5.57 + 2.13

Figure 9.23 Changing holdup on reactive trays.

Number of Stripping Trays. The base case has 4 stripping trays and requires a reflux ratio of 2.947. The program would not converge when fewer stripping trays were used. Increasing the number over the range from 4 to 12 resulted in a decrease in the reflux ratio to 2.885. Thus, the number of stripping trays has little effect as long as there is more than the minimum.

Fresh Feed Location for C4. In the base case the C4 feed is introduced at the bottom of the reactive zone on stage 20. Feeding this stream higher in the column reduced the reflux ratio only slightly. The reflux ratio is 2.947 at stage 20 and 2.900 at stage 15. The program would not converge for higher locations.

Other Parameters. We were unsuccessful in trying to change the reactive tray holdup (Fig. 9.23), the number of reactive trays, the number of stripping trays, or the location of the ethanol fresh feed. The program either would not converge or produced Fortran errors and shut down.

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