Reactor design models

Figure 1.6 The onion model of process design. A reactor design is needed before the separation ind recycle system can be designed, and so on. (From Smith and Linnhoff, Trans. IChemE, CkERD, 66 195, 1988 reproduced by permission of the Institution of Chemical Engineers.)...

Remarks The aim here was not the description of the mechanism of the real methanol synthesis, where CO2 may have a significant role. Here we created the simplest mechanistic scheme requiring only that it should represent the known laws of thermodynamics, kinetics in general, and mathematics in exact form without approximations. This was done for the purpose of testing our own skills in kinetic modeling and reactor design on an exact mathematical description of a reaction rate that does not even invoke the rate-limiting step assumption. 

Modeling of Chemical Kinetics and Reactor Design Appendix Heat Combustion... 

The kinetics of a complex catalytic reaction can be derived from the results obtained by a separate study of single reactions. This is important in modeling the course of a catalytic process starting from laboratory data and in obtaining parameters for catalytic reactor design. The method of isolation of reactions renders it possible to discover also some other reaction paths which were not originally considered in the reaction network. 

Friis and Hamielec (48) offered some comments on the continuous reactor design problem suggesting that the dispersed particles have the same residence time distribution as the dispersing fluid and the system can be modeled as a segregated CSTR reactor. 

To do this we developed a computer model to predict the kinetic conditions during the runaway stage. The kinetic model is used to estimate the reaction rates, temperatures, pressures, viscosities, conversions, and other variables which influence reactor design. 

Manufacturing economics require that many devices be fabricated simultaneously in large reactors. Uniformity of treatment from point to point is extremely important, and the possibility of concentration gradients in the gas phase must be considered. For some reactor designs, standard models such as axial dispersion may be suitable for describing mixing in the gas phase. More typically, many vapor deposition reactors have such low L/R ratios that two-dimensional dispersion must be considered. A pseudo-steady model is... 

Reactor design usually begins in the laboratory with a kinetic study. Data are taken in small-scale, specially designed equipment that hopefully (but not inevitably) approximates an ideal, isothermal reactor batch, perfectly mixed stirred tank, or piston flow. The laboratory data are fit to a kinetic model using the methods of Chapter 7. The kinetic model is then combined with a transport model to give the overall design. 

Four elements of microchannel scale-up models will be described pressure-drop design, heat-transfer design, reactor design, and mechanical and manufacturing designs. 

The use of integrated reactor and heat-transfer models is essential for scale-up. Figure 11.7 shows an early reactor design for the same chemistry that was developed without the use of integrated models. Other unoptimized designs with temperature spikes have also been reported [12,44]. Integrated models were used to... 

Boundary layer similarity solution treatments have been used extensively to develop analytical models for CVD processes (2fl.). These have been useful In correlating experimental observations (e.g. fi.). However, because of the oversimplified fiow description they cannot be used to extrapolate to new process conditions or for reactor design. Moreover, they cannot predict transverse variations In film thickness which may occur even In the absence of secondary fiows because of the presence of side walls. Two-dimensional fully parabolized transport equations have been used to predict velocity, concentration and temperature profiles along the length of horizontal reactors for SI CVD (17,30- 32). Although these models are detailed, they can neither capture the effect of buoyancy driven secondary fiows or transverse thickness variations caused by the side walls. Thus, large scale simulation of 3D models are needed to obtain a realistic picture of horizontal reactor performance. 

Simulation models are essential tools for reactor design and optimization. A general simulation model consists of a reactor and a reaction model [1]. The reactor model accounts for the reactor type and for the flow pattern in the reactor, while the reaction or kinetic model describes the kinetics of the chemical reactions occurring. 

Kinetic Rate Lam y/Vfateriat Balance reaction/deactivation/ reactor design equation, heat/mass transpat/ fluid-flow model,... 

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