Adiabatic reactor tubular, with plug flow

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. 

Ogunye and Ray (1971a,b) have formulated the optimal control problem for tubular reactors with catalyst decay via a weak maximum principle for this distributed system. Detailed numerical examples have been calculated for both adiabatic and isothermal reactors. For irreversible reactions, constant conversion policies are found to not always be optimal. A practical technique for on-line optimal control for fixed bed catalytic reactors, has been suggested by Brisk and Barton (1977). Lovland (1977) derived a simple maximum principle for the optimal flow control of plug flow processes. 

F to 500°F in a 1-2 parallel-counterflow heat exchanger with a mean overall heat transfer coefficient of 75 Btu/hr ft T.lt is converted to C by the exothermic reaction, A -(- B C, in an adiabatic plug-flow tubular reactor (Figure 4.30). For a process simulator, prepare a simulation flowsheet and show the calcula-1 tion sequence to determine ... 

Thus, even in an adiabatic mode of tubular turbulent chlorination reactor operation (without heat removal), the temperature growth in the reaction zone in the case of BR chlorination (12-15% solution) with molecular chlorine in a tubular reactor, operating in the optimum plug-flow mode in turbulent flows, does not exceed 2 1 °C. The process can be thought to proceed under quasi-isothermal conditions and does not require external or internal heat removal, or special stirring devices for heat and mass exchange intensification. 

We now consider a homogeneous first-order reaction conduced in a plug-flow, tubular reactor. The process is adiabatic. We will now be concerned with the fluid velocity through the reactor instead of the agitation of the fluid. We will also be concerned with the reactor s diameter D and its length L as well, but not its volume per se. The reaction remains the same the effective reaction rate constant is defined as... 

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