impurities change significantly. The distillate impurity climbs from the desired 2 mol% isobutane level to over 3 mol%. The bottoms stream becomes overly pure. Using the CC/TC cascade control structure, the distillate purity is maintained. The setpoint of the temperature controller is decreased by the composition controller to drive the distillate impurity to 2 mol% isobutane.
These results illustrate that single-end temperature control provides stable base-level regulatory control of the column. However, product purities change somewhat when feed composition changes.
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