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Figure 9.9 (Continued).

Figure 9.9 (Continued).

Figure 9.11 Design spec for distillate.

Adding more stripping trays reduces energy consumption and increases MTBE production. However, the improvements become increasingly smaller above about nine trays.

Other Parameters. Attempts to explore the number of reactive stages were unsuccessful because the program would not converge. The same occurred when the number of rectifying stages was changed.

Aspen Plus sometimes has trouble converging standard conventional distillation columns, particularly with design specifications. Convergence problems with reactive distillation columns are encountered even more frequently.

9.1.6 Chemical Equilibrium Model

In the previous sections we utilized the kinetic subroutine supplied by Aspen Technology, which uses a kinetic expression for the reaction rate. It is interesting to compare this column design with the results when chemical equilibrium is assumed on the reactive trays. This is done in Aspen Plus by simply specifying that the reaction is Equilibrium on the Edit Reactions window, as shown in the upper picture of Figure 9.15. The lower picture shows that the chemical equilibrium constant is calculated from the Gibbs free energies.

Figure 9.12 Steady-state conditions with kinetic model.

Figure 9.12 Steady-state conditions with kinetic model.

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