Tube-wall reactor reactant conversion

A numerical example was used to examine the desired product yield versus reactant conversion behavior in a tube-wall reactor described above. Values assumed for the physical and chemical properties and the operating conditions are ... 

The reactor will be designed to operate at a conversion of 80% and have a production rate of 6,000 Ib/day of phthalic anhydride. It will be a multitube type (illustrated in Fig. 13-1) with heat-transfer salt circulated through the jacket. The temperature of the entering reactants will be raised to 340°C by preheating, and the circulating heat-transfer salt will maintain the inside of the reactor-tube walls at 340°C. 

In a similar manner, the temperature can vary with radial position, even if the reactor is adiabatic. If the reaction is exothermic, the temperature close to the wall will be relatively high, since the reactant conversion is high in this region. Conversely, the temperature will be relatively low at the center of the tube, where the residence time and the reactant conversion are lowest. The situation is shown schematically in Figure 10-3. 

This comparison focuses on the comer regions in square ducts that are nonexistent in tubes. In both configurations, the momentum boundary layer thickness is substantial (i.e., Effective/2) for fully developed laminar flow. The no-slip boundary condition for viscous flow near the walls increases the mass transfer boundary layer thickness and reduces the flux of reactants toward the catalytic surface relative to plug flow. This effect is significant in the comer regions of the channel with square cross section. Since the entire active surface in heterogeneous tubular reactors is equally accessible to reactants, one predicts larger conversion in tubes via equation (23-71) ... 

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