12.3.1 Column Configuration

For the decomposition reaction A , B + C, we consider the case when the reactant is the intermediate boiler, that is, IK , LK + HK. With a one-reactant, two-product reaction system, the column has a bottoms product and a top product because the two products B and C are the lightest and heaviest boilers, respectively. Figure 12.47 provides the flowsheet. Steady-state conditions and design parameters are given in Table 12.4. This is the optimal design in terms of TAC as discussed in Chapter 6. Figure 12.48 contains composition profiles and the fraction of total conversion on tray i (Ri/Rt) in the reactive zone. Figure 12.49 gives the temperature profile.

The column diameter is calculated from the sizing relationships given in Chapter 6, which gives a diameter of 0.92 m. A liquid height of 0.05 m is assumed for each tray. Tray holdup on the reactive trays is 909 mol. The holdups in the column base and reflux drum are sized to give a 5-min residence time when the liquid level is held at 50%.

Three alternative control structures are explored in the following sections. The objective is to maintain the specified purities of the top product at 98 mol% B and the bottoms product at 98 mol% C. The load disturbances that are considered are production rate changes and feed composition variations.

TABLE 12.4 Steady-State Conditions and Design Parameters for TAC Optimum Case

Fresh feed flowrate of A (mol/s)

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