference to reaction. In review of the various approaches to modeling nonideal flow effects on reactor performance, however, we find that in fact a number of these have already been treated, although perhaps with different applications in mind. The classes of reactor models we have treated are... 

Work was also performed with a mixed batch reactor to gain insight into the effects of agitation on batch systems and the possible influence of fluid velocity on hemicellulose removal. For these tests, a 1-L Parr bomb constructed of Carpenter-20 (Parr Instruments, Moline, IL) was fitted with a flat-blade impeller on a one-piece shaft and operated at varying speeds using a Parr DC motor drive (A1750HC, Parr Instruments, Moline, IL) (62),... 

Models can also be used for parameter sensitivity analysis. Due to the complexity of reaction networks and hydrodynamics, the effects of various factors on the reactor performance are complex. Model analysis provides a guiding tool for process development. The effects of PCa on the yield of acrylonitrile are shown in Fig. 30. As shown, when Pe is less than 0.05, the yield of acrylonitrile changes marginally with Pea, and the reactor can be considered well mixed. When Pea is greater than 10, the yield of acrylonitrile is almost the same as that in a plug-flow reactor. Model simulation also reveal the existence of a Pea-sensitive range... 

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