Effect of Reactant Feed Location

The base case number is Ns = Nr = 5. Table 2.5 shows how vapor boilup changes with the number of fractionating trays. As expected from our experience with conventional distillation, with fewer than three trays, vapor boilup begins to increase sharply. 

There was a very slight increase when a very large numbers of trays were used, which was unexpected. This was because there was less heavier B near the top of the column and less lighter A near the bottom, which makes the separation somewhat more difficult. As we will see in Chapter 5, which studies a different chemical system, this unexpected effect can become more pronounced. 

The final design parameter to be studied in this chapter is the locations of the two fresh feed-streams. Up to this point we have assumed that the lighter reactant fresh feed Fqa is introduced on the bottom tray of the reactive zone (Ns +1) and the heavier reactant fresh feed Fob is introduced on the top tray of the reactive zone (Ns -I- 1 -I- Nrx)- This configuration seems like a logical choice. However, the fresh feeds could be introduced on trays inside the reactive zone. The question is how this affects the design, primarily in terms of energy consumption because this is our major economic performance criterion. 

The base case location of the fresh feed of reactant B is on tray 14 because there are five stripping trays and nine reactive trays. Several cases were run with lower feed tray locations. There was little effect on the vapor boilup as indicated in Table 2.6. The location of the heavy feed does not seem to have as large an effect as that of the light feed unless the feed is introduced quite far down in the reactive zone. 

The impacts of a number of important kinetic, phase equilibrium, and design parameters have been explored in the chapter. Most of the parameters have effects that are logical and follow our experience with conventional distillation. 

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