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In-Depth Information
Figure 11.19
RadFrac design specification.
Figure 11.20
RadFrac vary form.
RadFracExample3 illustrates the use of design specifications in conjunction with the
normal end specifications of RadFRac. In this case the distillate rate and reflux ratio are
permitted to vary, with the aim of achieving composition targets of the distillate and
bottoms composition of 0.95 mole fraction methanol and 0.01 mole fraction methanol,
respectively. The solution shows that for the limits of the perturbed variables the
bottoms composition is obtained and the overhead specification is close and probably
acceptable. Note that the Aspen Plus results show many errors, but in a practical sense
they are meaningless. These results are obtained by using two implementations of the
Design Spec and Vary functions. The final values of the reflux ratio and the distillate
rate are given in the report.
The remaining design questions are: Are the number of stages nearly optimal? Where
is the best feed location? RadFrac addresses these questions by selecting NQ Curves
under the list of options for the entry Distl1. The setup of this capability is shown in
Figure 11.21 and is illustrated at Examples//Example3a. In this example, many errors,
