CONTROL AND DYNAMICS OF HEAT-INTEGRATED DISTILLATION COLUMNS (MULTIVARIABLE)

Three different heat-integrated distillation processes (FS, LSF and LSR) have been studied to find the best configuration for binary separations. Steady-state energy consumptions were compared over a range of feed compositions and relative volatilities. Both moderate and high product purities were studied.;The LSR configuration consists of two columns that are heat-integrated in the reverse direction to process flows. All the feed is introduced into the first low pressure column. Approximately half of the light component is taken overhead in each column. This LSR scheme was found to be the best in terms of steady-state energy savings, dynamic controllability and insensitivity to modeling errors for most of the separations studied.;Unexpectedly, the more complex and interacting LSR scheme was found to be dynamically as good as the single column and in some cases even better. This improved dynamic performance is felt to be the result of the more reversible nature of the LSR configuration. The process interactions tend to let the process handle load disturbances more easily.;A procedure for designing SISO controllers in a multivariable environment was also developed. It can be used to determine the fundamental limitations of control structure, select the best variable pairing and find reasonable tuning constants for each loop.;The dynamic controllability of these two-column heat-integrated designs was also explored for the methanol-water separation. The dynamic performances of the complex heat-integrated systems were compared with the dynamic performance of a conventional single column. Disturbances in both feed composition and feed flow were studied.