H 390 380 370 360 350

Tray

Figure 2.6 Effect of number of reactive trays on temperature profile.

Tray

Figure 2.6 Effect of number of reactive trays on temperature profile.

These high concentrations require more vapor boilup and reflux to keep reactant B from escaping out of the top and reactant A from dropping out of the bottom of the column.

This phenomenon is one of the most intriguing aspects of reactive distillation design. Adding more reactive trays does not always produce a more economical design, even if the increase in capital cost is ignored.

There are also control implications. As we will see in later chapters, the dynamic controllability of a reactive distillation column is improved by adding more reactive trays. Thus, as is true in many chemical processes, there is a conflict between steady-state design and dynamic controllability. The column with 9 reactive trays is the steady-state economic optimum. However, as we will demonstrate in Chapter 10, a column with 13 reactive trays provides better dynamic performance in terms of the ability to maintain conversion and product purities in the face of disturbances in throughput and feed compositions.

The reactive distillation process provides an excellent example of the ever-present interaction between design and control. Both steady-state and dynamic aspects of a chemical process must be considered at all stages of the development and commercialization of a chemical process: laboratory, pilot plant, and plant.

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