M13.9 Summary

In this chapter, we have focused on "conventional control" of distillation columns, where reflux is manipulated to control distillate composition and reboiler vapor boil-up rate is manipulated to control bottoms composition. The RGA indicates that this is the only satisfactory pairing for this strategy. We have found that this process is very sensitive to the multivariable direction of the manipulated inputs (open loop), or the setpoints (closed loop). The SVD is a useful mathematical tool for finding the strongest and weakest directions for a multivariable process.