Nonadiabatic plug flow reactor

To sum up, it is sufficient to treat an adiabatic reactor as a plug-flow reactor. If the axial dispersion effect is to be included, only the heat dispersion term needs to be added. In the case of nonadiabatic, nonisothermal reactors, axial dispersion terms can be neglected in comparison to the radial dispersion terms. In addition, the radial dispersion terms can often be neglected if the radial aspect ratio is small. The conservation equations for various cases are summarized in Table 9.1. 

NONISOTHERMAL, NONADIABATIC BATCH, AND PLUG-FLOW REACTORS... 

The flow patterns, composition profiles, and temperature profiles in a real tubular reactor can often be quite complex. Temperature and composition gradients can exist in both the axial and radial dimensions. Flow can be laminar or turbulent. Axial diffusion and conduction can occur. All of these potential complexities are eliminated when the plug flow assumption is made. A plug flow tubular reactor (PFR) assumes that the process fluid moves with a uniform velocity profile over the entire cross-sectional area of the reactor and no radial gradients exist. This assumption is fairly reasonable for adiabatic reactors. But for nonadiabatic reactors, radial temperature gradients are inherent features. If tube diameters are kept small, the plug flow assumption in more correct. Nevertheless the PFR can be used for many systems, and this idealized tubular reactor will be assumed in the examples considered in this book. We also assume that there is no axial conduction or diffusion. 

All simulators provide one-dimensional, plug-flow models that neglect axial dispersion Thus, there are no radial gradients of temperature, composition, or pressure and mass diffusion and heat conduction do not occur in the axial direction. Operation of the reactor can bt adiabatic, isothermal, or nonadiabatic, nonisothermal. For the latter, heat transfer to or fron the reacting mixture occurs along the length of the reactor. 

A successful application of the plug-flow heterogeneous model has been reported by Cappelli and coworkers (1972). Their simulation results show excellent agreement between the model predictions and the data that they obtained from a nonadiabatic industrial reactor for the synthesis of methanol from CO and Hj. The work by Dumez and Froment (1976) is another example of the application of the plug-flow heterogeneous model to an industrial reactor. 

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