Analysis for Dual Temperature Control

In order to understand why the CS1 control stmcture fails for feed composition disturbances, a series of runs are made using steady-state simulations in Aspen Plus. Feed composition is varied from its design value of 50 mol% acetone. The distillate and bottoms compositions 

The temperature on Stage 3 in the extractive column is controlled by manipulating the reflux-to-feed ratio. 

An average temperature in the solvent recovery column is calculated using Stages 3,4, and 5. This becomes the process variable in the temperature controller TC2 that changes the reboiler heat input-to-feed ratio. 

These results illustrate that the dual-temperatore control stmctore provides effective regulatory control of this maximum-boiling azeotropic system in the face of very large disturbances. 

---