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Figure 13.5
Constraint.
a display similar to Figure 13.1. Although this example does not require a constraint,
an example of the formulation of a constraint is shown in Figure 13.5. Results of
the example above are given at Chapter Thirteen Examples/ExampleOne. In this case
the nature of DSTWU does not permit simultaneous variation of the reflux ratio and
the number of stages required; however, for the case of varying the reflux ratio only,
the results show that a tall column with a relatively low reflux ratio produces the lowest
value of the objective function.
Although results are available at the Optimization block, additional results at Con-
vergence/Convergence under the tab Iterations show values of the objective function
and the independent variable through the solution process.
13.2 WORKSHOPS
Workshop 13.1
Propane at 14.7 psi and 200
◦
F is to be compressed to 120 psi
with two single-stage polytropic compressors, using the ASME method, separated by
a cooler that reduces the first compressor's outlet temperature to 200
◦
F. Develop an
optimization that will select the outlet pressure of the first compressor such that the
work required for the system is minimized. The polytropic efficiency for both com-
pressors is 0.72 and their mechanic efficiency is 1.0. The minimum allowable work
for both compressors is 10 hp.
Workshop 13.2a
The process shown in Figure 13.6 is to be optimized with respect
to the pressure of the flash, the column internal reflux ratio, and its distillate to feed
ratio. In preparation it is necessary to develop a series of process models in steps.
A key element of the process is the requirement that the column vapor product be
compressed to the operating pressure of the flash, which for model development is 150
psi. The flash is to operate adiabatically. It is necessary that a Fortran statement in a
calculator block be written to accomplish this. Once the code has been written, the
sequence tab is selected and the appropriate option to be employed upon execution is
configured. The column has 10 theoretical stages with the feed on stage 5. The column
