AN EXPERIMENTAL COMPARISON OF 4 CONTROL-STRUCTURES FOR 2-POINT CONTROL OF DISTILLATION

An experimental 15-plate pilot-plant distillation column has been used to study four control strategies for two-point control of distillation. The control schemes consist of two single-input/single output (SISO) loops. The schemes are labeled after the manipulators used: (L,V), (D,V), (D/(L plus D), V), and (D/(L plus D),V/B). The best control quality for feed composition disturbances was obtained with the scheme (D/(L plus D),V) and by far the worst with (D,V). The difference between the three best schemes was small. The two-ratio scheme (D/(L plus D),V/B) was clearly the most difficult one to implement on the column studied. The control structure chosen for a distillation column may strongly influence the sensitivity of the column to disturbances such as changes in feed composition or in feed flow rate.