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Tray

Tray

Figure 5.31 Effect of NR and NS on temperature profile.

this number is decreased from 5 to 4, there is a sharp jump in vapor boilup. There are also large increases in the fresh feed of A and of the impurity of A in the distillate. Thus, both energy and yield considerations indicate that there is a very hard lower constraint on the number of separation stages.

Figures 5.31 and 5.32 give temperature and composition profiles for three values of separation stages. The NR = NS = 4 case shows a composition profile with high concentrations of heavy C component in the reactive zone, which raises temperatures. The concentrations of A are also large, but the concentrations of I are small. Because A and I have the same volatility, their opposite changes in compositions tend to cancel each other.

Note the increase in the composition of A in the rectifying section for the NR = NS = 4 case. A large amount of A is escaping from the top of the reactive zone, but the rectifying trays are only able to keep heavier components B and C from leaving in the distillate.

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